Bøger udgivet af Cuvillier

One of the most impressive large rivers worldwide is in Egypt the river Nile known since ages for its intense anthropogenic use as well as for increasing pollution along its course from spring to estuary forming presumably a strong gradient of pollutants. Effective management of the river Nile in a manner that supports a sustainable economy and society with sufficient quantity and quality of water is essential. In order to do this, however, improved water quality monitoring is necessary to facilitate resource protection and to understand ecological changes within ecosystems. In past decades, aquatic monitoring programs dealt only with the measurement of physical and chemical variables. Physicochemical analyses alone are insufficient to provide the information about water quality and it is essential to use biological test systems (biomonitoring) with living cells or organisms that provide a general response to the pollutants present in the sample. Biomonitoring takes advantage of the knowledge that chemicals that have entered the organisms leave biomarkers reflecting this exposure. Biomarkers have been proposed as sensitive tools for detecting environmental exposure and adverse effects of toxic anthropogenic chemicals on aquatic organisms. Biomarkers may take many forms ¿ from the assessment of chemical residues in the tissues of living organisms (bioaccumulation level), through to assaying specific biological end points based on changes to various biochemical, physiological, morphological or behavioral characteristics in organisms, as well as traditional ecological community attributes such as abundance and diversity. Biomarkers at the molecular level tend to respond first, followed by responses at the cellular (biochemical), morphological/histological and whole-body levels. Thus, by monitoring molecular, biochemical and physiological parameters biomarkers can be used as an early warning system and the potential harm of an agent can be assessed before more severe disturbances/consequences occur. Within this book, in the interest of clarity, the early warning biomarkers are limited as ¿rapidly-responding biomarkers¿ to the sub-organismic changes, such as bioaccumulation biomarkers, molecular biomarkers, biochemical biomarkers, physiological biomarkers, and morphological/histological biomarkers, that can be measured in cells, body fluids, tissues or organs within an organism and are indicative of xenobiotic exposure and/or effect.

The main aim of the research presented in this thesis was to expand the substrate scope of the iridium-catalyzed asymmetric hydrogenation, which represents an extremely useful methodology for the enantioselective synthesis of chiral molecules.While this chemistry has been developed and investigated mainly for the hydrogenation of unfunctionalized olefins, so far only little attention has been given to functionalized olefins. Therefore, the different research projects presented in this thesis dealt with the application of iridium catalysts to the reduction of particularly valuable substrates that are difficult to hydrogenate enantioselectively with other methods.The first chapter of this thesis gives a general introduction on asymmetric hydrogenation and the role of iridium catalysts in this context. The following two chapters deal with the investigation of new substrates in the iridium-catalyzed asymmetric hydrogenation using various N,Pligands developed in the Pfaltz group,and give an account of the superior results that have been obtained with such catalysts compared to thoserepresenting the state-of-the-art. In particular, chapter twoconcerns the reduction of vinylsilanes, for which the judicious choice of the best catalyst for each specific substrate was required to achieve good results in term of both chemical and optical yield. On the contrary, a pyridinyl phosphitine bearing a 2,6-difluorophenyl group on the oxazoline ringwas best suited for a broad array of 2-alkyl- and aryl- substituted maleic acid dimethyldiester, as reported in chapter three. Such process turned out to be enantioconvergent, allowing the hydrogenation of mixtures of maleates and fumarates in high enantiomeric excesses.In chapter fourthe deployment of environmentally friendly solvents such as THF and 2-MeTHF in the iridium-catalyzed asymmetric hydrogenation of 3,3-disubstituted allylic alcohols is described. Finally, chapter five of this dissertation deals with the development of new NHC ligands for the iridium-catalyzed asymmetric hydrogenation of acid-labile substrates such as tert-butyloxycarbonyl protected allylic alcohols. Experimental details and characterization of the substances discussed in the main body of this manuscript is reported in the experimental section that constitutes chapter six.

