On the existence of soliton-like collective modes in liquid water at the viscoelastic crossover.

The problem of large-density variations in supercooled and ambient water has been widely discussed in the past years. Recent studies have indicated the possibility of nanometer-sized density variations on the subpicosecond and picosecond time scales. The nature of fluctuating density heterogeneities remains a highly debated issue. In the present work, we address the problem of possible association of such density variations with the dynamics of terahertz longitudinal acoustic-like modes in liquid water. Our study is based on the fact that the subpicosecond dynamics of liquid water are essentially governed by the structural relaxation. Using a mode coupling theory approach, we found that for typical values of parameters of liquid water, the dynamic mechanism coming from the combination of the structural relaxation process and the finiteness of the amplitude of terahertz longitudinal acoustic-like mode gives rise to a soliton-like collective mode on a temperature-dependent nanometer length scale. The characteristics of this mode are consistent with the estimates of the amplitudes and temperature-dependent correlation lengths of density fluctuations in liquid water obtained in experiments and simulations. Thus, the fully dynamic mechanism could contribute to the formation and dynamics of fluctuating density heterogeneities. The soliton-like collective excitations suggested by our analysis may be relevant to different phenomena connected with supercooled water and can be expected to be associated with some ultrafast biological processes.

Tidal variations of background ionizing radiation and circadian timing of the suprachiasmatic nucleus clock.

Recently, correlations of different physiological processes in humans with variations in the local lunisolar gravitational tide force have been observed under highly controlled laboratory conditions. Understanding of the physical nature of this phenomenon needs a comprehensive study of its possible molecular mechanisms. One of the possible timing cues is the strong periodic variation of the emanation fields of radon-222 and its progeny produced by tidal deformations of geological environment. In the present work, we argue that this variation could induce temporal modulation of radiation-induced bystander signaling pathways associated with fundamental regulators of gene expression in the suprachiasmatic nucleus clock.

Dynamic structure factor of a lipid bilayer in the presence of a high electric field.

The influence of a high average electric field (∼1 V/nm) in the hydrophobic interior of a bilayer lipid membrane on short-wavelength in-plane phononic motions of lipid chains is considered. The average electric field is assumed to be nearly constant on a picosecond time scale and a nanometer length scale. This field may be induced, for instance, by externally applied subnanosecond electric pulses or the membrane dipole potential. Using a generalized hydrodynamic approach, we derive a corresponding electrohydrodynamic model generalized to high wave numbers. In the considered approximation, all electric field effects are reduced only to a constant contribution to the generalized isothermal compressibility modulus. The corresponding dynamic structure factor for a lipid bilayer is derived. We show that due to polarization effects, the high field can critically impact the dynamics of longitudinal acousticlike modes at wave numbers near the major peak of the static structure factor. We estimate quantitatively that for typical lipid bilayers, transverse high electric fields can cause strong phonon energy softening, enhancement of phonon population, and formation of a gap in the dispersion of excitation frequency. The results obtained agree with simulations of the initiation of lipid bilayer electropores, suggesting that the proposed model reproduces the essential features of the field's impact on atomic density fluctuations. The proposed mechanism may have significant implications for the understanding of electroporation, passive molecular transport, and spontaneous pore formation in lipid bilayers.

Nonequilibrium dynamic structure factor of a lipid bilayer in the presence of an in-plane temperature gradient.

There is rapidly increasing evidence that nanoscale temperature heterogeneities are involved in important biological processes. Combining nanoheating and nanoscale thermosensors forms the basis of emerging unique methods of cell therapy, tissue engineering, and regenerative medicine. Understanding corresponding phenomena seems to require a mesoscopic nonequilibrium hydrodynamic theory. In this paper, a Langevin-type model of dynamics of phonon modes propagating along a bilayer lipid membrane in the presence of an in-plane temperature gradient is proposed. Corresponding quantitative estimates for the Brillouin components of the nonequilibrium dynamic structure factor and the equal-time longitudinal momentum-density correlation function for a lipid bilayer are obtained. The analysis reveals that for typical values of parameters of lipid bilayer, the longitudinal temperature gradient of the order of 5qK for wave numbers q from 0.01 to 1nm^{-1} induces significant asymmetry of the Brillouin components of the dynamic structure factor and long-range spatial correlations in the plane of the bilayer. The corresponding membrane temperature gradients seem to be typical or achievable for cellular processes responsible for intracellular temperature variations and such external physical impacts as high-intensity electromagnetic pulses or heating of membrane-associated nanoparticles.

[Tidal variations of radon activity as a possible factor for synchronization of biological processes].

Possible scenarios for synchronization of some biological processes with variations in Lunar-Solar gravitational tide acceleration, based on the trigger influence of the tidal force on geological environment and the relevant modulation of the emanation and activity fields of radon and other radioactive elements, are considered. Mechanisms and models of sensitivity of biological systems to the tidal variations of natural background radiation, including mitochondrial permeability transition, generation of reactive oxygen species and reactive nitrogen species, bystander factors, secondary biogenic radiation, modulation of cell signaling and rhythmic gene expression, are discussed.

[The Kupershtokh-Medvedev electrostrictive instability as possible mechanism of initiation of phase transitions, domains and pores in lipid membranes and influence of microwave irradiation on cell].

One of the possible mechanisms of initiation of local phase transitions and formation of nonuniform structure of biological and model lipid membranes is suggested. It is based on anisotropic electrohydrodynamic instability of Kupershtokh and Medvedev in strong electric field relative to density perturbations. This mechanism may clarify initial stages of formation of membrane domains and pores, some aspects of cell signalization and influence of microwave irradiation of nonthermal intensity on living organisms.