Showing papers by "Moscow Institute of Physics and Technology published in 2006"

Plasma assisted ignition and combustion

Abstract: In recent decades particular interest in applications of nonequilibrium plasma for the problems of plasma-assisted ignition and plasma-assisted combustion has been observed. A great amount of experimental data has been accumulated during this period which provided the grounds for using low temperature plasma of nonequilibrium gas discharges for a number of applications at conditions of high speed flows and also at conditions similar to automotive engines. The paper is aimed at reviewing the data obtained and discusses their treatment. Basic possibilities of low temperature plasma to ignite gas mixtures are evaluated and historical references highlighting pioneering works in the area are presented. The first part of the review discusses plasmas applied to plasma-assisted ignition and combustion. The paper pays special attention to experimental and theoretical analysis of some plasma parameters, such as reduced electric field, electron density and energy branching for different gas discharges. Streamers, pulsed nanosecond discharges, dielectric barrier discharges, radio frequency discharges and atmospheric pressure glow discharges are considered. The second part depicts applications of discharges to reduce the ignition delay time of combustible mixtures, to ignite transonic and supersonic flows, to intensify ignition and to sustain combustion of lean mixtures. The results obtained by different authors are cited, and ways of numerical modelling are discussed. Finally, the paper draws some conclusions on the main achievements and prospects of future investigations in the field.

Laser-plasma acceleration of quasi-monoenergetic protons from microstructured targets

Abstract: Particle acceleration based on high intensity laser systems (a process known as laser-plasma acceleration) has achieved high quality particle beams that compare favourably with conventional acceleration techniques in terms of emittance, brightness and pulse duration. A long-term difficulty associated with laser-plasma acceleration--the very broad, exponential energy spectrum of the emitted particles--has been overcome recently for electron beams. Here we report analogous results for ions, specifically the production of quasi-monoenergetic proton beams using laser-plasma accelerators. Reliable and reproducible laser-accelerated ion beams were achieved by intense laser irradiation of solid microstructured targets. This proof-of-principle experiment serves to illuminate the role of laser-generated plasmas as feasible particle sources. Scalability studies show that, owing to their compact size and reasonable cost, such table-top laser systems with high repetition rates could contribute to the development of new generations of particle injectors that may be suitable for medical proton therapy.

3.77-5.05-μm tunable solid-state lasers based on Fe/sup 2+/-doped ZnSe crystals operating at low and room temperatures

Abstract: Spectroscopic properties and lasing of Fe:ZnSe and co-doped Fe:Cr:ZnSe crystals in the mid-infrared spectral range were studied at room and low temperatures. Using a free-running Er:YAG laser as a pump source, the output energy of the thermoelectrically cooled Fe:ZnSe laser was 142 mJ with 30% slope efficiency at T=220 K. Passive Q-switched oscillation of Er:YAG laser with Fe:ZnSe crystal was demonstrated and used as a pump source for a Fe:ZnSe laser system. Room-temperature (RT) gain-switched lasing of Fe:ZnSe was achieved in microchip and selective cavity configurations using Q-switched Er:YAG and Raman-shifted Nd:YAG lasers as pump sources. The microchip laser threshold of 100 mJ/cm2 was demonstrated using a Fe:ZnSe crystal without any reflection coatings. A slope efficiency of 13%, oscillation threshold of 1.3 mJ, and tunable oscillation of Fe:ZnSe laser systems over 3.95-5.05 mum spectral range were realized at RT

The left hand of brightness: past, present and future of negative index materials.

Abstract: Recent advances have brought negative index materials and their fascinating properties from their theoretical origins into the domain of experimental physics and device engineering.

Development of the signal in sensory rhodopsin and its transfer to the cognate transducer.

