7,143 research outputs found
SU(N) Wigner-Racah algebra for the matrix of second moments of embedded Gaussian unitary ensemble of random matrices
Recently Pluhar and Weidenmueller [Ann. Phys. (N.Y.) Vol 297, 344 (2002)]
showed that the eigenvectors of the matrix of second moments of embedded
Gaussian unitary ensemble of random matrices generated by k-body interactions
(EGUE(k)) for m fermions in N single particle states are SU(N) Wigner
coefficients and derived also an expression for the eigenvalues. Going beyond
this work, we will show that the eigenvalues of this matrix are square of a
SU(N) Racah coefficient and thus the matrix of second moments of EGUE(k) is
solved completely by SU(N) Wigner-Racah algebra.Comment: 16 page
Response of river-dominated delta channel networks to permanent changes in river discharge
Using numerical experiments, we investigate how river-dominated delta channel networks are likely to respond to changes in river discharge predicted to occur over the next century as a result of environmental change. Our results show for a change in discharge up to 60% of the initial value, a decrease results in distributary abandonment in the delta, whereas an increase does not significantly affect the network. However, an increase in discharge beyond a threshold of 60% results in channel creation and an increase in the density of the distributary network. This behavior is predicted by an analysis of an individual bifurcation subject to asymmetric water surface slopes in the bifurcate arms. Given that discharge in most river basins will change by less than 50% in the next century, our results suggest that deltas in areas of increased drought will be more likely to experience significant rearrangement of the delta channel network. Copyright 2010 by the American Geophysical Union
Angular-planar CMB power spectrum
Gaussianity and statistical isotropy of the Universe are modern cosmology's
minimal set of hypotheses. In this work we introduce a new statistical test to
detect observational deviations from this minimal set. By defining the
temperature correlation function over the whole celestial sphere, we are able
to independently quantify both angular and planar dependence (modulations) of
the CMB temperature power spectrum over different slices of this sphere. Given
that planar dependence leads to further modulations of the usual angular power
spectrum , this test can potentially reveal richer structures in the
morphology of the primordial temperature field. We have also constructed an
unbiased estimator for this angular-planar power spectrum which naturally
generalizes the estimator for the usual 's. With the help of a chi-square
analysis, we have used this estimator to search for observational deviations of
statistical isotropy in WMAP's 5 year release data set (ILC5), where we found
only slight anomalies on the angular scales and . Since this
angular-planar statistic is model-independent, it is ideal to employ in
searches of statistical anisotropy (e.g., contaminations from the galactic
plane) and to characterize non-Gaussianities.Comment: Replaced to match the published version. Journal-ref: Phys.Rev. D80
063525 (2009
Crafting a critical technical practice
In recent years, the category of practice-based research has become an essential component of discourse around public funding and evaluation of the arts in British higher education. When included under the umbrella of public policy concerned with the creative industries", technology researchers often find themselves collaborating with artists who consider their own participation to be a form of practice-based research. We are conducting a study under the Creator Digital Economies project asking whether technologists, themselves, should be considered as engaging in practice-based research, whether this occurs in collaborative situations, or even as a component of their own personal research [1]
Surfactant-induced migration of a spherical drop in Stokes flow
In Stokes flows, symmetry considerations dictate that a neutrally-buoyant
spherical particle will not migrate laterally with respect to the local flow
direction. We show that a loss of symmetry due to flow-induced surfactant
redistribution leads to cross-stream drift of a spherical drop in Poiseuille
flow. We derive analytical expressions for the migration velocity in the limit
of small non-uniformities in the surfactant distribution, corresponding to
weak-flow conditions or a high-viscosity drop. The analysis predicts that the
direction of migration is always towards the flow centerline.Comment: Significant extension with additional text, figures, equations, et
Implementation of optimal phase-covariant cloning machines
The optimal phase covariant cloning machine (PQCM) broadcasts the information
associated to an input qubit into a multi-qubit systems, exploiting a partial
a-priori knowledge of the input state. This additional a priori information
leads to a higher fidelity than for the universal cloning. The present article
first analyzes different experimental schemes to implement the 1->3 PQCM. The
method is then generalized to any 1->M machine for odd value of M by a
theoretical approach based on the general angular momentum formalism. Finally
different experimental schemes based either on linear or non-linear methods and
valid for single photon polarization encoded qubits are discussed.Comment: 7 pages, 3 figure
N=4 Supersymmetric Yang-Mills on S^3 in Plane Wave Matrix Model at Finite Temperature
We investigate the large N reduced model of gauge theory on a curved
spacetime through the plane wave matrix model. We formally derive the action of
the N=4 supersymmetric Yang-Mills theory on R \times S^3 from the plane wave
matrix model in the large N limit. Furthermore, we evaluate the effective
action of the plane wave matrix model up to the two-loop level at finite
temperature. We find that the effective action is consistent with the free
energy of the N=4 supersymmetric Yang-Mills theory on S^3 at high temperature
limit where the planar contributions dominate. We conclude that the plane wave
matrix model can be used as a large N reduced model to investigate
nonperturbative aspects of the N=4 supersymmetric Yang-Mills theory on R \times
S^3.Comment: 31pages: added comments and reference
Polarized entangled Bose-Einstein condensation
We consider a mixture of two distinct species of atoms of pseudospin-1/2 with
both intraspecies and Interspecies spin-exchange interactions, and find all the
ground stats in a general case of the parameters in the effective Hamiltonian.
In general, corresponding to the two species and two pseudo-spin states, there
are four orbital wave functions into which the atoms condense. We find that in
certain parameter regimes, the ground state is the so-called polarized
entangled Bose-Einstein condensation, i.e. in addition to condensation of
interspecies singlet pairs, there are unpaired atoms with spins polarized in
the same direction. The interspecies entanglement and polarization
significantly affect the generalized Gross-Pitaevskii equations governing the
four orbital wave functions into which the atoms condense, as an interesting
interplay between spin and orbital degrees of freedom.Comment: 14 pages, received by PRA on 27 October 201
Hypergraphic LP Relaxations for Steiner Trees
We investigate hypergraphic LP relaxations for the Steiner tree problem,
primarily the partition LP relaxation introduced by Koenemann et al. [Math.
Programming, 2009]. Specifically, we are interested in proving upper bounds on
the integrality gap of this LP, and studying its relation to other linear
relaxations. Our results are the following. Structural results: We extend the
technique of uncrossing, usually applied to families of sets, to families of
partitions. As a consequence we show that any basic feasible solution to the
partition LP formulation has sparse support. Although the number of variables
could be exponential, the number of positive variables is at most the number of
terminals. Relations with other relaxations: We show the equivalence of the
partition LP relaxation with other known hypergraphic relaxations. We also show
that these hypergraphic relaxations are equivalent to the well studied
bidirected cut relaxation, if the instance is quasibipartite. Integrality gap
upper bounds: We show an upper bound of sqrt(3) ~ 1.729 on the integrality gap
of these hypergraph relaxations in general graphs. In the special case of
uniformly quasibipartite instances, we show an improved upper bound of 73/60 ~
1.216. By our equivalence theorem, the latter result implies an improved upper
bound for the bidirected cut relaxation as well.Comment: Revised full version; a shorter version will appear at IPCO 2010
- …