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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.
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.
Metal-organic frameworks (MOFs) have gained increasing attention in the last four decades due to their versatility and unique properties. They are often used as catalysts because they combine advantageous properties of both heterogeneous and homogeneous catalysts. Noble metals are very active in catalysis, but they are expensive, sometimes toxic to the environment and very rare. Therefore, the demand for the substitution of noble metals by commonly available metals such as iron or cobalt is of interest. The complexity and versatility of MOF materials is further enhanced by the use of mixed-linker and mixed-metal approaches or post-synthetic modification reactions.
The aim of this PhD project was to synthesize and characterize MOF-based catalysts which contain Co and Fe and to test the resulting materials in the liquid phase oxidation reaction of alcohols. In the first part of this work, mixed-metal CPO-27(Co,Fe) with three different metal ratios and two different spatial distributions were prepared. The spatial distributions of the metals were either statistically distributed or a core-shell orientation. The resulting catalysts were characterized by powder X-ray diffraction, thermogravimetric analysis and ICP-OES analysis. The results confirmed that the catalysts were highly porous, corresponded to the CPO 27 structure and that the amounts of metals were close to the desired ratios. The materials were then tested in oxidation reactions of benzyl alcohol and 1-phenylethanol. For the parameter optimization, the highly active monometallic CPO-27(Co) catalyst was used and parameters such as temperature and the amount of catalyst, substrate or oxidant (air) were investigated. Bimetallic CPO-27(Co,Fe) catalysts were then tested with the optimized parameters and both conversion and selectivity were compared to the monometallic CPO 27(Co) reference. In general, the rare and expensive cobalt can be partially replaced by cheap but inactive iron without affecting the catalytic activity and in some cases, the distribution of the metals in the MOF lattice have an effect on the catalytic performance.
In the second part of this work, the previously synthesized CPO-27(Co,Fe) catalysts were thermally decomposed in an inert atmosphere to obtain metal species which are encapsulated in a porous carbonaceous matrix via the so called MOF-mediated synthesis. The decomposition was expected to result in unique materials that could not be synthesized by any other route. The resulting materials were characterized by powder X-ray diffraction, N2 physisorption and ICP-OES analysis. The characterization revealed differences between materials prepared from statistically distributed and core-shell-structured CPO-27(Co,Fe). These catalysts were also tested in the oxidation of benzyl alcohol and compared not only within this series but also with the CPO-27 precursors, showing that in some cases the thermally decomposed materials were even more catalytically active than their MOF precursors.
In the last part of this thesis, Co,Fe DUT-5-based catalysts with core-shell structure and statistical distribution, respectively, were synthesized. The first step was to prepare a DUT-5-based framework. For the statistically distributed material, 4,4'-biphenyldicarboxylate, 2,2' bipyridine-5,5'-dicarboxylate and 2-amino-4,4'-biphenyldicarboxylate linkers were mixed with an aluminum salt precursor. The 2,2'-bipyridine-5,5'-dicarboxylate linkers were then used to directly immobilize cobalt ions. The amine-functionalized linkers were post-synthetically modified with salicylaldehyde and the resulting chelating groups were finally used for the immobilization of iron ions. The core-shell backbone consisted of 4,4'-biphenyldicarboxylate and 2,2'-bipyridine-5,5'-dicarboxylate in the core. The first shell contained only unfunctionalized 4,4' biphenyldicarboxylate and the outer shell consisted of a mixture of 2 amino-4,4'-biphenyldicarboxylate and 4,4'-biphenyldicarboxylate linkers. The post-synthetic reactions were then performed analogously to the statistically distributed materials: (1) cobalt immobilization at the bipyridine linkers, (2) insertion of chelating groups at the amine linkers and (3) iron immobilization. All materials were thoroughly characterized after each synthesis step using powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, N2 physisorption and ICP-OES analysis. The linker ratios were calculated by 1H NMR of diluted samples. The results confirmed the formation of a porous material with a DUT-5 structure, but the spatial distribution could not be confirmed unambiguously by the methods used. Both materials were tested, together with a monometallic DUT-5 BPyDC(Co) reference, in oxidation reactions cinnamyl alcohol. The results showed significant differences between the statistically distributed and core-shell catalysts, providing evidence for the difference in spatial orientations and the symergistic effects of the two metals.
In summary, novel MOF materials containing Co and Fe were synthesized, characterized and tested in oxidation reactions of primary and secondary alcohols under aerobic conditions. The results confirmed that in some cases a part of rare cobalt could be replaced by cheap and widely available iron without decreasing the catalytic activity and selectivity. In addition, the spatial distribution of the metals can have a direct and massive influence on the catalytic properties and therefore, a thorough characterization is a very important part of the synthesis process.
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.
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.
Weyl points are point degeneracies that occur in momentum space of 3D periodic materials and are associated with a quantized topological charge. Here, the splitting of a quadratic (charge-2) Weyl point into two linear (charge-1) Weyl points in a 3D micro-printed photonic crystal is observed experimentally via Fourier-transform infrared spectroscopy. Using a theoretical analysis rooted in symmetry arguments, it is shown that this splitting occurs along high-symmetry directions in the Brillouin zone. This micro-scale observation and control of Weyl points is important for realizing robust topological devices in the near-infrared.
Based on experimental pure component data for the characterization of the isostructural imidazolate framework Potsdam (IFP) series reported in Part I, a model for the simulation of non-isothermal dynamic adsorption of CO2/CH4-mixtures in fixed-bed columns is presented in this Part II. The robustness of the model is examined and validated, by comparison to experimental breakthrough data at different process conditions, such as varying concentration, temperature, and pressure. Thereby, different predictive methods for the estimation of adsorption equilibria of mixtures are compared (RAST, IAST, ML). The results show that ideal behaviour can be assumed with good accuracy for the system under consideration, except for IFP-2, which shows significant deviations at increased pressures and temperatures. A detailed kinetic analysis reveals that mass transfer is significantly influenced by micropore diffusion. Thus, only for IFP-1 the dynamic separation of CO2 and CH4 is equilibrium-driven, while for the remaining IFPs the kinetic regime dominates the process, which in some cases increases the separation efficiency (IFP-2 to -7) but can also inhibit it (IFP-8). The determined intracrystalline diffusion coefficients show very good agreement with values for metal organic framework (MOF) compounds of similar structure reported in the literature.
It is known from the literature that freedom from macroscopic defects (voids) is an essential prerequisite for good mechanical properties of 3D-printed components manufactured using fused filament fabrication. The present study further shows that the morphology and mechanical properties of void free components are significantly influenced by the choice of process parameters. Components that were printed at low temperatures and high speeds show fair and inhomogeneous supermolecular morphology, clearly visible weld seams and a special flow-induced staggered structure of the individual strands laid-up. At higher magnification in the optical microscope, transcrystalline structures are visible starting from the contact area between the strands, that is, crystallization has started at the interface between the strands and is moving forward towards the center of the strands. In contrast, the samples printed at high temperatures and low speeds show a homogeneous supermolecular morphology with overall larger spherulites and a higher degree of crystallinity and compared to the specimens printed with the low temperature/high speed-set much better mechanical properties. A numerical simulation of the temperature at the contact point of the strand emerging from the hot nozzle and the cooled strand neighbor agrees well with the measured behavior. The thermal simulation thus enables the temperature to be calculated at any point in time in the welding contact and thus access to the local thermal conditions during joining, cooling and the formation of the morphology.
