Mean Relative Velocity Research Articles

Self-broadened half-widths and self-induced line shifts for water vapor transitions in the 3.2–17.76 μm spectral region via complex Robert–Bonamy theory

Water vapor in the Earth’s atmosphere is being studied in the 3.2–17.76 μm spectral region by the atmospheric infrared sounder (AIRS) on Aqua, the troposphere emission spectrometer (TES) and the high-resolution dynamics limb sounder (HIRDLS) on Aura, both part of the NASA EOS mission. However, the lack of sufficient data on spectral parameters will hamper the prospect of accurate retrievals of temperature and concentration profiles. The spectral parameters for thousands of water vapor transitions are required, which are hard to determine by measurements alone. As reported previously [Can. J. Chem. 82 (2004) 1013–1027], of the 10 602 measurements of H 2O self-broadening half-widths only 440 intercomparisons with more than 3 data points have estimated uncertainty less than 10%. In this work, we have employed the mean relative thermal velocity approximation of the complex implementation of Robert–Bonamy formalism to obtain the self-broadened half-widths and self-induced line shifts for 5442 water vapor transitions in the 3.2–17.76 μm region. The calculations are compared with the measurement database and trends in the half-widths and line shifts are studied.

Mutual Diffusion Coefficient in Binary Mixtures and the Lattice Gas Model

A modification of the elementary kinetic theory of a gas mixture in terms of the lattice gas model is proposed. It is assumed that molecules of components of the mixture are spherical and close in size. In calculating the diffusion flux of molecules through a selected plane, instead of the mean thermal velocity of molecules, the mean relative velocity of molecules of components of different types is used. In this case, the flux explicitly depends on the type of component with which a molecule collided last before intersecting the selected plane. The proposed modification allows one to derive an expression for the mutual diffusion coefficient of components of a binary mixture that at low densities of the mixture (as in a rarefied gas phase), is consistent with the expression obtained in the rigorous kinetic theory of gases.

Differentiation of Vascular Dementia and Alzheimer Disease

In brain perfusion studies, perfusion defects have been reported mainly in the temporal and parietal regions in patients with Alzheimer disease (AD), but it is known that the occipital cortex is partially preserved from metabolic defects in patients with AD, at least in the early stage of the disease. We therefore evaluated the reactivity of the posterior cerebral arteries during visual stimulation with transcranial Doppler ultrasonography (TDU). Fifteen patients with AD (mean age, 70 years), 12 patients with vascular dementia (VD) (mean age, 61.5 years), and 9 healthy control subjects (mean age, 58 years) were enrolled in the study. The reactivity of both posterior cerebral arteries during visual stimulation was measured with TDU. Reactivity was calculated by the differences in mean relative blood flow velocity (rBFv) between stimulation (vs) and rest (vr) divided by the resting value [rBFv = 100 x (vs - vr)/vr]. Significant increases of vascular reactivity were obtained during visual stimulation for each group (P < .001). There was no significant right or left side difference for vascular reactivity within the groups except in VD; therefore, values of the right and left sides were pooled for patients with AD and control subjects. Reactivity to visual stimulation was similar for the patients with AD (mean +/- SD, 38% +/- 2.2%) and control subjects (35% +/- 1.8%), but reactivity was found significantly decreased in both sides of patients with VD (25.7% +/- 2.1% for the left side and 24% +/- 2.6% for the right side) compared with the healthy control subjects and the patients with AD (P < .001). These results indicate that the occipital cortex is partially preserved in patients with AD and that functional TDU may be a valuable tool for differentiating VD and AD.

