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Dissertations / Theses on the topic 'Halo density'
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Lehner, Nicolas. "Interstellar gas and hot stars in low density environments." Thesis, Queen's University Belfast, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343034.
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Casas, Miranda Rigoberto Angel. "Statistics of the dark matter halo distribution in cosmic density fields." Diss., [S.l.] : [s.n.], 2002. http://edoc.ub.uni-muenchen.de/archive/00000098.
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Weiss, Jake. "The Stellar Density of the Major Substructure in the Milky Way Halo." Thesis, Rensselaer Polytechnic Institute, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10840515.
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<p> We develop, test, and apply a statistical photometric parallax method using main sequence turn off (MSTO) stars in the Sloan Digital Sky Survey (SDSS). We show using simulated data that if our density model is similar to the actual density distribution of our data, we can reliably determine the density model parameters of at least three major substructures in the Milky Way halo, and a smooth background component, using the computational resources available on MilkyWay@home (a twenty parameter fit). As a test for the new model, we fit the stellar density in SDSS stripe 19. After confirming that the model is working as intended on both simulated and observed SDSS stripe 19 data, we moved on to fitting stripes 10 through 23 in the SDSS north Galactic cap. We found an oblate halo with an average flattening of $0.58$. Seven streams were found in these fourteen stripes. The Sgr dwarf leading tidal tail detected in 8 stripes, with properties that are consistent with previous fits to the streams. The trailing tidal tail and the ''bifurcated'' stream were found at the previously identified distances. The Parallel Stream was traced across the sky at a distance of 15 kpc, and roughly tracks an orbit that was fit by previous authors to the Virgo Stellar Stream. A new stream, the Perpendicular Stream, was found at a distance of 15 kpc in the region of Virgo, but roughly perpendicular in orientation on the sky to the Parallel Stream. A stream possibly including the globular cluster NGC 5466 was also found at a distance between 5 and 15 kpc from the Sun.</p><p>
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Achitouv, Ixandra. "Halo mass function of dark matter halos : imprints of the initial matter density field and of the non-linear collapse." Paris 7, 2012. http://www.theses.fr/2012PA077245.
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Mastromarino, Claudio. "Shapes and density profiles of haloes in self-interacting dark matter cosmologies." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/24440/.
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We use cosmological simulation to test the differences of halo properties on the mass range that goes from Milky-Way-like to massive
elliptical galaxies in CDM and SIDM models. We use two distinct SIDM models, one with constant cross-section (σ/m = 1 cm^2 /g) and one with a velocity-dependent cross-section. The simulation set is made of 6 runs in total, which simulate the same volume of 50 Mpc^3, in CDM and the two SIDM models; moreover, for each of those, a DM-only and a full-hydrodynamic version is available. In particular, we focus on the analysis of density profiles and halo shapes at z = 0. We split
our sample into three mass bins to compare and average the features of haloes of comparable mass.
From DM-only simulations we find: 1) both SIDM models produce a central core in density profiles regardless of the halo mass; 2) both SIDM models make DM haloes rounder than in CDM counterpart for each mass bin.
From full-hydrodynamic simulations, we find that the inclusion of baryonic effects can modify these properties. Both for the density profiles and the halo shapes the baryon effects make the differences between the DM models less pronounced than in the DM-only case. Moreover, we find that the average final properties of the density profiles in full-hydrodynamic simulations depend on the considered mass bin: the most massive
shows a cored profile in the SIDM runs, while the less massive one shows a cuspier profile than in CDM. For the intermediate-mass bin, we find no differences in the density profile between the models.
Regarding the halo shapes, we find that the haloes in the SIDM models are more spherical than in the CDM counterpart also with the inclusion of the baryonic effects. However, while the differences between DM models in the density profiles are visible only at small radii (r < 10 kpc/h), we show that SIDM haloes remain more spherical than in CDM even in more external regions (r ∼ 60 − 100 kpc/h).
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Silva, Maurício Banaszeski da. "A physics-based statistical random telegraph noise model." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/150171.
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O Ruído de Baixa Frequência (LFN), tais como o ruído flicker e o Random Telegraph Noise (RTN), são limitadores de performance em muitos circuitos analógicos e digitais. Para transistores diminutos, a densidade espectral de potência do ruído pode variar muitas ordens de grandeza, impondo uma séria limitação na performance do circuito e também em sua confiabilidade. Nesta tese, nós propomos um novo modelo de RTN estatístico para descrever o ruído de baixa frequência em MOSFETs. Utilizando o modelo proposto, pode-se explicar e calcular o valor esperado e a variabilidade do ruído em função das polarizações, geometrias e dos parâmetros físicos do transistor. O modelo é validado através de inúmeros resultados experimentais para dispositivos com canais tipo n e p, e para diferentes tecnologias CMOS. É demonstrado que a estatística do ruído LFN dos dispositivos de canal tipo n e p podem ser descritos através do mesmo mecanismo. Através dos nossos resultados e do nosso modelo, nós mostramos que a densidade de armadilhas dos transistores de canal tipo p é fortemente dependente do nível de Fermi, enquanto para o transistor de tipo n a densidade de armadilhas pode ser considerada constante na energia. Também é mostrado e explicado, através do nosso modelo, o impacto do implante de halo nas estatísticas do ruído. Utilizando o modelo demonstra-se porque a variabilidade, denotado por σ[log(SId)], do RTN/LFN não segue uma dependência 1/√área; e fica demonstrado que o ruído, e sua variabilidade, encontrado em nossas medidas pode ser modelado utilizando parâmetros físicos. Além disso, o modelo proposto pode ser utilizado para calcular o percentil do ruído, o qual pode ser utilizado para prever ou alcançar certo rendimento do circuito.<br>Low Frequency Noise (LFN) and Random Telegraph Noise (RTN) are performance limiters in many analog and digital circuits. For small area devices, the noise power spectral density can easily vary by many orders of magnitude, imposing serious threat on circuit performance and possibly reliability. In this thesis, we propose a new RTN model to describe the statistics of the low frequency noise in MOSFETs. Using the proposed model, we can explain and calculate the Expected value and Variability of the noise as function of devices’ biases, geometry and physical parameters. The model is validated through numerous experimental results for n-channel and p-channel devices from different CMOS technology nodes. We show that the LFN statistics of n-channel and p-channel MOSFETs can be described by the same mechanism. From our results and model, we show that the trap density of the p-channel device is a strongly varying function of the Fermi level, whereas for the n-channel the trap density can be considered constant. We also show and explain, using the proposed model, the impact of the halo-implanted regions on the statistics of the noise. Using this model, we clarify why the variability, denoted by σ[log(SId)], of RTN/LFN doesn't follow a 1/√area dependence; and we demonstrate that the noise, and its variability, found in our measurements can be modeled using reasonable physical quantities. Moreover, the proposed model can be used to calculate the percentile quantity of the noise, which can be used to predict or to achieve certain circuit yield.
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Tsemekhman, Kiril. "Current distribution and density of states in the quantum hall effect /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/9737.
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Pinto, J. A. "Some aspects of geometric quantization and their physical basis." Thesis, University of St Andrews, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377329.
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Siddiki, Afif. "Model calculations of current and density distributions in dissipative Hall bars." Doctoral thesis, [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=980715725.
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Juan, Rovira Enric. "Analytic derivation of non-linear dark matter clustering from the filtering of the primordial density field." Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/395192.
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In this Thesis, we show how the properties of dark matter halos can be directly derived from the proper filtering of the primordial density field through the use of the CUSP formalism (ConflUent System of Peak trajectories). Although the CUSP formalism was first proposed in 1995, it was still incomplete.
In the present Thesis we give a general overview of the formalism, explaining its theoretical grounds and how it can be used to derive the typical properties of relaxed dark matter halos. We prove the existence of a one-to-one correspondence between halos and peaks despite the ellipsoidal collapse of peaks and we also show that halos formed through major mergers and accretion have the same properties, dependent on the properties of the respective progenitor peaks at the largest scale.
We also apply the CUSP formalism to study the growth of halos, showing that they grow inside-out. We also derive practical analytical expressions for the mass-concentration-shape NFW and Einasto relations over the whole mass and redshift range.
Finally, we have applied the CUSP formalism to study the halo mass and multiplicity functions, and their dependence on the exact mass definition used. We have shown that the FoF(0.2) halo finding algorithm is equivalent to the spherical virial overdensity one, which explains the privileged linking length equal to 0.2; we have shown why the virial radii of halos are close to the top-hat radii described by the spherical collapse model, and why the halo mass function is so close to the Press-Shechter form and, lastly, we have explained why the halo multiplicity function is closely universal in the two equivalent cases mentioned before.<br>En aquesta tesi demostrem com les propietats dels halos de matèria fosca poden ser derivades directament del camp primordial de densitat si s'usa un filtre adequat. En aquest marc, desenvolupem el formalisme CUSP (ConflUent System of Peak trajectories).
