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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Charakterisierung thermoreversibler Gele im Zentrifugalfeld - Characterization of thermoreversible gels in a centrifugal field

Kisters, Dirk 23 May 2001 (has links)
In the theoretical part of this work it is shown that the Lamm´s Differential Equation for polymer solutions can be extended to swollen polymer networks, if the phenomenological equations and the equation for the chemical potential of the polymer component in the network are taken into account. All differences for a transition from a polymer solution to a swollen polymer network can be assigned a "Elastically active coefficient E", which describes a deformation velocity with the same unit as the diffusion coefficient. In the practical part of this thesis some new improvements/developments regarding the Schlieren optical system are introduced and discussed. In the part "Results and Discussion" the results of the centrifugal measurements of gelatine gels are presented and discussed. The following evaluation of the centrifugal runs of polyacrylat gels (chemical networks) and the comparison with the results of the gelatine gels (physical networks) shows clearly that the new theory is suitable to describe the move ment of the polymer component in the network in a centrifugal field quantitatively as well as qualitatively.
32

Implementation und Verifikation eines generischen wissensbasierten Netzwiederaufbau-Systems - Implementation and verification of a generic knowledge based restoration system

Salek, Kambiz 23 May 2001 (has links)
Restoration of electrical power systems after severe disturbances is characterised by high time pressure and low experience of the operating personnel. The thesis describes a flexible approach for training and/or guidance of operators in system restoration, for the first time realised as a generic solution applicable to any given disturbance situation in any power system. Under consideration of the actual states of network and power units the system step by step suggests operational measures to be per-formed. The implementation also comprises components for knowledge acquisition, consistency check and explanation of reasoning; optionally an acoustic user dialogue can be activated. Coupling of the entire system with an operator training simulator gave the opportunity for verification with a large variety of scenarios on different power systems replicated under operational realism.
33

Elektrochemie supramolekularer Systeme - Electrochemistry of supramolecular systems

Uebe, Jochen 23 May 2001 (has links)
Host and guest compounds self-assemble to supramolecular complexes. Noncovalent bonding donor-acceptor-interactions of supramolecular complexes like that of J. F. Stoddart et al. can be weakened by redox reactions, but the complexes desintegrate. Here, it is described the reversed way. The initial reaction mixture contains a host and a potential guest compound not interacting with each other. The potential guest compound will be transferred in a real guest compound by electrochemical reduction and the supramolecular complexation is induced. Tetracationic, electronwithdrawing cyclophanes with two redoxactive units of 4,4-bipyridindiium respectively 2,7-diazapyrendiium act as host compounds, electronwithdrawing quinones as potential guest compounds. The host and guest compounds and their interaction in complex are characterized and studied by cyclic voltammetry and spectroelectrochemistry. It can be demonstrated that the reduction potentials are shifted, that the cyclophane and the guest compound form an inclusion complex and that the inclusion complexes are low soluble, exclusion complexes well soluble.
34

Methoden zur Dynamikerweiterung in der zweidimensionalen CMOS-Bildsensorik - Dynamic range expansion in CMOS imaging

Schrey, Olaf 25 May 2001 (has links)
Nearly 80% of the worldwide semiconductor market volume is covered by standard-CMOS-technology products. Due to the increasing demand on highly flexible, reliable and robust image sensors from many different industry parts, CMOS-technology has become more and more attractive, since it offers several features in contrast to the CCD-technology. The focus of this work lies on the development of high dynamic range CMOS image sensors suitable for industrial, automotive and consumer applications. The developed sensors should yield more powerful and cost-saving system solutions compared with CCD-sensor systems that are available from the market. The work concentrates on mainly linear CMOS-sensors offering a linear dependency between illumination and electronic signal representation. The developed sensors achieve a dynamic range of more than 90dB, which is much more than CCD´s have with 50-60dB. Two sensors are presented with the first one using a mixed logarithmic/linear characteristic and the second sensor working with a multi-illumination scheme using different exposure/integration times, resp. The work finishes with a discussion of the presented sensors and their underlying signal processing algorithms and a short outlook on future developments.
35

Einfluß ionisierender Strahlung auf die Funktionsfähigkeit faseroptischer Bragg-Gitter-Sensoren - Influence of ionizing radiation on the operativeness of fiber-optic Bragg-grating sensors

Pfeiffer, Frank 25 May 2001 (has links)
Fiber-optic Bragg-Grating sensors are often the only possibility to perform measurements under adverse environmental conditions, ionizing radiation among them. However, up to now no basic research has been carried out to determine the influence of ionizing radiation on the operativeness of Bragg-Grating-Sensors. Within this work gratings of type I have been written into 3 different singlemode-fibers, with different Ge-content, one of them hydrogen-loaded. Various kinds of ionizing radiation (electrons, photons, He-nuclei) of various energy have been applied to the gratings and grating-temperature-sensors with doses up to 90 MGy. Changees of grating-properties have been monitored before and after irradiation. Experiments show only slight increase of the Bragg-wavelength within the measurement-precision of 1E-03 nm. According to these changes which were also estimated by theoretical considerations, typical applications for grating-sensors with exposure to ionizing radiation have been examinded to tell whether the sensors will meet the specific demands of the respective application.
36

