Dissertations / Theses on the topic 'Binary energy'
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Dickinson, Hugh John. "Very high energy gamma-rays from binary systems." Thesis, Durham University, 2010. http://etheses.dur.ac.uk/290/.
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This thesis presents a study of the very high energy (VHE) gamma-ray emission from X-ray binary systems using the H.E.S.S. imaging atmospheric Cherenkov array. The historical background and basic principles of ground-based gamma-ray astronomy are briefly reviewed and an overview of the design and capabilities of the H.E.S.S. telescope system is presented. The broadband observational properties of X-ray binary systems and their relevance in a broader astrophysical context is also discussed. A review of the radiative emission mechanisms which relate to VHE gamma-ray emission in X-ray binaries is presented, with emphasis given to the leptonic emission processes of synchrotron radiation and inverse-Compton scattering. Intrinsic absorption processes which act to attenuate the emitted flux of VHE gamma-rays are also discussed. Three computer models are introduced which simulate aspects of the gamma-ray emission and absorption in X-ray binary systems. A detailed analysis of the VHE gamma-ray emission from the X-ray binary LS 5039 is presented and the relevant procedures for data selection, gamma-hadron separation and background estimation are discussed in some detail. Methods for the determination of detection significance and the calculation of gamma-ray fluxes are also reviewed and results are derived which apply specifically to LS 5039. A detailed temporal analysis of the gamma-ray signal from LS 5039 is presented, applying tests for secular, excess and periodic variability. Strong evidence is found for modulation of the observed gamma-ray flux on the orbital period of ~3.9 days. Following a brief discussion of the procedures required for spectral analysis of VHE gamma-ray data, results are presented for LS 5039 which reveal evidence for spectral variability which is correlated with the observed gamma-ray flux and therefore, the orbital phase of the binary system. The spectral and temporal characteristics of LS 5039 are then compared with the predictions of theoretical models in an attempt to explain the observed behaviour. Contemporaneous X-ray and VHE gamma-ray observations of three galactic microquasars using the Rossi X-ray Timing Explorer and H.E.S.S. are presented. Although no gamma-ray detections are reported, the observations permit the derivation of upper limits to the VHE gamma-ray flux which correspond to episodes of known X-ray behaviour. The X-ray characteristics of each target are compared with pre-existing observational data to infer the presence or otherwise of relativistic outflows at the H.E.S.S. observation epochs. The implications of the gamma-ray non-detections are then discussed in the context of these inferred system properties. The results of a survey of the VHE gamma-ray emission associated with the positions of 125 known X-ray binaries are presented. Although no conclusive detections were obtained, tentative indications were found for a population of faint, spectrally hard gamma-ray sources associated with high-mass X-ray binary systems. The inferred characteristics of the indicated population show broad agreement with the measured properties of known gamma-ray-emitting X-ray binary systems like LS 5039.
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Chu, Chiang-Kai. "Energy Redistribution with Controllable Binary State Latch Element." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/78336.
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An application of binary state latch device with proper real-time control algorithm for energy
redistribution application is introduced in this thesis. Unlike traditional tuned vibration
absorber, the latch device can be viewed as variable semi-active dampers such as magnetorheological
(MR) and piezoelectric friction dampers. The distinct difference between other
semi-active dampers and our latch device is that other semi-active dampers can provide continuous
resistance according to the amount of input current, however, the binary latch device
can only provide two different values of resistance - either the maximum or no resistance
at all. This property brings the latch possibly having higher maximum and minimum ratio
of resistance than MR dampers. As for the operating structure, the mechanism of latch
element is nearly the same as the piezoelectric friction dampers which the resistance force is
provided according to the normal force acting on two rough plates. Nonetheless, because of
the characteristic of the binary states output of the latch element, this make it very different
from the ordinary variable dampers. Since it is either being turned on or turned off, a novel
control law is required for shifting energy. Also, because of the simplicity of the binary states
output, it is very accessible to implement the controller on Field Programmable Gate Array
(FPGA). With this accessibility, it is promising to apply plenty of latch elements in the same
time for large scale application, such as multi-agent networks. In this thesis, an energy-based
analytic solution is proposed to illustrate the universal latch-off condition. And a latch-on
condition under ideal situations is discussed. At the end, a control law under nonideal condition
is being suggested for real-time periodically excited system. We found that energy
redistribution is achievable by using the proper control law under fairly broad conditions.Master of Science
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Vancea, Anisoara. "Energy and electron transfer on titania-silica binary oxides." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12152.
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Steady state reflectance and emission characteristics of anthracene adsorbed on silica gel and titania-silica mixed oxides have been investigated as a function of sample loading. Titania-silica mixed oxides with 1, 3, 5 and 10 wt. % TiO2 were prepared by two different methods: a dropwise method and a sol-gel route. Ground state diffuse reflectance and fluorescence emission spectra of anthracene adsorbed on titania-silica surfaces show a dependence on titania content. The absorption peaks of anthracene are difficult to resolve at higher titania content due to the increasing red-shift of the titania absorption edge. The absorption edge of titania is shifted to longer wavelengths and the band gap energy decreases with increasing the titania loading. Diffuse reflectance laser flash photolysis at 355 nm produces both the triplet and radical cation of anthracene and gives relevant information regarding the photochemical transients and the kinetics details of the surface photochemical processes. Energy dependence studies confirm the monophotonic nature of the triplet production, whereas the anthracene radical cation is formed by monophoton or multiphoton ionisation in the mixed titania-silica systems. Energy and electron transfer reactions of anthracene co-adsorbed with azulene as electron donor on silica sol-gel and titania-silica mixed oxides prepared by the sol-gel method with different titania content have been studied using the time-resolved diffuse reflectance laser flash photolysis technique. The fluorescence of excited anthracene adsorbed on silica sol-gel is quenched by the addition of azulene, while co-adsorption of azulene on titania-silica mixed oxides resulted in a decrease in the fluorescence intensity of the adsorbed anthracene due to the formation, at the same time, of anthracene radical cation and Ti3+ species on the titania-silica surface. Triplet-triplet energy transfer from the excited anthracene to ground state azulene and electron transfer from azulene to the anthracene radical cation have been investigated using a time-resolved diffuse reflectance laser flash photolysis technique following laser excitation at 355 nm. Bimolecular rate constants for energy and electron transfer between anthracene and azulene have been obtained. Kinetic analysis of the decay of the anthracene triplet state and radical cation show that the kinetic parameters depend on the titania content of the sample and the azulene concentration. This indicates that the rate of energy and electron transfer reactions increases as a function of azulene concentration and decreases with increasing titania content in titania-silica mixed oxides, whereas the observed rate of reaction on silica sol-gel is predominantly governed by the rate of diffusion of azulene. Electron transfer reactions in a ternary system using azulene for hole transfer between 9-anthracenecarboxylic acid radical cation as electron acceptor and perylene as electron donor were also studied in order to demonstrate the mobility of radical cations on the silica sol-gel and titania-silica surfaces. The co-adsorption of azulene as a molecule shuttle with 9-anthracenecarboxylic acid and perylene on both silica sol-gel and titania-silica systems has been shown to enhance the rate of electron transfer in this ternary system. Activation energies for energy and electron transfer on photoinduced bimolecular and termolecular processes on silica sol-gel and titania-silica mixed oxides have been measured. In bimolecular anthracene / azulene systems, at higher azulene loadings, the activation energies and the pre-exponential factors on titania-silica surfaces are the same for both energy and electron transfer and are comparable with the parameters extracted for azulene diffusion on silica Davisil suggesting that azulene diffuses across the silica Davisil and titania-silica mixed oxides surfaces, while at lower azulene loadings, ion-electron recombination dominates and the activation energy extracted is for this process. In a ternary 9-anthracenecarboxylic acid / azulene / perylene system, the activation energy for perylene diffusion is higher than that observed for the anthracene / azulene system, reflecting the lower mobility of the perylene molecule. In this study, a series of titania-silica samples with different loadings of titania (1 10 wt. %) prepared by the sol-gel method and also the pure TiO2 P25 Degussa have been used to study the photocatalytic degradation of 4-chlorophenol in aqueous solution under UV light irradiation. The absorption peak of 4-chlorophenol at 280 nm decreases with increasing titania content and finally disappeared suggesting that titania has a positive influence on the degradation of 4-chlorophenol. The investigated titania-silica mixed oxides prepared by the sol-gel method are less efficient photocatalysts for the degradation of 4-chlorophenol than TiO2 P25.
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Sinjab, Issam Musleh. "Energy transfer in W Ursae Majoris type contact binary stars." Thesis, University of Sussex, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.543317.
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This thesis investigates two problems concerned with contact binary stars: the mechanism of energy transfer and the evolutionary states in the W UMa-type contact binary systems. The observational and theoretical background is first reviewed. This highlights the importance of a proper treatment of energy transfer if W UMa stars are to be understood. Expressions for the ratio of the transferred luminosity to the primary's radiated and centrally generated luminosities are derived. An estimate of the size of the transfer rate in observed unevolved systems is determined. The implications of accurate mass-ratios are briefly discussed. The generalized transport equation is shown to contradict the requirements of the TRO theory. A more general formula is put forward. The sideways convection model is investigated critically and is found to work only in very deep A-type systems. The implications of this result on contact binaries' structure, stability and evolution are discussed. A variety of different energy transfer models are explored. Equilibrium circulation and turbulent conduction models require moderately deep A-type systems. The small- and large-scale models can, respectively, transfer enough energy in the shallow and moderately shallow W-type systems. Webbink's ideas of energy transfer are used to construct numerical contact binary models which for the first time use an explicit mechanism to represent the energy transfer process. The added complications caused by the implementation of such a mechanism rendered the procedure used to build numerical models ineffective. An alternative procedure is briefly discussed. Hazlehurst's dissipation mechanism is simulated numerically. We argue on the basis of our results that this mechanism is unworkable in its present form. We attribute this to a fundamental error in the formulation of the model and sketch a possible reformulation of the model in terms of the theory of thermals. The consequences of strict hydrostatic equilibrium for the overall structure of contact binaries are discussed. It is shown that imposition of strict hydrostatic equilibrium in the envelope requires (1) the observed anomalous M-L relation hold and (2) the contact phenomenon be considered as a single (severely distorted) configuration. A model is proposed which deviates markedly from hydrostatic equilibrium just below the envelope, with accelerating flow through the L, -point and a shock in the secondary component. A substantial amount of energy can be transferred, with conditions in the envelope remaining very close to hydrostatic equilibrium. The model works independently of the overlying envelope structure. We approach the second of our topics by investigating the evolutionary states in 9 A-type systems. Depending on their observed properties the systems are divided into two distinct groups. Group I members are evolved. Group II members belong to a distinct, still problematic category. The W-type system TX Cnc in Praesepe may be a pre-main sequence contact binary system. The implications of these results on the transfer mechanism are discussed.
