One-dimensional Velocity Distribution Research Articles

Fractional entropy-based models of one-dimensional velocity distributions in partially filled and fully filled pipe flows

Fractional entropy-based models of one-dimensional velocity distributions in partially filled and fully filled pipe flows

Investigation of gyrotron-based collective Thomson scattering for fast ion diagnostics in a compact high-field tokamak

As a promising method for fast ion diagnostics, collective Thomson scattering (CTS) can measure the one-dimensional velocity distribution of fast ions with high spatial and temporal resolution. The feasibility of diagnosing fast ions in a compact high-field tokamak by CTS was studied in this work, and the results showed that a wide range of probing frequencies could be applied. A high-frequency case and a low-frequency case were mainly considered for fast ion diagnostics in a compact high-field tokamak. The use of a high probing frequency could effectively avoid the refraction effect of the beams, while the application of a low probing frequency allows greater flexibility in the selection of scattering angle which may help to improve the spatial resolution. Based on typical plasma conditions (B 0 = 12.2 T, n e0 = 4.3 × 1020 m−3, T e0 = 22.2 keV, T i0 = 19.8 keV) for a compact high-field tokamak, a 220 GHz CTS diagnostic that utilizes a small scattering angle of θ = 30° and a 160 GHz CTS diagnostic that utilizes an orthogonal geometry were proposed. Further study showed that the high-frequency case could operate in a wider range of plasma conditions and provide more information on fast ions while the low-frequency case could achieve higher spatial resolution of the poloidal direction.

Application of the fractional entropy for one-dimensional velocity distribution with dip-phenomenon in open-channel turbulent flows

Application of the fractional entropy for one-dimensional velocity distribution with dip-phenomenon in open-channel turbulent flows

One-dimensional velocity distribution in seepage channel using Tsallis and Shannon entropy

One-dimensional velocity distribution in seepage channel using Tsallis and Shannon entropy

Physics of the high specific impulse alternative low power hybrid ion engine (alphie): Direct thrust measurements and plasma plume kinetics

The Alternative Low Power Ion Engine (alphie) is a high specific impulse plasma thruster different from conventional gridded ion engines (GIEs). It uses only one external cathode and ions and electrons flow through the open spaces of its two grids, whereas only ions are transported through the GIE ion optics. Ionizing electrons from the cathode move inward to the alphie ionization chamber and ions, which are neutralized by electrons from the same cathode, exit along the opposite direction. These currents together with the voltages applied to the grids produce a self-consistent electric field that accelerates the charges. The one-dimensional ion velocity distribution and the electron energy spectra in the collisionless alphie plasma plume are studied along its axial axis of symmetry. The thruster produces a mesothermal plasma flow with a non-monotone plasma potential profile along the axial direction. The ion populations observed are of those accelerated by the self-consistent electric field and a low velocity group that results from the charge exchange collisions in the thruster. Both populations remain essentially unaltered in the plasma flow. Conversely, the two electron groups observed merge along the axial direction of the plume following the changes in the plasma potential. The temperatures of ion populations are high by the neutral gas heating inside the thruster by high-energy ionizing electrons. The direct measurement of thrusts of 0.8–3.5 mN for argon gives 13 900–20 000 s specific impulses. These high values might be explained by the additional contribution to the thrust by the remaining non-ionized hot neutral gas effusion through the apertures of grids.

Discussion of “Estimation of one-dimensional velocity distribution by measuring velocity at two points” by Yeganeh and Heidari (2020)

The concept of information entropy together with the principle of maximum entropy to open channel flow is essentially based on some physical consideration of the problem under consideration. This paper is a discussion on Yeganeh and Heidari (2020)'s paper, who proposed a new approach for measuring vertical distribution of streamwise velocity in open channels. The discussers argue that their approach is conceptually incorrect and thus leads to a physically unrealistic situation. In addition, the discussers found some wrong mathematical expressions (which are assumed to be typos) written in the paper, and also point out that the authors did not cite some of the original papers on the topic.

Entropy-Based Velocity and Shear Stress Distributions for Trapezoidal Channel

AbstractA multitude of studies have derived one-dimensional velocity distributions, assuming open channels to be rectangular, and have extended their applications to rivers, canals, and other open ...

