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Novel Pseudocyclopeptides Containing 1,4-Disubstituted 1,2,3-Triazole Subunits for Anion Recognition (2017)

Disha Mungalpara

Anion recognition is one of the most rapidly growing areas in the field of Supramolecular Chemistry due to the vital role of anions in the environment, in biology and in industry. The development of new anion binding motifs that can also be combined with known ones in a novel receptor is a timely topic. In this context, we have synthesized three cyclic pseudopeptides 16, 17 and 18, containing conventional H-bond donors (amide) in combination with, respectively, triazole C–H or triazole C–I functions. All three receptors were synthesized by using a combination of peptide and click chemistry. Structural studies show that all three pseudopeptides adopt conformations with the triazole C-H or C-I groups pointing into the cavity center to allow them to contribute to binding. Quantitative binding studies showed that the cyclic pseudohexapeptide 1 coordinates to oxoanions (sulfate, dihydrogenphosphate, and hydrogenpyrophosphate) with different binding strengths and complex stoichiometries in 2.5 vol% water/DMSO. Anion selectivity of 16 significantly changes when the cavity size of this pseudopeptide is increased to obtain the larger analog 17. This pseudooctapeptide forms well defined complexes with protonated phosphate anions. The complexation involves sandwiching of a cyclic tetramer of dihydrogenphosphate or a dimer of dihydrogenpyrophosphate anions by two pseudopeptide rings. Both complexes were characterized structurally in the solid state. They are stable in solution (2.5 vol% water/DMSO) as result of the interaction between hydrogen bond donors of 17 and the oxygen atoms of the anionic aggregates. The complexes can also be transferred to the gas phase without decomposition. Anion selectivity of 16 was further altered by introducing iodine atom in the C5 position of the 1,4-disubstituted 1,2,3-triazole units. The corresponding cyclic pseudohexapeptide 18 features a smaller cavity diameter than 17 as a result of the iodide atoms and was therefore found to only coordinate to smaller spherical anions such as chloride. It forms 1:1 complexes with chloride, bromide and iodide in 2.5 vol% water/DMSO. Among the halides, 18 has highest affinity for chloride followed by bromide and iodide. The same stability trend was also observed in the gas phase by ESI/MS. Concluding, I prepared three new macrocyclic pseudopeptides during my PhD and characterized their complexes with anions in terms of structure and affinity. All of these pseudopeptides were shown to interact with phosphate-derived anions, which renders them unique among the anion receptors developed in the Kubik group before.

Cryo Tagging Infrared Spectroscopy and Temperature Controlled Kinetic Studies in a Tandem Trap Mass Spectrometer (2017)

Jennifer Mohrbach

In the present work, the interaction of diatomic molecules with charged transition metal clusters and complexes was investigated. Temperature controlled isothermal kinetic studies served to elucidate the adsorption behavior of transition metal clusters. Infrared multiple photon dissociation (IR-MPD) experiments in conjunction with density functional theory (DFT) computations enabled the analysis of adsorbate induced changes on the structure and spin multiplicity of transition metal cores. A tandem cryo trap setup was used for the kinetic and spectroscopic investigations of the given compounds as isolated species in the gas phase. The presented investigations enabled insight into the metal-adsorbate bonding and provided cluster size and adsorbate coverage dependent information on cluster surface morphologies.

Viscoelastic Modeling of Calving Processes at Antarctic Ice Shelves (2017)

Julia Christmann

In this thesis viscoelastic material models are established to investigate the nature of continuous calving processes at Antarctic ice shelves. Physics-based descriptions of calving require appropriate fracture criteria to separate icebergs from the remaining ice shelf. Hence, criteria of the stress, the strain, and the self-similarity criterion are considered within finite-element computations. Crucial parameters in the models to determine the position of calving are the accurate knowledge of the geometry, especially the freeboard height, while the material parameters mainly influence the time span between two successive calving events. The extension to nonlinear material models is necessary to properly analyze the internal forces also for large deformations that occur for longer times of the viscous ice flow.

