Non-Maxwellian Molecular Velocity Distribution at Large Knudsen Numbers
Shim, Jae Wan
2012-01-01
We have derived a non-Maxwellian molecular velocity distribution at large Knudsen numbers for ideal gas. This distribution approaches Maxwellian molecular velocity distribution as the Knudsen number approaches zero. We have found that the expectation value of the square of velocity is the same in the non-Maxwellian molecular velocity distribution as it is in the Maxwellian distribution; however, the expectation value of the speed is not the same.
Creating Non-Maxwellian Velocity Distributions in Ultracold Plasmas
Castro, J; McQuillen, P; Pohl, T; Killian, T C
2011-01-01
We present techniques to perturb, measure and model the ion velocity distribution in an ultracold neutral plasma produced by photoionization of strontium atoms. By optical pumping with circularly polarized light we promote ions with certain velocities to a different spin ground state, and probe the resulting perturbed velocity distribution through laser-induced fluorescence spectroscopy. We discuss various approaches to extract the velocity distribution from our measured spectra, and assess their quality through comparisons with molecular dynamic simulations
The auroral O+ non-Maxwellian velocity distribution function revisited
Directory of Open Access Journals (Sweden)
F. Leblanc
Full Text Available New characteristics of O+ ion velocity distribution functions in a background of atomic oxygen neutrals subjected to intense external electromagnetic forces are presented. The one dimensional (1-D distribution function along the magnetic field displays a core-halo shape which can be accurately fitted by a two Maxwellian model. The Maxwellian shape of the 1-D distribution function around a polar angle of 21 ± 1° from the magnetic field direction is confirmed, taking into account the accuracy of the Monte Carlo simulations. For the first time, the transition of the O+ 1-D distribution function from a core halo shape along the magnetic field direction to the well-known toroidal shape at large polar angles, through the Maxwellian shape at polar angle of 21 ± 1° is properly explained from a generic functional of the velocity moments at order 2 and 4.
Computing a non-Maxwellian velocity distribution from first principles.
Cáceres, Manuel O
2003-01-01
We investigate a family of single-particle anomalous velocity distribution by solving a particular class of stochastic Liouville equations. The stationary state is obtained analytically and the Maxwell-Boltzmann distribution is reobtained in a particular limit. We discuss the comparison with other different methods to obtain the stationary state. Extensions when the models cannot be solved in an exact way are also pointed out in connection with the one-ficton approximation.
Beausang, K V; Prunty, S L; Scannell, R; Beurskens, M N; Walsh, M J; de la Luna, E
2011-03-01
The present work is motivated by a long standing discrepancy between the electron temperature measurements of Thomson scattering (TS) and electron cyclotron emission (ECE) diagnostics for plasmas with strong auxiliary heating observed at both JET and TFTR above 6–7 keV, where in some cases the ECE electron temperature measurements can be 15%–20% higher than the TS measurements. Recent analysis based on ECE results at JET has shown evidence of distortions to the Maxwellian electron velocity distribution and a correlation with the TS and ECE discrepancies has been suggested. In this paper, a technique to determine the presence of non-Maxwellian behavior using TS diagnostics is outlined. The difficulties and limitations of modern TS system designs to determine the electron velocity distribution are also discussed. It is demonstrated that small deviations such as those suggested by previous ECE analysis could be potentially detected, depending on the spectral layout of the TS polychromators. The spectral layout of the JET high resolution Thomson scattering system is such that it could be used to determine these deviations between 1 and 6 keV, and the results presented here indicate that no evidence of non-Maxwellian behavior is observed in this range. In this paper, a modification to the current polychromator design is proposed, allowing non-Maxwellian distortions to be detected up to at least 10 keV.
Beausang, K. V.; Prunty, S. L.; Scannell, R.; Beurskens, M. N.; Walsh, M. J.; de La Luna, E.; Jet Efda Contributors
2011-03-01
The present work is motivated by a long standing discrepancy between the electron temperature measurements of Thomson scattering (TS) and electron cyclotron emission (ECE) diagnostics for plasmas with strong auxiliary heating observed at both JET and TFTR above 6-7 keV, where in some cases the ECE electron temperature measurements can be 15%-20% higher than the TS measurements. Recent analysis based on ECE results at JET has shown evidence of distortions to the Maxwellian electron velocity distribution and a correlation with the TS and ECE discrepancies has been suggested. In this paper, a technique to determine the presence of non-Maxwellian behavior using TS diagnostics is outlined. The difficulties and limitations of modern TS system designs to determine the electron velocity distribution are also discussed. It is demonstrated that small deviations such as those suggested by previous ECE analysis could be potentially detected, depending on the spectral layout of the TS polychromators. The spectral layout of the JET high resolution Thomson scattering system is such that it could be used to determine these deviations between 1 and 6 keV, and the results presented here indicate that no evidence of non-Maxwellian behavior is observed in this range. In this paper, a modification to the current polychromator design is proposed, allowing non-Maxwellian distortions to be detected up to at least 10 keV
A generalized AZ-non-Maxwellian velocity distribution function for space plasmas
Abid, A. A.; Khan, M. Z.; Lu, Quanming; Yap, S. L.
2017-03-01
A more generalized form of the non-Maxwellian distribution function, i.e., the AZ-distribution function is presented. Its fundamental properties are numerically observed by the variation of three parameters: α (rate of energetic particles on the shoulder), r (energetic particles on a broad shoulder), and q (superthermality on the tail of the velocity distribution curve of the plasma species). It has been observed that (i) the A Z - distribution function reduces to the ( r , q ) - distribution for α → 0 ; (ii) the A Z - distribution function reduces to the q - distribution for α → 0 , and r → 0 ; (iii) the A Z -distribution reduces to Cairns-distribution function for r → 0 , and q → ∞ ; (iv) the AZ-distribution reduces to Vasyliunas Cairns distribution for r → 0 , and q = κ + 1 ; (v) the AZ-distribution reduces to kappa distribution for α → 0 , r → 0 , and q = κ + 1 ; and (vi) finally, the AZ-distribution reduces to Maxwellian distribution for α → 0 , r → 0 , and q → ∞ . The uses of this more generalized A Z - distribution function in various space plasmas are briefly discussed.
Yin, L; Daughton, W; Albright, B J; Bezzerides, B; DuBois, D F; Kindel, J M; Vu, H X
2006-02-01
The parametric coupling involving backward stimulated scattering of a laser and electron beam acoustic modes (BAM) is described as observed in particle-in-cell (PIC) simulations. The BAM modes evolve from Langmuir waves (LW) as the electron velocity distribution is nonlinearly modified to be non-Maxwellian by backward stimulated Raman scattering (BSRS). With a marginal damping rate, BAM can be easily excited and allow an extended chirping in frequency to occur as later SRS pulses encounter modified distributions. Coincident with the emergence of this non-Maxwellian distribution is a rapid increase in BSRS reflectivities with laser intensities. Both the reflectivity scaling with laser intensity and the observed spectral features from PIC simulations are consistent with recent Trident experiments.
Roussel-Dupre, R.
1979-01-01
It was shown that, in the presence of the steep temperature gradients characteristic of EUV models of the solar transition region, the electron and proton velocity distribution functions are non-Maxwellian and are characterized by high energy tails. The magnitude of these tails are estimated for a model of the transition region and the heat flux is calculated at a maximum of 30 percent greater than predicted by collision-dominated theory.
Roussel-Dupre, R.
1979-01-01
Non-Maxwellian electron velocity distribution functions, previously computed for Dupree's model of the solar transition region are used to calculate ionization rates for ions of carbon, nitrogen, and oxygen. Ionization equilibrium populations for these ions are then computed and compared with similar calculations assuming Maxwellian distribution functions for the electrons. The results show that the ion populations change (compared to the values computed with a Maxwellian) in some cases by several orders of magnitude depending on the ion and its temperature of formation.
van Lammeren, A. C. A. P.; Barth, C. J.; Vanest, Q. C.; Schüller, F. C.
1992-01-01
The Thomson scattering spectrum represents the projection of the three-dimensional electron velocity distribution on the scattering vector. From this the local electron temperature and density can be derived. To determine the three-dimensional electron velocity distribution it is necessary to have s
Measurement of non-Maxwellian electron velocity distributions in a reflex discharge
Phipps, C. R., Jr.; Bershader, D.
1978-01-01
The results of a ruby laser Thomson scattering study of the space and time-resolved electron velocity distributions in a pulsed Penning discharge in hydrogen are presented. Electron densities were to the order of 10 to the 13th/cu cm and temperatures were roughly 3 eV. This point is just prior to the cessation of the discharge ohmic heating pulse. For magnetic strengths less than 200 G, Maxwellian distributions were found over an energy range six times thermal energy. Temperatures agreed with Langmuir probe data. For fields of 450 G, chaotic plasma potentials were observed to be unstable and the Thomson scattering showed that the electron velocity distributions had central temperatures of 2 eV and wing temperatures of 15-12 eV.
Burgi, A.
1987-01-01
A previous model has shown that in order to account for the charge state distribution in the low-speed solar wind, a high coronal temperature is necessary and that this temperature peak goes together with a peak of nx/np in the corona. In the present paper, one of the assumptions made previously, i.e., that coronal electrons are Maxwellian, is relaxed, and a much cooler model is presented, which could account for the same oxygen charge states in the solar wind due to the inclusion of non-Maxwellian electrons. Also, due to a different choice of the coronal magnetic field geometry, this model would show no enhancement of the coronal nx/np. Results of the two models are then compared, and observational tests to distinguish between the two scenarios are proposed: comparison of directly measured coronal Te to charge state measurements in the solar wind, determination of the coronal nx/np measurement of ion speeds in the acceleration region of the solar wind, and measurement of the frozen-in silicon charge state distribution.
Barth, C J
1988-07-15
A high-transmission (~45%) twenty-channel polychromator equipped with near-infrared sensitive photomultipliers has been constructed to record Thomson scattering spectra at the TORTUR tokamak. The high transmission was achieved by the use of mirrors instead of fiber optics to guide the spectrally resolved light to a set of photomultipliers. Spectral analysis is performed with a holographically ruled concave grating. Acceptable dimensions of the wavelength selection mirrors were obtained by magnifying the spectral image by a factor of 5 with a Mangin mirror. Electron temperatures up to 1000 eV at a density of 5 x 10(19) m(-3) can be measured with an accuracy of approximately l%. Both high sensitivity and high resolution enable the detection of irregularities in the velocity distribution. For example, satellites corresponding to partial densities of (5 +/- 1) x 10(17) m(-3) were found at 23 nm from the laser wavelength.
Che, H
2014-01-01
The formation of the observed core-halo feature in the solar wind electron velocity distribution function is a long-time puzzle. In this letter based on the current knowledge of nanoflares we show that the nanoflare-accelerated electron beams are likely to trigger a strong electron two-stream instability that generates kinetic Alfv\\'en wave and whistler wave turbulence, as we demonstrated in a previous paper. We further show that the core-halo feature produced during the origin of kinetic turbulence is likely to originate in the inner corona and can be preserved as the solar wind escapes to space along open field lines. We formulate a set of equations to describe the heating processes observed in the simulation and show that the core-halo temperature ratio of the solar wind is insensitive to the initial conditions in the corona and is related to the core-halo density ratio of the solar wind and to the quasi-saturation property of the two-stream instability at the time when the exponential decay ends. This rel...
Energy Technology Data Exchange (ETDEWEB)
Che, H.; Goldstein, M. L. [NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
2014-11-10
The formation of the observed core-halo feature in the solar wind electron velocity distribution function is a long-time puzzle. In this Letter, based on the current knowledge of nanoflares, we show that the nanoflare-accelerated electron beams are likely to trigger a strong electron two-stream instability that generates kinetic Alfvén wave and whistler wave turbulence, as we demonstrated in a previous paper. We further show that the core-halo feature produced during the origin of kinetic turbulence is likely to originate in the inner corona and can be preserved as the solar wind escapes to space along open field lines. We formulate a set of equations to describe the heating processes observed in the simulation and show that the core-halo temperature ratio of the solar wind is insensitive to the initial conditions in the corona and is related to the core-halo density ratio of the solar wind and to the quasi-saturation property of the two-stream instability at the time when the exponential decay ends. This relation can be extended to the more general core-halo-strahl feature in the solar wind. The temperature ratio between the core and hot components is nearly independent of the heliospheric distance to the Sun. We show that the core-halo relative drift previously reported is a relic of the fully saturated two-stream instability. Our theoretical results are consistent with the observations while new tests for this model are provided.
Kinetic corrections from analytic non-Maxwellian distribution functions in magnetized plasmas
Izacard, Olivier
2016-01-01
In magnetized plasma physics, almost all developed analytic theories assume a Maxwellian distribution function (MDF) and in some cases small deviations are described using the perturbation theory. The deviations with respect to the Maxwellian equilibrium, called kinetic effects, are required to be taken into account specially for fusion reactor plasmas. Generally, because the perturbation theory is not consistent with observed steady-state non-Maxwellians, these kinetic effects are numerically evaluated by very CPU-expensive codes, avoiding the analytic complexity of velocity phase space integrals. We develop here a new method based on analytic non-Maxwellian distribution functions constructed from non-orthogonal basis sets in order to (i) use as few parameters as possible, (ii) increase the efficiency to model numerical and experimental non-Maxwellians, (iii) help to understand unsolved problems such as diagnostics discrepancies from the physical interpretation of the parameters, and (iv) obtain analytic cor...
Weng, Su-Ming; Sheng, Zheng-Ming; Zhang, Jie
2009-11-01
Inverse bremsstrahlung (IB) absorption and evolution of the electron distribution function (EDF) in a wide laser intensity range (10;{12}-10;{17} W/cm;{2}) have been studied systematically by a two velocity-dimension Fokker-Planck code. It is found that Langdon's IB operator overestimates the absorption rate at high laser intensity, consequently with an overdistorted non-Maxwellian EDF. According to the small anisotropy of EDF in the oscillation frame, we introduce an IB operator which is similar to Langdon's but without the low laser intensity limit. This operator is appropriate for self-consistently tackling the nonlinear effects of high laser intensity as well as non-Maxwellian EDF. Particularly, our operator is capable of treating IB absorption properly in the indirect and direct-drive inertial confinement fusion schemes with the National Ignition Facility and Laser MegaJoule laser parameters at focused laser intensity beyond 10;{15} W/cm;{2} .
Kinetic corrections from analytic non-Maxwellian distribution functions in magnetized plasmas
Energy Technology Data Exchange (ETDEWEB)
Izacard, Olivier, E-mail: izacard@llnl.gov [Lawrence Livermore National Laboratory, 7000 East Avenue, L-637, Livermore, California 94550 (United States)
2016-08-15
In magnetized plasma physics, almost all developed analytic theories assume a Maxwellian distribution function (MDF) and in some cases small deviations are described using the perturbation theory. The deviations with respect to the Maxwellian equilibrium, called kinetic effects, are required to be taken into account especially for fusion reactor plasmas. Generally, because the perturbation theory is not consistent with observed steady-state non-Maxwellians, these kinetic effects are numerically evaluated by very central processing unit (CPU)-expensive codes, avoiding the analytic complexity of velocity phase space integrals. We develop here a new method based on analytic non-Maxwellian distribution functions constructed from non-orthogonal basis sets in order to (i) use as few parameters as possible, (ii) increase the efficiency to model numerical and experimental non-Maxwellians, (iii) help to understand unsolved problems such as diagnostics discrepancies from the physical interpretation of the parameters, and (iv) obtain analytic corrections due to kinetic effects given by a small number of terms and removing the numerical error of the evaluation of velocity phase space integrals. This work does not attempt to derive new physical effects even if it could be possible to discover one from the better understandings of some unsolved problems, but here we focus on the analytic prediction of kinetic corrections from analytic non-Maxwellians. As applications, examples of analytic kinetic corrections are shown for the secondary electron emission, the Langmuir probe characteristic curve, and the entropy. This is done by using three analytic representations of the distribution function: the Kappa distribution function, the bi-modal or a new interpreted non-Maxwellian distribution function (INMDF). The existence of INMDFs is proved by new understandings of the experimental discrepancy of the measured electron temperature between two diagnostics in JET. As main results, it
Kinetic corrections from analytic non-Maxwellian distribution functions in magnetized plasmas
Izacard, Olivier
2016-08-01
In magnetized plasma physics, almost all developed analytic theories assume a Maxwellian distribution function (MDF) and in some cases small deviations are described using the perturbation theory. The deviations with respect to the Maxwellian equilibrium, called kinetic effects, are required to be taken into account especially for fusion reactor plasmas. Generally, because the perturbation theory is not consistent with observed steady-state non-Maxwellians, these kinetic effects are numerically evaluated by very central processing unit (CPU)-expensive codes, avoiding the analytic complexity of velocity phase space integrals. We develop here a new method based on analytic non-Maxwellian distribution functions constructed from non-orthogonal basis sets in order to (i) use as few parameters as possible, (ii) increase the efficiency to model numerical and experimental non-Maxwellians, (iii) help to understand unsolved problems such as diagnostics discrepancies from the physical interpretation of the parameters, and (iv) obtain analytic corrections due to kinetic effects given by a small number of terms and removing the numerical error of the evaluation of velocity phase space integrals. This work does not attempt to derive new physical effects even if it could be possible to discover one from the better understandings of some unsolved problems, but here we focus on the analytic prediction of kinetic corrections from analytic non-Maxwellians. As applications, examples of analytic kinetic corrections are shown for the secondary electron emission, the Langmuir probe characteristic curve, and the entropy. This is done by using three analytic representations of the distribution function: the Kappa distribution function, the bi-modal or a new interpreted non-Maxwellian distribution function (INMDF). The existence of INMDFs is proved by new understandings of the experimental discrepancy of the measured electron temperature between two diagnostics in JET. As main results, it
Non-Maxwellian electron distributions in models of the solar atmosphere
Macneice, P.; Fontenla, J.; Ljepojevic, N. N.
1991-01-01
In this paper, the solar models of Fontenla et al. (1990) are extended to coronal temperatures using optically thin radiative losses and a semicircular loop geometry. The effects of a non-Maxwellian high-energy tail of the electron distribution function is tested by performing a Fokker-Planck calculation of the tail. The results show that the downward conductive heat flux is very clsoe to that given by Braginskii (1965) for small departures from a Maxwellian distribution. The effects of the high-energy tail of the electron distribution on element ionization are computed and found to be negligible for all ionization states of O, Ne, and Si. It is concluded that, for quiet sun loop models in stationary energy balance, the ionization state of all elements is not significantly affected by the non-Maxwellian tail of the electron velocity distribution, and that the heat flux can be computed by considering only small first-order departures from the Maxwellian distribution.
Muñoz, P. A.; J. Büchner
2016-01-01
Non-Maxwellian electron velocity space distribution functions (EVDF) are useful signatures of plasma conditions and non-local consequences of collisionless magnetic reconnection. In the past, EVDFs were obtained mainly for antiparallel reconnection and under the influence of weak guide-fields in the direction perpendicular to the reconnection plane. EVDFs are, however, not well known, yet, for oblique (or component-) reconnection in dependence on stronger guide-magnetic fields and for the exh...
Study of non-Maxwellian distributions of electron energies in the solar transition region
Liao, Lamei; He, Jian
2017-01-01
For accurate spectral diagnostics in the solar transition region, we discuss the electron energies for non-Maxwellian distributions both for and Druyvesteyn distributions. We analyze the difference between the κ and the Druyvesteyn distributions with the Maxwellian distribution and derive the expressions for the averaged collision strengths for the κ and the Druyvesteyn distributions. This discussion will be significant for spectral diagnostics of the electron density and temperature in the solar transition region.
Non-Maxwellian electron distributions in clusters of galaxies
Kaastra, J.S.; Bykov, A.M.; Werner, N.
2009-01-01
Context. Thermal X-ray spectra of clusters of galaxies and other sources are commonly calculated assuming Maxwellian electron distributions. There are situations where this approximation is not valid, for instance near interfaces of hot and cold gas and near shocks. Aims. The presence of non-thermal
Kinetic corrections from analytic non-Maxwellian distribution functions in magnetized plasmas
Izacard, Olivier
2016-01-01
In magnetized plasma physics, almost all developed analytic theories assume a Maxwellian distribution function (MDF) and in some cases small deviations are described using the perturbation theory. The deviations with respect to the Maxwellian equilibrium, called kinetic effects, are required to be taken into account specially for fusion reactor plasmas. Generally, because the perturbation theory is not consistent with observed steady-state non-Maxwellians, these kinetic effects are numericall...
Sehar, Sumbul; Nouman Sarwar, Qureshi Muhammad
2016-04-01
In many physical situations such as space or laboratory plasmas a hot low-density electron populations can be generated superimposed on the bulk cold population, resulting in a particle distribution function consisting of a dense cold part and hot superthermal tail. Space observations show that electron distributions are often observed with flat top at low energies and high energy tails. The appropriate distribution to model such non-Maxwellian features is the generalized (r,q) distribution function which in limiting forms can be reduced to kappa and Maxwellian distribution functions. In this study, Kinetic model is employed to study the electron-acoustic and ion-ion acoustic instabilities in four component plasma with generalized (r,q) distribution function for both magnetized and unmagnetized plasmas. Departure of plasma from Maxwellian distributions significantly alters the growth rates as compared to the Maxwellian plasma. Significant growth observed for highly non-Maxwellian distributions as well as plasmas with higher dense and hot electron population. Existence of weak damping is also established when the distribution contains broadened flat tops at the low energies or tends to be Maxwellian. These results may be applied in both experimental and space physics regimes.
Muñoz, P A
2016-01-01
Non-Maxwellian electron velocity space distribution functions (EVDF) are useful signatures of plasma conditions and non-local consequences of collisionless magnetic reconnection. In the past, the evolution of the EVDFs was investigated mainly for antiparallel or weak-guide-field reconnection. The shape of EVDFs is, however, not well known yet for oblique (or component-) reconnection in dependence on a finite guide magnetic field component perpendicular to the reconnection plane. In view of the multi-spacecraft mission MMS, we derive the non-Maxwellian features of EVDFs formed by collisionless magnetic reconnection starting from very weak ($b_g\\approx0$) up to very strong ($b_g=8$) guide-field strengths $b_g$, taking into account the feedback of the self-generated turbulence. For this sake, we carry out 2.5D fully-kinetic Particle-in-Cell (PiC) simulations using the ACRONYM code. We obtained anisotropic EVDFs and the distribution of electron beams propagating along the separatrices as well as in the exhaust re...
Dzifcakova, Elena
2013-01-01
New data for calculation of the ionization and recombination rates have have been published in the past few years. Most of these are included in CHIANTI database. We used these data to calculate collisional ionization and recombination rates for the non-Maxwellian kappa-distributions with an enhanced number of particles in the high-energy tail, which have been detected in the solar transition region and the solar wind. Ionization equilibria for elements H to Zn are derived. The kappa-distributions significantly influence both the ionization and recombination rates and widen the ion abundance peaks. In comparison with Maxwellian distribution, the ion abundance peaks can also be shifted to lower or higher temperatures. The updated ionization equilibrium calculations result in large changes for several ions, notably Fe VIII--XIV. The results are supplied in electronic form compatible with the CHIANTI database.
Owocki, S. P.; Scudder, J. D.
1983-01-01
Analytic expressions are derived for ionization and recombination rates in a parameterized non-Maxwellian electron velocity distribution with an enhanced high-energy tail. These expressions are then used in investigating the effect of such an enhancement in the high-energy tail of the coronal electron velocity distribution on the oxygen and iron ionization balances, O(+6) - O(+7) and Fe(+11) - Fe(+12). Relative to a Maxwellian of the same mean electron energy, the degree of ionization allowed by such a distribution is found to be either unchanged or slightly decreased for iron but often substantially increased for oxygen. The greater sensitivity of oxygen ionization balance to the high-energy distribution tail derives from the higher oxygen ionization threshold energy. It is noted that the electron temperature inferred from a measurement of the oxygen ionization ratio, O(+6)/O(+7), could indeed overestimate the actual coronal electron temperature by nearly 10 to the 6th K if the coronal electron distribution is incorrectly assumed to be Maxwellian.
Toncian, T; McCary, E; Meadows, A; Arefiev, A V; Blakeney, J; Serratto, K; Kuk, D; Chester, C; Roycroft, R; Gao, L; Fu, H; Yan, X Q; Schreiber, J; Pomerantz, I; Bernstein, A; Quevedo, H; Dyer, G; Ditmire, T; Hegelich, B M
2015-01-01
The irradiation of few nm thick targets by a finite-contrast high-intensity short-pulse laser results in a strong pre-expansion of these targets at the arrival time of the main pulse. The targets decompress to near and lower than critical densities plasmas extending over few micrometers, i.e. multiple wavelengths. The interaction of the main pulse with such a highly localized but inhomogeneous target leads to the generation of a short channel and further self-focusing of the laser beam. Experiments at the GHOST laser system at UT Austin using such targets measured non-Maxwellian, peaked electron distribution with large bunch charge and high electron density in the laser propagation direction. These results are reproduced in 2D PIC simulations using the EPOCH code, identifying Direct Laser Acceleration (DLA) as the responsible mechanism. This is the first time that DLA has been observed to produce peaked spectra as opposed to broad, maxwellian spectra observed in earlier experiments. This high-density electron...
Non-Maxwellian electron distributions by direct laser acceleration in near-critical plasmas
Toncian, T.; Wang, C.; Arefiev, A.; McCary, E.; Meadows, A.; Blakeney, J.; Chester, C.; Roycroft, R.; Fu, H.; Yan, X. Q.; Schreiber, J.; Pomerantz, I.; Quevedo, H.; Dyer, G.; Gaul, E.; Ditmire, T.; Hegelich, B. M.
2015-11-01
The irradiation of few nm thick targets by a finite-contrast high-intensity short-pulse laser results in a strong pre-expansion of these targets at the arrival time of the main pulse. The targets will decompress to near and lower than critical electron densities plasmas extending over lengths of few micrometers. The laser-matter interaction of the main pulse with such a highly localized but inhomogeneous the target leads to the generation of a channel and further self focussing of the laser beam. As measured in a experiment conducted with the GHOST laser system at UT Austin, 2D PIC simulations predict Direct Laser Acceleration of non-Maxwellian electron distribution in the laser propagation direction for such targets. The hereby high density electron bunches have potential applications as injector beams for a further wakefield acceleration stage. This work was supported by NNSA cooperative agreement DE-NA0002008, the DARPA's PULSE program (12-63-PULSE-FP014) and the AFOSR (FA9550-14-1-0045).
Muñoz, P. A.; Büchner, J.
2016-10-01
Non-Maxwellian electron velocity space distribution functions (EVDFs) are useful signatures of plasma conditions and non-local consequences of collisionless magnetic reconnection. In the past, EVDFs were obtained mainly for antiparallel reconnection and under the influence of weak guide-fields in the direction perpendicular to the reconnection plane. EVDFs are, however, not well known, yet, for oblique (or component-) reconnection in case and in dependence on stronger guide-magnetic fields and for the exhaust (outflow) region of reconnection away from the diffusion region. In view of the multi-spacecraft Magnetospheric Multiscale Mission (MMS), we derived the non-Maxwellian EVDFs of collisionless magnetic reconnection in dependence on the guide-field strength bg from small ( b g ≈ 0 ) to very strong (bg = 8) guide-fields, taking into account the feedback of the self-generated turbulence. For this sake, we carried out 2.5D fully kinetic Particle-in-Cell simulations using the ACRONYM code. We obtained anisotropic EVDFs and electron beams propagating along the separatrices as well as in the exhaust region of reconnection. The beams are anisotropic with a higher temperature in the direction perpendicular rather than parallel to the local magnetic field. The beams propagate in the direction opposite to the background electrons and cause instabilities. We also obtained the guide-field dependence of the relative electron-beam drift speed, threshold, and properties of the resulting streaming instabilities including the strongly non-linear saturation of the self-generated plasma turbulence. This turbulence and its non-linear feedback cause non-adiabatic parallel electron acceleration. We further obtained the resulting EVDFs due to the non-linear feedback of the saturated self-generated turbulence near the separatrices and in the exhaust region of reconnection in dependence on the guide field strength. We found that the influence of the self-generated plasma turbulence
Survey for non-Maxwellian plasma in Jupiter's magnetosheath
Mihalov, J. D.; Wolfe, J. H.; Frank, L. A.
1976-01-01
Ames Research Center plasma-analyzer high resolution ion spectra, obtained during the traversals of Jupiter's magnetosheath by Pioneer 10 and 11, are examined for non-Maxwellian characteristics. Many examples are found of proton velocity distributions that are Maxwellian down to an observational limit set by the relative helium flux. However, clear deviations from a Maxwellian velocity distribution sometimes are observed. Most often, these non-Maxwellian proton velocity distributions seem to be enhanced on the low-energy side of the peak, in comparison with a Maxwellian distribution. Even less often, however, the high-energy side of the peak seems to be enhanced. A different type of non-Maxwellian spectrum is also seen occasionally near the times of bow-shock crossings, and it exhibits features of both solar-wind and high-temperature magnetosheath proton spectra combined.
Institute of Scientific and Technical Information of China (English)
M.N.S.Qureshi; S.Sehar; H.A.Shah; J.B.Cao
2013-01-01
In many physical situations where a laser or electron beam passes through a dense plasma,hot low-density electron populations can be generated,resulting in a particle distribution function consisting of a dense cold population and a small hot population.Presence of such low-density electron distributions can alter the wave damping rate.A kinetic model is employed to study the Landau damping of Langmuir waves when a small hot electron population is present in the dense cold electron population with non-Maxwellian distribution functions.Departure of plasma from Maxwellian distributions significantly alters the damping rates as compared to the Maxwellian plasma.Strong damping is found for highly non-Maxwellian distributions as well as plasmas with a higher density and hot electron population.Existence of weak damping is also established when the distribution contains broadened flat tops at the low energies or tends to be Maxwellian.These results may be applied in both experimental and space physics regimes.
Fleishman, Gregory D
2013-01-01
Currently there is a concern about ability of the classical thermal (Maxwellian) distribution to describe quasi-steady-state plasma in solar atmosphere including active regions. In particular, other distributions have been proposed to better fit observations, for example, kappa- and $n$-distributions. If present, these distributions will generate radio emissions with different observable properties compared with the classical gyroresonance (GR) or free-free emission, which implies a way of remote detecting these non-Maxwellian distributions in the radio observations. Here we present analytically derived GR and free-free emissivities and absorption coefficients for the kappa- and $n$-distributions and discuss their properties, which are in fact remarkably different from each other and from the classical Maxwellian plasma. In particular, the radio brightness temperature from a gyrolayer increases with the optical depth $\\tau$ for kappa-distribution, but decreases with $\\tau$ for $n$-distribution. This property ...
The ionization state in a gas with a non-Maxwellian electron distribution
Owocki, S. P.; Scudder, J. D.
1981-01-01
The inferred degree of ionization of a gas is often used in astrophysics as a diagnostic of the gas temperature. In the solar transition region and corona, in the outer atmospheres of cool stars, and in some portions of the interstellar medium), photoionization can be neglected, and the ionization state is fixed by the balance between ion-electron collisional ionization and dielectronic and/or radiative recombination. Under these conditions, higher degrees of ionization result from higher energy ion-electron collisions which are common in a high temperature gas. Actually, ionization occurs through collisions with electrons that have kinetic energies greater than the ionization potential of the given ion, and so the ionization rate depends on to the number of such high-energy electrons in the tail of the electron velocity distribution. High-velocity electrons move across large distances between effective coulomb collisions, and, in a strong temperature or density gradient, the tail can be overpopulated relative to Maxwell-Boltzmann distribution of equivalent energy density. Thus, the ionization rate can also be greatly increased. These effects for a parameterized form of the electron distribution function with an enhanced high-velocity tail, namely the kappa distribution are illustrated.
Dust heating by Alfvén waves using non-Maxwellian distribution function
Energy Technology Data Exchange (ETDEWEB)
Zubia, K. [Department of Physics, Government College University, Lahore 54000 (Pakistan); Shah, H. A. [Department of Physics, Forman Christian College, Lahore 54600 (Pakistan); Yoon, P. H. [Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742 (United States); School of Space Research, Kyung Hee University, Yongin, Gyeonggi 446-701 (Korea, Republic of)
2015-08-15
Quasilinear theory is employed in order to evaluate the resonant heating rate by Alfvén waves, of multiple species dust particles in a hot, collisionless, and magnetized plasma, with the underlying assumption that the dust velocity distribution function can be modeled by a generalized (r, q) distribution function. The kinetic linear dispersion relation for the electromagnetic dust cyclotron Alfvén waves is derived, and the dependence of the heating rate on the magnetic field, mass, and density of the dust species is subsequently investigated. The heating rate and its dependence on the spectral indices r and q of the distribution function are also investigated. It is found that the heating is sensitive to negative value of spectral index r.
Generalized fluid theory including non-Maxwellian kinetic effects
Izacard, Olivier
2017-04-01
The results obtained by the plasma physics community for the validation and the prediction of turbulence and transport in magnetized plasmas come mainly from the use of very central processing unit (CPU)-consuming particle-in-cell or (gyro)kinetic codes which naturally include non-Maxwellian kinetic effects. To date, fluid codes are not considered to be relevant for the description of these kinetic effects. Here, after revisiting the limitations of the current fluid theory developed in the 19th century, we generalize the fluid theory including kinetic effects such as non-Maxwellian super-thermal tails with as few fluid equations as possible. The collisionless and collisional fluid closures from the nonlinear Landau Fokker-Planck collision operator are shown for an arbitrary collisionality. Indeed, the first fluid models associated with two examples of collisionless fluid closures are obtained by assuming an analytic non-Maxwellian distribution function (e.g. the INMDF (Izacard, O. 2016b Kinetic corrections from analytic non-Maxwellian distribution functions in magnetized plasmas. Phys. Plasmas 23, 082504) that stands for interpreted non-Maxwellian distribution function). One of the main differences with the literature is our analytic representation of the distribution function in the velocity phase space with as few hidden variables as possible thanks to the use of non-orthogonal basis sets. These new non-Maxwellian fluid equations could initiate the next generation of fluid codes including kinetic effects and can be expanded to other scientific disciplines such as astrophysics, condensed matter or hydrodynamics. As a validation test, we perform a numerical simulation based on a minimal reduced INMDF fluid model. The result of this test is the discovery of the origin of particle and heat diffusion. The diffusion is due to the competition between a growing INMDF on short time scales due to spatial gradients and the thermalization on longer time scales. The results
Mendoza, C
2014-01-01
The classic optical nebular diagnostics [N II], [O II], [O III], [S II], [S III], and [Ar III] are employed to search for evidence of non-Maxwellian electron distributions, namely $\\kappa$~distributions, in a sample of well-observed Galactic H II regions. By computing new effective collision strengths for all these systems and A-values when necessary (e.g. S II), and by comparing with previous collisional and radiative datasets, we have been able to obtain realistic estimates of the electron-temperature dispersion caused by the atomic data, which in most cases are not larger than $\\sim 10$%. If the uncertainties due to both observation and atomic data are then taken into account, it is plausible to determine for some systems a representative average temperature while in others there are at least two plasma excitation regions. For the latter, it is found that the diagnostic temperature differences in the high-excitation region, e.g. $T_e$(O III), $T_e$(S III), and $T_e$(Ar III), cannot be conciliated by invoki...
Dudik, Jaroslav; Dzifcakova, Elena; Del Zanna, Giulio; Williams, David R; Karlicky, Marian; Mason, Helen E; Lorincik, Juraj; Kotrc, Pavel; Farnik, Frantisek; Zemanova, Alena
2015-01-01
We report on the SDO/AIA and Hinode/EIS observations of a transient coronal loop. The loop brightens up in the same location after the disappearance of an arcade formed during a B8.9-class microflare three hours earlier. EIS captures this loop during its brightening phase as observed in most of the AIA filters. We use the AIA data to study the evolution of the loop, as well as to perform the DEM diagnostics as a function of $\\kappa$. Fe XI--XIII lines observed by EIS are used to perform the diagnostics of electron density and subsequently the diagnostics of $\\kappa$. Using ratios involving the Fe XI 257.772\\AA selfblend, we diagnose $\\kappa$ $\\lesssim$ 2, i.e., an extremely non-Maxwellian distribution. Using the predicted Fe line intensities derived from the DEMs as a function of $\\kappa$, we show that, with decreasing $\\kappa$, all combinations of ratios of line intensities converge to the observed values, confirming the diagnosed $\\kappa$ $\\lesssim$ 2. These results represent the first positive diagnostics ...
The non-Maxwellian energy distribution of ions in the warm Io torus
Richardson, J. D.; Siscoe, G. L.
1983-01-01
Observations of Io's torus indicate that the majority of ions have energies of 55-75 eV, with a high-energy tail extending up to the corotation energy. It was found that such a distribution can be established via the Coulomb cooling of ions heated at the corotation energy onto the cold 5-eV electrons. The energy E(asterisk) of the main body of the ions and the shape of the energy distribution are functions of the transport loss time. Matching E(asterisk) with the data (E/asterisk/ = 55-75 eV) requires transport loss times in the range 25-1000 days.
Generalized fluid theory including non-Maxwellian kinetic effects
Energy Technology Data Exchange (ETDEWEB)
Izacard, Olivier
2017-03-29
The results obtained by the plasma physics community for the validation and the prediction of turbulence and transport in magnetized plasmas come mainly from the use of very central processing unit (CPU)-consuming particle-in-cell or (gyro)kinetic codes which naturally include non-Maxwellian kinetic effects. To date, fluid codes are not considered to be relevant for the description of these kinetic effects. Here, after revisiting the limitations of the current fluid theory developed in the 19th century, we generalize the fluid theory including kinetic effects such as non-Maxwellian super-thermal tails with as few fluid equations as possible. The collisionless and collisional fluid closures from the nonlinear Landau Fokker–Planck collision operator are shown for an arbitrary collisionality. Indeed, the first fluid models associated with two examples of collisionless fluid closures are obtained by assuming an analytic non-Maxwellian distribution function (e.g. the INMDF (Izacard, O. 2016b Kinetic corrections from analytic non-Maxwellian distribution functions in magnetized plasmas.
Nonlinear ion-acoustic solitary waves with warm ions and non-Maxwellian electrons in space plasmas
Hussain Shah, Khalid; Qureshi, Nouman
2017-04-01
Electrons velocity distributions are often observed with non-Maxwellian features such flat tops at low energies and/or superthermal tails at high energies from different regions of near Earth plasmas such as Earth's bow shock, auroral zone and magnetosphere by numerous satellites. Such non-Maxwellian distributions are well modelled by generalized (r,q) distribution or Cairns distribution. Solitons are nonlinear solitary structures and are integral part of space plasmas. In this paper, we present a fluid model containing Cairns (r,q) distributed non-Maxwellian electrons and derive the Sagdeev potential for fully nonlinear fluid equations. We found that compressive solitons can be developed in such a plasma. The results from our model can be used to interpret solitary structures in space plasmas when electrons are obeying the non-Maxwellian flat tops along with the high energy tails.
Dzifčáková, Elena; Kotrč, Pavel; Fárník, František; Zemanová, Alena
2015-01-01
The non-Maxwellian $\\kappa$-distributions have been detected in the solar transition region and flares. These distributions are characterized by a high-energy tail and a near-Maxwellian core and are known to have significant impact on the resulting optically thin spectra arising from collisionally dominated astrophysical plasmas. We developed the KAPPA package (http://kappa.asu.cas.cz) for synthesis of such line and continuum spectra. The package is based on the freely available CHIANTI database and software, and can be used in a similar manner. Ionization and recombination rates together with the ionization equilibria are provided for a range of $\\kappa$ values. Distribution-averaged collision strengths for excitation are obtained by an approximate method for all transitions in all ions available within CHIANTI. The validity of this approximate method is tested by comparison with direct calculations. Typical precisions of better than 5% are found, with all cases being within 10%. Tools for calculation of syn...
Ljepojevic, N. N.; Macneice, P.
1988-01-01
The high-velocity tail of the electron distribution has been calculated by solving the high-velocity form of the Landau equation for a thermal structure representative of a flaring coronal loop. These calculations show an enhancement of the tail population above Maxwellian for electrons moving down the temperature gradient. The results obtained are used to test the reliability of the BGK approximation. The comparison shows that the BGK technique can estimate contributions to the heat flux from the high-energy tail to within an order of magnitude.
Falconer, D. A.; Davila, J. M.
1999-01-01
We examine the idea that the corona is heated by a population of nonthermal particles. An upper limit on the size of the nonthermal population is derived by assuming that all of the radiation and conduction losses in the corona are provided by the nonthermal tail of the particle distribution. Only a very small percentage of nonthermal particles are allowed. These particles have a negligable effect on temperature sensitive line ratios typically observed in the EUV (Extreme Ultraviolet Radiation).
Consequences of entropy bifurcation in non-Maxwellian astrophysical environments
Directory of Open Access Journals (Sweden)
M. P. Leubner
2008-07-01
Full Text Available Non-extensive systems, accounting for long-range interactions and correlations, are fundamentally related to non-Maxwellian distributions where a duality of equilibria appears in two families, the non-extensive thermodynamic equilibria and the kinetic equilibria. Both states emerge out of particular entropy generalization leading to a class of probability distributions, where bifurcation into two stationary states is naturally introduced by finite positive or negative values of the involved entropic index kappa. The limiting Boltzmann-Gibbs-Shannon state (BGS, neglecting any kind of interactions within the system, is subject to infinite entropic index and thus characterized by self-duality. Fundamental consequences of non-extensive entropy bifurcation, manifest in different astrophysical environments, as particular core-halo patterns of solar wind velocity distributions, the probability distributions of the differences of the fluctuations in plasma turbulence as well as the structure of density distributions in stellar gravitational equilibrium are discussed. In all cases a lower entropy core is accompanied by a higher entropy halo state as compared to the standard BGS solution. Data analysis and comparison with high resolution observations significantly support the theoretical requirement of non-extensive entropy generalization when dealing with systems subject to long-range interactions and correlations.
Collisionless damping of electron waves in non-Maxwellian plasma
Soshnikov, V. N.
2007-01-01
In this paper we have criticized the so-called Landau damping theory. We have analyzed solutions of the standard dispersion equations for longitudinal (electric) and transversal (electromagnetic and electron) waves in half-infinite slab of the uniform collisionless plasmas with non-Maxwellian and Maxwellian-like electron energy distribution functions. One considered the most typical cases of both the delta-function type distribution function (the plasma stream with monochromatic electrons) an...
Chen, J.; Lee, Y. C.
1985-01-01
In the present investigation, a general integro-differential formalism is derived for the study of the collisionless tearing mode in a highly non-Maxwellian neutral sheet in which both electrons and ions are treated kinetically. The obtained formalism is applied to a specific non-Maxwellian distribution. The dispersion relation for the considered system is determined, taking into account the fundamental harmonic of the orbital frequency. It is found that the dispersion relation is dominated by the electrons. The results are presented in a number of graphs. The growth rates of non-Maxwellian distributions are generally much greater than the growth rate of the conventional isotropic tearing instability.
Generalized fluid theory including non-Maxwellian kinetic effects
Izacard, Olivier
2016-01-01
The results obtained by the plasma physics community for the validation and the prediction of turbulence and transport in magnetized plasma come mainly from the use of very CPU-consuming particle-in-cell or (gyro)kinetic codes which naturally include non-Maxwellian kinetic effects. To date, fluid codes are not considered to be relevant for the description of these kinetic effects. Here, after revisiting the limitations of the current fluid theory developed in the 19th century, we generalize the fluid theory including kinetic effects such as non-Maxwellian super-thermal tails with as few fluid equations as possible. The collisionless and collisional fluid closures from the nonlinear Landau Fokker-Planck collision operator are shown for an arbitrary collisionality. Indeed, the first fluid models associated with two examples of collisionless fluid closures are obtained by assuming an analytic non-Maxwellian distribution function (e.g., the INMDF [O. Izacard, Phys. Plasmas 23, 082504 (2016)]). One of the main dif...
Non-Maxwellian background effects in gyrokinetic simulations with GENE
Di Siena, A.; Görier, T.; Doerk, H.; Citrin, J.; Johnson, T.; Schneider, M.; Poli, E.; Contributors, JET
2016-11-01
The interaction between fast particles and core turbulence has been established as a central issue for a tokamak reactor. Recent results predict significant enhancement of electromagnetic stabilisation of ITG turbulence in the presence of fast ions. However, most of these simulations were performed with the assumption of equivalent Maxwellian distributed particles, whereas to rigorously model fast ions, a non-Maxwellian background distribution function is needed. To this aim, the underlying equations in the gyrokinetic code GENE have been re-derived and implemented for a completely general background distribution function. After verification studies, a previous investigation on a particular JET plasma has been revised with linear simulations. The plasma is composed by Deuterium, electron, Carbon impurities, NBI fast Deuterium and ICRH 3He. Fast particle distributions have been modelled with a number of different analytic choices in order to study the impact of non-Maxwellian distributions on the plasma turbulence: slowing down and anisotropic Maxwellian. Linear growth rates are studied as a function of the wave number and compared with those obtained using an equivalent Maxwellian. Generally, the choice of the 3He distribution seems to have a stronger impact on the microinstabilities than that of the fast Deuterium.
Driven phase space vortices in plasmas with nonextensive velocity distribution
Trivedi, Pallavi; Ganesh, Rajaraman
2017-03-01
The evolution of chirp-driven electrostatic waves in unmagnetized plasmas is numerically investigated by using a one-dimensional (1D) Vlasov-poisson solver with periodic boundary conditions. The initial velocity distribution of the 1D plasma is assumed to be governed by nonextensive q distribution [C. Tsallis, J. Stat. Phys. 52, 479 (1988)]. For an infinitesimal amplitude of an external drive, we investigate the effects of chirp driven dynamics that leads to the formation of giant phase space vortices (PSV) for both Maxwellian (q = 1) and non-Maxwellian ( q ≠ 1 ) plasmas. For non-Maxwellian plasmas, the formation of giant PSV with multiple extrema and phase velocities is shown to be dependent on the strength of "q". Novel features such as "shark"-like and transient "honeycomb"-like structures in phase space are discussed. Wherever relevant, we compare our results with previous work.
The Use of Langmuir Probes in Non-Maxwellian Space Plasmas
Hoegy, Walter R.; Brace, Larry H.
1998-01-01
Disturbance of the Maxwellian plasma may occur in the vicinity of a spacecraft due to photoemission, interactions between the spacecraft and thermospheric gases, or electron emissions from other devices on the spacecraft. Significant non-maxwellian plasma distributions may also occur in nature as a mixture of ionospheric and magnetospheric plasmas or secondaries produced by photoionization in the thermosphere or auroral precipitation. The general formulas for current collection (volt-ampere curves) by planar, cylindrical, and spherical Langmuir probes in isotropic and anisotropic non-maxwellian plasmas are examined. Examples are given of how one may identify and remove the non-maxwellian components in the Langmuir probe current to permit the ionospheric parameters to be determined. Theoretical volt-ampere curves presented for typical examples of non-maxwellian distributions include: two-temperature plasmas and a thermal plasma with an energetic electron beam. If the non-ionospheric electrons are Maxwellian at a temperature distinct from that of the ionosphere electrons, the volt-ampere curves can be fitted directly to obtain the temperatures and densities of both electron components without resorting to differenting the current. For an arbitrary isotropic distribution, the current for retarded particles is shown to be identical for the three geometries. For anisotropic distributions, the three probe geometries are not equally suited for measuring the ionospheric electron temperature and density or for determining the distribution function in the presence of non-maxwellian back-round electrons.
Dudík, J; Mason, H E; Dzifčáková, E
2014-01-01
We investigate the possibility of diagnosing the degree of departure from the Maxwellian distribution using single-ion spectra originating in astrophysical plasmas in collisional ionization equilibrium. New atomic data for excitation of Fe IX-XIII are integrated under the assumption of a kappa-distribution of electron energies. Diagnostic methods using lines of a single ion formed at any wavelength are explored. Such methods minimize uncertainties from the ionization and recombination rates, as well as the possible presence of non-equilibrium ionization. Approximations to the collision strengths are also investigated. The calculated intensities of most of the Fe IX-XIII EUV lines show consistent behaviour with kappa at constant temperature. Intensities of these lines decrease with kappa, with the vast majority of ratios of strong lines showing little or no sensitivity to kappa. Several of the line ratios, especially involving temperature-sensitive lines, show a sensitivity to kappa that is of the order of sev...
Ion-dust streaming instability with non-Maxwellian ions
Energy Technology Data Exchange (ETDEWEB)
Kählert, Hanno, E-mail: kaehlert@theo-physik.uni-kiel.de [Institut für Theoretische Physik und Astrophysik, Christian-Albrechts-Universität zu Kiel, Leibnizstr. 15, 24098 Kiel (Germany)
2015-07-15
The influence of non-Maxwellian ions on the ion-dust streaming instability in a complex plasma is investigated. The ion susceptibility employed for the calculations self-consistently accounts for the acceleration of the ions by a homogeneous background electric field and their collisions with neutral gas particles via a Bhatnagar-Gross-Krook collision term [e.g., A. V. Ivlev et al., Phys. Rev. E 71, 016405 (2005)], leading to significant deviations from a shifted Maxwellian distribution. The dispersion relation and the properties of the most unstable mode are studied in detail and compared with the Maxwellian case. The largest deviations occur at low to intermediate ion-neutral damping. In particular, the growth rate of the instability for ion streaming below the Bohm speed is found to be lower than in the case of Maxwellian ions, yet remains on a significant level even for fast ion flows above the Bohm speed.
Population densities of hydrogenlike ions in a non-Maxwellian plasma.
Ashbourn, J M
2001-04-01
In this paper we examine the effects of non-Maxwellian electron energy distributions on the population densities of excited atomic levels for hydrogenlike ions. We model the electron energy distribution function by two Maxwellian finite elements, one approximating the bulk distribution with temperature T(b) and the other the tail distribution with temperature T(t). We present results for various T(b)/T(t) ratios for Si XIV.
Behaviour of ion velocity distributions for a simple collision model
St-Maurice, J.-P.; Schunk, R. W.
1974-01-01
Calculation of the ion velocity distributions for a weakly ionized plasma subjected to crossed electric and magnetic fields. An exact solution to Boltzmann's equation has been obtained by replacing the Boltzmann collision integral with a simple relaxation model. At altitudes above about 150 km, where the ion collision frequency is much less than the ion cyclotron frequency, the ion distribution takes the shape of a torus in velocity space for electric fields greater than 40 mV/m. This shape persists for one to two hours after application of the electric field. At altitudes where the ion collision and cyclotron frequencies are approximately equal (about 120 km), the ion velocity distribution is shaped like a bean for large electric field strengths. This bean-shaped distribution persists throughout the lifetime of ionospheric electric fields. These highly non-Maxwellian ion velocity distributions may have an appreciable affect on the interpretation of ion temperature measurements.
Kinetic non-Maxwellians, from theory to experiments
Izacard, Olivier
2016-10-01
This contribution shows strong progresses on the analytic prediction of some kinetic effects (e.g., presence of super-thermal particles) on a selection of theories which usually assume a Maxwellian distribution function (MDF). The new method developed is based on the use of non-orthogonal basis sets to represent analytic non-Maxwellian distribution functions (NMDFs). This choice is motivated by its efficiency to model experimental and numerical NMDFs computed by PIC or Fokker-Plank codes and its capability to extract physical interpretation. We particularly introduce an interpreted NMDF which helped to understand the origin of the TS-ECE discrepancy (up to 20% on the electron temperature due to less than 2% of non-thermalized particles) observed in JET and TFTR. Additional results are discussed such as the inconsistency of the empirical SEE formula with a MDF, and the replacement of a diffusion ad-hoc coefficient by NMDFs. Finally, we show inclusion of kinetic effects in generalized fluid models and we focus our discussion on experimental perspectives toward NSTX-U measurements of NMDFs with different diagnostics. A part of this work is disseminated in Refs.. Footnote: LLNL-ABS-702319 Supported by U.S. Department of Energy Contract No. DE-AC52-07NA27344.
Nonlinear kinetic Alfvén waves with non-Maxwellian electron population in space plasmas
Masood, W.; Qureshi, M. N. S.; Yoon, P. H.; Shah, H. A.
2015-01-01
The present work discusses the effects of non-Maxwellian electron distributions on kinetic Alfvén waves in low-beta plasmas. Making use of the two-potential theory and employing the Sagdeev potential approach, the existence of solitary kinetic Alfvén waves having arbitrary amplitude is investigated. It is found that the use of non-Maxwellian population of electrons in the study of kinetic Alfvén waves leads to solutions corresponding to solitary structures that do not exist for Maxwellian electrons. The present investigation solves the riddle of plasma density fluctuations associated with strong electromagnetic perturbations observed by the Freja satellite. The present findings can also be applied to regions of space where various satellite missions have observed the presence of suprathermal populations of plasma species and where the low β assumption is valid.
A model for ion-acoustic solitary waves with streaming non-Maxwellian electrons in space plasmas
Khalid Hussain, Shah; Nouman Sarwar, Qureshi Muhammad
2016-04-01
Solitons are nonlinear solitary structures and are integral part of space plasmas. Such nonlinear structures, accompanied by streaming electrons are frequently observed by various satellites in different regions of near Earth plasmas such as Earth's bow shock, magnetopause, auroral zone, etc. In this paper, we present a fluid model consisting streaming non-Maxwellian electrons along the magnetic field and derived the Sagdeev potential for fully nonlinear fluid equations. We found that compressive solitons can be developed in such a plasma. The results from our model can be used to interpret solitary structures in space plasmas when there is streaming electron obeying the non-Maxwellian distributions
Ignition threshold for non-Maxwellian plasmas
Energy Technology Data Exchange (ETDEWEB)
Hay, Michael J., E-mail: hay@princeton.edu [Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey 08544 (United States); Fisch, Nathaniel J. [Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey 08544 (United States); Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)
2015-11-15
An optically thin p-{sup 11}B plasma loses more energy to bremsstrahlung than it gains from fusion reactions, unless the ion temperature can be elevated above the electron temperature. In thermal plasmas, the temperature differences required are possible in small Coulomb logarithm regimes, characterized by high density and low temperature. Ignition could be reached more easily if the fusion reactivity can be improved with nonthermal ion distributions. To establish an upper bound for the potential utility of a nonthermal distribution, we consider a monoenergetic beam with particle energy selected to maximize the beam-thermal reactivity. Comparing deuterium-tritium (DT) and p-{sup 11}B, the minimum Lawson criteria and minimum ρR required for inertial confinement fusion (ICF) volume ignition are calculated with and without the nonthermal feature. It turns out that channeling fusion alpha energy to maintain such a beam facilitates ignition at lower densities and ρR, improves reactivity at constant pressure, and could be used to remove helium ash. On the other hand, the reactivity gains that could be realized in DT plasmas are significant, the excess electron density in p-{sup 11}B plasmas increases the recirculated power cost to maintain a nonthermal feature and thereby constrains its utility to ash removal.
Ignition threshold for non-Maxwellian plasmas
Hay, Michael J
2015-01-01
An optically thin $p$-$^{11}$B plasma loses more energy to bremsstrahlung than it gains from fusion reactions, unless the ion temperature can be elevated above the electron temperature. In thermal plasmas, the temperature differences required are possible in small Coulomb logarithm regimes, characterized by high density and low temperature. The minimum Lawson criterion for thermal $p$-$^{11}$B plasmas and the minimum $\\rho R$ required for ICF volume ignition are calculated. Ignition could be reached more easily if the fusion reactivity can be improved with nonthermal ion distributions. To establish an upper bound for this utility, we consider a monoenergetic beam with particle energy selected to maximize the beam- thermal reactivity. Channeling fusion alpha energy to maintain such a beam facilitates ignition at lower densities and $\\rho R$, improves reactivity at constant pressure, and could be used to remove helium ash. The gains realized with a beam thus establish an upper bound for the reductions in igniti...
Sensitivity of ICF ignition conditions to non-Maxwellian DT fusion reactivity
Directory of Open Access Journals (Sweden)
Garbett W.J.
2013-11-01
Full Text Available The hotspot ignition conditions in ICF are determined by considering the power balance between fusion energy deposition and energy loss terms. Uncertainty in any of these terms has potential to modify the ignition conditions, changing the optimum ignition capsule design. This paper considers the impact of changes to the DT fusion reaction rate due to non-thermal ion energy distributions. The DT fusion reactivity has been evaluated for a class of non-Maxwellian distributions representing a perturbation to the tail of a thermal distribution. The resulting reactivity has been used to determine hotspot ignition conditions as a function of the characteristic parameter of the modified distribution.
Lee, Jungpyo; Wright, John; Bonoli, Paul; Harvey, Robert
2015-11-01
We describe a numerical model for the propagation and absorption of ion cyclotron waves in a tokamak with a non-Maxwellian velocity space distribution function. The non-Maxwellian distribution is calculated by solving Maxwell's equations and the Fokker-Plank equation self-consistently. This approach will be useful to interpret measurements of minority hydrogen tail formation during ICRF heating experiments in Alcator C-Mod. To couple the Maxwell equation solver with Fokker-Plank equation solver, the quasilinear diffusion coefficients for the fundamental ion cyclotron absorption and the first harmonic absorption are calculated. In a previous study, the all-orders spectral algorithm wave solver (AORSA) was coupled with the Fokker-Plank code (CQL3D) to find the self-consistent non-Maxwellian distribution. We derive the modified quasilinear diffusion coefficients for the finite Larmor radius (FLR) approximation using a significantly faster wave solver (TORIC) following the approach by Jaeger. The coupled TORIC-CQL3D model will be compared against results from AORSA-CQL3D in order to verify the accuracy of the reduced FLR physics in TORIC. Work supported by US Department of Energy Contract No. DE-FC02-01ER54648.
Observations of the velocity distribution of solar wind ions
Ogilvie, K. W.; Bochsler, P.; Geiss, J.; Coplan, M. A.
1980-01-01
Measurements made by the Isee 3 ion composition experiment have been used to determine the kinetic temperatures of 3He(++), 4He(++), 16O(6+), and 16O(7+) in the solar wind. It is found that these temperatures generally obey the relation that T(i)/m(i) equals const, but fluctuations, some of which are caused by dynamical effects in the flow, are observed. The temperature of oxygen sometimes rises above 10 K, which is very strong evidence for heating outside the collisional region of the corona. The tendency toward equal temperatures per nucleon occurs everywhere where collisions are unimportant, suggesting that the temperatures are set up close to the sun rather than elsewhere in the interplanetary medium. The velocity distribution function of helium is observed to be non-Maxwellian, with a pronounced high velocity tail.
On the rogue waves propagation in non-Maxwellian complex space plasmas
El-Tantawy, S. A.; El-Awady, E. I.; Tribeche, M.
2015-11-01
The implications of the non-Maxwellian electron distributions (nonthermal/or suprathermal/or nonextensive distributions) are examined on the dust-ion acoustic (DIA) rogue/freak waves in a dusty warm plasma. Using a reductive perturbation technique, the basic set of fluid equations is reduced to a nonlinear Schrödinger equation. The latter is used to study the nonlinear evolution of modulationally unstable DIA wavepackets and to describe the rogue waves (RWs) propagation. Rogue waves are large-amplitude short-lived wave groups, routinely observed in space plasmas. The possible region for the rogue waves to exist is defined precisely for typical parameters of space plasmas. It is shown that the RWs strengthen for decreasing plasma nonthermality and increasing superthermality. For nonextensive electrons, the RWs amplitude exhibits a bit more complex behavior, depending on the entropic index q. Moreover, our numerical results reveal that the RWs exist with all values of the ion-to-electron temperature ratio σ for nonthermal and superthermal distributions and there is no limitation for the freak waves to propagate in both two distributions in the present plasma system. But, for nonextensive electron distribution, the bright- and dark-type waves can propagate in this case, which means that there is a limitation for the existence of freak waves. Our systematic investigation should be useful in understanding the properties of DIA solitary waves that may occur in non-Maxwellian space plasmas.
