459 research outputs found
Gamow-Teller sum rule in relativistic nuclear models
Relativistic corrections are investigated to the Gamow-Teller(GT) sum rule
with respect to the difference between the and transition
strengths in nuclei. Since the sum rule requires the complete set of the
nuclear states, the relativistic corrections come from the anti-nucleon degrees
of freedom. In the relativistic mean field approximation, the total GT
strengths carried by the nucleon sector is quenched by about 12% in nuclear
matter, while by about 8% in finite nuclei, compared to the sum rule value. The
coupling between the particle-hole states with the nucleon-antinucleon states
is also discussed with the relativistic random phase approximation, where the
divergence of the response function is renormalized with use of the counter
terms in the Lagrangian. It is shown that the approximation to neglect the
divergence, like the no-sea approximation extensively used so far, is
unphysical, from the sum-rule point of view.Comment: 12 pages, Brief review for Mod. Phys. Lett. A, using ws-mpla.cl
Discriminating the Progenitor Type of Supernova Remnants with Iron K-Shell Emission
Supernova remnants (SNRs) retain crucial information about both their parent
explosion and circumstellar material left behind by their progenitor. However,
the complexity of the interaction between supernova ejecta and ambient medium
often blurs this information, and it is not uncommon for the basic progenitor
type (Ia or core-collapse) of well-studied remnants to remain uncertain. Here
we present a powerful new observational diagnostic to discriminate between
progenitor types and constrain the ambient medium density of SNRs solely using
Fe K-shell X-ray emission. We analyze all extant Suzaku observations of SNRs
and detect Fe K alpha emission from 23 young or middle-aged remnants, including
five first detections (IC 443, G292.0+1.8, G337.2-0.7, N49, and N63A). The Fe K
alpha centroids clearly separate progenitor types, with the Fe-rich ejecta in
Type Ia remnants being significantly less ionized than in core-collapse SNRs.
Within each progenitor group, the Fe K alpha luminosity and centroid are well
correlated, with more luminous objects having more highly ionized Fe. Our
results indicate that there is a strong connection between explosion type and
ambient medium density, and suggest that Type Ia supernova progenitors do not
substantially modify their surroundings at radii of up to several parsecs. We
also detect a K-shell radiative recombination continuum of Fe in W49B and IC
443, implying a strong circumstellar interaction in the early evolutionary
phases of these core-collapse remnants.Comment: Accepted by ApJL; 5 pages with just 1 table and 1 figur
Precise measurement of positronium hyperfine splitting using the Zeeman effect
Positronium is an ideal system for the research of the quantum
electrodynamics (QED) in bound state. The hyperfine splitting (HFS) of
positronium, , gives a good test of the bound state
calculations and probes new physics beyond the Standard Model. A new method of
QED calculations has revealed the discrepancy by 15\,ppm (3.9) of
between the QED prediction and the experimental
average. There would be possibility of new physics or common systematic
uncertainties in the previous all experiments. We describe a new experiment to
reduce possible systematic uncertainties and will provide an independent check
of the discrepancy. We are now taking data and the current result of
has been obtained so far. A measurement with a precision of (ppm) is
expected within a year.Comment: 8 pages, 8 figures, 2 tables, proceeding of LEAP2011, accepted by
Hyperfine Interaction
Analysis of Oscillator Neural Networks for Sparsely Coded Phase Patterns
We study a simple extended model of oscillator neural networks capable of
storing sparsely coded phase patterns, in which information is encoded both in
the mean firing rate and in the timing of spikes. Applying the methods of
statistical neurodynamics to our model, we theoretically investigate the
model's associative memory capability by evaluating its maximum storage
capacities and deriving its basins of attraction. It is shown that, as in the
Hopfield model, the storage capacity diverges as the activity level decreases.
We consider various practically and theoretically important cases. For example,
it is revealed that a dynamically adjusted threshold mechanism enhances the
retrieval ability of the associative memory. It is also found that, under
suitable conditions, the network can recall patterns even in the case that
patterns with different activity levels are stored at the same time. In
addition, we examine the robustness with respect to damage of the synaptic
connections. The validity of these theoretical results is confirmed by
reasonable agreement with numerical simulations.Comment: 23 pages, 11 figure
Frequent Detection of Anti-Tubercular-Glycolipid-IgG and -IgA Antibodies in Healthcare Workers with Latent Tuberculosis Infection in the Philippines
Anti-tubercular-glycolipid-IgG (TBGL-IgG) and -IgA (TBGL-IgA) antibodies, and the QuantiFERON-TB Gold test (QFT) were compared in healthcare workers (HCWs, n = 31) and asymptomatic human immunodeficiency virus-carriers (HIV-AC, n = 56) in Manila. In HCWs, 48%, 51%, and 19% were positive in QFT, TBGL-IgG, and -IgA, respectively. The TBGL-IgG positivity was significantly higher (P = 0.02) in QFT-positive than QFT-negative HCWs. Both TBGL-IgG- and -IgA-positive cases were only found in QFT-positive HCWs (27%). The plasma IFN-γ levels positively correlated with TBGL-IgA titers (r = 0.74, P = 0.005), but not TBGL-IgG titers in this group, indicating that mucosal immunity is involved in LTBI in immunocompetent individuals. The QFT positivity in HIV-AC was 31% in those with CD4+ cell counts >350/μL and 12.5% in low CD4 group (<350/μL). 59 % and 29% were positive for TBGL-IgG and -IgA, respectively, in HIV-AC, but no association was found between QFT and TBGL assays. TBGL-IgG-positive rates in QFT-positive and QFT-negative HIV-AC were 61% and 58%, and those of TBGL-IgA were 23% and 30%, respectively. The titers of TBGL-IgA were associated with serum IgA (P = 0.02) in HIV-AC.
