1,490 research outputs found
All Transients, All the Time: Real-Time Radio Transient Detection with Interferometric Closure Quantities
We demonstrate a new technique for detecting radio transients based on
interferometric closure quantities. The technique uses the bispectrum, the
product of visibilities around a closed-loop of baselines of an interferometer.
The bispectrum is calibration independent, resistant to interference, and
computationally efficient, so it can be built into correlators for real-time
transient detection. Our technique could find celestial transients anywhere in
the field of view and localize them to arcsecond precision. At the Karl G.
Jansky Very Large Array (VLA), such a system would have a high survey speed and
a 5-sigma sensitivity of 38 mJy on 10 ms timescales with 1 GHz of bandwidth.
The ability to localize dispersed millisecond pulses to arcsecond precision in
large volumes of interferometer data has several unique science applications.
Localizing individual pulses from Galactic pulsars will help find X-ray
counterparts that define their physical properties, while finding host galaxies
of extragalactic transients will measure the electron density of the
intergalactic medium with a single dispersed pulse. Exoplanets and active stars
have distinct millisecond variability that can be used to identify them and
probe their magnetospheres. We use millisecond time scale visibilities from the
Allen Telescope Array (ATA) and VLA to show that the bispectrum can detect
dispersed pulses and reject local interference. The computational and data
efficiency of the bispectrum will help find transients on a range of time
scales with next-generation radio interferometers.Comment: Accepted to ApJ. 8 pages, 5 figures, 2 tables. Revised to include
discussion of non-Gaussian statistics of techniqu
Assessing policy stability in Iraq: a fuzzy approach to modeling preferences
The first Council of Representatives elected under the new Iraqi Constitution was unable to pass legislation required to achieve the political benchmarks set by the government. We argue that the exercise of a qualified veto by the three-member Presidency Council essentially required near unanimity among the nine parties of the governing coalition. Given the policy positions of these parties, unanimity was not possible. Our analysis makes use of a fuzzy veto players model. The placement of the government parties along a single dimension based on fuzzy preference measures derived from party text data reveals no common area of agreement
Analysis of Cardiac Ion Channels to Understand Arrhythmias Which Lead to Sudden Cardiac Death
There are 300,000-400,000 fatalities attributed to sudden cardiac death every year in the U.S. due to a lack of sufficient research on mechanisms causing arrhythmias1. Malfunctions with the ion channels in the heart may lead to lethal arrhythmias. The purpose of this work is to study ion channels and evaluate malfunctions relative to normally functioning hearts. Plasmid insertion in E. coli assayed whether functional ion channels reach the membrane, and confocal fluorescent microscopy was used to illuminate cellular functionality. In addition, genetic analysis was used to determine the extent of hereditary factors in sudden cardiac death. Genes that encode for the voltage-gated sodium, potassium, and calcium ion channels were analyzed at the genetic level using isolated DNA samples and traditional Sanger sequencing methods to identify mutations that may be responsible for sudden cardiac death syndromes. For example, Long QT syndrome, Short QT syndrome, and Brugada syndrome are caused by mutations in these ion channels. Once these mutations are identified, genetic engineering techniques can be used in the generation of new heart cells from the stem cells found in somatic tissue. Generation of such heart cells is important because it could lead to the development of personalized treatment for degenerative diseases such as heart failure in the future.
