• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 306
  • 26
  • 10
  • 4
  • 4
  • 4
  • 3
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 367
  • 245
  • 245
  • 65
  • 47
  • 37
  • 37
  • 37
  • 35
  • 34
  • 22
  • 22
  • 22
  • 21
  • 19
  • 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.
141

Erzeugung ultrakurzer elektrischer Impulse auf nichtlinearen Leitungsstrukturen - Generation of short electrical pulses on nonlinear transmission lines

Huelsewede, Ralf 18 September 2001 (has links)
In this work the generation of shock-waves and short electrical pulses on nonlinear transmission lines (NLTL) showing transients down to 3.6 ps and amplitudes of 1V - are presented. Special emphasis is layed upon the development of monolithic integration of planar schottky-diodes and coplanar waveguide structures based on InP-semiconductor material. The methods of simulating nonliear propagation effects on NLTL, designing and technology of NLTL and at last the experimental investigations in order to measure the generatred transients both in the time domain and frequency domain are shown in detail.
142

Ni/Mg/Al catalysts derived from hydrotalcite-type precursors for the partial oxidation of propane - Ni/Mg/Al-Katalysatoren hergestellt aus hydrotalkitartigen Prekursoren für die partielle Oxiadtion von Propan

Schulze, Kai 24 September 2001 (has links)
Ni/Mg/Al containing anionic clays of hydrotalcite-type structure with varying Ni/Mg ratio and constant Al content were synthesised by coprecipitation. Their composition and structure was determined by elemental analysis, XRD, TG-MS and DSC. Their calcination at 700-1000°C resulted in the transformation into the corresponding mixed metal oxides, with their structure depending on the calcination temperature. Temperature programmed reduction/oxidation and high temperature XRD studies were applied to study their reducibility, Ni dispersion and the oxidation of the formed metallic nickel particles. The partial oxidation of propane to syngas could be successfully performed at temperatures between 600 and 900°C over reduced Ni containing catalysts. The conversion of propane and the yield of syngas increased with increasing reaction temperature. The catalysts with a low to medium Ni content exhibited better catalytic performance than those with a higher Ni content or a conventional steam reforming catalyst used as reference. Coking was found to decrease with increasing reaction temperature and to increase with increasing Ni content. Since several factors characterising the catalysts (BET surface area, Mg content and available Ni surface) follow the same or the opposite trend with the Ni content, it was impossible to differentiate between these properties and their effect on the catalyst performance or coking. By the use of the best catalyst an at least two-fold increase in the yield of carbon monoxide and eight-fold increase in the yield of hydrogen was observed compared with the non-catalytic reaction. Further investigations were performed to study the influence of the feed ratio and the space velocity.
143

Erstellung und Validierung einer kombinierten NIR/Raman-Bibliothek zur Identitätskontrolle organischer und anorganischer Substanzen - Creation and validation of a combined NIR/Raman-library for identity control of organic and inorganic substances

Mandal, Oliver 02 October 2001 (has links)
Due to legal requests in future the identity control of products will not only be required in pharmaceutical industry but also in chemical industry. Therefore the demands on the analytical methods are very high. The company Merck realized an identity control tool by combining NIR and Raman spectroscopy. This Tool is suited for identification of a broad range of organic and inorganic substances. In this work different chemometric methods and data pretreatments were tested. The NIR and the Raman library have been optimized and the validation results visualized. Alternatives as binary coding and wavelet transformation, which lead to data compression at the same time, were tested
144

Molekulare Mangan-,Eisen- und Cobalt-Komplexe mit neuartigen Metall-Chalcogen-Gerüsten - Molecular manganese-, iron- and cobalt-complexes with novell metal-chalcogenides frameworks

