1,792 research outputs found
Simulation of cosmic irradiation conditions in thick target arrangements
One approach to simulate 2-pi irradiation conditions of planetary surfaces which has been widely applied in the past are bombardments of so called thick targets. A very large thick target was exposed recently to 2.1 GeV protons at the Bevatron-Bevalac in Berkeley. In a 100x100x180 cm steel-surrounded granodiorite target radioactive medium and high energy spallation products of the incident primary and of secondary particles were analyzed along the beam axis down to depths of 140 g/cm(2) in targets such as Cu, Ni, Co, Fe, T, Si, SiO2 and Al. Activities of these nuclides were exclusively determined via instrumental gamma-ray spectroscopy. Relative yields of neutron capture and spallation products induced in Co and Cu targets during the thick target bombardment are shown as a function of depth. The majority of the medium energy products such as Co-58 from Co targets exhibit a maximum at shallow depths of 40-60 g/cm(2) and then decrease exponentially. In a comparable 600 MeV proton bombarded thick target such a slight maximum for medium energy products was not observed. Rather, Co-58 activities in Co decreased steadily with the highest activity at the surface. The activities of the n-capture product Co-60 increase steadily starting at the surface. This indicates the rapidly growing flux of low energy neutrons within the target
G+++ Invariant Formulation of Gravity and M-Theories: Exact BPS Solutions
We present a tentative formulation of theories of gravity with suitable
matter content, including in particular pure gravity in D dimensions, the
bosonic effective actions of M-theory and of the bosonic string, in terms of
actions invariant under very-extended Kac-Moody algebras G+++. We conjecture
that they host additional degrees of freedom not contained in the conventional
theories. The actions are constructed in a recursive way from a level expansion
for all very-extended algebras G+++. They constitute non-linear realisations on
cosets, a priori unrelated to space-time, obtained from a modified Chevalley
involution. Exact solutions are found for all G+++. They describe the algebraic
properties of BPS extremal branes, Kaluza-Klein waves and Kaluza-Klein
monopoles. They illustrate the generalisation to all G+++ invariant theories of
the well-known duality properties of string theories by expressing duality as
Weyl invariance in G+++. Space-time is expected to be generated dynamically. In
the level decomposition of E8+++ = E11, one may indeed select an A10
representation of generators Pa which appears to engender space-time
translations by inducing infinite towers of fields interpretable as field
derivatives in space and time.Comment: Latex 45 pages, 1 figure. Discussion on pages 19 and 20 altered.
Appendix B amplified. 4 footnotes added. 2 references added. Acknowledgments
updated. Additional minor correction
QCD Corrections to Vector-Boson Fusion Processes in Warped Higgsless Models
We discuss the signatures of a representative Higgsless model with ideal
fermion delocalization in vector-boson fusion processes, focusing on the gold-
and silver-plated decay modes of the gauge bosons at the CERN-Large Hadron
Collider. For this purpose, we have developed a fully-flexible parton-level
Monte-Carlo program, which allows for the calculation of cross sections and
kinematic distributions within experimentally feasible selection cuts at
NLO-QCD accuracy. We find that Kaluza-Klein resonances give rise to very
distinctive distributions of the decay leptons. Similar to the Standard Model
case, within the Higgsless scenario the perturbative treatment of the
vector-boson scattering processes is under excellent control.Comment: 22 pages, 20 figure
NLO QCD corrections to processes with multiple electroweak bosons
The VBFNLO program package is a collection of Monte Carlo programs for the
calculation of NLO QCD corrections to vector boson fusion cross sections,
double and triple vector boson production, or the production of two electroweak
bosons in association with an additional jet. An overview is given of the
processes and features implemented in VBFNLO. WWgamma and Wgamma jet production
are discussed as examples.Comment: 6 pages, 3 figures; talk given at RADCOR 2009 - 9th International
Symposium on Radiative Corrections (Applications of Quantum Field Theory to
Phenomenology), October 25 - 30 2009, Ascona, Switzerlan
Numerical calculations of the phase diagram of cubic blue phases in cholesteric liquid crystals
We study the static properties of cubic blue phases by numerically minimising
the three-dimensional, Landau-de Gennes free energy for a cholesteric liquid
crystal close to the isotropic-cholesteric phase transition. Thus we are able
to refine the powerful but approximate, semi-analytic frameworks that have been
used previously. We obtain the equilibrium phase diagram and discuss it in
relation to previous results. We find that the value of the chirality above
which blue phases appear is shifted by 20% (towards experimentally more
accessible regions) with respect to previous estimates. We also find that the
region of stability of the O5 structure -- which has not been observed
experimentally -- shrinks, while that of BP I (O8-) increases thus giving the
correct order of appearance of blue phases at small chirality. We also study
the approach to equilibrium starting from the infinite chirality solutions and
we find that in some cases the disclination network has to assemble during the
equilibration. In these situations disclinations are formed via the merging of
isolated aligned defects.Comment: 16 pages, 5 figures. Accepted for publication in Phys. Rev.
