176,465 research outputs found
A Minimal Periods Algorithm with Applications
Kosaraju in ``Computation of squares in a string'' briefly described a
linear-time algorithm for computing the minimal squares starting at each
position in a word. Using the same construction of suffix trees, we generalize
his result and describe in detail how to compute in O(k|w|)-time the minimal
k-th power, with period of length larger than s, starting at each position in a
word w for arbitrary exponent and integer . We provide the
complete proof of correctness of the algorithm, which is somehow not completely
clear in Kosaraju's original paper. The algorithm can be used as a sub-routine
to detect certain types of pseudo-patterns in words, which is our original
intention to study the generalization.Comment: 14 page
Finding the Leftmost Critical Factorization on Unordered Alphabet
We present a linear time and space algorithm computing the leftmost critical
factorization of a given string on an unordered alphabet.Comment: 13 pages, 13 figures (accepted to Theor. Comp. Sci.
Little Boxes: A Dynamic Optimization Approach for Enhanced Cloud Infrastructures
The increasing demand for diverse, mobile applications with various degrees
of Quality of Service requirements meets the increasing elasticity of on-demand
resource provisioning in virtualized cloud computing infrastructures. This
paper provides a dynamic optimization approach for enhanced cloud
infrastructures, based on the concept of cloudlets, which are located at
hotspot areas throughout a metropolitan area. In conjunction, we consider
classical remote data centers that are rigid with respect to QoS but provide
nearly abundant computation resources. Given fluctuating user demands, we
optimize the cloudlet placement over a finite time horizon from a cloud
infrastructure provider's perspective. By the means of a custom tailed
heuristic approach, we are able to reduce the computational effort compared to
the exact approach by at least three orders of magnitude, while maintaining a
high solution quality with a moderate cost increase of 5.8% or less
Universal quantum computation and simulation using any entangling Hamiltonian and local unitaries
What interactions are sufficient to simulate arbitrary quantum dynamics in a
composite quantum system? We provide an efficient algorithm to simulate any
desired two-body Hamiltonian evolution using any fixed two-body entangling
n-qubit Hamiltonian and local unitaries. It follows that universal quantum
computation can be performed using any entangling interaction and local unitary
operations.Comment: Added references to NMR refocusing and to earlier work by Leung et al
and Jones and Knil
Oscillatory secular modes: The thermal micropulses
Stars in the narrow mass range of about 2.5 and 3.5 solar masses can develop
a thermally unstable He-burning shell during its ignition phase. We study, from
the point of view secular stability theory, these so called thermal micropulses
and we investigate their properties; the thermal pulses constitute a convenient
conceptual laboratory to look thoroughly into the physical properties of a
helium-burning shell during the whole thermally pulsing episode. Linear
stability analyses were performed on a large number of 3 solar-mass star models
at around the end of their core helium-burning and the beginning of the
double-shell burning phase. The stellar models were not assumed to be in
thermal equilibrium. The thermal mircopulses, and we conjecture all other
thermal pulse episodes encountered by shell-burning stars, can be understood as
the nonlinear finite-amplitude realization of an oscillatory secular
instability that prevails during the whole thermal pulsing episode. Hence, the
cyclic nature of the thermal pulses can be traced back to a linear instability
concept.Comment: To be published - essentially footnote-free - in Astronomy &
Astrophysic
Global bifurcation for the Whitham equation
We prove the existence of a global bifurcation branch of -periodic,
smooth, traveling-wave solutions of the Whitham equation. It is shown that any
subset of solutions in the global branch contains a sequence which converges
uniformly to some solution of H\"older class , . Bifurcation formulas are given, as well as some properties along
the global bifurcation branch. In addition, a spectral scheme for computing
approximations to those waves is put forward, and several numerical results
along the global bifurcation branch are presented, including the presence of a
turning point and a `highest', cusped wave. Both analytic and numerical results
are compared to traveling-wave solutions of the KdV equation
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