Abstract: The microbial phototaxis receptor sensory rhodopsin II (NpSRII, also named phoborhodopsin) mediates the photophobic response of the haloarchaeon Natronomonas pharaonis1,2 by modulating the swimming behaviour of the bacterium3. After excitation by blue-green light NpSRII triggers, by means of a tightly bound transducer protein (NpHtrII), a signal transduction chain homologous with the two-component system of eubacterial chemotaxis4. Two molecules of NpSRII and two molecules of NpHtrII form a 2:2 complex in membranes as shown by electron paramagnetic resonance5 and X-ray structure analysis6. Here we present X-ray structures of the photocycle intermediates K and late M (M2) explaining the evolution of the signal in the receptor after retinal isomerization and the transfer of the signal to the transducer in the complex. The formation of late M has been correlated with the formation of the signalling state2,7. The observed structural rearrangements allow us to propose the following mechanism for the light-induced activation of the signalling complex. On excitation by light, retinal isomerization leads in the K state to a rearrangement of a water cluster that partly disconnects two helices of the receptor. In the transition to late M the changes in the hydrogen bond network proceed further. Thus, in late M state an altered tertiary structure establishes the signalling state of the receptor. The transducer responds to the activation of the receptor by a clockwise rotation of about 15° of helix TM2 and a displacement of this helix by 0.9 A at the cytoplasmic surface.

The effective acceleration of plasma outflow in the paraboloidal magnetic field

Abstract: The problem of the efficiency of particle acceleration for a paraboloidal poloidal magnetic field is considered within the approach of steady axisymmetric magnetohydrodynamic (MHD) flow. For the large Michel magnetization parameter σ it is possible to linearize the stream equation near the force-free solution and to solve the problem self-consistently as was done by Beskin, Kuznetsova & Rafikov for a monopole magnetic field. It is shown that, on the fast magnetosonic surface (FMS), the particle Lorentz factor y does not exceed the standard value σ 1/3 . On the other hand, in the supersonic region, the Lorentz factor grows with the distance z from the equatorial plane as y ≈ (z/R L ) 1/2 up to the distance z ≈ σ 2 R L , where R L = c/Ω F is the radius of the light cylinder. Thus, the maximal Lorentz factor is γ max ≈ σ, which corresponds to almost the full conversion of the Poynting energy flux into the particle kinetic one.

Deterministic microscopic three-phase traffic flow models

Abstract: Two different deterministic microscopic traffic flow models, which are in the context of the Kerner's there-phase traffic theory, are introduced. In an acceleration time delay model (ATD model), different time delays in driver acceleration associated with driver behaviour in various local driving situations are explicitly incorporated into the model. Vehicle acceleration depends on local traffic situation, i.e., whether a driver is within the free flow or synchronized flow or else wide moving jam traffic phase. In a speed adaptation model (SA model), vehicle speed adaptation occurs in synchronized flow depending on driving conditions. It is found that the ATD and SA models show spatiotemporal congested traffic patterns that are adequate with empirical results. In the ATD and SA models, the onset of congestion in free flow at a freeway bottleneck is associated with a first-order phase transition from free flow to synchronized flow; moving jams emerge spontaneously in synchronized flow only. Differences between the ATD and SA models are studied. A comparison of the ATD and SA models with stochastic models in the context of three-phase traffic theory is made. A critical discussion of earlier traffic flow theories and models based on the fundamental diagram approach is presented.

Mars water vapor abundance from SPICAM IR spectrometer: Seasonal and geographic distributions

Abstract: Received 2 February 2006; revised 7 July 2006; accepted 11 July 2006; published 26 September 2006. [1] The near-IR channel of SPICAM experiment on Mars Express spacecraft is a 800-g acousto-optic tunable filter (AOTF)–based spectrometer operating in the spectral range of 1–1.7 mm with resolving power of � 2000. It was put aboard as an auxiliary channel dedicated to nadir H2O measurements in the 1.37-mm spectral band. This primary scientific goal of the experiment is achieved though successful water vapor retrievals, resulting in spatial and seasonal distributions of H2O. We present the results of H2O retrieval from January 2004 (Ls = 330� ) to December 2005 (Ls = 340� ), covering the entire Martian year. The seasonal trend of water vapor obtained by SPICAM IR is consistent with TES results and reveals disagreement with MAWD results related to south pole maximum. The main feature of SPICAM measurements is globally smaller water vapor abundance for all seasons and locations including polar regions, as compared to other data. The maximum abundance is 50–55 precipitable microns at the north pole and 13–16 precipitable microns (pr mm) at the south pole. The northern tropical maximum amounts to 12–15 pr mm. Possible reasons for the disagreements are discussed.

