970 resultados para Physics, Fluids
Resumo:
The Lennard-Jones Devonshire 1 (LJD) single particle theory for liquids is extended and applied to the anharmonic solid in a high temperature limit. The exact free energy for the crystal is expressed as a convergent series of terms involving larger and larger sets of contiguous particles called cell-clusters. The motions of all the particles within cell-clusters are correlated to each other and lead to non-trivial integrals of orders 3, 6, 9, ... 3N. For the first time the six dimensional integral has been calculated to high accuracy using a Lennard-Jones (6-12) pair interaction between nearest neighbours only for the f.c.c. lattice. The thermodynamic properties predicted by this model agree well with experimental results for solid Xenon.
Resumo:
The diffusion of Co60 in the body centered cubic beta phase of a ZrSOTi SO alloy has been studied at 900, 1200, and 1440C. The results confirm earlier unpublished data obtained by Kidson17 The temperature dependence of the diffusion coefficient is unusual and suggests that at least two and possibly three mechanisms may be operative Annealing of the specimen in the high B.C.C. region prior to the deposition of the tracer results in a large reduction in the diffusion coefficient. The possible significance of this effect is discussed in terms of rapid transport along dislocation network.
Resumo:
UANL
Resumo:
Tesis (Doctor en Ingeniera de Materiales) UANL, 2014.
Resumo:
Vers la fin du 19me sicle, le moine et rformateur hindou Swami Vivekananda affirma que la science moderne convergeait vers l'Advaita Vedanta, un important courant philosophique et religieux de l'hindouisme. Au cours des dcennies suivantes, suite aux apports scientifiques rvolutionnaires de la thorie de la relativit d'Einstein et de la physique quantique, un nombre croissant d'auteurs soutenaient que d'importants "parallles" pouvaient tre tracs entre l'Advaita Vedanta et la physique moderne. Encore aujourd'hui, de tels rapprochements sont faits, particulirement en relation avec la physique quantique. Cette thse examine de manire critique ces rapprochements travers l'tude comparative dtaille de deux concepts: le concept d'akasa dans l'Advaita Vedanta et celui de vide en physique quantique. L'nonc examin est celui selon lequel ces deux concepts pointeraient vers une mme ralit: un substratum omniprsent et subtil duquel mergent et auquel retournent ultimement les divers constituants de l'univers. Sur la base de cette tude comparative, la thse argumente que des comparaisons de nature conceptuelle favorisent rarement la mise en place d'un vritable dialogue entre l'Advaita Vedanta et la physique moderne. Une autre voie d'approche serait de prendre en considration les limites pistmologiques respectivement rencontres par ces disciplines dans leur approche du "rel-en-soi" ou de la "ralit ultime." Une attention particulire sera porte sur l'pistmologie et le problme de la nature de la ralit dans l'Advaita Vedanta, ainsi que sur le ralisme scientifique et les implications philosophiques de la non-sparabilit en physique quantique.
Resumo:
Cette thse sintresse la modlisation magntohydrodynamique des coulements de fluides conducteurs dlectricit multi-chelles en mettant lemphase sur deux applications particulires de la physique solaire: la modlisation des mcanismes des variations de lirradiance via la simulation de la dynamo globale et la reconnexion magntique. Les variations de lirradiance sur les priodes des jours, des mois et du cycle solaire de 11 ans sont trs bien expliques par le passage des rgions actives la surface du Soleil. Cependant, lorigine ultime des variations se droulant sur les priodes dcadales et multi-dcadales demeure un sujet controvers. En particulier, une certaine cole de pense affirme quune partie de ces variations long-terme doit provenir dune modulation de la structure thermodynamique globale de ltoile, et que les seuls effets de surface sont incapables dexpliquer la totalit des fluctuations. Nous prsentons une simulation globale de la convection solaire produisant un cycle magntique similaire en plusieurs aspects celui du Soleil, dans laquelle le flux thermique convectif varie en phase avec l energie magntique. La corrlation positive entre le flux convectif et lnergie magntique supporte donc lide quune modulation de la structure thermodynamique puisse contribuer aux variations long-terme de lirradiance. Nous analysons cette simulation dans le but didentifier le mcanisme physique responsable de la corrlation en question et pour prdire de potentiels effets observationnels rsultant de la modulation structurelle. La reconnexion magntique est au coeur du mcanisme de plusieurs phnomnes de la physique solaire dont les ruptions et les jections de masse, et pourrait expliquer les tempratures extrmes caractrisant la couronne. Une correction aux trajectoires du schma semi-Lagrangien classique est prsente, qui est base sur la solution une quation aux drives partielles nonlinaire du second ordre: lquation de Monge-Ampre. Celle-ci prvient lintersection des trajectoires et assure la stabilit numrique des simulations de reconnexion magntique pour un cas de magnto-fluide relaxant vers un tat dquilibre.
