2,688 research outputs found
A theorem of Tits type for compact Kahler manifolds
We prove a theorem of Tits type about automorphism groups for compact Kahler
manifolds, which has been conjectured in the paper [KOZ].Comment: Inventiones Mathematicae (to appear), 11 page
Pairing effect on the giant dipole resonance width at low temperature
The width of the giant dipole resonance (GDR) at finite temperature T in
Sn-120 is calculated within the Phonon Damping Model including the neutron
thermal pairing gap determined from the modified BCS theory. It is shown that
the effect of thermal pairing causes a smaller GDR width at T below 2 MeV as
compared to the one obtained neglecting pairing. This improves significantly
the agreement between theory and experiment including the most recent data
point at T = 1 MeV.Comment: 8 pages, 5 figures to be published in Physical Review
Time resolved fission in metal clusters
We explore from a theoretical point of view pump and probe (P&P) analysis for
fission of metal clusters where probe pulses are generalized to allow for
scanning various frequencies. We show that it is possible to measure the time
the system needs to develop to scission. This is achieved by a proper choice of
both delay and frequency of the probe pulse. A more detailed analysis even
allows to access the various intermediate stages of the fission process.Comment: 4 pages, 4 figure
Dynamics of metal clusters in rare gas clusters
We investigate the dynamics of Na clusters embedded in Ar matrices. We use a
hierarchical approach, accounting microscopically for the cluster's degrees of
freedom and more coarsely for the matrix. The dynamical polarizability of the
Ar atoms and the strong Pauli-repulsion exerted by the Ar-electrons are taken
into account. We discuss the impact of the matrix on the cluster gross
properties and on its optical response. We then consider a realistic case of
irradiation by a moderately intense laser and discuss the impact of the matrix
on the hindrance of the explosion, as well as a possible pump probe scenario
for analyzing dynamical responses.Comment: Proceedings of the 30th International Workshop on Condensed Matter
Theories, Dresden, June 05 - 10, 2006, World Scientific. 3 figure
Exchange Interaction and in Alkaline-earth-metal-oxide-based DMS without Magnetic Impurities: First Principle Pseudo-SIC and Monte Carlo Calculation
The prospects of half-metallic ferromagnetism being induced by the
incorporation of C atoms into alkaline-earth-metal-oxides are investigated by
the first principle calculation. The origin of the ferromagnetism is discussed
through the calculation of the electronic structure and exchange coupling
constant by using the pseudo-potential-like self-interaction-corrected local
spin density method. The Curie temperature () is also predicted by
employing the Monte Carlo simulation. It is shown that by taking the electron
self-interaction into account, the half-metallic ferromagnetism induced by C in
the host materials is more stabilized in comparison with the standard LDA case,
and the C's electron states in the bandgap become more localized resulting
in the predominance of the short-ranged exchange interaction. While the
ferromagnetism in MgOC is stabilized due to the exchange
interaction of the -nearest neighbor pairs and might be suppressed by the
anti-ferromagnetic super-exchange interaction at higher , the ferromagnetism
in CaOC, SrOC, and BaOC is stabilized by
both the - and -nearest neighbor pairs, and monotonously
increases with the C concentration.Comment: 5 pages, 5 figure
New method for measuring azimuthal distributions in nucleus-nucleus collisions
The methods currently used to measure azimuthal distributions of particles in
heavy ion collisions assume that all azimuthal correlations between particles
result from their correlation with the reaction plane. However, other
correlations exist, and it is safe to neglect them only if azimuthal
anisotropies are much larger than 1/sqrt(N), with N the total number of
particles emitted in the collision. This condition is not satisfied at
ultrarelativistic energies. We propose a new method, based on a cumulant
expansion of multiparticle azimuthal correlations, which allows to measure much
smaller values of azimuthal anisotropies, down to 1/N. It is simple to
implement and can be used to measure both integrated and differential flow.
Furthermore, this method automatically eliminates the major systematic errors,
which are due to azimuthal asymmetries in the detector acceptance.Comment: final version (misprints corrected), to be published in Phys.Rev.
PO-0772: Multi-center validation of a model for prostate tumor delineation using multi-parametric MRI
Population of isomers in decay of the giant dipole resonance
The value of an isomeric ratio (IR) in N=81 isotones (Ba, Ce,
Nd and Sm) is studied by means of the ( reaction.
This quantity measures a probability to populate the isomeric state in respect
to the ground state population. In ( reactions, the giant dipole
resonance (GDR) is excited and after its decay by a neutron emission, the
nucleus has an excitation energy of a few MeV. The forthcoming decay
by direct or cascade transitions deexcites the nucleus into an isomeric or
ground state. It has been observed experimentally that the IR for Ba
and Ce equals about 0.13 while in two heavier isotones it is even less
than half the size. To explain this effect, the structure of the excited states
in the energy region up to 6.5 MeV has been calculated within the Quasiparticle
Phonon Model. Many states are found connected to the ground and isomeric states
by , and transitions. The single-particle component of the wave
function is responsible for the large values of the transitions. The calculated
value of the isomeric ratio is in very good agreement with the experimental
data for all isotones. A slightly different value of maximum energy with which
the nuclei rest after neutron decay of the GDR is responsible for the reported
effect of the A-dependence of the IR.Comment: 16 pages, 4 Fig
Scalar ground-state observables in the random phase approximation
We calculate the ground-state expectation value of scalar observables in the
matrix formulation of the random phase approximation (RPA). Our expression,
derived using the quasiboson approximation, is a straightforward generalization
of the RPA correlation energy. We test the reliability of our expression by
comparing against full diagonalization in 0 h-bar omega shell-model spaces. In
general the RPA values are an improvement over mean-field (Hartree-Fock)
results, but are not always consistent with shell-model results. We also
consider exact symmetries broken in the mean-field state and whether or not
they are restored in RPA.Comment: 7 pages, 3 figure
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