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Dynamical change under slowly changing conditions: the quantum Kruskal–Neishtadt–Henrard theorem
(2022)
Adiabatic approximations break down classically when a constant-energy contour splits into separate contours, forcing the system to choose which daughter contour to follow; the choices often represent qualitatively different behavior, so that slowly changing conditions induce a sudden and drastic change in dynamics. The Kruskal–Neishtadt–Henrard (KNH) theorem relates the probability of each choice to the rates at which the phase space areas enclosed by the different contours are changing. This represents a connection within closed-system mechanics, and without dynamical chaos, between spontaneous change and increase in phase space measure, as required by the Second Law of Thermodynamics. Quantum mechanically, in contrast, dynamical tunneling allows adiabaticity to persist, for very slow parameter change, through a classical splitting of energy contours; the classical and adiabatic limits fail to commute. Here we show that a quantum form of the KNH theorem holds nonetheless, due to unitarity.
Experimental observation of a dissipative phase transition in a multi-mode many-body quantum system
(2022)
Dissipative phase transitions are a characteristic feature of open systems. One of the paradigmatic examples for a first order dissipative phase transition is the driven nonlinear single-mode optical resonator. In this work, we study a realization with an ultracold bosonic quantum gas, which generalizes the single-mode system to many modes and stronger interactions. We measure the effective Liouvillian gap of the system and find evidence for a first order dissipative phase transition. Due to the multi-mode nature of the system, the microscopic dynamics is much richer and allows us to identify a non-equilibrium condensation process.
Individual quantum emitters form a fundamental building block for emerging quantum technologies. Collective effects of emitters, such as superradiance, might improve the performance of applications even further. When scaling materials to larger sizes, however, the optical density of states is modified by the surrounding material, and the collective coupling in small domains might be covered by transitions to bulk properties due to the presence of multiple collectively emitting domains, which inhomogeneously add. Here, we probe the optical properties of nitrogen vacancy centers in agglomerates of nanodiamonds. We quantify the transition from individual emitters to bulk emission by fluorescence lifetime measurements, and find a transition to occur on a length scale of \(\sim \!3\) wavelengths around the emitter. While our lifetime measurements are consistent with superradiant decay, the second-order correlation function, which is a standard measure to reveal collective properties, fails to probe collective effects for our case of an ensemble of collectively contributing domains to the emission. Therefore, we propose and apply a new measure to trace collective effects based on the intensity fluctuations of the emitted light. Our work points toward systematically studying collective effects in a scalable solid-state quantum system, and using them for quantum optical applications in agglomerates of highly-doped nanodiamonds.
Within this paper, electro-mechanical long-term tests on a thrust bearing were presented. The effects of an additional electrical load on the bearing raceways and the used lubricant were investigated. Chemical investigations and viscosity measurements were presented, which show the changes in the lubricant. These investigations were compared with the electrical loads and the occurring raceway damage. In addition, a comparison was made with mechanical reference tests. This procedure makes it possible to classify the changes that occur due to the electrical load and to distinguish the effects from each other. The background to these investigations is the increased occurrence of parasitic currents in electric motors, which can lead to damage to machine elements. The phenomena that occur here are new challenges in the development of drive trains
Surface alloys are a highly flexible class of low dimensional materials with the opportunity to tune and control the spin and charge carrier functionalities on the nanoscale. Here, we focus on the atomic and mesoscopic structural details of three distinct binary rare-earth-noble metals (NM) surface alloys by employing scanning tunneling microscopy and low energy electron diffraction. Using Dysprosium as the guest element on fcc(111) NM substrates, we identify the formation of non-commensurate surface alloy superstructures, which lead to homogeneous moiré patterns for DyCu2/Cu(111) and DyAu2/Au(111), while an inhomogeneous one is found for DyAg2/Ag(111). The local structure was analyzed for these samples and the observed differences are discussed in the light of the lattice mismatches of the alloy layer with respect to the underlying substrate. For the particularly intriguing case of a DyAg2 surface alloy, the surface alloy layer does not show a uniform long-range periodic structure, but consists of local hexagonal tiles separated by extended domain walls, which occur likely to relieve the in-plane strain within the DyAg2 surface alloy layer. Our findings clearly demonstrate that surface alloying is an intriguing tool to tailor the local atomic structure as well as the mesoscopic moiré structures of metallic heterostructures.
Spin transport and spin dynamics after femtosecond laser pulse irradiation of iron (Fe) are studied using a kinetic Monte Carlo model. This model simulates spin dependent dynamics by taking into account two interaction processes during nonequilibrium: elastic electron–lattice scattering, where only the direction of the excited electrons changes, and inelastic electron–electron scattering processes, where secondary electrons are generated. An analysis of the spin dependent particle kinetics inside the material shows that a smaller elastic scattering time leads to a larger spatial spread of electrons in the material, whereas generation of secondary electrons extends the time span for superdiffusive transport and increases the spin current density.
Since the advent of experiments with photon Bose–Einstein condensates (phBECs) in dye-filled microcavities in 2010, many investigations have focussed upon the emerging effective photon–photon interaction. Despite its smallness, it can be identified to stem from two physically distinct mechanisms. On the one hand, a Kerr nonlinearity of the dye medium yields a photon–photon contact interaction. On the other hand, a heating of the dye medium leads to an additional thermo-optic interaction, which is both delayed and non-local. The latter turns out to represent the leading contribution to the effective interaction for the current 2D experiments. Here we analyse theoretically how the effective photon–photon interaction increases when the system dimension is reduced from 2D to 1D. To this end, we consider an anisotropic harmonic trapping potential and determine via a variational approach how the properties of the phBEC in general, and both aforementioned interaction mechanisms in particular, change with increasing anisotropy. We find that the thermo-optic interaction strength increases at first linearly with the trap aspect ratio and later on saturates at a certain value of the trap aspect ratio. Furthermore, in the strong 1D limit the roles of both interactions get reversed as the thermo-optic interaction remains saturated and the contact Kerr interaction becomes the leading interaction mechanism. Finally, we discuss how the predicted effects can be measured experimentally.
Photon Bose–Einstein condensates are characterised by a quite weak interaction, so they behave nearly as an ideal Bose gas. Moreover, since the current experiments are conducted in a microcavity, the longitudinal motion is frozen out and the photon gas represents effectively a two-dimensional trapped gas of massive bosons. In this paper we focus on a harmonically confined ideal Bose gas in two dimensions, where the anisotropy of the confinement allows for a dimensional crossover. If the confinement in one direction is strong enough so that this squeezed direction is frozen out, then only one degree of freedom survives and the system can be considered to be quasi-one dimensional. In view of an experimental set-up we work out analytically the thermodynamic properties for such a system with a finite number of photons. In particular, we focus on examining the dimensional information which is contained in the respective thermodynamic quantities.
As shown in recent experiments (Lienhard et al 2020 Phys. Rev. X 10 021031), spin–orbit coupling in systems of Rydberg atoms can give rise to density-dependent Peierls phases in second-order hoppings of Rydberg spin excitations and nearest-neighbor repulsion. We here study theoretically a one-dimensional zig-zag ladder system of such spin–orbit coupled Rydberg atoms at half filling. The second-order hopping is shown to be associated with an effective gauge field, which in mean-field approximation is static and homogeneous. Beyond the mean-field level the gauge potential attains a transverse quantum component whose amplitude is dynamical and linked to density modulations. We here study the effects of this to the possible ground-state phases of the system. In a phase where strong repulsion leads to a density wave, we find that as a consequence of the induced quantum gauge field a regular pattern of current vortices is formed. However also in the absence of density–density interactions the quantum gauge field attains a non-vanishing amplitude. Above a certain critical strength of the second-order hopping the energy gain due to gauge-field induced transport overcomes the energy cost from the associated build-up of density modulations leading to a spontaneous generation of the quantum gauge field.
We investigate small tantalum clusters Tan+, n = 2–4, for their capability to cleave N2 adsorption spontaneously. We utilize infrared photon dissociation (IR-PD) spectroscopy of isolated and size selected clusters under cryogenic conditions within a buffer gas filled ion trap, and we augment our experiments by quantum chemical simulations (at DFT level). All Tan+ clusters, n = 2–4, seem to cleave N2 efficiently. We confirm and extend a previous study under ambient conditions on Ta2+ cluster [Geng et al., Proc. Natl. Acad. Sci. U. S. A. 115, 11680–11687 (2018)]. Our cryo studies and the concomitant DFT simulations of the tantalum trimer Ta3+ suggest cleavage of the first and activation of the second and third N2 molecule across surmountable barriers and along much-involved multidimensional reaction paths. We unravel the underlying reaction processes and the intermediates involved. The study of the N2 adsorbate complexes of Ta4+ presented here extends our earlier study and previously published spectra from (4,m), m = 1–5 [Fries et al., Phys. Chem. Chem. Phys. 23(19), 11345–11354 (2021)], up to m = 12. We confirm the priory published double activation and nitride formation, succeeded by single side-on N2 coordination. Significant red shifts of IR-PD bands from these side-on coordinated μ2-κN:κN,N N2 ligands correlate with the degree of tilting towards the second coordinating Ta center. All subsequently attaching N2 adsorbates onto Ta4+ coordinate in an end-on fashion, and we find clear evidence for co-existence of end-on coordination isomers. The study of stepwise N2 adsorption revealed adsorption limits m(max) of [Tan(N2)m]+ which increase with n, and kinetic fits revealed significant N2 desorption rates upon higher N2 loads. The enhanced absolute rate constants of the very first adsorbate steps kabs(n,0) of the small Ta3+ and Ta4+ clusters independently suggest dissociative N2 adsorption and likely N2 cleavage into Ta nitrides.
We present an IR-PD study of tantalum cluster adsorbate complexes [Tan(N2)m]+, abbreviated (n,m), n = 5–8. We utilize infrared spectroscopy of isolated and size selected clusters as prepared and characterized by a cryogenic tandem ion trap setup, and we augment our experiments with quantum chemical simulations at the level of density functional theory. The cluster adsorbate complexes (n,m) reveal vibrational bands above 2000 cm−1, which indicate end-on coordinated μ1-N2 oscillators, and bands below 2000 cm−1, which indicate side-on μ2-κN:κN,N coordinated ones. We observe a general increase in spectral complexity and an inhomogeneous broadening, mainly towards the red, at certain points of N2 loading m, which originates from an increasingly higher amount of double and triple N2 coordination at Ta sites, eventually at all of them. Other than the small tantalum clusters Tan+, n = 2–4, the IR-PD spectra of the initial N2 adsorbate species (n,1), n = 5–8, provide strong evidence for a lack of spontaneous N2 cleavage. Spontaneous N2 cleavage by Tan+, n = 5–8, seems suppressed. Therefore, the ability of a small Ta cluster to cleave dinitrogen disappears with one more tantalum core atom. The study of stepwise N2 adsorption on size selected Tan+, n = 5–8 clusters revealed adsorption limits m(max) of [Tan(N2)m]+ that are independent of cluster size within this size range. Cryo-adsorption kinetics at 26 K allowed for kinetic fits to consecutive N2 adsorption steps, and the fits revealed significant N2 desorption rates upon higher N2 loads, and the cluster adsorbate complexes eventually reached equilibrium. Some enhanced N2 desorption rates point towards likely adsorbate shell reorganization, and there is also some evidence for the coexistence of isomeric cluster adsorbate complexes.
Finding new energy-efficient methods for exciting magnetization dynamics is one of the key challenges in magnonics. In this work, we present an approach to excite the gyrotropic dynamics of magnetic vortices through the phenomenon of inverse magnetostriction, also known as the Villari effect. We develop an analytical model based on the Thiele formalism that describes the gyrotropic motion of the vortex core including the energy contributions due to inverse magnetostriction. Based on this model, we predict excitations of the vortex core resonances by surface acoustic waves whose frequency is resonant with the frequency of the vortex core. We verify the model's prediction using micromagnetic simulations and show the dependence of the vortex core's oscillation radius on the surface acoustic wave amplitude and the static bias field. Our study contributes to the advancement of energy-efficient magnetic excitations by relying on voltage-induced driven dynamics, which is an alternative to conventional current-induced excitations.