Lattice Boltzmann methods [1] have been extended beyond their initial usage in transport problems, and can be used to solve a broader range of partial differential equations, e.g. the wave equation [2]. Thereby they can be utilized for fracture mechanics [3]. In the context of antiplane shear deformation we previously examined a stationary crack [4, 5] with a finite width. In this work we present two implementation strategies for non-mesh conforming boundary conditions, for which the bounding geometry does not need to adhere to the underlying lattice. This rectifies problems in modeling the crack. A numerical example shows the improvement compared to the previous results.
The influence of the specimen size of ultra-high-performance fibre-reinforced concrete samples on the spatial distribution and orientation of the steel fibres is investigated. Specimens of varying size are produced by using the same protocol. They are imaged by micro-computed tomography to perform a statistical analysis of the spatial arrangement of the fibres. The tensile strength of the specimens is measured by tensile tests on subspecimens of equal size. The results are correlated to geometric characteristics of the fibre systems determined from the image data. Increasing the specimen size results in a larger variability of the local fibre geometry. This effect was most prominent when increasing the height of the specimens.
The formation of protein aggregates is a hallmark of neurodegenerative diseases. Observations on patient samples and model systems demonstrated links between aggregate formation and declining mitochondrial functionality, but causalities remain unclear. We used Saccharomyces cerevisiae to analyze how mitochondrial processes regulate the behavior of aggregation‐prone polyQ protein derived from human huntingtin. Expression of Q97‐GFP rapidly led to insoluble cytosolic aggregates and cell death. Although aggregation impaired mitochondrial respiration only slightly, it considerably interfered with the import of mitochondrial precursor proteins. Mutants in the import component Mia40 were hypersensitive to Q97‐GFP, whereas Mia40 overexpression strongly suppressed the formation of toxic Q97‐GFP aggregates both in yeast and in human cells. Based on these observations, we propose that the post‐translational import of mitochondrial precursor proteins into mitochondria competes with aggregation‐prone cytosolic proteins for chaperones and proteasome capacity. Mia40 regulates this competition as it has a rate‐limiting role in mitochondrial protein import. Therefore, Mia40 is a dynamic regulator in mitochondrial biogenesis that can be exploited to stabilize cytosolic proteostasis.
As additive manufacturing offers only low surface quality, a subsequent machining of functional and highly loaded areas is required. Thus, a sound knowledge of the interrelation between the additive and subtractive manufacturing process as well as the resulting mechanical properties is indispensable. In this work, specimens were manufactured by using laser-based powder bed fusion (L-PBF) with substantially different sets of process parameters as well as subsequent grinding (G) or milling (M). Despite the substantially different surface topographies, the fatigue tests revealed only a slight influence of the subtractive manufacturing on the fatigue behavior, whereas the different laser-based powder bed fusion process parameters led to pronounced changes in fatigue strength. In contrast, a significant influence of subtractive finishing on the fatigue properties of the defect-free continuously cast (CC) reference specimens was observed. This can be explained by a dominating influence of process-induced defects in laser-based powder bed fusion material, which overruled the influence of surface machining. However, although both laser-based powder bed fusion parameter sets resulted in substantial defects, one set yielded similar fatigue strength compared to continuously cast specimens.
We show that every convergent power series with monomial extended Jacobian ideal is right equivalent to a Thom–Sebastiani polynomial. This solves a problem posed by Hauser and Schicho. On the combinatorial side, we introduce a notion of Jacobian semigroup ideal involving a transversal matroid. For any such ideal, we construct a defining Thom–Sebastiani polynomial. On the analytic side, we show that power series with a quasihomogeneous extended Jacobian ideal are strongly Euler homogeneous. Due to a Mather–Yau-type theorem, such power series are determined by their Jacobian ideal up to right equivalence.
An FEM-based physical force model is an important step to obtain a full understanding of the grinding process itself. Such a physical force model is already under development and is based on Abaqus-FEM. In order to examine basic material behavior and material parameters for such a physical force model and to validate it, scratch tests have been carried out with single grains. However, the current physical force model is only designed for grinding processes that do not require cooling lubricants. Therefore, the aim of this work is to extend this physical force model in such a way that grinding processes with cooling lubricants can also be considered. In order to include the cooling lubricants in the FEM model, it is essential to carry out scratch tests with cooling lubricants in addition to the scratch tests in a dry environment. The aim is to identify basic mechanisms in connection with cooling lubricants, which are needed to expand the FEM model and to create a data basis for subsequent validation.
The German energy mix, which provides an overview of the sources of electricity available in Germany, is changing as a result of the expansion of renewable energy sources. With this shift towards sustainable energy sources such as wind and solar power, the electricity market situation is also in flux. Whereas in the past there were few uncertainties in electricity generation and only demand was subject to stochastic uncertainties, generation is now subject to stochastic fluctuations as well, especially due to weather dependency. To provide a supportive framework for this different situation, the electricity market has introduced, among other things, the intraday market, products with half-hourly and quarter-hourly time slices, and a modified balancing energy market design. As a result, both electricity price forecasting and optimization issues remain topical.
In this thesis, we first address intraday market modeling and intraday index forecasting. To do so, we move to the level of individual bids in the intraday market and use them to model the limit order books of intraday products. Based on statistics of the modeled limit order books, we present a novel estimator for the intraday indices. Especially for less liquid products, the order book statistics contain relevant information that allows for significantly more accurate predictions in comparison to the benchmark estimator.
Unlike the intraday market, the day ahead market allows smaller companies without their own trading department to participate since it is operated as a market with daily auctions. We optimize the flexibility offer of such a small company in the day ahead market and model the prices with a stochastic multi-factor model already used in the industry. To make this model accessible for stochastic optimization, we discretize it in time and space using scenario trees. Here we present existing algorithms for scenario tree generation as well as our own extensions and adaptations. These are based on the nested distance, which measures the distance between two distributions of stochastic processes. Based on the resulting scenario trees, we apply the stochastic optimization methods of stochastic programming, dynamic programming, and reinforcement learning to illustrate in which context the methods are appropriate.
Diafiltration of Highly Concentrated Suspensions with Fine Particles by Dynamic Disk Filtration
(2021)
A method for washing highly concentrated suspensions with fine particles by using a filter with overlapping disks was studied. For the experiments, alumina and titanium dioxide suspensions were used. It was demonstrated that the used suspensions have non-Newtonian behavior. The viscosity is influenced by the type of particle system, the solid concentration, and the shear rate. The washing process is operated in a discontinuous and a continuous way. The rotation of the disks and the shear flow across their surface prevents the formation of a filter cake and facilitates the handling of suspensions. The shear stresses at the filter disk and the rheology of the processed suspensions are both influenced by the type of particle system, the solid concentration, and the process parameters.
In the present study, tribological properties of PEEK/CF/nanosilica composites with distinct amounts of silica nanoparticles against steel were studied by using a block-on-ring tribometer followed by the characterizations of associated transfer films and polymer worn surfaces. The results demonstrate that the content of silica nanoparticles exerts an obvious influence on the friction and wear properties of PEEK/CF/nanosilica composites. Under low-load conditions, the friction coefficient and specific wear rate exhibit opposite dependence on the nanosilica content. The friction coefficient decreases with increasing nanofiller content, while the specific wear rate increases with enhancing nanosilica loading. When the load conditions were changed toward high values, the divergence of the tribological properties becomes insignificant, which show less dependence on the nanosilica loading. Taking into account the practical applications of such composites, the composite containing 2 wt.% silica nanoparticles can serve as an excellent candidate for manufacturing tribological components in the practical applications.
