Vladimir V. Shuvalov

Astronomical and physical aspects of the Chelyabinsk event (February 15, 2013)

Various observational data including infrasound, seismic, optical (onboard) monitoring, ground video and photo records, and evidence from witnesses of the Chelyabinsk event on February 15, 2013, have been analyzed. The extensive material gathered has provided a base for investigations of the physical properties of the object, the results of which are discussed. A bolide light curve is constructed, which shows a multiplicity of flashes. Estimations of the energy of the meteoroid explosion, which took place in the atmosphere at an altitude of about 23 km, show evidence of the formation of a high-power shock wave equivalent to 300–500 kilotons of TNT. The object diameter corresponding to this energy falls within the range 16–19 m. The trajectory of the meteor is outlined. It is preliminarily concluded that the Chelyabinsk meteorite was a representative the Apollo asteroid family.

Reaction pattern of photosystem II: oxidative water cleavage and protein flexibility.

This short communication addresses three topics of photosynthetic water cleavage in Photosystem II (PS II): (a) effect of protonation in the acidic range on the extent of the ‘fast’ ns kinetics of P680+· reduction by YZ, (b) mechanism of O–O bond formation and (c) role of protein flexibility in the functional integrity of PS II. Based on measurements of light-induced absorption changes and quasielastic neutron scattering in combination with mechanistic considerations, evidence is presented for the protein acting as a functionally active constituent of the water cleavage machinery, in particular, for directed local proton transfer. A specific flexibility emerging above a threshold of about 230 K is an indispensable prerequisite for oxygen evolution and plastoquinol formation.

Evidence that histidine forms a coordination bond to the A0A and A0B chlorophylls and a second H-bond to the A1A and A1B phylloquinones in M688HPsaA and M668HPsaB variants of Synechocystis sp. PCC 6803

The axial ligands of the acceptor chlorophylls, A(0A) and A(0B), in Photosystem I are the Met sulfur atoms of M688(PsaA) and M668(PsaB). To determine the role of the Met, His variants were generated in Synechocystis sp. PCC 6803. Molecular dynamics simulations on M688H(PsaA) show that there exist low energy conformations with the His coordinated to A(0A) and possibly H-bonded to A(1A). Transient EPR studies on M688H(PsaA) indicate a more symmetrical electron spin distribution in the A(1A) phyllosemiquinone ring consistent with the presence of an H-bond to the C1 carbonyl. Ultrafast optical studies on the variants show that the 150fs charge separation between P₇₀₀ and A(0) remains unaffected. Studies on the ns timescale show that 57% of the electrons are transferred from A(0A)(-) to A(1A) in M688H(PsaA) and 48% from A(0B)(-) to A(1B) in M668H(PsaB); the remainder recombine with P₇₀₀(+) with 1/e times of 25ns and 37ns, respectively. Those electrons that reach A(1A) and A(1B) in the branch carrying the mutation are not transferred to FX, but recombine with P₇₀₀(+) with 1/e times of ~15μs and ~5μs, respectively. Hence, the His is coordinated to A0 in all populations, but in a second population, the His may be additionally H-bonded to A(1). Electron transfer from A(0) to A(1) occurs only in the latter, but the higher redox potentials of A(0) and A(1) as a result of the stronger coordination bond to A(0) and the proposed second H-bond to A(1) preclude electron transfer to the Fe/S clusters.

Formation of spatial solitons and spatial shock waves in photorefractive crystals

An analytical model, which describes the drift and diffusion mechanisms for the formation of the nonlinear response (local and nonlocal nonlinearities) of photorefractive crystals on the microscopic level, is constructed. New types of stable self-consistent distributions of the light field intensity, i.e., spatial solitons, are found. The trajectories of their motion (self-bending) are calculated, and the possibility of observing a new nonlinear-optical effect in photorefractive crystals, viz., the formation of spatial shock waves, is demonstrated. The modulation instability appearing when plane waves propagate in photorefractive crystals is analyzed, and the characteristic spatial scales of the light field distribution formed as a result of self-interaction (fanning) are determined. The results of the analysis are confirmed by computer simulation data.

