1,047 research outputs found
Collisional Semiclassical Aproximations in Phase-Space Representation
The Gaussian Wave-Packet phase-space representation is used to show that the
expansion in powers of of the quantum Liouville propagator leads, in
the zeroth order term, to results close to those obtained in the statistical
quasiclassical method of Lee and Scully in the Weyl-Wigner picture. It is also
verified that propagating the Wigner distribution along the classical
trajectories the amount of error is less than that coming from propagating the
Gaussian distribution along classical trajectories.Comment: 20 pages, REVTEX, no figures, 3 tables include
Timed Consistent Network Updates
Network updates such as policy and routing changes occur frequently in
Software Defined Networks (SDN). Updates should be performed consistently,
preventing temporary disruptions, and should require as little overhead as
possible. Scalability is increasingly becoming an essential requirement in SDN.
In this paper we propose to use time-triggered network updates to achieve
consistent updates. Our proposed solution requires lower overhead than existing
update approaches, without compromising the consistency during the update. We
demonstrate that accurate time enables far more scalable consistent updates in
SDN than previously available. In addition, it provides the SDN programmer with
fine-grained control over the tradeoff between consistency and scalability.Comment: This technical report is an extended version of the paper "Timed
Consistent Network Updates", which was accepted to the ACM SIGCOMM Symposium
on SDN Research (SOSR) '15, Santa Clara, CA, US, June 201
An Optimal Self-Stabilizing Firing Squad
Consider a fully connected network where up to processes may crash, and
all processes start in an arbitrary memory state. The self-stabilizing firing
squad problem consists of eventually guaranteeing simultaneous response to an
external input. This is modeled by requiring that the non-crashed processes
"fire" simultaneously if some correct process received an external "GO" input,
and that they only fire as a response to some process receiving such an input.
This paper presents FireAlg, the first self-stabilizing firing squad algorithm.
The FireAlg algorithm is optimal in two respects: (a) Once the algorithm is
in a safe state, it fires in response to a GO input as fast as any other
algorithm does, and (b) Starting from an arbitrary state, it converges to a
safe state as fast as any other algorithm does.Comment: Shorter version to appear in SSS0
Optical bistability in sideband output modes induced by squeezed vacuum
We consider two-level atoms in a ring cavity interacting with a broadband
squeezed vacuum centered at frequency and an input monochromatic
driving field at frequency . We show that, besides the central mode
(at \o), many other {\em sideband modes} are produced at the output, with
frequencies shifted from by multiples of .
Here we analyze the optical bistability of the two nearest sideband modes, one
red-shifted and the other blue-shifted.Comment: Replaced with final published versio
Dynamical Casimir effect for a massless scalar field between two concentric spherical shells
In this work we consider the dynamical Casimir effect for a massless scalar
field -- under Dirichlet boundary conditions -- between two concentric
spherical shells. We obtain a general expression for the average number of
particle creation, for an arbitrary law of radial motion of the spherical
shells, using two distinct methods: by computing the density operator of the
system and by calculating the Bogoliubov coefficients. We apply our general
expression to breathing modes: when only one of the shells oscillates and when
both shells oscillate in or out of phase. We also analyze the number of
particle production and compare it with the results for the case of plane
geometry.Comment: Final version. To apear in Physical Review
Whatâs so bad about scientism?
In their attempt to defend philosophy from accusations of uselessness made by prominent scientists, such as Stephen Hawking, some philosophers respond with the charge of âscientism.â This charge makes endorsing a scientistic stance, a mistake by definition. For this reason, it begs the question against these critics of philosophy, or anyone who is inclined to endorse a scientistic stance, and turns the scientism debate into a verbal dispute. In this paper, I propose a different definition of scientism, and thus a new way of looking at the scientism debate. Those philosophers who seek to defend philosophy against accusations of uselessness would do philosophy a much better service, I submit, if they were to engage with the definition of scientism put forth in this paper, rather than simply make it analytic that scientism is a mistake
The Wigner function associated to the Rogers-Szego polynomials
We show here that besides the well known Hermite polynomials, the q-deformed
harmonic oscillator algebra admits another function space associated to a
particular family of q-polynomials, namely the Rogers-Szego polynomials. Their
main properties are presented, the associated Wigner function is calculated and
its properties are discussed. It is shown that the angle probability density
obtained from the Wigner function is a well-behaved function defined in the
interval [-Pi,Pi), while the action probability only assumes integer values
greater or equal than zero. It is emphasized the fact that the width of the
angle probability density is governed by the free parameter q characterizing
the polynomial.Comment: 12 pages, 2 (mathemathica) figure
- âŠ