Varactor diodes have been proposed as active tuning elements of reconfigurable metasurfaces in the Ka-band. However, their experimental realization in this frequency range has not been demonstrated yet. We report the implementation of such a reconfigurable intelligent surface (RIS) made of 20 × 20 unit cells. By active tuning of the bias voltage of the varactors, the phase of the backward diffracted wave can be continuously tuned between 0 ° and 180 °. Thus, the phase tuning can be independently controlled for each unit cell. The frequency working range of the RIS is 1.1 GHz (from 30.6 to 31.7 GHz). As an illustration of the practical use, we demonstrate continuous beam steering of microwave radiation at 31 GHz in a defined propagation plane.
Rapid-prototyping of microscopic thermal landscapes in Brillouin light scattering spectroscopy
(2023)
Since temperature and its spatial, and temporal variations affect a wide range of physical properties of material systems, they can be used to create reconfigurable spatial structures of various types in physical and biological objects. This paper presents an experimental optical setup for creating tunable two-dimensional temperature patterns on a micrometer scale. As an example of its practical application, we have produced temperature-induced magnetization landscapes in ferrimagnetic yttrium iron garnet films and investigated them using micro-focused Brillouin light scattering spectroscopy. It is shown that, due to the temperature dependence of the magnon spectrum, spatial temperature distributions can be visualized even for microscale thermal patterns.
The concept of building logically functional networks employing spintronics or magnetic heterostructures is becoming more and more popular today. Incorporating logical segments into a circuit needs physical bonds between the magnetic molecules or clusters involved. In this framework, we systematically study ultrafast laser-induced spin-manipulation scenarios on a closed system of three carbon chains to which three Ni atoms are attached. After the inclusion of spin–orbit coupling and an external magnetic field, different ultrafast spin dynamics scenarios involving spin-flip and long-distance spin-transfer processes are achieved by various appropriately well-tailored time-resolved laser pulses within subpicosecond timescales. We additionally study the various effects of an external magnetic field on spin-flip and spin-transfer processes. Moreover, we obtain spin-dynamics processes induced by a double laser pulse, rather than a single one. We suggest enhancing the spatial addressability of spin-flip and spin-transfer processes. The findings presented in this article will improve our knowledge of the magnetic properties of carbon-based magnetic molecular structures. They also support the relevant experimental realization of spin dynamics and their potential applications in future molecular spintronics devices.
Mass transfer through fluid interfaces is an important phenomenon in industrial applications as well as in naturally occurring processes. In this work, we investigate the mass transfer across vapor–liquid interfaces in binary mixtures using molecular dynamics simulations. We investigate the influence of interfacial properties on mass transfer by studying three binary azeotropic mixtures known to have different interfacial behaviors. Emphasis is placed on the effect of the intermolecular interactions by choosing mixtures with the same pure components but different cross-interactions such that different azeotropic behaviors are obtained. The molar flux is created by utilizing a non-stationary molecular dynamics simulation approach, where particles of one component are inserted into the vapor phase over a short period of time before the system’s response to this insertion is monitored. From a direct comparison of the density profiles and the flux profiles in close proximity to the interface, we analyze the particles’ tendency to accumulate in the interfacial region throughout the different stages of the simulation. We find that for mixtures with strong attractive cross-interactions, the inserted particles are efficiently transported into the liquid phase. For systems with weak attractive cross-interactions, the inserted particles show a tendency to accumulate in the interfacial region, and the flux through the system is lower. The results from this work indicate that the accumulation of particles at the interface can act as a hindrance to mass transfer, which has practical relevance in technical processes.
This paper is concerned with a theoretical analysis of the behavior of optically excited spin currents in bilayer and multilayer systems of ferromagnetic and normal metals. As the propagation, control, and manipulation of the spin currents created in ferromagnets by femtosecond optical pulses is of particular interest, we examine the influence of different thicknesses of the constituent layers for the case of electrons excited several electronvolts above the Fermi level. Using a Monte-Carlo simulation framework for such highly excited electrons, we first examine the spatiotemporal characteristics of the spin current density driven in a Fe layer, where the absorption profile of the light pulse plays an important role. Further, we examine how the combination of light absorption profile, spin-dependent transmission probabilities, and iron layer thickness affects spin current density in a Fe/Au bilayer system. For high-energy electrons studied here, the interface and secondary electron generation have a small influence on spin transport in the bilayer system. However, we find that spin injection from one layer to another is most effective within a certain range of iron layer thicknesses.
Colloidal nanorods based on CdS or CdSe, functionalized with metal particles, have proven to be efficient catalysts for light-driven hydrogen evolution. Seeded CdSe@CdS nanorods have shown increasing performance with increasing rod length. This observation was rationalized by the increasing lifetime of the separated charges, as a large distance between holes localized in the CdSe seed and electrons localized at the metal tip decreases their recombination rate. However, the impact of nanorod length on the electron-to-tip localization efficiency or pathway remained an open question. Therefore, we investigated the photo-induced electron transfer to the metal in a series of Ni-tipped CdSe@CdS nanorods with varying length. We find that the transfer processes occurring from the region close to the semiconductor–metal interface, the rod region, and the CdSe seed region depend in different ways on the rods’ length. The rate of the fastest process from excitonic states generated directly at the interface is independent of the rod length, but the relative amplitude decreases with increasing rod length, as the weight of the interface region is decreasing. The transfer of electrons to the metal tip from excitons generated in the CdS rod region depends strongly on the length of the nanorods, which indicates an electron transport-limited process, i.e., electron diffusion toward the interface region, followed by fast interface crossing. The transfer originating from the CdSe excitonic states again shows no significant length dependence in its time constant, as it is probably limited by the rate of overcoming the shallow confinement in the CdSe seed.
A set of molecular models for the alkali nitrates (LiNO3, NaNO3, KNO3, RbNO3, and CsNO3) in aqueous solutions is presented and used for predicting the thermophysical properties of these solutions with molecular dynamics simulations. The set of models is obtained from a combination of a model for the nitrate anion from the literature with a set of models for the alkali cations developed in previous works of our group. The water model is SPC/E and the Lorentz–Berthelot combining rules are used for describing the unlike interactions. This combination is shown to yield fair predictions of thermophysical and structural properties of the studied aqueous solutions, namely the density, the water activity and the mean ionic activity coefficient, the self-diffusion coefficients of the ions, and radial distribution functions, which were studied at 298 K and 1 bar; except for the density of the solutions of all five nitrates and the activity properties of solutions of NaNO3, which were also studied at 333 K. For calculating the water the activity and the mean ionic activity coefficient, the OPAS (osmotic pressure for the activity of selvents) method was applied. The new models extend an ion model family for the alkali halides developed in previous works of our group in a consistent way.
We propose a hybrid magnonic-oscillator system based on the combination of a spin transfer auto-oscillator and a magnonic waveguide to open new perspectives for spin-wave based circuits. The system is composed of a spin transfer oscillator based on a vortex state which is dipolarly coupled to a nanoscale spin-wave waveguide with longitudinal magnetization. In its auto-oscillating regime, the oscillator emits coherent spin waves with tunable and controllable frequencies, directions, and amplitudes into the waveguide. We demonstrate the principle of this method using micromagnetic simulations and show that reconfiguration of the system is possible by changing the chirality and polarity of the magnetic vortex. Spin waves are emitted into the waveguide with high non-reciprocity and the preferred direction depends on the core polarity of the vortex. In contrast, different vortex chiralities lead to different amplitudes of the emitted waves. Our findings open up a novel way to design an agile spintronic device for the coherent and tunable generation of propagating spin waves.
Confinement of Bose–Einstein magnon condensates in adjustable complex magnetization landscapes
(2022)
Coherent wave states such as Bose–Einstein condensates (BECs), which spontaneously form in an overpopulated magnon gas even at room temperature, have considerable potential for wave-based computing and information processing at microwave frequencies. The ability to control the transport properties of magnon BECs plays an essential role in their practical use. Here, we demonstrate the spatiotemporal control of the BEC density distribution through the excitation of magnon supercurrents in an inhomogeneously magnetized yttrium iron garnet film. The BEC is created by microwave parametric pumping and probed by Brillouin light scattering spectroscopy. The desired magnetization profile is prepared by heating the film with optical patterns projected onto its surface using a phase-based wavefront modulation technique. Specifically, we observe a pronounced spatially localized magnon accumulation caused by magnon supercurrents flowing toward each other originating in two heated regions. This accumulation effect increases the BEC lifetime due to the constant influx of condensed magnons into the confinement region. The shown approach to manipulate coherent waves provides an opportunity to extend the lifetime of freely evolving magnon BECs, create dynamic magnon textures, and study the interaction of magnon condensates formed in different regions of the sample.
We present a robust, fiber-based endoscope with a silver direct-laser-written structure for radio frequency (RF) emission next to the optical fiber facet. Thereby, we are able to excite and probe a sample, such as nitrogen-vacancy (NV) centers in diamond, with RF and optical signals simultaneously and specifically measure the fluorescence of the sample fully through the fiber. At our targeted frequency range of around 2.9 GHz, the facet of the fiber core is in the near-field of the RF-guiding silver structure, which comes with the advantage of an optimal RF intensity decreasing rapidly with the distance. By creating a silver structure on the cladding of the optical fiber, we achieve the minimal possible distance between an optically excited and detected sample and an antenna structure without affecting the optical performance of the fiber. This allows us to realize a high RF amplitude at the sample’s position when considering an endoscope solution with integrated optical and RF access. The capabilities of the endoscope are quantified by optically detected magnetic resonance (ODMR) measurements of an NV-doped microdiamond that we probe as a practical use case. We demonstrate a magnetic sensitivity of our device of 17.8 nT/Hz when measuring the ODMR exclusively through our fiber and compare the sensitivity to a measurement using a confocal microscope. Moreover, the application of our device is not limited to NV centers in diamonds. Similar endoscope-like devices combining optical excitation and detection with radio frequency or microwave antenna could be used as a powerful tool for measuring a variety of fluorescent particles that have so far only been investigated with bulky and large optical setups. Furthermore, our endoscope points toward precise distance measurements based on Rabi oscillations.
Schlafschwierigkeiten und Insomnie stellen ein gesellschaftlich zunehmendes Phänomen dar. Studierende sind hiervon überdurchschnittlich häufig betroffen, mehr als ein Drittel beklagt eine niedrige Schlafqualität. In diesem Kontext erwiesen sich vor allem achtsamkeitsbasierte Interventionen als hilfreich. Wirksame, neuere Forschungsansätze widmen sich der Untersuchung mobiler Gesundheitsanwendungen. Daran anknüpfend setzt sich die Studie zum Ziel, die Effektivität einer achtsamkeitsbasierten Intervention mittels Meditations-App („7Mind“) in Bezug auf Schlafschwierigkeiten zu evaluieren. Studierende wurden randomisiert der Treatment- oder Wartelisten-Kontrollgruppe zugeordnet. Baseline-Messung, Post-Messung (2 Wochen) und Follow-up-Messung (4 Wochen) wurden mit Selbstberichtfragebogen zu den Variablen Schlafqualität, Insomnie-Schweregrad, Achtsamkeit, Tagesmüdigkeit, Stress und Lebensqualität untersucht. Die Intervention sollte 14 Tage 20 Minuten täglich absolviert werden. Von 53 Studierenden mit Baseline-Messung füllten 35 die Post-Messung und 28 alle Messzeitpunkte aus. Im Anschluss an das Training zeigten sich zwischen den Gruppen signifikante Unterschiede bezüglich der Schlafparameter (p < .001), wohingegen die Achtsamkeit unverändert blieb. Dafür wies letztere eine signifikante Zeit x Gruppe Interaktion auf (p = .018). In Bezug auf den Schlaf ergaben sich hohe Effektstärken, welche auch zum Follow-up-Zeitpunkt persistierten (d= 2.36). Die Variablen Tagesmüdigkeit,
Stress und Lebensqualität waren hochsignifikant mit der Schlafqualität korreliert (p < .001).
Mobile achtsamkeitsbasierte Interventionen stellen eine ökonomische Alternative dar, um Studierende mit Schlafschwierigkeiten zu unterstützen. Zukünftige Schritte inkludieren die Überprüfung über einen längeren Zeitraum und mit einer größeren Reichweite.