Amb aquesta tesi completem aquest tractament analític de la formació no lineal d'estructura en el nostre Univers. En primer lloc, fem un resum del formalisme i les seves bases teòriques, explicant com pot ser usat per trobar les propietats típiques dels halos. Alhora demostrem l'existència d'una correspondència unívoca entre pics de densitat i halos. També es demostra que les propietats dels halos relaxats són les mateixes tant si s'han format per fusions o per acreció pura, ja que aquestes només depenen de les propietats dels pics progenitors de major escala. D'aquesta manera, entenem perquè les propietats típiques dels halos de matèria fosca depenen només de la seva massa i del temps. Un cop establert el formalisme CUSP, aquest ha estat usat, en primer lloc, per estudiar el creixement dels halos de matèria fosca. En particular, hem demostrat que els halos creixen de dins cap a fora, punt crucial en el desenvolupament del formalisme CUSP. També hem estudiat els dominis de validesa de la configuració de tipus NFW i Einasto per als perfils de densitat dels halos, establint alhora unes relacions analítiques per a les relacions massa-concentració-forma. Finalment, també hem aplicat el formalisme CUSP per a estudiar les funcions de massa i multiplicitat, i la dependència d'aquestes amb la definició de massa usada. Hem demostrat que l'algoritme de cerca d'halos FOF (0.2) (molt usat en simulacions numèriques) és equivalent a la definició de sobredensitat virial. També hem demostrat el motiu pel qual els radis virials dels halos són similars als top-hat del col·lapse esfèric i perquè la funció de masses dels halos és tan similar a la de Press-Shechter. Finalment, hem explicat el motiu pel qual la funció de multiplicitat dels halos és pràcticament universal en els dos casos equivalents descrits anterioment.
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Tsikata, Sedina. "Small-scale electron density fluctuations in the hall thruster, investigated by collective light scattering." Palaiseau, Ecole polytechnique, 2009. http://tel.archives-ouvertes.fr/docs/00/48/40/27/PDF/thesis.pdf.
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Les oscillations dans le plasma d'un propulseur à effet Hall sont susceptibles de provoquer le transport anormal à travers des lignes du champ magnétique. La théorie cinétique linéaire montre qu'en particulier certaines oscillations, de fréquence de l'ordre du mégahertz et de longueur d'onde millimétrique, peuvent jouer un rôle important dans le transport anormal. Les échelles caractéristiques de ces fluctuations ne sont pas détectables par des outils standards comme les sondes. Ce travail décrit pour la première fois l'utilisation d'un diagnostic de diffusion collective (PRAXIS) conçu pour l'étude du plasma du propulseur, qui a mené à l'identification des modes instables dans le plasma. Deux modes hautes fréquences ont été identifiés, se propageant dans les directions azimutale et axiale, avec des longueurs d'onde millimétriques et des fréquences de l'ordre du mégahertz. Les directions de propagation et les ouvertures angulaires de ces modes ont été déterminées. Le mode azimutal, identifié dans la théorie comme agent principal du transport, possède des composantes anti-parallèles au champ magnétique et parallèles au champ électrique et se propage dans une ouverture angulaire très restreinte. Le mode axial montre des caractéristiques liées à la vitesse et la divergence du faisceau d'ions. Le niveau de fluctuation de la densité est associé à une grande amplitude du champ électrique fluctuant. Les résultats des expériences sont en accord avec les prévisions théoriques et apportent de nouvelles informations, permettant ainsi d'améliorer et de développer des modèles pour les deux modes<br>Anomalous electron transport across magnetic field lines in the Hall thruster plasma is believed to be due in part to plasma oscillations. Oscillations of frequencies on the order of a few megahertz and of wavelengths on the order of a millimeter have been shown to be likely to lead to transport. Measurements of fluctuations at these length scales is, however, beyond the reach of conventional thruster diagnostics such as probes. This work describes the first application of a specially-designed collective light scattering diagnostic (PRAXIS) to the measurement of electron density fluctuations and the subsequent identification of unstable modes in the thruster plasma. Two main high frequency modes are identified, propagating azimuthally and axially, of millimetric length scales and megahertz frequencies. The propagation directions and angular openings of the modes are determined. The azimuthallypropagating mode, believed to be responsible for transport, is shown to have wave vector components antiparallel to the magnetic field and parallel to the electric field, and to propagate within an extremely limited region. The axially-propagating mode is shown to have features closely related to the ion beam velocity and divergence. The electron density fluctuation level is calculated and is associated with a high electric field amplitude. The experiments, confirming a number of predictions arising from linear kinetic theory, also provide much additional information permitting the improvement and development of models for both modes
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Hollandsworth, Carl B. "Full and half sandwich compounds of dimolybdenum and ditungsten." The Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=osu1095455882.
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GOERBIG, Mark Oliver. "Etude theorique des phases de densite inhomogene dans les systemes a effet Hall quantique." Phd thesis, Université Paris Sud - Paris XI, 2004. http://tel.archives-ouvertes.fr/tel-00007072.
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L'objet de cette these est l'etude des differentes phases solides electroniques et liquides quantiques, que l'on trouve dans des systemes electroniques bi-dimensionnels exposes a un champ magnetique perpendiculaire. La formation de ces phases est due aà la repulsion coulombienne entre les electrons restreints a un niveau de Landau partiellement rempli. Les calculs d'energie de cette these permettent de comprendre des etudes experimentales recentes, qui ont mis en evidence un comportement non monotone de la resistance transverse (de Hall). Cet effet est du a des transitions multiples de premier ordre entre les phases en competition. La deduction d'un modele de fermions composites en interaction - les quasi-particules responsables de l'effet Hall quantique fractionnaire - permet de plus l'etude de nouvelles phases qui paraissent a fort champ magnetique. En particulier, un effet Hall quantique fractionnaire a des valeurs inhabituelles du champ a ete identifie comme la manifestation d'une deuxieme generation de fermions composites.
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Goerbig, Mark Oliver. "Etude théorique des phases de densité inhomogène dans les systèmes à effet Hall quantique." Paris 11, 2004. http://www.theses.fr/2004PA112109.
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L'objet de cette thèse est l'étude des différentes phases solides électroniques et liquides quantiques, que l'on trouve dans des systèmes électroniques bi-dimensionnels exposés à un champ magnétique perpendiculaire. La formation de ces phases est due à la répulsion coulombienne entre les électrons restreints à un niveau de Landau partiellement rempli. Les calculs d'énergie de cette thèse permettent de comprendre des études expérimentales récentes, qui ont mis en évidence un comportement non monotone de la résistance transverse (de Hall). Cet effet est dû à des transitions multiples de premier ordre entre les phases en compétition. La déduction d'un modèle de fermions composites en interaction - les quasi-particules responsables de l'effet Hall quantique fractionnaire - permet de plus l'étude de nouvelles phases qui paraissent à fort champ magnétique. En particulier, un effet Hall quantique fractionnaire a des valeurs inhabituelles du champ a été identifié comme a manifestation d'une deuxième génération de fermions composites<br>The issue of this thesis is the study of the different electron-solid and quantum-liquid phases, which are found in two-dimensional electron systems under a perpendicular magnetic field. The formation of these phases is due to the strong Coulomb repulsion between the electrons of a partially filled Landau level. The energy calculations of the thesis allow one to understand recent experimental investigations, which have revealed a non-monotonic behaviour of the transverse (Hall) resistance. This effect is due to multiple first-order transitions between the competing phases. The derivation of a model of interacting composite fermions - the quasiparticles responsible for the fractional quantum Hall effect - furthermore allows for the study of new phases, which occur at high magnetic fields. Most saliently, a recently observed fractional quantum Hall effect at unusual values of the field has been identified as the manifestation of a second generation of composite fermions
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de, Naray Rachel Kuzio. "High resolution optical velocity fields of low surface brightness galaxies and the density profiles of dark matter halos." College Park, Md. : University of Maryland, 2007. http://hdl.handle.net/1903/7239.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2007.<br>Thesis research directed by: Astronomy. 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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Lim, Hojun. "Meso-Scale Modeling of Polycrystal Deformation." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1275400049.
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Nasser, Abbass. "Spectrum sensing for half and full-duplex interweave cognitive radio systems." Thesis, Brest, 2017. http://www.theses.fr/2017BRES0006/document.
