21,811 research outputs found
An experimental study of the temporal statistics of radio signals scattered by rain
A fixed-beam bistatic CW experiment designed to measure the temporal statistics of the volume reflectivity produced by hydrometeors at several selected altitudes, scattering angles, and at two frequencies (3.6 and 7.8 GHz) is described. Surface rain gauge data, local meteorological data, surveillance S-band radar, and great-circle path propagation measurements were also made to describe the general weather and propagation conditions and to distinguish precipitation scatter signals from those caused by ducting and other nonhydrometeor scatter mechanisms. The data analysis procedures were designed to provide an assessment of a one-year sample of data with a time resolution of one minute. The cumulative distributions of the bistatic signals for all of the rainy minutes during this period are presented for the several path geometries
Effective-Hamiltonian parameters for \emph{ab initio} energy-level calculations of SrCl:Yb and CsCaBr:Yb
Calculated energy levels from recent \emph{ab initio} studies of the
electronic structure of SrCl:Yb and CsCaBr:Yb are
fitted with a semi-empirical "crystal-field" Hamiltonian, which acts within the
model space . Parameters are obtained for the
minima of the potential-energy curves for each energy level and also for a
range of anion-cation separations. The parameters are compared with published
results parameters fitted to experimental data and to atomic calculations. The
states with significant character give a good approximation of the
impurity-trapped exciton states that appear in the \emph{ab initio}
calculations.Comment: Minor revisio
Highly effective yet simple transmembrane anion transporters based upon ortho-phenylenediamine bis-ureas
Simple, highly fluorinated receptors are shown to function as highly effective transmembrane anion antiporters with the most active transporters rivalling the transport efficacy of natural anion transporter prodigiosin for bicarbonate
Cellular automaton model of precipitation/dissolution coupled with solute transport
Precipitation/dissolution reactions coupled with solute transport are
modelled as a cellular automaton in which solute molecules perform a random
walk on a regular lattice and react according to a local probabilistic rule.
Stationary solid particles dissolve with a certain probability and, provided
solid is already present or the solution is saturated, solute particles have a
probability to precipitate. In our simulation of the dissolution of a solid
block inside uniformly flowing water we obtain solid precipitation downstream
from the original solid edge, in contrast to the standard reaction-transport
equations. The observed effect is the result of fluctuations in solute density
and diminishes when we average over a larger ensemble. The additional
precipitation of solid is accompanied by a substantial reduction in the
relatively small solute concentration. The model is appropriate for the study
of the r\^ole of intrinsic fluctuations in the presence of reaction thresholds
and can be employed to investigate porosity changes associated with the
carbonation of cement.Comment: LaTeX file, 13 pages. To appear in Journal of Statistical Physics
(Proceedings of Lattice Gas'94, June 1994, Princeton). Figures available from
author. Requests may be submitted by E-mail ([email protected]) or ordinary
mail (Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
Field Tests of Some Liming Treatments for Growing Burley Tobacco on Acid Soils
A major problem in the production of tobacco on acid soils in Kentucky is manganese toxicity, despite the fact that it can be easily prevented. Since manganese toxicity is caused by high levels of soil acidity, prevention of soil acidity by liming is the best method of control. And soil testing is the only way to determine how acid a field has become
The CLIC Programme: Towards a Staged e+e- Linear Collider Exploring the Terascale : CLIC Conceptual Design Report
This report describes the exploration of fundamental questions in particle
physics at the energy frontier with a future TeV-scale e+e- linear collider
based on the Compact Linear Collider (CLIC) two-beam acceleration technology. A
high-luminosity high-energy e+e- collider allows for the exploration of
Standard Model physics, such as precise measurements of the Higgs, top and
gauge sectors, as well as for a multitude of searches for New Physics, either
through direct discovery or indirectly, via high-precision observables. Given
the current state of knowledge, following the observation of a 125 GeV
Higgs-like particle at the LHC, and pending further LHC results at 8 TeV and 14
