Quantum dynamics in strong fluctuating fields

A large number of multifaceted quantum transport processes in molecular systems and physical nanosystems can be treated in terms of quantum relaxation processes which couple to one or several fluctuating environments. A thermal equilibrium environment can conveniently be modelled by a thermal bath of harmonic oscillators. An archetype situation provides a two-state dissipative quantum dynamics, commonly known under the label of a spin-boson dynamics. An interesting and nontrivial physical situation emerges, however, when the quantum dynamics evolves far away from thermal equilibrium. This occurs, for example, when a charge transferring medium possesses nonequilibrium degrees of freedom, or when a strong time-dependent control field is applied externally. Accordingly, certain parameters of underlying quantum subsystem acquire stochastic character. Herein, we review the general theoretical framework which is based on the method of projector operators, yielding the quantum master equations for systems that are exposed to strong external fields. This allows one to investigate on a common basis the influence of nonequilibrium fluctuations and periodic electrical fields on quantum transport processes. Most importantly, such strong fluctuating fields induce a whole variety of nonlinear and nonequilibrium phenomena. A characteristic feature of such dynamics is the absence of thermal (quantum) detailed balance.Comment: review article, Advances in Physics (2005), in pres

Загальна теорія іонних каналів з багатократною заселеністю

У статті представлений загальний теоретичний підхід, що дозволяє описати провідність іонних каналів з множинною заселеністю. Він базується на реальній структурі калієвого каналу KcsA, але не обмежується даним каналом. Показано, що рух іонів у селективному фільтрі каналу є істотно колективним і може бути редукованим до руху єдиної квазічастинки - квазііону. Концепція квазііонів дозволяє пояснити явище безбар'єрної виштовхувальної провідності в селективному фільтрі та уникнути повного опису руху індивідуальних іонів у багатоіонному каналі, що значно спрощує задачу. Показано, що квазііони є фактичними переносниками заряду в каналі.We present a general theoretical approach, which explains the conductance in the ion channel with multiple occupancy. The model is based on the design of KcsA K* channel, but not limited to it. We show that the motion of the ions in the selective filter is concerted and can be reduced to the motion of a single quasiparticle called quasi-ion. The concept of quasi-ions provides an elegant explanation of barrier-less "knock-on" conduction in the selectivity filter and allows us to avoid explicit description of the motion of individual ions in the multi-ion channel. The quasi-ions perform actual charge transfer in the channel

Holographic interferometry as a method to study conformational changes in macromolecules

This paper concerns with our measurements of reaction center (RC) volume changes in the course of photoactivation using the method of holographic interferometry. As a principal value, we studied changes of a solution refraction index (Δn) influenced by the sample volume expansion due to temperature changes (ΔnT), light absorption (Δnabs) and changes in the volume of photoactive molecules (DnV). Using the scheme of temperature compensation we could reduce the task to the case ΔnT <<Δnabs, ΔnV. At RC concentrations close to 10¹⁵ cm-³, our experimental setup enabled to register the shift of an interference pattern up to 0.1 of the bandwidth. Our estimations for the case of a protein solution yields in relative changes in the molecular volume within 10-³...10-²

Semi-quantitative model of the gating of KcsA ion channel. 2. Dynamic self-organization model of the gating

The aim of this series of papers is to develop the semi-quantitative theory of the gating of KcsA channel. Methods. For this purpose available structural and electrophysiological data and the results of molecular dynamics simulations were used in the context of the concept of dynamical self-organization. In the second paper we describe the principles of dynamic self-organization and develop the theory of KcsA channel gating based on this concept. Conclusions. Present work is the first successful attempt of combining the structure and dynamics of real protein and the general concept of dynamic self-organizatio