Rear Region Research Articles

Intracellular free calcium responses during chemotaxis of Dictyostelium cells.

A calcium ion indicator, fura-2 bovine serum albumin, was introduced into Dictyostelium discoideum cells by electroporation. The concentration of intracellular calcium ions ([Ca2+]i) increased transiently in vegetative cells upon stimulation with submicromolar concentrations of folic acid, a chemoattractant for this organism at the vegetative stage. Similar [Ca2+]i responses were also observed in aggregation-competent cells upon stimulation with subnanomolar concentrations of cAMP, a chemoattractant at the aggregation stage. The [Ca2+]i response caused by cAMP was 2.1 times higher than that caused by folic acid. The magnitude of these responses depended on the concentration of Ca2+ in the external buffer. The presence of magnesium ions inhibited the [Ca2+]i responses in a dose-dependent manner. [Ca2+]i was higher in the rear region than in the anterior region of cells freely migrating on the surface, although such a gradient was not always maintained. When aggregation competent cells were locally stimulated by the application of a microcapillary containing cAMP, the cells extended pseudopods toward the microcapillary. In these cases, an increase in [Ca2+]i was transiently observed in the region opposite to the tip of the capillary. At the slug stage, [Ca2+]i was higher in prestalk cells than in prespore cells of slugs. The possibility that the [Ca2+]i is spatially regulated within a cell was discussed.

Flow separation patterns over an F-14A aircraft wing

Computational results of flow over an F-14A wing based on a thin-layer Navier-Stokes method are presented, and the resulting flow separation patterns are discussed. A zonal approach is employed that allows a condensed grid for viscous calculations near the wing surface. The F-14A wing is fixed with a sweep angle of 20 deg and travels at an altitude of 45,000 ft above sea level at Mach 0.6 and at sea level at Mach 0.1 with various angles of attack. These conditions, which yield a Reynolds number of 8.95 x 10 6 at both altitudes, allow evaluation of the effect of Mach number on flow separation patterns with fixed Reynolds number. Massive flow separation occurs at Mach 0.6 at an angle of attack of 10 deg. At Mach 0.1, with the same Reynolds number, the rear region massive separation disappears, but a strong leading-edge separation emerges. Consequently, the lift and drag values are far more stable at low speed as the angle of attack increases.

10 直接シミュレーションモンテカルロ法における分子移動の可視化

Molecule motion is visualized by sequential expression of molecular position at each time step in direct simulation of monte carlo method. Exhausted gas molecules from a nozzle are impinged on a circular disk, held perpendicualarly and coaxially with the nozzle. Few molecules do not intrude into the rear region of the disk.

Theoretical optimization of a split septaless xenon ionization detector for dual-energy chest radiography.

It is proposed that digital scanned projection radiography of the chest be performed by using an energy-sensitive septaless xenon ionization detector (SXID) to obtain dual-energy images. The proposed detector is composed of a front region, sensitive to low-energy x rays, and a rear region, sensitive to high-energy x rays, separated by a suitable filter layer. We have developed a simple, precise theoretical formulation for dual-energy optimization, and applied it to the split SXID. We describe the variation of optimum detector performance with source kilovoltage and filtration (material and thickness), and hence heat loading, under conditions of constant exposure and constant dose. We estimate dose as the average absorbed dose to an equivalent water layer of suitable thickness, assuming slab geometry, so that the calculation is as simple as that for exposure.

乱流はん点内の渦構造

The structures of the streamwise vortices and transverse vortices in a turbulent spot are investigated using two visualization techniques that utilize fluorescent dye excited by a sheet of laser light (2 watt argon laser).The results indicate that (1) a number of the streamwise vortices and transverse vortices which have some scales, exist in the turbulent spot, (2) small scale transverse vortex exists at the top of the stream-wise vortex, (3) large scale transverse vortices are formed at the rear region of the turbulent spot, and (4) low speed streak exists in the root of a pair of the counterrotating streamwise vortices near the wall.

Characteristics of Free Surface Shock Waves around Wedge Models (Second Report)

Characteristics of free surface shock waves were experimentally investigated with wedge models whose half-entrance angle is from 5 to 45 degree. Measurements of wave configuration and distribution of velocity components and pressure were undertaken. The wave configuration is ruled by Froude number based on draft, but there exists some scale effect on and behind the wave front, being connected with dissipative property of free surface shock waves. Remarkable features of the structure of free surface shock wave are occurrence of energy deficit at the wave front as a result of ultimate wave steepening, its diffusion in the rear region and partially hydrostatic pressure distribution.