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En raison de la demande croissante de services de communication sans fil et de la limitation des ressources de spectre, la radio cognitive (CR) a été initialement proposée pour résoudre la pénurie de spectre. CR divise les systèmes transmetteurs-récepteurs de communication en deux catégories : les Utilisateurs Principaux (PU) et les Utilisateurs Secondaires (SU). PU a le droit légal d'utiliser la bande spectrale, tandis que SU est un utilisateur opportuniste qui peut transmettre sur cette bande chaque fois qu'elle est vacante afin d'éviter toute interférence avec le signal de PU. De ce fait, la détection des activités de PU devient une priorité principale pour toute CR.Le Spectrum Sensing devient ainsi une partie importante d’un système CR, qui surveille les transmissions de PU. En effet, le Spectrum Sensing joue un rôle essentiel dans le mécanisme du fonctionnement du CR en localisant les canaux disponibles et, d'autre part, en protégeant les canaux occupés des interférences de la transmission SU. En fait, Spectrum Sensing a gagné beaucoup d'attention au cours de la dernière décennie, et de nombreux algorithmes sont proposés. Concernant la fiabilité de la performance, plusieurs défis comme le faible rapport signal sur bruit, l'incertitude de bruit (NU), la durée de détection du spectre, etc. Cette thèse aborde les défis de la détection du spectre et apporte quelques solutions. De nouveaux détecteurs basés sur la détection des caractéristiques cyclo-stationnaires et la densité spectrale de puissance (PSD) du signal de PU sont présentés. Un algorithme de test de signification de corrélation canonique (CCST) est proposé pour effectuer une détection cyclo-stationnaire. CCST peut détecter la présence des caractéristiques cycliques communes parmi les versions retardées du signal reçu. Ce test peut révéler la présence d'un signal cyclo-stationnaire dans le signal de mélange reçu. Une autre méthode de détection basée sur la PSD cumulative est proposée. En supposant que le bruit est blanc (sa PSD est plate), la PSD cumulative s'approche d'une droite. Cette forme devient non linéaire pour les signaux de télécommunication. Distinguer la forme cumulative PSD peut donc conduire à diagnostiquer l'état du canal.La radio cognitive Full-Duplex (FD-CR) a également été étudiée dans ce manuscrit, où plusieurs défis sont analysés en proposant de nouvelles contributions. Le fonctionnement FD permet au CR d'éviter la période de silence pendant la détection du spectre. Dans le système CR classique, le SU cesse de transmettre pendant la détection du spectre afin de ne pas affecter la fiabilité de détection. Dans FD-CR, SU peut éliminer la réflexion de son signal transmis et en même temps réaliser le Spectrum Sensing. En raison de certaines limitations, le résidu de l'auto-interférence ne peut pas être complètement annulé, alors la crédibilité de la détection du spectre est fortement affectée. Afin de réduire la puissance résiduelle, une nouvelle architecture de récepteur SU est élaborée pour atténuer les imperfections du circuit (comme le bruit de phase et la distorsion non linéaire de l'amplificateur à faible bruit du récepteur). La nouvelle architecture montre sa robustesse en assurant une détection fiable et en améliorant le débit de SU<br>Due to the increasing demand of wireless communication services and the limitation in the spectrum resources, Cognitive Radio (CR) has been initially proposed in order to solve the spectrum scarcity. CR divides the communication transceiver into two categories: the Primary (PU) or the Secondary (SU) Users. PU has the legal right to use the spectrum bandwidth, while SU is an opportunistic user that can transmit on that bandwidth whenever it is vacant in order to avoid any interference to the signal of PU. Hence the detection of PU becomes a main priority for CR systems. The Spectrum Sensing is the part of the CR system, which monitors the PU activities. Spectrum Sensing plays an essential role in the mechanism of the CR functioning. It provides CR with the available channel in order to access them, and on the other hand, it protects occupied channels from the interference of the SU transmission. In fact, Spectrum Sensing has gained a lot of attention in the last decade, and numerous algorithms are proposed to perform it. Concerning the reliability of the performance, several challenges have been addressed, such as the low Signal to Noise Ratio (SNR), the Noise Uncertainty (NU), the Spectrum Sensing duration, etc. This dissertation addresses the Spectrum Sensing challenges and some solutions are proposed. New detectors based on Cyclo-Stationary Features detection and the Power Spectral Density (PSD) of the PU are presented. CanonicalCorrelation Significance Test (CCST) algorithm is proposed to perform cyclo-stationary detection. CCST can detect the presence of the common cyclic features among the delayed versions of the received signal. This test can reveal the presence of a cyclo-stationary signal in the received mixture signal. Another detection method based on the cumulative PSD is proposed. By assuming the whiteness of the noise (its PSD is at), the cumulative PSD approaches a straight line. This shape becomes non-linear when a telecommunication signal is present in the received mixture. Distinguishing the Cumulative PSD shape may lead to diagnose the channel status.Full-Duplex Cognitive Radio (FD-CR) has been also studied in this manuscript, where several challenges are analyzed by proposing a new contribution. FD functioning permits CR to avoid the silence period during the Spectrum Sensing. In classical CR system, SU stops transmitting during the Spectrum Sensing in order to do not affect the detection reliability. In FD-CR, SU can eliminate the reflection of its transmitted signal and at the same time achieving the Spectrum Sensing. Due to some limitations, the residual of the Self Interference cannot be completely cancelled, then the Spectrum Sensing credibility is highly affected. In order to reduce the residual power, a new SU receiver architecture is worked out to mitigate the hardware imperfections (such as the Phase Noise and the Non-Linear Distortion of the receiver Low-Noise Amplifier). The new architecture shows its robustness by ensuring a reliable detection and enhancing the throughput of SU
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Collignon, Clément. "De la densité des fluides électroniques dans deux oxydes supraconducteurs." Thèse, Université de Sherbrooke, 2017. http://hdl.handle.net/11143/11636.
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Cette thèse se décompose en deux parties.
Dans la première, nous nous intéressons au premier champ critique, Hc1, du titanate de strontium, que nous mesurons à l’aide d’un réseau de microsondes de Hall taille dans un gaz bidimensionnel. La valeur du premier champ critique nous permet alors d’évaluer la densité superfluide à six différents dopages couvrant l’ensemble du dôme supraconducteur. À bas dopage, nous trouvons que celle-ci correspond à la densité de porteurs dans l’état normal tandis qu’au-delà du dopage optimal, celle-ci chute drastiquement. En plaçant nos résultats dans le contexte de la loi de Homes, nous voyons que cette chute s’explique par l’entrée dans la limite sale. Un lissage multibande de Hc1(T), dans ce contexte semble également indiquer que la supraconductivité émerge de la bande la plus basse et est seulement induite dans les deux autres bandes.
Dans la seconde partie, nous regardons l’évolution de la densité de porteurs, n, du cuprate Nd-LSCO. Nous mesurons ainsi six échantillons de dopages proches du point critique pseudogap, p*, via trois sondes de transport : effet Hall, résistivité et effet Seebeck. Nous trouvons que n chute de 1+p a p a l’entrée dans la phase pseudogap. En comparant les différentes sondes, nous montrons que cette chute est due à une reconstruction de la surface de fermi et qu’il existe sûrement des poches d’électrons et de trous juste en dessous de p*. Ceci est en accord, entre autres, avec un scénario antiferromagnétique. Finalement, nous trouvons que la mobilité est inchangée à l’entrée dans la phase pseudogap et que les mesures de transports semblent insensibles à la divergence de la masse effective vue par chaleur spécifique.
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Van, Den Berg Tineke. "Conductivité de spin et effets magnétiques dans les systèmes quantiques désordonnés." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4812/document.
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Dans une première partie nous explorerons les effets d'impuretés désordonnées et paramagnétiques sur l'effet spin-Hall intrinsèque dans un gaz d'électrons bi-dimensionnel avec un couplage spin-orbite de Rashba. A faible désordre, la conductivité de spin-Hall reste proche de sa valeur d'échantillon pur, comme le montrent un calcul analytique de réponse linéaire et une étude numérique. De fortes fluctuations sont toutefois observées, elles augmentent avec l'importance du désordre. Pour caractériser la dynamique d'un paquet d'onde sur un réseau, nous mesurons sa taille, le taux de participation inverse, et sa dimension de corrélation. Le système subit une transition de localisation à une valeur critique du désordre. Dans le régime localisé, la densité locale d'états n'est plus uniforme et ne coïncide plus avec la densité totale d'états. Une corrélation antiferromagnétique entre les impuretés et les électrons de conduction est observée. Après la transition de localisation, la conductivité de spin augmente significativement. La première correction quantique dans le formalisme de réponse linéaire, contribue positivement à la conductivité de spin-Hall. Dans une seconde partie, le modèle de Hubbard avec double échange avec corrélations électroniques est étudié par la méthode du champ moyen dynamique (DMFT) dans l'approximation de non-croisement pour la résolution du problème d'impureté (NCA). Autour du quart remplissage, un polaron orbital est observé et décrit à l'aide d'un Hamiltonien effectif. Le double échange dans les semi-conducteurs magnétiques dilués est étudié dans l'approximation du potentiel cohérent (CPA)<br>Spintronics is a research area that is concerned with the storage and transfer of information by means of electron spins. In the first part we investigated the intrinsic spin Hall effect in the presence of disordered magnetic impurities in a paramagnetic state in a two dimensional electron gas with Rashba spin-orbit coupling. In the presence of weak magnetic disorder the spin Hall conductivity stays close to its universal (clean system) value, as shown by analytical linear response calculations and numerical simulations. Heavy spin conductivity fluctuations are observed, that increase with disorder strength. To investigate the spreading of a wavepacket on a lattice we measure the wavepacket width, the inverse participation ratio and the (2)-fractal dimension. It is shown the system undergoes a localization transition at a critical disorder strength. In the localized regime the local density of states is not uniform anymore. An anti-ferromagnetic correlation between electron spins and impurity magnetic moments is observed. Beyond the localization transition the spin conductivity increases significantly. The first quantum (Cooperon) corrections in the linear response formalism are shown to contribute positively to the spin Hall conductivity. In the second part the double exchange Hubbard model for correlated electron systems is studied using dynamical mean field theory (DMFT) with the non-crossing approximation (NCA). Around quarter filling an orbital polaron is observed, numerically and in an effective Hamiltonian. Double exchange in dilute magnetic semiconductors is studied using the coherent potential approximation (CPA)
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Yao, Liangbin. "HIGH CURRENT DENSITY LOW VOLTAGE ISOLATED DC-DC CONVERTERSWITH FAST TRANSIENT RESPONSE." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3205.
