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Computational Studies of Structure, Stability and Properties of Nanoporous Framework Materials
No full textFramework materials are extended structures that are built into destined nanoscale architectures using molecular building units. Reticular synthesis methods allow stitching of a large variety of molecules into predicted networks. Porosity is an obvious outcome of the stitching process. These materials are classified and named according to the chemical composition of the building blocks. For instance, Metal-Organic Frameworks (MOFs) consists of metal-oxide centers that are linked together by organic entities. The stitching process is straight-forward, so that there are already thousands of them synthesized. Controlled growth of MOFs on substrates leads to what is known as surface-MOFs (SURMOFs). A low-weight, metal-free version of MOFs is known as Covalent Organic Frameworks (COFs). They consist of light elements such as boron, oxygen, silicon, nitrogen, carbon and hydrogen atoms. Diamond-like structures with a variety of linear organic linkers between tetrahedral nodes is called Porous Aromatic Frameworks (PAFs). The thesis is composed of computational studies of the above mentioned classes of materials. The significance of such studies lies in the insights that it gives about the structure-property relationships. Density Functional Theory (DFT) and its Tight-Binding approximate method (DFTB) were used in order to perform extensive calculations on finite and periodic structures of several frameworks. DFTB provides an ab-initio base on periodic structure calculations of very large crystals which are typically studied only using force-field methods. The accuracy of this approximate method is validated prior to reasoning. As the materials are energized from building units and coordination (or binding), stability vs. structure is discussed. Energy of formation and mechanical strength are particularly calculated. Using dispersion corrected (DC)-Self Consistent Charge (SCC) DFTB, we asserted that 2D COFs should have a layer arrangement different from experimental suggestions. Our arguments supported by simulated PXRDs were later verified using higher level theories in the literature. Another benchmark is giving an insightful view on the recently reported difference in symmetries of two-dimensional MOFs and SURMOFs. The result of it shows an extra-ordinary role of linkers in SURMOFs, providing metastability. Electronic properties of all the materials and hydrogen adsorption capacities of PAFs are discussed. COFs, PAFs and many of the MOFs are semiconductors. HOMO-LUMO gaps of molecular units have crucial influence in the band gaps of the solids. Density of states (DOS) of solids corresponds to that of cluster models. Designed PAFs give a large choice of adsorption capacities; one of them exceeds the DOE (US) 2005 target. Generally, the studies covered under the scheme of the thesis illustrate the structure, stability and properties of framework materials
Structural and functional changes of insect eyes in cases of miniaturization
No full textIn spite of the numerous studies on insect compound eyes within the last 100 years, astonishingly the number of investigations specifically dealing with the eyes of species of small body size is near to negligible. Moreover, conclusions by Warrant and McIntyre (1993) and Meyer-Rochow and Gál (2004), based on theoretical optical examinations, suggested that an unlimited eye size reduction was not possible; a suggestion that begged the question as to how the tiniest insects might deal with these restrictions. To demonstrate that optical and structural modifications are widespread, a detailed study of eye miniaturizations involving tiny lepidopteran and hymenopteran species and a quest to determine limiting factors seemed timely and interesting. The main goals of the present work were therefore A) to test through the description of ultrastructural and functional design features of compound eyes of different species of tiny lepidopterans, the prediction of Meyer-Rochow and Gál (2004) that the possession of a superposition type of eye was of no benefit to small eyes B) to describe possible adaptations occurring in these eye of reduced size and C) to carve out through a comparative analysis of eyes of different size, the impacting factors that set the limits for the miniaturization of compound eyes generally. The present work revealed that the conclusions reached by Meyer-Rochow and Gál (2004) based on their theoretical approach holds true and adaptations in small eyes are manifest in form of an intermediate eye type, combining features of apposition and superposition optics. The intermediate eye type is described and discussed in detail as well as the functional consequences resulting from it. Furthermore, adaptations recognizable in the investigated eyes as a consequence of miniaturization are discussed on a functional basis, as is the aspect of limiting factors operating on the smallest possible optics generally
