3,536 research outputs found
A study of atmosphere-ionosphere-magnetosphere coupling
The properties of low energy plasma in the magnetosphere were predicted. The effects of wave particle interactions involving the concept of plasmons are studied, and quantum mechanical formulations are used for the processes occurring and bulk energization of the low energy plasma are investigated through the concept of the energy momentum tensor for the plasma and its electromagnetic environment
Toward a unified description of hadro- and photoproduction amplitudes
The near-term objectives of the research program at the Data Analysis Center
are established within the context of the existing partial wave analyses
available through the online suite of analysis and database codes accessible
through SAID, the Scattering Analysis Interactive Database. This presentation
reviews the efforts to determine a model independent method to obtain sets of
partial wave amplitudes for strong and electromagnetic reactions, the
interpretation of the amplitudes in terms of the excited states of the nucleon,
the role of new precision unpolarized and polarized data, and new developments
aimed at determining the photoproduction mulitpoles in a unitary,
coupled-channel approach. The Chew-Mandelstam technique is discussed and
applied to the problem of the S-wave pion- and eta-photoproduction amplitudes.
The resulting eta production amplitudes exhibit the expected resonant behavior
near the eta production threshold. Application of this method to a unified
description of the hadro- and photoproduction amplitudes is discussed.Comment: 4 pages, 1 figure, invited talk for the 12th International Conference
on Meson-Nucleon Physics and the Structure of the Nucleon (MENU 2010),
Williamsburg, Virginia, 31 May - 4 Jun 201
Effect of Sigma-beam Asymmetry Data on Fits to Single Pion Photoproduction off Neutron
We investigate the influence of new GRAAL Sigma-beam asymmetry measurements
on the neutron in multipole fits to the single-pion photoproduction database.
Results are compared to those found with the addition of a double-polarization
quantity associated with the sum rule.Comment: 4 pages, 4 figures, 1 table; v2/v3: minor corrections; Presented at
the 8th Workshop on the Physics of Excited Nucleons (NSTAR2011), Newport
News, USA, May 201
Unified Chew-Mandelstam SAID analysis of pion photoproduction data
A unified description of single-pion photoproduction data, together with
pion- and eta-hadroproduction data, has been achieved in a Chew-Mandelstam
parametrization which is consistent with unitarity at the two-body level.
Energy-dependent and single-energy partial wave analyses of pion
photoproduction data have been performed and compared to previous SAID fits and
multipoles from the Mainz and Bonn-Gatchina groups.Comment: 11 pages, 9 figures, and 2 table
Accomplishments of the NASA Johnson Space Center portion of the soil moisture project in fiscal year 1981
The NASA/JSC ground scatterometer system was used in a row structure and row direction effects experiment to understand these effects on radar remote sensing of soil moisture. Also, a modification of the scatterometer system was begun and is continuing, to allow cross-polarization experiments to be conducted in fiscal years 1982 and 1983. Preprocessing of the 1978 agricultural soil moisture experiment (ASME) data was completed. Preparations for analysis of the ASME data is fiscal year 1982 were completed. A radar image simulation procedure developed by the University of Kansas is being improved. Profile soil moisture model outputs were compared quantitatively for the same soil and climate conditions. A new model was developed and tested to predict the soil moisture characteristic (water tension versus volumetric soil moisture content) from particle-size distribution and bulk density data. Relationships between surface-zone soil moisture, surface flux, and subsurface moisture conditions are being studied as well as the ways in which measured soil moisture (as obtained from remote sensing) can be used for agricultural applications
Parameterization dependence of T matrix poles and eigenphases from a fit to piN elastic scattering data
We compare fits to piN elastic scattering data, based on a Chew-Mandelstam
K-matrix formalism. Resonances, characterized by T-matrix poles, are compared
in fits generated with and without explicit Chew-Mandelstam K-matrix poles.