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Mykhailenko, T. P., and A. H. Omar. "Energy efficienсy of binary cycle power plant for the refinery." Thesis, Видавництво СумДУ, 2012. http://essuir.sumdu.edu.ua/handle/123456789/25763.
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Molina, Lumbreras Edgar. "Modeling and observations of relativistic outflows in high-energy binary systems." Doctoral thesis, Universitat de Barcelona, 2021. http://hdl.handle.net/10803/672686.
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Some binary systems consisting of a compact object, which can be either a neutron star or a black hole, and typically a non-degenerate companion star, have been shown to emit broadband radiation from radio up to gamma-ray frequencies. These systems are normally classified as X-ray or gamma-ray binaries, depending on the frequency at which their emission has its maximum. Unlike with stars, a big part of the observed emission cannot be explained by thermal radiation, and therefore non-thermal radiative processes need to be invoked. The interactions between the star and the compact object may result in the launching of outflows of plasma originating around the compact object position. These outflows can attain speeds close to the speed of light, and be an efficient site for acceleration of charged particles up to relativistic energies. A part of the non-thermal emission observed from X-ray and gamma-ray binaries comes precisely from the non-thermal radiative cooling of these accelerated particles. Additionally, when the companion star is very massive, it produces a strong stellar wind that interacts with the aforementioned relativistic outflows, modifying both their dynamical and radiative evolution.
The main theoretical objective of this thesis is the study the interactions between the outflows of X-ray and gamma- ray binary systems and the stellar wind of a massive companion star. For this purpose, we developed versatile semi- analytical models that give a complete view of these interactions for different kinds of systems. The results of the theoretical modeling include broadband spectral energy distributions and light curves that are directly comparable with the observational data. Radio sky maps are also obtained for the large-scale emission of the outflows. The latter allows to directly visualize the dynamical effect of the stellar wind in the outflow trajectory, which acquires a helical or spiral-like pattern. This modified trajectory gives rise to asymmetries in the light curves at different energy ranges, as well as changes in the spectral energy distributions mostly due to variations of angle-dependent processes influencing the outflow emission.
From the observational point of view, this thesis focuses on the analysis of the potential very high-energy gamma-ray emission above 100 GeV of the X-ray binary MAXI J1820+070, as seen by the MAGIC telescopes. The analysis is done through a custom software developed by MAGIC, which allows to reconstruct the arrival direction and energy of a gamma ray from the Cherenkov light emitted by the electromagnetic cascade that the gamma ray generates when it enters the atmosphere of the Earth. The observational results consist on a multiwavelength study of MAXI J1820+070 in the form of light curves and spectral energy distributions that use data from a number of telescopes at radio, optical, X-ray and gamma-ray frequencies. The source is not detected in gamma-rays above 100 MeV, and only flux upper limits can be given for those energies. Nevertheless, the obtained upper limits, together with the observed fluxes at other frequencies, are enough to constrain significantly the properties of a potential gamma-ray emitter in MAXI J1820+070.
In conclusion, this thesis deepens in our understanding of the interactions between the stellar wind and the outflows of high-energy binary systems. It shows that these interactions must be taken into account in order to properly characterize the subset of those binary systems hosting a massive companion star, in which a powerful stellar wind is present. In this thesis, it is also shown that observations in high-energy and very high-energy gamma rays of X-ray and gamma-ray binary systems allow to set meaningful limits to the outflow properties, even when the sources are not detected and only upper limits in the flux are obtained.A la nostra Galàxia, existeixen sistemes binaris formats per un objecte compacte i una estrella companya típicament no degenerada que emeten a freqüències des de ràdio fins a raigs gamma. Les interaccions entre l'estrella i l'objecte compacte poden resultar en el llançament d'outflows de plasma originats al voltant de l'objecte compacte, els quals poden adquirir velocitats properes a la de la llum. Quan l'estrella companya és molt massiva, aquesta genera un fort vent estel·lar que interacciona amb els outflows i els afecta tant dinàmicament com radiativa. El principal objectiu d'aquesta tesi des del punt de vista teòric és l'estudi de les interaccions entre els outflows de sistemes binaris i el vent estel·lar d'una companya massiva. Per això, hem desenvolupat una sèrie de models semi- analítics que donen una visió completa d'aquestes interaccions en diferents tipus d'escenaris. Els resultats de la modelització teòrica inclouen prediccions per a les distribucions espectrals d'energia i corbes de llum, així com mapes ràdio per a l'emissió a gran escala dels outflows. En relació a la part observacional, aquesta tesi es focalitza en l'anàlisi de l'emissió potencial de raigs gamma de molt alta energia de la binària MAXI J1820+070, observada amb els telescopis MAGIC. Els resultats observacionals consisteixen en un estudi multifreqüència de la font de ràdia a raigs gamma. Tot i que la font no es detecta per sobre dels 100 MeV, els resultats obtinguts permeten limitar les propietats d'un emissor potencial de raigs gamma a MAXI J1820+070. En conclusió, aquesta tesi profunditza en el coneixement de les interaccions entre el vent estel·lar i els outflows de sistemes binaris d'altes energies. També es conclou que les observacions en raigs gamma de sistemes binaris permeten limitar de manera important les propietats dels outflows, fins i tot quan les fonts no son detectades.
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Snyder, Kenneth A. "Energy localization and transport in binary isotopically disordered Fermi-Pasta-Ulam chains." College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/2643.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2005.Thesis research directed by: Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Schlenker, Stefan. "Very high energy gamma rays from the binary pulsar PSR B1259-63." Doctoral thesis, [S.l. : s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=976502267.
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Edwards, Philip Gregory. "A search for ultra high energy gamma ray emission from binary X-ray systems." Title page, contents and summary only, 1988. http://web4.library.adelaide.edu.au/theses/09PH/09phe266.pdf.
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Chan, Ryan James. "Mean-Field Parameter Study of Radiation-Induced Segregation in a Binary Metal Alloy." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/96606.
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The purpose of this thesis is to broaden the tools and knowledge available for understanding the behavior of metals under irradiation to aid in the pursuit of advanced materials for deployment in Generation IV (Gen-IV) nuclear reactor designs. A mean-field study is conducted on a body-centered cubic (BCC) A-B binary metal alloy system. The performance of the simulated metal system is measured by assessing the degree of segregation that occurs at the grain boundary (GB) in the center of the one-dimensional simulation box. This mean-field method was developed using rate theory equations to observe the diffusion of defects and solute atoms in the binary BCC alloy modeled after a section of planes in the <100> direction of α-iron. The method in this thesis is adapted from a previous radiation-induced segregation (RIS) study that was similarly validated against thermal segregation isotherms.
This adapted simulation code was used to study RIS by varying the initial values and conditions across ranges relevant to Generation IV reactor designs. The simulations run with this code were centered around segregation energy and the diffusion coefficient relationships between defects and solute atoms. The most influential conditions applied to both the segregation energy and diffusion coefficient relationship test suites were the temperature and dose rate. The interplay of the various segregation energies, manipulated diffusion coefficients, temperatures, and dose rates is explored in this thesis. The code used in this thesis is presented as a modular framework for further parameter study with a clear direction for more complex alloys.Master of Science
The growing electricity demand for more efficient, safe, reliable, and sustainable means of power generation requires research and subsequent implementation of advanced Generation IV (Gen-IV) nuclear reactor designs. These proposed designs operate under significantly more strenuous conditions from the perspective of materials used in constructing the reactor. Materials inside the reactor will experience temperatures, pressures, and radiation doses greatly exceeding those of previous generations: Gen II through III+. Metals are employed in almost every component inside a reactor and are particularly susceptible to the demanding conditions due to their tendency to lose their ductility under these stressors. This thesis presents a diffusion-based code that models a binary metal alloy under conditions similar to those expected in Gen-IV reactors. The results of the code give insight into the prevalence of a phenomenon known as radiation induced segregation (RIS) in metals under these Gen-IV relevant conditions. The values input into the code have significant effects on the resulting RIS behavior of the metal alloy. This thesis presents correlations between the initial parameters and the amount of segregation this alloy experiences. The results of this thesis allow a sort of mapping of material parameters and operating conditions so that materials can be designed for optimal performance over the lifespan of the next generation of nuclear reactors. The code in this thesis was developed with the expectation that its modularity would be expanded upon to apply to more complex alloys under a broader range of initial conditions.
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Polcer, James. "Generalized Bathtub Hazard Models for Binary-Transformed Climate Data." TopSCHOLAR®, 2011. http://digitalcommons.wku.edu/theses/1060.
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In this study, we use a hazard-based modeling as an alternative statistical framework to time series methods as applied to climate data. Data collected from the Kentucky Mesonet will be used to study the distributional properties of the duration of high and low-energy wind events relative to an arbitrary threshold. Our objectiveswere to fit bathtub models proposed in literature, propose a generalized bathtub model, apply these models to Kentucky Mesonet data, and make recommendations as to feasibility of wind power generation. Using two different thresholds (1.8 and 10 mph respectively), results show that the Hjorth bathtub model consistently performed better than all other models considered with coefficient of R-squared values at 0.95 or higher. However, fewer sites and months could be included in the analysis when we increased our threshold to 10 mph. Based on a 10 mph threshold, Bowling Green (FARM), Hopkinsville (PGHL), and Columbia (CMBA) posted the top 3 wind duration times in February of 2009. Further studies needed to establish long-term trends.
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Mullick, Kelley Anne. "Binary Nucleation of n-butanol and Deuterium Oxide Conducted in Supersonic Nozzles." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1324247960.
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Bhatta, Fanindra P. "Phase Separation in Binary Lipid Monolayers Bilayers: Experiment and Theory." Kent State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=kent1322501214.