Seidel, Renate Magdalene 10 October 2001 (has links)
The possibility of synthesis of (poly-)chalcogenide and chalcogenolate ions to manganese, iron and cobalt was expanded with the introduction of the donor ligand carbon monoxide. The metal atoms get than greater coordination numbers. So it was possible to synthesise new metal frameworks, p. e. Co11E7 in the complexes [Ph4P]2[Co11Se7(CO)10] and [Ph4P]2[Co11Te7(CO)10], in which the cobalt atoms built a inner centred pentagonal prism. In the examined reaction systems Mn2(CO)10/Na2Sex/Kat, Fe(CO)5/Na2Ex/Kat and Co2(CO)8/Na2Ex/Kat (E = Se or Te; x = 1 or 2; Kat = Ph4PCl or PPNCl) succeeded the synthesis of [Co6Se8(CO)6]-/2-anions as first anionic clusters of the M6E8L6 class. The difference between the new [Co6Se8(CO)4]- anion and the M6E8L6-complex class is the extraordinary compressed Co6-oktaeder and considerable shorter Co-Co-distances. In addition to the higher mentioned compounds it was possible to synthesise and characterize unambiguous with the aid of single crystal x-ray crystallography the following complexes: [Ph4P]2[Fe3Te(CO)9]; [Ph4P][Fe3EH(CO)9] für E=Se,Te; [Ph4P]2 [Fe4Te2(CO)14]; [Ph4P]2 [Fe6Se6(CO)12]; [Ph4P]2 [Mn3Se2(CO)9]. Worth mentioning is also the unusual square pyramidal coordination of the manganese atom in the [Ph4P][Mn(CO)5] crystal. Until now were only penta carbonyl complexes known with a trigonal bipyramidal coordination.
145

Thermodynamische Eigenschaften semirigider Polymere und deren Anwendung in faseroptischen Detektoren - Thermodynamic properties of semirigid polymers and their applications in fibre optical detectors

Woelke, Ralf 12 October 2001 (has links)
In the following thesis the thermotropic phase transition behaviour and structure-property-relations of semiflexible polyesters were investigated. These materials can be used in fibre optical blood-pressure sensors as resonator materials in a Fabry-Perot-Interferometer. PVT-measurements were carried out to determine the thermodynamic parameters alphaV(T) and kappa(P), and the validity of the Ehrenfest equations at glass transition temperatures was verified. These latter investigations showed no thermodynamic second order transition. By using alphaV(T) and kappa(P) for the calculation of the resonator-length-difference, the temperature- and pressure behaviour of the investigated polyesters was simulated. This simulation showed that small variations in the resonator length from increasing pressure agrees with the empirically determined values. An increasing number of methylene groups in the sidechain of the spacer molecule resulted in decreased melting- and glass transition temperature, which revealed the possibility to prepare thin polymer-films with 5-10 micrometer in diameter at low temperatures.
146

Vertikale Wanderwellenmodulatoren auf Quantenfilmbasis für die optische Informationsverarbeitung - Vertical travelling-wave modulators using quantum-well material for optical information processing

Wingen, Georg 12 October 2001 (has links)
The vertical optical travelling-wave modulator represents a new high-frequency element for optical data processing. The modulator is designed for a wavelength of 1200 nm and combines the layered structure of vertical optical modulators based on pseudomorphic InGaAs/GaAs quantum-wells with microwave lines from the MMIC technology. The quantum confined Stark effect is used to modulate the optical signal. The multiple quantum-well structure is embedded into an asymmetrical Fabry-Perot resonator built from a Bragg reflector and an aluminum layer to increase the electrooptical effect. The modulators produces a reflectivity change of 0,28. Large scale travelling-wave modulators are capable of critical frequencies higher than 40 GHz. By varying the width of the central conductor of the microwave line, the slow-wave factor could be varied experimentally between 4.8 and 12,7. The applied microwave produces a modulation lattice along the microwave line which can be used in a high frequency beam-steering element for optical information processing
147

Economic Relations Between Germany and Japan : an Analysis of Recent Data <br>Duisburger Papiere zur Ostasienwirtschaft ; 61 (2002)