The study investigated the influences of wood modification on the properties of Polyvinyl chloride (PVC) based Wood Polymer Composites (WPC). Various ethanolamines, L-arginine, pre-hydrolyzed and monomeric aminosilane, melamine and acetic anhydride treatment were used to improve the adhesion between wood and polymer as well as water absorption behavior and resistance to basidiomycetes. Amine based treatments were chosen to change the nature of wood from acidic to basic in order to increase the compatibility with the acidic polymer. Treated and untreated wood flour, PVC and additives were dry blended in a mixer. The dry blend was compounded to granulate by counter-rotating twin screw extrusion and compression moulded into panels using a hydraulic press.Elemental analysis (nitrogen content) via gas chromatography showed expected fixation of aminosilane and melamine treatment. The nitrogen fixation of ethanolamine and L-arginine treated material were obviously reduced, whereas the amount and reactivity of the aminogroups influenced the fixation behavior. With increasing content of amino-groups and reactivity, the fixation was improved. Fourier transform infrared (FTIR) analyses revealed interactions between monoethanolamine and cell wall components. The amine based treatments changed the nature of wood from acidic to basic. An improvement of the interphase was detected via mechanical property testing. Tensile strength, elongation at break and unnotched impact strength of the composite were obviously increased by Larginine, ethanolamine and aminosilane treatments. It has to be considered that amine based treatments (monoethanolamine in this study) led to reduced thermal stability of the composite. Thermogravimetric analysis showed a decrease of onset temperature with increasing monoethanolamine content. Water repellence of the composite was improved by melamine, pre-hydrolyzed aminosilane and acetic acid treatment. Treated and untreated composites revealed high resistance against basidiomycetes. Due to the low initial moisture content and low weight loss of untreated and treated composites, no effect of the various modifications was distinguished.

This Journal examines the state of African developmentsince independence. It compares the past and thepresent and addresses the issues systematically. Mostof the materials in this Journal were based on otheractivists and IAHRAC interventions on issues relating toHuman Right abuses. Some of the materials were alsocollected from already existing journals and issues onAfrica affairs especially from the UN point of view.The Journal dwells on the role of leaders with specialemphasis on some countries as well as the role of individualsin various countries¿ development. The materialsin this Journal critically reviewed the factors hinderingAfricäs development and encouraged leaders to takemeaningful steps forward, after fifty years of independence.The materials in this Journal are written by severalhuman rights activists and intellectuals from differentacademic domains. This Journal will be useful for individualsand academic institutions whose role is to promotedemocracy in both developed and developing countries.It is our aim that readers understand the effects of goodgovernance, political change in various African countriesand the problems affecting food insecurity in thecontinent.

Various health problems are associated with the disruption of circadian rhythms. In particular,psychological disturbances often show disrupted sleep-wake cycles as a symptom,suggesting a relation between a disrupted circadian clock and mental health problems suchas affective disorders, schizophrenia and addictive disorders. The mentioned vital clockworkis sustained by specific circadian oscillatory expression of clock genes ¿ which controlthemselves via transcriptional/translational feedback loops ¿ and influences behavioural,biochemical and physiological circadian rhythms. Increasing evidence suggests aninteraction of these so-called clock genes and glucocorticoids. For this reason, we wereinterested in the question of whether the cortisol response after awakening is associated withthe gene expression of the clock genes hPER1 and hPER2, in particular hPER1, given thatits DNA sequence disposes of a glucocorticoid-responsive element and is therefore mostlikely influenced by glucocorticoids.Data 1: We investigated thirty-one healthy men aged 20-30 combining microbiological andpsychometric methods. We measured the amount of mRNA of hPER1 and hPER2 on twoconsecutive mornings as well as twelve hours later in the evenings of the same days. Tomeasure the increase of cortisol after awakening, we sampled cortisol levels immediatelyafter, 30 minutes after and 60 minutes after awakening on both mornings. Additionally,subjects filled in questionnaires to assess their level of chronic stress. We found anassociation between the gene expression of hPER1 and age as well as the increase ofcortisol in the morning, whereas the gene expression of hPER2 seems to be associatedprimarily with age and levels of chronic stress.Data 2: Furthermore, since numerous mental health problems are associated with adisruption of the sleep-wake cycle, a disturbance of the circadian clock on a molecular levelseems likely. Simultaneously, psychosocial stress is considered as a major factor in theetiology of several mental health problems. For this reason, we aimed to investigate theputative cortisol-mediated influence of acute and chronic psychosocial stress on the geneexpression of hPER1 in thirty-one healthy men. Our findings suggest that firstly, acutepsychosocial stress influences the expression of hPER1, and secondly, chronic stressinvolves heightened gene expression of hPER1.

