A Dicke Type Model for Equilibrium BEC Superradiance

We study the effect of electromagnetic radiation on the condensate of a Bose gas. In an earlier paper we considered the problem for two simple models showing the cooperative effect between Bose–Einstein condensation and superradiance. In this paper we formalize the model suggested by Ketterle et al. in which the Bose condensate particles have a two level structure. We present a soluble microscopic Dicke type model describing a thermodynamically stable system. We find the equilibrium states of the system and compute the thermodynamic functions giving explicit formulæ expressing the cooperative effect between Bose–Einstein condensation and superradiance.     

3D KMC simulations of crater growth during the reduction of oxide nanoislands on metal surfaces

The homoepitaxial growth of Cu nanocraters induced by thermal reduction of Cu₂O nanoislands on Cu(100) surfaces is simulated using a three-dimensional (3D) kinetic Monte Carlo (KMC) model by incorporating surface diffusion, attachment and detachment Cu adatoms dislodged from reducing Cu₂O islands. The craters are observed to grow continuously in rim height and rim slopes while remaining relatively constant in rim width in the course of the oxide decomposition. Such a growth behavior is attributed to the climbing uphill of Cu adatoms released from the perimeter of the reducing Cu₂O island at the crater bottom. The observed decay of the rim height and slopes after completion of the reduction of oxide islands suggests that these surface craters are thermodynamically unstable at high temperatures.     

Gradient plasticity for thermo-mechanical processes in metals with length and time scales

A thermodynamically consistent framework is developed in order to characterize the mechanical and thermal behavior of metals in small volume and on the fast transient time. In this regard, an enhanced gradient plasticity theory is coupled with the application of a micromorphic approach to the temperature variable. A physically based yield function based on the concept of thermal activation energy and the dislocation interaction mechanisms including nonlinear hardening is taken into consideration in the derivation. The effect of the material microstructural interface between two materials is also incorporated in the formulation with both temperature and rate effects. In order to accurately address the strengthening and hardening mechanisms, the theory is developed based on the decomposition of the mechanical state variables into energetic and dissipative counterparts which endowed the constitutive equations to have both energetic and dissipative gradient length scales for the bulk material and the interface. Moreover, the microstructural interaction effect in the fast transient process is addressed by incorporating two time scales into the microscopic heat equation. The numerical example of thin film on elastic substrate or a single phase bicrystal under uniform tension is addressed here. The effects of individual counterparts of the framework on the thermal and mechanical responses are investigated. The model is also compared with experimental results.     

Thermodynamically guided nonequilibrium Monte Carlo method for generating realistic shear flows in polymeric systems

A thermodynamically guided atomistic Monte Carlo methodology is presented for simulating systems beyond equilibrium by expanding the statistical ensemble to include a tensorial variable accounting for the overall structure of the system subjected to flow. For a given shear rate, the corresponding tensorial conjugate field is determined iteratively through independent nonequilibrium molecular dynamics simulations. Test simulations for the effect of flow on the conformation of a C50H102 polyethylene liquid show that the two methods (expanded Monte Carlo and nonequilibrium molecular dynamics) provide identical results.     

Simple method of optimizing structural parameters of system of solid spheres for the calculation of liquid radial function

A thermodynamically consistent representation, in terms of the equation of state, is obtained for the coefficients of the Wertheim-Till direct correlation functions for a system of solid spheres modeling the microstructure of a simple liquid. It is shown that use of the equation of state in Karnahan — Sterling form significantly improves the results for the radial function, giving good agreement with the results of the semiempirical Verlet-Weis approximation for the data of a numerical experiment on a system of solid spheres. Optimization of the sphere diameter using the entropic method proposed earlier is shown to ensure agreement of the nodes of the radial function of the liquid with experimental data. The agreement of the method proposed with other known methods for the calculation and optimization of the radial function of solid spheres is discussed, and its advantages are noted.Thanks are due to Professor V. I. Shimulis for his constant interest in the work.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 28–32, June, 1977.     

Cooling capacity optimization of a waste heat absorption refrigeration cycle

A finite-time endoreversible heat-driven absorption refrigerator is modeled thermodynamically in this paper. The refrigerator uses low-temperature waste heat directly to provide a cooling effect. The maximum cooling capacity delivered by the absorption system is analyzed.     

Lattice vibrations induced by a polarizable impurity atom in polar crystals

The effect of a polarizable impurity atom on the frequency of optical vibrations of a polar crystal is calculated. The impurity-lattice interaction is treated by considering lattice polarization as discrete in contrast to earlier methods based on continuum approximation. In the appropriate limit, our result goes over exactly to the result of earlier approximation.     

Effect of curvature on a statistical model of quark-gluon-plasma fireball in the hadronic medium

The free energy of a quark-gluon plasma fireball in the hadronic medium is calculated in the Ramanathan et al statistical model after incorporating the effect of curvature. The result with the inclusion of curvature is found to produce significant improvements in all the parameters we calculated with respect to the earlier results. The surface tension with this curvature effect is found to be 0.17T _c³, which is two times the earlier value of surface tension which is 0.078T _c³, and this new result is nearly close to the lattice value 0.24T _c³. As far as transition is concerned, a thermodynamic variable like entropy shows weakly first-order phase transition and it shows continuity in the behaviour of specific heat.     