SPICAM IR acousto-optic spectrometer experiment on Mars Express

Abstract: SPICAV IR, a part of SPICAV/SOIR suite on Venus Express, is a compact single pixel spectrometer for the spectral range of 0.65–1.7 mm based on acousto-optical tunable filter (AOTF) technology. SPICAV IR is derived from SPICAM IR operating on Mars Express, the first AOTF spectrometer in the deep space, and adapted for Venus atmosphere measurements. The spectrometer sequentially measures spectra of reflected solar radiation from Venus on the dayside and the emitted Venus radiation in spectral ‘‘windows’’ on the nightside, and works also in solar occultation mode. The spectral range is 0.65– 1.1 mm with spectral resolution of 7.8 cm � 1 , and 1–1.7 mm with spectral resolution of 5.2 cm � 1 .A description of this near-IR instrument, its calibration, in-flight performances, and the modes of operations on Venus’ orbit are presented. A brief overview of the science measurements is given: water vapor measurements in the mesosphere on the day-side and near surface on the nightside, mapping of the O2(a 1 Dg) emission at 1.27 mm, aerosol studies via polarization and scattering solar radiation at the day-side, and measurements of aerosol properties at the tops of the clouds in solar occultations.

Regulation of mitochondria distribution by RhoA and formins

Abstract: The distribution of mitochondria is strictly controlled by the cell because of their vital role in energy supply, regulation of cytosolic Ca2+ concentration and apoptosis. We employed cultured mammalian CV-1 cells and Drosophila BG2-C2 neuronal cells with enhanced green fluorescent protein (EGFP)-tagged mitochondria to investigate the regulation of their movement and anchorage. We show here that lysophosphatidic acid (LPA) inhibits fast mitochondrial movements in CV-1 cells acting through the small GTPase RhoA. The action of RhoA is mediated by its downstream effectors: formin-homology family members mDia1 in mammalian cells and diaphanous in Drosophila. Overexpression of constitutively active mutant forms of formins leads to dramatic loss of mitochondrial motility and to their anchorage to actin microfilaments. Conversely, depletion of endogenous diaphanous protein in BG2-C2 cells by RNA interference (RNAi) stimulates the mitochondrial movement. These effects are not simply explained by increased cytoplasm viscosity resulting from an increased F-actin concentration since stimulators of Arp2/3-dependent actin polymerization and jasplakinolide do not cause inhibition. The observed effects are highly specific to mitochondria since perturbations of diaphanous or mDia1 have no effect on movement of other membrane organelles. Thus, mitochondrial movement is controlled by the small GTPase RhoA and this control is mediated by formins.

Plasma-assisted combustion

Abstract: This paper presents an overview of experimental and numerical investigations of the nonequilibrium cold plasma generated under high overvoltage and further usage of this plasma for plasma-assisted combustion. Here, two different types of the discharge are considered: a streamer under high pres- sure and the so-called fast ionization wave (FIW) at low pressure. The comprehensive experimental investigation of the processes of alkane slow oxida- tion in mixtures with oxygen and air under nanosecond uniform discharge has been per- formed. The kinetics of alkane oxidation has been measured from methane to decane in stoichiometric and lean mixtures with oxygen and air at room temperature under the action of high-voltage nanosecond uniform discharge. The efficiency of nanosecond discharges as active particles generator for plasma-as- sisted combustion and ignition has been investigated. The study of nanosecond barrier dis- charge influence on a flame propagation and flame blow-off velocity has been carried out. With energy input negligible in comparison with the burner's chemical power, a double flame blow-off velocity increase has been obtained. A signicant shift of the ignition delay time in comparison with the autoignition has been registered for all mixtures. Detonation initiating by high-voltage gas discharge has been demonstrated. The energy deposition in the discharge ranged from 70 mJ to 12 J. The ignition delay time, the velocity of the flame front propagation, and the electrical characteristics of the discharge have been measured during the experiments. Under the conditions of the experiment, three modes of the flame front propagation have been observed, i.e., deflagration, transient detonation, and Chapman-Jouguet detonation. The efficiency of the pulsed nanosecond discharge to defla- gration-to-detonation transition (DDT) control has been shown to be very high.

