11,561 research outputs found
Dissipative preparation of entanglement in optical cavities
We propose a novel scheme for the preparation of a maximally entangled state
of two atoms in an optical cavity. Starting from an arbitrary initial state, a
singlet state is prepared as the unique fixed point of a dissipative quantum
dynamical process. In our scheme, cavity decay is no longer undesirable, but
plays an integral part in the dynamics. As a result, we get a qualitative
improvement in the scaling of the fidelity with the cavity parameters. Our
analysis indicates that dissipative state preparation is more than just a new
conceptual approach, but can allow for significant improvement as compared to
preparation protocols based on coherent unitary dynamics.Comment: 4 pages, 2 figure
Mesoscale structure of 11-20 km winds
Wind speed and direction profiles by tracking spherical superpressure balloon
Interhemispheric comparison of atmospheric circulation features as evaluated from Nimbus satellite data. A comparison of the structure and flow characteristics of the upper troposphere and stratosphere of the Northern and Southern Hemispheres
The general circulations of the Northern and Southern Hemispheres are compared with regard to the upper troposphere and stratosphere, using atmospheric structure obtained from multi-channel radiance data from the satellite infrared spectrometer instrument aboard the Nimbus 3 spacecraft. The inter-hemispheric comparisons are based on two months of data (one summer month and one winter month) in each hemisphere. Topics studied include: (1) mean meridional circulation in the Southern Hemisphere stratosphere; (2) magnitude and distribution of tropospheric eddy heat flux; (3) relative importance of standing and transient eddies in the two hemispheres; (4) magnitudes of energy cycle components; and (5) the relation of vortex structure to the breakdown climatology of the Antarctic stratospheric polar vortex
Automatic Error Localization for Software using Deductive Verification
Even competent programmers make mistakes. Automatic verification can detect
errors, but leaves the frustrating task of finding the erroneous line of code
to the user. This paper presents an automatic approach for identifying
potential error locations in software. It is based on a deductive verification
engine, which detects errors in functions annotated with pre- and
post-conditions. Using an automatic theorem prover, our approach finds
expressions in the code that can be modified such that the program satisfies
its specification. Scalability is achieved by analyzing each function in
isolation. We have implemented our approach in the widely used Frama-C
framework and present first experimental results. This is an extended version
of [8], featuring an additional appendix.Comment: This is an extended version of [8], featuring an additional appendi
On the Observation of Phase Transitions in Collisions of Elementary Matter
We investigate the excitation function of directed flow, which can provide a
clear signature of the creation of the QGP and demonstrate that the minimum of
the directed flow does not correspond to the softest point of the EoS for
isentropic expansion. A novel technique measuring the compactness is introduced
to determine the QGP transition in relativistic-heavy ion collisions: The QGP
transition will lead to higher compression and therefore to higher compactness
of the source in coordinate space. This effect can be observed by pion
interferometry. We propose to measure the compactness of the source in the
appropriate principal axis frame of the compactness tensor in coordinate space.Comment: LaTeX, 8 pages, 6 figures, Conference proceedings to CRIS 2000, 3rd
Catania Relativistic Ion Studie
Explaining Violation Traces with Finite State Natural Language Generation Models
An essential element of any verification technique is that of identifying and
communicating to the user, system behaviour which leads to a deviation from the
expected behaviour. Such behaviours are typically made available as long traces
of system actions which would benefit from a natural language explanation of
the trace and especially in the context of business logic level specifications.
In this paper we present a natural language generation model which can be used
to explain such traces. A key idea is that the explanation language is a CNL
that is, formally speaking, regular language susceptible transformations that
can be expressed with finite state machinery. At the same time it admits
various forms of abstraction and simplification which contribute to the
naturalness of explanations that are communicated to the user
Entropy Production in Collisions of Relativistic Heavy Ions -- a signal for Quark-Gluon Plasma phase transition?
Entropy production in the compression stage of heavy ion collisions is
discussed within three distinct macroscopic models (i.e. generalized RHTA,
geometrical overlap model and three-fluid hydrodynamics). We find that within
these models \sim 80% or more of the experimentally observed final-state
entropy is created in the early stage. It is thus likely followed by a nearly
isentropic expansion. We employ an equation of state with a first-order phase
transition. For low net baryon density, the entropy density exhibits a jump at
the phase boundary. However, the excitation function of the specific entropy
per net baryon, S/A, does not reflect this jump. This is due to the fact that
for final states (of the compression) in the mixed phase, the baryon density
\rho_B increases with \sqrt{s}, but not the temperature T. Calculations within
the three-fluid model show that a large fraction of the entropy is produced by
nuclear shockwaves in the projectile and target. With increasing beam energy,
this fraction of S/A decreases. At \sqrt{s}=20 AGeV it is on the order of the
entropy of the newly produced particles around midrapidity. Hadron ratios are
calculated for the entropy values produced initially at beam energies from 2 to
200 AGeV.Comment: 17 pages, 8 figures, uses epsfig.sty; Submitted to Nucl.Phys.
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