Robust Precoder Design in Wireless Networks
No full textThe ever shrinking cell sizes to accommodate more users make the performance of wireless cellular networks interference limited. To mitigate inter-cell interference in downlink transmissions, many researchers have studied coordinated signal processing across base stations assuming perfect channel knowledge at the transmitter side. This unrealistic assumption necessitates the development of robust multi-cell precoding techniques to cope with channel estimation errors and quantization errors in practical transmission. In existing literature, robust precoder designs for single-cell downlink transmissions have been extensively investigated, where intercell interference was treated as background noise. However, robust multi-cell signal processing has not been adequately explored. The main focus of this thesis is to develop a framework to design robust precoders for various wireless networks with different kinds of channel models. Specifically, we consider both worst-case and stochastic approaches for multiple-input-single-output (MISO) systems. In the first part of the thesis, worst-case approach that is suitable to account for quantization errors is employed. Initially, robust precoders are designed applying semidefinite relaxation (SDR) techniques for amplify-and-forward (AF) networks. Later, we apply more sophisticated techniques via S-procedure to develop robust beamformers for multi-cell networks. It is also shown that the developed methods can be easily extended to multi-cell cognitive radio (CR) networks. In the second half, the probabilistic approach to accommodate channel estimation errors is considered. Conservative bounds to the optimal objective are derived and efficiently solved via convex optimization methods. The proposed algorithms that can be efficiently computed either solve uninvestigated problems or provide improved performance as compared to the existing state- of-the-art techniques
Software Assistance for Preoperative Risk Assessment and Intraoperative Support in Liver Resection Surgery
No full textThis thesis contributes to the field of computer-assisted liver surgery with a focus on surgical planning and intraoperative support. Resection planning for liver surgery has become an essential tool in the clinical routine. Based on 3D reconstructions from radiologic images of the patient, different resection plans can be simulated and assessed before an intervention. During an intervention, surgical navigation systems align the planning information with the patient's liver and thus support the realization of a preoperative plan. New techniques for preoperative risk assessment in liver surgery are presented in this work. Thereby, the determination of safety margins around tumors is addressed which is a challenging task for surgeons. The spatial relation of tumors to the intrahepatic vascular anatomy and the amount of remnant liver volume are important factors when deciding whether a tumor-free safety margin can be achieved. Besides a method to define safety margins with uniform width, a method to define non-uniform safety margins is proposed while considering robustness and sensitivity of vascular risk. In addition, techniques for intraoperative support of liver interventions are introduced. First, the intraoperative adaptation of surgical planning data is focused. A software assistant to quickly adapt risk analyses and resection proposals in case of intraoperatively detected findings is presented. In this context, appropriate interfaces for surgeon-computer interaction and an approach for automatic generation of virtual resection surfaces are proposed. Second, new visualization techniques designed for intraoperative use are addressed. Intraoperative visualizations have to follow specific requirements such as the workflow and cognitive load of the surgeon, which together call for a context-driven reduction of complexity and a focus on critical areas. Therefore, surgical risk maps and an approach for illustrative augmented reality are presented. The developed visualization techniques provide a new and objective basis for the assessment of risks during liver surgery. Third, new techniques for auditory support for navigated liver surgery are introduced. Auditory support has the potential to reduce the dependency on visual presentations and freeing the surgeon to focus attention on the situs rather than on a monitor. The transfer of these methods from academic research to applicability in clinical routine was an important goal of this dissertation project. A great value was set on including clinicians in the development process by using their feedback to define design requirements, creating new concepts, and finally evaluating the developed methods in a clinical environment. Therefore, the development was accompanied by a number of clinically oriented tests
