186 research outputs found
Pulsations powered by hydrogen shell burning in white dwarfs
In the absence of a third dredge-up episode during the asymptotic giant
branch phase, white dwarf models evolved from low-metallicity progenitors have
a thick hydrogen envelope, which makes hydrogen shell burning be the most
important energy source. We investigate the pulsational stability of white
dwarf models with thick envelopes to see whether nonradial -mode pulsations
are triggered by hydrogen burning, with the aim of placing constraints on
hydrogen shell burning in cool white dwarfs and on a third dredge-up during the
asymptotic giant branch evolution of their progenitor stars. We construct
white-dwarf sequences from low-metallicity progenitors by means of full
evolutionary calculations, and analyze their pulsation stability for the models
in the range of effective temperatures
K. We demonstrate that, for white dwarf models with masses M_{\star} \lesssim
0.71\,\rm M_{\sun} and effective temperatures K that evolved from low-metallicity progenitors (,
, and ) the dipole () and quadrupole ()
modes are excited mostly due to the hydrogen-burning shell through the
-mechanism, in addition to other modes driven by either the
or the convective driving mechanism. However, the
mechanism is insufficient to drive these modes in white dwarfs evolved from
solar-metallicity progenitors. We suggest that efforts should be made to
observe the dipole mode in white dwarfs associated with low-metallicity
environments, such as globular clusters and/or the galactic halo, to place
constraints on hydrogen shell burning in cool white dwarfs and the third
dredge-up episode during the preceding asymptotic giant branch phase.Comment: 6 pages, 4 figures, 1 table. To be published in Astronomy and
Astrophysic
Antenna-Coupled Terahertz Microbolometers with Meander Structures: the Comparison of Titanium and Platinum Thermistors
Characterization of H5N1 influenza viruses isolated from humans in vitro
Since December 1997, highly pathogenic avian influenza A H5N1viruses have swept through poultry populations across Asian countries and been transmitted into African and European countries. We characterized 6 avian influenza H5N1 viruses isolated from humans in 2004 in Thailand. A highly pathogenic (HP) KAN353 strain showed faster replication and higher virulence in embryonated eggs compared to other strains, especially compared to the low pathogenic (LP) SP83 strain. HP KAN353 also showed strong cytopathogenicity compared to SP83 in Madin-Darby canine kidney cells. Interestingly, LP SP83 induced smaller plaques compared to other strains, especially HP KAN353. PB2 amino acid 627E may contribute to low virulence, whereas either PB2 amino acid 627 K or the combination of 627E/701N seems to be associated with high virulence. The in vitro assays used in this study may provide the basis for assessing the pathogenesis of influenza H5N1 viruses in vivo
Fatal Cases of Influenza A(H3N2) in Children: Insights from Whole Genome Sequence Analysis
During the Northern Hemisphere winter of 2003–2004 the emergence of a novel influenza antigenic variant, A/Fujian/411/2002-like(H3N2), was associated with an unusually high number of fatalities in children. Seventeen fatal cases in the UK were laboratory confirmed for Fujian/411-like viruses. To look for phylogenetic patterns and genetic markers that might be associated with increased virulence, sequencing and phylogenetic analysis of the whole genomes of 63 viruses isolated from fatal cases and non fatal “control” cases was undertaken. The analysis revealed the circulation of two main genetic groups, I and II, both of which contained viruses from fatal cases. No associated amino acid substitutions could be linked with an exclusive or higher occurrence in fatal cases. The Fujian/411-like viruses in genetic groups I and II completely displaced other A(H3N2) viruses, but they disappeared after 2004. This study shows that two A(H3N2) virus genotypes circulated exclusively during the winter of 2003–2004 in the UK and caused an unusually high number of deaths in children. Host factors related to immune state and differences in genetic background between patients may also play important roles in determining the outcome of an influenza infection
Corrosion Resistance Evaluation of HVOF Produced Hydroxyapatite and TiO2-hydroxyapatite Coatings in Hanks' Solution
The luminous and dark matter content of disk galaxies
For a compiled sample of disk galaxies with available photometry (B and K
bands), velocity line-widths and HI integral fluxes, several parameters which
trace the luminous, baryonic and dark matter contents were inferred. We
investigated how these parameters do vary with different galaxy properties, and
confronted the results with predictions of galaxy evolutionary models in the
context of the LCDM cosmogony. The ratio of disk-to-total maximum circular
velocity, vd/vt, depends mainly on the central disk surface density Sig_d (or
surface brightness, SB), increasing roughly as Sig_d^0.15. While a fraction of
high SB galaxies have a vd/vt ratio corresponding to the maximum disk solution,
the low SB are completely dark matter dominated. The trend is similar for the
models, although they have slightly smaller vd/vt ratios than observations. An
analysis of residuals of the vd/vt-Sig_d relation shows that vd/vt tends to
decrease as the galaxy is redder, more luminous (massive), and of earlier type.
