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The CD spectra of dispersion particles with the “re-entrant” packing of ds DNA have been compared to the CD spectra of particles with the cholesteric ordering of these molecules. The intercalation of daunomycin (DAU) between base pairs of DNA leads to an appearance of new additional band in the CD spectra. The linking of DNA in the single particles by (DAU-copper) nanobridges transforms the “liquid-like” structures of the both particles into the “rigid” state. These effects prove the existence of the cholesteric structure in “re-entrant” DNA phase.

The dispersions were obtained as a result of phase exclusion of the DNA molecules from aqueous-salt-PEG-containing solutions. The CD spectra have shown cholesteric and hexagonal packing of the DNA in single dispersion particles at room temperature. The phase transition of the hexagonal → the “re-entrant” cholesteric packing of DNA takes place at elevated temperature. The texture of the “re-entrant” phase does not demonstrate attributes of DNA cholesteric phase. Alternative reasons of such discrepancy are discussed in the presented Letter.

In this work we reconsider the problem discussed by Caldeira and Leggett (CL), and generalize their results for a quantum oscillator coupled bilinearly to a reservoir with dense discrete spectrum of harmonic oscillators. We show that for such systems dynamic evolution of any state of the CL Hamiltonian consists of recurrence cycles with partial revivals of the initial state amplitude. This revival or Loschmidt echo appears in each cycle due to reverse (from the reservoir) transitions (not existing in the limit of a macroscopic bath). Width and number of the Loschmidt echo components increase with the recurrence cycle number, eventually leading to irregular, stochastic-like time evolution. Standard for continuous spectrum thermal bath CL dynamics dissipative dynamics (exponential decay) takes place only within the initial cycle. In terms of the effective CL Hamiltonian, where the reservoir degrees of freedom are integrated out, our results mean oscillatory (time periodic) behavior of the effective mass. Only in the initial cycle, we found the known for CL Hamiltonian exponential in time increase of the effective mass. We do believe that the basic ideas inspiring our work can be applied to a large variety of interesting nano-systems and molecular complexes., 5 pages, 2 figures

A simple model for ultrafast and efficient photoisomerization reactions is presented. In this model, the relevant region of the potential results from double crossing of two harmonic 1D diabatic potentials with opposite curvature. The eigenvalue problem is solved within a semiclassical approximation using the method of connection matrices, and the propagation of wave packets, expanded over these semiclassical eigenfunctions, is calculated. Within this model, fast double non-adiabatic transitions through both crossing points circumvent slow tunneling through the potential barrier. The extension to real systems makes this model relevant for the design of bi-stable photochromic materials.

We investigate possible ordered phases in a magnetic field in quasi-one-dimensional conductors ( Q 1 D ). Long ago [I.E. Dzyaloshinskii, E.I. Kats, JETP 28 (1969) 178] we found that sufficiently strong external magnetic field leads to instability of the Fermi state with an arbitrarily weak repulsion between the particles. In the present communication we generalize this idea and provide more details to assign a physical meaning to such a state. We show that without umklapp processes the found instability corresponds to antiferromagnetic (spin density wave) order, whereas umklapp processes favor to Cooper pairing.

A simple model for charge transfer in one-dimensional donor ( D ) – bridges ( B n ) – acceptor ( A ) systems is proposed. The model describes the charge transfer as the conjunction of two non-dichotomic (and probabilistically competing) mechanisms: direct D – A tunneling and incoherent hopping. An analytical expression of the charge transfer rate k ET is derived for this model, and seemingly contradictory observations of a strong followed by a weak influence of D – A distance on k ET are readily reproduced.

We discuss the weak crystallization of a liquid or a liquid crystal which is a first-order phase transition close to a continuous one. Such a phase transition is accompanied by the softening of the order parameter, describing the short-wavelength density modulation. The softening occurring in the vicinity of certain lines or surfaces in the reciprocal space induces a number of characteristic peculiarities of the transition. Quantitatively the softening may be characterized by the value of the gap, figuring in the expression for the pair correlator of fluctuations of the order parameter. The value of the gap is small near the phase transition temperature and possesses a complex behaviour. A peculiarity of the weak crystallization is the important role of fluctuations of the order parameter accounted for by a large phase volume of the fluctuations. We investigate the behaviour of the gap both in the framework of mean field approximation and with the effects of fluctuations taken into account. The theory enables us to construct the phase diagram of the system which appears to be rather reach for all the considered cases. In this diagram there arise (depending on the strength of the anisotropy and fluctuations) both crystalline phases of different symmetry and smectic, columnar and quasicrystalline phases. The dynamics of the order parameter is pure relaxational and the respective kinetic coefficient proves to be insensitive to the phase transition, therefore the relaxation time is inversely proportional to the gap. All physical characteristics of the system in some degree depend on the proximity to the transition point. For example the heat capacity and the compressibility of the system have singular contributions which may be expressed explicitly through the value of the gap. The most singular behaviour near the phase transition is inherent in the bulk viscosity coefficients determining the sound attenuation.

The peculiarities of the weak first-order phase transition smectic-A-crystal are studied. The analysis is made on the basis of the Landau expansion. The role of the fluctuations of the order parameter is considered. There are qualitative differences of the transition picture from the results of the mean-field theory. The phase diagram of the system is found for different values of the parameters entering the Landau expansion. The anomalous behaviour of the elasticity moduli, heat capacity and viscosity coefficients in the vicinity of the phase transition point is considered.

A second order smectic A-smectic C phase transition in a 3D space has been analyzed by the renorm-group technique. The Frank moduli considered in the one-loop approximation have been shown to remain stable, which is valid for the region 7 3 /τ) 2 (τ is the dimensionless vicinity to the transition point). The critical indices describing temperature-variation of the compression modulus of smectic layers, susceptibility and heat capacity are calculated. The indices of the Frank moduli are found in a two-loop approximation. The isotropic critical point is shown to be stable.

An effective action which makes it possible to take into account dynamic fluctuation effects in smectics-C is constructed. The effects associated with displacements of smectic layers are the most important. The influence of these fluctuations on the dynamics of the director is studied. The corresponding terms in the effective action are constructed and their renormalization is found. The renormalization spectrum of the director mode is obtained.