Design improvement by a simulative investigation of the locomotion of a snake-like soft robot
(2021)
This work aims to improve the design of a snake-like soft robot in terms of its velocity of locomotion by a geometric model. Therefore, we determine the locomotion of the snake-like soft robot as the result of a given excitation curvature and a given friction anisotropy between the robot and the ground.Varying the design parameters of the robot in the model allows to identify important parameters to increase the velocity of locomotion of the snake-like soft robot. Whereas its body design is sufficient, the transverse friction of its artificial skin is the main parameter to be improved. The transverse friction can be adjusted by turning the scales of the artificial skin. The velocity of locomotion of the robot increases significantly by this simple trick.
Formaldehyde is an important chemical that is mostly handled in aqueous solutions, which generally also contain methanol; furthermore, also solutions of formaldehyde in other alcohols are used. The density of these solutions is an important thermophysical property. The available models of the density of formaldehyde-containing solutions, however, all have shortcomings, such as a poor accuracy or a limited range of applicability. Therefore, in the present work, a new model of the density in systems of the type (formaldehyde + water + alcohol) was developed. The alcohols that are presently included in the new model are methanol, 1-propanol, and isoprenol; an extension to other alcohols is straightforward. The model was developed using literature data and extensive new density data measured in this work covering binary, ternary, and quarternary solutions of formaldehyde in water, methanol, 1-propanol, and isoprenol at temperatures of 283−333 K and formaldehyde concentrations of 0.06 − 0.30 g g−1.
Metastable austenitic CrNi steels undergo phase transformation when loaded or deformed plastically. In the current work a macroscopic and phenomenological constitutive model is presented to model the strain induced transformation of austenite to martensite. The approach is based on the previous works of Olsen and Cohen [1] & Stringfellow et al. [2]. The kinetics of the phase transformation is modelled based on the assumption that the intersections of the shear bands in the austenitic phase, act as potential martensite nucleation locations. Evolution of the shear band density and their intersections are modelled using the plastic strain in the austenitic phase. The probability of the intersection creating martensite is given by a Gaussian cumulative distribution, which in turn depends on the temperature and stress triaxiality. The resulting stress- strain behavior considers the volume fraction, plastic strains and the strain hardening parameters of the individual phases as internal variables. An explicit formulation of the material model is implemented as a user subroutine in a bi-linear element formulation of FEM. Some of the required material parameters are estimated by fitting experimental stress-strain and martensite volume evolution curves. For the purpose of illustrating the model's behavior, boundary value problems of components with structured surfaces are presented.
The Lattice Boltzmann Method (LBM), e.g. in [1] and [2], can be interpreted as an alternative method for the numerical solution of certain partial differential equations that is not restricted to its origin in computational fluid mechanics. The interpretation of the LBM as a general numerical tool allows to extend the LBM to solid mechanics as well, see e.g. [3], which is concerned with the simulation of elastic solids under simplified deformation assumptions, and [4] as well as [5] which propose LBMs for the general plane strain case. In previous works on a LBM for plain strain such as [5], the treatment of practically relevant boundary conditions like Neumann and Dirichlet type boundary conditions is not the main focus and thus periodic conditions or absorbing layers are specified to simulate numerical examples. In this work, we show how Neumann and Dirichlet type boundary conditions are implemented in our LBM for plane strain from [4].
Automated investment management: Comparing the design and performance of international robo-managers
(2021)
Robo-managers offer automated asset management; however, their overall performance is highly debated. We analyze 15 robo-managers from Germany, the United States and the United Kingdom by conducting a comprehensive qualitative and quantitative study. The qualitative comparison shows considerable differences between the various robo-managers, not only across but also within countries. The quantitative evaluation utilizes different measures to evaluate the performance of the robo-manager sample. Our results indicate that each country has one particularly favourable robo-manager. Furthermore, we find that the costs and characteristics of rebalancing measures have only a small effect on performance.
Spin Hamiltonian parameters of a pentanuclear Os Ni cyanometallate complex are derived from ab initio wave function based calculations, namely valence-type configuration interaction calculations with a complete active space including spin-orbit interaction (CASOCI) in a single-step procedure. While fits of experimental data performed so far could reproduce the data but the resulting parameters were not satisfactory, the parameters derived in the present work reproduce experimental data and at the same time have a reasonable size. The one-centre parameters (local matrices and single-ion zero field splitting tensors) are within an expected range, the anisotropic exchange parameters obtained in this work for an Os−Ni pair are not exceedingly large but determine the low-T part of the experimental χT curve. Exchange interactions (both isotropic and anisotropic) obtained from CASOCI have to be scaled by a factor of 2.5 to obtain agreement with experiment, a known deficiency of such types of calculation. After scaling the parameters, the isotropic Os−Ni exchange coupling constant is cm−1 and the D parameter of the (nearly axial) anisotropic Os−Ni exchange is −1, so anisotropic exchange is larger in absolute size than isotropic exchange. The negative value of the isotropic J (indicating antiferromagnetic coupling) seemingly contradicts the large-temperature behaviour of the temperature dependent susceptibility curve, but this is caused by the negative g value of the Os centres. This negative g value is a universal feature of a pseudo-octahedral coordination with configuration and strong spin-orbit interaction. Knowing the size of these exchange interactions is important because Os(CN) is a versatile building block for the synthesis of / magnetic materials.
Finishing processes result in changes of near-surface morphology, which strongly influences the fatigue behavior of components. Especially, roller bearings show a high dependency of the lifetime on surface roughness and the residual stress state in the subsurface volume. To analyze the influence of different finishing processes on the near-surface morphology, including the residual stress state, roller bearing rings made of AISI 52100 are finished in this work using hard turning, rough grinding, and fine grinding. In addition, fatigue specimens made of AISI 52100 and finished by cryogenic hard turning are investigated. For each condition, the residual stresses are determined at different distances from the surface, showing pronounced compressive stresses for all conditions. While the ground roller bearing rings show highest compressive residual stresses at the surface, the hard turned bearing ring and the cryogenic hard turned fatigue specimens reveal maximum compressive stresses in the subsurface volume. Moreover, cyclic indentation tests (CITs) are conducted in the different subsurface volumes, showing a higher cyclic plasticity in relation to the respective initial state, which is assumed to be caused by finishing-induced compressive residual stresses. Thus, the presented results indicate a high potential of CITs to efficiently characterize the residual stress state.
Surface wetting can be described by using phase field models [1]. In these models, often either the contact angle or the surface tensions between the solid and the fluid are prescribed directly on the wall in order to represent the solid-fluid interaction. However, the interaction of the wall and the fluid are not strictly local. The influence of the wall, which can be described by wall potentials [2], reaches out into the fluid, which is the reason for the formation of adsorbate layers. The investigation shows how such a wall potential can be included into a phase field model of wetting. It is found that by considering this energy contribution, the model is able to capture the adsorbate layer.