Chemical interferences on the atomization yield of high reduction potential elements : Signal suppression in the plasma source spectrometry

Liu, Jian 25 May 2001 (has links)
In inductively coupled plasma spectrometry, signal suppression by acids has been recognized for a long time. It is always explained as the physical effects on the sampling processes, plasma conditions, and aerosol properties. In some cases, signal suppression apparently relates to the chemical properties of element. However, there was no publication discussed this phenomenon. In this work, it has been proven that mercury signal suppression depends on the plasma properties and nitric acid concentration. It relates to the atomization yield of mercury compounds, which is governed by the red-ox equilibrium in the central channel of plasma. Mercury complex formation equilibrium has been proven to exert in the heated droplets in plasma. The equilibrium state is governed by the complex formation with ammonium nitrate, the complex dissociation by nitric acid, and the heat obtained from plasma. Mercury halogen complex is not sensitive to the changes in acidity. Therefore, it is able to keep mercury free from nitric acid interferences and unify mercury atomization in the central channel of plasma. Similar to mercury, the uncertain signal and memory effect of platinum group elements and gold mainly arises from the chemical interference on the atomization efficiency. It not only depends on nitric acid concentration, but also on the standard reduction potential (Eo) of precious metal species in solution. Chemical interference on the spectrometric signals is governed by the robustness of the plasma, the capabilities to ingest aerosol and to protect foreign disturbance. The robustness of plasma is not equal to the excitation conditions. It has been observed that nitric acid has no significant interferences on mercury signal intensity of MIP-OES. When wet aerosol enters into the resonant cavity, it is completely desolvated in the powerful electromagnetic field. Liquid phase instantly disappears from the plasma observation zone. No doubt, the chemical equilibrium does not exist. In conclusion, chemical reactions exist in the plasma and interference the spectrometric signal. The best way to overcome the chemical matrix interferences in the plasma source spectrometry is to realize the controllable atomization.
37

On the number of injective indecomposable modules

Toerner, Guenter & Brungs, Hans-Heinrich 27 May 2002 (has links)
For every natural number m there exists a ring R with a completely prime ideal P so that there are exactly m non-isomorphic indecomposable injective right R-modules with P as associated prime ideal.
38

Spectral properties of two-slanted matrices

Berg, Lothar & Plonka, Gerlind 27 May 2002 (has links)
For two-slanted matrices, there is shown the close connection between their spectral properties and the zeros of their corresponding symbols. The results are applied to two-scale difference equations.
39

World views of mathematics held by university teachers of mathematics science

Grigutsch, Stefan & Toerner, Guenter 27 May 2002 (has links)
The present empirical study deals with the question of the (world) view of mathematics (i.e. the image of mathematics) held by university mathematics teachers in countries of German as a first lan-guage. The basis of this study is a voluntary survey by means of a closed questionnaire of 119 persons during an annual meeting of mathematicians. This questionnaire was on the whole employed for two other studies on mathematics teachers (N= 300) and pupils (N=1650). Four to five dimensions were defined by means of factor analysis and subsequently verified as relevant dimensions of the view of mathematics. These dimensions can be called the formalism aspect, the schema aspect, the process aspect, the application aspect and the Platonism aspect of mathematics. Attitudes towards these aspects differ on average, so that the "average" view of mathematics of university teachers is clearly accentuated in these five aspects. The process aspect acclaims the highest agreement, whereby the aspects formalism and application claim an average to above average assessment. In contrast, the Platonic aspect receives only weak to very weak agreement, and the schema aspect is on the whole rejected. Furthermore the structure of the view of mathematics resulting out of the relations between the dimensions is investigated. The part of the view of mathematics that is considered here contains two different viewpoints in content, namely the static view of mathematics as a system and the dynamic view of mathematics as a process. In contrast to the observa-tions in the other two populations the two viewpoints are not opposites. Mathematics is in the view of university teachers a comple-mentary toge-therness of both viewpoints. Their view of mathematics is insofar broader differentiated than the two other populations.
40

Untersuchung von Technologien für Farbfilter und Mikrolinsen zur monolithischen Integration in CMOS-Fotosensorarrays - Technological investigation of colour filters and microlenses for the monolithic integration in CMOS-photodetector arrays

Schicketanz, Peter 30 May 2001 (has links)
In this thesis two methods for the manufacturing of optical elements for the monolithic integration in CMOS image sensors are described. Polymeric micro colour filters and refractive micro lenses are presented. The colour filters were made of polyimid thin films with the colours Cyan, Yellow and Magenta. 9 x 9 um^2 filters were deposited on previously planarised CMOS substrates. Optical constants are measured by spectroscopic ellipsometry. The optical constants were used to calculate the colour sensor responses which are in good agreement with the experimental values. Raytracing calculations are used to evaluate the improvement of the responsivity by the use of microlenses. It is shown that the architecture of the pixel layout have to be considered to adapt the lens parameters. For the fabrication of the lenses Polymethyl-Methacrylat (PMMA) was used as a hight transparent material. By the melting of PMMA structures the lenses were obtained. A microlens array was deposited on a glass plate to determine the focal length by the following procedure. By illuminating the microlens array with laser light the focused beam was analysed with a microscope objective. It is estimated that the improvement in responsivity could be as high as 30 % with such a PMMA microlens array.

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