Interfacial properties of binary azeotropic mixtures of Lennard-Jones truncated and shifted fluids were studied by molecular dynamics (MD) simulation and density gradient theory (DGT) in combination with an equation of state. Three binary mixtures were investigated, which differ in the energetic cross interaction parameter that yields different types of azeotropic behavior. This study covers a wide temperature and composition range. Mixture A exhibits a heteroazeotrope at low temperatures, which changes to a low-boiling azeotrope at high temperatures, mixture B exhibits a low-boiling azeotrope, and mixture C exhibits a high-boiling azeotrope. The phase behavior and fluid interfacial properties as well as their relation were studied. Vapor–liquid, liquid–liquid, and vapor–liquid–liquid equilibria and interfaces were considered. Density profiles, the surface tension, the interfacial thickness, as well as the relative adsorption and enrichment of the components at the interface were studied. The results obtained from the two independent methods (MD and DGT) are overall in good agreement. The results provide insights into the relation of the phase behavior, particularly the azeotropic behavior, of simple fluid mixtures and the corresponding interfacial properties. Strong enrichment was found for the mixture with a heteroazeotrope in the vicinity of the three-phase equilibrium, which is related to a wetting transition.
We report on the resonant excitation of spin waves in micro-structured magnetic thin films by short-wavelength surface acoustic waves (SAWs). The spin waves as well as the acoustic waves are studied by micro-focused Brillouin light scattering spectroscopy. At low magnetic bias fields, a resonant phonon–magnon conversion is possible, which results in the excitation of short-wavelength spin waves. Using micromagnetic simulations, we verify that during this excitation both energy and linear momentum are conserved and fully transferred from the SAW to the spin wave. This conversion can already be detected after an interaction length of a few micrometers. Thus, our findings pave the way for miniaturized magneto-elastic spin-wave emitters for magnon computing.
We study the influence of transport effects on time- and space-resolved magnetization dynamics in a laser-excited thick nickel film. We explicitly include diffusive heat transport and spin-resolved charge transport as well as Seebeck and Peltier effects and calculate the dynamics of spin-dependent electronic temperatures, chemical potentials, lattice temperatures, and magnetization. We find that transport has an influence on the magnetization dynamics closer to the excited surface as well as in regions deeper than the penetration depth of the laser. We reveal that, for higher absorbed fluences and in the presence of transport, thick magnetic films show a quenching time nearly independent of depth, though the magnitude of quenching is depth-dependent.
We investigate ultrafast spin dynamics due to exchange, electron–phonon and Elliott–Yafet spin-flip scattering in a model with a simple band structure and ferromagnetically coupled electronic sublattices (or more generally, subsystems). We show that this incoherent model of electronic dynamics leads to sublattice magnetization changes in opposite directions after ultrashort-pulse excitation. This prominent feature on an ultrafast timescale is related to a transfer of energy and angular momentum between the subsystems due to exchange scattering. Our calculations illustrate a possible incoherent mechanism that works in addition to the coherent optically induced spin transfer mechanism.
Spin waves in yttrium iron garnet (YIG) nano-structures attract increasing attention from the perspective of novel magnon-based data processing applications. For short wavelengths needed in small-scale devices, the group velocity is directly proportional to the spin-wave exchange stiffness constant λex. Using wave vector resolved Brillouin light scattering spectroscopy, we directly measure λex in Ga-substituted YIG thin films and show that it is about three times larger than for pure YIG. Consequently, the spin-wave group velocity overcomes the one in pure YIG for wavenumbers k > 4 rad/μm, and the ratio between the velocities reaches a constant value of around 3.4 for all k > 20 rad/μm. As revealed by vibrating-sample magnetometry and ferromagnetic resonance spectroscopy, Ga:YIG films with thicknesses down to 59 nm have a low Gilbert damping (α<10−3), a decreased saturation magnetization μ0MS≈20 mT, and a pronounced out-of-plane uniaxial anisotropy of about μ0Hu1≈95 mT, which leads to an out-of-plane easy axis. Thus, Ga:YIG opens access to fast and isotropic spin-wave transport for all wavelengths in nano-scale systems independently of dipolar effects.
In this work, we present a method to microscopically investigate the liquid–vapor interfaces on the bottom side of droplets, which were placed on superhydrophobic structures, so that wetting in the Cassie–Baxter (CB) state occurred. These interfaces are hard to access optically, especially when an opaque substrate material is used, which is usually the case for technical applications. In that case, the menisci have to be observed through the droplet, which substantially deteriorates the imaging quality. Other methods that circumvent these distortions, such as optical coherence tomography, are restricted to a resolution of several micrometers. Confocal or fluorescence microscopy additionally requires a transparent substrate. To measure the liquid–vapor interfaces formed in the Cassie–Baxter state with high accuracy liquid droplets of a monomer solution that chemically reacts to form the elastomer, polydimethylsiloxane was placed on structured surfaces. Because double reentrant structures were used, wetting occurred in the Cassie–Baxter state despite the low surface tension of the monomer solution. After curing, it was possible to remove the solid droplets from the surface and investigate them using confocal microscopy, which provides an excellent height resolution of 10 nm. Test structures such as arrays of stripes and holes with variable spacing or diameter were used to investigate the impact of their geometry on the liquid–vapor interfaces formed in the CB state. Although the maximum height of the menisci on the droplet's bottom side is in the region of several 10 μm, the 10 nm resolution is required to adequately compare their topography with simplified theoretical models.
The magnetic response of a ferromagnet after an ultrafast optical excitation can be connected to the underlying electronic dynamics either via primary excitation processes during the laser pulse or via secondary collision processes. In the latter case, the information on the details of the excitation is lost and, therefore, the electron dynamics can be described using quasi-equilibrium concepts. In this work, we study the effect of the pump photon energy on the ultrafast demagnetization dynamics in ferromagnetic nickel. We find that the magnetization dynamics for similar absorbed energies for a range of pump photon energies are almost identical and depend only on the absorbed energy. This is in stark contrast to characteristic differences in the optically excited electronic distributions, as calculated from the band structure. In addition, the measured fluence-dependent dynamics can be reproduced with a model based on local temperatures. These findings indicate that it is mainly secondary processes that are responsible for the observed demagnetization dynamics.
We present a study of stepwise cryogenic N2 adsorption on size-selected Fen+ (n = 8–20) clusters within a hexapole collision cell held at T = 21–28 K. The stoichiometries of the observed adsorption limits and the kinetic fits of stepwise N2 uptake reveal cluster size-dependent variations that characterize four structural regions. Exploratory density functional theory studies support tentative structural assignment in terms of icosahedral, hexagonal antiprismatic, and closely packed structural motifs. There are three particularly noteworthy cases, Fe13+ with a peculiar metastable adsorption limit, Fe17+ with unprecedented nitrogen phobia (inefficient N2 adsorption), and Fe18+ with an isomeric mixture that undergoes relaxation upon considerable N2 uptake.
Cryo infrared spectroscopy of N2 adsorption onto bimetallic rhodium–iron clusters in isolation
(2021)
We investigated the N2 adsorption behavior of bimetallic rhodium–iron cluster cations [RhiFej(N2)m]+ by means of InfraRed MultiplePhotoDissociation (IR-MPD) spectroscopy in comparison with density functional theory (DFT) modeling. This approach allows us to refine our kinetic results [Ehrhard et al., J. Chem. Phys. (in press)] to enhance our conclusions. We focus on a selection of cluster adsorbate complexes within the ranges of i = j = 3–8 and m = 1–10. For i = j = 3, 4, DFT suggests alloy structures in the case of i = j = 4 of high (D2d) symmetry: Rh–Fe bonds are preferred instead of Fe–Fe bonds or Rh–Rh bonds. N2 adsorption and IR-MPD studies reveal strong evidence for preferential adsorption to Rh sites and mere secondary adsorption to Fe. In some cases, we observe adsorption isomers. With the help of modeling the cluster adsorbate complex [Rh3Fe3(N2)7]+, we find clear evidence that the position of IR bands allows for an element specific assignment of an adsorption site. We transfer these findings to the [Rh4Fe4(N2)m]+ cluster adsorbate complex where the first four N2 molecules are exclusively adsorbed to the Rh atoms. The spectra of the larger adsorbates reveal N2 adsorption onto the Fe atoms. Thus, the spectroscopic findings are well interpreted for the smaller clusters in terms of computed structures, and both compare well to those of our accompanying kinetic study [Ehrhard et al., J. Chem. Phys. (in press)]. In contrast to our previous studies of bare rhodium clusters, the present investigations do not provide any indication for a spin quench in [RhiFej(N2)m]+ upon stepwise N2 adsorption.
Many amphibians and insects have a biphasic life cycle, linking aquatic and terrestrial ecosystems. In temperate wetlands, insect communities are largely dominated by midges, such as non-biting chironomids and mosquitoes. Particularly chironomids and their aquatic larvae play a key role for both aquatic and terrestrial predators, e.g., dragonflies and damselflies (Odonata), birds, riparian spiders and amphibians. Therefore, adverse effects on chironomid larvae induced by pesticides or biocides can have implications on food webs across ecosystem boundaries.
In floodplains of the Upper Rhine Valley in southwest Germany, the biocide Bacillus thuringiensis var. israelensis (Bti) has been applied for over 40 years to reduce nuisance by mass emergence of mosquitoes. Due to its specific mode of action, Bti is presumed to be a more environmentally friendly alternative to non-selective, highly toxic pesticides used in the past. However, research on indirect effects of Bti on non-target organisms inhabiting these wetlands is still relatively scarce. The aim of this thesis was the investigation of direct and indirect effects of Bti on non-target organisms and, consequently, bottom-up effects on aquatic food webs and propagation to the terrestrial ecosystem. Effects were examined in outdoor floodplain pond mesocosms (FPMs) with natural flora and fauna communities.
Benthic macroinvertebrate communities were significantly altered in Bti-treated FPMs, largely due to the reduction of chironomid density by over 40% compared to untreated FPMs. Sampling of exuviae indicated that the emergence of Libellulidae (Odonata) was reduced by Bti, while larger Aeshnidae were not affected. This finding suggested increased intraguild predation (predation of competing predators) in Bti-treated FPMs as a result of decreased prey availability, i.e. chironomid larvae. This conclusion was partly confirmed in food web analyses using stable isotopes of C and N and fatty acids, with Aeshnidae experiencing a slight diet shift towards larger prey (i.e., newts, Aeshnidae) in Bti-treated FPMs. In contrast, the diet proportions of newt larvae were not affected by Bti treatment, but showed a marginal trend in lower omega-6 fatty acid content. Analyses of oxidative stress biomarkers did not reveal any direct effects of Bti on common frog tadpoles under natural climatic conditions.
This thesis emphasizes that adverse effects of Bti on the base of aquatic-terrestrial food webs, i.e., reduction of larval chironomids, can have implications for higher trophic levels and cascade to terrestrial ecosystems. Affected organisms also include species of concern, such as protected Odonata species. In view of the global insect and amphibian decline, the large-scale use of Bti in (partially protected) wetlands should be carefully considered.
We report the N2 cryo adsorption kinetics of selected gas phase mixed rhodium–iron clusters [RhiFej]+ in the range of i = 3–8 and j = 3–8 in 26 K He buffer gas by the use of a cryo tandem RF-hexapole trap–Fourier transform ion cyclotron resonance mass spectrometer. From kinetic data and fits, we extract relative rate constants for each N2 adsorption step and possible desorption steps. We find significant trends in adsorption behavior, which reveal adsorption limits, intermittent adsorption limits, and equilibrium reactions. For those steps, which are in equilibrium, we determine the Gibbs free energies. We conclude on likely ligand shell reorganization and some weakly bound N2 ligands for clusters where multiple N2 adsorbates are in equilibrium. The relative rate constants are transferred to absolute rate constants, which are slightly smaller than the collision rate constants calculated by the average dipole orientation (Langevin) theory. The calculated sticking probabilities increase, in general, with the size of the clusters and decrease with the level of N2 adsorption, in particular, when reaching an adsorption/desorption equilibrium. We receive further evidence on cluster size dependent properties, such as cluster geometries and metal atom distributions within the clusters through the accompanying spectroscopic and computational study on the equiatomic i = j clusters [Klein et al., J. Chem. Phys. 156, 014302 (2022)].
