Showing papers by "Moscow Institute of Physics and Technology published in 1997"

Ionization rates and energy and angular distributions at the barrier-suppression ionization of complex atoms and atomic ions

Abstract: Analytical expressions are obtained for energy and angular distributions of ejected electrons at the barrier-suppression and tunneling ionization of complex atoms and atomic ions by low-frequency strong electromagnetic radiation. The results reduce to previously known expressions in the case of the ground state of the hydrogen atom. Both linear and circular polarizations of the electromagnetic field are considered. The ionization rates are found by integration over angles and energies of the ejected electron in the case of barrier-suppression ionization of complex atoms and atomic ions. The barrier-suppression results reduce correctly to the tunneling results of the Ammosov–Delone–Krainov approach in the limit of weak fields compared with the barrier-suppression fields.

Asymptotic theory of traffic jams

Abstract: Based on singular perturbation methods, an asymptotic theory of traffic jams of large amplitude is developed in this work. Simple equations describing the form of traffic jams of large amplitude are found. The theory leads to analytical formulas for the characteristic parameters of traffic flow that are independent of road length, vehicle density of the initial traffic flow, or other initial conditions. Analytical investigations have been made showing that, in agreement with earlier numerical results (Kerner and Konhauser, 1994), the boundary flux at which a traffic jam can still exist is equal to the flux in the flow from a jam. The manner in which the shape of a traffic jam evolves due to changes in initial vehicle density is analytically studied. Simple analytical formulas are obtained for parameters of narrow traffic jams capable of forming in a limited interval of vehicle densities. A comparison is also made between results of the present analytical theory of traffic jams, the theory of shock waves in gas dynamics, the classical Lighthill-Whitham theory of kinematic waves (1955), and the recently discovered experimental features and characteristics of wide traffic jams in traffic.

The ionization kinetics and electric field in the leader channel in long air gaps

Abstract: A kinetic model for the ionization processes in high-temperature air in a strong electric field is developed. The model is used to study numerically the problem of the relaxation of the plasma properties in atmospheric-pressure air to a new steady state after an instantaneous change in the gas temperature between 300 and 1000 - 6000 K. Our simulation shows that the electrical properties of the plasma under the conditions of the leader being a long spark nearly follow the local value of the gas temperature. The reduced field E/N in the leader channel is found to decrease considerably as the gas temperature T increases from 1000 to 6000 K. The decrease in E/N is caused by the formation of NO molecules with low ionization energy at T 4500 K. As a result, the value of E/N falls to 10 Td at T = 5000 K and to 1.5 Td at T = 6000 K for a current of 1 A and a channel radius of 0.1 cm. This agrees well with the experimental evidence showing that the leader bridges very long air gaps (about 200 m) at a moderate applied voltage (< 5 MV).

Non-extremal Intersecting p-branes in Various Dimensions

Abstract: Non-extremal intersecting p-brane solutions of gravity coupled with several antisymmetric fields and dilatons in various space-time dimensions are constructed. The construction uses the same algebraic method of finding solutions as in the extremal case and a modified "no-force" conditions. We justify the "deformation" prescription. It is shown that the non-extremal intersecting p-brane solutions satisfy harmonic superposition rule and the intersections of non-extremal p-branes are specified by the same characteristic equations for the incidence matrices as for the extremal p-branes. We show that S-duality holds for non-extremal p-brane solutions. Generalized T-duality takes place under additional restrictions to the parameters of the theory which are the same as in the extremal case.

Experiments on rf band communications using chaos

Abstract: This paper presents experimental results of wire-line and wireless analog information transmission in RF band via chaos using standard signal formation and reception methods.

Mass-correlated Delayed Extraction in Linear Time-of-Flight Mass Spectrometers

Abstract: Theoretical analysis and model calculations were directed to find a means of extending the Wiley-McLarens principles of velocity focusing to wide range mass spectra. Both the cases of time-profiled single-field and double-field operation modes were considered. High mass accuracy over about a 10-fold ratio of masses at high (M0) and low (m0) ends of spectrum is attainable with a single-field ion source in the case of matrix-assisted laser desorption ionization (MALDI). This range ratio increases by a factor of 10 using the double-field operation mode. In the latter case, mass resolution increases at least by a factor of 7 compared with the standard delayed extraction mode in typical MALDI conditions. Application to a combined single-field/double-field operation mode enables the maintenance of accuracy parameters over a mass ratio M0/m0 of about 1000. © 1997 John Wiley & Sons, Ltd.

Properties of Intersecting p-branes in Various Dimensions

Abstract: General properties of intersecting extremal p-brane solutions of gravity coupled with dilatons and several different d-form fields in arbitrary space-time dimensions are considered. It is show that heuristically expected properties of the intersecting p-branes follow from the explicit formulae for solutions. In particular, harmonic superposition and S-duality hold for all p-brane solutions. Generalized T-duality takes place under additional restrictions on the initial theory parameters .