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Sidro, Martín Núria. "Discovery and characterization of the binary system LSI +61º303 in very high energy gamma-rays with MAGIC." Doctoral thesis, Universitat Autònoma de Barcelona, 2008. http://hdl.handle.net/10803/3402.
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Seaton, Robert Leonard. "The influence of temperature and composition on the activation energy for creep in binary aluminum lithium alloys." Thesis, Monterey, California: Naval Postgraduate School, 1990. http://hdl.handle.net/10945/27666.
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Approved for public release; distribution is unlimited.With the fast pace of technology in the aerospace industry, there are increasing demands for higher strength and stiffness in structural materials but with reduced weight and improved formability. Aluminum alloys have been widely used in the construction of aerospace vehicles because of their high strength to weight ratio, forming characteristics and corrosion resistance. An investigation was conducted to determine the temperature and composition dependence on the activation energy for creep of A1-0.5wt.pct.lithium, A1-1.Owt.pct.Li, and A1-2. Owt.pc+.Li alloys. A series of isothermal tests were conducted utilizing constant true stress creep tests, with nominal temperatures ranging from 300 C to 500 C. Temperature cycling tests involved a range of 10 C for each test. Experimental results indicate all three alloys behave as a class II alloy (pure metal class) with a stress exponent, n, approximately equal to 5. In addition, subgrain formation was observed in association with the primary stage of creep. The activation energy for creep of the A1-0.5wt.pct.Li and A1-1.Owt.pct.Li alloys was observed to b essentially the same as that for pure Aluminum.
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Seaton, Robert L. "The influence of temperature and composition on the activation energy for creep in binary aluminum lithium alloys." Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA242299.
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Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, December 1990.Thesis Advisor(s): McNelley, Terry R. ; Kalu, Peter N. "December 1990." Description based on title screen as viewed on April 2, 2010. DTIC Identifier(s): Aluminum alloys, lithium, creep, binary alloys, strength weight ratio, stress tests, stress strain relations, microstructure, aerospace craft, isothermal tests, theses. Author(s) subject terms: Temperature, composition, activation energy, creep binary aluminum lithium alloys. Includes bibliographical references (p. 89-90). Also available in print.
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Zagorac, Dejan [Verfasser], and Martin [Akademischer Betreuer] Jansen. "Energy landscape investigations of chemical matter and structure prediction of binary inorganic solids / Dejan Zagorac. Betreuer: Martin Jansen." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2012. http://d-nb.info/1026684633/34.
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Lim, Mook Tzeng. "Hydrodynamics of a Cold Model of a Dual Fluidized Bed Gasification Plant." Thesis, University of Canterbury. Chemical and Process Engineering, 2012. http://hdl.handle.net/10092/6287.
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Biomass energy is increasingly used to reduce the dependence on fossil fuels and reduce the impact of greenhouse gas emissions on global warming. Fluidized bed
gasification converts solid biomass into gaseous fuels that can be used for combustion or liquid fuels synthesis. The efficiency of biomass gasification is directly affected by the fluidized bed hydrodynamics. For example, the solids recirculation rate through the system is an important parameter that affects the heat and mass transfer rates. In this study, a cold model of a dual fluidized bed (DFB) biomass gasification plant was designed using scaling laws, and was constructed to investigate the hydrodynamics of
industrial DFBs. A DFB consists of a bubbling fluidized bed (BFB), where biomass is gasified to produce syngas, and a circulating fluidized bed (CFB) where the residues of
gasification are combusted. The investigation was divided into Phase I and II. In Phase I, an operational map was developed for the CFB to define operational boundaries for
steady state operation of the plant. An empirical model was developed to predict the solids mass flow rate out of the CFB riser, which is an empirical function of the exit
opening width, the CFB diameter, and a newly introduced aerodynamic factor. The correlation coefficient, R2 for the empirical function was 0.8327. The aerodynamic
factor accounts for the particle inertia and clustering effects at the exit of the CFB riser. Results from Phase I also showed that increasing the fluidizing velocities increased the solids circulation rate and affected the pressure drop over various points in the CFB plant
due to redistribution of solids with the system. A critical assessment was performed on published correlations found in the literature to determine how accurately they predicted
the hydrodynamics in the CFB riser. By comparing predicted and experimental results, the correlations were found to be inaccurate for the conditions and configuration of the
CFB tested in this study. For example, the solids velocity was not accurately predicted by published correlations due to unaccounted particle clustering effects. The main issue
with the published correlations was a lack of generality, so that the correlations only applied for predicting fluidizing behaviour in the equipment they were developed in. In Phase II, an operational map was developed for the DFB, which incorporated both the CFB and the BFB. Experiments with a binary mixture representing sand and char in an industrial gasifier showed a blocking effect in the connecting chute between the CFB and BFB by the material representing char, which was larger and less dense than the material representing sand. A computational fluid dynamics (CFD) based design tool for modelling the cold model CFB cyclone was developed and validated by comparing the predicted and experimental cyclone pressure drop. The correlation coefficient for the CFD pressure drop prediction was 0.7755. The design tool contained information about the grid resolution and the time step required for modelling the cyclone accurately.
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Soudens, Franschke A. "A modified Adams fusion method for the synthesis of binary metal oxide catalysts for the oxygen evolution reaction." University of Western Cape, 2020. http://hdl.handle.net/11394/8231.
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>Magister Scientiae - MScThe majority of the global energy is sourced from conventional fossil fuels. The high demand for energy is accelerating along with the depletion of these fossil fuels. Hence, the shift to renewable energy sources and technology becomes indispensable. Hydrogen is considered a promising alternative to fossil fuels. Polymer electrolyte membrane water electrolysers offer an environmentally friendly technique for the production of hydrogen from renewable energy sources. However, the high overpotential and acidic environment at the anode is one of the challenges faced by polymer electrolyte membrane water electrolysers. This harsh environment requires distinct electrocatalysts which currently consist of expensive precious metals such as Ir, Ru and their oxides.
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Liu, Xinye. "Binary metal organic framework derived hierarchical hollow Ni3S2/Co9S8/N-doped carbon composite with superior sodium storage performance." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1489784678856585.
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Woo, Tim. "A Scalable, Secure, and Energy-Efficient Image Representation for Wireless Systems." Thesis, University of Waterloo, 2004. http://hdl.handle.net/10012/940.
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The recent growth in wireless communications presents a new challenge to multimedia communications. Digital image transmission is a very common form of multimedia communication. Due to limited bandwidth and broadcast nature of the wireless medium, it is necessary to compress and encrypt images before they are sent. On the other hand, it is important to efficiently utilize the limited energy in wireless devices. In a wireless device, two major sources of energy consumption are energy used for computation and energy used for transmission. Computation energy can be reduced by minimizing the time spent on compression and encryption. Transmission energy can be reduced by sending a smaller image file that is obtained by compressing the original highest quality image. Image quality is often sacrificed in the compression process. Therefore, users should have the flexibility to control the image quality to determine whether such a tradeoff is acceptable. It is also desirable for users to have control over image quality in different areas of the image so that less important areas can be compressed more, while retaining the details in important areas. To reduce computations for encryption, a partial encryption scheme can be employed to encrypt only the critical parts of an image file, without sacrificing security. This thesis proposes a scalable and secure image representation scheme that allows users to select different image quality and security levels. The binary space partitioning (BSP) tree presentation is selected because this representation allows convenient compression and scalable encryption. The Advanced Encryption Standard (AES) is chosen as the encryption algorithm because it is fast and secure. Our experimental result shows that our new tree construction method and our pruning formula reduces execution time, hence computation energy, by about 90%. Our image quality prediction model accurately predicts image quality to within 2-3dB of the actual image PSNR.
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Divi, Suresh Chandra. "Heat capacity measurements of pure and binary organic "plastic crystal" thermal energy storage materials and calculation of excess molar heat capacities." abstract and full text PDF (free order & download UNR users only), 2005. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1433411.
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Clarke, Joshua. "Optimal design of geothermal power plants." VCU Scholars Compass, 2014. http://scholarscompass.vcu.edu/etd/3472.
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The optimal design of geothermal power plants across the entire spectrum of meaningful geothermal brine temperatures and climates is investigated, while accounting for vital real-world constraints that are typically ignored in the existing literature. The constrained design space of both double-flash and binary geothermal power plants is visualized, and it is seen that inclusion of real-world constraints is vital to determining the optimal feasible design of a geothermal power plant. The effect of varying condenser temperature on optimum plant performance and optimal design specifications is analyzed. It is shown that condenser temperature has a significant effect on optimal plant design as well. The optimum specific work output and corresponding optimal design of geothermal power plants across the entire range of brine temperatures and condenser temperatures is illustrated and tabulated, allowing a scientifically sound assessment of both feasibility and appropriate plant design under any set of conditions. The performance of genetic algorithms and particle swarm optimization are compared with respect to the constrained, non-linear, simulation-based optimization of a prototypical geothermal power plant, and particle swarm optimization is shown to perform significantly better than genetic algorithms. The Pareto-optimal front of specific work output and specific heat exchanger area is visualized and tabulated for binary and double-flash plants across the full range of potential geothermal brine inlet conditions and climates, allowing investigation of the specific trade-offs required between specific work output and specific heat exchanger area. In addition to the novel data, this dissertation research illustrates the development and use of a sophisticated analysis tool, based on multi-objective particle swarm optimization, for the optimal design of geothermal power plants.
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Yekoladio, Peni Junior. "Thermodynamic optimization of sustainable energy system : application to the optimal design of heat exchangers for geothermal power systems." Diss., University of Pretoria, 2013. http://hdl.handle.net/2263/31615.
