650 research outputs found
On the origin of HE0107-5240, the most iron deficient star presently known
We show that the "puzzling" chemical composition observed in the extremely
metal poor star HE0107-5240 may be naturally explained by the concurrent
pollution of at least two supernovae. In the simplest possible model a
supernova of quite low mass (~15 Msun), underwent a "normal" explosion and
ejected ~0.06 Msun of 56Ni while a second one was massive enough (~35 Msun) to
experience a strong fall back that locked in a compact remnant all the
carbon-oxygen core. In a more general scenario, the pristine gas clouds were
polluted by one or more supernovae of relatively low mass (less than ~25 Msun).
The successive explosion of a quite massive star experiencing an extended fall
back would have largely raised the abundances of the light elements in its
close neighborhood.Comment: 10 pages; 3 figures; accepted for publication in the The
Astrophysical Journal Letter
C/O white dwarfs of very low mass: 0.33-0.5 Mo
The standard lower limit for the mass of white dwarfs (WDs) with a C/O core
is roughly 0.5 Mo. In the present work we investigated the possibility to form
C/O WDs with mass as low as 0.33 Mo. Both the pre-WD and the cooling evolution
of such nonstandard models will be described.Comment: Submitted to the "Proceedings of the 16th European White Dwarf
Workshop" (to be published JPCS). 7 pages including 13 figure
On the Origin of the Early Solar System Radioactivities. Problems with the AGB and Massive Star Scenarios
Recent improvements in stellar models for intermediate-mass and massive stars
are recalled, together with their expectations for the synthesis of radioactive
nuclei of lifetime Myr, in order to re-examine the origins
of now extinct radioactivities, which were alive in the solar nebula. The
Galactic inheritance broadly explains most of them, especially if -process
nuclei are produced by neutron star merging according to recent models.
Instead, Al, Ca, Cs and possibly Fe require
nucleosynthesis events close to the solar formation. We outline the persisting
difficulties to account for these nuclei by Intermediate Mass Stars (2
M/M). Models of their final stages now
predict the ubiquitous formation of a C reservoir as a neutron capture
source; hence, even in presence of Al production from Deep Mixing or Hot
Bottom Burning, the ratio Al/Pd remains incompatible with
measured data, with a large excess in Pd. This is shown for two recent
approaches to Deep Mixing. Even a late contamination by a Massive Star meets
problems. In fact, inhomogeneous addition of Supernova debris predicts
non-measured excesses on stable isotopes. Revisions invoking specific low-mass
supernovae and/or the sequential contamination of the pre-solar molecular cloud
might be affected by similar problems, although our conclusions here are
weakened by our schematic approach to the addition of SN ejecta. The limited
parameter space remaining to be explored for solving this puzzle is discussed.Comment: Accepted for publication on Ap
The centrosomal kinase NEK2 is a novel splicing factor kinase involved in cell survival
NEK2 is a serine/threonine kinase that promotes centrosome splitting and ensures correct chromosome segregation during the G2/M phase of the cell cycle, through phosphorylation of specific substrates. Aberrant expression and activity of NEK2 in cancer cells lead to dysregulation of the centrosome cycle and aneuploidy. Thus, a tight regulation of NEK2 function is needed during cell cycle progression. In this study, we found that NEK2 localizes in the nucleus of cancer cells derived from several tissues. In particular, NEK2 co-localizes in splicing speckles with SRSF1 and SRSF2. Moreover, NEK2 interacts with several splicing factors and phosphorylates some of them, including the oncogenic SRSF1 protein. Overexpression of NEK2 induces phosphorylation of endogenous SR proteins and affects the splicing activity of SRSF1 toward reporter minigenes and endogenous targets, independently of SRPK1. Conversely, knockdown of NEK2, like that of SRSF1, induces expression of pro-apoptotic variants from SRSF1-target genes and sensitizes cells to apoptosis. Our results identify NEK2 as a novel splicing factor kinase and suggest that part of its oncogenic activity may be ascribed to its ability to modulate alternative splicing, a key step in gene expression regulation that is frequently altered in cancer cells
PrevalĂȘncia de parasitismo por Toxocara canis em cĂŁes e presença de ovos de Toxocara sp. no solo de localidades pĂșblicas da zona urbana do municĂpio de Londrina, Estado do ParanĂĄ, Brasil
Out of 158 dogs submitted to coprological examination or necropsy, 70 (44.30%) were found to be infected by Toxocara canis, the prevalence being higher among puppies with and up to 6 months of age. Out of 15 soil samples taken from public places atended by children, ova of Toxocara species were found in 60% indicating the possibility of transmission of toxocaral infection to humans through ova containing larvae.De um total de 158 cĂŁes examinados, atravĂ©s de exame parasitolĂłgico de fezes ou necropsia, 70 (44,30%) mostraram-se infectados por Toxocara canis, predominando a infecção nos animais com atĂ© 6 meses de idade. AtravĂ©s do exame de amostras de terra de localidades pĂșblicas utilizadas por crianças para diversĂŁo, demonstrou-se a presença de ovos de Toxocara sp. em 60% das amostras, evidenciando a possibilidade de ocorrer infecção humana, ingestĂŁo de ovos larvados do helminto
PrevalĂȘncia de parasitismo por Toxocara canis em cĂŁes e presença de ovos de Toxocara sp. no solo de localidades pĂșblicas da zona urbana do municĂpio de Londrina, Estado do ParanĂĄ, Brasil
Out of 158 dogs submitted to coprological examination or necropsy, 70 (44.30%) were found to be infected by Toxocara canis, the prevalence being higher among puppies with and up to 6 months of age. Out of 15 soil samples taken from public places atended by children, ova of Toxocara species were found in 60% indicating the possibility of transmission of toxocaral infection to humans through ova containing larvae.De um total de 158 cĂŁes examinados, atravĂ©s de exame parasitolĂłgico de fezes ou necropsia, 70 (44,30%) mostraram-se infectados por Toxocara canis, predominando a infecção nos animais com atĂ© 6 meses de idade. AtravĂ©s do exame de amostras de terra de localidades pĂșblicas utilizadas por crianças para diversĂŁo, demonstrou-se a presença de ovos de Toxocara sp. em 60% das amostras, evidenciando a possibilidade de ocorrer infecção humana, ingestĂŁo de ovos larvados do helminto
TOPoS: II. On the bimodality of carbon abundance in CEMP stars. Implications on the early chemical evolution of galaxies
In the course of the TOPoS (Turn Off Primordial Stars) survey, aimed at
discovering the lowest metallicity stars, we have found several carbon-enhanced
metal-poor (CEMP) stars. We here present our analysis of six CEMP stars.
