279 research outputs found
Time dependent dirac equation with relativistic mean field dynamics applied to heavy ion scattering
We treat the relativistic propagation of nucleons coupled to scalar- and vector-meson fields in a mean-field approximation. The time-dependent Dirac and mean-meson-field equations are solved numerically in three dimensions. Collisions of 16O(300, 600, and 1200 MeV/nucleon) + 16O are studied for various impact parameters. The results are compared to other recent theoretical approaches. The calculations predict spallation, large transverse-momentum transfer, and positive-angle sidewards flow, in qualitative agreement with the data in this energy regime
The Skyrme energy functional and low lying 2+ states in Sn, Cd and Te isotopes
We study the predictive power of Skyrme forces with respect to low lying
quadrupole spectra along the chains of Sn, Cd, and Te isotopes. Excitation
energies and B(E2) values for the lowest quadrupole states are computed from a
collective Schroedinger equation which as deduced through collective path
generated by constraint Skyrme-Hartree-Fock (SHF) plus self-consistent cranking
for the dynamical response. We compare the results from four different Skyrme
forces, all treated with two different pairing forces (volume versus
density-dependent pairing). The region around the neutron shell closure N=82 is
very sensitive to changes in the Skyrme while the mid-shell isotopes in the
region N<82 depend mainly on the adjustment of pairing. The neutron rich
isotopes are most sensitive and depend on both aspects
On the equivalence of pairing correlations and intrinsic vortical currents in rotating nuclei
The present paper establishes a link between pairing correlations in rotating
nuclei and collective vortical modes in the intrinsic frame. We show that the
latter can be embodied by a simple S-type coupling a la Chandrasekhar between
rotational and intrinsic vortical collective modes. This results from a
comparison between the solutions of microscopic calculations within the HFB and
the HF Routhian formalisms. The HF Routhian solutions are constrained to have
the same Kelvin circulation expectation value as the HFB ones. It is shown in
several mass regions, pairing regimes, and for various spin values that this
procedure yields moments of inertia, angular velocities, and current
distributions which are very similar within both formalisms. We finally present
perspectives for further studies.Comment: 8 pages, 4 figures, submitted to Phys. Rev.
Augmented Lagrangian Method for Constrained Nuclear Density Functional Theory
The augmented Lagrangiam method (ALM), widely used in quantum chemistry
constrained optimization problems, is applied in the context of the nuclear
Density Functional Theory (DFT) in the self-consistent constrained Skyrme
Hartree-Fock-Bogoliubov (CHFB) variant. The ALM allows precise calculations of
multidimensional energy surfaces in the space of collective coordinates that
are needed to, e.g., determine fission pathways and saddle points; it improves
accuracy of computed derivatives with respect to collective variables that are
used to determine collective inertia; and is well adapted to supercomputer
applications.Comment: 6 pages, 3 figures; to appear in Eur. Phys. J.
Recommended from our members
Relativistic mean-field theories and nuclear properties
The nucleus is described as consisting of relativistic nucleons and explicit mesonic degrees-of-freedom which are considered to be the relativistic generalization of the Skyrme force. The meson-parameters can be adjusted such that the model gives an excellent description of spherical nuclear ground states, first axially symmetric deformed calculations are presented. Dynamic calculations of relativistic /sup 16/O-/sup 16/O scattering are also done; they show pronounced effects of the mesonic degrees-of-freedom. 24 refs., 3 figs., 3 tabs
Self-consistent anisotropic oscillator with cranked angular and vortex velocities
The Kelvin circulation is the kinematical Hermitian observable that measures
the true character of nuclear rotation. For the anisotropic oscillator, mean
field solutions with fixed angular momentum and Kelvin circulation are derived
in analytic form. The cranking Lagrange multipliers corresponding to the two
constraints are the angular and vortex velocities. Self-consistent solutions
are reported with a constraint to constant volume.Comment: 12 pages, LaTex/RevTex, Phys. Rev. C4
Medium effects in high energy heavy-ion collisions
The change of hadron properties in dense matter based on various theoretical
approaches are reviewed. Incorporating these medium effects in the relativistic
transport model, which treats consistently the change of hadron masses and
energies in dense matter via the scalar and vector fields, heavy-ion collisions
at energies available from SIS/GSI, AGS/BNL, and SPS/CERN are studied. This
model is seen to provide satisfactory explanations for the observed enhancement
of kaon, antikaon, and antiproton yields as well as soft pions in the
transverse direction from the SIS experiments. In the AGS heavy-ion
experiments, it can account for the enhanced ratio, the difference
in the slope parameters of the and transverse kinetic energy
spectra, and the lower apparent temperature of antiprotons than that of
protons. This model also provides possible explanations for the observed
enhancement of low-mass dileptons, phi mesons, and antilambdas in heavy-ion
collisions at SPS energies. Furthermore, the change of hadron properties in hot
dense matter leads to new signatures of the quark-gluon plasma to hadronic
matter transition in future ultrarelativistic heavy-ion collisions at RHIC/BNL.Comment: RevTeX, 65 pages, including 25 postscript figures, invited topical
review for Journal of Physics G: Nuclear and Particle Physic
Seafloor biodiversity of Canada's three oceans: patterns, hotspots and potential drivers
Aim
We examined the relationships between bathymetry, latitude and energy and the diversity of marine benthic invertebrates across wide environmental ranges of Canada's three oceans.
