52,367 research outputs found
Gravitational Waves from Phase Transition of Accreting Neutron Stars
We propose that when neutron stars in low-mass X-ray binaries accrete
sufficient mass and become millisecond pulsars, the interiors of these stars
may undergo phase transitions, which excite stellar radial oscillations. We
show that the radial oscillations will be mainly damped by gravitational-wave
radiation instead of internal viscosity. The gravitational waves can be
detected by the advanced Laser Interferometer Gravitational-Wave Observatory at
a rate of about three events per year.Comment: Latex, article style, approximately 10 page
Electron-positron energy deposition rate from neutrino pair annihilation on the rotation axis of neutron and quark stars
We investigate the deposition of energy due to the annihilations of neutrinos
and antineutrinos on the rotation axis of rotating neutron and quark stars,
respectively. The source of the neutrinos is assumed to be a neutrino-cooled
accretion disk around the compact object. Under the assumption of the
separability of the neutrino null geodesic equation of motion we obtain the
general relativistic expression of the energy deposition rate for arbitrary
stationary and axisymmetric space-times. The neutrino trajectories are obtained
by using a ray tracing algorithm, based on numerically solving the
Hamilton-Jacobi equation for neutrinos by reversing the proper time evolution.
We obtain the energy deposition rates for several classes of rotating neutron
stars, described by different equations of state of the neutron matter, and for
quark stars, described by the MIT bag model equation of state and in the CFL
(Color-Flavor-Locked) phase, respectively. The electron-positron energy
deposition rate on the rotation axis of rotating neutron and quark stars is
studied for two accretion disk models (isothermal disk and accretion disk in
thermodynamical equilibrium). Rotation and general relativistic effects modify
the total annihilation rate of the neutrino-antineutrino pairs on the rotation
axis of compact stellar, as measured by an observer at infinity. The
differences in the equations of state for neutron and quark matter also have
important effects on the spatial distribution of the energy deposition rate by
neutrino-antineutrino annihilation.Comment: 38 pages, 9 figures, accepted for publication in MNRA
Spatiotemporal Patterns and Predictability of Cyberattacks
Y.C.L. was supported by Air Force Office of Scientific Research (AFOSR) under grant no. FA9550-10-1-0083 and Army Research Office (ARO) under grant no. W911NF-14-1-0504. S.X. was supported by Army Research Office (ARO) under grant no. W911NF-13-1-0141. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewedPublisher PD
Subzone control method of stratum ventilation for thermal comfort improvement
The conventional control method of a collective ventilation (e.g., stratum ventilation) controls the averaged thermal environment in the occupied zone to satisfy the averaged thermal preference of a group of occupants. However, the averaged thermal environment in the occupied zone is not the same as the microclimates of the occupants, because the thermal environment in the occupied zone is not absolutely uniform. Moreover, the averaged thermal preference of the occupants could deviate from the individual thermal preferences, because the occupants could have different individual thermal preferences. This study proposes a subzone control method for stratum ventilation to improve thermal comfort. The proposed method divides the occupied zone into subzones, and controls the microclimates of the subzones to satisfy the thermal preferences of the respective subzones. Experiments in a stratum-ventilated classroom are conducted to model and validate the Predicted Mean Votes (PMVs) of the subzones, with a mean absolute error between 0.05 scale and 0.14 scale. Using the PMV models, the supply air parameters are optimized to minimize the deviation between the PMVs of the subzones and the respective thermal preferences. Case studies show that the proposed method can fulfill the thermal constraints of all subzones for thermal comfort, while the conventional method fails. The proposed method further improves thermal comfort by reducing the deviation of the achieved PMVs of subzones from the preferred ones by 17.6%â41.5% as compared with the conventional method. The proposed method is also promising for other collective ventilations (e.g., mixing ventilation and displacement ventilation)
An experimental study on a motion sensing system for sports training
In sports science, motion data collected from athletes is
used to derive key performance characteristics, such as stride length
and stride frequency, that are vital coaching support information. The
sensors for use must be more accurate, must capture more vigorous
events, and have strict weight and size requirements, since they must
not themselves affect performance. These requirements mean each
wireless sensor device is necessarily resource poor and yet must be
capable of communicating a considerable amount of data, contending
for the bandwidth with other sensors on the body. This paper analyses
the results of a set of network traffic experiments that were designed
to investigate the suitability of conventional wireless motion sensing
system design ïżœ which generally assumes in-network processing - as
an efficient and scalable design for use in sports training
Compressing Inertial Motion Data in Wireless Sensing Systems â An Initial Experiment
The use of wireless inertial motion sensors, such as accelerometers, for supporting medical care and sportâs training, has been under investigation in recent years. As the number of sensors (or their sampling rates) increases, compressing data at source(s) (i.e. at the sensors), i.e. reducing the quantity of data that needs to be transmitted between the on-body sensors and the remote repository, would be essential especially in a bandwidth-limited wireless environment. This paper presents a set of compression experiment results on a set of inertial motion data collected during running exercises. As a starting point, we selected a set of common compression algorithms to experiment with. Our results show that, conventional lossy compression algorithms would achieve a desirable compression ratio with an acceptable time delay. The results also show that the quality of the decompressed data is within acceptable range
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