1,678 research outputs found
Full abstraction for fair testing in CCS
In previous work with Pous, we defined a semantics for CCS which may both be
viewed as an innocent presheaf semantics and as a concurrent game semantics. It
is here proved that a behavioural equivalence induced by this semantics on CCS
processes is fully abstract for fair testing equivalence. The proof relies on a
new algebraic notion called playground, which represents the 'rule of the
game'. From any playground, two languages, equipped with labelled transition
systems, are derived, as well as a strong, functional bisimulation between
them.Comment: 15 pages, to appear in CALCO '13. To appear Lecture notes in computer
science (2013
Growth, processing, and optical properties of epitaxial Er_2O_3 on silicon
Erbium-doped materials have been investigated for generating and amplifying light in low-power chip-scale optical networks on silicon, but several effects limit their performance in dense microphotonic applications. Stoichiometric ionic crystals are a potential alternative that achieve an Er^(3+) density 100× greater. We report the growth, processing, material characterization, and optical properties of single-crystal Er_2O_3 epitaxially grown on silicon. A peak Er^(3+) resonant absorption of 364 dB/cm at 1535nm with minimal background loss places a high limit on potential gain. Using high-quality microdisk resonators, we conduct thorough C/L-band radiative efficiency and lifetime measurements and observe strong upconverted luminescence near 550 and 670 nm
Is life a thermal horizon ?
This talk aims at questioning the vanishing of Unruh temperature for an
inertial observer in Minkovski spacetime with finite lifetime, arguing that in
the non eternal case the existence of a causal horizon is not linked to the
non-vanishing of the acceleration. This is illustrated by a previous result,
the diamonds temperature, that adapts the algebraic approach of Unruh effect to
the finite case.Comment: Proceedings of the conference DICE 2006, Piombino september 200
A Bisognano-Wichmann-like Theorem in a Certain Case of a Non Bifurcate Event Horizon related to an Extreme Reissner-Nordstr\"om Black Hole
Thermal Wightman functions of a massless scalar field are studied within the
framework of a ``near horizon'' static background model of an extremal R-N
black hole. This model is built up by using global Carter-like coordinates over
an infinite set of Bertotti-Robinson submanifolds glued together. The
analytical extendibility beyond the horizon is imposed as constraints on
(thermal) Wightman's functions defined on a Bertotti-Robinson sub manifold. It
turns out that only the Bertotti-Robinson vacuum state, i.e. , satisfies
the above requirement. Furthermore the extension of this state onto the whole
manifold is proved to coincide exactly with the vacuum state in the global
Carter-like coordinates. Hence a theorem similar to Bisognano-Wichmann theorem
for the Minkowski space-time in terms of Wightman functions holds with
vanishing ``Unruh-Rindler temperature''. Furtermore, the Carter-like vacuum
restricted to a Bertotti-Robinson region, resulting a pure state there, has
vanishing entropy despite of the presence of event horizons. Some comments on
the real extreme R-N black hole are given
Quantum macrostatistical picture of nonequilibrium steady states
We employ a quantum macrostatistical treatment of irreversible processes to
prove that, in nonequilibrium steady states, (a) the hydrodynamical observables
execute a generalised Onsager-Machlup process and (b) the spatial correlations
of these observables are generically of long range. The key assumptions behind
these results are a nonequilibrium version of Onsager's regression hypothesis,
together with certain hypotheses of chaoticity and local equilibrium for
hydrodynamical fluctuations.Comment: TeX, 13 page
The quaternary structure of the amidase from Geobacillus pallidus RAPc8 is revealed by its crystal packing
The amidase from Geobacillus pallidus RAPc8, a moderate thermophile, is a member of the nitrilase enzyme superfamily. It converts amides to the corresponding acids and ammonia and has application as an industrial catalyst. RAPc8 amidase has been cloned and functionally expressed in Escherichia coli and has been purified by heat treatment and a number of chromatographic steps. The enzyme was crystallized using the hanging-drop vapour-diffusion method. Crystals produced in the presence of 1.2 M sodium citrate, 400 mM NaCl, 100 mM sodium acetate pH 5.6 were selected for X-ray diffraction studies. A data set having acceptable statistics to 1.96 Å resolution was collected under cryoconditions using an in-house X-ray source. The space group was determined to be primitive cubic P4232, with unit-cell parameter a = 130.49 (±0.05) Å. The structure was solved by molecular replacement using the backbone of the hypothetical protein PH0642 from Pyrococcus horikoshii (PDB code 1j31 ) with all non-identical side chains substituted with alanine as a probe. There is one subunit per asymmetric unit. The subunits are packed as trimers of dimers with D3 point-group symmetry around the threefold axis in such a way that the dimer interface seen in the homologues is preserved