Collisional depolarization of OH(A) studied by Zeeman quantum beat spectroscopy

The depolarization of the rotational angular momentum of electronically excited OH(2Σ) radicals through collisions with water molecules has been measured using Zeeman quantum beat spectroscopy. The new data have permitted the evaluation of OH(A) state-specific quenching and angular momentum depolarization cross-sections for superthermal OH(A) radicals with mean relative velocities centred around 3500 m s-1. The quenching cross-sections are compared both with values available in the literature, and with predictions based on a simple harpoon model, and are found to be in good qualitative accord with previous findings. For the lowest rotational levels studied, the depolarization cross-sections (which include contributions from both elastic and inelastic processes in OH(A)) are found to approach ∼100 Å2, only slightly below the high-temperature cross-sections for rotational energy transfer determined elsewhere. The data suggest that under the present conditions rotational energy transfer is accompanied by significant depolarization. The cross-section for the translational moderation of superthermal OH(X) by water is also determined in the present study.

Muscular Strength And Power In Children 3-7 Years Old

Muscular performance of many types have been determined for adults and post-pubescents. Few data exist concerning muscle kinetics and kinematics for prepubescent children. PURPOSE The purpose of the present study was to determine absolute and relative (adjusted for body mass) strength, mean power, and mean velocity for upper and lower body resistance exercises in young boys and girls. METHODS Boys and girls (ages 3–7 yrs) were tested for 1 repetition maximum (1 RM) strength for the chest press and leg press exercises. Weight machines were modified to accommodate the smaller dimensions and lower strength levels of the children. An external dynamometer (Fitronics; Bratislava, Slovakia) was interfaced with the machines and loads were set at 70% 1 RM to determine mean power and mean velocity. The effects of gender and age were determined via ANOVA (p ≤ 05). RESULTS No gender differences were observed for any variable at any age. 1 RM strength, mean power, and mean velocity sig. increased across ages. With one exception, these increases disappeared when results were adjusted for body mass. Relative mean velocity actually decreased for the leg press exercise. Test data indicated children from 3–7 yrs are capable of performing strength and power tests, but may require more attempts than adults, and may need to attempt maximal loads more than once. CONCLUSION These results provide the first data on muscular strength, power and velocity in very young children. Gender differences were not apparent for these ages. Muscle strength and power was associated with increasing body mass, while relative velocity actually decreased in a manner similar to the decreasing body mass index. It appears that muscular strength and power during this stage of development are primarily dependent on increasing body mass, whereas velocity is influenced by additional variable(s), perhaps the increases in stature during these ages. In this age range, it appears that forcerelated variables are dependent primarily on size.

Muscular Strength And Power In Children 3-7 Years Old

Muscular performance of many types have been determined for adults and post-pubescents. Few data exist concerning muscle kinetics and kinematics for prepubescent children. PURPOSE The purpose of the present study was to determine absolute and relative (adjusted for body mass) strength, mean power, and mean velocity for upper and lower body resistance exercises in young boys and girls. METHODS Boys and girls (ages 3–7 yrs) were tested for 1 repetition maximum (1 RM) strength for the chest press and leg press exercises. Weight machines were modified to accommodate the smaller dimensions and lower strength levels of the children. An external dynamometer (Fitronics; Bratislava, Slovakia) was interfaced with the machines and loads were set at 70% 1 RM to determine mean power and mean velocity. The effects of gender and age were determined via ANOVA (p ≤ 05). RESULTS No gender differences were observed for any variable at any age. 1 RM strength, mean power, and mean velocity sig. increased across ages. With one exception, these increases disappeared when results were adjusted for body mass. Relative mean velocity actually decreased for the leg press exercise. Test data indicated children from 3–7 yrs are capable of performing strength and power tests, but may require more attempts than adults, and may need to attempt maximal loads more than once. CONCLUSION These results provide the first data on muscular strength, power and velocity in very young children. Gender differences were not apparent for these ages. Muscle strength and power was associated with increasing body mass, while relative velocity actually decreased in a manner similar to the decreasing body mass index. It appears that muscular strength and power during this stage of development are primarily dependent on increasing body mass, whereas velocity is influenced by additional variable(s), perhaps the increases in stature during these ages. In this age range, it appears that forcerelated variables are dependent primarily on size.

