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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.
41

Klassische und quantenmechanische Beschreibung von Singularitäten in der Verteilung der Zeitverzögerung von 2D-Streusystemen / Classical and quantum-mechanical description of singularities in the time-delay distribution of 2D scattering systems

Majewsky, Stefan 07 May 2012 (has links) (PDF)
Die Zeitverzögerung bei der Streuung in zwei Dimensionen ist eine Funktion von zwei unabhängigen Parametern. Wenn diese Funktion Sattelpunkte aufweist, so hat der entsprechende Funktionswert theoretisch ein unendlich großes Gewicht in der Wahrscheinlichkeitsverteilung der Zeitverzögerungen. Dieser Zusammenhang soll analytisch und numerisch nachgewiesen und detailliert beschrieben werden. Insbesondere soll die klassische und quantenmechanische Wahrscheinlichkeitsverteilung der Zeitverzögerung für ein Modellsystem aus mehreren nichtüberlappenden zentralsymmetrischen Potentialen berechnet werden. Erwartete Ergebnisse sind Aussagen über die Parameterwerte, bei denen der oben genannte Effekt zu beobachten ist sowie Näherungsformeln für die Verteilung der Zeitverzögerung in der Nähe der Singularitäten. Außerdem soll die quantenmechanisch zu erwartende Glättung der Verteilungsfunktion quantitativ beschrieben werden. / For scattering problems in two dimensions, time-delay is a function of two independent parameters. If this function features saddle points, the corresponding function value should theoretically have an infinite weight in the probability distribution of time-delays. This correlation shall be confirmed analytically and numerically and studied in-depth. In particular, the classical and quantum-mechanical probability distribution of time-delays shall be calculated for a model system consisting of multiple non-overlapping potentials with rotational symmetry. We expect to obtain information about the parameter values where the aforementioned effects can be observed, and analytical approximations for the time-delay distribution near the singularities. Furthermore, the smoothing of the distribution in the quantummechanical regime shall be quantified.
42

Charakterisierung grundlegender Verbrennungseigenschaften von alternativen Treibstoffen und Treibstoffkomponenten

Richter, Sandra 08 May 2019 (has links)
Im Rahmen dieser Arbeit wurden die laminaren Flammengeschwindigkeit und die Zündverzugszeit für verschiedene alternative Treibstoffe und Treibstoffkomponenten experimentell bestimmt. Mit Farnesan, Alcohol-to-Jet SPK, Alcohol-to-Jet SKA und ReadiJet wurden vier verschiedene alternative Treibstoffe untersucht, die sich durch ihre Herkunft und in ihrer Zusammensetzung unterscheiden. Die Betrachtung einzelner Treibstoffkomponenten diente der Untersuchung inwieweit die Molekülstruktur einen Einfluss auf die Verbrennungseigenschaften hat. Dazu wurde aus jeder der vier Hauptstrukturgruppen (n-Alkane, iso-Alkane, Cycloalkane und Aromaten) jeweils ein Vertreter ausgewählt: n-Dodecan, Isooctan, n-Propylcyclohexan und n-Propylbenzol. Alle erhaltenen Ergebnisse worden mit Jet A-1, einem realen Treibstoff, verglichen. Aus den einzelnen Komponenten wurde auch ein aromatenfreies Surrogat hergestellt von welchem die Verbrennungseigenschaften ebenfalls experimentell untersucht wurden. Für das Surrogat wie auch seine Komponenten wurden die laminare Flammengeschwindigkeit und die Zündverzugszeit zusätzlich in einer Modellierung berechnet.:SYMBOLVERZEICHNIS ABKÜRZUNGSVERZEICHNIS 1 EINLEITUNG 2 GRUNDLAGEN ZUR VERBRENNUNG VON TREIBSTOFFEN 2.1 Laminare Flammen und Zündprozesse 2.2 Vorgänge bei der Oxidation von Kohlenwasserstoffen 2.3 Schadstoffbildung 3 UNTERSUCHTE TREIBSTOFFE 3.1 Jet A‐1 3.2 Alternative Treibstoffe 3.3 Treibstoffkomponenten 4 EXPERIMENTE 4.1 Einführung 4.2 Laminare Flammengeschwindigkeit 4.2.1 Einführung zur Messung der laminaren Flammengeschwindigkeit 4.2.2 Anwendung der Winkelmethode 4.2.3 Einfluss der Streckung auf laminare Flammen 4.2.4 Versuchsaufbau und Durchführung der Messung 4.2.5 Messergebnisse 4.3 Zündverzugszeit 4.3.1 Einführung zur Messung der Zündverzugszeit 4.3.2 Funktionsprinzip eines Stoßrohres 4.3.3 Versuchsaufbau und Durchführung der Messung 4.3.4 Messergebnisse 5 ZUSAMMENHANG ZWISCHEN STRUKTUR UND REAKTIVITÄT 5.1 Vergleich von n‐Dodecan und Isooctan 5.2 Vergleich von n‐Propylcyclohexan und n‐Propylbenzol 6 BERECHNUNG DER VERBRENNUNGSEIGENSCHAFTEN 6.1 DLR‐Mechanismus 6.2 Berechnung der laminaren Flammengeschwindigkeit 6.3 Berechnung der Zündverzugszeit 7 ZUSAMMENFASSUNG 8 FAZIT UND AUSBLICK 9 LITERATURVERZEICHNIS ABBILDUNGSVERZEICHNIS TABELLENVERZEICHNIS ANHANG
43

