15,378 research outputs found
Scattering of accelerated wave packets
Wave-packet scattering from a stationary potential is significantly modified
when the wave-packet is subject to an external time-dependent force during the
interaction. In the semiclassical limit, wave--packet motion is simply
described by Newtonian equations and the external force can, for example,
cancel the potential force making a potential barrier transparent. Here we
consider wave-packet scattering from reflectionless potentials, where in
general the potential becomes reflective when probed by an accelerated
wave-packet. In the particular case of the recently-introduced class of complex
Kramers-Kronig potentials we show that a broad class of time dependent forces
can be applied without inducing any scattering, while there is a breakdown of
the reflectionless property when there is a broadband distribution of initial
particle momentum, involving both positive and negative components.Comment: 13 pages, 4 figures, to appear in Phys. Rev.
Planck-scale effects on WIMP dark matter
There exists a widely known conjecture that gravitational effects violate
global symmetries. We study the effect of global-symmetry violating
higher-dimension operators induced by Planck-scale physics on the properties of
WIMP dark matter. Using an effective description, we show that the lifetime of
the WIMP dark matter candidate can satisfy cosmological bounds under reasonable
assumptions regarding the strength of the dimension-five operators. On the
other hand, the indirect WIMP dark matter detection signal is significantly
enhanced due to new decay channels.Comment: 12 pages, 4 figures. Version accepted for publication in Frontier
Observation of surface states with algebraic localization
We introduce and experimentally demonstrate a class of surface bound states
with algebraic decay in a one-dimensional tight-binding lattice. Such states
have an energy embedded in the spectrum of scattered states and are
structurally stable against perturbations of lattice parameters. Experimental
demonstration of surface states with algebraic localization is presented in an
array of evanescently-coupled optical waveguides with tailored coupling rates.Comment: revised version with Supplemental Material, to appear in Phys. Rev.
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Scanning laser techniques for characterisation of different surface breaking defect geometries
Measurements using a laser scanning system consisting of a pulsed Nd:YAG laser to generate surface ultrasonic
waves and an interferometer to detect the surface displacement, are presented for different samples and defect geometries. We show, ďŹrstly, details of the interaction of Rayleigh waves in thick samples with machined slots inclined at an angle to the surface normal, or with simple branched geometries, scanning the generation source over the defect (SLLS) or scanning the detection point over the defect (SLD). Secondly, we discuss effects of Lamb waves interacting with V-shaped defects in thin samples. The results from these measurements have shown that the signal enhancement found in the near-ďŹeld in both cases can be used to position the defect and gain an idea of its geometry, and have shown this to be a suitable ďŹngerprint of the presence of the defect
Bi-large neutrino mixing and the Cabibbo angle
Recent measurements of the neutrino mixing angles cast doubt on the validity
of the so-far popular tri-bimaximal mixing ansatz. We propose a parametrization
for the neutrino mixing matrix where the reactor angle seeds the large solar
and atmospheric mixing angles, equal to each other in first approximation. We
suggest such bi-large mixing pattern as a model building standard, realized
when the leading order value of the reactor angle equals the Cabibbo angle.Comment: 4 pages, 2 figs. v2: matches version appearing in Phys.Rev.D, rapid
communication
Comparison of Methods for Determining the Composition of Pyrolysis Products from the Degradation of Ablative Composites. Status report.
Determining composition of pyrolysis products from degradation of ablative material
National evaluation of the neighbourhood nurseries: impact report
This study assessed the impact of NNI on parental employment, use of formal childcare, and take-up of benefits and tax credits, particularly for disadvantaged groups such as lone parents, low income families and ethnic minority groups
The Timing Counter of the MEG experiment: calibration and performance
The MEG detector is designed to test Lepton Flavor Violation in the
decay down to a Branching Ratio of a few
. The decay topology consists in the coincident emission of a
monochromatic photon in direction opposite to a monochromatic positron. A
precise measurement of the relative time is crucial to suppress
the background. The Timing Counter (TC) is designed to precisely measure the
time of arrival of the and to provide information to the trigger system.
It consists of two sectors up and down stream the decay target, each consisting
of two layers. The outer one made of scintillating bars and the inner one of
scintillating fibers. Their design criteria and performances are described.Comment: Presented at the 12th Topical Seminar on Innovative Particle and
Radiation Detectors (IPRD10) 7 - 10 June 2010, Siena. Accepted by Nuclear
Physics B (Proceedings Supplements) (2011)tal
Scaling of the conductance in gold nanotubes
A new form of gold nanobridges has been recently observed in ultrahigh-vacuum
experiments, where the gold atoms rearrange to build helical nanotubes, akin in
some respects to carbon nanotubes. The good reproducibility of these wires and
their unexpected stability will allow for conductance measurements and make
them promising candidates for future applications . We present here a study of
the transport properties of these nanotubes in order to understand the role of
chirality and of the different orbitals in quantum transport observables. The
conductance per atomic row shows a light decreasing trend as the diameter
grows, which is also shown through an analytical formula based on a one-orbital
model.Comment: 5 pages, 6 figure
Length-weight relationships of Cuban marine fishes
A total of 140 sets of parameters (a and b) of the length-weight relationships (LWR) of the form W=aL super(b) are presented for fishes caught in Cuban waters. These parameters cover 94 species of fish belonging to 43 families. Most of the parameters were compiled from 107 sets of published and unpublished studies. Twenty-five sets of parameters were from personal communications through colleagues in Cuba, while the remaining eight sets were estimated by the authors from unpublished data
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