Strong-driving-assisted multipartite entanglement in cavity QED
We propose a method of generating multipartite entanglement by considering
the interaction of a system of N two-level atoms in a cavity of high quality
factor with a strong classical driving field. It is shown that, with a
judicious choice of the cavity detuning and the applied coherent field
detuning, vacuum Rabi coupling produces a large number of important
multipartite entangled states. It is even possible to produce entangled states
involving different cavity modes. Tuning of parameters also permits us to
switch from Jaynes-Cummings to anti-Jaynes-Cummings like interaction.Comment: Last version with minor changes and added references. Accepted for
publication in Phys. Rev. Letter
Measurement of Particle Parameters in Thermal Spray Systems
Particle parameters are important in the optimization of plasma and flame spray processes that involve fine powders. Such processes include plasma and flame spraying, spheroidizing, and chemical processes in which the material is introduced in the form of fine powders or the final product is in the form of a fine powder, e.g. plasma synthesis of ceramics. To fully characterize the particle flow field, it is necessary to measure the particle size, velocity, and number density. In many cases, it is necessary to measure simultaneously several parameters that are strongly coupled such as particle size and temperature, or size and velocity. In this paper we will describe a laser based measurement technique for simultaneously obtaining the in-flight size, velocity, and temperature of small particles entrained in a flow field
Classical phase-space descriptions of continuous-variable teleportation
The nonnegative Wigner function of all quantum states involved in
teleportation of Gaussian states using the standard continuous-variable
teleportation protocol means that there is a local realistic phase-space
description of the process. This includes the coherent states teleported up to
now in experiments. We extend the phase-space description to teleportation of
non-Gaussian states using the standard protocol and conclude that teleportation
of non-Gaussian states with fidelity of 2/3 is a "gold standard" for this kind
of teleportation.Comment: New version contains minor changes requested by journal referee
Inelastic scattering of light by a cold trapped atom: Effects of the quantum center-of-mass motion
The light scattered by a cold trapped ion, which is in the stationary state
of laser cooling, presents features due to the mechanical effects of
atom-photon interaction. These features appear as additional peaks (sidebands)
in the spectrum of resonance fluorescence. Among these sidebands the literature
has discussed the Stokes and anti-Stokes components, namely the sidebands of
the elastic peak. In this manuscript we show that the motion also gives rise to
sidebands of the inelastic peaks. These are not always visible, but, as we
show, can be measured in parameter regimes which are experimentally accessible.Comment: 10 pages, 4 figures, submitted to Phys. Rev.
Information transfer through a one-atom micromaser
We consider a realistic model for the one-atom micromaser consisting of a
cavity maintained in a steady state by the streaming of two-level Rydberg atoms
passing one at a time through it. We show that it is possible to monitor the
robust entanglement generated between two successive experimental atoms passing
through the cavity by the control decoherence parameters. We calculate the
entanglement of formation of the joint two-atom state as a function of the
micromaser pump parameter. We find that this is in direct correspondence with
the difference of the Shannon entropy of the cavity photons before and after
the passage of the atoms for a reasonable range of dissipation parameters. It
is thus possible to demonstrate information transfer between the cavity and the
atoms through this set-up.Comment: Revtex, 5 pages, 2 encapsulated ps figures; added discussion on
information transfer in relation with cavity photon statistics; typos
corrected; Accepted for Publicaiton in Europhysics Letter
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