M31, better known as the Andromeda Galaxy, is the nearest grand spiral galaxy. Its proximity allows us to reach high spatial resolutions and study it in great detail. Already early analysis of the polarized emission has shown that the turbulent and large-scale magnetic field is concentrated in a ring-like structure at 10 kpc radius. The presence of a regular field over such long distances can be explained by galactic dynamo theory. However, the structure of the M31¿s large-scale magnetic field is unusually simple. An almost purely axisymmetric field is not known from any other spiral galaxy.The aim of this work is to provide new clues to the understanding of M31¿s magnetic field structure, by utilizing new methods for data analysis, better resolutions and higher sensitivities than ever before, and by advancing into new wavelength regimes.

The function of membrane proteins is mainly dependend on their aggregational behavior. Some are active as monomers, whereas others need to assemble into oligomeric states.1 In this context, molecular recognition, which is realized within the membrane and in the adjacent water layer, is crucial to achieve a specific assembly. In order to establish a well defined model system to study assembly processes in membranes, a recently reported D,Lalternating double helical hairpin construct in structural analogy to the natural antibiotic gramicidin A was utilized.[2,3] Recogntion at the membrane/water interface was addressed via met al complex formation as well as duplex formation of a short PNA sequence. To achieve recognition within the bilayer, nucleobases or polar amino acid residues, respectively, were introduced in the center of the hairpin TMD. Additionally, fluorophores were attached applying an orthogonal protecting group strategy. The functionalized TMDs were reconstituted in large unilamellar vesicles (LUVs). The in membrane pore formation by adopting 5.6 double helices was investigated using CD spectroscopy and the dynamic aggregation process was determined using fluorescence probes for Fluorescence Resonance Energy Transfer (FRET). For orientational studies as well as distance measurements of membrane incorporatedpeptide homodimer structures, spin probes were introduced within the lead structure. These homodimers were incorporated in LUVs and the 5.6 structure was determined via CD analysis. Further investigation will be performed applying EPR measurements.

In this thesis, we consider mechanical problems with nonmonotone contact, like adhesive problems, delamination problems, bilateral contact problems with nonmonotone friction law, nonmonotone unilateral contact, etc. In all of them the contact phenomena are described by nonmonotone and multivalued laws, which can be expressed by means of the Clarke subdifferential of a locally Lipschitz function called a nonconvex, nonsmooth superpotential. Problems involving such laws give rise to hemivariational inequalities introduced for the first time by the engineer Panagiotopoulos in the eighties.In this work, we combine the regularization techniques with the finite element method to approximate a special class of hemivariational inequalities with maximum (resp. minimum) superpotential. Using some classes of smoothing approximations for nonsmooth functions based on convolution, we provide a regularization procedure to smooth the nonsmooth superpotential. The non-differentiable functional is approximated by a family of differentiable ones. Convergence of the solution based on the regularized problem to the solution of the original problem is shown. Then, the finite element approach for the regularized problem is analysed and convergence results are given. As an application we consider some model examples from continuum mechanics with nonmonotone contact and present some numerical results.

In this thesis four challenging problems concerning metal- or metalloid-containing systems were carefully studied in order to explain their properties, reactivities and selectivities. The first project focused on the dialkylzinc additions to unsaturated aldehydes. The reaction was proved to have bimetallic intermediates. The experimentally observed non-linear effect was addressed to the differences in stability of various zinc-ligand aggregates. Furthermore, the differences in regioselectivity between cinnamaldehyde and N-formylbenzylimine were traced back to the differences in the ¿-conjugation of both compounds. In contrary, the stereoselectivity of the reaction was controlled by the paracyclophane unit as well as by bulky substituents in the side-chain of the ligand. Based on these findings, a set of modifications for the ligand system were proposed and tested in silico. One of the compounds is expected to be superior to any previous catalysts. An important outcome from this study is the survey of methods used in calculations of reaction barrier heights. It is shown that economic DFT calculations, when extended by empirical dispersion corrections allow for the prediction of stereoselectivities. However, the prediction of the regioselectivities is a much more demanding task and only a consistent treatment of electron correlation can yield qualitative agreement with experimental findings. In this case, the computationally more expensive ¿ but even for large systems still applicable ¿ LPNO-CEPA/1 approach seems to be an efficient and reliable choice.

