Showing papers by "Moscow Institute of Physics and Technology published in 2005"
TL;DR: It has been demonstrated that the electric field in the streamer head is hardly affected by the pressure decrease, while the electron concentration decreases with pressure by an order of magnitude.
Abstract: The results are given of an experimental investigation of a cathode-directed streamer discharge in synthetic air in the pressure range from 760 to 300 torr and their comparison with the results of direct numerical simulation in a 2D hydrodynamic approximation. The pattern of discharge branching upon variation of pressure is investigated experimentally. The results are given of comparison of the predicted and measured values of anode current, streamer propagation velocity, and channel diameter. It has been demonstrated that the electric field in the streamer head is hardly affected by the pressure decrease, while the electron concentration decreases with pressure by an order of magnitude. At the same time, production of chemical species in a cathode-directed streamer discharge varies at a rate of at least the second power of inverse pressure.
327 citations
TL;DR: In this paper, a critical analysis of photoionization as the major process for seed electron production ahead of the cathode-directed streamer has been made, and the results of analytical estimates and full three-dimensional simulations confirm that the seed charge distribution in the undisturbed gap has an effect on the streamer head formation and leads to the branching phenomena.
Abstract: A critical analysis of photoionization as the major process for seed electron production ahead of the cathode-directed streamer has been made. The accumulation of ions between pulses and fast electron detachment in an electric field could be an effective source of seed electrons for repetitively pulsed discharges in electronegative gases. Measurements and two-dimensional calculations in the hydrodynamic approximation of streamer parameters in air (anode current, propagation velocity and radiative channel diameter) can only agree if one assumes uniform background pre-ionization and not by taking into account only the photoionization process generally adopted for pulsed discharges in air. The results of analytical estimates and full three-dimensional simulations confirm that the seed charge distribution in the undisturbed gap has an effect on the streamer head formation and leads to the streamer branching phenomena.
197 citations
31 Oct 2005
TL;DR: A new construction of rank codes is presented, which defines new codes and includes known codes, and it is argued that these are different codes.
Abstract: The only known construction of error-correcting codes in rank metric was proposed in 1985. These were codes with fast decoding algorithm. We present a new construction of rank codes, which defines new codes and includes known codes. This is a generalization of E.M. Gabidulin, 1985. Though the new codes seem to be very similar to subcodes of known rank codes, we argue that these are different codes. A fast decoding algorithm is described
155 citations
TL;DR: In this article, a robust modification of the elliptic relaxation model was developed to obtain homogeneous boundary conditions at a wall for both ¯ v 2 and f. The modification is based on both a change of variables and alteration of the governing equations.
Abstract: The elliptic relaxation approach of Durbin (Durbin, P.A., J. Theor. Comput. Fluid. Dyn. 3 (1991) 1-13), which accounts for wall blocking effects on the Reynolds stresses, is analysed herein from the numerical stability point of view, in the form of the ¯ v 2 − f . This model has been shown to perform very well on many challenging test cases such as separated, impinging and bluff-body flows, and including heat transfer. However, numerical convergence of the original model suggested by Durbin is quite difficult due to the boundary conditions requiring a coupling of variables at walls. A 'code-friendly' version of the model was suggested by Lien and Durbin (Lien, F.S. and Durbin, P.A., Non linear k −e −v 2 modelling with application to high-lift. In: Proceedings of the Summer Program 1996, Stanford University (1996), pp. 5-22) which removes the need of this coupling to allow a segregated numerical procedure, but with somewhat less accurate predictions. A robust modification of the model is developed to obtain homogeneous boundary conditions at a wall for both ¯ v 2 and f . The modification is based on both a change of variables and alteration of the governing equations. The new version is tested on a channel, a diffuser flow and flow over periodic hills and shown to reproduce the better results of the original model, while retaining the easier convergence properties of the 'code-friendly' version. Ke yw ords: turbulence, ¯ v 2 − f model, robust modification, near-wall flow.
116 citations
TL;DR: Simultaneous measurements of neutrons result in zero yield, which proves the observation of neutronless fusion reactions in the authors' experiments.
