1,472 research outputs found
Effect of Nitrate, Acetate and Hydrogen on Native Perchlorate-reducing Microbial Communities and Their Activity in Vadose Soil
The effect of nitrate, acetate, and hydrogen on native perchlorate-reducing bacteria (PRB) was examined by conducting microcosm tests using vadose soil collected from a perchlorate-contaminated site. The rate of perchlorate reduction was enhanced by hydrogen amendment and inhibited by acetate amendment, compared with unamendment. Nitrate was reduced before perchlorate in all amendments. In hydrogen-amended and unamended soils, nitrate delayed perchlorate reduction, suggesting that the PRB preferentially use nitrate as an electron acceptor. In contrast, nitrate eliminated the inhibitory effect of acetate amendment on perchlorate reduction and increased the rate and the extent, possibly because the preceding nitrate reduction/denitrification decreased the acetate concentration that was inhibitory to the native PRB. In hydrogen-amended and unamended soils, perchlorate reductase gene (pcrA) copies, representing PRB densities, increased with either perchlorate or nitrate reduction, suggesting that either perchlorate or nitrate stimulates the growth of the PRB. In contrast, in acetate-amended soil pcrA increased only when perchlorate was depleted: a large portion of the PRB may have not utilized nitrate in this amendment. Nitrate addition did not alter the distribution of the dominant pcrA clones in hydrogen-amended soil, likely because of the functional redundancy of PRB as nitrate-reducers/denitrifiers, whereas acetate selected different pcrA clones from those with hydrogen amendment
Uma tentativa de cultivo de rotavĂrus humano em cultura de leucĂłcitos humano (Nota PrĂ©via)
Experimentos preliminares da permissividade de cultura de leucĂłcitos humanos estimulados com mitĂłgeno frente a infecção pelo rotavirus humano foram realizados por microscopia eletrĂŽnica. Observamos que, cĂ©lulas mo-nonucleadas, mantidas em cultura, apĂłs estimulação com fitohemaglutinina (PHA) colhidas 36 horas pĂłs-infecção apresentavam muitas partĂculas virais no citoplasma. Verificamos, tambĂ©m, muitas partĂculas virais associadas a fragmentos celulares, vĂĄrias cĂ©lulas em degeneração e alguns linfĂłcitos pequenos intactos. NĂŁo presenciamos partĂculas virais em cĂ©lulas colhidas previamente (12 e 24 horas p.i.) e nas culturas controle (sem tratamento com PHA). Sugerimos que o rotavirus humano pode se replicar em culturas de leucĂłcitos humanos estimulados com PHA
Construction of Highly Accurate Models of Rotating Neutron Stars: Comparison of Three Different Numerical Schemes
We conduct a direct comparison of three different representative numerical codes for constructing models of rapidly rotating neutron stars in general relativity. Our aim is to evaluate the accuracy of the codes and to investigate how the accuracy is affected by the choice of interpolation, domain of integration and equation of state. In all three codes, the same physical parameters, equations of state and interpolation method are used. We construct 25 selected models for polytropic equations of state and 22 models with realistic neutron star matter equations of state. The three codes agree well with each other (typical agreement is better than 0.1% to 0.01%) for most models, except for the extreme assumption of uniform density stars. We conclude that the codes can be used for the construction of highly accurate initial data configurations for polytropes of index N > 0.5 (which typically correspond to realistic neutron stars), when the domain of integration includes all space and for realistic equations with no phase transitions. With the exception of the uniform density case, the obtained values of physical parameters for the models considered in this paper can be regarded as ``standard'' and we display them in detail for all models
Precise half-life measurement of 110Sn and 109In isotopes
The half-lives of 110Sn and 109In isotopes have been measured with high
precision. The results are T1/2 =4.173 +- 0.023 h for 110Sn and T1/2 = 4.167
+-0.018 h for 109In. The precision of the half-lives has been increased by a
factor of 5 with respect to the literature values which makes results of the
recently measured 106Cd(alpha,gamma)110Sn and 106Cd(alpha,p)109In cross
sections more reliable.Comment: 3 pages, 2 figures, accepted for publication in Phys. Rev C as brief
repor
The Sunyaev-Zeldovich Effect and Its Cosmological Significance
Comptonization of the cosmic microwave background (CMB) radiation by hot gas
in clusters of galaxies - the Sunyaev-Zeldovich (S-Z) effect - is of great
astrophysical and cosmological significance. In recent years observations of
the effect have improved tremendously; high signal-to-noise images of the
effect (at low microwave frequencies) can now be obtained by ground-based
interferometric arrays. In the near future, high frequency measurements of the
effect will be made with bolomateric arrays during long duration balloon
flights. Towards the end of the decade the PLANCK satellite will extensive S-Z
surveys over a wide frequency range. Along with the improved observational
capabilities, the theoretical description of the effect and its more precise
use as a probe have been considerably advanced. I review the current status of
theoretical and observational work on the effect, and the main results from its
use as a cosmological probe.Comment: Invited review; in proceedings of the Erice NATO/ASI `Astrophysical
Sources of High Energy Particles and Radiation'; 11 pages, 3 figure
Dynamical model for Pion - Nucleon Bremsstrahlung
A dynamical model based on effective Lagrangians is proposed to describe the
bremsstrahlung reaction at low energies. The
degrees of freedom are incorporated in a way consistent with
both, electromagnetic gauge invariance and invariance under contact
transformations. The model also includes the initial and final state
rescattering of hadrons via a T-matrix with off-shell effects. The differential cross sections are calculated using three different
T-matrix models and the results are compared with the soft photon
approximation, and with experimental data. The aim of this analysis is to test
the off-shell behavior of the different T-matrices under consideration.Comment: 16 pages, latex, 6 eps figures. Accepted for publication in Physical
Review
Pressure-driven instability in auroral images to create auroral patches
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Quasifree Pion Electroproduction from Nuclei in the Region
We present calculations of the reaction in the
distorted wave impulse approximation. The reaction allows for the study of the
production process in the nuclear medium without being obscured by the details
of nuclear transition densities. First, a pion electroproduction operator
suitable for nuclear calculations is obtained by extending the Blomqvist-Laget
photoproduction operator to the virtual photon case. The operator is gauge
invariant, unitary, reference frame independent, and describes the existing
data reasonably well. Then it is applied in nuclei to predict nuclear cross
sections under a variety of kinematic arrangements. Issues such as the effects
of gauge-fixing, the interference of the resonance with the
background, sensitivities to the quadrupole component of the
excitation and to the electromagnetic form factors, the role of final-state
interactions, are studied in detail. Methods on how to experimentally separate
the various pieces in the coincidence cross section are suggested. Finally, the
model is compared to a recent SLAC experiment.Comment: 27 pages in REVTEX, plus 22 PS figures embedded using psfig.sty
(included), uuencode
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