Fracture phenomena can be described by a phase field model in which an independent scalar field variable in addition to the mechanical displacement is considered [3]. This field approximates crack surfaces as a continuous transition zone from a value that indicates intact material to another value that represents the crack. For an accurate approximation of cracks, narrow transition zones resulting in steep gradients of the fracture field are required. This necessitates a high mesh density in finite element simulations, which leads to an increased computational effort. In order to circumvent this problem without forfeiting accuracy, exponential shape functions were introduced in the discretization of the phase field variable, see [4]. These special shape functions allow for a better approximation of steep gradients of the phase field with less elements as compared to standard Lagrange elements. Unfortunately, the orientation of the exponential shape functions is not uniquely determined and needs to be set up in the correct way in order to improve the approximation of smooth cracks. This work solves the issue by adaptively reorientating the exponential shape functions according to the nodal values of the phase field gradient in each element. Furthermore, a local approach is pursued that uses exponential shape function only in the vicinity of the crack, whereas standard bilinear shape function are used away from the crack.
Nucleophilic substitution of [(η5-cyclopentadienyl)(η6-chlorobenzene)iron(II)] hexafluorophosphate with sodium imidazolate resulted in the formation of [(η5-cyclopentadienyl)(η6-phenyl)iron(II)]imidazole hexafluorophosphate. The corresponding dicationic imidazolium salt, which was obtained by treating this imidazole precursor with methyl iodide, underwent cyclometallation with bis[dichlorido(η5-1,2,3,4,5-pentamethylcyclopentadienyl]iridium(III) in the presence of triethyl amine. The resulting bimetallic iridium(III) complex is the first example of an NHC complex bearing a cationic and cyclometallated [(η5-cyclopentadienyl)(η6-phenyl)iron(II)]+ substituent. As its iron(II) precursors, the bimetallic iridium(III) complex was fully characterized by means of spectroscopy, elemental analysis and single crystal X-ray diffraction. In addition, it was investigated in a catalytic study, wherein it showed high activity in transfer hydrogenation compared to its neutral analogue having a simple phenyl instead of a cationic [(η5-cyclopentadienyl)(η6-phenyl)iron(II)]+ unit at the NHC ligand.
VIPP proteins aid thylakoid biogenesis and membrane maintenance in cyanobacteria, algae, and plants. Some members of the Chlorophyceae contain two VIPP paralogs termed VIPP1 and VIPP2, which originate from an early gene duplication event during the evolution of green algae. VIPP2 is barely expressed under nonstress conditions but accumulates in cells exposed to high light intensities or H2O2, during recovery from heat stress, and in mutants with defective integration (alb3.1) or translocation (secA) of thylakoid membrane proteins. Recombinant VIPP2 forms rod-like structures in vitro and shows a strong affinity for phosphatidylinositol phosphate. Under stress conditions, >70% of VIPP2 is present in membrane fractions and localizes to chloroplast membranes. A vipp2 knock-out mutant displays no growth phenotypes and no defects in the biogenesis or repair of photosystem II. However, after exposure to high light intensities, the vipp2 mutant accumulates less HSP22E/F and more LHCSR3 protein and transcript. This suggests that VIPP2 modulates a retrograde signal for the expression of nuclear genes HSP22E/F and LHCSR3. Immunoprecipitation of VIPP2 from solubilized cells and membrane-enriched fractions revealed major interactions with VIPP1 and minor interactions with HSP22E/F. Our data support a distinct role of VIPP2 in sensing and coping with chloroplast membrane stress.
The Griffith-Ley oxidation of alcohols to aldehydes and ketones is performed with either RuCl3 ⋅ (H2O)x or a highly stable, well-defined ruthenium catalyst and with cheap trimethylamine N-oxide (TMAO) as the oxygen source. The use of n-heptane as the solvent, which forms a second phase with TMAO and a part of the alcohol, allows the reactions to be performed with a minimum amount of catalyst. This results in high local concentrations and thus to very rapid conversions. Detailed quantum chemical calculations suggest, that the Griffith-Ley oxidation not necessarily requires high oxidation states of ruthenium but can also proceed with RuII/RuIV species.
Most mitochondrial proteins are synthesized in the cytosol and subsequently translocated as unfolded polypeptides into mitochondria. Cytosolic chaperones maintain precursor proteins in an import-competent state. This post-translational import reaction is under surveillance of the cytosolic ubiquitin-proteasome system, which carries out several distinguishable activities. On the one hand, the proteasome degrades nonproductive protein precursors from the cytosol and nucleus, import intermediates that are stuck in mitochondrial translocases, and misfolded or damaged proteins from the outer membrane and the intermembrane space. These surveillance activities of the proteasome are essential for mitochondrial functionality, as well as cellular fitness and survival. On the other hand, the proteasome competes with mitochondria for nonimported cytosolic precursor proteins, which can compromise mitochondrial biogenesis. In order to balance the positive and negative effects of the cytosolic protein quality control system on mitochondria, mitochondrial import efficiency directly regulates the capacity of the proteasome via transcription factor Rpn4 in yeast and nuclear respiratory factor (Nrf) 1 and 2 in animal cells. In this review, we provide a thorough overview of how the proteasome regulates mitochondrial biogenesis.
Both solid particles and column diameter affect the gas holdup and flow regimes in slurry bubble columns, but investigations of the combined effects are not to be found. This study shows the simultaneous impacts on the overall gas holdup and flow regime transitions and determines the dominant effects in slurry bubble columns on the centi-scale containing solid particle concentrations up to 20 vol %. Additional tomography measurements are presented to visualize the gas phase flow and the spatial gas phase distribution in the column.
Sulfinate salts have attracted considerable attentions due to their versatile reactivity. They have emerged as highly useful building blocks for the construction of all kinds of sulfonyl-group containing molecules, such as sulfones or sulfonamides, and for the construction of various carbon–carbon- and carbon–heteroatom-bonds via sulfur dioxide (SO2) extrusion. Herein, we want to summarize the latest developments in the synthesis of sulfinate salts. Both improvement of classical methods and the development of various novel protocols will be discussed. Also selected one-pot methods directly utilizing in situ generated sulfinate salts as intermediates will be covered in this review article.
The applicability of laser-induced dye fluorescence (LIF) and rainbow schlieren deflectometry (RSD) for qualitative, non-invasive real-time visualization of spatial concentration distributions in two standard reference systems is presented. The combination of LIF and RSD enables measurements inside and outside of droplets and is able to overcome limitations of both measurement techniques. Experimental results in the presence of interfacial phenomena are compared and the connection between inner and outer effects is shown during droplet production at a capillary.
Image-based measurement techniques become increasingly popular and expedite digitalization in chemical engineering. This article demonstrates their potential by testing two inline probes, namely modified optical multimode online probe (OMOP) and process microscope. Validations are performed with static monodisperse standards (9.2 µm to 406 µm) and fast-moving droplets (68.6 µm to 860.7 µm; 24.5 m s−1 to 11 m s−1). Screening of a lithography attests both probes great distortion-free image quality. A 1951 USAF chart attests a low optical resolution of 8 µm or 7 µm with respect to the OMOP or process microscope, respectively. The modified OMOP and process microscope reaches accuracies of 7.6 % or 5.9 % for particles and 8.2 % or 6.8 % for droplets.
