704 research outputs found
Gauge Field Fluctuations and First-Order Phase Transition in Color Superconductivity
We study the gauge field fluctuations in dense quark matter and determine the
temperature of the induced first-order phase transition to the
color-superconducting phase in weak coupling. We find that the local
approximation of the coupling between the gauge potential and the order
parameter, employed in the Ginzburg-Landau theory, has to be modified by
restoring the full momentum dependence of the polarization function of gluons
in the superconducting phase.Comment: 5 pages, 1 figure, Revtex, we have modified our conclusions for the
metallic superconducto
Delay, Reliability, and Throughput Based QoS Profile: A MAC Layer Performance Optimization Mechanism for Biomedical Applications in Wireless Body Area Sensor Networks
Recently, increasing demand for remote healthcare monitoring systems poses a specific set of Quality of Services (QoS) requirements to the MAC layer protocols and standards (IEEE 802.15.6, IEEE 802.15.4, etc.) of Wireless Body Area Sensor Networks (WBASNs). They mainly include time bounded services (latency), reliable data transmission, fair channel distribution, and specified data rates. The existing MAC protocols of WBASNs are lack of a specific set of QoS. To address this, the paper proposes a QoS profile named delay, reliability, and throughput (DRT). The QoS values computed through DRT profile provide maximum reliability of data transmission within an acceptable latency and data rates. The DRT is based on the carrier sense multiple access with collision avoidance (CSMA/CA) channel access mechanism and considers IEEE 802.15.4 (low-rate WPAN) and IEEE 802.15.6 (WBASN). Further, a detailed performance analysis of different frequency bands is done which are standardized for WBASNs, that is, 420âMHz, 868âMHz, 2.4âGHz, and so forth. Finally, a series of experiments are conducted to produce statistical results for DRT profile with respect to delay, reliability, and packet delivery ratio (PDR). The calculated results are verified through extensive simulations in the CASTALIA 3.2 framework using the OMNET++ network simulator.</jats:p
IEEE 802.15.4 Frame Aggregation Enhancement to Provide High Performance in Life-Critical Patient Monitoring Systems
In wireless body area sensor networks (WBASNs), Quality of Service (QoS) provision for
patient monitoring systems in terms of time-critical deadlines, high throughput and energy efficiency
is a challenging task. The periodic data from these systems generates a large number of small
packets in a short time period which needs an efficient channel access mechanism. The IEEE 802.15.4
standard is recommended for low power devices and widely used for many wireless sensor networks
applications. It provides a hybrid channel access mechanism at the Media Access Control (MAC) layer
which plays a key role in overall successful transmission in WBASNs. There are many WBASNâs MAC
protocols that use this hybrid channel access mechanism in variety of sensor applications. However,
these protocols are less efficient for patient monitoring systems where life critical data requires limited
delay, high throughput and energy efficient communication simultaneously. To address these issues,
this paper proposes a frame aggregation scheme by using the aggregated-MAC protocol data unit
(A-MPDU) which works with the IEEE 802.15.4 MAC layer. To implement the scheme accurately, we
develop a traffic patterns analysis mechanism to understand the requirements of the sensor nodes in
patient monitoring systems, then model the channel access to find the performance gap on the basis of
obtained requirements, finally propose the design based on the needs of patient monitoring systems.
The mechanism is initially verified using numerical modelling and then simulation is conducted
using NS2.29, Castalia 3.2 and OMNeT++. The proposed scheme provides the optimal performance
considering the required QoS
Absence of the London limit for the first-order phase transition to a color superconductor
We study the effects of gauge-field fluctuations on the free energy of a
homogeneous color superconductor in the color-flavor-locked (CFL) phase.
