7,853 research outputs found
Nanomechanics of a Hydrogen Molecule Suspended between Two Equally Charged Tips
Geometric configuration and energy of a hydrogen molecule centered between
two point-shaped tips of equal charge are calculated with the variational
quantum Monte-Carlo (QMC) method without the restriction of the
Born-Oppenheimer (BO) approximation. Ground state nuclear distribution,
stability, and low vibrational excitation are investigated. Ground state
results predict significant deviations from the BO treatment that is based on a
potential energy surface (PES) obtained with the same QMC accuracy. The quantum
mechanical distribution of molecular axis direction and bond length at a
sub-nanometer level is fundamental for understanding nanomechanical dynamics
with embedded hydrogen. Because of the tips' arrangement, cylindrical symmetry
yields a uniform azimuthal distribution of the molecular axis vector relative
to the tip-tip axis. With approaching tips towards each other, the QMC sampling
shows an increasing loss of spherical symmetry with the molecular axis still
uniformly distributed over the azimuthal angle but peaked at the tip-tip
direction for negative tip charge while peaked at the equatorial plane for
positive charge. This directional behavior can be switched between both stable
configurations by changing the sign of the tip charge and by controlling the
tip-tip distance. This suggests an application in the field of molecular
machines.Comment: 20 pages, 10 figure
A current and capital budget for the ministry of health for the second five-year national development plan 1991-1995
A research paper on costing for the Zimbabwe Ministry of Health for the development period 1991 to 1995.The aim of this paper is to provide an estimate of the current and capital budgets for the Zimbabwe health sector over the period 1991-1995, coinciding with the second Five-Year National Development Plan, while taking into account the country’s population growth rate. Emphasis in the health sector will be on primary health care (PHC), defined by the World Health Organisation (1978) as essential health care based on politically and scientifically sound and socially acceptable methods and technology, made universally accessible to individuals and families in the community through their full participation and at costs that the community and the country can afford to maintain at every stage of their self- determination.
The capital budget shows expenditures whose returns extend beyond a year (usually planned for several years). These involve equipment replacement, plant extension, product improvement and new products. The current budget includes salaries, health personnel training costs and health facility maintenance costs
Assessing the accuracy of Hartree-Fock-Bogoliubov calculations by use of mass relations
The accuracy of three different sets of Hartree-Fock-Bogoliubov calculations
of nuclear binding energies is systematically evaluated. To emphasize minor
fluctuations, a second order, four-point mass relation, which almost completely
eliminates smooth aspects of the binding energy, is introduced. Applying this
mass relation yields more scattered results for the calculated binding
energies. By examining the Gaussian distributions of the non-smooth aspects
which remain, structural differences can be detected between measured and
calculated binding energies. Substructures in regions of rapidly changing
deformation, specifically around and , are clearly
seen for the measured values, but are missing from the calculations. A similar
three-point mass relation is used to emphasize odd-even effects. A clear
decrease with neutron excess is seen continuing outside the experimentally
known region for the calculations.Comment: 13 pages, 9 figures, published versio
Structure and decay at rapid proton capture waiting points
We investigate the region of the nuclear chart around from a
three-body perspective, where we compute reaction rates for the radiative
capture of two protons. One key quantity is here the photon dissociation cross
section for the inverse process where two protons are liberated from the
borromean nucleus by photon bombardment. We find a number of peaks at low
photon energy in this cross section where each peak is located at the energy
corresponding to population of a three-body resonance. Thus, for these energies
the decay or capture processes proceed through these resonances. However, the
next step in the dissociation process still has the option of following several
paths, that is either sequential decay by emission of one proton at a time with
an intermediate two-body resonance as stepping stone, or direct decay into the
continuum of both protons simultaneously. The astrophysical reaction rate is
obtained by folding of the cross section as function of energy with the
occupation probability for a Maxwell-Boltzmann temperature distribution. The
reaction rate is then a function of temperature, and of course depending on the
underlying three-body bound state and resonance structures. We show that a very
simple formula at low temperature reproduces the elaborate numerically computed
reaction rate.Comment: 4 pages, 3 figures, conference proceedings, publishe
Hadronization corrections to helicity components of the fragmentation function
In the hadronic decays of Z, gluon emission leads to the appearance of the
longitudinal component of the fragmentation function, F_L. Measurement of F_L
and the transverse component, F_T, could thus provide an insight into the gluon
fragmentation function. However, hadronization corrections at low x can be
significant. Here we present a method of accounting for such corrections, using
the JETSET event generator as illustration.Comment: 11 pages, 5 figure
Emergence of clusters: Halos, Efimov states, and experimental signals
We investigate emergence of halos and Efimov states in nuclei by use of a
newly designed model which combines self-consistent mean-field and three-body
descriptions. Recent interest in neutron heavy calcium isotopes makes Ca
(Ca+n+n) an ideal realistic candidate on the neutron dripline, and we
use it as a representative example that illustrates our broadly applicable
conclusions. By smooth variation of the interactions we simulate the crossover
from well-bound systems to structures beyond the threshold of binding, and find
that halo-configurations emerge from the mean-field structure for three-body
binding energy less than keV. Strong evidence is provided that Efimov
states cannot exist in nuclei. The structure that bears the most resemblance to
an Efimov state is a giant halo extending beyond the neutron-core scattering
length. We show that the observable large-distance decay properties of the wave
function can differ substantially from the bulk part at short distances, and
that this evolution can be traced with our combination of few- and many-body
formalisms. This connection is vital for interpretation of measurements such as
those where an initial state is populated in a reaction or by a beta-decay.Comment: 5 pages, 5 figures, under revie
Combined few-body and mean-field model for nuclei
The challenging nuclear many-body problem is discussed along with
classifications and qualitative descriptions of existing methods and models. We
present detailed derivations of a new method where cluster correlations
co-exist with an underlying mean-field described core-structure. The variation
of an antisymmetrized product of cluster and core wave functions and a given
nuclear interaction, provide sets of self-consistent equations of motion.
After the applications on dripline nuclei we discuss perspectives with
improvements and applications. In the conclusion we summarize while emphasizing
the merits of consistently treating both short- and large-distance properties,
few- and many-body correlations, ordinary nuclear structure, and concepts of
halos and Efimov states
A combined mean-field and three-body model tested on the O-nucleus
We combine few- and many-body degrees of freedom in a model applicable to
both bound and continuum states and adaptable to different subfields of
physics. We formulate a self-consistent three-body model for a core-nucleus
surrounded by two valence nucleons. We treat the core in the mean-field
approximation and use the same effective Skyrme interaction between both core
and valence nucleons. We apply the model to O where we reproduce the
known experimental data as well as phenomenological models with more
parameters. The decay of the ground state is found to proceed directly into the
continuum without effect of the virtual sequential decay through the well
reproduced -resonance of O.Comment: 5 pages, 5 figures, under revie
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