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Mysakovych T.S.,Institute for Condensed Matter Physics
Journal of Physics Condensed Matter | Year: 2010

The phase transitions at finite temperatures in the systems described by the Bose-Fermi-Hubbard model are investigated in this work in the framework of the self-consistent random phase approximation. The case of the hard-core bosons is considered and the pseudospin formalism is used. The density-density correlator is calculated in the random phase approximation and the possibilities of transitions from superfluid to supersolid phases are investigated. It is shown that the transitions between uniform and charge-ordered phases can be of the second or the first order, depending on the system parameters. © 2010 IOP Publishing Ltd.

Kastelic M.,University of Ljubljana | Kalyuzhnyi Y.V.,Institute for Condensed Matter Physics | Hribar-Lee B.,University of Ljubljana | Dil K.A.,State University of New York at Stony Brook | Vlachy V.,University of Ljubljana
Proceedings of the National Academy of Sciences of the United States of America | Year: 2015

Protein aggregation is broadly important in diseases and in formulations of biological drugs. Here, we develop a theoretical model for reversible protein-protein aggregation in salt solutions. We treat proteins as hard spheres having square-well-energy binding sites, using Wertheim's thermodynamic perturbation theory. The necessary condition required for such modeling to be realistic is that proteins in solution during the experiment remain in their compact form. Within this limitation our model gives accurate liquid-liquid coexistence curves for lysozyme and γ IIIa-crystallin solutions in respective buffers. It provides good fits to the cloud-point curves of lysozyme in buffer-salt mixtures as a function of the type and concentration of salt. It than predicts full coexistence curves, osmotic compressibilities, and second virial coefficients under such conditions. This treatment may also be relevant to protein crystallization. © 2015, National Academy of Sciences. All rights reserved.

Ignatyuk V.V.,Institute for Condensed Matter Physics | Morozov V.G.,Moscow State Technical University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2015

The influence of the initial preparation on dephasing in open quantum dynamics is studied using an exactly solvable model of a two-level system (qubit) interacting with a bosonic bath. It is found that, for some classes of nonselective preparation measurements, qubit-bath correlations lead to a significant enhancement of coherence in the qubit at the initial stage of evolution. The time behavior of the qubit purity and entropy in the regime of enhancement of coherence is considered for different temperatures and coupling strengths. © 2015 American Physical Society.

Ignatyuk V.V.,Institute for Condensed Matter Physics
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2011

We consider surface diffusion of a single particle, which performs site-to-site under-barrier hopping, fulfils intrasite motion between the ground and the first excited states within a quantum well, and interacts with surface phonons. On the basis of quantum kinetic equations for one-particle distribution functions, we study the coherent and incoherent motion of the adparticle. In the latter case, we derive the generalized diffusion coefficients and study various dynamic regimes of the adparticle. The critical values of the coupling constant Gcr(T,Ω), which separate domains with possible recrossing from those with the monotonic motion of the adparticle, are calculated as functions of temperature T and vibrational frequency Ω. These domains are found to coincide with the regions where the experimentally observed diffusion coefficients change their behavior from weakly dependent on T to quite a sensitive function of the temperature. We also evaluate the off-diagonal distribution functions both in the Markovian limit and when the memory effects become important. The obtained results are discussed in the context of the "long tails" problem of the generalized diffusion coefficients, the recrossing/multiple crossing phenomena, and an eventual interrelation between the adparticle dynamics at short times and the temperature dependence of the diffusion coefficients measured experimentally. © 2011 American Physical Society.

Yaremko Y.,Institute for Condensed Matter Physics
Electronic Journal of Theoretical Physics | Year: 2012

A renormalization scheme which relies on energy-momentum and angular momentum balance equations is applied to the derivation of effective equation of motion for a massless point-like charge. Unlike the massive case, the rates of radiated energymomentum and angular momentum tend to infinity whenever the source is accelerated. The external electromagnetic fields which do not change the velocity of the particle admit only its presence within the interaction area. The effective equation of motion is the equation on eigenvalues and eigenvectors of the electromagnetic tensor. The massless charges move along base line determined by the eigenvectors when the effective equation of motion possesses uniform solutions. It is interesting that the same solution arises in Rylov's model of magnetosphere of a rapidly rotating neutron star (pulsar). © Electronic Journal of Theoretical Physics.

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