Temporal and spatial changes of polar substorms and infrasonic wave emissions

By use of auroral infrasonic wave (AIW) records observed at the Syowa station, Antarctica, the relations between the AIW emissions and the auroral substorms were studied separately in the cases of emissions in the dusk, dawn and midnight. For this purpose, contour maps of the horizontal magnetic vectors at the time of AIW emissions were compared with the equivalent current systems. The followings are found. The existence of substorm activity is always found at the time of AIW emissions, but its strength has only minor relations to their occurrence. The condition for the occurrence of the emission depends largely on the manner how the disturbed region moves. The AIWs are emitted when the disturbed region moves with a supersonic speed and the trace direction of the wave roughly coincides with the direction of the traveling disturbance. While the morning and the evening AIWs are emitted from the rear region of the traveling disturbance, the midnight one from the front region. The AIW emissions tend to synchronize with the overhead crossing of the electrojet current and at that time the current causes the rotational change in the horizontal magnetic vectors on the ground.

A note on the asymptotic physical optic solution to the scattered fields from a paraboloidal reflector

The asymptotic physical optic (APO) formulation for the scattered fields from a paraboloid has been found to give results which agree with experiment except in the rear region. The disagreement here is due to the inexact nature of the assumed geometric optic (GO) edge currents as used in APO. A means of correcting for the error in these currents is given here by appealing to the equivalent half plane problem of Sommerfeld. This correction method is called CAPO (corrected APO). The resulting corrected diffraction coefficients are shown to be numerically indistinguishable from those of GTD. Comparisons of predicted E - and H -plane field patterns, based on these corrected results, with measurements in the rear region are given and shown to be quite acceptable; the corrections having negligible effect elsewhere. The static nature (in the sense of implicitly ignoring slope diffraction) of APO, GTD, and CAPO is discussed.

Mass transfer to the rear of a sphere in Stokes flow

Mass transfer to a sphere, including the rear region, in Stokes flow and at large Péclet numbers, is investigated. By the singular-perturbation technique, six distinct regions of different mass-transfer mechanisms are found. One of these regions, the diffusion layer, has already been solved by the boundary-layer method. Another area, the region at the rear of the sphere, is solved here. The local Nusselt number at the rear stagnation point is found to be 1·192. To predict the mass transfer rate everywhere on the sphere, a composite solution can be formed from the boundary-layer solution and the rear-region solution. In heat- and mass-transfer problems, the method used here complements the boundary-layer methods in predicting the heat- or mass-transfer rate at the rear of an axisymmetric object.

Membrane potentials in Amoeba proteus.

ABSTRACT Amoebae can be penetrated by microelectrodes at either end. One records voltage and the other supplies alternating current. Step-like increases in alternating voltage superimposed on potentials recorded by the voltage electrode when in either the pseudopod or rear region demonstrate that low potentials recorded from a pseudopod and high ones from the rear region exist across a discrete impedance barrier. The only structure so far shown to fulfil this function is the plasma membrane. A resistance inserted in the earth path monitors current flowing through the system and confirms observations made when recording with single electrodes that there is a reduction of electrode resistance when the cell is entered. Pronounced depolarization in the rear region is shown when the currentcarrying electrode penetrates the pseudopod, but not vice versa. Morphological changes associated with membrane potential reversal are illustrated. Consideration is given to the role of step-like potential changes in movement.

Further investigations into membrane potentials in amoebae

1. 1. The present work confirms the findings of Bingley and Thompson and Batueva that membrane potentials recorded from the tip of an advancing pseudopod are less negative than those recorded from the rear region. Photographic records are presented. 2. 2. Pseudopods streaming forward exhibit low potentials −24.5 mV s.d. ± 2.7 compared to the rear region −64.2 mV s.d. ± 4.4. 3. 3. Mechanical stimulation in the rear region produced a partial depolarization of the membrane. 4. 4. Breakage of a microelectrode while inside the cell was often followed by a positive membrane potential excursion of up to +70 mV. The cell expanded and water appeared to enter the cell. Photographic traces show the course of this potential change which shows some of the characteristics of an action potential. 5. 5. Electrode resistance was continuously monitored while membrane potentials were recorded. Increases in this during penetration suggest that there is only one resistive barrier, probably the cell membrane through which the electrode passes, whether it is in the pseudopod or rear region.

CONTRIBUTIONS TO SURVIVAL MADE BY BODY CELLS OF GENETICALLY DIFFERENTIATED STRAINS OF MICE FOLLOWING X-IRRADIATIONS

1. The influence of x-irradiation absorbed in three body regions and in the combinations of these regions has been measured by three subsequent responses: survival to radiation, natural resistance to disease and ability to acquire resistance following contact with the disease agent, S. typhimurium. The effects of irradiation are presented in this paper. Papers on natural and acquired resistance will follow. The experiment was designed as a factorial with five genetically differentiated strains of mice, S, Z, K, Q and Ba; four levels of radiation: 0 r, 320 r, 480 r and 640 r; eight treatment groups and two sexes. All mice were 46 ± 3 days of age when irradiated from a 250 pkv x-ray source operated at 30 ma with 0.25 mm. Cu + 1 mm. A1 filter at a dose rate averaging 170 r/minute. For the initial treatment the strains and sexes were well balanced, at least 50 mice in each of the 25 different treatment groups. The bodies of the mice were marked off in three regions, head h, mid m, and rear r, each comprising ...