4,930 research outputs found
Time of flight mass spectrometer with feedback means from the detector to the low source and a specific counter Patent
Design and characteristics of time of flight mass spectrometer to measure or analyze gases at low pressures and time of flight of single gas molecul
Effects of heavy ions on electron temperatures in the solar corona and solar wind
The effects of the reduction in the thermal conductivity due to heavy ions on electron temperatures in the solar corona and solar wind are examined. Large enhancements of heavy ions in the corona appear to be necessary to give appreciable changes in the thermal gradient of the electrons
Interplanetary magnetic fields as a cause of comet tails
Interplanetary magnetic fields as cause of comet tail
Isospin-projected nuclear level densities by the shell model Monte Carlo method
We have developed an efficient isospin projection method in the shell model
Monte Carlo approach for isospin-conserving Hamiltonians. For isoscalar
observables this projection method has the advantage of being exact sample by
sample. The isospin projection method allows us to take into account the proper
isospin dependence of the nuclear interaction, thus avoiding a sign problem
that such an interaction introduces in unprojected calculations. We apply our
method in the calculation of the isospin dependence of level densities in the
complete shell. We find that isospin-dependent corrections to the
total level density are particularly important for nuclei.Comment: 5 pages including 4 figure
Binomial level densities
It is shown that nuclear level densities in a finite space are described by a
continuous binomial function, determined by the first three moments of the
Hamiltonian, and the dimensionality of the underlying vector space.
Experimental values for Mn, Fe, and Ni are very well
reproduced by the binomial form, which turns out to be almost perfectly
approximated by Bethe's formula with backshift. A proof is given that binomial
densities reproduce the low moments of Hamiltonians of any rank: A strong form
of the famous central limit result of Mon and French. Conditions under which
the proof may be extended to the full spectrum are examined.Comment: 4 pages 2 figures Second version (previous not totally superseeded
Quantum number projection at finite temperature via thermofield dynamics
Applying the thermo field dynamics, we reformulate exact quantum number
projection in the finite-temperature Hartree-Fock-Bogoliubov theory. Explicit
formulae are derived for the simultaneous projection of particle number and
angular momentum, in parallel to the zero-temperature case. We also propose a
practical method for the variation-after-projection calculation, by
approximating entropy without conflict with the Peierls inequality. The quantum
number projection in the finite-temperature mean-field theory will be useful to
study effects of quantum fluctuations associated with the conservation laws on
thermal properties of nuclei.Comment: 27 pages, using revtex4, to be published in PR
Parity Dependence of Nuclear Level Densities
A simple formula for the ratio of the number of odd- and even-parity states
as a function of temperature is derived. This formula is used to calculate the
ratio of level densities of opposite parities as a function of excitation
energy. We test the formula with quantum Monte Carlo shell model calculations
in the -shell. The formula describes well the transition from low
excitation energies where a single parity dominates to high excitations where
the two densities are equal.Comment: 14 pages, 4 eps figures included, RevTe
RKKY interaction between adsorbed magnetic impurities in graphene: Symmetry and strain effects
The growing interest in carbon-based spintronics has stimulated a number of
recent theoretical studies on the RKKY interaction in graphene, with the aim of
determining the most energetically favourable alignments between embedded
magnetic moments. The RKKY interaction in undoped graphene decays faster than
expected for conventional two-dimensional materials and recent studies suggest
that the adsorption configurations favoured by many transition-metal impurities
may lead to even shorter ranged decays and possible sign-changing oscillations.
Here we show that these features emerge in a mathematically transparent manner
when the symmetry of the configurations is included in the calculation.
Furthermore, we show that by breaking the symmetry of the graphene lattice, via
uniaxial strain, the decay rate, and hence the range, of the RKKY interaction
can be significantly altered. Our results suggest that magnetic interactions
between adsorbed impurities in graphene can be manipulated by careful strain
engineering of such systems.Comment: 12 pages, 6 figures, submitte
Conductance of graphene nanoribbon junctions and the tight binding model
Planar carbon-based electronic devices, including metal/semiconductor junctions, transistors and interconnects, can now be formed from patterned sheets of graphene. Most simulations of charge transport within graphene-based electronic devices assume an energy band structure based on a nearest-neighbour tight binding analysis. In this paper, the energy band structure and conductance of graphene nanoribbons and metal/semiconductor junctions are obtained using a third nearest-neighbour tight binding analysis in conjunction with an efficient nonequilibrium Greenâs function formalism. We find significant differences in both the energy band structure and conductance obtained with the two approximations
Total and Parity-Projected Level Densities of Iron-Region Nuclei in the Auxiliary Fields Monte Carlo Shell Model
We use the auxiliary-fields Monte Carlo method for the shell model in the
complete -shell to calculate level densities. We introduce
parity projection techniques which enable us to calculate the parity dependence
of the level density. Results are presented for Fe, where the calculated
total level density is found to be in remarkable agreement with the
experimental level density. The parity-projected densities are well described
by a backshifted Bethe formula, but with significant dependence of the
single-particle level-density and backshift parameters on parity. We compare
our exact results with those of the thermal Hartree-Fock approximation.Comment: 14 pages, 3 Postscript figures included, RevTe
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