10,843 research outputs found
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
On "the authentic damping mechanism" of the phonon damping model
Some general features of the phonon damping model are presented. It is
concluded that the fits performed within this model have no physical content
Neutron transition strengths of states in the neutron rich Oxygen isotopes determined from inelastic proton scattering
A coupled-channel analysis of the O data has been
performed to determine the neutron transition strengths of 2 states in
Oxygen targets, using the microscopic optical potential and inelastic form
factor calculated in the folding model. A complex density- and \emph{isospin}
dependent version of the CDM3Y6 interaction was constructed, based on the
Brueckner-Hatree-Fock calculation of nuclear matter, for the folding model
input. Given an accurate isovector density dependence of the CDM3Y6
interaction, the isoscalar () and isovector () deformation
lengths of 2 states in O have been extracted from the
folding model analysis of the data. A specific -dependence of
and has been established which can be linked to the
neutron shell closure occurring at approaching 16. The strongest isovector
deformation was found for 2 state in O, with about 2.5
times larger than , which indicates a strong core polarization by the
valence neutrons in O. The ratios of the neutron/proton transition
matrix elements () determined for 2 states in O have
been compared to those deduced from the mirror symmetry, using the measured
values of 2 states in the proton rich Ne and Mg
nuclei, to discuss the isospin impurity in the excitation of the
and isobars.Comment: Version accepted for publication in Physical Review
Scanning optical pyrometer for measuring temperatures in hollow cathodes
Life-limiting processes in hollow cathodes are determined largely by the temperature of the electron emitter. To support cathode life assessment, a noncontact temperature measurement technique which employs a stepper motor-driven fiber optic probe was developed. The probe is driven inside the hollow cathode and collects light radiated by the hot interior surface of the emitter. Ratio pyrometry is used to determine the axial temperature profile. Thermocouples on the orifice plate provide measurements of the external temperature during cathode operation and are used to calibrate the pyrometer system in situ with a small oven enclosing the externally heated cathode. The diagnostic method and initial measurements of the temperature distribution in a hollow cathode are discussed
Effect of growth conditions on optical properties of CdSe/ZnSe single quantum dots
In this work, we have investigated the optical properties of two samples of
CdSe quantum dots by using submicro-photoluminescence spectroscopy. The effect
of vicinal-surface GaAs substrates on their properties has been also assessed.
The thinner sample, grown on a substrate with vicinal surface, includes only
dots with a diameter of less than 10 nm (type A islands). Islands of an average
diameter of about 16 nm (type B islands) that are related to a phase transition
via a Stranski-Krastanow growth process are also distributed in the thicker
sample grown on an oriented substrate. We have studied the evolution of
lineshapes of PL spectra for these two samples by improving spatial resolution
that was achieved using nanoapertures or mesa structures. It was found that the
use of a substrate with the vicinal surface leads to the suppression of
excitonic PL emitted from a wetting layer.Comment: 2pages, 2 figures, Proceedings of International Conference On
Superlattices Nano-Structures And Nano-Devices, July, Toulouse, France, to
appear in the special issue of Physica
Singularity Free Inhomogeneous Models with Heat Flow
We present a class of singularity free exact cosmological solutions of
Einstein's equations describing a perfect fluid with heat flow. It is obtained
as generalization of the Senovilla class [1] corresponding to incoherent
radiation field. The spacetime is cylindrically symmetric and globally regular.Comment: 6 pages, TeX, to appear in Class.Quant.Gra
Competing magnetic fluctuations in Sr3Ru2O7 probed by Ti doping
We report the effect of nonmagnetic Ti4+ impurities on the electronic and
magnetic properties of Sr3Ru2O7. Small amounts of Ti suppress the
characteristic peak in magnetic susceptibility near 16 K and result in a sharp
upturn in specific heat. The metamagnetic quantum phase transition and related
anomalous features are quickly smeared out by small amounts of Ti. These
results provide strong evidence for the existence of competing magnetic
fluctuations in the ground state of Sr3Ru2O7. Ti doping suppresses the low
temperature antiferromagnetic interactions that arise from Fermi surface
nesting, leaving the system in a state dominated by ferromagnetic fluctuations.Comment: 5 pages, 4 figures, 1 tabl
Photoluminescence and photoluminescence excitation studies of lateral size effects in Zn_{1-x}Mn_xSe/ZnSe quantum disc samples of different radii
Quantum disc structures (with diameters of 200 nm and 100 nm) were prepared
from a Zn_{0.72}Mn_{0.28}Se/ZnSe single quantum well structure by electron beam
lithography followed by an etching procedure which combined dry and wet etching
techniques. The quantum disc structures and the parent structure were studied
by photoluminescence and photoluminescence excitation spectroscopy. For the
light-hole excitons in the quantum well region, shifts of the energy positions
are observed following fabrication of the discs, confirming that strain
relaxation occurs in the pillars. The light-hole exciton lines also sharpen
following disc fabrication: this is due to an interplay between strain effects
(related to dislocations) and the lateral size of the discs. A further
consequence of the small lateral sizes of the discs is that the intensity of
the donor-bound exciton emission from the disc is found to decrease with the
disc radius. These size-related effects occur before the disc radius is reduced
to dimensions necessary for lateral quantum confinement to occur but will
remain important when the discs are made small enough to be considered as
quantum dots.Comment: LaTeX2e, 13 pages, 6 figures (epsfig
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