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Notes: Molecular dynamics simulations are carried out to determine the effects of channel wall structure on water and ion properties. We compare hydrophobic (Lennard-Jones 5-3 and atomic) and molecular-hydrophilic cylindrical pores of 2–6 Å in effective radius, relevant to the study of most significant biological ion channels including gramicidin A, ACh, and potassium channels, and to the study of many microporous materials. Large variations in levels of self-diffusion and rotational correlation within hydrophobic channels are explained in terms of water geometry, hydrogen bonding, and dipole correlation. The differing levels of water structure and self-diffusion in hydrophobic and hydrophilic pores arise because of marked differences in the preferred orientation of water dipole moments, and due to hydrogen bonding with molecules on the pore lining. Axial sodium ion diffusion does not experience large variations with pore size, despite anomalous stability in moderate-sized hydrophobic pores. We attribute this to the ability of ions to diffuse along troughs of water density. Ion diffusion along the pore axis exhibits a general increase with channel radius in hydrophobic channels but remains fairly low in hydrophilic channels. © 1999 American Institute of Physics.

Notes: In order to study the rotational motion of a vortex ring or the locomotion of bacteria, which propel their cells by rotating their long curved filaments called flagella, the low-Reynolds-number flow resulting from the rotation of a torus is studied. The velocity field is obtained by distributing uniform rotlets along a circle with the rotlet directions tangent to the circle. It is found that the effect of curvature of this ring distribution of uniform rotlets is to displace this rotlet ring from the center of the cross section toward the outside of the torus in the normal direction. The net force exerted on the surrounding fluid by the rotational torus is zero. The net torque acting on the fluid is also zero.

Notes: In this paper we are concerned with the wave generation by a singular forcelet in a viscous fluid of finite depth, where the singularity is located far from the bottom and not very near the free surface. In the first part of this work, the image system of an Oseenlet bounded by a no-slip wall, is considered. It is found that the resultant velocity field can be described by a planar distribution of vertical Oseen doublets and a negative Oseenlet located at the mirror point of the singularity with respect to the plane wall. In the second part of the work we deal with the generation of waves by these solutions. By imposing the linearized free-surface conditions on the solutions obtained from the first part, the wave generated is shown to exhibit the Kelvin ship wave pattern that agrees with observation. The effects of water depth and of submergence on the wave amplitude are also investigated. © 1997 American Institute of Physics.

Notes: The free-surface flow generated by an impulsively accelerating, surface-piercing, vertical plate has been studied experimentally in an open channel of constant depth. The flat vertical plate is fixed on a towing carriage that is set off by suddenly dropping a weight bucket through a connecting steel cable in a pulley system. The free-surface profile in front of the plate and the pressure distribution on the plate surface are measured for three different accelerations of the plate. A capacitance-type wave gauge is used to measure the variations of the water surface, while a variable reluctance pressure transducer is used to measure the pressure on the plate surface. The acceleration of the plate is obtained by means of an accelerometer. All response voltage outputs are recorded on an IBM PC-XT personal computer with a data-acquisition electrical board. Experimental measurements are compared with the numerical, viscous-flow results of Yang and Chwang (IIHR Report No. 332; Iowa Institute of Hydraulic Research, The University of Iowa, 1989) and the analytical, inviscid-flow solution of Chwang [Phys. Fluids 26, 383 (1983)]. The agreement of the free-surface profile and the pressure distribution between the numerical results and the present experimental measurements is fairly good. However, the inviscid-flow solution overpredicts the wave amplitude and the pressure distribution on the plate. In the physical experiments, the water surface is observed to rise in front of the vertical plate where the potential-flow theory becomes singular.

Notes: The development of a swirling round laminar jet in an unbounded viscous fluid is investigated in this Brief Communication by applying the unsteady Stokes equations instead of the full Navier–Stokes equations. The solutions corresponding to a constant linear-momentum source, an impulsive linear-momentum source, and constant and impulsive angular-momentum sources are presented. Since the Stokes equations are linear, these results can be superimposed together. For a constant linear-momentum source and a constant angular-momentum source, the present results reduce to the Stokeslet and rotlet solutions, which are the singular solutions of the Stokes equations, respectively, as time approaches infinity. It is also found that the developing flow field due to a linear-momentum source at the initial stage is irrotational and has a dipolelike structure. However, the developing flow field due to an angular-momentum source is immediately rotational and the magnitude of the velocity is exponentially small.

