STATISTICAL MECHANICS

Author: RUIZ LÓPEZ GUIOMAR.
Year: 2004.
University: COMPLUTENSE DE MADRID.
Place of defense: FACULTAD CIENCIAS FÍSICAS.
Place of preparation: FACULTAD CIENCIAS FÍSICAS.

Summary: This is an original contribution to the study of fluids complejos.Analizar by analytical methods, integral equations and numerical simulation transitions fluido-fluido a system of particles that interact with a potential pal that depends on the density and temperature. The polymorphism of a fluid monocomponente discusses with a potential model containing a part which is an attractive power inverse index is a function not of densidad.Como second monotonous example discusses a fluid monocomponente described by the potential DLVO, as a model potential cash for the study of dissolution colloidal stabilized in the electric charge. Along the report detailing the methods and equations that describe a complex fluid through a fluid monocomponente with effective interactions, the results differ from traditional to be obtained from the statistical physics of the atomic fluids.

Author: JIMÉNEZ DE CISNEROS BAILLY BAILLIÈRE BORJA.
Year: 2004.
University: COMPLUTENSE DE MADRID.
Place of defense: FACULTAD DE CIENCIAS FÍSICAS.
Place of preparation: FACULTAD DE CIENCIAS FÍSICAS.

Summary: The thesis deals with the thermodynamic aspects of different transport processes which have their origin in correcting fluctuations not balance. The first three chapters are dedicated to engines brownianos or "ratchets." In Chapter 1 provides a review of the effect "ratchet" and its main applications. The following two chapters focus on the thermodynamics of the engines brownianos. Here we analyze the energy flows have been established between the particles brownianas and environs. This analysis depends on the nature of the shocks moving particles brownianas out of balance. Therefore classified engines brownianos according disruptions have a mechanical nature, chemical or thermal. For each of these types of engines are discussed different strategies that would allow them to operate in a manner reversible. Moreover, in chapter 2, which deals with engines brownianos isotermos subjected to mechanical shocks and chemical proposes a potential chemical thermodynamics based on generalized dependent on the position of the particle and, in the case of chemical engines, also coordinates internal . Adopting the assumption of local equilibrium, and with the sole help of the Fokker-Planck equation and the reaction - diffusion equations, we obtain the entropy production of these engines, and it is shown to be an amount not negative. This will check the compatibility of the theory of engines brownianos with the second law of thermodynamics. Chapter 3 deals with the problem of piston adiabatic. Some recent results show some similarities between the behavior of adiabáticos piston engines and thermal brownianos. This chapter proposes a widespread problem of adiabatic piston which can be interpreted as a real engine. The problem of piston adiabatic also relates to issues atafien the foundations of the thermostatic. It is a widespread opinion that the thermostatic is unable to predict alone reaching steady state systems subject to internal adiabáticas ligatures. En.el Chapter 3 presents a solution to that problem using purely Thermostatics; is adapting the principle of maximum entropy to systems with internal adiabáticas ligatures. That theory is contrasted with molecular dynamics simulations in a two-dimensional model of adiabatic piston separating two gases disk drives. Chapter 5 is devoted to the phenomenon of negative absolute mobility. Specifically, we discuss two simple modifications of a model engine Brownian resulting in the occurrence of negative absolute mobility Check such conduct is consistent with the second law of thermodynamics. Finally, in Chapter 6 presents the findings.

Author: ESCUDERO LIÉBANA CARLOS.
Year: 2004.
University: NACIONAL DE EDUCACIÓN A DISTANCIA.
Place of defense: FACULTAD DE CIENCIAS UNED.
Place of preparation: FACULTAD DE CIENCIAS UNED..

Summary: This dissertation deals dobre how you can extrapolate different methods of theoretical physics and applying them to solve problems biological framed within the context of the dynamics of populations. The issues addressed include the effect of seasonal variation on the dynamics of populations, biological extinction of a species, the spread of disease and the study of fronts and migration. The methods used are the most varied and include the use of ordinary differential equations, partial derivatives in equations, dynamical systems theory, ordinary differential equations, integrals functional quantum field theories and equations teachers. The use of new methods and the expansion of some existing ones has led to new findings and conclusions beyond the scope of the classic methodology for the quantitative study of the dynamics of biological populations.

Author: ARES GARCIA SAUL.
Year: 2004.
University: CARLOS III DE MADRID.
Place of defense: ESCUELA POLITECNICA SUPERIOR.
Place of preparation: UNIVERSIDAD CARLOS III DE MADRI.

