21,074 research outputs found
On the propagation of plane waves above an impedance surface
The propagation of grazing incidence plane waves along a finite impedance boundary is investigated. A solution of the semi-infinite problem, where a harmonic motion, parallel to the boundary, is imposed along a line perpendicular to the boundary, is obtained. This solution consists of quasiplane waves, waves moving parallel to the boundary with amplitude and phase variations perpendicular to the boundary. Several approximations to the full solution are considered
Positioning of self-assembled Ge islands on stripe-patterned Si (001) substrates
Self-assembled Ge islands were grown on stripe-patterned Si (001) substrates
by solid source molecular beam epitaxy. The surface morphology obtained by
atomic force microscopy (AFM) and cross-sectional transmission electron
microscopy images (TEM) shows that the Ge islands are preferentially grown at
the sidewalls of pure Si stripes along [-110] direction at 650o C or along the
trenches, whereas most of the Ge islands are formed on the top terrace when the
patterned stripes are covered by a strained GeSi buffer layer. Reducing the
growth temperature to 600oC results in a nucleation of Ge islands both on the
top terrace and at the sidewall of pure Si stripes. A qualitative analysis,
based on the growth kinetics, demonstrates that the step structure of the
stripes, the external strain field and the local critical wetting layer
thickness for the islands formation contribute to the preferential positioning
of Ge islands on the stripes.Comment: 10 pages, 7 figures, 1 table, the original paper is in print in J.
Appl. Phy
Supercurrent transferring through c-axis cuprate Josephson junctions with thick normal-metal-bridge
With simple but exactly solvable model, we investigate the supercurrent
transferring through the c-axis cuprate superconductor-normal
metal-superconductor junctions with the clean normal metal much thicker than
its coherence length. It is shown that the supercurrent as a function of
thickness of the normal metal decreases much slower than the exponential
decaying expected by the proximity effect. The present result may account for
the giant proximity effect observed in the c-axis cuprate SNS junctions.Comment: 6 pages, 4 figure
Direct measurement of product of the electron mobility and mean free drift time of CdZnTe semiconductors using position sensitive single polarity charge sensing detectors
This article describes novel techniques to directly measure the electron mobility and mean free drift time product μeτeμeτe in semiconductor detectors. These methods are based on newly developed single polarity charge sensing and depth sensing techniques. Compared with conventional methods based on the Hecht relation, the new methods do not involve curve fitting, are less sensitive to the variation of pulse rise times, and allow the use of higher energy γ rays typical of many applications. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70289/2/JAPIAU-84-10-5566-1.pd
Generarized Cubic Model for BaTiO-like Ferroelectric Substance
We propose an order-disorder type microscopic model for BaTiO-like
Ferroelectric Substance. Our model has three phase transitions and four phases.
The symmetry and directions of the polarizations of the ordered phases agree
with the experimental results of BaTiO. The intermediate phases in our
model are known as an incompletely ordered phase, which appears in a
generalized clock model.Comment: 6 pages, 4figure
Vorticity Budget of Weak Thermal Convection in Keplerian disks
By employing the equations of mean-square vorticity (enstrophy) fluctuations
in strong shear flows, we demonstrate that unlike energy production of
turbulent vorticity in nonrotating shear flows, the turbulent vorticity of weak
convection in Keplerian disks cannot gain energy from vortex stretching/tilting
by background shear unless the asscoiated Reynolds stresses are negative. This
is because the epicyclic motion is an energy sink of the radial component of
mean-square turbulent vorticity in Keplerian disks when Reynolds stresses are
positive. Consequently, weak convection cannot be self-sustained in Keplerian
flows. This agrees with the results implied from the equations of mean-square
velocity fluctuations in strong shear flows. Our analysis also sheds light on
the explanation of the simulation result in which positive kinetic helicity is
produced by the Balbus-Hawley instability in a vertically stratified Keplerian
disk. We also comment on the possibility of outward angular momentum transport
by strong convection based on azimuthal pressure perturbations and directions
of energy cascade.Comment: 8 pages, 1 figure, emulateapj.sty, revised version in response to
referee's comments, accepted by Ap
Gravitational Lensing by Wormholes
Gravitational lensing by traversable Lorentzian wormholes is a ew possibility
which is analyzed here in the strong field limit. Wormhole solutions are
considered in the Einstein minimally coupled theory and in the brane world
model. The observables in both the theories show significant differences from
those arising in the Schwarzschild black hole lensing. As a corollary, it
follows that wormholes with zero Keplerian mass exhibit lensing properties
which are qualitatively (though not quantitatively) the same as those of a
Schwarzschild black hole. Some special features of the considered solutions are
pointed out.Comment: 20 pages, no figure
Method of convex rigid frames and applications in studies of multipartite quNit pure-states
In this Letter we suggest a method of convex rigid frames in the studies of
the multipartite quNit pure-states. We illustrate what are the convex rigid
frames and what is the method of convex rigid frames. As the applications we
use this method to solve some basic problems and give some new results (three
theorems): The problem of the partial separability of the multipartite quNit
pure-states and its geometric explanation; The problem of the classification of
the multipartite quNit pure-states, and give a perfect explanation of the local
unitary transformations; Thirdly, we discuss the invariants of classes and give
a possible physical explanation.Comment: 6 pages, no figur
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