TeV, a linear e+e- collider built and operated in centre-of-mass energy stages
from a few-hundred GeV up to a few TeV will be an ideal physics exploration
tool, complementing the LHC. In this document, an overview of the physics
potential of CLIC is given. Two example scenarios are presented for a CLIC
accelerator built in three main stages of 500 GeV, 1.4 (1.5) TeV, and 3 TeV,
together with operating schemes that will make full use of the machine capacity
to explore the physics. The accelerator design, construction, and performance
are presented, as well as the layout and performance of the experiments. The
proposed staging example is accompanied by cost estimates of the accelerator
and detectors and by estimates of operating parameters, such as power
consumption. The resulting physics potential and measurement precisions are
illustrated through detector simulations under realistic beam conditions.Comment: 84 pages, published as CERN Yellow Report
https://cdsweb.cern.ch/record/147522
The importance of tau leptons for supersymmetry searches at the Tevatron
Supersymmetry is perhaps most effectively probed at the Tevatron through
production and decay of weak gauginos. Most of the analyses of weak gaugino
observables require electrons or muons in the final state. However, it is
possible that the gauginos will decay primarily to tau leptons, thus
complicating the search for supersymmetry. The motivating reasons for high tau
multiplicity final states are discussed in three approaches to supersymmetry
model building: minimal supergravity, gauge mediated supersymmetry breaking,
and more minimal supersymmetry. The concept of ``e/mu/tau candidate'' is
introduced, and an observable with three e/mu/tau candidates is defined in
analog to the trilepton observable. The maximum mass reach for supersymmetry is
then estimated when gaugino decays to tau leptons have full branching fraction.Comment: 9 pages, latex, 2 figures. Presented at the D0 New Phenomena
Workshop, UC Davis, 26-28 March 199
On Virtual Displacement and Virtual Work in Lagrangian Dynamics
The confusion and ambiguity encountered by students, in understanding virtual
displacement and virtual work, is discussed in this article. A definition of
virtual displacement is presented that allows one to express them explicitly
for holonomic (velocity independent), non-holonomic (velocity dependent),
scleronomous (time independent) and rheonomous (time dependent) constraints. It
is observed that for holonomic, scleronomous constraints, the virtual
displacements are the displacements allowed by the constraints. However, this
is not so for a general class of constraints. For simple physical systems, it
is shown that, the work done by the constraint forces on virtual displacements
is zero. This motivates Lagrange's extension of d'Alembert's principle to
system of particles in constrained motion. However a similar zero work
principle does not hold for the allowed displacements. It is also demonstrated
that d'Alembert's principle of zero virtual work is necessary for the
solvability of a constrained mechanical problem. We identify this special class
of constraints, physically realized and solvable, as {\it the ideal
constraints}. The concept of virtual displacement and the principle of zero
virtual work by constraint forces are central to both Lagrange's method of
undetermined multipliers, and Lagrange's equations in generalized coordinates.Comment: 12 pages, 10 figures. This article is based on an earlier article
physics/0410123. It includes new figures, equations and logical conten
Comparison of 32-site exact diagonalization results and ARPES spectral functions for the AFM insulator
We explore the success of various versions of the one-band t-J model in
explaining the full spectral functions found in angle-resolved photoemission
spectra for the prototypical, quasi two-dimensional, tetragonal,
antiferromagnetic insulator . After presenting arguments
justifying our extraction of from the experimental data, we rely
on exact-diagonalization results from studies of a square 32-site lattice, the
largest cluster for which such information is presently available, to perform
this comparison. Our work leads us to believe that (i) a one-band model that
includes hopping out to third-nearest neighbours, as well three-site,
spin-dependent hopping, can indeed explain not only the dispersion relation,
but also the quasiparticle lifetimes -- only in the neighbourhood of do we find disagreement; (ii) an energy-dependent broadening
function, , is important in accounting for the
incoherent contributions to the spectral functions.Comment: 8 pages, Revtex
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