Showing papers by "Russian Academy of Sciences published in 1990"

Cold denaturation of proteins.

Abstract: This article summarizes all experimental facts concerning the cold denaturation of single-domain, multi-domain, and multimeric globular proteins in aqueous solutions with and without urea and guanidine hydrochloride. The facts obtained by various experimental techniques are analyzed thermodynamically and it is shown that the cold denaturation is a general phenomenon caused by the very specific and strongly termperature-dependent interaction of protein nonpolar groups with water. Hydration of these groups, in contrast to expectations, is favorable thermodynamically, i.e., the Gibbs energy of hydration is negative and increases in magnitude at a temperature decrease. As a result, the polypeptide chain, tightly packed in a compact native structure, unfolds at a sufficiently low temperature, exposing internal nonpolar groups to water. The reev-aluation of the hydration effect on the base of direct calorimetric studies of protein denaturation and of transfer of non-polar compounds into water leads to r...

Diamond inclusions in garnets from metamorphic rocks: a new environment for diamond formation

Abstract: DIAMONDS commonly occur in kimberlites, lamproites and alluvial sediments derived from these rocks. More recently, diamonds (or their graphite pseudomorphs) have been discovered in ultramafic massifs1 and picrites2. Here we report the occurrence of diamonds in situ in crustal rocks: highly retrograded high-pressure metamorphic garnet–pyroxene and pyroxene–carbonate–garnet rocks, biotite gneisses and schists from the Kokchetav massif, northern Kazakhstan, USSR. The diamonds are cubo-octahedral, averaging 12 μm in size, and occur in zircons, and with euhedral graphite as inclusions in unzoned garnets. We believe that the zircon and garnet matrices protected these diamonds from retrogressive transformation to graphite. Mica, rutile, titanite, clinopyroxene, kyanite and zircon also occur as inclusions in garnet, often intergrown with the diamonds. Equilibration relations of inclusions and host garnets indicate that both diamonds and graphite crystallized from a fluid phase under static conditions at pressures of ⩾40 kbar and temperatures >900–1,000 °C.

Quantitative IR spectrophotometry of peptide compounds in water (H2O) solutions. I. Spectral parameters of amino acid residue absorption bands.

Abstract: Infrared spectra of the amino acid residues in H2O solution have been obtained in the 1800-1400-cm-1 region. It has been established that amino acid residues of arginine, asparagine, glutamine, aspartic and glutamic acids, lysine, tyrosine, histidine, and phenylalanine have intensive absorption in this spectral region. Infrared spectra for a set of model compounds have been measured. On the basis of these data, spectral parameters of amino acid residue absorption bands have been determined.

Common features of protein unfolding and dissolution of hydrophobic compounds

Abstract: Protein unfolding and the dissolution of hydrophobic compounds (including solids, liquids, and gases) in water are characterized by a linear relation between entropy change and heat capacity change. The same slope is found for various classes of compounds, whereas the intercept depends on the particular class. The feature common to these processes is exposure of hydrophobic groups to water. These observations make possible the assignment of the heat capacity change to hydrophobic solvation and lead to the description of protein stability in terms of a hydrophobic and a nonhydrophobic contribution. A general representation of protein stability is given by the heat capacity change and the temperature.

Palaeoclimatological and chronological implications of the Vostok core dust record

Abstract: THE2,083-m Vostok ice core recovered by the Soviet Antarctic expeditions has provided much information of climatic and environmental interest, for a period covering a full glacial–inter-glacial cycle1–6. Here we present and discuss the dust record obtained down to 2,202 m, the final depth to which this core was extended in 1986. First, we document the fact that major changes in aeolian deposits, as recorded in the Vostok core, appear to be of global significance and confirm the existence of a link between high-latitude aeolian deposits and the Earth's orbital parameters7,8. Second, we propose atmospheric dust as a strati-graphic marker to compare timing with other records of palaeocli-mate, and use the magnetic-susceptibility profile measured along the RC11-120 Indian Ocean core9 for this purpose, assuming that major dust events correspond to common aeolian inputs. This approach indicates that the Vostok and marine records were roughly in phase at the previous glacial–interglacial transition.

