75,499 research outputs found
Secure Key Distribution by Swapping Quantum Entanglement
We report two key distribution schemes achieved by swapping quantum
entanglement. Using two Bell states, two bits of secret key can be shared
between two distant parties that play symmetric and equal roles. We also
address eavesdropping attacks against the schemes.Comment: 4 pages, 2 figures, 3 tables. The revised version will appear in
Phys. Rev.
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A QoS monitoring system in a heterogeneous multi-domain DVB-H platform
The MobileTV, IPTV, and DVB standards (DVB-H/T) have been defined to offer mobile users interactive multimedia services with quality of service (QoS) consistency analogous to TV services. However, the market has yet to provide effective and economical solutions for the real-time delivery of such services to the corresponding transmitters over multi-domain IP networks. The monitoring system proposed in this paper enables the QoS in the IP networks involved in the delivery of real-time multimedia content to the transmitters to be ascertained. The system utilizes the QoS parameters defined in MPEG-2 Transport Streams to detect problems occurring in the heterogeneous multi-domain IP networks. The ability to detect problems having an adverse effect on QoS allows appropriate control actions to be determined to recover the QoS across the composite IP network. The design and implementation of the proposed QoS-Monitoring system (QoS-MS) is presented, followed by analysis of experimental results that demonstrate the feasibility of the system
Unitary transformation for the system of a particle in a linear potential
A unitary operator which relates the system of a particle in a linear
potential with time-dependent parameters to that of a free particle, has been
given. This operator, closely related to the one which is responsible for the
existence of coherent states for a harmonic oscillator, is used to find a
general wave packet described by an Airy function. The kernel (propagator) and
a complete set of Hermite-Gaussian type wave functions are also given.Comment: Europhysics Letters (in press
Massive star evolution in close binaries:conditions for homogeneous chemical evolution
We investigate the impact of tidal interactions, before any mass transfer, on
various properties of the stellar models. We study the conditions for obtaining
homogeneous evolution triggered by tidal interactions, and for avoiding any
Roche lobe overflow during the Main-Sequence phase. We consider the case of
rotating stars computed with a strong coupling mediated by an interior magnetic
field. In models without any tidal interaction (single stars and wide
binaries), homogeneous evolution in solid body rotating models is obtained when
two conditions are realized: the initial rotation must be high enough, the loss
of angular momentum by stellar winds should be modest. This last point favors
metal-poor fast rotating stars. In models with tidal interactions, homogeneous
evolution is obtained when rotation imposed by synchronization is high enough
(typically a time-averaged surface velocities during the Main-Sequence phase
above 250 km s), whatever the mass losses. In close binaries, mixing is
stronger at higher than at lower metallicities. Homogeneous evolution is thus
favored at higher metallicities. Roche lobe overflow avoidance is favored at
lower metallicities due to the fact that stars with less metals remain more
compact. We study also the impact of different processes for the angular
momentum transport on the surface abundances and velocities in single and close
binaries. In models where strong internal coupling is assumed, strong surface
enrichments are always associated to high surface velocities in binary or
single star models. In contrast, models computed with mild coupling may produce
strong surface enrichments associated to low surface velocities. Close binary
models may be of interest for explaining homogeneous massive stars, fast
rotating Wolf-Rayet stars, and progenitors of long soft gamma ray bursts, even
at high metallicities.Comment: 21 pages, 13 figures, 3 tables, accepted for publication in Astronomy
and Astrophysic
Determining SUSY Parameters in Chargino Pair-Production in Collisions
In most supersymmetric theories, charginos , mixtures
of charged color-neutral gauginos and higgsinos, belong to the class of the
lightest supersymmetric particles. They are easy to observe at
colliders. By measuring the total cross sections and the left-right asymmetries
with polarized electron beams in , the chargino masses and the gaugino-higgsino mixing angles can be
determined. From these observables the fundamental SUSY parameters can be
derived: the SU(2) gaugino mass , the modulus and
of the higgsino mass parameter, and , the ratio of the
vacuum expectation values of the two neutral Higgs doublet fields. The
solutions are unique; the CP-violating phase can be determined
uniquely by analyzing effects due to the normal polarization of the charginos.Comment: 20 pages, 4 figures, uses axodraw.st
Close binary evolution I. The tidally induced shear mixing in rotating binaries
We study how tides in a binary system induce some specific internal shear
mixing, able to substantially modify the evolution of close binaries prior to
mass transfer. We construct numerical models accounting for tidal interactions,
meridional circulation, transport of angular momentum, shears and horizontal
turbulence and consider a variety of orbital periods and initial rotation
velocities. Depending on orbital periods and rotation velocities, tidal effects
may spin down (spin down Case) or spin up (spin up Case) the axial rotation. In
both cases, tides may induce a large internal differential rotation. The
resulting tidally induced shear mixing (TISM) is so efficient that the internal
distributions of angular velocity and chemical elements are greatly influenced.
The evolutionary tracks are modified, and in both cases of spin down and spin
up, large amounts of nitrogen can be transported to the stellar surfaces before
any binary mass transfer. Meridional circulation, when properly treated as an
advection, always tends to counteract the tidal interaction, tending to spin up
the surface when it is braked down and vice versa. As a consequence, the times
needed for the axial angular velocity to become equal to the orbital angular
velocity may be larger than given by typical synchronization timescales. Also,
due to meridional circulation some differential rotation remains in tidally
locked binary systems.Comment: 10 pages, 18 figures, Accepted for publication in Astronomy and
Astrophysic
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