11,355 research outputs found
Adiabatic and Non-Adiabatic Contributions to the Free Energy from the Electron-Phonon Interaction for Na, K, Al, and Pb
We calculate the adiabatic contributions to the free energy due to the
electron--phonon interaction at intermediate temperatures, for the elemental metals Na, K, Al, and Pb. Using our
previously published results for the nonadiabatic contributions we show that
the adiabatic contribution, which is proportional to at low
temperatures and goes as at high temperatures, dominates the
nonadiabatic contribution for temperatures above a cross--over temperature,
, which is between 0.5 and 0.8 , where is the melting
temperature of the metal. The nonadiabatic contribution falls as for
temperatures roughly above the average phonon frequency.Comment: Updated versio
On Zurek's derivation of the Born rule
Recently, W. H. Zurek presented a novel derivation of the Born rule based on
a mechanism termed environment-assisted invariance, or "envariance" [W. H.
Zurek, Phys. Rev. Lett. 90(2), 120404 (2003)]. We review this approach and
identify fundamental assumptions that have implicitly entered into it,
emphasizing issues that any such derivation is likely to face.Comment: 8 pages; v2: minor clarifications added; v3: reference to Zurek's
quant-ph/0405161 added. To appear in Foundations of Physics (Cushing Volume
Nucleon, and excited states in lattice QCD
The energies of the excited states of the Nucleon, and are
computed in lattice QCD, using two light quarks and one strange quark on
anisotropic lattices. The calculation is performed at three values of the light
quark mass, corresponding to pion masses = 392(4), 438(3) and 521(3)
MeV. We employ the variational method with a large basis of interpolating
operators enabling six energies in each irreducible representation of the
lattice to be distinguished clearly. We compare our calculation with the
low-lying experimental spectrum, with which we find reasonable agreement in the
pattern of states. The need to include operators that couple to the expected
multi-hadron states in the spectrum is clearly identified.Comment: Revised for publication. References added, Table VI expanded to add
strange baryon multiparticle thresholds and multiparticle thresholds added to
Figs. 4, 5 and 6. 15 pages, 6 figure
Proton Drip-Line Calculations and the Rp-process
One-proton and two-proton separation energies are calculated for proton-rich
nuclei in the region . The method is based on Skyrme Hartree-Fock
calculations of Coulomb displacement energies of mirror nuclei in combination
with the experimental masses of the neutron-rich nuclei. The implications for
the proton drip line and the astrophysical rp-process are discussed. This is
done within the framework of a detailed analysis of the sensitivity of rp
process calculations in type I X-ray burst models on nuclear masses. We find
that the remaining mass uncertainties, in particular for some nuclei with
, still lead to large uncertainties in calculations of X-ray burst light
curves. Further experimental or theoretical improvements of nuclear mass data
are necessary before observed X-ray burst light curves can be used to obtain
quantitative constraints on ignition conditions and neutron star properties. We
identify a list of nuclei for which improved mass data would be most important.Comment: 20 pages, 9 figures, 2 table
Liquid state properties from first principles DFT calculations: Static properties
In order to test the Vibration-Transit (V-T) theory of liquid dynamics, ab
initio density functional theory (DFT) calculations of thermodynamic properties
of Na and Cu are performed and compared with experimental data. The
calculations are done for the crystal at T = 0 and T_m, and for the liquid at
T_m. The key theoretical quantities for crystal and liquid are the structural
potential and the dynamical matrix, both as function of volume. The theoretical
equations are presented, as well as details of the DFT computations. The
properties compared with experiment are the equilibrium volume, the isothermal
bulk modulus, the internal energy and the entropy. The agreement of theory with
experiment is uniformly good. Our primary conclusion is that the application of
DFT to V-T theory is feasible, and the resulting liquid calculations achieve
the same level of accuracy as does ab initio lattice dynamics for crystals.
Moreover, given the well established reliability of DFT, the present results
provide a significant confirmation of V-T theory itself.Comment: 9 pages, 3 figures, 5 tables, edited to more closely match published
versio
KECK HIRES Spectroscopy of APM 08279+5255
With an optical R-band magnitude of 15.2, the recently discovered z=3.911 BAL
quasar APM 08279+5255 is an exceptionally bright high redshift source. Its
brightness has allowed us to acquire a high signal-to-noise ratio (~100), high
resolution (~6 km/s) spectrum using the HIRES echelle spectrograph on the 10-m
Keck I telescope. Given the quality of the data, these observations provide an
unprecedented view of associated and intervening absorption systems. Here we
announce the availability of this spectrum to the general astronomical
community and present a brief analysis of some of its main features.Comment: 21 pages including 5 figures. Accepted for publication by PAS
Dynamics of monatomic liquids
We present a theory of the dynamics of monatomic liquids built on two basic
ideas: (1) The potential surface of the liquid contains three classes of
intersecting nearly-harmonic valleys, one of which (the ``random'' class)
vastly outnumbers the others and all whose members have the same depth and
normal mode spectrum; and (2) the motion of particles in the liquid can be
decomposed into oscillations in a single many-body valley, and nearly
instantaneous inter-valley transitions called transits. We review the
thermodynamic data which led to the theory, and we discuss the results of
molecular dynamics (MD) simulations of sodium and Lennard-Jones argon which
support the theory in more detail. Then we apply the theory to problems in
equilibrium and nonequilibrium statistical mechanics, and we compare the
results to experimental data and MD simulations. We also discuss our work in
comparison with the QNM and INM research programs and suggest directions for
future research.Comment: 53 pages, 16 figures. Differs from published version in using
American English spelling and grammar (published version uses British
English
Estimating the nuclear level density with the Monte Carlo shell model
A method for making realistic estimates of the density of levels in even-even
nuclei is presented making use of the Monte Carlo shell model (MCSM). The
procedure follows three basic steps: (1) computation of the thermal energy with
the MCSM, (2) evaluation of the partition function by integrating the thermal
energy, and (3) evaluating the level density by performing the inverse Laplace
transform of the partition function using Maximum Entropy reconstruction
techniques. It is found that results obtained with schematic interactions,
which do not have a sign problem in the MCSM, compare well with realistic
shell-model interactions provided an important isospin dependence is accounted
for.Comment: 14 pages, 3 postscript figures. Latex with RevTex. Submitted as a
rapid communication to Phys. Rev.
Extrapolation of neutron-rich isotope cross-sections from projectile fragmentation
Using the measured fragmentation cross sections produced from the 48Ca and
64Ni beams at 140 MeV per nucleon on 9Be and 181Ta targets, we find that the
cross sections of unmeasured neutron rich nuclei can be extrapolated using a
systematic trend involving the average binding energy. The extrapolated
cross-sections will be very useful in planning experiments with neutron rich
isotopes produced from projectile fragmentation. The proposed method is general
and could be applied to other fragmentation systems including those used in
other radioactive ion beam facilities.Comment: accepted for publication in Europhysics Letter
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