Showing papers by "Moscow State University published in 2004"

The current-phase relation in Josephson junctions

Abstract: This review provides a theoretical basis for understanding the current-phase relation (CPhiR) for the stationary (dc) Josephson effect in various types of superconducting junctions The authors summarize recent theoretical developments with an emphasis on the fundamental physical mechanisms of the deviations of the CPhiR from the standard sinusoidal form A new experimental tool for measuring the CPhiR is described and its practical applications are discussed The method allows one to measure the electrical currents in Josephson junctions with a small coupling energy as compared to the thermal energy A number of examples illustrate the importance of the CPhiR measurements for both fundamental physics and applications

Glycogen synthase kinase-3β mediates convergence of protection signaling to inhibit the mitochondrial permeability transition pore

Abstract: Environmental stresses converge on the mitochondria that can trigger or inhibit cell death. Excitable, postmitotic cells, in response to sublethal noxious stress, engage mechanisms that afford protection from subsequent insults. We show that reoxygenation after prolonged hypoxia reduces the reactive oxygen species (ROS) threshold for the mitochondrial permeability transition (MPT) in cardiomyocytes and that cell survival is steeply negatively correlated with the fraction of depolarized mitochondria. Cell protection that exhibits a memory (preconditioning) results from triggered mitochondrial swelling that causes enhanced substrate oxidation and ROS production, leading to redox activation of PKC, which inhibits glycogen synthase kinase-3beta (GSK-3beta). Alternatively, receptor tyrosine kinase or certain G protein-coupled receptor activation elicits cell protection (without mitochondrial swelling or durable memory) by inhibiting GSK-3beta, via protein kinase B/Akt and mTOR/p70(s6k) pathways, PKC pathways, or protein kinase A pathways. The convergence of these pathways via inhibition of GSK-3beta on the end effector, the permeability transition pore complex, to limit MPT induction is the general mechanism of cardiomyocyte protection.

Heavy fermion superconductivity and magnetic order in noncentrosymmetric CePt3Si.

Abstract: CePt3Si is a novel heavy fermion superconductor, crystallizing in the CePt3B structure as a tetragonally distorted low symmetry variant of the AuCu3 structure type. CePt3Si exhibits antiferromagnetic order at T(N) approximately 2.2 K and enters into a heavy fermion superconducting state at T(c) approximately 0.75 K. Large values of H(')(c2) approximately -8.5 T/K and H(c2)(0) approximately 5 T refer to heavy quasiparticles forming Cooper pairs. Hitherto, CePt3Si is the first heavy fermion superconductor without a center of symmetry.

SUSY Les Houches accord: interfacing SUSY spectrum calculators, decay packages, and event generators

Abstract: An accord specifying a unique set of conventions for supersymmetric extensions of the Standard Model together with generic file structures for 1) supersymmetric model specifications and input parameters, 2) electroweak scale supersymmetric mass and coupling spectra, and 3) decay tables is presented, to provide a universal interface between spectrum calculation programs, decay packages, and high energy physics event generators.

CompHEP 4.4 - Automatic Computations from Lagrangians to Events

Abstract: We present a new version of the CompHEP program (version 4.4). We describe shortly new issues implemented in this version, namely, simplification of quark flavor combinatorics for the evaluation of hadronic processes, Les Houches Accord-based CompHEP-PYTHIA interface, processing the color configurations of events, implementation of MSSM, symbolical and numerical batch modes, etc. We discuss how the CompHEP program is used for preparing event generators for various physical processes. We mention a few concrete physics examples for CompHEP-based generators prepared for the LHC and Tevatron.

Mechanism of stochastic resonance

Abstract: Stochastic resonance in an overdamped oscillator is considered theoretically. It has been shown that a seeming resonance is actually caused by a noise-induced change in the effective stiffness and damping factor with respect to a signal. For a certain noise intensity, the effective stiffness is minimal, which leads to a nonmonotonic variation of the output-signal amplitude as a function of noise intensity. It is substantial that the position of the minimum of the effective stiffness and its value depend strongly on the signal frequency. The results are compared with similar processes for vibrational resonance. Considerable differences between these phenomena are indicated.