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With the rapid development of microprocessor and semiconductor technology, industry continues to update the requirements for power supplies. For telecommunication and computing system applications, power supplies require increasing current level while the supply voltage keeps decreasing. For example, the Intel's CPU core voltage decreased from 2 volt in 1999 to 1 volt in 2005 while the supply current increased from 20A in 1999 to up to 100A in 2005. As a result, low-voltage high-current high efficiency dc-dc converters with high power-density are demanded for state-of-the-art applications and also the future applications. Half-bridge dc-dc converter with current-doubler rectification is regarded as a good topology that is suitable for high-current low-voltage applications. There are three control schemes for half-bridge dc-dc converters and in order to provide a valid unified analog model for optimal compensator design, the analog state-space modeling and small signal modeling are studied in the dissertation and unified state-space and analog small signal model are derived. In addition, the digital control gains a lot of attentions due to its flexibility and re-programmability. In this dissertation, a unified digital small signal model for half-bridge dc-dc converter with current doubler rectifier is also developed and the digital compensator based on the derived model is implemented and verified by the experiments with the TI DSP chip. In addition, although current doubler rectifier is widely used in industry, the key issue is the current sharing between two inductors. The current imbalance is well studied and solved in non-isolated multi-phase buck converters, yet few discusse this issue in the current doubler rectification topology within academia and industry. This dissertation analyze the current sharing issue in comparison with multi-phase buck and one modified current doubler rectifier topology is proposed to achieve passive current sharing. The performance is evaluated with half bridge dc-dc converter; good current sharing is achieved without additional circuitry. Due to increasing demands for high-efficiency high-power-density low-voltage high current topologies for future applications, the thermal management is challenging. Since the secondary-side conduction loss dominates the overall power loss in low-voltage high-current isolated dc-dc converters, a novel current tripler rectification topology is proposed. Theoretical analysis, comparison and experimental results verify that the proposed rectification technique has good thermal management and well-distributed power dissipation, simplified magnetic design and low copper loss for inductors and transformer. That is due to the fact that the load current is better distributed in three inductors and the rms current in transformer windings is reduced. Another challenge in telecommunication and computing applications is fast transient response of the converter to the increasing slew-rate of load current change. For instance, from Intel's roadmap, it can be observed that the current slew rate of the age regulator has dramatically increased from 25A/uS in 1999 to 400A/us in 2005. One of the solutions to achieve fast transient response is secondary-side control technique to eliminate the delay of optocoupler to increase the system bandwidth. Active-clamp half bridge dc-dc converter with secondary-side control is presented and one industry standard 16th prototype is built and tested; good efficiency and transient response are shown in the experimental section. However, one key issue for implementation of secondary-side control is start-up. A new zero-voltage-switching buck-flyback isolated dc-dc converter with synchronous rectification is proposed, and it is only suitable for start-up circuit for secondary-side controlled converter, but also for house-keeping power supplies and standalone power supplies requiring multi-outputs.<br>Ph.D.<br>School of Electrical Engineering and Computer Science<br>Engineering and Computer Science<br>Electrical Engineering PhD
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Júnior, Gerson Ferreira. "Ferromagnetismo no regime Hall quântico inteiro via teoria do funcional de densidade." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-31082011-100156/.
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O efeito Hall quântico surge em gases de elétrons bidimensionais (2DEG) na presença de altos campos magnéticos B. O campo magnético quantiza o movimento planar dos elétrons em órbitas ciclotrônicas caracterizadas pelos níveis de Landau. Neste regime a resistividade transversal (ou Hall) ρxy em função de B exibe platôs em submúltiplos inteiros de e2/h, i.e., ρxy = ν-1 e2/h, sendo ν o fator de preenchimento dos níveis de Landau. Por sua vez, a resistividade longitudinal ρxx apresenta picos nas transições entre platôs de ρxy. Em primeira instância, ρxx é uma medida indireta da densidade de estados no nível de Fermi g(εF), e os picos dos mesmos indicam cruzamentos do nível de Fermi εF com niveis de Landau. Assim, o diagrama de densidade de elétrons n2D e B dos picos de ρxx ~ g(εF) fornece um mapa topológico da estrutura eletrônica do sistema. Em sistemas de duas subbandas, ρxx(n2D, B) exibe estruturas em forma de anel devido a cruzamentos de níveis de Landau de subbandas distintas [experimentos do grupo do Prof. Jiang (UCLA)]. Estes cruzamentos podem ainda levar a instabilidades ferromagnéticas. Investigamos estas instabilidades usando a teoria do funcional da densidade (DFT) para o cálculo da estrutura eletrônica, e o modelo de Ando (formalismo de Kubo) para o cálculo de ρxx e ρxy. Para temperaturas mais altas (340 mK) obtemos as estruturas em forma de anel em ρxx. Para temperaturas mais baixas (70 mK), observamos uma quebra dos anéis devido a transições de fase ferromagnéticas. Variando-se o ângulo θ de B com relação ao 2DEG observa-se o encolhimento do anel. Nossos resultados mostram que o ângulo de colapso total do anel depende de uma competição entre o termo de troca da interação de Coulomb (princípio de Pauli) e cruzamentos evitados devido ao ângulo θ finito. As transições de fase exibem ainda o fenômeno de histerese. Na região de instabilidade ferromagnética obtemos diferentes soluções variando B de forma crescente ou decrescente. Estas soluções possuem energias total diferentes, de forma que representam estados fundamental e excitado de muitos corpos. Esta observação, juntamente com resultados anteriores do grupo [Freire & Egues (2007)], representam as primeiras realizações teóricas da previsão da possibilidade de estados excitados como mínimos locais do funcional de energia do estado fundamental [Perdew & Levy (1985)]. O modelo aqui proposto fornece excelente acordo com os experimentos considerados. Adicionalmente, a observação sistemática e experimentalmente verificada dos estados excitados valida as previsões de Perdew & Levy. Aplicamos ainda estas mesmas ideias no cálculo da estrutura eletrônica e condutância de fios quânticos na presença de campos magnéticos, mostrando que cruzamentos de modos transversais também exibem instabilidades ferromagnéticas observadas em experimentos recentes [Dissertação de Mestrado de Filipe Sammarco, IFSC/USP], fortalecendo a validade do modelo apresentado nesta tese.<br>The quantum Hall effect arises in two dimensional electron gases (2DEG) under high magnetic fields B. The magnetic field quantizes the planar motion of the electrons into cyclotron orbits given by the Landau levels. In this regime the transversal (Hall) resistivity ρxy shows plateaus as a function of B at integer sub-multiples of e2/h, i.e., ρxy = ν-1 e2/h, where n is the filling factor of the Landau levels. The longitudinal resistivity ρxx shows peaks at the transition between the plateaus of ρxy. In principle, ρxx is an indirect measure of the density of states at the Fermi level g(εF), so that the peaks indicate when the Fermi level εF crosses a Landau level. Therefore, a density-B-field diagram n2D-B of the ρxx ~ g(εF) peaks shows a topological map of the electronic structure of the system. In two-subband systems, ρxx( n2D, B) shows ringlike structures due to crossings of spin-split Landau levels from distinct subbands [experiments from the group of Prof. Jiang (UCLA)] that could lead to ferromagnetic instabilities. We study these instabilities using the density functional theory (DFT) to calculate the electronic structure, and Ando\'s model (Kubo formalism) for ρxx and ρxy. At higher temperatures (340 mK) we also obtain the ringlike structures in ρxx. At lower temperatures (70 mK) we see broken rings due to quantum Hall ferromagnetic phase transitions. Tilting B by theta with respect to the 2DEG normal we find that the ring structure shrinks. Our results show that the angle of full collapse depends on a competition between the exchange term from the Coulomb interaction (Pauli principle) and the anticrossing of Landau levels due to the finite angle theta. Additionally, at the instabilities we observe hysteresis. Sweeping the B field up or down near these regions we obtain two different solutions with distinct total energies, corresponding to the ground state and an excited state of the many-body system. This result, together with previous results of our group [Freire & Egues (2007)], are the first realizations of the theoretical prediction of the possibility of excited states as local minima of the ground state energy functional [Perdew & Levy (1985)]. The model proposed here shows an excellent agreement with the experiments. Additionally, the systematic and experimentally verified observation of excited states corroborates the predictions of Perdew & Levy. Similar ideas as presented here when applied to the electronic structure and conductance of quantum wires with an in-plane magnetic field show ferromagnetic instabilities at crossings of the wire transverse modes [Master Thesis of Filipe Sammarco, IFSC/USP], also with excellent experimental agreement. This strengthen the range of validity of the model proposed in this Thesis.
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Van, Den Berg Tineke. "Conductivité de spin et effets magnétiques dans les systèmes quantiques désordonnés." Electronic Thesis or Diss., Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4812.
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Dans une première partie nous explorerons les effets d'impuretés désordonnées et paramagnétiques sur l'effet spin-Hall intrinsèque dans un gaz d'électrons bi-dimensionnel avec un couplage spin-orbite de Rashba. A faible désordre, la conductivité de spin-Hall reste proche de sa valeur d'échantillon pur, comme le montrent un calcul analytique de réponse linéaire et une étude numérique. De fortes fluctuations sont toutefois observées, elles augmentent avec l'importance du désordre. Pour caractériser la dynamique d'un paquet d'onde sur un réseau, nous mesurons sa taille, le taux de participation inverse, et sa dimension de corrélation. Le système subit une transition de localisation à une valeur critique du désordre. Dans le régime localisé, la densité locale d'états n'est plus uniforme et ne coïncide plus avec la densité totale d'états. Une corrélation antiferromagnétique entre les impuretés et les électrons de conduction est observée. Après la transition de localisation, la conductivité de spin augmente significativement. La première correction quantique dans le formalisme de réponse linéaire, contribue positivement à la conductivité de spin-Hall. Dans une seconde partie, le modèle de Hubbard avec double échange avec corrélations électroniques est étudié par la méthode du champ moyen dynamique (DMFT) dans l'approximation de non-croisement pour la résolution du problème d'impureté (NCA). Autour du quart remplissage, un polaron orbital est observé et décrit à l'aide d'un Hamiltonien effectif. Le double échange dans les semi-conducteurs magnétiques dilués est étudié dans l'approximation du potentiel cohérent (CPA)<br>Spintronics is a research area that is concerned with the storage and transfer of information by means of electron spins. In the first part we investigated the intrinsic spin Hall effect in the presence of disordered magnetic impurities in a paramagnetic state in a two dimensional electron gas with Rashba spin-orbit coupling. In the presence of weak magnetic disorder the spin Hall conductivity stays close to its universal (clean system) value, as shown by analytical linear response calculations and numerical simulations. Heavy spin conductivity fluctuations are observed, that increase with disorder strength. To investigate the spreading of a wavepacket on a lattice we measure the wavepacket width, the inverse participation ratio and the (2)-fractal dimension. It is shown the system undergoes a localization transition at a critical disorder strength. In the localized regime the local density of states is not uniform anymore. An anti-ferromagnetic correlation between electron spins and impurity magnetic moments is observed. Beyond the localization transition the spin conductivity increases significantly. The first quantum (Cooperon) corrections in the linear response formalism are shown to contribute positively to the spin Hall conductivity. In the second part the double exchange Hubbard model for correlated electron systems is studied using dynamical mean field theory (DMFT) with the non-crossing approximation (NCA). Around quarter filling an orbital polaron is observed, numerically and in an effective Hamiltonian. Double exchange in dilute magnetic semiconductors is studied using the coherent potential approximation (CPA)
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Kumar, Manish. "High density and high reliability thin film embedded capacitors on organic and silicon substrates." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26655.