An Intersection-Theoretic Approach to Correspondence Problems in Tropical Geometry (2016)

Andreas Gross

The main theme of this thesis is the interplay between algebraic and tropical intersection theory, especially in the context of enumerative geometry. We begin by exploiting well-known results about tropicalizations of subvarieties of algebraic tori to give a simple proof of Nishinou and Siebert’s correspondence theorem for rational curves through given points in toric varieties. Afterwards, we extend this correspondence by additionally allowing intersections with psi-classes. We do this by constructing a tropicalization map for cycle classes on toroidal embeddings. It maps algebraic cycle classes to elements of the Chow group of the cone complex of the toroidal embedding, that is to weighted polyhedral complexes, which are balanced with respect to an appropriate map to a vector space, modulo a naturally defined equivalence relation. We then show that tropicalization respects basic intersection-theoretic operations like intersections with boundary divisors and apply this to the appropriate moduli spaces to obtain our correspondence theorem. Trying to apply similar methods in higher genera inevitably confronts us with moduli spaces which are not toroidal. This motivates the last part of this thesis, where we construct tropicalizations of cycles on fine logarithmic schemes. The logarithmic point of view also motivates our interpretation of tropical intersection theory as the dualization of the intersection theory of Kato fans. This duality gives a new perspective on the tropicalization map; namely, as the dualization of a pull-back via the characteristic morphism of a logarithmic scheme.

Magnetic and Structural Characterization of Isolated Gaseous Ions by XMCD and IRMPD Spectroscopy (2017)

Joachim Hewer

This thesis comprises four independent research studies on the magnetic and structural characterization of isolated ions in the gas phase. The electrospray ionization (ESI) technique is used for the transfer of (multi-)metallic complexes and organic molecules from solution into the gas phase. The subsequent storage of molecular ions in ion traps allows for a variety of spectroscopic methods in order to investigate the intrinsic properties of the isolated species void of solvent, crystal lattice, bulk or supporting surface effects. The magnetic properties of metal complexes are elucidated by gas phase X-ray magnetic circular dichroism (XMCD) spectroscopy. The element selective technique in combination with sum rule analysis allows for a separate determination of spin and orbital magnetic moments at different metal centers. Structural investigations on isolated molecular ions in terms of coordination sphere, binding motifs and hydrogen bonds are conducted using infrared multiple photon dissociation (IRMPD) spectroscopy. A resonant two color IRMPD technique serves to increase fragmentation yields, overcome dissociation bottlenecks and reveal otherwise dark bands. Comparison of experimental IRMPD spectra with calculated harmonic absorption spectra by density functional theory (DFT) provides structural assignments for a profound understanding of intra- and intermolecular interactions.

Conception and First Implementation of Novel Sensory Signal Conditioning and Digital Conversion Electronics Based on Spiking Neuron Ensembles for Inherently Robust Processing in Aggressively Scaled Integration Technologies (2017)