Manufacturing techniques that can produce surfaces with a defined microstructure are in the focus of current research efforts. The ability to manufacture such surfaces gives rise to the need for numerical models that can predict the wetting properties of a given microstructure and can help to optimize these surfaces with respect to certain wetting properties. The present phase field (PF) model for wetting is linked to molecular dynamics (MD) simulations by the usage of the MD based perturbed Lennard-Jones truncated and shifted (PeTS) equation of state as well as a MD based viscosity correlation. The lower computational effort of the PF simulations compared to MD simulations enables the model to simulate wetting scenarios on the microscale.
In this work we illustrate the ability of a phase field model for fatigue crack growth in terms of extension capability to various amplitude loading and mean stress effects. The additional energy density contribution accounting for the energy associated with fatigue is modified in order to provide a more general model. Results obtained from numerical fatigue crack growth simulations are briefly presented and discussed.
Herein, experimental demonstration of the parallel parametric generation of spin waves in a microscaled yttrium iron garnet waveguide with nanoscale thickness is presented. Using Brillouin light scattering microscopy, the parametric excitation of the first and second waveguide modes by a stripline microwave pumping source is observed. Micromagnetic simulations reveal the wave vector of the parametrically generated spin waves. Based on analytical calculations, which are in excellent agreement with experiments and simulations, it is proved that the spin-wave radiation losses are the determinative term of the parametric instability threshold in this miniaturized system. The used method enables the direct excitation and amplification of nanometer spin waves dominated by exchange interactions. The presented results pave the way for integrated magnonics based on insulating nanomagnets.
A palladium-catalyzed three-component synthesis of α-arylglycines from benzoic acids, sulfonamides and glyoxylic acid is reported. This novel reaction offers straightforward access to the important arylglycine motif in good yields and high structural diversity. By replacing boronic with carboxylic acids as nucleophilic component, this method can be considered as a more sustainable version of the classical Petasis reaction for synthesis of arylglycines.
In this work, we investigate the locomotion of a snake-like soft robot in terms of its design. Therefore the backbone of the robot is represented by a curve in plane which is actuated by a given curvature. By adding anisotropic friction between robot and surface the robot “moves” on the surface.
With this simple model we are able to predict the locomotion of the robot for certain sets of parameters. This allows to evaluate the influence of design changes and hence to facilitate the design process. As an example, we discuss results concerning the precision of actuation, the bending radius of the robot and the influence of friction between robot and surface.
In cold regions of the earth, like Antarctica, Greenland or mountains at high altitude, the annual amount of deposited snow exceeds the amount of snow melting. Snow, which is more than one year old, is called firn. Over time firn transforms into ice by a sintering process, mainly driven by overburden pressure and temperature. This ultimately leads to the formation of glaciers and ice sheets.
We simulate firn densification based on the processes of sintering. The constitutive law represents grain boundary sliding, dislocation creep and diffusion. These mechanisms sum up to the overall densification which leads to the transformation of snow to ice. The model aims at obtaining a physics driven simulation tool for firn densification which provides data for a wider range of areas. It will contribute to develop better models and better understanding of the cryosphere.
The Lattice Boltzmann Method (LBM), e.g. in [3] and [4], can be interpreted as an alternative method for the numerical solution of partial differential equations. The LBM is usually applied to solve fluid flows. However, the interpretation of the LBM as a general numerical tool, allows to extend the LBM to solid mechanics as well. In this spirit, the LBM has been studied in recent years. First publications [5], [6] present a LBM scheme for the numerical solution of the dynamic behavior of a linear elastic solid under simplified deformation assumptions. For so-called anti-plane shear deformation, the only non-zero displacement component is governed by the two-dimensional wave equation. In this work, the existing LBM for the two-dimensional wave equation is extended to more general plane strain problems. The algorithm reduces the plane strain problem to the solution of two separate wave equations for the volume dilatation and the non-zero component of the rotation vector, respectively.
Enantiomerically pure, C2-symmetric 2,6-bis(pyrazol-3-yl) pyridine ligands were obtained by treatment of diethyl-2,6-pyridinedicarbonate with (1R,4R)-(+)-camphor in the presence of NaH followed by ring closure with hydrazine. After twofold N-alkylation at the pyrazole rings, the addition of iron(II) chloride led to the according pentacoordinate dichloridoiron(II) complexes. All intermediates of the ligand synthesis, the ligands bearing NCH3 and NCH2C6H5 groups and the derived iron(II) complexes were structurally characterized by means of X-ray structure analysis. In-situ reaction with iron(II) carboxylates resulted in the formation of iron(II) carboxylate complexes, which turned out to be highly active in the hydrosilylation of acetophenone. However, even at room temperature, the enantiomeric excess of the product 1-phenylethanol is poor. 57Fe Mössbauer spectroscopy gave an insight into the species formed during catalysis.
This DFG-funded research project aimed to gain a better understanding of the mechanisms of the W-Cl repair principle within the framework of fundamental investigations, to contribute to the creation of the necessary basis for a broader application of the repair principle in practice. The focus was on the development of a model to describe the chloride redistribution after the application of a system sealing surface protective coating. On the basis of Fick's second law of diffusion, a mathematical model with a self-contained analytical solution was developed, with the help of which the chloride redistribution after application of a system sealing surface protective coating can be calculated under the idealized assumption of complete water saturation of the concrete. Furthermore, the influence of the dehydration of the concrete, expected as a result of the application of the repair principle W-Cl, on the chloride redistribution was investigated. On the basis of laboratory tests and numerical simulations, material-specific reduction functions were developed to quantify the relationship between the chloride diffusion coefficient and the ambient humidity.
In this paper, the relationship between production parameters of ultra high performance fiber-reinforced concrete (UHPFRC) and the spatial distribution and orientation of the steel fibers is investigated. UHPFRC specimens with varying fiber diameter, fiber volume fraction, and rheology of the mixture are produced. Additionally, casting is performed from the side or the middle of the formwork. Imaging by micro computed tomography allows for a statistical analysis of the spatial arrangement of the fibers in the test specimens. The flexural behavior and the load capacity of the specimens are analyzed by four point bending tests. The results of the bending tests are well explained by characteristics of the fiber systems determined from the image data.
Virtual Possibilities: Exploring the Role of Emerging Technologies in Work and Learning Environments
(2024)
The present work aims to investigate whether virtual reality can support learning as well as vocational work environments. To this end, four studies were conducted, with the first set investigating the demands for vocational workers and the impact of input methods on participant performance. These studies laid the foundation needed to create studies incorporating virtual reality research. The second set of studies was concerned with the impact of virtual reality on learning performance as well as the influence of binaural stimuli presentation on task performance. Results of each study are discussed individually and in conjunction with one another. The four studies are further supplemented with further research conducted by the author as well as an analysis of the growing field of virtual reality-based research. The thesis closes by embedding the discussed work into the scientific landscape and tries to give an outlook for virtual reality-based use cases in the future.
The fundamental differences in hydrodynamics of the froth and spray regime account for the ongoing interest in search for the point of phase inversion. This short communication presents a new approach for identification of phase inversion on sieve trays in terms of an image-based measurement technique. Image analysis of entrained droplets reveals a distinct increase in Sauter mean diameter and droplet frequency during phase inversion. Further measurement methods like pressure drop, gravimetric analysis of entrained liquid, froth height assessment and photographic observation of the flow regime serve as a reference value and complement the discussion. A flow map based on the experimental data comprises each regime and shows a good agreement with phase inversion correlations from literature.