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The present work addresses the thermodynamic optimization of small binary-cycle geothermal power plants. The optimization process and entropy generation minimization analysis were performed to minimize the overall exergy loss of the power plant, and the irreversibilities associated with heat transfer and fluid friction caused by the system components. The effect of the geothermal resource temperature to impact on the cycle power output was studied, and it was found that the maximum cycle power output increases exponentially with the geothermal resource temperature. In addition, an optimal turbine inlet temperature was determined, and observed to increase almost linearly with the increase in the geothermal heat source. Furthermore, a coaxial geothermal heat exchanger was modeled and sized for minimum pumping power and maximum extracted heat energy. The geofluid circulation flow rate was also optimized, subject to a nearly linear increase in geothermal gradient. In both limits of the fully turbulent and laminar fully-developed flows, a nearly identical diameter ratio of the coaxial pipes was determined irrespective of the flow regime, whereas the optimal geofluid mass flow rate increased exponentially with the Reynolds number. SeveORCs were observed to yield maximum cycle power output. The addition of an IHE and/or an Oral organic Rankine Cycles were also considered as part of the study. The basic types of the FOH improved significantly the effectiveness of the conversion of the available geothermal energy into useful work, and increased the thermal efficiency of the geothermal power plant. Therefore, the regenerative ORCs were preferred for high-grade geothermal heat. In addition, a performance analysis of several organic fluids was conducted under saturation temperature and subcritical pressure operating conditions of the turbine. Organic fluids with higher boiling point temperature, such as n-pentane, were recommended for the basic type of ORCs, whereas those with lower vapour specific heat capacity, such as butane, were more suitable for the regenerative ORCs.Dissertation (MEng)--University of Pretoria, 2013.
Mechanical and Aeronautical Engineering
unrestricted
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Jerlerud, Pérez Rosa. "Thermodynamic Database for Zirconium Alloys." Doctoral thesis, KTH, Materialvetenskap, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3918.
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For many decades zirconium alloys have been commonly used in the nuclear power industry as fuel cladding material. Besides their good corrosion resistance and acceptable mechanical properties the main reason for using these alloys is the low neutron absorption. Zirconium alloys are exposed to a very severe environment during the nuclear fission process and there is a demand for better design of this material. To meet this requirement a thermodynamic database is useful to support material designers. In this thesis some aspects of the development of a thermodynamic database for zirconium alloys are presented. A thermodynamic database represents an important facility in applying thermodynamic equilibrium calculations for a given material providing: 1) relevant information about the thermodynamic properties of the alloys e.g. amount and composition of phases, oxygen activity, heat capacity etc, and 2) significant information for the manufacturing process e.g. heat treatment temperature. The basic information in the database is first the unary data, i.e. pure elements; those are taken from the compilation of the Scientific Group Thermodata Europe (SGTE) and then the binary and ternary systems. All phases present in those binary and ternary systems are described by means of the Gibbs energy as a function of composition and temperature. Many of those binary systems have been taken from published or unpublished works and others have been assessed in the present work. The elements included in the databse are: C, Fe, Cr, Nb, Ni, Mo, O, Si, Sn, and Zr + H, and the assessment performed under this thesis are: Cr-Sn, Mo-Zr, Sn-Zr, Fe-Nb-Zr and Nb-O-Zr. All the calculations have been made using Thermo-Calc software and the representation of the Gibbs energy obtained by applying Calphad technique with some use of ab initio calculations.QC 20100902
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Pascual, Marc. "Etude hydrodynamique des mélanges binaires thermosensibles." Thesis, Université Paris sciences et lettres, 2020. http://www.theses.fr/2020UPSLS009.
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La nanofluidique marque l'émergence de nouvelles technologies prometteuses pour la production d'énergies bleues. Ces énergies renouvelables à faible impact environnemental exploitent l'entropie de mélange de l'eau douce et l'eau salée, par exemple à l'estuaire d'un fleuve, pour générer de l'électricité. La diffusio-osmose (écoulement associé au déplacement diffusiophorétique) est un candidat sérieux pour la génération de courants électriques. Ce phénomène prend naissance à l'intérieur même des nanopores d’une membrane, et son intensité est directement liée à la charge de surface du matériau. Les mélanges binaires thermosensibles eau-liquide ionique sont une alternative aux fleuves et océans pour générer un gradient salin. L'état monophasique ou biphasique du mélange est contrôlé par la température; dans le cas présent la nature LCST du fluide induit une démixtion par chauffage.Nos travaux se concentrent sur la séparation de phase du mélange en cavité microfluidique, où nous montrons qu'un gradient de confinement ou de température sont une aide précieuse pour isoler sélectivement les deux phases. Nous mesurons également l'intensité des courants diffusio-osmotiques avec ces solutions de liquides ioniques dans des nanopores uniques et des membranes multiporesNanofluidics marks the emergence of promising new technologies for the production of blue energies. These renewable energies with low environmental impact harness the entropy of mixing of fresh and salt water, for example at the estuary of a river, to generate electricity. Diffusio-osmosis (which flow is associated with diffusiophoretic displacement) is a serious candidate for the generation of electric currents. This phenomenon stems from osmotic effects inside the nanopores of the membrane and its intensity is directly linked to the surface charge of the material. Waterionic liquid thermoresponsive binary mixtures are an alternative to rivers and oceans to generate a salt gradient. The monophasic or biphasic state of the mixture is controlled by temperature; in the present case the LCST nature of the fluid induces a demixing by heating. Our work focuses on the phase separation of the mixture in a microfluidic cavity, where we show that a confinement or temperature gradient is a precious help to selectively isolate the two phases. We also measure the intensity of diffusio-osmotic currents with these solutions of ionic liquids in single nanopores and multi-pore membranes
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Chakrabarti, Dwaipayan. "Slow Dynamics In Soft Condensed Matter : From Supercooled Liquids To Thermotropic Liquid Crystals." Thesis, Indian Institute of Science, 2006. http://hdl.handle.net/2005/292.
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This thesis, which contains fourteen chapters in two parts, presents theoretical and computer simulation studies of dynamics in supercooled liquids and thermotropic liquid crystals. These two apparently diverse physical systems are unified by a startling similarity in their complex slow dynamics. Part I consists of six chapters on supercooled liquids while Part II comprises seven chapters on thermotropic liquid crystals. The fourteenth chapter provides a concluding note.
Part I starts with an introduction to supercooled liquids given in chapter 1. This chapter discusses basic features of supercooled liquids and the glass transition and portrays some of the theoretical frameworks and formalisms that are widely recognized to have contributed to our present understanding.
Chapter 2 introduces a new model of binary mixture in order to study dynamics across the supercooled regime. The system consists of an equimolar mixture of the Lennard-Jones spheres and the Gay-Berne ellipsoids of revolution, and thus one of its components has orientational degrees of freedom (ODOF). A decoupling between trans-lational diffusion and rotational diffusion is found to occur below a temperature where the second rank orientational correlation time starts showing a steady deviation from the Arrhenius temperature behavior. At low temperatures, the optical Kerr effect (OKE) signal derived from the system shows a short-to-intermediate time power law decay with a very weak dependence on temperature, if at all, of the power law exponent as has been observed experimentally. At the lowest temperature investigated, jump motion is found to occur in both the translational and orientational degrees of freedom.
Chapter 3 studies how the binary mixture, introduced in the previous chapter, explores its underlying potential energy landscape. The study reveals correlations between the decoupling phenomena, observed almost universally in supercooled molecular liquids, and the manner of exploration of the energy landscape of the system. A significant deviation from the Debye model of rotational diffusion in the dynamics of ODOF is found to begin at a temperature at which the average inherent structure energy of the system starts falling as the temperature decreases. Further, the coupling between rotational diffusion and translational diffusion breaks down at a still lower temperature, where a change occurs in the temperature dependence of the average inherent structure energy.
Chapters 4-6 describe analytical and numerical approaches to solve kinetic models of glassy dynamics for various observables. The β process is modeled as a thermally activated event in a two-level system and the a process is described as a β relaxation mediated cooperative transition in a double-well. The model resembles a landscape picture, conceived by Stillinger [Science 267, 1935 (1995)], where the a process is assumed to involve a concerted series of the β processes, the latter being identified as elementary relaxations involving transitions between contiguous basins. For suitable choice of parameter values, the model could reproduce many of the experimentally observed features of anomalous heat capacity behavior during a temperature cycle through the glass transition as described in chapter 4. The overshoot of the heat capacity during the heating scan that marks the glass transition is found to be caused by a delayed energy relaxation. Chapter 5 shows that the model can also predict a frequency dependent heat capacity that reflects the two-step relaxation behavior. The high-frequency peak in the heat capacity spectra appears with considerably larger amplitude than the low-frequency peak, the latter being due to the a relaxation. The model, when simplified with a modified description of the a process that involves an irreversible escape from a metabasin, can be solved analytically for the relaxation time. This version of the model captures salient features of the structural relaxation in glassy systems as described in chapter 6.
In Part II, thermotropic liquid crystals are studied in molecular dynamics simulations using primarily the family of the Gay-Berne model systems. To start with, chapter 7 provides a brief introduction to thermotropic liquid crystals, especially from the perspective of the issues discussed in the following chapters. This chapter ends up with a detail description of the family of the Gay-Berne models.
Chapter 8 demonstrates that a model system for calamitic liquid crystal (comprising rod-like molecules) could capture the short-to-intermediate time power law decay in the OKE signal near the isotropic-nematic (I-N) phase transition as observed experimentally. The single-particle second rank orientational time correlation function (OTCF) for the model liquid crystalline system is also found to sustain a power law decay regime in the isotropic phase near the I-N transition. On transit across the I-N phase boundary, two power law decay regimes, separated by a plateau, emerge giving rise to a step-like feature in the single-particle second rank OTCF. When the time evolution of the rotational non-Gaussian parameter is monitored as a diagnostic of spatially heterogeneous dynamics, a dominant peak is found to appear following a shoulder at short times, signaling the growth of pseudonematic domains. These observations are compared with those relevant ones obtained for the supercooled binary mixture, as discussed in chapter 2, in the spirit of the analogy suggested recently by Fayer and coworkers [J. Chem. Phys. 118, 9303 (2003)].
In chapter 9, orientational dynamics across the I-N transition are investigated in a variety of model systems of thermotropic liquid crystals. A model discotic system that consists of disc-like molecules as well as a lattice system have been considered in the quest of a universal short-to-intermediate time power law decay in orientational relaxation, if any. A surprisingly general power law decay at short to intermediate times in orientational relaxation is observed in all these systems. While the power law decay of the OKE signal has been recently observed experimentally in calamitic systems near the I-N phase boundary and in the nematic phase by Fayer and coworkers [J. Chem. Phys. 116, 6339 (2002), J. Phys. Chem. B 109, 6514 (2005)], the prediction for the discotic system can be tested in experiments.
