818 research outputs found
Condensing Nielsen-Olesen strings and the vortex-boson duality in 3+1 and higher dimensions
The vortex-boson (or Abelian-Higgs, XY) duality in 2+1 dimensions
demonstrates that the quantum disordered superfluid is equivalent to an ordered
superconductor and the other way around. Such a duality structure should be
ubiquitous but in 3+1 (and higher) dimensions a precise formulation of the
duality is lacking. The problem is that the topological defects become extended
objects, strings in 3+1D. We argue how the condensate of such vortex strings
must behave from the known physics of the disordered superfluid, namely the
Bose-Mott insulator. A flaw in earlier proposals is repaired, and a more direct
viewpoint, avoiding gauge fields, in terms of the physical supercurrent is laid
out, that also easily generalizes to higher-dimensional and more complicated
systems. Furthermore topological defects are readily identified; we demonstrate
that the Bose-Mott insulator supports line defects, which may be seen in cold
atom experiments.Comment: LaTeX, 25 pages, 5 figures; several revisions and addition
Stochastic Differential Equations for Quantum Dynamics of Spin-Boson Networks
The quantum dynamics of open many-body systems poses a challenge for
computational approaches. Here we develop a stochastic scheme based on the
positive P phase-space representation to study the nonequilibrium dynamics of
coupled spin-boson networks that are driven and dissipative. Such problems are
at the forefront of experimental research in cavity and solid state
realizations of quantum optics, as well as cold atom physics, trapped ions and
superconducting circuits. We demonstrate and test our method on a driven,
dissipative two-site system, each site involving a spin coupled to a photonic
mode, with photons hopping between the sites, where we find good agreement with
Monte Carlo Wavefunction simulations. In addition to numerically reproducing
features recently observed in an experiment [Phys. Rev. X 4, 031043 (2014)], we
also predict a novel steady state quantum dynamical phase transition for an
asymmetric configuration of drive and dissipation.Comment: 15 pages, 8 figure
The Berry phase of dislocations in graphene and valley conserving decoherence
We demonstrate that dislocations in the graphene lattice give rise to
electron Berry phases equivalent to quantized values {0,1/3,-1/3} in units of
the flux quantum, but with an opposite sign for the two valleys. An elementary
scale consideration of a graphene Aharonov-Bohm ring equipped with valley
filters on both terminals, encircling a dislocation, says that in the regime
where the intervalley mean free path is large compared to the intravalley phase
coherence length, such that the valley quantum numbers can be regarded as
conserved on the relevant scale, the coherent valley-polarized currents
sensitive to the topological phases have to traverse the device many times
before both valleys contribute, and this is not possible at intermediate
temperatures where the latter length becomes of order of the device size, thus
leading to an apparent violation of the basic law of linear transport that
magnetoconductance is even in the applied flux. We discuss this discrepancy in
the Feynman path picture of dephasing, when addressing the transition from
quantum to classical dissipative transport. We also investigate this device in
the scattering matrix formalism, accounting for the effects of decoherence by
the Buttiker dephasing voltage probe type model which conserves the valleys,
where the magnetoconductance remains even in the flux, also when different
decoherence times are allowed for the individual, time reversal connected,
valleys.Comment: 14 pages, 7 figures; revised text, added figure, accepted for
publication by PR
Efficient Enumeration of Non-Equivalent Squares in Partial Words with Few Holes
International audienceA partial word is a word with holes (also called don't cares: special symbols which match any symbol). A p-square is a partial word matching at least one standard square without holes (called a full square). Two p-squares are called equivalent if they match the same sets of full squares. Denote by psquares(T) the number of non-equivalent p-squares which are subwords of a partial word T. Let PSQUARES k (n) be the maximum value of psquares(T) over all partial words of length n with k holes. We show asympthotically tight bounds: c1 · min(nk 2 , n 2) ≤ PSQUARES k (n) ≤ c2 · min(nk 2 , n 2) for some constants c1, c2 > 0. We also present an algorithm that computes psquares(T) in O(nk 3) time for a partial word T of length n with k holes. In particular, our algorithm runs in linear time for k = O(1) and its time complexity near-matches the maximum number of non-equivalent p-squares
