Changes In Velocity Distribution Research Articles

Effects of melatonin supplementation on exercise-induced changes in conduction velocity distributions

The mammalian nervous system processes complex information to control complex behaviors. Since the speed of transport of information can be a life-saving phenomenon, it is extremely important to stabilize the rate of these processes. This study aims to investigate the protective effects of melatonin supplementation on acute heavy exercise-induced changes in the nerve conduction velocity distributions (CVD). Remodeling of the sciatic nerve due to heavy exercise demonstrates not only an increase in some parameters (rheobase and chronaxie), but also decreases in maximum depolarization, total area under the compound action potential (CAP), fall-down phase of CAP kinetics and speed of the intermediately conducting group. Acute heavy exercise-induced decreases in the contribution of nerve fibers were mainly found between 1.0 and 1.7 interstimulus interval (ISI) values (46-52 m/s). Presupplementation with melatonin, a powerful antioxidant for nervous tissues, protects the sciatic nerve against all of the aforementioned changes. Presupplementation not only protects the nerve cells from exercise-induced damage, but also increases the contribution of nerve fibers with conduction velocities of 46-52 m/s.

Effect of wind speed and load power factor variation on optimal sizing of the machine and converters for double output induction generator based stand-alone wind energy conversion systems

In this paper, an algorithm for finding out the optimal ratings of the machine and power electronic converters of a wind turbine driven stand-alone double output induction generator based variable speed constant frequency generation system is reported, which seeks to minimize the cost of energy generation. The nonlinear constrained optimization technique employed includes, among others, the reactive power balance constraints, which are not often considered for stand-alone systems. For this purpose, the load power factor is modeled as a random variable with known probability density function. The total energy captured is calculated for a given wind velocity density function and load power factor density function. The proposed method finally finds the optimum combination of machine and converter ratings, which results in minimum cost of energy. The effects of changes in load power factor and wind velocity distribution are also discussed in detail.

소수력발전용 횡류수차의 러너 블레이드 깃수에 따른 성능해석

Performance improvement of Small hydro turbine is a very important subject to solve in the stage of introduction and development of the turbine. Cross-flow hydro turbine should be also studied more in detail for the turbine performance in order to extend the sites of application. In order to improve the turbine performance, the effect of the turbine shape on the turbine performance should be examined. Therefore, the effect of runner blade number on the turbine performance is investigated by use of a commercial CFD code. The results show that runner blade number gives remarkable effect on the efficiency and output power of the turbine. Pressure on the surface of the runner blade changes considerably by the blade number at Stage 1, but relatively small change of velocity distribution occurs in the flow passage.

Rheological Characteristics for Thin Film Elastohydrodynamic Lubrication with Non-Newtonian Lubricants

AbstractThe modified Reynolds equation for power law fluid is derived from the viscous adsorption theory for thin film elastohydrodynamic lubrication (TFEHL). The differences between classical non-Newtonian EHL and non-Newtonian TFEHL are discussed. Results show that the proposed model can reasonably calculate the pressure distribution, the film thickness, the velocity distribution and the average viscosity under thin film lubrication. The thickness (δ), the viscosity (m1), and the flow index (n1) of the adsorption layer influence significantly the lubrication characteristics of the contact conjunction. Furthermore, the film thickness increases with the increase of n1 and the film thickness affected by m1 is greater than that affected by n1, but the effect of n1 produces a very small difference in the pressure distributions. In addition, the greater n1, the smaller the change of velocity distribution in the adsorption layer, and the greater the change of velocity distribution in the middle layer. The larger δ and n1, the larger the deviation on log (film thickness) vs. log (speed) produced in the very thin film regime. In the region of the flow index ratio between 1.0 and 1.3, the difference in film thickness is significant. When the flow index of the adsorption layer is 1.6 times greater than the flow index of the middle layer, the adsorption layer is generally looked upon as a “solid-like”.

Three-Dimensional Numerical Calculations on Liquid-Metal Magneto-hydrodynamic Flow through Circular Pipe in Magnetic-Field Inlet-Region

Three-dimensional numerical calculations have been performed on liquid-metal magnetohydrodynamic (MHD) flows through a circular pipe in the inlet region of the applied magnetic field, including a sufficient calculation region upstream in the magnetic field section. The continuity equation, the momentum equation including the Lorentz force term, and the induction equation derived from basic equations in the electromagnetism have been solved numerically. Along the flow axis (i.e., the channel axis), the pressure decreases slightly as a normal non-MHD flow, increases once, thereafter, decreases sharply, and finally decreases as a fully-developed MHD flow. The sharp decrease in the pressure, resulting in a large pressure drop in the inlet region is due to the increase in the induced electric current in this region compared with that in the fully-developed region. The velocity distribution changes from a parabolic profile of a laminar non-MHD flow to a profile with peaks near the walls parallel to the magnetic field, and finally to a flat profile of a fully-developed MHD flow.

