19,322 research outputs found
The Decay Lifetime of Polarized Fermions in Flight
Based on the parity violation in Standard model, we study the dependence of
lifetime on the helicity of an initial-state fermion in weak interactions. It
is pointed out that if the initial fermions in the decays are longitudinally
polarized, then the decay lifetime of left-handed polarized fermions is
different from that of right-handed polarized fermions in flight with a same
velocity in a same inertial system.Comment: 7 pages, Late
Adaptive medium access control for VoIP services in IEEE 802.11 WLANs
Abstract- Voice over Internet Protocol (VoIP) is an important service with strict Quality-of-Service (QoS) requirements in Wireless Local Area Networks (WLANs). The popular Distributed Coordination Function (DCF) of IEEE 802.11 Medium Access Control (MAC) protocol adopts a Binary Exponential Back-off (BEB) procedure to reduce the packet collision probability in WLANs. In DCF, the size of contention window is doubled upon a collision regardless of the network loads. This paper presents an adaptive MAC scheme to improve the QoS of VoIP in WLANs. This scheme applies a threshold of the collision rate to switch between two different functions for increasing the size of contention window based on the status of network loads. The performance of this scheme is investigated and compared to the original DCF using the network simulator NS-2. The performance results reveal that the adaptive scheme is able to achieve the higher throughput and medium utilization as well as lower access delay and packet loss probability than the original DCF
An effective ant-colony based routing algorithm for mobile ad-hoc network
An effective Ant-Colony based routing algorithm for mobile ad-hoc network is proposed in this paper. In this routing scheme, each path is marked by path grade, which is calculated from the combination of multiple constrained QoS parameters such as the time delay, packet loss rate and bandwidth, etc. packet routing is decided by the path grade and the queue buffer length of the node. The advantage of this scheme is that it can effectively improve the packet delivery ratio and reduce the end-to-end delay. The simulation results show that our proposed algorithm can improve the packet delivery ratio by 9%-22% and the end-to-end delay can be reduced by 14%-16% as compared with the conventional QAODV and ARA routing schemes
Antiparticle in Light of Einstein-Podolsky-Rosen Paradox and Klein Paradox
The original version of Einstein-Podolsky-Rosen (EPR) paradox and the Klein
paradox of Klein-Gordon (KG) equation are discussed to show the necessity of
existence of antiparticle with its wavefunction being fixed unambiguously. No
concept of "hole" is needed.Comment: 4 pages, 0 figures. Accepted by Chinese Phys. Let
Ellipsometry noise spectrum, suspension transfer function measurement and closed-loop control of the suspension system in the Q & A experiment
The Q & A experiment, aiming at the detection of vacuum birefringence
predicted by quantum electrodynamics, consists mainly of a suspended 3.5 m
Fabry-Perot cavity, a rotating permanent dipole magnet and an ellipsometer. The
2.3 T magnet can rotate up to 10 rev/s, introducing an ellipticity signal at
twice the rotation frequency. The X-pendulum gives a good isolation ratio for
seismic noise above its main resonant frequency 0.3 Hz. At present, the
ellipsometry noise decreases with frequency, from 1*10^{-5} rad Hz^{-1/2} at 5
Hz, 2*10^{-6} rad Hz^{-1/2} at 20 Hz to 5*10^{-7} rad Hz^{-1/2} at 40 Hz. The
shape of the noise spectrum indicates possible improvement can be made by
further reducing the movement between the cavity mirrors. From the preliminary
result of yaw motion alignment control, it can be seen that some peaks due to
yaw motion of the cavity mirror was suppressed. In this paper, we first give a
schematic view of the Q & A experiment, and then present the measurement of
transfer function of the compound X-pendulum-double pendulum suspension. A
closed-loop control was carried out to verify the validity of the measured
transfer functions. The ellipsometry noise spectra with and without yaw
alignment control and the newest improvement is presented.Comment: 7 pages, 5 figures, presented in 6th Edoardo Amaldi Conference on
Gravitational Waves, June 2005, Okinawa Japan and submitted to Journal of
Physics: Conference Series. Some modifications are made according to the
referee's comments: mainly to explain the relation between the displacement
of cavity mirror and the ellipticity noise spectru
Doping dependence of heat transport in the iron-arsenide superconductor Ba(FeCo)As: from isotropic to strongly -dependent gap structure
The temperature and magnetic field dependence of the in-plane thermal
conductivity of the iron-arsenide superconductor
Ba(FeCo)As was measured down to mK and up to
T as a function of Co concentration in the range 0.048 0.114. In zero magnetic field, a negligible residual linear term in
as at all shows that there are no zero-energy
quasiparticles and hence the superconducting gap has no nodes in the -plane
anywhere in the phase diagram. However, the field dependence of
reveals a systematic evolution of the superconducting gap with doping , from
large everywhere on the Fermi surface in the underdoped regime, as evidenced by
a flat at , to strongly -dependent in the overdoped
regime, where a small magnetic field can induce a large residual linear term,
indicative of a deep minimum in the gap magnitude somewhere on the Fermi
surface. This shows that the superconducting gap structure has a strongly
-dependent amplitude around the Fermi surface only outside the
antiferromagnetic/orthorhombic phase.Comment: version accepted for publication in Physical Review Letters; new
title, minor revision, revised fig.1, and updated reference
Observation of a pressure-induced transition from interlayer ferromagnetism to intralayer antiferromagnetism in Sr4Ru3O10
Sr4Ru3O10 is a Ruddlesden-Popper compound with triple Ru-O perovskite layers
separated by Sr-O alkali layers. This compound presents a rare coexistence of
interlayer (c-axis) ferromagnetism and intralayer (basal-plane) metamagnetism
at ambient pressure. Here we report the observation of pressure-induced,
intralayer itinerant antiferromagnetism arising from the interlayer
ferromagnetism. The application of modest hydrostatic pressure generates an
anisotropy that causes a flattening and a tilting of RuO6 octahedra. All
magnetic and transport results from this study indicate these lattice
distortions diminish the c-axis ferromagnetism and basal-plane metamagnetism,
and induce a basal-plane antiferromagnetic state. The unusually large
magnetoelastic coupling and pressure tunability of Sr4Ru3O10 makes it a unique
model system for studies of itinerant magnetism.Comment: 6 figure
Three-Dimensional Time-Resolved Trajectories from Laboratory Insect Swarms
Aggregations of animals display complex and dynamic behaviour, both at the individual level and on the level of the group as a whole. Often, this behaviour is collective, so that the group exhibits properties that are distinct from those of the individuals. In insect swarms, the motion of individuals is typically convoluted, and swarms display neither net polarization nor correlation. The swarms themselves, however, remain nearly stationary and maintain their cohesion even in noisy natural environments. This behaviour stands in contrast with other forms of collective animal behaviour, such as flocking, schooling, or herding, where the motion of individuals is more coordinated, and thus swarms provide a powerful way to study the underpinnings of collective behaviour as distinct from global order. Here, we provide a data set of three-dimensional, time-resolved trajectories, including positions, velocities, and accelerations, of individual insects in laboratory insect swarms. The data can be used to study the collective as a whole as well as the dynamics and behaviour of individuals within the swarm
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