Gluonic fluctuations induce a strong first-order phase transition, in contrast
to electronic superconductors where this transition is weakly first order. The
critical temperature for this transition is larger than the one corresponding
to the diquark pairing instability. The physical reason is that the gluonic
Meissner masses suppress long-wavelength fluctuations as compared to the normal
conducting phase where gluons are massless, which stabilizes the
superconducting phase. In weak coupling, we analytically compute the
temperatures associated with the limits of metastability of the normal and
superconducting phases, as well as the latent heat associated with the
first-order phase transition. We then extrapolate our results to intermediate
densities and numerically evaluate the temperature of the fluctuation-induced
first-order phase transition, as well as the discontinuity of the diquark
condensate at the critical point. We find that the London limit of magnetic
interactions is absent in color superconductivity.Comment: 14 pages, 5 figure
Precise determination of stellar parameters of the ZZ Ceti and DAZ white dwarf GD 133 through asteroseismology
An increasing number of white dwarf stars show atmospheric chemical
composition polluted by heavy elements accreted from debris disk material. The
existence of such debris disks strongly suggests the presence of one or more
planet(s) whose gravitational interaction with rocky planetesimals is
responsible for their disruption by tidal effect. The ZZ Ceti pulsator and
polluted DAZ white dwarf GD 133 is a good candidate for searching for such a
potential planet. We started in 2011 a photometric follow-up of its pulsations.
As a result of this work in progress, we used the data gathered from 2011 to
2015 to make an asteroseismological analysis of GD 133, providing the star
parameters from a best fit model with / = 0.630 0.002,
= 12400 K 70 K, log() = -2.00 0.02,
log() = -4.50 0.02 and determining a rotation period of
7 days.Comment: 10 pages, 13 figures, accepted by MNRA
Discerning Aggregation in Homogeneous Ensembles: A General Description of Photon Counting Spectroscopy in Diffusing Systems
In order to discern aggregation in solutions, we present a quantum mechanical
analog of the photon statistics from fluorescent molecules diffusing through a
focused beam. A generating functional is developed to fully describe the
experimental physical system as well as the statistics. Histograms of the
measured time delay between photon counts are fit by an analytical solution
describing the static as well as diffusing regimes. To determine empirical
fitting parameters, fluorescence correlation spectroscopy is used in parallel
to the photon counting. For expedient analysis, we find that the distribution's
deviation from a single Poisson shows a difference between two single fluor
moments or a double fluor aggregate of the same total intensities. Initial
studies were performed on fixed-state aggregates limited to dimerization.
However preliminary results on reactive species suggest that the method can be
used to characterize any aggregating system.Comment: 30 pages, 5 figure
Linearized Gravity in Isotropic Coordinates in the Brane World
We solve the Einstein equations in the Randall-Sundrum framework using an
isotropic ansatz for the metric and obtain an exact expression to first order
in the gravitational coupling. The solution is free from metric singularities
away from the source and it satisfies the Israel matching condition on a
straight brane. At distances far away from the source and on the physical brane
this solution coincides with the 4-D Schwarzschild metric in isotropic
coordinates. Furthermore we show that the extension of the standard
Schwarzschild horizon in the bulk is tubular for any diagonal form of the
metric while there is no restriction for the extension of the Schwarzschild
horizon in isotropic coordinates.Comment: 13 pages, plain Te
The Subleading Term of the Strong Coupling Expansion of the Heavy-Quark Potential in a Super Yang-Mills Plasma
Applying the AdS/CFT correspondence, the expansion of the heavy-quark
potential of the supersymmetric Yang-Mills theory at large is
carried out to the sub-leading term in the large 't Hooft coupling at nonzero
temperatures. The strong coupling corresponds to the semi-classical expansion
of the string-sigma model, the gravity dual of the Wilson loop operator, with
the sub-leading term expressed in terms of functional determinants of
fluctuations. The contributions of these determinants are evaluated
numerically.Comment: 17 pages in JHEP3, typos fixed, updated version to be published in
JHE
Path integral solution for an angle-dependent anharmonic oscillator
We have given a straightforward method to solve the problem of noncentral
anharmonic oscillator in three dimensions. The relative propagator is presented
by means of path integrals in spherical coordinates. By making an adequate
change of time we were able to separate the angular motion from the radial one.
The relative propagator is then exactly calculated. The energy spectrum and the
corresponding wave functions are obtained.Comment: Corrected typos and mistakes, To appear in Communications in
Theoretical Physic
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