484 research outputs found
reaction near threshold
We analyze the total cross section data for near threshold
measured recently at SATURNE. Using an effective range approximation for the
on-shell S-wave final state interaction we extract from these data the
modulus fm of the threshold transition amplitude
. We present a calculation of various (tree-level) meson exchange
diagrams contributing to . It is essential that -emission from
the anomalous -vertex interferes destructively with
-emission from the proton lines. The contribution of scalar
-meson exchange to turns out to be negligibly small. Without
introducing off-shell meson-nucleon form factors the experimental value
fm can be reproduced with an -coupling constant
of . The results of the present approach agree qualitatively
with the J\"ulich model. We also perform a combined analysis of the reactions
and near threshold.Comment: Latex-file 6 pages, 2 Figure
Development of an improved oxygen electrode for use in alkaline H2-O2 fuel cells Quarterly report, Apr. 1 - Jun. 30, 1967
Preparation of institial compounds of transition metals for hydrogen oxygen fuel cell cathode
Global Grid User Support Building a worldwide distributed user support infrastructure
The organisation and management of the user support in a global escience computing infrastructure such as EGEE (Enabling Grids for E-sciencE), a series of EU projects, is one of the challenges of the Grid. Given the widely distributed nature of the organisation, and the spread of expertise for installing, configuring, managing and troubleshooting the Grid middleware services, a standard centralised model could not be deployed in EGEE. This paper presents the model used in EGEE for building a reliable infrastructure for user, virtual organisation and operations support. A short overview of EGEE is given. The model for supporting a production quality infrastructure for scientific applications will be described in detail. The advantages of the chosen model will be presented and the possible difficulties will be discussed. In this paper we will also describe a scheme of how knowledge management can be used in Grid user support and first steps towards a realisation in the framework of the EGEE user support infrastructure
Electronic Structure of Te and As Covered Si(211)
Electronic and atomic structures of the clean, and As and Te covered Si(211)
surface are studied using pseudopotential density functional method. The clean
surface is found to have (2 X 1) and rebonded (1 X 1) reconstructions as stable
surface structures, but no \pi-bonded chain reconstruction. Binding energies of
As and Te adatoms at a number of symmetry sites on the ideal and (2 X 1)
reconstructed surfaces have been calculated because of their importance in the
epitaxial growth of CdTe and other materials on the Si(211) surface. The
special symmetry sites on these surfaces having the highest binding energies
for isolated As and Te adatoms are identified. But more significantly, several
sites are found to be nearly degenerate in binding energy values. This has
important consequences for epitaxial growth processes. Optimal structures
calculated for 0.5 ML of As and Te coverage reveal that the As adatoms dimerize
on the surface while the Te adatoms do not. However, both As and Te covered
surfaces are found to be metallic in nature.Comment: 17 pages, 9 figures, accepted for publication in Phys. Rev.
Knowledge Management and Semantics in Global Grid User Support
The organisation and management of the user support in a global escience computing infrastructure such as EGEE (Enabling Grids for E-sciencE), a series of EU projects, is one of the challenges of the Grid. Given the widely distributed nature of the organisation, and the spread of expertise for installing, configuring, managing and troubleshooting the Grid middleware services, a standard centralised model could not be deployed in EGEE. This paper presents the model used in EGEE for building a reliable infrastructure for user, virtual organisation and operations support. A short overview of EGEE is given. The model for supporting a production quality infrastructure for scientific applications will be described in detail. The advantages of the chosen model will be presented and the possible difficulties will be discussed. In this paper we will also describe a scheme of how knowledge management can be used in Grid user support and first steps towards a realisation in the framework of the EGEE user support infrastructure
Rendimiento y calidad fisiológica de la semilla de Brachiaria spp. en los llanos colombianos
186 accesiones de 9 especies de Brachiaria, se establecieron en un diseño de franjas divididas, con 2 repeticiones, para evaluar 2 niveles de fertilidad: a) el recomendado para establecer pasturas; b) el nivel para establecer un sistema integrado arroz-pastos. En el tercer año se evaluó el potencial de rendimiento de semillas. En las pruebas de germinación y latencia se evaluó el efecto de 2 tratamientos: 1) Agua y 2) Semilla escarificada en ácido sulfúrico; las de b. humidicola se trataron con Nitrato de Potasio. El rendimiento promedio y el Peso Unidad de las semillas no presentaron diferencias significativas (P186 accessions of 9 species of Brachiaria were established in a design of fringes divided on 2 repetitions. In the third year seeds were evaluated to test their potencial under 2 different fertility levels: a) One recommended in order to establish pastures; b) Other in order to establish a system composed rice-pasture. The yield and the seed weight unit did not present significant differences (
Functional approach to the electromagnetic response function: the Longitudinal Channel
In this paper we address the (charge) longitudinal electromagnetic response
for a homogeneous system of nucleons interacting via meson exchanges in the
functional framework. This approach warrants consistency if the calculation is
carried on order-by-order in the mesonic loop expansion with RPA-dressed
mesonic propagators. At the 1-loop order and considering pion, rho and omega
exchanges we obtain a quenching of the response, in line with the experimental
results.Comment: RevTeX, 18 figures available upon request - to be published in
Physical Review
Ultrafast Optical-Pump Terahertz-Probe Spectroscopy of the Carrier Relaxation and Recombination Dynamics in Epitaxial Graphene
The ultrafast relaxation and recombination dynamics of photogenerated
electrons and holes in epitaxial graphene are studied using optical-pump
Terahertz-probe spectroscopy. The conductivity in graphene at Terahertz
frequencies depends on the carrier concentration as well as the carrier
distribution in energy. Time-resolved studies of the conductivity can therefore
be used to probe the dynamics associated with carrier intraband relaxation and
interband recombination. We report the electron-hole recombination times in
epitaxial graphene for the first time. Our results show that carrier cooling
occurs on sub-picosecond time scales and that interband recombination times are
carrier density dependent.Comment: 4 pages, 5 figure
The high-energy hadron spin-flip amplitude at small momentum transfer and new AN data from RHIC
In the case of elastic high-energy hadron-hadron scattering, the impact of
the large-distance contributions on the behaviour of the slopes of the
spin-non-flip and of the spin-flip amplitudes is analysed. It is shown that the
long tail of the hadronic potential in impact parameter space leads to a value
of the slope of the reduced spin-flip amplitude larger than that of the
spin-non-flip amplitude. This effect is taken into account in the calculation
of the analysing power in proton-nucleus reactions at high energies. It is
shown that the preliminary measurement of AN obtained by the E950 Collaboration
indeed favour a spin-flip-amplitude with a large slope. Predictions for AN at
pL = 250 GeV/c are given.Comment: 16 pages, 5 figures, a few typos fixed in v.
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