Three-Dimensional Numerical Calculations on Liquid-Metal Magneto-hydrodynamic Flow through Circular Pipe in Magnetic-Field Inlet-Region

Three-dimensional numerical calculations have been performed on liquid-metal magnetohydrodynamic (MHD) flows through a circular pipe in the inlet region of the applied magnetic field, including a sufficient calculation region upstream in the magnetic field section. The continuity equation, the momentum equation including the Lorentz force term, and the induction equation derived from basic equations in the electromagnetism have been solved numerically. Along the flow axis (i.e., the channel axis), the pressure decreases slightly as a normal non-MHD flow, increases once, thereafter, decreases sharply, and finally decreases as a fully-developed MHD flow. The sharp decrease in the pressure, resulting in a large pressure drop in the inlet region is due to the increase in the induced electric current in this region compared with that in the fully-developed region. The velocity distribution changes from a parabolic profile of a laminar non-MHD flow to a profile with peaks near the walls parallel to the magnetic field, and finally to a flat profile of a fully-developed MHD flow.

Molecular dynamics study of velocity distribution and local temperature change during rapid cooling processes in excimer-laser annealed silicon

Molecular dynamics (MD) simulations have been performed to investigate velocity distribution of atoms and local temperature changes during rapid cooling processes in excimer-laser annealed Si. The interatomic forces were calculated using the Tersoff potential, and the rapid cooling processes were simulated by determining the atomic movements with a combination of Langevin and Newton equations using a MD cell with the size of 48.9 × 48.9 × 97.8 Å 3. The local velocity distribution during rapid cooling processes was found to be the Maxwell–Boltzmann type, and the steady-state temperature distribution was obtained within 100 ps.

Accelerated electrons in the LLBL as observed by Interball on February 15, 1996

We analyze electron observations in the low latitude boundary layer (LLBL) with the Interball Tail satellite under a southward–duskward magnetosheath magnetic field. It is well known that the LLBL is characterized by bi-directional electron velocity distributions, which leads to an enhancement of the electron temperature. It is also well known that the electron temperature within the LLBL increases with a decrease of the LLBL number density. We found that the parallel electron velocity distribution changes self-consistently with varying number density. Namely, the shape of the parallel velocity distribution does not change in a log–log scale indicating that electron parallel velocities increase proportionately as the number density decreases. This suggests a possible role for the Fermi acceleration mechanism. We also discuss the LLBL topology that is provided by electron velocity distributions.

Does the conduction velocity distribution change along the nerve?*1

Does the conduction velocity distribution change along the nerve?*1

Three-Dimensional Numerical Calculations on Liquid-Metal Magnetohydrodynamic Flow in Magnetic-Field Inlet-Region

Three-dimensional numerical calculations have been performed on liquid-metal magnetohydrodynamic (MHD) flow through a rectangular channel in the inlet region of the applied magnetic field, including a region upstream the magnetic field section. The continuity equation, the momentum equation including the Lorentz force term and the induction equation have been solved numerically. The induction equation is derived from Maxwell's equations and Ohm's law in electromagnetism. The discretization of the equations is carried out by the finite difference method, and the solution procedure follows the MAC method. Along the flow axis (i.e. the channel axis), the pressure decreases slightly as normal non-MHD flow, increases once, thereafter decreases sharply and finally decreases as fully-developed MHD flow. The sharp decrease in the pressure, resulting in a large pressure drop, in the inlet region is due to increase in the induced electric current in this region comparing with that in the fully-developed region. In the inlet region, the flow velocity distribution changes from a parabolic profile of a laminar non-MHD flow to a flat profile of a fully-developed MHD flow.

Does the conduction velocity distribution change along the nerve?