Location
Canadian Pacific, Arctic and Atlantic Oceans from the intertidal zone to upper bathyal depths, encompassing 13 marine ecoregions.
Methods
We compiled 35 benthic datasets that encompass 3,337 taxa (70% identified to species and 21% to genus) from 13,172 samples spanning 6,117 sites. Partitioning the analyses by different gear types, ecoregions or sites, we used Hill numbers to examine spatial patterns in 뱉diversity. We used resampling and extrapolation to standardized sampling effort and examined the effects of depth, latitude, chemical energy (export particulate organic carbon [POC] flux), thermal energy (bottom temperature) and seasonality of primary production on the benthic biodiversity.
Results
The Canadian Arctic harboured the highest benthic diversity (e.g. epifauna and common and dominant infauna species), whereas the lowest diversity was found in the Atlantic. The Puget Trough (Pacific), Beaufort Sea, Arctic Archipelago, Hudson Bay, Northern Labrador and Southern Grand Bank (Atlantic) were the âhotspots" of diversity among the ecoregions. The infauna and epifauna both exhibited humpâshaped diversityâdepth relationships, with peak diversity near shelf breaks; latitude (positively) predicted infaunal diversity, albeit weakly. Food supply, as inferred from primary production and depth, was more important than thermal energy in controlling diversity patterns. Limitations with respect to calculating POC flux in coastal (e.g. terrestrial runoff) and iceâcovered regions or biological interactions may explain the negative POC fluxâinfaunal diversity relationship.
Main Conclusions
We show previously unreported diversity hotspots in the Canadian Arctic and in other ecoregions. Our analyses reveal potential controlling mechanisms of largeâscale benthic biodiversity patterns in Canada's three oceans, which are inconsistent with the prevailing view of seafloor energyâdiversity relationships. These results provide insightful information for conservation that can help to implement further MPA networks
Camilla: A Centaur reconnaissance and impact mission concept
Centaurs, minor planets with a semi-major axis between the orbits of Jupiter and Neptune (5â30 AU), are thought to be among the most diverse small bodies in the solar system. These important targets for future missions may have recently been Kuiper Belt Objects (KBOs), which are thought to be chemically and physically primitive remnants of the early solar system. While the Kuiper Belt spans distances of 30â50 AU, making direct observations difficult, Centaurs' proximity to the Earth and Sun make them more accessible targets for robotic missions. Thus, we outline a mission concept designed to reconnoiter 10199 Chariklo, the largest Centaur and smallest ringed body yet discovered. Named for a legendary Centaur tamer, the conceptual Camilla mission is designed to fit under the cost cap of the National Aeronautics and Space Administration (NASA) New Frontiers program, leveraging a conservative payload to support a foundational scientific investigation to these primitive bodies. Specifically, the single flyby encounter utilizes a combined high-resolution camera/VIS-IR mapping spectrometer, a sub-mm point spectrometer, and a UV mapping spectrometer. In addition, the mission concept utilizes a kinetic impactor, which would provide the first opportunity to sample the composition of potentially primitive subsurface material beyond Saturn, thus providing key insights into solar system origins. Such a flyby of the Chariklo system would provide a linchpin in the understanding of small body composition, evolution, and transport of materials in the solar system
The BenBioDen database, a global database for meio-, macro- and megabenthic biomass and densities
Benthic fauna refers to all fauna that live in or on the seafloor, which researchers typically divide into size classes meiobenthos (32/64â”mâ0.5/1âmm), macrobenthos (250â”mâ1âcm), and megabenthos (>1âcm). Benthic fauna play important roles in bioturbation activity, mineralization of organic matter, and in marine food webs. Evaluating their role in these ecosystem functions requires knowledge of their global distribution and biomass. We therefore established the BenBioDen database, the largest open-access database for marine benthic biomass and density data compiled so far. In total, it includes 11,792 georeferenced benthic biomass and 51,559 benthic density records from 384 and 600 studies, respectively. We selected all references following the procedure for systematic reviews and meta-analyses, and report biomass records as grams of wet mass, dry mass, or ash-free dry mass, or carbon per m2 and as abundance records as individuals per m2. This database provides a point of reference for future studies on the distribution and biomass of benthic fauna
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