Momentum Transfer Between Polydisperse Particles in Dense Granular Flow

We perform molecular dynamics (MD) simulations (based on the soft-sphere model) of a model dry granular system consisting of two types of spherical particles differing in size and/or density to characterize particle-particle momentum transfer (solid drag). The velocity difference between two types of particles is specified in the initial conditions, and the evolution of relative mean velocity and the velocity fluctuations in terms of granular temperature are quantified. The dependence of the momentum transfer is studied as a function of volume fraction, size and density ratio of the two types of particles, inelasticity, and friction coefficient. An existing continuum model of particle-particle momentum transfer is compared to the MD simulations. A modified continuum solid drag model is suggested for a limited range of parameters.

430 攪拌槽内における平パドル翼周りの乱流渦構造(S35-3 乱流渦構造(3),S35 乱流渦構造)

Complex turbulence field around a flat paddle impeller in a stirred vessel was investigated experimentally with LDA measurement and phase averaging analysis. The relative mean velocity filed against the flat paddle was obtained and detailed examination was made on the production mechanism of Reynolds shear stress. Containing inflexion point, the relative velocity profile in downstream direction evolves like separated shear layer. Reynolds shear stress profile has a large peak, however, the location unnecessary coincides that of the maximum mean velocity gradient. There is the case that the large Reynolds shear stress occurs around boundary between inflow and outflow behind the edge of flat paddle. It is expected that quasi-periodic inflow and outflow contribute Reynolds shear stress production.

Effect of turbulence on the drag and lift of a particle

A direct numerical simulation (DNS) is used to study the effect of a freestream isotropic turbulent flow on the drag and lift forces on a spherical particle. The particle diameter is about 1.5–10 times the Kolmogorov scale, the particle Reynolds number is about 60–600, and the freestream turbulence intensity is about 10%–25%. The isotropic turbulent field considered here is stationary, i.e., frozen in time. It is shown that the freestream turbulence does not have a substantial and systematic effect on the time-averaged mean drag. The standard drag correlation based on the instantaneous or mean relative velocity results in a reasonably accurate prediction of the mean drag obtained from the DNS. However, the accuracy of prediction of the instantaneous drag decreases with increasing particle size. For the smaller particles, the low frequency oscillations in the DNS drag are well captured by the standard drag, but for the larger particles significant differences exist even for the low frequency components. Inclusion of the added-mass and history forces, computed based on the fluid velocity at the center of the particle, does not improve the prediction. Different estimates of the fluid velocity seen by the particle are examined. It is shown that the mean drag is insensitive to the fluid velocity measured at the particle center, or obtained by averaging over a fluid volume of the order of the particle size. The fluctuations diminish as the size of the averaging volume increases. The effect of increasing freestream turbulence intensity for the same particle size is studied. Fluctuations in the drag and lift forces are shown to scale with the mean drag and freestream intensity. The standard drag without the added-mass and history forces provides the best approximation to the DNS result.

An Estimate ofmwithout Conventional Priors

Using mean relative peculiar velocity measurements for pairs of galaxies, we estimate the cosmological density parameter Ωm and the amplitude of density fluctuations σ8. Our results suggest that our statistic is a robust and reproducible measure of the mean pairwise velocity and thereby the Ωm parameter. We get Ωm = 0.30 and σ8 = 1.13. These estimates do not depend on prior assumptions on the adiabaticity of the initial density fluctuations, the ionization history, or the values of other cosmological parameters.

