4,797 research outputs found
Systematic study of deformed nuclei at the drip lines and beyond
An improved prescription for choosing a transformed harmonic oscillator (THO)
basis for use in configuration-space Hartree-Fock-Bogoliubov (HFB) calculations
is presented. The new HFB+THO framework that follows accurately reproduces the
results of coordinate-space HFB calculations for spherical nuclei, including
those that are weakly bound. Furthermore, it is fully automated, facilitating
its use in systematic investigations of large sets of nuclei throughout the
periodic table. As a first application, we have carried out calculations using
the Skyrme Force SLy4 and volume pairing, with exact particle number projection
following application of the Lipkin-Nogami prescription. Calculations were
performed for all even-even nuclei from the proton drip line to the neutron
drip line having proton numbers Z=2,4,...,108 and neutron numbers
N=2,4,...,188. We focus on nuclei near the neutron drip line and find that
there exist numerous particle-bound even-even nuclei (i.e., nuclei with
negative Fermi energies) that have at the same time negative two-neutron
separation energies. This phenomenon, which was earlier noted for light nuclei,
is attributed to bound shape isomers beyond the drip line.Comment: 12 ReVTeX4 pages, 6 EPS figures. See also
http://www.fuw.edu.pl/~dobaczew/thodri/thodri.htm
Who is that? Brain networks and mechanisms for identifying individuals
Social animals can identify conspecifics by many forms of sensory input. However, whether the neuronal computations that support this ability to identify individuals rely on modality-independent convergence or involve ongoing synergistic interactions along the multiple sensory streams remains controversial. Direct neuronal measurements at relevant brain sites could address such questions, but this requires better bridging the work in humans and animal models. Here, we overview recent studies in nonhuman primates on voice and face identity-sensitive pathways and evaluate the correspondences to relevant findings in humans. This synthesis provides insights into converging sensory streams in the primate anterior temporal lobe (ATL) for identity processing. Furthermore, we advance a model and suggest how alternative neuronal mechanisms could be tested
Local structure of In_(0.5)Ga_(0.5)As from joint high-resolution and differential pair distribution function analysis
High resolution total and indium differential atomic pair distribution
functions (PDFs) for In_(0.5)Ga_(0.5)As alloys have been obtained by high
energy and anomalous x-ray diffraction experiments, respectively. The first
peak in the total PDF is resolved as a doublet due to the presence of two
distinct bond lengths, In-As and Ga-As. The In differential PDF, which involves
only atomic pairs containing In, yields chemical specific information and helps
ease the structure data interpretation. Both PDFs have been fit with structure
models and the way in that the underlying cubic zinc-blende lattice of
In_(0.5)Ga_(0.5)As semiconductor alloy distorts locally to accommodate the
distinct In-As and Ga-As bond lengths present has been quantified.Comment: 9 pages, 7 figur
Self-consistent Skyrme QRPA for use in axially-symmetric nuclei of arbitrary mass
We describe a new implementation of the quasiparticle random phase
approximation (QRPA) in axially-symmetric deformed nuclei with Skyrme and
volume-pairing energy-density functionals. After using a variety of tests to
demonstrate the accuracy of the code in ^{24,26}Mg and ^{16}O, we report the
first fully self-consistent application of the Skyrme QRPA to a heavy deformed
nucleus, calculating strength distributions for several K^pi in ^{172}Yb. We
present energy-weighted sums, properties of gamma-vibrational and low-energy
K^pi=0^+ states, and the complete isovector E1 strength function. The QRPA
calculation reproduces the properties of the low-lying 2^+ states as well or
better than it typically does in spherical nuclei.Comment: 5 pages, 6 figure
Polyhedral units and network connectivity in calcium aluminosilicate glasses from high-energy x-ray diffraction
Structure factors for Cax/2AlxSi1-xO2 glasses (x=0,0.25,0.5,0.67) extended to
a wave vector of magnitude Q= 40 1/A have been obtained by high-energy x-ray
diffraction. For the first time, it is possible to resolve the contributions of
Si-O, Al-O and Ca-O coordination polyhedra to the experimental atomic pair
distribution functions (PDF). It has been found that both Si and Al are
four-fold coordinated and so participate in a continuous tetrahedral network at
low values of x. The number of network breaking defects in the form of
non-bridging oxygens (NBO's) increases slowly with x until x=0.5 (NBO's ~ 10%
at x=0.5). By x=0.67 the network breaking defects become significant as
evidenced by the significant drop in the average coordination number of Si. By
contrast, Al-O tetrahedra remain free of NBO's and fully integrated in the
Al/Si-O network for all values of x. Calcium maintains a rather uniform
coordination sphere of approximately 5 oxygen atoms for all values of x. The
results suggest that not only Si/Al-O tetrahedra but Ca-O polyhedra, too, play
a role in determining the glassy structure
Reward cues readily direct monkeys’ auditory performance resulting in broad auditory cortex modulation and interaction with sites along cholinergic and dopaminergic pathways
In natural settings, the prospect of reward often influences the focus of our attention, but how cognitive and motivational systems influence sensory cortex is not well understood. Also, challenges in training nonhuman animals on cognitive tasks complicate cross-species comparisons and interpreting results on the neurobiological bases of cognition. Incentivized attention tasks could expedite training and evaluate the impact of attention on sensory cortex. Here we develop an Incentivized Attention Paradigm (IAP) and use it to show that macaque monkeys readily learn to use auditory or visual reward cues, drastically influencing their performance within a simple auditory task. Next, this paradigm was used with functional neuroimaging to measure activation modulation in the monkey auditory cortex. The results show modulation of extensive auditory cortical regions throughout primary and non-primary regions, which although a hallmark of attentional modulation in human auditory cortex, has not been studied or observed as broadly in prior data from nonhuman animals. Psycho-physiological interactions were identified between the observed auditory cortex effects and regions including basal forebrain sites along acetylcholinergic and dopaminergic pathways. The findings reveal the impact and regional interactions in the primate brain during an incentivized attention engaging auditory task.Peer reviewe
Sum Rule Approach to the Isoscalar Giant Monopole Resonance in Drip Line Nuclei
Using the density-dependent Hartree-Fock approximation and Skyrme forces
together with the scaling method and constrained Hartree-Fock calculations, we
obtain the average energies of the isoscalar giant monopole resonance. The
calculations are done along several isotopic chains from the proton to the
neutron drip lines. It is found that while approaching the neutron drip line,
the scaled and the constrained energies decrease and the resonance width
increases. Similar but smaller effects arise near the proton drip line,
although only for the lighter isotopic chains. A qualitatively good agreement
is found between our sum rule description and the presently existing random
phase approximation results. The ability of the semiclassical approximations of
the Thomas-Fermi type, which properly describe the average energy of the
isoscalar giant monopole resonance for stable nuclei, to predict average
properties for nuclei near the drip lines is also analyzed. We show that when
hbar corrections are included, the semiclassical estimates reproduce, on
average, the quantal excitation energies of the giant monopole resonance for
nuclei with extreme isospin values.Comment: 31 pages, 12 figures, revtex4; some changes in text and figure
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