Abstract: The yield of $\ensuremath{\alpha}$ particles in neutronless fusion reactions $^{11}\mathrm{B}+p$ in plasmas produced by picosecond laser pulses with the peak intensity of $2\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$ has been observed. Experiments were carried out on the ``Neodymium'' laser facility at the pulse energy of $10--12\phantom{\rule{0.3em}{0ex}}\mathrm{J}$ and pulse duration of $1.5\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$. The composite targets $^{11}\mathrm{B}+{(\mathrm{C}{\mathrm{H}}_{2})}_{n}$ were used. The yield of ${10}^{3}$ $\ensuremath{\alpha}$ particles per pulse has been observed. The energy spectrum of $\ensuremath{\alpha}$ particles contains two maxima: at $3--4\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ and at $6--10\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$. The first of these peaks corresponds to the secondary ${\ensuremath{\alpha}}_{12}$ particles at the decay of the intermediate first excited state of $^{8}\mathrm{Be}$, whereas the second peak demonstrates generation of ${\ensuremath{\alpha}}_{1}$ particles in the reaction $^{11}\mathrm{B}+p$ with the production of this excited state. Simultaneous measurements of neutrons result in zero yield, which proves the observation of neutronless fusion reactions in our experiments.
114 citations
10 Jan 2005
102 citations
TL;DR: It is shown that the molecular phenomena affect acoustic characteristics of micro-channels and pores starting from relatively small Knudsen numbers Kn > 0.01, especially at low frequencies.
Abstract: Analytical solutions describing propagation of monochromatic acoustic waves inside long pores of simple geometries and narrow flat slits are obtained with accounting for gas rarefaction effects. It is assumed that molecular nature of gas is important in Knudsen layers near solid boundaries. Outside the Knudsen layers, the continuum approach is used. This model allows for extension of acoustic analysis to regions of low pressures and microscopic cross-sectional sizes of channels. The problem is solved using linearized Navier-Stokes equations with the boundary conditions that resulted from the first-order approximation with respect to small Knudsen number Kn. For slits and pores of circular and square cross sections, the theoretical dependencies of the dynamic density in the low-frequency range are compared with those that resulted from known experimental data on steady-state flows of rarefied gases in uniform channels. Despite the formal restriction Kn 0.01, especially at low frequencies. The obtained results may be used for analyses of acoustic properties of waveguides, perforated panels, micro-channels and pores in wide range of gas pressures as well as for stationary flows of rarefied gases through long uniform pipes etc.
69 citations
TL;DR: Particle-in-cell simulations show that the inhomogeneity scale of the plasma produced in the interaction of high-power laser radiation with gas targets is of fundamental importance for ion acceleration as discussed by the authors.
Abstract: Particle-in-cell simulations show that the inhomogeneity scale of the plasma produced in the interaction of high-power laser radiation with gas targets is of fundamental importance for ion acceleration. In a plasma slab with sharp boundaries, the quasistatic magnetic field and the associated electron vortex structure produced by fast electron beams both expand along the slab boundary in a direction perpendicular to the plasma density gradient, forming an extended region with a quasistatic electric field, in which the ions are accelerated. In a plasma with a smooth density distribution, the dipole magnetic field can propagate toward the lower plasma density in the propagation direction of the laser pulse. In this case, the electron density in an electric current filament at the axis of the magnetic dipole decreases to values at which the charge quasineutrality condition fails to hold. In electric fields generated by this process, the ions are accelerated to energies substantially higher than those characteristic of plasma configurations with sharp boundaries.
65 citations
TL;DR: In this article, the authors used the shock-tube technique to measure the ignition delay time of a lean mixture of n-pentane and air in a wide range of temperatures from 867 to 1534 K and pressures from 11 to 530 atm.
64 citations
TL;DR: This note considers a society that partitions itself into disjoint jurisdictions, each choosing a location of its public project and a taxation scheme to finance it, and imposes two principles, egalitarianism and efficiency, that require the equalization of the total cost for all agents in the same jurisdiction.