Bondi-Metzner-Sachs symmetry, holography on null-surfaces and area proportionality of "light-slice" entropy
It is shown that certain kinds of behavior, which hitherto were expected to
be characteristic for classical gravity and quantum field theory in curved
spacetime, as the infinite dimensional Bondi-Metzner-Sachs symmetry, holography
on event horizons and an area proportionality of entropy, have in fact an
unnoticed presence in Minkowski QFT. This casts new light on the fundamental
question whether the volume propotionality of heat bath entropy and the
(logarithmically corrected) dimensionless area law obeyed by
localization-induced thermal behavior are different geometric parametrizations
which share a common primordeal algebraic origin. Strong arguments are
presented that these two different thermal manifestations can be directly
related, this is in fact the main aim of this paper. It will be demonstrated
that QFT beyond the Lagrangian quantization setting receives crucial new
impulses from holography onto horizons. The present paper is part of a project
aimed at elucidating the enormous physical range of "modular localization". The
latter does not only extend from standard Hamitonian heat bath thermal states
to thermal aspects of causal- or event- horizons addressed in this paper. It
also includes the recent understanding of the crossing property of formfactors
whose intriguing similarity with thermal properties was, although sometimes
noticed, only sufficiently understood in the modular llocalization setting.Comment: 42 pages, changes, addition of new results and new references, in
this form the paper will appear in Foundations of Physic
Fluctuation-dissipation theorem and the Unruh effect of scalar and Dirac fields
We present a simple and systematic method to calculate the Rindler noise,
which is relevant to the analysis of the Unruh effect, by using the
fluctuation-dissipative theorem. To do this, we calculate the dissipative
coefficient explicitly from the equations of motion of the detector and the
field. This method gives not only the correct answer but also a hint as to the
origin of the apparent statistics inversion effect. Moreover, this method is
generalized to the Dirac field, by using the fermionic fluctuation-dissipation
theorem. We can thus confirm that the fermionic fluctuation-dissipation theorem
is working properly.Comment: 26 page
Diamonds's Temperature: Unruh effect for bounded trajectories and thermal time hypothesis
We study the Unruh effect for an observer with a finite lifetime, using the
thermal time hypothesis. The thermal time hypothesis maintains that: (i) time
is the physical quantity determined by the flow defined by a state over an
observable algebra, and (ii) when this flow is proportional to a geometric flow
in spacetime, temperature is the ratio between flow parameter and proper time.
An eternal accelerated Unruh observer has access to the local algebra
associated to a Rindler wedge. The flow defined by the Minkowski vacuum of a
field theory over this algebra is proportional to a flow in spacetime and the
associated temperature is the Unruh temperature. An observer with a finite
lifetime has access to the local observable algebra associated to a finite
spacetime region called a "diamond". The flow defined by the Minkowski vacuum
of a (four dimensional, conformally invariant) quantum field theory over this
algebra is also proportional to a flow in spacetime. The associated temperature
generalizes the Unruh temperature to finite lifetime observers.
Furthermore, this temperature does not vanish even in the limit in which the
acceleration is zero. The temperature associated to an inertial observer with
lifetime T, which we denote as "diamond's temperature", is 2hbar/(pi k_b
T).This temperature is related to the fact that a finite lifetime observer does
not have access to all the degrees of freedom of the quantum field theory.Comment: One reference correcte
Experiments on a videotape atom chip: fragmentation and transport studies
This paper reports on experiments with ultra-cold rubidium atoms confined in
microscopic magnetic traps created using a piece of periodically-magnetized
videotape mounted on an atom chip. The roughness of the confining potential is
studied with atomic clouds at temperatures of a few microKelvin and at
distances between 30 and 80 microns from the videotape-chip surface. The
inhomogeneities in the magnetic field created by the magnetized videotape close
to the central region of the chip are characterized in this way. In addition,
we demonstrate a novel transport mechanism whereby we convey cold atoms
confined in arrays of videotape magnetic micro-traps over distances as large as
~ 1 cm parallel to the chip surface. This conveying mechanism enables us to
survey the surface of the chip and observe potential-roughness effects across
different regions.Comment: 29 pages, 22 figures
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