Abhaya Chandra Kammara Subramanyam

”In contemporary electronics 80% of a chip may perform digital functions but the 20% of analog functions may take 80% of the development time.” [1]. Aggravating this, the demands on analog design is increasing with rapid technology scaling. Most designs have moved away from analog to digital domains, where possible, however, interacting with the environment will always require analog to digital data conversion. Adding to this problem, the number of sensors used in consumer and industry related products are rapidly increasing. Designers of ADCs are dealing with this problem in several ways, the most important is the migration towards digital designs and time domain techniques. Time to Digital Converters (TDC) are becoming increasingly popular for robust signal processing. Biological neurons make use of spikes, which carry spike timing information and will not be affected by the problems related to technology scaling. Neuromorphic ADCs still remain exotic with few implementations in sub-micron technologies Table 2.7. Even among these few designs, the strengths of biological neurons are rarely exploited. From a previous work [2], LUCOS, a high dynamic range image sensor, the efficiency of spike processing has been validated. The ideas from this work can be generalized to make a highly effective sensor signal conditioning system, which carries the promise to be robust to technology scaling. The goal of this work is to create a novel spiking neural ADC as a novel form of a Multi-Sensor Signal Conditioning and Conversion system, which • Will be able to interface with or be a part of a System on Chip with traditional analog or advanced digital components. • Will have a graceful degradation. • Will be robust to noise and jitter related problems. • Will be able to learn and adapt to static errors and dynamic errors. • Will be capable of self-repair, self-monitoring and self-calibration Sensory systems in humans and other animals analyze the environment using several techniques. These techniques have been evolved and perfected to help the animal sur- vive. Different animals specialize in different sense organs, however, the peripheral neural network architectures remain similar among various animal species with few ex- ceptions. While there are many biological sensing techniques present, most popularly used engineering techniques are based on intensity detection, frequency detection, and edge detection. These techniques are used with traditional analog processing (e.g., colorvi sensors using filters), and with biological techniques (e.g. LUCOS chip [2]). The local- ization capability of animals has never been fully utilized. One of the most important capabilities for animals, vertebrates or invertebrates, is the capability for localization. The object of localization can be predator, prey, sources of water, or food. Since these are basic necessities for survival, they evolve much faster due to the survival of the fittest. In fact, localization capabilities, even if the sensors are different, have convergently evolved to have same processing methods (coincidence detection) in their peripheral neurons (for e.g., forked tongue of a snake, antennae of a cockroach, acoustic localization in fishes and mammals). This convergent evolution increases the validity of the technique. In this work, localization concepts based on acoustic localization and tropotaxis are investigated and employed for creation of novel ADCs. Unlike intensity and frequency detection, which are not linear (for e.g. eyes saturate in bright light, loose color perception in low light), localization is inherently linear. This is mainly because the accurate localization of predator or prey can be the difference between life and death for an animal. Figure 1 visually explains the ADC concept proposed in this work. This has two parts. (1) Sensor to Spike(time) Conversion (SSC), (2) Spike(time) to Digital Conversion(SDC). Both of the structures have been designed with models of biological neurons. The combination of these two structures is called SSDC. To efficiently implement the proposed concept, a comparison of several biological neural models is made and two models are shortlisted. Various synapse structures are also studied. From this study, Leaky Integrate and Fire neuron (LIF) is chosen since it fulfills all the requirements of the proposed structure. The analog neuron and synapse designs from Indiveri et. al. [3], [4] were taken, and simulations were conducted using cadence and the behavioral equivalence with biological counterpart was checked. The LIF neuron had features, that were not required for the proposed approach. A simple LIF neuron stripped of these features and was designed to be as fast as allowed by the technology. The SDC was designed with the neural building blocks and the delays were designed using buffer chains. This SDC converts incoming Time Interval Code (TIC) to sparse place coding using coincidence detection. Coincidence detection is a property of spiking neurons, which is a time domain equivalent of a Gaussian Kernel. The SDC is designed to have an online reconfigurable Gaussian kernel width, weight, threshold, and refractory period. The advantage of sparse place codes, which contain rank order coding wasvii Figure 1: ADC as a localization problem (right), Jeffress model of sound localization visualized (left). The values t 1 and t 2 indicate the time taken from the source to s1 and s2 respectively. described in our work [5]. A time based winner take all circuit with memory was created based on a previous work [6] for reading out of sparse place codes asynchronously. The SSC was also initially designed with the same building blocks. Additionally, a differential synapse was designed for better SSC. The sensor element considered wasviii a Wheatstone full bridge AMR sensor AFF755 from Sensitec GmbH. A reconfigurable version of the synapse was also designed for a more generic sensor interface. The first prototype chip SSDCα was designed with 257 modules of coincidence detectors realizing the SDC and the SSC. Since the spike times are the most important information, the spikes can be treated as digital pulses. This provides the capability for digital communication between analog modules. This creates a lot of freedom for use of digital processing between the discussed analog modules. This advantage is fully exploited in the design of SSDCα. Three SSC modules are multiplexed to the SDC. These SSC modules also provide outputs from the chip simultaneously. A rising edge detecting fixed pulse width generation circuit is used to create pulses that are best suited for efficient performance of the SDC. The delay lines are made reconfigurable to increase robustness and modify the span of the SDC. The readout technique used in the first prototype is a relatively slow but safe shift register. It is used to analyze the characteristics of the core work. This will be replaced by faster alternatives discussed in the work. The area of the chip is 8.5 mm 2 . It has a sampling rate from DC to 150 kHz. It has a resolution from 8-bit to 13-bit. It has 28,200 transistors on the chip. It has been designed in 350 nm CMOS technology from ams. The chip has been manufactured and tested with a sampling rate of 10 kHz and a theoretical resolution of 8 bits. However, due to the limitations of our Time-Interval-Generator, we are able to confirm for only 4 bits of resolution. The key novel contributions of this work are • Neuromorphic implementation of AD conversion as a localization problem based on sound localization and tropotaxis concepts found in nature. • Coincidence detection with sparse place coding to enhance resolution. • Graceful degradation without redundant elements, inherent robustness to noise, which helps in scaling of technologies • Amenable to local adaptation and self-x features. Conceptual goals have all been fulfilled, with the exception of adaptation. The feasibility for local adaptation has been shown with promising results and further investigation is required for future work. This thesis work acts as a baseline, paving the way for R&D in a new direction. The chip design has used 350 nm ams hitkit as a vehicle to prove the functionality of the core concept. The concept can be easily ported to present aggressively-scaled-technologies and future technologies.