Elevations of TBGL-IgG and -IgA were related to latent tuberculosis infection in HCWs, but careful interpretation is necessary in HIV-AC
A model for selection of eyespots on butterfly wings
The development of eyespots on the wing surface of butterflies of the family Nympalidae is one of the most studied examples of biological pattern formation.However, little is known about the mechanism that determines the number and precise locations of eyespots on the wing. Eyespots develop around signaling centers, called foci, that are located equidistant from wing veins along the midline of a wing cell (an area bounded by veins). A fundamental question that remains unsolved is, why a certain wing cell develops an eyespot, while other wing cells do not. We illustrate that the key to understanding focus point selection may be in the venation system of the wing disc. Our main hypothesis is that changes in morphogen concentration along the proximal boundary veins of wing cells govern focus point selection. Based on previous studies, we focus on a spatially two-dimensional reaction-diffusion system model posed in the interior of each wing cell that describes the formation of focus points. Using finite element based numerical simulations, we demonstrate that variation in the proximal boundary condition is sufficient to robustly select whether an eyespot focus point forms in otherwise identical wing cells. We also illustrate that this behavior is robust to small perturbations in the parameters and geometry and moderate levels of noise. Hence, we suggest that an anterior-posterior pattern of morphogen concentration along the proximal vein may be the main determinant of the distribution of focus points on the wing surface. In order to complete our model, we propose a two stage reaction-diffusion system model, in which an one-dimensional surface reaction-diffusion system, posed on the proximal vein, generates the morphogen concentrations that act as non-homogeneous Dirichlet (i.e., fixed) boundary conditions for the two-dimensional reaction-diffusion model posed in the wing cells. The two-stage model appears capable of generating focus point distributions observed in nature.
We therefore conclude that changes in the proximal boundary conditions are sufficient to explain the empirically observed distribution of eyespot focus points on the entire wing surface. The model predicts, subject to experimental verification, that the source strength of the activator at the proximal boundary should be lower in wing cells in which focus points form than in those that lack focus points. The model suggests that the number and locations of eyespot foci on the wing disc could be largely controlled by two kinds of gradients along two different directions, that is, the first one is the gradient in spatially varying parameters such as the reaction rate along the anterior-posterior direction on the proximal boundary of the wing cells, and the second one is the gradient in source values of the activator along the veins in the proximal-distal direction of the wing cell
Efeitos da aplicação do boro em solos sob vegetação de cerrado
The present was carried out with the objective of studying the effects of boron applications on Red Yellow Latosol - sandy phase and on Regossol (Quartzosas Sand) under "Cerrado" vegetation of São Simão, São Paulo, State. Chemical determinations of soluble boron were made on soil samples of the experimental area collected before and after dolomitic line applications. Complementary biological tests of boron were also made, employing sunflower (Helianthus annus L.). Simultaneously, fold experiment was carried and with dry (Phaseolus vulgaris L.) to study boron applications. The main conclusions were the followings: 1 - Biologycal tests with sumflower were correlated with chemical analysis indicating that both soil units were slightly or no boron deficient. 2 - The soil classified how Regosol (Quartzous Sand) showed a larger Boron content than the Red Yellow Latosol-sandy phase. 3 - There has been no response of dry beans to boron on both soils.O presente trabalho teve como objetivo estudar os efeitos da aplicação de boro em duas unidades de solo cobertas com vegetação de cerrado, classificadas co-como, Latossolo Vermelho Amarelo-fase arenosa e Regossolo (Areas Quartzosas), que ocorrem no município de São Simão, no Estado de São Paulo. Foram feitas determinações químicas de boro solúvel em amostras colhidas nas áreas experimentais antes e depois do tratamento dos solos com calagem. As determinações do boro foram complementados com testes biológicos do girassol (Helianthus annuus L.). Simultaneamente foram conduzidos ensaios de campo para estudos sobre a aplicação de doses crescentes de boro no feijoeiro (Phaseolus vulgaris L.). As conclusões do trabalho foram as seguintes: 1 - O teste do girassol apresentou boa concordância com os testes químicos, indicando que as duas unidades de solo são ligeiramente deficientes ou não deficientes em boro. 2 - O solo classificado como Regossolo (Areias Quartzosas) mostrou-se mais elevado em boro do que o Latossol Vermelho Amarelo - fase arenosa. 3 - Não houve efeito da aplicação de boro na produção do feijoeiro
Analysis of excitation and coherent amplitude enhancement of surface acoustic waves by the phase velocity scanning method
Nonlinearity of Mechanochemical Motions in Motor Proteins
The assumption of linear response of protein molecules to thermal noise or
structural perturbations, such as ligand binding or detachment, is broadly used
in the studies of protein dynamics. Conformational motions in proteins are
traditionally analyzed in terms of normal modes and experimental data on
thermal fluctuations in such macromolecules is also usually interpreted in
terms of the excitation of normal modes. We have chosen two important protein
motors - myosin V and kinesin KIF1A - and performed numerical investigations of
their conformational relaxation properties within the coarse-grained elastic
network approximation. We have found that the linearity assumption is deficient
for ligand-induced conformational motions and can even be violated for
characteristic thermal fluctuations. The deficiency is particularly pronounced
in KIF1A where the normal mode description fails completely in describing
functional mechanochemical motions. These results indicate that important
assumptions of the theory of protein dynamics may need to be reconsidered.
Neither a single normal mode, nor a superposition of such modes yield an
approximation of strongly nonlinear dynamics.Comment: 10 pages, 6 figure
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