8,687 research outputs found
Anomalous kinetics of attractive reactions
We investigate the kinetics of reaction with the local attractive
interaction between opposite species in one spatial dimension. The attractive
interaction leads to isotropic diffusions inside segregated single species
domains, and accelerates the reactions of opposite species at the domain
boundaries. At equal initial densities of and , we analytically and
numerically show that the density of particles (), the size of domains
(), the distance between the closest neighbor of same species
(), and the distance between adjacent opposite species ()
scale in time as , , and respectively. These dynamical exponents form a new
universality class distinguished from the class of uniformly driven systems of
hard-core particles.Comment: 4 pages, 4 figure
The Resonance Peak in SrRuO: Signature of Spin Triplet Pairing
We study the dynamical spin susceptibility, , in the
normal and superconducting state of SrRuO. In the normal state, we find
a peak in the vicinity of in agreement with
recent inelastic neutron scattering (INS) experiments. We predict that for spin
triplet pairing in the superconducting state a {\it resonance peak} appears in
the out-of-plane component of , but is absent in the in-plane component.
In contrast, no resonance peak is expected for spin singlet pairing.Comment: 4 pages, 4 figures, final versio
Kundt spacetimes as solutions of topologically massive gravity
We obtain new solutions of topologically massive gravity. We find the general
Kundt solutions, which in three dimensions are spacetimes admitting an
expansion-free null geodesic congruence. The solutions are generically of
algebraic type II, but special cases are types III, N or D. Those of type D are
the known spacelike-squashed AdS_3 solutions, and of type N are the known AdS
pp-waves or new solutions. Those of types II and III are the first known
solutions of these algebraic types. We present explicitly the Kundt solutions
that are CSI spacetimes, for which all scalar polynomial curvature invariants
are constant, whereas for the general case we reduce the field equations to a
series of ordinary differential equations. The CSI solutions of types II and
III are deformations of spacelike-squashed AdS_3 and the round AdS_3,
respectively.Comment: 30 pages. This material has come from splitting v1 of arXiv:0906.3559
into 2 separate papers. v2: minor changes
Actions of the braid group, and new algebraic proofs of results of Dehornoy and Larue
This article surveys many standard results about the braid group with
emphasis on simplifying the usual algebraic proofs.
We use van der Waerden's trick to illuminate the Artin-Magnus proof of the
classic presentation of the algebraic mapping-class group of a punctured disc.
We give a simple, new proof of the Dehornoy-Larue braid-group trichotomy,
and, hence, recover the Dehornoy right-ordering of the braid group.
We then turn to the Birman-Hilden theorem concerning braid-group actions on
free products of cyclic groups, and the consequences derived by Perron-Vannier,
and the connections with the Wada representations. We recall the very simple
Crisp-Paris proof of the Birman-Hilden theorem that uses the Larue-Shpilrain
technique. Studying ends of free groups permits a deeper understanding of the
braid group; this gives us a generalization of the Birman-Hilden theorem.
Studying Jordan curves in the punctured disc permits a still deeper
understanding of the braid group; this gave Larue, in his PhD thesis,
correspondingly deeper results, and, in an appendix, we recall the essence of
Larue's thesis, giving simpler combinatorial proofs.Comment: 51`pages, 13 figure
Attractiveness of periodic orbits in parametrically forced systemswith time-increasing friction
We consider dissipative one-dimensional systems subject to a periodic force
and study numerically how a time-varying friction affects the dynamics. As a
model system, particularly suited for numerical analysis, we investigate the
driven cubic oscillator in the presence of friction. We find that, if the
damping coefficient increases in time up to a final constant value, then the
basins of attraction of the leading resonances are larger than they would have
been if the coefficient had been fixed at that value since the beginning. From
a quantitative point of view, the scenario depends both on the final value and
the growth rate of the damping coefficient. The relevance of the results for
the spin-orbit model are discussed in some detail.Comment: 30 pages, 6 figure
Enabling Proactive Adaptation through Just-in-time Testing of Conversational Services
Service-based applications (SBAs) will increasingly be composed of third-party services available over the Internet. Reacting to failures of those third-party services by dynamically adapting the SBAs will become a key enabler for ensuring reliability. Determining when to adapt an SBA is especially challenging in the presence of conversational (aka. stateful) services. A conversational service might fail in the middle of an invocation sequence, in which case adapting the SBA might be costly; e.g., due to the necessary state transfer to an alternative service. In this paper we propose just-in-time testing of conversational services as a novel approach to detect potential problems and to proactively trigger adaptations, thereby preventing costly compensation activities. The approach is based on a framework for online testing and a formal test-generation method which guarantees functional correctness for conversational services. The applicability of the approach is discussed with respect to its underlying assumptions and its performance. The benefits of the approach are demonstrated using a realistic example
Symmetries of supergravity black holes
We investigate Killing tensors for various black hole solutions of
supergravity theories. Rotating black holes of an ungauged theory, toroidally
compactified heterotic supergravity, with NUT parameters and two U(1) gauge
fields are constructed. If both charges are set equal, then the solutions
simplify, and then there are concise expressions for rank-2 conformal
Killing-Stackel tensors. These are induced by rank-2 Killing-Stackel tensors of
a conformally related metric that possesses a separability structure. We
directly verify the separation of the Hamilton-Jacobi equation on this
conformally related metric, and of the null Hamilton-Jacobi and massless
Klein-Gordon equations on the "physical" metric. Similar results are found for
more general solutions; we mainly focus on those with certain charge
combinations equal in gauged supergravity, but also consider some other
solutions.Comment: 36 pages; v2: minor changes; v3: slightly shorte
Charged rotating black holes in six-dimensional gauged supergravity
We obtain non-extremal charged rotating black holes in six-dimensional SU(2)
gauged supergravity with two independent angular momenta and one U(1) charge.
These include supersymmetric black holes without naked closed timelike curves.Comment: 9 pages; v2: minor change
Equal charge black holes and seven dimensional gauged supergravity
We present various supergravity black holes of different dimensions with some
U(1) charges set equal in a simple, common form. Black hole solutions of seven
dimensional U(1)^2 gauged supergravity with three independent angular momenta
and two equal U(1) charges are obtained. We investigate the thermodynamics and
the BPS limit of this solution, and find that there are rotating supersymmetric
black holes without naked closed timelike curves. There are also supersymmetric
topological soliton solutions without naked closed timelike curves that have a
smooth geometry.Comment: 24 pages; v2, v3: minor change
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