19,139 research outputs found
The covert set-cover problem with application to Network Discovery
We address a version of the set-cover problem where we do not know the sets
initially (and hence referred to as covert) but we can query an element to find
out which sets contain this element as well as query a set to know the
elements. We want to find a small set-cover using a minimal number of such
queries. We present a Monte Carlo randomized algorithm that approximates an
optimal set-cover of size within factor with high probability
using queries where is the input size.
We apply this technique to the network discovery problem that involves
certifying all the edges and non-edges of an unknown -vertices graph based
on layered-graph queries from a minimal number of vertices. By reducing it to
the covert set-cover problem we present an -competitive Monte
Carlo randomized algorithm for the covert version of network discovery problem.
The previously best known algorithm has a competitive ratio of and therefore our result achieves an exponential improvement
Soliton solution in dilaton-Maxwell gravity
The inverse scattering problem method application to construction of exact
solution for Maxwell dilaton gravity system ia considered. By use of Belinsky
and Zakharov L - A pair the solution of the theory is constructed. The rotating
Kerr - like configuration with NUT - parameter is obtained.Comment: 8 pages in LaTex; published in Gen. Rel. Grav. pp. 32 (2000)
2219-222
Gapless points of dimerized quantum spin chains: analytical and numerical studies
We study the locations of the gapless points which occur for quantum spin
chains of finite length (with a twisted boundary condition) at particular
values of the nearest neighbor dimerization, as a function of the spin S and
the number of sites. For strong dimerization and large values of S, a tunneling
calculation reproduces the same results as those obtained from more involved
field theoretic methods using the non-linear sigma-model approach. A different
analytical calculation of the matrix element between the two Neel states gives
a set of gapless points; for strong dimerization, these differ significantly
from the tunneling values. Finally, the exact diagonalization method for a
finite number of sites yields a set of gapless points which are in good
agreement with the Neel state calculations for all values of the dimerization,
but the agreement with the tunneling values is not very good even for large S.
This raises questions about possible corrections to the tunneling results.Comment: Revtex4, 10 pages including 5 figure
Taxation by Auction: Fund-Raising by 19th Century Indian Guilds
We describe a unique institution used by 19th century Indian guilds to raise funds: The guild members agreed that on a particular day all but one of their shops would be shut. An auction would be held to determine which one shop would remain open, and the winning bid would go to the guild funds. We compare this “taxation by auction” mechanism with more conventional tax schemes and show that under certain conditions, not only will a majority of the guild members prefer to be taxed via an auction, but that this form of taxation will be more equitable than other forms.Auctions, Fund-Raising, Indian Guilds, Taxation
Counterterms, critical gravity and holography
We consider counterterms for odd dimensional holographic CFTs. These
counterterms are derived by demanding cut-off independence of the CFT partition
function on and . The same choice of counterterms
leads to a cut-off independent Schwarzschild black hole entropy. When treated
as independent actions, these counterterm actions resemble critical theories of
gravity, i.e., higher curvature gravity theories where the additional massive
spin-2 modes become massless. Equivalently, in the context of AdS/CFT, these
are theories where at least one of the central charges associated with the
trace anomaly vanishes. Connections between these theories and logarithmic CFTs
are discussed. For a specific choice of parameters, the theories arising from
counterterms are non-dynamical and resemble a DBI generalization of gravity.
For even dimensional CFTs, analogous counterterms cancel log-independent
cut-off dependence.Comment: 28 pages, v2: references added, v3: minor changes, version to appear
in PR
Chiral Dirac fermions on the lattice using Geometric Discretisation
A new approach to the problem of doubling is presented with the Dirac-Kahler
(DK) theory as a starting point and using Geometric Discretisation providing us
with a new way of extracting the Dirac field in the discrete setting of a
hyper-cubic complex.Comment: Lattice2003(Chiral), 3 page
Turbulent flow in graphene
We demonstrate the possibility of a turbulent flow of electrons in graphene
in the hydrodynamic region, by calculating the corresponding turbulent
probability density function. This is used to calculate the contribution of the
turbulent flow to the conductivity within a quantum Boltzmann approach. The
dependence of the conductivity on the system parameters arising from the
turbulent flow is very different from that due to scattering.Comment: 4 pages, Latex file, Journal versio
Solitons on compact and noncompact spaces in large noncommutativity
We study solutions at the minima of scalar field potentials for Moyal spaces
and torii in the large non-commutativity and interprete these solitons in terms
of non-BPS D-branes of string theory. We derive a mass spectrum formula linking
different D-branes together on quantum torii and suggest that it describes
general systems of D-brane bound states extending the D2-D0 one. Then we
propose a shape for the effective potential approaching these quasi-stable
bound states. We give the gauge symmetries of these systems of branes and show
that they depend on the quantum torii representations.Comment: 25 pages, Latex, 1 figure (use epsfig.sty), corrected formul
Black Hole Entropy Function and the Attractor Mechanism in Higher Derivative Gravity
We study extremal black hole solutions in D dimensions with near horizon
geometry AdS_2\times S^{D-2} in higher derivative gravity coupled to other
scalar, vector and anti-symmetric tensor fields. We define an entropy function
by integrating the Lagrangian density over S^{D-2} for a general AdS_2\times
S^{D-2} background, taking the Legendre transform of the resulting function
with respect to the parameters labelling the electric fields, and multiplying
the result by a factor of 2\pi. We show that the values of the scalar fields at
the horizon as well as the sizes of AdS_2 and S^{D-2} are determined by
extremizing this entropy function with respect to the corresponding parameters,
and the entropy of the black hole is given by the value of the entropy function
at this extremum. Our analysis relies on the analysis of the equations of
motion and does not directly make use of supersymmetry or specific structure of
the higher derivative terms.Comment: LaTeX file, 12page
Time Delay Induced Death in Coupled Limit Cycle Oscillators
We investigate the dynamical behaviour of two limit cycle oscillators that
interact with each other via time delayed coupling and find that time delay can
lead to amplitude death of the oscillators even if they have the same
frequency. We demonstrate that this novel regime of amplitude "death" also
exists for large collections of coupled identical oscillators and provide
quantitative measures of this death region in the parameter space of coupling
strength and time delay. Its implication for certain biological and physical
applications is also pointed out.Comment: 4 aps formatted revtex pages; 3 figures; to be published in Phys.
Rev. Let
- …