An Integral Equation Theory for the Widom–Rowlinson Mixture

The Widom–Rowlinson mixture is a two-component fluid in which like species do not interact and unlike species interact via a hard-core repulsion. As the density is increased, this fluid phase separates. Standard integral equation approaches, such as the Percus–Yevick or hypernetted chain, or thermodynamically self-consistent hybirds of these two, make very inaccurate predictions for the location of this critical point in the three-dimensional model. In this article we suggest a family of new approximations for this model that rely on incorporating terms in the density expansion of the direct correlation function into the closure approximation. We show that the simplest of these closures is significantly more accurate than previous theories for the structure and thermodynamics of the fluid.     

Variational Principle in the Theory of Partial Distribution Functions

We have constructed thermodynamically consistent theory of correlations in a classical equilibrium system. The theory is based on a variational principle for thermodynamic potential, as functional of correlation functions. Both the thermodynamic potential and correlation functions are determined simultaneously from a uniform variation problem for this functional. We have offered also methods of consecutive approximations system construction for the solution of the obtained variational problem.     

Excluded volume effect for the nuclear matter equation of state

We present the thermodynamically consistent procedure to introduce the excluded volume effect into the equation of state of nuclear matter. Implications are discussed in the framework of a mean-field model for hadrons with eigenvolume.     

Dilute Bose gas: short-range particle correlations and ultraviolet divergence

The modified Bogoliubov model where the primordial interaction is replaced by the t matrix is reinvestigated. It is shown to provide a negative value of the kinetic energy for a strongly interacting dilute Bose gas, contrary to the original Bogoliubov model. To clear up the origin of this failure, the correct values of the kinetic and interaction energies of a dilute Bose gas are calculated. It is demonstrated that both the problem of the negative kinetic energy and the ultraviolet divergence, dating back to the well-known paper of Lee, Yang and Huang, is connected with an inadequate picture of the short-range boson correlations. These correlations are reconsidered within the thermodynamically consistent model proposed earlier by the present authors. Found results are in absolute agreement with the data of the Monte-Carlo calculations for the hard-sphere Bose gas. Received 10 February 2000 and Received in final form 28 November 2000     

Relativistic and thermodynamically consistent treatment for the finite volume effect of nucleons in nuclear matter

A previous thermodynamically consistent procedure for considering the finite volume effect of nucleons in nuclear matter is developed to be relativistic. Parameters are determined by fitting all five empirical data for normal nuclear matter. The resulting nuclear equations of state may be used in researches for neutron stars and for phase transitions between nuclear matter and quarkgluon plasma.     

Relativistic and Thermodynamically Consistent Treatment for Finite-Volume Effect of Nucleons in Nuclear Matter (I) General Formulation

A previous thermodynamically consistent procedure for considering the finite volume effect of nucleons in nuclear matter is developed to be relativistic. Parameters are determined by fitting all five empirical data for normd nuclear matter. The resulting nuclear equations of state may be used in researches for neutron stars and for phase transitions between nuclear matter and quark-gluon plasma.     

Magnetoelastic effects in rare earth metals and alloys near magnetic phase transitions

Magnetoelastocaloric effects in rare earth metals and alloys have been thermodynamically investigated. It is found that these magnets, along with the ordinary elastocaloric effect, exhibit a giant magnetoelastocaloric effect near the magnetic ordering temperatures, which is proportional to the temperature derivative of spontaneous magnetostriction.     

Influence of surface ordering on the wetting of structured liquids

The substrate is shown to induce substantial ordering in diblock copolymer thin films above the bulk order-disorder transition (ODT) where, thermodynamically, a phase mixed state is favored. Initially, uniform films reorganize to form a hierarchy of transient surface patterns and stable film thicknesses that depend on the initial film thickness and on the substrate. Self-consistent field calculations of the free energy of the system for different situations, depending on the relative tendency for the different block components to be attracted to the substrate and/or free surface, provide an explanation of the formation of the stable film thicknesses. A continuum picture proposed earlier by Brochard et al.rovides an explanation of the wetting characteristics of this system. In some cases the ordering destabilizes the film so that dewetting occurs (wetting autophobicity), whereas in other cases the surface ordering results in a kinetic stabilization of a film that would otherwise dewet. Received 3 August 2001 and Received in final form 1 November 2001     

The problem of consistency of equations of state and a new method for their thermodynamic matching

The problem of the thermodynamic consistency of equations of state obtained by using distribution functions is considered. The effect of thermodynamic consistency of equations on the accuracy of their calculations is determined. It is shown that the velocity of convergence of the thermodynamically consistent perturbation theory series in the general case is determined by the behavior of the distribution functions in the total range of the coordinate changes. A new method for the full thermodynamic consistency of equations of state obtained on the basis of thermodynamics perturbation theory is proposed.     

Phase behavior and charge regulation of weak polyelectrolyte grafted layers

The stability of weak polyelectrolytes end grafted to a planar surface has been studied with a molecular theory. The effective quality of the solvent is found to depend on the interplay between polymer grafting density, acid-base equilibrium, and salt concentration. Our results reveal that increasing salt concentration results in a thermodynamically more stable layer. This reverse salt effect is due to the competition between the solvent quality and the dual role of the ionic strength in screening the electrostatic interactions (reducing stability with increasing salt concentration), and regulating the charge on the polymer (increasing charge with increasing salt concentration). Grafted weak polyelectrolyte layers are found to be thermodynamically unstable at intermediate surface coverages. Additionally, it is established that the increased solubility of the layer at low surface coverage is due to the relatively large charge of the grafted polymers. The range of stability of the film with regard to polymer surface coverage, temperature, bulk pH and salt concentration is demonstrated.