On the rogue waves propagation in non-Maxwellian complex space plasmas
Energy Technology Data Exchange (ETDEWEB)
El-Tantawy, S. A., E-mail: samireltantawy@yahoo.com; El-Awady, E. I., E-mail: eielawady@hotmail.com [Department of Physics, Faculty of Science, Port Said University, Port Said 42521 (Egypt); Tribeche, M., E-mail: mouloudtribeche@yahoo.fr, E-mail: mtribeche@usthb.dz [Plasma Physics Group, Theoretical Physics Laboratory, Faculty of Physics, University of Bab-Ezzouar, USTHB, BP 32, El Alia, Algiers 16111 (Algeria)
2015-11-15
The implications of the non-Maxwellian electron distributions (nonthermal/or suprathermal/or nonextensive distributions) are examined on the dust-ion acoustic (DIA) rogue/freak waves in a dusty warm plasma. Using a reductive perturbation technique, the basic set of fluid equations is reduced to a nonlinear Schrödinger equation. The latter is used to study the nonlinear evolution of modulationally unstable DIA wavepackets and to describe the rogue waves (RWs) propagation. Rogue waves are large-amplitude short-lived wave groups, routinely observed in space plasmas. The possible region for the rogue waves to exist is defined precisely for typical parameters of space plasmas. It is shown that the RWs strengthen for decreasing plasma nonthermality and increasing superthermality. For nonextensive electrons, the RWs amplitude exhibits a bit more complex behavior, depending on the entropic index q. Moreover, our numerical results reveal that the RWs exist with all values of the ion-to-electron temperature ratio σ for nonthermal and superthermal distributions and there is no limitation for the freak waves to propagate in both two distributions in the present plasma system. But, for nonextensive electron distribution, the bright- and dark-type waves can propagate in this case, which means that there is a limitation for the existence of freak waves. Our systematic investigation should be useful in understanding the properties of DIA solitary waves that may occur in non-Maxwellian space plasmas.
Generalized fluid theory including non-Maxwellian kinetic effects
Izacard, Olivier
2016-01-01
The results obtained by the plasma physics community for the validation and the prediction of turbulence and transport in magnetized plasma come mainly from the use of very CPU-consuming particle-in-cell or (gyro)kinetic codes which naturally include non-Maxwellian kinetic effects. To date, fluid codes are not considered to be relevant for the description of these kinetic effects. Here, after revisiting the limitations of the current fluid theory developed in the 19th century, we generalize t...
Energy Technology Data Exchange (ETDEWEB)
Ahmad, Ali [National Centre for Physics, Shahdara Valley Road, Islamabad (Pakistan); Masood, W. [National Centre for Physics, Shahdara Valley Road, Islamabad (Pakistan); COMSATS Institute of Information Technology, Park Road, Chak Shahzad, Islamabad (Pakistan)
2016-05-15
Linear and nonlinear electrostatic ion acoustic waves in a weakly relativistic magnetorotating plasma in the presence of non-Maxwellian electrons and warm ions have been examined. The system under consideration has yielded two solutions, namely, the fast and slow acoustic modes which have been observed to depend on the streaming velocity, ion to electron temperature ratio, and the nonthermality parameter of the non-Maxwellian electrons. Using the multiple time scale analysis, we have derived the three dimensional nonlinear Zakharov–Kuznetsov equation and also presented its solution. Both compressive and rarefactive solitary structures have been found in consonance with the satellite observations. It has been observed that although the linear dispersion relation gives both fast and slow ion acoustic waves, the solitary structures form only for the fast acoustic mode. The dependence of the characteristics of the solitary structures on several plasma parameters has also been explored. The present investigation may be beneficial to understanding the rotating plasma environments such as those found in the planetary magnetospheres of Saturn and Jupiter.
Jaeger, E. F.
2005-10-01
High-performance burning plasma devices such as ITER will contain significant concentrations of non-thermal plasma particles arising from fusion reactions, neutral beam injection, and wave-driven diffusion in velocity space. Initial studies in 1-D [1] and experimental results [2] show that non-thermal energetic ions can significantly alter wave propagation and absorption in the ion cyclotron range of frequencies. In addition, these ions can absorb power at high harmonics of the cyclotron frequency where conventional 2-D global-wave models are not valid. In this work, the all-orders, full-wave solver AORSA [3] is generalized to treat non-Maxwellian velocity distributions. Quasi-linear diffusion coefficients are derived directly from the global wave fields and used to calculate the energetic ion velocity distribution with the CQL3D Fokker-Planck code [4]. Alternately, the quasi-linear coefficients can be calculated numerically by integrating the Lorentz force equations along particle orbits. Self-consistency between the wave electric field and resonant ion distribution function is achieved by iterating between the full-wave and Fokker-Planck solutions.[1] R. J. Dumont, C. K. Phillips and D. N. Smithe, Phys. Plasmas 12, 042508 (2005).[2] A. L. Rosenberg, J. E. Menard, J. R. Wilson, et al., Phys. Plasmas 11, 2441(2004).[3] E. F. Jaeger, L. A. Berry, J. R. Myra, et al., Phys. Rev. Lett. 90, 195001-1 (2003).[4] R. W. Harvey and M. G. McCoy, in Proceedings of the IAEA Technical Committee Meeting on Advances in Simulation and Modeling of Thermonuclear Plasmas (IAEA, Montreal, 1992).
Cylindrical and spherical soliton collision of electron-acoustic waves in non-Maxwellian plasma
El-Labany, S. K.; Sabry, R.; Moslem, W. M.; Elghmaz, E. A.
2014-02-01
Generation of quasielastic electron-acoustic (EA) waves head-on collision are investigated in non-planar (cylindrical/spherical) plasma composed of cold electrons fluid, hot electrons obeying nonthermal distribution, and stationary ions. The cylindrical/spherical Korteweg-de Vries (KdV) equations describing two bidirectional EA waves are derived and solved analytically. Numerical investigation have shown that only positive electron-acoustic (EA) structures can propagate and collide. The analytical phase shift |Δ A | due to the non-Maxwellian (nonthermal) electrons is different from the Maxwellian case. Both the hot-to-cold electron number density ratio α and nonthermal parameter β have opposite effect on the phase shift behavior. The phase shift of the spherical EA waves is smaller than the cylindrical case, which indicates that the former is more stable for collision. The relevance of the present study to EA waves propagating in the Earth's auroral zone is highlighted.
Directory of Open Access Journals (Sweden)
D. Hubert
Full Text Available New results on the information that can be extracted from simulated non-Maxwellian incoherent radar spectra are presented. The cases of a pure ionosphere and of a composite ionosphere typical of a given altitude of the auroral F region are considered. In the case of a pure ionosphere of NO^{+} or O^{+} ions it has been shown that the electron temperature and the electron density can be derived from a Maxwellian analysis of radar spectra measured at aspect angles of 0° or 21° respectively; the ion temperature and ion temperature anisotropy can be derived from a non- constraining model such as the 1D Raman fitting of a complementary measurement made at an aspect angle larger than 0° for the NO^{+} ions, or at an aspect angle larger than 21° for the O^{+} ions. Moreover with such measurements at large aspect angles, the shape of the velocity ion distribution functions can simultaneously be inferred. The case of a composite ionosphere of atomic O^{+} and molecular NO^{+ }ions is a difficult challenge which requires simultaneously a complementary measurement of the electron temperature to provide the ion composition and the electron density from the incoherent radar spectra at a specific aspect angle of 21°; hence, a model dependent routine is necessary to derive the ion temperatures and ion temperature anisotropies. In the case where the electron temperature is not given, a routine which depends on ion distribution models is required first: the better the ion distribution models are, the more accurately derived the plasma parameters will be. In both cases of a composite ionosphere, the 1D Raman fitting can be used to keep a check on the validity of the results provided by the ion distribution model dependent routine.
Further observations on resonance cones in non-Maxwellian plasmas
Thiemann, H.; Singh, N.
1983-01-01
Results on the angular distribution of the electrostatic potential of a pulsating point charge in a warm magnetized plasma permeated by an electron beam are presented. The theoretical formulation for a finite magnetic field is given, and the solution of the resonance cone dispersion relation is presented. Numerical results on the angular distribution of the potential are shown, and the propagation of waves outside the resonance cones is described. It is demonstrated that with the inclusions of a finite magnetic field, the field patterns of a point charge are qualitatively similar to those obtained for a uniaxial plasma. The Cerenkov radiation occurs at angles much smaller than the cold-cone angle, even with the finite magnetic field. When the beam velocity is well above the thermal velocity of the background electrons, a characteristic wave propagation occurs between the cold-cone angles.
Multicomponent plasma expansion into vacuum with non-Maxwellian electrons
Elkamash, Ibrahem; Kourakis, Ioannis
2016-10-01
The expansion of a collisionless plasma into vacuum has been widely studied since the early works of Gurevich et al and Allen and coworkers. It has received momentum in recent years, in particular in the context of ultraintense laser pulse interaction with a solid target, in an effort to elucidate the generation of high energy ion beams. In most present day experiments, laser produced plasmas contain several ion species, due to increasingly complicated composite targets. Anderson et al have studied the isothermal expansion of a two-ion-species plasma. As in most earlier works, the electrons were assumed to be isothermal throughout the expansion. However, in more realistic situations, the evolution of laser produced plasmas into vacuum is mainly governed by nonthermal electrons. These electrons are characterized by particle distribution functions with high energy tails, which may significantly deviate from the Maxwellian distribution. In this paper, we present a theoretical model for plasma expansion of two component plasma with nonthermal electrons, modelled by a kappa-type distribution. The superthermal effect on the ion density, velocity and the electric field is investigated. It is shown that energetic electrons have a significant effecton the expansion dynamics of the plasma. This work was supported from CPP/QUB funding. One of us (I.S. Elkamash) acknowledges financial support by an Egyptian Government fellowship.
Shielding effect and wakefield pattern of a moving test charge in a non-Maxwellian dusty plasma
Energy Technology Data Exchange (ETDEWEB)
Ali, S. [National Centre for Physics (NCP), Quaid-e-Azam University Campus, Shahdra Valley Road, Islamabad 44000 (Pakistan); Khan, S. [National Centre for Physics (NCP), Quaid-e-Azam University Campus, Shahdra Valley Road, Islamabad 44000 (Pakistan); Department of Physics, Gomal University, Dera Ismail Khan 29050 (Pakistan)
2013-07-15
By using the Vlasov-Poisson equations, we calculate an expression for the electrostatic potential caused by a test charge in an unmagnetized non-Maxwellian dusty plasma, whose constituents are the superthermal hot-electrons, the mobile cold-electrons with a neutralizing background of cold ions, and charge fluctuating isolated dust grains. The superthermality effects due to hot electrons not only modify the dielectric constant of the electron-acoustic waves but also significantly affect the electrostatic potential. The latter can be decomposed into the Debye-Hückel and oscillatory wake potentials. Analytical and numerical results reveal that the Debye-Hückel and wakefield potentials converge to the Maxwellian case for large values of superthermality parameter. Furthermore, the plasma parameters play a vital role in the formation of shielding and wakefield pattern in a two-electron temperature plasma. The present results should be important for laboratory and space dusty plasmas, where hot-electrons can be assumed to follow the non-Maxwellian distribution function.
On heat conduction in multicomponent, non-Maxwellian spherically symmetric solar wind plasmas
Cuperman, S.; Dryer, M.
1985-01-01
A generalized expression for the steady-state heat flux in multicomponent, moderately non-Maxwellian spherically symmetric plasmas is presented and discussed. The work was motivated by the inability of the simple, Fourier-type formula for the thermal conductivity to explain the observed correlations in the solar wind. The results hold for situations not far from local thermodynamic equilibrium. The generalized expression includes not only correlations that have been observed but also correlations not sought for previously.
Intrinsic rotation driven by non-Maxwellian equilibria in Tokamak plasmas.
Barnes, M; Parra, F I; Lee, J P; Belli, E A; Nave, M F F; White, A E
2013-08-02
The effect of small deviations from a Maxwellian equilibrium on turbulent momentum transport in tokamak plasmas is considered. These non-Maxwellian features, arising from diamagnetic effects, introduce a strong dependence of the radial flux of cocurrent toroidal angular momentum on collisionality: As the plasma goes from nearly collisionless to weakly collisional, the flux reverses direction from radially inward to outward. This indicates a collisionality-dependent transition from peaked to hollow rotation profiles, consistent with experimental observations of intrinsic rotation.
Intrinsic rotation driven by non-Maxwellian equilibria in tokamak plasmas
Barnes, M; Lee, J P; Belli, E A; Nave, M F F; White, A E
2013-01-01
The effect of small deviations from a Maxwellian equilibrium on turbulent momentum transport in tokamak plasmas is considered. These non-Maxwellian features, arising from diamagnetic effects, introduce a strong dependence of the radial flux of co-current toroidal angular momentum on collisionality: As the plasma goes from nearly collisionless to weakly collisional, the flux reverses direction from radially inward to outward. This indicates a collisionality-dependent transition from peaked to hollow rotation profiles, consistent with experimental observations of intrinsic rotation.
Electron Velocity Distribution Function in Magnetic Clouds in the Solar Wind
Nieves-Chinchil, Teresa; Vinas, Adolfo F.; Bale, Stuart D.
2006-01-01
We present a study of the kinetic properties of the electron velocity distribution functions within magnetic clouds, since they are the dominant thermal component. The study is based on high time resolution data from the GSFC WIND/SWE electron spectrometer and the Berkeley 3DP electron plasma instruments. Recent studies on magnetic clouds have shown observational evidence of anti-correlation between the total electron density and electron temperature, which suggest a polytrope law P(sub e) = alpha(Nu(sub e) (sup gamma)) for electrons with the constant gamma approximates 0.5 non-Maxwellian electron distributions (i.e. non-thermal) within magnetic clouds. These works suggested that the non-thermal electrons can contribute as much as 50% of the total electron pressure within magnetic clouds. We have revisited some of the magnetic cloud events previously studied and attempted to quantify the nature of the non-thermal electrons by modeling the electron velocity distribution function using a kappa distribution function to characterize the kinetic non-thermal effects. If non-thermal tail effects are the source for the anti-correlation between the moment electron temperature and density and if the kappa distribution is a reasonable representative model of non-thermal effects, then the electron velocity distribution within magnetic clouds should show indication for small K-values when gamma < 1.
Distributional Monte Carlo Methods for the Boltzmann Equation
2013-03-01
become the first to possess non - Maxwellian distributions, and therefore become the only location where 112 collisions are required to be calculated... Maxwellian . . . . . . . . . . . . . . . . . 16 fMB Maxwell-Boltzmann Density . . . . . . . . . . . . . . . . . . . . . . . . 16 nMB Maxwell-Boltzmann...is equivalent to assuming that millions of actual particles all share the exact velocity vector. This assumption is non -physical in the sense that
Barghouthi, I. A.; Barakat, A. R.; Schunk, R. W.
1994-01-01
Non-Maxwellian ion velocity distribution functions have been theoretically predicted and confirmed by observations, to occur at high latitudes. These distributions deviate from Maxwellian due to the combined effect of the E x B drift and ion-neutral collisions. At high altitude and/or for solar maximum conditions, the ion-to-neutral density ratio increases and, hence, the role of ion self-collisions becomes appreciable. A Monte Carlo simulation was used to investigate the behavior of O(+) ions that are E x B-drifting through a background of neutral O, with the effect of O(+) (Coulomb) self-collisions included. Wide ranges of the ion-to-neutral density ratio n(sub i)/n(sub n) and the electrostatic field E were considered in order to investigate the change of ion behavior with solar cycle and with altitude. For low altitudes and/or solar minimum (n(sub i)/n(sub n) less than or equal to 10(exp -5)), the effect of self-collisions is negligible. For higher values of n(sub i)/n(sub n), the effect of self-collisions becomes significant and, hence, the non-Maxwellian features of the O(+) distribution are reduced. The Monte Carlo results were compared to those that used simplified collision models in order to assess their validity. In general, the simple collision models tend to be more accurate for low E and for high n(sub i)/n(sub n).
Adnan, Muhammad; Qamar, Anisa; Mahmood, Shahzad; Kourakis, Ioannis
2017-03-01
The dynamical characteristics of large amplitude ion-acoustic waves are investigated in a magnetized plasma comprising ions presenting space asymmetry in the equation of state and non-Maxwellian electrons. The anisotropic ion pressure is defined using the double adiabatic Chew-Golberger-Low theory. An excess in the superthermal component of the electron population is assumed, in agreement with long-tailed (energetic electron) distribution observations in space plasmas; this is modeled via a kappa-type distribution function. Large electrostatic excitations are assumed to propagate in a direction oblique to the external magnetic field. In the linear (small amplitude) regime, two electrostatic modes are shown to exist. The properties of arbitrary amplitude (nonlinear) obliquely propagating ion-acoustic solitary excitations are thus investigated via a pseudomechanical energy balance analogy, by adopting a Sagdeev potential approach. The combined effect of the ion pressure anisotropy and excess superthermal electrons is shown to alter the parameter region where solitary waves can exist. An excess in the suprathermal particles is thus shown to be associated with solitary waves, which are narrower, faster, and of larger amplitude. Ion pressure anisotropy, on the other hand, affects the amplitude of the solitary waves, which become weaker (in strength), wider (in spatial extension), and thus slower in comparison with the cold ion case.
The Pulsar Kick Velocity Distribution
Hansen, B M S; Hansen, Brad M. S.
1997-01-01
We analyse the sample of pulsar proper motions, taking detailed account of the selection effects of the original surveys. We treat censored data using survival statistics. From a comparison of our results with Monte Carlo simulations, we find that the mean birth speed of a pulsar is 250-300 km/s, rather than the 450 km/s foundby Lyne & Lorimer (1994). The resultant distribution is consistent with a maxwellian with dispersion $ \\sigma_v = 190 km/s$. Despite the large birth velocities, we find that the pulsars with long characteristic ages show the asymmetric drift, indicating that they are dynamically old. These pulsars may result from the low velocity tail of the younger population, although modified by their origin in binaries and by evolution in the galactic potential.
AtomDB and PyAtomDB: Atomic Data and Modelling Tools for High Energy and Non-Maxwellian Plasmas
Foster, Adam; Smith, Randall K.; Brickhouse, Nancy S.; Cui, Xiaohong
2016-04-01
The release of AtomDB 3 included a large wealth of inner shell ionization and excitation data allowing accurate modeling of non-equilibrium plasmas. We describe the newly calculated data and compare it to published literature data. We apply the new models to existing supernova remnant data such as W49B and N132D. We further outline progress towards AtomDB 3.1, including a new energy-dependent charge exchange cross sections.We present newly developed models for the spectra of electron-electron bremsstrahlung and those due to non-Maxwellian electron distributions.Finally, we present our new atomic database access tools, released as PyAtomDB, allowing powerful use of the underlying fundamental atomic data as well as the spectral emissivities.
A method to deconvolve stellar rotational velocities
Cure, Michel; Cassetti, Julia; Christen, Alejandra
2014-01-01
Rotational speed is an important physical parameter of stars and knowing the distribution of stellar rotational velocities is essential for the understanding stellar evolution. However, it cannot be measured directly but the convolution of the rotational speed and the sine of the inclination angle, $v \\sin i$. We developed a method to deconvolve this inverse problem and obtain the cumulative distribution function (CDF) for stellar rotational velocities extending the work of Chandrasekhar & M\\"unch (1950). This method is applied a) to theoretical synthetic data recovering the original velocity distribution with very small error; b) to a sample of about 12.000 field main--sequence stars, corroborating that the velocity distribution function is non--Maxwellian, but is better described by distributions based on the concept of maximum entropy, such as Tsallis or Kaniadakis distribution functions. This is a very robust and novel method that deconvolve the rotational velocity cumulative distribution function fro...
Model description of non-Maxwellian nuclear processes in the solar interior
Voronchev, Victor T; Watanabe, Yukinobu
2016-01-01
A consistent model for the description of non-Maxwellian nuclear processes in the solar core triggered by fast reaction-produced particles is formulated. It essentially extends an approach to study suprathermal solar reactions discussed previously [Phys. Rev. C 91, 028801 (2015)] and refines its predictions. The model is applied to examine in detail the slowing-down of 8.7-MeV alpha particles produced in the 7Li(p,alpha)alpha reaction of the pp chain, and to study suprathermal processes in the solar CNO cycle induced by them. The influence of electron degeneracy and electron screening on suprathermal reactions through in-flight reaction probability and fast particle emission rate is clarified. In particular, these effects account for a 20% increase of the 14N(alpha,p)17O reaction rate at R 18F of nuclear flow transforms to abnormal sequential flow 14N --> 17O --> 18F, and the 14N(alpha,p)17O reaction rate exceeds the rate of 17O burn up through conventional 17O(p,alpha)14N and 17O(p,gamma)18F processes. It i...
Energy Technology Data Exchange (ETDEWEB)
Haque, Q. [Theoretical Physics Division, PINSTECH, P.O. Nilore, Islamabad (Pakistan); Zakir, U. [Department of Physics, University of Peshawar, Khyber Pakhtun Khwa 25000 (Pakistan); Department of Physics, University of Malakand, Khyber Pakhtun Khwa 18800 (Pakistan); Qamar, A. [Department of Physics, University of Peshawar, Khyber Pakhtun Khwa 25000 (Pakistan)
2015-12-15
Linear and nonlinear dynamics of electron temperature gradient mode along with parallel electron dynamics is investigated by considering hydrodynamic electrons and non-Maxwellian ions. It is noticed that the growth rate of η{sub e}-mode driven linear instability decreases by increasing the value of spectral index and increases by reducing the ion/electron temperature ratio along the magnetic field lines. The eigen mode dispersion relation is also found in the ballooning mode limit. Stationary solutions in the form of dipolar vortices are obtained for both circular and elliptic boundary conditions. It is shown that the dynamics of both circular and elliptic vortices changes with the inclusion of inhomogeneity and non-Maxwellian effects.
Emission of fast non-Maxwellian hydrogen atoms in low-density laboratory plasma
Brandt, Christian; Marchuk, Oleksandr; Pospieszczyk, Albrecht; Dickheuer, Sven
2017-03-01
The source of strong and broad emission of the Balmer-α line in mixed plasmas of hydrogen (or deuterium) and noble gases in front of metallic surfaces is a subject of controversial discussion of many plasma types. In this work the excitation source of the Balmer lines is investigated by means of optical emission spectroscopy in the plasma device PSI-2. Neutral fast non-Maxwellian hydrogen atoms are produced by acceleration of hydrogen ions towards an electrode immersed into the plasma. By variation of the electrode potential the energy of ions and in turn of reflected fast atoms can be varied in the range of 40-300 eV. The fast atoms in front of the electrode are observed simultaneously by an Echelle spectrometer (0.001 nm/channel) and by an imaging spectrometer (0.01 nm/channel) up to few cm in the plasma. Intense excitation channels of the Balmer lines are observed when hydrogen is mixed with argon or with krypton. Especially in Ar-H and Ar-D mixed plasmas the emission of fast hydrogen atoms is very strong. Intermixing hydrogen with other noble gases (He, Ne or Xe) one observes the same effect however the emission is one order of magnitude less compared to Kr-H or Kr-D plasmas. It is shown, that the key process, impacting this emission, is the binary collision between the fast neutral hydrogen atom and the noble gas atom. Two possible sources of excitation are discussed in details: one is the excitation of hydrogen atoms by argon atoms in the ground state and the second one is the process of the so-called excitation transfer between the metastable states of noble gases and hydrogen. In the latter case the atomic data for excitation of Balmer lines are still not available in literature. Further experimental investigations are required to conclude on the source process of fast atom emission.
Directory of Open Access Journals (Sweden)
P. Guio
Full Text Available The plasma dispersion function and the reduced velocity distribution function are calculated numerically for any arbitrary velocity distribution function with cylindrical symmetry along the magnetic field. The electron velocity distribution is separated into two distributions representing the distribution of the ambient electrons and the suprathermal electrons. The velocity distribution function of the ambient electrons is modelled by a near-Maxwellian distribution function in presence of a temperature gradient and a potential electric field. The velocity distribution function of the suprathermal electrons is derived from a numerical model of the angular energy flux spectrum obtained by solving the transport equation of electrons. The numerical method used to calculate the plasma dispersion function and the reduced velocity distribution is described. The numerical code is used with simulated data to evaluate the Doppler frequency asymmetry between the up- and downshifted plasma lines of the incoherent-scatter plasma lines at different wave vectors. It is shown that the observed Doppler asymmetry is more dependent on deviation from the Maxwellian through the thermal part for high-frequency radars, while for low-frequency radars the Doppler asymmetry depends more on the presence of a suprathermal population. It is also seen that the full evaluation of the plasma dispersion function gives larger Doppler asymmetry than the heat flow approximation for Langmuir waves with phase velocity about three to six times the mean thermal velocity. For such waves the moment expansion of the dispersion function is not fully valid and the full calculation of the dispersion function is needed.
Key words. Non-Maxwellian electron velocity distribution · Incoherent scatter plasma lines · EISCAT · Dielectric response function
Slowly moving test charge in two-electron component non-Maxwellian plasma
Energy Technology Data Exchange (ETDEWEB)
Ali, S. [National Centre for Physics (NCP), Quaid-e-Azam University Campus, Shahdra Valley Road, Islamabad 44000 (Pakistan); Eliasson, B. [SUPA, Physics Department, University of Strathclyde, Glasgow G4 0NG, Scotland (United Kingdom)
2015-08-15
Potential distributions around a slowly moving test charge are calculated by taking into account the electron-acoustic waves in an unmagnetized plasma. Considering a neutralizing background of static positive ions, the supra-thermal hot and cold electrons are described by the Vlasov equations to account for the Kappa (power-law in velocity space) and Maxwell equilibrium distributions. Fourier analysis further leads to the derivation of electrostatic potential showing the impact of supra-thermal hot electrons. The test charge moves slowly in comparison with the hot and cold electron thermal speeds and is therefore shielded by the electrons. This gives rise to a short-range Debye-Hückel potential decaying exponentially with distance and to a far field potential decaying as inverse third power of the distance from the test charge. The results are relevant for both laboratory and space plasmas, where supra-thermal hot electrons with power-law distributions have been observed.
Slowly moving test charge in two-electron component non-Maxwellian plasma
Ali, S.; Eliasson, B.
2015-08-01
Potential distributions around a slowly moving test charge are calculated by taking into account the electron-acoustic waves in an unmagnetized plasma. Considering a neutralizing background of static positive ions, the supra-thermal hot and cold electrons are described by the Vlasov equations to account for the Kappa (power-law in velocity space) and Maxwell equilibrium distributions. Fourier analysis further leads to the derivation of electrostatic potential showing the impact of supra-thermal hot electrons. The test charge moves slowly in comparison with the hot and cold electron thermal speeds and is therefore shielded by the electrons. This gives rise to a short-range Debye-Hückel potential decaying exponentially with distance and to a far field potential decaying as inverse third power of the distance from the test charge. The results are relevant for both laboratory and space plasmas, where supra-thermal hot electrons with power-law distributions have been observed.
Unstable density distribution associated with equatorial plasma bubble
Kherani, E. A.; Bharuthram, R.; Singh, S.; Lakhina, G. S.; de Meneses, F. Carlos
2016-04-01
In this work, we present a simulation study of equatorial plasma bubble (EPB) in the evening time ionosphere. The fluid simulation is performed with a high grid resolution, enabling us to probe the steepened updrafting density structures inside EPB. Inside the density depletion that eventually evolves as EPB, both density and updraft are functions of space from which the density as implicit function of updraft velocity or the density distribution function is constructed. In the present study, this distribution function and the corresponding probability distribution function are found to evolve from Maxwellian to non-Maxwellian as the initial small depletion grows to EPB. This non-Maxwellian distribution is of a gentle-bump type, in confirmation with the recently reported distribution within EPB from space-borne measurements that offer favorable condition for small scale kinetic instabilities.
The Velocity Distribution of Isolated Radio Pulsars
Arzoumanian, Z; Cordes, J M
2002-01-01
(Abridged) We infer the velocity distribution of radio pulsars by modelling their birth, evolution, and detection in large-scale 0.4 GHz pulsar surveys, and by comparing model distributions of measurable pulsar properties with survey data using a likelihood function. We test models that characterize a population's birth rate, luminosity, shutoff of radio emission, birth locations, and birth velocities. We infer that the radio beam luminosity (i) is comparable to the energy flux of relativistic particles in models for spin-driven magnetospheres, signifying that radio emission losses reach nearly 100% for the oldest pulsars; and (ii) scales approximately as sqrt(Edot) which, in magnetosphere models, is proportional to the voltage drop available for acceleration of particles. We find that a two-component velocity distribution with characteristic velocities of 90 km/s and 500 km/s is greatly preferred to any one-component distribution. We explore some consequences of the preferred birth velocity distribution: (i)...
New electromagnetic mode in a non-Maxwellian high-beta plasma
Urrutia, J. M.; Stenzel, R. L.
1984-01-01
An electromagnetic (EM) mode outside of the electron cyclotron frequency in a dense plasma discharge is reported. The experimental plasma was generated in a weak, uniform magnetic field and natural magnetic fluctuations were monitored and examined for cross correlations. Wave dispersion, propagation direction polarization and the electron velocity distribution were also derived. The fluctuations observed were neither cyclotron harmonic waves nor whistlers and consisted of circularly polarized waves propagating along field lines in 3-6 cm diam flux tubes. The mode was carried away from the cathode by streaming energetic electrons. The results may be pertinent in studies of EM modes in auroral arcs or magnetic fluctuations in tokamaks with runaway electrons.
Heat flux in a non-Maxwellian plasma. [in realistic solar coronal loop
Ljepojevic, N. N.; Macneice, P.
1989-01-01
A hybrid numerical scheme is applied to solve the Landau equation for the electron distribution function over all velocity space. Evidence is presented for the first time of the degree and character of the failure of the classical Spitzer-Haerm heat flux approximation in a realistic solar coronal loop structure. In the loop model used, the failure is so severe at some points that the role of the heat flux in the plasma's energy balance is completely misinterpreted. In the lower corona the Spitzer-Haerm approximation predicts that the heat flux should act as an energy source, whereas the more accurate distribution functions calculated here show this to be an energy sink.
Alves, M. V.; Barbosa, M. V. G.; Simoes, F. J. L., Jr.
2016-12-01
Observations have shown that several regions in space plasmas exhibit non-Maxwellian distributions with high energy superthermal tails. Kappa velocity distribution functions can describe many of these regions and have been used since the 60's. They suit well to represent superthermal tails in solar wind as well as to obtain plasma parameters of plasma within planetary magnetospheres. A set of initial velocities following kappa distribution functions is used in KEMPO1 particle simulation code to analyze the normal modes of wave propagation. Initial conditions are determined using observed characteristics for Saturńs magnetosphere. Two electron species with different temperatures and densities and ions as a third species are used. Each electron population is described by a different kappa index. Particular attention is given to perpendicular propagation, Bernstein modes, and parallel propagation, Langmuir and electron-acoustic modes. The dispersion relation for the Bernstein modes is strongly influenced by the shape of the velocity distribution and consequently by the value of kappa index. Simulation results are compared with numerical solutions of the dispersion relation obtained in the literature and they are in good agreement.
Velocity distributions in dilute granular systems.
van Zon, J S; MacKintosh, F C
2005-11-01
We investigate the idea that velocity distributions in granular gases are determined mainly by eta, the coefficient of restitution and q, which measures the relative importance of heating (or energy input) to collisions. To this end, we study by numerical simulation the properties of inelastic gases as functions of eta, concentration phi, and particle number N with various heating mechanisms. For a wide range of parameters, we find Gaussian velocity distributions for uniform heating and non-Gaussian velocity distributions for boundary heating. Comparison between these results and velocity distributions obtained by other heating mechanisms and for a simple model of a granular gas without spatial degrees of freedom, shows that uniform and boundary heating can be understood as different limits of q, with q>1 and q < or approximately 1 respectively. We review the literature for evidence of the role of q in the recent experiments.
Kappa distributions: theory and applications in space plasmas
Pierrard, V
2010-01-01
Particle velocity distribution functions (VDF) in space plasmas often show non Maxwellian suprathermal tails decreasing as a power law of the velocity. Such distributions are well fitted by the so-called Kappa distribution. The presence of such distributions in different space plasmas suggests a universal mechanism for the creation of such suprathermal tails. Different theories have been proposed and are recalled in this review paper. The suprathermal particles have important consequences concerning the acceleration and the temperature that are well evidenced by the kinetic approach where no closure requires the distributions to be nearly Maxwellians. Moreover, the presence of the suprathermal particles take an important role in the wave-particle interactions.
Directory of Open Access Journals (Sweden)
A. R. Barakat
Full Text Available Non-Maxwellian ion velocity distribution functions have been theoretically predicted and confirmed by observations, to occur at high latitudes. These distributions deviate from Maxwellian due to the combined effect of the E×B drift and ion-neutral collisions. The majority of previous literature, in which the effect of ion self-collisions was neglected, established a clear picture for the ion distribution under a wide range of conditions. At high altitudes and/or for solar maximum conditions, the ion-to-neutral density ratio increases and, hence, the role of ion self-collisions becomes appreciable. A Monte Carlo simulation was used to investigate the behaviour of O^{+} ions that are E×B-drifting through a background of neutral O, with the effect of O^{+} (Coulomb self-collisions included. Wide ranges of the ion-to-neutral density ratio n_{i}/n_{n} and the electrostatic field E were considered in order to investigate the change of ion behaviour with solar cycle and with altitude. For low altitudes and/or solar minimum (n_{i}/n_{n}≤ 10^{-5}, the effect of self-collisions is negligible. For higher values of n_{i}/n_{n}, the effect of self-collisions becomes significant and, hence, the non-Maxwellian features of the O^{+} distribution are reduced. For example, the parallel temperature T_{iVert} increases, the perpendicular temperature T_{i⊥} decreases, the temperature anisotropy approaches unity and the toroidal features of the ion distribution function become less pronounced. Also, as E increases, the ion-neutral collision rate increases, while the ion-ion collision rate decreases. Therefore, the effect of ion self-collisions is reduced. Finally, the
Velocity Distributions in Inelastic Granular Gases with Continuous Size Distributions
Institute of Scientific and Technical Information of China (English)
LI Rui; ZHANG Duan-Ming; LI Zhi-Hao
2011-01-01
We study by numerical simulation the property of velocity distributions of granular gases with a power-law size distribution, driven by uniform heating and boundary heating. It is found that the form of velocity distribution is primarily controlled by the restitution coefficient -q and q, the ratio between the average number of heatings and the average number of collisions in the system. Furthermore, we show that uniform and boundary heating can be understood as different limits of q, with q ? 1 and q >1 and q≤1,respectively.
Kinetics of metastable atoms and non-Maxwellian electrons in two-temperature plasmas
Kunc, J. A.; Soon, W. H.
1990-01-01
Numerical and analytical solutions of the electron Boltzmann equation in two-temperature steady-state helium plasma are studied in a broad range of conditions T(a) = 5,000-20,000 K, T(e) = 10,000-20,000 K; N(a) = 10 to the 10th - 10 to the 18th per cu cm. The WKB analytical solution is found to be satisfactory in most situations. The deviation of the electron distribution from Maxwellian and a possibility of raising of the tail of the distribution in presence of sources of fast electrons is also discussed.
Kinetic relaxation of a non-Maxwellian monatomic gas in a state of gross rest
Baganoff, D.
1993-01-01
The kinetic relaxation of a monatomic gas in a state of gross rest is studied by use of Maxwell's second-order moment equation. The molecular models considered range from the hard sphere to the Maxwell molecule. The development is exact for an ellipsoidal distribution and becomes a good approximation for more general distributions. The results show that the relaxation of second-order moments is nearly exponential for power-law molecules and that the characteristic time mu/p appears as the principal controlling parameter while the power-law constant plays a secondary role. Comparisons between results of numerical simulations using Bird's direct simulation Monte Carlo method and theory show excellent agreement for both hard-sphere and Maxwell molecules.
Lázár, M; Shukla, P K
2008-01-01
Counterstreaming plasma structures are widely present in laboratory experiments and astrophysical systems, and they are investigated either to prevent unstable modes arising in beam-plasma experiments or to prove the existence of large scale magnetic fields in astrophysical objects. Filamentation instability arises in a counterstreaming plasma and is responsible for the magnetization of the plasma. Filamentationally unstable mode is described by assuming that each of the counterstreaming plasmas has an isotropic Lorentzian (kappa) distribution. In this case, the filamentation instability growth rate can reach a maximum value markedly larger than that for a a plasma with a Maxwellian distribution function. This behaviour is opposite to what was observed for the Weibel instability growth rate in a bi-kappa plasma, which is always smaller than that obtained for a bi-Maxwellian plasma. The approach is further generalized for a counterstreaming plasma with a bi-kappa temperature anisotropy. In this case, the filam...
Antonelli, Cristian; Mecozzi, Antonio
2004-05-15
We give an analytical expression for the probability density function of the differential group delay for a concatenation of Maxwellian fiber sections and an arbitrary number of lumped elements with constant and isotropically oriented birefringence. When the contribution of the average squared of the constant birefringence elements is a significant fraction of the total, we show that the outage probability can be significantly overestimated if the probability density function of the differential group delay is approximated by a Maxwellian distribution.
Dust kinetic Alfvén waves and streaming instability in a non-Maxwellian magnetoplasma
Energy Technology Data Exchange (ETDEWEB)
Rubab, N.; Jaffer, G. [Department of Space Science, Institute of Space Technology (IST), Islamabad Expressway, Islamabad 44000 (Pakistan); Ali, S. [National Centre for Physics (NCP) at Quaid-i-Azam University Campus, Shahdra Valley Road, Islamabad 44000 (Pakistan)
2014-06-15
The dust kinetic Alfvén wave (DKAW) instability is studied in a uniform dusty magnetoplasma by incorporating the superthermality effects of the electrons and perpendicularly streaming κ-distributed ions. The dispersion relation of the DKAW instability is investigated in the low-β{sub d} Lorentzian plasma limit. The solutions are analyzed for various scenarios of dusty and dusty-free plasmas. It is shown that the presence of dust particles and the cross-field superthermal ions sensibly modify the dispersion characteristics of the low-frequency DKAW. The present results are only valid for a frequency regime well below the dust cyclotron frequency. Numerical calculations are carried out for the growth rates by taking different dust parameters into account. It is found that the nonthermality is more effective for the dust kinetic Alfvén waves in the perpendicular direction as compared to the parallel one. The relevance of the results to the low-β{sub d} regions of space and astrophysical plasmas is highlighted.
Theoretical models of non-Maxwellian equilibria for one-dimensional collisionless plasmas
Allanson, O.; Neukirch, T.; Wilson, F.; Troscheit, S.
2016-12-01
It is ideal to use exact equilibrium solutions of the steady state Vlasov-Maxwell system to intialise collsionless simulations. However, exact equilibrium distribution functions (DFs) for a given macroscopic configuration are typically unknown, and it is common to resort to using `flow-shifted' Maxwellian DFs in their stead. These DFs may be consistent with a macrosopic system with the target number density and current density, but could well have inaccurate higher order moments. We present recent theoretical work on the `inverse problem in Vlasov-Maxwell equilibria', namely calculating an exact solution of the Vlasov equation for a specific given magnetic field. In particular, we focus on one-dimensional geometries in Cartesian (current sheets) coordinates.1. From 1D fields to Vlasov equilibria: Theory and application of Hermite Polynomials: (O. Allanson, T. Neukirch, S. Troscheit and F. Wilson, Journal of Plasma Physics, 82, 905820306 (2016) [28 pages, Open Access] )2. An exact collisionless equilibrium for the Force-Free Harris Sheet with low plasma beta: (O. Allanson, T. Neukirch, F. Wilson and S. Troscheit, Physics of Plasmas, 22, 102116 (2015) [11 pages, Open Access])3. Neutral and non-neutral collisionless plasma equilibria for twisted flux tubes: The Gold-Hoyle model in a background field (O. Allanson, F. Wilson and T. Neukirch, (2016)) (accepted, Physics of Plasmas)
Energy Technology Data Exchange (ETDEWEB)
Tereshchenko, V.D.; Tereshchanko, E.D. (Polar Geophysical Inst., Murmansk (USSR)); Kohl, H. (Max-Planck-Inst. fuer Aeronomie, Katlenburg-Lindau (West Germany))
1991-10-01
In this paper the formulas for the ion distribution as well as the spectrum of radio waves scattered in a magnetized plasma with a strong electric field are derived. It is shown that the presence of the electric field in the ionosphere leads to an anisotropic ion velocity distribution and, therefore, to untypical incoherent scatter spectra for the F region of the polar ionosphere which are caused by ion-neutral together with ion-ion collisions. The effect of ion-ion collisions, which has not been taken into account so far, is to reduce the anisotropy of the ion velocity distribution. Estimates of the ion-ion collision frequency derived from EISCAT measurements show that this may happen above about 300 km.
Solar wind driven dust acoustic instability with Lorentzian kappa distribution
Energy Technology Data Exchange (ETDEWEB)
Arshad, Kashif [National Center for Physics (NCP), Quaid-i-Azam University Campus, Shahdra Valley Road, Islamabad 44000 (Pakistan); Pakistan Institute of Engineering and Applied Sciences, P.O. Nilore, Islamabad and University of Wah, Wah Cantt 47040 (Pakistan); Ehsan, Zahida, E-mail: Ehsan.zahida@gmail.com [National Center for Physics (NCP), Quaid-i-Azam University Campus, Shahdra Valley Road, Islamabad 44000 (Pakistan); Universita degli Studi del Molise, 86090 Pesche - IS (Italy); INFN Sezione di Napoli, 80126 Napoli (Italy); Department of Physics, COMSATS Institute of Information Technology (CIIT), Defence Road, Off Raiwind Road, Lahore 86090 (Pakistan); Khan, S. A. [National Center for Physics (NCP), Quaid-i-Azam University Campus, Shahdra Valley Road, Islamabad 44000 (Pakistan); Mahmood, S. [Theoretical Plasma Physics Division, PINSTEC, PO Box Nilore, Islamabad 44000 (Pakistan)
2014-02-15
In a three species electron-ion-dust plasma following a generalized non-Maxwellian distribution function (Lorentzian or kappa), it is shown that a kinetic instability of dust-acoustic mode exists. The instability threshold is affected when such (quasineutral) plasma permeates through another static plasma. Such case is of interest when the solar wind is streaming through the cometary plasma in the presence of interstellar dust. In the limits of phase velocity of the waves larger and smaller than the thermal velocity of dust particles, the dispersion properties and growth rate of dust-acoustic mode are investigated analytically with validation via numerical analysis.
Two dimensional velocity distribution in open channels using Renyi entropy
Kumbhakar, Manotosh; Ghoshal, Koeli
2016-05-01
In this study, the entropy concept is employed for describing the two-dimensional velocity distribution in an open channel. Using the principle of maximum entropy, the velocity distribution is derived by maximizing the Renyi entropy by assuming dimensionless velocity as a random variable. The derived velocity equation is capable of describing the variation of velocity along both the vertical and transverse directions with maximum velocity occurring on or below the water surface. The developed model of velocity distribution is tested with field and laboratory observations and is also compared with existing entropy-based velocity distributions. The present model has shown good agreement with the observed data and its prediction accuracy is comparable with the other existing models.
Concentration of the velocity distribution of pulsed neutron beams
Kitaguchi, Masaaki; Shimizu, Hirohiko M
2016-01-01
The velocity of neutrons from a pulsed neutron source is well-defined as a function of their arrival time. Electromagnetic neutron accelerator/decelerator synchronized with the neutron time-of-flight is capable of selectively changing the neutron velocity and concentrating the velocity distribution. Possible enhancement of the neutron intensity at a specific neutron velocity by orders of magnitude is discussed together with an experimental design.
Incoherent scatter spectra from plasma of a 13-moment approximation distribution function
Institute of Scientific and Technical Information of China (English)
2008-01-01
The function and physical mechanism of heat flow and the viscous stress in the velocity distribution function expanded by Maxwellian distribution are presented. With the introduction of effective temperature Tf, incoherent scatter spectra from plasma for electromagnetic wave in arbitrary line of sight are given. The effect of asymmetry and anisotropy provided by heat flow and the viscous stress on power spectra is discussed. Radar spectra are calculated for different cases of electric field, direction, collision frequency and temperature. The effect of heat flow and the viscous stress on inversion results is analyzed. With a large electric field, the character of non-Maxwellian must be considered.
Experimental velocity distributions in a granular submonolayer
Cadillo-Martínez, Alejandra T.; Sánchez, Rodrigo
2017-01-01
Experimental speed distributions are obtained for driven granular submonolayers of binary mixtures of single spheres and dimers of spheres. The results are well-described by a distribution originally developed for a single-species one-dimensional system. This suggests that such a distribution may be extended to other mixtures such as systems exhibiting aggregation and dissociation.
Experimental investigation of particle velocity distributions in windblown sand movement
Institute of Scientific and Technical Information of China (English)
2008-01-01
With the PDPA(Phase Doppler Particle Analyzer) measurement technology,the probability distributions of particle impact and lift-off velocities on bed surface and the particle velocity distributions at different heights are detected in a wind tunnel. The results show that the probability distribution of impact and lift-off velocities of sand grains can be expressed by a log-normal function,and that of impact and lift-off angles complies with an exponential function. The mean impact angle is between 28° and 39°,and the mean lift-off angle ranges from 30° to 44°. The mean lift-off velocity is 0.81-0.9 times the mean impact velocity. The proportion of backward-impacting particles is 0.05-0.11,and that of backward-entrained particles ranges from 0.04 to 0.13. The probability distribution of particle horizontal velocity at 4 mm height is positive skew,the horizontal velocity of particles at 20 mm height varies widely,and the variation of the particle horizontal velocity at 80 mm height is less than that at 20 mm height. The probability distribution of particle vertical velocity at different heights can be described as a normal function.
Quantitative velocity distributions via nuclear magnetic resonance flow metering
O'Neill, Keelan T.; Fridjonsson, Einar O.; Stanwix, Paul L.; Johns, Michael L.
2016-08-01
We demonstrate the use of Tikhonov regularisation as a data inversion technique to determine the velocity distributions of flowing liquid streams. Regularisation is applied to the signal produced by a nuclear magnetic resonance (NMR) flow measurement system consisting of a pre-polarising permanent magnet located upstream of an Earth's magnetic field NMR detection coil. A simple free induction decay (FID) NMR signal is measured for the flowing stream in what is effectively a 'time-of-flight' measurement. The FID signal is then modelled as a function of fluid velocity and acquisition time, enabling determination of the velocity probability distributions via regularisation. The mean values of these velocity distributions were successfully validated against in-line rotameters. The ability to quantify multi-modal velocity distributions was also demonstrated using a two-pipe system.
Two-Dimensional Distributed Velocity Collision Avoidance
2014-02-11
trigonometry . For convex polygon agents, the tangents are found by iterating over each point, calculating the z-component of the cross product between a...the modifications to the basic VO to favor the source bot’s current velocity (i.e., encourage the bot to change course as little as possible). To...the source agent on a collision course . However, if ignore factors are used, then A2 is more important (i.e., has a lower ignore factor), and so the
Reconstructing the three-dimensional local dark matter velocity distribution
Kavanagh, Bradley J
2016-01-01
Directionally sensitive dark matter (DM) direct detection experiments present the only way to observe the full three-dimensional velocity distribution of the Milky Way halo local to Earth. In this work we compare methods for extracting information about the local DM velocity distribution from a set of recoil directions and energies in a range of hypothetical directional and non-directional experiments. We compare a model independent empirical parameterisation of the velocity distribution based on an angular discretisation with a model dependent approach which assumes knowledge of the functional form of the distribution. The methods are tested under three distinct halo models which cover a range of possible phase space structures for the local velocity distribution: a smooth Maxwellian halo, a tidal stream and a debris flow. In each case we use simulated directional data to attempt to reconstruct the shape and parameters describing each model as well as the DM particle properties. We find that the empirical pa...
Reconstructing the three-dimensional local dark matter velocity distribution
Kavanagh, Bradley J.; O'Hare, Ciaran A. J.
2016-12-01
Directionally sensitive dark matter (DM) direct detection experiments present the only way to observe the full three-dimensional velocity distribution of the Milky Way halo local to Earth. In this work we compare methods for extracting information about the local DM velocity distribution from a set of recoil directions and energies in a range of hypothetical directional and nondirectional experiments. We compare a model-independent empirical parametrization of the velocity distribution based on an angular discretization with a model-dependent approach which assumes knowledge of the functional form of the distribution. The methods are tested under three distinct halo models which cover a range of possible phase space structures for the local velocity distribution: a smooth Maxwellian halo, a tidal stream and a debris flow. In each case we use simulated directional data to attempt to reconstruct the shape and parameters describing each model as well as the DM particle properties. We find that the empirical parametrization is able to make accurate unbiased reconstructions of the DM mass and cross section as well as capture features in the underlying velocity distribution in certain directions without any assumptions about its true functional form. We also find that by extracting directionally averaged velocity parameters with this method one can discriminate between halo models with different classes of substructure.
How required reserve ratio affects distribution and velocity of money
Xi, Ning; Ding, Ning; Wang, Yougui
2005-11-01
In this paper the dependence of wealth distribution and the velocity of money on the required reserve ratio is examined based on a random transfer model of money and computer simulations. A fractional reserve banking system is introduced to the model where money creation can be achieved by bank loans and the monetary aggregate is determined by the monetary base and the required reserve ratio. It is shown that monetary wealth follows asymmetric Laplace distribution and latency time of money follows exponential distribution. The expression of monetary wealth distribution and that of the velocity of money in terms of the required reserve ratio are presented in a good agreement with simulation results.
How Required Reserve Ratio Affects Distribution and Velocity of Money
Xi, N; Wang, Y; Xi, Ning; Ding, Ning; Wang, Yougui
2005-01-01
In this paper the dependence of wealth distribution and the velocity of money on the required reserve ratio is examined based on a random transfer model of money and computer simulations. A fractional reserve banking system is introduced to the model where money creation can be achieved by bank loans and the monetary aggregate is determined by the monetary base and the required reserve ratio. It is shown that monetary wealth follows asymmetric Laplace distribution and latency time of money follows exponential distribution. The expression of monetary wealth distribution and that of the velocity of money in terms of the required reserve ratio are presented in a good agreement with simulation results.
The velocity distribution of SDSS satellites in MOND
Angus, Garry; Tiret, Olivier; Combes, Francoise; Zhao, HongSheng
2007-01-01
The recent SDSS measured velocity distribution of satellite galaxies has been modelled in the context of MOND. We show that even when the extra constraint of adhering to the projected satellite number density profile is added, the two line of sight (los) velocity dispersion profiles presented in Klypin & Prada (2007) can be matched simply with a radially varying anisotropy. Interestingly, the anisotropies required to fit the los velocity dispersions are remarkably similar to the anisotropies generated by dissipationless collapse simulations in MOND. The mass-to-light ratios of the two host galaxies used are sensible and positivity of the distribution function is satisfied.
SPIDER - IX. Classifying galaxy groups according to their velocity distribution
Ribeiro, A. L. B.; de Carvalho, R. R.; Trevisan, M.; Capelato, H. V.; La Barbera, F.; Lopes, P. A. A.; Schilling, A. C.
2013-09-01
We introduce a new method to study the velocity distribution of galaxy systems, the Hellinger Distance (HD), designed for detecting departures from a Gaussian velocity distribution. Testing different approaches to measure normality of a distribution, we conclude that HD is the least vulnerable method to type I and II statistical errors. We define a relaxed galactic system as the one with unimodal velocity distribution and a normality deviation below a critical value (HD ) and the Gaussianity of the velocity distribution of the groups. Bright galaxies (Mr ≤ -20.7) residing in the inner and outer regions of groups do not show significant differences in the listed quantities regardless if the group has a Gaussian (G) or a Non-Gaussian (NG) velocity distribution. However, the situation is significantly different when we examine the faint galaxies (-20.7 < Mr ≤ -17.9). In G groups, there is a remarkable difference between the galaxy properties of the inner and outer galaxy populations, testifying how the environment is affecting the galaxies. Instead, in NG groups there is no segregation between the properties of galaxies in the inner and outer regions, showing that the properties of these galaxies still reflect the physical processes prevailing in the environment where they were found earlier.
Stark, A; Fox, W; Egedal, J; Grulke, O; Klinger, T
2005-12-02
Observations in space and laboratory plasmas suggest magnetic reconnection as a mechanism for ion heating and formation of non-Maxwellian ion velocity distribution functions (IVDF). Laser-induced fluorescence measurements of the IVDF parallel to the X line of a periodically driven reconnection experiment are presented. A time-resolved analysis yields the evolution of the IVDF within a reconnection cycle. It is shown that reconnection causes a strong increase of the ion temperature, where the strongest increase is found at the maximum reconnection rate. Monte Carlo simulations demonstrate that ion heating is a consequence of the in-plane electric field that forms around the X line in response to reconnection.
Shear Profiles and Velocity Distribution in Dense Shear Granular Flow
Institute of Scientific and Technical Information of China (English)
WANG Deng-Ming; ZHOU You-He
2009-01-01
We perform DEM simulations to investigate the influence of the packing fraction γ on the,shape of mean tan-gential velocity profile in a 2D annular dense shear granular flow. There is a critical packing fraction γc. For γ < γc, the mean tangential velocity profile shows a roughly exponential decay from the shearing boundary and is almost invariant to the imposed shear rate. However, for γ γc, the tangential velocity profile exhibits a rate-dependence feature and changes from linear to nonlinear gradually with the increasing shear rate. Fhrther-more, the distributions of normalized tangential velocities at different positions along radial direction exhibit the Gaussian or the composite Gaussian distributing features.
Shaping the distribution of vertical velocities of antihydrogen in GBAR
Dufour, G.; Lambrecht, A.; Nesvizhevsky, V.V.; Reynaud, S.; Voronin, A.Yu.
2014-01-30
GBAR is a project aiming at measuring the free fall acceleration of gravity for antimatter, namely antihydrogen atoms ($\\overline{\\mathrm{H}}$). Precision of this timing experiment depends crucially on the dispersion of initial vertical velocities of the atoms as well as on the reliable control of their distribution. We propose to use a new method for shaping the distribution of vertical velocities of $\\overline{\\mathrm{H}}$, which improves these factors simultaneously. The method is based on quantum reflection of elastically and specularly bouncing $\\overline{\\mathrm{H}}$ with small initial vertical velocity on a bottom mirror disk, and absorption of atoms with large initial vertical velocities on a top rough disk. We estimate statistical and systematic uncertainties, and show that the accuracy for measuring the free fall acceleration $\\overline{g}$ of $\\overline{\\mathrm{H}}$ could be pushed below $10^{-3}$ under realistic experimental conditions.
Shaping the distribution of vertical velocities of antihydrogen in GBAR
Dufour, G.; Debu, P.; Lambrecht, A.; Nesvizhevsky, V. V.; Reynaud, S.; Voronin, A. Yu.
2014-01-01
GBAR is a project aiming at measuring the free-fall acceleration of gravity for antimatter, namely antihydrogen atoms (). The precision of this timing experiment depends crucially on the dispersion of initial vertical velocities of the atoms as well as on the reliable control of their distribution. We propose to use a new method for shaping the distribution of the vertical velocities of , which improves these factors simultaneously. The method is based on quantum reflection of elastically and specularly bouncing with small initial vertical velocity on a bottom mirror disk, and absorption of atoms with large initial vertical velocities on a top rough disk. We estimate statistical and systematic uncertainties, and we show that the accuracy for measuring the free fall acceleration of could be pushed below under realistic experimental conditions.
Motion of Euglena gracilis: Active fluctuations and velocity distribution
Romanczuk, P.; Romensky, M.; Scholz, D.; Lobaskin, V.; Schimansky-Geier, L.
2015-07-01
We study the velocity distribution of unicellular swimming algae Euglena gracilis using optical microscopy and active Brownian particle theory. To characterize a peculiar feature of the experimentally observed distribution at small velocities we use the concept of active fluctuations, which was recently proposed for the description of stochastically self-propelled particles [Romanczuk, P. and Schimansky-Geier, L., Phys. Rev. Lett. 106, 230601 (2011)]. In this concept, the fluctuating forces arise due to internal random performance of the propulsive motor. The fluctuating forces are directed in parallel to the heading direction, in which the propulsion acts. In the theory, we introduce the active motion via the depot model [Schweitzer, et al., Phys. Rev. Lett. 80(23), 5044 (1998)]. We demonstrate that the theoretical predictions based on the depot model with active fluctuations are consistent with the experimentally observed velocity distributions. In addition to the model with additive active noise, we obtain theoretical results for a constant propulsion with multiplicative noise.
Motion of Euglena Gracilis: Active Fluctuations and Velocity Distribution
Romanczuk, Pawel; Scholz, Dimitri; Lobaskin, Vladimir; Schimansky-Geier, Lutz
2015-01-01
We study the velocity distribution of unicellular swimming algae Euglena gracilis using optical microscopy and theory. To characterize a peculiar feature of the experimentally observed distribution at small velocities we use the concept of active fluctuations, which was recently proposed for the description of stochastically self-propelled particles [Romanczuk, P. and Schimansky-Geier, L., Phys. Rev. Lett. 106, 230601 (2011)]. In this concept, the fluctuating forces arise due to internal random performance of the propulsive motor. The fluctuating forces are directed in parallel to the heading direction, in which the propulsion acts. In the theory, we introduce the active motion via the depot model [Schweitzer et al., Phys. Rev. Lett. 80, 23, 5044 (1998)]. We demonstrate that the theoretical predictions based on the depot model with active fluctuations are consistent with the experimentally observed velocity distributions. In addition to the model with additive active noise, we obtain theoretical results for a...
Kappa distributions in the presence of a potential energy
Livadiotis, George
2016-10-01
Classical particle systems reside at thermal equilibrium with their velocity distribution function stabilized into a Maxwell distribution. On the contrary, collisionless and correlated particle systems, such as geophysical, space, and astrophysical plasmas, are characterized by a non-Maxwellian behavior, typically described by the so-called kappa distributions, or combinations thereof. Empirical kappa distributions have become increasingly widespread across plasma physics. A breakthrough in the field came with the connection of kappa distributions to non-extensive statistical mechanics. Understanding the statistical origin of kappa distributions was the cornerstone of further theoretical developments and applications, one of which is the generalization to the phase-space kappa distributions of a Hamiltonian with non-zero potentials. We present the theory behind the phase-space kappa distributions and discuss three important applications in collisionless plasmas: (i) origin of polytropic relation; (ii) gravitational field; (iii) barometric relation (i.e., pressure vs. altitude); and (iv) plasma magnetization.
Power exponential velocity distributions in disordered porous media
Matyka, Maciej; Koza, Zbigniew
2016-01-01
Velocity distribution functions link the micro- and macro-level theories of fluid flow through porous media. Here we study them for the fluid absolute velocity and its longitudinal and lateral components relative to the macroscopic flow direction in a model of a random porous medium. We claim that all distributions follow the power exponential law controlled by an exponent $\\gamma$ and a shift parameter $u_0$ and examine how these parameters depend on the porosity. We find that $\\gamma$ has a universal value $1/2$ at the percolation threshold and grows with the porosity, but never exceeds 2.
