37 research outputs found
Strong Phase Separation in a Model of Sedimenting Lattices
We study the steady state resulting from instabilities in crystals driven
through a dissipative medium, for instance, a colloidal crystal which is
steadily sedimenting through a viscous fluid. The problem involves two coupled
fields, the density and the tilt; the latter describes the orientation of the
mass tensor with respect to the driving field. We map the problem to a 1-d
lattice model with two coupled species of spins evolving through conserved
dynamics. In the steady state of this model each of the two species shows
macroscopic phase separation. This phase separation is robust and survives at
all temperatures or noise levels--- hence the term Strong Phase Separation.
This sort of phase separation can be understood in terms of barriers to
remixing which grow with system size and result in a logarithmically slow
approach to the steady state. In a particular symmetric limit, it is shown that
the condition of detailed balance holds with a Hamiltonian which has
infinite-ranged interactions, even though the initial model has only local
dynamics. The long-ranged character of the interactions is responsible for
phase separation, and for the fact that it persists at all temperatures.
Possible experimental tests of the phenomenon are discussed.Comment: To appear in Phys Rev E (1 January 2000), 16 pages, RevTex, uses
epsf, three ps figure
Determination of pi-N scattering lengths from pionic hydrogen and pionic deuterium data
The pi-N s-wave scattering lengths have been inferred from a joint analysis
of the pionic hydrogen and the pionic deuterium x-ray data using a
non-relativistic approach in which the pi-N interaction is simulated by a
short-ranged potential. The pi-d scattering length has been calculated exactly
by solving the Faddeev equations and also by using a static approximation. It
has been shown that the same very accurate static formula for pi-d scattering
length can be derived (i) from a set of boundary conditions; (ii) by a
reduction of Faddeev equations; and (iii) through a summation of Feynman
diagrams. By imposing the requirement that the pi-d scattering length,
resulting from Faddeev-type calculation, be in agreement with pionic deuterium
data, we obtain bounds on the pi-N scattering lengths. The dominant source of
uncertainty on the deduced values of the pi-N scattering lengths are the
experimental errors in the pionic hydrogen data.Comment: RevTeX, 20 pages,4 PostScript figure
P-wave excited baryons from pion- and photo-induced hyperon production
We report evidence for , , ,
, , and , and find
indications that might have a companion state at 1970\,MeV. The
controversial is not seen. The evidence is derived from a
study of data on pion- and photo-induced hyperon production, but other data are
included as well. Most of the resonances reported here were found in the
Karlsruhe-Helsinki (KH84) and the Carnegie-Mellon (CM) analyses but were
challenged recently by the Data Analysis Center at GWU. Our analysis is
constrained by the energy independent scattering amplitudes from either
KH84 or GWU. The two amplitudes from KH84 or GWU, respectively, lead to
slightly different branching ratios of contributing resonances but the
debated resonances are required in both series of fits.Comment: 22 pages, 28 figures. Some additional sets of data are adde
Spallation Neutron Production by 0.8, 1.2 and 1.6 GeV Protons on various Targets
Spallation neutron production in proton induced reactions on Al, Fe, Zr, W,
Pb and Th targets at 1.2 GeV and on Fe and Pb at 0.8, and 1.6 GeV measured at
the SATURNE accelerator in Saclay is reported. The experimental
double-differential cross-sections are compared with calculations performed
with different intra-nuclear cascade models implemented in high energy
transport codes. The broad angular coverage also allowed the determination of
average neutron multiplicities above 2 MeV. Deficiencies in some of the models
commonly used for applications are pointed out.Comment: 20 pages, 32 figures, revised version, accepted fpr publication in
Phys. Rev.
Photoproduction of pions and properties of baryon resonances from a Bonn-Gatchina partial wave analysis
Masses, widths and photocouplings of baryon resonances are determined in a
coupled-channel partial wave analysis of a large variety of data. The
Bonn-Gatchina partial wave formalism is extended to include a decomposition of
t- and u-exchange amplitudes into individual partial waves. The multipole
transition amplitudes for and are
given and compared to results from other analyses.Comment: 18 pages, 14 figure
Dependence of calculated binding energies and widths of -mesic nuclei on treatment of subthreshold -nucleon interaction
We demonstrate that the binding energies and widths of eta-mesic nuclei
depend strongly on subthreshold eta-N interaction. This strong dependence is
made evident from comparing three different eta-nucleus optical potentials: (1)
a microscopic optical potential taking into account the full effects of
off-shell eta-nucleon interactions; (2) a factorization approximation to the
microscopic optical potential where a downward energy shift parameter is
introduced to approximate the subthreshold eta-nucleon interaction; and (3) an
optical potential using on-shell eta-nucleon scattering length as the
interaction input. Our analysis indicates that the in-medium N
interaction for bound-state formation is about 30 MeV below the free-space
N threshold, which causes a substantial reduction of the attractive force
between the and nucleon with respect to that implied by the scattering
length. Consequently, the scattering-length approach overpredicts the binding
energies and caution must be exercised when these latter predictions are used
as guide in searching for -nucleus bound states. We also show that
final-state-interaction analysis cannot provide an unequivocal determination of
the existence of -nucleus bound state. More direct measurements are,
therefore, necessary.Comment: 28 pages, 1 figur
Properties of baryon resonances from a multichannel partial wave analysis
Properties of nucleon and resonances are derived from a multichannel
partial wave analysis. The statistical significance of pion and photo-induced
inelastic reactions off protons are studied in a multichannel partial-wave
analysis.Comment: 12 pages, 8 Table