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Thesis (M.S.)--Materials Science and Engineering, Georgia Institute of Technology, 2009.<br>Committee Chair: Tummala Rao; Committee Member: Pulugurtha Raj; Committee Member: Wong C P. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Tsikata, Sedina. "Fluctuations de densité électronique à petite échelle dans un propulseur à effet Hall, investigué par la méthode de diffusion collective." Phd thesis, Ecole Polytechnique X, 2009. http://tel.archives-ouvertes.fr/tel-00484027.
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Les oscillations dans le plasma d'un propulseur à effet Hall sont susceptibles de provoquer le transport anormal à travers des lignes du champ magnétique. La théorie cinétique linéaire montre qu'en particulier certaines oscillations, de fréquence de l'ordre du mégahertz et de longueur d'onde millimétrique, peuvent jouer un rôle important dans le transport anormal. Les échelles caractéristiques de ces fluctuations ne sont pas détectables par des outils standards comme les sondes. Ce travail décrit pour la première fois l'utilisation d'un diagnostic de diffusion collective (PRAXIS) conçu pour l'étude du plasma du propulseur, qui a mené à l'identification des modes instables dans le plasma. Deux modes hautes fréquences ont été identifiés, se propageant dans les directions azimutale et axiale, avec des longueurs d'onde millimétriques et des fréquences de l'ordre du mégahertz. Les directions de propagation et les ouvertures angulaires de ces modes ont été déterminées. Le mode azimutal, identifié dans la théorie comme agent principal du transport, possède des composantes anti-parallèles au champ magnétique et parallèles au champ électrique et se propage dans une ouverture angulaire très restreinte. Le mode axial montre des caractéristiques liées à la vitesse et la divergence du faisceau d'ions. Le niveau de fluctuation de la densité est associé à une grande amplitude du champ électrique fluctuant. Les résultats des expériences sont en accord avec les prévisions théoriques et apportent de nouvelles informations, permettant ainsi d'améliorer et de développer des modèles pour les deux modes.
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Demouge, Annabelle. "Étude galvanomagnétique de l'alliage semi-métallique Bi-Sb (4 at. % Sb) entre 77 K et 300 K." Vandoeuvre-les-Nancy, INPL, 1996. http://docnum.univ-lorraine.fr/public/INPL_T_1996_DEMOUGE_A.pdf.
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Les alliages Bi-Sb sont des matériaux thermoélectriques performants entre 50 K et 250 K, mais leurs propriétés fondamentales sont mal connues, en particulier les concentrations et les mobilités des porteurs, ainsi que la structure de bandes. La présence de deux types de porteurs, électrons et trous, nécessite une étude galvanomagnétique. Nous avons élaboré des lingots de Bi-Sb (4 at. % Sb) par la méthode THM et découpe des échantillons monocristallins et homogènes pour les différentes orientations nécessaires aux mesures des douze coefficients du tenseur galvanomagnétique. Nous avons ensuite réalisé le montage permettant les mesures de magnétorésistivité sous faible champ magnétique entre 77 K et 300 K. Un modèle ellipsoïdal non parabolique à deux bandes et un programme de calcul ont été développés pour permettre d'atteindre les concentrations et les mobilités des porteurs. Les résultats obtenus montrent des concentrations de porteurs dans l'alliage croissant entre 77 K et 300 K de 0,6 10^23m-3 a 6,7 10^23m-3, ce qui traduit une augmentation de l'énergie de recouvrement dans le semi-métal et une énergie de fermi plus faible que dans le bismuth pur. Les valeurs des mobilités des électrons à 77 K sont: #1 220 m2/v. S, #2 < 1 m2/v. S, #3 130 m2/v. S, et pour les trous #1 60 m2/v. S et #3 <1 m2/v. S. L'angle d'inclinaison des ellipsoïdes d'électrons est voisin de 7 quelle que soit la température. Les facteurs de Hall et de magnétorésistance A et M des électrons restent proches de l'unité et montrent une dépendance énergétique modérée du temps de relaxation. Nous donnons enfin les équations permettant de déterminer la structure de bandes de l'alliage semi-métallique Bi#0, 96Sb#0,#0#4 entre 77 K et 300 K
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Machkour, Deshayes Nadia. "Méthode de déconvolution appliquée à l'étude de la densité surfacique d'un arc électrique de coupure basse tension à partir de mesures magnétiques." Clermont-Ferrand 2, 2003. http://www.theses.fr/2003CLF22456.
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L'étude consiste à mettre en place une méthode qui permet de reconstituer la densité du courant dans un arc électrique de coupure basse tension, à partir des mesures ponctuelles de l'induction magnétique créée par le dispositif de coupure. Ces mesures sont réalisées grâce à l'utilisation des capteurs à effet Hall placés en dehors du trajet de l'arc. Pour cette étude, nous avons supposé l'arc électrique modélisé par une nappe de courant rectangulaire, de densité variable dans la direction de propagation de l'arc. Les autres éléments du circuit sont assimilés à des segments de courant rectilignes et filiformes. Nous avons montré que l'induction magnétique créée par l'arc représente un produit de convolution entre sa densité du courant et une fonction qui dépend de la géométrie du dispositif de coupure et du modèle pris par l'arc. Cette méthode permet aussi de calculer les dimensions de l'arc, déterminer sa position ainsi que sa conductivité électrique. Celle-ci est utilisée pour estimer la température de l'arc. Nous avons appliqué cette méthode pour étudier le comportement de l'arc en fonction du courant présumé et l'espace interélectrode
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Wang, Haihang. "PAOFLOW-Aided Computational Materials Design." Thesis, University of North Texas, 2019. https://digital.library.unt.edu/ark:/67531/metadc1609102/.
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Functional materials are essential to human welfare and to provide foundations for emerging industries. As an alternative route to experimental materials discovery, computational materials designs are playing an increasingly significant role in the whole discovery process. In this work, we use an in-house developed python utility: PAOFLOW, which generates finite basis Hamiltonians from the projection of first principles plane-wave pseudopotential wavefunctions on pseudo atomic orbitals(PAO) for post-process calculation on various properties such as the band structures, density of states, complex dielectric constants, diffusive and anomalous spin and charge transport coefficients. In particular, we calculated the dielectric function of Sr-, Pb-, and Bi-substituted BaSnO3 over wide concentration ranges. Together with some high-throughput experimental study, our result indicates the importance of considering the mixed-valence nature and clustering effects upon substitution of BaSnO3 with Pb and Bi. We also studied two prototype ferroelectric rashba semiconductors, GeTe and SnTe, and found the spin Hall conductivity(SHC) can be large either in ferroelectric or paraelectric structure phase. Upon doping, the polar displacements in GeTe can be sustained up to a critical hole concentration while the tiny distortions in SnTe vanish at a minimal level of doping. Moreover, we investigated the sensitivity of two dimensional group-IV monochalcogenides to external strain and doping, which reveal for the first time giant intrinsic SHC in these materials, providing a new route for the design of highly tunable spintronics devices based on two-dimensional materials.
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Yu, Geliang. "Transport properties of graphene based van der Waals heterostructures." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/transport-properties-of-graphene-based-van-der-waals-heterostructures(5cbb782f-4d49-42da-a05e-15b26606e263).html.
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In the past few years, led by graphene, a large variety of two dimensional (2D) materials have been discovered to exhibit astonishing properties. By assembling 2D materials with different designs, we are able to construct novel artificial van der Waals (vdW) heterostructures to explore new fundamental physics and potential applications for future technology. This thesis describes several novel vdW heterostructures and their fundamental properties. At the beginning, the basic properties of some 2D materials and assembled vdW heterostructures are introduced, together with the fabrication procedure and transport measurement setups. Then the graphene based capacitors on hBN (hexagonal Boron Nitride) substrate are studied, where quantum capacitance measurements are applied to determine the density of states and many body effects. Meanwhile, quantum capacitance measurement is also used to search for alternative substrates to hBN which allow graphene to exhibit micrometer-scale ballistic transport. We found that graphene placed on top of MoS2 and TaS2 show comparable mobilities up to 60,000cm2/Vs. After that, the graphene/hBN superlattices are studied. With a Hall bar structure based on the superlattices, we find that new Dirac minibands appear away from the main Dirac cone with pronounced peaks in the resistivity and are accompanied by reversal of the Hall effects. With the capacitive structure based on the superlattices, quantum capacitance measurement is used to directly probe the density states in the graphene/hBN superlattices, and we observe a clear replica spectrum, the Hofstadter-butterfly fan diagram, together with the suppression of quantum Hall Ferromagnetism. In the final part, we report on the existence of the valley current in the graphene/hBN superlattice structure. The topological current originating from graphene’s two valleys flows in opposite directions due to the broken inversion symmetry in the graphene/hBN superlattice, meaning an open band gap in graphene.
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Nübler, Johannes [Verfasser], and David [Akademischer Betreuer] Wharam. "Density Dependence of the v=5/2 Fractional Quantum Hall Effect - Compressibility of a Two-dimensional Electron System under Microwave Irradiation / Johannes Nübler ; Betreuer: David Wharam." Tübingen : Universitätsbibliothek Tübingen, 2011. http://d-nb.info/1162699248/34.