Leo, M; Leo, R A; Tempesta, P; Tsallis, C
2012-03-01
In a recent paper [M. Leo, R. A. Leo, and P. Tempesta, J. Stat. Mech. (2011) P03003], it has been shown that the π/2-mode exact nonlinear solution of the Fermi-Pasta-Ulam β system, with periodic boundary conditions, admits two energy density thresholds. For values of the energy density ε below or above these thresholds, the solution is stable. Between them, the behavior of the solution is unstable, first recurrent and then chaotic. In this paper, we study the chaotic behavior between the two thresholds from a statistical point of view, by analyzing the distribution function of a dynamical variable that is zero when the solution is stable and fluctuates around zero when it is unstable. For mesoscopic systems clear numerical evidence emerges that near the second threshold, in a large range of the energy density, the numerical distribution is fitted accurately with a q-Gaussian distribution for very large integration times, suggesting the existence of a quasistationary state possessing a weakly chaotic behavior. A normal distribution is recovered in the thermodynamic limit.
How Required Reserve Ratio Affects Distribution and Velocity of Money
Ning Xi; Ning Ding; Yougui Wang
2005-01-01
In this paper the dependence of wealth distribution and the velocity of money on the required reserve ratio is examined based on a random transfer model of money and computer simulations. A fractional reserve banking system is introduced to the model where money creation can be achieved by bank loans and the monetary aggregate is determined by the monetary base and the required reserve ratio. It is shown that monetary wealth follows asymmetric Laplace distribution and latency time of money fo...
How Required Reserve Ratio Affects Distribution and Velocity of Money
Ning Xi; Ning Ding; Yougui Wang
2005-01-01
In this paper the dependence of wealth distribution and the velocity of money on the required reserve ratio is examined based on a random transfer model of money and computer simulations. A fractional reserve banking system is introduced to the model where money creation can be achieved by bank loans and the monetary aggregate is determined by the monetary base and the required reserve ratio. It is shown that monetary wealth follows asymmetric Laplace distribution and latency time of money fo...
Local pulsars : A note on the birth-velocity distribution
Blaauw, A; Ramachandran, R
1998-01-01
We explore a simple model for the representation of the observed distributions of the motions, and the characteristic ages of the local population of pulsars. The principal difference from earlier models is the introduction of a unique value, S, for the kick velocity with which pulsars are born. We
Suprathermal electron distributions in the solar transition region
Vocks, C; Mann, G
2016-01-01
Suprathermal tails are a common feature of solar wind electron velocity distributions, and are expected in the solar corona. From the corona, suprathermal electrons can propagate through the steep temperature gradient of the transition region towards the chromosphere, and lead to non-Maxwellian electron velocity distribution functions (VDFs) with pronounced suprathermal tails. We calculate the evolution of a coronal electron distribution through the transition region in order to quantify the suprathermal electron population there. A kinetic model for electrons is used which is based on solving the Boltzmann-Vlasov equation for electrons including Coulomb collisions with both ions and electrons. Initial and chromospheric boundary conditions are Maxwellian VDFs with densities and temperatures based on a background fluid model. The coronal boundary condition has been adopted from earlier studies of suprathermal electron formation in coronal loops. The model results show the presence of strong suprathermal tails ...
A nonextensive entropy approach to kappa-distributions
Leubner, M P
2002-01-01
Most astrophysical plasmas are observed to have velocity distribution functions exhibiting non-Maxwellian suprathermal tails. The high energy particle populations are accurately represented by the family of kappa-distributions where the use of these distributions has been unjustly criticized because of a perceived lack of theoretical justification. We show that distributions very close to kappa-distributions are a consequence of the generalized entropy favored by nonextensive statistics, which provides the missing link for power-law models of non-thermal features from fundamental physics. With regard to the the physical basis supplied by the Tsallis nonextensive entropy formalism we propose that this slightly modified functional form, qualitatively similar to the traditional kappa-distribution, be used in fitting particle spectra in the future.
Actin filaments on myosin beds: The velocity distribution
Bourdieu, L.; Magnasco, M. O.; Winkelmann, D. A.; Libchaber, A.
1995-12-01
In vitro studies of actin filaments sliding on a myosin-coated surface are analyzed, filament by filament, at a sampling rate of 30 per second. For each filament, the mean arc length coordinate is computed and histograms of instantaneous velocities, along the arc length, are established. Two types of motion are observed, depending on the experimental conditions. The first one is characterized by a homogeneous flow, with well defined velocities. In this regime, specific defects are a constitutive part of the flow. It is observed at high temperature, at high myosin coverage, and with a particular mode of attachment of myosin to the surface. The second regime shows no clear velocity selection, but a broadband distribution. It is characterized by high friction and is observed at low temperature or low myosin density. (c) 1995 The American Physical Society
PROBABILITY DISTRIBUTION FUNCTION OF NEAR-WALL TURBULENT VELOCITY FLUCTUATIONS
Institute of Scientific and Technical Information of China (English)
无
2005-01-01
By large eddy simulation (LES), turbulent databases of channel flows at different Reynolds numbers were established. Then, the probability distribution functions of the streamwise and wall-normal velocity fluctuations were obtained and compared with the corresponding normal distributions. By hypothesis test, the deviation from the normal distribution was analyzed quantitatively. The skewness and flatness factors were also calculated. And the variations of these two factors in the viscous sublayer, buffer layer and log-law layer were discussed. Still illustrated were the relations between the probability distribution functions and the burst events-sweep of high-speed fluids and ejection of low-speed fluids-in the viscous sub-layer, buffer layer and loglaw layer. Finally the variations of the probability distribution functions with Reynolds number were examined.
Whistler Waves Driven by Anisotropic Strahl Velocity Distributions: Cluster Observations
Vinas, A.F.; Gurgiolo, C.; Nieves-Chinchilla, T.; Gary, S. P.; Goldstein, M. L.
2010-01-01
Observed properties of the strahl using high resolution 3D electron velocity distribution data obtained from the Cluster/PEACE experiment are used to investigate its linear stability. An automated method to isolate the strahl is used to allow its moments to be computed independent of the solar wind core+halo. Results show that the strahl can have a high temperature anisotropy (T(perpindicular)/T(parallell) approximately > 2). This anisotropy is shown to be an important free energy source for the excitation of high frequency whistler waves. The analysis suggests that the resultant whistler waves are strong enough to regulate the electron velocity distributions in the solar wind through pitch-angle scattering
Distributed Velocity-Dependent Protocol for Multihop Cellular Sensor Networks
Directory of Open Access Journals (Sweden)
Jagyasi Bhushan
2009-01-01
Full Text Available Abstract Cell phones are embedded with sensors form a Cellular Sensor Network which can be used to localize a moving event. The inherent mobility of the application and of the cell phone users warrants distributed structure-free data aggregation and on-the-fly routing. We propose a Distributed Velocity-Dependent (DVD protocol to localize a moving event using a Multihop Cellular Sensor Network (MCSN. DVD is based on a novel form of connectivity determined by the waiting time of nodes for a Random Waypoint (RWP distribution of cell phone users. This paper analyzes the time-stationary and spatial distribution of the proposed waiting time to explain the superior event localization and delay performances of DVD over the existing Randomized Waiting (RW protocol. A sensitivity analysis is also performed to compare the performance of DVD with RW and the existing Centralized approach.
Distributed Velocity-Dependent Protocol for Multihop Cellular Sensor Networks
Directory of Open Access Journals (Sweden)
Deepthi Chander
2009-01-01
Full Text Available Cell phones are embedded with sensors form a Cellular Sensor Network which can be used to localize a moving event. The inherent mobility of the application and of the cell phone users warrants distributed structure-free data aggregation and on-the-fly routing. We propose a Distributed Velocity-Dependent (DVD protocol to localize a moving event using a Multihop Cellular Sensor Network (MCSN. DVD is based on a novel form of connectivity determined by the waiting time of nodes for a Random Waypoint (RWP distribution of cell phone users. This paper analyzes the time-stationary and spatial distribution of the proposed waiting time to explain the superior event localization and delay performances of DVD over the existing Randomized Waiting (RW protocol. A sensitivity analysis is also performed to compare the performance of DVD with RW and the existing Centralized approach.
Barakat, A. R.; Schunk, R. W.
1982-01-01
A wide variety of plasma flow conditions is found in aeronomy and space plasma physics. Transport equations based on an isotropic Maxwellian vilecity distribution function can be used to describe plasma flows which contain 'small' temperature anisotropies. However, for plasma flows characterized by large temperature anisotropies, transport equations based on an anisotropic bi-Maxwellian (or two-temperature) velocity distribution function are expected to provide a much better description of the plasma transport properties. The present investigation is concerned with the extent to which transport equations based on both Maxwellian and bi-Maxwellian series expansions can describe plasma flows characterized by non-Maxwellian velocity distributions, giving particular attention to a modelling of the anisotropic character of the distribution function. The obtained results should provide clues as to the extent to which a given series expansion can account for the anisotropic character of a plasma.
Mechanism of proton anisotropic velocity distribution in the solar wind
Institute of Scientific and Technical Information of China (English)
AO; Xianzhi(敖先志); SHEN; Ji(沈迹); TU; Chuanyi(涂传诒)
2003-01-01
Although it has been long that spacecraft observed the anisotropy of velocity protons in the solar wind, there is still not a reasonable explanation. In this paper we try to give an explanation from the diffusion plateau of protoncyclotron resonance predicted by the quasi-linear theory for the resonance between the protons and the parallel propagating waves. We consider the effect of dispersion relation on diffusion plateau and notice that the diffusion plateau we have got by using cold plasma dispersion relation accords with the density contours in the velocity phase space detected at 0.3 AU in fast solar wind. For explaining proton distributions obtained in the fast solar wind from 0.7 AU to 1 AU hot plasma dispersion relation should be considered. We also give a theoretical relation of proton thermal anisotropy A and plasma parameter β.
Measurements of parallel electron velocity distributions using whistler wave absorption.
Thuecks, D J; Skiff, F; Kletzing, C A
2012-08-01
We describe a diagnostic to measure the parallel electron velocity distribution in a magnetized plasma that is overdense (ω(pe) > ω(ce)). This technique utilizes resonant absorption of whistler waves by electrons with velocities parallel to a background magnetic field. The whistler waves were launched and received by a pair of dipole antennas immersed in a cylindrical discharge plasma at two positions along an axial background magnetic field. The whistler wave frequency was swept from somewhat below and up to the electron cyclotron frequency ω(ce). As the frequency was swept, the wave was resonantly absorbed by the part of the electron phase space density which was Doppler shifted into resonance according to the relation ω - k([parallel])v([parallel]) = ω(ce). The measured absorption is directly related to the reduced parallel electron distribution function integrated along the wave trajectory. The background theory and initial results from this diagnostic are presented here. Though this diagnostic is best suited to detect tail populations of the parallel electron distribution function, these first results show that this diagnostic is also rather successful in measuring the bulk plasma density and temperature both during the plasma discharge and into the afterglow.
Settling-velocity specific SOC distribution on hillslopes
DEFF Research Database (Denmark)
Hu, Yaxian; Berhe, Asmeret Asefaw; Fogel, Marilyn L.;
The net effect of soil erosion by water, as a sink or source of atmospheric CO2, is determined by the spatial (re-)distribution and stability of eroded soil organic carbon (SOC). The depositional position of eroded SOC is a function of the transport distances of soil fractions where the SOC...... is stored. In theory, the transport distances of soil fractions are related to their settling velocities under given flow conditions. Yet, very few field investigations have been conducted to examine the actual movement of eroded soil fractions along hillslopes, let alone the re-distribution pattern of SOC...... shows a coarsening effect immediately below the eroding slope, followed by a fining trend at the slope tail. The 13C values of soil fractions were more positive at the footslope than on the slope shoulder or at the slope tail, suggesting enhanced decomposition rate of fresh SOC input at the footslope...
Settling-velocity specific SOC distribution on hillslopes
Hu, Yaxian; Asefaw Berhe, Asmeret; Fogel, Marilyn L.; Heckrath, Goswin J.; Kuhn, Nikolaus J.
2016-04-01
The net effect of soil erosion by water, as a sink or source of atmospheric CO2, is determined by the spatial (re-)distribution and stability of eroded soil organic carbon (SOC). The depositional position of eroded SOC is a function of the transport distances of soil fractions where the SOC is stored. In theory, the transport distances of soil fractions are related to their settling velocities under given flow conditions. Yet, very few field investigations have been conducted to examine the actual movement of eroded soil fractions along hillslopes, let alone the re-distribution pattern of SOC fractions. Eroding sandy soils and sediment were sampled after a series of rainfall events along a slope on a freshly seeded cropland in Jutland, Denmark. All the soil samples were fractionated into five settling classes using a settling tube apparatus. The spatial distribution of soil settling classes shows a coarsening effect immediately below the eroding slope, followed by a fining trend at the slope tail. The δ13C values of soil fractions were more positive at the footslope than on the slope shoulder or at the slope tail, suggesting enhanced decomposition rate of fresh SOC input at the footslope during or after erosion-induced transport. Overall, our results illustrate that immediate deposition of fast settling soil fractions and the associated SOC at footslopes must be appropriately accounted for in attempts to quantify the role of soil erosion in terrestrial carbon sequestration. A SOC erodibility parameter based on actual settling velocity distribution of eroded fractions is needed to better calibrate soil erosion models.
Kikuchi, K.; Barakat, A.; St-Maurice, J.-P.
1989-01-01
Monte Carlo simulations of ion velocity distributions in the high-latitude F region have been performed in order to improve the calculation of incoherent radar spectra in the auroral ionosphere. The results confirm that when the ion temperature becomes large due to frictional heating in the presence of collisions with the neutral background constituent, F region spectra evolve from a normal double hump, to a triple hump, to a spectrum with a single maximum. An empirical approach is developed to overcome the inadequacy of the Maxwellian assumption for the case of radar aspect angles of between 30 and 70 deg.
Fine velocity structures collisional dissipation in plasmas
Pezzi, Oreste; Valentini, Francesco; Veltri, Pierluigi
2016-04-01
In a weakly collisional plasma, such as the solar wind, collisions are usually considered far too weak to produce any significant effect on the plasma dynamics [1]. However, the estimation of collisionality is often based on the restrictive assumption that the particle velocity distribution function (VDF) shape is close to Maxwellian [2]. On the other hand, in situ spacecraft measurements in the solar wind [3], as well as kinetic numerical experiments [4], indicate that marked non-Maxwellian features develop in the three-dimensional VDFs, (temperature anisotropies, generation of particle beams, ring-like modulations etc.) as a result of the kinetic turbulent cascade of energy towards short spatial scales. Therefore, since collisional effects are proportional to the velocity gradients of the VDF, the collisionless hypothesis may fail locally in velocity space. Here, the existence of several characteristic times during the collisional relaxation of fine velocity structures is investigated by means of Eulerian numerical simulations of a spatially homogeneous force-free weakly collisional plasma. The effect of smoothing out velocity gradients on the evolution of global quantities, such as temperature and entropy, is discussed, suggesting that plasma collisionality can increase locally due to the velocity space deformation of the particle velocity distribution. In particular, by means of Eulerian simulations of collisional relaxation of a spatially homogeneous force-free plasma, in which collisions among particles of the same species are modeled through the complete Landau operator, we show that the system entropy growth occurs over several time scales, inversely proportional to the steepness of the velocity gradients in the VDF. We report clear evidences that fine velocity structures are dissipated by collisions in a time much shorter than global non-Maxwellian features, like, for example, temperature anisotropies. Moreover we indicate that, if small-scale structures
Discretising the velocity distribution for directional dark matter experiments
Kavanagh, Bradley J
2015-01-01
Dark matter (DM) direct detection experiments which are directionally-sensitive may be the only method of probing the full velocity distribution function (VDF) of the Galactic DM halo. We present an angular basis for the DM VDF which can be used to parametrise the distribution in order to mitigate astrophysical uncertainties in future directional experiments and extract information about the DM halo. This basis consists of discretising the VDF in a series of angular bins, with the VDF being only a function of the DM speed $v$ within each bin. In contrast to other methods, such as spherical harmonic expansions, the use of this basis allows us to guarantee that the resulting VDF is everywhere positive and therefore physical. We present a recipe for calculating the event rates corresponding to the discrete VDF for an arbitrary number of angular bins $N$ and investigate the discretisation error which is introduced in this way. For smooth, Standard Halo Model-like distribution functions, only $N=3$ angular bins ar...
Electron velocity distribution and lion roars in the magnetosheath
Directory of Open Access Journals (Sweden)
W. Masood
2006-07-01
Full Text Available Whistler waves which are termed "lion roars" in the magnetosheath are studied using data obtained by the Spectrum Analyser (SA of the Spatio-Temporal Analysis of Field Fluctuations (STAFF experiment aboard Cluster. Kinetic theory is then employed to obtain the theoretical expression for the whistler wave with electron temperature anisotropy which is believed to trigger lion roars in the magnetosheath. This allows us to compare theory and data. This paper for the first time studies the details of the electron velocity distribution function as measured by the Plasma Electron And Current Experiment (PEACE in order to investigate the underlying causes for the different types of lion roars found in the data. Our results show that while some instances of lion roars could be locally generated, the source of others must be more remote regions of the magnetosheath.
LASER ULTRASONIC FOR MEASUREMENTS OF VELOCITY DISTRIBUTION IN PIPES
Directory of Open Access Journals (Sweden)
M. Navarrete
2004-12-01
Full Text Available The present work describes the development of a photoacoustic flowmeter with probe-beam deflection. A pulsedlaser beam produces an acoustic pulse, whose propagation is registered by its deflection effects on two cw probebeams. The acoustic pulse in a flowing fluid is produced by absorption of a laser pulse (30 ns, 1.1 mJ focused overa path flow line. The acoustic propagations, along and against the flow, are monitored by two cw probe beams. Inthe interaction, the probe beam undergoes a transient deflection that is detected by a fast response photodiode.The velocity distribution data profile of a square pipe is obtained by means of the acoustic pulse arrival timemeasured through its cross section applying the cylindrical shockwave model developed by Vlasses. The profilesdetermined with this experimental technique are compared with two turbulent pipe flow models.
On the distribution of sound velocity in a section of Vzag in the Bay of Bengal
Directory of Open Access Journals (Sweden)
J.Siva Rama Sastry
1956-04-01
Full Text Available The vertical sound velocity distribution in a section of Visakhapatnam in the Bay of Bengal has been computed making use of Kuwahara's tables. In an attempt to find out the corrections to the echo-sounder readings the average sound velocity distribution is computed together with the sound velocity profiles taking the spot values only. The physical oceanography of the area in relation to the sound velocity distribution is discussed.
Calculation of a velocity distribution from particle trajectory end-points.
Rasmussen, Lowell A.
1983-01-01
The longitudinal component of the velocity of a particle at or near a glacier surface is considered, its position as a function of time being termed its trajectory. Functional relationships are derived for obtaining the trajectory from the spatial distribution of velocity and for obtaining the velocity distribution from the trajectory. It is established that the trajectory end-points impose only an integral condition on the velocity distribution and that no individual point on the velocity distribution can be determined if only the end-points are known.-from Author
Complete velocity distribution in river cross-sections measured by acoustic instruments
Cheng, R.T.; Gartner, J.W.; ,
2003-01-01
To fully understand the hydraulic properties of natural rivers, velocity distribution in the river cross-section should be studied in detail. The measurement task is not straightforward because there is not an instrument that can measure the velocity distribution covering the entire cross-section. Particularly, the velocities in regions near the free surface and in the bottom boundary layer are difficult to measure, and yet the velocity properties in these regions play the most significant role in characterizing the hydraulic properties. To further characterize river hydraulics, two acoustic instruments, namely, an acoustic Doppler current profiler (ADCP), and a "BoogieDopp" (BD) were used on fixed platforms to measure the detailed velocity profiles across the river. Typically, 20 to 25 stations were used to represent a river cross-section. At each station, water velocity profiles were measured independently and/or concurrently by an ADCP and a BD. The measured velocity properties were compared and used in computation of river discharge. In a tow-tank evaluation of a BD, it has been confirmed that BD is capable of measuring water velocity at about 11 cm below the free-surface. Therefore, the surface velocity distribution across the river was extracted from the BD velocity measurements and used to compute the river discharge. These detailed velocity profiles and the composite velocity distribution were used to assess the validity of the classic theories of velocity distributions, conventional river discharge measurement methods, and for estimates of channel bottom roughness.
An Unbiased Estimator of Peculiar Velocity with Gaussian Distributed Errors for Precision Cosmology
Watkins, Richard
2014-01-01
We introduce a new estimator of the peculiar velocity of a galaxy or group of galaxies from redshift and distance estimates. This estimator results in peculiar velocity estimates which are statistically unbiased and that have errors that are Gaussian distributed, thus meeting the assumptions of analyses that rely on individual peculiar velocities. We apply this estimator to the SFI++ and the Cosmicflows-2 catalogs of galaxy distances and, using the fact that peculiar velocity estimates of distant galaxies are error dominated, examine their error distributions, The adoption of the new estimator significantly improves the accuracy and validity of studies of the large-scale peculiar velocity field and eliminates potential systematic biases, thus helping to bring peculiar velocity analysis into the era of precision cosmology. In addition, our method of examining the distribution of velocity errors should provide a useful check of the statistics of large peculiar velocity catalogs, particularly those that are comp...
Institute of Scientific and Technical Information of China (English)
何正勤; 丁志峰; 叶太兰; 孙为国; 张乃铃
2002-01-01
Based on the long period digital surface wave data recorded by 11 CDSN stations and 11 IRIS stations, the dispersion curves of the group velocities of fundamental mode Rayleigh waves along 647 paths, with the periods from 10 s to 92 s, were measured by multi-filter. Their distribution at 25 central periods within the region of 18((54(N, 70(~140(E was inverted by Dimtar-Yanovskaya method. Within the period from 10 s to 15.9 s, the group velocity distribution is laterally inhomogeneous and is closely related to geotectonic units, with two low velocity zones located in the Tarim basin and the East China Sea and its north regions, respectively. From 21 s to 33 s, the framework of tectonic blocks is revealed. From 36.6 s to 40 s, the lithospheric subdivision of the Chinese mainland is obviously uncovered, with distinct boundaries among the South-North seismic belt, the Tibetan plateau, the North China, the South China and the Northeast China. Four cross-sections of group velocity distribution with period along 30(N, 38(N, 90(E and 120(E, are discussed, respectively, which display the basic features of the crust and upper mantle of the Chinese mainland and its neighboring regions. There are distinguished velocity differences among the different tectonic blocks. There are low-velocity-zones (LVZ) in the middle crust of the eastern Tibetan plateau, high velocity featured as stable platform in the Tarim basin and the Yangtze platform, shallow and thick low-velocity-zone in the upper mantle of the North China. The upper mantle LVZ in the East China Sea and the Japan Sea is related to the frictional heat from the subduction of the Philippine slab and the strong extension since the Himalayan orogenic period.
Benson, Robert F.; Vinas, Adolfo, F.; Fainberg, Joseph; Osherovich, Vladimir A.; Purser, Carola M.; Galkin, Ivan A.; Reinisch, Bodo W.
2011-01-01
Magnetosphere sounders stimulate plasma resonances between the harmonics of the electron cyclotron frequency and above the upper-hybrid frequency. More than three decades ago they were recognized as equivalent to ionospheric topside-sounder-stimulated resonances, designated as Qn resonances a decade earlier, with one important difference: the magnetospheric Qn frequencies often indicated that the background electron-velocity distribution was non-Maxwellian. Interpretations based on bi-Maxwellian and kappa distributions have been proposed. Here we expand on the latter, which requires fewer free parameters, by comparing kappa-derived Qn frequencies with observations from the Radio Plasma Imager on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite.
Impact of Excitation and Reaction Processes on FRC Thruster Efficiency
2013-06-01
bimodality essentially disappears after about 50 µs, but the ion distribution function is still visibly non - Maxwellian even after 1 ms. The neutral atom...manifested in differences in their translational temperatures as well as in non - Maxwellian distribution functions. The elector and ion velocity...electron, and neutral temperatures strongly differ, and the ion and neutral gas distribution function is strongly non - Maxwellian . The electron velocity
Tsujido, S.; Arakawa, M.; Suzuki, A. I.; Yasui, M.
2014-07-01
Introduction: Regolith formation on asteroids is caused by successive impacts of small bodies. The ejecta velocity distribution during the crater formation process is one of the most important physical properties related to the surface-evolution process, and the distribution is also necessary to reconstruct the planetary-accretion process among planetesimals. The surface of small bodies, such as asteroids and planetesimals in the solar system, could have varying porosity, strength, and density, and the impact velocity could vary across a wide range from a few tens of m/s to several km/s. Therefore, it is necessary to conduct impact experiments by changing the physical properties of the target and the projectile in a wide velocity range in order to constrain the crater-formation process applicable to the small bodies in the solar system. Housen and Holsapple (2011) compiled the data of ejecta velocity distribution with various impact velocities, porosities, grain sizes, grain shapes, and strengths of the targets, and they improved their ejecta scaling law. But the ejecta velocity data is not enough for varying projectile densities and for impact velocities less than 1 km/s. In this study, to investigate the projectile density dependence of the ejecta velocity distribution at a low velocity region, we conducted impact experiments with projectile densities from 1.1 to 11.3 g/cm^3. Then, we try to determine the effect of projectile density on the ejecta velocity distribution by means of the observation of each individual ejecta grain. Experimental methods: We made impact cratering experiments by using a vertical-type one-stage light-gas gun (V-LGG) set at Kobe University. Targets were quartz sand (irregular shape) and glass beads (spherical shape) with the grain size of 500 μ m (porosity 44.7 %). The target container with the size of 30 cm was set in a large vacuum chamber with air pressure less than 10^3 Pa. The projectile materials that we used were lead, copper
Empirical Study of Traffic Velocity Distribution and its Effect on VANETs Connectivity
Abuelenin, Sherif M
2015-01-01
In this article we use real traffic data to confirm that vehicle velocities follow Gaussian distribution in steady state traffic regimes (free-flow, and congestion). We also show that in the transition between free-flow and congestion, the velocity distribution is better modeled by generalized extreme value distribution (GEV). We study the effect of the different models on estimating the probability distribution of connectivity duration between vehicles in vehicular ad-hoc networks.
Velocity distribution measurements in atomic beams generated using laser induced back-ablation
Denning, A; Lee, S; Ammonson, M; Bergeson, S D
2008-01-01
We present measurements of the velocity distribution of calcium atoms in an atomic beam generated using a dual-stage laser back-ablation apparatus. Distributions are measured using a velocity selective Doppler time-of-flight technique. They are Boltzmann-like with rms velocities corresponding to temperatures above the melting point for calcium. Contrary to a recent report in the literature, this method does not generate a sub-thermal atomic beam.
2001-01-01
The relativistic corrections to the Maxwellian velocity distribution are needed for standard solar models. Relativistic equilibrium velocity distribution, if adopted in standard solar models, will lower solar neutrino fluxes and change solar neutrino energy spectra but keep solar sound speeds. It is possibly a solution to the solar neutrino problem.
Evaluating gas transfer velocity parameterizations using upper ocean radon distributions
Bender, Michael L.; Kinter, Saul; Cassar, Nicolas; Wanninkhof, Rik
2011-02-01
Sea-air fluxes of gases are commonly calculated from the product of the gas transfer velocity (k) and the departure of the seawater concentration from atmospheric equilibrium. Gas transfer velocities, generally parameterized in terms of wind speed, continue to have considerable uncertainties, partly because of limited field data. Here we evaluate commonly used gas transfer parameterizations using a historical data set of 222Rn measurements at 105 stations occupied on Eltanin cruises and the Geosecs program. We make this evaluation with wind speed estimates from meteorological reanalysis products (from National Centers for Environmental Prediction and European Centre for Medium-Range Weather Forecasting) that were not available when the 22Rn data were originally published. We calculate gas transfer velocities from the parameterizations by taking into account winds in the period prior to the date that 222Rn profiles were sampled. Invoking prior wind speed histories leads to much better agreement than simply calculating parameterized gas transfer velocities from wind speeds on the day of sample collection. For individual samples from the Atlantic Ocean, where reanalyzed winds agree best with observations, three similar recent parameterizations give k values for individual stations with an rms difference of ˜40% from values calculated using 222Rn data. Agreement of basin averages is much better. For the global data set, the average difference between k constrained by 222Rn and calculated from the various parameterizations ranges from -0.2 to +0.9 m/d (average, 2.9 m/d). Averaging over large domains, and working with gas data collected in recent years when reanalyzed winds are more accurate, will further decrease the uncertainties in sea-air fluxes.
Ion and electron velocity distributions within flux transfer events
Thomsen, M. F.; Stansberry, J. A.; Bame, S. J.; Fuselier, S. A.; Gosling, J. T.
1987-01-01
The detailed nature of the thermal and suprathermal ion and electron distributions within magnetic flux transfer events (FTEs) is examined. Examples of both magnetosheath FTEs and magnetospheric FTEs are discussed. The detailed distributions confirm that FTEs contain a mixture of magnetosheath and magnetospheric plasmas. To lowest order, the distributions are consistent with a simple superposition of the two interpenetrating populations, with no strong interactions between them. To first order, some interesting differences appear, especially in the electron distributions, suggesting that considerable pitch angle scattering and some electron energy diffusion are also occurring. These observations should provide a useful test of analytical and numerical studies of interpenetrating plasmas.
Spanwise loading distribution and wake velocity surveys of a semi-span wing
Felker, F. F., III; Piziali, R. A.; Gall, J. K.
1982-01-01
The spanwise distribution of bound circulation on a semi-span wing and the flow velocities in its wake were measured in a wind tunnel. Particular attention was given to documenting the flow velocities in and around the development tip vortex. A two-component laser velocimeter was used to make the velocity measurements. The spanwise distribution of bound circulation, three components of the time-averaged velocities throughout the near wake their standard deviations, and the integrated forces and moments on a metric tip as measured by an internal strain gage balance are presented without discussion.
Search for a Lorentz invariant velocity distribution of a relativistic gas
Curado, Evaldo M F; Soares, Ivano Damiao
2016-01-01
We examine numerically and analytically the problem of the relativistic velocity distribution in a 1-dim relativistic gas in thermal equilibrium. Our derivation is based on the special theory of relativity, the central limit theorem and the Lobachevsky structure of the velocity space of the theory, where the rapidity variable plays a crucial role. For v^2/c^2 << 1 and 1/\\beta = k_B T/ m_0 c^2 << 1 the distribution tends to the Maxwell-Boltzmann distribution.
Cup anemometer calibration: effect of flow velocity distribution
Piccato, A.; Spazzini, P. G.; Malvano, R.
2011-10-01
The effects of different working conditions and specifically of different velocity profiles on the output of a commercial cup anemometer were analysed experimentally. A simple mathematical model is also presented and provides results in line with the experiments. Results show that a cup anemometer with certain geometrical features can be calibrated through a rotating drag rig by correcting for the bias on the instrument output. The increase in uncertainty caused by this systematic correction was evaluated and applied to the results. The correction was validated by checking the compatibility of calibrations of a cup anemometer at the rotating rig and in a wind tunnel.
2014-01-01
The traditional mine microseism locating methods are mainly based on the assumption that the wave velocity is uniform through the space, which leads to some errors for the assumption goes against the laws of nature. In this paper, the wave velocity is regarded as a random variable, and the probability distribution information of the wave velocity is fused into the traditional locating method. This paper puts forwards the microseism source location method for the undersea mining on condition o...
Precision measurement of transverse velocity distribution of a strontium atomic beam
Gao, F.; H. Liu; Xu, P.; X. Tian; Y. Wang; Ren, J; Haibin Wu; Hong Chang
2014-01-01
We measure the transverse velocity distribution in a thermal Sr atomic beam precisely by velocity-selective saturated fluorescence spectroscopy. The use of an ultrastable laser system and the narrow intercombination transition line of Sr atoms mean that the resolution of the measured velocity can reach 0.13 m/s, corresponding to 90$\\mu K$ in energy units. The experimental results are in very good agreement with the results of theoretical calculations. Based on the spectroscopic techniques use...
Velocity statistics of dynamic spinners in out-of-equilibrium magnetic suspensions.
Snezhko, Alexey; Aranson, Igor S
2015-08-14
We report on the velocity statistics of an out-of-equilibrium magnetic suspension in a spinner phase confined at a liquid interface. The suspension is energized by a uniaxial alternating magnetic field applied parallel to the interface. In a certain range of the magnetic field parameters the system spontaneously undergoes a transition into a dynamic spinner phase (ensemble of hydrodynamically coupled magnetic micro-rotors) comprised of two subsystems: self-assembled spinning chains and a gas of rotating single particles. Both subsystems coexist in a dynamic equilibrium via continuous exchange of the particles. Spinners excite surface flows that significantly increase particle velocity correlations in the system. For both subsystems the velocity distributions are strongly non-Maxwellian with nearly exponential high-energy tails, P(v) ∼ exp(-|v/v0|). The kurtosis, the measure of the deviation from the Gaussian statistics, is influenced by the frequency of the external magnetic field. We show that in the single-particle gas the dissipation is mostly collisional, whereas the viscous damping dominates over collisional dissipation for the self-assembled spinners. The dissipation increases with the frequency of the applied magnetic field. Our results provide insights into non-trivial dissipation mechanisms determining self-assembly processes in out-of-equilibrium magnetic suspensions.
Local Pulsars; A note on the Birth-Velocity Distribution
Blaauw, A.; Ramachandran, R.
1998-01-01
Submitted to: Astron. Astrophys. Abstract: We explore a simple model for the representation of the observed distributions of the motions, and the characteristic ages of the local population of pulsars. The principal difference from earlier models is the introduction of a unique value, S, for the kic
DEFF Research Database (Denmark)
Nielsen, Stefan Kragh; Bindslev, Henrik; Porte, L.
2008-01-01
of scattering locations and different resolved velocity components can be measured. The temporal resolution is 4 ms while the spatial resolution is similar to 10 cm depending on the scattering geometry. Fast-ion velocity distributions in a variety of scenarios are measured, including the evolution...
The three-dimensional distributions of tangential velocity and total- temperature in vortex tubes
DEFF Research Database (Denmark)
Linderstrøm-Lang, C.U.
1971-01-01
physical requirements and which at the same time lead to realistic tangential velocity gradients. The total-temperature distribution in both the axial and radial directions is calculated from such secondary flow functions and corresponding tangential velocity results on the basis of an approximate...
Vilquin, A.; Boudet, J. F.; Kellay, H.
2016-01-01
International audience; Velocity distributions in normal shock waves obtained in dilute granular flows are studied. These distributions cannot be described by a simple functional shape and are believed to be bimodal. Our results show that these distributions are not strictly bimodal but a trimodal distribution is shown to be sufficient. The usual Mott-Smith bimodal description of these distributions, developed for molecular gases, and based on the coexistence of two subpopulations (a superson...
Fu, X.; Waters, T.; Gary, S. P.
2014-12-01
Collisionless space plasmas often deviate from Maxwellian-like velocity distributions. To study kinetic waves and instabilities in such plasmas, the dispersion relation, which depends on the velocity distribution, needs to be solved numerically. Most current dispersion solvers (e.g. WHAMP) take advantage of mathematical properties of the Gaussian (or generalized Lorentzian) function, and assume that the velocity distributions can be modeled by a combination of several drift-Maxwellian (or drift-Lorentzian) components. In this study we are developing a kinetic dispersion solver that admits nearly arbitrary non-relativistic parallel velocity distributions. A key part of any dispersion solver is the evaluation of a Hilbert transform of the velocity distribution function and its derivative along Landau contours. Our new solver builds upon a recent method to compute the Hilbert transform accurately and efficiently using the fast Fourier transform, while simultaneously treating the singularities arising from resonances analytically. We have benchmarked our new solver against other codes dealing with Maxwellian distributions. As an example usage of our code, we will show results for several instabilities that occur for electron velocity distributions observed in the solar wind.
Non-axisymmetric vertical velocity dispersion distributions produced by bars
Du, Min; Debattista, Victor P
2016-01-01
In barred galaxies, the contours of stellar velocity dispersions ($\\sigma$) are generally expected to be oval and aligned with the orientation of bars. However, many double-barred (S2B) galaxies exhibit distinct $\\sigma$ peaks on the minor axis of inner bar, which we termed "$\\sigma$-humps," while two local $\\sigma$ minima are present close to the ends of inner bars, i.e., "$\\sigma$-hollows." Analysis of numerical simulations shows that $\\sigma_z$-humps or hollows should play an important role in generating the observed $\\sigma$-humps+hollows in low-inclination galaxies. In order to systematically investigate the properties of $\\sigma_z$ in barred galaxies, we apply the vertical Jeans equation to a group of well-designed three-dimensional bar+disk(+bulge) models. A vertically thin bar can lower $\\sigma_z$ along the bar and enhance it perpendicular to the bar, thus generating $\\sigma_z$-humps+hollows. Such a result suggests that $\\sigma_z$-humps+hollows can be generated by the purely dynamical response of star...
Numerical Investigation of Developing Velocity Distributions in Open Channel Flows
Directory of Open Access Journals (Sweden)
Usman Ghani
2014-04-01
Full Text Available The velocity profiles in open channel flows start developing after entering into the channel for quite some length. All types of laboratory experiments for open channel flows are carried out in the fully developed flow regions which exist at some length downstream the inlet. In this research work an attempt has been made to investigate the impact of roughness and slope of the channel bed on the length required for establishment of fully developed flow in an open channel. A range of different roughness values along with various slopes were considered for this purpose. It was observed that an increase in roughness results in reduction of development length; and development length reduces drastically when roughness reaches to the range normally encountered in open channel flows with emergent vegetation or natural river flows. However, it was observed that the change of slope did not have any noticeable effect on development length. This work suggests that CFD (Computational Fluid Dynamics technique can be used for getting a reliable development length before performing an experimental work
Orthogonal Vertical Velocity Dispersion Distributions Produced by Bars
Du, Min; Shen, Juntai; Debattista, Victor P.; de Lorenzo-Cáceres, Adriana
2017-02-01
In barred galaxies, the contours of stellar velocity dispersions (σ) are generally expected to be oval and aligned with the orientation of bars. However, many double-barred (S2B) galaxies exhibit distinct σ peaks on the minor axis of the inner bar, which we termed “σ-humps,” while two local σ minima are present close to the ends of inner bars, i.e., “σ-hollows.” Analysis of numerical simulations shows that {σ }z-humps or hollows should play an important role in generating the observed σ-humps+hollows in low-inclination galaxies. In order to systematically investigate the properties of {σ }z in barred galaxies, we apply the vertical Jeans equation to a group of well-designed three-dimensional bar+disk(+bulge) models. A vertically thin bar can lower {σ }z along the bar and enhance it perpendicular to the bar, thus generating {σ }z-humps+hollows. Such a result suggests that {σ }z-humps+hollows can be generated by the purely dynamical response of stars in the presence of a sufficiently massive, vertically thin bar, even without an outer bar. Using self-consistent N-body simulations, we verify the existence of vertically thin bars in the nuclear-barred and S2B models that generate prominent σ-humps+hollows. Thus, the ubiquitous presence of σ-humps+hollows in S2Bs implies that inner bars are vertically thin. The addition of a bulge makes the {σ }z-humps more ambiguous and thus tends to somewhat hide the {σ }z-humps+hollows. We show that {σ }z may be used as a kinematic diagnostic of stellar components that have different thicknesses, providing a direct perspective on the morphology and thickness of nearly face-on bars and bulges with integral field unit spectroscopy.
CFD Simulation of Air Velocity Distribution in Occupied Livestock Buildings
DEFF Research Database (Denmark)
Svidt, Kjeld; Zhang, G.; Bjerg, B.
In modem livestock buildings the design of the ventilation systems is important in order to obtain good air distribution. The use of Computational Fluid Dynamics for predicting the air flow and air quality makes it possible to include the effect of room geometry, equipment and occupants in the de......In modem livestock buildings the design of the ventilation systems is important in order to obtain good air distribution. The use of Computational Fluid Dynamics for predicting the air flow and air quality makes it possible to include the effect of room geometry, equipment and occupants...... in the design of ventilation systems. However, it is not appropriate to include the detailed geometry of a large group of lying or standing animals affecting the air flow in the building. It is necessary to have relatively simple models of the animals, which are easier to implement in the computer models....... In this study laboratory measurements in a ventilated test room with "pig simulators" are compared with CFD-simulations....
Breaking through: The effects of a velocity distribution on barriers to dust growth
Windmark, Fredrik; Ormel, Chris; Dullemond, Cornelis P
2012-01-01
It is unknown how far dust growth can proceed by coagulation. Obstacles to collisional growth are the fragmentation and bouncing barriers. However, in all previous simulations of the dust-size evolution in protoplanetary disks, only the mean collision velocity has been considered, neglecting that a small but possibly important fraction of the collisions will occur at both much lower and higher velocities. We study the effect of the probability distribution of impact velocities on the collisional dust growth barriers. Assuming a Maxwellian velocity distribution for colliding particles to determine the fraction of sticking, bouncing, and fragmentation, we implement this in a dust-size evolution code. We also calculate the probability of growing through the barriers and the growth timescale in these regimes. We find that the collisional growth barriers are not as sharp as previously thought. With the existence of low-velocity collisions, a small fraction of the particles manage to grow to masses orders of magnit...
Electric Field-Induced Fluid Velocity Field Distribution in DNA Solution
Institute of Scientific and Technical Information of China (English)
ZHANG Ling-Yun; WANG Peng-Ye
2008-01-01
We present an analytical solution for fluid velocity field distribution of polyelectrolyte DNA. Both the electric field force and the viscous force in the DNA solution are considered under a suitable boundary condition. The solution of electric potential is analytically obtained by using the linearized Poisson-Boltzmann equation. The fluid velocity along the electric field is dependent on the cylindrical radius and concentration. It is shown that the electric field-induced fluid velocity will be increased with the increasing cylindrical radius, whose distribution also varies with the concentration
Velocity distribution measurements in a fishway like open channel by Laser Doppler Anemometry (LDA)
Sayeed-Bin-Asad, S. M.; Lundström, T. S.; Andersson, A. G.; Hellström, J. G. I.
2016-03-01
Experiments in an open channel flume with placing a vertical half cylinder barrier have been performed in order to investigate how the upstream velocity profiles are affected by a barrier. An experimental technique using Laser Doppler Velocimetry (LDV) was adopted to measure these velocity distributions in the channel for four different discharge rates. Velocity profiles were measured very close to wall and at 25, 50 and 100 mm upstream of the cylinder wall. For comparing these profiles with well-known logarithmic velocity profiles, velocity profiles were also measured in smooth open channel flow for all same four discharge rates. The results indicate that regaining the logarithmic velocity profiles upstream of the half cylindrical barrier occurs at 100 mm upstream of the cylinder wall.
Velocity distribution measurements in a fishway like open channel by Laser Doppler Anemometry (LDA
Directory of Open Access Journals (Sweden)
Sayeed-Bin-Asad S.M.
2016-01-01
Full Text Available Experiments in an open channel flume with placing a vertical half cylinder barrier have been performed in order to investigate how the upstream velocity profiles are affected by a barrier. An experimental technique using Laser Doppler Velocimetry (LDV was adopted to measure these velocity distributions in the channel for four different discharge rates. Velocity profiles were measured very close to wall and at 25, 50 and 100 mm upstream of the cylinder wall. For comparing these profiles with well-known logarithmic velocity profiles, velocity profiles were also measured in smooth open channel flow for all same four discharge rates. The results indicate that regaining the logarithmic velocity profiles upstream of the half cylindrical barrier occurs at 100 mm upstream of the cylinder wall.
Asymmetric Velocity Distributions from Halo Density Profiles in the Eddington Approach
Directory of Open Access Journals (Sweden)
J. D. Vergados
2015-01-01
Full Text Available We show how to obtain the energy distribution f(E in our vicinity starting from WIMP density profiles in a self-consistent way by employing the Eddington approach and adding reasonable angular momentum dependent terms in the expression of the energy. We then show how we can obtain the velocity dispersions and the asymmetry parameter β in terms of the parameters describing the angular momentum dependence. From this expression, for f(E, we proceed to construct an axially symmetric WIMP a velocity distribution, which, for a gravitationally bound system, automatically has a velocity upper bound and is characterized by the same asymmetriy β. This approach is tested and clarified by constructing analytic expressions in a simple model, with adequate structure. We then show how such velocity distributions can be used in determining the event rates, including modulation, in both the standard and the directional WIMP searches.
Rodríguez, Y; Bautista, M A; Mendoza, C
2016-01-01
After an extensive assessment of the effective collision strengths available to model the He-like triplet of C V, N VI, O VII, Ne IX, Mg XI and Si XIII in collisionally dominated plasmas, new accurate effective collision strengths are reported for Ne IX. The uncertainty intervals of the density and temperature diagnostics due to the atomic data errors are also determined for both Maxwell-Boltzmann and $\\kappa$ electron-energy distributions. It is shown that these uncertainty bands limit the temperature range where the temperature line-ratio diagnostic can be applied and its effectiveness to discern the electron-energy distribution type. These findings are benchmarked with Chandra and XMM-Newton spectra of stellar coronae and with tokamak measurements.
A benchmark of the He-like triplet for ions with 6 ≤ Z ≤ 14 in Maxwellian and non-Maxwellian plasmas
Rodríguez, Y.; Gatuzz, E.; Bautista, M. A.; Mendoza, C.
2016-09-01
After an extensive assessment of the effective collision strengths available to model the He-like triplet of C V, N VI, O VII, Ne IX, Mg XI and Si XIII in collisionally dominated plasmas, new accurate effective collision strengths are reported for Ne IX. The uncertainty intervals of the density and temperature diagnostics due to the atomic data errors are also determined for both Maxwell-Boltzmann and κ electron-energy distributions. It is shown that these uncertainty bands limit the temperature range where the temperature line-ratio diagnostic can be applied and its effectiveness to discern the electron-energy distribution type. These findings are benchmarked with Chandra and XMM-Newton spectra of stellar coronae and with tokamak measurements.
Energy Technology Data Exchange (ETDEWEB)
El-Tantawy, S. A., E-mail: samireltantawy@yahoo.com [Department of Physics, Faculty of Science, Port Said University, Port Said 42521 (Egypt); Moslem, W. M., E-mail: wmmoslem@hotmail.com [Department of Physics, Faculty of Science, Port Said University, Port Said 42521 (Egypt); Centre for Theoretical Physics, The British University in Egypt (BUE), El-Shorouk City, Cairo (Egypt)
2014-05-15
Solitons (small-amplitude long-lived waves) collision and rogue waves (large-amplitude short-lived waves) in non-Maxwellian electron-positron-ion plasma have been investigated. For the solitons collision, the extended Poincaré-Lighthill-Kuo perturbation method is used to derive the coupled Korteweg-de Vries (KdV) equations with the quadratic nonlinearities and their corresponding phase shifts. The calculations reveal that both positive and negative polarity solitons can propagate in the present model. At critical value of plasma parameters, the coefficients of the quadratic nonlinearities disappear. Therefore, the coupled modified KdV (mKdV) equations with cubic nonlinearities and their corresponding phase shifts have been derived. The effects of the electron-to-positron temperature ratio, the ion-to-electron temperature ratio, the positron-to-ion concentration, and the nonextensive parameter on the colliding solitons profiles and their corresponding phase shifts are examined. Moreover, generation of ion-acoustic rogue waves from small-amplitude initial perturbations in plasmas is studied in the framework of the mKdV equation. The properties of the ion-acoustic rogue waves are examined within a nonlinear Schrödinger equation (NLSE) that has been derived from the mKdV equation. The dependence of the rogue wave profile on the relevant physical parameters has been investigated. Furthermore, it is found that the NLSE that has been derived from the KdV equation cannot support the propagation of rogue waves.
Energy Technology Data Exchange (ETDEWEB)
Durand, O.; Soulard, L. [CEA, DAM, DIF, F-91297 Arpajon (France)
2015-04-28
The mass (volume and areal densities) versus velocity as well as the size versus velocity distributions of a shock-induced cloud of particles are investigated using large scale molecular dynamics simulations. A generic three-dimensional tin crystal with a sinusoidal free surface roughness (single wavelength) is set in contact with vacuum and shock-loaded so that it melts directly on shock. At the reflection of the shock wave onto the perturbations of the free surface, two-dimensional sheets/jets of liquid metal are ejected. The simulations show that the distributions may be described by an analytical model based on the propagation of a fragmentation zone, from the tip of the sheets to the free surface, in which the kinetic energy of the atoms decreases as this zone comes closer to the free surface on late times. As this kinetic energy drives (i) the (self-similar) expansion of the zone once it has broken away from the sheet and (ii) the average size of the particles which result from fragmentation in the zone, the ejected mass and the average size of the particles progressively increase in the cloud as fragmentation occurs closer to the free surface. Though relative to nanometric scales, our model may help in the analysis of experimental profiles.
The observational distribution of internal velocity dispersions in nearby galaxy clusters
Fadda, D; Giuricin, G; Mardirossian, F; Mezzetti, M; Fadda, Dario; Girardi, Marisa; Giuricin, Giuliano; Mardirossian, Fabio; Mezzetti, Marino
1996-01-01
We analyze the internal velocity dispersions of a sample of 172 nearby galaxy clusters (z 800 km/s). We estimate that our distributions is complete for at least a dispersion greater than 650 km/s. In this completeness range a power law fit is in fair agreement with results coming from the X-ray temperature distributions.
Non-local velocity distribution function and one-flight approximation
Energy Technology Data Exchange (ETDEWEB)
Bakunin, O.G. [FOM Instituut voor Plasmafysica ' Rijnhuizen' , Associate Euroatom-FOM, 3430 BE Nieuwegein (Netherlands) and Russian Research Center ' Kurchatov Institute' , Nuclear Fusion Institute, sq. Kurchatova 1, 123182 Moscow (Russian Federation)]. E-mail: oleg_bakunin@yahoo.com
2004-09-13
The functional equation describing the collisionless particle velocity distribution function f(V) is considered in the framework of probabilistic approach. The key element of the collisionless particles description is using the waiting time distribution {psi}(t). The solution of the considered functional is obtained for several model functions {psi}(t) and it leads to the power form tails of the velocity distribution f(V). It is possible to adopt considered functional to the Laplace transformation form that allows us to accord 'collision' and 'collisionless' description. This Laplace form of the functional yields the Levy-Smirnov velocity distribution function with the characteristic exponent aL=1/2.
Impact of velocity distribution assumption on simplified laser speckle imaging equation
Ramirez-San-Juan, Julio C; Ramos-Garcia, Ruben; Guizar-Iturbide, Ileana; Martinez-Niconoff, Gabriel; Choi, Bernard
2012-01-01
Since blood flow is tightly coupled to the health status of biological tissue, several instruments have been developed to monitor blood flow and perfusion dynamics. One such instrument is laser speckle imaging. The goal of this study was to evaluate the use of two velocity distribution assumptions (Lorentzian- and Gaussian-based) to calculate speckle flow index (SFI) values. When the normalized autocorrelation function for the Lorentzian and Gaussian velocity distributions satisfy the same definition of correlation time, then the same velocity range is predicted for low speckle contrast (0 < C < 0.6) and predict different flow velocity range for high contrast. Our derived equations form the basis for simplified calculations of SFI values. PMID:18542407
Ribeiro, A L B; de Carvalho, R R; La Barbera, F; Trevisan, M; Lopes, P A; Capelato, H V
2013-01-01
We introduce a new method to study the velocity distribution of galaxy systems, the Hellinger Distance (HD) - designed for detecting departures from a Gaussian velocity distribution. We define a relaxed galactic system as the one with unimodal velocity distribution and a normality deviation below a critical value (HD= 20) systems are significantly larger than in low multiplicity ones (N) and the gaussianity of the velocity distribution of the groups. Bright galaxies (M_r <=-20.7) residing in the inner and outer regions of groups, do not show significant differences in the listed quantities regardless if the group has a Gaussian (G) or a Non-Gaussian (NG) velocity distribution. However, the situation is significantly different when we examine the faint galaxies (-20.7
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
On the basis of model test and theoretical analysis of velocity and pressure distributions,an hypothesis is presented that the distribution of tangential velocity in radial direction seems to be a combinational distribution of a quasi-free vortex and a quasi-forced vortex for the discharge tunnel of rotary-obstruction composite inner energy dissipation.The variations of corresponding parameters about the hypothesis are obtained under test conditions in this paper.The formula of pressure distribution in radial direction is deduced theoretically,and the theoretical values of pressure distribution computed by the formula are well consistent with the measured ones,showing that the formula is correct and can be applied to the computation and analysis of pressure distribution of this discharge tunnel.
Energy Technology Data Exchange (ETDEWEB)
Mandel, Kaisey S.; Kirshner, Robert P. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Foley, Ryan J., E-mail: kmandel@cfa.harvard.edu [Astronomy Department, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801 (United States)
2014-12-20
We investigate the statistical dependence of the peak intrinsic colors of Type Ia supernovae (SNe Ia) on their expansion velocities at maximum light, measured from the Si II λ6355 spectral feature. We construct a new hierarchical Bayesian regression model, accounting for the random effects of intrinsic scatter, measurement error, and reddening by host galaxy dust, and implement a Gibbs sampler and deviance information criteria to estimate the correlation. The method is applied to the apparent colors from BVRI light curves and Si II velocity data for 79 nearby SNe Ia. The apparent color distributions of high-velocity (HV) and normal velocity (NV) supernovae exhibit significant discrepancies for B – V and B – R, but not other colors. Hence, they are likely due to intrinsic color differences originating in the B band, rather than dust reddening. The mean intrinsic B – V and B – R color differences between HV and NV groups are 0.06 ± 0.02 and 0.09 ± 0.02 mag, respectively. A linear model finds significant slopes of –0.021 ± 0.006 and –0.030 ± 0.009 mag (10{sup 3} km s{sup –1}){sup –1} for intrinsic B – V and B – R colors versus velocity, respectively. Because the ejecta velocity distribution is skewed toward high velocities, these effects imply non-Gaussian intrinsic color distributions with skewness up to +0.3. Accounting for the intrinsic-color-velocity correlation results in corrections to A{sub V} extinction estimates as large as –0.12 mag for HV SNe Ia and +0.06 mag for NV events. Velocity measurements from SN Ia spectra have the potential to diminish systematic errors from the confounding of intrinsic colors and dust reddening affecting supernova distances.
Pham-Van-diep, Gerald C.; Erwin, Daniel A.
1989-01-01
Velocity distribution functions in normal shock waves in argon and helium are calculated using Monte Carlo direct simulation. These are compared with experimental results for argon at M = 7.18 and for helium at M = 1.59 and 20. For both argon and helium, the variable-hard-sphere (VHS) model is used for the elastic scattering cross section, with the velocity dependence derived from a viscosity-temperature power-law relationship in the way normally used by Bird (1976).
Precision measurement of transverse velocity distribution of a Strontium atomic beam
Gao, F; Xu, P; Tian, X; Wang, Y; Ren, J; Wu, Haibin; Chang, Hong
2013-01-01
We measure precisely the transverse velocity distribution in a thermal Sr atomic beam with a velocity selective saturated fluorescence spectroscopy. By using the ultrastable laser system and narrow intercombination transition line of Sr atoms, the resolution of the velocity measured can be reached 0.13m/s, corresponding to 90$\\mu K$ in energy unit. The experimental results are agreement very well with a theoretical calculation. With the spectroscopic techniques, the absolute frequency of the intercombination transition of $^{88}$Sr is measured by an optical-frequency comb generator referenced to the SI second through an H maser, which is given by 434 829 121 318(10)kHz.
Galactic Subsystems on the Basis of Cumulative Distribution of Space Velocities
Directory of Open Access Journals (Sweden)
Vidojević, S.
2008-12-01
Full Text Available A sample containing $4,614$ stars with available space velocities and high-quality kinematical data from the Arihip Catalogue is formed. For the purpose of distinguishing galactic subsystems the cumulative distribution of space velocities is studied. The fractions of the three subsystems are found to be: thin disc 92\\%, thick disc 6\\% and halo 2\\%. These results are verified by analysing the elements of velocity ellipsoids and the shape and size of the galactocentric orbits of the sample stars, i.e. the planar and vertical eccentricities of the orbits.
Origins and properties of kappa distributions in space plasmas
Livadiotis, George
2016-07-01
Classical particle systems reside at thermal equilibrium with their velocity distribution function stabilized into a Maxwell distribution. On the contrary, collisionless and correlated particle systems, such as the space and astrophysical plasmas, are characterized by a non-Maxwellian behavior, typically described by the so-called kappa distributions. Empirical kappa distributions have become increasingly widespread across space and plasma physics. However, a breakthrough in the field came with the connection of kappa distributions to the solid statistical framework of Tsallis non-extensive statistical mechanics. Understanding the statistical origin of kappa distributions was the cornerstone of further theoretical developments and applications, some of which will be presented in this talk: (i) The physical meaning of thermal parameters, e.g., temperature and kappa index; (ii) the multi-particle description of kappa distributions; (iii) the phase-space kappa distribution of a Hamiltonian with non-zero potential; (iv) the Sackur-Tetrode entropy for kappa distributions, and (v) the new quantization constant, h _{*}˜10 ^{-22} Js.
Clustering and velocity distributions in granular gases cooling by solid friction.
Das, Prasenjit; Puri, Sanjay; Schwartz, Moshe
2016-09-01
We present large-scale molecular dynamics simulations to study the free evolution of granular gases. Initially, the density of particles is homogeneous and the velocity follows a Maxwell-Boltzmann (MB) distribution. The system cools down due to solid friction between the granular particles. The density remains homogeneous, and the velocity distribution remains MB at early times, while the kinetic energy of the system decays with time. However, fluctuations in the density and velocity fields grow, and the system evolves via formation of clusters in the density field and the local ordering of velocity field, consistent with the onset of plug flow. This is accompanied by a transition of the velocity distribution function from MB to non-MB behavior. We used equal-time correlation functions and structure factors of the density and velocity fields to study the morphology of clustering. From the correlation functions, we obtain the cluster size, L, as a function of time, t. We show that it exhibits power law growth with L(t)∼t^{1/3}.
Clustering and velocity distributions in granular gases cooling by solid friction
Das, Prasenjit; Puri, Sanjay; Schwartz, Moshe
2016-09-01
We present large-scale molecular dynamics simulations to study the free evolution of granular gases. Initially, the density of particles is homogeneous and the velocity follows a Maxwell-Boltzmann (MB) distribution. The system cools down due to solid friction between the granular particles. The density remains homogeneous, and the velocity distribution remains MB at early times, while the kinetic energy of the system decays with time. However, fluctuations in the density and velocity fields grow, and the system evolves via formation of clusters in the density field and the local ordering of velocity field, consistent with the onset of plug flow. This is accompanied by a transition of the velocity distribution function from MB to non-MB behavior. We used equal-time correlation functions and structure factors of the density and velocity fields to study the morphology of clustering. From the correlation functions, we obtain the cluster size, L , as a function of time, t . We show that it exhibits power law growth with L (t ) ˜t1 /3 .
Boschan, A; Annichini, M; Gauthier, G
2016-01-01
A study on the spatial organization and velocity fluctuations of non Brownian spherical particles settling at low Reynolds number in a vertical Hele-Shaw cell is reported. The particle volume fraction ranged from 0.005 to 0.05, while the distance between cell plates ranged from 5 to 15 times the particle radius. Particle tracking revealed that particles were not uniformly distributed in space but assembled in transient settling clusters. The population distribution of these clusters followed an exponential law. The measured velocity fluctuations are in agreement with that predicted theoretically for spherical clusters, from the balance between the apparent weight and the drag force. This result suggests that particle clustering, more than a spatial distribution of particles derived from random and independent events, is at the origin of the velocity fluctuations.
Gurgiolo, Chris; Vinas, Adolfo F.