The main objective of this thesis is to analyze combustion instabilities in a matrixburner. The various tools that exist for analyzing thermoacoustic instabilities areapplied to the matrix burner with multiple flames. The principal goals are to determinethe primary causes of combustion instabilities in the burner and to exploreways of controlling such instabilities in order to prevent damage to the burner.To achieve these goals, the stability map of the burner obtained from measurementsis analyzed. This is followed by the analysis of the aerodynamics of the cold flowusing CFD. Results obtained from CFD are validated with PIV and LDA resultsfrom measurements. Critical are the centerline axial velocity inside the combustionchamber and the recirculation zones on the walls of the combustion chamber andthose between the various slots of the matrix burner.Cold flow simulations are followed by reactive flow simulations for both gaseous andliquid fuels. A detailed atomization model is developed for the liquid fuel case fromexperimental data. Two combustion models, namely, the combined finite rate/eddydissipation model and the finite rate chemistry model are compared in the CFDsimulations of combustion instabilities and validation with measurements are done.The latter is chosen over the former because it accounts for chemistry and it is notnumerically dissipative. Two CFD softwares, Fluent and CFX are also compared todetermine which is better at capturing acoustics. System identification using CFDis used to determine the flame transfer function and the acoustic transfer matrix.This is followed by the use of acoustic forcing and fuel modulation on the primaryand pilot in order to limit the amplitude of the instabilities inside the matrix burnercombustor.The 1D acoustic network is used to determine the longitudinal eigenmodes of thematrix burner. This is followed by the use of 3D finite element method (FEM) andfluid-structure interaction (FSI) to determine whether a coupling exist between thefluid and structure of the matrix burner combustor and vice versa.Finally, Full harmonic analysis is performed for the rectangular combustor and theresults obtained are validated with analytical results. This is followed by the 3Dstructure modal analysis of the full matrix burner test rig.

The infrared spectral region between wavelengths of 2 and 6 µm is of great importance in molecular physics. Molecules with an X-H bond (X being carbon, nitrogen or oxygen) exhibit strong vibrational transitions there, but also linear carbon clusters Cn (n=2,3,¿). Many combination bands and overtones of low-energy vibrational modes also occur in this spectral range. Analyses of these spectral features allow ¿ if highly resolved ¿ for example the prediction of pure rotational transitions in the sub-mm wavelength regime, or help understanding the internal dynamics of the molecule.To provide radiation sources with extremely large frequency coverage, two optical parametric oscillator (OPO) systems in the wavelength regions from 2.5 to 4.1 µm and from 4.7 to 5.4 µm have been set up and characterized in this thesis. The OPO system around 5 µm wavelength is the only one in this spectral region used in high-resolution spectroscopy up to now. Both of the OPO systems have been shown to be ideal tools for spectroscopic studies delivering highly accurate transition frequencies of transient molecules, using the following example cases:The rovibrational spectrum of the fundamental cation CH2D+ around 3.2 µm wavelength has been measured with unprecedented spectral resolution and frequency accuracy. The combination of the OPO as radiation source with a cold ion trap to produce and store the ions has been proven to have a high predictive power for pure rotational transition frequencies of CH2D+. Located at around 100 to 200 GHz, these are of great importance in astrophysics.The V3 fundamental vibration of Si2C3 around 5.1 µm wavelength has been measured using the OPO and a newly built jet spectrometer for the production of transient molecules. Molecular parameters have been determined with high precision. An associated hot band originating from the V7 vibrational bending mode has been resolved and analyzed for the first time.The pure carbon clusters C3 and C7 have also been examined. For the first time, a combination band of C3 and an associated hot band were detected around 3.0 µm wavelength in the gas phase. Their analyses yield valuable information about the potential energy surface of C3. Analysis of the V5 mode of C7 delivered further proof of its rigidity, which was put into question by earlier works. Last but not least, a previously unknown associated hot band of C7 has been detected and analyzed.

Proof complexity focuses on the complexity of theorem proving procedures, atopic which is tightly linked to questions from computational complexity (theseparation of complexity classes), first-order arithmetic theories (bounded arithmetic),and practical questions as automated theorem proving. One fascinatingquestion in proof complexity is whether powerful computational resources as randomnessor oracle access can shorten proofs or speed up proof search. In thisdissertation we investigated these questions for proof systems that use a limitedamount of non-uniform information (advice). This model is very interesting as¿-in contrast to the classical setting¿-it admits an optimal proof system as recentlyshown by Cook and Krajícek. We give a complete complexity-theoretic classificationof all languages admitting polynomially bounded proof systems with adviceand explore whether the advice can be simplified or even eliminated while stillpreserving the power of the system.Propositional proof systems enjoy a close connection to bounded arithmetic.Cook and Krajícek (JSL¿07) use the correspondence between proof systems withadvice and arithmetic theories to obtain a very strong Karp-Lipton collapse resultin bounded arithmetic: if SAT has polynomial-size Boolean circuits, then thepolynomial hierarchy collapses to the Boolean hierarchy. Here we show that thiscollapse consequence is in fact optimal with respect to the theory PV, therebyanswering a question of Cook and Krajícek.The second main topic of this dissertation is parameterized proof complexity, aparadigm developed by Dantchev, Martin, and Szeider (FOCS¿07) which transfersthe highly successful approach of parameterized complexity to the study of prooflengths. In this thesis we introduce a powerful two player game to model andstudy the complexity of proofs in a tree-like Resolution system in a setting arisingfrom parameterized complexity. This game is also applicable to show stronglower bounds in other tree-like proof systems. Moreover, we obtain the first lowerbound to the general dag-like Parameterized Resolution system for the pigeonholeprinciple and study a variant of the DPLL algorithm in the parameterized setting.