Slip velocity and drag law in a liquid‐liquid homogeneous dispersed flow

AbstractLocal measurements of phase velocities and phase fraction in a dense liquid‐liquid homogeneous flow were done based on an application of PIV with a refractive index matching technique. This technique allowed to measure simultaneously both phase velocities and phase fraction fields, as well as the drop mean diameter in a vertical cocurrent flow of n‐heptane dispersed in an aqueous solution of glycerin. The evolution of the relative velocity as a function of the phase fraction (0–0.4) was studied with moderate particle Reynolds numbers (10–100) for drops behaving as spherical rigid particles. A local drag coefficient was derived from these measurements. The calculated mean relative velocity as a function of the local phase fraction with existing classical drag coefficient laws showed significant discrepancies with the measurements overestimated. Thus, the drag coefficient variation rate as a function of the phase fraction was underestimated by the models. The evolution of the normalized velocity (by the terminal velocity) as a function of the phase fraction was predicted correctly with mixture viscosity models in a creeping flow regime.

A Unified Approach for Designing a Radial Flow Gas Turbine

Radial flow turbo machines have been used for a long time in a variety of applications such as turbochargers, cryogenics, auxiliary power units, and air conditioning of aircraft cabins. Hence numerous papers have been written on the design and performance of these machines. The only justification for yet another paper is that it would describe a unified approach for designing a single stage inward flow radial turbine comprising a rotor and the casing. The current turbine is designed to drive a direct-coupled permanent magnet high-speed alternator running at 60000 rpm and developing a maximum of 60 kW electrical power. The freedom of choice of the tip diameter and the tip width of the rotor that would be necessary for optimum isentropic efficiency of the turbine stage was restricted by the specified rotational speed and power output. Hence, an optimization procedure was developed to determine the principal dimension of the rotor. The mean relative velocity in the rotor passages in the direction of the flow would be accelerated but flow velocity on the blade surfaces experiences a significant space rate of deceleration. The rate of deceleration can be controlled by means of a proper choice of the axial length of the rotor. A prescribed mean stream velocity distribution procedure was used to spread the rate of deceleration of the mean flow velocity along the meridional length of the flow passages. The nozzle-less volute casing was designed to satisfy the mass flow rate, energy and angular momentum equations simultaneously. This paper describes the work undertaken to design both the rotor and the casing. The work was motivated by the growing interest in developing gas turbine based hybrid power plant for road vehicles. The authors believe that the paper would lead to a stimulating discussion.

Rheology of suspensions with high particle inertia and moderate fluid inertia

We consider the averaged flow properties of a suspension in which the Reynolds number based on the particle diameter is finite so that the inertia of the fluid phase is important. When the inertia of the particles is sufficiently large, their trajectories, between successive particle collisions, are only weakly affected by the interstitial fluid. If the particle collisions are nearly elastic the particle velocity distribution is close to an isotropic Maxwellian. The rheological properties of the suspension can then be determined using kinetic theory, provided that one knows the granular temperature (energy contained in the particle velocity fluctuations). This energy results from a balance of the shear work with the loss due to the viscous dissipation in the interstitial fluid and the dissipation due to inelastic collisions. We use lattice-Boltzmann simulations to calculate the viscous dissipation as a function of particle volume fraction and Reynolds number (based on the particle diameter and granular temperature). The Reynolds stress induced in the interstitial fluid by the random motion of the particles is also determined. We also consider the case where the interstitial fluid is moving relative to the particles, as would occur if the particles experienced an external body force. Owing to the nonlinearity of the equations of motion for the interstitial fluid, there is a coupling between the viscous dissipation caused by the fluctuating motion of the particles and the drag associated with a mean relative motion of the two phases, and this coupling is explored by computing the dissipation and mean drag for a range of values of the Reynolds numbers based on the mean relative velocity and the granular temperature.

Measurement of local flow characteristics in buoyancy-driven bubbly flow at high void fraction

The sedimentation of a homogeneous dispersion of gas bubbles in water is studied, using double optical probe and hot-film anemometry, for high bubble Reynolds number (300–500), and high void fraction α (0–0.3). An experimental device has been specially designed to produce a uniform swarm of monodisperse bubbles without recirculating motions in the liquid phase. It is found that the evolution of the rise velocity of the bubbles is very similar to the sedimentation of particles in dense regimes, the hindrance function being characterized by scaling in α 1/3. The fluctuating kinetic in the liquid, once scaled by the mean relative gas velocity, exhibits a remarkable linear evolution with the void fraction. Moreover, the energy associated with the agitation of the bubbles reaches a maximum value when the distance between bubbles decreases.