Chapter 10 presents the energy landscape view of phase transitions and slow dynamics in thermotropic liquid crystals by determining the inherent structures of a family of one-component Gay-Berne model systems. This study throws light on the interplay between the orientational order and the translational order in the mesophases the systems exhibit. The onset of the growth of the orientational order in the parent phase is found to induce a translational order, resulting in a smectic-like layer in the underlying inherent structures. The inherent structures, surprisingly, never seem to sustain orientational order alone if the parent nematic phase is sandwiched between the high-temperature isotropic phase and the low-temperature smectic phase. The Arrhenius temperature dependence of the orientational relaxation time breaks down near the I-N transition and this breakdown is found to occur at a temperature below which the system explores increasingly deeper potential energy minima. There exists a remarkable similarity in the manner of exploration of the potential energy landscape between the Gay-Berne systems studied here and the well known Kob-Andersen binary mixture reported previously [Nature, 393, 554 (1998)].
In search of a dynamical signature of the coupling between orientational order and translational order, anisotropic translational diffusion in the nematic phase has been investigated in the Gay-Berne model systems as described in chapter 11. The translational diffusion coefficient parallel to the director D// is found to first increase and then decrease as the temperature drops through the nematic phase. This reversal occurs where the smectic order parameter of the underlying inherent structures becomes significant for the first time. The non-monotonic temperature behavior of D// can thus be viewed from an energy landscape analysis as a dynamical signature of the coupling between orientational and translational order at the microscopic level. Such a view is likely to form the foundation of a theoretical framework to explain the anisotropic translation diffusion.
Chapter 12 investigates the validity of the Debye model of rotational diffusion near the I-N phase boundary with a molecular dynamics simulation study of a Gay-Berne model system for calamitic liquid crystals. The Debye model is found to break down near the I-N phase transition. The breakdown, unlike the one observed in supercooled molecular liquids where a jump diffusion model is often invoked, is attributed to the growth of orientational pair correlation. A mode-coupling theory analysis is provided in support of the explanation.
Chapter 13 presents a molecular dynamics study of a binary mixture of prolate ellipsoids of revolution with different aspect ratios interacting with each other through a generalized Gay-Berne potential. Such a study allows to investigate directly the aspect ratio dependence of the dynamical behavior.
In the concluding note, chapter 14 starts with a brief summary of the outcome of the thesis and ends up with suggestion of a few relevant problems that may prove worthwhile to be addressed in future.
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Joch, Vítězslav. "Nízkoenergiový rozptyl iontů inertních plynů na zlatých strukturách." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2011. http://www.nusl.cz/ntk/nusl-229500.
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This diploma thesis deals with comparison of experimental and simulated low energy ion scattering spectra. There is a theoretical description of basic principles of low energy ion scattering and description of the spectrometer, which is situated at Institute of physical engineering. It is shown, how to prepare samples using the colloidal gold solution. The deposition of gold nanoparticles is characterized. The usage and meaning of time and energy spectra of low energy ion scattering is explained. There is also shown the effect of channeling in Si substrate.
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Leser, Eva [Verfasser], Christian [Akademischer Betreuer] Stegmann, Christian Gutachter] Stegmann, Jörn [Gutachter] [Wilms, and Marek [Gutachter] Kowalski. "Eta Carinae : detection and characterisation of the first colliding-wind binary in very-high-energy gamma-rays with H.E.S.S. / Eva Leser ; Gutachter: Christian Stegmann, Jörn Wilms, Marek Kowalski ; Betreuer: Christian Stegmann." Potsdam : Universität Potsdam, 2018. http://d-nb.info/121840471X/34.
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Leser, Eva [Verfasser], Christian [Akademischer Betreuer] Stegmann, Christian [Gutachter] Stegmann, Jörn [Gutachter] Wilms, and Marek [Gutachter] Kowalski. "Eta Carinae : detection and characterisation of the first colliding-wind binary in very-high-energy gamma-rays with H.E.S.S. / Eva Leser ; Gutachter: Christian Stegmann, Jörn Wilms, Marek Kowalski ; Betreuer: Christian Stegmann." Potsdam : Universität Potsdam, 2018. http://d-nb.info/121840471X/34.
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Birgersson, Evert. "Determination of binary fission-fragment yields in the reaction 251Cf(nth, f) and Verification of nuclear reaction theory predictions of fission-fragment distributions in the reaction 238U(n, f)." Doctoral thesis, Örebro : Institutionen för naturvetenskap Department of Natural Sciences, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-1474.
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Sushch, Iurii. "Modeling the emission of the Galactic very high energy [gamma]-ray sources G1.9+0.3, G330.2+1.0, HESS J1303-631 and PSR B1259-63/LS 2883 observed with H.E.S.S." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://dx.doi.org/10.18452/16674.
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Abbildende Cherenkov-Teleskope haben in den letzten Jahren eine groẞe Anzahl neuer Gammastrahlungsquellen im Bereich sehr hoher Energien (VHE, very high energy, E>100 GeV) entdeckt. Diese Studie behandelt Vertreter von drei unterschiedlichen Klassen von galaktischen Gammastrahlungsquellen: die Supernova-Überreste G1.9+0.3 und G330.2+1.0, den Pulsarwind-Nebel HESS J1303-631 und das Binärsystem PSR B1259-63/LS 2883. Für alle Objekte werden die Analyse der H.E.S.S.-Daten und die Modellierung der Emission unter Einbeziehung von Daten aus anderen Wellenlängenbereichen dargestellt.Recently, imaging atmospheric Cherenkov telescopes have discovered numerous new sources representing various source classes in the very high energy (VHE; E>100 GeV) sky. This work presents studies of representatives of three types of Galactic VHE emitters: the Supernova remnants G1.9+0.3 and G330.2+1.0, the pulsar wind nebula HESS J1303-631 and the binary system PSR B1259-63/LS 2883. The analysis of the H.E.S.S. data and the broadband emission modeling are presented.
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Siellez, Karelle. "Les systèmes binaires compacts comme sources de multimessagers : taux, distribution, émissions." Thesis, Nice, 2015. http://www.theses.fr/2015NICE4055.
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La coalescence d'objets compacts (étoiles à neutrons entre elles ou étoile à neutrons avec un trou noir) émet des ondes gravitationnelles et on pense qu’elle produit un sursaut gamma court. Avec l'arrivée des détecteurs d'ondes gravitationnelles de seconde génération, on s'attend à détecter ce signal, qui est l'un des mieux modélisé.L'observation en coïncidence des ondes gravitationnelles émises par ce système et de l'émission électromagnétique sera une source d'informations considérable pour la compréhension de ces phénomènes, de leur progéniteur et du moteur central. Le but de ma thèse a été d’estimer ce taux de détections en coïncidence attendus en fonction des différents instruments. La première méthode se base sur les observations, j’ai donc sélectionné et étudié un échantillon de 31 sursauts gamma courts possédant une mesure de distance. Après avoir dérivé un taux local isotropique du nombre de sursauts gamma courts pour différents satellites, j’ai utilisé la seconde méthode de Monte Carlo avec la simulation de cette population de sursauts gamma courts. La différence entre les taux dérivés des observations et celui venant des simulations est expliqué par la présence d'une sous-population à bas redshift qui était sous-estimée auparavant. Cette thèse montre la faisabilité d'une étude en coïncidence et les stratégies observationnelles à adopter. La compréhension de notre échantillon de sursauts gamma courts, avec une nouvelle sous-population à bas redshift et basse-luminosité, est cruciale dans la préparation de ces détections simultanéesThe coalescence of compact binaries (two neutron stars or a neutron star and a black hole) emits gravitational waves and are thought to produce a short Gamma-Ray Burst (sGRB). With the second generation of gravitational waves detector, the detection in coincidence of both electromagnetic and gravitational emission will open a new window in astrophysics; the multimessenger area. It will allow the understanding of this phenomena, their progenitor and central engine. The goal of this thesis was to made an estimation of the coincident rate for different instruments, using two different method. The first one was based on the oberservations. Thus, I selected a sample of 31 sGRBs of known redshift based on specific criteria. After studying the spectral, temporal and host properties, I derived the isotropic local rate corrected from all known biases. This result was then applied to different satellites and gravitational detectors. After that I simulated this population to confirm this coincident rate with the Monte Carlo simulations. The difference between the two results is explained by a low-redshift population that can't be reproduce by the simulations, and was underestimated before. After tested different parameters for the model, I conclude that this non reproducible population of faint sGRBs at low redshift might be due to an other sort of progenitor. This thesis shows the feasibility of a coincident detection and the observational strategy that should be adopted. The understanding of our sample of sGRB is crucial in the preparation of this coincident detection
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Martins, Marcio Marques. "Influência de parâmetros moleculares em funções de correlação temporal na dinâmica de solvatação mecânica." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2004. http://hdl.handle.net/10183/6896.
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No presente trabalho descrevemos nossos resultados relativos à investigação da dinâmica de solvatação mecânica por meio de simulações por dinâmica molecular, respeitando o regime da resposta linear, em sistemas-modelo de argônio líquido com um soluto monoatômico ou diatômico dissolvido. Estudamos sistematicamente a influência dos parâmetros moleculares dos solutos (tamanho, polarizabilidade) e da densidade frente a vários modelos de solvatação. Funções de Correlação Temporal da Energia de Solvatação foram calculadas com relação à correlações de n-corpos (n = 2; 3) distinguindo interações repulsivas e atrativas para ambos os sistemas líquidos. Também obtivemos segundas derivadas temporais dessas funções referindo-se à parcelas translacionais, rotacionais e roto-translacionais na solução do diatômico. Encontramos que funções de correlação temporal coletivas podem ser razoavelmente bem aproximadas por correlações binárias a densidades baixas e, a densidades altas, correlações ternárias tornam-se mais importantes produzindo um descorrelacionamento mais rápido das funções coletivas devido a efeitos de cancelamento parciais. As funções de correlação para interações repulsivas e atrativas exibem comportamentos dinâmicos independentes do modelo de solvatação devido a fatores de escalonamento linear que afetam apenas as amplitudes das dessas funções de correlação temporal. Em geral, os sistemas com grau de liberdade rotacional apresentam tempos de correlação mais curtos para a dinâmica coletiva e tempos de correlação mais longos para as funções binárias e ternárias. Finalmente, esse estudo mostra que os sistemas contendo o diatômico relaxam-se predominantemente por mecanismos translacionais binários em modelos de solvatação envolvendo alterações apenas na polarizabilidade do soluto, e por mecanismos rotacionais atrativos binários em modelos envolvendo alterações no comprimento de ligação.In the present work, we describe our results concerning our molecular dynamics investigation of the mechanical solvation dynamics within the linear response regime in model systems composed by liquid argon with a monoatomic or diatomic solute. The effect of molecular parameters (size, polarizability) and density has been elucidated for various solvation models. Time Correlation Functions for the solvation energy were calculated and separated into n-body (n = 2; 3) contributions distinguishing repulsive and attractive interactions in both liquid systems. In addition, we computed second time derivatives of these functions in order to describe translational, rotational, and roto-translational portions in the solutions containing the diatomics. We found that collective time correlation functions are well described by binary correlations at low liquid densities and, at high densities, ternary correlations become more important producing faster decaying collective time correlation functions due to partial cancellation effects. The repulsive and attractive time correlation functions exhibit a dynamic behavior that is independent on the solvation model due to linear scaling factors that only affect the absolute amplitudes of these functions. In general, the systems involving a rotational degree of freedom furnish smaller correlation times for the collective solvation dynamics, but stronger correlated two-body and three-body terms. Finally, this study shows that the solvation dynamics for the solution containing the diatomics relaxes predominatly by binary translational mechanisms when solvation models involving changes only in the polarizability parameter are considered. Binary attractive rotational mechanism become important in models with changes in the bond length.