Mean fields and fluctuation moments in unstably stratified turbulent boundary layers

Abstract: The earliest results concerning the turbulence structure in a turbulent boundary layer with very unstable thermal stratification are due to Prandtl (1932). These results were developed further and made more precise by Obukhov (1946, 1960), Monin & Obukhov (1954) and Priestley (1954, 1955, 1956, 1960). All of these authors dealt with a surface layer of the Earth's atmosphere on hot summer days. Such a layer is the most easily accessible example of an unstably stratified boundary layer and it will be the main concern in this paper too. The theoretical predictions by the above-mentioned authors seemed at first to be confirmed by the available experimental data but in the late 1960s it became clear that at least some of the predictions disagreed strongly with the experimental information.A more elaborate theory was proposed by Betchov & Yaglom (1971) who used a suggestion of Zilitinkevich (1971). According to this theory, within an unstably stratified boundary layer there are three special sublayers where turbulence structure is self-preserving and obeys rather simple power laws. The new theory explained the disagreement between some of the deductions from the old theory and the data. However, the data available in 1971 were insufficient for the confirmation of the new theory and it was even supposed by Betchov & Yaglom (1971) that their theory could not be applied to atmospheric surface layers on hot summer days.Much new experimental data concerning unstably stratified boundary layers has been obtained in recent years; in particular, extensive experimental information was collected during the summers of 1981–1987 at the Tsimlyansk Field Station of the Moscow Institute of Atmospheric Physics. This paper is a survey of the deductions from the theory by Betchov & Yaglom which concern the mean fields and the one-point fluctuation moments in unstably stratified boundary layers, and a comparison of these deductions with the data available in 1989. It is shown that the data agree more or less satisfactorily with the theoretical predictions and permit one to obtain estimates for a number of coefficients that enter the theoretical equations.

Optical-damage-resistant LiNbO(3):Zn crystal.

Abstract: Zinc doping is shown to reduce the photorefraction in LiNbO3:Zn. The damage-resistant crystal LiNbO3:Zn has demonstrated a conversion efficiency of approximately 50% for frequency doubling of 1.06-μm radiation. The dependence of optical characteristics on the ZnO concentration in the melt reveals a sharp change of the optical properties at the threshold concentration of 4–6 mol % Zn. The optical and nonlinear-optical data of LiNbO3:Zn are similar to those of LiNbO3:Mg, but the former shows better optical performance.

Quantitative IR spectrophotometry of peptide compounds in water (H2O) solutions. II. Amide absorption bands of polypeptides and fibrous proteins in α‐, β‐, and random coil conformations

Abstract: Infrared spectra of poly(D,L-alanine), poly(L-glutamic acid), poly(L-lysine), silk fibroin, and tropomyosin have been registered for various conformations of the polypeptide chain. Assuming additivity of the main- and side-chain absorption, spectral parameters of amide I and II absorption bands corresponding to alpha-, beta-, and random coil conformations have been derived. The amide I band parameters for H2O and D2O have been compared.

Loop averages and partition functions in U(N) gauge theory on two-dimensional manifolds

Abstract: Loop averages and partition functions in the U(N) gauge theory are calculated for loops without intersections on arbitrary two-dimensional manifolds including nonorientable ones. The physical quantities are directly expressed through geometrical characteristics of a manifold (areas enclosed by loops and the genus) and gauge group parameters (Casimir eigenvalues and dimensions of the irreducible representations). It is shown that, from the physical quantities’ point of view, non-orientability of the manifold is equivalent to its non-compactness.

Behavioral indicators of sublethal toxicity in rainbow trout

Abstract: Four measures of behavior-spontaneous swimming activity, swimming capacity, feeding behavior, and vulnerability to predation-were assessed as indicators of sublethal toxicity in rainbow trout (Oncorhynchus mykiss) in 96-hr exposures to sublethal concentrations of six agricultural chemicals: carbaryl, chlordane, dimethylamine salt of 2,4-dichlorophenoxyacetic acid (2,4-DMA), tributyl phosphorotrithioate (DBF 1), methyl parathion, and pentachlorophenol. After exposures, behavioral changes consistently demonstrated sublethal toxicity, but effects on specific behaviors varied with contaminants and their concentrations were altered by the water quality criterion concentration for chlordane (2 μg/L), and at a concentration of DEF (5 μg/L) that had previously been shown to inhibit growth and survival after a 90-day exposure. Feeding behavior was inhibited most by exposure to DEF, 2,4-DMA, and methyl parathion. Vulnerability to predation was heightened most by exposure to carbaryl and pentachlorophenol. Although all chemicals inhibited spontaneous swimming activity, only carbaryl, DEF, and 2,4-DMA influenced swimming capacity.