Nerve conduction velocity distribution (CVD) is a very useful tool to examine the state and function of nerves. Only one record of compound action potential (CAP) may be sufficient to determine the CVD if the shape functions of the single fiber action potentials (SFAP) of fibers are known. Otherwise, CAP recordings from different locations are necessary to determine CVD. In this case, we confront the problem of whether the shape of the CVD changes along the nerve, because many methods that attempt to determine the CVD are based on the assumption that the CVD is invariant along the nerve. There is not a complete solution to this problem, but there are many suggestions allied with the recording conditions to minimise this effect. The other effect that may influence both shapes of CAP and CVD along the nerve is the volume conductor effect. If a suitable model could isolate and eliminate the volume conductor effect, then the spatial variation of CVD may be attributed to the natural conditions of the nerve. In this study, we followed a procedure to eliminate volume conductor effect and then applied our previously published model to examine the spatial variations in CVD. The results show that CVDs estimated at discrete points along the nerve trunk have significantly different patterns. Consequently, it may be concluded that CVD is not uniform along an isolated nerve trunk contrary to the assumptions of the most CVD estimation methods.

High speed, wide velocity dynamic range Doppler optical coherence tomography (Part II): Imaging in vivo cardiac dynamics of Xenopus laevis

We previously reported a Doppler optical coherence tomography (DOCT) system design [1] for high-speed imaging with wide velocity dynamic range (up to 28.5 dB when acquiring 8 frames per second), operating at 1.3 m with a coherence length of 13.5 m. Using a developmental biology model (Xenopus laevis), here we test the DOCT system's ability to image cardiac dynamics in an embryo in vivo, with a simple hand-held scanner at 4 ~ 16 frames per second. In particular, we show that high fidelity DOCT movies can be obtained by increasing the reference arm scanning rate (~8 kHz). Utilizing a combination of four display modes (B-mode, color-Doppler, velocity variance, and Doppler spectrum), we show that DOCT can detect changes in velocity distribution during heart cycles, measure the velocity gradient in the embryo, and distinguish blood flow Doppler signal from heart wall motions.

Heat Transfer Enhancement and Pressure Loss in the Channel with a Vortex Generator

Using the time-space averaged momentum and energy equations obtained in the preceding report, a theoretical relation was derived to estimate the drag increase and the heat-transfer enhancement in the channel with a turbulence promoter. The investigation of the relation and the results of DNS for the channel with a wing-type vortex generator (VG) show that the heat-transfer efficiency η (i. e., the ratio of the heat transfer enhancement to the drag increase from the smooth channel) is larger when VG is installed in the laminar flow than in the turbulent flow from the following reasons. (I) The large pressure drag on VG in the turbulent flow decreases η. (II) The change of velocity distribution from the laminar parabolic one increases the convective heat transfer near the wall. This effect raises η without the penalty of drag increase.

톱니형 휜이 부착된 원주의 근접후류특성 연구 (II) - 시간평균 유동장 비교 -

The measurements of velocity vectors are made in the near wake(X/d=5.0) of a circular cylinder with serrated fins. Velocity of fluid which flow through fins decreases as increasing fin height and freestream velocity and decreasing tin pitch. Therefore the velocity distribution at X/d=0.0 has lower gradient with increasing treestream velocity and fin height and decreasing fin pitch. The discontinuity of the streamwise velocity gradient is observed near the fin edge and causes significant changes in V-component velocity distribution in the near wake. This change attributes to the differences in Strouhal number and entraintment flow behavior. Increased turbulent intensity around a circular cylinder due to the serrated fins and entrainment flow are important factors for the recovery of velocity defect. The widths of velocity and turbulent intensity distribution of fin tubes are wider than those of a circular cylinder. The normalized velocity and turbulent intensity distributions with a hydraulic diameter which is proposed in this paper are in closer agreement with those of a circular cylinder.

Internal Flow in a Centrifugal Pump of a Low Specific Speed with Semi-Open Impeller.

The internal flow in a centrifugal pump with semi-open impeller is visualized and measured by PTV method. In this pump, the design type number is 0.244 of low specific speed. The experimental results of two impellers whose outlet angles are 30 and 90 degree are compared. At the outlet of impeller, most of the quantity of fluid flows out along the pressure side of the vane, but some climbs over the top of the vane and flows into the suction side through the tip clearance. When the total quantity is changed, the meridian velocity distribution changes only near the tongue area, and in other area the meridian velocity is almost same. When the quantity becomes small, large vortices are produced between vanes, and this vortex reduces the tangential velocity at the outlet of impeller. This causes the reduce of theoretical head and instability in the performance curve.