Besides chemical synthesis routes, nanoparticles can be produced in top-down processes nowadays. Stirred media mills are commonly used to break particles down to the nanometer range. Thereby, their stabilization against agglomeration plays a major role to obtain nanoparticle suspensions with the desired properties. Whereas different stabilization methods have been a subject of much research in the last few years, the breakage behavior of nanoparticles is not well understood for the time being. A discrepancy exists between the common state of the art that particles cannot be comminuted below the brittle-to-ductile transition size, which is in the range of a few µm for ceramic particles, and the experimental findings of particles sizes in the nanometer range. In this work, long term grinding experiments of different oxide and non-oxide inorganic materials were carried out to investigate the breakage behavior in the nanometer range. By means of X-ray diffraction analysis and TEM investigations, the evolution of the internal microstructure of the particles was followed during the grinding treatment. A strong correlation between the microstructure and the fracture ability was found. In addition, the existence of a true grinding limit, where no further fracture takes place, and the influence of process and environmental conditions was demonstrated. A physical explanation of the grinding limit originates from changes in the defect structure below a critical crystallite size.Besides the breakage behavior of brittle ceramics, the grindability of graphite particles as a typical layered material was also investigated. The strong anisotropy of the bond forces in the crystal results in a selective size reduction during the grinding process. By adjusting the process conditions in a way that the acting forces overcome the attractive van der Waals forces between the graphene sheets without breaking them, the production of thinnest flakes with high aspect ratios is allowed. The size reduction was realized as a kind of peeling process. Various analysis techniques such as AFM, Raman spectroscopy, TEM or XPS were employed to characterize the delaminated sheets, especially to determine the exact number of layers. Furthermore, information about the yield of delaminated sheets was given and first examples of application are presented.

Die Entwicklung von innovativen Lösungen durch Freiwillige in Online Communities ¿ sogenannten ¿Open Collaberative Innovation¿ (OCI) Communities ¿ hat beachtliche Aufmerksamkeit durch die Wissenschaftsgemeinde erfahren. Ein Grund dafür ist, dass viele dieser Communities extrem erfolgreich sind, wie die Beispiele von Wikipedia oder unzähligen Open Source Communities zur Softwareentwicklung zeigen. Eine der Kernfragen bei der Erforschung dieses Phänomens ist die Problematik der Governance in solchen Communities. Governance umfasst die Mechanismen zur Koordination der Arbeit und zur Sicherung des Austausches zwischen verschiedenen Akteuren. Zusätzlich versuchen immer mehr Firmen die Vorteile von OCI Communities zu nutzen, indem sie entweder eigene Communities gründen oder mit bestehenden interagieren. Diese Entwicklung hat direkte Auswirkung auf die Frage der Governance, da sich der Fokus von einer reinen Selbststeuerung der Community hin zu einer externen Steuerung durch die Firma verschiebt. Die folgende Arbeit untersucht dieses Problem, indem die die Auswirkung von zwei verschiedenen Governance Ausprägungen (exogen vs. endogen) in einer Innovations-Community gegenüber gestellt wird. Dies wird mittels eines Experiments erörtert. Communities of volunteers creating innovative outcomes, so called open collaborative innovation (OCI) communities, have received considerably scholarly attention. Attention, because such communities have shown extremely successful as the outstanding examples of Wikipedia and numerous open source communities producing software confirm. When investigating OCI communities¿ one key question is governance, that is, the way the community coordinates work and safeguards their interactions. Recently, a growing number of firms have started to make use of OCI communities, either by sponsoring or interacting with them. The emergence of firms shifts the focus from self-governance of volunteers to external, firm initiated, governance of communities.The following book examines this issue, by contrasting two modes of governance (exogenous vs. endogenous governance) within a community. The question is investigated through an experimental approach.