Klassische und quantenmechanische Beschreibung von Singularitäten in der Verteilung der Zeitverzögerung von 2D-Streusystemen

Majewsky, Stefan 20 February 2012 (has links)
Die Zeitverzögerung bei der Streuung in zwei Dimensionen ist eine Funktion von zwei unabhängigen Parametern. Wenn diese Funktion Sattelpunkte aufweist, so hat der entsprechende Funktionswert theoretisch ein unendlich großes Gewicht in der Wahrscheinlichkeitsverteilung der Zeitverzögerungen. Dieser Zusammenhang soll analytisch und numerisch nachgewiesen und detailliert beschrieben werden. Insbesondere soll die klassische und quantenmechanische Wahrscheinlichkeitsverteilung der Zeitverzögerung für ein Modellsystem aus mehreren nichtüberlappenden zentralsymmetrischen Potentialen berechnet werden. Erwartete Ergebnisse sind Aussagen über die Parameterwerte, bei denen der oben genannte Effekt zu beobachten ist sowie Näherungsformeln für die Verteilung der Zeitverzögerung in der Nähe der Singularitäten. Außerdem soll die quantenmechanisch zu erwartende Glättung der Verteilungsfunktion quantitativ beschrieben werden.:1 Einleitung 2 Zeitverzögerung in klassischen Streusystemen 2.1 Definition durch die Wirkung 2.2 Geometrisch motivierte Definitionen 2.2.1 Eigentliche Zeitverzögerung 2.2.2 Definition über retardierten Ort 2.2.3 Definition über Aufenthaltszeit 2.2.4 Numerische Bestimmung der Zeitverzögerung 2.3 Zeitverzögerungsfunktion und -verteilung 2.4 Rechenregeln 2.4.1 Koordinatensystemwechsel 2.4.2 Verkettung 3 Klassische Modellsysteme 3.1 Harte Scheibe 3.2 Verschobene harte Scheibe 3.2.1 Verhalten in der Umgebung von stationären Punkten 3.3 Weiches Scheibenpaar 3.3.1 Sattelpunkte 3.3.2 Extrempunkte 3.3.3 Zusammenfassung 4 Quantenmechanische Zeitverzögerung 4.1 Quantisierung der klassischen Definition 4.1.1 Definition über Aufenthaltszeit 4.1.2 Wigner-Smith-Matrix 4.1.3 Numerische Umsetzung 4.2 Einheitenlose Formulierung 4.3 Gegenüberstellung von Zeitentwicklungsmethoden 4.4 Split-Operator-Methode 4.4.1 Parameterwahl 4.4.2 Zur Abschätzung des systematischen Fehlers 4.5 Unterdrückung der periodischen Randbedingung 4.6 Harte Potentiale 5 Quantenmechanische Modellsysteme 5.1 Stationäre Punkte 5.2 Unschärfeeffekte 5.3 Numerische Ungenauigkeiten 5.3.1 Skalierungsverhalten der numerischen Methoden 5.4 Zusammenfassung der Ergebnisse 6 Zusammenfassung und Ausblick Anhang A Verhalten der Verteilung einer Funktion in der Nähe stationärer Punkte A.1 Umgebung eines Sattelpunktes A.2 Umgebung