Wess-Zumino-Witten model as a theory of free fields

Abstract: The free field representation or "bosonization" rule1 for Wess-Zumino-Witten model (WZWM) with arbitrary Kac-Moody algebra and arbitrary central charge is discussed. Energy-momentum tensor, arising from Sugawara construction, is quadratic in the fields. In this way, all known formulae for conformal blocks and correlators may be easily reproduced as certain linear combinations of correlators of these free fields. Generalization to conformal blocks on arbitrary Riemann surfaces is straightforward. However, projection rules in the spirit of Ref. 2 are not specified. The special role of βγ systems is emphasized. From the mathematical point of view, the construction involved represents generators of Kac-Moody (KM) algebra in terms of generators of a Heisenberg one. If WZW Lagrangian is considered as d−1 of Kirillov form on an orbit of KM algebra,3 then the free fields of interest (i.e. generators of the Heisenberg algebra) diagonalize Kirillov form and the action. Reduction of KM algebra within the same construction should naturally lead to arbitrary coset models.

Implications of thermodynamics of protein folding for evolution of primary sequences.

Abstract: NATURAL proteins exhibit essentially two-state thermodynamics, with one stable fold that dominates thermodynamically over a vast number of possible folds, a number that increases exponentially with the size of the protein. Here we address the question of whether this feature of proteins is a rare property selected by evolution or whether it is in fact true of a significant proportion of all possible protein sequences. Using statistical procedures developed to study spin glasses, we show that, given certain assumptions, the probability that a randomly synthesized protein chain will have a dominant fold (which is the global minimum of free energy) is a function of temperature, and that below a critical temperature the probability rapidly increases as the temperature decreases. Our results suggest that a significant proportion of all possible protein sequences could have a thermodynamically dominant fold.

Geochemistry of the Siberian Trap of the Noril'sk area, USSR, with implications for the relative contributions of crust and mantle to flood basalt magmatism

Abstract: The sequence investigated of the Siberian Trap at Noril'sk, USSR, consists of at least 45 flows that have been divided into six lava suites. The lower three suites consist of alkalic to subalkalic basalts (the Ivakinsky suite), overlain by nonporphyritic basalts (the Syverminsky suite), and porphyritic and picritic basalts (the Gudchikhinsky suite). The upper three suites are tholeiitic. The uppermost 750 m of dominantly non-porphyritic basalt belong to the Mokulaevsky suite and are characterized by a nearly constant Mg number (0.54–0.56), SiO2 (48.2–49.1 wt%), Ce (12–18 ppm), and Ce/Yb (5–8). The underlying 1100 m of dominantly porphyritic basalt belong to the Morongovsky and Nadezhdinsky suites. There is a continuous increase in SiO2 (48.1–55.2 wt%), Ce (12–41 ppm), and Ce/Yb (5–18) from the top of the Mokulaevsky to the base of the Nadezhdinsky with little change in the Mg number (0.53–0.59). Mokulaevsky magmas have trace element signatures similar to slightly contaminated transitional type mid-ocean ridge basalts. The change in major and trace element geochemistry in the upper three suites is consistent with a decline in the degree of anatexis and assimilation of tonalitic upper crust by Mokulaevsky magma. The Nadezhdinsky and underlaying lavas thicken within and thus appear to be related to an elongate basin centred on the Noril'sk-Talnakh mining camp. The Mokulaevsky and Morongovsky lavas thicken to the east and appear to be related to a basin centred more than 100 km to the east of the Noril'sk region; these magmas may have risen up out of a different conduit system.

Cauchy problem in spacetimes with closed timelike curves.