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Bugnard, Jean-Marc. "Ségrégation, reconstructions et ordre partiel aux surfaces des alliages de platine-cobalt." Université Joseph Fourier (Grenoble), 1995. http://www.theses.fr/1995GRE10025.
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Structure et composition superficielles des faces (100), (110) et (111) d'alliages de platine-cobalt ont ete determinees par diffraction d'electrons lents. On trouve, pour les faces non reconstruites un comportement semblable a celui du platine-nickel avec un profil de composition oscillant sur les premiers plans, pour les faces denses de faibles relaxations des distances interplans accompagnees d'un enrichissement en platine du premier plan et pour la face ouverte (110) de fortes relaxations avec enrichissement superficiel en cobalt. Sur la face (100) du pt25co75 nous avons mis en evidence un nouveau mode de reconstruction avec des deplacements lateraux des atomes dans le plan. Ce travail montre, en outre, que la diffraction d'electrons lents est sensible a l'ordre local malgre l'absence de surstructures sur le diagramme de diffraction et met en evidence l'existence d'un tel ordre sur l'ensemble des faces des alliages de platine-cobalt que j'ai etudie
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Fernández-Díaz, Álvaro, Christel Baier, Clara Benac-Earle, and Lars-Åke Fredlund. "Static Partial Order Reduction for Probabilistic Concurrent Systems." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-121261.
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Sound criteria for partial order reduction for probabilistic concurrent systems have been presented in the literature. Their realization relies on a depth-first search-based approach for generating the reduced model. The drawback of this dynamic approach is that it can hardly be combined with other techniques to tackle the state explosion problem, e.g., symbolic probabilistic model checking with multi-terminal variants of binary decision diagrams. Following the approach presented by Kurshan et al. for non-probabilistic systems, we study partial order reduction techniques for probabilistic concurrent systems that can be realized by a static analysis. The idea is to inject the reduction criteria into the control flow graphs of the processes of the system to be analyzed. We provide the theoretical foundations of static partial order reduction for probabilistic concurrent systems and present algorithms to realize them. Finally, we report on some experimental results.
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Fernández-Díaz, Álvaro, Christel Baier, Clara Benac-Earle, and Lars-Åke Fredlund. "Static Partial Order Reduction for Probabilistic Concurrent Systems." Technische Universität Dresden, 2012. https://tud.qucosa.de/id/qucosa%3A26083.
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Sound criteria for partial order reduction for probabilistic concurrent systems have been presented in the literature. Their realization relies on a depth-first search-based approach for generating the reduced model. The drawback of this dynamic approach is that it can hardly be combined with other techniques to tackle the state explosion problem, e.g., symbolic probabilistic model checking with multi-terminal variants of binary decision diagrams. Following the approach presented by Kurshan et al. for non-probabilistic systems, we study partial order reduction techniques for probabilistic concurrent systems that can be realized by a static analysis. The idea is to inject the reduction criteria into the control flow graphs of the processes of the system to be analyzed. We provide the theoretical foundations of static partial order reduction for probabilistic concurrent systems and present algorithms to realize them. Finally, we report on some experimental results.
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Zhang, Qiaofu. "Use Diffusion Multiples to Investigate Diffusion and Precipitation Behavior in Binary Systems." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1483702959561522.
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Terquem, Caroline. "Déformation des disques circumstellaires par effet de marée : application aux objets stellaires jeunes." Phd thesis, Grenoble 1, 1993. http://tel.archives-ouvertes.fr/tel-00686407.
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Les observations des étoiles de type T Tauri ont mis en évidence le très grand nombre de systèmes binaires parmi cette classe d'objets stellaires jeunes. Cette constatation, associée à celle de l'influence de la déformation des disques circumstellaires sur les distributions spectrales d'énergie des T Tauri, nous a conduit à étudier les effets de marée dans les sytèmes binaires d'étoiles jeunes. Dans un premier temps, nous avons donc calculé la perturbation engendrée par des effets de marée dans un disque circumstellaire, auto-gravitant ou d'accrétion. De façon à obtenir un développement analytique, nous avons dans cette étude supposé la perturbation faible. Pour évaluer l'incidence de cette déformation sur la distribution spectrale d'énergie, nous avons ensuite calculé l'énergie émise dans une direction donnée par le système constitué du disque déformé et de l'étoile située en son centre. Cette étude a quant à elle été menée dans le cas d'une déformation d'amplitude quelconque, et rien n'a été négligé du point de vue géométrique, c'est-à-dire qu'ont été prises en considération l'ombre portée par le disque sur l'étoile et celle portée par l'étoile sur le disque. Puis nous avons appliqué ces deux études aux systèmes binaires d'étoiles jeunes de type T Tauri. Nous avons ainsi montré que dans le cas de faibles perturbations, c'est-àdire de systèmes binaires dans lesquels la séparation entre les deux composantes est supérieure ou de l'ordre de la centaine d'unités astronomiques, les effets de marée dans le disque circumstellaire ont une incidence tout à fait significative sur le domaine submillimétrique de la distribution spectrale d'énergie. Pour évaluer l'influence de ces effets dans les systèmes binaires plus serrés, nous avons ensuite décrit la déformation de manière paramétrique. Les distributions spectrales d'énergie obtenues alors nous conduisent à proposer une nouvelle interprétation des observations d'objets stellaires jeunes de classe I, et nous permettent également de reproduire des distributions spectrales d'énergie d'étoiles de type T Tauri ayant un fort excès dans l'infra-rouge. Enfin, nous abordons de façon préliminaire le problème de l'influence de la déformation sur le taux d'accrétion dans le disque.
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WEHREY-AUGUSTIN, FABIENNE. "Oxydo-reduction du neptunium dans les melanges phosphate tributylique-dodecane." Université Louis Pasteur (Strasbourg) (1971-2008), 1988. http://www.theses.fr/1988STR13007.
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Etude des reactions de dismutation et d'oxydation (parhno::(3)) de np(v) dans les melanges tbp-dodecane. La dismutation de np(v) en milieu perchlorique est une reaction d'ordre 2 par rapport a np. Cinetique et energie d'activation de la reaction
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Vanelle, Eric. "Ecrantage du champ piézo-électrique dans les puits quantiques CdTe/CdZnTe : étude dynamique." Université Joseph Fourier (Grenoble), 1995. http://www.theses.fr/1995GRE10212.
Full textAbstract:
Les puits quantiques cdte/cdmnte que nous avons etudies ont la particularite d'etre piezo-electriques. Les contraintes exercees par les barrieres sur le puits de cdte provoquent l'apparition d'un champ piezo-electrique de l'ordre de 10#7 v/m dans le puits quantique si l'axe de croissance est polaire pour la structure blende de zinc, ce qui est le cas des structures <111> etudiees. Ce champ a pour effet principal d'incliner les bandes de conduction et de valence, et de decaler vers le rouge l'energie des transitions excitonique et bande a bande, par rapport au puits carre correspondant. Les electrons et les trous photo-crees sont alors separes spatialement et tendent a creer un champ electrique qui s'oppose au champ piezo-electrique permanent. Nous avons etudie en dynamique, tant en photoluminescence qu'en absorption, les mecanismes d'ecrantage de ce champ piezo-electrique et, entre autres, les modulations induites sur les energies de transition, en fonction de la densite de porteurs photo-crees. Des deplacements d'environ 10 mev sont observes, et interpretes theoriquement comme resultant bien d'un ecrantage du champ piezo-electrique. Les experiences resolues en temps montrent de plus le caractere ultra-rapide (<100 fs) de ce phenomene. Nous mettons en evidence le comportement particulier des excitons dans ce type de structures, qui, par bien des aspects, est tres proche de celui des paires libres notamment au niveau de l'efficacite d'ecrantage et des collisions exciton-exciton. Enfin, nous montrons que le champ piezo-electrique permet une tres forte augmentation des effets du couplage aux phonons acoustiques
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Duc, Nguyen Manh. "Approche électronique de l'ordre local dans les alliages à base de métaux de transition." Grenoble 1, 1986. http://www.theses.fr/1986GRE10072.
Full textAbstract:
Modèle de calcul de l'énergie électronique des alliages à base de métaux de transition. Ce modèle est base sur un hamiltonien de liaisons fortes et prend en compte les effets d'hybridation s-d. Calcul de la densité d'états électroniques et des énergies de cohésion. Pour les alliages amorphes de deux métaux de transition, un ordre chimique local est établi. Conséquences sur la densité d'états électronique. Corrélation entre structure électronique et coefficient de hall. Mise en évidence d'une forte hybridation sp-d pour les alliages entre métaux de transition et métaux polyvalents
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Bessoud, Agnès. "Analyse des interactions dans des alliages à base de métaux de transition." Grenoble INPG, 1989. http://www.theses.fr/1989INPG0091.