Large–scale geographical variation confirms that climate change causes birds to lay earlier

Abstract: Advances in the phenology of organisms are often attributed to climate change, but alternatively, may reflect a publication bias towards advances and may be caused by environmental factors unrelated to climate change. Both factors are investigated using the breeding dates of 25 long-term studied populations of Ficedula flycatchers across Europe. Trends in spring temperature varied markedly between study sites, and across populations the advancement of laying date was stronger in areas where the spring temperatures increased more, giving support to the theory that climate change causally affects breeding date advancement.

Observation and properties of the X(3872) decaying to J/ψπ+π- in pp̄ collisions at √s = 1.96 TeV

Abstract: We report the observation of the X(3872) in the J/psipi(+)pi(-) channel, with J/psi decaying to mu(+)mu(-), in p (p) over bar collisions at roots=1.96 TeV. Using approximately 230 pb(-1) of data collected with the Run II D0 detector, we observe 522+/-100 X(3872) candidates. The mass difference between the X(3872) state and the J/psi is measured to be 774.9+/-3.1(stat)+/-3.0(syst) MeV/c(2). We have investigated the production and decay characteristics of the X(3872) and find them to be similar to those of the psi(2S) state.

Porous calcium carbonate microparticles as templates for encapsulation of bioactive compounds

Abstract: The paper describes the preparation and characterisation of porous calcium carbonate microparticles with an average size of 5 µm and their use for encapsulation of biomacromolecules. The average pore size of about 30–50 nm enables size selective and time-dependent permeation of different macromolecules. Layer-by-layer adsorption of polyelectrolytes into these particles followed by core dissolution leads to formation of interconnecting networks (matrix-like structure) made of polyelectrolyte complexes. The structure can be used for accumulation of bio-macromolecules, mainly proteins. Besides the inter-polyelectrolyte structure templated on porous CaCO3 microparticles the microgel particles (“ghost”) can also be made inside by complexing alginate and calcium. The adsorption of biomacromolecules inside the porous calcium carbonate particles is presumably regulated by electrostatic interactions on the microparticle surface within pores and protein–protein interactions. Protein adsorption into CaCO3 microparticle voids together with layer-by-layer assembly of biopolymers provide a way for fabrication of completely biocompatible microcapsules envisaging their use as biomaterials.

Prussian Blue based nanoelectrode arrays for H2O2 detection

Abstract: We propose to form nanoelectrode arrays by deposition of the electrocatalyst through lyotropic liquid crystalline templates onto inert electrode support. Whereas Prussian Blue is known to be a superior electrocatalyst in hydrogen peroxide reduction, carbon materials used as electrode support demonstrate only a minor activity. We report on the possibility for nanostructuring of Prussian Blue by its electrochemical deposition through lyotropic liquid crystalline templates, which is noticed from atomic force microscopy images of the resulting surfaces. The resulting Prussian Blue based nanoelectrode arrays in flow injection analysis mode demonstrate a sub-part-per-billion detection limit (1 × 10-8 M) and a linear calibration range starting exactly from the detection limit and extending over 6 orders of magnitude of H2O2 concentrations (1 × 10-8 to 1 × 10-2 M), which are the most advantageous analytical performances in hydrogen peroxide electroanalysis.

The Yana RHS site: humans in the Arctic before the last glacial maximum.

Abstract: A newly discovered Paleolithic site on the Yana River, Siberia, at 71°N, lies well above the Arctic circle and dates to 27,000 radiocarbon years before present, during glacial times. This age is twice that of other known human occupations in any Arctic region. Artifacts at the site include a rare rhinoceros foreshaft, other mammoth foreshafts, and a wide variety of tools and flakes. This site shows that people adapted to this harsh, high-latitude, Late Pleistocene environment much earlier than previously thought.

