4,090 research outputs found
Chaotic Waveguide-Based Resonators for Microlasers
We propose the construction of highly directional emission microlasers using
two-dimensional high-index semiconductor waveguides as {\it open} resonators.
The prototype waveguide is formed by two collinear leads connected to a cavity
of certain shape. The proposed lasing mechanism requires that the shape of the
cavity yield mixed chaotic ray dynamics so as to have the appropiate (phase
space) resonance islands. These islands allow, via Heisenberg's uncertainty
principle, the appearance of quasi bound states (QBS) which, in turn,
propitiate the lasing mechanism. The energy values of the QBS are found through
the solution of the Helmholtz equation. We use classical ray dynamics to
predict the direction and intensity of the lasing produced by such open
resonators for typical values of the index of refraction.Comment: 5 pages, 5 figure
Classical versus Quantum Structure of the Scattering Probability Matrix. Chaotic wave-guides
The purely classical counterpart of the Scattering Probability Matrix (SPM)
of the quantum scattering matrix is defined for 2D
quantum waveguides for an arbitrary number of propagating modes . We compare
the quantum and classical structures of for a waveguide
with generic Hamiltonian chaos. It is shown that even for a moderate number of
channels, knowledge of the classical structure of the SPM allows us to predict
the global structure of the quantum one and, hence, understand important
quantum transport properties of waveguides in terms of purely classical
dynamics. It is also shown that the SPM, being an intensity measure, can give
additional dynamical information to that obtained by the Poincar\`{e} maps.Comment: 9 pages, 9 figure
Formation of a disk-structure and jets in the symbiotic prototype Z And during its 2006-2010 active phase
We present an analysis of spectrophotometric observations of the latest cycle
of activity of the symbiotic binary Z And from 2006 to 2010. We estimate the
temperature of the hot component of Z And to be \approx 150000 - 170000 K at
minimum brightness, decreasing to \approx 90000 K at the brightness maximum.
Our estimate of the electron density in the gaseous nebula is
N_{e}=10^{10}-10^{12} cm^{-3} in the region of formation of lines of neutral
helium and 10^6-10^7 cm^{-3} in the region of formation of the [OIII] and
[NeIII] nebular lines. A trend for the gas density derived from helium lines to
increase and the gas density derived from [OIII] and [NeIII] lines to
simultaneously decrease with increasing brightness of the system was observed.
Our estimates show that the ratios of the theoretical and observed fluxes in
the [OIII] and [NeIII] lines agree best when the O/Ne ratio is similar to its
value for planetary nebulae. The model spectral energy distribution showed
that, in addition to a cool component and gaseous nebula, a relatively cool
pseudophotosphere (5250-11 500 K) is present in the system. The simultaneous
presence of a relatively cool pseudophotosphere and high-ionization spectral
lines is probably related to a disk-like structure of the pseudophotosphere.