Transitional Justice is increasingly consolidating as a legal framework directed at providing an answer as to how to deal with the serious violations of human rights committed during a warlike conflict or a dictatorship. In order to achieve this goal, transitional justice resorts to measures which must have the victim¿s rights as a limit. The victim¿s perspective is emphasized in the context of transitional justice due to the special characteristics of physical and psychological harm that they suffered during the constitutional break. Thus, victims¿ rights constitute a schema of reference for determining the admissibility of a political measure enacted during the transition or the re-thinking of traditional legal institutions. It is precisely in this context that the statute of limitations must be questioned with regards to the criminal prosecution of core crimes.

The theme for this year¿s Tropentag, ¿Agricultural development within the rural-urban continuum¿ has a very special significance. The question of how agricultural production will respond to the dramatic shift in the rural-urban continuum is not only highly relevant but also vital for the future. In developing countries, rural areas still have the highest birth rates. Therefore, even with a high rural exodus, the absolute population in these areas will experience an increase lasting far into the next decade. The size of the rural population will not start to fall until later in this century. On the other hand, cities are growing at an unprecedented rate. From the estimated global population of 9.6 billion in 2050, 70% will be urban inhabitants. Already today the demand for food from a growing urban population in the developing countries is huge. A large middle-class is forming in the cities of these countries too, with a growing appetite for better quality, high protein foods. Must this increased overall demand be primarily met by buying on world markets? Or could local agriculture provide sufficient goods to cover the growing demand? Increased urbanization offers huge opportunities for development, not only for cities but also for rural areas and for agriculture. Urbanisation gives many small farmers the opportunity to make the leap from subsistence farming to producing for urban markets. This opportunity to earn an income can, for many families in rural areas, be the decisive step away from poverty and hunger. At the same time, new forms of ¿urban agriculture¿ are also offering interesting opportunities for development in the growing cities.

Die Finite-Elemente-Simulation ist ein wichtiges numerisches Werkzeug zur Verbesserung des Verständnisses des Spanbildungsprozesses. Mit dieser Methode können komplexe Bearbeitungsprozesse mit komplexen Span-Morphologien simuliert werden. Eine wichtige Herausforderung bei der Modellierung spanender Bearbeitungsverfahren ist, dass keine Materialparameter bekannt sind, die das Werkstoffverhalten unter stark variierenden Dehnungen, Dehnungsgeschwindigkeiten und Temperaturen vorhersagen können. Während eines Fließspanbildungsprozesses können Dehnungen von bis zu 200%, sowie Dehnungsgeschwindigkeiten in der Größenordnung von 105 s¿1 und Temperaturerhöhungen im Bereich von mehreren 100 ¿C auftreten. Im Vergleich dazu können experimentelle Methoden wie der Split-Hopkinson-Pressure-Bar-Test (SHPB) in der Regel Dehnungen von bis zu 50% und Dehnungsgeschwindigkeiten in der Größenordnung von 103 s¿1 erreichen. Diese Tests können dazu genutzt werden, um mittels Datenanpassungsmethoden die Materialparameter aus den experimentellen Daten zu bestimmen. Aufgrund der großen Extrapolationsbereiche stimmen die Ergebnisse der Zerspanungssimulationen in der Regel nicht besonders gut mit den experimentellen Ergebnissen überein.Zuerst werden die Schwierigkeiten der Verwendung der Materialparameter, die aus Standard-Experimenten bestimmt werden, für die Zerspanungssimulationen von drei verschiedenen Werkstoffen aufgezeigt. Die Johnson-Cook-Parameter werden für Ti-15-3-3-3, Ti-6246 und Alloy 625 aus SHPB-Experimenten bestimmt. Diese werden anschließend verwendet, um die Spanbildung mit Hilfe der Finite-Elemente-Methode zu simulieren. Für Ti-15-3-3-3 und Ti-6246 wird die Bildung eines segmentierten Spans beobachtet. Für Alloy 625 wird die Materialfestigkeit bei hohen Dehnungen vom Johnson-Cook-Modell überschätzt, wodurch in der Simulation die Bildung eines Fließspans vorhergesagt wird. Daher wird ein modifiziertes Johnson-Cook-Modell für die Zerspanungssimulationen verwendet, resultierend in einer segmentierten Spanform. Die durchschnittlichen Schnittkräfte werden in den drei Fällen im Rahmen von 20% der experimentell erhaltenen Werte vorhergesagt. Es gibt deutliche Unterschiede in den vorhergesagten und den experimentell ermittelten Spanformen. Diese Unterschiede können auf die Schwierigkeit der Vorhersage des Materialverhaltens unter den während spanender Bearbeitung vorherrschenden Bedingungen zurückgeführt werden.Dieses Problem wird durch die Verwendung einer inversen Parameterbestimmungsmethode beseitigt, da auf diese Weise die Materialparameter direkt aus den Zerspanungsprozessen identifiziert werden. Die Spanformen und die Schnittkräfte der Simulation werden durch die systematische Variation der Materialparameter mit den entsprechenden Werten aus den Standardexperimenten abgestimmt. Die Robustheit des Verfahrens wird durch die Identifizierung von Parametern für zwei verschiedene Materialien, sowie die Durchführung von Optimierungen von verschiedenen Ausgangspunkten getestet. Ebenfalls werden Studien durchgeführt, um die Konvergenz zu verbessern, und um den Berechnungsaufwand zu reduzieren. Die Lösung, die aus dem inversen Identifikationsalgorithmus vorhergesagt wird, kann ebenfalls durch die Kenntnis des Einflusses der Spannungs-Dehnungs-Kurven auf die Spanformen und die Schnittkräfte verbessert werden, was auch den Berechnungsaufwand verringern kann.Es hat sich gezeigt, dass viele Parametersätze identifiziert werden können, die ähnliche Spanformen und Schnittkräfte zur Folge haben. Dies ist darin begründet, dass alle Parametersätze im Gebiet der Zerspanungverfahren die gleiche Fließspannungskurve wiedergeben. Um Parameter zu bestimmen, die über einen möglichst großen Bereich gültig sind, werden sich stark unterscheidende Schneidbedingungen für den Identifikationsprozess gewählt.

