Velocity Vw Research Articles

A Hydrodynamic Model for the Formation of the Galactic Center “Minicavity”

The minicavity in the streamer to the southwest of the dynamical center of the Galaxy and the unique, nonthermal radio source Sgr A* appear to be physically connected by a chain of plasma that may be in transit from the latter to the former. Recent observations at radio and infrared wavelengths have provided clear evidence that the cavity has an opening radius of ~1'' ≈ 0.04 pc and radiates with a power Lcav ≈ 6 × 1037 ergs s-1. Here, we model the formation of the cavity as the result of an impact between the streamer gas and the post-bow shock gas collimated by a massive (~106 M☉) black hole coincident with Sgr A*. Multiwavelength observations, including those of He I, Brα, and Brγ line emission in the inner ~0.3 pc region of the Galaxy provide strong evidence for the presence of an ambient Galactic center wind with velocity vw ≈ 500-700 km s-1 and mass-loss rate ~3-4 × 10-3 M☉ yr-1. We show that the Bondi-Hoyle process responsible for the accretion of ~1022 g s-1 by Sgr A* also produces a downstream, focused flow with a radius very similar to that of the minicavity and a mechanical luminosity about 2.5 larger than Lcav. In addition, the size and density of the blobs appear to be consistent with the gas characteristics in this flow.

Polymer Brushes in Strong Shear Flow

ABSTRACTPolymers end-grafted to a surface in the presence of a shear flow are studied by molecular dynamics simulations. The solvent velocity field is observed to penetrate only a short distance into the brush consistent with predictions based on self-consistent field theory. The deformation of the brush is small except when the shear rate γ is very large. In this limit, while some of the polymer chains are stretched in the direction of flow, the brush height actually decreases slightly, in contrast to several theoretical predictions. When two surfaces bearing end-grafted chains are brought into contact, the normal force increases rapidly with decreasing plate separation, while the shear force is significantly smaller. For low relative velocityvwof the two walls, the surfaces slide pass each other with almost no change in the chain's radius of gyration or the amount of interpenetration, while for very largevw, there is significant stretching and some disentanglement of the chains. The results are in qualitatively good agreement with recent experiments using the surface force apparatus.

The Presupernova H [CSC]ii[/CSC] Region around SN 1987A

The slow expansion of the bright ring around SN 1987A and the large size estimated for the radio source at an age of ~1500 days suggest a low mass-loss rate, , from the blue supergiant progenitor star; we adopt = 7.5 × 10-8 M☉ yr-1 and a wind velocity vw = 450 km s-1 as standard values. This wind density would not give substantial radio free-free absorption during the first few days when low-frequency absorption was observed, but the turnover can be attributed to synchrotron self-absorption. The X-ray and radio emission observed since 1990 require that the supernova shock be interacting with denser gas than that in the free wind. We propose that it is interacting with an H II region created by the B3 Ia progenitor star in the swept-up red supergiant wind. The H II region extends from a radius rII ≈ 3 × 1017 cm to the ring radius R = 6 × 1017 cm in the equatorial plane and has a hydrogen density ~102 cm-3. The shock front will not reach the dense ring until the year 2005 ± 3. The X-ray luminosity should slowly increase until that time. The equatorial ionization front is trapped in the swept-up gas; the dense ring and its associated bipolar nebula are the initially neutral part of the shell. In the polar direction, the ionization front broke out of the swept-up gas, and there is no dense neutral shell, consistent with the observed lack of a thin shell in that direction.

Leukocyte-Endothelial Cell Adhesive Interactions: Role of Xanthine Oxidase-Derived Oxidants

The objective of this study was to determine whether agents that either scavenge or inhibit the production of oxygen radicals can alter the adhesive interactions between leukocytes and venular endothelium elicited by ischemia-reperfusion. Cat mesenteric and intestinal blood flows were reduced to 20% of baseline for 1 hr, followed by 1 hr of reperfusion. Sixty minutes after reperfusion, red blood cell velocity (Vr), leukocyte rolling velocity (Vw), and the number of adherent leukocytes were measured in mesenteric venules. Then, either manganese-superoxide dismutase (Mn-SOD), catalase, desferrioxamine, or oxypurinol was administered intravascularly. Ten minutes later, repeat measurements were obtained and compared with pretreatment values. Catalase, Mn-SOD, and oxypurinol significantly attenuated neutrophil adherence while neither inactivated-catalase nor desferrioxamine altered the reperfusion-induced leukocyte adhesion. The ratio of Vw to erythrocyte velocity, an index of the fracture stress between rolling leukocytes and venular endothelium, was not altered by any of the agents studied. These results and data in the literature indicate that many of the agents that are commonly used to either scavenge or inhibit the production of oxygen radicals in postischemic tissues exert a significant inhibitory influence on leukocyte adhesion to microvascular endothelium in vivo. Our results are also consistent with the view that xanthine oxidase-derived oxidants contribute to the leukocyte-endothelial cell adhesive interactions associated with reperfusion of ischemic tissues.