On the nature of EIT waves, EUV dimmings and their link to CMEs

Abstract: EIT waves and extreme-ultraviolet (EUV) dimmings attract particular attention as they frequently accompany Coronal Mass Ejections (CMEs) We present several examples of EIT waves and EUV dimmings with particular morphologies previously unreported in the literature We report for the first time an EIT wave in the Fe XV (284 A) bandpass of the SOHO/EIT instrument The observations of this event confirm previous results that an EIT wave is a purely coronal phenomenon that does not propagate in the transition region plasma Two EIT wave events initiated close to the solar limb are investigated, thus per- mitting us to see simultaneously the wave and the magnetic configuration of the CME These observations suggest that EIT wave can be regarded as a bimodal phenomenon The wave mode represents a wave-like propagating disturbance Its char- acteristic features are propagation of a bright front to large distances from dimming sites and quasi-circular appearance The eruptive mode is the propagation of a dimming and of an EIT wave as a result of successive opening of magnetic field lines during the CME lift-off It can be identified by noting the expansion of a dimming and the appearance of another dimming ahead of a bright front We reveal the temperature structure of the EUV dimmings that appeared after the classical EIT wave event on May 12, 1997, using differential emission measure (DEM) maps obtained through the analysis of images in four EIT bandpasses The part of the CME mass contained in the low corona observed by the EIT is estimated to be about 10 15 g It appears that around 50% of this total CME mass in the low corona is contained outside of transient coronal holes It is shown that at present it is difficult to reconcile all the observational facts into a coherent physical model In particular, the physical nature of the wave mode of EIT waves remains elusive

Detector description and performance for the first coincidence observations between LIGO and GEO

Abstract: For 17 days in August and September 2002, the LIGO and GEO interferometer gravitational wave detectors were operated in coincidence to produce their first data for scientific analysis. Although the detectors were still far from their design sensitivity levels, the data can be used to place better upper limits on the flux of gravitational waves incident on the earth than previous direct measurements. This paper describes the instruments and the data in some detail, as a companion to analysis papers based on the first data.

Biosensors for life quality. Design, development and applications

Abstract: Biosensors, combining a selective biological recognition element and a sensitive transducer, are versatile analytical tools applied more and more in different fields, such as medicine, food quality and safety control, and environment pollution monitoring. They are expected to play an increasingly important role in the improvement of life quality. In this context, the present work covers recent approaches in design and development of biosensors applied for analysis of real samples of medical, environmental or industrial relevance. The described sensors meet the sensitivity, selectivity, and response time required by their applications. Moreover, they are designed to avoid contamination of the monitored systems with undesirable components and to minimise the damage of living organisms (when it comes to in vivo monitoring). (C) 2004 Elsevier B.V. All rights reserved. (Less)

The twilight of Heliozoa and rise of Rhizaria, an emerging supergroup of amoeboid eukaryotes

Abstract: Recent molecular phylogenetic studies revealed the extraordinary diversity of single-celled eukaryotes. However, the proper assessment of this diversity and accurate reconstruction of the eukaryote phylogeny are still impeded by the lack of molecular data for some major groups of easily identifiable and cultivable protists. Among them, amoeboid eukaryotes have been notably absent from molecular phylogenies, despite their diversity, complexity, and abundance. To partly fill this phylogenetic gap, we present here combined small-subunit ribosomal RNA and actin sequence data for the three main groups of “Heliozoa” (Actinophryida, Centrohelida, and Desmothoracida), the heliozoan-like Sticholonche, and the radiolarian group Polycystinea. Phylogenetic analyses of our sequences demonstrate the polyphyly of heliozoans, which branch either as an independent eukaryotic lineage (Centrohelida), within stramenopiles (Actinophryida), or among cercozoans (Desmothoracida), in broad agreement with previous ultrastructure-based studies. Our data also provide solid evidence for the existence of the Rhizaria, an emerging supergroup of mainly amoeboid eukaryotes that includes desmothoracid heliozoans, all radiolarians, Sticholonche, and foraminiferans, as well as various filose and reticulose amoebae and some flagellates.