Chirped elliptically polarized waves in an isotropic gyrotropic nonlinear medium: approximate solution to the propagation problem

An approximate solution to the nonintegrable propagation problem for chirped elliptically polarized waves in an isotropic gyrotropic medium with local and non-local parts of the cubic nonlinear optical response and second order frequency dispersion has been obtained. Conditions for excitation of waves with periodic changes in the polarization state (chirped elliptically polarized cnoidal waves) and implementation of aperiodic propagation regimes similar to polarization ‘chaos’ have been determined.

Biharmonic pumping technique for YBaCuO energy spectrum research in the vicinity of the phase transition

Abstract The temperature dependence of η(Ω) (here η is the self-diffraction process efficiency, Ω is the frequency detuning of the biharmonic pumping components) for HTSC Y-Ba-Cu-O thin films in the vicinity of the superconductive transition point Θc has been investigated. It is shown that the specific “dip” in η(Ω) for temperatures Θ (1- Θ Θ C ) 1 2 (here kB is the Boltzmann constant) for the temperature range 80 K ⩽Θ⩽ΘC is correct A = 3.12+0.22-0.26 consistent with the BCS weak-coupling limit (A ≅3.06) and ΘC = 91.0+1.3-0.9 K have been found.

Particular periodic solutions to a nonintegrable system of Schrödinger nonlinear equations and their eigenvalues

Particular solutions to the general case of a nonintegrable system of Schrödinger nonlinear equations in the form of a family of cnoidal waves are found on the assumption of linear relationship between the squared moduli of the orthogonal components of a vector field. The domains of existence of solutions and the corresponding spectra of eigenvalues are determined.

Nonlinear spectroscopy of YBaCuO and Ni thin films by a biharmonic pumping technique

Abstract High temperature superconducting (HTSC) (YBaCuO, critical temperature Tc=87 K) and metal (Ni) thin films are investigated by a picosecond spectrometer with two tunable dye lasers. The selfdiffraction process efficiency η versus the biharmonic pumping component detuning Ω has been measured at temperatures Θ=300 and 80 K. For the HTSC films at Θ=80 K a well-defined dip on the disperion curve η(Ω) for − 10 > Ω > −50 cm−1 is found. The upper limit of the region of this dip corresponds to a value of 2Δ of the superconducting energy gap. At 10 cm −1 no such effect is found. In other respects all obtained dispersion curves resemble each other. These curves consist of a central peak ( η∼10 −7 , |Ω| × 10 cm −1 ) and wide wings ( η∼10 −9 , |Ω| > 10 cm −1 ) with a complex interference structure. The YBaCuO film resonances coincide with the phonon mode frequencies (120, 335 and 580 cm−1). It is also shown that the photoexcitation kinetics must consist of some components. The characteristic timme of the most “ultrafast” component below 5 fs has been estimated and a complex subpicosecond quantum beat presence has been predicted.

Stationary and monstationary nonlinear spectroscopy of GaSe

Abstract An effective complex investigation of semiconductors by means of nonlinear spectroscopy is reported. The main nonlinearity physical mechanisms are investigated and characteristic times of some relaxation processes are measured in GaSe at 293 K.

Spatial Solitons and Shock Waves in Photorefractive Crystals with Nonlocal Nonlinearity

An analytical model has been developed to describe both drift and diffusion mechanisms of nonlinear response (local and nonlocal components of nonlinearity) of photorefractive crystals (PRCs) on a microscopic level. Some types of stable self-consistent distributions of light intensity — bright and dark photorefractive spatial solitons — have been considered. Paths of their propagation (self-bending) have been calculated and a possibility of formation of a new type of soliton-like distributions — spatial shock waves — has been shown. Analysis of plane wave modulation instability has been performed and specific spatial scales of light distribution, resulting from self-action processes (fanning), have been calculated. All the analytical results have been confirmed using computer simulation.