34,881 research outputs found
Turbulent boundary layer around a group of obstacles in the direction of flow
Results of an investigation of a boundary layer in a turbulent flow on the surface of a wall having a group of obstacles on the path of flow are presented with regard to the mean velocity field, velocity distribution of the two dimensional flow, wall surface shear stresses and Reynolds stresses measured in a downstream cross section where an interference of boundary layers takes place in a flow around adjacent obstacles arranged on the path of flow
Thermodynamics of Extended Bodies in Special Relativity
Relativistic thermodynamics is generalized to accommodate four dimensional
rotation in a flat spacetime. An extended body can be in equilibrium when its
each element moves along a Killing flow. There are three types of basic Killing
flows in a flat spacetime, each of which corresponds to translational motion,
spatial rotation, and constant linear acceleration; spatial rotation and
constant linear acceleration are regarded as four dimensional rotation.
Translational motion has been mainly investigated in the past literature of
relativistic thermodynamics. Thermodynamics of the other two is derived in the
present paper.Comment: 8 pages, no figur
Gravitational Radiation from Cylindrical Naked Singularity
We construct an approximate solution which describes the gravitational
emission from a naked singularity formed by the gravitational collapse of a
cylindrical thick shell composed of dust. The assumed situation is that the
collapsing speed of the dust is very large. In this situation, the metric
variables are obtained approximately by a kind of linear perturbation analysis
in the background Morgan solution which describes the motion of cylindrical
null dust. The most important problem in this study is what boundary conditions
for metric and matter variables should be imposed at the naked singularity. We
find a boundary condition that all the metric and matter variables are
everywhere finite at least up to the first order approximation. This implies
that the spacetime singularity formed by this high-speed dust collapse is very
similar to that formed by the null dust and thus the gravitational emission
from a naked singularity formed by the cylindrical dust collapse can be gentle.Comment: 20 pages, 1 figur
Two Phase Collective Modes in Josephson Vortex Lattice in Intrinsic Josephson Junction BiSrCaCuO
Josephson plasma excitations in the high superconductor
BiSrCaCuO have been investigated in a wide microwave
frequency region (9.8 -- 75 GHz), in particular, in magnetic field applied
parallel to the plane of the single crystal. In sharp contrast to the case
for magnetic fields parallel to the c axis or tilted from the plane, it
was found that there are two kinds of resonance modes, which are split in
energy and possess two distinctly different magnetic field dependences. One
always lies higher in energy than the other and has a shallow minimum at about
0.8 kOe, then increases linearly with magnetic field. On the other hand,
another mode begins to appear only in a magnetic field (from a few kOe and
higher) and has a weakly decreasing tendency with increasing magnetic field. By
comparing with a recent theoretical model the higher energy mode can naturally
be attributed to the Josephson plasma resonance mode propagating along the
primitive reciprocal lattice vector of the Josephson vortex lattice, whereas
the lower frequency mode is assigned to the novel phase collective mode of the
Josephson vortex lattice, which has never been observed before.Comment: 11 pages and 10 figure
Leaf area index and topographical effects on turburlent diffusion in a deciduous forest
In order to investigate turbulent diffusion in a deciduous forest canopy, wind velocity
measurements were conducted from late autumn of 2009 to early spring of 2010, using an observation tower
20 m in height located in the campus of Kanazawa University. Four sonic anemometers mounted on the
tower recorded the average wind velocities and temperatures, as well as their fluctuations, at four different
heights simultaneously. Two different types of data sets were selected, in which the wind velocities, wind
bearings and atmospheric stabilities were all similar, but the Leaf Area Indexes (LAI's) were different.
Vertical profiles of average wind velocities were found to have an approximately exponential profile in each
case. The characteristic length scales of turbulence were evaluated by both von Karman's method and the
integral time scale deduced from the autocorrelation from time-series analyses. Both methods produced
comparable values of eddy diffusivity for the cases with some foliage during late autumn, but some
discrepancy in the upper canopy layer was observed when the trees did not have their leaves in early spring.
It was also found that the eddy diffusivities generally take greater values at higher positions, where the wind
speeds are large. Anisotropy of eddy diffusivities between the vertical and horizontal components was also
observed, particularly in the cases when the canopy does not have leaves, when the horizontal eddy
diffusivities are generally larger than the vertical ones. On the other hand, the anisotropy is less visible when
the trees have some foliage during autumn. The effects of topography on the turbulent diffusion were also
investigated, including evaluation of the non-zero time-averaged vertical wind velocities. The results show
that the effects are marginal for both cases, and can be neglected as far as diffusion in the canopy is
concerned
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