Liquid breakup at the surface of turbulent round liquid jets in still gases

An experimental study of liquid column breakup lengths and turbulent primary breakup properties at the surface of turbulent round liquid jets in still air at standard temperature and pressure is described. Jet exit conditions were limited to non-cavitating water and ethanol flows, long length/diameter ratio (greater than 40:1) constant-diameter round injector passages, jet exit Reynolds numbers of 5000–200,000, jet exit Weber numbers of 235–270,000 and liquid/gas density ratios of 690 and 860, at conditions where direct effects of viscosity were small (e.g., liquid jet Ohnesorge numbers were smaller than 0.0053). Three liquid column breakup modes were observed, as follows: a weakly turbulent Rayleigh-like breakup mode observed at small jet exit Weber and Reynolds numbers, a turbulent breakup mode observed at moderate jet exit Weber numbers, and an aerodynamic bag/shear breakup mode observed at large jet Weber numbers. The turbulent primary liquid column breakup mode was associated with conditions where drop diameters resulting from turbulent primary breakup along the liquid surface were comparable to the diameter of the liquid column itself. The bag/shear liquid column breakup mode was observed when liquid turbulence caused large deformations of the liquid column so that portions of it were in a gaseous cross flow; this resulted in bag or shear liquid column breakup, very similar to the breakup of non-turbulent liquid jets in gaseous cross flow. Mean streamwise drop velocities after breakup were comparable to mean streamwise velocities within the jet whereas mean cross stream drop velocities after breakup were comparable to cross stream velocity fluctuations within the liquid. Rates of primary breakup at the liquid surface are reported as surface efficiency factors (the fraction of the maximum possible cross stream drop liquid flux at the surface based on the mean relative cross stream velocity of the drops at the surface and the liquid density). The resulting surface efficiency factors varied from small values near the onset of liquid surface breakup to values of the order of unity as conditions near breakup of the liquid column as a whole were approached.

East-West scattering level asymmetry of the solar corona

Coronal radio sounding experiments with spacecraft near solar conjunction show a steady tendency toward enhanced radio frequency fluctuations during the ingress phase with respect to the egress phase. This behavior can be explained by the higher mean relative velocity of the solar wind density inhomogeneities traversing the radio ray path. Indeed, the relative velocity is the sum of the velocity of the inhomogeneities (solar wind +/− possible wave velocity) plus the ray path velocity during ingress and the difference of these components during egress. There are isolated exceptions to this rule (e.g., the Galileo spacecraft conjunctions in 1994/95 and 1995/96). These anomalous cases, which were observed in the years preceeding solar activity minimum, can be explained by the strongly asymmetric structure of the rotating corona over the course of the conjunction.

Analytical Evaluation of the Maxwell–Boltzmann Velocity Average in Pressure-Broadened Half-Width Calculations

For the first time the half-width within the complex Robert–Bonamy (CRB) formalism is calculated without making the mean relative thermal velocity approximation. The application is to the nitrogen-broadened half-width of the 500.4-GHz transition (342 32←341 33) of the ground vibrational state of ozone. For each state of the perturber, the optical cross sections are determined at a number of velocities with the intermolecular potential taken as a sum of electrostatic contributions and Lennard–Jones (6–12) atom–atom components. The dynamics of the collision process are correct to second order in time. Using a nonlinear least-squares fitting method, the optical cross sections are fit to a double power law, which allows the velocity integral for the half-width to be done analytically. The results are compared with the mean relative thermal velocity complex Robert–Bonamy calculations and with measurement. The temperature dependence of the half-width, which is necessary for reduction of remotely sensed data, is determined from both methods and compared with experiment.

