14,927 research outputs found
Longitudinal profiles of Extensive Air Showers with inclusion of charm and bottom particles
Charm and bottom particles are rare in Extensive Air Showers but the effect
of its presence can be radical in the development of the Extensive Air Showers
(EAS). If such particles arise with a large fraction of the primary energy,
they can reach large atmospheric depths, depositing its energy in deeper layers
of the atmosphere. As a consequence, the EAS observables (, and
) will be modified, as well as the shape of the longitudinal profile
of the energy deposited in the atmosphere. In this paper, we will modify the
CORSIKA Monte Carlo by the inclusion of charm and bottom production in the
first interaction of the primary cosmic ray. Results for different selections
of the typical values of the heavy particles and distinct production
models will be presented.Comment: Replacement of tex file by the correct versio
The Challenge of Light-Front Quantisation: Recent Results
We explain what is the challenge of light-front quantisation, and how we can
now answer it because of recent progress in solving the problem of zero modes
in the case of non-Abelian gauge theories. We also give a description of the
light-front Hamiltonian for SU(2) finite volume gluodynamics resulting from
this recent solution to the problem of light-front zero modes.Comment: 17 pages, lecture delivered by GBP at the XXXIV PNPI Winter School,
Repino, St.Petersburg, Russia, February 14-20, 2000, version to appear in the
Proceeding
Role of Rotations on Surface Diffusion of Water Trimers on Pd\{111\}
Diffusion barriers for a cluster of three water molecules on Pd(111) have
been estimated from ab-initio Density Functional Theory. A model for the
diffusion of the trimer based in rotations yields a simple explanation of why
the cluster can diffuse faster than a single water molecule by a factor
. This model is based on the differences between the adsorption
geometry for the three monomers forming the cluster. One member interacts
strongly with the surface and sits closer to the surface (d) while the other
two interact weakly and stay at a larger separation from the surface (u). The
trimer rotates nearly freely around the axis determined by the d monomer.
Translations of the whole trimer imply breaking the strong interaction of the d
monomer with the surface. Alternatively, thermal fluctuations exchange the
actual monomer sitting closer to the surface with a lower energetic cost.
Rotations around different axis introduce a diffusion mechanism where a strong
interaction is kept along the diffusion path between the water molecule
defining the axis of rotation and the Pd underneath.Comment: water ; monomer ; trimer ; water clusters ; diffusion ; rotation
assisted ; Pd\{111\} ; ab-initio ; density functional theor
Transverse momentum spectra and elliptic flow in ideal hydrodynamics and geometric scaling
In an ideal hydrodynamic model, with an equation of state where the
confinement-deconfinement transition is a cross-over at , we
have simulated =200 GeV Au+Au collisions. Simultaneous description of
the experimental charged particle's spectra and elliptic flow require
that in central (0-10%) Au+Au collisions, initial energy density scales with
the binary collision number density. In less central collisions, experimental
data demand scaling with the participant density. Simulation studies also
indicate that in central collisions viscous effects are minimal.Comment: 4 pages, 3 figures
Anderson localization of solitons in optical lattices with random frequency modulation
We report on phenomenon of Anderson-type localization of walking solitons in
optical lattices with random frequency modulation, manifested as dramatic
enhancement of soliton trapping probability on lattice inhomogeneities with
growth of the frequency fluctuation level. The localization process is strongly
sensitive to the lattice depth since in shallow lattices walking solitons
experience random refraction and/or multiple scattering in contrast to
relatively deep lattices, where solitons are typically immobilized in the
vicinity of local minimums on modulation frequency.Comment: 13 pages, 4 figures, to appear in Physical Review
Isomeric effects in the gas-phase reactions of dichloroethene, C2H2Cl2, with a series of cations
A study of the reactions of a series of gas-phase cations (NH, HO, SF, CF, CF, SF5, SF, SF, CF, SF, O, Xe, NO, CO, Kr, CO, N, N, Ar, F and Ne) with the three structural isomers of dichloroethene, i.e. 1,1-CHCl, cis-1,2-CHCl and trans-1,2-CHCl is reported. The recombination energy of these ions spans the range 4.7-21.6 eV. Reaction rate coefficients and product branching ratios have been measured at 298 K in a selected ion flow tube. Collisional rate coefficients are calculated by modified average dipole orientation theory and compared with experimental data. Thermochemistry and mass balance have been used to predict the most feasible neutral products. Threshold photoelectron-photoion coincidence spectra have also been obtained for the three isomers of CHCl with photon energies in the range 10-23 eV. The fragment ion branching ratios have been compared with those of the flow tube study to determine the importance of long-range charge transfer. A strong influence of the isomeric structure of dichloroethene on the products of ion-molecule reactions has been observed for HO, CF, and CF. For 1,1-CHCl the reaction with HO proceeds at the collisional rate with the only ionic product being 1,1-CHClH. However, the same reaction yields two more ionic products in the case of cis-1,2- and trans-1,2-CHCl, but only proceeds with 14 % and 18 % efficiency, respectively. The CF reaction proceeds with 56-80 % efficiency, the only ionic product for 1,1-CHCl being CHCl formed via Cl- abstraction, whereas the only ionic product for both 1,2-isomers is CHCl corresponding to a breaking of the C=C double bond. Less profound isomeric effects, but still resulting in different products for 1,1- and 1,2-CHCl isomers, have been found in the reactions of SF, CO, CO, N, and Ar. Although these five ions have recombination energies above the ionization energy of any of the CHCl isomers and hence the threshold for long-range charge transfer, the results suggest that the formation of a collision complex at short range between these ions and CHCl is responsible for the observed effects
On the Cholesky Decomposition for electron propagator methods: General aspects and application on C60
To treat the electronic structure of large molecules by electron propagator
methods we developed a parallel computer program called P-RICD. The
program exploits the sparsity of the two-electron integral matrix by using
Cholesky decomposition techniques. The advantage of these techniques is that
the error introduced is controlled only by one parameter which can be chosen as
small as needed. We verify the tolerance of electron propagator methods to the
Cholesky decomposition threshold and demonstrate the power of the
P-RICD program for a representative example (C60). All decomposition
schemes addressed in the literature are investigated. Even with moderate
thresholds the maximal error encountered in the calculated electron affinities
and ionization potentials amount to a few meV only, and the error becomes
negligible for small thresholds.Comment: 30 pages, 6 figures submitted to J.Chem. Phy
Vortices and quasiparticles near the "superconductor-insulator" transition in thin films
We study the low temperature behavior of an amorphous superconducting film
driven normal by a perpendicular magnetic field (B). For this purpose we
introduce a new two-fluid formulation consisting of fermionized field induced
vortices and electrically neutralized Bogoliubov quasiparticles (spinons)
interacting via a long-ranged statistical interaction. This approach allows us
to access a novel non-Fermi liquid phase which naturally interpolates between
the low B superconductor and the high B normal metal. We discuss the transport,
thermodynamic, and tunneling properties of the resulting "vortex metal" phase.Comment: 4 pages, 1 figure, references adde
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