• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 75
  • 58
  • 28
  • 8
  • 7
  • 5
  • 2
  • Tagged with
  • 285
  • 74
  • 55
  • 55
  • 55
  • 40
  • 39
  • 39
  • 39
  • 39
  • 39
  • 39
  • 39
  • 38
  • 37
  • 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.
241

Space Radiation Environment And Radiation Hardness Assurance Tests Of Electronic Components To Be Used In Space Missions

Amutkan, Ozge 01 July 2010 (has links) (PDF)
Space radiation is significantly harmful to electronic Components. The operating time, duration and orbit of the space mission are affected by the characteristic of the radiation environment. The aging and the performance of the electronic components are modified by radiation. The performance of the space systems such as electronic units, sensors, power and power subsystem units, batteries, payload equipments, communication units, remote sensing instruments, data handling units, externally located units, and propulsion subsystem units is determined by the properly functioning of various electronic systems. Such systems are highly sensitive against space radiation. The space radiation can cause damage to electronic components or functional failure on the electronics. A precisely methodology is needed to ensure that space radiation is not a threat on the functionality and performance of the electronics during their operational lives. This methodology is called as &rdquo / Radiation Hardness Assurance&rdquo / . In this thesis, the hardening of electronics against space radiation is discussed. This thesis describes the space radiation environments, physical mechanisms, effects of space radiation, models of the space radiation environment, simulation of the Total Ionizing Dose, and &rdquo / Radiation Hardness Assurance&rdquo / which covers Total Ionizing Dose and Single Event Effects testing and analyzing of the electronics.
242

Lepton Flavor Violation In The Two Higgs Doublet Model

Sundu, Hayriye 01 June 2007 (has links) (PDF)
The lepton flavor violating interactions are interesting in the sense that they are sensitive the physics beyond the standard model and they ensure considerable information about the restrictions of the free parameters, with the help of the possible accurate measurements. In this work, we investigate the lepton flavor violating H+ ! W+l and the lepton flavor conserving H+ ! W+l decays in the general two Higgs doublet model and we estimate decay widths of these decays. After that, we analyze lepton flavor violating decay ! i in the same model and calculate its branching ratio. We observe that the experimental results of the processes under consideration can give comprehensive information about the physics beyond the standard model and the existing free parameters.
243

Scalar Mesons In Radiative Phi-meson Decays Into Charged K-meson States

Ozturk, Fahri 01 June 2008 (has links) (PDF)
The role of $f_{0}(980)$ and $a_{0}(980)$ scalar meson intermediate states in the mechanism of radiative $phi (1020)$ meson decay into two charged $K (494)$ mesons and a photon $phirightarrow K^{+} + K^{-} + gamma$ is investigated. For the contribution of scalar meson intermediate state two models are considered. In the kaon-loop model, the scalar meson intermediate state couples the final state to the initial $phi$ meson through a charged kaon-loop. The second model, called no-structure model, consist of point-like coupling of intermediate scalar meson state to the initial state. It is found that in the kaon-loop model, scalar meson intermediate state results in a considerable modification of the pure Bremsstrahlung photon spectrum.
244

Properties Of Light And Heavy Baryons In Light Cone Qcd Sum Rules Formalism

Azizi, Kazem 01 March 2009 (has links) (PDF)
In this thesis, we investigate the masses, form factors and magnetic dipole moments of some light octet, decuplet and heavy baryons containing a single heavy quark in the framework of the light cone QCD sum rules. The magnetic dipole moments can be measured considering radiative transitions within a multiplet or between multiplets. Analyzing the transitions among the baryons and calculating the above mentioned parameters can give us insight into the structure of those baryons. In analyzing the aforementioned processes, the transition form factors play a crucial role. In this thesis, the form factors for these transitions are calculated using the light cone QCD sum rules approach. In the limit when the light quark masses are equal, mu = md = ms, QCD has an SU(3) flavour symmetry which can be used to classify the light baryons. This classification results in the light decuplet, octet and singlet baryons. The baryons containing single heavy quark, on the other hand, can be classified according to the spin of the light degrees of freedom in the heavy quark limit, mQ -&gt / infinity. QCD at low energies, when the baryons are formed, is a non-perturbative theory. Hence, for phenomenology of the baryons, the QCD sum rules as a more powerful non-perturbative approach is used. Understanding the properties of nucleons is one of the main objectives of QCD. To investigate the properties of the nucleons, the axial N-Delta(1232) transition form factors are calculated within the light cone QCD sum rules method. A comparison of our results on those form factors with the predictions of lattice QCD and quark model is presented. The nucleon electromagnetic form factors are also calculated in the same framework using the most general form of the nucleon interpolating current. Using two forms of the distribution amplitudes (DA&rsquo / s), predictions for the form factors are presented and compared with existing experimental data. It is shown that our results describe the existing experimental data remarkably well. Another important property of the baryons is their magnetic moments. The magnetic moments of the heavy Xi_Q (Q = b or c) baryons containing a single charm or bottom quark are calculated within the light cone QCD sum rules approach. A comparison of our results with the predictions of other approaches, such as relativistic and nonrelativistic quark models, hyper central model, Chiral perturbation theory, soliton and skyrmion models is presented. Moreover, inspired by the results of recent experimental discoveries for charm and bottom baryons, the masses and magnetic moments of the heavy baryons with J^2P = 3/2^+ containing a single heavy quark are studied also within the light cone QCD sum rules method. Our results on the masses of heavy baryons are in good agreement with predictions of other approaches, as well as with the existing experimental values. Our predictions on the masses of the states, which are not experimentally discovered yet, can be tested in the future experiments. A comparison of our results on the magnetic moments of these baryons and the hyper central model predictions is also presented.
245

