25,431 research outputs found
A study of image quality for radar image processing
Methods developed for image quality metrics are reviewed with focus on basic interpretation or recognition elements including: tone or color; shape; pattern; size; shadow; texture; site; association or context; and resolution. Seven metrics are believed to show promise as a way of characterizing the quality of an image: (1) the dynamic range of intensities in the displayed image; (2) the system signal-to-noise ratio; (3) the system spatial bandwidth or bandpass; (4) the system resolution or acutance; (5) the normalized-mean-square-error as a measure of geometric fidelity; (6) the perceptual mean square error; and (7) the radar threshold quality factor. Selective levels of degradation are being applied to simulated synthetic radar images to test the validity of these metrics
Bandgap and effective mass of epitaxial cadmium oxide
The bandgap and band-edge effective mass of single crystal cadmium oxide, epitaxially grown by metal-organic vapor-phase epitaxy, are determined from infrared reflectivity, ultraviolet/visible absorption, and Hall effect measurements. Analysis and simulation of the optical data, including effects of band nonparabolicity, Moss-Burstein band filling and bandgap renormalization, reveal room temperature bandgap and band-edge effective mass values of 2.16±0.02 eV and 0.21±0.01m0 respectively
Bound whispering gallery modes in circular arrays of dielectric spherical particles
Low-dimensional ordered arrays of optical elements can possess bound modes
having an extremely high quality factor. Typically, these arrays consist of
metal elements which have significantly high light absorption thus restricting
performance. In this paper we address the following question: can bound modes
be formed in dielectric systems where the absorption of light is negligible?
Our investigation of circular arrays of spherical particles shows that (1) high
quality modes in an array of 10 or more particles can be attained at least for
a refractive index , so optical materials like TiO or GaAs can
be used; (2) the most bound modes have nearly transverse polarization
perpendicular to the circular plane; (3) in a particularly interesting case of
TiO particles (rutile phase, ), the quality factor of the most
bound mode increases almost by an order of magnitude with the addition of 10
extra particles, while for particles made of GaAs the quality factor increases
by almost two orders of magnitude with the addition of ten extra particles. We
hope that this preliminary study will stimulate experimental investigations of
bound modes in low-dimensional arrays of dielectric particles.Comment: Submitted to Physical Review
Atomic swelling upon compression
The hydrogen atom under the pressure of a spherical penetrable confinement
potential of a decreasing radius is explored, as a case study. A novel
counter-intuitive effect of atomic swelling rather than shrinking with
decreasing is unraveled, when reaches, and remains smaller
than, a certain critical value. Upon swelling, the size of the atom is shown to
increase by an order of magnitude, or more, compared to the size of the free
atom. Examples of changes of photoabsorption properties of confined hydrogen
atom upon its swelling are uncovered and demonstrated.Comment: 5 pages, 4 figure
Anisotropic Magnetoresistance components in (Ga,Mn)As
Our experimental and theoretical study of the non-crystalline and crystalline
components of the anisotropic magnetoresistance (AMR) in (Ga,Mn)As is aimed at
exploring the basic physical aspects of this relativistic transport effect. The
non-crystalline AMR reflects anisotropic lifetimes of the holes due to
polarized Mn impurities while the crystalline AMR is associated with valence
band warping. We find that the sign of the non-crystalline AMR is determined by
the form of spin-orbit coupling in the host band and by the relative strengths
of the non-magnetic and magnetic contributions to the impurity potential. We
develop experimental methods directly yielding the non-crystalline and
crystalline AMR components which are then independently analyzed. We report the
observation of an AMR dominated by a large uniaxial crystalline component and
show that AMR can be modified by local strain relaxation. We discuss generic
implications of our experimental and theoretical findings including predictions
for non-crystalline AMR sign reversals in dilute moment systems.Comment: 4 pages, 3 figures. Phys. Rev. Lett. in pres
Mass-Radius Relationships for Solid Exoplanets
We use new interior models of cold planets to investigate the mass-radius
relationships of solid exoplanets, considering planets made primarily of iron,
silicates, water, and carbon compounds. We find that the mass-radius
relationships for cold terrestrial-mass planets of all compositions we
considered follow a generic functional form that is not a simple power law:
for up to , where and are scaled mass and radius
values. This functional form arises because the common building blocks of solid
planets all have equations of state that are well approximated by a modified
polytrope of the form .