Algorithmic decision-making (ADM) systems have come to support, pre-empt or substitute for human decisions in manifold areas, with potentially significant impacts on individuals' lives. Achieving transparency and accountability has been formulated as a general goal regarding the use of these systems. However, concrete applications differ widely in the degree of risk and the accountability problems they entail for data subjects. The present paper addresses this variation and presents a framework that differentiates regulatory requirements for a range of ADM system uses. It draws on agency theory to conceptualize accountability challenges from the point of view of data subjects with the purpose to systematize instruments for safeguarding algorithmic accountability. The paper furthermore shows how such instruments can be matched to applications of ADM based on a risk matrix. The resulting comprehensive framework can guide the evaluation of ADM systems and the choice of suitable regulatory provisions.
We describe a novel technique for the simultaneous visualization of multiple scalar fields, e.g. representing the members of an ensemble, based on their contour trees. Using tree alignments, a graph-theoretic concept similar to edit distance mappings, we identify commonalities across multiple contour trees and leverage these to obtain a layout that can represent all trees simultaneously in an easy-to-interpret, minimally-cluttered manner. We describe a heuristic algorithm to compute tree alignments for a given similarity metric, and give an algorithm to compute a joint layout of the resulting aligned contour trees. We apply our approach to the visualization of scalar field ensembles, discuss basic visualization and interaction possibilities, and demonstrate results on several analytic and real-world examples.
Synchrotron-based nuclear resonance vibrational spectroscopy (NRVS) using the Mössbauer isotope 161Dy has been employed for the first time to study the vibrational properties of a single-molecule magnet (SMM) incorporating DyIII, namely [Dy(Cy3PO)2(H2O)5]Br3⋅2 (Cy3PO)⋅2 H2O ⋅2 EtOH. The experimental partial phonon density of states (pDOS), which includes all vibrational modes involving a displacement of the DyIII ion, was reproduced by means of simulations using density functional theory (DFT), enabling the assignment of all intramolecular vibrational modes. This study proves that 161Dy NRVS is a powerful experimental tool with significant potential to help to clarify the role of phonons in SMMs.
This article proposes a new clock-dependent gain-scheduled dynamic output feedback controller for delayed linear parameter varying systems with piecewise constant parameters. The proposed controller guarantees ℒ2-performance. By employing a clock-dependent Lyapunov–Krasovskii functional, a sufficient condition for the existence of the controller is provided in terms of clock- and parameter-dependent linear matrix inequalities. A case study on output feedback control of delayed switched systems is also provided. To illustrate the efficacy of the result, it is applied to a practical VTOL helicopter model.
The generation of liquid-liquid dispersions with defined droplet size distributions is an important aspect for process equipment design. In this work, two centrifugal pumps with different impeller diameters were used to generate dispersions at selected operating points for a paraffin oil-water system. The droplet break-up phenomena within the centrifugal pumps were analyzed using a transparent pump design in combination with high-speed imaging. Droplet size distributions at centrifugal pump discharge nozzle were recorded with optical probe measurement technologies and evaluated by means of image processing using a neural network. The influence of impeller diameter, rotational speed, volumetric flow rate and dispersed phase fraction are discussed. Experimental data is correlated using fluid properties, operating data as well as centrifugal pump dimensions. The correlations developed from results of this work serve as a basis for the equipment design of centrifugal pumps.
Microcrystalline cellulose pellets for oral drug delivery are often produced by a combined wet extrusion-spheronization process. During the entire process, the cylindrical as well as the spherical pellets are exposed to various stresses resulting in a change of their shape and size due to plastic deformation and breakage. In this work, the effect of moisture content of pellets on their mechanical behavior is studied. In static compression tests, the strong influence of water content on deformation behavior of pellets is confirmed. Moreover, impact tests are performed using a setup consisting of three high-speed cameras to record pellet-wall collisions. Material properties, such as stiffness, restitution coefficient, breakage force, and displacement, were analyzed depending on the water content.
Microbial planktonic communities are the basis of food webs in aquatic ecosystems since they contribute substantially to primary production and nutrient recycling. Network analyses of DNA metabarcoding data sets emerged as a powerful tool to untangle the complex ecological relationships among the key players in food webs. In this study, we evaluated co-occurrence networks constructed from time-series metabarcoding data sets (12 months, biweekly sampling) of protistan plankton communities in surface layers (epilimnion) and bottom waters (hypolimnion) of two temperate deep lakes, Lake Mondsee (Austria) and Lake Zurich (Switzerland). Lake Zurich plankton communities were less tightly connected, more fragmented and had a higher susceptibility to a species extinction scenario compared to Lake Mondsee communities. We interpret these results as a lower robustness of Lake Zurich protistan plankton to environmental stressors, especially stressors resulting from climate change. In all networks, the phylum Ciliophora contributed the highest number of nodes, among them several in key positions of the networks. Associations in ciliate-specific subnetworks resembled autecological species-specific traits that indicate adaptions to specific environmental conditions. We demonstrate the strength of co-occurrence network analyses to deepen our understanding of plankton community dynamics in lakes and indicate biotic relationships, which resulted in new hypotheses that may guide future research in climate-stressed ecosystems.
A highly water-dispersible heterogeneous Brønsted acid surfactant was prepared by synthesis of a bi-functional anisotropic Janus-type material. The catalyst comprises ionic functionalities on one side and propyl-SO3H groups on the other. The novel material was investigated as a green substitute of a homogeneous acidic phase transfer catalyst (PTC). The activity of the catalyst was investigated for the aqueous-phase oxidation of cyclohexene to adipic acid with 30 % hydrogen peroxide even in a decagram-scale. It can also be used for the synthesis of some other carboxylic acid derivatives as well as diethyl phthalate.
A characterisation of the spaces \({\mathcal {G}}_K\) and \({\mathcal {G}}_K'\) introduced in Grothaus et al. (Methods Funct Anal Topol 3(2):46–64, 1997) and Potthoff and Timpel (Potential Anal 4(6):637–654, 1995) is given. A first characterisation of these spaces provided in Grothaus et al. (Methods Funct Anal Topol 3(2):46–64, 1997) uses the concepts of holomorphy on infinite dimensional spaces. We, instead, give a characterisation in terms of U-functionals, i.e., classic holomorphic function on the one dimensional field of complex numbers. We apply our new characterisation to derive new results concerning a stochastic transport equation and the stochastic heat equation with multiplicative noise.
Machining is very common in industry, e.g. automotive industry and aerospace industry, which is a nonlinear dynamic problem including large deformations, large strain, large strain rates and high temperatures, that implies some difficulties for numerical methods such as Finite element method. One way to simulate such kind of problems is the Particle Finite Element Method (PFEM) which combines the advantages of continuum mechanics and discrete modeling techniques. In this work we introduce an improved PFEM called the Adaptive Particle Finite Element Method (A-PFEM). The A-PFEM introduces particles and removes wrong elements along the numerical simulation to improve accuracy, precision, decrease computing time and resolve the phenomena that take place in machining in multiple scales. At the end of this paper, some examples are present to show the performance of the A-PFEM.
