8,951 research outputs found
Matter-wave interferometer for large molecules
We demonstrate a near-field Talbot-Lau interferometer for C-70 fullerene
molecules. Such interferometers are particularly suitable for larger masses.
Using three free-standing gold gratings of one micrometer period and a
transversally incoherent but velocity-selected molecular beam, we achieve an
interference fringe visibility of 40 % with high count rate. Both the high
visibility and its velocity dependence are in good agreement with a quantum
simulation that takes into account the van der Waals interaction of the
molecules with the gratings and are in striking contrast to a classical moire
model.Comment: revtex4, 4 pages, 3 figure
Model dependence of single-energy fits to pion photoproduction data
Model dependence of multipole analysis has been explored through
energy-dependent and single-energy fits to pion photoproduction data. The MAID
energy-dependent solution has been used as input for an event generator
producing realistic pseudo data. These were fitted using the SAID
parametrization approach to determine single-energy and energy-dependent
solutions over a range of lab photon energies from 200 to 1200 MeV. The
resulting solutions were found to be consistent with the input amplitudes from
MAID. Fits with a -squared per datum of unity or less were generally
achieved. We discuss energy regions where consistent results are expected, and
explore the sensitivity of fits to the number of included single- and
double-polarization observables. The influence of Watson's theorem is examined
in detail.Comment: 12 pages, 8 figure
The energies and residues of the nucleon resonances N(1535) and N(1650)
We extract pole positions for the N(1535) and N(1650) resonances using two
different models. The positions are determined from fits to different subsets
of the existing , and data
and found to be 1515(10)--i85(15)MeV and 1660(10)--i65(10)MeV, when the data is
described in terms of two poles. Sensitivity to the choice of fitted data is
explored. The corresponding and residues of these poles
are also extracted.Comment: 9 page
Where are the missing members of the baryon antidecuplet?
We analyze what consequences has the observation of exotic pentaquark baryons
on the location of the non-exotic baryons belonging to the antidecuplet. We
suggest that there must be a new nucleon state at 1650-1690 MeV and a new Sigma
baryon at 1760-1810 MeV.Comment: 5 pages, 1 figure. Missing reference adde
Multipole Amplitudes of Pion Photoproduction on Nucleons up to 2GeV within Dispersion Relations and Unitary Isobar Model
Two approaches for analysis of pion photo- and electroproduction on nucleons
in the resonance energy region are checked at using the results of
GWU(VPI) partial-wave analysis of photoproduction data. The approaches are
based on dispersion relations and unitary isobar model. Within dispersion
relations good description of photoproduction multipoles is obtained up to
. Within unitary isobar model, modified with increasing energy by
incorporation of Regge poles, and with unified Breit-Wigner parametrization of
resonance contributions, good description of photoproduction multipoles is
obtained up to .Comment: 23 pages, LaTe
A cost-efficient biogeochemical model for estuaries: a case-study of a funnel-shaped system
The hydrodynamics exerts an important influence on the biogeochemical functioning of estuarine systems. Comparative studies have long recognized this tight coupling and, for instance, have attempted to correlate key estuarine biogeochemical processes to simple hydrodynamic properties, such as the residence time or the tidal forcing. Yet, these correlations fail to resolve the estuarine spatio-temporal variability and do not provide powerful means to disentangle the complex interplay of multiple reaction and transport processes. In this context, reaction-transport models (RTMs) are useful tools to resolve the variability inherent to the estuarine environment. They ideally complement field observations, because their integrative power provides the required extrapolation means for a system-scale analysis over the entire spectrum of changing forcing conditions, including the long-term response to land-use and climate changes. However, RTM simulations are associated with high computational costs, especially when the biogeochemical dynamics are to be resolved on a regional or global scale. Furthermore, specific data requirements, such as boundary conditions or bathymetric and geometric information may limit their applicability.Here, a generic one-dimensional RTM approach which relies on idealized geometries to support the estuarine physics is used to quantify the biogeochemical dynamics. The model is cost-efficient and requires only a limited number of readily available input data. The approach is applied to a case-study of a funnel-shaped estuary (The Scheldt, BE/NL) and is tested by comparing integrative measures of the estuarine biogeochemical functioning (e.g. Net Ecosystem Metabolism, integrated CO2 fluxes) with those derived from observations (Frankignoulle et al., 1996, 1998) and highly-resolved model simulations (Vanderborght et al., 2002; Arndt et al., 2009). The method provides a robust quantitative tool to carry sensitivity and uncertainty analyses and to investigate the estuarine biogeochemistry at the regional scale
Updated resonance photo-decay amplitudes to 2 GeV
We present the results of an energy-dependent and set of single-energy
partial-wave analyses of single-pion photoproduction data. These analyses
extend from threshold to 2 GeV in the laboratory photon energy, and update our
previous analyses to 1.8 GeV. Photo-decay amplitudes are extracted for the
baryon resonances within this energy range. We consider two photoproduction sum
rules and the contributions of two additional resonance candidates found in our
most recent analysis of elastic scattering data. Comparisons are made
with previous analyses.Comment: Revtex, 26 pages, 3 figures. Postscript figures available from
ftp://clsaid.phys.vt.edu/pub/pr or indirectly from
http://clsaid.phys.vt.edu/~CAPS
Search for anisotropic effects of hcp solid helium on optical lines of cesium impurities
The anisotropic effect of a hcp 4He solid matrix on cesium atoms has been
proposed as a tool to reveal the parity violating anapole moment of its
nucleus. It should also result in splitting the D2 optical excitation line in a
way depending on the light polarization. An experimental investigation has been
set up using oriented hcp helium crystals in which cesium metal grains are
embedded. Atoms are created by laser sputtering from this grains. Optical
absorption spectra of the D2 line have been recorded in the temperature range
of 1.0 to 1.4 K at liquid/solid coexistence pressure by monitoring the
fluorescence on the D2 line at 950 nm. No significant effect of the light
polarization has been found, suggesting a statistically isotropic disordered
solid environment for the cesium atoms.Comment: The original publication will be available at
http://www.springerlink.co
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