The pseudophotosphere formed very rapidly, over several weeks, during a period
of increasing brightness of Z And. We infer that in 2009, as in 2006, the
activity of the system was accompanied by a collimated bipolar ejection of
matter. In contrast to the situation in 2006, the jets were detected even
before the system reached its maximum brightness. Moreover, components with
velocities close to 1200 km/s disappeared at the maximum, while those with
velocities close to 1800 km/s appeared.Comment: 18 pages, 19 figures, Accepted for publication in Astronomy Report
Signal-averaged P wave analysis for delineation of interatrial conduction â Further validation of the method
<p>Abstract</p> <p>Background</p> <p>The study was designed to investigate the effect of different measuring methodologies on the estimation of P wave duration. The recording length required to ensure reproducibility in unfiltered, signal-averaged P wave analysis was also investigated. An algorithm for automated classification was designed and its reproducibility of manual P wave morphology classification investigated.</p> <p>Methods</p> <p>Twelve-lead ECG recordings (1 kHz sampling frequency, 0.625 <it>ÎŒ</it>V resolution) from 131 healthy subjects were used. Orthogonal leads were derived using the inverse Dower transform. Magnification (100 times), baseline filtering (0.5 Hz high-pass and 50 Hz bandstop filters), signal averaging (10 seconds) and bandpass filtering (40â250 Hz) were used to investigate the effect of methodology on the estimated P wave duration. Unfiltered, signal averaged P wave analysis was performed to determine the required recording length (6 minutes to 10 s) and the reproducibility of the P wave morphology classification procedure. Manual classification was carried out by two experts on two separate occasions each. The performance of the automated classification algorithm was evaluated using the joint decision of the two experts (i.e., the consensus of the two experts).</p> <p>Results</p> <p>The estimate of the P wave duration increased in each step as a result of magnification, baseline filtering and averaging (100 ± 18 vs. 131 ± 12 ms; P < 0.0001). The estimate of the duration of the bandpass-filtered P wave was dependent on the noise cut-off value: 119 ± 15 ms (0.2 <it>ÎŒ</it>V), 138 ± 13 ms (0.1 <it>ÎŒ</it>V) and 143 ± 18 ms (0.05 <it>ÎŒ</it>V). (P = 0.01 for all comparisons).</p> <p>The mean errors associated with the P wave morphology parameters were comparable in all segments analysed regardless of recording length (95% limits of agreement within 0 ± 20% (mean ± SD)). The results of the 6-min analyses were comparable to those obtained at the other recording lengths (6 min to 10 s).</p> <p>The intra-rater classification reproducibility was 96%, while the interrater reproducibility was 94%. The automated classification algorithm agreed with the manual classification in 90% of the cases.</p> <p>Conclusion</p> <p>The methodology used has profound effects on the estimation of P wave duration, and the method used must therefore be validated before any inferences can be made about P wave duration. This has implications in the interpretation of multiple studies where P wave duration is assessed, and conclusions with respect to normal values are drawn.</p> <p>P wave morphology and duration assessed using unfiltered, signal-averaged P wave analysis have high reproducibility, which is unaffected by the length of the recording. In the present study, the performance of the proposed automated classification algorithm, providing total reproducibility, showed excellent agreement with manually defined P wave morphologies.</p
Signature of Chaotic Diffusion in Band Spectra
We investigate the two-point correlations in the band spectra of spatially
periodic systems that exhibit chaotic diffusion in the classical limit. By
including level pairs pertaining to non-identical quasimomenta, we define form
factors with the winding number as a spatial argument. For times smaller than
the Heisenberg time, they are related to the full space-time dependence of the
classical diffusion propagator. They approach constant asymptotes via a regime,
reflecting quantal ballistic motion, where they decay by a factor proportional
to the number of unit cells. We derive a universal scaling function for the
long-time behaviour. Our results are substantiated by a numerical study of the
kicked rotor on a torus and a quasi-one-dimensional billiard chain.Comment: 8 pages, REVTeX, 5 figures (eps
Analytic models and forward scattering from accelerator to cosmic-ray energies
Analytic models for hadron-hadron scattering are characterized by analytical
parametrizations for the forward amplitudes and the use of dispersion relation
techniques to study the total cross section and the
parameter. In this paper we investigate four aspects related to the application
of the model to and scattering, from accelerator to cosmic-ray
energies: 1) the effect of different estimations for from
cosmic-ray experiments; 2) the differences between individual and global