Downstream process intensification by innovative material development
No full textDue to the development of industrial biotechnology where the high level of the desired product is a reality now, there is a need for efficient purification process design of these entities. The integration of a few downstream processing steps could be the solution to achieve highly pure bio-molecules in less time and with fewer resources. This thesis is based on intensification and integration of downstream processing via incorporation of innovative materials to the separation process. Innovative 3D megaporous and imprinted materials were synthesized by free radical initiation of vinyl monomers. A rigid three-dimensional mega porous monolithic structure was produced by polymerization of selected monomers in the presence of a highly soluble cross-linking agent. The megaporous materials bottleneck is a lower binding capacity of bio-molecules, which renders them useless at the industrial level. Particle embedding, direct chemical synthesis or grafting (radiation-induced and chemical induced) was incorporated to enhance the binding capacity. The material was now able to integrate capture and early purification steps and thus was able to be used for process intensification and integration at an industrial level. Various functionalities were incorporated into the megaporous material after grafting of glycidyl methacrylate to the pore surface. In ion-exchange mode, the dynamic binding capacity for cation-exchanger reached 353 mg per g (10% breakthrough) and 507 mg per g (50% breakthrough) and for anion-exchanger was 58 mg per g. In the form of a metal affinity material, it was able to purify 12 mg per g of His-tagged protein, which shows a single band on SDS-PAGE that confirms the purity and integrity of the target protein. The affinity material was created by covalent immobilization of short peptide on the megaporous backbone, which has the affinity for Immuno globulin. The material was compatible with the routine affinity material possessing protein A ligand, which was synthesized and fabricated in the same way of megaporous material. Finally, the megaporous material was used for enzyme immobilization. Lysozyme supported on a grafted body showed extensive clarification activity against a Micrococcus lysodekticus suspension in the flow-through mode. This experiment proved the materials ability to allow the passage of whole cells without clogging the packed bed. Both protein capture and biocatalysis applications are conceivable with the 3D-megaporous materials. Overall, the system was competent to be used efficiently under chromatographic conditions and thus could be efficiently used for process intensification. A process was designed for the direct capture of low molecular weight bio-molecule (carminic acid, CA); the same adsorbent was not feasible to be used for purification of low molecular weight substances. Therefore, an innovative rigid 3-D beaded molecularly imprinted megaporous material was synthesized by radical polymerization of monomer and cross-linker for process intensification of low molecular weight bio-molecules. The synthesis strategy developed here was a novel method based on the non - covalent approach, which resulted in highly specific particles possessing the high binding capacity. The observed data (surface area, charge, imprinting factor, selectivity factor, maximum capacity and maximum available binding sites) indicates that the imprinted adsorbent could be conveniently utilized for the recovery of CA from cochineal extract in the finite bath mode of operation. The material was able specifically to capture CA from clarified extract in a single step. Mass transfer limitation is the major problem that renders the use of adsorbents from industrial level. In the materials produced here, the mass transfer resistance was evaluated and it was observed that most of the resistances come from the pore diffusion. The increase in the bulk movements was enough to overcome the resistance
Surface energetics of protein adsorption onto chromatographic supports