2009-01-01
This paper presents a spherical harmonic analysis of the plasma velocity distribution function using high-angular, energy, and time resolution Cluster data obtained from the PEACE spectrometer instrument to demonstrate how this analysis models the particle distribution function and its moments and anisotropies. The results show that spherical harmonic analysis produced a robust physical representation model of the velocity distribution function, resolving the main features of the measured distributions. From the spherical harmonic analysis, a minimum set of nine spectral coefficients was obtained from which the moment (up to the heat flux), anisotropy, and asymmetry calculations of the velocity distribution function were obtained. The spherical harmonic method provides a potentially effective "compression" technique that can be easily carried out onboard a spacecraft to determine the moments and anisotropies of the particle velocity distribution function for any species. These calculations were implemented using three different approaches, namely, the standard traditional integration, the spherical harmonic (SPH) spectral coefficients integration, and the singular value decomposition (SVD) on the spherical harmonic methods. A comparison among the various methods shows that both SPH and SVD approaches provide remarkable agreement with the standard moment integration method.
Measurements of neutral and ion velocity distribution functions in a Hall thruster
Svarnas, Panagiotis; Romadanov, Iavn; Diallo, Ahmed; Raitses, Yevgeny
2015-11-01
Hall thruster is a plasma device for space propulsion. It utilizes a cross-field discharge to generate a partially ionized weakly collisional plasma with magnetized electrons and non-magnetized ions. The ions are accelerated by the electric field to produce the thrust. There is a relatively large number of studies devoted to characterization of accelerated ions, including measurements of ion velocity distribution function using laser-induced fluorescence diagnostic. Interactions of these accelerated ions with neutral atoms in the thruster and the thruster plume is a subject of on-going studies, which require combined monitoring of ion and neutral velocity distributions. Herein, laser-induced fluorescence technique has been employed to study neutral and single-charged ion velocity distribution functions in a 200 W cylindrical Hall thruster operating with xenon propellant. An optical system is installed in the vacuum chamber enabling spatially resolved axial velocity measurements. The fluorescence signals are well separated from the plasma background emission by modulating the laser beam and using lock-in detectors. Measured velocity distribution functions of neutral atoms and ions at different operating parameters of the thruster are reported and analyzed. This work was supported by DOE contract DE-AC02-09CH11466.
VELOCITY DISTRIBUTION IN TRAPEZOID-SECTION OPEN CHANNEL FLOW WITH A NEW REYNOLDS-STRESS EXPRESSION
Institute of Scientific and Technical Information of China (English)
Ma Zheng
2003-01-01
By considering that the coherent structure is the main cause of the Reynolds stress, a new Reynolds stress expression was given. On this basis the velocity distribution in the trapezoid-section open channel flow was worked out with the pseudo-spectral method. The results were compared with experimental data and the influence of the ratio of length to width of the cross-section and the lateral inclination on the velocity distribution was analyzed. This model can be used the large flux in rivers and open channes.
Chow, V. W.; Mendis, D. A.; Rosenberg, M.
1993-01-01
By virtue of being generally immersed in a plasma environment, cosmic dust is necessarily electrically charged. The fact that secondary emission plays an important role in determining the equilibrium grain potential has long been recognized, but the fact that the grain size plays a crucial role in this equilibrium potential, when secondary emission is important, has not been widely appreciated. Using both conducting and insulating spherical grains of various sizes and also both Maxwellian and generalized Lorentzian plasmas (which are believed to represent certain space plasmas), we have made a detailed study of this problem. In general, we find that the secondary emission yield delta increases with decreasing size and becomes very large for grains whose dimensions are comparable to the primary electron penetration depth, such as in the case of the very small grains observed at comet Halley and inferred in the interstellar medium. Moreover, we observed that delta is larger for insulators and equilibrium potentials are generally more positive when the plasma has a broad non-Maxwellian tail. Interestingly, we find that for thermal energies that are expected in several cosmic regions, grains of different sizes can have opposite charge, the smaller ones being positive while the larger ones are negative. This may have important consequences for grain accretion in polydisperse dusty space plasmas.
Jiang, Yulin; Li, Bin; Chen, Jie
2016-01-01
The flow velocity distribution in partially-filled circular pipe was investigated in this paper. The velocity profile is different from full-filled pipe flow, since the flow is driven by gravity, not by pressure. The research findings show that the position of maximum flow is below the water surface, and varies with the water depth. In the region of near tube wall, the fluid velocity is mainly influenced by the friction of the wall and the pipe bottom slope, and the variation of velocity is similar to full-filled pipe. But near the free water surface, the velocity distribution is mainly affected by the contractive tube wall and the secondary flow, and the variation of the velocity is relatively small. Literature retrieval results show relatively less research has been shown on the practical expression to describe the velocity distribution of partially-filled circular pipe. An expression of two-dimensional (2D) velocity distribution in partially-filled circular pipe flow was derived based on the principle of maximum entropy (POME). Different entropies were compared according to fluid knowledge, and non-extensive entropy was chosen. A new cumulative distribution function (CDF) of partially-filled circular pipe velocity in terms of flow depth was hypothesized. Combined with the CDF hypothesis, the 2D velocity distribution was derived, and the position of maximum velocity distribution was analyzed. The experimental results show that the estimated velocity values based on the principle of maximum Tsallis wavelet entropy are in good agreement with measured values.
Influence of anisotropy on velocity and age distribution at Scharffenbergbotnen blue ice area
Directory of Open Access Journals (Sweden)
T. Zwinger
2013-06-01
Full Text Available We use a full-Stokes thermo-mechanically coupled ice-flow model to study the dynamics of the glacier inside Scharffenbergbotnen valley, Dronning Maud Land, Antarctica. The domain encompasses a high accumulation rate region and, downstream a sublimation-dominated bare ice ablation area. The ablation ice area is notable for having old ice at its surface since the vertical velocity is upwards, and horizontal velocities are almost stagnant there. We compare the model simulation with field observations of velocities and the age distribution of the surface ice. A satisfactory match with simulations using an isotropic flow law was not found because of too high horizontal velocities and too slow vertical ones. However, the existence of a pronounced ice fabric may explain the present day surface velocity distribution in the inner Scharffenbergbotnen blue ice area. Near absence of data on the temporal evolution of Scharffenbergbotnen since the Late Glacial Maximum necessitates exploration of the impact of anisotropy using prescribed ice fabrics: isotropic, single maximum, and linear variation with depth, in both two-dimensional and three dimensional flow models. The realistic velocity field simulated with a non-collinear orthotropic flow law, however produced surface ages in significant disagreement with the few reliable age measurements and suggests that the age field is not in a steady state and that the present distribution is a result of a flow reorganization at about 15 000 yr BP. In order to fully understand the surface age distribution a transient simulation starting from the Late Glacial Maximum including the correct initial conditions for geometry, age, fabric and temperature distribution would be needed. It is the first time that the importance of anisotropy has been demonstrated in the ice dynamics of a blue ice area. This is useful to understand ice flow in order to better interpret archives of ancient ice for paleoclimate research.
Holzer, T.L.; Bennett, M.J.; Noce, T.E.; Tinsley, J. C.
2005-01-01
Shear-wave velocities of shallow surficial geologic units were measured at 210 sites in a 140-km2 area in the greater Oakland, California, area near the margin of San Francisco Bay. Differences between average values of shear-wave velocity for each geologic unit computed by alternative approaches were in general smaller than the observed variability. Averages estimated by arithmetic mean, geometric mean, and slowness differed by 1 to 8%, while coefficients of variation ranged from 14 to 25%. With the exception of the younger Bay mud that underlies San Francisco Bay, velocities of the geologic units are approximately constant with depth. This suggests that shear-wave velocities measured at different depths in these surficial geologic units do not need to be normalized to account for overburden stress in order to compute average values. The depth dependence of the velocity of the younger Bay mud most likely is caused by consolidation. Velocities of each geologic unit are consistent with a normal statistical distribution. Average values increase with geologic age, as has been previously reported. Velocities below the water table are about 7% less than those above it. ?? 2005, Earthquake Engineering Research Institute.
Institute of Scientific and Technical Information of China (English)
KNIGHT; Donald; W
2009-01-01
Natural rivers are commonly characterized by a main channel for primary flow conveyance and a floodplain, often partially covered with vegetation such as shrubs or trees, to carry extra flow during floods. The hydraulic resistance due to vegetation on the floodplain typically causes a further reduction of flow velocity and increases the velocity difference between the main channel and the floodplain. As a consequence a strong lateral shear layer leads to the exchange of mass and momentum between the main channel and floodplain, which in turn affects the overall channel conveyance and certain fluvial processes. The prediction of the lateral velocity distribution is important for many flood alleviation schemes, as well as for studies on sediment transport and dispersion in such channels. The present paper proposes a method for predicting the depth-averaged velocity in compound channels with partially vegetated floodplains, based on an analytical solution to the depth-integrated Reynolds-Averaged Navier-Stokes equation with a term included to account for the effects of vegetation. The vegetation is modelled via an additional term in the momentum equation to account for the additional drag force. The method includes the effects of bed friction, drag force, lateral turbulence and secondary flows, via four coefficients f, CD, λ & Γ respectively. The predicted lateral distributions of depth-averaged velocity agree well with the experimental data. The analytical solutions can also be used to predict the distribution of boundary shear stresses, which adds additional weight to the method proposed.
Influence of bank vegetation and gravel bed on velocity and Reynolds stress distributions
Institute of Scientific and Technical Information of China (English)
Hossein AFZALIMEHR; Subhasish DEY
2009-01-01
This paper presents the results of a laboratory flume experimental study on the interaction of bank vegetation and gravel bed on the flow velocity (primarily on the location of the maximum velocity, Umax) and the Reynolds stress distributions. The results reveal that the dip of the maximum velocity below the water surface is up to 35% of flow depth and the difference between Umax and the velocity at the water surface is considerable in the presence of vegetation on the walls. The zone of the log-law varies from y/h=2 up to 15 percent of flow depth and it does not depend on distance from the wall. Deviation of the velocity profile in the outer layer over a gravel bed with vegetation cover on the walls is much larger than the case of flow over a gravel bed without vegetation cover on the walls. The presence of vegetation on the walls changes uniform flow to non-uniform flow. This fact can be explained by considering the nonlinear Reynolds stress distribution and location of maximum velocity in each profile at different distances across the flume. The Reynolds stress distributions at the distance 0.02 m from the wall have negative values and away from the wall, they change the sign taking positive values with specific convex form with apex in higher location. Average of von Karman constant κ for this study is equal to 0.16. Based on κ=0.16, the methods of Clauser and the Reynolds stress are compatible for determination of shear velocity.
Distributed tracking for networked Euler-Lagrange systems without velocity measurements
Institute of Scientific and Technical Information of China (English)
Qingkai Yang; Hao Fang; Yutian Mao; Jie Huang
2014-01-01
The problem of distributed coordinated tracking control for networked Euler-Lagrange systems without velocity measure-ments is investigated. Under the condition that only a portion of the fol owers have access to the leader, sliding mode estimators are developed to estimate the states of the dynamic leader in fi-nite time. To cope with the absence of velocity measurements, the distributed observers which only use position information are designed. Based on the outputs of the estimators and observers, distributed tracking control laws are proposed such that al the fol-lowers with parameter uncertainties can track the dynamic leader under a directed graph containing a spanning tree. It is shown that the distributed observer-control er guarantees asymptotical stabil-ity of the closed-loop system. Numerical simulations are worked out to il ustrate the effectiveness of the control laws.
Anisotropic q-Gaussian velocity distributions in LambdaCDM halos
Silva, L Beraldo e; Duarte, M; Peirani, S; Boué, G
2013-01-01
The knowledge of the velocity distribution function (VDF) of dark matter (DM) halos is required for calibrating the direct DM detection experiments and useful for recovering the mass profile from the observed distribution of tracers in projected phase space when the VDF has unknown anisotropy. Unfortunately, the VDF of halos in LambdaCDM dissipationless cosmological simulations is still poorly known. We consider the q-Gaussian (Tsallis) family of VDFs, among which the Gaussian is a special case. We extend the q-Gaussian to anisotropic VDFs by considering the isotropic set of dimensionless spherical velocity components normalized by the velocity dispersion along that component. We test our anisotropic VDF on 90 cluster-mass halos of a dissipationless cosmological simulation. While our anisotropic q-Gaussian model adequately reproduces the VDF averaged in spherical shells with radii greater than 2 virial radii, no q-Gaussian model can adequately represent the VDF in spherical shells of radius smaller than 2 vir...
Experimental Study on the Distribution of Velocity and Pressure near a Submarine Pipeline
Institute of Scientific and Technical Information of China (English)
HAN Yan; SHI Bing; REN Xingyue; JING Xiaodong
2009-01-01
As a transport means of oil and gas the submarine pipeline has many merits, such as continuous delivery, large conveying capacity, convenient management, etc. A tube was chosen in our study to simulate the submarine pipeline in the experiments. A high accuracy instrument ADV and high precision point-type pressure sensors were used to measure the parameters of the flow field, including the pressure distribution, velocities at seven cross sections near the submarine pipeline with five different clearance ratios, and twelve dynamic pressure values around the pipeline. The pressure distributions and velocity changes around the pipe under different flow velocities and clearance ratios were analyzed. These results might be useful for further study of submarine pipeline erosion and protection.
Ion velocity distributions within the LLBL and their possible implication to multiple reconnections
Directory of Open Access Journals (Sweden)
O. L. Vaisberg
2004-01-01
Full Text Available We analyze two LLBL crossings made by the Interball-Tail satellite under a southward or variable magnetosheath magnetic field: one crossing on the flank of the magnetosphere, and another one closer to the subsolar point. Three different types of ion velocity distributions within the LLBL are observed: (a D-shaped distributions, (b ion velocity distributions consisting of two counter-streaming components of magnetosheath-type, and (c distributions with three components, one of which has nearly zero parallel velocity and two counter-streaming components. Only the (a type fits to the single magnetic flux tube formed by reconnection between the magnetospheric and magnetosheath magnetic fields. We argue that two counter-streaming magnetosheath-like ion components observed by Interball within the LLBL cannot be explained by the reflection of the ions from the magnetic mirror deeper within the magnetosphere. Types (b and (c ion velocity distributions would form within spiral magnetic flux tubes consisting of a mixture of alternating segments originating from the magnetosheath and from magnetospheric plasma. The shapes of ion velocity distributions and their evolution with decreasing number density in the LLBL indicate that a significant part of the LLBL is located on magnetic field lines of long spiral flux tube islands at the magnetopause, as has been proposed and found to occur in magnetopause simulations. We consider these observations as evidence for multiple reconnection Χ-lines between magnetosheath and magnetospheric flux tubes.
Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; solar wind-magnetosphere interactions
Vasyliunas-Cairns distribution function for space plasma species
Abid, A. A.; Ali, S.; Du, J.; Mamun, A. A.
2015-08-01
A more generalized form of non-Maxwellian distribution function (that can be named as Vasyliunas-Cairns distribution function) is introduced. Its basic properties are numerically analyzed by the variation of two important parameters, namely, α (which shows the amount of energetic particles present in the plasma system) and κ (which shows the superthermality of the plasma species). It has been observed that (i) for α → 0 ( κ → ∞ ), the Vasyliunas-Cairns distribution function reduces to the Vasyliunas or κ (Cairns or nonthermal) distribution function; (ii) for α → 0 and κ → ∞ , it reduces to the Maxwellian distribution function; and (iii) the effect of the parameter α (κ) significantly modifies the basic properties of the Vasyliunas (Cairns) distribution function. The applications of this generalized non-Maxwellian distribution function (Vasyliunas-Cairns distribution function) in different space plasma situations are briefly discussed.
Pressure anisotropy and small spatial scales induced by velocity shear
Del Sarto, Daniele; Califano, Francesco
2015-01-01
Non-Maxwellian metaequilibria can exist in low-collisionality plasmas as evidenced by satellite and laboratory measurements. By including the full pressure tensor dynamics in a fluid plasma model, we show that a sheared velocity field can provide an effective mechanism that makes an initial isotropic state anisotropic and agyrotropic. We discuss how the propagation of magneto-elastic waves can affect the pressure tensor anisotropization and its spatial filamentation which are due to the action of both the magnetic field and flow strain tensor. We support this analysis by a numerical integration of the nonlinear equations describing the pressure tensor evolution.
Gas-kinetic numerical method for solving mesoscopic velocity distribution function equation
Institute of Scientific and Technical Information of China (English)
Zhihui Li; Hanxin Zhang
2007-01-01
A gas-kinetic numerical method for directly solving the mesoscopic velocity distribution function equation is presented and applied to the study of three-dimensional complex flows and micro-channel flows covering various flow regimes. The unified velocity distribution function equation describing gas transport phenomena from rarefied transition to continuumflow regimes can be presented on the basis of the kinetic Boltzmann-Shakhov model equation. The gas-kinetic finite-difference schemes for the velocity distribution function are constructed by developing a discrete velocity ordinate method of gas kinetic theory and an unsteady time-splitting technique from computational fluid dynamics. Gas-kinetic boundary conditions and numerical modeling can be established by directly manipulating on the mesoscopic velocity distribution function. A new Gauss-type discrete velocity numerical integration method can be developed and adopted to attack complex flows with different Mach numbers. HPF parallel strategy suitable for the gas-kinetic numerical method is investigated and adopted to solve three-dimensional complex problems. High Mach number flows around three-dimensional bodies are computed preliminarily with massive scale parallel. It is noteworthy and of practical importance that the HPF parallel algorithm for solving three-dimensional complex problems can be effectively developed to cover various flow regimes. On the other hand, the gas-kinetic numerical method is extended and used to study micro-channel gas flows including the classical Couette flow, the Poiseuillechannel flow and pressure-driven gas flows in twodimensional short micro-channels. The numerical experience shows that the gas-kinetic algorithm may be a powerful tool in the numerical simulation of microscale gas flows occuring in the Micro-Electro-Mechanical System (MEMS).
Relaxation Time of the Particle Beam with an Anisotropic Velocity Distribution
Directory of Open Access Journals (Sweden)
V.P. Vechirka
2012-11-01
Full Text Available The computer experiment for study of the relaxation time of the beam particles with an anisotropic velocity distribution is performed by the molecular dynamics. Obtained results agree with the characteristic times of thermal relaxation in plasma for the electronic coolers in modern storage rings.
Velocity-space tomography of the fast-ion distribution function
DEFF Research Database (Denmark)
Jacobsen, Asger Schou; Salewski, Mirko; Geiger, Benedikt;
2013-01-01
Fast ions play an important role in heating the plasma in a magnetic confinement fusion device. Fast-ion Dα(FIDA) spectroscopy diagnoses fast ions in small measurement volumes. Spectra measured by a FIDA diagnostic can be related to the 2D fast-ion velocity distribution function. A single FIDA vi...
Electron Velocity Distributions Measured with Soft-X-Ray PHA at RTP
Da Cruz, D. F.; Meijer, J. H.; Donne, A. J. H.
1992-01-01
A soft x-ray pulse height analysis (PHA) system is begin used at the Rijhuizen Tokamak Project to study the electron velocity distribution. A liquid nitrogen cooled Si(Li) detector is used to view the plasma along a tangential line of sight. A gas cell in combination with Al foils is used for filter
Sodium Atoms in the Lunar Exotail: Observed Velocity and Spatial Distributions
Line, Michael R.; Mierkiewicz, E. J.; Oliversen, R. J.; Wilson, J. K.; Haffner, L. M.; Roesler, F. L.
2011-01-01
The lunar sodium tail extends long distances due to radiation pressure on sodium atoms in the lunar exosphere. Our earlier observations determined the average radial velocity of sodium atoms moving down the lunar tail beyond Earth along the Sun-Moon-Earth line (i.e., the anti-lunar point) to be 12.4 km/s. Here we use the Wisconsin H-alpha Mapper to obtain the first kinematically resolved maps of the intensity and velocity distribution of this emission over a 15 x times 15 deg region on the sky near the anti-lunar point. We present both spatially and spectrally resolved observations obtained over four nights around new moon in October 2007. The spatial distribution of the sodium atoms is elongated along the ecliptic with the location of the peak intensity drifting 3 degrees east along the ecliptic per night. Preliminary modeling results suggest that the spatial and velocity distributions in the sodium exotail are sensitive to the near surface lunar sodium velocity distribution and that observations of this sort along with detailed modeling offer new opportunities to describe the time history of lunar surface sputtering over several days.
Tomography of fast-ion velocity-space distributions from synthetic CTS and FIDA measurements
DEFF Research Database (Denmark)
Salewski, Mirko; Geiger, B.; Nielsen, Stefan Kragh;
2012-01-01
We compute tomographies of 2D fast-ion velocity distribution functions from synthetic collective Thomson scattering (CTS) and fast-ion D (FIDA) 1D measurements using a new reconstruction prescription. Contradicting conventional wisdom we demonstrate that one single 1D CTS or FIDA view suffices to...
Directory of Open Access Journals (Sweden)
M. P. Sulzer
2004-01-01
Full Text Available We report the observation and analysis of ionization flashes associated with the decay of meteoroids (so-called head echos detected by the Arecibo 430 MHz radar during regular ionospheric observations in the spring and autumn equinoxes. These two periods allow pointing well-above and nearly-into the ecliptic plane at dawn when the event rate maximizes. The observation of many thousands of events allows a statistical interpretation of the results, which show that there is a strong tendency for the observed meteoroids to come from the apex as has been previously reported (Chau and Woodman, 2004. The velocity distributions agree with Janches et al. (2003a when they are directly comparable, but the azimuth scan used in these observations allows a new perspective. We have constructed a simple statistical model which takes meteor velocities as input and gives radar line of sight velocities as output. The intent is to explain the fastest part of the velocity distribution. Since the speeds interpreted from the measurements are distributed fairly narrowly about nearly 60 km s-1, double the speed of the earth in its orbit, is consistent with the interpretation that many of the meteoroids seen by the Arecibo radar are moving in orbits about the sun with similar parameters as the earth, but in the retrograde direction. However, it is the directional information obtained from the beam-swinging radar experiment and the speed that together provide the evidence for this interpretation. Some aspects of the measured velocity distributions suggest that this is not a complete description even for the fast part of the distribution, and it certainly says nothing about the slow part first described in Janches et al. (2003a. Furthermore, we cannot conclude anything about the entire dust population since there are probably selection effects that restrict the observations to a subset of the population.
Institute of Scientific and Technical Information of China (English)
FU Xudong; WANG Guangqian; KANG Zhicheng; FEI Xiangjun
2007-01-01
Characteristics of planar velocity distribution of viscous debris flow were analyzed using the measured data at Jiangjia Ravine, Yunnan, China. The velocity data were measured through using two radar velocimeters. The cross-sectional mean velocities were calculated and used to examine Kang et al's (2004) relationship, which was established for converting the flow velocity at river centerline measured by a radar velocimeter into the mean velocity based on the stop-watch method. The velocity coefficient, K, defined by the ratio of the mean velocity to the maximum velocity, ranges from 0.2 to 0.6. Kang et al's (2004) relationship was found being inapplicable to flows with K smaller than 0.43. This paper contributes to show the complexity of the planar velocity distribution of viscous debris flows and the applicability of Kang et al's relationship.
Institute of Scientific and Technical Information of China (English)
LI ShuangMing; FU HengZhi
2007-01-01
Liquid concentration distribution is seriously affected by an abruptly changing pulling velocity under directional solidification. Theoretical and numerical investigations indicate that at the pulling velocity jumping from V0 to V, the solidification system does not achieve the pulling velocity V immediately, and it goes through a non-steady-state transition zone. As the pulling velocity abruptly increases (V/V0 ＞ 1), interface liquid concentration firstly increases to the maximum and then decreases to the steady-state value. The magnitude of interface liquid concentration at the beginning increases with V/V0, the initial pulling velocity V0 and the temperature gradient GL in the liquid. At the same time, solute diffusion length reduces with V/V0 and GL. In contrast, the minimum of interface liquid concentration falls with V/V0 at the pulling velocity decreasing abruptly. As the interface liquid concentration enriched at V/V0 ＞ 1 is more than the value required for the planar interface to keep stable, the solid/liquid interface may become unstable. The analytical results are in agreement with the numerical calculation results of Al-2%Cu alloy.
Institute of Scientific and Technical Information of China (English)
2007-01-01
Liquid concentration distribution is seriously affected by an abruptly changing pulling velocity under directional solidification. Theoretical and numerical investi-gations indicate that at the pulling velocity jumping from V0 to V, the solidification system does not achieve the pulling velocity V immediately, and it goes through a non-steady-state transition zone. As the pulling velocity abruptly increases (V/V0 > 1), interface liquid concentration firstly increases to the maximum and then de-creases to the steady-state value. The magnitude of interface liquid concentration at the beginning increases with V/V0, the initial pulling velocity V0 and the tem-perature gradient GL in the liquid. At the same time, solute diffusion length reduces with V/V0 and GL. In contrast, the minimum of interface liquid concentration falls with V/V0 at the pulling velocity decreasing abruptly. As the interface liquid con-centration enriched at V/V0 > 1 is more than the value required for the planar inter-face to keep stable, the solid/liquid interface may become unstable. The analytical results are in agreement with the numerical calculation results of Al-2%Cu alloy.
Velocity Distribution Measurement Using Pixel-Pixel Cross Correlation of Electrical Tomography
Institute of Scientific and Technical Information of China (English)
DENGXiang; PENGLihui; YAODanya; ZHANGBaofen
2004-01-01
Electrical tomography (ET) provides a novel means of visualizing the internal behavior of twophase flow in industrial process. Using a dual-sensingplane Electrical resistance tomography (ERT) or Electrical capacitance tomography (ECT) system, the raw data of two different section images can be acquired synchronously and the two images reflecting the inner medium distribution respectively can also be reconstructed by using imaging algorithm. Further, the analysis of pixel-pixel cross correlation is able to be setup and the measurement of velocity distribution of two-phase flow could be achieved. The principle is described in the paper. The FFT algorithm for gray value computation and cross correlation function calculation is also introduced. Some experimental results of velocity distribution measurement using pixelpixel cross correlation in vertical slug flow are presented.
Wu, C. Y. R.; Chen, F. Z.
1993-01-01
The velocity distributions of H and OH fragments produced through solar photodissociation of gaseous H2O molecules under collisionless conditions are presented. The calculations are carried out using: the most recently available absolute partial cross sections for the production of H and OH through photodissociation of H2O from its absorption onset at 1860 A down to 500 A; the newly available vibrational and rotational energy distributions of both the excited and ground state OH photofragments; the calculated cross sections for the total dissociation processes; and the integrated solar flux in 10 A increments from 500 to 1860 A in the continuum regions and the specific wavelength and flux at the bright solar lines. The calculated results show that the H atoms and the OH radicals produced exhibit multiple velocity groups. Since most current cometary modeling uses a single velocity of 20 km/sec associated with the photodissociation of H2O, the present results may be useful in interpreting the many peaks observed in the velocity distributions of the H Lyman alpha and H alpha of comets.
Wu, C. Y. R.; Chen, F. Z.
1993-01-01
The velocity distributions of H and OH fragments produced through solar photodissociation of gaseous H2O molecules under collisionless conditions are presented. The calculations are carried out using: the most recently available absolute partial cross sections for the production of H and OH through photodissociation of H2O from its absorption onset at 1860 A down to 500 A; the newly available vibrational and rotational energy distributions of both the excited and ground state OH photofragments; the calculated cross sections for the total dissociation processes; and the integrated solar flux in 10 A increments from 500 to 1860 A in the continuum regions and the specific wavelength and flux at the bright solar lines. The calculated results show that the H atoms and the OH radicals produced exhibit multiple velocity groups. Since most current cometary modeling uses a single velocity of 20 km/sec associated with the photodissociation of H2O, the present results may be useful in interpreting the many peaks observed in the velocity distributions of the H Lyman alpha and H alpha of comets.
Vilquin, A.; Boudet, J. F.; Kellay, H.
2016-08-01
Velocity distributions in normal shock waves obtained in dilute granular flows are studied. These distributions cannot be described by a simple functional shape and are believed to be bimodal. Our results show that these distributions are not strictly bimodal but a trimodal distribution is shown to be sufficient. The usual Mott-Smith bimodal description of these distributions, developed for molecular gases, and based on the coexistence of two subpopulations (a supersonic and a subsonic population) in the shock front, can be modified by adding a third subpopulation. Our experiments show that this additional population results from collisions between the supersonic and subsonic subpopulations. We propose a simple approach incorporating the role of this third intermediate population to model the measured probability distributions and apply it to granular shocks as well as shocks in molecular gases.
Shan, Chung-Lin
2014-01-01
In this paper, we extended our earlier work on the reconstruction of the (time-averaged) one-dimensional velocity distribution of Galactic Weakly Interacting Massive Particles (WIMPs) and introduce the Bayesian fitting procedure to the theoretically predicted velocity distribution functions. In this reconstruction process, the (rough) velocity distribution reconstructed by using raw data from direct Dark Matter detection experiments directly, i.e. measured recoil energies, with one or more different target materials, has been used as "reconstructed-input" information. By assuming a fitting velocity distribution function and scanning the parameter space based on the Bayesian analysis, the astronomical characteristic parameters, e.g. the Solar and Earth's orbital velocities, will be pinned down as the output results. Our Monte-Carlo simulations show that this Bayesian scanning procedure could reconstruct the true (input) WIMP velocity distribution function pretty precisely with negligible systematic deviations ...
Velocity distribution of flow with submerged flexible vegetations based on mixing-length approach
Institute of Scientific and Technical Information of China (English)
Wen-xin HUAI; Jie HAN; Yu-hong ZENG; Xiang AN; Zhong-dong QIAN
2009-01-01
By choosing a PVC slice to simulate flexible vegetation, we carried out ex-periments in an open channel with submerged flexible vegetation. A 3D acoustic Doppler velocimeter (micro ADV) was used to measure local flow velocities and Reynolds stress. The results show that hydraulic characteristics in non-vegetation and vegetation layers are totally different. In a region above the vegetation, Reynolds stress distribution is linear, and the measured velocity profile is a classical logarithmic one. Based on the concept of new-riverbed, the river compression parameter representing the impact of vegetation on river is given, and a new assumption of mixing length expression is made. The formula for time-averaged velocity derived from the expression requires less parameters and simple calculation, and is useful in applications.
Late Quaternary climate-change velocity: Implications for modern distributions and communities
DEFF Research Database (Denmark)
Sandel, Brody Steven; Dalsgaard, Bo; Arge, Lars Allan
a global map of climate-change velocity since the Last Glacial Maximum and used this measure of climate instability to address a number of classic hypotheses. Results/Conclusions We show that historical climate-change velocity is related to a wide range of characteristics of modern distributions......Background/Question/Methods Climate-change velocity is a measure of the rate of climate change that incorporates small-scale climate variation such as that found along topographic gradients. As a measure of climate instability, it has several advantages, including describing the minimum migration...... rate required to track changing conditions and explicitly capturing the buffering effect of topography on climate change. Variation in climate stability has long been hypothesized as a possible driver of large-scale ecological patterns including diversity and range size gradients. We calculated...
Precision measurement of transverse velocity distribution of a strontium atomic beam
Gao, F.; Liu, H.; Xu, P.; Tian, X.; Wang, Y.; Ren, J.; Wu, Haibin; Chang, Hong
2014-02-01
We measure the transverse velocity distribution in a thermal Sr atomic beam precisely by velocity-selective saturated fluorescence spectroscopy. The use of an ultrastable laser system and the narrow intercombination transition line of Sr atoms mean that the resolution of the measured velocity can reach 0.13 m/s, corresponding to 90 μK in energy units. The experimental results are in very good agreement with the results of theoretical calculations. Based on the spectroscopic techniques used here, the absolute frequency of the intercombination transition of 88Sr is measured using an optical-frequency comb generator referenced to the SI second through an H maser, and is given as 434 829 121 318(10) kHz.
Precision measurement of transverse velocity distribution of a strontium atomic beam
Directory of Open Access Journals (Sweden)
F. Gao
2014-02-01
Full Text Available We measure the transverse velocity distribution in a thermal Sr atomic beam precisely by velocity-selective saturated fluorescence spectroscopy. The use of an ultrastable laser system and the narrow intercombination transition line of Sr atoms mean that the resolution of the measured velocity can reach 0.13 m/s, corresponding to 90 μK in energy units. The experimental results are in very good agreement with the results of theoretical calculations. Based on the spectroscopic techniques used here, the absolute frequency of the intercombination transition of 88Sr is measured using an optical-frequency comb generator referenced to the SI second through an H maser, and is given as 434 829 121 318(10 kHz.
Su, Huaizhi; Tian, Shiguang; Cui, Shusheng; Yang, Meng; Wen, Zhiping; Xie, Wei
2016-09-01
In order to systematically investigate the general principle and method of monitoring seepage velocity in the hydraulic engineering, the theoretical analysis and physical experiment were implemented based on distributed fiber-optic temperature sensing (DTS) technology. During the coupling influence analyses between seepage field and temperature field in the embankment dam or dike engineering, a simplified model was constructed to describe the coupling relationship of two fields. Different arrangement schemes of optical fiber and measuring approaches of temperature were applied on the model. The inversion analysis idea was further used. The theoretical method of monitoring seepage velocity in the hydraulic engineering was finally proposed. A new concept, namely the effective thermal conductivity, was proposed referring to the thermal conductivity coefficient in the transient hot-wire method. The influence of heat conduction and seepage could be well reflected by this new concept, which was proved to be a potential approach to develop an empirical method monitoring seepage velocity in the hydraulic engineering.
Electron velocity distribution functions from the solar wind to the corona
Maksimovic, M.; Pierrard, V.; Lemaire, J.; Larson, D.
1999-06-01
Typical electron velocity distribution functions observed at 1 AU from the Sun by the instrument 3DP aboard of WIND are used as boundary conditions to determine the electron velocity distribution function at 4 solar radii in the corona. The velocity distribution functions (VDF) at low altitude are obtained by solving the Fokker-Planck equation, using two different sets of boundary conditions. The first set typically corresponds to a VDF observed in a low speed solar wind flow (i.e., characterized by ``core'' and ``halo'' electrons); the second one corresponds to high speed solar wind (i.e. characterized by ``core,'' ``halo'' and ``strahl'' populations). We use the observed electron VDFs as test particles which are submitted to external forces and Coulomb collisions with a background plasma. Closer to the Sun, the relative density of the core electrons is found to increase compared to the densities of the halo population. Nevertheless, we find that in order to match the observed distributions at 1 AU, suprathermal tails have to be present in the VDF of the test electron at low altitudes in the corona. Note that the present work has been submitted to Journal of Geophysical Research [6]. This is the reason why we present here only an extended summary.
Institute of Scientific and Technical Information of China (English)
TANG XiaoNan; KNIGHT Donald W
2009-01-01
Natural rivers are commonly characterized by a main channel for primary flow conveyance and a floodplain, often partially covered with vegetation such as shrubs or trees, to carry extra flow during floods.The hydraulic resistance due to vegetation on the floodplain typically causes a further reduction of flow velocity and increases the velocity difference between the main channel and the floodplain.As a consequence a strong lateral shear layer leads to the exchange of mass and momentum between the main channel and floodplain, which in turn affects the overall channel conveyance and certain fluvial processes.The prediction of the lateral velocity distribution is important for many flood alleviation schemes, as well as for studies on sediment transport and dispersion in such channels.The present paper proposes a method for predicting the depth-averaged velocity in compound channels with par-tially vegetated floodplains, based on an analytical solution to the depth-integrated Reynolds-Averaged Navier-Stokes equation with a term included to account for the effects of vegetation.The vegetation is modelled via an additional term in the momentum equation to account for the additional drag force.The method includes the effects of bed friction, drag force, lateral turbulence and secondary flows, via four coefficients f, C_D,λ & Г respectively.The predicted lateral distributions of depth-averaged velocity agree well with the experimental data.The analytical solutions can also be used to predict the distribu-tion of boundary shear stresses, which adds additional weight to the method proposed.
Mandel, Kaisey S; Kirshner, Robert P
2014-01-01
We investigate the correlations between the peak intrinsic colors of Type Ia supernovae (SN Ia) and their expansion velocities at maximum light, measured from the Si II 6355 A spectral feature. We construct a new hierarchical Bayesian regression model and Gibbs sampler to estimate the dependence of the intrinsic colors of a SN Ia on its ejecta velocity, while accounting for the random effects of intrinsic scatter, measurement error, and reddening by host galaxy dust. The method is applied to the apparent color data from BVRI light curves and Si II velocity data for 79 nearby SN Ia. Comparison of the apparent color distributions of high velocity (HV) and normal velocity (NV) supernovae reveals significant discrepancies in B-V and B-R, but not other colors. Hence, they are likely due to intrinsic color differences originating in the B-band, rather than dust reddening. The mean intrinsic B-V and B-R color differences between HV and NV groups are 0.06 +/- 0.02 and 0.09 +/- 0.02 mag, respectively. Under a linear m...
Gopalan, Balaji; Shaffer, Frank
2013-11-01
Fluid flows that are loaded with high concentration of solid particles are common in oil and chemical processing industries. However, the opaque nature of the flow fields and the complex nature of the flow have hampered the experimental and computational study of these processes. This has led to the development of a number of customized experimental techniques for high concentration particle flows for evaluation and improvement of CFD models. This includes techniques that track few individual particles, measures average particle velocity over a small sample volume and those over a large sample volume. In this work novel high speed PIV (HsPIV), with individual particle tracking, was utilized to measure velocities of individual particles in gas-particle flow fields at the walls circulating and bubbling fluidized bed. The HsPIV measurement technique has the ability to simultaneously recognize and track thousands of individual particles in flows of high particle concentration. To determine the effect of the size of the sample volume on particle velocity measurements, the PDF of Lagrangian particle velocity was compared with the PDF of Eulerian for different domain sizes over a range of flow conditions. The results will show that measured particle velocity distribution can vary from technique to technique and this bias has to be accounted in comparison with CFD simulations.
The Velocity Distribution Function of Galaxy Clusters as a Cosmological Probe
Ntampaka, M; Cisewski, J; Price, L C
2016-01-01
We present a new approach for quantifying the abundance of galaxy clusters and constraining cosmological parameters using dynamical measurements. In the standard method, galaxy line-of-sight (LOS) velocities, $v$, or velocity dispersions are used to infer cluster masses, $M$, in order to quantify the halo mass function (HMF), $dn(M)/d\\log(M)$, which is strongly affected by mass measurement errors. In our new method, the probability distribution of velocities for each cluster in the sample are summed to create a new statistic called the velocity distribution function (VDF), $dn(v)/dv$. The VDF can be measured more directly and precisely than the HMF and it can also be robustly predicted with cosmological simulations which capture the dynamics of subhalos or galaxies. We apply these two methods to mock cluster catalogs and forecast the bias and constraints on the matter density parameter $\\Omega_m$ and the amplitude of matter fluctuations $\\sigma_8$ in flat $\\Lambda$CDM cosmologies. For an example observation o...
Inversion of Seismic Velocities to obtain the Crack and Pore Aspect Ratio Distribution
Zimmerman, R. W.; David, E. C.
2010-12-01
During a hydrostatic experiment, in the elastic regime, P and S elastic wave velocities measured on rock samples generally increase with pressure and reach asymptotic values at high pressures. This increase of seismic velocities with confining pressure is known to be caused by the closure of compliant pores, such as flat “cracks”, and therefore the high-pressure values of the velocities must reflect only the influence of stiff, “equant” pores. If the pores are assumed to be spheroids, the use of an effective medium theory, combined with a crack closure model, gives a model to relate the elastic properties to the microstructure at each pressure. Therefore, the pressure dependence of elastic velocities can be inverted to obtain the pore aspect ratio distribution. This is done more easily using data obtained in dry experiments, since pore fluids have a strong effect on velocities and to some extent mask the effect of the pore geometry. However, thus far most models have used restrictive assumptions, such as assuming that the stiff pores are spherical, or the interactions between inclusions can be neglected (such as Morlier’s method), which is unfortunately not realistic in most cases. Others methods, such as the one developed by Cheng and Toksoz (1979), assume that the rock contains a discrete distribution of crack aspect ratios, and are complicated to implement numerically. Moreover, in most work only the dry data have been inverted, or jointly the dry and wet data, but it seems that few works have tried to look in detail at a consistent pore model, that remains simple and is able to predict the dependence of Vp and Vs under saturated conditions, based on data collected on dry rocks. We assume that the rock contains a distribution of cracks with different aspect ratios, and two families of stiff pores, each with their own finite aspect ratio. We use this model to invert the wavespeeds to obtain aspect ratio distributions of some isotropic sandstones (Berea
Directory of Open Access Journals (Sweden)
Kai Yan
2015-01-01
Full Text Available A predictive model for droplet size and velocity distributions of a pressure swirl atomizer has been proposed based on the maximum entropy formalism (MEF. The constraint conditions of the MEF model include the conservation laws of mass, momentum, and energy. The effects of liquid swirling strength, Weber number, gas-to-liquid axial velocity ratio and gas-to-liquid density ratio on the droplet size and velocity distributions of a pressure swirl atomizer are investigated. Results show that model based on maximum entropy formalism works well to predict droplet size and velocity distributions under different spray conditions. Liquid swirling strength, Weber number, gas-to-liquid axial velocity ratio and gas-to-liquid density ratio have different effects on droplet size and velocity distributions of a pressure swirl atomizer.
Non-Gaussian velocity distributions - The effect on virial mass estimates of galaxy groups
Ribeiro, Andre L B; Trevisan, Marina
2011-01-01
We present a study of 9 galaxy groups with evidence for non-Gaussianity in their velocity distributions out to 4R200. This sample is taken from 57 groups selected from the 2PIGG catalog of galaxy groups. Statistical analysis indicates that non-Gaussian groups have masses significantly higher than Gaussian groups. We also have found that all non-Gaussian systems seem to be composed of multiple velocity modes. Besides, our results indicate that multimodal groups should be considered as a set of individual units with their own properties. In particular, we have found that the mass distribution of such units are similar to that of Gaussian groups. Our results reinforce the idea of non-Gaussian systems as complex structures in the phase space, likely corresponding to secondary infall aggregations at a stage before virialization. The understanding of these objects is relevant for cosmological studies using groups and clusters through the mass function evolution.
Measurement of Velocity Distribution in Atomic Beam by Diode Laser with Narrow Line width
Institute of Scientific and Technical Information of China (English)
CHEN Jingbiao; WANG Fengzhi; YANG Donghai; WANG YiQiu
2001-01-01
In this paper, by using the detecting laser beam interacts with the atomic beam at a sharp angle and the Doppler frequency shift effect, the velocity distribution in cesium atomic beam is measured with a diode laser of narrow linewidth of 1 MHz. The effects of the atomic natural line width and cycling transition detecting factor on the measured results have been analyzed. Finally, the measured results have been compared with the theoretical calculation.
Energy Technology Data Exchange (ETDEWEB)
Rader, D.J.; Benson, D.A.
1995-05-01
This report presents the results of an experimental study of the aerosol produced by the combustion of high-velocity molten-uranium droplets produced by the simultaneous heating and electromagnetic launch of uranium wires. These tests are intended to simulate the reduction of high-velocity fragments into aerosol in high-explosive detonations or reactor accidents involving nuclear materials. As reported earlier, the resulting aerosol consists mainly of web-like chain agglomerates. A condensation nucleus counter was used to investigate the decay of the total particle concentration due to coagulation and losses. Number size distributions based on mobility equivalent diameter obtained soon after launch with a Differential Mobility Particle Sizer showed lognormal distributions with an initial count median diameter (CMD) of 0.3 {mu}m and a geometric standard deviation, {sigma}{sub g} of about 2; the CMD was found to increase and {sigma}{sub g} decrease with time due to coagulation. Mass size distributions based on aerodynamic diameter were obtained for the first time with a Microorifice Uniform Deposit Impactor, which showed lognormal distributions with mass median aerodynamic diameters of about 0.5 {mu}m and an aerodynamic geometric standard deviation of about 2. Approximate methods for converting between number and mass distributions and between mobility and aerodynamic equivalent diameters are presented.
The velocity distribution of pickup He{sup +} measured at 0.3 AU by MESSENGER
Energy Technology Data Exchange (ETDEWEB)
Gershman, Daniel J. [Geospace Physics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Fisk, Lennard A.; Gloeckler, George; Raines, Jim M.; Slavin, James A.; Zurbuchen, Thomas H. [Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI 48109 (United States); Solomon, Sean C., E-mail: djgersh@umich.edu [Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015 (United States)
2014-06-20
During its interplanetary trajectory in 2007-2009, the MErcury Surface, Space ENvrionment, GEochemistry, and Ranging (MESSENGER) spacecraft passed through the gravitational focusing cone for interstellar helium multiple times at a heliocentric distance R ≈ 0.3 AU. Observations of He{sup +} interstellar pickup ions made by the Fast Imaging Plasma Spectrometer sensor on MESSENGER during these transits provide a glimpse into the structure of newly formed inner heliospheric pickup-ion distributions. This close to the Sun, these ions are picked up in a nearly radial interplanetary magnetic field. Compared with the near-Earth environment, pickup ions observed near 0.3 AU will not have had sufficient time to be energized substantially. Such an environment results in a nearly pristine velocity distribution function that should depend only on pickup-ion injection velocities (related to the interstellar gas), pitch-angle scattering, and cooling processes. From measured energy-per-charge spectra obtained during multiple spacecraft observational geometries, we have deduced the phase-space density of He{sup +} as a function of magnetic pitch angle. Our measurements are most consistent with a distribution that decreases nearly monotonically with increasing pitch angle, rather than the more commonly modeled isotropic or hemispherically symmetric forms. These results imply that pitch-angle scattering of He{sup +} may not be instantaneous, as is often assumed, and instead may reflect the velocity distribution of initially injected particles. In a slow solar wind stream, we find a parallel-scattering mean free path of λ {sub ||} ∼ 0.1 AU and a He{sup +} production rate of ∼0.05 m{sup –3} s{sup –1} within 0.3 AU.
The Analysis of the Moments of the Velocity Distribution in the Gaia Sphere
Romero-Gomez, M.; Figueras, F.; Antoja, T.; Roca-Fabrega, S.; Abedi, H.; Aguilar, L.
2016-10-01
The good precision in radial velocities provided by the WEAVE instrument (at ING), together with the proper motions obtained by the Gaia (ESA) mission, will allow the kinematic study of the end of the bar region. This is a rich, kinematically speaking, region that could help answer the big question regarding the one bar or two bar problem. Therefore, with Gaia and WEAVE, we are not limited to the study of the bar overdensity, but we can use all the 6D phase space. We are currently working on the analysis of the moments of the velocity distribution function in the Gaia sphere, about 4-5 kpc from the Sun, to try to obtain information on the potential of the Galaxy.
Filaments from the galaxy distribution and from the velocity field in the local universe
Libeskind, Noam I; Hoffman, Yehuda; Tully, R Brent; Courtois, Helene
2015-01-01
The cosmic web that characterizes the large-scale structure of the Universe can be quantified by a variety of methods. For example, large redshift surveys can be used in combination with point process algorithms to extract long curvilinear filaments in the galaxy distribution. Alternatively, given a full 3D reconstruction of the velocity field, kinematic techniques can be used to decompose the web into voids, sheets, filaments and knots. In this paper we look at how two such algorithms - the Bisous model and the velocity shear web - compare with each other in the local Universe (within 100 Mpc), finding good agreement. This is both remarkable and comforting, given that the two methods are radically different in ideology and applied to completely independent and different data sets. Unsurprisingly, the methods are in better agreement when applied to unbiased and complete data sets, like cosmological simulations, than when applied to observational samples. We conclude that more observational data is needed to i...
Large scale characterization of the stellar velocity distribution in the galactic disk
Directory of Open Access Journals (Sweden)
Romero-Gómez M.
2012-02-01
Full Text Available Test particle simulations of Milky Way type galactic disks are being conducted to map the evolution of the stellar large scale kinematic response to the bar and spiral structure. Second and third order moments of the velocity distribution function prove to be good indicators of both, the velocity ellipsoid misalignment near the arms and the bar, and the degree of kinematic substructure in the UV plane, that is, the presence of moving groups. A large scale analysis all through the galactic disk allows to establish the kinematic behavior near resonances and the correlation between the kinematic parameters and properties of the non-axisymmetric components, such as its transient nature or its mass overdensity. N-body simulaions are being run in order to test these results in self-consistent models.
Energy Technology Data Exchange (ETDEWEB)
Buss, R.J.
1979-04-01
The study of seven radical-molecule reactions using the crossed molecular beam technique with supersonic nozzle beams is reported. Product angular and velocity distributions were obtained and compared with statistical calculations in order to identify dynamical features of the reactions. In the reaction of chlorine and fluorine atoms with vinyl bromide, the product energy distributions are found to deviate from predictions of the statistical model. A similar effect is observed in the reaction of chlorine atoms with 1, 2 and 3-bromopropene. The reaction of oxygen atoms with ICl and CF/sub 3/I has been used to obtain an improved value of the IO bond energy, 55.0 +- 2.0 kcal mol/sup -1/. In all reactions studied, the product energy and angular distributions are found to be coupled, and this is attributed to a kinematic effect of the conservation of angular momentum.
The Velocity Distribution Function of Galaxy Clusters as a Cosmological Probe
Ntampaka, M.; Trac, H.; Cisewski, J.; Price, L. C.
2017-01-01
We present a new approach for quantifying the abundance of galaxy clusters and constraining cosmological parameters using dynamical measurements. In the standard method, galaxy line-of-sight velocities, v, or velocity dispersions are used to infer cluster masses, M, to quantify the halo mass function (HMF), {dn}(M)/d{log}(M), which is strongly affected by mass measurement errors. In our new method, the probability distributions of velocities for each cluster in the sample are summed to create a new statistic called the velocity distribution function (VDF), {dn}(v)/{dv}. The VDF can be measured more directly and precisely than the HMF and can be robustly predicted with cosmological simulations that capture the dynamics of subhalos or galaxies. We apply these two methods to realistic (ideal) mock cluster catalogs with (without) interlopers and forecast the bias and constraints on the matter density parameter Ωm and the amplitude of matter fluctuations σ8 in flat ΛCDM cosmologies. For an example observation of 200 massive clusters, the VDF with (without) interloping galaxies constrains the parameter combination {σ }8 {{{Ω }}}m0.29(0.29)=0.589+/- 0.014 (0.584+/- 0.011) and shows only minor bias. However, the HMF with interlopers is biased to low Ωm and high σ8 and the fiducial model lies well outside of the forecast constraints, prior to accounting for Eddington bias. When the VDF is combined with constraints from the cosmic microwave background, the degeneracy between cosmological parameters can be significantly reduced. Upcoming spectroscopic surveys that probe larger volumes and fainter magnitudes will provide clusters for applying the VDF as a cosmological probe.
The velocity distribution of interstellar gas observed in strong UV absorption lines
Cowie, L. L.; York, D. G.
1978-01-01
Observations of three strong interstellar UV absorption lines of N I (1199 A), N II (1083 A), and Si III (1206 A) in 47 stars of widely varying distance and a variety of spectral types are analyzed to obtain a velocity distribution function for the interstellar gas. A technique based on the maximum and minimum velocities observed along a line of sight is adopted because of heavy line blending, and results are discussed for both power-law and exponential distribution functions. The expected distribution of radiative-phase supernova remnants (SNRs) in the interstellar medium is calculated as a function of SNR birthrate and of the interstellar density in which they evolve. The results are combined with observed distance estimates, and it is shown that an interstellar density in excess of 0.1 per cu cm would be required to keep the SNRs sufficiently confined so that their cross sections are consistent with the observed number of components. The alternative possibility is considered that SNRs do not enter the radiative phase before escaping from the Galaxy or colliding with neighboring remnants.
Observations of the He+ pickup ion torus velocity distribution function with SOHO/CELIAS/CTOF
Taut, Andreas; Berger, Lars; Bochsler, Peter; Drews, Christian; Klecker, Berndt; Wimmer-Schweingruber, Robert F.
2016-03-01
Interstellar PickUp Ions (PUIs) are created from neutrals coming from the interstellar medium that get ionized inside the heliosphere. Once ionized, the freshly created ions are injected into the magnetized solar wind plasma with a highly anisotropic torus-shaped Velocity Distribution Function (VDF). It has been commonly assumed that wave-particle interactions rapidly destroy this torus by isotropizing the distribution in one hemisphere of velocity space. However, recent observations of a He+ torus distribution using PLASTIC on STEREO showed that the assumption of a rapid isotropization is oversimplified. The aim of this work is to complement these studies. Using He+ data from the Charge Time-Of-Flight (CTOF) sensor of the Charge, ELement, and Isotope Analysis System (CELIAS) on-board the SOlar and Heliospheric Observatory (SOHO) and magnetic field data from the Magnetic Field Investigation (MFI) magnetometer of the WIND spacecraft, we derive the projected 1-D VDF of He+ for different magnetic field configurations. Depending on the magnetic field direction, the initial torus VDF lies inside CTOF's aperture or not. By comparing the VDFs derived under different magnetic field directions with each other we reveal an anisotropic signature of the He+ VDF.
Brevoort, Maurice J.
1937-01-01
In the design of a cowling a certain pressure drop across the cylinders of a radial air-cooled engine is made available. Baffles are designed to make use of this available pressure drop for cooling. The problem of cooling an air-cooled engine cylinder has been treated, for the most part, from considerations of a large heat-transfer coefficient. The knowledge of the precise cylinder characteristics that give a maximum heat-transfer coefficient should be the first consideration. The next problem is to distribute this ability to cool so that the cylinder cools uniformly. This report takes up the problem of the design of a baffle for a model cylinder. A study has been made of the important principles involved in the operation of a baffle for an engine cylinder and shows that the cooling can be improved 20% by using a correctly designed baffle. Such a gain is as effective in cooling the cylinder with the improved baffle as a 65% increase in pressure drop across the standard baffle and fin tips.
Wang, Huihui; Sukhomlinov, Vladimir S.; Kaganovich, Igor D.; Mustafaev, Alexander S.
2017-02-01
Based on accurate representation of the He+-He angular differential scattering cross sections consisting of both elastic and charge exchange collisions, we performed detailed numerical simulations of the ion velocity distribution functions (IVDF) by Monte Carlo collision method (MCC). The results of simulations are validated by comparison with the experimental data of the ion mobility and the transverse diffusion. The IVDF simulation study shows that due to significant effect of scattering in elastic collisions IVDF cannot be separated into product of two independent IVDFs in the transverse and parallel to the electric field directions.
Superstatistical velocity distributions of cold trapped ions in molecular dynamics simulations
Rouse, I
2015-01-01
We present a realistic molecular-dynamics treatment of laser-cooled ions in radiofrequency ion traps which avoids previously made simplifications such as modeling laser cooling as a friction force and combining individual heating mechanisms into a single effective heating force. Based on this implementation, we show that infrequent energetic collisions of single ions with background gas molecules lead to pronounced heating of the entire ion ensemble and a time-varying secular ensemble temperature which manifests itself in a superstatistical time-averaged velocity distribution of the ions. The effect of this finding on the experimental determination of ion temperatures and rate constants for cold chemical reactions is discussed.
Turbulence-Induced Relative Velocity of Dust Particles III: The Probability Distribution
Pan, Liubin; Scalo, John
2014-01-01
Motivated by its important role in the collisional growth of dust particles in protoplanetary disks, we investigate the probability distribution function (PDF) of the relative velocity of inertial particles suspended in turbulent flows. Using the simulation from our previous work, we compute the relative velocity PDF as a function of the friction timescales, tau_p1 and tau_p2, of two particles of arbitrary sizes. The friction time of particles included in the simulation ranges from 0.1 tau_eta to 54T_L, with tau_eta and T_L the Kolmogorov time and the Lagrangian correlation time of the flow, respectively. The relative velocity PDF is generically non-Gaussian, exhibiting fat tails. For a fixed value of tau_p1, the PDF is the fattest for equal-size particles (tau_p2~tau_p1), and becomes thinner at both tau_p2tau_p1. Defining f as the friction time ratio of the smaller particle to the larger one, we find that, at a given f in 1/2>T_L). These features are successfully explained by the Pan & Padoan model. Usin...
Line-of-sight velocity distributions of low-luminosity elliptical galaxies
Halliday, C E; Kuntschner, H; Birkinshaw, M; Bender, R; Saglia, R P; Baggley, G; Davies, Roger L.; Kuntschner, Harald; Bender, Ralf; Baggley, Glenn
2001-01-01
The shape of the line-of-sight velocity distribution (LOSVD) is measured for a sample of 14 elliptical galaxies, predominantly low-luminosity ellipticals. The sample is dominated by galaxies in the Virgo cluster but also contains ellipticals in nearby groups and low density environments. The parameterization of the LOSVD due to Gerhard and van der Marel and Franx is adopted, which measures the asymmetrical and symmetrical deviations of the LOSVD from a Gaussian by the amplitudes h3 and h4 of the Gauss-Hermite series. Rotation, velocity dispersion, h3 and h4 are determined as a function of radius for both major and minor axes. Non-Gaussian LOSVDs are found for all galaxies along the major axes. Deviations from a Gaussian LOSVD along the minor axis are of much lower amplitude if present at all. Central decreases in velocity dispersion are found for three galaxies. Two galaxies have kinematically-decoupled cores: NGC 4458 and the well-known case of NGC 3608.
Yu, Wenwu; Chen, Guanrong; Cao, Ming
Using tools from algebraic graph theory and nonsmooth analysis in combination with ideas of collective potential functions, velocity consensus and navigation feedback, a distributed leader-follower flocking algorithm for multi-agent dynamical systems with time-varying velocities is developed where
Effects of projectile track charging on the H - secondary ion velocity distribution
Iza, P.; Farenzena, L. S.; da Silveira, E. F.
2007-03-01
The bombardment of insulating targets by MeV projectiles produces a positive track delivering secondary electrons to the solid. These electrons are eventually captured by adsorbed hydrogen-containing molecules, inducing fragmentation and initiating the H- secondary ion emission. The dynamics of this process is very sensitive to the track electric field and depends on the emission site and on the H- initial velocity. In this work, a model, based on a time-depending track potential followed by secondary electron induced desorption - SEID, is employed to describe the production and dynamics of H- secondary ion emission. It is shown that depending on how fast the track neutralization occurs, the movement of H- ions may be accelerated, decelerated or even aborted. Trajectories, angular distributions and energy distributions are predicted and compared with experimental data obtained for water ice bombarded by 1.7 MeV nitrogen ions.
Steffen, Jason H
2015-01-01
Motivated by recent discussions, both in private and in the literature, we use a Monte Carlo simulation of planetary systems to investigate sources of bias in determining the mass-radius distribution of exoplanets for the two primary techniques used to measure planetary masses---Radial Velocities (RVs) and Transit Timing Variations (TTVs). We assert that mass measurements derived from these two methods are comparably reliable---as the physics underlying their respective signals is well understood. Nevertheless, their sensitivity to planet mass varies with the properties of the planets themselves. We find that for a given planet size, the RV method tends to find planets with higher mass while the sensitivity of TTVs is more uniform. This ``sensitivity bias'' implies that a complete census of TTV systems is likely to yield a more robust estimate of the mass-radius distribution provided there are not important physical differences between planets near and far from mean-motion resonance. We discuss differences in...
Markov random field modelling for fluid distributions from the seismic velocity structures
Kuwatani, T.; Nagata, K.; Okada, M.; Toriumi, M.
