26,878 research outputs found
A search for the superburst oscillation signal in the regular thermonuclear bursts of 4U 1636-536
Burst oscillations are brightness asymmetries that develop in the burning
ocean during thermonuclear bursts on accreting neutron stars. They have been
observed during H/He-triggered (Type I) bursts and Carbon-triggered
superbursts. The mechanism responsible is not unknown, but the dominant burst
oscillation frequency is typically within a few Hz of the spin frequency, where
this is independently known. One of the best-studied burst oscillation sources,
4U 1636-536, has oscillations at in both its regular Type I
bursts and in one superburst. Recently however, Strohmayer \& Mahmoodifar
reported the discovery of an additional signal at a higher frequency,
, during the superburst. This higher frequency is consistent
with the predictions for several types of global ocean mode, one of the
possible burst oscillation mechanisms. If this is the case then the same
physical mechanism may operate in the normal Type I bursts of this source. In
this paper we report a stacked search for periodic signals in the regular Type
I bursts: we found no significant signal at the higher frequency, with upper
limits for the single trial root mean square (rms) fractional amplitude of
0.57(6)\%. Our analysis did however reveal that the dominant
burst oscillation signal is present at a weak level even in the sample of
bursts where it cannot be detected in individual bursts. This indicates that
any cutoff in the burst oscillation mechanism occurs below the detection
threshold of existing X-ray telescopes.Comment: 6 pages, 2 figures. Accepted for publication by Ap
Gauge and Yukawa mediated supersymmetry breaking in the triplet seesaw scenario
We propose a novel supersymmetric unified scenario of the triplet seesaw
mechanism where the exchange of the heavy triplets generates both neutrino
masses and soft supersymmetry breaking terms. Our framework is very predictive
since it relates neutrino mass parameters, lepton flavour violation in the
slepton sector, sparticle and Higgs spectra and electroweak symmetry breakdown.
The phenomenological viability and experimental signatures in lepton flavor
violating processes are discussed.Comment: 11 pages, 3 eps figs. Comments and references added. Final version to
be published in Phys. Rev. Let
Radiation from a charge circulating inside a waveguide with dielectric filling
The emitted power of the radiation from a charged particle moving uniformly
on a circle inside a cylindrical waveguide is considered. The expressions for
the energy flux of the radiation passing through the waveguide cross-section
are derived for both TE and TM waves. The results of the numerical evaluation
are presented for the number of emitted quanta depending on the waveguide
radius, the radius of the charge rotation orbit and dielectric permittivity of
the filling medium. These results are compared with the corresponding
quantities for the synchrotron radiation in a homogeneous medium.Comment: 10 pages, Latex, four EPS figure
HE 1327-2326, An Unevolved Star With Fe/H <-5.0. III. Does Its Atmosphere Reflect Its Natal Composition?
Based on spectroscopic constraints derived from nonlocal thermodynamic equilibrium line formation, we explore the likely range of stellar parameters (T-eff and log g) for the hyper-metal-poor (HMP) star HE 1327-2326. Combining the constraints from Balmer line profiles and the Ca I/II ionization equilibrium, a subgiant stage of evolution is indicated. This result is further supported by spectrophotometric observations of the Balmer jump. If a higher T-eff value was used (as favored by some photometric calibrations), the spectroscopic analysis would indicate a turnoff-point stage of evolution. Using a stellar-structure code that treats the effects of atomic diffusion throughout the star in detail, we evolve a low-mass model star to reach the Hertzsprung-Russell-diagram position of HE 1327-2326 after roughly 13 Gyr. While the surface abundances are modified significantly (by more than 1 dex for the case of uninhibited diffusion), such corrections cannot resolve the discrepancy between the abundance inferred from the nondetection of the Li I resonance line at 6707 angstrom and the Wilkinson Microwave Anisotropy Probe based primordial lithium abundance. As there are numerous processes that can destroy lithium, any cosmological interpretation of a lower-than-expected lithium abundance at the lowest metallicities will have to await sample sizes of unevolved HMP stars that are 1 order of magnitude larger. The situation remains equally inconclusive concerning atomic-diffusion corrections. Here, attempts have to be made to better constrain internal mixing processes, both observationally and by means of sophisticated modeling. With constraints on additional mixing processes taken from a recent globular-cluster study, the likeliest scenario is that HE 1327-2326's surface abundances have undergone mild depletion (of order 0.2 dex).Swedish Research Council (Vetenskapradet)Presidium RAS Programme "Origin and evolution of stars and the Galaxy"Deutsche Forschungsgemeinschaft GE 490/34-1W. J. McDonald Fellowship of the McDonald ObservatoryJSPS 18104003McDonald Observator
Intermediate reading exercises for use with the Durrell Analysis of Reading Difficulty.
Thesis (Ed.M.)--Boston Universit
Early Interferon-γ Production in Human Lymphocyte Subsets in Response to Nontyphoidal Salmonella Demonstrates Inherent Capacity in Innate Cells
Background
Nontyphoidal Salmonellae frequently cause life-threatening bacteremia in sub-Saharan Africa. Young children and HIV-infected adults are particularly susceptible. High case-fatality rates and increasing antibiotic resistance require new approaches to the management of this disease. Impaired cellular immunity caused by defects in the T helper 1 pathway lead to intracellular disease with Salmonella that can be countered by IFNγ administration. This report identifies the lymphocyte subsets that produce IFNγ early in Salmonella infection.
Methodology
Intracellular cytokine staining was used to identify IFNγ production in blood lymphocyte subsets of ten healthy adults with antibodies to Salmonella (as evidence of immunity to Salmonella), in response to stimulation with live and heat-killed preparations of the D23580 invasive African isolate of Salmonella Typhimurium. The absolute number of IFNγ-producing cells in innate, innate-like and adaptive lymphocyte subpopulations was determined.
Principal Findings
Early IFNγ production was found in the innate/innate-like lymphocyte subsets: γδ-T cells, NK cells and NK-like T cells. Significantly higher percentages of such cells produced IFNγ compared to adaptive αβ-T cells (Student's t test, P<0.001 and ≤0.02 for each innate subset compared, respectively, with CD4+- and CD8+-T cells). The absolute numbers of IFNγ-producing cells showed similar differences. The proportion of IFNγ-producing γδ-T cells, but not other lymphocytes, was significantly higher when stimulated with live compared with heat-killed bacteria (P<0.0001).
Conclusion/Significance
Our findings indicate an inherent capacity of innate/innate-like lymphocyte subsets to produce IFNγ early in the response to Salmonella infection. This may serve to control intracellular infection and reduce the threat of extracellular spread of disease with bacteremia which becomes life-threatening in the absence of protective antibody. These innate cells may also help mitigate against the effect on IFNγ production of depletion of Salmonella-specific CD4+-T lymphocytes in HIV infection
- …