Non-destructive testing (NDT) and inspection of the blast furnace refractory lining by stress wave propagation technique
Generally speaking, a blast furnace is the main equipment in Ironmaking and the campaign life of a blast furnace depends on its remaining hearth refractory lining [1]. The Acousto Ultrasonic- Echo (AU-E) is a stress wave propagation technique that uses time and frequency data analysis to determine coarse-grained material thicknesses, such as refractory and stave materials in operating blast furnaces. A mechanical impact on the surface of the structure (via a hammer or a mechanical impactor) generates a stress pulse, propagating into the furnace layers. The wave is partially reflected by the change in refractory layer properties, but the main pulse propagates through the solid refractory layers until its energy dissipates. The signal is mainly reflected by the refractory/ molten metal interface, or alternatively by the build up/air or molten metal interfaces that are formed between internal layers or at external boundaries. In this paper, we describe the AU-E technique in details and demonstrate a few results that are indicative of the technique reliability and accuracy
Expansion of neopterin and beta2-microglobulin in cerebrospinal fluid reaches maximum levels early and late in the course of human immunodeficiency virus infection
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Sets Represented as the Length-n Factors of a Word
In this paper we consider the following problems: how many different subsets
of Sigma^n can occur as set of all length-n factors of a finite word? If a
subset is representable, how long a word do we need to represent it? How many
such subsets are represented by words of length t? For the first problem, we
give upper and lower bounds of the form alpha^(2^n) in the binary case. For the
second problem, we give a weak upper bound and some experimental data. For the
third problem, we give a closed-form formula in the case where n <= t < 2n.
Algorithmic variants of these problems have previously been studied under the
name "shortest common superstring"
Science-Driven Entrepreneurship in the Islamic World
The paper under review delineates the scenario, perspective and the future trends of science –Driven Entrepreneurship in the Islamic world. It digs outthe factors causing the sluggishness and suggests the plan of action for the renaissance of indigenous science –driven entrepreneurship with grafting ofthe modern scientific high tech marketing techniques on it. The paper highlights that entrepreneurship is both the cause and consequence ofeconomic growth, technological advancement and conceptual innovations and they are interknitted, interconnected and interwoven with one-another.The economic, political, social and religious components of the society influence the science driven entrepreneurship in the Islamic World. It depictsthe present situation and flashes back on the glaring Islamic era when Islamic Civilization was a beacon light and an icon scientific innovation,technological advancement and an improved entrepreneurship of that time, for the rest of the world. It was the time when almost the important seats ofscientific centers were filled with Muslim Scientists and the world was hovered over with the lucrative Muslim trading networks. The paperdiagnoses the pitfalls that caused the Islamic World lagging behind and provides food for the thoughts of scientists and experts pertaining to theEntrepreneurship Research and Policy Networks, the world over. It points out that all leading Muslim Scientists should have been more conscious andcommitted to commercializing their scientific and technological productions. It is high time for the Muslim Think Tank to synergize the efforts for thepromotion and development of scientific knowledge, technological advancement and an improved entrepreneurship. The paper concludes bysuggesting a tetra-pod model for the social reengineering process to improve the science driven entrepreneurship in the World of Islam
Factorization in Formal Languages
We consider several novel aspects of unique factorization in formal
languages. We reprove the familiar fact that the set uf(L) of words having
unique factorization into elements of L is regular if L is regular, and from
this deduce an quadratic upper and lower bound on the length of the shortest
word not in uf(L). We observe that uf(L) need not be context-free if L is
context-free.
Next, we consider variations on unique factorization. We define a notion of
"semi-unique" factorization, where every factorization has the same number of
terms, and show that, if L is regular or even finite, the set of words having
such a factorization need not be context-free. Finally, we consider additional
variations, such as unique factorization "up to permutation" and "up to
subset"
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