Pascha, Werner 22 October 2002 (has links)
The author takes a close look at bilateral German-Japanese trade and direct investment data, employing various techniques (intensity indicators, RCA, intra-industry trade). It turns out that German-Japanese trade and FDI links are indeed rather limited, as has frequently been stated. A number of somewhat surprising pieces of evidence do emerge, though. For competitive industries and with respect to emerging opportunities, the bilateral figures do show a healthy performance
148

Institutionenökonomische Anmerkungen zur Einbettung von Korruption in das Ordnungssystem chinesischer Guangxi-Netzwerke <br>Duisburger Papiere zur Ostasienwirtschaft ; 60 (2001)

Schramm, Matthias ; Taube, Markus 22 October 2002 (has links)
In jüngster Zeit ist das Phänomen der Korruption in der VR China wieder verstärkt in das Blickfeld gerückt. Wie allen ökonomischen Austauschbeziehungen, so stellt sich auch korrupten Transaktionen das Problem der Absicherung derselben gegen opportunistisches Verhalten. In diesem Beitrag werden die chinesischen Guanxi-Netzwerke als eine sowohl in funktionaler als auch transaktionstheoretischer Hinsicht optimale Lösung dieses Ordnungsproblems identifiziert. Dies resultiert daraus, dass Guanxi-Netzwerke es vermögen, durch die Bindung von Investitionen in social capital stark risikobehaftete Austauschbeziehungen in sich selbst durchsetzende Verträge zu transformieren. Die durch den forcierten Aufbau eines Rechtssystems in der VR China aufgeworfene Frage, ob hierdurch Guanxi-Netzwerke verdängt und somit letztlich auch das Phänomen der Korruption zurückgeführt werden könnte, wird abschlägig beantwortet. Eine Analyse der einen derartigen institutionellen Wandlungsprozess determinierenden Faktoren institutionelle L eistungsfähigkeit, Kostenstrukturen, Pfadabhängigkeit und embeddedness zeigt, dass eine substantielle Verdrängung der Guanxi-Netzwerke auch bei weiterer Stärkung des chinesischen Rechtssystems nicht zu erwarten ist. Von dieser Seite her kann also kein Impuls zur Reduzierung des Korruptionsphänomens in der VR China erwartet werden.
149

Economic Relations between Germany and Mainland China, 1979 - 2000 <br>Duisburger Papiere zur Ostasienwirtschaft ; 59 (2001)

Taube, Markus 22 October 2002 (has links)
In the course of the last twenty plus years the intensity of economic exchange between China and Germany has increased dramatically. This development was triggered off most of all by the economic policy changes introduced by Deng Xiaoping in 1978. Since then, China has freed itself from its former self-imposed isolation and gradually integrated with the world economy. The market-oriented transformation process initiated in China in the late seventies created the preconditions for the resumption of economic contacts that had been largely stagnant in the preceding years. The gradual establishment of a market-based economic framework has step-by-step contributed to an economic environment that has allowed economic actors to exploit the comparative advantages of the economies concerned and enlarge the scope of labor division with China.
150

Untersuchungen zur Leistungsfähigkeit der Ionenmobilitätsspektrometrie als Detektionsverfahren für flüchtige Thermolyseprodukte bei der Entstehung von Bränden - Investigations about the Performance of Ion Mobility Spectrometry as a Detection method for volatile Thermolysis Products during Fire Development

Schumann, Achim 29 October 2001 (has links)
The present work describes the use of Ion Mobility Spectrometry (IMS) as a detection method for specific thermolysis products with respect to the early recognition of fires. By using additional analytic methods such as simultaneous differential thermal analysis/thermogravimetry (DTA/TG), gas chromatography/mass spectrometry (GC/MS) and Infrared spectrometry (IR) the specific thermolysis products depent on the temperature of the fire load were characterized and identified. While considering possible interference like e.g. varying atmospheric humidity the limits of detection and determination of the detectable gasses by IMS were determined.

Page generated in 0.0412 seconds