Nuclear Spinodal Instabilities In Stochastic Mean-field Approaches

Er, Nuray 01 August 2009 (has links) (PDF)
Nuclear spinodal instabilities are investigated in non-relativistic and relativistic stochastic mean-field approaches for charge asymmetric and charge symmetric nuclear matter. Quantum statistical effect on the growth of instabilities are calculated in non-relativistic approach. Due to quantal effects, in both symmetric and asymmetric matter, dominant unstable modes shift towards longer wavelengths and modes with wave numbers larger than the Fermi momentum are strongly suppressed. As a result of quantum statistical effects, in particular at lower temperatures, amplitude of density fluctuations grows larger than those calculated in semi-classical approximation. Relativistic calculations in the semi-classical limit are compared with the results of non-relativistic calculations based on Skyrme-type effective interactions under similar conditions. A qualitative difference appears in the unstable response of the system: the system exhibits most unstable behavior at higher baryon densities around $rho_{B}=0.4 rho_{0}$ in the relativistic approach while most unstable behavior occurs at lower baryon densities around $rho_{B}=0.2 rho_{0}$ in the non-relativistic calculations.
246

Spinodal Instabilities In Symmetric Nuclear Matter Within A Density-dependent Relativistic Mean-field Approach

Danisman, Betul 01 August 2011 (has links) (PDF)
The nuclear matter liquid-gas phase transition is expected to be a signal of nuclear spinodal instabilities as a result of density fluctuations. Nuclear spinodal instabilities in symmetric nuclear matter are studied within a stochastic relativistic density-dependent model in semi-classical approximation. We use two parameterization for the Lagrange density, DDME1 and TW sets. The early growth of density fluctuations is investigated by employing relativistic Vlasov equation based on QHD and discussed the cluster size of the condensations from the early growth of density correlation functions. Expectations are that hot nuclear matter behaves unstable around &rho / b &asymp / &rho / 0/4 (below the saturation density) and at low temperatures. We therefore present our results at low temperature T=1 MeV and at higher temperature T=5 MeV, and also at a lower initial baryon density &rho / b = 0.2 &rho / 0 and a higher value &rho / b = 0.4 &rho / 0 where unstable behavior is within them. Calculations in density-dependent model are compared with the other calculations obtained in a relativistic non-linear model and in a Skyrme type nonivrelativistic model. Our results are consistent with them. Qualitatively similar results show that the physics of the quantities are model-independent. The size of clusterization is estimated in two ways, by using half-wavelength of the most unstable mode and from the width of correlation function at half maximum. Furthermore, the average speed of condensing fragments during the initial phase of spinodal decomposition are determined by using the current density correlation functions.
247

Analysis Of Kappa Meson In Light Cone Qcd Sum Rules

Baytemir, Gulsen 01 September 2011 (has links) (PDF)
In the present work some hadronic properties of the scalar &kappa / meson are studied. Using the QCD sum rules approach, which is a nonperturbative method, the mass and the overlap amplitude of this meson are calculated. As well as the mass and the overlap amplitude, &kappa / &rarr / K^+&pi / ^&minus / decay is also studied. For this decay the coupling constant g_&kappa / K^+&pi / ^&minus / is obtained using light cone QCD sum rules which is an extension of the QCD sum rules method. Moreover, the coupling constant is calculated using the experimental decay width and it is compared with the value obtained in light cone QCD sum rules approach. The result of the calculation of g_&kappa / K^+&pi / ^&minus / , the one obtained from light cone QCD sum rules approach, is also applied to acquire the f_0 &minus / &sigma / scalar mixing angle, &theta / s, using the ratio g^2 (&kappa / &rarr / K^+&pi / ^&minus / )/g^2 (&sigma / &rarr / &pi / &pi / ) obtained from experimental decay width. The value of scalar mixing angle is also compared with its experimental results.
248