Infrared photodissociation (IR-PD) spectra of iron cluster dinitrogen adsorbate complexes [Fen(N2)m]+ for n = 8–20 reveal slightly redshifted IR active bands in the region of 2200–2340 cm−1. These bands mostly relate to stretching vibrations of end-on coordinated N2 chromophores, a μ1,end end-on binding motif. Density Functional Theory (DFT) modeling and detailed analysis of n = 13 complexes are consistent with an icosahedral Fe13+ core structure. The first adsorbate shell closure at (n,m) = (13,12)—as recognized by the accompanying paper on the kinetics of N2 uptake by cationic iron clusters—comes with extensive IR-PD band broadening resulting from enhanced couplings among adjacent N2 adsorbates. DFT modeling predicts spin quenching by N2 adsorption as evidenced by the shift of the computed spin minima among possible spin states (spin valleys). The IR-PD spectrum of (17,1) surprisingly reveals an absence of any structure but efficient non-resonant fragmentation, which might indicate some weakly bound (roaming) N2 adsorbate. The multiple and broad bands of (17,m) for all other cases than (17,1) and (17,7) indicate a high degree of variation in N2 binding motifs and couplings. In contrast, the (17,7) spectrum of six sharp bands suggests pairwise equivalent N2 adsorbates. The IR-PD spectra of (18,m) reveal additional features in the 2120–2200 cm−1 region, which we associate with a μ1,side side-on motif. Some additional features in the (18,m) spectra at high N2 loads indicate a μ1,tilt tilted end-on adsorption motif.
We discuss the realization of a magnonic version of the STImulated-Raman-Adiabatic-Passage (m-STIRAP) mechanism using micromagnetic simulations. We consider the propagation of magnons in curved magnonic directional couplers. Our results demonstrate that quantum-classical analogy phenomena are accessible in magnonics. Specifically, the inherent advantages of the STIRAP mechanism, associated with dark states, can now be utilized in magnonics. Applications of this effect for future magnonic device functionalities and designs are discussed.
Semiconductor multilayer and device fabrication is a complex task in electronics and opto-electronics. Layer dry etching is one of the process steps to achieve a specific lateral device design. In situ and real-time monitoring of etch depth will be necessary if high precision in etch depth is required. Nondestructive optical techniques are the methods of choice. Reflectance anisotropy spectroscopy equipment has been used to monitor the accurate etch depth during reactive ion etching of III/V semiconductor samples in situ and real time. For this purpose, temporal Fabry–Perot oscillations due to the etch-related shrinking thickness of the uppermost layer have been exploited. Earlier, we have already reported an etch-depth resolution of ±16.0 nm. By the use of a quadruple-Vernier-scale measurement and an evaluation protocol, now we even improve the in situ real-time etch-depth resolution by a factor of 20, i.e., nominally down to ±0.8 nm.
Magnonics attracts increasing attention in the view of low-energy computation technologies based on spin waves. Recently, spin-wave propagation in longitudinally magnetized nano-scaled spin-wave conduits was demonstrated, proving the fundamental feasibility of magnonics at the sub-100 nm scale. Transversely magnetized nano-conduits, which are of great interest in this regard as they offer a large group velocity and a potentially chirality-based protected transport of energy, have not yet been investigated due to their complex internal magnetic field distribution. Here, we present a study of propagating spin waves in a transversely magnetized nanoscopic yttrium iron garnet conduit of 50 nm width. Space and time-resolved microfocused Brillouin-light-scattering spectroscopy is employed to measure the spin-wave group velocity and decay length. A long-range spin-wave propagation is observed with a decay length of up to (8.0 ± 1.5) μm and a large spin-wave lifetime of up to (44.7 ± 9.1) ns. The results are supported with micromagnetic simulations, revealing a broad single-mode frequency range and the absence of a mode localized to the edges. Furthermore, a frequency nonreciprocity for counter-propagating spin waves is observed in the simulations and the experiment, caused by the trapezoidal cross section of the structure. The revealed long-distance spin-wave propagation on the nano-scale is particularly interesting for an application in spin-wave devices, allowing for long-distance transport of information in magnonic circuits and low-energy device architectures.
Examination of laminar Couette flow with obstacles by a low-cost particle image velocimetry setup
(2021)
For many technical applications, a detailed analysis of the fluid mechanical properties is necessary, for which computational fluid dynamics (CFD) simulations are used. However, even though flow simulations are becoming faster and more accurate, validation through experimentation is essential. One way of validation is to use Particle Image Velocimetry (PIV), an imaging technique that can visualize the flow field and measure flow velocities. Since the measuring equipment of commercial systems is very expensive, we propose a low-cost PIV setup that is also affordable for small scientific institutions. In addition to the quality of the acquired images, the reliability and comparability between experiment and simulation are also important issues. Therefore, in this work, we compare the image acquisition quality of the proposed low-cost PIV system with two- and three-dimensional CFD simulations for a laminar Couette flow and a laminar flow around square and hexagonal obstacles with very good agreement. In addition, we analyzed the transferability of 2D and 3D CFD simulations with experiments by measuring the velocity field and found that experimentally determined flow velocities often cannot be used to validate idealized (2D) simulations due to the spatial flow that occurs. However, if the non-ideal conditions of the experiment are considered in the (3D) simulation, a good comparability is given and an experimental validation is possible, for which the presented low-cost PIV system is well suitable.
In situ condition monitoring of rotary shaft seals could significantly improve the reliability of future seals in numerous applications. A superficial application of strain gauges capturing the state of deformation could offer a cost-effective retrofit solution for indirect measurements of central operational parameters. Within a simulative investigation of the sealing system, possible sensor positions for determination of the preload as well as the friction torque prevailing in the sealing contact are therefore identified as two parameters directly related to the operating condition. Further investigations of the potential sensor signal with focus on its time-dependent behavior prove the theoretical feasibility of the measurement concepts developed and provide promising prospects for an initial technical implementation.
A building's indoor climate is an essential input variable for a variety of building physics computational models, simulations, and analyses. Precise knowledge of the indoor climate is necessary to minimize the risk of mold or moisture damage and is required to ensure minimum heat insulation standards in buildings. Detailed data are especially necessary for the progressive application of transient calculations, for example, concerning thermal comfort or energy consumption. While the properties of building materials and the (local) outdoor climate are known, only rudimentary information about the dynamic indoor climate is available. Most existing information in the literature about indoor climate is fairly general and forgoes a differentiation between climatic region, occupancy profile, and the utilization of rooms. In this paper, we report on indoor climate measurements in naturally ventilated apartments over a period of 1 year. The measurement results complement the existing data to provide accurate indoor climate data in buildings. The measured values of indoor temperature and relative humidity serve to derive the dew point temperature and moisture load whereby dynamic time-dependent regression functions are determined for these parameters. The evaluations are carried out separately according to room use. The comparison of living rooms and bedrooms indicates a great influence of room use on the indoor climate in residential buildings. The determined indoor climate model can be used for the planning of buildings and simulations. The classification into living rooms and bedrooms makes it possible to take user behavior into account more realistically in building physics simulations. The minimum thermal insulation in residential buildings can also be checked and designed based on realistic data. The prediction interval describes the limits in which residential rooms are free of damage with a high probability. In this way, the indoor climate model describes an approach to examine and evaluate simulation results regarding condensation risk and mold damage in naturally ventilated rooms.
Magnetic heterostructures consisting of single-crystal yttrium iron garnet (YIG) films coated with platinum are widely used in spin-wave experiments related to spintronic phenomena such as the spin-transfer-torque, spin-Hall, and spin-Seebeck effects. However, spin waves in YIG/Pt bilayers experience much stronger attenuation than in bare YIG films. For micrometer-thick YIG films, this effect is caused by microwave eddy currents in the Pt layer. This paper reports that by employing an excitation configuration in which the YIG film faces the metal plate of the microstrip antenna structure, the eddy currents in Pt are shunted and the transmission of the Damon–Eschbach surface spin wave is greatly improved. The reduction in spin-wave attenuation persists even when the Pt coating is separated from the ground plate by a thin dielectric layer. This makes the proposed excitation configuration suitable for injection of an electric current into the Pt layer and thus for application in spintronics devices. The theoretical analysis carried out within the framework of the electrodynamic approach reveals how the platinum nanolayer and the nearby highly conductive metal plate affect the group velocity and the lifetime of the Damon–Eshbach surface wave and how these two wavelength-dependent quantities determine the transmission characteristics of the spin-wave device.
A novel core–shell species for the adsorption-based separation of carbon dioxide (CO2) from methane (CH4) is introduced by hydrothermal synthesis of Ni-MOF-74 on mesoporous spherical Al2O3 carrier substrate. The material was characterized and the shell thickness determined by means of optical and scanning electron microscopy as well as volumetric adsorption and fluid displacement experiments. Kinetic experiments with Ni-MOF-74@Al2O3 core–shell composites carried out at 303.15 K and at pressures up to 10 bar expose remarkably dominating uptake rates for CO2 over CH4. In the contrary Ni-MOF-74@Al2O3 appears to be unselective according to equilibrium data at the same conditions. Dynamic breakthrough experiments of binary CH4/CO2-mixtures (at 303.15 K and 5 bar) prove the prevailing effect of adsorption kinetics and the storage function of the mesoporous core. This statement is supported by a considerable boost in CO2-selectivity and capacity compared to adsorption equilibria measured on pure Ni-MOF-74 by the factor of 55.02 and up to 2.42, respectively.
Surface wetting can be simulated using a phase field approach which describes the continuous liquid-gas transition with the help of an order parameter. In this publication, wetting of non-planar surfaces is investigated based on a phase field model by Diewald et al. [1, 2]. Different scenarios of droplets on rough surfaces are simulated. The static equilibrium for those scenarios is calculated using an Allen-Cahn evolution equation. The influence of the surface morphology on the resulting contact angle is investigated while the width of the phase transition from liquid to gas is varied as a model parameter.
The great flexibility of direct laser writing (DLW) arises from the possibility to fabricate precise three-dimensional structures on very small scales as well as the broad range of applicable materials. However, there is still a vast number of promising materials, which are currently inaccessible requiring the continuous development of novel photoresists. Herein, a new bio-sourced resist is reported that uses the monomeric unit of chitin, N-acetyl-D-glucosamine, paving the way from existing hydrogel resists based on animal carbohydrates to a new class of non-hydrogel ones. In addition, it is shown that the combined use of two photoinitiators is advantageous over the use of a single one. In this approach, the first photoinitiator is a good two-photon absorber at the applied wavelength, while the second photoinitiator exhibits poor two-photon absorbtion abilities, but is better suited for cross-linking of the monomer. The first photoinitiator absorbs the light acting as a sensitizer and transfers the energy to the second initiator, which subsequently forms a radical and initializes the polymerization. This sensitization effect enables a new route to utilize reactive photointiators with a small two-photon absorption cross section for DLW without changing their chemical structure.
Starting from [(η5-cyclopentadienyl)(η6-phenyl)iron(II)]imidazole, dicationic imidazolium salts were prepared by N-alkylation. Reaction of these compounds with basic metal precursors such as mesityl copper(I) or palladium(II) acetate led to mono respectively dicationic transition metal NHC complexes (NHC=N-heterocyclic carbene). Transmetalation using the copper(I) complexes opened up the access to NHC gold(I) compounds. PEPPSI-type NHC complexes of palladium(II) and platinum(II) were prepared by offering a neutral pyridine ligand to the transition metal center. A rhodium(I) NHC complex was accessible by deprotonation of the dicationic imidazolium precursor and subsequent treatment with [(COD)Rh(μ2-Cl)]2 (COD=1,5-cyclooctadiene). The new NHC complexes were investigated by means of NMR spectroscopy, mass spectrometry as well as single crystal X-ray structure analysis. Both, the palladium(II) containing PEPPSI-type and the gold(I) complex, were investigated for their catalytic properties in typical model reactions such as cyclization reactions, Suzuki coupling and cyanation. In addition, a selenium adduct was synthesized in order to study the electronic properties of the underlying ligand backbone. Based on the chemical shift in the 77Se NMR spectrum, it is evident that these NHC ligands possess rather poor π-acidity.