Microscopic features of moving traffic jams.

Abstract: Empirical and numerical microscopic features of moving traffic jams are presented. Based on a single vehicle data analysis, it is found that within wide moving jams, i.e., between the upstream and downstream jam fronts there is a complex microscopic spatiotemporal structure. This jam structure consists of alternations of regions in which traffic flow is interrupted and flow states of low speeds associated with "moving blanks" within the jam. Moving blanks within a wide moving jam resemble electron holes in the valence band of semiconductors: As the moving blanks that propagate upstream appear due to downstream vehicle motion within the jam, so appearance of electron holes moving with the electric field results from electron motion against the electric field in the valence band of semiconductors. Empirical features of moving blanks are found. Based on microscopic models in the context of the Kerner's three-phase traffic theory, physical reasons for moving blanks emergence within wide moving jams are disclosed. Microscopic nonlinear effects of moving jam emergence, propagation, and dissolution as well as a diverse variety of hysteresis effects in freeway traffic associated with phase transitions and congested traffic propagation are numerically investigated. Microscopic structure of moving jam fronts is numerically studied and compared with empirical results.

Annihilation Emission from the Galactic Black Hole

Abstract: Both diffuse high-energy gamma rays and an extended electron-positron annihilation line emission have been observed in the Galactic Center (GC) region. Although X-ray observations indicate that the Galactic black hole Sgr A* is inactive now, we suggest that Sgr A* can become active when a captured star is tidally disrupted and matter is accreted into the black hole. As a consequence the Galactic black hole could be a powerful source of relativistic protons. We are able to explain the current observed diffuse gamma rays and the very detailed 511 keV annihilation line of secondary positrons by p-p collisions of such protons, with appropriate injection times and energy. Relativistic protons could have been injected into the ambient material if the black hole captured a 50 M☉ star at several tens times 106 yr ago. An alternative possibility is that the black hole continues to capture stars with ~1 M☉ every 105 yr. Secondary positrons produced by p-p collisions at energies 30 MeV are cooled down to thermal energies by Coulomb collisions and are annihilated in the warm neutral and ionized phases of the interstellar medium with temperatures about several eV, because the annihilation cross section reaches its maximum at these temperatures. It takes about 10 million years for the positrons to cool down to thermal temperatures so that they can diffuse into a very large extended region around the GC. A much more recent star capture may also be able to account for recent TeV observations within 10 pc of the GC, as well as for the unidentified GeV gamma-ray sources found by EGRET at GC. The spectral difference between the GeV and TeV flux could be explained naturally in this model as well.

Efficient lasing in a Fe2+:ZnSe crystal at room temperature

Abstract: Efficient room-temperature lasing is obtained in a Fe2+:ZnSe crystal pumped by 2.9364-?m giant pulses from an Er:YAG laser. The slope efficiency of a Fe2+:ZnSe laser with respect to the absorbed pump energy is 13%. The laser with a dispersion resonator can be continuously tuned from 3.95 to 5.05 ?m. The luminescence lifetime of the 5T2 level of the Fe2+ ion in a ZnSe matrix at room temperature is measured to be 355?15 ns.

Direct numerical simulation of disturbances generated by periodic suction-blowing in a hypersonic boundary layer

Abstract: A numerical algorithm and code are developed and applied to direct numerical simulation (DNS) of unsteady two-dimensional flow fields relevant to stability of the hypersonic boundary layer. An implicit second-order finite-volume technique is used for solving the compressible Navier–Stokes equations. Numerical simulation of disturbances generated by a periodic suction-blowing on a flat plate is performed at free-stream Mach number 6. For small forcing amplitudes, the second-mode growth rates predicted by DNS agree well with the growth rates resulted from the linear stability theory (LST) including nonparallel effects. This shows that numerical method allows for simulation of unstable processes despite its dissipative features. Calculations at large forcing amplitudes illustrate nonlinear dynamics of the disturbance flow field. DNS predicts a nonlinear saturation of fundamental harmonic and rapid growth of higher harmonics. These results are consistent with the experimental data of Stetson and Kimmel obtained on a sharp cone at the free-stream Mach number 8.

