Showing papers by "Moscow State University published in 1991"

RSFQ logic/memory family: a new Josephson-junction technology for sub-terahertz-clock-frequency digital systems

Abstract: Recent developments concerning the rapid single-flux-quantum (RSFQ) circuit family are reviewed. Elementary cells in this circuit family can generate, pass, memorize, and reproduce picosecond voltage pulses with a nominally quantized area corresponding to transfer of a single magnetic flux quantum across a Josephson junction. Functionally, each cell can be viewed as a combination of a logic gate and an output latch (register) controlled by clock pulses, which are physically similar to the signal pulses. Hand-shaking style of local exchange by the clock pulses enables one to increase complexity of the LSI RSFQ systems without loss of operating speed. The simplest components of the RSFQ circuitry have been experimentally tested at clock frequencies exceeding 100 GHz, and an increase of the speed beyond 300 GHz is expected as a result of using an up-to-date fabrication technology. This review includes a discussion of possible future developments and applications of this novel, ultrafast digital technology. >

Real surface area measurements in electrochemistry

Abstract: Electrode reaction rates and most double layer parameters are extensive quantities and have to be referred to the unit area of the interface. Knowledge of the real surface area of electrodes is therefore needed. Different methods have been proposed to normalize experimental data specifically with solid electrodes. Some of them are not sufficiently justified from a physical point of view. A few of them are definitely questionable. The purpose of this document is to scrutinize the basis on which the various methods and approaches rest, in order to assess their relevance to the specific electrochemical situation and, as far as possible, their absolute reliability

Discrete versions of some classical integrable systems and factorization of matrix polynomials

Abstract: Discrete versions of several classical integrable systems are investigated, such as a discrete analogue of the higher dimensional force-free spinning top (Euler-Arnold equations), the Heisenberg chain with classical spins and a new discrete system on the Stiefel manifold. The integrability is shown with the help of a Lax-pair representation which is found via a factorization of certain matrix polynomials. The complete description of the dynamics is given in terms of Abelian functions; the flow becomes linear on a Prym variety corresponding to a spectral curve. The approach is also applied to the billiard problem in the interior of anN-dimensional ellipsoid.

Colour transparency and scaling properties of nuclear shadowing in deep inelastic scattering

Abstract: We present the perturbative QCD analysis of nuclear shadowing in the deep inelastic scattering at smallx in terms of the spatial wave function ofq $$\bar q$$ fluctuations of virtual photons. The wave function formalism makes it quite obvious that shadowing is the scaling, rather than the higher twist, 1/Q 2, effect, contrary to a numerous recent claims. We demonstrate explicitly how the scaling shadowing comes from the large, hadronic, size quarkantiquark pairs even in the limit ofQ 2→∞, and why it should very slowly, ∞1/log (Q 2/m 2) decrease at very largeQ 2. We argue in favor of the scaling triple-pomeron contribution to the nuclear shadowing and present predictions for a cross section of diffraction dissociation of virtual photons and for the mass spectrum of diffraction excitation, which can be checked at HERA and Fermilab. We predict strikingly different scaling properties of diffraction dissociation and nuclear shadowing for the longitudinal and transverse photons. Our, numerial predictions for shadowing are in good agreement with the recent EMC data.

Universal R-matrix for quantized (super)algebras

Abstract: For quantum deformations of finite-dimensional contragredient Lie (super)algebras we give an explicit formula for the universalR-matrix. This formula generalizes the analogous formulae for quantized semisimple Lie algebras obtained by M. Rosso, A. N. Kirillov, and N. Reshetikhin, Ya. S. Soibelman, and S. Z. Levendorskii. Our approach is based on careful analysis of quantized rank 1 and 2 (super)algebras, a combinatorial structure of the root systems and algebraic properties ofq-exponential functions. We don't use quantum Weyl group.

Theory of single-electron charging of quantum wells and dots.

Abstract: Single-electron charging effects similar to those in small-area metallic tunnel junctions should take place in semiconductor heterostructures, in particular, small-area quantum wells. Our analysis shows that dc current-voltage characteristics of such a well should exhibit an interplay between single-electron charging and energy-quantization effects. Relative magnitude of the single-electron charging effects is determined by the same parameter which scales multielectron charging in the conventional (large-area) quantum wells.

Transition temperatures of superconductor-ferromagnet superlattices

Abstract: The transition temperature ${\mathit{T}}_{\mathit{c}}$ of superconductor-ferromagnet superlattices is calculated by solving exactly the Usadel equations. Characteristic ground-state configurations are predicted with nontrivial phase difference 0cphi\ensuremath{\le}\ensuremath{\pi} between neighboring superconducting layers. An unusual oscillatory dependence of ${\mathit{T}}_{\mathit{c}}$ on the ferromagnetic-layer thickness is obtained. For short-period superlattices it is found that the transition changes from second to first order. A comparison of theoretical results with experimental data for V/Fe superlattices is given.