Janus materials are anisotropic nano- and microarchitectures with two different faces consisting of distinguishable or opposite physicochemical properties. In parallel with the discovery of new methods for the fabrication of these materials, decisive progress has been made in their application, for example, in biological science, catalysis, pharmaceuticals, and, more recently, in battery technology. This Minireview systematically covers recent and significant achievements in the application of task-specific Janus nanomaterials as heterogeneous catalysts in various types of chemical reactions, including reduction, oxidative desulfurization and dye degradation, asymmetric catalysis, biomass transformation, cascade reactions, oxidation, transition-metal-catalyzed cross-coupling reactions, electro- and photocatalytic reactions, as well as gas-phase reactions. Finally, an outlook on possible future applications is given.
The folding of newly synthesized polypeptides requires the coordinated action of molecular chaperones. Prokaryotic cells and the chloroplasts of plant cells possess the ribosome-associated chaperone trigger factor, which binds nascent polypeptides at their exit stage from the ribosomal tunnel. The structure of bacterial trigger factor has been well characterized and it has a dragon-shaped conformation, with flexible domains responsible for ribosome binding, peptidyl-prolyl cis–trans isomerization (PPIase) activity and substrate protein binding. Chloroplast trigger-factor sequences have diversified from those of their bacterial orthologs and their molecular mechanism in plant organelles has been little investigated to date. Here, the crystal structure of the plastidic trigger factor from the green alga Chlamydomonas reinhardtii is presented at 2.6 Å resolution. Due to the high intramolecular flexibility of the protein, diffraction to this resolution was only achieved using a protein that lacked the N-terminal ribosome-binding domain. The eukaryotic trigger factor from C. reinhardtii exhibits a comparable dragon-shaped conformation to its bacterial counterpart. However, the C-terminal chaperone domain displays distinct charge distributions, with altered positioning of the helical arms and a specifically altered charge distribution along the surface responsible for substrate binding. While the PPIase domain shows a highly conserved structure compared with other PPIases, its rather weak activity and an unusual orientation towards the C-terminal domain points to specific adaptations of eukaryotic trigger factor for function in chloroplasts.
An improved route for the highly stereoselective synthesis of (Z)-2-oxyenamides is reported. The desired products can be accessed in only three steps from aminoacetaldehyde dimethyl acetal as common, readily available building block in a highly modular fashion. The improved procedure has been applied to the synthesis of various acylated and sufonylated oxyenamides. Mechanistic and theoretical studies provide a conclusive rationale for the observed stereoselectivities.
Scaled boundary isogeometric analysis (SB-IGA) describes the computational domain by proper boundary NURBS together with a well-defined scaling center; see [5]. More precisely, we consider star convex domains whose domain boundaries correspond to a sequence of NURBS curves and the interior is determined by a scaling of the boundary segments with respect to a chosen scaling center. However, providing a decomposition into star shaped blocks one can utilize SB-IGA also for more general shapes. Even though several geometries can be described by a single patch, in applications frequently there appear multipatch structures. Whereas a C0 continuous patch coupling can be achieved relatively easily, the situation becomes more complicated if higher regularity is required. Consequently, a suitable coupling method is inevitably needed for analyses that require global C1 continuity.In this contribution we apply the concept of analysis-suitable G1 parametrizations [2] to the framework of SB-IGA for the C1 coupling of planar domains with a special consideration of the scaling center. We obtain globally C1 regular basis functions and this enables us to handle problems such as the Kirchhoff-Love plate and shell, where smooth coupling is an issue. Furthermore, the boundary representation within SB-IGA makes the method suitable for the concept of trimming. In particular, we see the possibility to extend the coupling procedure to study trimmed plates and shells.The approach was implemented using the GeoPDEs package [1] and its performance was tested on several numerical examples. Finally, we discuss the advantages and disadvantages of the proposed method and outline future perspectives.
Print path-dependent contact temperature dependency for 3D printing using fused filament fabrication
(2022)
This paper focuses on the effects of different time spans and thus different contact temperatures when a molten strand contacts an adjacent already solidified strand in a plane during 3D printing with fused filament fabrication. For this purpose, both the manufacturing parameters and the geometry of the component are systematically varied and the effect on morphology and mechanical properties is investigated. The results clearly show that even with identical printing parameters, the transitions between the individual layers are much more visible with long time spans until fusion and lead to low mechanical properties. In contrast, short spans lead to hardly visible welds and high mechanical properties. Transferring the findings to different component sizes ultimately verifies that the average temperature at the time of contact between the already solidified and the currently deposited strand is decisive for component quality. In order to generate high component qualities, this finding must therefore be taken into account in the future in the path generation strategy, i.e., in so-called slicing.
Methods for predicting Henry's law constants Hij are important as experimental data are scarce. We introduce a new machine learning approach for such predictions: matrix completion methods (MCMs) and demonstrate its applicability using a data base that contains experimental Hij values for 101 solutes i and 247 solvents j at 298 K. Data on Hij are only available for 2661 systems i + j. These Hij are stored in a 101 × 247 matrix; the task of the MCM is to predict the missing entries. First, an entirely data-driven MCM is presented. Its predictive performance, evaluated using leave-one-out analysis, is similar to that of the Predictive Soave-Redlich-Kwong equation-of-state (PSRK-EoS), which, however, cannot be applied to all studied systems. Furthermore, a hybrid of MCM and PSRK-EoS is developed in a Bayesian framework, which yields an unprecedented performance for the prediction of Hij of the studied data set.
Based on conservation of resources theory, this paper examines the mediating mechanisms in the relationship between digital affordances and employee corporate entrepreneurship participation likelihood. Findings from an experimental study with 207 employees show a statistically significant and positive indirect effect of digital affordances on employee corporate entrepreneurship participation likelihood through employee-perceived information technology support for innovation and a statistically significant and—contrary to our expectations—positive indirect effect through employee-perceived work overload. Results are corroborated by insights from in-depth interviews with senior managers. They provide support for digital affordances as action potentials that are associated with resource gains that in turn foster employee corporate entrepreneurship participation likelihood.
Overexpression of the vacuolar sugar transporter TST1 in Arabidopsis leads to higher seed lipid levels and higher total seed yield per plant. However, effects on fruit biomass have not been observed in crop plants like melon, strawberry, cotton, apple, or tomato with increased tonoplast sugar transporter (TST) activity. Thus, it was unclear whether overexpression of TST in selected crops might lead to increased fruit yield, as observed in Arabidopsis. Here, we report that constitutive overexpression of TST1 from sugar beet in the important crop species Camelina sativa (false flax) resembles the seed characteristics observed for Arabidopsis upon increased TST activity. These effects go along with a stimulation of sugar export from source leaves and not only provoke optimised seed properties like higher lipid levels and increased overall seed yield per plant, but also modify the root architecture of BvTST1 overexpressing Camelina lines. Such mutants grew longer primary roots and showed an increased number of lateral roots, especially when developed under conditions of limited water supply. These changes in root properties result in a stabilisation of total seed yield under drought conditions. In summary, we demonstrate that increased vacuolar TST activity may lead to optimised yield of an oil-seed crop species with high levels of healthy ω3 fatty acids in storage lipids. Moreover, since BvTST1 overexpressing Camelina mutants, in addition, exhibit optimised yield under limited water availability, we might devise a strategy to create crops with improved tolerance against drought, representing one of the most challenging environmental cues today and in future.
Living systems incessantly engage in the regulation of their cellular processes to fulfill their biological functions. Beyond development-related adjustments or cell cycle oscillations, environmental fluctuations compel the system to reorganize metabolic pathways, structural components, or molecular repair and reconstitution mechanisms. These responses manifest across diverse temporal scales, necessitating an intricate regulatory orchestration. Time series experiments have become increasingly popular for charting the chronological order and elucidating the underlying mechanisms. In the era of high-throughput technologies, the majority of cellular molecules can be analyzed in one fell swoop, generating a comprehensive snapshot of the status quo of most present molecules. Methodological advancements also permit the monitoring not only of molecular abundances but also the functional status of transcripts and proteins. However, due to the still high efforts associated with such experiments, the number of measured time points and the replication of measurements remains limited. Resulting datasets contain signals from thousands of molecules, yet they are sparse in temporal resolution and are often imprecise due to biological variability and technical measurement inaccuracies.
This thesis explores the complexities arising from the examination of short time series data and introduces pioneering tools that offer fresh insights into the realm of biological time series analysis. The broad spectrum of analytic possibilities ranges from a molecule-centric investigation of individual time courses to a holistic aggregation of the system’s response to its main characteristics. By creating a modeling framework that applies domain-specific constraints, time-course signals can be transformed from a series of discrete data points into a continuous curve. These curves align with current biological conjectures about molecule kinetics being smooth and devoid of superfluous oscillations. Noise present at individual time points is judiciously accounted for during curve fitting, mitigating the impact of time points with high variance on the curve. Subsequent classification is based on the features of these curves (extreme points and inflection points) and ensures a reduction in data amount and complexity. Succinct labels assigned to each molecule's kinetics encapsulate the signal's most notable features. Besides this modeling approach, an innovative enrichment strategy is introduced, that is independent of prior data partitioning and capable of segregating the temporal response into its thermodynamically relevant components. This approach allows for a continuous assessment of each molecule's contribution to these components, obviating the need for exclusive allocation. The application of various analytical approaches to heat acclimation experiments in Chlamydomonas highlights the relevance and potential of time series experiments and specifically tailored analysis techniques. The integration of different system levels has led to the identification of regulatory peculiarities, such as an increased correlation between transcripts and corresponding proteins during acclimation responses. These and other insights may herald new avenues of research that could ultimately enhance plant robustness in the face of increasing environmental perturbations.
The growing popularity of time series experiments necessitates dedicated analytical approaches that empower researchers and analysts to decipher patterns, discern trends, and unravel the underlying structures within the data, facilitating predictions and the derivation of meaningful conclusions that could potentially build bridges between the interweaved systems levels.
Cyanobacteria oxygenated Earth's atmosphere ~2.4 billion years ago, during the Great Oxygenation Event (GOE), through oxygenic photosynthesis. Their high iron requirement was presumably met by high levels of Fe(II) in the anoxic Archean environment. We found that many deeply branching Cyanobacteria, including two Gloeobacter and four Pseudanabaena spp., cannot synthesize the Fe(II) specific transporter, FeoB. Phylogenetic and relaxed molecular clock analyses find evidence that FeoB and the Fe(III) transporters, cFTR1 and FutB, were present in Proterozoic, but not earlier Archaean lineages of Cyanobacteria. Furthermore Pseudanabaena sp. PCC7367, an early diverging marine, benthic strain grown under simulated Archean conditions, constitutively expressed cftr1, even after the addition of Fe(II). Our genetic profiling suggests that, prior to the GOE, ancestral Cyanobacteria may have utilized alternative metal iron transporters such as ZIP, NRAMP, or FicI, and possibly also scavenged exogenous siderophore bound Fe(III), as they only acquired the necessary Fe(II) and Fe(III) transporters during the Proterozoic. Given that Cyanobacteria arose 3.3–3.6 billion years ago, it is possible that limitations in iron uptake may have contributed to the delay in their expansion during the Archean, and hence the oxygenation of the early Earth.
In selective laser melting (SLM), a powdered material is locally melted by a laser and, after cooling, forms a coherent solid structure that enables the production of complex geometries with various materials. The process involves extreme heating and cooling rates and, thus, large temperature gradients, which lead to anisotropic material properties on the macroscopic scale and, in the worst case, reduced mechanical properties. In order to reliably predict the final mechanical component properties, simulations can be performed at different time and length scales. Enormous computational resources are often required to perform such simulations. In order to transform these simulations into suitable surrogate models, the generated data must be compressed and evaluated in a suitable way. This paper shows first preliminary work and a possible new data description of such simulations.
In diesem Beitrag stellt sich die Nachwuchswissenschaftlerin Dr.-Ing. Dorina Strieth vom Lehrgebiet Bioverfahrenstechnik der TU Kaiserslautern vor. Neben aktuellen Forschungsarbeiten und Lehraktivität berichtet sie über die Notwendigkeit des Wissenstransfers in die Zivilgesellschaft. Fachlich berichtet sie von aktuellen Ergebnissen der intelligenten Nutzung phototropher Biofilme sowie dem Potenzial zur biotechnologischen Herstellung nachhaltiger Baumaterialien.