2011-12-01
Recent development of geophysical observations, such as seismic tomography, seismic reflection method and geomagnetic method, provide us detailed images of the earth's interior. However, it has still been difficult to interpret these data geologically, including predicting lithology and fluid distributions, mainly because (1) available data usually have large noise and uncertainty, and (2) the number of observable parameters is usually smaller than the number of target parameters. Therefore, the statistical analyses of geophysical data sets are essential for the objective and quantitative geological interpretation. We propose the use of Markov random field (MRF) model to geophysical image data as an alternative to classical deterministic approaches. The MRF model is a Bayesian stochastic model using a generalized form of Markov Chains, and is often applied to the analysis of images, particularly in the detection of visual patterns or textures. The MRF model assumes that the spatial gradients of physical properties are relatively small compared to the observational noises. By hyperparameter estimation, the variances of noises can be appropriately estimated only from available data sets without prior information about observational noises. In this study, we try to image the fluid distributions based on the seismic velocity structure by using the Markov random field model. According to Nakajima et al. (2005), seismic velocities (Vp and Vs) are expressed as functions of porosity and pore geometry using the unified formulation proposed by Takei (2002). Additionally, the spatial continuity of porosity and pore geometry is incorporated by Gaussian Markov Chains as prior probabilities. The most probable estimation can be obtained by maximizing the posterior probability of the fluid distribution given the observed velocity structures. In the present study, the steepest descent method was implemented in order to minimize the free energy (i.e. maximize the posterior
The ion velocity distribution of tokamak plasmas: Rutherford scattering at TEXTOR
Energy Technology Data Exchange (ETDEWEB)
Tammen, H.F.
1995-01-10
One of the most promising ways to gererate electricity in the next century on a large scale is nuclear fusion. In this process two light nuclei fuse and create a new nucleus with a smaller mass than the total mass of the original nuclei, the mass deficit is released in the form of kinetic energy. Research into this field has already been carried out for some decades now, and will have to continue for several more decades before a commercially viable fusion reactor can be build. In order to obtain fusion, fuels of extremely high temperatures are needed to overcome the repulsive force of the nuclei involved. Under these circumstances the fuel is fully ionized: it consists of ions and electrons and is in the plasma state. The problem of confining such a hot substance is solved by using strong magnetic fields. One specific magnetic configuration, in common use, is called the tokamak. The plasma in this machine has a toroidal, i.e. doughnut shaped, configuration. For understanding the physical processes which take place in the plasma, a good temporally and spatially resolved knowledge of both the ion and electron velocity distribution is required. The situation concerning the electrons is favourable, but this is not the case for the ions. To improve the existing knowledge of the ion velocity distribution in tokamak plasmas, a Rutherford scattering diagnostic (RUSC), designed and built by the FOM-Institute for Plasmaphysics `Rijnhuizen`, was installed at the TEXTOR tokamak in Juelich (D). The principle of the diagnostic is as follows. A beam of monoenergetic particles (30 keV, He) is injected vertically into the plasma. A small part of these particles collides elastically with the moving plasma ions. By determining the energy of a scattered beam particle under a certain angle (7 ), the initial velocity of the plasma ion in one direction can be computed. (orig./WL).
Vu, Huong T.; Chakrabarti, Shaon; Hinczewski, Michael; Thirumalai, D.
2016-08-01
Fluctuations in the physical properties of biological machines are inextricably linked to their functions. Distributions of run lengths and velocities of processive molecular motors, like kinesin-1, are accessible through single-molecule techniques, but rigorous theoretical models for these probabilities are lacking. Here, we derive exact analytic results for a kinetic model to predict the resistive force (F )-dependent velocity [P (v )] and run length [P (n )] distribution functions of generic finitely processive molecular motors. Our theory quantitatively explains the zero force kinesin-1 data for both P (n ) and P (v ) using the detachment rate as the only parameter. In addition, we predict the F dependence of these quantities. At nonzero F , P (v ) is non-Gaussian and is bimodal with peaks at positive and negative values of v , which is due to the discrete step size of kinesin-1. Although the predictions are based on analyses of kinesin-1 data, our results are general and should hold for any processive motor, which walks on a track by taking discrete steps.
Institute of Scientific and Technical Information of China (English)
Wenfei Wu; Xuan Wu; Yanhui Feng; Xinxin Zhang
2007-01-01
In order to obtain a better understanding of flow characteristics of displacement ventilation, the three-dimensional numerical models are developed using the CFD technology. The numerical simulation results are verified by experiments, based on this, the velocity and temperature distribution of three-dimensional displacement ventilation system with single and double heat sources are studied. Velocity and temperature fields under two different cases of heat source are analyzed and compared. The numerical results show that there are three layers in vertical temperature fields of displacement ventilation system with single or double heat sources, and the vertical temperature distribution of single heat source is different from that of double heat sources. When indoor load is large, the comfort requirement of people indoor can't be satisfied with displacement ventilation system only, thus an additional refrigeration system is necessary. Furthermore, under the condition of two heat sources, the displacement ventilation parameters can't be computed simply according to single heat source inlet parameters, therefore the interaction between heat sources should be considered.
Revised Model of the Steady-state Solar Wind Halo Electron Velocity Distribution Function
Yoon, Peter H.; Kim, Sunjung; Choe, G. S.; moon, Y.-J.
2016-08-01
A recent study discussed the steady-state model for solar wind electrons during quiet time conditions. The electrons emanating from the Sun are treated in a composite three-population model—the low-energy Maxwellian core with an energy range of tens of eV, the intermediate ˜102-103 eV energy-range (“halo”) electrons, and the high ˜103-105 eV energy-range (“super-halo”) electrons. In the model, the intermediate energy halo electrons are assumed to be in resonance with transverse EM fluctuations in the whistler frequency range (˜102 Hz), while the high-energy super-halo electrons are presumed to be in steady-state wave-particle resonance with higher-frequency electrostatic fluctuations in the Langmuir frequency range (˜105 Hz). A comparison with STEREO and WIND spacecraft data was also made. However, ignoring the influence of Langmuir fluctuations on the halo population turns out to be an unjustifiable assumption. The present paper rectifies the previous approach by including both Langmuir and whistler fluctuations in the construction of the steady-state velocity distribution function for the halo population, and demonstrates that the role of whistler-range fluctuation is minimal unless the fluctuation intensity is arbitrarily raised. This implies that the Langmuir-range fluctuations, known as the quasi thermal noise, are important for both halo and super-halo electron velocity distribution.
Effect of velocity and temperature distribution at the hole exit on film cooling of turbine blades
Garg, Vijay K.; Gaugler, Raymond E.
1995-01-01
An existing three-dimensional Navier-Stokes code, modified to include film cooling considerations, has been used to study the effect of coolant velocity and temperature distribution at the hole exit on the heat transfer coefficient on three-film-cooled turbine blades, namely, the C3X vane, the VKI rotor, and the ACE rotor. Results are also compared with the experimental data for all the blades. Moreover, Mayle's transition criterion, Forest's model for augmentation of leading edge heat transfer due to freestream turbulence, and Crawford's model for augmentation of eddy viscosity due to film cooling are used. Use of Mayle's and Forest's models is relevant only for the ACE rotor due to the absence of showerhead cooling on this rotor. It is found that, in some cases, the effect of distribution of coolant velocity and temperature at the hole exit can be as much as 60% on the heat transfer coefficient at the blade suction surface, and 50% at the pressure surface. Also, different effects are observed on the pressure and suction surface depending upon the blade as well as upon the hole shape, conical or cylindrical.
Non-Gaussian velocity distributions - the effect on virial mass estimates of galaxy groups
Ribeiro, A. L. B.; Lopes, P. A. A.; Trevisan, M.
2011-05-01
We present a study of nine galaxy groups with evidence for non-Gaussianity in their velocity distributions out to 4R200. This sample is taken from the 57 groups selected from the 2dF Percolation-Inferred Galaxy Groups (2PIGG) catalogue of galaxy groups. Statistical analysis indicates that the non-Gaussian groups have masses significantly higher than that of the Gaussian groups. We also have found that all non-Gaussian systems seem to be composed of multiple velocity modes. Besides, our results indicate that multimodal groups should be considered as a set of individual units with their own properties. In particular, we have found that the mass distributions of such units are similar to that of the Gaussian groups. Our results reinforce the idea of non-Gaussian systems as complex structures in the phase space, likely corresponding to secondary infall aggregations at a stage before virialization. The understanding of these objects is relevant for cosmological studies using groups and clusters through the mass function evolution.
Production of a double-humped ion velocity distribution function in a single-ended Q-machine
DEFF Research Database (Denmark)
Andersen, S.A.; Jensen, Vagn Orla; Michelsen, Poul
1970-01-01
An experimental method of producing a double-humped velocity distribution function for the ions in a Q-machine is described. The method is based on charge exchange processes between neutral ceasium and the ions in a ceasium plasma.......An experimental method of producing a double-humped velocity distribution function for the ions in a Q-machine is described. The method is based on charge exchange processes between neutral ceasium and the ions in a ceasium plasma....
S. D. Bergeson; Lyon, M
2016-01-01
We report measurements of the ion velocity distribution in an ultracold neutral plasma derived from a dense, cold Rydberg gas in a MOT. The Rydberg atoms are excited using a resonant two-step excitation pathway with lasers of 4 ns duration. The plasma forms spontaneously and rapidly. The rms width of the ion velocity distribution is determined by measuring laser-induced fluorescence (LIF) of the ions. The measured excitation efficiency is compared with a Monte-Carlo wavefunction calculation, ...
Božnic, D. K.; Nedeljkovic, N. N.
2010-07-01
We analyze the ionization dynamics of slow hydrogenlike Rydberg atoms (principal quantum number n >> 1 ) approaching solid surface in a weak electric field. The recently obtained etalon-equation method results for the simulation of experimental signal are used to investigate the influence of the initial velocity distribution. It is demonstrated that an agreement with the experimental signal can be obtained with the broadened velocity distributions.
Modelling the transverse distribution of velocity and suspended sediment in tidal estuaries
Huijts, K. M. H.
2011-01-01
An estuary is a semi-enclosed coastal body of water which has a free connection with the open sea and within which sea water is measurably diluted with fresh water derived from land drainage. Examples are the Western Scheldt River Estuary and the Chesapeake Bay. Within these environments complex patterns of velocity and suspended sediments are observed in the transversal plane (across-estuary and vertical), and sediments are trapped laterally (across-estuary). The transverse structure of velocity is relevant to the transport of salt, sediment, contaminants, oxygen and other material. High sediment concentrations affect water quality, ecology and wildlife, and may cause siltation of navigation channels and harbors. This work aims at a fundamental understanding of the transverse distributions of estuarine velocity and suspended sediment. The thesis provides two-dimensional (cross-sectional) analytical models to identify the effect of individual forcing mechanisms on the transverse distribution of velocity and suspended sediment in tidally-dominated estuaries. The models are based on the shallow water equations and sediment mass balance. Considered are the residual and the semi-diurnal tidal components of the along-estuary, across-estuary and vertical velocity and of the suspended sediment concentration. The models apply to partially to well-mixed tidal estuaries, relatively uniform along-channel conditions and weakly to moderately nonlinear flow. Horizontal density gradients are prescribed based on numerical or observational data. The analytical flows are decomposed into components induced by individual mechanisms. Considered are tides, horizontal residual density gradients, river discharge, stokes return flow, wind, the earth’s rotation, tidal variations in the across-channel density gradient and channel curvature. In addition, two tidally rectified along-channel residual flow mechanisms are considered, which result from net advection of along-channel tidal
Min, Kyungguk; Liu, Kaijun
2016-04-01
Fast magnetosonic waves in Earth's inner magnetosphere, which have as their source ion Bernstein instabilities, are driven by hot proton velocity distributions (fp) with ∂fp(v⊥)/∂v⊥>0. Two typical types of distributions with such features are ring and shell velocity distributions. Both have been used in studies of ion Bernstein instabilities and fast magnetosonic waves, but the differences between instabilities driven by the two types of distributions have not been thoroughly addressed. The present study uses linear kinetic theory to examine and understand these differences. It is found that the growth rate pattern is primarily determined by the cyclotron resonance condition and the structure of the velocity distribution in gyroaveraged velocity space. For ring-driven Bernstein instabilities, as the parallel wave number (k∥) increases, the discrete unstable modes approximately follow the corresponding proton cyclotron harmonic frequencies while they become broader in frequency space. At sufficiently large k∥, the neighboring discrete modes merge into a continuum. In contrast, for shell-driven Bernstein instabilities, the curved geometry of the shell velocity distribution in gyroaveraged velocity space results in a complex alternating pattern of growth and damping rates in frequency and wave number space and confines the unstable Bernstein modes to relatively small k∥. In addition, when k∥ increases, the unstable modes are no longer limited to the proton cyclotron harmonic frequencies. The local growth rate peak near an exact harmonic at small k∥ bifurcates into two local peaks on both sides of the harmonic when k∥ becomes large.
Information hidden in the velocity distribution of ions and the exact kinetic Bohm criterion
Tsankov, Tsanko V.; Czarnetzki, Uwe
2017-05-01
Non-equilibrium distribution functions of electrons and ions play an important role in plasma physics. A prominent example is the kinetic Bohm criterion. Since its first introduction it has been controversial for theoretical reasons and due to the lack of experimental data, in particular on the ion distribution function. Here we resolve the theoretical as well as the experimental difficulties by an exact solution of the kinetic Boltzmann equation including charge exchange collisions and ionization. This also allows for the first time non-invasive measurement of spatially resolved ion velocity distributions, absolute values of the ion and electron densities, temperatures, and mean energies as well as the electric field and the plasma potential in the entire plasma. The non-invasive access to the spatially resolved distribution functions of electrons and ions is applied to the problem of the kinetic Bohm criterion. Theoretically a so far missing term in the criterion is derived and shown to be of key importance. With the new term the validity of the kinetic criterion at high collisionality and its agreement with the fluid picture are restored. All findings are supported by experimental data, theory and a numerical model with excellent agreement throughout.
Dhanya, M. B.; Bhardwaj, Anil; Futaana, Yoshifumi; Barabash, Stas; Alok, Abhinaw; Wieser, Martin; Holmström, Mats; Wurz, Peter
2016-06-01
Due to the high absorption of solar wind plasma on the lunar dayside, a large scale wake structure is formed downstream of the Moon. However, recent in-situ observations have revealed the presence of protons in the near-lunar wake (100 km to 200 km from the surface). The solar wind, either directly or after interaction with the lunar surface (including magnetic anomalies), is the source of these protons in the near-wake region. Using the entire data from the SWIM sensor of the SARA experiment onboard Chandrayaan-1, we analyzed the velocity distribution of the protons observed in the near-lunar wake. The average velocity distribution functions, computed in the solar wind rest frame, were further separated based on the angle between the upstream solar wind velocity and the IMF. Although the protons enter the wake parallel as well as perpendicular to the IMF, the velocity distribution were not identical for the different IMF orientations, indicating the control of IMF in the proton entry processes. Several proton populations were identified from the velocity distribution and their possible entry mechanism were inferred based on the characteristics of the velocity distribution. These entry mechanisms include (i) diffusion of solar wind protons into the wake along IMF, (ii) the solar wind protons with finite gyro-radii that are aided by the wake boundary electric field, (iii) solar wind protons with gyro-radii larger than lunar radii from the tail of the solar wind velocity distribution, and (iv) scattering of solar wind protons from the dayside lunar surface or from magnetic anomalies. In order to gain more insight into the entry mechanisms associated with different populations, backtracing is carried out for each of these populations. For most of the populations, the source of the protons obtained from backtracing is found to be in agreement with that inferred from the velocity distribution. There are few populations that could not be explained by the known mechanisms
National Oceanic and Atmospheric Administration, Department of Commerce — Wind direction/velocity and current direction/velocity data were collected using current meter casts in a world wide distribution from December 6, 1970 to October...
Directory of Open Access Journals (Sweden)
O. Jakubov
2013-09-01
Full Text Available Common techniques for position-velocity-time estimation in satellite navigation, iterative least squares and the extended Kalman filter, involve matrix operations. The matrix inversion and inclusion of a matrix library pose requirements on a computational power and operating platform of the navigation processor. In this paper, we introduce a novel distributed algorithm suitable for implementation in simple parallel processing units each for a tracked satellite. Such a unit performs only scalar sum, subtraction, multiplication, and division. The algorithm can be efficiently implemented in hardware logic. Given the fast position-velocity-time estimator, frequent estimates can foster dynamic performance of a vector tracking receiver. The algorithm has been designed from a factor graph representing the extended Kalman filter by splitting vector nodes into scalar ones resulting in a cyclic graph with few iterations needed. Monte Carlo simulations have been conducted to investigate convergence and accuracy. Simulation case studies for a vector tracking architecture and experimental measurements with a real-time software receiver developed at CTU in Prague were conducted. The algorithm offers compromises in stability, accuracy, and complexity depending on the number of iterations. In scenarios with a large number of tracked satellites, it can outperform the traditional methods at low complexity.
Kr II and Xe II axial velocity distribution functions in a cross-field ion source
Lejeune, A.; Bourgeois, G.; Mazouffre, S.
2012-07-01
Laser induced fluorescence measurements were carried out in a cross-field ion source to examine the behaviour of the axial ion velocity distribution functions (VDFs) in the expanding plasma. In the present paper, we focus on the axial VDFs of Kr II and Xe II ions. We examine the contourplots in a 1D-phase space (x,vx) representation in front of the exhaust channel and along the centerline of the ion source. The main ion beam, whose momentum corresponds to the ions that are accelerated through the whole potential drop, is observed. A secondary structure reveals the ions coming from the opposite side of the channel. We show that the formation of the neutralized ion flow is governed by the annular geometry. The assumption of a collisionless shock or a double layer due to supersonic beam interaction is not necessary. A non-negligible fraction of slow ions originates in local ionization or charge-exchange collision events between ions of the expanding plasma and atoms of the background residual gas. Slow ions that are produced near the centerline in the vicinity of the exit plane are accelerated toward the source body with a negative velocity leading to a high sputtering of front face. On the contrary, the ions that are produced in the vicinity of the channel exit plane are partially accelerated by the extended electric field.
Taut, Andreas; Wimmer-Schweingruber, Robert; Berger, Lars; Drews, Christian
2016-07-01
Interstellar pickup ions in the heliosphere exhibit a characteristic suprathermal Velocity Distribution Function (VDF). This is the result of their injection into the solar wind as a highly anisotropic torus distribution which is continuously modulated by pitch-angle scattering and cooling processes. As the impact of these processes on the pickup ion VDF depends on present and past solar wind conditions, the pickup ion VDF is not static but variable in shape and intensity. Using the good counting statistics of the Charge-Time-Of-Flight sensor onboard SOHO we were able to resolve a systematic variability of the He^+ VDF. On the one hand the intensity of freshly created pickup ions near the injection speed increases during magnetic field configurations in which the initial torus distribution lies inside the sensor's aperture. This complements our studies showing a persisting anisotropy of the He^+ VDF and introduces a limit for the efficiency of pitch-angle scattering. On the other hand we observe anomalous shapes of the He^+ VDF in the vicinity of stream interaction regions, where the VDF tends to be shifted towards higher speeds. These observations may be explained by a modified cooling behaviour in these regions. Furthermore we observe an enhancement of ions above the injection speed that were likely accelerated in compression regions. Here, we present our observations and discuss the implications on the processes named above.
Lao, Hai-Ling; Lacey, Roy A
2016-01-01
We analyze the transverse momentum ($p_T$) spectra of identified particles ($\\pi^{\\pm}$, $K^{\\pm}$, $p$, and $\\bar p$) produced in gold-gold (Au-Au) and lead-lead (Pb-Pb) collisions over a $\\sqrt{s_{NN}}$ (center-of-mass energy per nucleon pair) range from 14.5 GeV [one of the Relativistic Heavy Ion Collider (RHIC) energies] to 2.76 TeV [one of the Large Hadron Collider (LHC) energies]. For the spectra with a narrow $p_T$ range, an improved Tsallis distribution which is in fact the Tsallis distribution with radial flow is used. For the spectra with a wide $p_T$ range, a superposition of the improved Tsallis distribution and an inverse power-law is used. Both the extracted kinetic freeze-out temperature ($T_0$) and radial flow velocity ($\\beta_T$) increase with the increase of $\\sqrt{s_{NN}}$, which indicate a higher excitation and larger expansion of the interesting system at the LHC. Both the values of $T_0$ and $\\beta_T$ in central collisions are slightly larger than those in peripheral collisions, and they...
The complex velocity distribution of galaxies in Abell 1689: implications for CDM mass modelling
Lokas, E L; Wojtak, R; Moles, M; Gottlöber, S; Lokas, Ewa L.; Prada, Francisco; Wojtak, Radoslaw; Moles, Mariano; Gottloeber, Stefan
2006-01-01
The Abell 1689 galaxy cluster has recently become a subject of intensive study. Thanks to its intermediate redshift (z=0.183) its mass distribution can be reconstructed using numerous methods including gravitational lensing, galaxy kinematics and X-ray imaging. The methods used to yield conflicting mass estimates in the past and recently the cluster mass distribution has been claimed to be in conflict with standard CDM scenarios due to rather large concentration and steep mass profile obtained from detailed studies of Broadhurst et al. using lensing. By studying in detail the kinematics of about 200 galaxies with measured redshifts in the vicinity of the cluster we show that the cluster is probably surrounded by a few structures, quite distant from each other, but aligned along the line of sight. We support our arguments by referring to cosmological N-body simulations and showing explicitly that distant, non-interacting haloes can produce entangled multi-peak line-of-sight velocity distributions similar to th...
Energy Technology Data Exchange (ETDEWEB)
Gupta, D.; Gota, H.; Hayashi, R.; Kiyashko, V.; Morehouse, M.; Primavera, S. [Tri Alpha Energy, Inc., Rancho Santa Margarita, California 92688 (United States); Bolte, N. [Tri Alpha Energy, Inc., Rancho Santa Margarita, California 92688 (United States); Department of Physics and Astronomy, University of California, Irvine, California 92697 (United States); Marsili, P. [Department of Physics, University of Pisa, Largo B. Pontecorvo 3, 56127 Pisa (Italy); Roche, T. [Department of Physics and Astronomy, University of California, Irvine, California 92697 (United States); Wessel, F. [Department of Physics and Astronomy, University of California, Irvine, California 92697 (United States); Tri Alpha Energy, Inc., Rancho Santa Margarita, California 92688 (United States)
2010-10-15
One aim of the flux-coil generated field reversed configuration at Tri Alpha Energy (TAE) is to establish the plasma where the ion rotational energy is greater than the ion thermal energy. To verify this, an optical diagnostic was developed to simultaneously measure the Doppler velocity-shift and line-broadening using a 0.75 m, 1800 groves/mm, spectrometer. The output spectrum is magnified and imaged onto a 16-channel photomultiplier tube (PMT) array. The individual PMT outputs are coupled to high-gain, high-frequency, transimpedance amplifiers, providing fast-time response. The Doppler spectroscopy measurements, along with a survey spectrometer and photodiode-light detector, form a suite of diagnostics that provide insights into the time evolution of the plasma-ion distribution and current when accelerated by an azimuthal-electric field.
Particle Paths of Lagrangian Velocity Distribution Simulating the Spiral Arms of Galaxy M51
Institute of Scientific and Technical Information of China (English)
Tzu-Fang Chen; Georgios H. Vatistas; Sui Lin
2008-01-01
Galaxies are huge families of stars held together by their own gravities. The system M51 is a spiral galaxy. It possesses billions of stars. The range of the spiral arms extends hundred thousand light years. The present study is in an attempt in using the particle paths of the Lagrangian flow field to simulate the spiral arms of Galaxy M51.The Lagrangian flow field is introduced. The initial locations of fluid particles in the space between two concentric cylinders are first specified. Then a linear velocity distribution of the fluid particles is used with different angle rotations of the particles to obtain the particle paths in the Lagrangian diagram. For simulating the spiral arms of Galaxy M51, the Lagrangian M51 diagram is developed. The particle paths of the Lagrangian M51 diagram agree quite well with the spiral arms of Galaxy M51.
Velocity distribution of carbon and oxygen atoms in front of a tokamak limiter
Bogen, P.; Rusbüldt, D.
1992-12-01
From the Doppler-broadened emission profiles of a CI line ( 3P 2→ 3P 20, λ=909.5 nm) and of an OI line ( 3P 2,1,0→ 3S 10, λ=844.6 nm), the velocity distribution of carbon and oxygen atoms in front of a graphite limiter has been deduced. For the π-component of the CI line, the Zeeman splitting is negligible, but for the π-components of the OI line, the Paschen-Back effect has to be taken into account. The contribution of chemical and physical sputtering to the release of impurities under various experimental conditions has been investigated at the tip of the limiter. For C atoms, chemical sputtering dominates at low boundary temperatures, and physical sputtering at high temperature. For oxygen, chemical sputtering is always indicated to be the more efficient process.
Gupta, D; Bolte, N; Gota, H; Hayashi, R; Kiyashko, V; Marsili, P; Morehouse, M; Primavera, S; Roche, T; Wessel, F
2010-10-01
One aim of the flux-coil generated field reversed configuration at Tri Alpha Energy (TAE) is to establish the plasma where the ion rotational energy is greater than the ion thermal energy. To verify this, an optical diagnostic was developed to simultaneously measure the Doppler velocity-shift and line-broadening using a 0.75 m, 1800 groves/mm, spectrometer. The output spectrum is magnified and imaged onto a 16-channel photomultiplier tube (PMT) array. The individual PMT outputs are coupled to high-gain, high-frequency, transimpedance amplifiers, providing fast-time response. The Doppler spectroscopy measurements, along with a survey spectrometer and photodiode-light detector, form a suite of diagnostics that provide insights into the time evolution of the plasma-ion distribution and current when accelerated by an azimuthal-electric field.
Han, Zheng; Chen, Guangqi; Li, Yange; Wang, Wei; Zhang, Hong
2015-07-01
The estimation of debris-flow velocity in a cross-section is of primary importance due to its correlation to impact force, run up and superelevation. However, previous methods sometimes neglect the observed asymmetric velocity distribution, and consequently underestimate the debris-flow velocity. This paper presents a new approach for exploring the debris-flow velocity distribution in a cross-section. The presented approach uses an iteration algorithm based on the Riemann integral method to search an approximate solution to the unknown flow surface. The established laws for vertical velocity profile are compared and subsequently integrated to analyze the velocity distribution in the cross-section. The major benefit of the presented approach is that natural channels typically with irregular beds and superelevations can be taken into account, and the resulting approximation by the approach well replicates the direct integral solution. The approach is programmed in MATLAB environment, and the code is open to the public. A well-documented debris-flow event in Sichuan Province, China, is used to demonstrate the presented approach. Results show that the solutions of the flow surface and the mean velocity well reproduce the investigated results. Discussion regarding the model sensitivity and the source of errors concludes the paper.
Wu, XueHong; Chang, ZhiJuan; Ma, QiuYang; Lu, YanLi; Yin, XueMei
2016-08-01
This paper focuses on improving the performance of the vertical open refrigerated display cabinets (VORDC) by optimizing the structure of deflector, which is affected by inlet velocity and velocity distribution of air curtains. The results show that the temperature of products located at the front and at the rear reduces as the increases of inlet velocity of air curtains. The increase of the inlet velocity of air curtains can strengthen the disturbance inside the VORDC, and also decrease the temperature of products inside the VORDC; the increase of the outer velocity of air curtain will exacerbate the disturbance outside the VORDC and decrease air curtain's performance. The present study can provide a theoretical foundation for the design of VORDC.
Sonin, V.; Ustimenko, A.; Kuibin, P.; Litvinov, I.; Shtork, S.
2016-11-01
One of the mechanisms of generation of powerful pressure pulsations in the circuit of the turbine is a precessing vortex core, formed behind the runner at the operation points with partial or forced loads, when the flow has significant residual swirl. To study periodic pressure pulsations behind the runner the authors of this paper use approaches of experimental modeling and methods of computational fluid dynamics. The influence of velocity distributions at the output of the hydro turbine runner on pressure pulsations was studied based on analysis of the existing and possible velocity distributions in hydraulic turbines and selection of the distribution in the extended range. Preliminary numerical calculations have showed that the velocity distribution can be modeled without reproduction of the entire geometry of the circuit, using a combination of two blade cascades of the rotor and stator. Experimental verification of numerical results was carried out in an air bench, using the method of 3D-printing for fabrication of the blade cascades and the geometry of the draft tube of hydraulic turbine. Measurements of the velocity field at the input to a draft tube cone and registration of pressure pulsations due to precessing vortex core have allowed building correlations between the velocity distribution character and the amplitude-frequency characteristics of the pulsations.
Xie, Ji-Wei
2016-01-01
Many multiple-planet systems have been found by the Kepler transit survey and various radial velocity (RV) surveys. Kepler planets show an asymmetric feature, namely, there are small but significant deficits/excesses of planet pairs with orbital period spacing slightly narrow/wide of the exact resonance, particularly near the first order mean motion resonance (MMR), such as 2:1 and 3:2 MMR. Similarly, if not exactly the same, an asymmetric feature (pileup wide of 2:1 MMR) is also seen in RV planets, but only for massive ones. We analytically and numerically study planets' orbital evolutions near and in the MMR. We find that their orbital period ratios could be asymmetrically distributed around the MMR center regardless of dissipation. In the case of no dissipation, Kepler planets' asymmetric orbital distribution could be partly reproduced for 3:2 MMR but not for 2:1 MMR, implying that dissipation might be more important to the latter. The pileup of massive RV planets just wide of 2:1 MMR is found to be consis...
Steffen, Jason H.
2016-04-01
Motivated by recent discussions, both in private and in the literature, we use a Monte Carlo simulation of planetary systems to investigate sources of bias in determining the mass-radius distribution of exoplanets for the two primary techniques used to measure planetary masses - radial velocities (RVs) and transit timing variations (TTVs). We assert that mass measurements derived from these two methods are comparably reliable - as the physics underlying their respective signals is well understood. Nevertheless, their sensitivity to planet mass varies with the properties of the planets themselves. We find that for a given planet size, the RV method tends to find planets with higher mass while the sensitivity of TTVs is more uniform. This `sensitivity bias' implies that a complete census of TTV systems is likely to yield a more robust estimate of the mass-radius distribution provided there are not important physical differences between planets near and far from mean-motion resonance. We discuss differences in the sensitivity of the two methods with orbital period and system architecture, which may compound the discrepancies between them (e.g. short-period planets detectable by RVs may be more dense due to atmospheric loss). We advocate for continued mass measurements using both approaches as a means both to measure the masses of more planets and to identify potential differences in planet structure that may result from their dynamical and environmental histories.
Hosokawa, Iwao
2007-01-01
A decaying homogeneous isotropic turbulence is treated on the combined bases of the Kolmogorov hypothesis and the cross-independence hypothesis (for a closure of the Monin-Lundgren (ML) hierarchy of many-point velocity distributions) in turbulence. Similarity solutions for one- and two-point velocity distributions are obtained in the viscous, inertial and large-scale ranges of separation distance, from which we can give a reasonable picture of longitudinal and transverse velocity autocorrelation functions for any Reynolds number, even though they are distant from exact solutions of the infinite ML hierarchy. Possibility of non-similarity solutions with other reasonable and more realistic features is unveiled within the same theoretical framework. The cross-independence hypothesis is proved to be inconsistent with the Kolmogorov [1941b. Dissipation of energy in locally isotropic turbulence. Dokl. Akad. Nauk SSSR 32, 16-18.] theory in the inertial range. This is the main factor by which our special strategy (described in Introduction) is taken for solving this problem.
Predicted Impacts of Proton Temperature Anisotropy on Solar Wind Turbulence
Klein, Kristopher G; Howes, Gregory G.
2015-01-01
Particle velocity distributions measured in the weakly collisional solar wind are frequently found to be non-Maxwellian, but how these non-Maxwellian distributions impact the physics of plasma turbulence in the solar wind remains unanswered. Using numerical solutions of the linear dispersion relation for a collisionless plasma with a bi-Maxwellian proton velocity distribution, we present a unified framework for the four proton temperature anisotropy instabilities, identifying the associated s...
Meng, Yiqing; Lucas, Gary P.
2017-05-01
This paper presents the design and implementation of an inductive flow tomography (IFT) system, employing a multi-electrode electromagnetic flow meter (EMFM) and novel reconstruction techniques, for measuring the local water velocity distribution in water continuous single and multiphase flows. A series of experiments were carried out in vertical-upward and upward-inclined single phase water flows and ‘water continuous’ gas-water and oil-gas-water flows in which the velocity profiles ranged from axisymmetric (single phase and vertical-upward multiphase flows) to highly asymmetric (upward-inclined multiphase flows). Using potential difference measurements obtained from the electrode array of the EMFM, local axial velocity distributions of the continuous water phase were reconstructed using two different IFT reconstruction algorithms denoted RT#1, which assumes that the overall water velocity profile comprises the sum of a series of polynomial velocity components, and RT#2, which is similar to RT#1 but which assumes that the zero’th order velocity component may be replaced by an axisymmetric ‘power law’ velocity distribution. During each experiment, measurement of the local water volume fraction distribution was also made using the well-established technique of electrical resistance tomography (ERT). By integrating the product of the local axial water velocity and the local water volume fraction in the cross section an estimate of the water volumetric flow rate was made which was compared with a reference measurement of the water volumetric flow rate. In vertical upward flows RT#2 was found to give rise to water velocity profiles which are consistent with the previous literature although the profiles obtained in the multiphase flows had relatively higher central velocity peaks than was observed for the single phase profiles. This observation was almost certainly a result of the transfer of axial momentum from the less dense dispersed phases to the water
Taut, A.; Drews, C.; Berger, L.; Wimmer-Schweingruber, R. F.
2015-12-01
The 1D Velocity Distribution Function (VDF) of He+ pickup ions shows two distinct populations that reflect the sources of these ions. The highly suprathermal population is the result of the ionization and pickup of almost resting interstellar neutrals that are injected into the solar wind as a highly anisotropic torus distribution. The nearly thermalized population is centered around the solar wind bulk speed and is mainly attributed to inner-source pickup ions that originate in the inner heliosphere. It is generally believed that the initial torus distribution of interstellar pickup ions is rapidly isotropized by resonant wave-particle interactions, but recent observations by Drews et al. (2015) of a torus-like VDF strongly limit this isotropization. This in turn means that more observational data is needed to further characterize the kinetic behavior of pickup ions. In this study we use data from the Charge-Time-Of-Flight sensor on-board SOHO. As this sensor offers unrivaled counting statistics for He+ together with a sufficient mass-per-charge resolution it is well-suited for investigating the He+ VDF on comparatively short timescales. We combine this data with the high resolution magnetic field data from WIND via an extrapolation to the location of SOHO. With this combination of instruments we investigate the He+ VDF for time periods of different solar wind speeds, magnetic field directions, and wave power. We find a systematic trend of the short-term He+ VDF with these parameters. Especially by varying the considered magnetic field directions we observe a 1D projection of the anisotropic torus-like VDF. In addition, we investigate stream interaction regions and coronal mass ejections. In the latter we observe an excess of inner-source He+ that is accompanied by a significant increase of heavy pickup ion count rates. This may be linked to the as yet ill understood production mechanism of inner-source pickup ions.
Kuznetsov, A V
2013-01-01
A model describing the propagation of positive injury signals from the lesion site in an axon towards the neuron soma is described. It is assumed that these signals are driven by dynein molecular motors. An analytical solution that accounts for the probability density function (pdf) of a dynein velocity distribution is obtained. Two examples of pdf of dynein velocity distributions that follow from the results published in Ross et al. (2006, Processive bidirectional motion of dynein-dynactin complexes in vitro. Nat Cell Biol. 8:562-570) and Deinhardt et al. (2006, Rab5 and Rab7 control endocytic sorting along the axonal retrograde transport pathway. Neuron 52:293-305) are considered. The effect of dynein velocity distribution on the rate of spreading of the signal wave is discussed. It is demonstrated that the obtained solution can be applied to the problem of how neurons measure the distance between the lesion site and the neuron soma.
Dhanya, M B; Futaana, Yoshifumi; Barabash, Stas; Alok, Abhinaw; Wieser, Martin; Holmström, Mats; Wurz, Peter
2016-01-01
Due to the high absorption of solar wind plasma on the lunar dayside, a large scale wake structure is formed downstream of the Moon. However, recent in-situ observations have revealed the presence of protons in the near-lunar wake (100 km to 200 km from the surface). The solar wind, either directly or after interaction with the lunar surface (including magnetic anomalies), is the source of these protons in the near-wake region. Using the entire data from the SWIM sensor of the SARA experiment onboard Chandrayaan-1, we analysed the velocity distribution of the protons observed in the near-lunar wake. The average velocity distribution functions, computed in the solar wind rest frame, were further separated based on the angle between the upstream solar wind velocity and the IMF. Several proton populations were identified from the velocity distribution and their possible entry mechanism were inferred based on the characteristics of the velocity distribution. These entry mechanisms include (i) diffusion of solar w...
Energy Technology Data Exchange (ETDEWEB)
Clark, G
2003-04-28
This report describes a feasibility study. We are interested in calculating the angular and linear velocities of a re-entry vehicle using six acceleration signals from a distributed accelerometer inertial measurement unit (DAIMU). Earlier work showed that angular and linear velocity calculation using classic nonlinear ordinary differential equation (ODE) solvers is not practically feasible, due to mathematical and numerical difficulties. This report demonstrates the theoretical feasibility of using model-based nonlinear state estimation techniques to obtain the angular and linear velocities in this problem. Practical numerical and calibration issues require additional work to resolve. We show that the six accelerometers in the DAIMU are not sufficient to provide observability, so additional measurements of the system states are required (e.g. from a Global Positioning System (GPS) unit). Given the constraint that our system cannot use GPS, we propose using the existing on-board 3-axis magnetometer to measure angular velocity. We further show that the six nonlinear ODE's for the vehicle kinematics can be decoupled into three ODE's in the angular velocity and three ODE's in the linear velocity. This allows us to formulate a three-state Gauss-Markov system model for the angular velocities, using the magnetometer signals in the measurement model. This re-formulated model is observable, allowing us to build an Extended Kalman Filter (EKF) for estimating the angular velocities. Given the angular velocity estimates from the EKF, the three ODE's for the linear velocity become algebraic, and the linear velocity can be calculated by numerical integration. Thus, we do not need direct measurements of the linear velocity to provide observability, and the technique is mathematically feasible. Using a simulation example, we show that the estimator adds value over the numerical ODE solver in the presence of measurement noise. Calculating the velocities in the
Johnson, Christian I; Kobayashi, Chiaki; Kunder, Andrea; Pilachowski, Catherine A; Koch, Andreas; De Propris, Roberto
2013-01-01
We present radial velocities and chemical abundance ratios of [Fe/H], [O/Fe], [Si/Fe], and [Ca/Fe] for 264 red giant branch (RGB) stars in three Galactic bulge off-axis fields located near (l,b)=(-5.5,-7), (-4,-9), and (+8.5,+9). The results are based on equivalent width and spectrum synthesis analyses of moderate resolution (R~18,000), high signal-to-noise ratio (S/N~75-300) spectra obtained with the Hydra spectrographs on the Blanco 4m and WIYN 3.5m telescopes. The targets were selected from the blue side of the giant branch to avoid cool stars that would be strongly affected by CN and TiO; however, a comparison of the color-metallicity distribution in literature samples suggests our selection of bluer targets should not present a significant bias against metal-rich stars. We find a full range in metallicity that spans [Fe/H]\\approx-1.5 to +0.5, and that, in accordance with the previously observed minor-axis vertical metallicity gradient, the median [Fe/H] also declines with increasing Galactic latitude in ...
Temporal Evolution of Ion Velocity Distribution Function in a Pulsed Helicon Source
Hardin, Robert; Biloiu, Costel; Compton, Chris; Keesee, Amy; Scime, Earl; Heard, John
2004-11-01
We report measurements of the time resolved ion velocity distribution function (ivdf) in a pulsed helicon plasma source using laser induced fluorescence (LIF). Our LIF laser system consists of a 6 W Coherent Innova 300 argon-ion laser that pumps a Coherent 899 tunable ring dye laser tuned to 611.49 nm. The 611.49 nm (air wavelength) photons pump the Ar II 3d^2G_9/2 metastable state to the 4p^2F_7/2 state that decays to the 4s^2D_5/2 state by emitting 460.96 nm photons. The helicon plasma source is pulsed on for 100 ms with a 50% duty cycle. The background emission was subtracted from the fluorescent emission in two different ways: either the laser was mechanically chopped at with a frequency much longer than the rf pulse and lock in amplification employed or multiple acquisitions (typically 50) of pulsed emission with both the laser on and off were obtained. For most plasma conditions, both the parallel and perpendicular ivdf reach equilibrium by 5 ms into the rf pulse. Time dependent measurements of the ivdf will be presented for a range of rf powers, magnetic field strengths, and neutral pressures.
Energy Technology Data Exchange (ETDEWEB)
Cunge, G., E-mail: gilles.cunge@cea.fr; Darnon, M.; Dubois, J.; Bezard, P.; Mourey, O.; Petit-Etienne, C.; Vallier, L.; Despiau-Pujo, E.; Sadeghi, N. [Laboratoire des Technologies de la Microélectronique, CNRS, 17 rue des Martyrs, 38054 Grenoble (France)
2016-02-29
Several issues associated with plasma etching of high aspect ratio structures originate from the ions' bombardment of the sidewalls of the feature. The off normal angle incident ions are primarily due to their temperature at the sheath edge and possibly to charging effects. We have measured the ion velocity distribution function (IVDF) at the wafer surface in an industrial inductively coupled plasma reactor by using multigrid retarding field analyzers (RFA) in front of which we place 400 μm thick capillary plates with holes of 25, 50, and 100 μm diameters. The RFA then probes IVDF at the exit of the holes with Aspect Ratios (AR) of 16, 8, and 4, respectively. The results show that the ion flux dramatically drops with the increase in AR. By comparing the measured IVDF with an analytical model, we concluded that the ion temperature is 0.27 eV in our plasma conditions. The charging effects are also observed and are shown to significantly reduce the ion energy at the bottom of the feature but only with a “minor” effect on the ion flux and the shape of the IVDF.
High-resolution observations of the spatial and velocity distribution of cometary hydrogen
Brown, Michael E.; Spinrad, Hyron
1992-01-01
We have obtained high velocity and spatial resolution long-slit H alpha spectra of comets Austin (1989c1) and Levy (1990c). Spectra of both comets clearly show the existence of a low velocity thermalized component of hydrogen gas. The amount of slow hydrogen is estimated for comet Austin. The Levy spectrum shows an unusual high-velocity spatially-confined blob of hydrogen emission of unknown origin.
Velocity and suspended solids distributions in an oval-shaped channel with a side bank
Larrarte, Frédérique
2015-01-01
This study focuses on field measurements of both the velocity and total suspended solids within a combined sewer through use of a two-dimensional sampler called Hydre. The paper begins by presenting this instrument and its experimental applications. The discussion centers on the recorded velocities and concentrations; moreover, analyses of results demonstrate the ability of this Hydre device to provide robust suspended solids and velocity profiles in sewers for a range of flow conditions.
Mamon, Gary A; Murante, Giuseppe
2010-01-01
When clusters of galaxies are viewed in projection, one cannot avoid picking up foreground/background interlopers, that lie within the virial cone (VC), but outside the virial sphere. Structural and kinematic deprojection equations are not known for an expanding Universe, where the Hubble flow (HF) stretches the line-of-sight distribution of velocities. We analyze 93 mock relaxed clusters, built from a cosmological simulation. The stacked mock cluster is well fit by an m=5 Einasto DM density profile, with velocity anisotropy (VA) close to the Mamon-Lokas model with anisotropy radius equal to that of density slope -2. The surface density of interlopers is nearly flat out to the virial radius, while their velocity distribution shows a dominant gaussian cluster-outskirts component and a flat field component. This distribution of interlopers in PPS is nearly universal in mass. A local kappa=2.7 sigma velocity cut returns the line-of-sight velocity dispersion profile (LOSVDP) expected from the NFW density and VA p...
Rehme, K.
1987-03-01
The velocity, turbulence, and temperature distributions in nuclear fuel element bundles of nuclear reactors were investigated. The mean velocity, the wall shear stresses, and the turbulence were measured in two wall subchannels of a rod bundle of four parallel rods, arranged in a rectangular channel, for three axial planes. A spacer grid was inserted in the rod bundle, for ratios between the distance spacer grid/measuring plane and the hydraulic diameter (LIDh) of 40.4, 32.8 and 16.9. The Reynolds number was 145,000. The results show that the distributions of the velocity and the turbulence are affected by the spacer grid, already for LIDh = 40.4. The effects of the spacer grid increase with decreasing distance to the spacer grid.
Determination and shaping of the ion-velocity distribution function in a single-ended Q machine
DEFF Research Database (Denmark)
Andersen, S.A.; Jensen, Vagn Orla; Michelsen, Poul
1971-01-01
An electrostatic energy analyzer with a resolution better than 0.03 eV was constructed. This analyzer was used to determine the ion-velocity distribution function at different densities and plate temperatures in a single-ended Q machine. In all regions good agreement with theoretical predictions......% in single-ended Q machines...
DEFF Research Database (Denmark)
Jacobsen, T.V.; Nielsen, Peter V.
Measurements are performed in a full-scale test room with displacement ventilation with focus on the velocity and temperature field in the region close to the inlet device. Investigations based on these detailed measurements have been made in order to see if it is possible to describe the velocity...
Furbish, David J.; Schmeeckle, Mark; Schumer, Rina; Fathel, Siobhan L.
2016-01-01
We describe the most likely forms of the probability distributions of bed load particle velocities, accelerations, hop distances, and travel times, in a manner that formally appeals to inferential statistics while honoring mechanical and kinematic constraints imposed by equilibrium transport conditions. The analysis is based on E. Jaynes's elaboration of the implications of the similarity between the Gibbs entropy in statistical mechanics and the Shannon entropy in information theory. By maximizing the information entropy of a distribution subject to known constraints on its moments, our choice of the form of the distribution is unbiased. The analysis suggests that particle velocities and travel times are exponentially distributed and that particle accelerations follow a Laplace distribution with zero mean. Particle hop distances, viewed alone, ought to be distributed exponentially. However, the covariance between hop distances and travel times precludes this result. Instead, the covariance structure suggests that hop distances follow a Weibull distribution. These distributions are consistent with high-resolution measurements obtained from high-speed imaging of bed load particle motions. The analysis brings us closer to choosing distributions based on our mechanical insight.
Energy Technology Data Exchange (ETDEWEB)
Lee, Jounghun [Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul 151-747 (Korea, Republic of); Choi, Yun-Young, E-mail: jounghun@astro.snu.ac.kr, E-mail: yy.choi@khu.ac.kr [Department of Astronomy and Space Science, Kyung Hee University, Gyeonggi 446-701 (Korea, Republic of)
2015-02-01
We report a detection of the effect of the large-scale velocity shear on the spatial distributions of the galactic satellites around the isolated hosts. Identifying the isolated galactic systems, each of which consists of a single host galaxy and its satellites, from the Seventh Data Release of the Sloan Digital Sky Survey and reconstructing linearly the velocity shear field in the local universe, we measure the alignments between the relative positions of the satellites from their isolated hosts and the principal axes of the local velocity shear tensors projected onto the plane of sky. We find a clear signal that the galactic satellites in isolated systems are located preferentially along the directions of the minor principal axes of the large-scale velocity shear field. Those galactic satellites that are spirals, are brighter, are located at distances larger than the projected virial radii of the hosts, and belong to the spiral hosts yield stronger alignment signals, which implies that the alignment strength depends on the formation and accretion epochs of the galactic satellites. It is also shown that the alignment strength is quite insensitive to the cosmic web environment, as well as the size and luminosity of the isolated hosts. Although this result is consistent with the numerical finding of Libeskind et al. based on an N-body experiment, owing to the very low significance of the observed signals, it remains inconclusive whether or not the velocity shear effect on the satellite distribution is truly universal.
Prediction of Fluid Velocity Distribution near a Rising Bubble%上升气泡附近液体速度分布的预测
Institute of Scientific and Technical Information of China (English)
成弘; 周明
2002-01-01
A model is presented for predicting the fluid velocity distribution around a rising bubble which startsfrom rest on a distillation column tray by considering the unsteady fluid flow based on the method of streamfunction. Experimental measurement of the velocity distribution by using whole field digitized PIV (particle imagevelocimetry) method is briefly described. The velocity distribution predicted by the present model is in betteragreement with the measurements than the others models published in literature.
Late Quaternary climate-change velocity: Implications for modern distributions and communities
DEFF Research Database (Denmark)
Sandel, Brody Steven; Dalsgaard, Bo; Arge, Lars Allan;
Background/Question/Methods Climate-change velocity is a measure of the rate of climate change that incorporates small-scale climate variation such as that found along topographic gradients. As a measure of climate instability, it has several advantages, including describing the minimum migration...... and communities, typically more so than traditionally used climate anomalies. Some key results include apparent extinctions of small-ranged and weakly-dispersing species from high-velocity regions, more specialized mutualistic networks in low-velocity regions and an increased importance of stability where current...
Gayen, Bishakhdatta; Alam, Meheboob
2011-08-01
From particle simulations of a sheared frictional granular gas, we show that the Coulomb friction can have dramatic effects on orientational correlation as well as on both the translational and angular velocity distribution functions even in the Boltzmann (dilute) limit. The dependence of orientational correlation on friction coefficient (μ) is found to be nonmonotonic, and the Coulomb friction plays a dual role of enhancing or diminishing the orientational correlation, depending on the value of the tangential restitution coefficient (which characterizes the roughness of particles). From the sticking limit (i.e., with no sliding contact) of rough particles, decreasing the Coulomb friction is found to reduce the density and spatial velocity correlations which, together with diminished orientational correlation for small enough μ, are responsible for the transition from non-gaussian to gaussian distribution functions in the double limit of small friction (μ→0) and nearly elastic particles (e→1). This double limit in fact corresponds to perfectly smooth particles, and hence the maxwellian (gaussian) is indeed a solution of the Boltzmann equation for a frictional granular gas in the limit of elastic collisions and zero Coulomb friction at any roughness. The high-velocity tails of both distribution functions seem to follow stretched exponentials even in the presence of Coulomb friction, and the related velocity exponents deviate strongly from a gaussian with increasing friction.
Ancellet, Gerard M.; Menzies, Robert T.; Grant, William B.
1989-01-01
A pulsed CO2 lidar with coherent detection has been used to measure the correlation time of backscatter from an ensemble of atmospheric aerosol particles which are illuminated by the pulsed radiation. The correlation time of the backscatter of the return signal, which is directly related to the velocity spectral width, can be used to study the velocity structure constant of atmospheric turbulence and wind shear. Various techniques for correlation time measurement are discussed, and several measurement results are presented for the technique using the information contained in the statistical distribution of a set of lidar return signal intensities.
Estimation of the Radial Distribution of the Tangential Velocity in a Vortex Chamber
Institute of Scientific and Technical Information of China (English)
Akira OGAWA; Tsuyoshi IKARI; Hiroyuki MURAKAMI; Kouhei SATHO
2009-01-01
The estimation of maximum tangential velocity becomes a very important factor for the estimation of performances of the vortex chamber. In this paper, a proposed flow model of how to estimate the maximum tangential velocity in the special form of the vortex chamber is described in detail. The pressure drop basing upon the rapid expansion by flowing from the inlet pipe into the cyclone body is estimated as half of the dynamic pressure in the inlet pipe.
Gartrell, L. R.; Rhodes, D. B.
1980-01-01
A rapid scanning two dimensional laser velocimeter (LV) has been used to measure simultaneously the vortex vertical and axial velocity distributions in the Langley Vortex Research Facility. This system utilized a two dimensional Bragg cell for removing flow direction ambiguity by translating the optical frequency for each velocity component, which was separated by band-pass filters. A rotational scan mechanism provided an incremental rapid scan to compensate for the large displacement of the vortex with time. The data were processed with a digital counter and an on-line minicomputer. Vaporized kerosene (0.5 micron to 5 micron particle sizes) was used for flow visualization and LV scattering centers. The overall measured mean-velocity uncertainity is less than 2 percent. These measurements were obtained from ensemble averaging of individual realizations.
Energy Technology Data Exchange (ETDEWEB)
Wittig, C.
1987-01-01
We developed a method of sub-Doppler resolution spectroscopy that is useful for determining kinetic energy distributions. With 'conventional' Doppler spectroscopy, it is almost impossible to obtain an accurate distribution from a line profile, even with the highest resolution, except when the distribution is quite simple (e.g., a delta function). This is due to the lineshape deriving from velocity components along the wave-vector of the probe radiation, k/sub probe/. However, by choosing only those species whose velocities are essentially parallel (or antiparallel) to k/sub probe/, this handicap is overcome. Here, one obtains the kinetic energy distribution along k/sub probe/, and the resolution is limited only by our ability to reject species with velocity components perpendicular to k/sub probe/. This rejection is done by spatial and temporal discrimination, using counterpropagating, overlapped, pulsed photolysis and probe sources. At long delays, molecules are detected which are aligned with k/sub probe/. We call the method velocity-aligned Doppler spectroscopy (VADS). We have perused several cases involving photodissociation of small molecules, in each case detecting H-atoms using sequential 2-photon ionization via Lyman-..cap alpha... We discern structure in the kinetic energy distribution which is attributed to internal excitation of the 'other' fragment, and resolution is limited by the dye laser bandwidth. In the case of HBr, we resolve the Br spin-orbit states, and with H/sub 2/S, we resolve the SH vibrational levels. 38 refs., 7 figs.
Institute of Scientific and Technical Information of China (English)
Deng Xiao-wei; Liu Jiong-tian; Wang Yong-tian; Cao Yi-jun
2013-01-01
Laboratory experiments have been conducted to study the flow field in a cyclone static micro-bubble flotation column.The method of Particle Image Velocimetry (PIV) was used.The flow field velocity distribution in both cross section and longitudinal section within cyclonic zone was studied for different circulating volumes.The cross sectional vortex was also analyzed.The results show that in cross section as the circulating volume increases from 0.187 to 0.350 m3/h,the flow velocity ranges from 0 to 0.68 m/s.The flow field is mainly a non-vortex potential flow that forms a free vortex without outside energy input.In the cyclonic region the vortex deviates from the center of the flotation column because a single tangential opening introduces circulating fluid into the column.The tangential component of the velocity plays a defining role in the cross section.In the longitudinal section the velocity ranges from 0 to 0.08 m/s.The flow velocity increases as does the circulating volume.Advantageous mineral separation conditions arise from the combined effects of cyclonic flow in cross and longitudinal section.
Energy distributions of electrons in electron beam produced nitrogen plasmas
Energy Technology Data Exchange (ETDEWEB)
Suhre, D.R.
1976-01-01
A theory was developed which predicts the equilibrium electron energy distributions resulting from the injection of an electron beam into molecular nitrogen. The results were highly non-Maxwellian with a depletion region existing near 2.5 eV. Using these distributions, fractional power transfers to various excitation processes were calculated. The theory was verified experimentally by using Langmuir probes to measure the electron energy distributions produced by a beam generated by a cold cathode discharge in low pressure nitrogen. The distributions were measured in absolute units and compared directly with theory. All of the major features of the theory were found to be present in the measurements.
Institute of Scientific and Technical Information of China (English)
Bin Du; Jiayun Zhang; Tuping Zhou; Qifeng Shu
2003-01-01
The upward bubble velocity and the pierce length distributions in a sectional water model of the copper convener in Guixi Smelter in Jiangxi, China, were measured using a two-contact electro-resistivity probe. In the case of using a single tuyere, the bubble velocity distribution along longitudinal direction was similar to that derived from Guassian function. Beyond the center of the longitudinal range, the bubble pierce length exhibited a sudden increase. The upward bubble velocity at a specified location could go up to meters per second. Its probability at a fixed location obeys a lognormal function; the bubble pierce length there varies bellow a few centimeters. In the case of using multi-tuyeres, the upward bubble velocity was roughly uniform right above the tuyeres and showed a slow decrease beyond this region. The bubble pierce length within both of these two regions was roughly uniform. Its average value in the former region, however, was found to be somewhat lower than that in the later.
DEFF Research Database (Denmark)
Jørgensen, L. W.; Sillesen, Alfred Hegaard
1979-01-01
The Doppler-broadened profile of the He II 4685.75 AA line was measured along a chord in a rotating plasma, transverse to the magnetic field. Using a single-particle orbit picture, the corresponding velocity spectrum of ions confirm the measurements, so it can be concluded that the single......-particle orbit picture is valid for the discharge period under investigation, except for the first few microseconds during breakdown when a strong interaction between plasma and remaining neutral gas takes place by Alfvens critical velocity mechanism. A simple relation is given between the measured half......-width and shift of the Doppler profile and the macroscopic quantities of ion velocity and energy. Several Doppler-broadened profiles are shown for different plasma parameters....
Ryan, Russell E., Jr.; Thorman, Paul A.; Schmidt, Sarah J.; Cohen, Seth H.; Hathi, Nimish P.; Holwerda, Benne W.; Lunine, Jonathan I.; Pirzkal, Nor; Windhorst, Rogier A.; Young, Erick
2017-09-01
We present a Monte Carlo simulation designed to predict the vertical velocity dispersion of brown dwarfs in the Milky Way. We show that since these stars are constantly cooling, the velocity dispersion has a noticeable trend with the spectral type. With realistic assumptions for the initial mass function, star formation history, and the cooling models, we show that the velocity dispersion is roughly consistent with what is observed for M dwarfs, decreases to cooler spectral types, and increases again for the coolest types in our study (∼T9). We predict a minimum in the velocity dispersions for L/T transition objects, however, the detailed properties of the minimum predominately depend on the star formation history. Since this trend is due to brown dwarf cooling, we expect that the velocity dispersion as a function of spectral type should deviate from the constancy around the hydrogen-burning limit. We convert from velocity dispersion to vertical scale height using standard disk models and present similar trends in disk thickness as a function of spectral type. We suggest that future, wide-field photometric and/or spectroscopic missions may collect sizable samples of distant (∼ 1 kpc) dwarfs that span the hydrogen-burning limit. As such, we speculate that such observations may provide a unique way of constraining the average spectral type of hydrogen burning. Support for program #13266 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under the NASA contract NAS 5-26555.
Bergeson, Scott; Lyon, Mary
2016-05-01
We report measurements of the ion velocity distribution in an ultracold neutral plasma derived from a dense, cold Rydberg gas in a MOT. The Rydberg atoms are excited using a resonant two-step excitation pathway with lasers of 4 ns duration. The plasma forms spontaneously and rapidly. The rms width of the ion velocity distribution is determined by measuring laser-induced fluorescence (LIF) of the ions. The measured excitation efficiency is compared with a Monte-Carlo wavefunction calculation, and significant differences are observed. We discuss the conditions for blockaded Rydberg excitation and the subsequent spatial ordering of Rydberg atom domains. While the blockade interaction is greater than the Rabi frequency in portions of the atomic sample, no evidence for spatial ordering is observed. This research is supported in part by the Air Force Office of Scientific Research (Grant No. FA9950-12- 0308) and by the National Science Foundation (Grant No. PHY-1404488).
Bergeson, S D
2016-01-01
We report measurements of the ion velocity distribution in an ultracold neutral plasma derived from a dense, cold Rydberg gas in a MOT. The Rydberg atoms are excited using a resonant two-step excitation pathway with lasers of 4 ns duration. The plasma forms spontaneously and rapidly. The rms width of the ion velocity distribution is determined by measuring laser-induced fluorescence (LIF) of the ions. The measured excitation efficiency is compared with a Monte-Carlo wavefunction calculation, and significant differences are observed. We discuss the conditions for blockaded Rydberg excitation and the subsequent spatial ordering of Rydberg atom domains. While the blockade interaction is greater than the Rabi frequency in portions of the atomic sample, no evidence for spatial ordering is observed.