eines Extremums B Zeitverzögerung für das weiche Scheibenpaar / For scattering problems in two dimensions, time-delay is a function of two independent parameters. If this function features saddle points, the corresponding function value should theoretically have an infinite weight in the probability distribution of time-delays. This correlation shall be confirmed analytically and numerically and studied in-depth. In particular, the classical and quantum-mechanical probability distribution of time-delays shall be calculated for a model system consisting of multiple non-overlapping potentials with rotational symmetry. We expect to obtain information about the parameter values where the aforementioned effects can be observed, and analytical approximations for the time-delay distribution near the singularities. Furthermore, the smoothing of the distribution in the quantummechanical regime shall be quantified.:1 Einleitung 2 Zeitverzögerung in klassischen Streusystemen 2.1 Definition durch die Wirkung 2.2 Geometrisch motivierte Definitionen 2.2.1 Eigentliche Zeitverzögerung 2.2.2 Definition über retardierten Ort 2.2.3 Definition über Aufenthaltszeit 2.2.4 Numerische Bestimmung der Zeitverzögerung 2.3 Zeitverzögerungsfunktion und -verteilung 2.4 Rechenregeln 2.4.1 Koordinatensystemwechsel 2.4.2 Verkettung 3 Klassische Modellsysteme 3.1 Harte Scheibe 3.2 Verschobene harte Scheibe 3.2.1 Verhalten in der Umgebung von stationären Punkten 3.3 Weiches Scheibenpaar 3.3.1 Sattelpunkte 3.3.2 Extrempunkte 3.3.3 Zusammenfassung 4 Quantenmechanische Zeitverzögerung 4.1 Quantisierung der klassischen Definition 4.1.1 Definition über Aufenthaltszeit 4.1.2 Wigner-Smith-Matrix 4.1.3 Numerische Umsetzung 4.2 Einheitenlose Formulierung 4.3 Gegenüberstellung von Zeitentwicklungsmethoden 4.4 Split-Operator-Methode 4.4.1 Parameterwahl 4.4.2 Zur Abschätzung des systematischen Fehlers 4.5 Unterdrückung der periodischen Randbedingung 4.6 Harte Potentiale 5 Quantenmechanische Modellsysteme 5.1 Stationäre Punkte 5.2 Unschärfeeffekte 5.3 Numerische Ungenauigkeiten 5.3.1 Skalierungsverhalten der numerischen Methoden 5.4 Zusammenfassung der Ergebnisse 6 Zusammenfassung und Ausblick Anhang A Verhalten der Verteilung einer Funktion in der Nähe stationärer Punkte A.1 Umgebung eines Sattelpunktes A.2 Umgebung eines Extremums B Zeitverzögerung für das weiche Scheibenpaar
44

Experiment and Simulation of Autoignition in Jet Flames and its Relevance to Flame Stabilization and Structure

