574 research outputs found
The long journey from the giant-monopole resonance to the nuclear-matter incompressibility
Differences in the density dependence of the symmetry energy predicted by
nonrelativistic and relativistic models are suggested, at least in part, as the
culprit for the discrepancy in the values of the compression modulus of
symmetric nuclear matter extracted from the energy of the giant monopole
resonance in 208Pb. ``Best-fit'' relativistic models, with stiffer symmetry
energies than Skyrme interactions, consistently predict higher compression
moduli than nonrelativistic approaches. Relativistic models with compression
moduli in the physically acceptable range of K=200-300 MeV are used to compute
the distribution of isoscalar monopole strength in 208Pb. When the symmetry
energy is artificially softened in one of these models, in an attempt to
simulate the symmetry energy of Skyrme interactions, a lower value for the
compression modulus is indeed obtained. It is concluded that the proposed
measurement of the neutron skin in 208Pb, aimed at constraining the density
dependence of the symmetry energy and recently correlated to the structure of
neutron stars, will also become instrumental in the determination of the
compression modulus of nuclear matter.Comment: 9 pages with 2 (eps) figure
Self-consistent description of nuclear compressional modes
Isoscalar monopole and dipole compressional modes are computed for a variety
of closed-shell nuclei in a relativistic random-phase approximation to three
different parametrizations of the Walecka model with scalar self-interactions.
Particular emphasis is placed on the role of self-consistency which by itself,
and with little else, guarantees the decoupling of the spurious
isoscalar-dipole strength from the physical response and the conservation of
the vector current. A powerful new relation is introduced to quantify the
violation of the vector current in terms of various ground-state form-factors.
For the isoscalar-dipole mode two distinct regions are clearly identified: (i)
a high-energy component that is sensitive to the size of the nucleus and scales
with the compressibility of the model and (ii) a low-energy component that is
insensitivity to the nuclear compressibility. A fairly good description of both
compressional modes is obtained by using a ``soft'' parametrization having a
compression modulus of K=224 MeV.Comment: 28 pages and 10 figures; submitted to PR
Neutron Hole States of Mo-99
Journals published by the American Physical Society can be found at http://publish.aps.org
Spin-Orbit Splitting in Non-Relativistic and Relativistic Self-Consistent Models
The splitting of single-particle energies between spin-orbit partners in
nuclei is examined in the framework of different self-consistent approachs,
non-relativistic as well as relativistic. Analytical expressions of spin-orbit
potentials are given for various cases. Proton spin-orbit splittings are
calculated along some isotopic chains (O, Ca, Sn) and they are compared with
existing data. It is found that the isotopic dependence of the relativistic
mean field predictions is similar to that of some Skyrme forces while the
relativistic Hartree-Fock approach leads to a very different dependence due to
the strong non-locality.Comment: 12 pages, RevTeX, 4 new figs.in .zip format, unchanged conclusions,
Phys. ReV.
Caloric curves and critical behavior in nuclei
Data from a number of different experimental measurements have been used to
construct caloric curves for five different regions of nuclear mass. These
curves are qualitatively similar and exhibit plateaus at the higher excitation
energies. The limiting temperatures represented by the plateaus decrease with
increasing nuclear mass and are in very good agreement with results of recent
calculations employing either a chiral symmetry model or the Gogny interaction.