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Calcul, a partir d'un hamiltonien de liaisons fortes et de la methode de l'amas-reseau de bethe, de la structure electronique et l'energie de formation d'alliages binaires de structure cubique centree ou cubique a faces centrees. En utilisant l'entropie de configuration traitee par la methode variationnelle des amas, l'energie libre de formation a ete obtenue par minimisation par rapport au parametre d'ordre a courte distance
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Bosch, i. Ramon Valentí. "Broadband emission from high energy processes in microquasars." Doctoral thesis, Universitat de Barcelona, 2006. http://hdl.handle.net/10803/746.
Full textAbstract:
Microquasars are X-ray binary systems that present relativistic radio jets.These systems consist on a normal star and a compact object, where the latter accretes matter from the former powering the mentioned relativistic jets.
Microquasars are known to emit at all the wavelengths from radio to soft gamma-ray energies. Moreover, these objects are nowadays turning out as a new galactic population of high-energy and very high energy gamma-ray emitters.
Although the mechanisms behind gamma-ray emission are still not known, it seems that the production site should be the jet itself.
We have explored several scenarios linked to gamma-ray production, modeling the non-thermal radiation produced in microquasar jets in the entire spectrum, from radio to TeV energies. We have developed leptonic models to reproduce the emission thought to come from the inner parts of the jet, close to the compact object, taking also into account the radiation at lower energies. Moreover, we have studied the extended broadband emission that could be produced via leptonic and hadronic interactions in nearby clouds bombarded by microquasar jet accelerated protons.
We show that microquasars could be behind a significant fraction of the gamma and cosmic rays generated within the Galaxy. Gamma-ray emission from jets could be observed presenting complicated spectra and patterns of variability. The emission should be affected by variable accretion and jet ejection, particle acceleration changes, photon photon absorption in dense ambient photon fields, and other effects linked to the geometry involved in the emitting and absorbing processes. Concerning extended emission from microquasar nearby regions, radiation, convection and diffusion timescales, as well as the particle acceleration efficiencies, are of primary importance to characterize their emission properties.
Multiwavelength and multiparticle observations are required to properly understand the involved physics. This will be possible with the new instrumentation at work or to come, which will allow to improve theoretical modeling up to unexpected levels.
"Emissió multi-longitud d'ona per processos d'alta energia als microquàsars"
Els microquàsars són sistemes formats per dos objectes, un d'ells és una estrella normal, l'altre pot ser una estrella de neutrons o un forat negre. Si no presenten majors peculiaritats, aquests objectes són anomenats binàries de raigs X, ja que són sistemes binaris que emeten fortament en X. Si aquestes binàries de raigs X presenten dolls relativistes que emeten en ràdio, llavors s'anomenen microquàsars. Aquests dolls s'originen amb la participació de forts camps magnètics presents al veïnatge de l'objecte compacte, i poden emetre en tot l'espectre electromagnètic. Durant el desenvolupament d'aquesta tesi, s'han investigat els mecanismes d'emissió d'alta i molt energia als microquàsars, tenint en compte també la radiació a energies més baixes. Es conclou que es poden explicar els fluxos gamma observats als microquàsars assumint continguts
d'energia en les partícules emissores raonables encara que més grans que aquells que serien suficients per explicar només la part ràdio. De fet, els microquàsars podrien ser una fracció important de les fonts no identificades variables al pla galàctic. Amb la introducció d'acceleració de partícules i absorció per creació de parelles, es pot explicar de manera elegant l'espectre multi-longitud d'ona d'un microquàsar, des de ràdio fins a raigs gamma de molt alta energia. Es important fer notar que, si protons relativistes abandonessin els dolls quan aquests interactuen amb el medi circumdant, el flux de raigs còsmics a les regions properes seria incrementat de forma significativa, cosa que mostra la rellevància dels microquàsars com a acceleradors de raigs còsmics. Això també podria generar emissió multi longitud d'ona si els mencionats protons interactuessin amb el medi circumdant. El treball presentat mostra la riquesa de la física involucrada en l'estudi dels microquàsars, i posa de manifest que l'estudi del fenomen microquàsar ha de recórrer un llarg camí abans de ser comprés de manera global. En qualsevol cas, degut a les excitants perspectives en el camp teòric i observacional, el viatge cap a una bona comprensió d'aquests objectes promet grans avenços en el futur proper.
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Chassagne, Francis. "Etude de l'ordre à courte distance dans la solution solide gamma Ni-Al." Paris 6, 1986. http://www.theses.fr/1986PA066098.
Full textAbstract:
Etude par mesures quantitatives de diffusion en diffraction de rayons X de l'état de l'ordre local dans les alliages binaires Ni-10,5 et 7,3% at Al. Description de la méthode d'étude. Calcul des potentiels d'interaction de paires par comparaison de l'intensité d'ordre à courte distance avec la susceptibilité du modèle de champ moyen de paires sur un réseau cubique à faces centrées à champ non nul. Détermination de l'énergie d'interface précipitée.
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Grieshaber, Wolfgang. "Caractérisation d'interfaces et effet polaron magnétique excitonique dans les hétérostructures de semiconducteurs semimagnétiques CdMnTe/CdTe." Université Joseph Fourier (Grenoble), 1995. http://www.theses.fr/1995GRE10040.
Full textAbstract:
L'etalement des interfaces dans des heterostructures cdte/cdmnte a ete determine par mesures de l'effet zeeman des transitions excitoniques dans le puits de cdte. Cette methode magneto-optique est sensible a la correlation de position d'ions mn en sites de premiers voisins et permet une caracterisation a l'echelle de la distance interatomique. Deux effets (extrinseque et intrinseque) expliquent quantitativement l'exaltation de l'aimantation aux interfaces. L'effet extrinseque est du a l'etalement des interfaces selon l'axe de croissance ; l'effet intrinseque est pris en compte en attribuant a chaque ion mn dans une monocouche l'aimantation qu'il aurait dans le massif avec le meme nombre de premiers voisins. Dans des echantillons a barrieres magnetiques epaisses on peut determiner l'etalement: i) l'interface cdte/cdmnte est plus etalee que son opposee, ii) l'etalement augmente avec la temperature de depot, iii) la stoechiometrie des flux et les arrets de croissance influe peu sur l'etalement. Dans des echantillons avec nominalement 1 monocouche magnetique, la contribution de l'effet intrinseque devient non negligeable. Nous avons observe la formation du polaron magnetique excitonique dans des heterostructures cd#1#-#xmn#xte/cd#1#-#ymn#yte (y-x0. 25) avec differentes concentrations x et largeurs de puits l. Les observations resolues en temps ainsi qu'en excitation continue montrent que i) le polaron devient observable dans des puits avec x<0. 1 en excitation continue alors qu'il ne l'est pas dans le massif de meme concentration, ii) la diminution de la largeur de puits fait augmenter l'energie polaron au-dessus de la valeur qu'elle a dans le massif de meme composition. Un modele a une particule qui admet un potentiel de prelocalisation qui depend uniquement de la concentration x et qui agit dans le plan des couches rend bien compte des mesures en fonction de l et de la temperature
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Mandray, Ariane. "Etude magnéto-optique de centres D- confinés dans des multi-puits quantiques GaAs/AlGaAs." Université Joseph Fourier (Grenoble), 1994. http://www.theses.fr/1994GRE10075.
Full textAbstract:
Le centre d#-, ou ion donneur negatif, est l'analogue en physique du solide de l'ion hydrogene negatif h#-. Il s'agit donc d'un systeme correle simple, avec seulement deux electrons. Les transitions magneto-optiques permettant l'etude des donneurs peu profonds (neutres ou charges negativement) dans les multi-puits gaas/algaas se situent dans la gamme de l'infra-rouge lointain. Notre appareillage experimental est essentiellement constitue d'un spectrometre a transformee de fourier, couple a un aimant supraconducteur ou resistif. Nous avons etudie le mecanisme de formation des centres d#- confines dans des multi-puits quantiques. Dans cette configuration, contrairement au materiau massif, les centres d#- sont formes par construction, ce qui permet leur etude a l'equilibre thermodynamique. L'importance de la geometrie de dopage est soulignee, et la possibilite de realiser un dopage d#- de puits quantiques est mise en evidence. Le spectre d'energie des centres d#- confines a ete etudie pour une large gamme de champs magnetiques (jusqu'a 20 t) et pour differentes largeurs de puits. Ces mesures permettent d'observer, outre la non-parabolicite de bande de gaas, les effets de correlation electronique augmentes par la baisse de dimensionalite. L'etude des centres d#- en presence de desordre d'alliage dans des puits de al-gaas met en evidence la possibilite de coexistence, dans ce type de systeme, de centres profonds et de centres peu profonds, tous deux charges negativement
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Murach, Thomas. "Monoscopic Analysis of H.E.S.S. Phase II Data on PSR B1259–63/LS 2883." Doctoral thesis, Humboldt-Universität zu Berlin, 2017. http://dx.doi.org/10.18452/18484.
