Compression of ultrashort UV pulses in a self-defocusing gas

Compression of UV femtosecond laser pulses focused into a gas cell filled with xenon is reported numerically. With a large negative Kerr index and normal dispersion, xenon promotes temporal modulational instability (MI) which can be monitored to shorten ~ 100 fs pulses to robust, singly-peaked waveforms exhibiting a fourfold compression factor. Combining standard MI theory with a variational approach allows us to predict the beam parameters suitable for efficient compression. At powers < 30 MW, nonlinear dispersion is shown to shift the pulse temporal profile to the rear zone.Comment: 4 pages, 4 figure

A new color change to improve the coloring of a graph

AbstractFor some special classes of graphs an optimal coloring can be obtained by the “Kempe method”: color as many vertices as possible with q given colors, and then make one of these colors available for an uncolored vertex x0 by interchanging the two colors of a “bicolor component”. It is well known that in general these interchanges cannot lead to an optimal coloring.We shall define here another type of color changes which can always lead to an optimal coloring. The basic tool is the concept of an “odd alternating sequence”

Fuzzy Bigraphs: An Exercise in Fuzzy Communicating Agents

Bigraphs and their algebra is a model of concurrency. Fuzzy bigraphs are a generalization of birgraphs intended to be a model of concurrency that incorporates vagueness. More specifically, this model assumes that agents are similar, communication is not perfect, and, in general, everything is or happens to some degree.Comment: 11 pages, 3 figure

q_T Uncertainties for W and Z Production

Analysis of semi-inclusive DIS hadroproduction suggests broadening of transverse momentum distributions at small x below 1E-3 ~ 1E-2 which can be modeled in the Collins-Soper-Sterman formalism by a modification of impact parameter dependent parton densities. We investigate these consequences for the production of electroweak bosons at the Tevatron and the LHC. If substantial small-x broadening is observed in forward Z boson production in the Tevatron Run-2, it will strongly affect the predicted q_T distributions for W and Z boson production at the LHC.Comment: 4 pages, 2 figures; contribution to the XIII International Workshop on Deep Inelastic Scattering (DIS 2005

Natural linewidth analysis of d-band photoemission from Ag(110)

We report a high-resolution angle-resolved study of photoemission linewidths observed for Ag(110). A careful data analysis yields k$-resolved upper limits for the inverse inelastic lifetimes of$d$-holes at the X-point of the bulk band structure. At the upper$d$-band edge the hole-lifetime is$\tau_h \geq 22 $fs, i.e. more than one order of magnitude larger than predicted for a free-electron gas. Following calculations for$d$-hole dynamics in Cu (I.\ Campillo et al., Phys. Rev. Lett., in press) we interpret the lifetime enhancement by a small scattering cross-section of $d$- and $sp$-states below the Fermi level. With increasing distance to $E_F$ the $d$-hole lifetimes get shorter because of the rapidly increasing density of d-states and contributions of intra-$d$-band scattering processes, but remain clearly above free-electron-model predictions.Comment: 14 pages, 7 figure

A combinatorial problem in logic

AbstractThis short note is an application of some theorems of graph theory to the problem of the minimum number of counter-examples needed to show that a special class of theories is complete

Neutrino-Nucleus Cross Section Measurements using Stopped Pions and Low Energy Beta Beams

Two new facilities have recently been proposed to measure low energy neutrino-nucleus cross sections, the nu-SNS (Spallation Neutron Source) and low energy beta beams. The former produces neutrinos by pion decay at rest, while the latter produces neutrinos from the beta decays of accelerated ions. One of the uses of neutrino-nucleus cross section measurements is for supernova studies, where typical neutrino energies are 10s of MeV. In this energy range there are many different components to the nuclear response and this makes the theoretical interpretation of the results of such an experiment complex. Although even one measurement on a heavy nucleus such as lead is much anticipated, more than one data set would be still better. We suggest that this can be done by breaking the electron spectrum down into the parts produced in coincidence with one or two neutrons, running a beta beam at more than one energy, comparing the spectra produced with pions and a beta beam or any combination of these.Comment: 6 pages, 6 figure