Nanoparticle-Filled Thermoplastics and Thermoplastic Elastomer: Structure-Property Relationships (2012)

Ruijuan Zhou

The present work focuses on the structure-property relationships of particulate-filled thermoplastics and thermoplastic elastomer (TPE). In this work two thermoplastics and one TPE were used as polymer matrices, i.e. amorphous bisphenol-A polycarbonate (PC), semi-crystalline isotactic polypropylene (iPP), and a block copolymer poly(butylene terephthalate)-block-poly(tetramethylene glycol) TPE(PBT-PTMG). For PC, a selected type of various Aerosil® nano-SiO2 types was used as filler to improve the thermal and mechanical properties by maintaining the transparency of PC matrix. Different types of SiO2 and TiO2 nanoparticles with different surface polarity were used for iPP. The goal was to examine the influence of surface polarity and chemical nature of nanoparticles on the thermal, mechanical and morphological properties of iPP composites. For TPE(PBT-PTMG), three TiO2 particles were used, i.e. one grade with hydroxyl groups on the particle surface and the other two grades are surface-modified with metal and metal oxides, respectively. The influence of primary size and dispersion quality of TiO2 particles on the properties of TPE(PBT-PTMG)/TiO2 composites were determined and discussed. All polymer composites were produced by direct melt blending in a twin-screw extruder via masterbatch technique. The dispersion of particles was examined by using scanning electron microscopy (SEM) and micro-computerized tomography (μCT). The thermal and crystalline properties of polymer composites were characterized by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The mechanical and thermomechanical properties were determined by using mechanical tensile testing, compact tension and Charpy impact as well as dynamic-mechanical thermal analysis (DMTA). The SEM results show that the unpolar-surface modified nanoparticles are better dispersed in polymer matrices as iPP than polar-surface nanoparticles, especially in case of using Aeroxide® TiO2 nanoparticles. The Aeroxide® TiO2 nanoparticles with a polar surface due to Ti-OH groups result in a very high degree of agglomeration in both iPP and TPE matrices because of strong van der Waals interactions among particles (hydrogen bonding). Compared to unmodified Aeroxide® TiO2 nanoparticles, the other grades of surface modified TiO2 particles are very homogenously dispersed in used iPP and TPE(PBT-PTMG). The incorporation of SiO2 nanoparticles into bisphenol-A PC significantly increases the mechanical properties of PC/SiO2 nanocomposites, particularly the resistance against environmental stress crazing (ESC). However, the transparency of PC/SiO2 nanocomposites decreases with increasing nanoparticle content and size due to a mismatch of infractive indices of PC and SiO2 particles. The different surface polarity of nanoparticles in iPP shows evident influence on properties of iPP composites. Among iPP/SiO2 nanocomposites, the nanocomposite containing SiO2 nanoparticles with a higher degree of hydrophobicity shows improved fracture and impact toughness compared to the other iPP/SiO2 composites. The TPE(PBT-PTMG)/TiO2 composites show much better thermal and mechanical properties than neat TPE(PBT-PTMG) due to strong chemical interactions between polymer matrix and TiO2 particles. In addition, better dispersion quality of TiO2 particles in used TPE(PBT-PTMG) leads to dramatically improved mechanical properties of TPE(PBT-PTMG)/TiO2 composites.

Induction Welding of Fiber Reinforced Thermoplastic Polymer Composites to Metals (2007)

Rudi Velthuis

Water-Mediated Melt Compounding to Produce Thermoplastic Polymer-Based Nanocomposites: Structure-Property Relationships (2008)