Photo-stimulated desorption of rare gas atoms adsorbed on Si(100) surfaces modified with oxygen and deuterium

Photo-stimulated desorption of rare gas atoms (Xe and Kr) adsorbed on Si(100) surfaces has been investigated in the photon energy range of 1.16 eV to 6.43 eV. Rare gas atoms are photodesorbed from a clean surface and their velocity distribution is well represented by a Maxwellian with the average kinetic energy, 〈EK〉=0.07 eV. When the surface is modified by oxygen or deuterium, the desorption yield increases and the velocity distribution changes dramatically. Upon oxidation with one monolayer oxygen the velocity distribution shows two nonthermal components with 〈EK〉=0.85 and 0.25 eV, while only one component with 〈EK〉=0.17 eV for the mono-deuterated surface. The velocity component with 〈EK〉=0.85 eV has a threshold at hν∼3.5 eV. The origin of the component is understood by assuming the excitation from the ground state of a rare gas adsorbate to an excited state where electron transfer occurs from the adsorbate to the substrate. On the other hand, the other nonthermal desorption components do not show such remarkable wavelength dependence; they appear in the entire range of photon energies used in this study and do not show any significant changes in their velocity distributions. The origins of these components are discussed in terms of substrate-mediated excitation.

An Analytical Solution for Incompressible Flow Through Parallel Multiple Jets

A theoretical model of multiple jet flow is introduced based on the thin shear layer theory. The analytical solution has been obtained by using Prandtl’s mixing length hypothesis. The results show that along the streamline direction, the axial velocity decreases gradually like a single jet and in the transverse direction, the velocity distribution changes as a cosinoidal function, in which the velocity amplitude decreases with increasing x, gradually approaching a flat profile. It is also shown that the distance at which the individual jets begin to merge increases with increasing pitch, s. For the special cases when the pitch, s is zero, the row of multiple jets becomes equivalent to a single jet. Finally, the predictive results are found to agree well with experimental data in the fully developed turbulent flow region.

710 円形噴流初期領域における二次フィルム流の影響 : 二次フィルム流による速度分布及びエントレンメントの変化(流体工学II)

710 円形噴流初期領域における二次フィルム流の影響 : 二次フィルム流による速度分布及びエントレンメントの変化(流体工学II)

PRESSURE DROP AND HEAT TRANSFER IN PACKED BEDS WITH SMALL TUBE-TO-PARTICLE DIAMETER RATIO

Measurements of overall voidage, velocity distribution, and pressure drop in cylindrical packed beds of spherical particles in which the tube-to-particle diameter ranged from 5 to 50 and the particle Reynolds number ranged from 30 to 1,700 are reported. Owing to the change in the packing structure within the bed, the overall voidage decreases with increasing diameter ratio, becoming constant for values of the latter greater than about 16. After exit from the bed, the velocity distribution changes continuously with distance downstream of the bed, toward that typical of flow in an empty pipe. As such, measurements made above the bed are not truly representative of flow within the bed. The pressure drop across the bed can be correlated by the Ergun-type equation, but the coefficients in this equation vary with diameter ratio. These variations can be explained by considering the effect of the tube wall on the local packing structure. Results of measurements on the heat transfer from an electrically heated rod, placed coaxially within an annular bed of spherical particles, to air flowing in an outer annulus external to the can containing the particles are presented for a range of channel Reynolds number between 4 x 103 and 1.7 x 104. The use of a porous can instead of a smooth, nonporous one results in an increase in the rate of heat transfer, and this effect increases with increasing Reynolds number.

Lorentz's model with dissipative collisions

Propagation of a particle accelerated by an external field through a scattering medium is studied within the generalized Lorentz model allowing inelastic collisions. Energy losses at collisions are proportional to (1− α 2), where 0⩽ α⩽1 is the restitution coefficient. For α=1 (elastic collisions) there is no stationary state. It is proved in one dimension that when α<1 the stationary state exists . The corresponding velocity distribution changes from a highly asymmetric half-Gaussian ( α=0) to an asymptotically symmetric distribution ∼exp[−(1− α) v 4/2], for α→1. The identical scaling behavior in the limit of weak inelasticity is derived in three dimensions by a self-consistent perturbation analysis, in accordance with the behavior of rigorously evaluated moments. The dependence on the external field scales out in any dimension, predicting, in particular, the stationary current to be proportional to the square root of the external acceleration.