Monotonicity Criteria for Difference Schemes Designed for Hyperbolic Equations

Abstract: Previously formulated monotonicity criteria for explicit two-level difference schemes designed for hyperbolic equations (S.K. Godunov’s, A. Harten’s (TVD schemes), characteristic criteria) are extended to multileveled, including implicit, stencils. The characteristic monotonicity criterion is used to develop a universal algorithm for constructing high-order accurate nonlinear monotone schemes (for an arbitrary form of the desired solution) based on their analysis in the space of grid functions. Several new fourth-to-third-order accurate monotone difference schemes on a compact three-level stencil and nonexpanding (three-point) stencils are proposed for an extended system, which ensures their monotonicity for both the desired function and its derivatives. The difference schemes are tested using the characteristic monotonicity criterion and are extended to systems of hyperbolic equations.

IR differential-absorption lidars for ecological monitoring of the environment

Abstract: A review of studies on lidar sensing of the environment by the method of IR differential absorption is presented The differential-absorption method is described and its various applications are considered A comparison of this method with other methods of lidar sensing showed that a differential-absorption lidar successfully supplements a Raman lidar The basic parameters are presented for IR lidars fabricated recently by various research groups The outlook for the IR lidar sensing of the atmosphere is discussed

Criterion for traffic phases in single vehicle data and empirical test of a microscopic three-phase traffic theory

Abstract: Based on empirical and numerical microscopic analyses, the physical nature of a qualitatively different behaviour of the wide moving jam phase in comparison with the synchronized flow phase—microscopic traffic flow interruption within the wide moving jam phase—is found. A microscopic criterion for distinguishing the synchronized flow and wide moving jam phases in single vehicle data measured at a single freeway location is presented. Based on this criterion, empirical microscopic classification of different local congested traffic states is performed. Simulations made show that the microscopic criterion and macroscopic spatiotemporal objective criteria lead to the same identification of the synchronized flow and wide moving jam phases in congested traffic. Microscopic models in the context of three-phase traffic theory have been tested based on the microscopic criterion for the phases in congested traffic. It is found that microscopic three-phase traffic models can explain both microscopic and macroscopic empirical congested pattern features. It is obtained that microscopic frequency distributions for vehicle speed difference as well as fundamental diagrams and speed correlation functions can depend on the spatial co-ordinate considerably. It turns out that microscopic optimal velocity (OV) functions and time headway distributions are not necessarily qualitatively different, even if local congested traffic states are qualitatively different. The reason for this is that important spatiotemporal features of congested traffic patterns are lost in these as well as in many other macroscopic and microscopic traffic characteristics, which are widely used as the empirical basis for a test of traffic flow models, specifically, cellular automata traffic flow models.

Observation of O2 1.27 μm dayglow by SPICAM IR: Seasonal distribution for the first Martian year of Mars Express

Abstract: [1] The O2(a1Δg) molecule is a result of the photodissociation of ozone in the Martian atmosphere and may be used as a tracer for atmospheric ozone mostly above ∼20 km since the singlet delta state is quenched by carbon dioxide at lower altitudes. The SPICAM IR acousto-optic tunable filter (AOTF) spectrometer is a part of the SPICAM experiment onboard Mars Express. It is able to measure the O2 singlet delta emission band at 1.27 μm with a resolving power of ∼2200. We present the first seasonal map of the O2 emission covering the entire Martian year. Maximal values of O2 emission are observed during late winter to early spring at high latitudes in both hemispheres. We report the highest dayglow intensity of 30 MR in the southern hemisphere (70°–80°S latitudes) at Ls = 185°–195° and of 26 MR in the north polar regions (latitudes 70°–80°N) at Ls = 10°–20°. The lowest emissions are measured during the southern hemisphere summer near perihelion (Ls = 270°–330°), with an upper limit of 1–2 MR. At low latitudes (30°S–30°N) the seasonal evolution of the O2 emission shows a distinct maximum (5–7 MR) near aphelion. This is consistent with the maximum in O3 occurring at this time of the year, which has been reported from Earth, from satellite, or by modeling studies. The comparison of our results with previous measurements carried out from Earth shows quantitative differences that can be attributed to differences in local time of the observation or interannual variability of the Martian ozone layer.