Anomalous frequency shift of negative muon spin precession in n-type silicon

Abstract: The dependence of the residual polarization of negative muons in n‐type Si with impurity concentration (1.6\pm 0.2)\times 1013\ cm-3 on temperature in the 10–300 K range has been investigated. Measurements were carried out in external magnetic field of 0.08 T transverse to the muon spin. Muon spin relaxation and frequency shift were observed at temperatures below 30 K. The relaxation rate at 30 K is equal to 0.25\pm 0.08\,μ s-1. The frequency shift at 20 K is equal to 7\times 10-3. Both the relaxation rate and the frequency shift grow with decrease of temperature. Below 30 K the relaxation rate is well described by the dependence \varLambda=bT-q, where q=2.8.

Variability analysis of HIV-1 gp120 V3 region: II. Hierarchy of taxons.

Abstract: In the previous work (M. Yu. Shchelkanov, A. N. Yudin, A. V. Antonov, N. S. Starikov, A. A. Vedenov, E. V. Karamov, J. Biomol. Struct. Dyn. 15, 217–229 (1997)) we have introduced the amino acid distribution function within HIV-1 taxons and Hamming-transformed Euclidean measures between their characteristics: consensus, subconsensus and sample mean. In this work the referred characteristics are used for hierarchical classification of amino acid sequences of gp120 V3 region belonging to different HIV-1 taxons. A comparative analysis of the results produced by various classification methods is carried out. Multidimensional scaling of distance matrix for the specified characteristics is used to visualize the pattern of HIV-1 variability.

Theory of muon spin depolarization in condensed phases of hydrogen isotopes

Abstract: A theory of muon spin depolarization in the molecular ion ( H2μ)+(( D_2μ)) formed in a crystalline phase of hydrogen isotopes is presented. It is shown that the molecular ion ( H_2μ)+ has no time to thermalize during the muon lifetime, but after \tau\ll \tau_μ has time to transit to the lowest energy levels of the vibration‐rotation spectrum. The depolarization of the muon spin is determined by the interaction of the ion’s electric dipole moment with the lattice and by spin‐rotation interactions VLS in the ion. This mechanism is analogous to that of “muonium”, replacing the hyperfine interaction by VLS. The results can explain the experimental data and in particular the absence of a strong isotopic effect.

Two-phase model of hydrolysis kinetics and its applications to anaerobic degradation of particulate organic matter

Abstract: The various equations of hydrolysis kinetics included into the generalized simulation model (METHANE) were tested on the anaerobic digestion of cellulose, sludge, and cattle manure. The good agreement between the model simulation results and experimental data was obtained. The Contois equation, taking into account a hydrolytic biomass, and the first-order equation with respect to the particulate substrate only, were shown to be the approximations of two-phase hydrolysis kinetics.

Variability analysis of HIV-1 gp120 V3 region: I. Point estimators for the amino acid distribution characteristics.

Abstract: Enumerating procedure for symbol sequences is proposed. Relationship between Hamming distance for symbol sequences and Euclidean distance for corresponding enumerations is established, and more universal Hamming-transformed Euclidean measure is constructed. A distribution function of amino acid substitutions and some of its point estimators (consensus, subconsensus, sample mean, sample central moments and asymmetry coefficient) are introduced. Hamming-transformed Euclidean measures between consensus, subconsensus and sample means for ten HIV-1 taxons of gp120 V3 regions are calculated. It is demonstrated that these taxons have a complicated pattern which is significant for their classification.

Theory of muon spin depolarization in crystalline phases of 3he

Abstract: As is obvious from the energetic point of view, positive muons must form the molecular ion ( He_2μ)+ in condensed phases of helium A theory of positive muon spin depolarization in crystalline phase of 3He in this model is devised The theory explains experimental results It is shown that the abrupt temperature dependence of the muon spin depolarization rate at T < 2 K which is observed in experiments is explained by spin–phonon interaction This interaction mechanism arises due to a modulation of the exchange interaction between host atoms of the 3He‐lattice

Resonance radiation transfer in dense dispersive media

Abstract: The theory of resonance radiation transfer in highly absorptive media is developed. The system of equations for generalized spectral “intensity” of radiation and population densities of excited states is obtained. The generalized “intensity” depends on frequency and wave number which are independent variables, and obeys simultaneously two equations. One of them has the form of a kinetic equation and the other one the form of a wave equation with a source in right hand side. The observable spectral intensity of radiation can be obtained from the generalized one by the proper integration over wave numbers; inside thick media it may be significantly higher than Planck intensity. The boundary conditions for the “intensity” are deduced and for inhomogeneous media it is shown that the residual intensity at the output of hot matter may be several orders of magnitude higher than according to the conventional theory. For optically thick media the spatial distribution of the excited atoms can be received with high accuracy from the well known Biberman-Holstein equations. A numerical code for solution of the proposed equations is developed and the results of simulations are compared with the experimental ones carried out with sodium vapour. The agreement with experiment is quite satisfactory. The possibility to observe the predicted effects in plasmas of multicharged ions is discussed.

Negative differential conductivity of electrons in He - Xe mixtures

Abstract: The drift velocity of electrons in He - Xe mixtures is calculated using the two-term expansion of the electron energy distribution function in Legendre polynomials. Collisions of electrons with ground-state and excited atoms are considered, together with Coulomb collisions. The calculations are performed under conditions when negative differential conductivity of electrons occurs. It is shown that concurrent effects of Coulomb collisions and of electron collisions with excited Xe atoms extend the region of parameters in the He - Xe mixtures where negative differential conductivity takes place.