MMS Observations of Accelerated Interstellar Pickup He+ Ions at an Interplanetary Shock

Abstract Interstellar pickup ions (PUI) are interstellar neutrals that have been ionized in transit through the heliosphere via charge exchange or photoionization. These new PUIs then “freeze” into the solar wind (SW) and move with the bulk SW velocity (V SW). They also begin to gyrate around the local magnetic field with V SW, resulting in a maximum PUI velocity of 2 ∗ V SW. Understanding how He+ PUIs are accelerated at shocks in space provides valuable insights into shock dynamics and shock acceleration mechanisms. On 2018 January 8, while the Magnetospheric Multiscale (MMS) Mission was in the SW, it observed the forward shock of a corotating interaction region. In this work, we analyze the upstream and downstream velocity distributions of He+ for this quasiperpendicular, marginally supercritical (θ Bn = 67°, M A = 2.8) interplanetary shock. We derive average two-dimensional pitch-angle distributions in the field-aligned SW frame, as well as reduced one-dimensional velocity distributions for selected upstream and downstream intervals. We find that the shock accelerates He+ largely perpendicular to the magnetic field, consistent with shock reflection. Furthermore, we derive a measured ratio of accelerated He+ ions by estimating a maximum speed in the downstream frame, above which we assume that He+ ions have been accelerated by their interaction with the shock. The measured acceleration ratio, R Measured = 0.14, is then compared to a theoretical ratio derived from a simple model of the upstream distribution, R Theoretical = 0.06.

Estimation of one-dimensional velocity distribution by measuring velocity at two points

The measurement of the velocity distribution and discharge in the open channels has always been an important issue in hydraulics. Unfortunately, flow measurement in the open channel is often expensive and sometimes produces poor results. There are many empirical methods to estimate the velocity distribution in a conduit, however, these methods are often applicable only to a narrow range of open channel conditions. In this paper, considering velocity as a random parameter, one-dimensional velocity distribution in open-channel has been derived based on the entropy concept and the principle of maximum entropy (POME). The entropy indexes (M, G, λ2 and λ*) are important parameters in entropy method to estimate velocity distribution and discharge in a conduit. A new approach is presented in this work for estimating the entropy parameters based on two-point velocity measurements. The approach for estimating the entropy parameters is tested for laboratory observations and velocity distribution and discharge are determined using Shannon, Renyi and Tsallis entropy methods. The present approach has shown good agreement with measured data. Also, the results showed that Tsallis entropy method is more accurate than other forms of entropy and the calculated values of NRMSE for estimated velocity profile and discharge are 7.86 and 8.8% respectively, showing a good simulation.

‘Observing’ unrelaxed clusters in dark matter simulations

ABSTRACT We present a detailed study of relaxed and unrelaxed galaxy clusters in a large dark matter only simulation. Recent work has demonstrated clear differences between the galaxy populations in clusters that have Gaussian velocity distributions (relaxed) compared to those that do not (unrelaxed). To directly compare with observations, we identify unrelaxed clusters in the simulations using one-dimensional velocity distributions. We show that non-Gaussian clusters have had recent major mergers and enhanced rates of galaxy infall relative to systems with Gaussian velocity profiles. Furthermore, we find that the fraction of non-Gaussian clusters increases strongly with cluster mass and modestly with redshift. For comparison, we also make use of three-dimensional information available in the simulations to explore the impact of projection on observational measurements. Differences between Gaussian and non-Gaussian clusters are much stronger when three-dimensional information is considered, which demonstrates that the strength of oberserved trends with cluster dynamics are diluted because observed velocity information is limited to one line-of-sight.

A Zeeman slower for diatomic molecules

We present a novel slowing scheme for beams of laser-coolable diatomic molecules reminiscent of Zeeman slowing of atomic beams. The scheme results in efficient compression of the one-dimensional velocity distribution to velocities trappable by magnetic or magneto-optical traps. We experimentally demonstrate our method in an atomic testbed and show an enhancement of flux below v = 35 m s−1 by a factor of ≈20 compared to white light slowing. 3D Monte Carlo simulations performed to model the experiment show excellent agreement. We apply the same simulations to the prototype molecule 88Sr19F and expect 15% of the initial flux to be continuously compressed in a narrow velocity window at around 10 m s−1. This is the first experimentally shown continuous and dissipative slowing technique in molecule-like level structures, promising to provide the missing link for the preparation of large ultracold molecular ensembles.

