1,359 research outputs found
Strong dineutron correlation in 8He and 18C
We study the spatial structure of four valence neutrons in the ground state
of He and C nuclei using a core+4 model. For this purpose, we
employ a density-dependent contact interaction among the valence neutrons, and
solve the five-body Hamiltonian in the Hartree-Fock-Bogoliubov (HFB)
approximation. We show that two neutrons with the coupled spin of =0 exhibit
a strong dineutron correlation around the surface of these nuclei, whereas the
correlation between the two dineutrons is much weaker. Our calculation
indicates that the probability of the (1p and [(1p
(p] configurations in the ground state wave function of He
nucleus is 34.9% and 23.7%, respectively. This is consistent with the recent
experimental finding with the He(He reaction, that is, the ground
state wave function of He deviates significantly from the pure
(1p structure.Comment: 10 pages, 9 figures, 3 table
Widths of Isobaric Analog Resonances: a microscopic approach
A self-consistent particle-phonon coupling model is used to investigate the
properties of the isobaric analog resonance in Bi. It is shown that
quantitative agreement with experimental data for the energy and the width can
be obtained if the effects of isospin-breaking nuclear forces are included, in
addition to the Coulomb force effects. A connection between microscopic model
predictions and doorway state approaches which make use of the isovector
monopole resonance, is established via a phenomenological ansatz for the
optical potential.Comment: 18 pages, 1 figure. To appear on Phys. Rev. C (tentatively scheduled
for June 1998
Microscopic Study of the Isoscalar Giant Monopole Resonance in Cd, Sn and Pb Isotopes
The isoscalar giant monopole resonance (ISGMR) in Cd, Sn and Pb isotopes has
been studied within the self-consistent Skyrme Hartree-Fock+BCS and
quasi-particle random phase approximation (QRPA). Three Skyrme parameter sets
are used in the calculations, i.e., SLy5, SkM* and SkP, since they are
characterized by different values of the compression modulus in symmetric
nuclear matter, namely K=230, 217, and 202 MeV, respectively. We also
investigate the effect of different types of pairing forces on the ISGMR in Cd,
Sn and Pb isotopes. The calculated peak energies and the strength distributions
of ISGMR are compared with available experimental data. We find that SkP fails
completely to describe the ISGMR strength distribution for all isotopes due to
its low value of the nuclear matter incompressibility, namely K=202 MeV. On the
other hand, the SLy5 parameter set, supplemented by an appropriate pairing
interaction, gives a reasonable description of the ISGMR in Cd and Pb isotopes.
A better description of ISGMR in Sn isotopes is achieved by the SkM*
interaction, that has a somewhat softer value of the nuclear incompressibility.Comment: Submitted to Phys. Rev.
Designing optimal discrete-feedback thermodynamic engines
Feedback can be utilized to convert information into useful work, making it
an effective tool for increasing the performance of thermodynamic engines.