Observation of an Exotic Baryon with S=+1 in Photoproduction from the Proton

Abstract: The reaction {gamma}p {yields} {pi}{sup +} K{sup -} K{sup +}n was studied at Jefferson Lab using a tagged photon beam with an energy range of 3-5.47 GeV. A narrow baryon state with strangeness S = +1 and mass M = 1555 {+-} 10 MeV/c{sup 2} was observed in the nK{sup +} invariant mass spectrum. The peak's width is consistent with the CLAS resolution (FWHM = 26 MeV/c{sup 2}), and its statistical significance is 7.8 {+-} 1.0 {sigma}. A baryon with positive strangeness has exotic structure and cannot be described in the framework of the naive constituent quark model. The mass of the observed state is consistent with the mass predicted by a chiral soliton model for the {Theta}{sup +} baryon. In addition, the pK{sup +} invariant mass distribution was analyzed in the reaction {gamma} p {yields} K{sup -} K{sup +}p with high statistics in search of doubly-charged exotic baryon states. No resonance structures were found in this spectrum.

Surface chemistry of nanodiamonds

Abstract: The experimental data available in the literature and the results obtained by the author in research into the structure of nanodiamonds and the physicochemical and chemical properties of their surface are generalized. An account is given of the problems concerning the chemical state and modification of the nanodiamond surface in gaseous and liquid media and the infiuence of modification on the sorption and catalytic properties of nanodiamonds, their compactibility, and sintering. The similarity and difference in the behavior of nanodiamonds and diamond macrocrystals in oxidation processes are discussed. The activation energies of oxidation of nanodiamonds by different reagents are determined in the absence and presence of catalysts.

Anabaena sensory rhodopsin: a photochromic color sensor at 2.0 A.

Abstract: Microbial sensory rhodopsins are a family of membrane-embedded photoreceptors in prokaryotic and eukaryotic organisms. Structures of archaeal rhodopsins, which function as light-driven ion pumps or photosensors, have been reported. We present the structure of a eubacterial rhodopsin, which differs from those of previously characterized archaeal rhodopsins in its chromophore and cytoplasmic-side portions. Anabaena sensory rhodopsin exhibits light-induced interconversion between stable 13-cis and all-trans states of the retinylidene protein. The ratio of its cis and trans chromophore forms depends on the wavelength of illumination, thus providing a mechanism for a single protein to signal the color of light, for example, to regulate color-sensitive processes such as chromatic adaptation in photosynthesis. Its cytoplasmic half channel, highly hydrophobic in the archaeal rhodopsins, contains numerous hydrophilic residues networked by water molecules, providing a connection from the photoactive site to the cytoplasmic surface believed to interact with the receptor's soluble 14-kilodalton transducer.

Circulating vaccine-derived polioviruses: current state of knowledge

Abstract: Within the past 4 years, poliomyelitis outbreaks associated with circulating vaccine-derived polioviruses (cVDPVs) have occurred in Hispaniola (2000-01), the Philippines (2001), and Madagascar (2001-02). Retrospective studies have also detected the circulation of endemic cVDPV in Egypt (1988-93) and the likely localized spread of oral poliovirus vaccine (OPV)-derived virus in Belarus (1965-66). Gaps in OPV coverage and the previous eradication of the corresponding serotype of indigenous wild poliovirus were the critical risk factors for all cVDPV outbreaks. The cVDPV outbreaks were stopped by mass immunization campaigns using OPV. To increase sensitivity for detecting vaccine-derived polioviruses (VDPVs), in 2001 the Global Polio Laboratory Network implemented additional testing requirements for all poliovirus isolates under investigation. This approach quickly led to the recognition of the Philippines and Madagascar cVDPV outbreaks, but of no other current outbreaks. The potential risk of cVDPV emergence has increased dramatically in recent years as wild poliovirus circulation has ceased in most of the world. The risk appears highest for the type 2 OPV strain because of its greater tendency to spread to contacts. The emergence of cVDPVs underscores the critical importance of eliminating the last pockets of wild poliovirus circulation, maintaining universally high levels of polio vaccine coverage, stopping OPV use as soon as it is safely possible to do so, and continuing sensitive poliovirus surveillance into the foreseeable future. Particular attention must be given to areas where the risks for wild poliovirus circulation have been highest, and where the highest rates of polio vaccine coverage must be maintained to suppress cVDPV emergence.

