948 research outputs found
Hamiltonians separable in cartesian coordinates and third-order integrals of motion
We present in this article all Hamiltonian systems in E(2) that are separable
in cartesian coordinates and that admit a third-order integral, both in quantum
and in classical mechanics. Many of these superintegrable systems are new, and
it is seen that there exists a relation between quantum superintegrable
potentials, invariant solutions of the Korteweg-De Vries equation and the
Painlev\'e transcendents.Comment: 19 pages, Will be published in J. Math. Phy
Fundamental limitations on "warp drive" spacetimes
"Warp drive" spacetimes are useful as "gedanken-experiments" that force us to
confront the foundations of general relativity, and among other things, to
precisely formulate the notion of "superluminal" communication. We verify the
non-perturbative violation of the classical energy conditions of the Alcubierre
and Natario warp drive spacetimes and apply linearized gravity to the
weak-field warp drive, testing the energy conditions to first and second order
of the non-relativistic warp-bubble velocity. We are primarily interested in a
secondary feature of the warp drive that has not previously been remarked upon,
if it could be built, the warp drive would be an example of a "reaction-less
drive". For both the Alcubierre and Natario warp drives we find that the
occurrence of significant energy condition violations is not just a high-speed
effect, but that the violations persist even at arbitrarily low speeds.
An interesting feature of this construction is that it is now meaningful to
place a finite mass spaceship at the center of the warp bubble, and compare the
warp field energy with the mass-energy of the spaceship. There is no hope of
doing this in Alcubierre's original version of the warp-field, since by
definition the point in the center of the warp bubble moves on a geodesic and
is "massless". That is, in Alcubierre's original formalism and in the Natario
formalism the spaceship is always treated as a test particle, while in the
linearized theory we can treat the spaceship as a finite mass object. For both
the Alcubierre and Natario warp drives we find that even at low speeds the net
(negative) energy stored in the warp fields must be a significant fraction of
the mass of the spaceship.Comment: 18 pages, Revtex4. V2: one reference added, some clarifying comments
and discussion, no physics changes, accepted for publication in Classical and
Quantum Gravit
Divide and concur: A general approach to constraint satisfaction
Many difficult computational problems involve the simultaneous satisfaction
of multiple constraints which are individually easy to satisfy. Such problems
occur in diffractive imaging, protein folding, constrained optimization (e.g.,
spin glasses), and satisfiability testing. We present a simple geometric
framework to express and solve such problems and apply it to two benchmarks. In
the first application (3SAT, a boolean satisfaction problem), the resulting
method exhibits similar performance scaling as a leading context-specific
algorithm (walksat). In the second application (sphere packing), the method
allowed us to find improved solutions to some old and well-studied optimization
problems. Based upon its simplicity and observed efficiency, we argue that this
framework provides a competitive alternative to stochastic methods such as
simulated annealing.Comment: 4 pages, 2 figure
Serologic evidence for the presence in Pteropus bats of a paramyxovirus related to equine morbillivirus.
Two outbreaks of a previously unknown disease in horses and humans occurred in Queensland in 1994. The outbreaks occurred within 1 month of each other in Brisbane and Mackay, which are approximately 1000 km apart. In the Brisbane incident, 21 horses were infected of which 14 died or were euthanized after severe clinical signs of an acute
respiratory disease. Two human cases were in patients with less well defined clinical signs; one patient died (1,2). In the Mackay incident two horses became seriously ill and died, and one person also died (3). Although it is now known that the two outbreaks occurred in August and September 1994, knowledge of the Mackay outbreak did not occur until late 1995 when the infected person died of a relapsing encephalitis. The name equine morbillivirus (EMV) has been proposed for a paramyxovirus isolated from four of the Brisbane horses and the first patient who died (2)
Surface stresses on a thin shell surrounding a traversable wormhole
We match an interior solution of a spherically symmetric traversable wormhole
to a unique exterior vacuum solution, with a generic cosmological constant, at
a junction interface, and the surface stresses on the thin shell are deduced.
In the spirit of minimizing the usage of exotic matter we determine regions in
which the weak and null energy conditions are satisfied on the junction
surface. The characteristics and several physical properties of the surface
stresses are explored, namely, regions where the sign of the tangential surface
pressure is positive and negative (surface tension) are determined. This is
done by expressing the tangential surface pressure as a function of several
parameters, namely, that of the matching radius, the redshift parameter, the
surface energy density and of the generic cosmological constant. An equation
governing the behavior of the radial pressure across the junction surface is
also deduced.Comment: 24 pages, 11 figures, LaTeX2e, IOP style files. Accepted for
publication in Classical and Quantum Gravity. V2: Four references added, now
25 page
Singularity confinement and algebraic integrability
Two important notions of integrability for discrete mappings are algebraic
integrability and singularity confinement, have been used for discrete
mappings. Algebraic integrability is related to the existence of sufficiently
many conserved quantities whereas singularity confinement is associated with
the local analysis of singularities. In this paper, the relationship between
these two notions is explored for birational autonomous mappings. Two types of
results are obtained: first, algebraically integrable mappings are shown to
have the singularity confinement property. Second, a proof of the non-existence
of algebraic conserved quantities of discrete systems based on the lack of
confinement property is given.Comment: 18 pages, no figur
Superintegrability with third order invariants in quantum and classical mechanics
We consider here the coexistence of first- and third-order integrals of
motion in two dimensional classical and quantum mechanics. We find explicitly
all potentials that admit such integrals, and all their integrals. Quantum
superintegrable systems are found that have no classical analog, i.e. the
potentials are proportional to \hbar^2, so their classical limit is free
motion.Comment: 15 page
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Landmine detection and imaging using Micropower Impulse Radar (MIR)
The Lawrence Livermore National Laboratory (LLNL) has developed radar and imaging technologies with potential applications in mine detection by the armed forces and other agencies involved in determining efforts. These new technologies use a patented ultra-wideband (impulse) radar technology that is compact, low-cost, and low power. Designated as Micropower hnpulse Radar, these compact, self-contained radars can easily be assembled into arrays to form complete ground penetrating radar imaging systems. LLNL has also developed tomographic reconstruction and signal processing software capable of producing high-resolution 2-D and 3-D images of objects buried in materials like soil or concrete from radar data. Preliminary test results have shown that a radar imaging system using these technologies has the ability to image both metallic and plastic land mine surrogate targets buried in 5 to 10 cm of moist soil. In dry soil, the system can detect buried objects to a depth of 30 cm and more. This report describes our initial test results and plans for future work
Remarks on the notion of quantum integrability
We discuss the notion of integrability in quantum mechanics. Starting from a
review of some definitions commonly used in the literature, we propose a
different set of criteria, leading to a classification of models in terms of
different integrability classes. We end by highlighting some of the expected
physical properties associated to models fulfilling the proposed criteria.Comment: 22 pages, no figures, Proceedings of Statphys 2
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