Attacking Group Protocols by Refuting Incorrect Inductive Conjectures

Automated tools for finding attacks on flawed security protocols often fail to deal adequately with group protocols. This is because the abstractions made to improve performance on fixed 2 or 3 party protocols either preclude the modelling of group protocols all together, or permit modelling only in a fixed scenario, which can prevent attacks from being discovered. This paper describes Coral, a tool for finding counterexamples to incorrect inductive conjectures, which we have used to model protocols for both group key agreement and group key management, without any restrictions on the scenario. We will show how we used Coral to discover 6 previously unknown attacks on 3 group protocols

Non-equilibrium dynamics: Studies of reflection of Bose-Einstein condensates

The study of the non-equilibrium dynamics in Bose-Einstein condensed gases has been dominated by the zero-temperature, mean field Gross-Pitaevskii formalism. Motivated by recent experiments on the reflection of condensates from silicon surfaces, we revisit the so-called {\em classical field} description of condensate dynamics, which incorporates the effects of quantum noise and can also be generalized to include thermal effects. The noise is included in a stochastic manner through the initial conditions. We show that the inclusion of such noise is important in the quantitative description of the recent reflection experiments

Rate of Diabetic Vitrectomy in a Defined Geographical Part of North East England

Purpose: To assess the yearly incidence of vitrectomy for proliferative diabetic retinopathy (PDR) over an 11-year period, in a geographically defined part of North East England. The time period covered the introduction of diabetic retinopathy screening. Methods: All patients undergoing vitrectomy for diabetic retinopathy in the Sunderland and South Tyneside area were recorded from 2000 to 2010. Incidence rates of vitrectomy specifically for the complications of PDR for the observed diabetic population, the estimated diabetic population and the population with known PDR were calculated. Results: There was a gradual and significant decline in the vitrectomy rate from 157 (95% confidence interval, CI, 135–187) to 103 (95% CI 98–109) per 100,000 of the observed diabetic population in 2000 and 2010 respectively. The rate in the estimated diabetic population showed no significant change at 68 (95% CI 48–87) in 2002 and 77 (95% CI 55–103) in 2010. The rate in the PDR population, which comprised 2.4% of the known diabetic population in 2002 and 1.8% in 2010, declined significantly from 7.7% in 2002 to 5.7% in 2010. Conclusion: This study evaluated vitrectomy rates for PDR in an area of North East England. There were apparent declining rates of vitrectomy for PDR following the introduction of diabetic retinopathy screening but these have to be interpreted in the light of several confounding factors

Classical and quantum regimes of two-dimensional turbulence in trapped Bose-Einstein condensates

We investigate two-dimensional turbulence in finite-temperature trapped Bose-Einstein condensates within damped Gross-Pitaevskii theory. Turbulence is produced via circular motion of a Gaussian potential barrier stirring the condensate. We systematically explore a range of stirring parameters and identify three regimes, characterized by the injection of distinct quantum vortex structures into the condensate: (A) periodic vortex dipole injection, (B) irregular injection of a mixture of vortex dipoles and co-rotating vortex clusters, and (C) continuous injection of oblique solitons that decay into vortex dipoles. Spectral analysis of the kinetic energy associated with vortices reveals that regime (B) can intermittently exhibit a Kolmogorov $k^{-5/3}$ power law over almost a decade of length or wavenumber ($k$) scales. The kinetic energy spectrum of regime (C) exhibits a clear $k^{-3/2}$ power law associated with an inertial range for weak-wave turbulence, and a $k^{-7/2}$ power law for high wavenumbers. We thus identify distinct regimes of forcing for generating either two-dimensional quantum turbulence or classical weak-wave turbulence that may be realizable experimentally.Comment: 11 pages, 10 figures. Minor updates to text and figures 1, 2 and

The Josephson plasmon as a Bogoliubov quasiparticle

We study the Josephson effect in alkali atomic gases within the two-mode approximation and show that there is a correspondence between the Bogoliubov description and the harmonic limit of the phase representation. We demonstrate that the quanta of the Josephson plasmon can be identified with the Bogoliubov excitations of the two-site Bose fluid. We thus establish a mapping between the Bogoliubov approximation for the many-body theory and the linearized pendulum Hamiltonian.Comment: 9 pages, LaTeX, submitted to J. Phys.