Mechanical properties of a hydraulic purse winch.

Relationships of velocity (Vw; m/s) and of effective force (Fw; kgw) of a hydraulic purse winch during fishing operation were obtained by using only the engine revolution (Ne; rpm) and the effec-tive output pressure of an oil pump (P-Po; kgw/cm2), respectively. Using the loaded (i.e. pulling the net) P (kgw/cm2) and the non-loaded (i.e. without pulling the net) Po (kgw/cm2) pressure of the pump, Vw and Fw could be expressed respectively as Vw=Kv(qp/qw)Ne and Fw=kfqw(P-Po), where ku and kf are constants, qp (l/rev) and qw (l/rev) are the displacement of the pump and the winch, respectively. Without using special instruments, Vw and Fw of the purse winch can be calculated applying the equations obtained. This simplified method is useful for the Third World Countries where sufficient instruments could not be provided for research works mainly due to economic problems.

Superoxide mediates reperfusion-induced leukocyte-endothelial cell interactions

The objective of this study was to determine whether superoxide mediates the leukocyte-endothelial cell interactions elicited by reperfusion (reoxygenation) of ischemic (hypoxic) tissues. Mesenteric and intestinal blood flows were reduced to 20% of control for 1 h, followed by 1 h of reperfusion. Sixty minutes after reperfusion, red blood cell velocity (Vr), leukocyte rolling velocity (Vw), and the number of adherent leukocytes were measured in mesenteric venules. Then, either human superoxide dismutase (hSOD), hydrogen peroxide-inactivated hSOD, or MoAb IB4 (a monoclonal antibody against the leukocyte adhesion molecule CD18) was injected intravenously. Ten minutes later, repeat measurements were obtained and compared with pretreatment values. hSOD attenuated reperfusion-induced neutrophil adherence and increased Vw/Vr, an index of the fracture stress between leukocytes and endothelium. Peroxide-inactivated hSOD did not alter any parameter. MoAb IB4 attenuated reperfusion-induced adherence but did not alter Vw/Vr. In a correlate study, cultured bovine microvascular endothelium was exposed to 30 min of anoxia, followed by 60 min of reoxygenation. Cat neutrophils were added during reoxygenation. Reoxygenation-induced leukocyte adherence was attenuated by either hSOD or MoAb IB4 but not by inactivated hSOD. Adherence of phorbol 12-myristate 13-acetate-activated cat neutrophils to plastic was unaffected by hSOD or inactive hSOD, yet MoAb IB4 virtually abolished the response. These results indicate that superoxide mediates reperfusion-induced leukocyte adherence and that endothelial cells are required for this superoxide-mediated adherence.

ＣＯ?S２?T溶接におけるシールド効果のテレビによる観察

The shape of the shielding gas stream of CO2 arc welding was visualized by the television system combined with the Schlieren optical apparatus. Some factors, such as the diameter of welding nozzle, the flow rate of shielding gas and the velocity of wind blow which influenced the core region of shielding gas and also the shielding area on the base metal surface, could be examined by this method. Gas analysis of shielding atmosphere and X-ray inspection of weld metal were also carried out to confirm the results obtained by this method.The following results were obtained.(a) In the area where the core region of shielding gas could be observed by the method, an enough CC2 concentration was measured, which could prevent the porosity of mild steel weld metal.. And the minimum CO2 concentration for preventing the porosity was found to be about 95 vol%.(b) An experimental formula, which included shielding distance toward the wind, crosssectional area of nozzle, shielding gas velocity (Vs) and wind velocity (Vw), was obtained. And the critical velocity ratio Vs/Vw, which was the minimum velocity ratio for preventing the porosity under the wind blow, was estimated as 1.62.1. The value was then confirmed by the X-ray inspection on the porosity of weld metal.