Suchart Siengchin

Nanotechnology is now recognized as one of the most promising areas for technological development in the 21st century. In materials research, the development of polymer nanocomposites is rapidly emerging as a multidisciplinary research activity whose results could widen the applications of polymers to the benefit of many different industries. Nanocomposites are a new class of composites that are particle-filled polymers for which at least one dimension of the dispersed particle is in the nanometer range. In the related area polymer/clay nanocomposites have attracted considerable interest because they often exhibit remarkable property improvements when compared to virgin polymer or conventional micro- and macro- composites. The present work addresses the toughening and reinforcement of thermoplastics via a novel method which allows us to achieve micro- and nanocomposites. In this work two matrices are used: amorphous polystyrene (PS) and semi-crystalline polyoxymethylene (POM). Polyurethane (PU) was selected as the toughening agent for POM and used in its latex form. It is noteworthy that the mean size of rubber latices is closely matched with that of conventional toughening agents, impact modifiers. Boehmite alumina and sodium fluorohectorite (FH) were used as reinforcements. One of the criteria for selecting these fillers was that they are water swellable/ dispersible and thus their nanoscale dispersion can be achieved also in aqueous polymer latex. A systematic study was performed on how to adapt discontinuousand continuous manufacturing techniques for the related nanocomposites. The dispersion of nanofillers was characterized by transmission, scanning electron and atomic force microcopy (TEM, SEM and AFM respectively), X-ray diffraction (XRD) techniques, and discussed. The crystallization of POM was studied by means of differential scanning calorimetry and polarized light optical microscopy (DSC and PLM, respectively). The mechanical and thermomechanical properties of the composites were determined in uniaxial tensile, dynamic-mechanical thermal analysis (DMTA), short-time creep tests, and thermogravimetric analysis (TGA). PS composites were produced first by a discontinuous manufacturing technique, whereby FH or alumina was incorporated in the PS matrix by melt blending with and without latex precompounding of PS latex with the nanofiller. It was found that direct melt mixing (DM) of the nanofillers with PS resulted in micro-, whereas the latex mediated pre-compounding (masterbatch technique, MB) in nanocomposites. FH was not intercalated by PS when prepared by DM. On the other hand, FH was well dispersed (mostly intercalated) in PS via the PS latex-mediated predispersion of FH following the MB route. The nanocomposites produced by MB outperformed the DM compounded microcomposites in respect to properties like stiffness, strength and ductility based on dynamic-mechanical and static tensile tests. It was found that the resistance to creep (summarized in master curves) of the nanocomposites were improved compared to those of the microcomposites. Master curves (creep compliance vs. time), constructed based on isothermal creep tests performed at different temperatures, showed that the nanofiller reinforcement affects mostly the initial creep compliance. Next, ternary composites composed of POM, PU and boehmite alumina were produced by melt blending with and without latex precompounding. Latex precompounding served for the predispersion of the alumina particles. The related MB was produced by mixing the PU latex with water dispersible boehmite alumina. The composites produced by the MB technique outperformed the DM compounded composites in respect to most of the thermal and mechanical characteristics. Toughened and/or reinforced PS- and POM-based composites have been successfully produced by a continuous extrusion technique, too. This technique resulted in good dispersion of both nanofillers (boehmite) and impact modifier (PU). Compared to the microcomposites obtained by conventional DM, the nanofiller dispersion became finer and uniform when using the water-mediated predispersion. The resulting structure markedly affected the mechanical properties (stiffness and creep resistance) of the corresponding composites. The impact resistance of POM was highly enhanced by the addition of PU rubber when manufactured by the continuous extrusion manufacturing technique. This was traced to the dispersed PU particle size being in the range required from conventional, impact modifiers.

Advanced in-situ Measurements within Sliding Contacts (2014)

Ron Sebastian

In recent years the field of polymer tribology experienced a tremendous development leading to an increased demand for highly sophisticated in-situ measurement methods. Therefore, advanced measurement techniques were developed and established in this study. Innovative approaches based on dynamic thermocouple, resistive electrical conductivity, and confocal distance measurement methods were developed in order to in-situ characterize both the temperature at sliding interfaces and real contact area, and furthermore the thickness of transfer films. Although dynamic thermocouple and real contact area measurement techniques were already used in similar applications for metallic sliding pairs, comprehensive modifications were necessary to meet the specific demands and characteristics of polymers and composites since they have significantly different thermal conductivities and contact kinematics. By using tribologically optimized PEEK compounds as reference a new measurement and calculation model for the dynamic thermocouple method was set up. This method allows the determination of hot spot temperatures for PEEK compounds, and it was found that they can reach up to 1000 °C in case of short carbon fibers present in the polymer. With regard to the non-isotropic characteristics of the polymer compound, the contact situation between short carbon fibers and steel counterbody could be successfully monitored by applying a resistive measurement method for the real contact area determination. Temperature compensation approaches were investigated for the transfer film layer thickness determination, resulting in in-situ measurements with a resolution of ~0.1 μm. In addition to a successful implementation of the measurement systems, failure mechanism processes were clarified for the PEEK compound used. For the first time in polymer tribology the behavior of the most interesting system parameters could be monitored simultaneously under increasing load conditions. It showed an increasing friction coefficient, wear rate, transfer film layer thickness, and specimen overall temperature when frictional energy exceeded the thermal transport capabilities of the specimen. In contrast, the real contact area between short carbon fibers and steel decreased due to the separation effect caused by the transfer film layer. Since the sliding contact was more and more matrix dominated, the hot spot temperatures on the fibers dropped, too. The results of this failure mechanism investigation already demonstrate the opportunities which the new measurement techniques provide for a deeper understanding of tribological processes, enabling improvements in material composition and application design.

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