One technique to describe the failure of mechanical structures is a phase field model for fracture. Phase field models for fracture consider an independent scalar field variable in addition to the mechanical displacement [1]. The phase field ansatz approximates crack surfaces as a continuous transition zone in which the phase field variable varies from a value that indicates intact material to another value that represents cracks. For a good approximation of cracks, these transition zones are required to be narrow, which leads to steep gradients in the fracture field. As a consequence, the required mesh density in a finite element simulation and thus the computational effort increases. In order to circumvent this efficiency problem, exponential shape functions were introduced in the discretization of the phase field variable, see [2]. Compared to the bilinear shape functions these special shape functions allow for a better approximation of the steep transition with less elements. Unfortunately, the exponential shape functions are not symmetric, which requires a certain orientation of elements relative to the crack surfaces. This adaptation is not uniquely determined and needs to be set up in the correct way in order to improve the approximation of smooth cracks. The issue is solved in this work by reorientating the exponential shape functions according to the nodal value of phase field gradient in a particular element. To be precise, this work discusses an adaptive algorithm that implements such a reorientation for 2d and 3d situations.
In grinding, the crystal grain size of the workpiece material is relatively same range compared to the removal depth. This raises a question if an anisotropic material model, which considers the effect of the crystal grain size and orientations, would better predict the process forces when compared to an isotropic material model. Initially, a simple micro-indentation process is chosen to compare the two models. In this work, a crystal plasticity model and an isotropic Johnson-Cooke plasticity model are employed to simulate micro-identation of a twinning induced plasticity (TWIP) steel. The results of the two models are compared using the force-displacement curves from the micro-indentation experiments. In the future, the study will be extended to describe the material removal process during a single grit scratch test.
A branch-and-cut approach and alternative formulations for thetraveling salesman problem with drone
(2020)
In this paper, we are interested in studying thetraveling salesman problem withdrone(TSP-D). Given a set of customers and a truck that is equipped with a singledrone, the TSP-D asks that all customers are served exactly once and minimal deliv-ery time is achieved. We provide two compact mixed integer linear programmingformulations that can be used to address instances with up to 10 customer within afew seconds. Notably, we introduce a third formulation for the TSP-D with an expo-nential number of constraints. The latter formulation is suitable to be solved by abranch-and-cut algorithm. Indeed, this approach can be used to find optimal solu-tions for several instances with up to 20 customers within 1 hour, thus challenging thecurrent state-of-the-art in solving the TSP-D. A detailed numerical study providesan in-depth comparison on the effectiveness of the proposed formulations. More-over, we reveal further details on the operational characteristics of a drone-assisteddelivery system. By using three different sets of benchmark instances, considera-tion is given to various assumptions that affect, for example, technological droneparameters and the impact of distance metrics.
In recent years, there has been a growing need for accurate 3D scene reconstruction. Recent developments in the automotive industry have led to the increased use of ADAS where 3D reconstruction techniques are used, for example, as part of a collision detection system. For such applications, scene geometry reconstruction is usually performed in the form of depth estimation, where distances to scene objects are obtained.
In general, depth estimation systems can be divided into active and passive. Both systems have their advantages and disadvantages, but passive systems are usually cheaper to produce and easier to assemble and integrate than active systems. Passive systems can be stereo- or multiple-view based. Up to a certain limit, increasing the number of views in multi-view systems usually results in improved depth estimation accuracy.
One potential problem for ensuring the reliability of multi-view systems is the need to accurately estimate the orientation of their optical sensors. One way to ensure sensor placement for multi-view systems is to rigidly fix the sensors at the manufacturing stage. Unlike arbitrary sensor placement, using of a simplified and known sensor placement geometry further simplifies the depth estimation.
We meet with the concept of light field, which parameterizes all visible light passing through all viewpoints by their intersection with angular and spatial planes. When applied to computer vision, this gives us a 2D set of 2D images, where the physical distances between each image are fixed and proportional to each other.
Existing light field depth estimation methods provide good accuracy, which is suitable for industrial applications. However, the main problems of these methods are related to their running time and resource requirements. Most of the algorithms presented in the literature are typically sharpened for accuracy, can only be run on high-performance machines and often require a significant amount of time to process and obtain results.
Real-world applications often have running time requirements. Also, often there is a power-consumption limitation. In this dissertation, we investigate the problem of building a depth estimation system with an light field camera that satisfies the operating time and power consumption constraints without significant loss of estimation accuracy.
First, an algorithm for calibrating light field cameras is proposed, together with an algorithm for automatic calibration refinement, that works on arbitrary captured scenes. An algorithm for classical geometric depth estimation using light field cameras is proposed. Ways to optimize the algorithm for real-time use without significant loss of accuracy are presented. Finally, the ways how the presented depth estimation methods can be extended using modern deep learning paradigms under the two previously mentioned constraints are shown.
Substrate channeling is a widespread mechanism in metabolic pathways to avoid decomposition of unstable intermediates, competing reactions, and to accelerate catalytic turnover. During the biosynthesis of light-harvesting phycobilins in cyanobacteria, two members of the ferredoxin-dependent bilin reductases are involved in the reduction of the open-chain tetrapyrrole biliverdin IXα to the pink pigment phycoerythrobilin. The first reaction is catalyzed by 15,16-dihydrobiliverdin:ferredoxin oxidoreductase and produces the unstable intermediate 15,16-dihydrobiliverdin (DHBV). This intermediate is subsequently converted by phycoerythrobilin:ferredoxin oxidoreductase to the final product phycoerythrobilin. Although substrate channeling has been postulated already a decade ago, detailed experimental evidence was missing. Using a new on-column assay employing immobilized enzyme in combination with UV-Vis and fluorescence spectroscopy revealed that both enzymes transiently interact and that transfer of the intermediate is facilitated by a significantly higher binding affinity of DHBV toward phycoerythrobilin:ferredoxin oxidoreductase. Concluding from the presented data, the intermediate DHBV is transferred via proximity channeling.
A novel method for the highly stereoselective synthesis of tetrahydropyrans is reported. This domino reaction is based on a twofold addition of enamides to aldehydes followed by a subsequent cyclization and furnishes fully substituted tetrahydropyrans in high yields. Three new σ-bonds and five continuous stereogenic centers are formed in this one-pot process with a remarkable degree of diastereoselectivity. In most cases, the formation of only one out of 16 possible diastereomers is observed. Two different stereoisomers can be accessed in a controlled fashion starting either from an E- or a Z-configured enamide.
Covering edges in networks
(2019)
In this paper we consider the covering problem on a networkG=(V,E)withedgedemands. The task is to cover a subsetJ⊆Eof the edges with a minimum numberof facilities within a predefined coverage radius. We focus on both the nodal andthe absolute version of this problem. In the latter, facilities may be placed every-where in the network. While there already exist polynomial time algorithms to solvethe problem on trees, we establish a finite dominating set (i.e., a finite subset ofpoints provably containing an optimal solution) for the absolute version in generalgraphs. Complexity and approximability results are given and a greedy strategy isproved to be a (1+ln(|J|))-approximate algorithm. Finally, the different approachesare compared in a computational study.
This contribution presents a novel approach to investigate entrainment in distillation and absorption columns. An image-based probe allows precise droplet detection at various radial and axial positions above trays. Validations achieve an aver-age error of 6.4 % (monospheres 9.2–114.4mm) and 3 % (monodisperse droplet stream up to 19 m s–1and 74.5mm).Experiments in a DN 450 cold flow test rig show an increasing (decreasing) share of larger droplets with higher gas (liq-uid) loads. Locally measured droplet sizes depend on probe position as well as tray design and enable an extrapolation tointegral entrainment rates.