Theoretische Fragestellungen zur Bewertung von Unternehmen

Lahmann, Alexander D. F. 31 January 2013 (has links)
Die vorliegende kumulative Dissertationsschrift beschäftigt sich mit theoretischen Fragestellungen der Finanzwissenschaft im Bereich des Asset Pricing und im Detail der Unternehmensbewertung. Dabei wird sowohl auf Problemstellungen der akademischen und praxisnahen Forschung eingegangen. Der erste Artikel beschäftigt sich mit der Fragestellung welche Implikationen die Annahme einer arithmetischen Brownschen Bewegung auf bestimmte Aspekte der Unternehmensbewertung hat. Es folgen drei Artikel die sich auf unterschiedlicher Weise mit der Zinsschrankenregelung auseinandersetzen. Die darauf folgenden zwei Artikel behandeln hauptsächlich die Modellierung von Insolvenz im Rahmen der Unternehmensbewertung bei Annahme verschiedener Finanzierungspolitiken. Der achte Artikel geht näher auf die Thematik der empirischen Bestätigung bestimmter Kapitalstrukturtheorien ein. Die Dissertation schließt mit einem Artikel zu wichtigen Parametern für die Unternehmensbewertung.
249

Aktuelle Themen in der Unternehmensbewertung

Arnold, Sven 31 January 2013 (has links)
Die vorliegende kumulative Dissertationsschrift beschäftigt sich mit finanzwissenschaftlichen Fragestellungen im Bereich der Unternehmensbewertung. Dabei wurden aktuelle Themen diskutiert, die in Theorie oder Praxis ungelöste Probleme darstellen. Hervorzuheben ist an dieser Stelle, dass sich die ersten drei Artikel mit dem Werteinfluss der Zinsschanke auf den Wert von fremdfinanzierungsbedingten Steuerersparnissen (Tax Shield) beschäftigen. Die drei darauf folgenden Artikel beschäftigen sich schwerpunktmäßig mit der konsistenten Modellierung von Finanzierungspolitiken und dem Werteinfluss der Insolvenzmöglichkeit von Unternehmen. Der siebte und achte Artikel haben die Kapitalstruktur und weitere wichtige Parameter für die Unternehmensbewertung zum Thema.
250

Ein Beitrag zum Entladungsverhalten langer Luftfunkenstrecken bei Blitzspannung / A Contribution to the Breakdown of Long Air Gaps by Lightning Voltages

Shirvani Boroujeni, Ali 26 February 2015 (has links) (PDF)
Für die Menschen zählen Gewitter mit Donner und Blitz zu den ältesten bekannten Phänomenen der Natur. Die Tatsache, dass Blitze dennoch bis heute nicht abschließend erforscht sind, liegt in dem äußerst komplexen, schnellen und stochastischen Verhalten der Blitzentladung begründet. Der Autor befasste sich in Rahmen dieser Arbeit u.a. mit der Entwicklung eines modernen Messsystems, durch das die Erfassung von sowohl elektrischen als auch optischen Parametern der im Nanosekundenbereich ablaufenden Prozesse der Entladungen möglich wurde. Es handelt sich um technisch anspruchsvolle Messungen von hohen Stoßspannungen und schwachen Vorentladungsströmen in einem großen Frequenzbereich. Außerdem gelang es durch eine geschickte Synchronisation, die Entladungsprozesse präzise und erstmalig in einer Fotosequenz aufzunehmen. Auf Grundlage der Messergebnisse konnte der Entladungsprozess in mehrere Phasen der Vorentladung unterteilt und beschrieben werden. Vor allem beweisen die Messergebnisse die Existenz einer kanalartigen Vorentladung, die nicht zwingend zu einem Durchschlag führt. Dieser Mechanismus, der bei langsam ansteigenden Spannungen als stabile Leaderentladung benannt und mit Thermoionisation gekennzeichnet ist, war bei Blitzstoßspannungen bisher umstritten. / The breakdown behavior of long air gaps by Lightning Voltages has been investigated and the results of a new measurement system are reported. A series of up to eight photos (made by a high-speed camera) have recorded the expansion of discharge activities during the breakdown process. The pre-discharge current and voltage have been measured as well. The modern measurement techniques have made possible the synchronization of the photos with the current and voltage measurements in nanosecond-ranges. The combination of the measured current, voltage, and photos can precisely explain the breakdown process. The experiments have been carried out with the lightning impulses up to 2.4 MV and the air gaps up to 4 m. Despite of such high voltages, the experimental system has been verified to be appropriate for measuring the pre-discharge current in mA-ranges.

Page generated in 0.0326 seconds