2,413 research outputs found
Coupling of phonons to a helium atom adsorbed on graphite
We compute the self-energy for a ^4He atom adsorbed on graphite to second order in the phonon coupling. The phonon contributions amount to several degrees Kelvin. The imaginary part corresponds to a lifetime of some 10^(-11) s
Nuclear Matter on a Lattice
We investigate nuclear matter on a cubic lattice. An exact thermal formalism
is applied to nucleons with a Hamiltonian that accommodates on-site and
next-neighbor parts of the central, spin- and isospin-exchange interactions. We
describe the nuclear matter Monte Carlo methods which contain elements from
shell model Monte Carlo methods and from numerical simulations of the Hubbard
model. We show that energy and basic saturation properties of nuclear matter
can be reproduced. Evidence of a first-order phase transition from an
uncorrelated Fermi gas to a clustered system is observed by computing
mechanical and thermodynamical quantities such as compressibility, heat
capacity, entropy and grand potential. We compare symmetry energy and first
sound velocities with literature and find reasonable agreement.Comment: 23 pages, 8 figures (some in color), to be submitted to Phys. Rev.
Lowest eigenvalue of the nuclear shell model Hamiltonian
In this paper we investigate regular patterns of matrix elements of the
nuclear shell model Hamiltonian , by sorting the diagonal matrix elements
from the smaller to larger values. By using simple plots of non-zero matrix
elements and lowest eigenvalues of artificially constructed "sub-matrices"
of , we propose a new and simple formula which predicts the lowest
eigenvalue with remarkable precisions.Comment: six pages, four figures, Physical Review C, in pres
Electron screening in molecular fusion reactions
Recent laboratory experiments have measured fusion cross sections at
center-of-mass energies low enough for the effects of atomic and molecular
electrons to be important. To extract the cross section for bare nuclei from
these data (as required for astrophysical applications), it is necessary to
understand these screening effects. We study electron screening effects in the
low-energy collisions of Z=1 nuclei with hydrogen molecules. Our model is based
on a dynamical evolution of the electron wavefunctions within the TDHF scheme,
while the motion of the nuclei is treated classically. We find that at the
currently accessible energies the screening effects depend strongly on the
molecular orientation. The screening is found to be larger for molecular
targets than for atomic targets, due to the reflection symmetry in the latter.
The results agree fairly well with data measured for deuteron collisions on
molecular deuterium and tritium targets.Comment: 15 Page RevTeX document, twelve postscript figures, now in a uufile
packag
Deformations and dilations of chaotic billiards, dissipation rate, and quasi-orthogonality of the boundary wavefunctions
We consider chaotic billiards in d dimensions, and study the matrix elements
M_{nm} corresponding to general deformations of the boundary. We analyze the
dependence of |M_{nm}|^2 on \omega = (E_n-E_m)/\hbar using semiclassical
considerations. This relates to an estimate of the energy dissipation rate when
the deformation is periodic at frequency \omega. We show that for dilations and
translations of the boundary, |M_{nm}|^2 vanishes like \omega^4 as \omega -> 0,
for rotations like \omega^2, whereas for generic deformations it goes to a
constant. Such special cases lead to quasi-orthogonality of the eigenstates on
the boundary.Comment: 4 pages, 3 figure
Branching ratios in low-energy deuteron-induced reactions
We consider (d,p) and (d,n) reactions on light nuclei at low energies. A simple estimate using the second-order distorted-wave Born approximation shows that Coulomb-induced predissociation of the deuteron influences the relative rate by less than 10%. This disagrees with a previous explanation of experiments involving 6Li targets and invalidates speculations about such effects in "cold fusion" experiments
Complex Langevin Equation and the Many-Fermion Problem
We study the utility of a complex Langevin (CL) equation as an alternative
for the Monte Carlo (MC) procedure in the evaluation of expectation values
occurring in fermionic many-body problems. We find that a CL approach is
natural in cases where non-positive definite probability measures occur, and
remains accurate even when the corresponding MC calculation develops a severe
``sign problem''. While the convergence of CL averages cannot be guaranteed in
principle, we show how convergent results can be obtained in three examples
ranging from simple one-dimensional integrals over quantum mechanical models to
a schematic shell model path integral.Comment: 19 pages, 10 PS figures embedded in tex
Broadening access to medical care during a severe influenza pandemic: The CDC Nurse Triage Line Project.
The impact of a severe influenza pandemic could be overwhelming to hospital emergency departments, clinics, and medical offices if large numbers of ill people were to simultaneously seek care. While current planning guidance to reduce surge on hospitals and other medical facilities during a pandemic largely focuses on improving the “supply” of medical care services, attention on reducing “demand” for such services is needed by better matching patient needs with alternative types and sites of care. Based on lessons learned during the 2009 H1N1 pandemic, the Centers for Disease Control and Prevention and its partners are currently exploring the acceptability and feasibility of using a coordinated network of nurse triage telephone lines during a pandemic to assess the health status of callers, help callers determine the most appropriate site for care (eg, hospital ED, outpatient center, home), disseminate information, provide clinical advice, and provide access to antiviral medications for ill people, if appropriate. As part of this effort, the integration and coordination of poison control centers, existing nurse advice lines, 2-1-1 information lines, and other hotlines are being investigated
Extrapolation method in shell model calculations with deformed basis
An extrapolation method in shell model calculations with deformed basis is
presented, which uses a scaling property of energy and energy variance for a
series of systematically approximated wave functions to the true one. Such
approximated wave functions are given by variation-after-projection method
concerning the full angular momentum projection. This extrapolation needs
energy variance, which amounts to the calculation of expectation value of
square of Hamiltonian . We present the method to evaluate this
matrix element and show that large reduction of its numerical computation can
be done by taking an advantage of time-reversal symmetry. The numerical tests
are presented for shell calculations with a realistic residual
interaction.Comment: 5 pages, 2 figures, accepted for publication in Phys. Rev.
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