Abstract: In this note we consider a society that partitions itself into disjoint jurisdictions, each choosing a location of its public project and a taxation scheme to finance it. The set of public project is multi-dimensional, and their costs could vary from jurisdiction to jurisdiction. We impose two principles, egalitarianism, that requires the equalization of the total cost for all agents in the same jurisdiction, and efficiency, that implies the minimization of the aggregate total cost within jurisdiction. We show that these two principles always yield a core-stable partition but a Nash stable partition may fail to exist.
60 citations
TL;DR: For the first time, the shear viscosity of dusty plasma liquid defined by the screened Coulomb interaction of dust particles is estimated on the basis of experimental data.
11 Mar 2005-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, a mechanism for efficient proton acceleration in the GeV energy range was proposed for low-energy neutrino sources and applications to non-conventional high intensity proton drivers and hence to low energy (10-200 MeV) neutrinos were discussed.
Abstract: A new mechanism is suggested for efficient proton acceleration in the GeV energy range; applications to non-conventional high intensity proton drivers and, hence, to low-energy (10–200 MeV) neutrino sources are discussed. In particular, we investigate possible uses of these sources to explore subdominant ν ¯ μ → ν ¯ e oscillations at the atmospheric scale and their CP conjugate. We emphasize the opportunity to develop these facilities in conjunction with projects for inertial confined nuclear fusion and neutron spallation sources.
TL;DR: In this paper, the reduced isotopic partition function ratio (β-factor) from the partial density of state (PDOS) obtained by inelastic nuclear resonant X-ray scattering (INRXS) in synchrotron radiation experiments was established.
TL;DR: How molecular dynamics simulations can elucidate structure-function relationships in bacteriorhodopsin (bR) involving water molecules is demonstrated and possible pathways for proton hopping and water movement inside bR are suggested.
TL;DR: In this article, the vibrational spectra of crystals of bismuth borates were obtained for the first time, and the spectra for Bi3B5O12 and BiB3O6 crystals measured in the range 30-1600 cm−1 at room temperature were refined.
Abstract: The vibrational spectra of crystals of bismuth borates Bi24B2O39, Bi4B2O9, BiBO3, and Bi2B8O15 were obtained for the first time, and the spectra of Bi3B5O12 and BiB3O6 crystals measured in the range 30–1600 cm−1 at room temperature were refined. The lines observed were assigned to the corresponding vibrational transitions on the basis of the theoretical group analysis and comparison of the obtained results with the vibrational spectra of borates of different composition. The complication of the structure of bismuth borates with increasing content of B2O3 was traced by the example of vibrational spectra.
TL;DR: In this article, a numerical simulation is used to investigate the effect of rod dimensions on lightning attachment to the lightning rod, and it is concluded that the efficacy of a lightning rod is almost independent of the rod radius in the range 0.05?5?cm.
Abstract: A numerical simulation is used to investigate the effect of rod dimensions on lightning attachment to the lightning rod. The effect is studied by considering a sequence of discharge processes, from a corona ignited in a slowly rising thundercloud electric field to the development of an upward leader in the electric field of an approaching downward leader. It is concluded that the efficacy of a lightning rod is almost independent of the rod radius in the range 0.05?5?cm. This is in agreement with measurements of the breakdown voltage in long laboratory rod-to-plane air gaps for various rod tip radii but is at variance with the conclusions reached by Moore et al (2000a Geophys. Res. Lett. 27 1487, 2000b J. Appl. Meteorol. 39 593, 2003 J. Appl. Meteorol. 42 984) from their observations under thunderstorm conditions.
TL;DR: The pattern found in the wake of the laser pulse shows unexpectedly regular modulations inside a long, finite width channel, which is interpreted as due to ion modulations developed during a two-stream instability excited by the return electric current generated by the wakefield.