We find that highly detailed planet interior models, including temperature
structure and phase changes, are not necessary to derive solid exoplanet bulk
composition from mass and radius measurements. For solid exoplanets with no
substantial atmosphere we have also found that: with 5% fractional uncertainty
in planet mass and radius it is possible to distinguish among planets composed
predominantly of iron or silicates or water ice but not more detailed
compositions; with ~5% uncertainty water ice planets with
water by mass may be identified; the minimum plausible planet size for a given
mass is that of a pure iron planet; and carbon planet mass-radius relationships
overlap with those of silicate and water planets due to similar zero-pressure
densities and equations of state. We propose a definition of "super Earths''
based on the clear distinction in radii between planets with significant gas
envelopes and those without.Comment: ApJ, in press, 33 pages including 16 figure
Monogamy of entanglement and other correlations
It has been observed by numerous authors that a quantum system being
entangled with another one limits its possible entanglement with a third
system: this has been dubbed the "monogamous nature of entanglement". In this
paper we present a simple identity which captures the trade-off between
entanglement and classical correlation, which can be used to derive rigorous
monogamy relations.
We also prove various other trade-offs of a monogamy nature for other
entanglement measures and secret and total correlation measures.Comment: 7 pages, revtex
Representations of the Canonical group, (the semi-direct product of the Unitary and Weyl-Heisenberg groups), acting as a dynamical group on noncommuting extended phase space
The unitary irreducible representations of the covering group of the Poincare
group P define the framework for much of particle physics on the physical
Minkowski space P/L, where L is the Lorentz group. While extraordinarily
successful, it does not provide a large enough group of symmetries to encompass
observed particles with a SU(3) classification. Born proposed the reciprocity
principle that states physics must be invariant under the reciprocity transform
that is heuristically {t,e,q,p}->{t,e,p,-q} where {t,e,q,p} are the time,
energy, position, and momentum degrees of freedom. This implies that there is
reciprocally conjugate relativity principle such that the rates of change of
momentum must be bounded by b, where b is a universal constant. The appropriate
group of dynamical symmetries that embodies this is the Canonical group C(1,3)
= U(1,3) *s H(1,3) and in this theory the non-commuting space Q= C(1,3)/
SU(1,3) is the physical quantum space endowed with a metric that is the second
Casimir invariant of the Canonical group, T^2 + E^2 - Q^2/c^2-P^2/b^2 +(2h
I/bc)(Y/bc -2) where {T,E,Q,P,I,Y} are the generators of the algebra of
Os(1,3). The idea is to study the representations of the Canonical dynamical
group using Mackey's theory to determine whether the representations can
encompass the spectrum of particle states. The unitary irreducible
representations of the Canonical group contain a direct product term that is a
representation of U(1,3) that Kalman has studied as a dynamical group for
hadrons. The U(1,3) representations contain discrete series that may be
decomposed into infinite ladders where the rungs are representations of U(3)
(finite dimensional) or C(2) (with degenerate U(1)* SU(2) finite dimensional
representations) corresponding to the rest or null frames.Comment: 25 pages; V2.3, PDF (Mathematica 4.1 source removed due to technical
problems); Submitted to J.Phys.
Water requirements of floodplain rivers and fisheries: existing decision support tools and pathways for development
Fisheries / Rivers / Flood plains / Hydrology / Ecology / Models / Decision support tools / Environmental impact assessment / Methodology / Databases
- âŠ