Al-Noman, Saeed M. 06 1900 (has links)
Autoignition characteristics of pre-vaporized iso-octane, primary reference fuels, gasolines, and dimethyl ether (DME) have been investigated experimentally in a coflow with elevated temperature of air. With the coflow air at relatively low initial temperatures below autoignition temperature Tauto, an external ignition source was required to stabilize the flame. Non-autoignited lifted flames had tribrachial edge structures and their liftoff heights correlated well with the jet velocity scaled by the stoichiometric laminar burning velocity, indicating the importance of the edge propagation speed on flame stabilization balanced with local flow velocity. At high initial temperatures over Tauto, the autoignited flames were stabilized without requiring an external ignition source. The autoignited lifted flames exhibited either tribrachial edge structures or Mild combustion behaviors depending on the level of fuel dilution. For the iso-octane and n-heptane fuels, two distinct transition behaviors were observed in the autoignition regime from a nozzle-attached flame to a lifted tribrachial-edge flame and then a sudden transition to lifted Mild combustion as the jet velocity increased at a certain fuel dilution level. The liftoff data of the autoignited flames with tribrachial edges were analyzed based on calculated ignition delay times for the pre-vaporized fuels. Analysis of the experimental data suggested that ignition delay time may be much less sensitive to initial temperature under atmospheric pressure conditions as compared with predictions. For the gasoline fuels for advanced combustion engines (FACEs), and primary reference fuels (PRFs), autoignited liftoff data were correlated with Research Octane Number and Cetane Number. For the DME fuel, planar laser-induced fluorescence (PLIF) of formaldehyde (CH2O) and CH* chemiluminescence were visualized qualitatively. In the autoignition regime for both tribrachial structure and mild combustion, formaldehyde were found mainly between the fuel nozzle and the lifted flame edge. On the other hand, they were formed just prior to the flame edge for the non-autoignited lifted flames. The effect of fuel pyrolysis and partial oxidation were found to be important in explaining autoignited liftoff heights, especially in the Mild combustion regime. Flame structures of autoignited flames were investigated numerically for syngas (CO/H2) and methane fuels. The simulations of syngas fuel accounting for the differential diffusion have been performed by adopting several kinetic mechanisms to test the models ability in predicting the flame behaviors observed previously. The results agreed well with the observed nozzle-attached flame characteristics in case of non-autoignited flames. For autoignited lifted flames in high temperature regime, a unique autoignition behavior can be predicted having HO2 and H2O2 radicals in a broad region between the nozzle and stabilized lifted flame edge. Autoignition characteristics of laminar nonpremixed methane jet flames in high- temperature coflow air were studied numerically. Several flame configurations were investigated by varying the initial temperature and fuel mole fraction. Characteristics of chemical kinetics structures for autoignited lifted flames were discussed based on the kinetic structures of homogeneous autoignition and flame propagation of premixed mixtures. Results showed that for autoignited lifted flame with tribrachial structure, a transition from autoignition to flame propagation modes occurs for reasonably stoichiometric mixtures. Characteristics of Mild combustion can be treated as an autoignited lean premixed lifted flame. Transition behavior from Mild combustion to a nozzle-attached flame was also investigated by increasing the fuel mole fraction.
45

Simulations And Experiments Of Plasma-Induced Effects In Silicon Detectors

Gomez L, Ana Maria January 2023 (has links)
When an atomic nucleus undergoes fission, two fragments with different mass and kinetic energy are emitted. The highly unstable fission fragments (FFs) evaporate prompt neutrons soon after the nucleus splits. A precise measurement of both, the mass yield distribution of the FFs and the average prompt neutron emission, $\bar{\nu}$, is important not only for current nuclear technologies but also for the development of future technologies such as Generation IV nuclear power plants. Moreover, the experimental determination of the mass yield distributions, both pre- and post-neutron emission, is valuable for testing fission models. Additionally, a precise measurement of the average neutron multiplicity as a function of the FFs mass, <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?$%5Cbar%7B%5Cnu%7D(A)$" data-classname="equation" data-title="" />, is crucial in the understanding of how the excitation energy is shared between nascent FFs.  The VElocity foR DIrect particle identification spectrometer (VERDI) is designed to achieve pre- and post-fission mass distributions with resolutions between 1-2 u. VERDI is a double-energy double-velocity instrument that consists of two arms. On each arm is operated one Microchannel Plate detector (MCP) for the collection of the FFs start time and up to 32 Passive Implanted Planar Silicon (PIPS) detectors for the stop time and energy detection of the FFs. However, challenges in the experimental measurements with VERDI arise due to the high degree of ionization (plasma) in the detector material from the interaction with the FFs. The plasma causes a delay in the charge carriers' migration for the signal start, known as the plasma delay time effect (PDT). Furthermore, the recombination of charge carriers in the plasma causes a shrinking in the signal's height, known as pulse height defect (PHD). This phenomenon leads to inaccuracies in the measurement of FFs mass distributions and increased systematic uncertainties.  Previous studies on PDT and PHD have shown varying behaviors across different detector types, which motivated dedicated studies in the type of PIPS detectors used in VERDI. An experimental campaign to characterize the PDT and PHD in PIPS detectors was conducted in the LOHENGRIN recoil separator, which is part of the ILL nuclear facility in Grenoble, France. Measurements of FFs in a range of masses between 80 u and 149 u, with energies between 20 MeV to 110 MeV, were taken to fully characterize six PIPS detectors. The resulting PDT and PHD values were 1 ns to 4 ns and 2 MeV to 10 MeV respectively. The PDT and PHD exhibited consistent energy and mass dependencies across the detectors, which enables the possibility of an event-by-event correction of VERDI data. In this thesis, the basis for discussing the results of the studies of the PDT and PHD effects will be presented.
46

