7,512 research outputs found
Multifacet holographic optical elements
New types of holographic optical elements, combining the flexibility of computer generated holograms with the large space bandwidth product and high diffraction efficiency of interferometrically recorded volume phase holograms, are demonstrated. The optical elements are recorded by subdividing a volume hologram film surface into numerous small areas (facets), each of which is individually exposed under computer control. Each facet is used to produce a portion of the desired final wavefront. Three different optical elements are demonstrated
Some triviality results for quasi-Einstein manifolds and Einstein warped products
In this paper we prove a number of triviality results for Einstein warped
products and quasi-Einstein manifolds using different techniques and under
assumptions of various nature. In particular we obtain and exploit gradient
estimates for solutions of weighted Poisson-type equations and adaptations to
the weighted setting of some Liouville-type theorems.Comment: 15 pages, fixed minor mistakes in Section
Stochastic evolution of four species in cyclic competition
We study the stochastic evolution of four species in cyclic competition in a
well mixed environment. In systems composed of a finite number of particles
these simple interaction rules result in a rich variety of extinction
scenarios, from single species domination to coexistence between
non-interacting species. Using exact results and numerical simulations we
discuss the temporal evolution of the system for different values of , for
different values of the reaction rates, as well as for different initial
conditions. As expected, the stochastic evolution is found to closely follow
the mean-field result for large , with notable deviations appearing in
proximity of extinction events. Different ways of characterizing and predicting
extinction events are discussed.Comment: 19 pages, 6 figures, submitted to J. Stat. Mec
Brief Note: The Status of Ermine (Mustela erminea) in Ohio
Author Institution: Ohio Cooperative Fish and Wildlife Research Unit, The Ohio State University and Ohio Department of Natural Resources, Division of WildlifeThe status of ermine as regular inhabitants of Ohio has been unclear. Previously, only three records were known from the state. In this study, size 0 leghold traps and 8 x 8 x 25 cm Sherman traps were used to capture five ermine in Ashtabula and Trumbull Counties during summer 1987 and two in Trumbull County in 1988. Ermine are permanent residents in at least Trumbull County
Black Holes, Branes and Superconformal Symmetry
The main focus of this lecture is on extended objects in adS*S bosonic
backgrounds with unbroken supersymmetry. The backgrounds are argued to be
exact, special consideration are given to the non-maximal supersymmetry case.
The near horizon superspace construction is explained. The superconformal
symmetry appears in the worldvolume actions as the superisometry of the near
horizon superspace, like the superPoincare symmetry of GS superstring and BST
supermembrane in the flat superspace. The issues in gauge fixing of local
kappa-symmetry are reviewed. We describe the features of the gauge-fixed IIB
superstring in adS(5)*S(5) background with RR 5-form. From a truncated boundary
version of it we derive an analytic N=2 off shell harmonic superspace of
Yang-Mills theory. The reality condition of the analytic subspace, which
includes the antipodal map on the sphere, has a simple meaning of the symmetry
of the string action in the curved space. The relevant issues of black holes
and superconformal mechanics are addressed.Comment: 34 pages, Latex. To be published in the Proceedings of a conference
held in Corfu, Greece in September 1998. Improvement in Sec. 3.
Scattering theory with finite-gap backgrounds: Transformation operators and characteristic properties of scattering data
We develop direct and inverse scattering theory for Jacobi operators (doubly
infinite second order difference operators) with steplike coefficients which
are asymptotically close to different finite-gap quasi-periodic coefficients on
different sides. We give necessary and sufficient conditions for the scattering
data in the case of perturbations with finite second (or higher) moment.Comment: 23 page
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