4,491 research outputs found
Spinning branes in Riemann-Cartan spacetime
We use the conservation law of the stress-energy and spin tensors to study
the motion of massive brane-like objects in Riemann-Cartan geometry. The
world-sheet equations and boundary conditions are obtained in a manifestly
covariant form. In the particle case, the resultant world-line equations turn
out to exhibit a novel spin-curvature coupling. In particular, the spin of a
zero-size particle does not couple to the background curvature. In the string
case, the world-sheet dynamics is studied for some special choices of spin and
torsion. As a result, the known coupling to the Kalb-Ramond antisymmetric
external field is obtained. Geometrically, the Kalb-Ramond field has been
recognized as a part of the torsion itself, rather than the torsion potential
The Environmental Implications of an Emerging Energy Technology: Photovoltaic Solar Cells – A Study of the Toxic Aspects
In-flight dissipation as a mechanism to suppress Fermi acceleration
Some dynamical properties of time-dependent driven elliptical-shaped billiard
are studied. It was shown that for the conservative time-dependent dynamics the
model exhibits the Fermi acceleration [Phys. Rev. Lett. 100, 014103 (2008)]. On
the other hand, it was observed that damping coefficients upon collisions
suppress such phenomenon [Phys. Rev. Lett. 104, 224101 (2010)]. Here, we
consider a dissipative model under the presence of in-flight dissipation due to
a drag force which is assumed to be proportional to the square of the
particle's velocity. Our results reinforce that dissipation leads to a phase
transition from unlimited to limited energy growth. The behaviour of the
average velocity is described using scaling arguments.Comment: 4 pages, 5 figure
A Backtracking-Based Algorithm for Computing Hypertree-Decompositions
Hypertree decompositions of hypergraphs are a generalization of tree
decompositions of graphs. The corresponding hypertree-width is a measure for
the cyclicity and therefore tractability of the encoded computation problem.
Many NP-hard decision and computation problems are known to be tractable on
instances whose structure corresponds to hypergraphs of bounded
hypertree-width. Intuitively, the smaller the hypertree-width, the faster the
computation problem can be solved. In this paper, we present the new
backtracking-based algorithm det-k-decomp for computing hypertree
decompositions of small width. Our benchmark evaluations have shown that
det-k-decomp significantly outperforms opt-k-decomp, the only exact hypertree
decomposition algorithm so far. Even compared to the best heuristic algorithm,
we obtained competitive results as long as the hypergraphs are not too large.Comment: 19 pages, 6 figures, 3 table
Optimal two-qubit gate for generation of random bipartite entanglement
We numerically study protocols consisting of repeated applications of two
qubit gates used for generating random pure states. A necessary number of steps
needed in order to generate states displaying bipartite entanglement typical of
random states is obtained. For generic two qubit entangling gate the decay rate
of purity is found to scale as and therefore of order steps
are necessary to reach random bipartite entanglement. We also numerically
identify the optimal two qubit gate for which the convergence is the fastest.
Perhaps surprisingly, applying the same good two qubit gate in addition to a
random single qubit rotations at each step leads to a faster generation of
entanglement than applying a random two qubit transformation at each step.Comment: 9 pages, 9 PS figures; published versio
Classical String in Curved Backgrounds
The Mathisson-Papapetrou method is originally used for derivation of the
particle world line equation from the covariant conservation of its
stress-energy tensor. We generalize this method to extended objects, such as a
string. Without specifying the type of matter the string is made of, we obtain
both the equations of motion and boundary conditions of the string. The world
sheet equations turn out to be more general than the familiar minimal surface
equations. In particular, they depend on the internal structure of the string.
The relevant cases are classified by examining canonical forms of the effective
2-dimensional stress-energy tensor. The case of homogeneously distributed
matter with the tension that equals its mass density is shown to define the
familiar Nambu-Goto dynamics. The other three cases include physically relevant
massive and massless strings, and unphysical tahyonic strings.Comment: 12 pages, REVTeX 4. Added a note and one referenc
Topological interactions in systems of mutually interlinked polymer rings
The topological interaction arising in interlinked polymeric rings such as
DNA catenanes is considered. More specifically, the free energy for a pair of
linked random walk rings is derived where the distance between two segments
each of which is part of a different ring is kept constant. The topology
conservation is imposed by the Gauss invariant. A previous approach (M.Otto,
T.A. Vilgis, Phys.Rev.Lett. {\bf 80}, 881 (1998)) to the problem is refined in
several ways. It is confirmed, that asymptotically, i.e. for large
where is average size of single random walk ring, the effective
topological interaction (free energy) scales .Comment: 16 pages, 3 figur
Anomalous diffusion and dynamical localization in a parabolic map
We study numerically classical and quantum dynamics of a piecewise parabolic
area preserving map on a cylinder which emerges from the bounce map of
elongated triangular billiards. The classical map exhibits anomalous diffusion.
Quantization of the same map results in a system with dynamical localization
and pure point spectrum.Comment: 4 pages in RevTeX (4 ps-figures included
Some properties of WKB series
We investigate some properties of the WKB series for arbitrary analytic
potentials and then specifically for potentials ( even), where more
explicit formulae for the WKB terms are derived. Our main new results are: (i)
We find the explicit functional form for the general WKB terms ,
where one has only to solve a general recursion relation for the rational
coefficients. (ii) We give a systematic algorithm for a dramatic simplification
of the integrated WKB terms that enter the energy
eigenvalue equation. (iii) We derive almost explicit formulae for the WKB terms
for the energy eigenvalues of the homogeneous power law potentials , where is even. In particular, we obtain effective algorithms to
compute and reduce the terms of these series.Comment: 18 pages, submitted to Journal of Physics A: Mathematical and Genera
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