Studying Lepton Family Violation in Lepton-Lepton Collisions

Abstract: In the context of the future high energy - high luminosity electron and muon colliders, all the relevant four-lepton processes with the lepton family violation (LFV) are systematically classified. The most general LFV effective lagrangians are found, and the helicity differential cross sections for the LFV processes are calculated. The six- and eight-lepton Standard Model (SM) backgrounds are discussed, and the LFV processes clean of the six-lepton background are picked out. The possibility to suppress the six-lepton SM background, when present, by the unnatural initial beam polarizations is investigated. It is shown that the four-lepton LFV processes are amenable to experimental study in the lepton-lepton collisions in the most favourable cases up to the underlying scale of order 100 TeV. Studying these processes should provide an essential part of the physics program for the next generation lepton colliders to unravel the outstanding flavour/family problem.

Selective gas detection using uncoated SAW delay lines

Abstract: Two approaches for gas recognition in binary mixtures have been developed for imcoated surface acoustic wave (SAW) sensors based on gas thermal conductivity principle. The first approach utilizes the difference thermal conductivity of the ambient atmosphere with respect to a reference gas as general property to test the responses of the sensing elements. Selecting the operating temperature and the reference gas, a single gas is distinctly detected. The second approach is based on the inherent property of the SAW devices, whose response is monitored by the temperature coefficient of delay (TCD). Choosing the operating temperature and the substrate material, the SAW response for a test gas is rejected. Experimental measurements are shown and discussed.

Variability Analysis of HIV-1 gp120 V3 Region: III. Distinctions Between Various Sets of Peptide Fragments Derived From the Sequences Belonging to Different HIV-1 Taxons

Abstract: Distinction criterion for various sets of fixed length peptide fragments and integral distinction measure for various sets of peptide fragments with different length and start position ranges have been introduced on the base of an enumeration procedure and a point estimators for the amino acid distribution characteristics introduced previously (M. Yu. Shchelkanov, A. N. Yudin, A. V. Antonov, N. S. Starikov, A. A. Vedenov, E. V. Karamov, J. Biomol. Struct. Dyn. 15, 231–241 (1997)). Differences between 6–10-mer peptides derived from the majority of HIV-1 taxon pairs are demonstrated to be located generally in the vicinity of the V3-loop top. This validates the suitability of V3 top mimicking synthetic peptides for HIV-1 serotyping. A significant difference between E subtype V3 C-terminus peptides and the corresponding peptides derived from the other subtypes has been demonstrated. Taking into account the Langerhans' cells tropism of E subtype virus variants we have hypothesized the influence of mut...

Disposition of Weapons-Grade Plutonium in Russia: Evaluation of Different Options

Abstract: The ongoing dismantlement of tens of thousands of nuclear weapons retired under the START I and START II treaties should result in over 60 tons of excess weapons-plutonium in Russia. Also, due to reprocessing of civil spent fuel, about 30 tons of reactor-grade plutonium is accumulated in Russia. This plutonium excess presents an international security problem. In the long term, the basic Russian approach for disposition of plutonium is to burn both weapons plutonium and civil plutonium in fast-neutron reactors. However due to the current political and economic situation in Russia, this plan cannot be realized any time soon. Under such conditions, the first priority should be placed on the establishment of a plutonium storage regime under bilateral or international control.

Photoelectric properties of Pb1-x-yGeySnxTe:In epitaxial films

Abstract: Epitaxial films Pb1-x-yGeySnxTe:In grown by 'hot wall' method on insulating substrates BaF2 are studied. Samples are made in Ukrainian Institute of Problems of the Study of Materials. Measurements of photoconductivity spectra and temperature dependence of resistance are carried out at different background fluxes. The correlation between a cutoff wavelength and thermoactivation energies of resistance of studied samples was observed. The observed phenomena are explained on the basis of a two-electron Indium impurity center model. Energies of local oscillations of impurity centers are determined.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Detection of laser damage to the surfaces of materials and coatings with the aid of an induced gas discharge

Abstract: A method for detection of laser damage to the surfaces of optical materials and coatings was investigated The damage was detected with the aid of a gas discharge induced by the products of a laser ablation plume A suitable selection of the parameters of the detection system made it possible to investigate laser surface damage at radiation intensities W>130 MW cm-2 (λ = 106 μm, tp=10 ns) A special feature of the electric response was that the result was determined solely by the occurrence of damage and not by its nature or by the laser damage threshold This feature makes the method suitable for automatic damage detection systems used in statistical investigations

Model for seawater optical characteristics at UV spectral region

Abstract: The goal of this work is development of a model for calculation of seawater optical characteristics at UV spectral range by using their values at visible region. Modified model based on physical factors caused optical properties of seawater is considered. Different models of spectral absorption have been compared at visible spectral region, and simple additive model is proposed. Contributions arising from different factors are calculated and analyzed.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.