The use of digital media in adult education is very heterogene-ous. To date, there are no empirical studies that have examined the possibility that media-related differences in media usage of adult educators could be in part due to differential media pedagogical attitudes of adult educators. Moreover, there is a lack of empirical evidence to support the understanding of what factors modulate differences in media pedagogical com-petencies of adult educators. In order to examine different the-oretical potentialities, in the present study, an online survey of adult educators (n = 626) was conducted to investigate the attitudes of adult educators in Germany toward their use of digital media. The results of the study indicate that there are influencing factors such as educational level or employment context on attitudes toward digital media.
Organic solutions of lithium bis(fluorosulfonyl)imide (LiFSI) are promising electrolytes for Li-ion batteries. Information on the diffusion coefficients of the species in these solutions is needed for battery design. Therefore, the self-diffusion coefficients in such solutions were studied experimentally with the pulsed-field gradient nuclear magnetic resonance technique. The self-diffusion coefficients of the ions Li+ and FSI− as well as those of the solvents were measured for LiFSI solutions in pure dimethyl carbonate and ethylene carbonate as well as in mixtures of these solvents at 298 K and ambient pressure. Despite the Li+ ion being the smallest species in the solution, its self-diffusion coefficient is the lowest as a result of its strong coordination with the solvent molecules.
The production of nylon-6.6 is one of the largest scale syntheses in industrial chemistry. The standard procedure is based on an energy consuming low-level conversion of cyclohexane to yield adipic acid in two steps that is converted to nylon-6.6 in a separate step. Therefore, there is a strong intent to optimize the synthetic route in an economic and ecologic matter. In this work, we present a one-pot oxygenation of cyclohexane with hydrogen peroxide and a µ4-oxido-copper cluster catalyst to yield dicarboxylic acids with adipic acid as the main product.
This paper provides experimental results on investigations for the validation of photo-grammetric strain measurements of ultra-high-performance concrete (UHPC)-prismssubjected to static and cyclic bending-tensile stress. For this purpose, 4 static and5 cyclic test series were performed. Damage progresses during loading are monitoredby means of a digital image correlation (DIC) system and a clip gauge. The control ofthe DIC by trigger lists and the measurement noise as a function of the measurementrate are examined. All static tests were performed force controlled with the same test-ingspeedandthesamemeasuringrateofDICandclipgauge.Allcyclictestswereperformed with the same upper and lower stress levels but with different loading rates.During the static tests, the DIC can be used to make accurate strain measurementsbefore UHPC failure. In the cyclic tests, the measurement noise of the DICdecreases with an increasing measuring rate. The tests performed confirm the con-trol of the DIC by trigger lists for cyclic tests on UHPC-prisms and show that themeasurement noise is negligible in static and cyclic tests.
The Atacama Desert is the driest non‐polar desert on Earth, presenting precarious conditions for biological activity. In the arid coastal belt, life is restricted to areas with fog events that cause almost daily wet–dry cycles. In such an area, we discov‐ered a hitherto unknown and unique ground covering biocenosis dominated by li‐chens, fungi, and algae attached to grit‐sized (~6 mm) quartz and granitoid stones. Comparable biocenosis forming a kind of a layer on top of soil and rock surfaces in general is summarized as cryptogamic ground covers (CGC) in literature. In contrast to known CGC from arid environments to which frequent cyclic wetting events are lethal, in the Atacama Desert every fog event is answered by photosynthetic activity of the soil community and thus considered as the desert's breath. Photosynthesis of the new CGC type is activated by the lowest amount of water known for such a community worldwide thus enabling the unique biocenosis to fulfill a variety of eco‐system services. In a considerable portion of the coastal Atacama Desert, it protects the soil from sporadically occurring splash erosion and contributes to the accumula‐tion of soil carbon and nitrogen as well as soil formation through bio‐weathering. The structure and function of the new CGC type are discussed, and we suggest the name grit–crust. We conclude that this type of CGC can be expected in all non‐polar fog deserts of the world and may resemble the cryptogam communities that shaped ancient Earth. It may thus represent a relevant player in current and ancient biogeo‐chemical cycling.
The increase of pluvial flooding has long been discussed to be a most probableoutcome of climate change. This has raised the question of necessary conse-quences in the design of urban drainage systems in order to secure adequateflood protection and resilience. Due to the uncertainties in future trends ofheavy rainfall events, the awareness of remaining risks of extreme pluvialflooding needs to be roused at responsible decision makers and the public aswell leading to the implementation of pluvial flood risk management (PFRM)concepts. The state of two core elements of PFRM in Germany are describedhere: flood hazard and risk evaluation and risk communication. In 2016 theguideline DWA-M 119 has been published to establish city-based PFRM con-cepts in specification of the European Flood Risk Management Directive(EU 2007). As core elements, the guidelines recommend a site-specific analysisand evaluation of flood hazards and potentials of flood damages to create floodhazard and flood risk maps. In the long run, PFRM needs to be established asa joint community effort and a requirement for more flood resilience. The riskcommunication within the administration and in the public requires a com-prehensible characterization and classification of heavy rainfall to illustrateevent extremity. The concept of a rainstorm severity index (RSI) instead of sta-tistical rainfall parameters appears to be promising to gain a better perceptionby affected citizens and non-hydrology-experts as well. A methodical approachis described to specify and assign site-specific rainfall depths within the sever-ity index scheme RSI12.This article is categorized under:
Engineering Water > Sustainable Engineering of Water
Engineering Water > Planning Water
Engineering Water > Methods
Measuring Particle Size Distributions in Multiphase Flows Using a Convolutional Neural Network
(2019)
The efficiency of many chemical engineering applications depends on the surface/volume ratio of the dispersed phase. Knowledge of this particle size distribution is a key factor for better process control. The challenge of measurements acquired by optical imaging techniques is the segmentation of overlapping particles, especially in high phase fraction flows. In this work, a convolutional neural network is trained to segment droplets in images acquired by a shadowgraphic approach. The network is trained on artificial images and implemented into a droplet size algorithm. The results are compared to an OpenSource segmentation approach.
Hajós' conjecture asserts that a simple Eulerian graph on n vertices can be decomposed into at most [(n-1)/2] cycles. The conjecture is only proved for graph classes in which every element contains vertices of degree 2 or 4. We develop new techniques to construct cycle decompositions. They work on the common neighborhood of two degree-6 vertices. With these techniques, we find structures that cannot occur in a minimal counterexample to Hajós' conjecture and verify the conjecture for Eulerian graphs of pathwidth at most 6. This implies that these graphs satisfy the small cycle double cover conjecture.
The interest in micro applications increases in recent years due to new methods of fabrication. One fabrication process is direct laser writing, which can fabricate high-precision structures in the micrometer range. The material properties of the micro structures are related to the writing parameters, such as laser power, scan speed, distance between written lines and writing direction. This work presents investigations of the thermal length expansion coefficients of a laser-written polymer in regard to laser power. To this end cantilever structures are fabricated. The small cantilevers are heated and their length expansions observed using a microscope. Images of the cantilevers at different temperatures are taken and by image post processing, the change in length and their coefficients of thermal expansion is determined.