75,902 research outputs found
Localization transitions in non-Hermitian quantum mechanics
We study the localization transitions which arise in both one and two
dimensions when quantum mechanical particles described by a random
Schr\"odinger equation are subjected to a constant imaginary vector potential.
A path-integral formulation relates the transition to flux lines depinned from
columnar defects by a transverse magnetic field in superconductors. The theory
predicts that the transverse Meissner effect is accompanied by stretched
exponential relaxation of the field into the bulk and a diverging penetration
depth at the transition.Comment: 4 pages (latex) with 3 figures (epsf) embedded in the text using the
style file epsf.st
Patterned Geometries and Hydrodynamics at the Vortex Bose Glass Transition
Patterned irradiation of cuprate superconductors with columnar defects allows
a new generation of experiments which can probe the properties of vortex
liquids by confining them to controlled geometries. Here we show that an
analysis of such experiments that combines an inhomogeneous Bose glass scaling
theory with the hydrodynamic description of viscous flow of vortex liquids can
be used to infer the critical behavior near the Bose glass transition. The
shear viscosity is predicted to diverge as at the Bose glass
transition, with the dynamical critical exponent.Comment: 5 pages, 4 figure
Terrestrial planet formation in low eccentricity warm-Jupiter systems
We examine the effect of giant planet migration on the formation of inner
terrestrial planet systems. We consider situations in which the giant planet
halts migration at semi-major axes in the range 0.13 - 1.7 AU due to gas disk
dispersal. An N-body code is employed that is linked to a viscous gas disk
algorithm capable of simulating: gas loss via accretion onto the central star
and photoevaporation; gap formation by the giant planet; type II migration of
the giant; optional type I migration of protoplanets; gas drag on
planetesimals. We find that most of the inner system planetary building blocks
survive the passage of the giant planet, either by being shepherded inward or
scattered into exterior orbits. Systems of one or more hot-Earths are predicted
to form and remain interior to the giant planet, especially if type II
migration has been limited, or where type I migration has affected
protoplanetary dynamics. Habitable planets in low eccentricity warm-Jupiter
systems appear possible if the giant planet makes a limited incursion into the
outer regions of the habitable zone (HZ), or traverses its entire width and
ceases migrating at a radial distance of less than half that of the HZ's inner
edge. We conclude that Type II migration does not prevent terrestrial planet
formation.Comment: Accepted for publication in A&A; 18 pages, 12 figures, 2 table
Computer-aided processing of LANDSAT MSS data for classification of forestlands
There are no author-identified significant results in this report
Structure and dynamics of topological defects in a glassy liquid on a negatively curved manifold
We study the low-temperature regime of an atomic liquid on the hyperbolic
plane by means of molecular dynamics simulation and we compare the results to a
continuum theory of defects in a negatively curved hexagonal background. In
agreement with the theory and previous results on positively curved (spherical)
surfaces, we find that the atomic configurations consist of isolated defect
structures, dubbed "grain boundary scars", that form around an irreducible
density of curvature-induced disclinations in an otherwise hexagonal
background. We investigate the structure and the dynamics of these grain
boundary scars
Design and implementation of a medium speed communications interface and protocol for a low cost, refreshed display computer
The design and implementation of hardware and software systems involved in using a 40,000 bit/second communication line as the connecting link between an IMLAC PDS 1-D display computer and a Univac 1108 computer system were described. The IMLAC consists of two independent processors sharing a common memory. The display processor generates the deflection and beam control currents as it interprets a program contained in the memory; the minicomputer has a general instruction set and is responsible for starting and stopping the display processor and for communicating with the outside world through the keyboard, teletype, light pen, and communication line. The processing time associated with each data byte was minimized by designing the input and output processes as finite state machines which automatically sequence from each state to the next. Several tests of the communication link and the IMLAC software were made using a special low capacity computer grade cable between the IMLAC and the Univac
An experimental investigation of vortex breakdown on a delta wing
An experimental investigation of vortex breakdown on delta wings at high angles is presented. Thin delta wings having sweep angles of 70, 75, 80 and 85 degrees are being studied. Smoke flow visualization and the laser light sheet technique are being used to obtain cross-sectional views of the leading edge vortices as they break down. At low tunnel speeds (as low as 3 m/s) details of the flow, which are usually imperceptible or blurred at higher speeds, can be clearly seen. A combination of lateral and longitudinal cross-sectional views provides information on the three dimensional nature of the vortex structure before, during and after breakdown. Whereas details of the flow are identified in still photographs, the dynamic characteristics of the breakdown process were recorded using high speed movies. Velocity measurements were obtained using a laser Doppler anemometer with the 70 degree delta wing at 30 degrees angle of attack. The measurements show that when breakdown occurs the core flow transforms from a jet-like flow to a wake-like flow
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