One approach to detect gravitational waves, which have been postulated by Albert Einstein in his General Theory of Relativity, is based on interferometric measurements oflength variations with a large-scale Michelson interferometer. The detection range of theseground-based observatories is currently limited to approx. 15 Megaparsec (Mpc) becauseof a reduced sensitivity at detection frequencies of 10 Hz ¿ 10 kHz by shot noise. Theselimitations can be overcome by an output power increase of the detector¿s light source,which will enhance the sensitivity by an order of magnitude. Thus, the possibility of detecting a gravitational wave will be raised by a factor of 1000 and the detection range will be increased to 150 Mpc, accordingly.In this work a laser systems is presented, which fulfills the free-running laser requirementson stability and beam quality required by the next generation of gravitational wave detectors for the first time. The developed laser system is based on a two-stage concept,supplemented with an active amplitude and frequency stabilization, which is not partof this work. A 35 W Nd:YVO4 amplifier system with an emission wavelength of 1064nm represents the frequency reference of the laser system and is used as the seed for aninjection-locked high power oscillator. This amplifier, which is based on a Master OscillatorPower Amplifier scheme, is already used in today¿s gravitational wave detectors and hasbeen proven to be reliable in long-term operation. The linearly polarized output power ofmore than 200 W is generated inside the oscillator stage, which consists of four Nd:YAGcrystals arranged in an asymmetric ring resonator configuration. To compensate for lossesdue to thermal birefringence inside the longitudinally pumped laser crystals, an imagingdepolarization compensation is used.

Während die landwirtschaftlichen Produktivitätsfortschritte von der Entwicklung der Gesamtwirtschaft eines Landes abhängen, spielt die effiziente Nutzung von landwirtschaftlichen Inputs eine wichtige Rolle für das Wachstum des Farmsektors. In Diskussionen über angemessene Politiken für Länder im Transformationsprozess ist auf diesen Unterschied oft hingewiesen worden. Dennoch gibt es bisher kaum quantitative Analysen der Effizienz der Ressourcennutzung während des Transformationsprozesses in den zentralasiatischen Ländern. Die vorliegende Studie ist eine der ersten, die für Usbekistan empirische Evidenz über die Effizienzniveaus bei der Produktion von Baumwolle, Weizen und Gemüse liefert. Auf der Basis von Querschnittsdaten des Landwirtschafts-Surveys von 2007 für die usbekischen Regionen Khorezm und Fergana wird die Ressourcennutzung der landwirtschaftlichen Betriebe untersucht. Methodisch kommen sowohl parametrische als auch nicht-parametrische Verfahren der ¿Frontier Analysis¿ zur Anwendung. Im Fall der Baumwollproduktion wurde ein theoretisch konsistentes Frontier-Modell entwickelt, um technische Effizienzniveaus zu messen und Gründe für Ineffizienz zu bestimmen. Die verwendete Analysetechnik erlaubt es, sowohl monotone als auch quasi-konkave Restriktionen in einem semiparametrischen Umfeld zu betrachten. Die empirischen Ergebnisse der Modelanalyse zeigen Effizienzniveaus von 85% bzw. 88% für Khorezm und Fergana. Sie belegen, dass es auch ohne die Einführung neuer Technologien Spielräume für eine Erhöhung der Baumwollproduktion gibt.