Resumo:
This thesis deals with some aspects of the Physics of the early universe, like phase transitions, bubble nucleations and premodial density perturbations which lead to the formation structures in the universe. Quantum aspects of the gravitational interaction play an essential role in retical high-energy physics. The questions of the quantum gravity are naturally connected with early universe and Grand Unification Theories. In spite of numerous efforts, the various problems of quantum gravity remain still unsolved. In this condition, the consideration of different quantum gravity models is an inevitable stage to study the quantum aspects of gravitational interaction. The important role of gravitationally coupled scalar field in the physics of the early universe is discussed in this thesis. The study shows that the scalar-gravitational coupling and the scalar curvature did play a crucial role in determining the nature of phase transitions that took place in the early universe. The key idea in studying the formation structure in the universe is that of gravitational instability.
Resumo:
An immense variety of problems in theoretical physics are of the non-linear type. Non~linear partial differential equations (NPDE) have almost become the rule rather than an exception in diverse branches of physics such as fluid mechanics, field theory, particle physics, statistical physics and optics, and the construction of exact solutions of these equations constitutes one of the most vigorous activities in theoretical physics today. The thesis entitled Some Non-linear Problems in Theoretical Physics addresses various aspects of this problem at the classical level. For obtaining exact solutions we have used mathematical tools like the bilinear operator method, base equation technique and similarity method with emphasis on its group theoretical aspects. The thesis deals with certain methods of finding exact solutions of a number of non-linear partial differential equations of importance to theoretical physics. Some of these new solutions are of relevance from the applications point of view in diverse branches such as elementary particle physics, field theory, solid state physics and non-linear optics and give some insight into the stable or unstable behavior of dynamical Systems The thesis consists of six chapters.
Resumo:
Self-sustained time-dependent current oscillations under dc voltage bias have been observed in recent experiments on n-doped semiconductor superlattices with sequential resonant tunneling. The current oscillations are caused by the motion and recycling of the domain wall separating low- and high-electric-field regions of the superlattice, as the analysis of a discrete drift model shows and experimental evidence supports. Numerical simulation shows that different nonlinear dynamical regimes of the domain wall appear when an external microwave signal is superimposed on the dc bias and its driving frequency and driving amplitude vary. On the frequency-amplitude parameter plane, there are regions of entrainment and quasiperiodicity forming Arnold tongues. Chaos is demonstrated to appear at the boundaries of the tongues and in the regions where they overlap. Coexistence of up to four electric-field domains randomly nucleated in space is detected under ac+dc driving.
Resumo:
Spatiotemporal chaos is predicted to occur in n-doped semiconductor superlattices with sequential resonant tunneling as their main charge transport mechanism. Under dc voltage bias, undamped time-dependent oscillations of the current (due to the motion and recycling of electric field domain walls) have been observed in recent experiments. Chaos is the result of forcing this natural oscillation by means of an appropriate external microwave signal.
Resumo:
Science is search for the laws of underlying phenomena of the nature. Engineering constructs the nature as we wish. Interestingly the huge engineering infrastructure like world wide web has grown in such a complex structure such that we need to see the fundamental science behind the structure and behaviour of these networks. This talk covers the science behind the complex networks like web, biological, social etc. The talk aim to discuss the basic theories that govern the static as well as the dynamics of such interesting networks
Resumo:
A detailed study of the electronic structure and bonding of the pentahalides of group 5 elements V, Nb, Ta, and element 105, hahnium (and Pa) has been carried out using relativistic molecular cluster Dirac-Slater discrete-variational method. A number of calculations have been performed for different geometries and molecular bond distances. The character of the bonding has been analyzed using the Mulliken population analysis of the molecular orbitals. It is shown that hahnium is a typical group 5 element. In a great number of properties it continues trends in the group. Some peculiarities in the electronic structure of HaCl_5 result from relativistic effects.
Resumo:
Relativistic self-consistent charge Dirac-Slater discrete variational method calculations have been done for the series of molecules MBr_5, where M = Nb, Ta, Pa, and element 105, Ha. The electronic structure data show that the trends within the group 5 pentabromides resemble those for the corresponding pentaclorides with the latter being more ionic. Estimation of the volatility of group 5 bromides has been done on the basis of the molecular orbital calculations. According to the results of the theoretical interpretation HaBr_5 seems to be more volatile than NbBr_5 and TaBr_5.