Boundary Layer Separation Plasma Control Using Low-Temperature Non-Equilibrium Plasma of Gas Discharge

Abstract: The influence of pulsed sliding discharge on the flow separation has been investigated. The high efficiency of pulsed discharge was shown within the velocity range from 20 to 110 m/s. The dynamics of discharge propagation with nanosecond time resolution was obtained. The influence of electrodes geometry was investigated. It was found that discharge affects flow separation while the electrodes were placed in parallel to the gas flow so the streamers propagated perpendicular to the flow. The conclusion was made that main mechanism of plasma influence is the boundary layer turbulization.

Vapour growth of II-VI single crystals doped by transition metals for mid-infrared lasers

Abstract: A modified vapour phase contact-free method to grow homogeneous single crystals of II-VI compounds doped by transition metals is presented. Single crystals of ZnSe:Cr, ZnSe:Fe, ZnSe:Co, ZnSe:Ni, CdSe:Cr, ZnTe:Cr, ZnS:Fe and ZnS:Mn with doping level up to 1019 cm–3 have been grown. Efficient lasing at about 2.5 and 4 µm with ZnSe:Cr and ZnSe:Fe crystals respectively has been achieved. Dependence of Fe2+:ZnSe laser characteristics on temperature is presented in more detail. A possibility of using Cr2+:ZnSe laser in intracavity laser spectroscopy is demonstrated. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Hypersonic Laminar Flow Control Using a Porous Coating of Random Microstructure

Abstract: It is shown that a passive porous coating of random structure (felt metal) significantly delays transition on a sharp cone at zero angle of attack in the Mach=12 wind tunnel. A semi-empirical method is developed to predict acoustic properties of randomly structured coatings including effects of gas rarefaction. This method simplifies calculations of the boundary conditions on the porous coating and solving the boundary-layer stability problem. The transition onset points on coated and uncoated cone surfaces are calculated using the -method. With this approach theoretical predictions agree satisfactorily with the experimental data. For the first time it is demonstrated that porous coatings of random microstructure, which are synergistic with fiber-ceramic thermal protection systems (TPS), can be used for hypersonic laminar-flow control. This provides symbiotic reduction of aeroheating and reduced skin friction drag. It also leads to a new family of lightweight TPS. N e

Construction of non-repeating frequency-hopping sequences with no-hit zone

Abstract: Based on finite field GF(p/sup m/), a new construction of frequency-hopping (FH) sequences with no-hit zone for quasi-synchronous FH code-division multiple-access systems to eliminate multiple-access interference is presented. These new FH patterns are non-repeating and possess ideal Hamming autocorrelation.

Passive Fe2+: ZnSe single-crystal Q switch for 3-mu m lasers

Abstract: Passive Q-switching of 3-μm lasers with the help of a Fe2+:ZnSe single crystal is demonstrated. The 6-mJ, 50-ns giant pulses are obtained from a 2.9364-μm Er:YAG laser by using this passive Q switch.

Single-cycle high-intensity electromagnetic pulse generation in the interaction of a plasma wakefield with regular nonlinear structures

Abstract: The interaction of regular nonlinear structures (such as subcycle solitons, electron vortices, and wake Langmuir waves) with a strong wake wave in a collisionless plasma can be exploited in order to produce ultrashort electromagnetic pulses. The electromagnetic field of the nonlinear structure is partially reflected by the electron density modulations of the incident wake wave and a single-cycle high-intensity electromagnetic pulse is formed. Due to the Doppler effect the length of this pulse is much shorter than that of the nonlinear structure. This process is illustrated with two-dimensional particle-in-cell simulations. The considered laser-plasma interaction regimes can be achieved in present day experiments and can be used for plasma diagnostics.