Agriculture remains the most important sector for promoting economic growth in developingcountries. In agriculture-based economies, the sector accounts for about 29% of the grossdomestic product (GDP) and employs 65% of the labor force (World Bank, 2007). About 75% ofthe world¿s poor live in rural areas, where agriculture is the main economic activity. Crosscountry comparison shows that GDP growth induced by agriculture is at least twice as effectivein reducing poverty as GDP growth outside agriculture (World Bank, 2007). Agriculture is,therefore, imperative in reducing mass poverty and food insecurity in developing countries.

Rapid urbanization in developing countries affects the social, economic and ecologic relationships between urban inhabitants. Even though urban and peri-urban agriculture (UPA) is well appreciated by the Food and Agriculture Organization (FAO) and United Nations (UN), it is often criticized due to its intensive mode of production and safety aspects. Only little is known about the UPA production system in the Mumbai Metropolitan Region (MMR). In order to characterize the various UPA production systems across MMR, a baseline survey was conducted in 2010 and further detailed investigations were conducted for general soil characterization and heavy metal signatures.Based on the results of a baseline survey of 165 households, the UPA production systems in the MMR were characterized according to their socio-economic, demographic, migratory and features related to production system. Five major UPA systems were detected: railway gardens, balcony gardens, terrace gardens, farms and ¿Tabelas¿ ¿ enclosures where buffalos and cows are reared for milk. A great diversity of vegetables, fruits, plantation crops and flowers prevail in these systems. The railway gardens in their majority (79%) were managed by migrants. The use of mineral fertilizers and pesticides prevalent in farms and railway gardens, while pesticide usage was absent in balcony and terrace gardens. The use of waste water among railway gardens accounted for 98% of the overall irrigation water usage; while the other production systems depend upon well water and tap water. Labor shortage is an increasing problem in UPA of MMR, while marketing channels are well organized and connected. In all cases studied, UPA systems contributed to food security and employment opportunities on limited land and helped to recycle organic waste.

Globalization requires companies to intelligently distribute work across time and space. Therefore, organizations increasingly turn to virtual teams (Majchrzak et al. 2005). Research defines virtual teams as groups of geographically distributed individuals that rely on information technology for accomplishing their work (Powell et al. 2004). Modern organizations increasingly require the formation of structurally diverse teams, where employees work with team members from different business units, overseas branches or delegates of other companies (Cummings 2004). Structurally diverse arrangements allow for sharing knowledge and integrating different perspectives to expedite implementation of new ideas and spark innovation across locations (Majchrzak et al. 2004). Moreover, facing increased market pressure to cut costs, companies increasingly outsource business functions to external providers. For this purpose, work teams of outsourcer and provider have to coordinate the provision of services and the transfer of business specific knowledge across time and space (Dibbern et al. 2008).In contrast to co-located teams, virtual teams hardly meet in person and therefore have to fully rely on information technology (Robert et al. 2009). Technology, however, severely limits the means of communication and thus tremendously changes the way people work together (Powell et al. 2004). Consequently, a plethora of studies have sought to investigate why collaboration in virtual teams is much more difficult than in co-located settings (Hinds and Bailey 2003; Powell et al. 2004). A fundamental problem of virtual collaboration is that team workers lack awareness about their team members¿ activities (Kraut et al. 2002). According to Dourish and Bellotti (1992, p. 107), awareness denotes the ¿¿ understanding of the activities of others,which provides a context of [ones] own activity¿. In co-located teams, peo ple learn about each other¿s activities by simply observing their team members carrying out a task, speaking about their activities in scheduled meetings as well as during chance encounters in the office space. In virtual teams, however, people cannot observe their colleagues and rarely meet in person (Kraut et al. 2002).