IEDF distortion and resolution considerations for RFEA operation at high voltages

Retarding field energy analyzers (RFEA) have been used extensively to measure the ion flux energy distribution function of plasmas. For consistency, the ion flux energy distribution function is referred to as the ion energy distribution function (IEDf) even though it more accurately represents the one-dimensional ion velocity distribution function. In the past, these devices have operated at voltages less than 1 kV. Higher operating voltages (>2 kV) are currently desired. For an RFEA to operate at these voltages, design changes are necessary that impact the energy resolution and cause space charge build-up. To investigate the effect the design changes have for a high voltage RFEA, electromagnetic simulations and particle-in-cell (PIC) simulations were used to analyze the electric field between the grids, the potential drop in the grid holes, and space charge build-up between the grids. Non-unique optimized dimensions for the RFEA increased the electric field uniformity. The optimization minimizes the electric field from distorting the IV curve or adversely affecting the energy resolution. It was found that a larger grid gap distance and smaller grid hole diameter decreases the potential drop in the grid holes improving energy resolution. IV curves from the PIC simulation were used to obtain space charge distorted IEDfs. The point at which space charge distorts the IV curve is dependent on the grid gap distance and incoming flux. Space charge build-up was found to only affect low energy ions which manifested by cutting off the low energy portion of the IEDf. To fix space charge distortions, the flux into the probe can be limited or it may be possible to account for the distortion when calculating the IEDf.

Dynamic material parameters of closed-cell foams under high-velocity impact

Cellular materials under high-velocity impact have highly localized deformation with the cells layer-wise collapse, which is usually characterized by the propagation of shock wave. Researches have shown that the shock wave speed is strongly dependent on the impact velocity, but the effect of the meso-structural and base-material parameters is unclear. In this study, the dynamic material parameters of closed-cell foams are investigated with cell-based finite element models. The one-dimensional velocity distribution along the loading direction is used to capture the propagation of shock front. The shock wave speed is thus determined and it exhibits a linear relationship with impact velocity when the impact velocity is high enough. The difference between the shock wave speed and the impact velocity is a dynamic material parameter of cellular material and the effect of meso-structural and base-material parameters on this dynamic material parameter is investigated with dimensional analysis. An expression of the dynamic material parameter with respect to the relative density and the base-material parameters is obtained. It shows that the dynamic material parameter intensively relies on the relative density and increases linearly with the relative density. The investigation of dynamic stresses with the aid of a shock model shows that the initial crushing stress increases in a power-law tendency with the increase of relative density. As a result, a stress–strain relation involving the relative density of material cellular and the yield stress and density of base material is obtained for the closed-cell foams considered. The effects of hardening behaviors of cell-wall material and gas trapped within cells are also considered. It is found that the dynamic material parameter exhibits nearly linear increase with the increase of hardening parameters of base material and initial gas pressure, while the dynamic initial crushing stress is independent of the strain-hardening parameter and the entrapped gas pressure but increases with the strain-rate hardening parameter linearly. These findings may be helpful for guiding the crashworthiness design of cellular materials and structures.

One-Dimensional velocity distribution in open channels using Renyi entropy

In this work, the concept of entropy based on probability is applied in modeling the vertical distribution of velocity in open channel turbulent flow. Using the principle of maximum entropy, one-dimensional velocity distribution is derived by maximizing the Renyi entropy subject to some constraints by assuming dimensionless velocity as a random variable. The Renyi entropy-based equation is capable of modeling the velocity distribution from the channel bed to the water surface. The derived 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 observed data and its prediction accuracy is superior than the other existing models.