Regular spatial structures in arrays of Bose-Einstein condensates induced by modulational instability

We show that the phenomenon of modulational instability in arrays of Bose-Einstein condensates confined to optical lattices gives rise to coherent spatial structures of localized excitations. These excitations represent thin disks in 1D, narrow tubes in 2D, and small hollows in 3D arrays, filled in with condensed atoms of much greater density compared to surrounding array sites. Aspects of the developed pattern depend on the initial distribution function of the condensate over the optical lattice, corresponding to particular points of the Brillouin zone. The long-time behavior of the spatial structures emerging due to modulational instability is characterized by the periodic recurrence to the initial low-density state in a finite optical lattice. We propose a simple way to retain the localized spatial structures with high atomic concentration, which may be of interest for applications. Theoretical model, based on the multiple scale expansion, describes the basic features of the phenomenon. Results of numerical simulations confirm the analytical predictions.Comment: 17 pages, 13 figure

New Wolf-Rayet Galaxies with Detection of WC Stars

We report the discovery of two new Wolf-Rayet (WR) galaxies: Mrk~1039, and F08208$+$2816. Two broad WR bumps at 5808\AA~ and 4650\AA~ indicate the presence of WCE and WNL star population in all two sources. We also confirm the presenceof WR features in Mrk~35, previously detected in a different position. The observed equivalent width of the WR bump at 4650\AA~ and the derived number ratios of WR/(WR$+$O) imply that star formation in these sources takes place inshort burst duration. Comparisons with the recent models of WR populations in young starbursts with the observed EW(\HeII)/EW(\CIV)/EW(WRbump) and their relative intensitie provide an indication that the stellar initial mass function in some WR galaxies might not be Salpeter-like. It is interesting to find that the luminous IRAS source, F08208$+$2816, has little dust reddening, probably because of the existence of a powerful superwind. By comparisons with other starbursts observed with the Hopkins Ultraviolet Telescope, F08208$+$2816 as a merging system renders a chance to study the contribution from young starbursts to the UV background radiation in universe.Comment: 22 pages, 6 figures, 4 tables, accepted by The Astrophysical Journa

Lassoing and corraling rooted phylogenetic trees

The construction of a dendogram on a set of individuals is a key component of a genomewide association study. However even with modern sequencing technologies the distances on the individuals required for the construction of such a structure may not always be reliable making it tempting to exclude them from an analysis. This, in turn, results in an input set for dendogram construction that consists of only partial distance information which raises the following fundamental question. For what subset of its leaf set can we reconstruct uniquely the dendogram from the distances that it induces on that subset. By formalizing a dendogram in terms of an edge-weighted, rooted phylogenetic tree on a pre-given finite set X with |X|>2 whose edge-weighting is equidistant and a set of partial distances on X in terms of a set L of 2-subsets of X, we investigate this problem in terms of when such a tree is lassoed, that is, uniquely determined by the elements in L. For this we consider four different formalizations of the idea of "uniquely determining" giving rise to four distinct types of lassos. We present characterizations for all of them in terms of the child-edge graphs of the interior vertices of such a tree. Our characterizations imply in particular that in case the tree in question is binary then all four types of lasso must coincide

The N boson time dependent problem: an exact approach with stochastic wave functions

We present a numerically tractable method to solve exactly the evolution of a N boson system with binary interactions. The density operator of the system rho is obtained as the stochastic average of particular operators |Psi_1><Psi_2| of the system. The states |Psi_{1,2}> are either Fock states |N:phi_{1,2}> or coherent states |coh:phi_{1,2}> with each particle in the state phi_{1,2}. We determine the conditions on the evolution of phi_{1,2} -which involves a stochastic element- under which we recover the exact evolution of rho. We discuss various possible implementations of these conditions. The well known positive P-representation arises as a particular case of the coherent state ansatz. We treat numerically two examples: a two-mode system and a one-dimensional harmonically confined gas. These examples, together with an analytical estimate of the noise, show that the Fock state ansatz is the most promising one in terms of precision and stability of the numerical solution.Comment: 21 pages, 5 figures, submitted to Phys.Rev.