Full textAbstract:
Cherenkov-Teleskope sind in der Lage, das schwache Cherenkovlicht aus Teilchenschauern zu detektieren, die von kosmischen Teilchen mit Energien von ca. 100 GeV bis 100 TeV in der Erdatmosphäre initiiert werden. Das Ziel ist die Detektion von Cherenkovlicht aus Schauern, die von Gammastrahlen erzeugt wurden, der größte Teil der Schauer stammt jedoch von geladenen Teilchen. Im Jahr 2012 wurde das H.E.S.S.-Observatorium in Namibia, bis dahin bestehend aus vier Teleskopen mit 100 m²-Spiegeln, um ein fünftes Teleskop mit einer Spiegelfläche von ca. 600 m² ergänzt. Aufgrund der großen Spiegelfläche besitzt dieses Teleskop die niedrigste Energieschwelle aller Teleskope dieser Art. In dieser Dissertation wird ein schneller Algorithmus namens MonoReco präsentiert, der grundlegende Eigenschaften der Gammastrahlen wie ihre Energien und Richtungen rekonstruieren kann. Dieser Algorithmus kann weiterhin unterscheiden, ob Schauer von Gammastrahlen oder von geladenen Teilchen der kosmischen Strahlung initiiert wurden. Diese Aufgaben werden mit mithilfe von künstlichen neuronalen Netzwerken erfüllt, welche ausschließlich die Momente der Intensitätsverteilungen in der Kamera des neuen Teleskops analysieren. Eine Energieschwelle von 59 GeV und Richtungsauflösungen von 0.1°-0.3° werden erreicht. Das Energiebias liegt bei wenigen Prozent, die Energieauflösung bei 20-30%. Unter anderem mit dem MonoReco-Algorithmus wurden Daten, die in der Zeit um das Periastron des Binärsystems PSR B1259-63/LS 2883 im Jahre 2014 genommen wurden, analysiert. Es handelt sich hierbei um einen Neutronenstern, der sich in einem 3,4-Jahres-Orbit um einen massereichen Stern mit einer den Stern umgebenden Scheibe aus Gas und Plasmen befindet. Zum ersten Mal konnte H.E.S.S. das Gammastrahlenspektrum dieses Systems bei Energien unterhalb von 200 GeV messen. Weiterhin wurde bei erstmaligen Beobachtungen zur Zeit des Periastrons ein lokales Flussminimum gemessen. Sowohl vor dem ersten als auch nach dem zweiten Transit des Neutronensterns durch die Scheibe wurden hohe Flüsse gemessen. Im zweiten Fall wurden Beobachtungen erstmals zeitgleich mit dem Fermi-LAT-Experiment durchgeführt, das wiederholt sehr hohe Flüsse in diesem Teil des Orbits messen konnte. Ein Vergleich der gemessenen Flüsse mit Vorhersagen eines leptonischen Modells zeigt gute Übereinstimmungen.Cherenkov telescopes can detect the faint Cherenkov light emitted by air showers that were initiated by cosmic particles with energies between approximately 100 GeV and 100 TeV in the Earth's atmosphere. Aiming for the detection of Cherenkov light emitted by gamma ray-initiated air showers, the vast majority of all detected showers are initiated by charged cosmic rays. In 2012 the H.E.S.S. observatory, until then comprising four telescopes with 100 m² mirrors each, was extended by adding a much larger fifth telescope with a very large mirror area of 600 m². Due to the large mirror area, this telescope has the lowest energy threshold of all telescopes of this kind. In this dissertation, a fast algorithm called MonoReco is presented that can reconstruct fundamental properties of the primary gamma rays like their direction or their energy. Furthermore, this algorithm can distinguish between air showers initiated either by gamma rays or by charged cosmic rays. Those tasks are accomplished with the help of artificial neural networks, which analyse moments of the intensity distributions in the camera of the new telescope exclusively. The energy threshold is 59 GeV and angular resolutions of 0.1°-0.3° are achieved. The energy reconstruction bias is at the level of a few percent, the energy resolution is at the level of 20-30%. Data taken around the 2014 periastron passage of the gamma-ray binary PSR B1259-63/LS 2883 were analysed with, among others, the MonoReco algorithm. This binary system comprises a neutron star in a 3.4 year orbit around a massive star with a circumstellar disk consisting of gas and plasma. For the first time the gamma-ray spectrum of this system could be measured by H.E.S.S. down to below 200 GeV. Furthermore, a local flux minimum could be measured during unprecedented measurements at the time of periastron. High fluxes were measured both before the first and after the second transit of the neutron star through the disk. In the second case measurements could be performed for the first time contemporaneously with the Fermi-LAT experiment, which has repeatedly detected very high fluxes at this part of the orbit. A good agreement between measured fluxes and predictions of a leptonic model is found.
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Marcote, Martin Benito. "Non-thermal emission from high-energy binaries through interferometric radio observations." Doctoral thesis, Universitat de Barcelona, 2015. http://hdl.handle.net/10803/336664.
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High-mass binary systems involve extreme environments that produce non-thermal emission from radio to gamma rays. Only three types of these systems are known to emit persistent gamma-ray emission: colliding-wind binaries, high-mass X-ray binaries and gamma-ray binaries. This thesis is focused on the radio emission of high-mass binary systems through interferometric observations, and we have explored several of these sources with low- and high-frequency radio observations, and very high-resolution VLBI ones.
We have studied the gamma-ray binary LS 5039 at low and high frequencies, and we have determined its spectra and light-curves in the frequency range of 0.15—15 GHz by analyzing radio observations from the VLA, GMRT and WSRT. We have observed that its spectrum is persistent along the time on day, month and year timescales, exhibiting a turnover at 0.5 GHz. The obtained quasi-simultaneous spectra reveal subtle differences between them. Synchrotron self-absorption can explain the observed spectra, but the Razin effect is necessary at some epochs. This is the first time that this effect is reported in a gamma-ray binary. With all these data and a simple model, we have estimated the physical properties of the radio emitting region, providing an estimation of its size, the magnetic field, the electron density, and the mass-loss rate of the companion star.
We have also explored the low-frequency emission of the gamma-ray binary LS I +61 303 through GMRT and LOFAR observations. We have detected for the first time a gamma-ray binary at a frequency as low as 150 MHz. We have also determined the light-curves of the source at 150, 235 and 610 MHz. These light-curves are modulated with the orbital and superorbital period, with a quasi-sinusoidal modulation along the orbital phase. The shifts observed between the orbital phases at which the maximum emission takes place at different frequencies have been modeled with a simple model, suggesting an expanding emitting region, with an expansion velocity close to the stellar wind one.
The gamma-ray binary HESS J0632+057 has been explored with a very high-resolution EVN observation to unveil the evolution of its radio emission along the orbit. However, the source was not detected, setting an upper-limit which is one order of magnitude below the radio emission detected in previous observations.
We have discovered a new colliding wind binary (HD 93129A) through a multiwavelength campaign with optical and LBA radio data. We have resolved the radio emission from the wind collision region, observing the expected bow-shaped structure. This source is one of the earliest, hottest, and most massive binary systems discovered up to now. We provide a rough estimation of the wind momentum rates ratio based on the observed structure. We have also observed an increase of the radio emission during the last years, as the system approaches to the periastron passage, which is estimated to take place in ~2024.
Finally, we performed radio observations on two new sources that were hypothesized to be gamma-ray binaries. On one hand, the star TYC 4051-1277-1 was initially proposed to be associated with a non-thermal radio source, but he have concluded that the radio emission is originated by a quasar. On the other hand, MWC 656 has been discovered to be the first Be/BH binary system. However, its radio emission remains undetected.
Based on these results, we have improved the knowledge of several high-energy binary systems through their radio emission, conducting for the first time detailed low-frequency estudies on these types of sources.Las binarias de alta energía son sistemas que producen emisión de rayos X y/o rayos gamma, debido a la presencia de un entorno suficientemente energético como para acelerar partículas hasta velocidades relativistas. Sólo tres tipos de binarias han sido detectadas en rayos gamma de forma persistente: binarias con colisión de vientos, binarias de rayos X de alta masa o binarias de rayos gamma. Todas ellas involucran una estrella masiva (con una masa superior a 8 veces la masa solar) y a otra estrella masiva o a un objeto compacto. Esta tesis está centrada en el estudio de la emisión radio de estos sistemas a través de observaciones con radio interferómetros. Se han estudiado dos binarias de rayos gamma a bajas frecuencias (LS 5039 y LS I +61 303), obteniendo sus curvas de luz y espectros. Éstos nos han permitido determinar propiedades físicas de la región emisora, como el campo magnético, la tasa de pérdida de masa, o la velocidad de expansión de dicha región. También hemos revelado la presencia del efecto Razin en la parte absorbida del espectro de LS 5039, siendo la primera vez que se detecta en una binaria de rayo gamma. Además, se ha detectado por primera vez una binaria de rayos gamma, LS I +61 303, a una frecuencia tan baja como 150 MHz. También se ha estudiado la binaria de rayos gamma HESS J0632+057 con observaciones radio de muy alta resolución, aunque la misma no ha sido detectada. Se ha descubierto una nueva binaria con colisión de vientos, HD 93129A, a través de observaciones radio de muy alta resolución y observaciones ópticas. Por último, se han llevado a cabo observaciones radio de dos fuentes que eran candidatas a ser binarias de rayos gamma.
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Vilela, Leticia Biagi. "Alocação ótima de indicadores de falta em redes de distribuição de energia elétrica utilizando modelagem matemática /." Ilha Solteira, 2018. http://hdl.handle.net/11449/157414.
Full textAbstract:
Orientador: Fábio Bertequini LeãoResumo: Neste trabalho propõe-se um modelo matemático de Programação Não Linear Binária (PNLB) para resolver o problema de alocação ótima de dispositivos indicadores de falta (OPFI – Optimal Placement of Fault Indicator Devices) em redes radiais de distribuição de energia elétrica. O problema é modelado por meio de uma função objetivo que considera dois custos conflitantes: o Custo da Energia Não Suprida (CENS) e o Custo de Investimento em Sensores (CINV). O modelo matemático proposto pode ser resolvido por métodos exatos e para todos os testes simulados foram utilizados os softwares de programação matemática AMPL (A Mathematical Programming Language) e KNITRO versão 9.0.0. Para validação do método proposto, são realizados testes em um sistema de distribuição de 19 barras, e em outros dois sistemas de 34 e 70 barras, sendo que nesses dois sistemas os indicadores de falta foram alocados apenas no tronco principal desses alimentadores. Os resultados obtidos mostram que o modelo matemático é adequado para resolver o problema formulado. Assim, o método proposto traz contribuição à literatura, visto que o problema da alocação ótima desses dispositivos tem sido resolvido principalmente por meio de técnicas meta-heurísticas.
Abstract: This paper proposes a Binary Nonlinear Programming model to solve the problem of Optimal Placement of Fault Indicator Devices (OPFI) in radial distribution networks. The problem is modeled by an objective function that considers two conflicting costs: Cost of Energy Not Supplied and Cost of Investing in Sensors. The proposed mathematical model can be solved by exact methods and for all the simulated tests the mathematical programming software AMPL (A Mathematical Programming Language) and KNITRO version 9.0.0 were used. For validation of the proposed method, tests are performed in a 19-bar distribution system, and in two other systems of 34 and 70 bars, where in these two systems fault indicators were only allocated to the main trunk of these feeders. The results obtained show that the mathematical model is adequate to solve the problem formulated. Thus, the proposed method brings contribution to the literature, since the problem of optimal allocation of these devices has been solved mainly by means of metaheuristic techniques.
Mestre