Denaturation capacity: a new quantitative criterion for selection of organic solvents as reaction media in biocatalysis

Abstract: The process of reversible denaturation of several proteins (alpha-chymotrypsin, trypsin, laccase, chymotrypsinogen, cytochrome c and myoglobin) by a broad series of organic solvents of different nature was investigated using both our own and literature data, based on the results of kinetic and spectroscopic measurements. In all systems studied, the denaturation proceeded in a threshold manner, i.e. an abrupt change in catalytic and/or spectroscopic properties of dissolved proteins was observed after a certain threshold concentration of the organic solvent had been reached. To account for the observed features of the denaturation process, a thermodynamic model of the reversible protein denaturation by organic solvents was developed, based on the widely accepted notion that an undisturbed water shell around the protein globule is a prerequisite for the retention of the native state of the protein. The quantitative treatment led to the equation relating the threshold concentration of the organic solvent with its physicochemical characteristics, such as hydrophobicity, solvating ability and molecular geometry. This equation described well the experimental data for all proteins tested. Based on the thermodynamic model of protein denaturation, a novel quantitative parameter characterizing the denaturing strength of organic solvents, called the denaturation capacity (DC), was suggested. Different organic solvents, arranged according to their DC values, form the DC scale of organic solvents which permits theoretical prediction of the threshold concentration of any organic solvent for a given protein. The validity of the DC scale for this kind of prediction was verified for all proteins tested and a large number of organic solvents. The experimental data for a few organic solvents, such as formamide and N-methylformamide, did not comply with equations describing the denaturation model. Such solvents form the group of so-called 'bad' solvents; reasons for the occurrence of 'bad' solvents are not yet clear. The DC scale was further extended to include also highly nonpolar solvents, in order to explain the well-known ability of enzymes to retain catalytic activity and stability in biphasic systems of the type water/water-immiscible organic solvent. It was quantitatively demonstrated that this ability is accounted for by the simple fact that nonpolar solvents are not sufficiently soluble in water to reach the inactivation threshold concentration.

Quantum Berezinian and the classical capelli identity

Abstract: We study a superanalogue of the Yangian of the Lie algebra gl m ℂ. We apply our constructions to invariant theory.

Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. II - An intensive study of NGC 5548 at optical wavelengths

Abstract: A large, international program of ground-based optical spectroscopy and photometry of the variable Seyfert 1 galaxy NGC 5548 undertaken in support of an IUE monitoring campaign is described. This contribution presents the data base and describes the methods used to correct for systematic differences between spectra from different sources. Optical continuum and H-beta emission-line light curves are derived from the spectra. The behavior of the optical continuum is qualitatively the same as the behavior of the ultraviolet continuum. Cross-correlation of the ultraviolet and optical continuum measurements does not reveal any significant lag between them. The h-beta emission-line variations show the same basic pattern as seen in the continuum and ultraviolet emission lines, with H-beta lagging behind the continuum by about 20 days. This is significantly larger than the about 10 day lag deduced for Ly-alpha.

Effect of structural and physico-chemical features of cellulosic substrates on the efficiency of enzymatic hydrolysis

Abstract: Effects of major physicochemical and structural parameters of cellulose on the rate and degree of its enzymatic hydrolysis were tested with cellulosic materials from various sources Some different pretreatments were: mechanical (milling), physical (X-ray irradiation), and chemical (cadoxen, H3PO4, H2SO4, NaOH, Fe2+/H2O2) The average size of cellulose particles and its degree of polymerization had little effect on the efficiency of enzymatic hydrolysis For samples of pure cellulose (cotton linter, microcrystalline cellulose, α-cellulose), increase in the specific surface area accessible to protein molecules and decrease in the crystallinity index accelerated the enzymatic hydrolysis (the correlation coefficients were 089 and 092, respectively) In the case of lignocellulose (bagasse), a quantitative linear relationship only between specific surface area and reactivity was observed

Inclusive particle production in 400 GeV/c pp-interactions

Abstract: We report on a study of inclusive particle production in pp-interactions at 400 GeV/c. The data are based on 472 K reconstructed events recorded in the NA 27 experiment using the LEBC-EHS facility at CERN. The production cross sections are determined of pseudo scalar (π±,0, η andK±), scalar (f0(975)), vector (ρ±,0(770), ω(783), ϕ(1020),K*0(892), and\(\bar K^{ * 0} \)(892)), and tensorf0 mesons, of protons and antiprotons, and theΔ++,+,0(1232), and Λ(1520) baryon resonances in the forward hemisphere of the center of mass system, as well as longitudinal and transverse momentum distributions. The results are compared with predictions of the FRITIOF model and with other experimental data.

Quantum effects and color transparency in charmonium photoproduction on nuclei.