Calcium and carbon are the only elements that can be measured in all six stars.
The range is -5.0<=[Ca/H]< -2.1 and 7.12<=A(C)<=8.65. For star SDSS J1742+2531
we were able to detect three FeI lines from which we deduced [Fe/H]=-4.80, from
four CaII lines we derived [Ca/H]=-4.56, and from synthesis of the G-band we
derived A(C)=7.26. For SDSS J1035+0641 we were not able to detect any iron
lines, yet we could place a robust (3sigma) upper limit of [Fe/H]< -5.0 and
measure the Ca abundance, with [Ca/H]=-5.0, and carbon, A(C)=6.90. No lithium
is detected in the spectrum of SDSS J1742+2531 or SDSS J1035+0641, which
implies a robust upper limit of A(Li)<1.8 for both stars. Our measured carbon
abundances confirm the bimodal distribution of carbon in CEMP stars,
identifying a high-carbon band and a low-carbon band. We propose an
interpretation of this bimodality according to which the stars on the
high-carbon band are the result of mass transfer from an AGB companion, while
the stars on the low-carbon band are genuine fossil records of a gas cloud that
has also been enriched by a faint supernova (SN) providing carbon and the
lighter elements. (Abridged)Comment: to be published on A&
AlteraçÔes de comportamento em Rattus norvegicus experimentalmente infectados por larvas de Toxocara canis
Toxocara canis is a common canine nematode parasite and one of its possible transmission mechanisms is the predation of infected rodents by canids. Fifty Rattus norvegicus were used to study behavioral alterations in rodents infected by T. canis larvae. The rats were divided into three groups: G1, 20 rats infected with 300 T. canis eggs; G2, 20 rats infected with 2,000 T. canis eggs; and G3, 10 non-infected rats. Thirty and 60 days post-infection, rats from all the groups were submitted to an open-field apparatus for five min and subsequently, to an elevated plus-maze apparatus, again for five min. The data obtained indicated improvement in mobility (total locomotion time and rearing frequency) and exploratory behavior in infected rats, principally in G2, which provides some support for the hypothesis that behavioral alterations in rodents infected by Toxocara canis larvae enhance the transmission rate of this ascarid to dogs.Toxocara canis Ă© um nematĂłdeo parasita habitual do intestino delgado de cĂŁes. Um dos mecanismos conhecidos de transmissĂŁo para cĂŁes Ă© representado pela predação de pequenos roedores que, como hospedeiros paratĂȘnicos albergam larvas de Toxocara canis em seus tecidos. Para avaliar a ocorrĂȘncia de alteraçÔes de comportamento em roedores infectados por Toxocara canis 50 exemplares de Rattus norvegicus foram utilizados no experimento. Os animais foram divididos em trĂȘs grupos: G1 - 20 ratos infectados com 300 ovos de Toxocara canis; G2 - 20 ratos infectados com 2.000 ovos de Toxocara canis e G3 - 10 ratos sem infecção. Trinta e 60 dias apĂłs a infecção avaliou-se a ocorrĂȘncia de alteraçÔes comportamentais nos trĂȘs grupos submetendo os animais, primeiramente, a uma arena de campo aberto durante cinco minutos e, a seguir, a labirinto em cruz elevado por mais cinco minutos. Os resultados obtidos indicaram aumento significativo da mobilidade (tempo total de movimentação e nĂșmero de vezes em que os animais se levantaram nas patas traseiras) e comportamento exploratĂłrio nos ratos infectados, principalmente nos pertencentes ao G2, sugerindo a ocorrĂȘncia de alteraçÔes comportamentais que favoreceriam a transmissĂŁo de Toxocara canis para canĂdeos por meio de relação presa-predador
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