5,336 research outputs found
LISA data analysis: The monochromatic binary detection and initial guess problems
We consider the detection and initial guess problems for the LISA
gravitational wave detector. The detection problem is the problem of how to
determine if there is a signal present in instrumental data and how to identify
it. Because of the Doppler and plane-precession spreading of the spectral power
of the LISA signal, the usual power spectrum approach to detection will have
difficulty identifying sources. A better method must be found. The initial
guess problem involves how to generate {\it a priori} values for the parameters
of a parameter-estimation problem that are close enough to the final values for
a linear least-squares estimator to converge to the correct result. A useful
approach to simultaneously solving the detection and initial guess problems for
LISA is to divide the sky into many pixels and to demodulate the Doppler
spreading for each set of pixel coordinates. The demodulated power spectra may
then be searched for spectral features. We demonstrate that the procedure works
well as a first step in the search for gravitational waves from monochromatic
binaries.Comment: 8 pages, 8 figure
Molecular Control of the Amount, Subcellular Location and Activity State of Translation Elongation Factor 2 (eEF-2) in Neurons Experiencing Stress
Eukaryotic elongation factor 2 (eEF-2) is an important regulator of the protein translation machinery wherein it controls the movement of the ribosome along the mRNA. The activity of eEF-2 is regulated by changes in cellular energy status and nutrient availability, and posttranslational modifications such as phosphorylation and mono-ADP-ribosylation. However, the mechanisms regulating protein translation under conditions of cellular stress in neurons are unknown. Here we show that when rat hippocampal neurons experience oxidative stress (lipid peroxidation induced by exposure to cumene hydroperoxide; CH), eEF-2 is hyperphosphorylated and ribosylated resulting in reduced translational activity. The degradation of eEF-2 requires calpain proteolytic activity and is accompanied by accumulation of eEF-2 in the nuclear compartment. The subcellular localization of both native and phosphorylated forms of eEF-2 is influenced by CRM1 and 14.3.3, respectively. In hippocampal neurons p53 interacts with non-phosphorylated (active) eEF-2, but not with its phosphorylated form. The p53 – eEF-2 complexes are present in cytoplasm and nucleus, and their abundance increases when neurons experience oxidative stress. The nuclear localization of active eEF-2 depends upon its interaction with p53, as cells lacking p53 contain less active eEF-2 in the nuclear compartment. Overexpression of eEF-2 in hippocampal neurons results in increased nuclear levels of eEF-2, and decreased cell death following exposure to CH. Our results reveal novel molecular mechanisms controlling the differential subcellular localization and activity state of eEF-2 that may influence the survival status of neurons during periods of elevated oxidative stress.España, Ministerio de Ciencia e Innovación BFU2010-20882.España, Ministerio de Educación, Cultura y Deporte postdoctoral fellowship (EX2009-0918
Price Indexes for Medical Care Goods and Services: An Overview of Measurement Issues
We review in considerable detail the conceptual and measurement issues that underlie construction of medical care price indexes in the U.S., particularly the medical care consumer price indexes (MCPIs) and medical-related producer price indexes (MPPIs). We outline salient features of the medical care marketplace, including the impacts of insurance, moral hazard, principal-agent relationships, technological progress and organizational changes. Since observed data are unlikely to correspond with efficient outcomes, we discuss implications of the failure of transactions data in this market to reveal reliable marginal valuations, and the consequent need to augment traditional transactions data with information based on cost-effectiveness and outcomes studies. We describe procedures currently used by the BLS in constructing MCPIs and MPPIs, including recent revisions, and then consider alternative notions of medical care output pricing that involve the price or cost of an episode of treatment, rather than prices of fixed bundles of inputs. We outline features of a proposed new experimental price index -- a medical care expenditure price index -- that is more suitable for evaluation and analyses of medical care cost changes, than are the current MCPIs and MPPIs. We conclude by suggesting future research and measurement issues that are most likely to be fruitful.
Angular Resolution of the LISA Gravitational Wave Detector
We calculate the angular resolution of the planned LISA detector, a
space-based laser interferometer for measuring low-frequency gravitational
waves from galactic and extragalactic sources. LISA is not a pointed
instrument; it is an all-sky monitor with a quadrupolar beam pattern. LISA will
measure simultaneously both polarization components of incoming gravitational
waves, so the data will consist of two time series. All physical properties of
the source, including its position, must be extracted from these time series.
LISA's angular resolution is therefore not a fixed quantity, but rather depends
on the type of signal and on how much other information must be extracted.