The models allow us to explain the physics of these results, which imply a
connexion between halo structure and luminous properties. The estimated
dynamical-to-baryon mass and dynamical mass-to-light ratios at a given radius,
for observations and models, decrease with the SB and do not correlate with the
galaxy scale, contrary to what has been reported in previous works, based on
the analysis of rotation curve shapes. We discuss this difference and state the
importance to solve the controversy on whether the dark and luminous contents
in disk galaxies depend on SB or luminosity. The broad agreement between models
and observations favors the LCDM scenario. However, the excess of dark matter
inside the optical region of disk galaxies remains as the main difficulty.
(abridged)Comment: 26 pages, 7 figures and 2 tables. Accepted for publication in A&
The N-Terminal Region of the PA Subunit of the RNA Polymerase of Influenza A/HongKong/156/97 (H5N1) Influences Promoter Binding
BACKGROUND: The RNA polymerase of influenza virus is a heterotrimeric complex of PB1, PB2 and PA subunits which cooperate in the transcription and replication of the viral genome. Previous research has shown that the N-terminal region of the PA subunit of influenza A/WSN/33 (H1N1) virus is involved in promoter binding. METHODOLOGY/PRINCIPAL FINDINGS: Here we extend our studies of the influenza RNA polymerase to that of influenza strains A/HongKong/156/97 (H5N1) and A/Vietnam/1194/04 (H5N1). Both H5N1 strains, originally isolated from patients in 1997 and 2004, showed significantly higher polymerase activity compared with two classical human strains, A/WSN/33 (H1N1) and A/NT/60/68 (H3N2) in vitro. This increased polymerase activity correlated with enhanced promoter binding. The N-terminal region of the PA subunit was the major determinant of this enhanced promoter activity. CONCLUSIONS/SIGNIFICANCE: Overall we suggest that the N-terminal region of the PA subunit of two recent H5N1 strains can influence promoter binding and we speculate this may be a factor in their virulence
Wear and corrosion interactions on titanium in oral environment : literature review
The oral cavity is a complex environment where corrosive substances from dietary, human saliva, and oral biofilms may accumulate in retentive areas of dental implant systems and prostheses promoting corrosion at their surfaces. Additionally, during mastication, micromovements may occur between prosthetic joints causing a relative motion between contacting surfaces, leading to wear. Both processes (wear and corrosion) result in a bio-tribocorrosion system once that occurs in contact with biological tissues and fluids. This review paper is focused on the aspects related to the corrosion and wear behavior of titanium-based structures in the oral environment. Furthermore, the clinical relevance of the oral environment is focused on the harmful effect that acidic substances and biofilms, formed in human saliva, may have on titanium surfaces. In fact, a progressive degradation of titanium by wear and corrosion (tribocorrosion) mechanisms can take place affecting the performance of titanium-based implant and prostheses. Also, the formation of wear debris and metallic ions due to the tribocorrosion phenomena can become toxic for human tissues. This review gathers knowledge from areas like materials sciences, microbiology, and dentistry contributing to a better understanding of bio-tribocorrosion processes in the oral environment.(undefined
Effect of herd size on subclinical infection of swine in Vietnam with influenza A viruses
Desenvolvimento micelial de Lentinula edodes como efeito da profundidade e suplementação do substrato
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