Abstract: We develop a rigorous quantum-mechanical treatment of color transparency effects in diffractive photoproduction of $\overline{c}c$ pairs on nuclei. The evolution of the $\overline{c}c$ wave function during propagation through a nucleus is more a considerable distortion of its form than a trivial attenuation. One of the manifestations of the quantum effects is a nuclear antishadowing of the ${\ensuremath{\psi}}^{\ensuremath{'}}$ yield, i.e., transparency above one. However, considerable nuclear shadowing is predicted for the photoproduction of $\frac{J}{\ensuremath{\psi}}$, which has a much smaller absorption cross section than ${\ensuremath{\psi}}^{\ensuremath{'}}$.

Observation of the bloch oscillations in an ultrasmall Josephson junction

Abstract: We have studied the low-temperature behavior of lead-alloy Josephson tunnel junctions with area S\ensuremath{\approxeq}0.01 \ensuremath{\mu}${\mathrm{m}}^{2}$, isolated from their electromagnetic environment by high-resistance metallic resistors inserted into the current and voltage leads. Under irradiation with microwaves frequencies, f=3.5--10 GHz, the dc differential resistance dV/dI, as a function of the dc current I, showed peaks at I=\ifmmode\pm\else\textpm\fi{}2ef. This effect, and other observations, arises due to the periodic electrical recharging of the junction by discrete Cooper pairs, and can be explained by the ``orthodox'' theory of Bloch oscillations.

PSCAN: personal superconductor circuit analyser

Abstract: The program PSCAN (personal superconductor circuit analyser) is briefly described. It uses the nodal Josephson phase approach which automatically accounts for peculiarities of superconductor circuits such as magnetic flux quantization and quantum interference. The program is able to perform five major types of analyses: transient, I-V curve, threshold curve, operation margin and time-delay.

DNA interpolyelectrolyte complexes as a tool for efficient cell transformation.

Abstract: A tool was developed for enhancement of plasmid penetration into an intact cell, based on increasing DNA hydrophobicity via inclusion into a soluble interpolyelectrolyte complex (IPC) with polycations. The characteristics of formation of DNA IPC with synthetic polycations [poly(N-ethyl-4-vinylpyridinium)bromide (PVP) and PVP modified with 3% of N-cetyl-4-vinylpyridinium units (PVP-C)] were studied using ultracentrifugation and polyacrylamide gel electrophoresis methods. The conditions were established under which the mixing of DNA and polycation aqueous solutions results in the self-assembly of soluble IPC species. Incorporation of DNA into IPC results in the enhancement of DNA binding with isolated Bacillus subtilis membranes. A considerable increase in the efficiency of transformation of B. subtilis cells with pBC16 plasmid resulted from incorporation of the plasmid into the IPC with PVP and CVP.

Hyperbolicity of groups with subquadratic isoperimetric inequality

Abstract: The author gives a simple and coherent proof of Gromov's statement on hyperbolicity of groups with subquadratic isoperimetric inequality.

Spherical Model of Color and Brightness Discrimination

Abstract: The most important problem confronting color science is the construction of a uniform color space, i.e., a geometrical model of color discrimination in which Euclidean distances between the points representing colors are proportional to perceived color differences. The traditional approach to the construction of a metric color space is based on the integration of just-noticeable color differences (Wyszecki & Stiles, 1982). Experimental data show, however, that the integral of just-noticeable differences between colors does not coincide with direct estimations of the subjective differences between the colors (Judd, 1967; Izmailov, 1980). We suggest another way to construct a uniform color space, namely, to analyze large color differences by multidimensional scaling. This paper reports three groups of experimental data of the measurement of large color differences. Based on these data, we suggest a new color space model taking into account nontraditional relations between threshold and suprathreshold differ...

The location of mRNA in the ribosomal 30S initiation complex; site-directed cross-linking of mRNA analogues carrying several photo-reactive labels simultaneously on either side of the AUG start codon.

Abstract: Messenger RNA molecules 30-35 bases long, with sequences related to the 5'-region of cro-mRNA from lambda-phage, were prepared by T7 transcription from synthetic DNA templates. Each mRNA contained five or six internal uridine residues, which were transcribed using a mixture of UTP and thio-UTP. Initiation complexes were formed with Escherichia coli 30S ribosomes in the presence or absence of tRNA(fMet), and cross-linking of the thio-U residues was induced by UV irradiation at wavelengths greater than 300 nm. The cross-linked ribosomal proteins were identified immunologically, and cross-linked regions of the 16S RNA were isolated by excision with ribonuclease H and suitable deoxyoligonucleotides. In both cases, the particular thio-U residue involved in the cross-link was identified by ribonuclease T1 fingerprinting of the (radioactive) mRNA in the isolated cross-linked complex. The principal results were that, at thio-U positions upstream of the AUG codon, specific cross-linking occurred to protein S7 and to the 3'-terminus of the 16S RNA, in agreement with similar experiments using 70S ribosomes. Less specific cross-linking was observed to proteins S1, S18 and S21 at various positions within the mRNA. Six bases downstream from the AUG codon, a tRNA-dependent cross-link was found to position approximately 1050 of the 16S RNA, but--in contrast to similar experiments with 70S ribosomes--no cross-linking was found to the 1390-1400 region.