Tracking waterborne microplastic (MP) in urban areas is a challenging task because of the various sources and transport pathways involved. Since MP occurs in low concentrations in most wastewater and stormwater streams, large sample volumes need to be captured, prepared, and carefully analyzed. The recent research in urban areas focused mainly on MP emissions at wastewater treatment plants (WWTPs), as obvious entry points into receiving waters. However, important transport pathways under wet-weather conditions are yet not been investigated thoroughly. In addition, the lack of comprehensive and comparable sampling strategies complicated the attempts for a deeper understanding of occurrence and sources. The goal of this paper is to (i) introduce and describe sampling strategies for MP at different locations in a municipal catchment area under dry and wet-weather conditions, (ii) quantify MP emissions from the entire catchment and two other smaller ones within the bigger catchment, and (iii) compare the emissions under dry and wet-weather conditions. WWTP has a high removal rate of MP (>96%), with an estimated emission rate of 189 kg/a or 0.94 g/[population equivalents (PEQ · a)], and polyethylene (PE) as the most abundant MP. The specific dry-weather emissions at a subcatchment were ≈30 g/(PEQ · a) higher than in the influent of WWTP with 23 g/(PEQ · a). Specific wet-weather emissions from large sub-catchment with higher traffic and population densities were 1952 g/(ha · a) higher than the emissions from smaller catchment (796 g/[ha · a]) with less population and traffic. The results suggest that wet-weather transport pathways are likely responsible for 2–4 times more MP emissions into receiving waters compared to dry-weather ones due to tire abrasion entered from streets through gullies. However, more investigations of wet-weather MP need to be carried out considering additional catchment attributes and storm event characteristics.
Model-based prediction is becoming increasingly important to meet the ever-increasing demands on manufacturing. In grinding, the prediction of the process forces and the generated surface by physical models are particularly important.Since cooling lubricants are almost always used on an industrial scale, the grinding model, developed at our institut, must be extended to include this component. Therefore, in order to implement cooling lubricants into the FEM-based model, it is first necessary to investigate the behaviors and effects of cooling lubricants in real experiments. Various influencing factors such as the scratching speed of individual abrasive grains in interaction with cooling lubricants need to be investigated. However, the existing physical grinding model is not limited exclusively to the prediction of the resulting forces. It is also supposed to be able to qualitatively predict the expected resulting surface of the workpiece. Hence, this paper will focus on the topographic characteristics that can occur in the scratch test due to different cooling lubricants and scratching speeds.Based on real experiments on a test rig for such scratch tests, it has been shown that different scratch speeds have a negligible influence on the topographical nature and expression of a scratch. In contrast, however, there is a direct influence of cooling lubricants on the topographic properties. This effect is additionally influenced by the viscosity of the cooling lubricant used.
In gravity separators, also known as settlers, two immiscible liquid phases separate due to differences in density. In extraction mixer-settler units, a dispersion needs to be separated within the separator unit. In order to overcome the hitherto purely experimental design, a knitted mesh adapted model as well as an automated test facility were developed in this work, which easily enable a scale-up to industrial units. An automation allows for a controlled investigation of knitted meshes as coalescing aids in settlers, and this was achieved via photo-optical probes with an optimized image analysis technique. It overcomes the limitations of neuronal network training based on manually annotating images using computer-generated image data. Therefore, the new methodology and setup are explained in detail, and the derivation and application of a new model to design separators with knitted meshes as coalescing aid is presented and compared to experimental results using meshes of different structures and materials. Finally, case studies and scale-up are discussed.
Within a biorefinery platform several conversion steps such as pretreatment, saccharification, fermentation and downstream processing are necessary to obtain the final bio-based product(s) from lignocellulosic biomass. The structural composition of the biomass, especially the lignin content, determines the necessary pretreatment steps. To obtain sugar monomers, the hydrolysis of lignocellulosic biomass is an essential step. This work examines the impact of different pretreatments on the sugar release during biocatalysis. Even without prior pretreatment the biocatalysis of low lignin biomass achieves glucose yields of up to 93 %, while the biocatalysis of high lignin biomass requires an upstream hydrothermal procedure to achieve a glucose yield of 74
Die Pandemie traf im Jahr 2020 auch die Kunstpädagogik unvorbereitet. Dem anfänglichen emergency remote teaching folgten elaboriertere Konzepte. Der Einsatz der Fachcommunity war immens – und hat die Disziplin allem Anschein nach dauerhaft verändert.
Die Publikation untersucht fachspezifische Erfahrungen aus der Pandemiezeit, kontextualisiert sie und entwickelt daraus Perspektiven. Dabei geht es nicht nur um den Gegensatz zwischen Präsenz- und Distanzformaten, sondern auch um grundsätzlichere Herausforderungen an das Fach. Die 28 Autor:innen u. a. aus den Bereichen Schule, Hochschule und Museum argumentieren und spekulieren in unterschiedlicher Weise, bisweilen auch zueinander im Widerspruch. Insgesamt ergibt sich so ein erstes Bild davon, was eine Kunstpädagogik nach der Pandemie ausmachen könnte.
Distributed message-passing systems have become ubiquitous and essential for our daily lives. Hence, designing and implementing them correctly is of utmost importance. This is, however, very challenging at the same time. In fact, it is well-known that verifying such systems is algorithmically undecidable in general due to the interplay of asynchronous communication (messages are buffered) and concurrency. When designing communication in a system, it is natural to start with a global protocol specification of the desired communication behaviour. In such a top-down approach, the implementability problem asks, given such a global protocol, if the specified behaviour can be implemented in a distributed setting without additional synchronisation. This problem has been studied from two perspectives in the literature. On the one hand, there are Multiparty Session Types (MSTs) from process algebra, with global types to specify protocols. Key to the MST approach is a so-called projection operator, which takes a global type and tries to project it onto every participant: if successful, the local specifications are safe to use. This approach is efficient but brittle. On the other hand, High-level Message Sequence Charts (HMSCs) study the implementability problem from an automata-theoretic perspective. They employ very few restrictions on protocol specifications, making the implementability problem for HMSCs undecidable in general. The work in this thesis is the first to formally build a bridge between the world of MSTs and HMSCs. To start, we present a generalised projection operator for sender-driven choice. This allows a sender to send to different receivers when branching, which is crucial to handle common communication patterns from distributed computing. Despite this first step, we also show that the classical MST projection approach is inherently incomplete. We present the first formal encoding from global types to HMSCs. With this, we prove decidability of the implementability problem for global types with sender-driven choice. Furthermore, we develop the first direct and complete projection operator for global types with sender-driven choice, using automata-theoretic techniques, and show its effectiveness with a prototype implementation. We are the first to provide an upper bound for the implementability problem for global types with sender-driven (or directed) choice and show it to be in PSPACE. We also provide a session type system that uses the results from our projection operator. Last, we introduce protocol state machines (PSMs) – an automata-based protocol specification formalism – that subsume both global types from MSTs and HMSCs with regard to expressivity. We use transformations on PSMs to show that many of the syntactic restrictions of global types are not restrictive in terms of protocol expressivity. We prove that the implementability problem for PSMs with mixed choice, which requires no dedicated sender for a branch but solely all labels to be distinct, is undecidable in general. With our results on expressivity, this answers an open question: the implementability problem for mixed-choice global types is undecidable in general.
Sound localization involves information analysis in the lateral superior olive (LSO), a conspicuous nucleus in the mammalian auditory brainstem. LSO neurons weigh interaural level differences (ILDs) through precise integration of glutamatergic excitation from the cochlear nucleus (CN) and glycinergic inhibition from the medial nucleus of the trapezoid body (MNTB). Sound sources can be localized even during sustained perception, an accomplishment that requires robust neurotransmission. Virtually nothing is known about the sustained performance and the temporal precision of MNTB–LSO inputs after postnatal day (P)12 (time of hearing onset) and whether acoustic experience guides development. Here we performed whole-cell patch-clamp recordings to investigate neurotransmission of single MNTB-LSO fibres upon sustained electrical stimulation (1–200 Hz/60 s) at P11 and P38 in wild-type (WT) and deaf otoferlin (Otof) knock-out (KO) mice. At P11, WT and KO inputs performed remarkably similarly. In WTs, the performance increased drastically between P11 and P38, e.g. manifested by an 8 to 11-fold higher replenishment rate (RR) of synaptic vesicles and action potential robustness. Together, these changes resulted in reliable and highly precise neurotransmission at frequencies ≤100 Hz. In contrast, KO inputs performed similarly at both ages, implying impaired synaptic maturation. Computational modelling confirmed the empirical observations and established a reduced RR per release site for P38 KOs. In conclusion, acoustic experience appears to contribute massively to the development of reliable neurotransmission, thereby forming the basis for effective ILD detection. Collectively, our results provide novel insights into experience-dependent maturation of inhibitory neurotransmission and auditory circuits at the synaptic level.
Development of a simple substitute model to describe the normal force of fluids in narrow gaps
(2023)
Fluids in narrow gaps are employed frequently in many applications. The motivation for their use is diverse and ranges from hydrodynamic lubrication in plain bearings to the transport of hard particles into the working gap for the purpose of machining workpiece surfaces in lapping processes. Depending on the focus of the analysis, it may be useful to investigate the entire pressure field or to calculate only individual quantities. For example, in sophisticated simulations it may be of interest to know the resulting force of a fluid as a function of the external system state in order to describe its damping characteristics. Especially for the simulation of flows in narrow gaps, the Reynolds equation is a convenient choice, which, in contrast to the more general Navier-Stokes equations, can lead to considerable savings in computational time because no three-dimensional discretization is required, but only a two-dimensional discretization. However, if not a highly detailed pressure field is of interest, but only simple relations such as the resulting force as a function of distance and velocity, and if this relation to be evaluated many times for different parameter combinations over a wide range of values, the use of a robust substitute model is a good choice. This article deals with the creation of such a substitute model based on the Reynolds equation taking cavitation into account.
Machine learning algorithms are widely applied to create powerful prediction models. With increasingly complex models, humans' ability to understand the decision function (that maps from a high-dimensional input space) is quickly exceeded. To explain a model's decisions, black-box methods have been proposed that provide either non-linear maps of the global topology of the decision boundary, or samples that allow approximating it locally. The former loses information about distances in input space, while the latter only provides statements about given samples, but lacks a focus on the underlying model for precise ‘What-If'-reasoning. In this paper, we integrate both approaches and propose an interactive exploration method using local linear maps of the decision space. We create the maps on high-dimensional hyperplanes—2D-slices of the high-dimensional parameter space—based on statistical and personal feature mutability and guided by feature importance. We complement the proposed workflow with established model inspection techniques to provide orientation and guidance. We demonstrate our approach on real-world datasets and illustrate that it allows identification of instance-based decision boundary structures and can answer multi-dimensional ‘What-If'-questions, thereby identifying counterfactual scenarios visually.
In the last decades, the phase field method has drawn much attention for its application in fracture mechanics because it offers a simple unified framework for crack propagation. The core idea of phase field models for fracture is to introduce a continuous scalar field representing the discontinuous crack. Recently, a phase field model for fatigue has been proposed along this path. The fatigue failure differs from the other fracture scenarios since cracks only occur after a considerable number of load cycles. As fracturing happens, changes of the material microstructure are involved, which causes the evolution of the structural configuration. Thus, a new mathematical description not based on traditional spatial coordinates but the material manifold is desired, which will serve as an elegant analysis tool to understand the energetic forces for crack propagation. Configurational forces are a suitable choice for this purpose, as they describe the energetic driving forces associated with phenomena changing the material itself. In this work, we present a phase field model for fatigue. Furthermore, the phase field fatigue model is analyzed within the concept of configurational forces, which provides a straightforward way to understand the phase field simulations of fatigue fracture.
Citizen conceptions of democracy and support for artificial intelligence in government and politics
(2022)
How much do citizens support artificial intelligence (AI) in government and politics at different levels of decision-making authority and to what extent is this AI support associated with citizens’ conceptions of democracy? Using original survey data from Germany, the analysis shows that people are overall sceptical toward using AI in the political realm. The findings suggest that how much citizens endorse democracy as liberal democracy as opposed to several of its disfigurations matters for AI support, but only in high-level politics. While a stronger commitment to liberal democracy is linked to lower support for AI, the findings contradict the idea that a technocratic notion of democracy lies behind greater acceptance of political AI uses. Acceptance is higher only among those holding reductionist conceptions of democracy which embody the idea that whatever works to accommodate people's views and preferences is fine. Populists, in turn, appear to be against AI in political decision making.