No full textProtein adsorption onto chromatographic supports has been studied utilizing the extended DLVO approach. Hydrophobic interaction chromatography was mainly explored due to it wide applicability in the recovery of a number of biologically significant macromolecules in its native form. The interactions between a number of selected model proteins and commercially available chromatographic beads i.e., Phenyl Sepharose 6 Fast Flow, Source 15 Phenyl, Toyopearl Phenyl 650-C and Toyopearl Butyl 650-C was studied via extended DLVO (XDLVO) calculations. The physicochemical properties of the proteins and the chromatographic beads, required for the calculations, are achieved by contact angle measurements and zeta potential determinations. Protein properties were investigated both at the hydrated and dehydrated state to achieve the colloidal-type calculation at the low and high salts. The mentioned approach allowed the calculations of interaction energy of proteins to chromatographic supports as a function of distance, at the operating buffer conditions. The XDLVO calculations were correlated with the actual separation behavior of the model proteins. The correlations plotted for all the chromatographic supports under study revealed that all the proteins can be segregated into two main groups; the proteins showing higher interaction energy minimum are eluting late in the chromatography while proteins showing low interaction energy are eluting earlier in the chromatographic experiments. Moreover, the calculations were able to expose the role of backbone chemistry harboring the same ligand and the effect of different ligands immobilized on the same supports. These studies have also shown the effect of the supporting surface used for protein immobilization. Thus, the XDLVO calculations were able to understand the underlying phenomenon and will suggest a broader tool to enhance a better understanding of the downstream bioprocessing, which will facilitate development, optimization and finally implementation of the bioprocess design
Parallels between Manufacturing Systems in Industrial Production and Metabolic Systems in Biological Cells : A Network Based Unifying Model from a Production Logistics Perspective
No full textProduction logistics is the planning, scheduling, and control of all activities in a manufacturing system. The management of operations and logistics in manufacturing systems faces numerous challenges, caused by growth, diversity, dynamics and complexity. At the same time, conflicting targets further detain of a favorable solution. Biological concepts, often developed under the term bionics, promise a new perspective on solution approaches, e.g., in terms of organization principles or heuristics. Metabolic systems have already been recognized by scientists as particularly suited systems for a transfer, because they share numerous properties with logistic systems regarding structure, functions, and goals. However, a detailed analysis of even a proof of the systemic similarity is missing. Additionally, there is currently no foundation for a systematic or structured way of transferring concepts from metabolism to logistics due to the lack of a matching of elements, functions, and goals between the two systems. The result of this work is a network-based model that is able to represent material flow and control procedures in manufacturing systems as well as metabolite flow and metabolic regulation in metabolic systems, the proof of its feasibility by modeling flow networks using real company and metabolic data sets, and the use of measures from complex network theory to identify fundamental commonalities and differences between the two systems that can help creating new ideas for a transfer of concepts from metabolic systems to manufacturing systems
Synthetic Approaches Towards Six-membered Hetero- and Carbocyclic Fluorinated Organophosphonates
No full textA series of CF2-containing alkynylphosphonates I-V have been employed in N,C-, O,C- and C,C-cyclizations with various 1,4-bipolar substrates to give polyfunctionalized hetero- and carbocyclic products, respectively. A variety of starting materials, such as 2-amino-3-formylchromones, 2-aminobenzaldehyde imines, 2-aminoacetophenones, 2-aminobenzophenones and 2-aminobenzonitriles were used as 1,4-bipolar substrates. As a result, we have synthesized novel polyfunctionalized pyridine/quinolines bearing difluoromethylated and phosphonate groups at 2- and 3-positions, respectively. Depending on the electrophilic center on these particular 1,4-bipolar substrates, the quinoline ring was substituted by H, CH3, CF3, Ph and NH2 groups at the 4-position. We have also demonstrated that symmetrical P(O)(OEt2)-acetylene VI reacting with 2-aminobenzonitriles led to 4-aminoquinolin-2,3-ylbisphosphonates. The reaction of VI with 2-aminobenzonitrile through unusual N,N-cyclization proceeded towards a 2,3-diphosphonate 1,4-benzodiazepine derivative in fairly good yield. The second section contains a study on O,C-cyclization of perfluoroalkyl alkynylphosphonates (CF3 I and C2F5 II) with 2-hydroxybenzaldehydes to afford chromenes. We showed that trialkyl amines (phosphines) as mediators provided the target 4H-chromenes; whereas PPh3 changed the regioselectivity resulting in 2H-chromenes carrying only CF3 group at the 2-position. We have also reported the isomerization process of 4H-chromenes into 2H-chromenes with almost quantitative yields. The third section concerns reactions of 1,4-bipolar substrates containing an acidic CH2 group (in-situ generated carbanion) with XF2C-acetylenes I-V via C,C-cyclization. The synthesis of polysubstituted benzene and naphthalene derivatives has thus been accomplished. Additionally, we have presented that the reaction of P(O)(OEt2)-acetylene VI with (2-cyanomethyl)benzonitrile underwent unexpected migration of one of the phosphonate groups. Finally, factors, such as substituents on the aryl ring as well as fluorinated groups in I-V, basic mediator and reaction media (solvents) that influence on the regioselectivity, specificity and efficiency of these hetero- and carbocyclization reactions have been disclosed