Diagonalization of the S matrix yields the eigenphase representation. While the
eigenphases can vary significantly for the different parameterizations, the
locations of most T-matrix poles are relatively stable.Comment: 6 pages, 3 figures, 1 tabl
Improving information/disturbance and estimation/distortion trade-offs with non universal protocols
We analyze in details a conditional measurement scheme based on linear
optical components, feed-forward loop and homodyne detection. The scheme may be
used to achieve two different tasks. On the one hand it allows the extraction
of information with minimum disturbance about a set of coherent states. On the
other hand, it represents a nondemolitive measurement scheme for the
annihilation operator, i.e. an indirect measurement of the Q-function. We
investigate the information/disturbance trade-off for state inference and
introduce the estimation/distortion trade-off to assess estimation of the
Q-function. For coherent states chosen from a Gaussian set we evaluate both
information/disturbance and estimation/distortion trade-offs and found that non
universal protocols may be optimized in order to achieve better performances
than universal ones. For Fock number states we prove that universal protocols
do not exist and evaluate the estimation/distortion trade-off for a thermal
distribution.Comment: 10 pages, 6 figures; published versio
Scaling in many-body systems and proton structure function
The observation of scaling in processes in which a weakly interacting probe
delivers large momentum to a many-body system simply reflects the
dominance of incoherent scattering off target constituents. While a suitably
defined scaling function may provide rich information on the internal dynamics
of the target, in general its extraction from the measured cross section
requires careful consideration of the nature of the interaction driving the
scattering process. The analysis of deep inelastic electron-proton scattering
in the target rest frame within standard many-body theory naturally leads to
the emergence of a scaling function that, unlike the commonly used structure
functions and , can be directly identified with the intrinsic proton
response.Comment: 11 pages, 4 figures. Proceedings of the 11th Conference on Recent
Progress in Many-Body Theories, Manchester, UK, July 9-13 200
Multiphoton communication in lossy channels with photon-number entangled states
We address binary and quaternary communication channels based on correlated
multiphoton two-mode states of radiation in the presence of losses. The
protocol are based on photon number correlations and realized upon choosing a
shared set of thresholds to convert the outcome of a joint photon number
measurement into a symbol from a discrete alphabet. In particular, we focus on
channels build using feasible photon-number entangled states (PNES) as two-mode
coherently-correlated (TMC) or twin-beam (TWB) states and compare their
performances with that of channels built using feasible classically correlated
(separable) states. We found that PNES provide larger channel capacity in the
presence of loss, and that TWB-based channels may transmit a larger amount of
information than TMC-based ones at fixed energy and overall loss. Optimized bit
discrimination thresholds, as well as the corresponding maximized mutual
information, are explicitly evaluated as a function of the beam intensity and
the loss parameter. The propagation of TMC and TWB in lossy channels is
analyzed and the joint photon number distribution is evaluated, showing that
the beam statistics, either sub-Poissonian for TMC or super-Poissonian for TWB,
is not altered by losses. Although entanglement is not strictly needed to
establish the channels, which are based on photon-number correlations owned
also by separable mixed states, purity of the support state is relevant to
increase security. The joint requirement of correlation and purity individuates
PNES as a suitable choice to build effective channels. The effects of losses on
channel security are briefly discussed.Comment: 8 pages, 19 figure
Toward a unified description of hadro- and photoproduction: S-wave pi- and eta-photoproduction amplitudes
The Chew-Mandelstam parameterization, which has been used extensively in the
two-body hadronic sector, is generalized in this exploratory study to the
electromagnetic sector by simultaneous fits to the pion- and
eta-photoproduction S-wave multipole amplitudes for center-of-mass energies
from the pion threshold through 1.61 GeV. We review the Chew-Mandelstam
parameterization in detail to clarify the theoretical content of the SAID
hadronic amplitude analysis and to place the proposed, generalized SAID
electromagnetic amplitudes in the context of earlier employed parameterized
forms. The parameterization is unitary at the two-body level, employing four
hadronic channels and the gamma-N electromagnetic channel. We compare the
resulting fit to the MAID parameterization and find qualitative agreement
though, numerically, the solution is somewhat different. Applications of the
extended parameterization to global fits of the photoproduction data and to
global fits of the combined hadronic and photoproduction data are discussed.Comment: 9 pages, 9 figures; added figures and tex
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