Securing data dissemination in vehicular ad hoc networks

Aldabbas, Hamza January 2012 (has links)
Vehicular ad hoc networks (VANETs) are a subclass of mobile ad hoc networks (MANETs) in which the mobile nodes are vehicles; these vehicles are autonomous systems connected by wireless communication on a peer-to-peer basis. They are self-organized, self-configured and self-controlled infrastructure-less networks. This kind of network has the advantage of being able to be set-up and deployed anywhere and anytime because it has no infrastructure set-up and no central administration. Distributing information between these vehicles over long ranges in such networks, however, is a very challenging task, since sharing information always has a risk attached to it especially when the information is confidential. The disclosure of such information to anyone else other than the intended parties could be extremely damaging, particularly in military applications where controlling the dissemination of messages is essential. This thesis therefore provides a review of the issue of security in VANET and MANET; it also surveys existing solutions for dissemination control. It highlights a particular area not adequately addressed until now: controlling information flow in VANETs. This thesis contributes a policy-based framework to control the dissemination of messages communicated between nodes in order to ensure that message remains confidential not only during transmission, but also after it has been communicated to another peer, and to keep the message contents private to an originator-defined subset of nodes in the VANET. This thesis presents a novel framework to control data dissemination in vehicle ad hoc networks in which policies are attached to messages as they are sent between peers. This is done by automatically attaching policies along with messages to specify how the information can be used by the receiver, so as to prevent disclosure of the messages other than consistent with the requirements of the originator. These requirements are represented as a set of policy rules that explicitly instructs recipients how the information contained in messages can be disseminated to other nodes in order to avoid unintended disclosure. This thesis describes the data dissemination policy language used in this work; and further describes the policy rules in order to be a suitable and understandable language for the framework to ensure the confidentiality requirement of the originator. This thesis also contributes a policy conflict resolution that allows the originator to be asked for up-to-date policies and preferences. The framework was evaluated using the Network Simulator (NS-2) to provide and check whether the privacy and confidentiality of the originators’ messages were met. A policy-based agent protocol and a new packet structure were implemented in this work to manage and enforce the policies attached to packets at every node in the VANET. Some case studies are presented in this thesis to show how data dissemination can be controlled based on the policy of the originator. The results of these case studies show the feasibility of our research to control the data dissemination between nodes in VANETs. NS-2 is also used to test the performance of the proposed policy-based agent protocol and demonstrate its effectiveness using various network performance metrics (average delay and overhead).
47

Vaporization and autoignition characteristics of ethanol and 1-propanol droplets : influence of water

