6,456 research outputs found
The pion electromagnetic form-factor in a QCD-inspired model
We present detailed numerical results for the pion space-like electromagnetic
form factor obtained within a recently proposed model of the pion
electromagnetic current in a confining light-front QCD-inspired model. The
model incorporates the vector meson dominance mechanism at the quark level,
where the dressed photon with decay in an interacting quark-antiquark
pair,wich absorbs the initial pion and produces the pion in the final state.Comment: Talk given in Light-Cone 2004, Amsterdam,NL., 16-20 August, 2004. To
appear in "Few-Body Systems". 4 pages, 2 figues eps, use Few-Body Sytems
latex styl
Feasibility study and design of a robust low-noise amplifier operating at millimeter-wave for high reliability applications
A feasibility study and the corresponding design flow for robust millimeter wave GaN LNAs is provided in this paper. Particular attention is devoted to the selection of the optimum geometry of the first stage active device. A trade-off is shown between noise performance and robustness requirements. The beneficial effects of source degenerative feedback are shown. The LNA's simulated performance are gain > 20B, NF < 1.7dB and power handling capability verified up to +20 dBm input power in CW operation. This design is well suited for operation in high reliability systems, such as space operation on airborne applications
Timelike and spacelike hadron form factors, Fock state components and light-front dynamics
A unified description of spacelike and timelike hadron form factors within a
light-front model was successfully applied to the pion. The model is extended
to the nucleon to study the role of pair production and of
nonvalence components in the nucleon form factors. Preliminary results in the
spacelike range are presented.Comment: 4 pages, espcrc1.sty. proceedings of FB XVIII (August 2006, Brazil),
to be published in Nucl. Phys.
Electromagnetic Hadron Form Factors and Higher Fock Components
Investigation of the spacelike and timelike electromagnetic form factors of
hadrons, within a relativistic microscopical model characterized by a small set
of hypothesis, could shed light on the components of hadron states beyond the
valence one. Our relativistic approach has been successfully applied first to
the pion and then the extension to the nucleon has been undertaken. The pion
case is shortly reviewed as an illustrative example for introducing the main
ingredients of our approach, and preliminary results for the nucleon in the
spacelike range are evaluated.Comment: 8 pages, 6 figs, espcrc1.sty included. Proceedings of Fifth
International Conference on Perspectives In Hadronic Physics, ICTP, May
22-26, 200
Electromagnetic form factors of the nucleon in spacelike and timelike regions
An approach for a unified description of the nucleon electromagnetic form
factors in spacelike and timelike regions is presented. The main ingredients of
our model are: a Mandelstam formula for the matrix elements of the nucleon
electromagnetic current; a 3-dimensional reduction of the problem on the
Light-Front performed within the so-called {\tt Propagator Pole Approximation}
({\bf PPA}), which consists in disregarding the analytical structure of the
Bethe-Salpeter amplitudes and of the quark-photon vertex function in the
integration over the minus components of the quark momenta; a dressed
photon vertex in the channel, where the photon is described by its
spin-1, hadronic component.Comment: 8 pages, 9 figs., macro added. Proceedings of the XI Conf. on
Problems in Theoretical Nuclear Physics, Cortona, Oct. 11-14, 200
Metabolic and cardiovascular adaptation, monkey. NASA SMD 3, project 76, experiment 44 conducted at NASA/JSC, 14-25 May 1977
The biomedical results from an experiment on a monkey subjected to space flight conditions are reported. A background history of the development and testing of an experiment system designed to permit measurement of physiological parameters in subhuman primates during continuous, comfortable, couch restraint for periods of up to 30 days is reviewed. Of major importance in the experimental design of the system was the use of a fiberglass pod, which could be sealed and subdivided into upper and lower parts, to monitor and control the physiological responses for various parts of the animal's body. The experiment was conducted within the Spacelab Simulator for a period of 11 days. Data recorded includes: Spacelab Simulator cabin temperature; ventilation rate; pod internal temperature; fraction percent oxygen; fraction percent carbon dioxide; oxygen consumption rate; carbon dioxide production rate; respiratory quotient; intrathoracic temperature; heart rate; mean aortic pressure; mean ventricular pressure; diurnal variation of parameters measured; comparison of mean preflight, flight, and postflight values of the parameters measured; and correlation matrix for the parameters measured
Deuteron Magnetic and Quadrupole Moments with a Poincar\'e Covariant Current Operator in the Front-Form Dynamics
The deuteron magnetic and quadrupole moments are unambiguosly determined
within the front-form Hamiltonian dynamics, by using a new current operator
which fulfills Poincar\'e, parity and time reversal covariance, together with
hermiticity and the continuity equation. For both quantities the usual
disagreement between theoretical and experimental results is largely removed.Comment: To appear in Phys. Rev. Let
Deep inelastic scattering and final state interaction in an exactly solvable relativistic model
In the theory of deep inelastic scattering (DIS) the final state interaction
(FSI) between the struck quark and the remnants of the target is usually
assumed to be negligible in the Bjorken limit. This assumption, still awaiting
a full validation within nonperturbative QCD, is investigated in a model
composed by two relativistic particles, interacting via a relativistic harmonic
oscillator potential, within light-cone hamiltonian dynamics. An
electromagnetic current operator whose matrix elements behave properly under
Poincar\'e transformations is adopted. It is shown that: i) the parton model is
recovered, once the standard parton model assumptions are adopted; and ii) when
relativistic, interacting eigenfunctions are exactly taken into account for
both the initial and final states, the values of the structure functions,
averaged over small, but finite intervals of the Bjorken variable , coincide
with the results of the parton model in the Bjorken limit.Comment: 26 pages, to appear in Phys. Rev. C (May 1998
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