Summary: In this report we studied several models made in one dimension. First we study the model sine-Gordon, it is appropriate to study the growth of solid surfaces, finding behavior of finite size similar to a transition phase thermodynamics. Then we introduced two models of the transition from wet surfaces. We used the version with disorder of these models to characterize the unit with the gene sequence of the DNA denaturation temperature. Combining one of the models wet with the sine-Gordon propose a new model, a version of which allows us to mess with making comparisons with the model sine-Gordon in two dimensions. Consequently we conjecture that the phase superrugosa model in two dimensions is actually a flat stage dominated by the disorder. Then, using the model Dauxois-Peyrard-Bishop, we studied the effect of bubbles in DNA denaturation. Our results are consistent with the pilot, which deduct a significant impact on the dynamics of bubbles. Finally, we propose a new model for studying the dynamics of forks DNA that allows us to test the existing interpretations on the experimental results.

Author: BENITEZ IGLESIAS RAUL.
Year: 2004.
University: POLITÉCNICA DE CATALUÑA.
Place of defense: Aula Màster (Edifici A3),.
Place of preparation: EDIFICI B5 DESPATX 111C Campus NORD.

Author: SERRANO ILLAN JUAN.
Year: 2004.
University: AUTÓNOMA DE MADRID.
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: In this thesis we studied the behavior of simple classical systems of a number of particles whose interactions have been described by various potential model with the potential of the well or the square of Yukawa attractive. We have studied the structural properties (radial distribution function, density profiles, etc.). Thermodynamic and (free energy, phase diagrams) of these systems, both through theory and using Monte Carlo simulation, depending on the extent of the interactions of the same . Besides a description of the mathematical formalism and techniques of computer simulation used, the thesis is divided into two parts. The first deals with the short-range interactions, defined as those whose range is comparable to the distance between the neighboring former, while the latter focuses on the interactions of medium or long-range, corresponding to the distance between the second and more distant neighbors . In the first part we summarize the properties of the systems and areas of hard drives and systems resulting from adding a part attractive to potential which describes. By adding this part attractive short-range systems can be seen in a transition isoestructural between phases of different densities. The theories are inadequate to the disturbances quantitative description of this transition in two-dimensional systems. That is why we need a very accurate description of the correlations between the positions of the particles, especially at short distances. This description is possible using the theory autoconsistente not perturbativa, to which we contributed in the work of this thesis. This theory also provides excellent results at the time to describe the thermodynamics of any system and constitutes an alternative to the simulation, because it can calculate all stages of a plot in a few minutes. In the second part of the thesis we have developed a theory based on the average Boltzmann factor for the system under study. From calculation of the partition function of a single particle beneath the potential for interaction generated by her neighbors along its continuous movement, we got the free energy of the system in a thermodynamic state without integrating along an entire process reversed. We have also predicted with this theory what is the degree of localization of particles as a function of temperature. In this second part of the thesis, we also predicted stability of several structures compact little in the particular case of potential downhole square, as the centered cubic structure in the body, centered tetragonal and hexagonal. We have demonstrated that the cubic structure centered on the faces loses its stability to a sufficiently low temperature. For the study of these structures have used a theory of turbulence and various simulations (at constant volume or pressure). Both theory and simulation have been adapted to the geometry of these structures. As a result of its implementation, we have found that a very simple system, as studied, can display a high degree of complexity in their phase diagrams, even if the interactions between its particles are of medium or long-range, depending on which such interactions have a unit with sharp enough distance.

Author: DINIS VIZCAÍNO LUIS IGNACIO.
Year: 2005.
University: COMPLUTENSE DE MADRID.
Place of defense: FACULTAD DE CIENCIAS FÍSICAS.
Place of preparation: FACULTAD DE CIENCIAS FÍSICAS.

Summary: This thesis has been studied critical issues concerning the rectification of thermal fluctuations: the control and optimization engines collective consisting of a large number of particles brownianas. We have analyzed various control protocols that are based on information on the position of the particles to improve transportation. At least one of these protocols could be used on an experimental realization of a Brownian motor in which the particles are monitored. Moreover, we have also studied optimization strategies in gambling groups closely associated with engines brownianos studied in the thesis. In the first part discusses some optimization strategies in the short term results are unexpected. For example, the election in each shift of the game more suitable for most produce losses for the entire set of players. After noting that this and other simple optimization strategies do not provide the maximum gain, it has tackled the problem of finding the optimal long-term strategy in the games group. Among the results that have been obtained stresses the solution to the problem opened dela determination of the optimal sequence for the games Parrondo. We have also obtained the best strategy for the games for both groups a finite number of players for a finite number of players between 1 and 100.