Experimental investigation of internal structure of open-channel flow with intense transport of sediment

Abstract Gravity-driven open-channel flows carrying coarse sediment over an erodible granular deposit are studied. Results of laboratory experiments with artificial sediments in a rectangular tilting flume are described and analyzed. Besides integral quantities such as flow rate of mixture, transport concentration of sediment and hydraulic gradient, the experiments include measurements of the one-dimensional velocity distribution across the flow. A vertical profile of the longitudinal component of local velocity is measured across the vertical axis of symmetry of a flume cross section using three independent measuring methods. Due to strong flow stratification, the velocity profile covers regions of very different local concentrations of sediment from virtually zero concentration to the maximum concentration of bed packing. The layered character of the flow results in a velocity distribution which tends to be different in the transport layer above the bed and in the sediment-free region between the top of the transport layer and the water surface. Velocity profiles and integral flow quantities are analyzed with the aim of evaluating the layered structure of the flow and identifying interfaces in the flow with a developed transport layer above the upper plane bed.

Reconstructing the WIMP velocity distribution from direct dark matter detection data with a nonnegligible threshold energy

In this paper, we investigate the modification of our expressions developed for the model-independent data analysis procedure of the reconstruction of the (time-averaged) one-dimensional velocity distribution of galactic weakly interacting massive particles (WIMPs) with a nonnegligible experimental threshold energy. Our numerical simulations show that, for a minimal reconstructable velocity of as high as [Formula: see text] km/s, our model-independent modification of the estimator for the normalization constant could provide precise reconstructed velocity distribution points to match the true WIMP velocity distribution with ≲ 10% bias.

Laser cooling without spontaneous emission.

This Letter reports the demonstration of laser cooling without spontaneous emission, and thereby addresses a significant controversy. It works by restricting the atom-light interaction to a time short compared to a cycle of absorption followed by natural decay. It is achieved by using the bichromatic force on an atomic transition with a relatively long excited state lifetime and a relatively short cooling time so that spontaneous emission effects are minimized. The observed width of the one-dimensional velocity distribution is reduced by ×2 thereby reducing the "temperature" by ×4. Moreover, our results comprise a compression in phase space because the spatial expansion of the atomic sample is limited. This accomplishment is of interest to direct laser cooling of molecules or in experiments where working space or time is limited.

AMIDAS-II: Upgrade of the AMIDAS package and website for direct Dark Matter detection experiments and phenomenology

In this paper, we give a detailed user's guide to the AMIDAS (A Model-Independent Data Analysis System) package and website, which is developed for online simulations and data analyses for direct Dark Matter detection experiments and phenomenology. Recently, the whole AMIDAS package and website system has been upgraded to the second phase: AMIDAS-II, for including the new developed Bayesian analysis technique. AMIDAS has the ability to do full Monte Carlo simulations as well as to analyze real/pseudo data sets either generated by another event generating programs or recorded in direct DM detection experiments. Moreover, the AMIDAS-II package can include several "user-defined" functions into the main code: the (fitting) one-dimensional WIMP velocity distribution function, the nuclear form factors for spin-independent and spin-dependent cross sections, artificial/experimental background spectrum for both of simulation and data analysis procedures, as well as different distribution functions needed in Bayesian analyses.

Design of the Collective Thomson scattering (CTS) system by using 170-GHz gyrotron in the KSTAR

The physics of energetic ions is one of the primary subjects to be understood toward the realization of a nuclear fusion power plant. Collective Thomson scattering (CTS) offers the possibility to diagnose the fast ions and the alpha particles in burning plasmas. Spatially- and temporally-resolved one-dimensional velocity distributions of the fast ions can be obtained from the scattered radiation with fewer geometric constraints by utilizing millimeter waves from a high-power gyrotron as a probe beam. We studied the feasibility of CTS fast-ion measurements in the KSTAR by calculating the spectral density functions. Based on that, we suggest a design for the CTS system that uses the currently-operating 170-GHz gyrotron for electron cyclotron heating (ECH) and electron cyclotron current drive (ECCD) in the KSTAR. The CTS system is presented as two subsystems: the antenna system and the heterodyne receiver system. The design procedure for an off-axis ellipsoidal mirror is described, and the CTS system requirements are discussed.

Bayesian reconstruction of the velocity distribution of weakly interacting massive particles from direct dark matter detection data

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 Galactic velocities, will be pinned down as the output results.