DISTRIBUTION AND ORIGIN OF HIGH-VELOCITY CLOUDS .3. CLOUDS, COMPLEXES AND POPULATIONS
WAKKER, BP; VANWOERDEN, H
1991-01-01
We present the first complete catalogue of high-velocity clouds (HVCs), followed by a classification of these clouds into complexes and populations. The catalogue will form the basis for comparisons with theoretical models. The study described here yields the following conclusions: (1) Differential
Velocity Distributions of Runaway Stars Produced by Supernovae in the Galaxy
Indian Academy of Sciences (India)
Abudusaimaitijiang Yisikandeer; Chunhua Zhu; Zhaojun Wang; Guoliang Lu
2016-09-01
Using a method of population synthesis, we investigate the runaway stars produced by disrupted binaries via asymmetric core collapse supernova explosions (CC-RASs) and thermonuclear supernova explosions (TN-RASs). We find the velocities of CC-RASs in the range of about 30--100 km s$^{−1}$. The runaway stars observed in the galaxy are possibly CC-RASs. Due to differences in stellar chemical components and structures, TN-RASs are divided into hydrogen-rich TN-RASs and helium-rich TN-RASs. The velocities of the former are about 100–500 km s$^{−1}$, while the velocities of the latter are mainly between 600 and 1100 km s$^{−1}$. The hypervelocity stars observed in the galaxy may originate from thermonuclear supernova explosions. Our results possibly cover the US 708 which is a compact helium star and travels with a velocity of 1157$\\pm$53 km s$^{−1}$ in our galaxy.
DEFF Research Database (Denmark)
Nielsen, Peter V.
The paper describes experiments with wall-mounted air terminal devices. The airflow from an air terminal device will influence the thermal comfort of the occupants and it is therefore important to develop an expression for this flow. The velocity at the floor is influenced by the flow rate to the...
DEFF Research Database (Denmark)
Nielsen, Peter Vilhelm
2000-01-01
The article describes experiments with wall-mounted air terminal devices. The airflow from an air terminal device influences the occupants' thermal comfort and, therefore, it is important to develop an expression for this flow in the occupied zone. The velocity at the floor is influenced by the f...
EXPERIMENTAL STUDY OF VELOCITY DISTRIBUTIONS IN THE TRANSITION REGION OF PIPES
Institute of Scientific and Technical Information of China (English)
LIU Yong-hui; DU Guang-sheng; LIU Li-ping; SHAO Zhu-feng; ZHAI Cheng-yuan
2011-01-01
The accuracy of an ultrasonic flowmeter meaurement depends on the profile-linear average velocity.But this velocity in the transition region is not available at the present.In this article,the velocity in the transition region in pipes is studied by experimental methods.The Particle Image Velocimetry ( PIV ) is used to measure the flow field in the transition region in pipes,and the measured results from PIV are in good agreement with the Westerwell's experimental data.Based on the experimental data of PIV,the curves of the profile-linear average velocity in the transition region against the Reynolds number in the range from 2 000 to 20 000 are obtained,and it is shown that the coefficient k is constant when the Reynolds number is in the range of 2 000-2 400 and 6 000-20 000,and the coefficient k is increasing when the Reynolds number is in the range of 2 400-6 000.The results of this article can be used to improve the measurement accuracy of the ultrasonic flowmeters and as a theoretical basis for the research on the transition flow.
DISTRIBUTION AND ORIGIN OF HIGH-VELOCITY CLOUDS .3. CLOUDS, COMPLEXES AND POPULATIONS
WAKKER, BP; VANWOERDEN, H
1991-01-01
We present the first complete catalogue of high-velocity clouds (HVCs), followed by a classification of these clouds into complexes and populations. The catalogue will form the basis for comparisons with theoretical models. The study described here yields the following conclusions: (1) Differential
Geospace Plasma Dynamics Laboratory Annual Task Report (FY11)
2012-03-01
and the other stability properties of the ion-cyclotron instability in various non - Maxwellian plasmas . For this purpose, analysis of the kinetic... Plasma Dynamics.” The goal of this research effort is to develop a detailed knowledge of the space environment by analyzing satellite data and...Furthermore, satellite-measured particle velocity distributions in the magnetosphere are often better modeled by non - Maxwellian distributions, such as
Burov, V. A.; Zotov, D. I.; Rumyantseva, O. D.
2014-07-01
A two-step algorithm is used to reconstruct the spatial distributions of the acoustic characteristics of soft biological tissues-the sound velocity and absorption coefficient. Knowing these distributions is urgent for early detection of benign and malignant neoplasms in biological tissues, primarily in the breast. At the first stage, large-scale distributions are estimated; at the second step, they are refined with a high resolution. Results of reconstruction on the base of model initial data are presented. The principal necessity of preliminary reconstruction of large-scale distributions followed by their being taken into account at the second step is illustrated. The use of CUDA technology for processing makes it possible to obtain final images of 1024 × 1024 samples in only a few minutes.
Directory of Open Access Journals (Sweden)
Francesco Zanlungo
Full Text Available We propose a way to introduce in microscopic pedestrian models a "social norm" in collision avoiding and overtaking, i.e. the tendency, shared by pedestrians belonging to the same culture, to avoid collisions and perform overtaking in a preferred direction. The "social norm" is implemented, regardless of the specific collision avoiding model, as a rotation in the perceived velocity vector of the opponent at the moment of computation of the collision avoiding strategy, and justified as an expectation that the opponent will follow the same "social norm" (for example a tendency to avoid on the left and overtake on the right, as proposed in this work for Japanese pedestrians. By comparing with real world data, we show that the introduction of this norm allows for a better reproduction of macroscopic pedestrian density and velocity patterns.
Influence of Generalized (r, q) Distribution Function on Electrostatic Waves
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
Non-Maxwellian particle distribution functions possessing high energy tail and shoulder in the profile of distribution function considerably change the damping characteristics of the waves. In the present paper Landau damping ofelectron plasma (Langmuir) waves and ion-acoustic waves in a hot, isotropic, unmagnetized plasma is studied with the generalized (r, q) distribution function. The results show that for the Langmuir oscillations Landau damping becomes severe as the spectral index r or q reduces. However, for the ion-acoustic waves Landau damping is more sensitive to the ion temperature than the spectral indices.
The Three-Dimensional Velocity Distribution of Wide Gap Taylor-Couette Flow Modelled by CFD
Directory of Open Access Journals (Sweden)
David Shina Adebayo
2016-01-01
Full Text Available A numerical investigation is conducted for the flow between two concentric cylinders with a wide gap, relevant to bearing chamber applications. This wide gap configuration has received comparatively less attention than narrow gap journal bearing type geometries. The flow in the gap between an inner rotating cylinder and an outer stationary cylinder has been modelled as an incompressible flow using an implicit finite volume RANS scheme with the realisable k-ε model. The model flow is above the critical Taylor number at which axisymmetric counterrotating Taylor vortices are formed. The tangential velocity profiles at all axial locations are different from typical journal bearing applications, where the velocity profiles are quasilinear. The predicted results led to two significant findings of impact in rotating machinery operations. Firstly, the axial variation of the tangential velocity gradient induces an axially varying shear stress, resulting in local bands of enhanced work input to the working fluid. This is likely to cause unwanted heat transfer on the surface in high torque turbomachinery applications. Secondly, the radial inflow at the axial end-wall boundaries is likely to promote the transport of debris to the junction between the end-collar and the rotating cylinder, causing the build-up of fouling in the seal.
Heymsfield, Gerald M.; Tian, Lin; Li, Lihua; Srivastava, C.
2005-01-01
Two techniques for retrieving the slope and intercept parameters of an assumed exponential raindrop size distribution (RSD), vertical air velocity, and attenuation by precipitation and water vapor in light stratiform rain using observations by airborne, nadir looking dual-wavelength (X-band, 3.2 cm and W-band, 3.2 mm) radars are presented. In both techniques, the slope parameter of the RSD and the vertical air velocity are retrieved using only the mean Doppler velocities at the two wavelengths. In the first method, the intercept of the RSD is estimated from the observed reflectivity at the longer wavelength assuming no attenuation at that wavelength. The attenuation of the shorter wavelength radiation by precipitation and water vapor are retrieved using the observed reflectivity at the shorter wavelength. In the second technique, it is assumed that the longer wavelength suffers attenuation only in the melting band. Then, assuming a distribution of water vapor, the melting band attenuation at both wavelengths and the rain attenuation at the shorter wavelength are retrieved. Results of the retrievals are discussed and several physically meaningful results are presented.
Eilerman, S; Anderson, J K; Reusch, J A; Liu, D; Fiksel, G; Polosatkin, S; Belykh, V
2012-10-01
An advanced neutral particle analyzer (ANPA) capable of simultaneously measuring hydrogen and deuterium ions of energies up to 45 keV has recently been developed for use on the Madison Symmetric Torus. The charge-to-mass separation allows for separate analysis of bulk deuterium ions and hydrogen ions injected with a 1 MW, 25 keV neutral beam. Orientation of the ANPA allows sampling of different regions of ion velocity space; a radial viewport favors collection of ions with high v(perpendicular)∕|v| while a recently installed tangential viewport favors ions with high v(||)∕|v|, such as those from the core-localized fast ion population created by the neutral beam. Signals are observed in the ANPA's highest energy channels during periodic magnetic reconnection events, which are drivers of anisotropic, non-Maxwellian ion energization in the reversed-field pinch. ANPA signal strength is dependent on the background neutral density, which also increases during magnetic reconnection events, so careful analysis must be performed to identify the true change in the ion distribution. A Monte Carlo neutral particle tracing code (NENE) is used to reconstruct neutral density profiles based on D(α) line emission, which is measured using a 16-chord filtered photodiode array.
Energy Technology Data Exchange (ETDEWEB)
Himpel, Michael, E-mail: himpel@physik.uni-greifswald.de; Killer, Carsten; Melzer, André [Institute of Physics, Ernst-Moritz-Arndt-University, 17489 Greifswald (Germany); Bockwoldt, Tim; Piel, Alexander [IEAP, Christian-Albrechts-Universität Kiel, D-24098 Kiel (Germany); Ole Menzel, Kristoffer [ABB Switzerland Ltd, Corporate Research Center, 5405 Dättwil (Switzerland)
2014-03-15
Experiments on dust-density waves have been performed in dusty plasmas under the microgravity conditions of parabolic flights. Three-dimensional measurements of a dust density wave on a single particle level are presented. The dust particles have been tracked for many oscillation periods. A Hilbert analysis is applied to obtain trajectory parameters such as oscillation amplitude and three-dimensional velocity amplitude. While the transverse motion is found to be thermal, the velocity distribution in wave propagation direction can be explained by harmonic oscillations with added Gaussian (thermal) noise. Additionally, it is shown that the wave properties can be reconstructed by means of a pseudo-stroboscopic approach. Finally, the energy dissipation mechanism from the kinetic oscillation energy to thermal motion is discussed and presented using phase-resolved analysis.
Institute of Scientific and Technical Information of China (English)
WANG Kai; SUN Feng-zhong; ZHAO Yuan-bin; GAO Ming; SHI Yue-tao
2008-01-01
A model for heat and mass transfer in a natural-draft wet cooling tower was established. Numerical simulation with the k-ε turbulent model was conducted. Distribution rules of air inlet aerodynamic field were studied. Field experiments were done in a cooling tower in power plant, and the test data was compared with the related results. The definition of characteristic air velocity was proposed and its influencing factors, such as the cross-wind velocity and circumferential angle, were quantitatively studied. It can be used to evaluate the performance of cooling tower and to calculate the ventilation quantity and resistance of air inlet. It is also a theoretical basis for cooling tower design and performance optimization.
Shells, holes, worms, high-velocity gas and the z-distribution of gas in galaxies.
Rand, R. J.
The author gives an overview of the current observational understanding of vertically extended gas components in spiral galaxies and the various phenomena which come under such names as shells, holes, worms, and high-velocity gas. For the most part, the focus is on recent high-resolution interferometric studies. The author concentrates on cold gas, and briefly on warm ionized gas, in the Milky Way and a few nearby spirals. Along the way, it is seen how phenomena such as worms and shells may be related to the formation and maintenance of the vertically extended components.
Parker, L.; Mellors, R. J.; Thurber, C. H.; Wang, H. F.; Zeng, X.
2015-12-01
A 762-meter Distributed Acoustic Sensing (DAS) array with a channel spacing of one meter was deployed at the Garner Valley Downhole Array in Southern California. The array was approximately rectangular with dimensions of 180 meters by 80 meters. The array also included two subdiagonals within the rectangle along which three-component geophones were co-located. Several active sources were deployed, including a 45-kN, swept-frequency, shear-mass shaker, which produced strong Rayleigh waves across the array. Both DAS and geophone traces were filtered in 2-Hz steps between 4 and 20 Hz to obtain phase velocities as a function of frequency from fitting the moveout of travel times over distances of 35 meters or longer. As an alternative to this traditional means of finding phase velocity, it is theoretically possible to find the Rayleigh-wave phase velocity at each point of co-location as the ratio of DAS and geophone responses, because DAS is sensitive to ground strain and geophones are sensitive to ground velocity, after suitable corrections for instrument response (Mikumo & Aki, 1964). The concept was tested in WPP, a seismic wave propagation program, by first validating and then using a 3D synthetic, full-waveform seismic model to simulate the effect of increased levels of noise and uncertainty as data go from ideal to more realistic. The results obtained from this study provide a better understanding of the DAS response and its potential for being combined with traditional seismometers for obtaining phase velocity at a single location. This analysis is part of the PoroTomo project (Poroelastic Tomography by Adjoint Inverse Modeling of Data from Seismology, Geodesy, and Hydrology, http://geoscience.wisc.edu/feigl/porotomo).
Barnes, J R; Jones, H R A; Pavlenko, Ya V; Jenkins, J S; Haswell, C A; Lohr, M E
2015-01-01
Since M4.5 - M9 dwarfs exhibit equatorial rotation velocities of order 10 km/s on average, radial velocity surveys targeting this stellar population will likely need to find methods to effectively remove starspot jitter. We present the first high resolution Doppler images of the M4.5 dwarf, GJ 791.2A, and the M9 dwarf, LP 944-20. The time series spectra of both objects reveal numerous line profile distortions over the rotation period of each star which we interpret as starspots. The transient distortions are modelled with spot/photosphere contrast ratios that correspond to model atmosphere temperature differences of Tphot-Tspot = 200 and 300 K. GJ 791.2A is a fully convective star with vsini = 35.1 km/s. Although we find more starspot structure at high latitudes, we reconstruct spots at a range of phases and latitudes with a mean spot filling of ~3%. LP 944-20 is one of the brightest known late-M dwarfs, with spectral type M9V and vsini = 30.8 km/s. Its spectral time series exhibits two dominant transient lin...
Singer, K. N.; Jolliff, B. L.; McKinnon, W. B.
2013-12-01
Title: Secondary Craters and the Size-Velocity Distribution of Ejected Fragments around Lunar Craters Measured Using LROC Images Authors: Kelsi N. Singer1, Bradley L. Jolliff1, and William B. McKinnon1 Affiliations: 1. Earth and Planetary Sciences, Washington University in St Louis, St. Louis, MO, United States. We report results from analyzing the size-velocity distribution (SVD) of secondary crater forming fragments from the 93 km diameter Copernicus impact. We measured the diameters of secondary craters and their distances from Copernicus using LROC Wide Angle Camera (WAC) and Narrow Angle Camera (NAC) image data. We then estimated the velocity and size of the ejecta fragment that formed each secondary crater from the range equation for a ballistic trajectory on a sphere and Schmidt-Holsapple scaling relations. Size scaling was carried out in the gravity regime for both non-porous and porous target material properties. We focus on the largest ejecta fragments (dfmax) at a given ejection velocity (υej) and fit the upper envelope of the SVD using quantile regression to an equation of the form dfmax = A*υej ^- β. The velocity exponent, β, describes how quickly fragment sizes fall off with increasing ejection velocity during crater excavation. For Copernicus, we measured 5800 secondary craters, at distances of up to 700 km (15 crater radii), corresponding to an ejecta fragment velocity of approximately 950 m/s. This mapping only includes secondary craters that are part of a radial chain or cluster. The two largest craters in chains near Copernicus that are likely to be secondaries are 6.4 and 5.2 km in diameter. We obtained a velocity exponent, β, of 2.2 × 0.1 for a non-porous surface. This result is similar to Vickery's [1987, GRL 14] determination of β = 1.9 × 0.2 for Copernicus using Lunar Orbiter IV data. The availability of WAC 100 m/pix global mosaics with illumination geometry optimized for morphology allows us to update and extend the work of Vickery
Agyrotropic pressure tensor induced by the plasma velocity shear
Pegoraro, Francesco; Del Sarto, Danele; Califano, Francesco
2016-10-01
We show that the spatial inhomogeneity of a shear flow in a fluid plasma is transferred to a pressure anisotropy that has both a gyrotropic and a non gyrotropic component. We investigate this process both analytically and numerically by including the full pressure tensor dynamics. We determine the time evolution of the pressure agyrotropy and in general of the pressure tensor anisotropization which arise from the action of both the magnetic eld and the flow strain tensor. This mechanism can affect the onset and development of shear-induced fluid instabilities in plasmas and is relevant to the understanding of the origin of some of the non-Maxwellian distribution functions evidenced both in Vlasov simulations and in space plasma measurements that exhibit pressure agyrotropy.
Sheared velocity flows as a source of pressure anisotropy in low collisionality plasmas
Del Sarto, Daniele; Pegoraro, Francesco; Cerri, Silvio Sergio; Califano, Francesco; Tenerani, Anna
2015-04-01
Non-Maxwellian metaequilibrium states may exist in low-collisionality plasmas as evidenced by direct (particle distributions) and indirect (e.g., instabilities driven by pressure anisotropy) satellite and laboratory measurements. These are directly observed in the solar wind (e.g. [1]), in magnetospheric reconnection events [2], in magnetically confined plasmas [3] or in simulations of Vlasov turbulence [4]. By including the full pressure tensor dynamics in a fluid plasma model, we show that a sheared velocity field can provide an effective mechanism that makes an initial isotropic state anisotropic. We discuss how the propagation of "magneto-elastic" waves can affect the pressure tensor anisotropization and the small scale formation that arise from the interplay between the gyrotropic terms due to the magnetic field and flow vorticity, and the non-gyropropic effect of the flow strain tensor. We support this analysis by a numerical integration of the nonlinear equations describing the pressure tensor evolution. This anisotropization mechanism might provide a good candidate for the understanding of the observed correlation between the presence of a sheared velocity flow and the signature of pressure anisotropies which are not yet explained within the standard models based e.g. on the CGL paradigm (see also [5]). Examples of these signatures are provided by the threshold lowering of ion-Weibel instabilities in the geomagnetic tail, observed in concomitance to the presence of a velocity shear in the near-earth plasma profile [6], or by the relatively stronger anisotropization measured for core protons in the fast solar wind [4,7] or in "space simulation" laboratory plasma experiments [3]. 1] E. Marsch et al., Journ. Geophys. Res. 109, A04120 (2004); Yu. V. Khotyainstev at el., Phys. Rev. Lett. 106, 165001 (2011). [2] N. Aunai et al., Ann. Geophys. 29, 1571 (2011); N. Aunai et al., Journ. Geophys. Res. 116, A09232 (2011). [3] E.E. Scime et al., Phys. Plasmas 7, 2157
Moorhead, A. V.; Brown, P. G.; Campbell-Brown, M. D.; Moser, D. E.; Blaauw, R. C.; Cooke, W. J.
2017-01-01
Meteoroids are known to damage spacecraft: they can crater or puncture components, disturb a spacecraft's attitude, and potentially create secondary electrical effects. Because the damage done depends on the speed, size, density, and direction of the impactor, accurate environment models are critical for mitigating meteoroid-related risks. Yet because meteoroid properties are derived from indirect observations such as meteors and impact craters, many characteristics of the meteoroid environment are uncertain. In this work, we present recent improvements to the meteoroid speed and density distributions. Our speed distribution is derived from observations made by the Canadian Meteor Orbit Radar. These observations are de-biased using modern descriptions of the ionization efficiency. Our approach yields a slower meteoroid population than previous analyses (see Fig. 1 for an example) and we compute the uncertainties associated with our derived distribution. We adopt a higher fidelity density distribution than that used by many older models. In our distribution, meteoroids with TJ less than 2 are assigned to a low-density population, while those with TJ greater than 2 have higher densities (see Fig. 2). This division and the distributions themselves are derived from the densities reported by Kikwaya et al. These changes have implications for the environment: for instance, the helion/antihelion sporadic sources have lower speeds than the apex and toroidal sources and originate from high-T(sub J) parent bodies. Our on-average slower and denser distributions thus imply that the helion and antihelion sources dominate the meteoroid environment even more completely than previously thought. Finally, for a given near-Earth meteoroid cratering rate, a slower meteoroid population produces a comparatively higher rate of satellite attitude disturbances.
Taut, A.; Drews, C.; Berger, L.; Peleikis, T.; Wimmer-Schweingruber, R. F.
2015-12-01
PickUp Ions (PUIs) are typically characterized by (1) their almost exclusively single charge state, (2) a highly non-thermal and anisotropic Velocity Distribution Function (VDF) [Drews et al., 2015], and (3) an extended source population of neutral atoms somewhere between the observer and the Sun. The origin of pickup ions ranges from sources only several solar radii away from the Sun, the so-called inner-source of pickup ions, up to a distance of several hundreds of astronomical units, the local interstellar medium. Their continuous production inside the heliosphere and complex interactions with the magnetized solar wind plasma leads to the development of non-thermal, anisotropic features of both the solar wind and pickup ion velocity distribution functions. In this study, we present observations of the VDF of He+, C+, N+, O+ and Ne+ pickup ions with PLASTIC on STEREO A. We have found a PUI flux increase during perpendicular configurations of the local magnetic field that is generally linked to the existence of a so-called torus-distribution [Drews et al., 2015] which is attributed to the production of PUIs close to the observer. A comparison of the PUI VDF between radial and perpendicular configurations of the local magnetic field vector is used to quantify the anisotropy of the PUI VDF and thereby enables us to estimate the mean free path for pitch-angle scattering of He, C, N, O and Ne pickup ions without the necessity of an over-simplified heliospheric model to describe the PUI phase space transport. Our results show a clear signature of a C+ torus signature at 1 AU as well as significant differences between the anisotropies of the He+ and O+ VDF. We will discuss our results in the light of recent studies about the nature of the inner-source of PUIs [Berger et al., 2015] and observations of the 2D VDF of He+[Drews et al., 2015]. Figure Caption: Velocity space diagrams of a pickup ion torus distribution as a (vx-vy)-projection (top left panel) and in the vz = 0
Impact of temperature-velocity distribution on fusion neutron peak shape
Munro, D. H.; Field, J. E.; Hatarik, R.; Peterson, J. L.; Hartouni, E. P.; Spears, B. K.; Kilkenny, J. D.
2017-05-01
Doppler broadening of the 14 MeV DT and 2.45 MeV DD fusion neutron lines has long been our best measure of temperature in a burning plasma. At the National Ignition Facility (NIF), yields are high enough and our neutron spectrometers accurate enough that we see finer details of the peak shape. For example, we can measure the shift of the peak due to the bulk motion of the plasma, and we see indications of non-thermal broadening, skew, and kurtosis of the peak caused by the variations of temperature and fluid velocity during burn. We can also distinguish spectral differences among several lines of sight. This paper will review the theory of fusion neutron line shape, show examples of non-Gaussian line shapes and directional variations in NIF data, and describe detailed spectral shapes we see in radiation-hydrodynamics simulations of implosions.
Velocity Distribution of Slurry in Horizontal Pipe When Solid Particles Sliding
Institute of Scientific and Technical Information of China (English)
ZhangShilin; XuZhenliang; Shaolongtan
2004-01-01
Based on the laws of momentum conservation and impulse in accelerating process, the distribution on speed of ununiform slurry flow in a horizontal pipe was studied. According to the momentum change of solid particles and conveying liquid of slurry flow during accelerating, and some effect factors, the relationship between the speed of solid particles and the speed of conveying liquid was obtained.When dealing with the friction between sliding solid particles and pipe, it is pivotal to reasonably distribute component of friction to each solid particle. The friction coefficient between solid particles was obtained by forces analysis and theoretic calculation, and can be used to calculate the friction force on every solid particle. The effect of friction on speed of ever), solid particle was investigated through the impulse law. The result is more accurate than that by using uniform friction on solid particles. It is completely new method to use above theory to get solid particles speed distribution, conveying liquid speed distribution and slurry speed distribution.
Energy Technology Data Exchange (ETDEWEB)
Din, Ghiyas Ud [Department of Nuclear Engineering, Pakistan Institute of Engineering and Applied Sciences (PIEAS), P.O. Nilore, Islamabad (Pakistan); Isotope Applications Division, Pakistan Institute of Nuclear Science and Technology (PINSTECH), P.O. Nilore, Islamabad (Pakistan)], E-mail: fac192@pieas.edu.pk; Chughtai, Imran Rafiq; Inayat, Mansoor Hameed [Department of Chemical and Materials Engineering, Pakistan Institute of Engineering and Applied Sciences (PIEAS), P.O. Nilore, Islamabad (Pakistan); Khan, Iqbal Hussain [Isotope Applications Division, Pakistan Institute of Nuclear Science and Technology (PINSTECH), P.O. Nilore, Islamabad (Pakistan)
2008-12-15
Axial dispersion, holdup and slip velocity of dispersed phase have been investigated for a range of dispersed and continuous phase superficial velocities in a pulsed sieve plate extraction column using radiotracer residence time distribution (RTD) analysis. Axial dispersion model (ADM) was used to simulate the hydrodynamics of the system. It has been observed that increase in dispersed phase superficial velocity results in a decrease in its axial dispersion and increase in its slip velocity while its holdup increases till a maximum asymptotic value is achieved. An increase in superficial velocity of continuous phase increases the axial dispersion and holdup of dispersed phase until a maximum value is obtained, while slip velocity of dispersed phase is found to decrease in the beginning and then it increases with increase in superficial velocity of continuous phase.
Wang, Huihui; Sukhomlinov, Vladimir S.; Kaganovich, Igor D.; Mustafaev, Alexander S.
2017-02-01
Using the Monte Carlo collision method, we have performed simulations of ion velocity distribution functions (IVDF) taking into account both elastic collisions and charge exchange collisions of ions with atoms in uniform electric fields for argon and helium background gases. The simulation results are verified by comparison with the experiment data of the ion mobilities and the ion transverse diffusion coefficients in argon and helium. The recently published experimental data for the first seven coefficients of the Legendre polynomial expansion of the ion energy and angular distribution functions are used to validate simulation results for IVDF. Good agreement between measured and simulated IVDFs shows that the developed simulation model can be used for accurate calculations of IVDFs.
Bourdin, Philippe-A.
2017-09-01
To understand the essential physics needed to reproduce magnetic reconnection events in 2.5-D particle-in-cell (PIC) simulations, we revisit the Geospace Environmental Modeling (GEM) setup. We set up a 2-D Harris current sheet (that also specifies the initial conditions) to evolve the reconnection of antiparallel magnetic fields. In contrast to the GEM setup, we use a much smaller initial perturbation to trigger the reconnection and evolve it more self-consistently. From PIC simulation data with high-quality particle statistics, we study a symmetric reconnection site, including separatrix layers, as well as the inflow and the outflow regions. The velocity distribution functions (VDFs) of electrons have a fine structure and vary strongly depending on their location within the reconnection setup. The goal is to start cataloging multidimensional fine-structured electron velocity distributions showing different reconnection processes in the Earth's magnetotail under various conditions. This will enable a direct comparison with observations from, e.g., the NASA Magnetospheric MultiScale (MMS) mission, to identify reconnection-related events. We find regions with strong non-gyrotropy also near the separatrix layer and provide a refined criterion to identify an electron diffusion region in the magnetotail. The good statistical significance of this work for relatively small analysis areas reveals the gradual changes within the fine structure of electron VDFs depending on their sampling site.
Impact of temperature-velocity distribution on fusion neutron peak shape
Munro, David
2016-10-01
Doppler broadening of the 14 MeV DT and 2.45 MeV DD fusion neutron lines has long been our best measure of temperature in a burning plasma. At the National Ignition Facility yields are high enough and our neutron spectrometers accurate enough that we see finer details of the peak shape. For example, we can measure the shift of the peak due to bulk motion of the plasma, and we see indications of non-thermal broadening, skew, and kurtosis of the peak caused by the variations of temperature and fluid velocity during burn. We can also distinguish spectral differences among several lines of sight. This talk will review the theory of fusion neutron line shape, show examples of non-Gaussian line shapes and directional variations in NIF data, and describe detailed spectral shapes we see in radhydro implosion simulations. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
The Numerical Investigation of Temperature and Velocity Distribution in the High-Bay Depot
Directory of Open Access Journals (Sweden)
Xuehong Wu
2014-07-01
Full Text Available High-bay depot plays an important role in the storage industry. Due to large and high space of high-bay depot, it is difficult to make temperature distribution uniform, which will influence the storage time of raw materials. In this paper, the aim is to find the reasonable air supply and energy-saving method; a supply-air method of high-bay depot is investigated as an example. The results show the radius and spacing of the supply-air inlet have great influence on temperature distribution. The temperature nonuniformity coefficient of summer is smaller than that of winter. The investigated results can provide a theoretical reference for the high-bay depot design and economic operation.
Energy Technology Data Exchange (ETDEWEB)
Buss, R.J.; Coggiola, M.J.; Lee, Y.T.
1978-12-01
Several methods currently used to study unimolecular decomposition in molecular beams are discussed. Experimental product angular and velocity distributions obtained for the reaction of F, Cl with C/sub 2/H/sub 3/Br are presented. The mechanism by which conservation of angular momemtum can cause coupling of the product angular and velocity distributions in dissociation of long-lived complexes is introduced. 14 references.
Energy Technology Data Exchange (ETDEWEB)
Vagin, K. Yu., E-mail: vagin@sci.lebedev.ru; Uryupin, S. A., E-mail: uryupin@sci.lebedev.ru [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)
2013-08-15
The reflection of a test electromagnetic pulse from the plasma formed as a result of tunnel ionization of atoms in the field of a circularly polarized high-power radiation pulse is analyzed using the kinetic approach to describe electron motion. It is shown that the reflected pulse is significantly amplified due to the development of Weibel instability. The amplification efficiency is determined by the maximum value of the instability growth rate, which depends on the degree of anisotropy of the photoelectron distribution function.
Non-Maxwellian background effects in gyrokinetic simulations with GENE
Di Siena, A.; Gorler, T.; Doerk, H.; Citrin, J.; Johnson, T.; Schneider, M.; Poli, E.; JET Contributors,
2016-01-01
The interaction between fast particles and core turbulence has been established as a central issue for a tokamak reactor. Recent results predict significant enhancement of electromagnetic stabilisation of ITG turbulence in the presence of fast ions. However, most of these simulations were performed
Essay on the Non-Maxwellian Theories of Electromagnetism
Dvoeglazov, V V
1996-01-01
In the first part of this paper we review several formalisms which give alternative ways for describing the light. They are: the formalism `baroque' and the Majorana-Oppenheimer form of electrodynamics, the Sachs' theory of Elementary Matter, the Dirac-Fock-Podol'sky model, its development by Staruszkiewicz, the Evans-Vigier ${\\bf B}^{(3)}$ field, the theory with an invariant evolution parameter of Horwitz, the analysis of the action-at-a-distance concept, presented recently by Chubykalo and Smirnov-Rueda, and the analysis of the claimed `longitudity' of the antisymmetric tensor field after quantization. The second part is devoted to the discussion of the Weinberg formalism and its recent development by Ahluwalia and myself.
Tsujido, Sayaka; Arakawa, Masahiko; Suzuki, Ayako I.; Yasui, Minami
2015-12-01
In order to clarify the effects of projectile density on ejecta velocity distributions for a granular target, impact cratering experiments on a quartz sand target were conducted by using eight types of projectiles with different densities ranging from 11 g cm-3 to 1.1 g cm-3, which were launched at about 200 m s-1 from a vertical gas gun at Kobe University. The scaling law of crater size, the ejection angle of ejecta grains, and the angle of the ejecta curtain were also investigated. The ejecta velocity distribution obtained from each projectile was well described by the π-scaling theory of v0/√{gR} =k2(x0/R)-1/μ, where v0, g, R and x0 are the ejection velocity, gravitational acceleration, crater radius and ejection position, respectively, and k2 and μ are constants mostly depending on target material properties (Housen, K.R., Holsapple, K.A. [2011]. Icarus 211, 856-875). The value of k2 was found to be almost constant at 0.7 for all projectiles except for the nylon projectile, while μ increased with the projectile density, from 0.43 for the low-density projectile to 0.6-0.7 for the high-density projectile. On the other hand, the π-scaling theory for crater size gave a μ value of 0.57, which was close to the average of the μ values obtained from ejecta velocity distributions. The ejection angle, θ, of each grain decreased slightly with distance, from higher than 45° near the impact point to 30-40° at 0.6 R. The ejecta curtain angle is controlled by the two elementary processes of ejecta velocity distribution and ejection angle; it gradually increased from 52° to 63° with the increase of the projectile density. The comparison of our experimental results with the theoretical model of the crater excavation flow known as the Z-model revealed that the relationship between μ and θ obtained by our experiments could not be described by the Z-model (Maxwell, D.E. [1977]. In: Roddy, D.J., Pepin, R.O., Merrill, R.B. (Eds.), Impact and Explosion Cratering
Dufton, P L; Dunstall, P R; Evans, C J; Brott, I; de Mink, S E; Howarth, I D; Kennedy, M; McEvoy, C; Potter, A T; Ramírez-Agudelo, O H; Sana, H; Simón-Díaz, S; Taylor, W; Vink, J S
2012-01-01
Aims: Projected rotational velocities (\\vsini) have been estimated for 334 targets in the VLT-FLAMES Tarantula survey that do not manifest significant radial velocity variations and are not supergiants. They have spectral types from approximately O9.5 to B3. The estimates have been analysed to infer the underlying rotational velocity distribution, which is critical for understanding the evolution of massive stars. Methods: Projected rotational velocities were deduced from the Fourier transforms of spectral lines, with upper limits also being obtained from profile fitting. For the narrower lined stars, metal and non-diffuse helium lines were adopted, and for the broader lined stars, both non-diffuse and diffuse helium lines; the estimates obtained using the different sets of lines are in good agreement. The uncertainty in the mean estimates is typically 4% for most targets. The iterative deconvolution procedure of Lucy has been used to deduce the probability density distribution of the rotational velocities. R...
Butsky, Iryna; Macciò, Andrea V.; Dutton, Aaron A.; Wang, Liang; Obreja, Aura; Stinson, Greg S.; Penzo, Camilla; Kang, Xi; Keller, Ben W.; Wadsley, James
2016-10-01
We use the NIHAO (Numerical Investigation of Hundred Astrophysical Objects) cosmological simulations to study the effects of galaxy formation on key properties of dark matter (DM) haloes. NIHAO consists of ≈90 high-resolution smoothed particle hydrodynamics simulations that include (metal-line) cooling, star formation, and feedback from massive stars and supernovae, and cover a wide stellar and halo mass range: 106 ≲ M*/M⊙ ≲ 1011(109.5 ≲ Mhalo/M⊙ ≲ 1012.5). When compared to DM-only simulations, the NIHAO haloes have similar shapes at the virial radius, Rvir, but are substantially rounder inside ≈0.1Rvir. In NIHAO simulations, c/a increases with halo mass and integrated star formation efficiency, reaching ˜0.8 at the Milky Way mass (compared to 0.5 in DM-only), providing a plausible solution to the long-standing conflict between observations and DM-only simulations. The radial profile of the phase-space Q parameter (ρ/σ3) is best fit with a single power law in DM-only simulations, but shows a flattening within ≈0.1Rvir for NIHAO for total masses M > 1011 M⊙. Finally, the global velocity distribution of DM is similar in both DM-only and NIHAO simulations, but in the solar neighbourhood, NIHAO galaxies deviate substantially from Maxwellian. The distribution is more symmetric, roughly Gaussian, with a peak that shifts to higher velocities for Milky Way mass haloes. We provide the distribution parameters which can be used for predictions for direct DM detection experiments. Our results underline the ability of the galaxy formation processes to modify the properties of DM haloes.
Osterday, Kathryn; Aliseda, Alberto; Lasheras, Juan
2009-11-01
The atomization of colloidal suspensions is of particular interest to the manufacturing of tablets and pills used as drug delivery systems by the pharmaceutical industry. At various stages in the manufacturing process, the tablets are coated with a spray of droplets produced by co-axial atomizers. The mechanisms of droplet size and spray formation in these types of atomizers are dominated by Kelvin-Helmholtz and Raleigh-Taylor instabilities for both low[1] and high[2] Ohnesorge numbers. We present detailed phase Doppler measurements of the Sauter Mean Diameter of the droplets produced by co-axial spray atomizers using water-based colloidal suspensions with solid concentrations ranging from fifteen to twenty percent and acetone-based colloidal suspensions with solid concentrations ranging from five to ten percent. Our results compare favorably with predictions by Aliseda's model. This suggests that the final size distribution is mainly determined by the instabilities caused by the sudden acceleration of the liquid interface. [1]Varga, C. M., et al. (2003) J. Fluid Mech. 497:405-434 [2]Aliseda, A. et al. (2008). J. Int. J. Multiphase Flow, 34(2), 161-175.
Kyoden, Tomoaki; Yasue, Youichi; Ishida, Hiroki; Akiguchi, Shunsuke; Andoh, Tsugunobu; Takada, Yogo; Teranishi, Tsunenobu; Hachiga, Tadashi
2015-01-01
A laser Doppler velocimeter (LDV) has been developed that is capable of performing two-dimensional (2D) cross-sectional measurements. It employs two horizontal laser light sheets that intersect at an angle of 13.3°. Since the intersection region is thin, it can be used to approximately determine the 2D flow field. An 8 × 8 array of optical fibers is used to simultaneously measure Doppler frequencies at 64 points. Experiments were conducted to assess the performance of the LDV, and it was found to be capable of obtaining spatial and temporal velocity information at multiple points in a flow field. The technique is fast, noninvasive, and accurate over long sampling periods. Furthermore, its applicability to an actual flow field was confirmed by measuring the temporal velocity distribution of a pulsatile flow in a rectangular flow channel with an obstruction. The proposed device is thus a useful, compact optical instrument for conducting simultaneous 2D cross-sectional multipoint measurements.
Directory of Open Access Journals (Sweden)
Samurović, S.
2009-12-01
Full Text Available In this paper we analyse the measurements of the absorption line-strength Lick indices in the early-type galaxy IC 1459. We use thelong-slit spectra of the elliptical galaxy IC 1459 from which its kinematicshad previously been extracted to calculate the Lick indices forthe observed spectral region (Mg$_2$, Fe5270, Fe5335 and H$_beta$. Weapply the usual procedure and correct the indices to the Lick spectralresolution and for the zero velocity dispersion. The procedure applied in thispaper also corrects to non-Gaussian line-of-sight velocity distribution(LOSVD observed in this galaxy, especially in its outer parts. The findingsof Kuntschner (2004 were tested and it is shown that the departures from theGaussian LOSVD may indeed cause erroneous determinations of the Lick indices. The impact of the introduction of non-Gaussian LOSVD differs for differentindices. For the galaxy IC~1459 it is shown that the iron indices areespecially sensitive when the correction due to anistropies is introduced: thecorrections for Fe5270 and Fe5335 are $sim 10$ and $sim 19$ percentlarger, respectively, than the corrections obtained in case of a pure Gaussian. The corrections for Mg$_2$ index are shown to be negligible and thecorrections of the H$_beta$ index due to anisotropies are also small (below$sim 4$ per cent at most.
Directory of Open Access Journals (Sweden)
Samurović Srđan
2009-01-01
Full Text Available In this paper we analyze the measurements of the absorption line-strength Lick indices in the early-type galaxy IC 1459. We use the long-slit spectra of the elliptical galaxy IC 1459 from which its kinematics had previously been extracted to calculate the Lick indices for the observed spectral region (Mg2, Fe5270, Fe5335 and Hβ. We apply the usual procedure and correct the indices to the Lick spectral resolution and for the zero velocity dispersion. The procedure applied in this paper also corrects to non-Gaussian line-of-sight velocity distribution (LOSVD observed in this galaxy, especially in its outer parts. The findings of Kuntschner (2004 were tested and it is shown that the departures from the Gaussian LOSVD may indeed cause erroneous determinations of the Lick indices. The impact of the introduction of non-Gaussian LOSVD differs for different indices. For the galaxy IC 1459 it is shown that the iron indices are especially sensitive when the correction due to anistropies is introduced: the corrections for Fe5270 and Fe5335 are ~10 and ~19 percent larger, respectively, than the corrections obtained in case of a pure Gaussian. The corrections for Mg2 index are shown to be negligible and the corrections of the Hβ index due to anisotropies are also small (below ~ 4 per cent at most.
Butsky, Iryna; Dutton, Aaron A; Wang, Liang; Stinson, Greg S; Penzo, Camilla; Kang, Xi; Keller, Ben W; Wadsley, James
2015-01-01
We show the effect of galaxy formation on the dark matter (DM) distribution across a wide range of halo masses. We focus on how baryon physics changes the dark matter halo shape, the so called "pseudo phase-space density distribution" and the velocity distribution within the virial radius, Rvir and in the solar neighborhood. This study is based on the NIHAO galaxy formation simulations, a large suite of cosmological zoom-in simulations. The galaxies reproduce key properties of observed galaxies, and hence offer unique insight into how baryons change the dark matter morphology and kinematics. When compared to dark matter only simulations, the NIHAO haloes have similar shapes at Rvir, but are substantially rounder inside ~0.1 Rvir. In DM-only simulations the inner halo has a minor-to-major axis ratio of c/a~0.5. In hydro simulations c/a increases with halo mass and integrated star formation efficiency, reaching ~0.8 at the Milky Way mass, reconciling a long-standing conflict between observations and DM only sim...
Spanwise lift distributions and wake velocity surveys of a semi-span wing with a discontinuous twist
Kumagai, Hiroyuki
1989-01-01
A wind tunnel test was conducted in the NASA-Ames 7 x 10 ft wind tunnel to investigate the lift distribution on a semispan wing with a discontinuous change in spanwise twist. The semispan wing had a tip with an adjustable pitch angle independent on the inboard section pitch angle simulating the free tip rotor blade when its free tip is at a deflected position. The spanwise lift distribution over the wing and the tip were measured and three component velocity surveys behind the wing were obtained with a 3-D laser Doppler velocimeter (LV) with the wing at one angle of attack and the tip deflected at different pitch angles. A six-component internal strain gage balance was also used to measure total forces and moments on the tip. The 3-D lift was computed from the 2-D lift distributions obtained from the LV and from the strain gage balance. The results from both experimental methods are shown to be in agreement with predictions made by a steady, 3-D panel code, VSAERO.
Burov, V. A.; Zotov, D. I.; Rumyantseva, O. D.
2015-03-01
The paper is devoted to implementing in a specific tomographic device a two-step algorithm designed to reconstruct the spatial distributions of the sound velocity and absorption coefficient, primarily in soft biological tissues. To generate the input data of the first and second steps, a correlation algorithm is used based on determination of the time shift in the signal propagation time in the presence of an object. The results of reconstruction are presented, which are based on data measured for objects-phantoms using a developed experimental ultrasound tomograph model. We discuss problems that arise during reconstruction with a low resolution at the first step of the algorithm, and we demonstrate the high spatial resolving power achieved at the second step.
Nouri Kadijani, M.; Abbasi, H.
2016-09-01
Dynamics of a dust layer suspending in a plasma and interacting through a Yukawa-type potential is considered. In the small affinity limit, the influence of an external white noise on the formation of Tsallis' velocity distribution function is studied through molecular dynamics simulation. The characteristic length of the noise is much smaller than the system size that causes a number of subsystems (islands) to be formed with the size similar to the noise one. The external noise leads to the temperature fluctuation in each island. Therefore, a stochastic formalism based on a Langevin equation for the fluctuating temperature is presented. The approach provides a dynamical reason how a fluctuating temperature takes a system to a unique class of quasi-equilibrium states. In particular, the dependence of the model systems on the noise parameters is explained. The non-extensive parameter is obtained through which the small affinity limit can be defined.
Perez, John Anthony
Averaged over appropriate space and time scales the dynamics of highly fluidized granular systems are often reminiscent of molecular fluid flows. As a result, theoretical efforts to describe these systems have borrowed heavily from continuum mechanics, particularly hydrodynamics. This has led to various proposed granular hydrodynamic theories which have been used to simulate granular materials in various states of confinement and excitation. These studies suggest that a continuum model for granular gasses can accurately reproduce the mean density, velocity and temperature profiles for an experimental granular gas. This thesis contributes to this body of work by presenting an experimental study of the hydrodynamic fields and velocity distributions within a vertically driven quasi-2D granular gas. We have taken pictures as fast as possible of a time-dependent granular gas using a high-speed CCD camera. We have extracted the positions and velocities of 57-564 particles per frame over 400 GB of raw images collected at 3700 fps. We used this data to compute the density, velocity and temperature fields as functions of time and space to a very high resolution. This approach led to the discovery of novel substructures within the hydrodynamic fields which would have been overlooked had we chosen to average over a drive cycle as earlier studies have done. In particular, the high spatial resolution available from our measurements reveals a serrated substructure in the shock waves which has not been reported before. This substructure is the result of collisional momentum transport . One of the current issues in formulating a granular continuum model is how to incorporate local and non-local dependencies between stress and strain correctly. In this thesis we demonstrate that the collisional transfer of momentum produces a non-local effect in the stress tensor which plays a major role in determining the mean flow. Current models have incorporated only the collisional or
Directory of Open Access Journals (Sweden)
Kristin M Kleisner
Full Text Available Many studies illustrate variable patterns in individual species distribution shifts in response to changing temperature. However, an assemblage, a group of species that shares a common environmental niche, will likely exhibit similar responses to climate changes, and these community-level responses may have significant implications for ecosystem function. Therefore, we examine the relationship between observed shifts of species in assemblages and regional climate velocity (i.e., the rate and direction of change of temperature isotherms. The assemblages are defined in two sub-regions of the U.S. Northeast Shelf that have heterogeneous oceanography and bathymetry using four decades of bottom trawl survey data and we explore temporal changes in distribution, spatial range extent, thermal habitat area, and biomass, within assemblages. These sub-regional analyses allow the dissection of the relative roles of regional climate velocity and local physiography in shaping observed distribution shifts. We find that assemblages of species associated with shallower, warmer waters tend to shift west-southwest and to shallower waters over time, possibly towards cooler temperatures in the semi-enclosed Gulf of Maine, while species assemblages associated with relatively cooler and deeper waters shift deeper, but with little latitudinal change. Conversely, species assemblages associated with warmer and shallower water on the broad, shallow continental shelf from the Mid-Atlantic Bight to Georges Bank shift strongly northeast along latitudinal gradients with little change in depth. Shifts in depth among the southern species associated with deeper and cooler waters are more variable, although predominantly shifts are toward deeper waters. In addition, spatial expansion and contraction of species assemblages in each region corresponds to the area of suitable thermal habitat, but is inversely related to assemblage biomass. This suggests that assemblage distribution
Lokajíček, T.; Kern, H.; Svitek, T.; Ivankina, T.
2014-06-01
Ultrasonic measurements of the 3D velocity distribution of P- and S-waves were performed on a spherical sample of a biotite gneiss from the Outokumpu scientific drill hole. Measurements were done at room temperature and pressures up to 400 and 70 MPa, respectively, in a pressure vessel with oil as a pressure medium. A modified transducer/sample assembly and the installation of a new mechanical system allowed simultaneous measurements of P- and S-wave velocities in 132 independent directions of the sphere on a net in steps of 15°. Proper signals for P- and S-waves could be recorded by coating the sample surface with a high-viscosity shear wave gel and by temporal point contacting of the transmitter and receiver transducers with the sample surface during the measurements. The 3D seismic measurements revealed a strong foliation-related directional dependence (anisotropy) of P- and S-wave velocities, which is confirmed by measurements in a multi-anvil apparatus on a cube-shaped specimen of the same rock. Both experimental approaches show a marked pressure sensitivity of P- and S-wave velocities and velocity anisotropies. With increasing pressure, P- and S-wave velocities increase non-linearly due to progressive closure of micro-cracks. The reverse is true for velocity anisotropy. 3D velocity calculations based on neutron diffraction measurements of crystallographic preferred orientation (CPO) of major minerals show that the intrinsic bulk anisotropy is basically caused by the CPO of biotite constituting about 23 vol.% of the rock. Including the shape of biotite grains and oriented low-aspect ratio microcracks into the modelling increases bulk anisotropy. An important finding from this study is that the measurements on the sample sphere and on the sample cube displayed distinct differences, particularly in shear wave velocities. It is assumed that the differences are due to the different geometries of the samples and the configuration of the transducer-sample assembly
Tuponogov, V. G.; Baskakov, A. P.
2013-11-01
The dependences of dimensionless fluidization velocities separating bubble, transition, and fast fluidization regimes on the properties of dispersed material for particles belonging to groups B and D (according to D. Geldart's classification) are presented. Correspondence between the considered dependences and experimental data obtained by different researchers and their correlation with critical fluidization velocities and particle terminal velocities are shown. The hydrodynamic mechanisms governing the saturation of fluidized bed with bubbles on reaching the transition fluidization velocity in installations having different sizes are considered. Factors due to which a bottom bubble layer disappears in narrow installations and is retained on large-diameter grids in an intense channel forming mode are explained. Experimental data are presented from which it is seen that the bubble layer hydrodynamics depends on the gas-distributing grid diameter and that this diameter has an insignificant influence on the fluidization velocity during the transition from a bubble to fast fluidization regime.
Khrabrov, Alexander V.; Kaganovich, Igor D.; Ventzek, Peter L. G.; Ranjan, Alok; Chen, Lee
2015-10-01
Low-pressure capacitively-coupled discharges with additional dc bias applied to a separate electrode are utilized in plasma-assisted etching for semiconductor device manufacturing. Measurements of the electron velocity distribution function (EVDF) of the flux impinging on the wafer, as well as in the plasma bulk, show a thermal population and additional peaks within a broad range of energies. That range extends from the thermal level up to the value for the ‘ballistic’ peak, corresponding to the bias potential. The non-thermal electron flux has been correlated to alleviating the electron shading effect and providing etch-resistance properties to masking photoresist layers. ‘Middle-energy peak electrons’ at energies of several hundred eV may provide an additional sustaining mechanism for the discharge. These features in the electron velocity (or energy) distribution functions are possibly caused by secondary electrons emitted from the electrodes and interacting with two high-voltage sheaths: a stationary sheath at the dc electrode and an oscillating self-biased sheath at the powered electrode. Since at those energies the mean free path for large-angle scattering (momentum relaxation length) is comparable to, or exceeds the size of the discharge gap, these ‘ballistic’ electrons will not be fully scattered by the background gas as they traverse the inter-electrode space. We have performed test-particle simulations in which the features in the EVDF of electrons impacting the RF electrode are fully resolved at all energies. An analytical model has been developed to predict existence of peaked and step-like structures in the EVDF. Those features can be explained by analyzing the kinematics of electron trajectories in the discharge gap. Step-like structures in the EVDF near the powered electrode appear due to accumulation of electrons emitted from the dc electrode within a portion of the RF cycle, and their subsequent release. Trapping occurs when the RF
Cardenas, M. Bayani; Ford, Aimee E.; Kaufman, Matthew H.; Kessler, Adam J.; Cook, Perran L. M.
2016-12-01
Many fish lay their eggs in nests, or redds, which they construct in sediment. The viability of eggs depends on many factors, particularly their oxygenation. Because dissolved oxygen is typically saturated within the stream channel, the dissolved oxygen distribution within the redd depends on whether or not hyporheic flow and transport occur within the sediment. We conducted a series of flume and numerical flow and age transport modeling experiments with the aim of understanding the effects of salmonid redds on the hyporheic transport of young oxygenated water. Hyporheic flow was visualized directly through dye injections. Dissolved oxygen throughout the fish nest was measured using a planar optode. Experiments were conducted at various open channel flow velocities in order to understand their effect on dissolved oxygen, and computational simulations considered various sediment textures and ambient groundwater upwelling rates to add process-level insight. We found that, as also shown by previous studies, the redd topography induces multiscale hyporheic flow that effectively flushes the egg pocket location with younger presumably oxygenated water; older water upwells and forms anoxic zones. This pattern persists even at the lowest channel flow rates and at small upwelling velocities of older ambient groundwater which splits the multiscale hyporheic flow cells into isolated pockets. Large groundwater upwelling rates can shut down all the hyporheic flushing. The relatively coarse texture of the redd further promotes hyporheic flushing of the redd sediment with oxygenated water. Thus, redd morphology and sediment texture optimally combine to induce hyporheic exchange flow that delivers young oxygenated water to the egg pocket.
Singer, Kelsi N.; McKinnon, William B.; Nowicki, L. T.
2013-09-01
We have mapped fields of secondary craters around three large primary craters on Europa and Ganymede and estimated the size and velocity of the fragments that formed the secondaries using updated scaling equations for ice impacts. We characterize the upper envelope of the fragment size-velocity distribution to obtain a function for the largest fragments at a given ejection velocity. Power-law velocity exponents found in our study of icy satellite secondary fields are compared to the exponents found for similar studies of mercurian, lunar, and martian craters; for all but basin-scale impacts, fragment size decreases more slowly with increasing ejection velocity than on rocky bodies. Spallation theory provides estimates of the size of ejected spall plates at a given velocity, but this theory predicts fragments considerably smaller than are necessary to form most of our observed secondaries. In general, ejecta fragment sizes scale with primary crater diameter and decrease with increasing ejection velocity, υej, by 1/υej or greater, and point-source scaling implies a relation between the two. The largest crater represented in any of these studies, Gilgamesh on Ganymede, exhibits a relatively steep velocity dependence. Extrapolating the results to the escape speed for each icy moon yields the size of the largest fragment that could later re-impact to form a so-called sesquinary crater, either on the parent moon or a neighboring satellite. We find that craters above 2 km in diameter on Europa and Ganymede are unlikely to be sesquinaries.
Zorec, J.; Frémat, Y.; Domiciano de Souza, A.; Royer, F.; Cidale, L.; Hubert, A.-M.; Semaan, T.; Martayan, C.; Cochetti, Y. R.; Arias, M. L.; Aidelman, Y.; Stee, P.
2016-11-01
Context. Among intermediate-mass and massive stars, Be stars are the fastest rotators in the main sequence (MS) and, as such, these stars are a cornerstone to validate models of structure and evolution of rotating stars. Several phenomena, however, induce under- or overestimations either of their apparent Vsini, or true velocity V. Aims: In the present contribution we aim at obtaining distributions of true rotational velocities corrected for systematic effects induced by the rapid rotation itself, macroturbulent velocities, and binarity. Methods: We study a set of 233 Be stars by assuming they have inclination angles distributed at random. We critically discuss the methods of Cranmer and Lucy-Richardson, which enable us to transform a distribution of projected velocities into another distribution of true rotational velocities, where the gravitational darkening effect on the Vsini parameter is considered in different ways. We conclude that iterative algorithm by Lucy-Richardson responds at best to the purposes of the present work, but it requires a thorough determination of the stellar fundamental parameters. Results: We conclude that once the mode of ratios of the true velocities of Be stars attains the value V/Vc ≃ 0.77 in the main-sequence (MS) evolutionary phase, it remains unchanged up to the end of the MS lifespan. The statistical corrections found on the distribution of ratios V/Vc for overestimations of Vsini, due to macroturbulent motions and binarity, produce a shift of this distribution toward lower values of V/Vc when Be stars in all MS evolutionary stages are considered together. The mode of the final distribution obtained is at V/Vc ≃ 0.65. This distribution has a nearly symmetric distribution and shows that the Be phenomenon is characterized by a wide range of true velocity ratios 0.3 ≲ V/Vc ≲ 0.95. It thus suggests that the probability that Be stars are critical rotators is extremely low. Conclusions: The corrections attempted in the present
DEFF Research Database (Denmark)
Salewski, Mirko; Geiger, B.; Jacobsen, Asger Schou
2014-01-01
We present the first measurement of a local fast-ion 2D velocity distribution function f(v‖, v⊥). To this end, we heated a plasma in ASDEX Upgrade by neutral beam injection and measured spectra of fast-ion Dα (FIDA) light from the plasma centre in three views simultaneously. The measured spectra ...
Février, Pierre; Simonin, Olivier; Squires, Kyle D.
2005-06-01
The velocity distribution of dilute suspensions of heavy particles in gas-solid turbulent flows is investigated. A statistical approach - the mesoscopic Eulerian formalism (MEF) - is developed in which an average conditioned on a realization of the turbulent carrier flow is introduced and enables a decomposition of the instantaneous particle velocity into two contributions. The first is a contribution from an underlying continuous turbulent velocity field shared by all the particles - the mesoscopic Eulerian particle velocity field (MEPVF) - that accounts for all particle-particle and fluid-particle two-point correlations. The second contribution corresponds to a distribution - the quasi-Brownian velocity distribution (QBVD) - that represents a random velocity component satisfying the molecular chaos assumption that is not spatially correlated and identified with each particle of the system. The MEF is used to investigate properties of statistically stationary particle-laden isotropic turbulence. The carrier flow is computed using direct numerical simulation (DNS) or large-eddy simulation (LES) with discrete particle tracking employed for the dispersed phase. Particle material densities are much larger than that of the fluid and the force of the fluid on the particle is assumed to reduce to the drag contribution. Computations are performed in the dilute regime for which the influences of inter-particle collisions and fluid-turbulence modulation are neglected. The simulations show that increases in particle inertia increase the contribution of the quasi-Brownian component to the particle velocity. The particle velocity field is correlated at larger length scales than the fluid, with the integral length scales of the MEPVF also increasing with particle inertia. Consistent with the previous work of Abrahamson (1975), the MEF shows that in the limiting case of large inertia, particle motion becomes stochastically equivalent to a Brownian motion with a random spatial
Dust charge fluctuation effects on Langmuir waves with kappa distributed electrons
Jamshidi, M.; Rouhani, M. R.; Hakimi Pajouh, H.
2016-03-01
Using a kinetic description, dust charge fluctuations due to the inelastic collisions between dust particles and plasma particles are studied in unmagnetized dusty plasmas. Most astrophysical and space plasmas are observed to have non-Maxwellian high energy tail. Therefore, a kappa distribution for electrons in the equilibrium is assumed. The dispersion relation and damping rates for Langmuir waves are obtained. Considering the dust charge fluctuations increases the damping rate of Langmuir waves. It is shown that the damping rate of Langmuir waves depends on the spectral index and the dust density parameter.
Nonthermal and suprathermal distributions as a consequence of superstatistics.
Ourabah, Kamel; Ait Gougam, Leila; Tribeche, Mouloud
2015-01-01
We propose to put the well-known nonthermal and suprathermal empirical distributions, used in plasma physics, onto a more rigorous foundation. Their use is frequently criticized because of a lack of formal derivation and physical explanation. A connection between these non-Maxwellian distributions and the Beck-Cohen superstatistics is suggested. They are perceived as a consequence of typical temperature fluctuations. We show that the suprathermal distribution is generated by the Γ distribution of the inverse temperature, in the same way as the Tsallis q statistics. The nonthermal distribution also follows from the χ(2) distribution, with a small variance. Our contribution provides a possible physical meaning for these ad hoc distributions.
