51,499 research outputs found
CARETS: A prototype regional environmental information system. Volume 7: Land use information and air quality planning
The author has identified the following significant results. The pilot air quality system provided data for updating information on the sources of point and area emissions of SO2 and particulate matter affecting the Norfolk-Portsmouth area of Virginia for 1971-72 winter and the annual 1972 period. During the 1971-72 winter, estimated SO2 amounts over an area with a SW-NE axis in the central section of Norfolk exceeded both primary and secondary levels
Dramatic impact of pumping mechanism on photon entanglement in microcavity
A theory of entangled photons emission from quantum dot in microcavity under
continuous and pulsed incoherent pumping is presented. It is shown that the
time-resolved two-photon correlations drastically depend on the pumping
mechanism: the continuous pumping quenches the polarization entanglement and
strongly suppresses photon correlation times. Analytical theory of the effect
is presented.Comment: 6 pages, 3 figure
Why a splitting in the final state cannot explain the GSI-Oscillations
In this paper, I give a pedagogical discussion of the GSI anomaly. Using two
different formulations, namely the intuitive Quantum Field Theory language of
the second quantized picture as well as the language of amplitudes, I clear up
the analogies and differences between the GSI anomaly and other processes (the
Double Slit experiment using photons, scattering, and
charged pion decay). In both formulations, the conclusion is reached that the
decay rate measured at GSI cannot oscillate if only Standard Model physics is
involved and the initial hydrogen-like ion is no coherent superposition of more
than one state (in case there is no new, yet unknown, mechanism at work).
Furthermore, a discussion of the Quantum Beat phenomenon will be given, which
is often assumed to be able to cause the observed oscillations. This is,
however, not possible for a splitting in the final state only.Comment: 10 pages, 3 figures; matches published version (except for some
stylistic ambiguities
Geometry of Valley Growth
Although amphitheater-shaped valley heads can be cut by groundwater flows
emerging from springs, recent geological evidence suggests that other processes
may also produce similar features, thus confounding the interpretations of such
valley heads on Earth and Mars. To better understand the origin of this
topographic form we combine field observations, laboratory experiments,
analysis of a high-resolution topographic map, and mathematical theory to
quantitatively characterize a class of physical phenomena that produce
amphitheater-shaped heads. The resulting geometric growth equation accurately
predicts the shape of decimeter-wide channels in laboratory experiments,
100-meter wide valleys in Florida and Idaho, and kilometer wide valleys on
Mars. We find that whenever the processes shaping a landscape favor the growth
of sharply protruding features, channels develop amphitheater-shaped heads with
an aspect ratio of pi
RascalC: A Jackknife Approach to Estimating Single and Multi-Tracer Galaxy Covariance Matrices
To make use of clustering statistics from large cosmological surveys,
accurate and precise covariance matrices are needed. We present a new code to
estimate large scale galaxy two-point correlation function (2PCF) covariances
in arbitrary survey geometries that, due to new sampling techniques, runs times faster than previous codes, computing finely-binned covariance
matrices with negligible noise in less than 100 CPU-hours. As in previous
works, non-Gaussianity is approximated via a small rescaling of shot-noise in
the theoretical model, calibrated by comparing jackknife survey covariances to
an associated jackknife model. The flexible code, RascalC, has been publicly
released, and automatically takes care of all necessary pre- and
post-processing, requiring only a single input dataset (without a prior 2PCF
model). Deviations between large scale model covariances from a mock survey and
those from a large suite of mocks are found to be be indistinguishable from
noise. In addition, the choice of input mock are shown to be irrelevant for
desired noise levels below mocks. Coupled with its generalization
to multi-tracer data-sets, this shows the algorithm to be an excellent tool for
analysis, reducing the need for large numbers of mock simulations to be
computed.Comment: 29 pages, 8 figures. Accepted by MNRAS. Code is available at
http://github.com/oliverphilcox/RascalC with documentation at
http://rascalc.readthedocs.io
Unsteady Crack Motion and Branching in a Phase-Field Model of Brittle Fracture
Crack propagation is studied numerically using a continuum phase-field
approach to mode III brittle fracture. The results shed light on the physics
that controls the speed of accelerating cracks and the characteristic branching
instability at a fraction of the wave speed.Comment: 11 pages, 4 figure
Determinant representation for a quantum correlation function of the lattice sine-Gordon model
We consider a completely integrable lattice regularization of the sine-Gordon
model with discrete space and continuous time. We derive a determinant
representation for a correlation function which in the continuum limit turns
into the correlation function of local fields. The determinant is then embedded
into a system of integrable integro-differential equations. The leading
asymptotic behaviour of the correlation function is described in terms of the
solution of a Riemann Hilbert Problem (RHP) related to the system of
integro-differential equations. The leading term in the asymptotical
decomposition of the solution of the RHP is obtained.Comment: 30 pages Latex2e, 2 Figures, epsf. Significantly extended and revised
versio
A Modified Magnitude System that Produces Well-Behaved Magnitudes, Colors, and Errors Even for Low Signal-to-Noise Ratio Measurements
We describe a modification of the usual definition of astronomical
magnitudes, replacing the usual logarithm with an inverse hyperbolic sine
function; we call these modified magnitudes `asinh magnitudes'. For objects
detected at signal-to-noise ratios of greater than about five, our modified
definition is essentially identical to the traditional one; for fainter objects
(including those with a formally negative flux) our definition is well behaved,
tending to a definite value with finite errors as the flux goes to zero.
This new definition is especially useful when considering the colors of faint
objects, as the difference of two `asinh' magnitudes measures the usual flux
ratio for bright objects, while avoiding the problems caused by dividing two
very uncertain values for faint objects.
The Sloan Digital Sky Survey (SDSS) data products will use this scheme to
express all magnitudes in their catalogs.Comment: 11 pages, including 3 postscript figures. Submitted to A
Electron interferometry with nano-gratings
We present an electron interferometer based on near-field diffraction from
two nanostructure gratings. Lau fringes are observed with an imaging detector,
and revivals in the fringe visibility occur as the separation between gratings
is increased from 0 to 3 mm. This verifies that electron beams diffracted by
nanostructures remain coherent after propagating farther than the Talbot length
= 1.2 mm, and hence is a proof of principle for the
function of a Talbot-Lau interferometer for electrons. Distorted fringes due to
a phase object demonstrates an application for this new type of electron
interferometer.Comment: 4 pgs, 6 figure
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