Abstract: Experimental investigations of the late-time ion structures formed in the wake of an ultrashort, intense laser pulse propagating in a tenuous plasma have been performed using the proton imaging technique. The pattern found in the wake of the laser pulse shows unexpectedly regular modulations inside a long, finite width channel. On the basis of extensive particle in cell simulations of the plasma evolution in the wake of the pulse, we interpret this pattern as due to ion modulations developed during a two-stream instability excited by the return electric current generated by the wakefield.
TL;DR: Two mathematical models of clot growth in the fluid flows have been considered and it is demonstrated that hydrodynamic flows can essentially affect the processes of blood coagulation, and consequently on the clot structure.
Abstract: Two mathematical models of clot growth in the fluid flows have been considered. The first one is the model of embolus growth in a wall-adjacent flow. The effect of hydrodynamic flows on proceeding chemical reactions and the backward effect of the growing clot on the flow are taken into account. The growing thrombus is assumed to be porous and having low permeability, that is in good agreement with experimental data. The exact solutions determining the distribution of a fluid velocity close to the embolus have been used. Numerical analysis of these solutions have demonstrated that hydrodynamic flows can essentially affect the processes of blood coagulation, and consequently on the clot structure. Their presence might lead to the destruction of chemical fronts having a cylindrical symmetry and formation of the so-called chemical spots. The second model describes the initial stage of thrombus growing in the hemorrhage into a natural internal space. It permits accounting for vessel geometry and provides studying the effects of geometric parameters on fluid flows and coagulation processes. The process of thrombus growth is shown to depend on the ratio of typical values of blood velocity in the vessel and rate of chemical reactions.
TL;DR: In this article, the effect of coronae on the initiation of an upward leader from the top of a fixed grounded structure that is exposed to the electric field produced by the storm-cloud and approaching downward leader was analyzed.
TL;DR: In this article, the specific features of a nonstationary corona discharge that develops in the electric field of a thundercloud and a downward lightning leader are analyzed, as well as possible mechanisms for the interaction of the corona space charge with an upward leader and prospects of using it to control downward lightning discharges.
Abstract: The interaction between the lightning leader and the space charge accumulated near the top of a ground object in the atmospheric electric field is considered using analytical and numerical models developed earlier to describe spark discharges in long laboratory gaps. The specific features of a nonstationary corona discharge that develops in the electric field of a thundercloud and a downward lightning leader are analyzed. Conditions for the development of an upward lightning discharge from a ground object and for the propagation of an upward-connecting leader from the object toward a downward lightning leader (the process determining the point of strike to the ground) are investigated. Possible mechanisms for the interaction of the corona space charge with an upward leader and prospects of using it to control downward lightning discharges are analyzed.
TL;DR: The first functional heterologous expression of SRII from H. salinarum provides the basis for studies with its cognate transducer HtrII to investigate the molecular processes involved in phototransduction as well as in chemotransduct.
TL;DR: In this article, the authors constructed N = 4 supersymmetric mechanics using the nonlinear chiral supermultiplet and demonstrated that the deformation of the connection results in the fermionic degrees of freedom with the background, and the bosonic potential.
TL;DR: In this article, the temperature dependence of the efficiency of a laser based on a Fe:ZnSe crystal grown from the vapour phase by the free-growth method was studied in the 85-255-K temperature range.
Abstract: The temperature dependence of the efficiency of a laser based on a Fe:ZnSe crystal grown from the vapour phase by the free-growth method is studied in the 85–255-K temperature range. As the temperature was increased, the slope efficiency of the laser with respect to absorbed energy decreased from 43% (at 85 K) down to 9% (at 255 K) and its emission spectrum shifted from 4.0 to 4.17 μm. Lasing was obtained in a Fe2+:ZnSe crystal cooled with a thermoelectric module down to ~220 K. In this case, the slope efficiency of the laser with respect to absorbed energy was 30%. The output energy of the thermoelectrically cooled laser was 142 mJ for the slope efficiency with respect to the incident pump energy equal to 21%.
Posted Content•
TL;DR: In this paper, a nucleation model for the breakdown phenomenon in freeway free traffic flow at an on-ramp bottleneck is presented, which is based on assumptions of three-phase traffic theory in which breakdown phenomenon is related to a first-order phase transition from the free flow phase to the synchronized flow phase.
