7,153 research outputs found
Scaling Function, Spectral Function and Nucleon Momentum Distribution in Nuclei
The link between the scaling function extracted from the analysis of (e,e')
cross sections and the spectral function/momentum distribution in nuclei is
revisited. Several descriptions of the spectral function based on the
independent particle model are employed, together with the inclusion of nucleon
correlations, and effects of the energy dependence arising from the width of
the hole states are investigated. Although some of these approaches provide
rough overall agreement with data, they are not found to be capable of
reproducing one of the distinctive features of the experimental scaling
function, namely its asymmetry. However, the addition of final-state
interactions, incorporated in the present study using either relativistic mean
field theory or via a complex optical potential, does lead to asymmetric
scaling functions in accordance with data. The present analysis seems to
indicate that final-state interactions constitute an essential ingredient and
are required to provide a proper description of the experimental scaling
function.Comment: 29 pages, 13 figures, accepted for publication in Physical Review
Caprellids (Crustacea: Amphipoda) from India
The caprellid fauna of India is investigated. A
total of 538 samples (including algae, seagrasses, sponges,
hydroids, ascidians, bryozoans, encrusted dead corals, coral
rubble, fine and coarse sediments) were collected from 39
stations along the coast of India, covering a wide diversity
of habitats from intertidal to 12 m water depth. A new
species (Jigurru longimanus n.sp.) is described, and figures
of the 11 valid species reported so far from India are given
together with a key for their identification. No caprellids
were found in sediments from the northeast (16–208N)
coast of India while they were abundant in the southeast
and west coast. Decreases in salinity due to river discharges
associated with lower values of oxygen, higher water
temperatures and lower nutrient inputs along the east coast
could explain these differences in caprellid composition
between the two coastlines. Significantly, lower abundance
of caprellids in India, as in other tropical ecosystems, is
probably related to the lack of species belonging to the
genus Caprella, which reach very high abundances in
temperate waters.Ministerio de Educación y Ciencia de España y fondos FEDER de la Unión Europea. CGL2007-60044/ BOSConsejería de Innovación, Ciencia y Empresa, Junta de Andalucía, España. P07-RNM-02524Ministry of Earth Sciences (MoES) de India. DOD/10-MLR/1/2002/DT 19.12.200
A note on the Guerra and Talagrand theorems for Mean Field Spin Glasses: the simple case of spherical models
The aim of this paper is to discuss the main ideas of the Talagrand proof of
the Parisi Ansatz for the free-energy of Mean Field Spin Glasses with a
physicist's approach. We consider the case of the spherical -spin model,
which has the following advantages: 1) the Parisi Ansatz takes the simple ``one
step replica symmetry breaking form'', 2) the replica free-energy as a function
of the order parameters is simple enough to allow for numerical maximization
with arbitrary precision. We present the essential ideas of the proof, we
stress its connections with the theory of effective potentials for glassy
systems, and we reduce the technically more difficult part of the Talagrand's
analysis to an explicit evaluation of the solution of a variational problem.Comment: 20 pages, 5 figures. Added references and minor language correction
Corona Virus Disease 19 (CoViD-19) impact on cardiovascular disease in a non-CoViD-19 emergency setting
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Charge and matter distributions and form factors of light, medium and heavy neutron-rich nuclei
Results of charge form factors calculations for several unstable neutron-rich
isotopes of light, medium and heavy nuclei (He, Li, Ni, Kr, Sn) are presented
and compared to those of stable isotopes in the same isotopic chain. For the
lighter isotopes (He and Li) the proton and neutron densities are obtained
within a microscopic large-scale shell-model, while for heavier ones Ni, Kr and
Sn the densities are calculated in deformed self-consistent mean-field Skyrme
HF+BCS method. We also compare proton densities to matter densities together
with their rms radii and diffuseness parameter values. Whenever possible
comparison of form factors, densities and rms radii with available experimental
data is also performed. Calculations of form factors are carried out both in
plane wave Born approximation (PWBA) and in distorted wave Born approximation
(DWBA). These form factors are suggested as predictions for the future
experiments on the electron-radioactive beam colliders where the effect of the
neutron halo or skin on the proton distributions in exotic nuclei is planned to
be studied and thereby the various theoretical models of exotic nuclei will be
tested.Comment: 26 pages, 11 figures, 3 tables, accepted for publication in Phys.
Rev.
Mutations In Sry And Wt1 Genes Required For Gonadal Development Are Not Responsible For Xy Partial Gonadal Dysgenesis.
The WT1 transcription factor regulates SRY expression during the initial steps of the sex determination process in humans, activating a gene cascade leading to testis differentiation. In addition to causing Wilms' tumor, mutations in WT1 are often responsible for urogenital defects in men, while SRY mutations are mainly related to 46,XY pure gonadal dysgenesis. In order to evaluate their role in abnormal testicular organogenesis, we screened for SRY and WT1 gene mutations in 10 children with XY partial gonadal dysgenesis, 2 of whom with a history of Wilms' tumor. The open reading frame and 360 bp of the 5' flanking sequence of the SRY gene, and the ten exons and intron boundaries of the WT1 gene were amplified by PCR of genomic DNA. Single-strand conformation polymorphism was initially used for WT1 mutation screening. Since shifts in fragment migration were only observed for intron/exon 4, the ten WT1 exons from all patients were sequenced manually. No mutations were detected in the SRY 5' untranslated region or within SRY open-reading frame sequences. WT1 sequencing revealed one missense mutation (D396N) in the ninth exon of a patient who also had Wilms' tumor. In addition, two silent point mutations were found in the first exon including one described here for the first time. Some non-coding sequence variations were detected, representing one new (IVS4+85A>G) and two already described (-7ATG T>G, IVS9-49 T>C) single nucleotide polymorphisms. Therefore, mutations in two major genes required for gonadal development, SRY and WT1, are not responsible for XY partial gonadal dysgenesis.3817-2
Charge density distributions and related form factors in neutron-rich light exotic nuclei
Charge form factors corresponding to proton density distributions in exotic
nuclei, such as He, Li, B and Be are calculated
and compared. The results can be used as tests of various theoretical models
for the exotic nuclei structure in possible future experiments using a
colliding electron-exotic nucleus storage ring. The result of such a comparison
would show the effect of the neutron halo or skin on the proton distributions
in exotic nuclei.Comment: 11 pages, 4 figures, to be published in International Journal of
Modern Physics
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