CFD-DEM Simulation of Superquadric Cylindrical Particles in a Spouted Bed and a Rotor Granulator
(2023)
The fluidization behavior of cylindrical particles in a spouted bed was first investigated experimentally using a camera setup. The obtained average spouted bed height was used to evaluate the accuracy of different drag models in CFD-DEM simulations with the superquadric approach to model the particle shape. The drag model according to Sanjeevi et al. showed the best agreement. With this model, cylindrical particles were simulated in a rotor granulator and the particle dynamics were compared with the fluidization of volume equivalent spherical particles.
Drawing on theorising on digital technologies as external enablers of entrepreneurial activities and an interactionist perspective on corporate entrepreneurship, this article examines the relationship between digital technology support and employee intrapreneurial behaviour. We propose that management support for innovation as an organisational characteristic and intrapreneurial self-efficacy as an individual characteristic moderate this relationship. Findings from a metric conjoint experiment with 1360 decisions nested within 85 employees showed that support by social media, support by collaborative technologies, and support by intelligent decision support systems were significant predictors of employee intrapreneurial behaviour. However, the relative impact of support by these digital technologies varied with different levels of management support for innovation and intrapreneurial self-efficacy.
Edit distances between merge trees of scalar fields have many applications in scientific visualization, such as ensemble analysis, feature tracking or symmetry detection. In this paper, we propose branch mappings, a novel approach to the construction of edit mappings for merge trees. Classic edit mappings match nodes or edges of two trees onto each other, and therefore have to either rely on branch decompositions of both trees or have to use auxiliary node properties to determine a matching. In contrast, branch mappings employ branch properties instead of node similarity information, and are independent of predetermined branch decompositions. Especially for topological features, which are typically based on branch properties, this allows a more intuitive distance measure which is also less susceptible to instabilities from small-scale perturbations. For trees with 𝒪(n) nodes, we describe an 𝒪(n4) algorithm for computing optimal branch mappings, which is faster than the only other branch decomposition-independent method in the literature by more than a linear factor. Furthermore, we compare the results of our method on synthetic and real-world examples to demonstrate its practicality and utility.
The direct regioselective C−H-functionalization of simple, unfunctionalized pyridines is considered a long-standing challenge in heterocyclic chemistry. Herein, we report a novel one-pot protocol for the C4-selective sulfonylation of pyridines via triflic anhydride (Tf2O) activation, base-mediated addition of a sulfinic acid salt, and subsequent elimination/re-aromatization. Contrary to previous approaches employing tailored blocking groups, positional selectivity can be controlled by using N-methylpiperidine as simple, readily available external base. This method offers a highly modular and streamlined access to C4-sulfonylated pyridines.
Janus-Materialien sind anisotrope Nano- und Mikroarchitekturen, die zwei verschiedene Seiten mit unterschiedlichen oder entgegengesetzten physikochemischen Eigenschaften aufweisen. Parallel zur Entwicklung neuer Methoden zur Herstellung dieser Materialien wurden entscheidende Fortschritte in Bezug auf Anwendungen erzielt, z. B. in der Biologie, der Katalyse, der Pharmazie und neuerdings auch in der Batterietechnologie. Dieser Kurzaufsatz stellt die jüngsten und wichtigsten Erfolge bei der Anwendung aufgabenspezifisch funktionalisierter Janus-Nanomaterialien im Bereich der heterogenen Katalyse für unterschiedliche chemische Transformationen vor. Er umfasst Reduktionreaktionen, oxidative Entschwefelung und Farbstoffabbau, asymmetrische Katalyse, Biomassetransformationen, Kaskadenreaktionen, Oxidationsreaktionen, übergangsmetallkatalysierte Kreuzkupplungsreaktionen, elektro- und photokatalytische Reaktionen sowie Gasphasenreaktionen. Zum Abschluss folgt ein Ausblick auf mögliche zukünftige Anwendungen.
Algorithms increasingly govern people's lives, including through rapidly spreading applications in the public sector. This paper sheds light on acceptance of algorithms used by the public sector emphasizing that algorithms, as parts of socio-technical systems, are always embedded in a specific social context. We show that citizens' acceptance of an algorithm is strongly shaped by how they evaluate aspects of this context, namely the personal importance of the specific problems an algorithm is supposed to help address and their trust in the organizations deploying the algorithm. The objective performance of presented algorithms affects acceptance much less in comparison. These findings are based on an original dataset from a survey covering two real-world applications, predictive policing and skin cancer prediction, with a sample of 2661 respondents from a representative German online panel. The results have important implications for the conditions under which citizens will accept algorithms in the public sector.
The development of algorithmic differentiation (AD) tools focuses mostly on handling floating point types in the target language. Taping optimizations in these tools mostly focus on specific operations like matrix vector products. Aggregated types like std::complex are usually handled by specifying the AD type as a template argument. This approach provides exact results, but prevents the use of expression templates. If AD tools are extended and specialized such that aggregated types can be added to the expression framework, then this will result in reduced memory utilization and improve the timing for applications where aggregated types such as complex number or matrix vector operations are used. Such an integration requires a reformulation of the stored data per expression and a rework of the tape evaluation process. We will demonstrate the overheads on a synthetic benchmark and show the improvement when aggregated types are handled properly by the expression framework of the AD tool.
A stereoselective synthesis of isoindolo[2,1-a]quinolin-11(5H)-ones containing three contiguous stereogenic centers is described. This Lewis-acid mediated reaction of enamides with N-aryl-acylimines affords the desired fused heterocyclic isoindolinones in high yields and diastereoselectivities. Scope and limitations of this method are discussed. The stereochemical outcome of this transformation indicates a stepwise reaction pathway.
The measurement of self-diffusion coefficients using pulsed-field gradient (PFG) nuclear magnetic resonance (NMR) spectroscopy is a well-established method. Recently, benchtop NMR spectrometers with gradient coils have also been used, which greatly simplify these measurements. However, a disadvantage of benchtop NMR spectrometers is the lower resolution of the acquired NMR signals compared to high-field NMR spectrometers, which requires sophisticated analysis methods. In this work, we use a recently developed quantum mechanical (QM) model-based approach for the estimation of self-diffusion coefficients from complex benchtop NMR data. With the knowledge of the species present in the mixture, signatures for each species are created and adjusted to the measured NMR signal. With this model-based approach, the self-diffusion coefficients of all species in the mixtures were estimated with a discrepancy of less than 2 % compared to self-diffusion coefficients estimated from high-field NMR data sets of the same mixtures. These results suggest benchtop NMR is a reliable tool for quantitative analysis of self-diffusion coefficients, even in complex mixtures.
We compute three-dimensional displacement vector fields to estimate the deformation of microstructural data sets in mechanical tests. For this, we extend the well-known optical flow by Brox et al. to three dimensions, with special focus on the discretization of nonlinear terms. We evaluate our method first by synthetically deforming foams and comparing against this ground truth and second with data sets of samples that underwent real mechanical tests. Our results are compared to those from state-of-the-art algorithms in materials science and medical image registration. By a thorough evaluation, we show that our proposed method is able to resolve the displacement best among all chosen comparison methods.
Coastal port-industrial areas are becoming increasingly significant due to urban shrinkage, population
decline, and climate change. To address social and economic issues and enhance climate resilience, it
is crucial to anticipate urban shrinkage in both stable and growing coastal areas that are undergoing
economic transformation. Urban planning can better understand the dynamics of planning for urban
shrinkage and climate resilience, as port-industrial areas have a large economic impact on nearby
coastal communities.
This dissertation examines the long-term implications of urban shrinkage in coastal port-industrial
areas in the context of climate change and sea level rise in England. The research problem is that
current urban policy does not adequately address the challenges of urban shrinkage and climate
resilience in these areas. The research questions are: What are the population changes in local areas
in England? What effect does population decline have on changing urbanisation patterns in older
industrial areas? What type of adaptation efforts were made in North East Lincolnshire, England, and
Bremerhaven, Germany, in response to the 2013 tidal surge, and how did this affect urban
shrinkage?
The dissertation applies an integrated concept of Shrinkage-Resilience as a framework for analysis.
The methodology includes a review of existing models and frameworks, as well as case studies of
international and local contexts. The findings suggest that between 2013-2019, 68% of older
industrial areas (including coastal ports) in England are undergoing changing urbanisation patterns
relative to population, land use, and green belt areas, and are key areas for urban policy, such as the
Levelling Up agenda. One of the areas, North East Lincolnshire is discussed and compared to
Bremerhaven. These examples demonstrate the link between Shrinkage-Resilience approaches and
their practical implementation in coastal port-industrial areas affected by urban shrinkage.
This research advances the scientific practice of urban planning and policy-making for shrinking cities
by introducing the approach of Shrinkage-Resilience, which emphasises the importance of
considering long-term social, economic, and environmental impacts in urban shrinkage contexts. This
approach is crucial in the transition to a more sustainable and inclusive society, where the welfare of
present and future generations, the environment, and economic development are taken into
account. The dissertation provides recommendations for urban planning to incorporate policy
changes for shrinking cities and coastal port-industrial areas worldwide, to include disaster risk
reduction and climate change adaptation approaches.
To increase situational awareness of the crane operator, the aim of this thesis is to develop a vision-based deep learning object detection from crane load-view using an adaptive perception in the construction area. Conventional worker detection methods are based on simple shape or color features from the worker's appearances. Nonetheless, these methods can fail to recognize the workers who do not wear the protective gears. To find out an image representation of the object from the top view manually or handcrafted feature is crucial. We, therefore, employed deep learning methods to automatically learn those features.
To yield optimal results, deep learning methods require mass amount of data.
Due to the data deficit especially in the construction domain, we developed the photorealistic world to create the data in addition to our samples collected from the real construction area. The simulated platform does not benefit only from diverse data types, but also concurrent research development which speeds up the pipeline at a low cost.
Our research findings indicate that the combination of synthetic and real training samples improved the state-of-the-art detector. In line with previous studies to bridge the gap between synthetic and real data, the results of preprocessed synthetic images are substantially better than using the raw data by approximately 10%.
Finding the right deep learning model for load-view detection is challenging.
By investigating our training data, it becomes evident that the majority of bounding box sizes are very small with a complex background.
In addition, we gave the priority to speed over accuracy based on the construction safety criteria. Finally, RetinaNet is chosen out of the three primary object detection models.
Nevertheless, the data-driven detection algorithm can fail to handle scale invariance, especially for detectors whose input size is changed in an extremely wide range.
The adaptive zoom feature can enhance the quality of the worker detection.
To avoid further data gathering and extensive retraining, the proposed automatic zoom method of the load-view crane camera supports the deep learning algorithm, specifically in the high scale variant problem. The finite state machine is employed for control strategies to adapt the zoom level to cope not only with inconsistent detection but also abrupt camera movement during lifting operation. Consequently, the detector is able to detect a small size object by smooth continuous zoom control without additional training.
The adaptive zoom control not only enhances the performance of the top-view object detection but also reduces the interaction of the crane operator with camera system, reducing the risk of fatality during load lifting operation.
We study the sensor fault estimation and accommodation problems in a data-driven \(\mathcal{H}_\infty\) setting, leading to a data-driven sensor fault-tolerant control scheme. First, we formulate the fault estimation problem as a finite-horizon minimax \(\mathcal{H}_\infty\)-optimization problem in a data-driven setup, whose solution yields the fault estimate. The estimated fault is then used for output compensation. This compensated output and the experimental input are used to achieve certain control objectives in a data-driven \(\mathcal{H}_\infty\) setting. Next, the data-driven \(\mathcal{H}_\infty\) fault estimation and control problems are solved using a subspace predictor-based approach. Finally, the proposed algorithm is applied to the steering subsystem of the remotely operated underwater vehicle.
Opposition parties under minority governments find themselves in a fundamental dilemma. They are competing with other parties, including the government, for electoral support while also having a common responsibility to make stable government work. This dilemma is especially pronounced for opposition parties signing support agreements with the government. While not formally in a coalition, they nonetheless publicly commit to supporting a government. They may thus be concerned about losing distinctiveness and have an interest in strategically timing cooperation with the minority government. The present paper tests whether this is the case using data on opposition party voting on committee proposals from 23 years of Swedish minority governments between 1991 and 2018. The findings indicate that support parties are less likely to support the government towards the beginning and end of the election cycle, that is, when public attention is intense – a pattern that is not observable for other opposition parties.
