3,460 research outputs found
Distinct difference configurations: multihop paths and key predistribution in sensor networks
A distinct difference configuration is a set of points in Z2 with the property that the vectors (difference vectors) connecting any two of the points are all distinct. Many specific examples of these configurations have been previously studied: the class of distinct difference configurations includes both Costas arrays and sonar sequences, for example. Motivated by an application of these structures in key predistribution for wireless sensor networks, we define the k-hop coverage of a distinct difference configuration to be the number of distinct vectors that can be expressed as the sum of k or fewer difference vectors. This is an important parameter when distinct difference configurations are used in the wireless sensor application, as this parameter describes the density of nodes that can be reached by a short secure path in the network. We provide upper and lower bounds for the k-hop coverage of a distinct difference configuration with m points, and exploit a connection with Bh sequences to construct configurations with maximal k-hop coverage. We also construct distinct difference configurations that enable all small vectors to be expressed as the sum of two of the difference vectors of the configuration, an important task for local secure connectivity in the application
Two-dimensional patterns with distinct differences; constructions, bounds, and maximal anticodes
A two-dimensional (2-D) grid with dots is called a configuration with distinct differences if any two lines which connect two dots are distinct either in their length or in their slope. These configurations are known to have many applications such as radar, sonar, physical alignment, and time-position synchronization. Rather than restricting dots to lie in a square or rectangle, as previously studied, we restrict the maximum distance between dots of the configuration; the motivation for this is a new application of such configurations to key distribution in wireless sensor networks. We consider configurations in the hexagonal grid as well as in the traditional square grid, with distances measured both in the Euclidean metric, and in the Manhattan or hexagonal metrics. We note that these configurations are confined inside maximal anticodes in the corresponding grid. We classify maximal anticodes for each diameter in each grid. We present upper bounds on the number of dots in a pattern with distinct differences contained in these maximal anticodes. Our bounds settle (in the negative) a question of Golomb and Taylor on the existence of honeycomb arrays of arbitrarily large size. We present constructions and lower bounds on the number of dots in configurations with distinct differences contained in various 2-D shapes (such as anticodes) by considering periodic configurations with distinct differences in the square grid
Shadowing Effects on Particle and Transverse Energy Production
The effect of shadowing on the early state of ultrarelativistic heavy ion
collisions and transverse energy production is discussed. Results are presented
for RHIC Au+Au collisions at GeV and LHC Pb+Pb collisions
at TeV.Comment: 4 pgs, 2 figures, presented at Quark Matter '9
Nucleons Properties at Finite Lattice Spacing in Chiral Perturbation Theory
Properties of the proton and neutron are studied in partially-quenched chiral
perturbation theory at finite lattice spacing. Masses, magnetic moments, the
matrix elements of isovector twist-2 operators and axial-vector currents are
examined at the one-loop level in a double expansion in the light-quark masses
and the lattice spacing. This work will be useful in extrapolating the results
of simulations using Wilson valence and sea quarks, as well as simulations
using Wilson sea quarks and Ginsparg-Wilson valence quarks, to the continuum.Comment: 16 pages LaTe
Subtilisin enzymes: A note on time-resolved fluorescence and circular dichroism properties
AbstractThis note briefly corrects previous information about the time-resolved fluorescence properties of preparations of subtilisin Carlsberg and subtilisin BPN′. We confirm the observation of segmental motion of the single tryptophan in subtilisin Carlsberg by analysis of the time-resolved fluorescence anisotropy, and present circular dichroism and spectroscopic data on the two proteins. Near-UV properties clearly differentiate between the two proteins. Far-UV circular dichroism confirms that the two subtilisins have closely similar secondary structure in solution; the multi-component analysis is consistent with the established X-ray conformations, but the quantitative agreement is still somewhat imperfect
Physics at Hadron Colliders
In this paper we summarize the results of the theory working group dedicated
to the analysis of production at hadron colliders.Comment: 7 pages, LaTe
Chaos and Energy Redistribution the Nonlinear Interaction of Two Spatio-Temporal Wave Triplets
In this paper we examine the spatio-temporal dynamics of two nonlinearly
coupled wave triplets sharing two common modes. Our basic findings are the
following. When spatial dependence is absent, the homogeneous manifold so
obtained can be chaotic or regular. If chaotic, it drives energy diffusion from
long to small wavelengths as soon as inhomogeneous perturbations are added to
the system. If regular, one may yet have two distinct cases: (i) energy
diffusion is again present if the inhomogeneous modes are linearly unstable and
triplets are effectively coupled; (ii) energy diffusion is absent if the
inhomogeneous modes are linearly stable or the triplets are uncoupled.Comment: 21 pages, 5 figures, accepted for publication in Physica D (1997
Structural modelling and testing of failed high energy pipe runs: 2D and 3D pipe whip
Copyright @ 2011 ElsevierThe sudden rupture of a high energy piping system is a safety-related issue and has been the subject of extensive study and discussed in several industrial reports (e.g. [2], [3] and [4]). The dynamic plastic response of the deforming pipe segment under the blow-down force of the escaping liquid is termed pipe whip. Because of the potential damage that such an event could cause, various geometric and kinematic features of this phenomenon have been modelled from the point of view of dynamic structural plasticity. After a comprehensive summary of the behaviour of in-plane deformation of pipe runs [9] and [10] that deform in 2D in a plane, the more complicated case of 3D out-of-plane deformation is discussed. Both experimental studies and modelling using analytical and FE methods have been carried out and they show that, for a good estimate of the “hazard zone” when unconstrained pipe whip motion could occur, a large displacement analysis is essential. The classical, rigid plastic, small deflection analysis (e.g. see [2] and [8]), is valid for estimating the initial failure mechanisms, however it is insufficient for describing the details and consequences of large deflection behaviour
Strongly Interacting W's and Z's and the Existence of a Heavy Fourth Generation of Fermions
By employing the dictum that axiomatic principles are devoid of predictive
power, we find that the elastic unitarity constraint, applied to strong
WW scattering, does not alter the assumed spectrum of intermediate
states. We consider intermediate states involving a heavy Higgs and heavy
fermions of a hypothetical fourth generation doublet. In contrast to recent
studies, we find no p-wave resonance, and therefore no violation of the S
parameter upper bound. We conclude that the elastic unitarity constraint sheds
no light on the existence of a heavy fourth generation.Comment: 8 pages including 4 uuencoded, tarred, and compressed postscript
figures, CPP-93-0
Staggered flux and stripes in doped antiferromagnets
We have numerically investigated whether or not a mean-field theory of spin
textures generate fictitious flux in the doped two dimensional -model.
First we consider the properties of uniform systems and then we extend the
investigation to include models of striped phases where a fictitious flux is
generated in the domain wall providing a possible source for lowering the
kinetic energy of the holes. We have compared the energetics of uniform systems
with stripes directed along the (10)- and (11)-directions of the lattice,
finding that phase-separation generically turns out to be energetically
favorable. In addition to the numerical calculations, we present topological
arguments relating flux and staggered flux to geometric properties of the spin
texture. The calculation is based on a projection of the electron operators of
the model into a spin texture with spinless fermions.Comment: RevTex, 19 pages including 20 figure
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