Abstract: The laws of physics might permit the existence, in the real Universe, of closed timelike curves (CTC’s). Macroscopic CTC’s might be a semiclassical consequence of Planck-scale, quantum gravitational, Lorentzian foam, if such foam exists. If CTC’s are permitted, then the semiclassical laws of physics (the laws with gravity classical and other fields quantized or classical) should be augmented by a principle of self-consistency, which states that a local solution to the equations of physics can occur in the real Universe only if it can be extended to be part of a global solution, one which is well defined throughout the (nonsingular regions of) classical spacetime. The consequences of this principle are explored for the Cauchy problem of the evolution of a classical, massless scalar field Φ (satisfying □Φ=0) in several model spacetimes with CTC’s. In general, self-consistency constrains the initial data for the field Φ. For a family of spacetimes with traversible wormholes, which initially possess no CTC’s and then evolve them to the future of a stable Cauchy horizon scrH, self-consistency seems to place no constraints on initial data for Φ that are posed on past null infinity, and none on data posed on spacelike slices which precede scrH. By contrast, initial data posed in the future of scrH, where the CTC’s reside, are constrained; but the constraints appear to be mild in the sense that in some neighborhood of every event one is free to specify initial data arbitrarily, with the initial data elsewhere being adjusted to guarantee self-consistent evolution. A spacetime whose self-consistency constraints have this property is defined to be ‘‘benign with respect to the scalar field Φ.’’ The question is posed as to whether benign spacetimes in some sense form a generic subset of all spacetimes with CTC’s. It is shown that in the set of flat, spatially and temporally closed, 2-dimensional spacetimes the benign ones are not generic. However, it seems likely that every 4-dimensional, asymptotically flat space-time that is stable and has a topology of the form R×(S-one point), where S is a closed 3-manifold, is benign. Wormhole spacetimes are of this type, with S=S^1×S^2. We suspect that these types of self-consistency behavior of the scalar field Φ are typical for noninteracting (linearly superposing), classical fields. However, interacting classical systems can behave quite differently, as is demonstrated by a study of the motion of a hard-sphere billiard ball in a wormhole spacetime with closed timelike curves: If the ball is classical, then some choices of initial data (some values of the ball’s initial position and velocity) give rise to unique, self-consistent motions of the ball; other choices produce two different self-consistent motions; and others might (but we are not yet sure) produce no self-consistent motions whatsoever. By contrast, in a path-integral formulation of the nonrelativistic quantum mechanics of such a billiard ball, there appears to be a unique, self-consistent set of probabilities for the outcomes of all measurements. This paper’s conclusion, that CTC’s may not be as nasty as people have assumed, is reinforced by the fact that they do not affect Gauss’s theorem and thus do not affect the derivation of global conservation laws from differential ones. The standard conservation laws remain valid globally, and in asymptotically flat, wormhole spacetimes they retain a natural, quasilocal interpretation.

Ultrashort-pulse propagation in optical fibers

Abstract: A more exact model is suggested for the description of nonlinear light propagation in fibers. In addition to the previously discussed self-phase modulation, parametric, dispersion, self-steepening, and Raman self-scattering effects, this model also takes into account the Stokes losses associated with the material excitation, the dependence of nonlinear effects on the light frequency, and the frequency dependence of the fiber mode area. The self-steepening effect is taken into account more correctly in comparison with previous models. The effects influence considerably the femtosecond soliton propagation. The model is generalized for the case of various fiber dispersion properties along the fiber length. The possibility of obtaining high-quality pulses of less than 15-fsec duration by compression of fundamental solitons with approximately 100-fsec duration in fibers with slowly decreasing dispersion is shown.

Aspera/Phobos measurements of the ion outflow from the MARTIAN ionosphere

Abstract: This report reviews the first results on the ionospheric ion outflow in the Martian magnetosphere by the ion composition experiment ASPERA on Phobos-2. The measurements show that Mars is characterized by a strong loss of plasma from its topside ionosphere. This loss results from both ion pick-up due to mass-loading of the solar wind in the Martian boundary layer and an acceleration mechanism, quite similar to that observed above the Earth's auroral oval, providing intense ionospheric O+ beams of energies up to several keV. A preliminary estimate of the ionospheric outflow from Mars indicates that the planet at present is losing oxygen at a rate of ≈3·1025 ions/s. This corresponds to an evacuation of its present total atmospheric oxygen content (contained in CO2 and O2) in less than 100 million years.

Universal Form of the Low-Energy (2 to 10 meV) Vibrational Spectrum of Glasses

Abstract: By means of inelastic cold neutron scattering the density of vibrational states (DVS) has been determined for a series of vitreous materials: SiO2, As2S3 and metallic glass Mg70Zn30. In the low-energy range of the spectrum (E ~ (2 ÷ 10) meV) for these materials DVS reveals a universal, but non-Debye form. The data obtained are compared to different models. A comparison with the Raman scattering data provides the spectral dependence for the coupling of the light to the vibrational excitations.

Three types of Photosystem II photoinactivation : I. Damaging processes on the acceptor side.

