Toy model of superconductivity

The model of hypothetical superconductivity, where the energy gap asymptotically approaches zero as temperature or magnetic field increases, has been proposed. Formally the critical temperature and the second critical field for such a superconductor is equal to infinity. Thus the material is in superconducting state always

Multimodal size distribution of Si nanoclusters in SiO₂ as manifestation of interaction in the space of sizes

This paper summarizes the results of experimental studies revealing a multimodal character of the function of size distribution of Si nanoclusters in light-emitting SiO₂:Si structures. To explain the nature of this multimodality, a “liquid” approach to the description of the coalescence stage based on taking into account the correlation effects caused by particle-particle interactions in the space of sizes is proposed. This approach is justified by a high concentration of solutions where the nuclei of the new phase are described by a multimodal function of size distribution.Узагальнені результати експериментальних досліджень, які засвідчують полімодальність функції розмірного розподілу кремнієвих наночасток в матриці SiO₂ в випадку сильного перенасичення розчину SiO2:Si кремнійовою компонентою. Для пояснення природи полімодальності запропоновано «рідинний» підхід в описі стадії коалесценції, який оснований на врахуванні процесів міжчастинкової взаємодії в просторі розмірів. Запропонований підхід може виявитись перспективним для розвитку фізичних основ керування спектральним складом і інтенсивністю випромінювання кремнійових випромінювачів світла.Обобщены результаты экспериментальных исследований, свидетельствующие о полимодальности функции размерного распределения кремниевых наночастиц в матрице SiO₂ в случае сильного пересыщения раствора SiO2:Si кремниевой составляющей. Для объяснения природы полимодальности предложен «жидкостный» подход в описании стадии коалесценции, основанный на учете процессов межчастичного взаимодействия в пространстве размеров. Предложенный подход перспективен для развития физических принципов управления спектральным составом и интенсивностью излучения кремниевых излучателей света

Brownian particle in non-equilibrium plasma

The stationary distribution function of Brownian particles in a nonequilibrium dusty plasma is calculated with regard to electron and ion absorption by grains. The distribution is shown to be considerably different from the distribution function of ordinary Brownian particles in thermal equilibrium. A criterion for the grain-structure formation in a nonequilibrium dusty plasma is derived.Знайдена стацiонарна функцiя розподiлу для Броунiвських частинок, що знаходяться в в нерiвноважнiй запорошенiй плазмi. Для цього використано нелiнiйне рiвняння Фоккера-Планка. Сила, що дiє на частинку, враховує безпосереднiй вплив плазми за рахунок змiни поля рухомої частинки при абсорбцiї зарядiв на її поверхнi та звичайне тертя порошинки в плазмi. Показано, що стацiонарна функцiя розподiлу по швидкостях для частинок не вiдповiдає рiвноважному розподiлу для звичайних Броунiвських частинок. Знайденi критерiї формування структур в системi таких частинок в нерiвноважнiй плазмi

Forces between elongated particles in a nematic colloid

Using molecular dynamics simulations we study the interactions between elongated colloidal particles (length to breath ratio ≫1) in a nematic host. The simulation results are compared to the results of a Landau–de Gennes elastic free energy. We find that depletion forces dominate for the sizes of the colloidal particles studied. The tangential component of the force, however, allows us to resolve the elastic contribution to the total interaction. We find that this contribution differs from the quadrupolar interaction predicted at large separations. The difference is due to the presence of nonlinear effects, namely, the change in the positions and structure of the defects and their annihilation at small separations

Peculiarities of the stochastic motion in antiferromagnetic nanoparticles

Antiferromagnetic (AFM) materials are widely used in spintronic devices as passive elements (for stabilization of ferromangetic layers) and as active elements (for information coding). In both cases switching between the different AFM states depends in a great extent from the environmental noise. In the present paper we derive the stochastic Langevin equations for an AFM vector and corresponding Fokker-Planck equation for distribution function in the phase space of generalised coordinate and momentum. Thermal noise is modeled by a random delta-correlated magnetic field that interacts with the dynamic magnetisation of AFM particle. We analyse in details a particular case of the collinear compensated AFM in the presence of spin-polarised current. The energy distribution function for normal modes in the vicinity of two equilibrium states (static and stationary) in sub- and super-critical regimes is found. It is shown that the noise-induced dynamics of AFM vector has pecuilarities compared to that of magnetisation vector in ferromagnets.Comment: Submitted to EPJ ST, presented at the 4-th Conference on Statistical Physics, Lviv, Ukraine, 201

Defect structures and torque on an elongated colloidal particle immersed in a liquid crystal host

Combining molecular dynamics and Monte Carlo simulation we study defect structures around an elongated colloidal particle embedded in a nematic liquid crystal host. By studying nematic ordering near the particle and the disclination core region we are able to examine the defect core structure and the difference between two simulation techniques. In addition, we also study the torque on a particle tilted with respect to the director, and modification of this torque when the particle is close to the cell wall

Experimental and Theoretical Challenges in the Search for the Quark Gluon Plasma: The STAR Collaboration's Critical Assessment of the Evidence from RHIC Collisions

We review the most important experimental results from the first three years of nucleus-nucleus collision studies at RHIC, with emphasis on results from the STAR experiment, and we assess their interpretation and comparison to theory. The theory-experiment comparison suggests that central Au+Au collisions at RHIC produce dense, rapidly thermalizing matter characterized by: (1) initial energy densities above the critical values predicted by lattice QCD for establishment of a Quark-Gluon Plasma (QGP); (2) nearly ideal fluid flow, marked by constituent interactions of very short mean free path, established most probably at a stage preceding hadron formation; and (3) opacity to jets. Many of the observations are consistent with models incorporating QGP formation in the early collision stages, and have not found ready explanation in a hadronic framework. However, the measurements themselves do not yet establish unequivocal evidence for a transition to this new form of matter. The theoretical treatment of the collision evolution, despite impressive successes, invokes a suite of distinct models, degrees of freedom and assumptions of as yet unknown quantitative consequence. We pose a set of important open questions, and suggest additional measurements, at least some of which should be addressed in order to establish a compelling basis to conclude definitively that thermalized, deconfined quark-gluon matter has been produced at RHIC.Comment: 101 pages, 37 figures; revised version to Nucl. Phys.

Brownian system in energy space

The main goal of this article is to present a simple way to describe non-equilibrium systems in energy space and to obtain new spacial solution that complements recent results of B.I. Lev and A.D. Kiselev, Phys. Rev. E 82, (2010) 031101. The novelty of this presentation is based on the kinetic equation which may be further used to describe the non-equilibrium systems, as Brownian system in the energy space. Starting with the basic kinetic equation and the Fokker-Plank equation for the distribution function of the macroscopic system in the energy space, we obtain steady states and fluctuation relations for the non-equilibrium systems. We further analyze properties of the stationary steady states and describe several nonlinear models of such systems

Pattern formation in the models with coupling between order parameter and its gradient

A possibility of pattern formation in the models of the first order phase transitions with coupling between the order parameter and its gradient is discussed. We use the standard model of phase transitions extended to the higher derivatives of the order parameter that makes possible to describe the formation of various spatial distributions of the order parameter after phase transition. An example of the simple model with coupling between the order parameter and its gradient is considered. The proposed model is analogical to the mechanical nonlinear oscillator with the coordinate-dependent mass or velocity-dependent elastic module. The exact solution of this model is obtained that can be used to predict the order parameter distribution in the case of a spinodal decomposition