Dhanya, M. B.; Barabash, Stas; Wieser, Martin; Holmström, Mats; Bhardwaj, Anil; Wurz, Peter; Alok, Abhinaw; Futaana, Yoshifumi
2016-07-01
Moon is an airless body with no global magnetic field, although regions of crustal magnetic fields known as magnetic anomalies exist on Moon. Solar wind, the magnetized plasma flow from the Sun, continuously impinges on Moon. Due to the high absorption of solar wind plasma on the lunar dayside, a large scale wake structure is formed downstream of the Moon. However, recent in-situ observations have revealed the presence of protons in the near-lunar wake (100 km to 200 km from the surface). The source of these protons have been found to be the solar wind that enter the wake either directly or after interaction with the lunar surface or with the magnetic anomalies. Using the entire data from the SWIM sensor, which was an ion-mass analyzer, of the SARA experiment onboard Chandrayaan-1, the characteristics of velocity distribution of these protons were investigated to understand the entry mechanisms to near lunar wake. The velocity distribution functions were computed in the two dimensional velocity space, namely in the directions parallel and perpendicular to the IMF (v_allel and v_perp) in the solar wind rest frame. Several proton populations were identified from the velocity distribution and their possible entry mechanism were inferred based on the characteristics of the velocity distribution. These entry mechanisms include (i) diffusion of solar wind protons into the wake along IMF, (ii) the solar wind protons with finite gyro-radii that are aided by the wake boundary electric field, (iii) solar wind protons with gyro-radii larger than lunar radii from the tail of the solar wind velocity distribution, and (iv) scattering of solar wind protons from the dayside lunar surface or from magnetic anomalies. In order to gain more insight into the entry mechanisms associated with different populations, the trajectories of the protons were computed backward in time (backtracing) for each of these populations. For most of the populations, the source mechanism obtained from
Institute of Scientific and Technical Information of China (English)
LI Hua; WANG Mi; WU Ying-xiang; MA Yi-xin; WILLIAMS Richard
2005-01-01
This paper presents the use of a high performance dual-plane electrical resistance tomography (ERT) system and a local dual-sensor conductance probe to measure the vertical upward oil-in-water pipe flows in which the mean oil volume fraction is up to 23.1%.A sensitivity coefficient back-projection (SBP) algorithm was adopted to reconstruct the flow distributions and a cross correlation method was applied to obtain the oil velocity distributions. The oil volume fraction and velocity distributions obtained from both measurement techniques were compared and good agreement was found, which indicates that the ERT technique can be used to measure the low fraction oil-water flows. Finally, the factors affecting measurement precision were discussed.
James, S. R.; Knox, H. A.; Ajo Franklin, J. B.; Johnson, T. C.; Morris, J.; Grubelich, M. C.; King, D. K.
2016-12-01
Knowledge of fracture systems, including locations, morphology, and evolution, is critical for groundwater management, contaminant transport, and energy applications such as reservoir development (i.e. tight shale and geothermal) and reservoir management (i.e. carbon sequestration and wastewater injection). It has long been understood that the presence of fractures reduces bulk seismic velocity, with waves traveling perpendicular to fracture planes experiencing the strongest velocity reduction. We present results from seismic interferometry using ambient seismic noise to detect velocity changes following fracture emplacement from two energetic stimulations. Distributed Acoustic Sensing (DAS) using fiber optic cables was used to record seismic arrivals at high spatial resolution ( 3 ft). Cables were grouted in the annulus of four cased monitoring boreholes surrounding the stimulation borehole at a radius of 4 feet. Ambient noise was recorded before and after each stimulation for 12-hour time periods. We used the Python package MSNoise to compute cross-correlations of all near-horizontal (less than 60°) channel pairs between boreholes and calculated the velocity change of each time period relative to initial conditions prior to stimulation. Results show an average velocity decrease of approximately 6% following the first fracturing event. Variations between channel pairs suggest some are more strongly affected than others, which is supported by evaluation of other geophysical data. These results show promise for locating fractures based on spatial variation in velocity changes. Unsurprisingly, results following the second stimulation are generally more scattered. Some velocities are further reduced compared to those after the first stimulation while others show a relative velocity increase. These results are roughly consistent with time-lapse seismic measurements conducted using active sources and classical sensors (e.g. hydrophones). Sandia National Laboratories is
Wakker, BP; vanWoerden, H
1997-01-01
High-velocity clouds (HVCs) consist of neutral hydrogen (HI) at velocities incompatible with a simple model of differential galactic rotation; in practice one uses \\v(LSR)\\ greater than or equal to 90 km/s to define HVCs. This review describes the main features of the sky and velocity distributions,
Bekeraité, S.; Walcher, C. J.; Falcón-Barroso, J.; Garcia Lorenzo, B.; Lyubenova, M.; Sánchez, S. F.; Spekkens, K.; van de Ven, G.; Wisotzki, L.; Ziegler, B.; Aguerri, J. A. L.; Barrera-Ballesteros, J.; Bland-Hawthorn, J.; Catalán-Torrecilla, C.; García-Benito, R.
2016-10-01
We measured the distribution in absolute magnitude - circular velocity space for a well-defined sample of 199 rotating galaxies of the Calar Alto Legacy Integral Field Area Survey (CALIFA) using their stellar kinematics. Our aim in this analysis is to avoid subjective selection criteria and to take volume and large-scale structure factors into account. Using stellar velocity fields instead of gas emission line kinematics allows including rapidly rotating early-type galaxies. Our initial sample contains 277 galaxies with available stellar velocity fields and growth curve r-band photometry. After rejecting 51 velocity fields that could not be modelled because of the low number of bins, foreground contamination, or significant interaction, we performed Markov chain Monte Carlo modelling of the velocity fields, from which we obtained the rotation curve and kinematic parameters and their realistic uncertainties. We performed an extinction correction and calculated the circular velocity vcirc accounting for the pressure support of a given galaxy. The resulting galaxy distribution on the Mr-vcirc plane was then modelled as a mixture of two distinct populations, allowing robust and reproducible rejection of outliers, a significant fraction of which are slow rotators. The selection effects are understood well enough that we were able to correct for the incompleteness of the sample. The 199 galaxies were weighted by volume and large-scale structure factors, which enabled us to fit a volume-corrected Tully-Fisher relation (TFR). More importantly, we also provide the volume-corrected distribution of galaxies in the Mr-vcirc plane, which can be compared with cosmological simulations. The joint distribution of the luminosity and circular velocity space densities, representative over the range of -20 > Mr > -22 mag, can place more stringent constraints on the galaxy formation and evolution scenarios than linear TFR fit parameters or the luminosity function alone. Galaxies main
Institute of Scientific and Technical Information of China (English)
Akira OGAWA; Tutomu OONO; Hayato OKABE; Noriaki AKIBA; Taketo OOYAGI
2005-01-01
@@ Vortex flow is applied to a cyclone dust collector, a vortex combustion chamber, and a vortex diode for vortex control. In order to apply the vortex flow to the industries, it is necessary to keep the stable flow condition and to estimate the response time of the transient flow process and also the intensity of the vortex flow. For control vortex flow, two types of vortex chamber with two inlet pipes were designed. One of them is to promote the vortex flow named as Co-Rotating Flow System and another one is to hinder the vortex flow named as Counter-Rotating Flow System. The pressure drops and the velocity distributions were measured for these vortex chambers. The estimation of the tangential velocity by the application of the angular momentum flux is compared with the measured velocity by a cylindrical Pitot-tube. The characteristics of the total pressure drop could be explained by introducing the circulation.
Plasma expansion into vacuum assuming a steplike electron energy distribution.
Kiefer, Thomas; Schlegel, Theodor; Kaluza, Malte C
2013-04-01
The expansion of a semi-infinite plasma slab into vacuum is analyzed with a hydrodynamic model implying a steplike electron energy distribution function. Analytic expressions for the maximum ion energy and the related ion distribution function are derived and compared with one-dimensional numerical simulations. The choice of the specific non-Maxwellian initial electron energy distribution automatically ensures the conservation of the total energy of the system. The estimated ion energies may differ by an order of magnitude from the values obtained with an adiabatic expansion model supposing a Maxwellian electron distribution. Furthermore, good agreement with data from experiments using laser pulses of ultrashort durations τ(L)Maxwellian electron distribution is assumed.
Energy Technology Data Exchange (ETDEWEB)
Xu, Z.; Koplitz, B.; Wittig, C.
1987-07-15
We report center-of-mass kinetic energy distributions for the 193 nm photodissociation of H/sub 2/S and HBr using the method of velocity--aligned Doppler spectroscopy. Nascent H atoms are detected by sequential two-photon photoionization via Lyman-..cap alpha.. (121.6 nm + 364.7 nm), and internal SH(X /sup 2/Pi) and Br excitations are observed directly in the H-atom kinetic energy distributions. The kinetic energy resolution is much better than in ''conventional'' sub-Doppler resolution spectroscopy and results from detecting spatially selected species whose velocities are aligned with the wave vector of the probe radiation, k/sub probe/, thereby providing a kinetic energy distribution for a specific laboratory direction. This improved resolution is achieved in the present experiments by using pulsed, collimated, and overlapped photolysis and probe beams, but the vital aspect of the technique involves increasing the delay between the two lasers in order to discriminate against species having velocity components perpendicular to k/sub probe/.
Winthaegen, P.L.A.; Verweij, J.M.
2003-01-01
The application of the empirical Eaton method to calibrated sonic well information and 3D seismic interval velocity data in the southeastern part of the Central North Sea Graben, using the Japsen (Glob. Planet. Change 24 (2000) 189) normal velocitydepth trend, resulted in the identification of an
DISTRIBUTION AND ORIGIN OF HIGH-VELOCITY CLOUDS .2. STATISTICAL-ANALYSIS OF THE WHOLE-SKY SURVEY
WAKKER, BP
1991-01-01
A sensitive, almost complete, whole-sky survey of high-velocity clouds (HVCs) has been made available by Bajaja et al. (1985) and Hulsbosch & Wakker (1988, Paper I). This paper (Paper II in a series on HVCs) is dedicated to the analysis of the statistical properties of these surveys. The main conclu
Winthaegen, P.L.A.; Verweij, J.M.
2003-01-01
The application of the empirical Eaton method to calibrated sonic well information and 3D seismic interval velocity data in the southeastern part of the Central North Sea Graben, using the Japsen (Glob. Planet. Change 24 (2000) 189) normal velocitydepth trend, resulted in the identification of an un
Wan, X.; Tse, P. W.; Xu, G. H.; Tao, T. F.; Zhang, Q.
2016-04-01
Most previous studies on nonlinear Lamb waves are conducted using mode pairs that satisfying strict phase velocity matching and non-zero power flux criteria. However, there are some limitations in existence. First, strict phase velocity matching is not existed in the whole frequency bandwidth; Second, excited center frequency is not always exactly equal to the true phase-velocity-matching frequency; Third, mode pairs are isolated and quite limited in number; Fourth, exciting a single desired primary mode is extremely difficult in practice and the received signal is quite difficult to process and interpret. And few attention has been paid to solving these shortcomings. In this paper, nonlinear S0 mode Lamb waves at low-frequency range satisfying approximate phase velocity matching is proposed for the purpose of overcoming these limitations. In analytical studies, the secondary amplitudes with the propagation distance considering the fundamental frequency, the maximum cumulative propagation distance (MCPD) with the fundamental frequency and the maximum linear cumulative propagation distance (MLCPD) using linear regression analysis are investigated. Based on analytical results, approximate phase velocity matching is quantitatively characterized as the relative phase velocity deviation less than a threshold value of 1%. Numerical studies are also conducted using tone burst as the excitation signal. The influences of center frequency and frequency bandwidth on the secondary amplitudes and MCPD are investigated. S1-S2 mode with the fundamental frequency at 1.8 MHz, the primary S0 mode at the center frequencies of 100 and 200 kHz are used respectively to calculate the ratios of nonlinear parameter of Al 6061-T6 to Al 7075-T651. The close agreement of the computed ratios to the actual value verifies the effectiveness of nonlinear S0 mode Lamb waves satisfying approximate phase velocity matching for characterizing the material nonlinearity. Moreover, the ratios derived from
Energy Technology Data Exchange (ETDEWEB)
A. Poerschke, R. Beach, T. Begg
2017-06-01
IBACOS investigated the performance of a small-diameter high-velocity heat pump system compared to a conventional system in a new construction triplex townhouse. A ductless heat pump system also was installed for comparison, but the homebuyer backed out because of aesthetic concerns about that system. In total, two buildings, having identical solar orientation and comprised of six townhomes, were monitored for comfort and energy performance.
Ho, Shirley
2010-01-01
Radial velocity (RV) observations of an exoplanet system giving a value of M_T sin(i) condition (ie. give information about) not only the planet's true mass M_T but also the value of sin(i) for that system (where i is the orbital inclination angle). Thus the value of sin(i) for a system with any particular observed value of M_T sin(i) cannot be assumed to be drawn randomly from a distribution corresponding to an isotropic i distribution, i.e. the presumptive prior distribution . Rather, the posterior distribution from which it is drawn depends on the intrinsic distribution of M_T for the exoplanet population being studied. We give a simple Bayesian derivation of this relationship and apply it to several "toy models" for the (currently unknown) intrinsic distribution of M_T. The results show that the effect can be an important one. For example, even for simple power-law distributions of M_T, the median value of sin(i) in an observed RV sample can vary between 0.860 and 0.023 (as compared to the 0.866 value for...
Evolution of The Proton Velocity Distribution due to Stochastic Heating in the Near-Sun Solar Wind
Klein, Kristopher G
2016-01-01
We investigate how the proton distribution function evolves when the protons undergo stochastic heating by strong, low-frequency, Alfv\\'en-wave turbulence under the assumption that $\\beta$ is small. We apply our analysis to protons undergoing stochastic heating in the supersonic fast solar wind and obtain proton distributions at heliocentric distances ranging from 4 to 30 solar radii. We find that the proton distribution develops non-Gaussian structure with a flat core and steep tail. For $r >5 \\ R_{\\rm S}$, the proton distribution is well approximated by a modified Moyal distribution. Comparisons with future measurements from \\emph{Solar Probe Plus} could be used to test whether stochastic heating is occurring in the solar-wind acceleration region.
Nishioka, T; Shikama, T; Nagamizo, S; Fujii, K; Zushi, H; Uchida, M; Iwamae, A; Tanaka, H; Maekawa, T; Hasuo, M
2013-07-01
The anisotropy of the electron velocity distribution function (EVDF) in plasmas can be deduced from the polarization of emissions induced by anisotropic electron-impact excitation. In this paper, we develop a compact thermal lithium atom beam source for spatially resolved measurements of the EVDF anisotropy in electron cyclotron resonance (ECR) plasmas. The beam system is designed such that the ejected beam has a slab shape, and the beam direction is variable. The divergence and flux of the beam are evaluated by experiments and calculations. The developed beam system is installed in an ECR plasma device with a cusp magnetic field, and the LiI 2s-2p emission (670.8 nm) is observed in low-pressure helium plasma. The two-dimensional distributions of the degree and direction of the polarization in the LiI emission are measured by a polarization imaging system. The evaluated polarization distribution suggests the spatial variation of the EVDF anisotropy.
Xu, Z.; Koplitz, B.; Wittig, C.
1987-07-01
We report center-of-mass kinetic energy distributions for the 193 nm photodissociation of H2S and HBr using the method of velocity-aligned Doppler spectroscopy. Nascent H atoms are detected by sequential two-photon photoionization via Lyman-α (121.6 nm + 364.7 nm), and internal SH(X 2Π) and Br excitations are observed directly in the H-atom kinetic energy distributions. The kinetic energy resolution is much better than in ``conventional'' sub-Doppler resolution spectroscopy and results from detecting spatially selected species whose velocities are aligned with the wave vector of the probe radiation, kprobe, thereby providing a kinetic energy distribution for a specific laboratory direction. This improved resolution is achieved in the present experiments by using pulsed, collimated, and overlapped photolysis and probe beams, but the vital aspect of the technique involves increasing the delay between the two lasers in order to discriminate against species having velocity components perpendicular to kprobe. In the case of HBr, we identify the Br(2P3/2) and Br(2P1/2) contributions and find that the Br(2P1/2) channel accounts for approximately 14% of the fragmentation associated with perpendicular electronic transitions. Concerning H2S, SH(X 2Π) vibrational structure is clearly evident in the H-atom kinetic energy distribution, and the SH vibrational distribution shows oscillations, with [v″=0]>[v″=1], [v″=1][v″=3], [v″=3][v″=5]. Such oscillatory behavior was predicted theoretically by Kulander. A simulation of our data places 32% of the SH in v″>0 (˜2700 cm-1, which is approximately 14% of the available energy, hν-D0), while the general features of our H2S data are in accord with the TOF study of van Veen et al. Presently, our measurements appear to be limited by the dye laser resolution (˜0.06 cm-1 at 364.7 nm), but a significant improvement of the laser bandwidth is possible using commercially available sources. The velocity-aligned Doppler
Li, Cheng; Kauffmann, Guinevere; Boerner, Gerhard; Kang, Xi; Wang, Lan; 10.1111/j.1365-2966.2007.11518.x
2008-01-01
By comparing semi-analytic galaxy catalogues with data from the Sloan Digital Sky Survey (SDSS), we show that current galaxy formation models reproduce qualitatively the dependence of galaxy clustering and pairwise peculiar velocities on luminosity, but some subtle discrepancies with the data still remain. The comparisons are carried out by constructing a large set of mock galaxy redshift surveys that have the same selection function as the SDSS Data Release Four (DR4). The mock surveys are based on two sets of semi-analytic catalogues presented by Croton et al. and Kang et al. From the mock catalogues, we measure the redshift-space projected two-point correlation function, the power spectrum, and the pairwise velocity dispersion (PVD) in Fourier space and in configuration space, for galaxies in different luminosity intervals. We then compare these theoretical predictions with the measurements derived from the SDSS DR4. On large scales and for galaxies brighter than L*, both sets of mock catalogues agree well...
Energy velocity and group velocity
Institute of Scientific and Technical Information of China (English)
陈宇
1995-01-01
A new Lagrangian method for studying the relationship between the energy velocity and the group velocity is described. It is proved that under the usual quasistatic electric field, the energy velocity is identical to the group velocity for acoustic waves in anisotropic piezoelectric (or non-piezoelectric) media.
The Distribution of Dark Matter in the Milky Way's Disk
Pillepich, Annalisa; Kuhlen, Michael; Guedes, Javiera; Madau, Piero
2014-04-01
We present an analysis of the effects of dissipational baryonic physics on the local dark matter (DM) distribution at the location of the Sun, with an emphasis on the consequences for direct detection experiments. Our work is based on a comparative analysis of two cosmological simulations with identical initial conditions of a Milky Way halo, one of which (Eris) is a full hydrodynamic simulation and the other (ErisDark) is a DM-only one. We find that in Eris two distinct processes lead to a 30% enhancement of DM in the disk plane at the location of the Sun: the accretion and disruption of satellites resulting in a DM component with net angular momentum, and the contraction of baryons pulling the DM into the disk plane without forcing it to co-rotate. Owing to its particularly quiescent merger history for dark halos of Milky Way mass, the co-rotating dark disk in Eris is less massive than what has been suggested by previous work, contributing only 9% of the local DM density. Yet, since the simulation results in a realistic Milky Way analog galaxy, its DM halo provides a plausible alternative to the Maxwellian standard halo model (SHM) commonly used in direct detection analyses. The speed distribution in Eris is broadened and shifted to higher speeds, compared to its DM-only twin simulation ErisDark. At high speeds f(v) falls more steeply in Eris than in ErisDark or the SHM, easing the tension between recent results from the CDMS-II and XENON100 experiments. The non-Maxwellian aspects of f(v) are still present, but much less pronounced in Eris than in the DM-only runs. The weak dark disk increases the time-averaged scattering rate by only a few percent at low recoil energies. On the high velocity tail, however, the increase in typical speeds due to baryonic contraction results in strongly enhanced mean scattering rates compared to ErisDark, although they are still suppressed compared to the SHM. Similar trends are seen regarding the amplitude of the annual modulation
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
@@ Numerical modelling of velocity and temperature fields in high-temperature KNbO3 melt of a loop-shaped Pt wire heater is carried out by using the commercial com putational code ANSYS for the mathematical solution of the governing equations.Based on the experimental boundary conditions and the Boussinesq approximation,the numerical modelling of a steady and two-dimensional model is applied to study the process under consideration of the buoyancy-driven convection condition. The result is compared with the previous experimental and theoretical data obtained in our laboratory, and the former is in agreement with the latter. Thus a theoretical guide for reasonable growth conditions is provided by studying in depth the real fluid flow effects in the crystal growth from the melt.
DEFF Research Database (Denmark)
Artemieva, Irina; Vinnik, Lev
2016-01-01
across) lowdensity (down to 3.34 g/cm3) and high-density (up to 3.41 g/cm3) anomalies. High (3.40–3.42 g/cm3) mantle densities beneath the Eastern Cape Fold belt require the presence of a significant amount of eclogite in the mantle, such as associated with subducted oceanic slabs. We find a strong...... the composition and rheology of the lithospheric mantle to make it unfavorable for consequent kimberlite eruptions. (5) Density anomalies in the lithospheric mantle show inverse correlation with seismic Vp, Vs velocities at 100–150 km depth. However, this correlation is weaker than reported in experimental...
Salewski, Mirko; Jacobsen, Asger Schou; Garcıa-Munoz, Manuel; Heidbrink, Bill; Korsholm, Soren Bang; Leipold, Frank; Madsen, Jens; Moseev, Dmitry; Nielsen, Stefan Kragh; Rasmussen, Jesper; Stejner, Morten; Tardini, Giovanni; Weiland, Markus
2015-01-01
We present the first measurement of a local fast-ion 2D velocity distribution function $f(v_\\parallel, v_\\perp)$. To this end, we heated a plasma in ASDEX Upgrade by neutral beam injection and measured spectra of fast-ion D-alpha (FIDA) light from the plasma center in three views simultaneously. The measured spectra agree very well with synthetic spectra calculated from a TRANSP/NUBEAM simulation. Based on the measured FIDA spectra alone, we infer $f(v_\\parallel, v_\\perp)$ by tomographic inversion. Salient features of our measurement of $f(v_\\parallel, v_\\perp)$ agree reasonably well with the simulation: the measured as well as the simulated $f(v_\\parallel, v_\\perp)$ are lopsided towards negative velocities parallel to the magnetic field, and they have similar shapes. Further, the peaks in the simulation of $f(v_\\parallel, v_\\perp)$ at full and half injection energies of the neutral beam also appear in the measurement at similar velocity-space locations. We expect that we can measure spectra in up to seven vi...
DEFF Research Database (Denmark)
Hansen, Kurt Schaldemose
2007-01-01
The statistical distribution of extreme wind excursions above a mean level, for a specified recurrence period, is of crucial importance in relation to design of wind sensitive structures. This is particularly true for wind turbine structures. Based on an assumption of a Gaussian "mother" distribu......The statistical distribution of extreme wind excursions above a mean level, for a specified recurrence period, is of crucial importance in relation to design of wind sensitive structures. This is particularly true for wind turbine structures. Based on an assumption of a Gaussian "mother...
Directory of Open Access Journals (Sweden)
Hong-fu Guo
2017-01-01
Full Text Available Particle size and distribution play an important role in ignition. The size and distribution of the cyclotetramethylene tetranitramine (HMX particles were investigated by Laser Particle Size Analyzer Malvern MS2000 before experiment and calculation. The mean size of particles is 161 μm. Minimum and maximum sizes are 80 μm and 263 μm, respectively. The distribution function is like a quadratic function. Based on the distribution of micron scale explosive particles, a microscopic model is established to describe the process of ignition of HMX particles under drop weight. Both temperature of contact zones and ignition probability of powder explosive can be predicted. The calculated results show that the temperature of the contact zones between the particles and the drop weight surface increases faster and higher than that of the contact zones between two neighboring particles. For HMX particles, with all other conditions being kept constant, if the drop height is less than 0.1 m, ignition probability will be close to 0. When the drop heights are 0.2 m and 0.3 m, the ignition probability is 0.27 and 0.64, respectively, whereas when the drop height is more than 0.4 m, ignition probability will be close to 0.82. In comparison with experimental results, the two curves are reasonably close to each other, which indicates our model has a certain degree of rationality.
Energy Technology Data Exchange (ETDEWEB)
Pascale, J. [CEA Centre d`Etudes de Saclay, 91 - Gif-sur-Yvette (France). Dept. de Recherche sur l`Etat Condense, les Atomes et les Molecules; Jacquet, E.; Boduch, P.; Chantepie, M.; Lecler, D. [Caen Univ., 14 (France). Lab. de Spectroscopie Atomique
1994-12-31
The effect of the velocity of the incident ions in the l-distributions of the electron capture in collisions of highly charged Ar{sup 8+} ions with a Li(2s) target is studied. These Ar{sup 8+} - Li(2s) collisions are experimentally studied by means of near UV and visible photon spectroscopy (200-600 nm) and theoretically analysed by means of three-body classical trajectory Monte-Carlo method. In addition to the effect of the projectile core, we show that the final nl-distributions are, for the most populated n = 8 and n = 9 states strongly energy dependent. (authors). 11 refs., 3 figs., 2 tabs.
Measures for Improving Velocity Distribution in Oxidation Ditch%改善氧化沟流速分布的措施
Institute of Scientific and Technical Information of China (English)
曹瑞钰; 付见中
2001-01-01
Velocity distribution in oxidation ditch can be improved by installing front baffle and back baffle based on researches and simulation tests,so that sludge deposit in the bottom of oxidation ditch can be eliminated.The velocity distribution diagrams of different cross-section before and after installing the baffles are presented in this paper.Moreover related suggestion on the problems appeared in design and construction of oxidation ditch is also given.%通过多年的研究和模拟试验，提出了加装前后导流板的措施以改善氧化沟的流速分布，消除目前氧化沟所存在的通病——池底积泥现象，而且很直观地给出了安装导流板前后的氧化沟各断面流速分布图。另外，还就目前氧化沟的设计和建造中出现的问题提出了相关的建议。
Bajkova, A T
2016-01-01
Three three-component (bulge, disk, halo) model Galactic gravitational potentials differing by the expression for the dark matter halo are considered. The central (bulge) and disk components are described by the Miyamoto-Nagai expressions. The Allen-Santill'an (I), Wilkinson-Evans (II), and Navarro-Frenk-White (III) models are used to describe the halo. A set of present-day observational data in the range of Galactocentric distances R from 0 to 200 kpc is used to refine the parameters of these models. The model rotation curves have been fitted to the observed velocities by taking into account the constraints on the local matter density \\rho_\\odotand the force K_{z=1.1} acting perpendicularly to the Galactic plane. The Galactic mass within a sphere of radius 50 kpc, M_G (R<=50 kpc)=(0.41+/-0.12)x10^12 M_\\odot, is shown to satisfy all three models. The differences between the models become increasingly significant with increasing radius R. In model I, the Galactic mass within a sphere of radius 200 kpc turns...
Yoganandan, Narayan; Fitzharris, Michael; Pintar, Frank A.; Stemper, Brian D.; Rinaldi, James; Maiman, Dennis J.; Fildes, Brian N.
2011-01-01
The objective of the study was to determine differences between the United States-based NASS and CIREN and Australia-based ANCIS databases in occupant-, crash-, and vehicle-related parameters for AIS 4+ head injuries in motor vehicle crashes. Logistic regression analysis was performed to examine roles of the change in velocity (DV), crash type (frontal, far-side, nearside, rear impact), seatbelt use, and occupant position, gender, age, stature, and body mass in cranial traumas. Belted and unbelted non-ejected occupant (age >16 years) data from 1997–2006 were used for the NASS and CIREN datasets, and 2000–2010 for ANCIS. Vehicle model year, and occupant position and demographics including body mass index (BMI) data were obtained. Injuries were coded using AIS 1990–1998 update. Similarities were apparent across all databases: mean demographics were close to the mid-size anthropometry, mean BMI was in the normal to overweight range, and representations of extreme variations were uncommon. Side impacts contributed to over one-half of the ensemble, implying susceptibility to head trauma in this mode. Odds of sustaining head injury increased by 4% per unit increase in DV (OR: 1.04, 95% CI: 1.03–1.04, pcrash- and occupant-related outcomes from the two continents indicate a worldwide need to revise the translation acceleration-based head injury criterion to include the angular component in an appropriate format for improved injury assessment and mitigation. PMID:22105402
Energy Technology Data Exchange (ETDEWEB)
2017-06-09
IBACOS investigated the performance of a small-diameter high velocity heat pump system compared to a conventional system in a new construction triplex townhouse. A ductless heat pump system also was installed for comparison, but the homebuyer backed out because of aesthetic concerns about that system. In total, two buildings, having identical solar orientation and comprised of six townhomes, were monitored for comfort and energy performance. Results show that the small-diameter system provides more uniform temperatures from floor to floor in the three-story townhome. No clear energy consumption benefit was observed from either system. The builder is continuing to explore the small-diameter system as its new standard system to provide better comfort and indoor air quality. The homebuilder also explored the possibility of shifting its townhome product to meet the U.S. Department of Energy Challenge Home National Program Requirements. Ultimately, the builder decided that adoption of these practices would be too disruptive midstream in the construction cycle. However, the townhomes met the ENERGY STAR Version 3.0 program requirements.
Energy Technology Data Exchange (ETDEWEB)
Bouzit, Omar, E-mail: omar.bouzit@yahoo.fr; Tribeche, Mouloud, E-mail: mouloudtribeche@yahoo.fr, E-mail: mtribeche@usthb.dz [Plasma Physics Group (PPG), Theoretical Physics Laboratory (TPL), Faculty of Physics, University of Bab-Ezzouar, U.S.T.H.B, B.P. 32, El Alia, Algiers 16111 (Algeria); Bains, A. S., E-mail: bainsphysics@yahoo.co.in [Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Saskatchewan S7N5E2 (Canada)
2015-08-15
Modulation instability of ion-acoustic waves (IAWs) is investigated in a collisionless unmagnetized one dimensional plasma, containing positive ions and electrons following the mixed nonextensive nonthermal distribution [Tribeche et al., Phys. Rev. E 85, 037401 (2012)]. Using the reductive perturbation technique, a nonlinear Schrödinger equation which governs the modulation instability of the IAWs is obtained. Valid range of plasma parameters has been fixed and their effects on the modulational instability discussed in detail. We find that the plasma supports both bright and dark solutions. The valid domain for the wave number k where instabilities set in varies with both nonextensive parameter q as well as non thermal parameter α. Moreover, the analysis is extended for the rational solutions of IAWs in the instability regime. Present study is useful for the understanding of IAWs in the region where such mixed distribution may exist.
1946-06-01
2 x 2 y y xx XT x y xy (l - Xii ^ - Iti */) <pyy . 0 (16) where subscripts denote partial differentiation. For the special case V = -1...Ya = Y0 + fi, x3 = Xo - 6. y3 = Yo« X* = Xo» Y* • Yo - s« 6 "being a small positive number. Denote the value of a function Q at ( xii y"i) hy...FEAXUHK Pnclass. |jun’lɞ| pj \\ 1$ I tablas , grapho AOSTOAOT LAHGUAGt Sng. po A method for computing pressure distribution along
山西地区面波相速度分布图像%Rayleigh-wave phase velocity distribution in Shanxi region
Institute of Scientific and Technical Information of China (English)
宋美琴; 何正勤; 郑勇; 吕芳; 刘春; 梁向军; 苏燕; 李丽
2013-01-01
In this work,seismic datas are taken from seismograms of over 100 earthquakes which are recorded from Feburary in 2009 to November in 2011 at 31 stations in Shanxi Province and other 6 broadband stations in adjacent areas,including Hebei,Henan,Shanxi and Neimeng Province.We obtained 350 high-quality Rayleigh wave phase velocity dispersion curves of fundamental mode by removing the duplicate paths and low quality data.The periods of the dispersion curves range from 8 to 75 seconds.Based on the method of Ditmar & Yanovskaya,we obtained phase velocity dispersion maps in 33 periods with resolution ranges from 40 to 50 km.We analyzed the phase velocity distribution maps at four representative periods and the phase velocity section maps along three profiles.The phase velocity maps reveal the lateral heterogeneity of the velocity structure and the phase speed variation with depth in the crust and the upper mantle of the Shanxi fault depression zone.The phase velocity map at 10 s clearly shows the spatial differences between the rift zone and the uplift zones in the two sides,presenting low phase velocity anomalies in the maximum depression regions near the centers of several basins inside the rift zone Moderate to strong earthquakes(M≥6)in Shanxi are mostly concentrated in the transitional zones where dramatic phase velocity changes occur at 15 s.At 20～26 s period,significant phase velocity difference can be observed across the latitude of 38°N,where phase velocity is higher in the south side than that in the north,which is in consistent with the variation pattern of Moho depth in the depression zone.This kind of velocity pattern keeps constant with the increase of period,which is consistent with the feature that the blocks in the north Shanxi is relatively weaker than those in the south.Along 113°E,the phase velocities at periods of 25～75 s are higher in the north side of latitude 38°N than in the south.This is consistent with the result of the lithospheric
Bajkova, A. T.; Bobylev, V. V.
2016-09-01
Three three-component (bulge, disk, halo) model Galactic gravitational potentials differing by the expression for the dark matter halo are considered. The central (bulge) and disk components are described by the Miyamoto-Nagai expressions. The Allen-Santillán (I), Wilkinson-Evans (II), and Navarro-Frenk-White (III) models are used to describe the halo. A set of present-day observational data in the range of Galactocentric distances R from 0 to 200 kpc is used to refine the parameters of thesemodels. For the Allen-Santillán model, a dimensionless coefficient γ has been included as a sought-for parameter for the first time. In the traditional and modified versions, γ = 2.0 and 6.3, respectively. Both versions are considered in this paper. The model rotation curves have been fitted to the observed velocities by taking into account the constraints on the local matter density ρ ⊙ = 0.1 M ⊙ pc-3 and the force K z =1.1/2 πG = 77 M ⊙ pc-2 acting perpendicularly to the Galactic plane. The Galactic mass within a sphere of radius 50 kpc, M G ( R ≤ 50 kpc) ≈ (0.41 ± 0.12) × 1012 M ⊙, is shown to satisfy all three models. The differences between the models become increasingly significant with increasing radius R. In model I, the Galactic mass within a sphere of radius 200 kpc at γ = 2.0 turns out to be greatest among the models considered, M G ( R ≤ 200 kpc) = (1.45 ±0.30)× 1012 M ⊙, M G ( R ≤ 200 kpc) = (1.29± 0.14)× 1012 M ⊙ at γ = 6.3, and the smallest value has been found in model II, M G ( R ≤ 200 kpc) = (0.61 ± 0.12) × 1012 M ⊙. In our view, model III is the best one among those considered, because it ensures the smallest residual between the data and the constructed model rotation curve provided that the constraints on the local parameters hold with a high accuracy. Here, the Galactic mass is M G ( R ≤ 200 kpc) = (0.75 ± 0.19) × 1012 M ⊙. A comparative analysis with the models by Irrgang et al. (2013), including those using
Figueroa-Vinas, Adolfo; Gurgiolo, Chris A.; Nieves-Chinchilla, Teresa; Goldstein, Melvyn L.
2010-01-01
It has been suggested by a number of authors that the solar wind electron halo can be formed by the scattering of the strahl. On frequent occasions we have observed in electron angular skymaps (Phi/Theta-plots) of the electron 3D velocity distribution functions) a bursty-filament of particles connecting the strahl to the solar wind core-halo. These are seen over a very limited energy range. When the magnetic field is well off the nominal solar wind flow direction such filaments are inconsistent with any local forces and are probably the result of strong scattering. Furthermore, observations indicates that the strahl component is frequently and significantly anisotropic (Tper/Tpal approx.2). This provides a possible free energy source for the excitation of whistler waves as a possible scattering mechanism. The empirical observational evidence between the halo and the strahl suggests that the strahl population may be, at least in part, the source of the halo component.
Validation and comparison of bend circulation velocity distribution formulas%弯道环流流速公式的验证与比较
Institute of Scientific and Technical Information of China (English)
李志威; 方春明; 邵佳
2011-01-01
弯道环流流速公式是弯道水力学理论研究的重要内容.给出了弯道环流流速公式的一般理论推导过程,归纳了国内外5种具有代表性的环流流速公式,即罗索夫斯基公式、张红武公式、Odgaard公式、孙东坡公式以及罗索夫斯基修正公式,并采用弯道水槽及模型资料予以验证和比较,同时对3种罗氏公式的近似式进行了验证.验证结果表明,罗氏公式的3种近似式中,只有丁君松的近似式是精度较高,其它两种均有较大偏差.5种代表性的环流流速公式,张红武公式的精度高和可靠性强,其次是罗氏公式和Odgaard公式,孙东坡公式与张红武的实测资料存在一定偏差,而罗索夫斯基修正公式的形式不尽合理,在近底区域与实测资料分歧较大,甚至与定性规律相悖.%The velocity distribution formula of bend secondary flow is still an important content of theoretical research of meandering rivers. The general deduction process of the circulation velocity formula is presented. This paper summarizes five representative circulation velocity formulas, namely Rozovskii's formula, Zhang Honghu's formula, Odgaard's formula, Sun Dongpo's formula and modified Rozovskii formula. The Rozovskii's and Zhang Hongwu's experimental data are used to validate and compare the five formulas, including three approximate expressions of Rozovskii's formula. The validation results show that the precision of Ding Junsong's approximate expressions is higher, and the deviation of other two experssions is larger. In five representative circulation velocity formulas, the precision and reliability of Zhang's formula is the best, followed by Rozovskii's and Odgaard's formulas, and Sun's formula is poorly accorded with Zhang Hongwu's experimental data. The format of approximate expressions of modified Rozovskiis formula may be unreasonable, and especially in near bed zone it is apparently anamorphic and inconsistent with the qualitative
Min, Kyungguk; Liu, Kaijun; Gary, S. Peter
2016-03-01
A ring-like proton velocity distribution with ∂fp(v⊥)/∂v⊥>0 and which is sufficiently anisotropic can excite two distinct types of growing modes in the inner magnetosphere: ion Bernstein instabilities with multiple ion cyclotron harmonics and quasi-perpendicular propagation and an Alfvén-cyclotron instability at frequencies below the proton cyclotron frequency and quasi-parallel propagation. Recent particle-in-cell simulations have demonstrated that even if the maximum linear growth rate of the latter instability is smaller than the corresponding growth of the former instability, the saturation levels of the fluctuating magnetic fields can be greater for the Alfvén-cyclotron instability than for the ion Bernstein instabilities. In this study, linear dispersion theory and two-dimensional particle-in-cell simulations are used to examine scalings of the linear growth rate and saturation level of the two types of growing modes as functions of the temperature anisotropy T⊥/T|| for a general ring-like proton distribution with a fixed ring speed of 2vA, where vA is the Alfvén speed. For the proton distribution parameters chosen, the maximum linear theory growth rate of the Alfvén-cyclotron waves is smaller than that of the fastest-growing Bernstein mode for the wide range of anisotropies (1≤T⊥/T||≤7) considered here. Yet the corresponding particle-in-cell simulations yield a higher saturation level of the fluctuating magnetic fields for the Alfvén-cyclotron instability than for the Bernstein modes as long as T⊥/T|| ≳ 3. Since fast magnetosonic waves with ion Bernstein instability properties observed in the magnetosphere are often not accompanied by electromagnetic ion cyclotron waves, the results of the present study indicate that the ring-like proton distributions responsible for the excitation of these fast magnetosonic waves should not be very anisotropic.
Effects of non-equilibrium particle distributions in deuterium-tritium burning
Energy Technology Data Exchange (ETDEWEB)
Michta, D; Graziani, F; Pruet, J; Luu, T
2009-08-18
We investigate the effects of non-equilibrium particle distributions resulting from rapid deuterium-tritium burning in plasmas using a Fokker-Planck code that incorporates small-angle Coulomb scattering, Brehmsstrahlung, Compton scattering, and thermal-nuclear burning. We find that in inertial confinement fusion environments, deviations away from Maxwellian distributions for either deuterium or tritium ions are small and result in 1% changes in the energy production rates. The deuterium and tritium effective temperatures are not equal, but differ by only about 2.5% near the time of peak burn rate. Simulations with high Z (Xe) dopants show that the dopant temperature closely tracks that of the fuel. On the other hand, fusion product ion distributions are highly non-Maxwellian, and careful treatments of energy-exchange between these ions and other particles is important for determining burn rates.
Self-Consistent Fokker-Planck Treatment Of Particle Distributions in Astrophysical Plasmas
Nayakshin, S; Nayakshin, Sergei; Melia, Fulvio
1997-01-01
High-energy, multi-component plasmas in which pair creation and annihilation, lepton-lepton scattering, lepton-proton scattering, and Comptonization all contribute to establishing the particle and photon distributions, are present in a broad range of compact astrophysical objects. Earlier work has included much of the microphysics needed to account for electron-photon and electron-proton interactions, but little has been done to handle the redistribution of the particles as a result of their Coulomb interaction with themselves in an arbitrary case. Our goal here is to use a Fokker-Planck approach in order to develop a fully self-consistent theory for the interaction of arbitrarily distributed particles and radiation to arrive at an accurate representation of the high-energy plasma in these sources. We conduct several tests representative of two dominant segments of parameter space and discuss physical implications of the non-Maxwellian distribution function. Approximate analytical forms for the electron distr...
The distribution of dark matter in the Milky Way's disk
Energy Technology Data Exchange (ETDEWEB)
Pillepich, Annalisa; Kuhlen, Michael; Madau, Piero [Department of Astronomy and Astrophysics, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Guedes, Javiera, E-mail: apillepich@cfa.harvard.edu [ETH Zurich, Institute for Astronomy, Wolfgang-Pauli-Strasse 27, CH-8049 Zurich (Switzerland)
2014-04-01
We present an analysis of the effects of dissipational baryonic physics on the local dark matter (DM) distribution at the location of the Sun, with an emphasis on the consequences for direct detection experiments. Our work is based on a comparative analysis of two cosmological simulations with identical initial conditions of a Milky Way halo, one of which (Eris) is a full hydrodynamic simulation and the other (ErisDark) is a DM-only one. We find that in Eris two distinct processes lead to a 30% enhancement of DM in the disk plane at the location of the Sun: the accretion and disruption of satellites resulting in a DM component with net angular momentum, and the contraction of baryons pulling the DM into the disk plane without forcing it to co-rotate. Owing to its particularly quiescent merger history for dark halos of Milky Way mass, the co-rotating dark disk in Eris is less massive than what has been suggested by previous work, contributing only 9% of the local DM density. Yet, since the simulation results in a realistic Milky Way analog galaxy, its DM halo provides a plausible alternative to the Maxwellian standard halo model (SHM) commonly used in direct detection analyses. The speed distribution in Eris is broadened and shifted to higher speeds, compared to its DM-only twin simulation ErisDark. At high speeds f(v) falls more steeply in Eris than in ErisDark or the SHM, easing the tension between recent results from the CDMS-II and XENON100 experiments. The non-Maxwellian aspects of f(v) are still present, but much less pronounced in Eris than in the DM-only runs. The weak dark disk increases the time-averaged scattering rate by only a few percent at low recoil energies. On the high velocity tail, however, the increase in typical speeds due to baryonic contraction results in strongly enhanced mean scattering rates compared to ErisDark, although they are still suppressed compared to the SHM. Similar trends are seen regarding the amplitude of the annual modulation
Modeling of Neutral Entrainment in an FRC Thruster
2012-07-01
nonequilibirum; ion, electron, and neutral temperatures strongly differ, and the electron distribution function is non - Maxwellian . This indicates that a...as keii = ∫ gσeii(g) fe(g)dg, (1) where g is the relative collision velocity and fe is the Maxwellian distribution function. For the charge exchange...plasma temperature and concentration of reacting species, non -equlibrium of their velocity distributions, and the relashionship between different reaction
Wojdowski, Patrick S; Kallman, Timothy R
2007-01-01
We present here X-ray spectra of the HMXB SMC X-1 obtained in an observation with the XMM observatory beginning before eclipse and ending near the end of eclipse. With the Reflection Grating Spectrometers (RGS) on board XMM, we observe emission lines from hydrogen-like and helium-like ions of nitrogen, oxygen, neon, magnesium, and silicon. Though the resolution of the RGS is sufficient to resolve the helium-like n=2->1 emission into three line components, only one of these components, the intercombination line, is detected in our data. The lack of flux in the forbidden lines of the helium-like triplets is explained by pumping by ultraviolet photons from the B0 star and, from this, we set an upper limit on the distance of the emitting ions from the star. The lack of observable flux in the resonance lines of the helium-like triplets indicate a lack of enhancement due to resonance line scattering and, from this, we derive a new observational constraint on the distribution of the wind in SMC X-1 in velocity and c...
Voitcu, Gabriel
2016-01-01
In this paper, we discuss the formation of ring-shaped and gyro-phase restricted velocity distribution functions (VDFs) at the edges of a cloud of protons injected into non-uniform distributions of the electromagnetic field. The velocity distribution function is reconstructed using the forward test-kinetic method. We consider two profiles of the electric field: (1) a non-uniform E-field obtained by solving the Laplace equation consistent with the conservation of the electric drift and (2) a constant and uniform E-field. In both cases, the magnetic field is similar to the solutions obtained for tangential discontinuities. The initial velocity distribution function is Liouville mapped along numerically integrated trajectories. The numerical results show the formation of an energy-dispersed structure due to the energy-dependent displacement of protons towards the edges of the cloud by the gradient-B drift. Another direct effect of the gradient-B drift is the formation of ring-shaped velocity distribution functio...
Minimal information in velocity space
Evrard, Guillaume
1995-01-01
Jaynes' transformation group principle is used to derive the objective prior for the velocity of a non-zero rest-mass particle. In the case of classical mechanics, invariance under the classical law of addition of velocities, leads to an improper constant prior over the unbounded velocity space of classical mechanics. The application of the relativistic law of addition of velocities leads to a less simple prior. It can however be rewritten as a uniform volumetric distribution if the relativistic velocity space is given a non-trivial metric.
Neutron Signatures of Non-Thermal Ion Distributions in Z-Pinch Driven ICF Plasmas
Knapp, Patrick; Jennings, Christopher; Sinars, Daniel
2012-10-01
In preparation for upcoming ICF experiments on the 26 MA Z machine (e.g., D2 gas puff, MagLIF [1]), we are studying the neutron energy spectra produced by magnetically-driven loads beyond the archetypal single temperature, uniform plasma. Z-pinch sources frequently exhibit evidence of unusual neutron spectra [2], which can be attributed to three-dimensional turbulent motion, high-energy beams, and other phenomena leading to non-Maxwellian ion distributions. Understanding the nature of our plasma neutron sources is critical for understanding how they scale with increasing current. We will show Monte Carlo and analytic calculations for plausible scenarios and discuss the corresponding signatures for the existing set of time-of-flight diagnostics on Z.[4pt] [1] S. A. Slutz et al. Phys. Plasmas 17, 056303 (2010)[0pt] [2] V.V. Vikhrev and V.D. Korolev, Plasma Dynamics, Vol. 33, No. 5 (2007)
Bretheim, Joel U; Gayme, Dennice F
2014-01-01
Numerical simulations of wall-turbulence using the restricted nonlinear (RNL) model generate realistic mean velocity profiles in plane Couette and channel flow at low Reynolds numbers. The results are less accurate at higher Re, and while a logarithmic region is observed, its von-K\\'arm\\'an constant is not consistent with the standard logarithmic law. In half-channel flow we show that limiting the streamwise-varying wavenumber support of RNL turbulence to one or few empirically determined modes improves its predictions considerably. In particular, the mean velocity profiles obtained with the band-limited RNL model follow standard logarithmic behavior for the higher Reynolds numbers in this study.
Iodine Plasma Species Measurements in a Hall Effect Thruster Plume
2013-04-01
vary across the plume. Furthermore, ion energy measurements here and historically show non - Maxwellian ion velocity distributions that vary with...related to beam composition or to non -uniformities in the gas flow distribution. Thus, thrust data are not reported...distribution is far from Maxwellian . D. Combined Probe The combined ESA/ExB probe was used to analyze specific populations selected from the ESA data
Maxwell's second- and third-order equations of transfer for non-Maxwellian gases
Baganoff, D.
1992-01-01
Condensed algebraic forms for Maxwell's second- and third-order equations of transfer are developed for the case of molecules described by either elastic hard spheres, inverse-power potentials, or by Bird's variable hard-sphere model. These hardly reduced, yet exact, equations provide a new point of origin, when using the moment method, in seeking approximate solutions in the kinetic theory of gases for molecular models that are physically more realistic than that provided by the Maxwell model. An important by-product of the analysis when using these second- and third-order relations is that a clear mathematical connection develops between Bird's variable hard-sphere model and that for the inverse-power potential.
Low-frequency sheath instability in a non-Maxwellian plasma with energetic ions.
Starodubtsev, Mikhail; Kamal-Al-Hassan, Md; Ito, Hiroaki; Yugami, Noboru; Nishida, Yasushi
2004-01-30
Spontaneous low-frequency oscillations have been observed in the circuit of a positively biased electrode when the ambient nonuniform plasma is irradiated by a microwave pulse of short duration, which is approximately equal to the ion-plasma period. The instability with its characteristic frequency below the ion-plasma frequency is driven by an accelerated ion component interacting with the sheath of the electrode. A qualitative model of the instability is suggested.
Dust acoustic and drift waves in a non-Maxwellian dusty plasma with dust charge fluctuation
Zakir, U.; Haque, Q.; Imtiaz, N.; Qamar, A.
2015-12-01
> ) on the wave dispersion and instability are presented. It is found that the presence of the non-thermal electron and ion populations reduce the growth rate of the instability which arises due to the dust charging effect. In addition, the nonlinear vortex solutions are also obtained. For illustration, the results are analysed by using the dusty plasma parameters of Saturn's magnetosphere.
Effect of non-maxwellians ions on dust acoustic dressed soliton
Amour, Rabia; Tribeche, Mouloud
2016-07-01
Dust is an ubiquitous component of space and astrophysical environments, occurring for example in planetary rings, comets and the Earth's ionosphere. Dusty plasmas are known to support a wide variety of ultra low-frequency wave modes. The most well studied of such modes are the so called dust-acoustic wave (DAW) and dust ion-acoustic wave (DIAW). The aim of this communication is to study a small-amplitude dust acoustic dressed solitons in a three component dusty plasma having electrons, suprathermal ions, and dust grains. We have then investigate the effect of ion suprathermality on small amplitude dust acoustic dressed wave and compared the result with the soliton's exact solution of the fourth order of pseudo-potential and K-dV soliton.
Institute of Scientific and Technical Information of China (English)
熊莉; 齐冰
2016-01-01
A new method based on fast Fourier transform, is presented to calculate ion velocity distribution by analyzing electromagnetic radiation signal from atmospheric nonequilibrium plasma. This method is based on a dipole model. Results show that the ion velocity distribution deviates from Maxwell distribution over time. The ion velocity and relative ion number fluctuate regularly with time.%通过测量大气压介质阻挡放电等离子体辐射信号，建立偶极子辐射模型，利用快速傅立叶变换，计算了大气压介质阻挡放电等离子体中离子速度分布。计算结果表明，速度分布偏离麦克斯韦分布，并且随着放电过程的进行，离子速度及相对离子数进行有规律的变化。
Statistics of Peculiar Velocities from Cosmic Strings
Moessner, R.
1995-01-01
We calculate the probability distribution of a single component of peculiar velocities due to cosmic strings, smoothed over regions with a radius of several $h^{-1}$ Mpc. The probability distribution is shown to be Gaussian to good accuracy, in agreement with the distribution of peculiar velocities deduced from the 1.9 Jy IRAS redshift survey. Using the normalization of parameters of the cosmic string model from CMB measurements, we show that the rms values for peculiar velocities inferred fr...
Energy Technology Data Exchange (ETDEWEB)
Yoon, Inkyoung; Ohm, Inyong [Seoul Nat’l Univ. of Science and Technology, Seoul (Korea, Republic of)
2017-02-15
This study is the second investigation on the steady flow characteristics of an SI engine with a semi-edge combustion chamber as a function of the port shape with varying evaluation positions. For this purpose, the planar velocity profiles were measured from 1.75B, 1.75 times of bore position apart from the bottom of head, to 6.00B positions using particle – image velocimetry. The flow patterns were examined with both a straight and a helical port. The velocity profiles, streamlines, and centers of swirl were almost the same at the same valve lift regardless of the measuring position, which is quite different from the case of the pent-roof combustion chamber. All the eccentricity values of the straight port were out of distortion criterion 0.15 through the lifts and the position. However, the values of the helical port exceeded the distortion criterion by up to 4 mm lift, but decreased rapidly above the 3.00B position and the 5 mm lift. There always existed a relative offset effect in the evaluation of the swirl coefficient using the PIV method due to the difference of the ideal impulse swirl meter velocity profile assumption, except for the cylinder-center-base estimation that was below 4 mm of the straight port. Finally, it was concluded that taking the center as an evaluation basis and the assumption about the axial velocity profile did not have any qualitative effect on swirl evaluation, but affected the value owing to the detailed profile.
The incomplete plasma dispersion function: properties and application to waves in bounded plasmas
Baalrud, Scott D.
2013-01-01
The incomplete plasma dispersion function is a generalization of the plasma dispersion function in which the defining integral spans a semi-infinite, rather than infinite, domain. It is useful for describing the linear dielectric response and wave dispersion in non-Maxwellian plasmas when the distribution functions can be approximated as Maxwellian over finite, or semi-infinite, intervals in velocity phase-space. A ubiquitous example is the depleted Maxwellian electron distribution found near...
Predicted Impacts of Proton Temperature Anisotropy on Solar Wind Turbulence
Klein, Kristopher G
2015-01-01
Particle velocity distributions measured in the weakly collisional solar wind are frequently found to be non-Maxwellian, but how these non-Maxwellian distributions impact the physics of plasma turbulence in the solar wind remains unanswered. Using numerical solutions of the linear dispersion relation for a collisionless plasma with a bi-Maxwellian proton velocity distribution, we present a unified framework for the four proton temperature anisotropy instabilities, identifying the associated stable eigenmodes, highlighting the unstable region of wavevector space, and presenting the properties of the growing eigenfunctions. Based on physical intuition gained from this framework, we address how the proton temperature anisotropy impacts the nonlinear dynamics of the \\Alfvenic fluctuations underlying the dominant cascade of energy from large to small scales and how the fluctuations driven by proton temperature anisotropy instabilities interact nonlinearly with each other and with the fluctuations of the large-scal...
Padidhapu, Rajendra; Brahmajirao, V
2016-01-01
We consider a coupled system of Navier Stokes, Maxwell Stefan and Poisson Boltzmann equations by incorporating the variation of dielectric constant, which governs the electro osmotic flow in nano channel, describing the evolution of the velocity, concentration and potential fields of dissolved constituents in an aqueous electrolyte solution. We apply the finite difference technique to solve one and two dimensional systems of these equations. The solutions give an extremely accurate prediction of the dielectric constant for a variety of salts and a wide range of concentrations.
Institute of Scientific and Technical Information of China (English)
蒋北寒; 杨克君; 曹叔尤; 陈梁
2012-01-01
天然河道中许多都是具有主槽和滩地的复式河槽，水流漫滩以后，复式河槽的水流结构发生复杂的变化。而天然河道漫滩上常常生长着各种植物，水中植被的存在增加了河床的阻力，如何确定流速分布和流量十分重要。本文基于植被作用下水流阻力的等效平衡原理，提出刚性植被等效附加阻力系数以及植被等效综合阻力系数的计算方法。通过运用SKM方法计算植被作用下的复式河槽垂线平均流速的横向分布，结果表明，本文提出的植被等效综合阻力系数的计算方法是可行的，能较好地确定植被作用下的复式河道垂线平均流速的横向分布。% Compound channels composed of the main channel and its associated floodplains widely exist in natural rivers. When water in the main channel flows in an out-of-bank manner onto the adjoining flood⁃plain, the flow structure is usually very complex. However, in natural rivers, floodplains and river banks are often home to many kinds of vegetation. Generally,such vegetation increases stabilization for banks and channels, but also increases the flow resistance and changes the velocity distribution and affects the dis⁃charge capacity. Hence,how to determine the velocity distribution and discharge become very important. In this paper, based on the equivalent balance of flow resistance, the equivalent additional resistance coeffi⁃cient and equivalent composite resistance coefficient of vegetated channels are proposed. Then using the Shiono and Knight method (SKM) together with the proposed equivalent composite resistance method, the lateral distribution of depth-averaged velocity in compound channels with vegetated floodplains are deter⁃mined. The results show that the computational method for composite resistance coefficient in the vegetated compound channel is feasible and can give good predictions for the velocity distribution for the type of
Energy Technology Data Exchange (ETDEWEB)
Nocente, M.; Rebai, M.; Gorini, G. [EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom); Dipartimento di Fisica “G. Occhialini,” Università degli Studi di Milano-Bicocca, Milano (Italy); Istituto di Fisica del Plasma “P. Caldirola,” Consiglio Nazionale delle Ricerche, Milano (Italy); Cazzaniga, C. [EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom); Istituto di Fisica del Plasma “P. Caldirola,” Consiglio Nazionale delle Ricerche, Milano (Italy); Rutherford Appleton Laboratory, ISIS Facility, Didcot (United Kingdom); Tardocchi, M.; Giacomelli, L.; Muraro, A. [EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom); Istituto di Fisica del Plasma “P. Caldirola,” Consiglio Nazionale delle Ricerche, Milano (Italy); Binda, F.; Eriksson, J. [EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom); Department of Physics and Astronomy, Uppsala University, Uppsala (Sweden); Sharapov, S. [EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom); CCFE, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB (United Kingdom); Collaboration: (EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom)
2015-10-15
Neutron spectroscopy measurements with a single crystal diamond detector have been carried out at JET, for the first time in an experiment aimed at accelerating deuterons to MeV energies with radio frequency heating at the third harmonic. Data are interpreted by means of the expected response function of the detector and are used to extract parameters of the highly non-Maxwellian distribution function generated in this scenario. A comparison with observations using a time of flight and liquid scintillator neutron spectrometers is also presented. The results demonstrate the capability of diamond detectors to contribute to fast ion physics studies at JET and are of more general relevance in view of the application of such detectors for spectroscopy measurements in the neutron camera of next step tokamak devices.
Nocente, M; Cazzaniga, C; Tardocchi, M; Binda, F; Eriksson, J; Giacomelli, L; Muraro, A; Rebai, M; Sharapov, S; Gorini, G
2015-10-01
Neutron spectroscopy measurements with a single crystal diamond detector have been carried out at JET, for the first time in an experiment aimed at accelerating deuterons to MeV energies with radio frequency heating at the third harmonic. Data are interpreted by means of the expected response function of the detector and are used to extract parameters of the highly non-Maxwellian distribution function generated in this scenario. A comparison with observations using a time of flight and liquid scintillator neutron spectrometers is also presented. The results demonstrate the capability of diamond detectors to contribute to fast ion physics studies at JET and are of more general relevance in view of the application of such detectors for spectroscopy measurements in the neutron camera of next step tokamak devices.