The Transition to Nonlinearity and New Constraints on Biasing

We present two new dynamical tests of the biasing hypothesis. The first is based on the amplitude and the shape of the galaxy-galaxy correlation function, xi g(r), where r is the separation of the galaxy pair. The second test uses the mean relative peculiar velocity for galaxy pairs, v12(r). This quantity is a measure of the rate of growth of clustering and it is related to the two-point correlation function for the matter density fluctuations, xi (r). Under the assumption that galaxies trace the mass (xi g = xi), the expected relative velocity can be calculated directly from the observed galaxy clustering. The above assumption can be tested by confronting the expected v12 with direct measurements from velocity-distance surveys. Both our methods are checked against N-body experiments and then compared with the xi g(r) and v12 estimated from the APM galaxy survey and the Mark III catalogue, respectively. Our results suggest that cosmological density parameter is low, omega m approximately 0.3, and that the APM galaxies trace the mass at separations r > or = 5 h-1, where h is the Hubble constant in units of 100 km s-1 Mpc. The present results agree with earlier studies, based on comparing higher-order correlations in the APM with weakly nonlinear perturbation theory. Both approaches constrain the linear bias factor to be within 20% of unity. If the existence of the feature we identified in the APM xi g(r)--the inflection point near xi g = 1--is confirmed by more accurate surveys, we may have discovered gravity's smoking gun: the long awaited "shoulder" in xi, generated by gravitational dynamics and predicted by Gott and Rees 25 years ago.

Semiclassical theory of alignment effects in near-resonant energy-transfer collisions of rare-gas atoms with aligned Rydberg atoms

Recent experiments [E. M. Spain et al., J. Chem. Phys 102, 24 (1995)] discovered alignment effects in cross sections for near-resonant energy-transfer collisions of Xe atoms with Ca Rydberg atoms at a single mean relative velocity. A collaborative quantum-mechanical study [W. Isaacs and M. A. Morrison, Phys. Rev. A 57, R9 (1998)] confirmed these findings and discovered pronounced oscillations in the velocity dependence of state-to-state cross sections. Collisions corresponding to the ${17d}_{{m}_{0}}\ensuremath{\rightarrow}{18p}_{m}$ transitions in the Ca-He system are here analyzed semiclassically. This analysis shows that the origin of these oscillations is a phase interference process unique to Rydberg target states. We further demonstrate the importance of retaining the energy defect and of using quantum-defect phase-shifted radial functions in calculations of alignment cross sections for Rydberg states.

Influence of the 3He isotope on the output parameters of theHe-Kr hollow cathode laser

The influence of the 3He isotope as a buffer gas on theoperating characteristics of the He-Kr hollow cathode laser is studied. Acomparison of the laser output power and gain on the KrII 469.4 nm andKrII 431.8 nm lines in 3He-Kr and 4He-Kr gas mixtures is made andan increase of 33% is observed in the case of the 3He-Kr gas mixture.A simple qualitative analysis of the plasma kinetics shows that theobserved increase of the laser output parameters is due to the increasedrate constant for the excitation transfer reaction and the increaseddensity of the He(2 3S1) metastable atoms and Kr ground state ions.The main reasons for this are the higher mean relative velocity of thecolliding particles and the higher rate of electron cooling in 3He-Krplasma.Peak output powers of 10 W and 1.5 W and small signal gains over thelosses of 85% m-1 and 64% m-1 are measured for the blue andviolet lines, respectively, from a 21 cm active length at 17.5 kPa 3Hepressure, 17 Pa Kr pressure and 96 A peak current. These values aresignificantly higher compared to earlier investigations. The operatingdischarge conditions are enlarged considerably; up to 21 kPa He pressureand 100 A peak current. The laser design chosen contributes to theachievement of this goal.