Notes: Wave disturbances caused by the uniform translatory motion of a submerged body on or beneath the free surface of a viscous fluid are investigated analytically. The submerged body is idealized as an Oseenlet or an Oseen doublet, and exact solutions in closed integral forms are obtained. Based on these exact solutions, asymptotic representations of the wave amplitude for large Reynolds numbers based on the deep-water wavelength at large distances downstream of the body are derived. The results obtained show explicitly the effect of the laminar wake on the amplitude and the phase of the surface waves thus created. © 1996 American Institute of Physics.

Notes: Two-dimensional solitary waves generated by a submerged body moving near the critical speed in a shallow water channel are studied numerically. The incompressible Navier–Stokes equations in a curvilinear free-surface-fitted coordinate system are solved by the finite difference method. The present numerical results are compared with the existing experimental data, and with the numerical solutions of two inviscid-flow models, i.e. the general Boussinesq equation and the forced Korteweg-de Vries equation. It is found that the viscous effect in the boundary layer around the body and on the bottom of the channel plays an important role in the generation of solitary waves on the free surface. Hence the Navier–Stokes solutions have a better agreement with the experimental data than those obtained from two inviscid-flow models. The effect of the submergence depth of the body on the waves generated is also investigated. It reveals that waves are insensitive to the submergence depth of the body, except for a small region quite close to the bottom of the water channel. © 1996 American Institute of Physics.

Notes: Quantum mechanical anharmonic oscillators and Hamiltonians for particles in external magnetic fields are related to representations of nilpotent groups. Using this connection the eigenfunctions of the quartic anharmonic oscillator with potential Vα(x)=(α+(x2/2))2 can be used to determine the eigenfunctions of a charged particle in a nonconstant magnetic field, of the form Bz=β2+β3x. The quartic anharmonic oscillator eigenvalues for low-lying states are obtained numerically and a function which interpolates between α(very-much-less-than)0 (a double harmonic oscillator) and α(very-much-greater-than)0 (a harmonic oscillator) is shown to give a good fit to the numerical data. Approximate expressions for the quartic anharmonic oscillator eigenfunctions are then used to get the eigenfunctions for the magnetic field Hamiltonian. © 1997 American Institute of Physics.

Notes: Calcium Channels and Temperature. Introduction: Lowering temperature greatly reduces calcium influx through calcium channels. Studies on a number of tissues demonstrate that the peak inward current, ICa exhibits Q10 values ranging from 1.8 to 3.5; however, it remains unclear which component(s) of calcium channel gating may give rise to this large temperature sensitivity. Components of gating that may affect channel availability include phosphorylation and changes in [Ca2+)i, processes that vary in pertinence depending on the channel examined. This study addresses this problem by examining the temperature sensitivity (from 34° to 14°C) of cardiac ICa under control conditions, during attenuation or activation of protein kinase A (PKA) activity, and when intracellular [Ca2+] has been elevated. Methods and Results: ICa was studied using the whole cell configuration of the patch clamp technique. In control, lowering temperature from 34° to 24°C resulted in a shift in the potential for maximum slope (Va and the peak current (Ymax) toward more positive membrane potentials. The Q10, values for the decrease in Ymax and the macroscopic slope conductance (Gmax), which reflects the number of available channels, were 3.15 ± 0.19 and 2.57 ± 0.13, respectively. At 0 mV the Ca2+ current decayed biexponentially, and the two time constants (T1 and T2) showed Q10 values of 1.79 ± 0.21 and 2.06 ± 038, while their contribution to the total current (I1 and I2) showed a Q10 of 5.99 ± 0.83 and 1.61 ± 0.22. In myocytes loaded with inhibitors of the PKA cycle sufficient to inhibit the increase of ICa to 1 μM isoprenaline, the Q10 values for some of the kinetic parameters were increased with the Q10 for I1 increasing to 17.06 ± 3.48. Stimulation of ICa by exposing myocytes to 1 μM isoprenaline reduced the temperature sensitivity of Ymax, Gmax, and I1, yielding respective values of 2.00 ± 0.18, 1.85 ± 0.07, and 2.04 ± 0.15. Raising [Ca2+], to enhance Ca2+i-dependent inactivation, while affecting inactivation and activation kinetics, affected temperature sensitivity little compared to control. The Q10 for time to peak changed little under experimental conditions (2.3 to 2.4) Conclusions: Increasing the phosphorylated states of calcium channels, but not Ca2+i-dependent inactivation, reduces temperature sensitivity of certain gating parameters. The data suggest that the rate of the transitions between the unavailable and also between the various closed states are changed in the opposite direction to that induced by PKA-dependent phosphorylation. Processes, e.g., inhibitory mechanisms, may be involved to maintain channels in unavailable or “unphosphorylated” states, and it may he these that contribute to the high Q10 of macroscopic channel currents.