Development of a Novel Mass Spectrometric Methodology for the Analysis of Hydrocarbon Content in Light Shredder Waste
No full textThe lack of a routine characterization method for non-volatile hydrocarbons has been an ongoing problem preventing mass spectrometry from the analysis of these hydrocarbons within many sources. Non-polar hydrocarbons are still difficult to be detected by mass spectrometry. Although several studies targeted this problem, lack of self-ionization has been limiting the ability of mass spectrometry to examine these hydrocarbons. A novel identification method for saturated straight-chain hydrocarbons in light shredder waste fraction under atmospheric pressure chemical ionization mass spectrometry (APCI-MS) has been developed. Ionization of alkanes under nitrogen gas source favoured hydrogen abstraction producing majorly (M-H)+ ions which are strictly corresponding to their respective series of n-alkanes between n-decane (C10) and n-tetracontane (C40). The method is shown to produce intact gas phase ions of n-alkane in both reference and real life waste samples. APCI-MS2 fragmentation data assisted in the structural verification of the n-alkanes investigated in both standard and waste mixtures. Additionally the total chemical composition of the light shredder waste fraction was translated by the same method. The mass spectrum displayed a bimodal distribution of odd and even mass ions with a molecular weight distribution range of m/z 200-900 Da. Molecular formulas for a 1000 unsaturated hydrocarbon compounds suggested a dehydrogenation process. The molecular masses were plotted on a Kendrick plot which was successfully employed for monitoring sample degradation. Another selection of high mass linear, branched and cyclic hydrocarbons, reported to be notoriously difficult to ionize, were examined during this study. Using optimized APCI conditions all of these analytes could be ionized without the use of an additional ionization aid and without fragmentation. This finding represents a promising step towards extending the applicability of mass spectrometry to complex non-polar hydrocarbon analyses
Itinerant Spin Dynamics in Structures of Reduced Dimensionality
No full textIn the present thesis results of the study of spin dynamics and quantum transport in disordered semiconductor quantum wires with spin-orbit coupling are presented. Starting from basic spin dynamics we derive the dependence of the weak localization correction to the conductance on the strength and the kind of spin-orbit interaction (linear and cubic Dresselhaus, as well as Rashba coupling), the width of the quantum wires as well as the mobility, temperature and Zeeman term. Furthermore, we exploit the connection found between the microscopic picture given by the Cooperon and the spin diffusion equation to extract the spin relaxation rate which shows the same wire dependencies as the weak localization correction. We also show how the result depends on the smoothness and the direction of the transverse confinement of the quantum wires. In this context we have addressed the question concerning long persisting or even persistent spin states in spintronic devices, presenting the corresponding optimal adjustment of spin orbit couplings of different kind and optimal alignment of the wire direction in semiconductor crystals. Experiments (Holleitner2006, Holleitner2007, Kunihashi2009a, Lehnen2007, hu05_4, Schapers2009) which report the dimensional reduction of the spin relaxation rate in agreement with previous results were raising new questions, in particular as regarding the crossover from diffusive to ballistic wires, which we answer using modified Cooperon equation. In addition, we focus on the intrinsic spin Hall effect, which is only due to spin-orbit coupling. Having shown the basic features with analytical calculations, we solve the spin Hall conductivity in presence of binary and block-distributed impurities (Anderson model). At this we apply the Kernel Polynomial Method, which allows for a finite size analysis of the metal-insulator transition and the calculation of spin Hall conductivity in large systems compared with those addressable with exact diagonalization