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Herath, Mudiyanselage Dimuthu Prasad Wijethunge. "Theoretical investigation of ferroelectric properties in 2D materials and their applications." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/235394/1/Dimuthu%2BWijethunge%2BThesis%283%29.pdf.
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This thesis examined two-dimensional ferroelectric materials and their applications using density functional theory calculations. The research has revealed several novel applications for 2D ferroelectric materials. It illustrated that ferroelectric materials can be used to modify electronic, photocatalytic and magnetic properties of two-dimensional materials. In addition to exploring applications, new two-dimensional ferroelectric material which exhibits metallic properties was discovered through high through output search. Two-dimensional ferroelectric metals are extremely rare and only handful of materials were ever discovered.
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Zamoum, Redouane. "Etude théorique des fluctuations de courant de l'admittance et de la densité d'états d'un nano-système en interaction." Phd thesis, Aix-Marseille Université, 2013. http://tel.archives-ouvertes.fr/tel-00881571.
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Dans notre thèse nous nous sommes intéressés à l'étude des fluctuations de courant, de l'admittance quantique ainsi que la densité d'états pour un nano système en interaction. Notre travail se divise en deux parties. Dans la première partie, nous avons étudié les fluctuations de courant et l'admittance pour un conducteur unidimensionnel, en décrivant le système par un liquide de Tomonaga-Luttinger. Nous avons utilisé les techniques de bosonisation et de refermionisation afin d'aboutir à des résultats exacts pour tous les régimes de température, toutes les valeurs de la tension appliquée et toute la gamme des fréquences. Les résultats obtenus sont appliqués à un conducteur cohérent couplé à un quantum de résistance, et aux états de bord dans le régime de l'effet Hall quantique fractionnaire. Dans le cas d'un conducteur cohérent, le bruit non symétrisé à fréquence finie exhibe un profil différent de celui de la théorie de la diffusion, et la conductance à fréquence finie est directement liée au courant. Dans le cas du régime de l'effet Hall quantique fractionnaire, nous avons pu établir que dans certaines limites, il existe une relation entre les corrélations de courant à l'admittance quantique. En particulier, les singularités qui apparaissent dans les corrélations de courant sont celles de l'admittance. Dans la deuxième partie, nous avons étudié un fil quantique connecté à deux réservoirs qui sont représentés par deux impuretés. Le système est décrit par un liquide de Tomonaga-Luttinger. Nous avons établi et résolu l'équation de Dyson pour la fonction de Green retardée. Ce qui permet de calculer la densité d'états pour un fil quantique homogène puis inhomogène. Dans le cas d'un paramètre d'interaction homogène, l'effet des impuretés modifie le profil de la densité d'états. Dans le cas d'un paramètre d'interaction inhomogène, le calcul de la densité d'états est plus difficile et une approche numérique est indispensable.
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Poilblanc, Didier. "Théorie des phases onde de densité de spin induites par le champ magnétique dans des conducteurs très anisotropes." Paris 11, 1988. http://www.theses.fr/1988PA112017.
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Le gaz électronique quasi-bidimensionnel très anisotrope, avec surface de Fermi ouverte est instable sous l'effet d'un champ magnétique uniforme appliqué dans la direction de plus faible conductivité, avec apparition d'une phase Onde de Densité de Spin ou de Charge. Le champ magnétique en quantifiant les orbites électroniques affecte fortement la structure du spectre de quasiparticules. Ce dernier est constitué de bandes de Landau séparées par des gaps qui sont régulièrement espacés en vecteur d'onde de 1/2x0, où x0 est la longueur magnétique, et qui oscillent avec le champ magnétique. La thermodynamique et les propriétés de l'état fondamental sont fortement modifiées par cette série de gaps : nous avons élaboré une description analytique de la phase ordonnée (dans l'approximation champ moyen), valable pour tout champ et toute température, nous permettant de décrire l'effet de cette série de gaps sur l'énergie libre, la chaleur spécifique ou l'aimantatin. Comme le spectre d'énergie, les fonctions de corrélation de spin ou de charge possèdent une structure fine à des vecteurs d'onde de l'ordre du vecteur d'onde magnétique 1/x0. Nous avons montré que les spectres d'onde de spin et de fluctuation de la phase (du paramètre d'ordre) possédaient, en plus du mode de Goldstone, une série de modes de type raton. Ceux-ci sont des minima locaux dans la relation de dispersion de l'énergie à des valeurs quantifiées n/ x0 (n entier) de l'impulsion (parallèle). Ces modes se situent, à toute température, dans le gap de quasiparticule au niveau de Fermi ; leurs positions relatives par rapport à ce même gap évoluent vers les basses énergies quand la température diminue. Chaque "magnétoroton" peut être considéré comme le précurseur des phases adjacentes qui sont stabilisées par une variation de champ magnétique. La quantification de l'effet Hall (EHQ)est un autre effet orbital directement relié à la structure du spectre de quasiparticule. Nous avons montré, de façon générale, que les phases ordonnées induites par le champ constituaient un nouveau mécanisme pour l'EHQ. La pertinence du modèle pour les sels de Bechgaard est discutée également.
33
Guyot, Hervé. "Etude des transitions d'onde de densité de charge et des propriétés de transport des oxydes de molybdène [êta]-Mo4O11 et [gamma]-Mo4O11." Grenoble 1, 1986. http://www.theses.fr/1986GRE10122.
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Montambaux, Gilles. "Contribution à l'étude des conducteurs quasi-unidimensionnels sous champ magnétique." Phd thesis, Université Paris Sud - Paris XI, 1985. http://tel.archives-ouvertes.fr/tel-00600617.
Full textAbstract:
Ce travail concerne les effets de champ magnétique sur le diagramme de phase des conducteurs quasi-unidimensionnels. Il s'agit de comprendre comment le champ magnétique peut détruire la phase métallique et induire une phase onde de densité de spin (ODS), comme observé expérimentalement dans les conducteurs organiques comme les sels de Bechgaard. La thèse est divisée en deux parties Le couplage Zeeman à un gaz d'électrons unidimensionnel gèle certains processus d'interaction et par conséquent modifie les fluctuations unidimensionnelles. L'évolution des différentes L'instabilités du gaz d'électrons (onde de densité de spin ou de charge, supraconductivité singulet ou triplet) est obtenue en fonction du champ magnétique et du potentiel chimique. Ce dernier a sur les degrés de libertés de charge au voisinage du demi-remplissage, le même effet que le champ magnétique sur les degrés de libertés de spin. Pour le gaz d'électrons quasi-1D, la formation d'une phase ODS dépend à la fois de la géométrie de la surface de Fermi (le " nesting ") et de la quantification des orbites induite pas le champ magnétique). Ce double mécanisme, baptisé le " nesting quantifié " a les conséquences suivantes : * Une série de transitions de phase quantiques du premier ordre entre des sous-phases ODS apparaît lorsque le champ augmente. * Chaque sous-phase est indexée par un nombre quantique n, qui correspond à n niveaux de Landau complètement remplis. * L'effet Hall est quantifié dans chaque sous-phase. * Cette théorie décrit pratiquement tous les phénomènes observés dans les phases induites par le champ dans les sels de Bechgaard.
35
Hyndman, Rhonda Jane. "Transport studies in p-type double quantum well samples." Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325711.
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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
37
Djerfi, Kheireddine. "Non-linear magnetoconductivity of the two-dimensional electron fluid and solid on liquid helium." Thesis, Royal Holloway, University of London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325526.
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Boujida, Mohamed. "Contribution à l'étude des propriétés de transport de quelques oxydes métalliques et supraconducteurs de basse dimensionnalité." Grenoble 1, 1988. http://www.theses.fr/1988GRE10157.
Full textAbstract:
Les proprietes de transport (magnetoconductivite, effet hall, ondes de densite de charge, ondes de densite de spin, transitions supraconductrices) des oxydes metalliques et supraconducteurs quasi-bidimensionnels sont etudiees a basse temperature
39
Giedigkeit, Rainer. "Strukturelle Ordnung und Unordnung in binären und ternären Verbindungen des Galliums mit Ytterbium und Palladium." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1201464467941-38198.
Full textAbstract:
Um einen besseren Zugang zum Verständnis struktureller Eigenschaften von den ternären Verbindungen des Systems Yb–Pd–Ga zu bekommen, wurden zunächst die Ordnungs- und Unordnungsbeziehungen sowie die chemische Bindung in den Kristallstrukturen binärer Pd–Ga- bzw. Yb–Ga-Verbindungen analysiert. Im Rahmen der phasenanalytischen Untersuchungen des binären Systems Yb–Ga konnte eine neue Verbindung charakterisiert werden (Ytterbiumpentagallid). Für den galliumreichen Teil des ternären Phasendiagramms Yb–Pd–Ga wurde ein isothermer Schnitt bei 600 °C erstellt (&gt; 50 At.-% Ga). Die Homogenitätsbereiche der untersuchten Verbindungen wurden metallographisch bzw. röntgenographisch bestimmt. Die Kristallstrukturen wurden aus Röntgen-Einkristalldaten bestimmt. In den Kristallstrukturen wurden drei unterschiedliche Arten von Unordnung beobachtet (Substitutionsunordnung, Symmetrie-Brechung, Positionsunordnung). Für eine Reihe von Verbindungen des Systems Yb–Pd–Ga wurde der elektronische Zustand von Yb bestimmt. Dies gelang mit Hilfe von Messungen der magnetischen Suszeptibilität bzw. mit der Röntgen-Absorptionsnahkantenspektroskopie.