Author: Díez Minguito Manuel.
Year: 2006.
University: GRANADA.
Place of defense: Facultad de Ciencias.
Place of preparation: Facultad de Ciencias.

Summary: The Statistical Mechanics is a discipline of Theoretical Physics which seeks to explain the dynamics of the macroscopic matter originated in the collective behavior of individual entities (microscopic). The greatest achievement of this discipline is the theory collectivities, which formally establishes the link between the microscopic and macroscopic properties for systems in balance. However, for systems outside the balance little is known in general. In this context, this thesis represents a new effort to understand the essential properties of systems far from equilibrium. Specifically, the main object is to study instabilities at various levels of description, forced systems, ie, kept away from equilibrium by an external agent. It focuses on two major classes of systems, fluids and gases diffusive trawl granular vibro-fluidicados. It looks through Monte Carlo simulations and theory of fields the effect of microscopic dynamics in the states of no-equilibrio resulting stationary. Precise estimates of critical parameters of the models being treated discuss the role of symmetries in the modeling of fluid out of balance. It proposes a new model microscopic no-reticular to study changes in anisotropic phase. This allows discuss exceptional properties and unrealistic models reticular previously proposed. Using Granular Hydrodynamics and Molecular Dynamics simulations characterize the rigidities of heterogeneous aggregation of particles and spontaneous symmetry breaking in a gas granular confined annular geometry. This study is intended to stimulate further experimental studies on phase separation granular. It is found that, surprisingly unlike molecular gas, the magnitude of fluctuations in the center of mass of the system does not decrease with the number of particles in the system.

Author: CASA DE JULIÁN MIGUEL ÁNGEL DE LA.
Year: 2006.
University: NACIONAL DE EDUCACIÓN A DISTANCIA.
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: This thesis is divided into two distinct parts. In the first, explores the resonance depends on the size of the system. This phenomenon is an extension of the classical stochastic resonance. While the stochastic resonance occurs in systems subjected to an external force and in which the size of the system plays no role (because the description of the system is in the thermodynamic limit), and is characterized by the correlation between system and the force is maximum intensity noise for a finite, non-zero, the resonance depends on the size of the system exploits the fact that in systems with a finite number of elements fluctuations scaled to the size of the system, setting the intensity of fluctuations, maximize the system's response to an external field for a given finite size of the system. In the second part, devoted to the relaxation of spiral waves in excitable media, presents results concerning the interaction between waves and spirals fronts levels in excitable media. The existence of solutions in the form of spiral wave is well known and, in the case of myocardial considered as a means excitable, are also well-known adverse effects, and that the presence of spirals is associated with ventricular tachycardia. Therefore, the elimination of spiral waves is an area of active research. This thesis shows how, under the right circumstances of action potential duration in both fronts, it can create complex patterns space in which the spiral is periodically diluted and confined to a small region of the system. These patterns can be grouped into two distinct classes and appear in an orderly fashion in the space of parameters. You may also find analytical expressions that can predict what pattern is apparent in functions of the values of the patterns.

Author: GOMEZ GARDEÑES JESUS.
Year: 2006.
University: ZARAGOZA.
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: This doctoral thesis deals with the study of systems of many elements (discrete systems) interacting. The phenomenology present in these systems is given by the presence of two key ingredients: (i) complex dynamics: The equations of motion that govern the evolution of the components are not linear so that we can rarely find analytical solutions. In the phase space of these systems can coexist different types of trajectories dynamics (multiestabilidad) and its topology can vary greatly depending on the parameters used in the equations. The combination of non-linear dynamics and systems of many degrees of freedom (such as those studied here) gives rise to emerging properties such as the existence of solutions localized in space, synchronization, chaos space, training patterns, etc. . (Ii) structural complexity: It refers to the existence of a high degree of randomness in the pattern of interactions between components. In most systems studied this randomness is presented in a way that the description of the influence of the environment on a single system element can not be described by an approximation field environment. The study of these two ingredients in widespread schemes will be carried out as separate (Parts I and II of this thesis) and combined (Part III). While the first two cases phenomenology introduced by each source of complexity has been the subject of extensive independent studies over the past aËnos, the combination of the two leads to an open field and enormously promising, where an interdisciplinary concerning the fields of application involves a massive effort of various scientific communities. In particular, this is the case study of the dynamics in biological systems whose analysis is difficult to deal with techniques exclusive to the Biochemistry, Physics Statistical Mathematics or Physics. Ultimately, the goal in this thesis is to study separately two sources of complexity inherent in many systems of interest to finally be able to tackle problems with new perspectives relevant to the physics of cellular processes, Neuroscience, Evolutionary Dynamics, etc. ..