808 research outputs found
Comparison of the ultrafast to slow time scale dynamics of three liquid crystals in the isotropic phase
The dynamics of three liquid crystals, 4'(pentyloxy)-4-biphenylcarbonitrile (5-OCB), 4'-pentyl-4-biphenylcarbonitrile (5-CB), and 1-isothiocyanato-(4-propylcyclohexyl)benzene (3-CHBT), are investigated from very short time (~1 ps) to very long time (>100 ns) as a function of temperature using optical heterodyne detected optical Kerr effect experiments. For all three liquid crystals, the data decay exponentially only on the longest time scale (>several ns). The temperature dependence of the long time scale exponential decays is described well by the Landau-de Gennes theory of the randomization of pseudonematic domains that exist in the isotropic phase of liquid crystals near the isotropic to nematic phase transition. At short time, all three liquid crystals display power law decays. Over the full range of times, the data for all three liquid crystals are fit with a model function that contains a short time power law. The power law exponents for the three liquid crystals range between 0.63 and 0.76, and the power law exponents are temperature independent over a wide range of temperatures. Integration of the fitting function gives the empirical polarizability-polarizability (orientational) correlation function. A preliminary theoretical treatment of collective motions yields a correlation function that indicates that the data can decay as a power law at short times. The power law component of the decay reflects intradomain dynamics
Inhomogeneity driven by Higgs instability in gapless superconductor
The fluctuations of the Higgs and pseudo Nambu-Goldstone fields in the 2SC
phase with mismatched pairing are described in the nonlinear realization
framework of the gauged Nambu--Jona-Lasinio model. In the gapless 2SC phase,
not only Nambu-Goldstone currents can be spontaneously generated, but the Higgs
field also exhibits instablity. The Nambu-Goldstone currents generation
indicates the formation of the single plane wave LOFF state and breaks rotation
symmetry, while the Higgs instability favors spatial inhomogeneity and breaks
translation invariance. In this paper, we focus on the Higgs instability which
has not drawn much attention yet. The Higgs instability cannot be removed
without a long range force, thus it persists in the gapless superfluidity and
induces phase separation. In the case of g2SC state, the Higgs instability can
only be partially removed by the electric Coulomb energy. However, it is not
excluded that the Higgs instability might be completely removed in the charge
neutral gCFL phase by the color Coulomb energy.Comment: 21 pages, 5 figure
Liquid crystal dynamics in the isotropic phase
The dynamics in the isotropic phase of the liquid crystal 1-isothiocyanato-(4-propylcyclohexyl) benzene (3-CHBT) are investigated from very short time (~1 ps) to very long time (>100 ns) as function of temperature. The data decay exponentially only on the longest time scale (>10 ns). The temperature dependence of the long time scale exponential decays is described well by the Landau-de Gennes theory of the randomization of pseudo-nematic domains that exist in the isotropic phase of liquid crystals near the isotropic to nematic phase transition. Over the full range of times, the data are fit with a model function that contains a short time power law. The power law exponent is temperature independent over a wide range of temperatures. Integration of the function gives the empirical polarizability-polarizability (orientational) correlation function. A preliminary theoretical treatment of collective motions yields a correlation function that indicates that the data can decay as a power law at short times. The power law component of the decay reflects intradomain dynamics
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
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, 420 MHz, 868 MHz, 2.4 GHz, 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 WBASN’s 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
MeCP2 regulates the timing of critical period plasticity that shapes functional connectivity in primary visual cortex
Mutations in methyl-CpG-binding protein 2 (MeCP2) cause Rett syndrome, an autism spectrum-associated disorder with a host of neurological and sensory symptoms, but the pathogenic mechanisms remain elusive. Neuronal circuits are shaped by experience during critical periods of heightened plasticity. The maturation of cortical GABA inhibitory circuitry, the parvalbumin+ (PV+) fast-spiking interneurons in particular, is a key component that regulates the initiation and termination of the critical period. Using MeCP2-null mice, we examined experience-dependent development of neural circuits in the primary visual cortex. The functional maturation of parvalbumin interneurons was accelerated upon vision onset, as indicated by elevated GABA synthetic enzymes, vesicular GABA transporter, perineuronal nets, and enhanced GABA transmission among PV interneurons. These changes correlated with a precocious onset and closure of critical period and deficient binocular visual function in mature animals. Reduction of GAD67 expression rescued the precocious opening of the critical period, suggesting its major role in MECP2-mediated regulation of experience-driven circuit development. Our results identify molecular changes in a defined cortical cell type and link aberrant developmental trajectory to functional deficits in a model of neuropsychiatric disorder
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