With direct laser writing micro structures can be manufactured by solidifying a photo resist when the laser beam triggers a photochemical reaction in the focal voxel. We have used direct laser writing to fabricate a thermally actuated microgripper, which can move its two cantilever like arms to grip micro-objects. One cantilever consists thereby of two strips with different coefficients of thermal expansion such that both cantilevers bends towards each other for an increasing temperature like a welded bimetal.This work investigates the impact of each cantilever's geometry on the gripping performance of the micro gripper theoretically. The tip deflection of the gripper is calculated by the analytical model of Timoshenko's theory of elasticity. After fabricaiton of the microgripper, its gripping performance is observed under the microscope while heated by a heating element.
The quality of risk reports: Integrating requirement levels of standard setters into text analysis
(2021)
The intention of this paper is to shed light on the analysis of financial disclosure through the integration of requirement levels. This in return will lead to the development of a general applicable evaluation methodology based on Bloom's taxonomy system. Therefore, it will be possible to explicitly consider the relevance of the given information. To underline the appropriateness of our method, we combine the requirement levels with a qualitative content analysis. Based on the German accounting standard DRS 20, we clarify the respective application of the requirement levels in the context of the qualitative content analysis. Hence, we will discuss the limitations of our developed approach. In addition, we analyze further areas of application in the context of qualitative analysis of financial disclosure. All things considered, it is evident that our chosen approach, through the integration of a taxonomy system, contributes to the validity of established text analyzing methods.
Firn describes the interstage product between snow and ice in cold regions of the earth, where annual snow fall exceeds the amount of snow melting. The continuing accumulation of snow leads to its densificiation due to overburden stress until it becomes ice. In the field of glaciology various attempts on simulating firn densification have been made and new models are still developed, as the knowledge of the firn column's density structure allows important derivations.
The presented study reassesses a model description for low density firn based on the process of grain boundary sliding presented by Alley in 1987 [1] using an optimisation approach. By comparing simulation results to 159 measured firn density profiles from Greenland and Antarctica it finds a possible additional dependency of the constitutive relation on the mean surface mass balance. This result is interpreted as an insufficient description of the stress regime.
Disorder and photonics have long been seen as natural adversaries and designers of optical systems have often driven systems to perfection by minimizing deviations from the ideal design. Especially in the field of photonic crystals and metamaterials but also for optical circuits, disorder has been avoided as a nuisance for many years. However, starting from the very robust structural colors found in nature, scientists learn to analyze and tailor disorder to achieve functionalities beyond what is possible with perfectly ordered or ideal systems alone. This review article covers theoretical and materials aspects of tailored disorder as well as experimental results. Furthermore selected examples are highlighted in greater detail, for which the intentional use of disorder adds additional functionality or provides novel functionality impossible without disorder.
A novel method for the synthesis of nitro fatty acids (NFAs), an intriguing class of endogenously occurring lipid mediators, is reported. This one-pot procedure enables the controlled and stereoselective construction of nitro fatty acids from a simple set of common building blocks in a highly facile manner. Thereby, this methodology offers a streamlined, highly modular access to naturally occurring nitro fatty acids as well as non-natural NFA derivatives.
Sulfones play a pivotal role in modern organic chemistry. They are highly versatile building blocks and find various applications as drugs, agrochemicals, or functional materials. Therefore, sustainable access to this class of molecules is of great interest. Herein, the goal was to provide a summary on recent developments in the field of sustainable sulfone synthesis. Advances and existing limitations in traditional approaches towards sulfones were reviewed on selected examples. Furthermore, novel emerging technologies for a more sustainable sulfone synthesis and future directions were discussed.
A concept for the quantification of cooperative effects in transition-metal complexes is presented. It is demonstrated for a series of novel N,N- (mononuclear) and C,N-coordinated homo- and heterometallic binuclear complexes based on the (2-dimethylamino)-4-(2-pyrimidinyl)pyrimidine ligand, which are accessible by applying roll-over cyclometallation. These iridium-, platinum-, and palladium-containing compounds are investigated with respect to their absorption and fluorescence spectra. The cooperative effects in the electronic absorptions, i. e., the energetic shifts between mononuclear and dinuclear complexes, and free ligands are analyzed on the basis of the lowest energy π-π* transitions and compared to calculated data, obtained from TD-DFT calculations. Furthermore the corresponding fluorescence spectra are presented and analyzed with respect to the concept of cooperativity.
Aquatic habitats are closely linked to the adjacent riparian area. Fluxes of nutrients, energy and matter through emerging aquatic insects are a key component of the aquatic subsidy to terrestrial systems. In fact, adult insects serve as high-quality prey for riparian predators. Stressors impacting the aquatic subsidy can thus translate to consequences for the receiving terrestrial food web, while mechanistic knowledge is extremely limited. Against this background, this thesis aimed at (i) assessing the impact of a model stressor specifically targeting insect emergence, that is the mosquito control agent Bacillus thuringiensis var. israelensis, on quantity, temporal dynamics and (ii) quality of emerging aquatic insects. For this purpose, outdoor floodplain pond mesocosms (n = 6) were employed. Since emergence is, in most cases, no point event but occurs over a longer period emergence was monitored over 3.5 months. The model stressor, i.e., Bti applied three times during spring at 2.88 × 10^9 ITU/ha, shifted the emergence time of aquatic insects, especially of non-biting midges (Diptera: Chironomidae), by ten days with a 26% reduced peak, while the nutrient content was not altered. On this basis, (ii) the propagation of the effects in aquatic subsidy emergence to riparian predators was investigated. Stable isotope analyses were used to assess the diet of a model predator, that is the web-building riparian spider Tetragnatha extensa. Results suggested changes in the composition of the spider’s diet to replace missing Chironomidae by other aquatic and terrestrial prey organisms pointing to further negative consequences. Finally, the thesis aimed at (iii) the understanding of processes underlying an altered emergence of aquatic subsidy mainly consisting of chironomids. Using a laboratory-based test design, populations of Chironomus riparius (n = 6) were assessed for their sensitivity towards Bti under different food qualities (high and low nutritious) before and after a long-term (six months) Bti exposure. Signs of phenotypic adaptation were observed in emergence time and nutrient content over multiple generations, resulting in changes in chironomids’ quantity and quality as food source. Overall, it can be concluded that direct and indirect effects of an aquatic stressor, as well as the adaptive response to it, can alter ecosystems at different levels, including individual, population and community level. Furthermore, this thesis highlights the importance of a temporal perspective when investigating the impact of aquatic stressors beyond ecosystem boundaries. It illustrates potential bottom-up effects on riparian predators through altered emergence of aquatic insects, feeding our understanding of meta-ecosystems and how stressors and their effects are transferred across systems. These insights will support efforts to protect and conserve natural ecosystems.
In nanobiotechnology, viral nanoparticles have come into focus as interesting nano building blocks. In this context, the formation of 2D and 3D structures is of particular interest. Herein, the creation of defined 2D patterns of an icosahedral plant virus, the tomato bushy stunt virus (TBSV), by means of different techniques is reported on: the top-down lithography ebeam and focused ion beam (FIB) as well as the bottom-up fluidic force microscope (FluidFM) approach. The obtained layer structures are imaged by scanning force and scanning electron microscopy. The data show that a defined 2D structure can successfully be created either top down by FIB or bottom up by FluidFM. Electron beam lithography is not able to remove viruses from the substrate under the chosen conditions. FIB has an advantage if larger areas covered with viruses combined with smaller areas without being desired. FluidFM is advantageous if only small areas with viruses are required. A further benefit is that the uncovered areas are not affected. The pattern formation in FluidFM is influenced not only by the spotting parameters, but in particular by the drying process. Deegan and Marangoni effects are shown to play a role if the spotted droplets are not very small.
A highly diastereoselective one-pot synthesis of the 1,3-diamino-2-alcohol unit bearing three continuous stereocenters is described. This method utilizes 2-oxyenamides as a novel type of building block for the rapid assembly of the 1,3-diamine scaffold containing an additional stereogenic oxygen functionality at the C2 position. A stereoselective preparation of the required (Z)-oxyenamides is reported as well.
In the present work, microfibrillar composites (MFCs) consisting of polypropylene (PP) and poly(ethylene terephthalate) (PET) were successfully produced by melt extrusion and cold stretching. The resulting filaments were then printed using fused filament fabrication. The morphological results demonstrate that the highly oriented PET fibrils after stretching are still well preserved in the printed components. Since the printing process defines the alignment of the fibrils in the final component the fibers can be perfectly adapted to the load paths. Comparative analyses of the mechanical properties reveal that the PET fibrils act as an effective reinforcement in the 3D printed components, resulting in the superior mechanical performance of the PP/PET MFCs compared to a PP/PET blend and a neat PP. Due to the combination of material and innovative processing, the study opens up a new way of using the morphology-based enormous potential of polymer fibers for lightweight, cost-effective and recyclable full polymer solutions in compact components.
Turbulence models, which are a means to fix the closure problem arising from Reynolds averaging of Navier-Stokes equations, are economical stop-gaps but suffer from accuracy issues. Modifying turbulence models by incorporating corrections in their functional form is one approach to improve their accuracy. We estimate correction functionals for the Spalart - Allmaras turbulence model, based on an inverse problem with PDE constraints emphasizing the issue of regularization.
Tribological systems are often characterized based on time-averaged quantities such as wear rates, friction coefficients and material properties. It is well known that some tribological metrics show variations depending on the laboratory conducting the study and the reproduction method selected. Perhaps the key to overcome this problem is to avoid a strong compression of the information generated. In this context, the arising forces and the coefficient of friction in three-body wear systems are investigated in more detail. The mean value of a time series of these physical quantities is only a single property and by no means an exhaustive description. A more detailed consideration of the variances could be a necessary condition to allow an appropriate comparison of tribological parameters and a correct interpretation of the properties of tribological systems. For this purpose, we examine two very simple tribological systems exemplarily and take a closer look at the properties of some characteristic process quantities.
Palladium-Catalyzed Decarboxylative 1,2-Addition of Carboxylic Acids to Glyoxylic Acid Esters
(2021)
The formation of C−C-bonds constitutes one of the most fundamental synthetic operations in organic chemistry. The nucleophilic addition of preformed organometallic reagents to an electrophilic carbonyl functionality represents a classical method for the selective construction of a C−C-bond. However, the synthesis and utilization of an organometallic reagent is associated with an unfavorable environmental profile. Herein, we disclose a Palladium-catalyzed decarboxylative 1,2-addition of carboxylic acids to glyoxylic acid esters. This novel method provides access to the mandelic acid scaffold in good yields. Easy-to-handle and readily available benzoic acids are utilized as more sustainable alternative to preformed organometallic nucleophiles.
Es wird eine hochgradig diastereoselektive Eintopf-Synthese der 1,3-Diamino-2-Alkohol-Einheit mit drei fortlaufenden Stereozentren beschrieben. Bei dieser Methode werden 2-Oxyenamide als neue Bausteine für den raschen Aufbau des 1,3-Diamin-Gerüsts, mit einer zusätzlichen stereogenen Sauerstofffunktionalität in C2-Position, eingesetzt. Zusätzlich wird über eine stereoselektive Synthese der erforderlichen (Z)-Oxyenamide berichtet.
Using the mixed-metal approach, a direct synthesis route at ambient pressure was developed for a new type of bimetallic metal-organic framework based on the CPO-27 structure. The structural characterization of CPO-27(Cu0.6−CS−Co0.4) using X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray mapping and X-ray absorption spectroscopy revealed that the Cu2+ and Co2+ ions were exclusively incorporated at the metal positions of the CPO-27 lattice, but with a core-shell distribution within the crystallites. The parent framework material was then utilized as a precursor for the generation of novel bimetallic carbon-supported materials using the controlled thermal decomposition in a reducing atmosphere. During this decomposition process, the distribution of the two metals remained the same, which resulted in unique needle-shaped particles with a high dispersion of cobalt at the periphery of the amorphous carbon and agglomerated copper particles in the inside.