Atmosphere of Mercury

THE recently released news concerning the possible atmosphere surrounding Mercury seems to have taken the astronomical community by surprise. It had generally been expected that because of the high temperatures (of the order of 450 K) existing there and also because of the low surface gravity, any atmosphere originally present, or any released from subsequent events on the surface would quickly evaporate since the random thermal speed of the atoms would be greater than the escape velocity. If VE is the escape velocity from Mercury, ρA the density of its atmosphere and A the surface area, then a simple computation indicates1,2 that the rate of mass loss from this atmosphere is where β = m/2 kT, k being Boltzmann's constant and m the atomic mass. All this ignores the solar wind which carries mass into the atmosphere. In reality the problem becomes a boundary layer problem in which the magnetic field of Mercury plays a part, but we can see simply that the main effect is to generate an atmosphere. If the wind has a density ρw and a velocity Vw, then it adds matter to Mercury at the rate and the stead state situation is given when Inserting the appropriate numerical values, β≈10−11, VE2≈ 2 × 1010, and Vw≈ 108 (all in c.g.s. units gives) There should therefore be a very tenuous atmosphere, basically composed of hydrogen being maintained in this way. Any helium and argon released by radioactivity would become trapped in this atmosphere and should be detected.

Effect of Uniform Suction on Laminar Film Condensation on a Porous Vertical Wall

The problem of film condensation on a porous wall has been solved by a boundary layer treatment. A dimensionless suction velocity parameter β, which is proportional to the uniform suction velocity vw and 1/4th the power of longitudinal coordinate (x1/4), is defined to characterize the process. The results are restricted to small values of β, as the solutions are given by power series expansion in β. The effects of uniform suction on heat transfer, condensation rate, film thickness, and velocity and temperature profiles are demonstrated through various examples. In general, uniform suction causes a substantial increase of heat transfer and condensation rate, especially at low subcooling and at high Prandtl numbers. The problem involves three governing parameters: subcooling, Prandtl number, and suction velocity. Comparison with the previous work of Jain and Bankoff is discussed.

Erratum: "Generalized Law of the Wall and Eddy-Viscosity Model for Wall Boundary Layers"

Based on the logarithmic velocity distribution at distances not so far from the wall, and a turbulent shear variation proportional to the cubic power of the wall distance in the immediate proximity of the wall, an analytical model for an eddy viscosity through the wall region is derived leading to a closed-form expression for the velocity distribution. An extension of the preceding analysis to include shear variation results in a generalized law of the wall which admits a Reynolds number effect on the velocity distribution. While many applications of the generalized solution are envisaged, as an example the velocity distribution for the case of injection or suction is considered. The theoretical results are shown to be in agreement with available experimental data. Nomenclature u — mean flow velocity (streamwise component) UT = friction velocity (local) UT = [r(y)/p]1/2 u* = wall friction velocity w* = (UT)W = [r(0)/p]1/2 u + = dimensionless mean flow velocity u + — u/u* u' = dummy variable for u + UT* — dimensionless friction velocity UT+ = ur/u* U = defined by Eq. (18) U' = dummy variable for U e = eddy viscosity e+ = dimensionless eddy viscosity e/v y = normal coordinate y+ = dimensionless normal coordinate y+ = yu*/v vw+ = dimensionless injection velocity vw+ = vw/u*

The fading of radio waves of medium and high frequencies

The fading of radio waves of medium and high frequencies returned from the ionosphere is analysed. The experimental data on high frequencies were recorded by the author at normal incidence using a pulse transmitter, and, when necessary, a circularly polarized receiving aerial. The medium-frequency records were made by the B.B.C. using continuous-wave transmissions from broadcasting stations at different distances up to 1 500 kilometres.A review is given of some theories suggested to explain the production of fading in terms of an ionosphere with varying irregularities in the horizontal plane. The theoretical nature of the fading curve, both with regard to the distribution of amplitude and the variation with time, is indicated, and is compared with experimental results.It is shown that all fading curves can be explained in terms of a wave which is the sum of a steady, specularly reflected component, and a random component with a Rayleigh distribution of amplitude. The relative magnitudes of these two components have been determined for a series of different conditions, and the results are summarized. It is also shown that the rate of variation of the amplitude of the received signal is approximately, but not exactly, in accord with the theories, and from this rate of change it is possible to calculate the “effective velocity” of the irregularities in the ionosphere. If the fading is caused by irregular “turbulent” motions of the irregularities, the “effective velocity” is the r.m.s. velocity of these motions; if it is due to a steady drift of the irregular ionosphere as a whole with a velocity vw, then the “effective velocity” is approximately equal to vw/14. The “effective velocities” deduced from 122 records made at vertical incidence, and 55 made at oblique incidence, lie between 0.3 and 8.0 m/sec and have an average value of 1.9 m/sec.