This agreement strongly favors a soft equation of state. Evidence is presented
that critical excitation energies and critical temperatures for nuclei can be
determined over a large mass range when the mass variations inherent in many
caloric curve measurements are taken into account.Comment: In response to referees comments we have improved the discussion of
the figures and added a new figure showing the relationship between the
effective level density and the excitation energy. The discussion has been
reordered and comments are made on recent data which support the hypothesis
of a mass dependence of caloric curve
Generator Coordinate Method Calculations for Ground and First Excited Collective States in He, O and Ca Nuclei
The main characteristics of the ground and, in particular, the first excited
monopole state in the He, O and Ca nuclei are studied
within the generator coordinate method using Skyrme-type effective forces and
three construction potentials, namely the harmonic-oscillator, the square-well
and Woods-Saxon potentials. Calculations of density distributions, radii,
nucleon momentum distributions, natural orbitals, occupation numbers and
depletions of the Fermi sea, as well as of pair density and momentum
distributions are carried out. A comparison of these quantities for both ground
and first excited monopole states with the available empirical data and with
the results of other theoretical methods are given and discussed in detail.Comment: 15 pages, LaTeX, 6 Postscript figures, submitted to EPJ
Nuclear matter incompressibility coefficient in relativistic and nonrelativistic microscopic models
We systematically analyze the recent claim that nonrelativistic and
relativistic mean field (RMF) based random phase approximation (RPA)
calculations for the centroid energy E_0 of the isoscalar giant monopole
resonance yield for the nuclear matter incompressibility coefficient, K_{nm},
values which differ by about 20%. For an appropriate comparison with the RMF
based RPA calculations, we obtain the parameters for the Skyrme force used in
the nonrelativistic model by adopting the same procedure as employed in the
determination of the NL3 parameter set of an effective Lagrangian used in the
RMF model. Our investigation suggest that the discrepancy between the values of
K_{nm} predicted by the relativistic and nonrelativistic models is
significantly less than 20%.Comment: Revtex file (13 pages), appearing in PRC-Rapid Com
Designing medical technology for developing countries
Resource-poor countries have markedly different healthcare systems. Many developed nations donate medical supplies to these countries, but this often does not meet the needs of the recipients. Our goal is to develop simple healthcare solutions that can be produced in-country so the developing area does not depend on outside sources for its supplies. Our group works on many projects, including sustainable woven grass neck braces and a variety of low-cost sensors. Our designs do not require frequent donations, minimize the use of consumables, and provide better detection and/or treatment of prevalent medical concerns. Our baby monitor will detect skin temperature and control a heating element based on the needs of the infant. Our low-cost glucometer operates with the use of test strips that can be printed for a penny with a standard inkjet printer. This will allow the hospital or clinic to print the strips themselves rather than depend on donated strips. Our bacterial sensor will measure resistance to quickly detect the quantity of bacteria in a sample. We seek sustainable solutions for in-house manufacturing to advance more self-sufficient healthcare systems
Collective excitations in the Unitary Correlation Operator Method and relativistic QRPA studies of exotic nuclei
The collective excitation phenomena in atomic nuclei are studied in two
different formulations of the Random Phase Approximation (RPA): (i) RPA based
on correlated realistic nucleon-nucleon interactions constructed within the
Unitary Correlation Operator Method (UCOM), and (ii) relativistic RPA (RRPA)
derived from effective Lagrangians with density-dependent meson-exchange
interactions. The former includes the dominant interaction-induced short-range
central and tensor correlations by means of an unitary transformation. It is
shown that UCOM-RPA correlations induced by collective nuclear vibrations
recover a part of the residual long-range correlations that are not explicitly
included in the UCOM Hartree-Fock ground state. Both RPA models are employed in
studies of the isoscalar monopole resonance (ISGMR) in closed-shell nuclei
across the nuclide chart, with an emphasis on the sensitivity of its properties
on the constraints for the range of the UCOM correlation functions. Within the
Relativistic Quasiparticle RPA (RQRPA) based on Relativistic Hartree-Bogoliubov
model, the occurrence of pronounced low-lying dipole excitations is predicted
in nuclei towards the proton drip-line. From the analysis of the transition
densities and the structure of the RQRPA amplitudes, it is shown that these
states correspond to the proton pygmy dipole resonance.Comment: 15 pages, 4 figures, submitted to Physics of Atomic Nuclei,
conference proceedings, "Frontiers in the Physics of Nucleus", St.
Petersburg, 28. June-1. July, 200
Effect of the momentum dependence of nuclear symmetry potential on the transverse and elliptic flows
In the framework of the isospin-dependent Boltzmann-Uehling-Uhlenbeck
transport model, effect of the momentum dependence of nuclear symmetry
potential on nuclear transverse and elliptic flows in the neutron-rich reaction
Sn+Sn at a beam energy of 400 MeV/nucleon is studied. We find
that the momentum dependence of nuclear symmetry potential affects the rapidity
distribution of the free neutron to proton ratio, the neutron and the proton
transverse flows as a function of rapidity. The momentum dependence of nuclear
symmetry potential affects the neutron-proton differential transverse flow more
evidently than the difference of neutron and proton transverse flows as well as
the difference of proton and neutron elliptic flows. It is thus better to probe
the symmetry energy by using the difference of neutron and proton flows since
the momentum dependence of nuclear symmetry potential is still an open
question. And it is better to probe the momentum dependence of nuclear symmetry
potential by using the neutron-proton differential transverse flow and the
rapidity distribution of the free neutron to proton ratio.Comment: 6 pages, 6 figures, to be published by EPJ
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