Using feedback reversibility as a guiding principle, we devise a method for
designing optimal feedback protocols for thermodynamic engines that extract all
the information gained during feedback as work. Our method is based on the
observation that in a feedback-reversible process the measurement and the
time-reversal of the ensuing protocol both prepare the system in the same
probabilistic state. We illustrate the utility of our method with two examples
of the multi-particle Szilard engine.Comment: 15 pages, 5 figures, submitted to New J. Phy
Extended Skyrme interaction (II): ground state of nuclei and of nuclear matter
We study the effect of time-odd components of the Skyrme energy density
functionals on the ground state of finite nuclei and in nuclear matter. The
spin-density dependent terms, which have been recently proposed as an extension
of the standard Skyrme interaction, are shown to change the total binding
energy of odd-nuclei by only few tenths of keV, while the time-odd components
of standard Skyrme interactions give an effect that is larger by one order of
magnitude. The HFB-17 mass formula based on a Skyrme parametrization is
adjusted including the new spin-density dependent terms. A comprehensive study
of binding energies in the whole mass table of 2149 nuclei gives a root mean
square (rms) deviation of 0.575 MeV between experimental data and the
calculated results, which is slightly better than the original HFB-17 mass
formula. From the analysis of the spin instabilities of nuclear matter,
restrictions on the parameters governing the spin-density dependent terms are
evaluated. We conclude that with the extended Skyrme interaction, the Landau
parameters and could be tuned with a large flexibility
without changing the ground-state properties in nuclei and in nuclear matter.Comment: 18 pages, 4 tables, 6 figure
Visible Luminescence from Octadecylsilane Monolayers on Silica Surfaces : Time-Resolved Photoluminescence Characterization
blue photoluminescence, nanometer-sized silica particles, time-resolved photoluminescenceWe have found that the adsorption of octadecyltrichlorosilane (OTS) monolayers on nanometer-sized silica particles yields a stable blue photoluminescence (PL) with a time scale of nanoseconds (N. Sagawa and T. Uchino, Appl. Phys. Lett. 87, 251923 (2005)). The observed PL intensity increases after curing at temperatures from 100 to 300 °C, suggesting that condensations between adjacent OTS molecules on the silica surface are related to the PL. The PL decay curve of the cured samples remains unchanged from 77 to 450 K, whereas the time-integrated PL intensity shows a monotonous decrease with increasing temperature. From these experimental results, a model of radiative and nonradiative process associated with the PL is presented
Study on the Prognosis of Tuberculous Meningitis Treated with Streptomycin in Children
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Mechanical and chemical spinodal instabilities in finite quantum systems
Self consistent quantum approaches are used to study the instabilities of
finite nuclear systems. The frequencies of multipole density fluctuations are
determined as a function of dilution and temperature, for several isotopes. The
spinodal region of the phase diagrams is determined and it appears that
instabilities are reduced by finite size effects. The role of surface and
volume instabilities is discussed. It is indicated that the important chemical
effects associated with mechanical disruption may lead to isospin
fractionation.Comment: 4 pages, 4 figure
Incompressibility of finite fermionic systems: stable and exotic atomic nuclei
The incompressibility of finite fermionic systems is investigated using
analytical approaches and microscopic models. The incompressibility of a system
is directly linked to the zero-point kinetic energy of constituent fermions,
and this is a universal feature of fermionic systems. In the case of atomic
nuclei, this implies a constant value of the incompressibility in medium-heavy
and heavy nuclei. The evolution of nuclear incompressibility along Sn and Pb
isotopic chains is analyzed using global microscopic models, based on both
non-relativistic and relativistic energy functionals. The result is an almost
constant incompressibility in stable nuclei and systems not far from stability,
and a steep decrease in nuclei with pronounced neutron excess, caused by the
emergence of a soft monopole mode in neutron-rich nuclei.Comment: 7 pages, 5 figure
Extended sudden approximation model for high-energy nucleon removal reactions
A model based on the sudden approximation has been developed to describe high
energy single nucleon removal reactions. Within this approach, which takes as
its starting point the formalism of Hansen \cite{Anne2}, the nucleon-removal
cross section and the full 3-dimensional momentum distributions of the core
fragments including absorption, diffraction, Coulomb and nuclear-Coulomb
interference amplitudes, have been calculated. The Coulomb breakup has been
treated to all orders for the dipole interaction. The model has been compared
to experimental data for a range of light, neutron-rich psd-shell nuclei. Good
agreement was found for both the inclusive cross sections and momentum
distributions. In the case of C, comparison is also made with the
results of calculations using the transfer-to-the-continuum model. The
calculated 3-dimensional momentum distributions exhibit longitudinal and
transverse momentum components that are strongly coupled by the reaction for
s-wave states, whilst no such effect is apparent for d-waves. Incomplete
detection of transverse momenta arising fromlimited experimental acceptances
thus leads to a narrowing of the longitudinal distributions for nuclei with
significant s-wave valence neutron configurations, as confirmed by the data.
Asymmetries in the longitudinal momentum distributions attributed to
diffractive dissociation are also explored.Comment: 16 figures, submitted to Phys. Rev.
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