Binti Saharin, Sanisah 04 February 2013 (has links) (PDF)
Detailed investigation of the vaporization of an isolated of ethanol and 1-propanol droplet was carried out in this experimental study. The experimental set-up consists of a heated chamber with a cross quartz fibers configuration as droplet support. An alcohol droplet is located at the intersection of the cross quartz fibre with a controlled initial diameter (300-600µm). Ambient temperature is varied from 298 to 973K at atmospheric pressure. The quasi-steady theory has been used to compare and to explain all experimental results. The real impact of the water concentration on the vaporization rate of an ethanol droplet is also examined, where two 'quasi-steady' periods are observed on the d2-curves, clearly showing that the vaporization of an ethanol droplet is accompanied by the simultaneous condensation of water vapour on the droplet surface and thus the temporal evolution of the droplet squared diameter exhibits an unsteady behavior. The histories of the instantaneous vaporization rates of both 1-propanol and ethanol droplets confirm this phenomenon. The autoignition experimental study of ethanol, 1-propanol and blends of ethanol and water have been carried out in a rapid compression machine at a compressed pressure of 30bar over a temperature range of 750-860K for stoichiometric mixture of fuel and air. The ignition delay times recorded show a significant decrease with increasing temperature. 1-propanol is more reactive than ethanol, which results in shorter ignition delay times. However, water addition to ethanol increases the reactivity of the mixture and results in a shorter ignition delay times than 1-propanol
48

Distanční ochrana využívající digitální vstupní data / Distance Protection Design Using Digital Input Data

Wannous, Kinan Hasan Wafaa January 2020 (has links)
Standard IEC 61850-9-2 definuje přenos vzorkovaných měřených hodnot (sampled measured values, SMV) prostřednictvím sítě Ethernet a využití SMV získaných ze slučovacích jednotek nebo přístrojových transformátorů. Implementace IEC 61850-9-2 závisí na vlastnostech datového souboru, jakými jsou časová synchronizace, počet vzorků a časový interval. Dizertační práce je zaměřena na algoritmy chránění a analýzu vlivu standardu IEC61850-9-2LE na fyzická zařízení ochran s analogově/digitálními vstupními daty o proudu a napětí. S ohledem na narůstající míru interakce mezi fyzickými zařízeními a komunikačními prvky byl navržen test pro analýzu komunikace pro rozvodnu využívající konvenční metody (analogové vstupy) a metody digitální založené na standardu IEC 61850-9-2. Práce dále popisuje funkci slučovací jednotky využívající standard IEC61850-9-2LE. Navržená metoda definuje zdroj SMV a analyzuje přenos dat. V rámci práce byl za využití softwaru Matlab naprogramován algoritmus ochrany. Vytvořený model je schopen vyhodnotit vliv harmonického zkreslení na funkci digitálních ochran a vliv přesycení proudového transformátoru na distanční ochranu. V práci jsou zhodnoceny i možnosti zrychlení testování systémů chránění s využitím neuronové sítě. Závěrečná kapitola se zabývá aplikacemi v reálném čase, využívajícími data z rozvodny v blízkosti Vysokého učení technického v Brně. K přenosu dat z rozvodny do univerzitní laboratoře je zde využíváno SMV přenášených optickým kabelem o délce 16 km. Aplikace je vytvořena v programu Matlab a je schopna číst data z ethernetového portu, dekódovat je, převést z formátu ASCII do desítkové soustavy a poté vykreslit průběhy proudu a napětí. Mezi vlastnosti aplikace se řadí jednoduchost použití, schopnost implementace funkcí distanční ochrany, výpočet RMS hodnot proudu a napětí a harmonického zkreslení, harmonická analýza prostřednictvím rychlé Fourierovy transformace a výpočet impedance poruchové smyčky. Všechny výpočty běží v reálném čase a provedena je i citlivostní analýza modelu.
49

Ověření biologických parametrů člověka pro robotickou vizuální teleprezenci / Validation of human body biological parameters for robotic visual telepresence

Cheparukhina, Anna January 2015 (has links)
This work presents a research in the field of robotic visual telepresence. At the beginning explains the principle of teleprezence and it makes classification of robots according to their properties and concepts. Furthermore, there is a review of modern existing robots. The following chapter discusses the human visual system, the basic parameters and functions including parameters of head movements. Subsequently have been selected critical parameters for visual telepresence. At the conclusion of the theoretical part were designed some experiments to validation of human body biological parameters. In the practical part was conducted measuring the extent and speed of head movements, eye distinction depending on the lighting and measurement of visual field man. Also, a series of experiments was performed for practical technical embodiment of the telepresence system rescue robot for class Orpheus.

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