Abstract: A nucleation model for the breakdown phenomenon in freeway free traffic flow at an on-ramp bottleneck is presented. This model, which can explain empirical results on the breakdown phenomenon, is based on assumptions of three-phase traffic theory in which the breakdown phenomenon is related to a first-order phase transition from the "free flow" phase to the "synchronized flow" phase. The main idea of this nucleation model is that random synchronized flow nucleation occurs within a metastable inhomogeneous steady state associated with a deterministic local perturbation in free flow, which can be considered "deterministic vehicle cluster" in free flow at the bottleneck. This deterministic vehicle cluster in free flow is motionless and exists permanent at the bottleneck due to the on-ramp inflow. In the nucleation model, traffic breakdown nucleation occurs through a random increase in vehicle number within this deterministic vehicle cluster, if the amplitude of the resulting random vehicle cluster exceeds some critical amplitude. The mean time delay and the associated nucleation rate of speed breakdown at the bottleneck are found and investigated. The nucleation rate of traffic breakdown as a function of the flow rates to the on-ramp and upstream of the bottleneck is studied. The nucleation model and the associated results exhibit qualitative different characteristics than those found earlier in other traffic flow nucleation models. Boundaries for speed breakdown in the diagram of congested patterns at the bottleneck are found. These boundaries are qualitatively correlated with numerical results of simulation of microscopic traffic flow models in the context of three-phase traffic theory.
TL;DR: In this article, a detailed kinetic model is constructed for hydrocarbon ignition, which includes ignition mechanisms for low, high, and intermediate (1000-1200 K) temperatures, and the effect of pressure on the mechanism of autoignition is demonstrated.
Abstract: Ignition delay time behind a reflected shock wave is measured for a lean propane-air mixture with an equivalence ratio of ϕ = 0.5 in wide temperature and pressure ranges (T = 880–1500 K, P = 2–500 atm). Ignition-delay activation energy data obtained in this study are compared with earlier data. A detailed kinetic model is constructed for hydrocarbon ignition, which includes ignition mechanisms for low, high, and intermediate (1000– 1200 K) temperatures. Each of the mechanisms is analyzed. The effect of pressure on the mechanism of autoignition is demonstrated.
TL;DR: In this paper, the authors reveal thermodynamic aspects of the problem through comparison of some available theoretical predictions for the uranium critical point parameters as well as to discuss in brief plausible versions to meet existing contradiction.
TL;DR: In this paper, the authors investigated how domain structures of the ferromagnet in superconductor-ferromagnetic heterostructures may change their transport properties and calculated the distribution of current induced by magnetic field of Bloch domain walls.
Abstract: We investigate how domain structures of the ferromagnet in superconductor-ferromagnet heterostructures may change their transport properties. We calculate the distribution of current in the superconductor induced by magnetic field of Bloch domain walls, e.g., find the ``lower critical'' magnetization of the ferromagnet that provides vortices in the superconductor.
TL;DR: In this paper, the interaction of the stellar wind with an unmagnetized planet was modeled using a three dimensional hybrid code as well as in the drift-kinetic approximation, and the effect of a interplanetary magnetic field oriented perpendicular to the incoming stellar wind was included.
TL;DR: In this paper, the structure and electrical characteristics of free vapor-air discharges with an electrolytic cathode and their relative transition were investigated at atmospheric pressure, and the basic physical processes which define the possible mechanism of maintaining a vapor air discharge with an ECC were revealed.
Abstract: Experimental investigation is performed of the structures and electrical characteristics of vapor-air discharges between a metal (solid, hollow, pointed) anode and an electrolytic cathode at atmospheric pressure. Singular features are revealed of free vapor-air discharges with an electrolytic cathode and their relative transition. Analysis and generalization of the experimental results enable one to reveal the basic physical processes which define the possible mechanism of maintaining a vapor-air discharge with an electrolytic cathode.
10 Jan 2005