Abstract: Oxygen evolving photosystem II particles were exposed to 100 and 250 W m−2 white light at 20°C under aerobic, anaerobic and strongly reducing (presence of dithionite) conditions. Three types of photoinactivation processes with different kinetics could be distinguished: (1) The fast process which occurs under strongly reducing (t 1/2≅1–3 min) and anaerobic conditions (t 1/2≅4–12 min). (2) The slow process (t 1/2≅15–40 min) and (3) the very slow process (t 1/2>100 min), both of which occur under all three sets of conditions. The fast process results in a parallel decline of variable fluorescence (F v) and of Hill reaction rate, accompanied by an antiparallel increase of constant fluorescence (F o). We assume that trapping of QA in a negatively charged stable state, (QA −)stab, is responsible for the effects observed. The slow process is characterized by a decline of maximal fluorescence (F m). In presence of oxygen this decline is due to the well known disappearance of F v which proceeds in parallel with the inhibition of the Hill reaction; F o remains essentially constant. Under anaerobic and reducing conditions the decline of F m represents the disappearance of the increment in F o generated by the fast process. We assume that the slow process consists in neutralization of the negative charge in the domain of QA in a manner that renders QA non-functional. The charge separation in the RC is still possible, but energy of excitation becomes thermally dissipated. The very slow photoinactivation process is linked to loss of charge separation ability of the PS II RC and will be analyzed in a forthcoming paper.

THREE-LOOP QCD CORRECTION TO THE CORRELATOR OF THE QUARK SCALAR CURRENTS AND Γtot(H0 → HADRONS)

Abstract: Analytical results of a re-evaluation of the massless three-loop next-to-leading QCD correction to the correlator of the quark scalar currents and Γtot(H0 → hadrons) are presented. The states of some other QCD perturbative results is discussed.

Relativistic multiwave Cherenkov generators

Abstract: A review of research on relativistic multiwave Cherenkov generators (MWCGs) is provided. Presented is the linear theory of these devices, allowing a detailed description of the multiwave interaction of a relativistic electron beam with an electromagnetic field in an electrodynamic superdimensional MWCG system. The results of theoretical research on the starting parameters of generation, power flows, and the structure of the radiated field in a MWCG of a 3-cm-wavelength band are reported. The experiments on obtaining and investigating high-power pulses of microwave radiation in a MWCG of 3-cm- and 8-mm-wavelength bands are described. In particular, the results of research on a MWCG with the power of 15 GW in a 3-cm-wavelength band and the power of 3 GW in a 8-mm-wavelength band are presented. The results of research on the spatial and temporal coherence of such generator radiation are reported. The possibility of conversion of the MWCG wavefield into a linearly polarized one is discussed. The investigation of the processes associated with the generation of high-power microwave radiation in a MWCG is described. >

Relative phase destabilization during interlimb coordination: the disruptive role of kinesthetic afferences induced by passive movement.

Abstract: The disruption of three patterns of two-limb coordination, involving cyclical flexion-extension movements performed in the same or in different directions, was investigated through application of passive movement to a third limb by the experimenter. The three patterns referred to the homologous, homolateral, and heterolateral (diagonal) limb combinations which were performed in the sagittal plane. The passive movement involved a spatiotemporal trajectory that differed from the movements controlled actively. Even though subjects were instructed to completely ignore the passive limb movement, the findings of experiment 1 demonstrated a moderate to severe destabilization of the two-limb patterns, as revealed by analyses of power spectra, relative phase, cycle duration, and amplitude. This disruption was more pronounced in the homolateral and heterolateral than in the homologous effector combinations, suggesting stronger coupling between homologous than nonhomologous limb pairs. Moreover, passive mobilization affected antiphase (nonisodirectional) movements more than inphase (isodirectional) movements, pointing to the differential stability of these patterns. Experiment 2 focused on homolateral coordination and demonstrated that withdrawal of visual information did not alter the effects induced by passive movement. It was therefore hypothesized that the generation of extra kinesthetic afferences through passive limb motion was primarily responsible for the detriment in interlimb coordination, possibly conflicting with the sensory information accompanying active movement production. In addition, it was demonstrated that the active limbs were more affected by their homologous passive counterpart than by their non-homologous counterpart, favoring the notion of “specific” interference. The findings are discussed in view of the potential role of kinesthetic afferences in human interlimb coordination, more specifically the preservance of relative phasing through a kinesthetic feedback loop.