(simultaneous) fits to and ; 3) the role of the
subtraction constant in the dispersion relations; 4) the effect of distinct
asymptotic inputs from different analytic models. This is done by using as a
framework the single Pomeron and the maximal Odderon parametrizations for the
total cross section. Our main conclusions are the following: 1) Despite the
small influence from different cosmic-ray estimations, the results allow us to
extract an upper bound for the soft pomeron intercept: ;
2) although global fits present good statistical results, in general, this
procedure constrains the rise of ; 3) the subtraction constant as
a free parameter affects the fit results at both low and high energies; 4)
independently of the cosmic-ray information used and the subtraction constant,
global fits with the odderon parametrization predict that, above GeV, becomes greater than , and
this result is in complete agreement with all the data presently available. In
particular, we infer at GeV and
at 500 GeV (BNL RHIC energies).Comment: 16 pages, 7 figures, aps-revtex, wording changes, corrected typos, to
appear in Physical Review
Constraining the Ratio in TeV Cosmic Rays with Observations of the Moon Shadow by HAWC
An indirect measurement of the antiproton flux in cosmic rays is possible as
the particles undergo deflection by the geomagnetic field. This effect can be
measured by studying the deficit in the flux, or shadow, created by the Moon as
it absorbs cosmic rays that are headed towards the Earth. The shadow is
displaced from the actual position of the Moon due to geomagnetic deflection,
which is a function of the energy and charge of the cosmic rays. The
displacement provides a natural tool for momentum/charge discrimination that
can be used to study the composition of cosmic rays. Using 33 months of data
comprising more than 80 billion cosmic rays measured by the High Altitude Water
Cherenkov (HAWC) observatory, we have analyzed the Moon shadow to search for
TeV antiprotons in cosmic rays. We present our first upper limits on the
fraction, which in the absence of any direct measurements, provide
the tightest available constraints of on the antiproton fraction for
energies between 1 and 10 TeV.Comment: 10 pages, 5 figures. Accepted by Physical Review
Journal Staff
We present the first measurements of the differential cross section d sigma/dp(T)(gamma) for the production of an isolated photon in association with at least two b-quark jets. The measurements consider photons with rapidities vertical bar y(gamma)vertical bar < 1.0 and transverse momenta 30 < p(T)(gamma) < 200 GeV. The b-quark jets are required to have p(T)(jet) > 15 GeVand vertical bar y(jet)vertical bar < 1.5. The ratio of differential production cross sections for gamma + 2 b-jets to gamma + b-jet as a function of p(T)(gamma) is also presented. The results are based on the proton-antiproton collision data at root s = 1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. The measured cross sections and their ratios are compared to the next- to- leading order perturbative QCD calculations as well as predictions based on the k(T)- factorization approach and those from the sherpa and pythia Monte Carlo event generators
The Sensitivity of HAWC to High-Mass Dark Matter Annihilations
The High Altitude Water Cherenkov (HAWC) observatory is a wide field-of-view
detector sensitive to gamma rays of 100 GeV to a few hundred TeV. Located in
central Mexico at 19 degrees North latitude and 4100 m above sea level, HAWC
will observe gamma rays and cosmic rays with an array of water Cherenkov
detectors. The full HAWC array is scheduled to be operational in Spring 2015.
In this paper, we study the HAWC sensitivity to the gamma-ray signatures of
high-mass (multi- TeV) dark matter annihilation. The HAWC observatory will be
sensitive to diverse searches for dark matter annihilation, including
annihilation from extended dark matter sources, the diffuse gamma-ray emission
from dark matter annihilation, and gamma-ray emission from non-luminous dark
matter subhalos. Here we consider the HAWC sensitivity to a subset of these
sources, including dwarf galaxies, the M31 galaxy, the Virgo cluster, and the
Galactic center. We simulate the HAWC response to gamma rays from these sources
in several well-motivated dark matter annihilation channels. If no gamma-ray
excess is observed, we show the limits HAWC can place on the dark matter
cross-section from these sources. In particular, in the case of dark matter
annihilation into gauge bosons, HAWC will be able to detect a narrow range of
dark matter masses to cross-sections below thermal. HAWC should also be
sensitive to non-thermal cross-sections for masses up to nearly 1000 TeV. The
constraints placed by HAWC on the dark matter cross-section from known sources
should be competitive with current limits in the mass range where HAWC has
similar sensitivity. HAWC can additionally explore higher dark matter masses
than are currently constrained.Comment: 15 pages, 4 figures, version to be published in PR
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