Kono, Akihiro; Sato, Toshinori; Shinohara, Masanao; Mochizuki, Kimihiro; Yamada, Tomoaki; Uehira, Kenji; Shinbo, Takashi; Machida, Yuuya; Hino, Ryota; Azuma, Ryosuke
2016-04-01
Off the Boso Peninsula, central Japan, where the Sagami Trough is in the south and the Japan Trench is in the east, there is a triple junction where the Pacific plate (PAC), the Philippine Sea plate (PHS) and the Honshu island arc (HIA) meet each other. In this region, the PAC subducts beneath the PHS and the HIA, and the PHS subducts beneath the HIA. Due to the subduction of 2 oceanic plates, numerous seismic events took place in the past. In order to understand these events, it is important to image structure of these plates. Hence, many researchers attempted to reveal the substructure from natural earthquakes and seismic experiments. Because most of the seismometers are placed inland area and the regular seismicity off Boso is inactive, it is difficult to reveal the precise substructure off Boso area using only natural earthquakes. Although several marine seismic experiments using active sources were conducted, vast area remains unclear off Boso Peninsula. In order to improve the situation, a marine seismic experiment, using airgun as an active source, was conducted from 30th July to 4th of August, 2009. The survey line has 216 km length and 20 Ocean Bottom Seismometers (OBSs) were placed on it. We estimated 2-D P-wave velocity structure from the airgun data using the PMDM (Progressive Model Development Method; Sato and Kenett, 2000) and the FAST (First Arrival Seismic Tomography ; Zelt and Barton, 1998). Furthermore, we identified the probable reflection phases from the data and estimated the location of reflectors using Travel time mapping method (Fujie et al. 2006). We found some reflection phases from the data, and the reflectors are located near the region where P-wave velocity is 5.0 km/s. We interpret that the reflectors indicate the plate boundary between the PHS and the HIA. The variation of the intensity of reflection along the upper surface of PHS seems to be consistent with the result from previous reflection seismic experiment conducted by Kimura et
Directory of Open Access Journals (Sweden)
Ju-Young Hong
2016-03-01
Full Text Available BackgroundMost type 2 diabetes mellitus patients are obese and have obesity related vascular complications. Exenatide treatment is well known for both decreasing glycated hemoglobin levels and reduction in body weight. So, this study aimed to determine the effects of exenatide on body composition, glycated hemoglobin levels, and vascular stiffness in obese type 2 diabetes mellitus patients.MethodsFor 1 month, 32 obese type 2 diabetes mellitus patients were administered 5 µg of exenatide twice daily. The dosage was then increased to 10 µg. Patients' height, body weight, glycated hemoglobin levels, lipid profile, pulse wave velocity (PWV, body mass index, fat mass, and muscle mass were measured by using Inbody at baseline and after 3 months of treatment.ResultsAfter 3 months of treatment, glycated hemoglobin levels decreased significantly (P=0.007. Triglyceride, total cholesterol, and low density lipoprotein levels decreased, while aspartate aminotransferase and alanine aminotransferase levels were no change. Body weight, and fat mass decreased significantly (P=0.002 and P=0.001, respectively, while interestingly, muscle mass did not decrease (P=0.289. In addition to, Waist-to-hip ratio and aortic PWV decreased significantly (P=0.006 and P=0.001, respectively.ConclusionEffects of short term exenatide use in obese type 2 diabetes mellitus with cardiometabolic high risk patients not only reduced body weight without muscle mass loss, body fat mass, and glycated hemoglobin levels but also improved aortic PWV in accordance with waist to hip ratio.
2012-07-16
non - Maxwellian . This indicates that a kinetic approach has to be used to model neutral entrainment in FRC thrusters. Strong impact of electron...radiative cooling can be problematic for high-Z plasma (due to a Z2 dependence) and in radiative non -equilibrium conditions (volumetric emission).1...dg, (1) where g is the relative collision velocity and fe is the Maxwellian distribution function. 2. Single charge exchange (SCX, A+ +A → A+A+) For
Multi-Scale Modeling of Novel Hall Thrusters: Understanding Physics of CHT and DCF Thrusters
2011-12-30
benefit of being able to capture not just a general non - Maxwellian velocity distribution space , but also radial variation in mass flux. B. Hybrid...continues to grow as more ions are accelerated from the bulk plasma towards the wall. This result is somewhat non -physical, since in a real device, the...The QN solution is non -physical, since the magnitude of the near-wall electric field is directly related to the cell spacing . The wall effect in the
Non-Intrusive, Time-Resolved Hall Thruster Near-Field Electron Temperature Measurements
2011-08-01
approximation. Another possible explanation for this disagreement is an initial non - Maxwellian electron energy distribution due to an insufficient...I828 and I834 /I828 methods in the beginning of the cycle may suggest an initial non - Maxwellian electron energy distribution or weaknesses in the...Temperature • Line Ratio Method Disagreement may be due to : – Issues with metastable approximations in that region of the cycle – Non - Maxwellian
Velocity anticipation in the optimal velocity model
Institute of Scientific and Technical Information of China (English)
DONG Li-yun; WENG Xu-dan; LI Qing-ding
2009-01-01
In this paper,the velocity anticipation in the optimal velocity model (OVM) is investigated.The driver adjusts the velocity of his vehicle by the desired headway,which depends on both instantaneous headway and relative velocity.The effect of relative velocity is measured by a sensitivity function.A specific form of the sensitivity function is supposed and the involved parameters are determined by the both numerical simulation and empirical data.It is shown that inclusion of velocity anticipation enhances the stability of traffic flow.Numerical simulations show a good agreement with empirical data.This model provides a better description of real traffic,including the acceleration process from standing states and the deceleration process approaching a stopped car.
Dust charging processes with a Cairns-Tsallis distribution function with negative ions
Energy Technology Data Exchange (ETDEWEB)
Abid, A. A., E-mail: abidaliabid1@hotmail.com [Applied Physics Department, Federal Urdu University of Arts, Science and Technology, Islamabad Campus, Islamabad 45320 (Pakistan); Khan, M. Z., E-mail: mzk-qau@yahoo.com [Applied Physics Department, Federal Urdu University of Arts, Science and Technology, Islamabad Campus, Islamabad 45320 (Pakistan); Plasma Technology Research Center, Department of Physics, Faculty of Science, University of Malaya, Kuala Lumpur 50603 (Malaysia); Yap, S. L. [Plasma Technology Research Center, Department of Physics, Faculty of Science, University of Malaya, Kuala Lumpur 50603 (Malaysia); Terças, H., E-mail: hugo.tercas@tecnico.ul.pt [Physics of Information Group, Instituto de Telecomunicações, Av. Rovisco Pais, Lisbon 1049-001 (Portugal); Mahmood, S. [Science Place, University of Saskatchewan, Saskatoon, Saskatchewan S7N5A2 (Canada)
2016-01-15
Dust grain charging processes are presented in a non-Maxwellian dusty plasma following the Cairns-Tsallis (q, α)–distribution, whose constituents are the electrons, as well as the positive/negative ions and negatively charged dust grains. For this purpose, we have solved the current balance equation for a negatively charged dust grain to achieve an equilibrium state value (viz., q{sub d} = constant) in the presence of Cairns-Tsallis (q, α)–distribution. In fact, the current balance equation becomes modified due to the Boltzmannian/streaming distributed negative ions. It is numerically found that the relevant plasma parameters, such as the spectral indexes q and α, the positive ion-to-electron temperature ratio, and the negative ion streaming speed (U{sub 0}) significantly affect the dust grain surface potential. It is also shown that in the limit q → 1 the Cairns-Tsallis reduces to the Cairns distribution; for α = 0 the Cairns-Tsallis distribution reduces to pure Tsallis distribution and the latter reduces to Maxwellian distribution for q → 1 and α = 0.
The Distribution of Dark Matter in the Milky Way's Disk
Kuhlen, Michael; Guedes, Javiera; Madau, Piero
2013-01-01
We present an analysis of the effects of dissipational baryonic physics on the local dark matter (DM) distribution at the location of the Sun, with an emphasis on the consequences for direct detection experiments. We find that two distinct processes lead to a 30% enhancement of DM in the disk plane: the accretion and disruption of satellites resulting in a DM component with net angular momentum and the contraction of baryons pulling DM into the disk plane without forcing it to co-rotate. The co-rotating dark disk in Eris is less massive than what has been suggested by previous work, contributing only 9% of the local DM density. The speed distribution in Eris is broadened and shifted to higher speeds compared to its DM-only twin simulation ErisDark. At high speeds f(v) falls more steeply in Eris than in ErisDark or the Standard Halo Model (SHM), easing the tension between recent results from the CDMS-II and XENON100 experiments. The non-Maxwellian aspects of f(v) are still present, but much less pronounced in ...
Jiang, Lanlan; Nishizawa, Osamu; Zhang, Yi; Park, Hyuck; Xue, Ziqiu
2016-12-01
Understanding the relationship between seismic wave velocity or attenuation and CO2 saturation is essential for CO2 storage in deep saline formations. In the present study, we describe a novel upright high-pressure vessel that is designed to keep a rock sample under reservoir conditions and simultaneously image the entire sample using a medical X-ray CT scanner. The pressure vessel is composed of low X-ray absorption materials: a carbon-fibre-enhanced polyetheretherketone (PEEK) cylinder and PEEK vessel closures supported by carbon-fibre-reinforced plastic (CFRP) joists. The temperature was controlled by a carbon-coated film heater and an aramid fibre thermal insulator. The assembled sample cell allows us to obtain high-resolution images of rock samples during CO2 drainage and brine imbibition under reservoir conditions. The rock sample was oriented vertical to the rotation axis of the CT scanner, and seismic wave paths were aligned parallel to the rotation axis to avoid shadows from the acoustic transducers. The reconstructed CO2 distribution images allow us to calculate the CO2 saturation in the first Fresnel zone along the ray path between transducers. A robust relationship between the seismic wave velocity or attenuation and the CO2 saturation in porous rock was obtained from experiments using this pressure vessel.
2013-06-01
states. The non -statistical nature implies either the equilibrium kinetics of the argon and electrons in the discharge are non - Maxwellian , the pop...and is shown in Figure 16. The clearly non - Maxwellian nature of the population distribution and the exclusion of the higher lying states are the...approaches the non - Maxwellian production and destruction rates of of the argon states in the discharge and is forcing them into a Boltzmann
Radio Emissions from Plasma with Electron Kappa-Distributions
Fleishman, G. D.; Kuznetsov, A. A.
2015-12-01
Gregory Fleishman (New Jersey Institute of Technology, Newark, USA)Alexey Kuznetsov (Institute of Solar-Terrestrial Physics, Irkutsk, Russia), Currently there is a concern about the ability of the classical thermal (Maxwellian) distribution to describe quasisteady-state plasma in the solar atmosphere, including active regions. In particular, other distributions have been proposed to better fit observations, for example, kappa-distributions. If present, these distributions will generate radio emissions with different observable properties compared with the classical gyroresonance (GR) or free-free emission, which implies a way of remotely detecting these kappa distributions in the radio observations. Here we present analytically derived GR and free-free emissivities and absorption coefficients for the kappa-distribution, and discuss their properties, which are in fact remarkably different from the classical Maxwellian plasma. In particular, the radio brightness temperature from a gyrolayer increases with the optical depth τ for kappa-distribution. This property has a remarkable consequence allowing a straightforward observational test: the GR radio emission from the non-Maxwellian distributions is supposed to be noticeably polarized even in the optically thick case, where the emission would have strictly zero polarization in the case of Maxwellian plasma. This offers a way of remote probing the plasma distribution in astrophysical sources, including solar active regions as a vivid example. In this report, we present analytical formulae and computer codes to calculate the emission parameters. We simulate the gyroresonance emission under the conditions typical of the solar active regions and compare the results for different electron distributions. We discuss the implications of our findings for interpretation of radio observations. This work was supported in part by NSF grants AGS-1250374 and AGS-1262772, NASA grant NNX14AC87G to New Jersey Institute of Technology
Turbulent Velocity Structure in Molecular Clouds
Ossenkopf, V; Ossenkopf, Volker; Low, Mordecai-Mark Mac
2002-01-01
We compare velocity structure observed in the Polaris Flare molecular cloud at scales ranging from 0.015 pc to 20 pc to the velocity structure of a suite of simulations of supersonic hydrodynamic and MHD turbulence computed with the ZEUS MHD code. We examine different methods of characterising the structure, including a scanning-beam size-linewidth relation, structure functions, velocity and velocity difference probability distribution functions (PDFs), and the Delta-variance wavelet transform, and use them to compare models and observations. The Delta-variance is most sensitive in detecting characteristic scales and varying scaling laws, but is limited in the observational application by its lack of intensity weighting. We compare the true velocity PDF in our models to simulated observations of velocity centroids and average line profiles in optically thin lines, and find that the line profiles reflect the true PDF better. The observed velocity structure is consistent with supersonic turbulence showing a com...
Radial velocity moments of dark matter haloes
Wojtak, R; Gottlöber, S; Mamon, G A; Wojtak, Radoslaw; Lokas, Ewa L.; Gottloeber, Stefan; Mamon, Gary A.
2005-01-01
Using cosmological N-body simulations we study the radial velocity distribution in dark matter haloes focusing on the lowest-order even moments, dispersion and kurtosis. We determine the properties of ten massive haloes in the simulation box approximating their density distribution by the NFW formula characterized by the virial mass and concentration. We also calculate the velocity anisotropy parameter of the haloes and find it mildly radial and increasing with distance from the halo centre. The radial velocity dispersion of the haloes shows a characteristic profile with a maximum, while the radial kurtosis profile decreases with distance starting from a value close to Gaussian near the centre. We therefore confirm that dark matter haloes possess intrinsically non-Gaussian, flat-topped velocity distributions. We find that the radial velocity moments of the simulated haloes are very well reproduced by the solutions of the Jeans equations obtained for the halo parameters with the anisotropy measured in the simu...
Institute of Scientific and Technical Information of China (English)
徐林荣; 韩征; 苏志满; 吴强
2012-01-01
以往研究表明,泥石流流速在沟道横断面上分布不均,但目前尚无理论依据,国内现行相关规范暂时建议在泥石流拦挡坝、排导槽等防治工程设计时,流速、荷载按均布考虑,这与实际的受荷情况有所差别,从而导致防治工程局部稳定性偏小,极易发生工程失效.为此,基于冲淤平衡原理、流体均质假设及沟道横断面形状的合理简化,结合雨洪修正法与形态断面法相关原理,演绎了沟道横断面任意位置流速计算公式的推导过程,并获取了泥石流流速的横向分布的非线性特征.通过四川省地震灾区理县甲司口沟泥石流防治工程的实例分析,发现横向上泥石流的中泓线流速与两侧流速相差达到300％.据此对拦砂坝进行了结构优化设计,在确保功能的前提下,提高了坝体稳定性系数约20％,节约了工程造价约5％.%Former researches indicate that the distribution of debris flow velocity is laterally asymmetrical. Due to a lack of a theoretical basis on it, velocity and load have to be calculated on uniform state advised by current design regulations when the debris flow dam and drainage canal are designed. It is different to the practical status, which may lead to the engineering failure due to the poor partial stability. Therefore, based on deposition-erosion equilibrium, isotropic fluid hypothesis and reasonable simplification for debris flow's gully cross-section, the nonlinearity features of debris flow velocity's lateral distribution was proposed by deducting the deducing process of the velocity calculation formula at any cross-section. With the instance analysis of debris flow mitigation and control work at earthquake-stricken areas in Lixian, Sichuan province, we found that the debris flow velocity at channel line is triple the one at either side, and conducted the structural optimization design for debris dam on the premise of ensuring its function, reducing the risk of the dam
Proton Cyclotron Instability Threshold Condition of Suprathermal Protons by Kappa Distribution
Institute of Scientific and Technical Information of China (English)
XIAO Fuliang; ZHOU Qinghua; HE Huiyong; TANG Lijun; FANG Jiayuan
2007-01-01
Observation has clearly shown that natural space plasmas generally possess a pronounced non-Maxwellian high-energy tail distribution that can be well modeled by a kappa distribution. In this study we investigate the proton cyclotron wave instability driven by the temperature anisotropy (T⊥/T||>1) of suprathermal protons modeled with a typical kappa distribution in the magnetosheath. It is found that as in the case for a regular bi-Maxwellian, the suprathermal proton temperature anisotropy is subject to the threshold condition of this proton cyclotron instability and the instability threshold condition satisfies a general form T⊥/T|| - 1 = S/βα||, with a very narrow range of the fitting parameters: 0.40 ≤ α ≤ 0.45, and a relatively sensitive variation 0.27 ≤ S ≤ 0.65, over 0.01 < β|| < 10. Furthermore, the difference in threshold conditions between the kappa distribution and the bi-Maxwellian distribution is found to be small for a relatively strong growth but becomes relatively obvious for a weak wave growth. The results may provide a deeper insight into the physics of this instability threshold for the proton cyclotron waves.
Velocity-aligned Doppler spectroscopy
Energy Technology Data Exchange (ETDEWEB)
Xu, Z.; Koplitz, B.; Wittig, C.
1989-03-01
The technique of velocity-aligned Doppler spectrosocopy (VADS) is presented and discussed. For photolysis/probe experiments with pulsed initiation, VADS can yield Doppler profiles for nascent photofragments that allow detailed center-of-mass (c.m.) kinetic energy distributions to be extracted. When compared with traditional forms of Doppler spectroscopy, the improvement in kinetic energy resolution is dramatic. Changes in the measured profiles are a consequence of spatial discrimination (i.e., focused and overlapping photolysis and probe beams) and delayed observation. These factors result in the selective detection of species whose velocities are aligned with the wave vector of the probe radiation k/sub pr/, thus revealing the speed distribution along k/sub pr/ rather than the distribution of nascent velocity components projected upon this direction. Mathematical details of the procedure used to model VADS are given, and experimental illustrations for HI, H/sub 2/S, and NH/sub 3/ photodissociation are presented. In these examples, pulsed photodissociation produces H atoms that are detected by sequential two-photon, two-frequency ionization via Lyman-..cap alpha.. with a pulsed laser (121.6+364.7 nm), and measuring the Lyman-..cap alpha.. Doppler profile as a function of probe delay reveals both internal and c.m. kinetic energy distributions for the photofragments. Strengths and weaknesses of VADS as a tool for investigating photofragmentation phenomena are also discussed.
Transverse Spectral Velocity Estimation
DEFF Research Database (Denmark)
Jensen, Jørgen Arendt
2014-01-01
A transverse oscillation (TO)-based method for calculating the velocity spectrum for fully transverse flow is described. Current methods yield the mean velocity at one position, whereas the new method reveals the transverse velocity spectrum as a function of time at one spatial location. A convex...
Velocity Fluctuations in Electrostatically Driven Granular Media
Aranson, I. S.; Olafsen, J. S.
2001-01-01
We study experimentally the particle velocity fluctuations in an electrostatically driven dilute granular gas. The experimentally obtained velocity distribution functions have strong deviations from Maxwellian form in a wide range of parameters. We have found that the tails of the distribution functions are consistent with a stretched exponential law with typical exponents of the order 3/2. Molecular dynamic simulations shows qualitative agreement with experimental data. Our results suggest t...
Algorithms for estimating blood velocities using ultrasound
DEFF Research Database (Denmark)
Jensen, Jørgen Arendt
2000-01-01
Ultrasound has been used intensively for the last 15 years for studying the hemodynamics of the human body. Systems for determining both the velocity distribution at one point of interest (spectral systems) and for displaying a map of velocity in real time have been constructed. A number of schemes...... have been developed for performing the estimation, and the various approaches are described. The current systems only display the velocity along the ultrasound beam direction and a velocity transverse to the beam is not detected. This is a major problem in these systems, since most blood vessels...
Analysis on Velocity Characteristics of Cavitation Flow Around Hydrofoil
Institute of Scientific and Technical Information of China (English)
LI Xiang-bin; LIU Shu-yan; WANG Guo-yu; ZHANG Bo; ZHANG Min-di
2010-01-01
The time-averaged velocity distributions in flows around a hydronautics hydrofoil were measured by using a digit-al particle image velocimeter (DPIV) system. The results show that the velocity distribution in the whole flow field depends on the development of cavitation structures with the decreasing of cavitation number. The high-fluctuation region with lower velocity relates to the cavitation area. The lowest velocity distribution in the cavity core becomes more uniform, and its in-fluence becomes smaller gradually as moving to downstream. The main-stream velocity distribution is even, then fluctuate and even at last. In the supercavitation stage, the fluid velocity in the cavitation region, corresponding to the front of the hydrofoil's suction surface, has a distribution close to the main stream, while the fluid velocity in other cavitation area is lower.
Ultrasound systems for blood velocity estimation
DEFF Research Database (Denmark)
Jensen, Jørgen Arendt
1998-01-01
color image of velocity at up to 20 to 60 frames a second. Both measurements are performedby repeatedly pulsing in the same direction and then usethe correlation from pulse to pulse to determine the velocity.The paper gives a simple model for the interactionbetween the ultrasound and the moving blood......Medical ultrasound scanners can be used both for displayinggray-scale images of the anatomy and for visualizing theblood flow dynamically in the body.The systems can interrogate the flow at a single position in the bodyand there find the velocity distribution over time. They can also show adynamic....... The calculation of the velocity distribution is then explainedalong with the different physical effects influencing the estimation.The estimation of mean velocities using auto- andcross-correlation for color flow mapping is also described....
Refinement of turbulent flow velocity characteristics
Directory of Open Access Journals (Sweden)
Y.V. Bryanskaya
2013-10-01
Full Text Available The basic laws of Prandtl semi-empirical turbulence theory were analyzed in the article. It was shown, that the Prandtl – Nikuradse logarithmic distribution of velocities are not strictly universal. The change of the first and second turbulence constants was analyzed on the basis of experimental data of I. Nikuradse. The logarithmic velocity profiles for smooth and rough pipes have been transformed. A united velocity logarithmic profile for flows in pipes, appropriate for any rate of hydraulic resistance was received. A more precise, consistent with the resistance laws, description of the kinematic structure of the flow with varying parameters of the velocity profiles was set. It was shown that the position of the average velocity point for the flow in pipe remained constant when the parameters of the velocity profile changed.
VELOCITY PROFILES OF TURBULENT OPEN CHANNEL FLOWS
Institute of Scientific and Technical Information of China (English)
WANG Dianchang; WANG Xingkui; YU Mingzhong; LI Danxun
2001-01-01
The log-law and the wake law of velocity profile for open channel flows are discussed and compared in this paper. Experimental data from eight sources are used to verify the velocity distribution models.The effect of bed level on the velocity profile is analyzed. A formula to calculate the maximum velocity is proposed. In the region of y ＜δm , the velocity profile approximately follows the log-law. For the region of y ＞δm , the effect of the aspect ratio is considered. A new velocity profile model on the basis of log-law that can unify all of the hydraulic bed roughness is presented.
Institute of Scientific and Technical Information of China (English)
王仁人; 万金领; 张锡朝; 刘云岗; 李国祥; 陆家祥; 顾宏中
2001-01-01
To measure the flow of double tongue-boards VGT turbine scroll with IFA300 hot - film anemometer and X probes a test device is designed.As the openness αA an d αB of the board A and B equal zero respectively,the throug h-flow velocity VX in the middle of flow path is similar to free vortex,but near the wall VX is less than the one estimated by free vortex.When αA is not zero,V X is larger than the one estimated.With different αA transverse-flow vel ocity VZ has similar distributions,and is 16 to 25 percentag e of VX.With Z increase and different αA,in the inner an d outer of flow path the radical -flow velocity VY has different distributions and is 25 to 30 percentage of VX.%设计了一种双舌型挡板VGT蜗壳内流场测试装置，用IFA300热膜风速仪X型探针测量了其速度 场。结果表明：(1)当A、B挡板开度αA＝00、αB＝00时，流道中间处通流 速度VX分布接近自由涡流规律，壁面处VX小于自由涡流估算值；当αA≠00 、αB＝00时，VX大于自由涡流估算值；(2)不同α B时，横流速度VZ分 布类似，VZ是VX的16％～25％；(3)α A变化时，随Z的 增加，在流道内侧和外侧径流速度VY分布不同，VY是VX的25％～3 0％。
Velocity selective optical pumping
Aminoff, C. G.; Pinard, M.
1982-01-01
We consider optical pumping with a quasi monochromatic tunable light beam, in the low intensity limit where a rate equation regime is obtained The velocity selective optical pumping (V.S.O.P.) introduces a correlation between atomic velocity and internal variables in the ground (or metastable) state. The aim of this article is to evaluate these atomic observables (orientation, alignment, population) as a function of velocity, using a phenomenological description of the relaxation effect of co...
Energy Technology Data Exchange (ETDEWEB)
Gasco, C. [Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas, CIEMAT, Departamento de Medio Ambiente, Avda. Complutense 22, Madrid 28040 (Spain); Anton, M.P. [Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas, CIEMAT, Departamento de Medio Ambiente, Avda. Complutense 22, Madrid 28040 (Spain)]. E-mail: maripaz.anton@ciemat.es; Pozuelo, M. [Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas, CIEMAT, Departamento de Medio Ambiente, Avda. Complutense 22, Madrid 28040 (Spain); Clemente, L. [Consejo Superior de Investigaciones Cientificas, Instituto de Recursos Naturales y Agrobiologia, CSIC-IRNA, Departamento de Geoecologia, Avda. Reina Mercedes s/n, Sevilla 41012 (Spain); Rodriguez, A. [Universidad de Huelva, Departamento de Geodinamica y Paleontologia, Avda. de las Fuerzas Armadas s/n, Huelva 21071 (Spain); Yanez, C. [Consejo Superior de Investigaciones Cientificas, Instituto de Recursos Naturales y Agrobiologia, CSIC-IRNA, Departamento de Geoecologia, Avda. Reina Mercedes s/n, Sevilla 41012 (Spain); Gonzalez, A. [Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas, CIEMAT, Departamento de Medio Ambiente, Avda. Complutense 22, Madrid 28040 (Spain); Meral, J. [Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas, CIEMAT, Departamento de Medio Ambiente, Avda. Complutense 22, Madrid 28040 (Spain)
2006-07-01
Within an extensive multinational and multidisciplinary project carried out in Donana National Park (Spain) to investigate its preservation and regeneration, the filling velocity of the salt marshes has been evaluated through the calculation of their average sediment accumulation rates. {sup 239+24}Pu and {sup 137}Cs from weapons testing fallout and total {sup 21}Pb distribution profiles and inventories have been determined in some of the most characteristic zones of the park, namely, the ponds (or 'lucios') and the waterjets (or 'canos'). Plutonium inventories range from 16 to 101 Bq m{sup -2}, {sup 137}Cs values fluctuate between 514 and 3758 Bq m{sup -2} and unsupported {sup 21}Pb values comprise between 124 and 9398 Bq m{sup -2}. Average sedimentation rates range from 3 to 5 mm y{sup -1} (1952-2002). These data are higher than those obtained by carbon dating for the period 6500 AD-present, estimated as 1.5-2 mm y{sup -1}, suggesting an increase in the accumulation of sediments and the alteration of the park's hydrodynamics caused by the re-channeling of the major rivers feeding the salt marshes.
DEFF Research Database (Denmark)
2000-01-01
Using a pulsed ultrasound field, the two-dimensional velocity vector can be determined with the invention. The method uses a transversally modulated ultrasound field for probing the moving medium under investigation. A modified autocorrelation approach is used in the velocity estimation. The new...
DEFF Research Database (Denmark)
2000-01-01
Using a pulsed ultrasound field, the two-dimensional velocity vector can be determined with the invention. The method uses a transversally modulated ultrasound field for probing the moving medium under investigation. A modified autocorrelation approach is used in the velocity estimation. The new...
Analyses of Current And Wave Forces on Velocity Caps
DEFF Research Database (Denmark)
Christensen, Erik Damgaard; Buhrkall, Jeppe; Eskesen, Mark C. D.
2015-01-01
) this paper investigates the current and wave forces on the velocity cap and the vertical cylinder. The Morison’s force model was used in the analyses of the extracted force time series in from the CFD model. Further the distribution of the inlet velocities around the velocity cap was also analyzed in detail...
Sukhinin, G I; Fedoseev, A V; Antipov, S N; Petrov, O F; Fortov, V E
2009-03-01
Dust-particles charging in a low-pressure glow discharge was investigated theoretically. The dust-particle charge was found on the basis of a developed self-consistent model taking into account the nonequilibrium character of electron distribution function and the formation of an ionic coat composed of bound or trapped ions around the dust particle. The dust-particle charge, the radial distributions of electron density, free and trapped ions densities, and the distribution of electrostatic potential were found. It was shown that the non-Maxwellian electron distribution function and collisional flux of trapped ions both reduce the dust-particle charge in comparison with that received with the help of the conventional orbital motion limited (OML) model. However, in rare collisional regimes in plasma when the collisional flux is negligible, the formation of ionic coat around a particle leads to a shielding of the proper charge of a dust particle. In low-pressure experiments, it is only possible to detect the effective charge of a dust particle that is equal to the difference between the proper charge of the particle and the charge of trapped ions. The calculated effective dust particle charge is in fairly good agreement with the experimental measurements of dust-particle charge dependence on gas pressure.
Superluminal Recession Velocities
Davis, T M; Davis, Tamara M.; Lineweaver, Charles H.
2000-01-01
Hubble's Law, v=HD (recession velocity is proportional to distance), is a theoretical result derived from the Friedmann-Robertson-Walker metric. v=HD applies at least as far as the particle horizon and in principle for all distances. Thus, galaxies with distances greater than D=c/H are receding from us with velocities greater than the speed of light and superluminal recession is a fundamental part of the general relativistic description of the expanding universe. This apparent contradiction of special relativity (SR) is often mistakenly remedied by converting redshift to velocity using SR. Here we show that galaxies with recession velocities faster than the speed of light are observable and that in all viable cosmological models, galaxies above a redshift of three are receding superluminally.
Perotti, Jose; Voska, Ned (Technical Monitor)
2002-01-01
This presentation provides an overview of the development of new hurricane wind sensor (Extreme Velocity Wind Sensor) for the Kennedy Space Center (KSC) which is designed to withstand winds of up to three hundred miles an hour. The proposed Extreme Velocity Wind Sensor contains no moveable components that would be exposed to extreme wind conditions. Topics covered include: need for new hurricane wind sensor, conceptual design, software applications, computational fluid dynamic simulations of design concept, preliminary performance tests, and project status.
宽喷幅风送式喷雾机空间气流速度分布规律%Law of spatial airflow velocity distribution for wide-swath air-blast sprayer
Institute of Scientific and Technical Information of China (English)
宋淑然; 洪添胜; 刘洪山; 阮耀灿; 陈建泽
2013-01-01
Spraying droplet adhesion and deposition were affected by the external flow field distribution of the air-blast sprayer. The swath of an air-blast sprayer can be expanded through expanding the duct and elongating rectangular outlet. In this paper, a wide-swath air-blast sprayer was applied as the experimental platform and its external airflow velocity field was tested. The duct of the wide-swath air-blast sprayer used in the experiment was made up of a cylindrical segment, a contractive segment, and an expanding segment. An axial fan was installed inside the cylindrical segment, and there were a semi-elliptical fluid director and distributors in the contractive segment. One end of the expanding segment was connected with contractive segment and the other was a rectangle outlet. The long side of the rectangle outlet was vertical to the ground and the axis of the duct was parallel to the ground simultaneously when testing was conducted. The airflow speed field of the wide-swath air-blast sprayer was tested indoors. The airflow speed sampling points were located with a sampling frame made up of lattices (11×11cm), and the airflow speed field and spray swath were tested in cross-sections 1m, 1.5m, 2m, and 2.5m away from the outlet. The average of ten testing wind speeds at each sample point was taken as the final speed of that point. The free turbulent jet theory was applied for data analysis. The distribution and variation mechanism of the wide-swath air-blast sprayer airflow velocity were obtained. The experimental results indicated that the relationship between the axial longitudinal time-averaged wind speed and the air blast distance of the wide-swath air-blast sprayer took on an attenuated power function with the fan power supply in different frequencies. The axial longitudinal time-averaged wind speed was in line with the attenuated power function regular pattern to which the axial longitudinal speed of the three-dimensional free turbulent jet was submitted. The
Bayliss, Matthew. B.; Zengo, Kyle; Ruel, Jonathan; Benson, Bradford A.; Bleem, Lindsey E.; Bocquet, Sebastian; Bulbul, Esra; Brodwin, Mark; Capasso, Raffaella; Chiu, I.-non; McDonald, Michael; Rapetti, David; Saro, Alex; Stalder, Brian; Stark, Antony A.; Strazzullo, Veronica; Stubbs, Christopher W.; Zenteno, Alfredo
2017-03-01
The velocity distribution of galaxies in clusters is not universal; rather, galaxies are segregated according to their spectral type and relative luminosity. We examine the velocity distributions of different populations of galaxies within 89 Sunyaev Zel’dovich (SZ) selected galaxy clusters spanning 0.28population. We find good agreement with simulations regarding the shape of the relationship between the measured velocity dispersion and the fraction of passive versus star-forming galaxies used to measure it, but we find a small offset between this relationship as measured in data and simulations, which suggests that our dispersions are systematically low by as much as 3% relative to simulations. We argue that this offset could be interpreted as a measurement of the effective velocity bias that describes the ratio of our observed velocity dispersions and the intrinsic velocity dispersion of dark matter particles in a published simulation result. Measuring velocity bias in this way suggests that large spectroscopic surveys can improve dispersion-based mass-observable scaling relations for cosmology even in the face of velocity biases, by quantifying and ultimately calibrating them out.
Balasubramaniam, K. S.; Keil, S. L.; Smaldone, L. A.
1996-05-01
We investigate the three dimensional structure of solar pores and their surroundings using high spatial and spectral resolution data. We present evidence that surface velocities decrease around pores with a corresponding increase in the line-of-sight (LOS) velocities. LOS velocities in pores increase with the strength of the magnetic field. Surface velocities show convergence toward a weak downflow which appear to trace boundaries resembling meso-granular and super granular flows. The observed magnetic fields in the pores appear near these boundaries. We analyze the vertical velocity structure in pores and show that they generally have downflows decreasing exponentially with height, with a scale height of about 90 km. Evidence is also presented for the expanding nature of flux tubes. Finally we describe a phenomenological model for pores. This work was supported by AFOSR Task 2311G3. LAS was partially supported by the Progetto Nazionale Astrofisica e Fisica Cosmica of MURST and Scambi Internazionali of the Universita degli Studi di Napoli Frederico II. National Solar Observatory, NOAO, is operated for the National Science Foundation by AURA, Inc.
Energy Technology Data Exchange (ETDEWEB)
Bayliss, Matthew.B. [MIT, MKI; Zengo, Kyle [Colby Coll.; Ruel, Jonathan [Harvard U., Phys. Dept.; Benson, Bradford A. [Fermilab; Bleem, Lindsey E. [Argonne; Bocquet, Sebastian [Argonne; Bulbul, Esra [MIT, MKI; Brodwin, Mark [Missouri U., Kansas City; Capasso, Raffaella [Munich, Tech. U., Universe; Chiu, I-non [Taiwan, Natl. Tsing Hua U.; McDonald, Michael [MIT, MKI; Rapetti, David [NASA, Ames; Saro, Alex [Munich, Tech. U., Universe; Stalder, Brian [Inst. Astron., Honolulu; Stark, Antony A. [Harvard-Smithsonian Ctr. Astrophys.; Strazzullo, Veronica [Munich, Tech. U., Universe; Stubbs, Christopher W. [Harvard-Smithsonian Ctr. Astrophys.; Zenteno, Alfredo [Cerro-Tololo InterAmerican Obs.
2016-12-08
The velocity distribution of galaxies in clusters is not universal; rather, galaxies are segregated according to their spectral type and relative luminosity. We examine the velocity distributions of different populations of galaxies within 89 Sunyaev Zel'dovich (SZ) selected galaxy clusters spanning $ 0.28 < z < 1.08$. Our sample is primarily draw from the SPT-GMOS spectroscopic survey, supplemented by additional published spectroscopy, resulting in a final spectroscopic sample of 4148 galaxy spectra---2868 cluster members. The velocity dispersion of star-forming cluster galaxies is $17\\pm4$% greater than that of passive cluster galaxies, and the velocity dispersion of bright ($m < m^{*}-0.5$) cluster galaxies is $11\\pm4$% lower than the velocity dispersion of our total member population. We find good agreement with simulations regarding the shape of the relationship between the measured velocity dispersion and the fraction of passive vs. star-forming galaxies used to measure it, but we find a small offset between this relationship as measured in data and simulations in which suggests that our dispersions are systematically low by as much as 3\\% relative to simulations. We argue that this offset could be interpreted as a measurement of the effective velocity bias that describes the ratio of our observed velocity dispersions and the intrinsic velocity dispersion of dark matter particles in a published simulation result. Measuring velocity bias in this way suggests that large spectroscopic surveys can improve dispersion-based mass-observable scaling relations for cosmology even in the face of velocity biases, by quantifying and ultimately calibrating them out.
Quantitative velocity modulation spectroscopy
Hodges, James N.; McCall, Benjamin J.
2016-05-01
Velocity Modulation Spectroscopy (VMS) is arguably the most important development in the 20th century for spectroscopic study of molecular ions. For decades, interpretation of VMS lineshapes has presented challenges due to the intrinsic covariance of fit parameters including velocity modulation amplitude, linewidth, and intensity. This limitation has stifled the growth of this technique into the quantitative realm. In this work, we show that subtle changes in the lineshape can be used to help address this complexity. This allows for determination of the linewidth, intensity relative to other transitions, velocity modulation amplitude, and electric field strength in the positive column of a glow discharge. Additionally, we explain the large homogeneous component of the linewidth that has been previously described. Using this component, the ion mobility can be determined.
Boosting Moving Object Indexing through Velocity Partitioning
Nguyen, Thi; Zhang, Rui; Ward, Phillip
2012-01-01
There have been intense research interests in moving object indexing in the past decade. However, existing work did not exploit the important property of skewed velocity distributions. In many real world scenarios, objects travel predominantly along only a few directions. Examples include vehicles on road networks, flights, people walking on the streets, etc. The search space for a query is heavily dependent on the velocity distribution of the objects grouped in the nodes of an index tree. Motivated by this observation, we propose the velocity partitioning (VP) technique, which exploits the skew in velocity distribution to speed up query processing using moving object indexes. The VP technique first identifies the "dominant velocity axes (DVAs)" using a combination of principal components analysis (PCA) and k-means clustering. Then, a moving object index (e.g., a TPR-tree) is created based on each DVA, using the DVA as an axis of the underlying coordinate system. An object is maintained in the index whose DVA...
Imaging thermal plasma mass and velocity analyzer
Yau, Andrew W.; Howarth, Andrew
2016-07-01
We present the design and principle of operation of the imaging ion mass and velocity analyzer on the Enhanced Polar Outflow Probe (e-POP), which measures low-energy (1-90 eV/e) ion mass composition (1-40 AMU/e) and velocity distributions using a hemispherical electrostatic analyzer (HEA), a time-of-flight (TOF) gate, and a pair of toroidal electrostatic deflectors (TED). The HEA and TOF gate measure the energy-per-charge and azimuth of each detected ion and the ion transit time inside the analyzer, respectively, providing the 2-D velocity distribution of each major ionospheric ion species and resolving the minor ion species under favorable conditions. The TED are in front of the TOF gate and optionally sample ions at different elevation angles up to ±60°, for measurement of 3-D velocity distribution. We present examples of observation data to illustrate the measurement capability of the analyzer, and show the occurrence of enhanced densities of heavy "minor" O++, N+, and molecular ions and intermittent, high-velocity (a few km/s) upward and downward flowing H+ ions in localized regions of the quiet time topside high-latitude ionosphere.
Velocity moments of dark matter haloes
Wojtak, R; Gottlöber, S; Mamon, G A; Wojtak, Radoslaw; Lokas, Ewa L.; Gottloeber, Stefan; Mamon, Gary A.
2006-01-01
Using cosmological N-body simulations we study the line-of-sight velocity distribution of dark matter haloes focusing on the lowest-order even moments, dispersion and kurtosis, and their application to estimate the mass profiles of cosmological structures. For each of the ten massive haloes selected from the simulation box we determine the virial mass, concentration and the anisotropy parameter. In order to emulate observations from each halo we choose randomly 300 particles and project their velocities and positions along the line of sight and on the surface of the sky, respectively. After removing interlopers we calculate the profiles of the line-of-sight velocity moments and fit them with the solutions of the Jeans equations. The estimates of virial mass, concentration parameter and velocity anisotropy obtained in this way are in good agreement with the values found from the full 3D analysis.
The Prescribed Velocity Method
DEFF Research Database (Denmark)
Nielsen, Peter Vilhelm
The- velocity level in a room ventilated by jet ventilation is strongly influenced by the supply conditions. The momentum flow in the supply jets controls the air movement in the room and, therefore, it is very important that the inlet conditions and the numerical method can generate a satisfactory...... description of this momentum flow. The Prescribed Velocity Method is a practical method for the description of an Air Terminal Device which will save grid points close to the opening and ensure the right level of the momentum flow....
Cirrus Crystal Terminal Velocities.
Heymsfield, Andrew J.; Iaquinta, Jean
2000-04-01
Cirrus crystal terminal velocities are of primary importance in determining the rate of transport of condensate from upper- to middle-tropospheric levels and profoundly influence the earth's radiation balance through their effect on the rate of buildup or decay of cirrus clouds. In this study, laboratory and field-based cirrus crystal drag coefficient data, as well as analytical descriptions of cirrus crystal shapes, are used to derive more physically based expressions for the velocities of cirrus crystals than have been available in the past.Polycrystals-often bullet rosettes-are shown to be the dominant crystal types in synoptically generated cirrus, with columns present in varying but relatively large percentages, depending on the cloud. The two critical parameters needed to calculate terminal velocity are the drag coefficient and the ratio of mass to cross-sectional area normal to their fall direction. Using measurements and calculations, it is shown that drag coefficients from theory and laboratory studies are applicable to crystals of the types found in cirrus. The ratio of the mass to area, which is shown to be relatively independent of the number of bullets in the rosette, is derived from an analytic model that represents bullet rosettes containing one to eight bullets in 19 primary geometric configurations. The ratio is also derived for columns. Using this information, a general set of equations is developed to calculate the terminal velocities and masses in terms of the aspect ratio (width divided by length), ice density, and rosette maximum dimension. Simple expressions for terminal velocity and mass as a function of bullet rosette maximum dimension are developed by incorporating new information on bullet aspect ratios.The general terminal velocity and mass relations are then applied to a case from the First International Satellite Cloud Climatology Project (ISCCP) Research Experiment (FIRE) 2, when size spectra from a balloon-borne ice crystal
Lie-Svendsen, O.; Leer, E.
1995-01-01
We have studied the evolution of the velocity distribution function of a test population of electrons in the solar corona and inner solar wind region, using a recently developed kinetic model. The model solves the time dependent, linear transport equation, with a Fokker-Planck collision operator to describe Coulomb collisions between the 'test population' and a thermal background of charged particles, using a finite differencing scheme. The model provides information on how non-Maxwellian features develop in the distribution function in the transition region from collision dominated to collisionless flow. By taking moments of the distribution the evolution of higher order moments, such as the heat flow, can be studied.
Velocity-selected molecular pulses produced by an electric guide
Sommer, Christian; Chervenkov, Sotir; van Buuren, Laurens D; Zeppenfeld, Martin; Pinkse, Pepijn W H; Rempe, Gerhard
2010-01-01
Electrostatic velocity filtering is a technique for the production of continuous guided beams of slow polar molecules from a thermal gas. We extended this technique to produce pulses of slow molecules with a narrow velocity distribution around a tunable velocity. The pulses are generated by sequentially switching the voltages on adjacent segments of an electric quadrupole guide synchronously with the molecules propagating at the desired velocity. This technique is demonstrated for deuterated ammonia (ND$_{3}$), delivering pulses with a velocity in the range of $20-100\\,\\rm{m/s}$ and a relative velocity spread of $(16\\pm 2)\\,%$ at FWHM. At velocities around $60\\,\\rm{m/s}$, the pulses contain up to $10^6$ molecules each. The data are well reproduced by Monte-Carlo simulations, which provide useful insight into the mechanisms of velocity selection.
Brand, Neal; Quintanilla, John A.
2013-01-01
Using a simultaneously falling softball as a stopwatch, the terminal velocity of a whiffle ball can be obtained to surprisingly high accuracy with only common household equipment. This classroom activity engages students in an apparently daunting task that nevertheless is tractable, using a simple model and mathematical techniques at their…
Analyses of Current And Wave Forces on Velocity Caps
DEFF Research Database (Denmark)
Christensen, Erik Damgaard; Buhrkall, Jeppe; Eskesen, Mark C. D.;
2015-01-01
Velocity caps are often used in connection with for instance offshore intake sea water for the use of for cooling water for power plants or as a source for desalinization plants. The intakes can also be used for river intakes. The velocity cap is placed on top of a vertical pipe. The vertical pipe......) this paper investigates the current and wave forces on the velocity cap and the vertical cylinder. The Morison’s force model was used in the analyses of the extracted force time series in from the CFD model. Further the distribution of the inlet velocities around the velocity cap was also analyzed in detail...
Accelerated radial Fourier-velocity encoding using compressed sensing
Energy Technology Data Exchange (ETDEWEB)
Hilbert, Fabian; Han, Dietbert [Wuerzburg Univ. (Germany). Inst. of Radiology; Wech, Tobias; Koestler, Herbert [Wuerzburg Univ. (Germany). Inst. of Radiology; Wuerzburg Univ. (Germany). Comprehensive Heart Failure Center (CHFC)
2014-10-01
Purpose:Phase Contrast Magnetic Resonance Imaging (MRI) is a tool for non-invasive determination of flow velocities inside blood vessels. Because Phase Contrast MRI only measures a single mean velocity per voxel, it is only applicable to vessels significantly larger than the voxel size. In contrast, Fourier Velocity Encoding measures the entire velocity distribution inside a voxel, but requires a much longer acquisition time. For accurate diagnosis of stenosis in vessels on the scale of spatial resolution, it is important to know the velocity distribution of a voxel. Our aim was to determine velocity distributions with accelerated Fourier Velocity Encoding in an acquisition time required for a conventional Phase Contrast image. Materials and Methods:We imaged the femoral artery of healthy volunteers with ECG - triggered, radial CINE acquisition. Data acquisition was accelerated by undersampling, while missing data were reconstructed by Compressed Sensing. Velocity spectra of the vessel were evaluated by high resolution Phase Contrast images and compared to spectra from fully sampled and undersampled Fourier Velocity Encoding. By means of undersampling, it was possible to reduce the scan time for Fourier Velocity Encoding to the duration required for a conventional Phase Contrast image. Results:Acquisition time for a fully sampled data set with 12 different Velocity Encodings was 40 min. By applying a 12.6 - fold retrospective undersampling, a data set was generated equal to 3:10 min acquisition time, which is similar to a conventional Phase Contrast measurement. Velocity spectra from fully sampled and undersampled Fourier Velocity Encoded images are in good agreement and show the same maximum velocities as compared to velocity maps from Phase Contrast measurements. Conclusion: Compressed Sensing proved to reliably reconstruct Fourier Velocity Encoded data. Our results indicate that Fourier Velocity Encoding allows an accurate determination of the velocity
Velocity structure and seismicity of southeastern Tennessee
Kaufmann, Ronald Douglas; Long, Leland Timothy
1996-04-01
The seismic zone in southeastern Tennessee is at the confluence of major crustal features, which have been interpreted largely from potential data, and their relation to seismicity could help us understand why major earthquakes sometimes occur in the eastern United States. In this paper we solve for the previously unknown velocity structure of the upper crust by an inversion of travel time residuals from relocated earthquakes. The gravity anomalies are included by using a linear relation between average anomalous density and average anomalous velocity. The velocity model demonstrates that the seismicity is concentrated in areas of average to below average velocity and does not appear to be associated with one of the previously identified major crustal features. The high-velocity zones mark areas that are generally lacking in seismicity. The association of earthquake hypocenters with regions of low-velocity crustal rocks is consistent with other intraplate seismic zones, and this association supports the conjecture that intraplate earthquakes occur in crust that may have been weakened. The velocity anomalies at midcrustal depths do not support the New York-Alabama (NY-AL) lineament as a linear feature extending through southeastern Tennessee and parallel to contours in gravity anomalies as originally proposed. A continuation of the (NY-AL) lineament to the southwest requires either a 15 degree southwestward change in direction or a displacement to be consistent with the velocity anomalies. The seismically active areas in southeastern Tennessee do not appear to be constrained by the major crustal features, but instead, the seismicity is characterized by the distribution of hypocenters and their association with low-velocity regions at midcrustal depths.
Wave propagation and group velocity
Brillouin, Léon
1960-01-01
Wave Propagation and Group Velocity contains papers on group velocity which were published during the First World War and are missing in many libraries. It introduces three different definitions of velocities: the group velocity of Lord Rayleigh, the signal velocity of Sommerfeld, and the velocity of energy transfer, which yields the rate of energy flow through a continuous wave and is strongly related to the characteristic impedance. These three velocities are identical for nonabsorbing media, but they differ considerably in an absorption band. Some examples are discussed in the last chapter
Distinct patterns of seasonal Greenland glacier velocity.
Moon, Twila; Joughin, Ian; Smith, Ben; van den Broeke, Michiel R; van de Berg, Willem Jan; Noël, Brice; Usher, Mika
2014-10-28
Predicting Greenland Ice Sheet mass loss due to ice dynamics requires a complete understanding of spatiotemporal velocity fluctuations and related control mechanisms. We present a 5 year record of seasonal velocity measurements for 55 marine-terminating glaciers distributed around the ice sheet margin, along with ice-front position and runoff data sets for each glacier. Among glaciers with substantial speed variations, we find three distinct seasonal velocity patterns. One pattern indicates relatively high glacier sensitivity to ice-front position. The other two patterns are more prevalent and appear to be meltwater controlled. These patterns reveal differences in which some subglacial systems likely transition seasonally from inefficient, distributed hydrologic networks to efficient, channelized drainage, while others do not. The difference may be determined by meltwater availability, which in some regions may be influenced by perennial firn aquifers. Our results highlight the need to understand subglacial meltwater availability on an ice sheet-wide scale to predict future dynamic changes. First multi-region seasonal velocity measurements show regional differencesSeasonal velocity fluctuations on most glaciers appear meltwater controlledSeasonal development of efficient subglacial drainage geographically divided.
Distinct patterns of seasonal Greenland glacier velocity
Moon, Twila; Joughin, Ian; Smith, Ben; van den Broeke, Michiel R; van de Berg, Willem Jan; Noël, Brice; Usher, Mika
2014-01-01
Predicting Greenland Ice Sheet mass loss due to ice dynamics requires a complete understanding of spatiotemporal velocity fluctuations and related control mechanisms. We present a 5 year record of seasonal velocity measurements for 55 marine-terminating glaciers distributed around the ice sheet margin, along with ice-front position and runoff data sets for each glacier. Among glaciers with substantial speed variations, we find three distinct seasonal velocity patterns. One pattern indicates relatively high glacier sensitivity to ice-front position. The other two patterns are more prevalent and appear to be meltwater controlled. These patterns reveal differences in which some subglacial systems likely transition seasonally from inefficient, distributed hydrologic networks to efficient, channelized drainage, while others do not. The difference may be determined by meltwater availability, which in some regions may be influenced by perennial firn aquifers. Our results highlight the need to understand subglacial meltwater availability on an ice sheet-wide scale to predict future dynamic changes. Key Points First multi-region seasonal velocity measurements show regional differences Seasonal velocity fluctuations on most glaciers appear meltwater controlled Seasonal development of efficient subglacial drainage geographically divided PMID:25821275
Velocity-aligned Doppler spectroscopy
Xu, Z.; Koplitz, B.; Wittig, C.
1989-03-01
The use of velocity-aligned Doppler spectroscopy (VADS) to measure center-of-mass kinetic-energy distributions of nascent photofragments produced in pulsed-initiation photolysis/probe experiments is described and demonstrated. In VADS, pulsed photolysis and probe laser beams counterpropagate through the ionization region of a time-of-flight mass spectrometer. The theoretical principles of VADS and the mathematical interpretation of VADS data are explained and illustrated with diagrams; the experimental setup is described; and results for the photodissociation of HI, H2S, and NH3 are presented in graphs and characterized in detail. VADS is shown to give much higher kinetic-energy resolution than conventional Doppler spectroscopy.
Roy, Arpita; Mahadevan, S.; Chakraborty, A.; Pathan, F. M.; Anandarao, B. G.
2010-01-01
The Physical Research Laboratory Advanced Radial-velocity All-sky Search (PARAS) is an efficient fiber-fed cross-dispersed high-resolution echelle spectrograph that will see first light in early 2010. This instrument is being built at the Physical Research laboratory (PRL) and will be attached to the 1.2m telescope at Gurushikhar Observatory at Mt. Abu, India. PARAS has a single-shot wavelength coverage of 370nm to 850nm at a spectral resolution of R 70000 and will be housed in a vacuum chamber (at 1x10-2 mbar pressure) in a highly temperature controlled environment. This renders the spectrograph extremely suitable for exoplanet searches with high velocity precision using the simultaneous Thorium-Argon wavelength calibration method. We are in the process of developing an automated data analysis pipeline for echelle data reduction and precise radial velocity extraction based on the REDUCE package of Piskunov & Valenti (2002), which is especially careful in dealing with CCD defects, extraneous noise, and cosmic ray spikes. Here we discuss the current status of the PARAS project and details and tests of the data analysis procedure, as well as results from ongoing PARAS commissioning activities.
Particle in cell calculation of plasma force on a small grain in a non-uniform collisional sheath
Hutchinson, I H
2013-01-01
The plasma force on grains of specified charge and height in a collisional plasma sheath are calculated using the multidimensional particle in cell code COPTIC. The background ion velocity distribution functions for the unperturbed sheath vary substantially with collisionality. The grain force is found to agree quite well with a combination of background electric field force plus ion drag force. However, the drag force must take account of the non-Maxwellian (and spatially varying) ion distribution function, and the collisional drag enhancement. It is shown how to translate the dimensionless results into practical equilibrium including other forces such as gravity.
POTENT Reconstruction from Mark III Velocities
Dekel, A.; Eldar, A.; Kolatt, T.; Yahil, A.; Willick, J. A.; Faber, S. M.; Courteau, S.; Burstein, D.
1999-09-01
We present an improved version of the POTENT method for reconstructing the cosmological velocity and mass density fields from radial peculiar velocities, test it with mock catalogs, and apply it to the Mark III Catalog of Galaxy Peculiar Velocities. The method is improved in several ways: (1) the inhomogeneous Malmquist bias is reduced by grouping and corrected statistically in either forward or inverse analyses of inferred distances, (2) the smoothing into a radial velocity field is optimized such that window and sampling biases are reduced, (3) the density field is derived from the velocity field using an improved weakly nonlinear approximation in Eulerian space, and (4) the computational errors are made negligible compared to the other errors. The method is carefully tested and optimized using realistic mock catalogs based on an N-body simulation that mimics our cosmological neighborhood, and the remaining systematic and random errors are evaluated quantitatively. The Mark III catalog, with ~3300 grouped galaxies, allows a reliable reconstruction with fixed Gaussian smoothing of 10-12 h-1 Mpc out to ~60 h-1 Mpc and beyond in some directions. We present maps of the three-dimensional velocity and mass-density fields and the corresponding errors. The typical systematic and random errors in the density fluctuations inside 40 h-1 Mpc are +/-0.13 and +/-0.18 (for Ω=1). In its gross features, the recovered mass distribution resembles the galaxy distribution in redshift surveys and the mass distribution in a similar POTENT analysis of a complementary velocity catalog (SFI), including such features as the Great Attractor, Perseus-Pisces, and the large void in between. The reconstruction inside ~40 h-1 Mpc is not affected much by a revised calibration of the distance indicators (VM2, tailored to match the velocities from the IRAS 1.2 Jy redshift survey). The volume-weighted bulk velocity within the sphere of radius 50 h-1 Mpc about the Local Group is V50=370+/-110 km s-1
Transverse velocity shifts in protostellar jets: rotation or velocity asymmetries?
De Colle, Fabio; Riera, Angels
2016-01-01
Observations of several protostellar jets show systematic differences in radial velocity transverse to the jet propagation direction, which have been interpreted as evidence of rotation in the jets. In this paper we discuss the origin of these velocity shifts, and show that they could be originated by rotation in the flow, or by side to side asymmetries in the shock velocity, which could be due to asymmetries in the jet ejection velocity/density or in the ambient medium. For typical poloidal jet velocities (~ 100-200 km/s), an asymmetry >~ 10% can produce velocity shifts comparable to those observed. We also present three dimensional numerical simulations of rotating, precessing and asymmetric jets, and show that, even though for a given jet there is a clear degeneracy between these effects, a statistical analysis of jets with different inclination angles can help to distinguish between the alternative origins of transverse velocity shifts. Our analysis indicate that side to side velocities asymmetries could ...
Human skeletal muscle fibre types and force: velocity properties.
MacIntosh, B R; Herzog, W; Suter, E; Wiley, J P; Sokolosky, J
1993-01-01
It has been reported that there is a relationship between power output and fibre type distribution in mixed muscle. The strength of this relationship is greater in the range of 3-8 rad.s-1 during knee extension compared to slower or faster angular knee extensor speeds. A mathematical model of the force: velocity properties of muscle with various combinations of fast- and slow-twitch fibres may provide insight into why specific velocities may give better predictions of fibre type distribution. In this paper, a mathematical model of the force:velocity relationship for mixed muscle is presented. This model demonstrates that peak power and optimal velocity should be predictive of fibre distribution and that the greatest fibre type discrimination in human knee extensor muscles should occur with measurement of power output at an angular velocity just greater than 7 rad.s-1. Measurements of torque:angular velocity relationships for knee extension on an isokinetic dynamometer and fibre type distribution in biopsies of vastus lateralis muscles were made on 31 subjects. Peak power and optimal velocity were determined in three ways: (1) direct measurement, (2) linear regression, and (3) fitting to the Hill equation. Estimation of peak power and optimal velocity using the Hill equation gave the best correlation with fibre type distribution (r < 0.5 for peak power or optimal velocity and percentage of fast-twitch fibres). The results of this study confirm that prediction of fibre type distribution is facilitated by measurement of peak power at optimal velocity and that fitting of the data to the Hill equation is a suitable method for evaluation of these parameters.
Dark Matter Velocity Spectroscopy.
Speckhard, Eric G; Ng, Kenny C Y; Beacom, John F; Laha, Ranjan
2016-01-22
Dark matter decays or annihilations that produce linelike spectra may be smoking-gun signals. However, even such distinctive signatures can be mimicked by astrophysical or instrumental causes. We show that velocity spectroscopy-the measurement of energy shifts induced by relative motion of source and observer-can separate these three causes with minimal theoretical uncertainties. The principal obstacle has been energy resolution, but upcoming experiments will have the precision needed. As an example, we show that the imminent Astro-H mission can use Milky Way observations to separate possible causes of the 3.5-keV line. We discuss other applications.
Minimum Length - Maximum Velocity
Panes, Boris
2011-01-01
We study a framework where the hypothesis of a minimum length in space-time is complemented with the notion of reference frame invariance. It turns out natural to interpret the action of the obtained reference frame transformations in the context of doubly special relativity. As a consequence of this formalism we find interesting connections between the minimum length properties and the modified velocity-energy relation for ultra-relativistic particles. For example we can predict the ratio between the minimum lengths in space and time using the results from OPERA about superluminal neutrinos.
Dark Matter Velocity Spectroscopy
Speckhard, Eric G; Beacom, John F; Laha, Ranjan
2016-01-01
Dark matter decays or annihilations that produce line-like spectra may be smoking-gun signals. However, even such distinctive signatures can be mimicked by astrophysical or instrumental causes. We show that velocity spectroscopy-the measurement of energy shifts induced by relative motion of source and observer-can separate these three causes with minimal theoretical uncertainties. The principal obstacle has been energy resolution, but upcoming and proposed experiments will make significant improvements. As an example, we show that the imminent Astro-H mission can use Milky Way observations to separate possible causes of the 3.5-keV line. We discuss other applications.
MAGNTY - Program for calculating velocities in magnified region of turbomachines
Katsanis, T.; Mc Nally, W.
1969-01-01
Computer program, MAGNFY, calculates the velocity distribution through the passage between and over blade surfaces of blade rows for turbines and compressors. Using the input of other programs, MAGNFY obtains velocities on smaller than normal finite difference mesh in any part of the blade-to-blade passage.