Rubart, M. et al., Mechanisms of Sudden Cardiac Death, 2005. J. clin. invest. 115(9):2305-2315
A Detailed Monte-Carlo Simulation for the Belle TOF System
We have developed a detailed Monte Carlo simulation program for the Belle TOF
system. Based on GEANT simulation, it takes account of all physics processes in
the TOF scintillation counters and readout electronics. The simulation
reproduces very well the performance of the Belle TOF system, including the
dE/dx response, the time walk effect, the time resolution, and the hit
efficiency due to beam background. In this report, we will describe the Belle
TOF simulation program in detail.Comment: To be submitted to NI
Detection and parameter estimation of binary neutron star merger remnants
Detection and parameter estimation of binary neutron star merger remnants can shed light on the physics of hot matter at supranuclear densities. Here we develop a fast, simple model that can generate gravitational waveforms, and show it can be used for both detection and parameter estimation of post-merger remnants. The model consists of three exponentially-damped sinusoids with a linear frequency-drift term. The median fitting factors between the model waveforms and numerical-relativity simulations exceed 0.90. We detect remnants at a post-merger signal-to-noise ratio of ≥7 using a Bayes-factor detection statistic with a threshold of 3000. We can constrain the primary post-merger frequency to ±^(1.4)_(1.2)% at post-merger signal-to-noise ratios of 15 with an increase in precision to ±^(0.3)_(0.2)% for post-merger signal-to-noise ratios of 50. The tidal coupling constant can be constrained to ±⁹₁₂% at post-merger signal-to-noise ratios of 15, and ±5% at post-merger signal-to-noise ratios of 50 using a hierarchical inference model
Detection and parameter estimation of binary neutron star merger remnants
Detection and parameter estimation of binary neutron star merger remnants can
shed light on the physics of hot matter at supranuclear densities. Here we
develop a fast, simple model that can generate gravitational waveforms, and
show it can be used for both detection and parameter estimation of post-merger
remnants. The model consists of three exponentially-damped sinusoids with a
linear frequency-drift term. The median fitting factors between the model
waveforms and numerical-relativity simulations exceed 0.90. We detect remnants
at a post-merger signal-to-noise ratio of using a Bayes-factor
detection statistic with a threshold of 3000. We can constrain the primary
post-merger frequency to at post-merger signal-to-noise
ratios of 15 with an increase in precision to for
post-merger signal-to-noise ratios of 50. The tidal coupling constant can be
constrained to at post-merger signal-to-noise ratios of 15,
and at post-merger signal-to-noise ratios of 50 using a hierarchical
inference model
Fermion Condensation Quantum Phase Transition versus Conventional Quantum Phase Transitions
The main features of fermion condensation quantum phase transition (FCQPT),
which are distinctive in several aspects from that of conventional quantum
phase transition (CQPT), are considered. We show that in contrast to CQPT,
whose physics in quantum critical region is dominated by thermal and quantum
fluctuations and characterized by the absence of quasiparticles, the physics of
a Fermi system near FCQPT or undergone FCQPT is controlled by the system of
quasiparticles resembling the Landau quasiparticles. Contrary to the Landau
quasiparticles, the effective mass of these quasiparticles strongly depends on
the temperature, magnetic fields, density, etc. This system of quasiparticles
having general properties determines the universal behavior of the Fermi system
in question. As a result, the universal behavior persists up to relatively high
temperatures comparatively to the case when such a behavior is determined by
CQPT. We analyze striking recent measurements of specific heat, charge and heat
transport used to study the nature of magnetic field-induced QCP in
heavy-fermion metal CeCoIn and show that the observed facts are in good
agreement with our scenario based on FCQPT and certainly seem to rule out the
critical fluctuations related with CQPT. Our general consideration suggests
that FCQPT and the emergence of novel quasiparticles near and behind FCQPT and
resembling the Landau quasiparticles are distinctive features intrinsic to
strongly correlated substances.Comment: 10 pages, Revtex, new references and facts are adde
Exposure to Household Air Pollution from Biomass Cookstoves and Levels of Fractional Exhaled Nitric Oxide (FeNO) among Honduran Women
Household air pollution is estimated to be responsible for nearly three million premature deaths annually. Measuring fractional exhaled nitric oxide (FeNO) may improve the limited understanding of the association of household air pollution and airway inflammation. We evaluated the cross-sectional association of FeNO with exposure to household air pollution (24-h average kitchen and personal fine particulate matter and black carbon; stove type) among 139 women in rural Honduras using traditional stoves or cleaner-burning Justastoves. We additionally evaluated interaction by age. Results were generally consistent with a null association; we did not observe a consistent pattern for interaction by age. Evidence from ambient and household air pollution regarding FeNO is inconsistent, and may be attributable to differing study populations, exposures, and FeNO measurement procedures (e.g., the flow rate used to measure FeNO)
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