40
Giedigkeit, Rainer. "Strukturelle Ordnung und Unordnung in binären und ternären Verbindungen des Galliums mit Ytterbium und Palladium." Doctoral thesis, Technische Universität Dresden, 2007. https://tud.qucosa.de/id/qucosa%3A24059.
Full textAbstract:
Um einen besseren Zugang zum Verständnis struktureller Eigenschaften von den ternären Verbindungen des Systems Yb–Pd–Ga zu bekommen, wurden zunächst die Ordnungs- und Unordnungsbeziehungen sowie die chemische Bindung in den Kristallstrukturen binärer Pd–Ga- bzw. Yb–Ga-Verbindungen analysiert. Im Rahmen der phasenanalytischen Untersuchungen des binären Systems Yb–Ga konnte eine neue Verbindung charakterisiert werden (Ytterbiumpentagallid). Für den galliumreichen Teil des ternären Phasendiagramms Yb–Pd–Ga wurde ein isothermer Schnitt bei 600 °C erstellt (&gt; 50 At.-% Ga). Die Homogenitätsbereiche der untersuchten Verbindungen wurden metallographisch bzw. röntgenographisch bestimmt. Die Kristallstrukturen wurden aus Röntgen-Einkristalldaten bestimmt. In den Kristallstrukturen wurden drei unterschiedliche Arten von Unordnung beobachtet (Substitutionsunordnung, Symmetrie-Brechung, Positionsunordnung). Für eine Reihe von Verbindungen des Systems Yb–Pd–Ga wurde der elektronische Zustand von Yb bestimmt. Dies gelang mit Hilfe von Messungen der magnetischen Suszeptibilität bzw. mit der Röntgen-Absorptionsnahkantenspektroskopie.
41
Ribeiro, Renan Augusto Pontes. "INVESTIGAÇÃO TEÓRICA DE MATERIAIS COM ESTRUTURA ILMENITA." UNIVERSIDADE ESTADUAL DE PONTA GROSSA, 2015. http://tede2.uepg.br/jspui/handle/prefix/2038.
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Previous issue date: 2015-03-12<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>The development of spintronic has motivated the research for new half-metallic magnetic materials due to multifunctionality of these compounds and the spin-based devices fabrication with increased performance as compared to the usual electronic devices. From this
perspective, we propose a theoretical investigation of FeBO3 (B = Ti, Zr, Hf, Si, Ge, Sn) ilmenite materials based on Density Functional Theory (DFT) within B3LYP hybrid
functional to investigate the B-site cation replacement effect on the structural, elastic, magnetic and electronic properties of ilmenite materials. Calculated structural parameters are in agreement with experimental results and shown that the unit cell volume can be controlled
by ionic radius of the B-site metals. The bond distances for FeO6 and BO6 octahedral clarify the Jahn-Teller distortion and Fe-O-B-O-Fe intermetallic connection. The elastic behavior was investigated from bulk modulus and showed that such results were influenced by different material densities. Furthermore, these quantities can be used for analyzing the thermodynamic stability of solids, proving that FeSnO3 and FeHfO3 are unstable due to the negative values for bulk modulus. The B-site radius effect is also evidenced on the magnetic property, where Fe(Ti, Si, Ge)O3 are antiferromagnetic, while Fe(Zr, Hf, Sn)O3 are ferromagnetic. The Mulliken population analysis and charge density maps show the charge corridor formation in
the [001] direction due to the intermetallic connection with the B-site metals and electronegativity affecting the stability of ilmenite materials. The Density of States and Band Structure profiles show that antiferromagnetics materials and FeZrO3 are convectional semiconductors, whereas FeHfO3 and FeSnO3 exhibit intrinsic half-metallic behavior, making them promising candidates for spintronic devices.<br>O desenvolvimento da spintrônica tem motivado a busca por novos materiais magnéticos com comportamento meio-metálico devido à multifuncionalidade desses compostos e ao desenvolvimento de dispositivos baseados no spin do elétron, proporcionando um aumento do desempenho em relação aos dispositivos eletrônicos usuais. Nesse trabalho, propomos a
investigação teórica, baseada na Teoria do Funcional de Densidade utilizando o funcional híbrido B3LYP, dos materiais FeBO3 (B = Ti, Zr, Hf, Si, Ge, Sn) na estrutura ilmenita com objetivo de esclarecer o efeito da substituição do cátion B sobre as propriedades estruturais,
elásticas, magnéticas e eletrônicas. Os parâmetros estruturais calculados se mostraram em concordância com resultados experimentais e teóricos, revelando que o volume da célula unitária é controlado pelo raio iônico do cátion B. As distâncias de ligação calculadas para os
octaedros FeO6 e BO6 indicam a existência do efeito de distorção Jahn-Teller e da conexão intermetálica Fe-O-B-O-Fe. O comportamento elástico foi investigado a partir do bulk modulus, indicando que tal entidade é dependente da densidade dos materiais e discute-se a
possibilidade de utilizar esse fator para análise da estabilidade termodinâmica de sólidos, sugerindo a instabilidade dos materiais FeSnO3 e FeHfO3 devido aos valores negativos de bulk modulus. O efeito do tamanho dos cátions B é evidenciado sobre as propriedades
magnéticas dos materiais, sendo que Fe(Ti, Si, Ge)O3 são antiferromagnéticos; enquanto que, Fe(Zr, Hf, Sn)O3 são ferromagnéticos. A análise populacional de Mulliken e os mapas de densidade de carga mostraram a formação de um corredor de carga nas conexões intermetálicas observadas na direção [001] e que a eletronegatividade dos cátions B afeta a estabilidade dos materiais com estrutura ilmenita. Os perfis de Densidade de Estados e
Estrutura de Bandas mostram que os materiais antiferromagnéticos e o FeZrO3 são semicondutores convencionais, entretanto, FeHfO3 e FeSnO3 exibem comportamento meiometálico intrínseco, tornando-os promissores candidatos para dispositivos spintrônicos,
porém, com outra estrutura.
42
Ribeiro, Renan Augusto Pontes. "Investigação teórica de materiais multiferróicos." Universidade Estadual de Ponta Grossa, 2019. http://tede2.uepg.br/jspui/handle/prefix/2760.
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Previous issue date: 2019-02-26<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>O desenvolvimento da spintrônica tem motivado a busca por novos materiais multiferróicos
devido à multifuncionalidade desses compostos associada ao acoplamento entre diferentes
ordens ferróicas em uma estrutura cristalina. No presente estudo, propomos a investigação
teórica, baseada na Teoria do Funcional de Densidade, dos materiais ATiO3 (A = Mn, Fe, Ni)
na estrutura R3c com objetivo de esclarecer o efeito da substituição do cátion A sobre as
propriedades estruturais, magnéticas e eletrônicas, bem como descrever diferentes mecanismos
de controle das propriedades multiferróicas baseados em arquiteturas de filmes-finos,
morfologia e controle de defeitos intrínsecos. Para uma maior compreensão dos efeitos
envolvidos nos materiais ATiO3, diferentes funcionais de troca e correlação foram investigados
e o funcional PBE0 apresentou os menores desvios, consequentemente, a melhor representação
comparado aos resultados experimentais. Com objetivo de investigar as propriedades
conectadas a filmes-finos dos materiais ATiO3, propomos uma metodologia inovadora que
permite descrever as deformações uni- e biaxial que se originam na região de interface entre o
filme e o substrato. Nesse caso, os resultados obtidos indicam que as distorções estruturais
induzem uma transição magnética para o NiTiO3, originando ordenamento ferromagnético a
partir de um critério magneto-estrutural associado a deformação dos clusters [MO6] que
reproduz satisfatoriamente os resultados experimentais reportados na literatura. De modo
análogo, para elucidar a relação entre o magnetismo e a morfologia dos materiais ATiO3,
combinamos cálculos de Energia de Superfície, Construção de Wulff e um formalismo
avançado para descrever o magnetismo superficial considerando a existência de spins não
compensados ao longo dos planos polares (100), (001), (101), (012), (111) e apolares (110). Os
resultados indicam que a redução do número de coordenação dos metais A e Ti para os planos
(001) e (111) resulta na transferência de carga entre os cátions A2+ e Ti4+, originando espécies
Ti3+ magnéticas que aumentam o magnetismo superficial ao longo desses planos. Além disso,
esse efeito é capaz de induzir uma alteração do caráter eletrônico para esses materiais,
permitindo indicar que a clivagem das superfícies contribui para o controle das propriedades
eletrônicas, reduzindo o valor de band-gap ou gerando comportamento meio-metálico. Os
mapas morfológicos obtidos indicam que o controle da exposição majoritária do plano (001)
para obtenção de discos hexagonais induz um aumento do magnetismo superficial para os
materiais ATiO3 em acordo com resultados experimentais, além de predizer diferentes
morfologias acessíveis com interessantes propriedades magnéticas. Ademais, o efeito de
defeitos intrínsecos como vacâncias de oxigênio no bulk e superfície apolar (110) dos materiais
ATiO3 foi investigado indicando que a redução do número de coordenação na região do defeito
induz que os elétrons remanescentes sejam localizados, principalmente, nos orbitais 3d vazios
dos cátions Ti vizinhos, gerando espécies [TiO5]ꞌ e [TiO4]ꞌ (3d1
) que possibilitam uma interação
ferromagnética nos materiais MnTiO3 e FeTiO3. A combinação entre os diferentes mecanismos
investigados permitiu estabelecer um guia científico para o estudo teórico de materiais
multiferróicos, contribuindo para descrever as potencialidades dos diferentes materiais bem
como predizer novos candidatos.<br>The development of spintronic has motivated the search for new multiferroic materials due to
the multifunctionality of these materials that are associated with the coupling of different ferroic
orders into a single crystalline structure. In the present study, we propose a theoretical
investigation, based on Density Functional Theory, of ATiO3 (A = Mn, Fe, Ni) materials in the
R3c structure in order to clarify the effect of A-site cation replacement on the structural,
magnetic and electronic properties, as well as to describe a different mechanism to control the
multiferroic properties based on thin-film architectures, morphology and point defects. For a
more comprehensive overview of the main effects involved on the ATiO3 materials several
exchange-correlation functionals were investigated, being the PBE0 the functional with
smallest deviations and, consequently, the best representation in comparison to the
experimental results. Aiming to describe the main fingerprints related with the creation of
ATiO3 thin-films, we propose an innovative methodology that allows to describe the uniaxial
and biaxial deformations originated in the interface region between the film and the substrate.