Information about the source position will be encoded in the measured signal in
three ways: 1) through the relative amplitudes and phases of the two
polarization components, 2) through the periodic Doppler shift imposed on the
signal by the detector's motion around the Sun, and 3) through the further
modulation of the signal caused by the detector's time-varying orientation. We
derive the basic formulae required to calculate the LISA's angular resolution
for a given source. We then evaluate for
two sources of particular interest: monchromatic sources and mergers of
supermassive black holes. For these two types of sources, we calculate (in the
high signal-to-noise approximation) the full variance-covariance matrix, which
gives the accuracy to which all source parameters can be measured. Since our
results on LISA's angular resolution depend mainly on gross features of the
detector geometry, orbit, and noise curve, we expect these results to be fairly
insensitive to modest changes in detector design that may occur between now and
launch. We also expect that our calculations could be easily modified to apply
to a modified design.Comment: 15 pages, 5 figures, RevTex 3.0 fil
Recovering the stationary phase condition for accurately obtaining scattering and tunneling times
The stationary phase method is often employed for computing tunneling {\em
phase} times of analytically-continuous {\em gaussian} or infinite-bandwidth
step pulses which collide with a potential barrier. The indiscriminate
utilization of this method without considering the barrier boundary effects
leads to some misconceptions in the interpretation of the phase times. After
reexamining the above barrier diffusion problem where we notice the wave packet
collision necessarily leads to the possibility of multiple reflected and
transmitted wave packets, we study the phase times for tunneling/reflecting
particles in a framework where an idea of multiple wave packet decomposition is
recovered. To partially overcome the analytical incongruities which rise up
when tunneling phase time expressions are obtained, we present a theoretical
exercise involving a symmetrical collision between two identical wave packets
and a one dimensional squared potential barrier where the scattered wave
packets can be recomposed by summing the amplitudes of simultaneously reflected
and transmitted waves.Comment: 32 pages, 5 figures, 1 tabl
Estimating the detectable rate of capture of stellar mass black holes by massive central black holes in normal galaxies
The capture and subsequent inspiral of stellar mass black holes on eccentric
orbits by central massive black holes, is one of the more interesting likely
sources of gravitational radiation detectable by LISA. We estimate the rate of
observable events and the associated uncertainties. A moderately favourable
mass function could provide many detectable bursts each year, and a detection
of at least one burst per year is very likely given our current understanding
of the populations in cores of normal spiral galaxies.Comment: 3 pages 2-column revtex Latex macro. No figures. Classical and
Quantum Gravity, accepte
CARS Temperature Measurements in a Hypersonic Propulsion Test Facility
Nonintrusive diagnostic measurements were performed in the supersonic reacting flow of the Hypersonic Propulsion Test Cell 2 at NASA-Langley. A Coherent Anti-stokes Raman Spectroscopy (CARS) system was assembled specifically for the test cell environment. System design considerations were: (1) test cell noise and vibration; (2) contamination from flow field or atmospheric borne dust; (3) unwanted laser or electrically induced combustion (inside or outside the duct); (4) efficient signal collection; (5) signal splitting to span the wide dynamic range present throughout the flow field; (6) movement of the sampling volume in the flow; and (7) modification of the scramjet model duct to permit optical access to the reacting flow with the CARS system. The flow in the duct was a nominal Mach 2 flow with static pressure near one atmosphere. A single perpendicular injector introduced hydrogen into the flow behind a rearward facing step. CARS data was obtained in three planes downstream of the injection region. At least 20 CARS data points were collected at each of the regularly spaced sampling locations in each data plane. Contour plots of scramjet combustor static temperature in a reacting flow region are presented
A New Waveform Consistency Test for Gravitational Wave Inspiral Searches
Searches for binary inspiral signals in data collected by interferometric
gravitational wave detectors utilize matched filtering techniques. Although
matched filtering is optimal in the case of stationary Gaussian noise, data
from real detectors often contains "glitches" and episodes of excess noise
which cause filter outputs to ring strongly. We review the standard \chi^2
statistic which is used to test whether the filter output has appropriate
contributions from several different frequency bands. We then propose a new
type of waveform consistency test which is based on the time history of the
filter output. We apply one such test to the data from the first LIGO science
run and show that it cleanly distinguishes between true inspiral waveforms and
large-amplitude false signals which managed to pass the standard \chi^2 test.Comment: 10 pages, 6 figures, submitted to Classical and Quantum Gravity for
the proceedings of the Eighth Gravitational Wave Data Analysis Workshop
(GWDAW-8
Choptuik scaling in six dimensions
We perform numerical simulations of the critical gravitational collapse of a
spherically symmetric scalar field in 6 dimensions. The critical solution has
discrete self-similarity. We find the critical exponent \gamma and the
self-similarity period \Delta.Comment: 8 pages, 3 figures RevTe
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