Space-time parity violation and magnetoelectric interactions in antiferromagnets

Abstract: The properties of antiferromagnetic materials with violated space-time parity are considered. Particular attention is given to the bismuth ferrite BiFeO3 ferroelectric magnet. This material is distinguished from other antiferromagnets in that the inversion center is absent in its crystal and magnetic structures. This circumstance gives rise to diversified and unusual properties, namely, to the appearance of a spatially modulated spin structure and to the unique possibility of the linear magnetoelectric effect coexisting with a weak ferromagnetic moment. The magnetic-induced phase transitions accompanied by the suppression of the modulated spin structure and appearance of a number of new and unusual effects are considered. These are the linear magnetoelectric effect and the appearance of a toroidal moment and a weak ferromagnetic moment of the magnetoelectric nature.

Synopsis of the interstellar He parameters from combined neutral gas, pickup ion and UV scattering observations and related consequences

Abstract: A coordinated effort to combine all three methods that are used to determine the physical parameters of interstellar gas in the heliosphere has been undertaken. In order to arrive at a consistent parameter set that agrees with the observations of neutral gas, pickup ions and UV backscattering we have combined data sets from coordinated observation campaigns over three years from 1998 through 2000. The key observations include pickup ions with ACE and Ulysses SWICS, neutral atoms with Ulysses GAS, as well as UV backscattering at the He focusing cone close to the Sun with SOHO UVCS and at I AU with EUVE. For the first time also the solar EUV irradiance that is responsible for photo ionization was monitored with SOHO CELIAS SEM, and the He I 58.4 nm line that illuminates He was observed simultaneously with SOHO SUMER. The solar wind conditions were monitored with SOHO, ACE, and WIND. Based on these data the modeling of the interstellar gas and its secondary products in the heliosphere has resulted in a consistent set of interstellar He parameters with much reduced uncertainties, which satisfy all observations, even extended to earlier data sets. It was also established that a substantial ionization in addition to photo ionization, most likely electron impact, is required, with increasing relative importance closer to the Sun. Furthermore, the total combined ionization rate varies significantly with solar latitude, requiring a fully three dimensional and time dependent treatment of the problem.

Tomography of temperature gradient metamorphism of snow and associated changes in heat conductivity

Abstract: Temperature gradient metamorphism is one of the dominant processes changing the structure of natural dry snow. The structure of snow regulates the thermal and mechanical properties. Physical models and numerical simulations of the evolution of the snow cover require a thorough understanding of the interplay between structure and physical properties. The structure of snow and the heat conductivity were measured simultaneously without disturbance in a miniature snow breeder. The structure was measured by microtomography, and heat conductivity by measuring heat fluxes and temperatures. A temperature gradient from 25 to 100 K m−1 was applied to the snow. The snow density range of the samples varied from 150 to 500 kg m−3. The density in the observed volume remained constant during the experiments under temperature gradient conditions. The structure was analysed with respect to the size of typical ice structures and air pores, specific surface area, curvature and anisotropy of the ice matrix. The temporal changes in structure and heat conductivity are compared. The heat conductivity changed by as much as twice its initial value, caused by changes in structure and texture, but not due to changes in density. This shows the enormous importance of structure in the evolution of the heat conductivity. The observed changes are not in good agreement with the current understanding of the metamorphic process, because heat conductivity increased during temperature gradient metamorphism, instead of the expected decrease due to a shrinking of the bonds. We also observed a plateau in the evolution of the heat conductivity coefficient, which indicates a quasi-steady state of the structural evolution with respect to thermophysical properties of snow. Copyright © 2004 John Wiley & Sons, Ltd.

Photocatalytic properties of titania powders prepared by hydrothermal method

Abstract: Nanocrystalline titania with particle size ∼20–50 nm and specific surface area ∼20–80 m 2 g −1 is prepared by hydrothermal treatment of aqueous TiOSO 4 , H 2 TiO(C 2 O 4 ) 2 , and TiO(NO 3 ) 2 solutions. The photocatalytic behavior of synthesized TiO 2 powders is studied in the reaction of phenol photodegradation in water and optimal characteristics of these materials are explored. The best photocatalytic activity was observed for a mixture of rutile (15%) and anatase (85%) prepared by high-temperature hydrolysis of aqueous TiOSO 4 solution.