In this case, the results indicate that structural distortions induce a magnetic transition for the
NiTiO3, originating ferromagnetic ordering from magneto-structural criteria, which is
associated to the deformation of the [MO6] clusters that reproduces satisfactorily the
experimental results reported in the literature. Similarly, in order to elucidate the relationship
between the magnetism and the morphology of the ATiO3 materials, we combined Surface
Energy, Wulff Construction, and an advanced formalism to describe surface magnetism by
considering the existence of uncompensated spins along the polar planes (100), (001), (101),
(012), (111) and non-polar (110). The results indicate that the reduction of the coordination for
both A and Ti metals along the (001) and (111) planes induces a charge transfer between the
A
2+
and Ti4+ cations, resulting in magnetic Ti3+ species that increase the superficial magnetism
along such planes. Moreover, this effect allowed a change in the electronic structure for these
materials, allowing to point out that the cleavage of the surfaces contribute to the control of the
electronic properties reducing the band-gap value or generating half-metallic behavior. The
morphological maps indicated that the control of the major exposure for the (001) surface to
obtain hexagonal discsinduces an increase of the superficial magnetism for the ATiO3 materials
according to experimental results, besides predicting different accessible morphologies with
interesting magnetic properties. In addition, the effect of intrinsic defects such as oxygen
vacancies on the bulk and non-polar (110) surface of the ATiO3 materials were investigated,
indicating that the reduction of coordination in the defect region induces the localization of the
remaining electrons in the empty 3d orbitals of neighboring Ti cations, generating [TiO5]'and
[TiO4]' (3d1
) species that allow a ferromagnetic interaction for MnTiO3 and FeTiO3 materials.
The combination of the different mechanisms investigated has allowed to stablish a scientific
guide for the theoretical study of multiferroic materials, contributing to describe the
potentialities of the different materials as well as to predict new candidates.
43
Sembach, Kenneth R. "Spectroscopic studies of low density gas in the Galactic disk and halo." 1992. http://catalog.hathitrust.org/api/volumes/oclc/28229221.html.
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Koda, Jun 1979. "Gravitational dynamics of halo formation in a collisional versus collisionless cold dark matter universe." 2009. http://hdl.handle.net/2152/9705.
Full textAbstract:
Flat cosmology with collisionless cold dark matter (CDM) and cosmological constant ([Lambda]CDM cosmology) may have some problems on small scales, even though it has been very successful on large scales. We study the effect of Self-Interacting Dark Matter (SIDM) hypothesis on the density profiles of halos. Collisionless CDM predicts cuspy density profiles toward the center, while observations of low mass galaxies prefer cored profiles. SIDM was proposed by Spergel & Steinhardt [161] as a possible solution to this cuspy profile problem on low-mass scales. On the other hand, observations and collisionless CDM agree on mass scales of galaxy clusters. It is also known that the SIDM hypothesis would contradict with X-ray and gravitational lensing observations of cluster of galaxies, if the cross section were too large. Our final goal is to find the range of SIDM scattering cross section models that are consistent with those astrophysical observations in two different mass scales. There are two theoretical approaches to compute the effect of self-interacting scattering -- Gravitational N-body simulation with Monte Carlo scattering and conducting fluid model; those two approaches, however, had not been confirmed to agree with each other. We first show that two methods are in reasonable agreement with each other for both isolated halos and for halos with realistic mass assembly history in an expanding [Lambda]CDM universe; the value of cross section necessary to have a maximally relaxed low-density core in [Lambda]CDM is in mutual agreement. We then develop a semianalytic model that predicts the time evolution of SIDM halo. Our semianalytic relaxation model enables us to understand how a SIDM halo would relax to a cored profile, and obtain an ensemble of SIDM halos from collisionless simulations with reasonable computational resources. We apply the semianalytic relaxation model to CDM halos, and compare the resulting statistical distribution of SIDM halos with astrophysical observations. We show that there exists a range of scattering cross sections that simultaneously solve the cuspy core problem on low-mass scales and satisfy the galaxy cluster observations. We also present that other potential conflicts between [Lambda]CDM and observations could be resolved in Part II and III.<br>text
45
Kennedy, HEATHER. "An Investigation of Neutral Hydrogen in Three Edge-on Spiral Galaxies." Thesis, 2009. http://hdl.handle.net/1974/5134.
Full textAbstract:
We present the results of a new and high sensitivity study of the neutral hydrogen (HI) gas in three early type edge-on spiral galaxies, NGC 4157, NGC 3600 and NGC 2683. All three galaxies reveal HI disks that extend nearly or more than twice the length of the optical disk, which ubiquitously reveal asymmetries and warps. We model each galaxy using a three-dimensional kinematic model to derive the empirical parameters of the density distribution functions and rotation curves. A Gaussian function is unanimously found to best represent the density distribution in the plane of the galaxies. We also find that there is in fact a thick HI disk extending into the halo of two of three of these galaxies with scale heights on kpc. scales. This gas suggests the existence of two separate widespread components: a thin, high intensity disk component, normally rotating, and a vast, low intensity halo component, rotating at slower velocities with respect to the disk. This vertical velocity gradient is perhaps our most significant finding in addition to the discovery of the two new HI halos. We also find an unevenly distributed small-scale component of the gas in the form of shell-like and filamentary structures that extend from the disk into the halo. In all three systems we find unique kinematic and structural peculiarities including an HI disk extending four times the optical disk, a declining rotation curve, a companion, expanding bubbles, disk warps, etc. Several physical parameters are derived such as neutral hydrogen and dynamic masses, systemic velocities, HI radii, HI halo masses, etc. All of our findings are investigated and discussed in depth for each of the three galaxies.<br>Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-09-03 19:47:31.786
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Hughes, Zak E., A. Baev, P. N. Prasad, and T. R. Walsh. "Halo-substituted azobenzenes adsorbed at Ag(111) and Au(111) interfaces: Structures and optical properties." 2017. http://hdl.handle.net/10454/15781.
Full textAbstract:
Yes<br>The adsorption of azobenzene (AB), ortho fluoro-azobenzene (FAB) and ortho chlor-azobenzol (ClAB), in both the cis and trans isomers, at the Au(111) and Ag(111) surfaces is investigated using plane-wave density functional calculations with the revPBE-vdW-DF functional. The resulting adsorption energies and internal structures of AB adsorbed to both metal surfaces are in broad agreement with available experimental data. In the gas phase, FAB and ClAB feature a significant reduction in the energy difference between the two isomeric states, compared with AB. This relative reduction in the energy difference is still significant for the adsorbed form of FAB but is only weakly apparent for ClAB. The absorption spectra of the molecules have also been calculated, with the halogen substituents generating significant changes in the gas phase, but only a modest difference for the adsorbed molecules.
47
Casas, Miranda Rigoberto Angel [Verfasser]. "Statistics of the dark matter halo distribution in cosmic density fields / vorgelegt von Rigoberto Angel Casas Miranda." 2002. http://d-nb.info/965761088/34.
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Ben, Bekhti Nadya [Verfasser]. "Low column density gas clumps in the inner and outer halo of the Milky Way / vorgelegt von Nadya Ben Bekhti." 2009. http://d-nb.info/994215592/34.
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GÓMEZ, DÍAZ LUIS GABRIEL. "Astrophysical implications of the fermionic dark matter in galaxies." Doctoral thesis, 2017. http://hdl.handle.net/11573/1011735.
Full textAbstract:
The main aim of this thesis is to use a fermionic dark matter (DM) model (the Ruffini-Arg\"uelles-Rueda (RAR) model) to describe the distribution of dark matter in galactic halos as an astrophysical probe of the fermionic nature of dark matter. My thesis work focuses then on testing possible effects that are caused by DM (and modeled by the RAR model) as well as their astrophysical implications. These effects are also compared with the ones provided by standard density profiles, such as the Navarro-Frenk-White and the pseudo isothermal profiles. My thesis work hence begins the exploration of this broad area by addressing one fundamental question: Is it possible to test and constrain the RAR model (and other DM models) by quantifying its gravitational interaction on some astrophysical systems? I response explicitly to this question, throughout the development of this thesis, presenting viable astrophysical scenarios.
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Ma, Yu-Ping, and 馬妤萍. "Half-level cells: enhancing flash read disturb management with adaptive cell-bit density." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/gcjyxw.
Full textAbstract:
碩士<br>國立交通大學<br>資訊科學與工程研究所<br>107<br>Read disturbance is a kind of noise generated by hardware characteristics while executing read operation. Accumulating a large amount of read disturbance may destroy existing data. Read refreshing use data migration to avoid data corruption, however it also induced a lot of erase count under read intensive workload. In-place reprogramming reduces cell-bit density to enhance read disturbance tolerance, but it can only handle a small amount of the read hot data which cause read refreshing when they stored in high-density cell. We further propose to increase block capacity by adjust cell-bit density, to reduce erase count induced by read refreshing.