8,256 research outputs found
A nonlinear detection algorithm for periodic signals in gravitational wave detectors
We present an algorithm for the detection of periodic sources of
gravitational waves with interferometric detectors that is based on a special
symmetry of the problem: the contributions to the phase modulation of the
signal from the earth rotation are exactly equal and opposite at any two
instants of time separated by half a sidereal day; the corresponding is true
for the contributions from the earth orbital motion for half a sidereal year,
assuming a circular orbit. The addition of phases through multiplications of
the shifted time series gives a demodulated signal; specific attention is given
to the reduction of noise mixing resulting from these multiplications. We
discuss the statistics of this algorithm for all-sky searches (which include a
parameterization of the source spin-down), in particular its optimal
sensitivity as a function of required computational power. Two specific
examples of all-sky searches (broad-band and narrow-band) are explored
numerically, and their performances are compared with the stack-slide technique
(P. R. Brady, T. Creighton, Phys. Rev. D, 61, 082001).Comment: 9 pages, 3 figures, to appear in Phys. Rev.
Is Steam a Modern Heating Medium or a Victorian Hangover?
In the UK many hospitals use steam as a heating medium. It is an accepted fact that steam can carry considerable amounts of heat energy, but is heating by steam really a cost effective and energy efficient method for hospital engineering services? This paper examines some steam and MTHW case studies in terms of energy and operation, and some quantifiable parameters for comparison of the two have been obtained. An important feature revealed by the study is that optimum energy and operational performance for both steam and MTHW systems is directly related to management and maintenance. Other factors affecting the choice of steam are also examined. For example, when choosing between steam and MTHW, how important a factor are those unique hospital applications such as laundries and sterilization equipment, that are traditionally provided for by steam? Interviews were conducted with engineering professionals at a large North-West hospital in order to consider the specialist health service applications for steam. The investigation concludes that although steam retains a Victorian image, in hospital applications its energy and financial performance costs are comparable, and sometimes better than hot water alternatives
Are HIV smartphone apps and online interventions fit for purpose?
Sexual health is an under-explored area of Human-Computer Interaction (HCI), particularly sexually transmitted infections such as HIV. Due to the stigma associated with these infections, people are often motivated to seek information online. With the rise of smartphone and web apps, there is enormous potential for technology to provide easily accessible information and resources. However, using online information raises important concerns about the trustworthiness of these resources and whether they are fit for purpose. We conducted a review of smartphone and web apps to investigate the landscape of currently available online apps and whether they meet the diverse needs of people seeking information on HIV online. Our functionality review revealed that existing technology interventions have a one-size-fits-all approach and do not support the breadth and complexity of HIV-related support needs. We argue that technology-based interventions need to signpost their offering and provide tailored support for different stages of HIV, including prevention, testing, diagnosis and management
Matching of the continuous gravitational wave in an all sky search
We investigate the matching of continuous gravitational wave (CGW) signals in
an all sky search with reference to Earth based laser interferometric
detectors. We consider the source location as the parameters of the signal
manifold and templates corresponding to different source locations. It has been
found that the matching of signals from locations in the sky that differ in
their co-latitude and longitude by radians decreases with source
frequency. We have also made an analysis with the other parameters affecting
the symmetries. We observe that it may not be relevant to take care of the
symmetries in the sky locations for the search of CGW from the output of
LIGO-I, GEO600 and TAMA detectors.Comment: 16 pages, 7 figures, 3 Tables, To appear in Int. J. Mod. Phys.
Do naked singularities generically occur in generalized theories of gravity?
A new mechanism for causing naked singularities is found in an effective
superstring theory. We investigate the gravitational collapse in a spherically
symmetric Einstein-Maxwell-dilaton system in the presence of a pure
cosmological constant "potential", where the system has no static black hole
solution. We show that once gravitational collapse occurs in the system, naked
singularities necessarily appear in the sense that the field equations break
down in the domain of outer communications. This suggests that in generalized
theories of gravity, the non-minimally coupled fields generically cause naked
singularities in the process of gravitational collapse if the system has no
static or stationary black hole solution.Comment: 4 pages including 2 eps figures, to be published in Physical Review
Letter
Price Discovery and the Accuracy of Consolidated Data Feeds in the U.S. Equity Markets
Both the scientific community and the popular press have paid much attention
to the speed of the Securities Information Processor, the data feed
consolidating all trades and quotes across the US stock market. Rather than the
speed of the Securities Information Processor, or SIP, we focus here on its
accuracy. Relying on Trade and Quote data, we provide various measures of SIP
latency relative to high-speed data feeds between exchanges, known as direct
feeds. We use first differences to highlight not only the divergence between
the direct feeds and the SIP, but also the fundamental inaccuracy of the SIP.
We find that as many as 60 percent or more of trades are reported out of
sequence for stocks with high trade volume, therefore skewing simple measures
such as returns. While not yet definitive, this analysis supports our
preliminary conclusion that the underlying infrastructure of the SIP is
currently unable to keep pace with the trading activity in today's stock
market.Comment: 18 pages, 20 figures, 2 table
Data analysis of gravitational-wave signals from spinning neutron stars. II. Accuracy of estimation of parameters
We examine the accuracy of estimation of parameters of the gravitational-wave
signals from spinning neutron stars that can be achieved from observations by
Earth-based laser interferometers. We consider a model of the signal consisting
of two narrowband components and including both phase and amplitude modulation.
We calculate approximate values of the rms errors of the parameter estimators
using the Fisher information matrix. We carry out extensive Monte Carlo
simulations and obtain cumulative distribution functions of rms errors of
astrophysically interesting parameters: amplitude of the signal, wobble angle,
position of the source in the sky, frequency, and spindown coefficients. We
consider both all-sky searches and directed searches. We also examine the
possibility of determination of neutron star proper motion. We perform
simulations for all laser-interferometric detectors that are currently under
construction and for several possible lengths of the observation time and sizes
of the parameter space. We find that observations of continuous
gravitational-wave signals from neutron stars by laser-interferometric
detectors will provide a very accurate information about their astrophysical
properties. We derive several simplified models of the signal that can be used
in the theoretical investigations of the data analysis schemes independently of
the physical mechanisms generating the gravitational-wave signal.Comment: LaTeX, 34 pages, 15 figures, submitted to Phys. Rev.
Quasi-normal modes of Schwarzschild-de Sitter black holes
The low-laying frequencies of characteristic quasi-normal modes (QNM) of
Schwarzschild-de Sitter (SdS) black holes have been calculated for fields of
different spin using the 6th-order WKB approximation and the approximation by
the P\"{o}shl-Teller potential. The well-known asymptotic formula for large
is generalized here on a case of the Schwarzchild-de Sitter black hole. In the
limit of the near extreme term the results given by both methods are
in a very good agreement, and in this limit fields of different spin decay with
the same rate.Comment: 9 pages, 1 ancillary Mathematica(R) noteboo
Data analysis of gravitational-wave signals from spinning neutron stars. IV. An all-sky search
We develop a set of data analysis tools for a realistic all-sky search for
continuous gravitational-wave signals. The methods that we present apply to
data from both the resonant bar detectors that are currently in operation and
the laser interferometric detectors that are in the final stages of
construction and commissioning. We show that with our techniques we shall be
able to perform an all-sky 2-day long coherent search of the narrow-band data
from the resonant bar EXPLORER with no loss of signals with the dimensionless
amplitude greater than .Comment: REVTeX, 26 pages, 1 figure, submitted to Phys. Rev.
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