The mechanism of generation, development and interaction of vortical structures, extracted as concentrated-vorticity regions, in homogeneous shear turbulence is investigated by the use of the results of a direct numerical simulation of the Navier-Stokes equation with 1283 grid points. Among others, a few of typical vortical structures are identified as important dynamical elements, namely longitudinal and lateral vortex tubes and vortex layers. They interact strongly with each other. Longitudinal vortex tubes are generated from a random fluctuating vorticity field through stretching of fluid elements caused by the mean linear shear. They are inclined toward the streamwise direction by rotational motion due to the mean shear. There is a small (about 10°) deviation in direction between the longitudinal vortex tubes and vorticity vectors therein, which makes the vorticity vectors turn toward the spanwise direction (against the mean vorticity) until the spanwise components of the fluctuating vorticity become comparable in magnitude with the mean vorticity. These longitudinal vortex tubes induce straining flows perpendicular to themselves which generate vortex layers with spanwise vorticity in planes spanned by the tubes and the spanwise axis. These vortex layers are unstable, and roll up into lateral vortex tubes with concentrated spanwise vorticity through the Kelvin-Helmholtz instability. All of these vortical structures, through strong mutual interactions, break down into a complicated smallscale random vorticity field. Throughout the simulated period an oblique stripe structure dominates the whole flow field: initially it is inclined at about 45° to the downstream and, as the flow develops, the inclination angle decreases but eventually stays at around 10°–20°.

Effect of compressibility on the stability of a vortex sheet in an ideal magnetofluid Phys. Fluids 16, 150 (1973);

High-voltage triode flat-panel display using field-emission nanotube-based thin films Field emission displays ͑FED͒ are drawing attention as one of the most promising flat panel displays. Currently, the development stage of Spindt-type FEDs with Mo emitter is close to an end. The monocolor Spindt-type FEDs are being supplied to the market, and the color FEDs are ready for mass production. FED is also expected as a low power consumed display device, because the power, in principle, is consuming at the light emitting part only. The present status of FEDs with Spindt type and nanocarbon emitters are reported in this article.

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The mechanism of wrap, tilt and stretch of vorticity lines around a strong thin straight vortex tube of circulation Γ starting with a vortex filament in a simple shear flow (U = SX 2 X 1 , S being a shear rate) is investigated analytically. An asymptotic expression for the vorticity field is obtained at a large Reynolds number Γ /ν 1, ν being the kinematic viscosity of fluid, and during the initial time S t 1 of evolution as well as S t (Γ /ν) 1/2 . The vortex tube, which is inclined from the streamwise (X 1 ) direction both in the vertical (X 2 ) and spanwise (X 3 ) directions, is tilted, stretched and diffused under the action of the uniform shear and viscosity. The simple shear vorticity is on the other hand, wrapped and stretched around the vortex tube by a swirling motion, induced by it to form double spiral vortex layers of high azimuthal vorticity of alternating sign. The magnitude of the azimuthal vorticity increases1/2 from the vortex tube. The spirals induce axial flows of the same spiral shape with alternate sign in adjacent spirals which in turn tilt the simple shear vorticity toward the axial direction. As a result, the vorticity lines wind helically around the vortex tube accompanied by conversion of vorticity of the simple shear to the axial direction. The axial vorticity increases in time as S 2 t, the direction of which is opposite to that of the vortexwhere the vorticity magnitude is strongest. In the near region r (Γ /ν) 1/3 (νt) 1/2 , on the other hand, a viscous cancellation takes place in tightly wrapped vorticity of alternate sign, which leads to the disappearance of the vorticity normal to the vortex tube. Only the axial component of the simple shear vorticity is left there, which is stretched by the simple shear flow itself. As a consequence, the vortex tube inclined toward the direction of the simple shear vorticity (a cyclonic vortex) is intensified, while the one oriented in the opposite direction (an anticyclonic vortex) is weakened. The growth rate of vorticity due to this effect attains a maximum (or minimum) value of ±S 2 /3 3/2 when the vortex tube is oriented in the direction of X 1 + X 2 ∓ X 3 . The present asymptotic solutions are expected to be closely related to the flow structures around intense vortex tubes observed in various kinds of turbulence such as helical winding of vorticity lines around a vortex tube, the dominance of cyclonic vortex tubes, the appearance of oppositesigned vorticity around streamwise vortices and a zig-zag arrangement of streamwise 116 G. Kawahara, S. Kida, M. Tanaka and S. Yanase vortices in homogeneous isotropic turbulence, homogeneous shear turbulence and near-wall turbulence.

The purpose of this study was to investigate the frequency of inpatient falls and to evaluate the risk factors of drugs in an academic hospital. The study population consisted of inpatients at Ehime University Hospital in Japan and the study was conducted from April 1st to October 31st, 2006. Children and teenagers (＜18 years old) were excluded. Inpatient falls were registered regularly with incident reports submitted by nurses and other hospital employees discovering the fall. Logistic regression techniques were used to estimate the odds ratios (OR) of the association of falls and drug use. Of the 4084 adult patients, 65 (1.6％) fell. An OR (unadjusted) for risk of falling were observed for various drug classes; hypnotics (OR 2.12; 95％ CI, 1.25 to 3.52), anxiolytic (OR 3.35; 95％ CI, 1.83 to 5.82), anti-Parkinson's (OR 5.79; 95％ CI, 1.71 to 14.80), narcotics (OR 3.08; 95％ CI, 1.06 to 7.11), hypotensives, diuretics (OR 2.39; 95％ CI, 1.42 to 3.95). A multivariate logistic regression analysis showed that inpatient falls were signiˆcantly associated with patients older than 70 years (OR, 2.25; 95％ CI, 1.35 to 3.77), with patients taking anxiolytic drugs (OR 2.36; 95％ CI, 1.24 to 4.25), and with patients taking anti-Parkinson's medication (OR 5.04; 95％ CI, 1.44 to 13.43). In conclusion, this study provides information regarding the relationship between fall-related accidents and drugs. Therefore, pharmacists should provide appropriate drug information related to the risk of falling to both patients and medical staŠ members.

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The dynamics of homogeneous shear turbulence laden with spherical finite-size particles is investigated using fully resolved numerical simulations to understand how the presence of particles modulates turbulent shear flows. We focus on a dilute flow laden with non-sedimenting particles whose diameter is slightly smaller than or comparable with those of vortex cores in turbulence. An immersed boundary method is adopted to represent a spherical finite-size particle. Numerical results show that the presence of particles augments the viscous dissipation of turbulence kinetic energy, which leads to a slower increase in the turbulence energy. Although the augmentation of energy dissipation occurs predominantly inside viscous layers surrounding particles in an initial period, the contribution from their outside becomes more significant due to the modification of turbulence structures as turbulence develops. It is found that the particles exhibit weak tendency to accumulate in vortex layers. The particles approaching and colliding with vortex layers induce large velocity fluctuations, which leads to the generation and shedding of thin vortex tubes. Newly generated vortex tubes interact with developed vortex tubes and layers, and modify the entire structure of the vorticity field.