985 research outputs found
On the nature of some SGRs and AXPs as rotation-powered neutron stars
We investigate the possibility that some SGRs/AXPs could be canonical
rotation-powered pulsars using realistic NS structure parameters instead of
fiducial values. We show that realistic NS parameters lowers the estimated
value of the magnetic field and radiation efficiency, ,
with respect to estimates based on fiducial NS parameters. We show that nine
SGRs/AXPs can be described as canonical pulsars driven by the NS rotational
energy, for computed in the soft (2--10~keV) X-ray band. We compute the
range of NS masses for which . We discuss the observed
hard X-ray emission in three sources of the group of nine potentially
rotation-powered NSs. This additional hard X-ray component dominates over the
soft one leading to in two of them. We show that 9
SGRs/AXPs can be rotation-powered NSs if we analyze their X-ray luminosity in
the soft 2--10~keV band. Interestingly, four of them show radio emission and
six have been associated with supernova remnants (including Swift J1834.9-0846
the first SGR observed with a surrounding wind nebula). These observations give
additional support to our results of a natural explanation of these sources in
terms of ordinary pulsars. Including the hard X-ray emission observed in three
sources of the group of potential rotation-powered NSs, this number of sources
with becomes seven. It remains open to verification
1) the accuracy of the estimated distances and 2) the possible contribution of
the associated supernova remnants to the hard X-ray emission.Comment: 11 pages, 14 figures, to appear in A&
Geodesic Deviation Equation in Bianchi Cosmologies
We present the Geodesic Deviation Equation (GDE) for the
Friedmann-Robertson-Walker(FRW) universe and we compare it with the equation
for Bianchi type I model. We justify consider this cosmological model due to
the recent importance the Bianchi Models have as alternative models in
cosmology. The main property of these models, solutions of Einstein Field
Equations (EFE) is that they are homogeneous as the FRW model but they are not
isotropic. We can see this because they have a non-null Weyl tensor in the GDE.Comment: Submitted to Journal of Physics: Conference Series (JPCS), ERE200
Oscilaciones acústicas y el espectro de potencias
En el paradigma actual de la cosmología, el modelo que goza de mayor aceptación, dadas las pruebas observacionales, es conocido como ΛCDM (Cosmic Microwave Background). Este modelo está dominado principalmente por dos constituyentes acerca de los cuales la física sabe muy poco: la energía oscura, con un 70 %, es la principal componente y la causante de la expansión acelerada del Universo, mientras que la materia oscura, con un 25 % aproximadamente, es la componente principal de las estructuras auto-gravitantes. En mucho menos proporción se tiene la componente bariónica, la principal constituyente de las estrellas y por ende de la parte luminosa de las galaxias. Otras especies con menor proporción son las constituyentes relativistas, entre las cuales se tienen los neutrinos y fotones. Después del periodo de expansión acelerada del universo, denominado periodo inflacionario, debido a las altas temperaturas el plasma primordial constituido de especies relativistas fue el componente dominante en el Universo. En ese plasma la materia bariónica se encuentra ionizada y se acopla a la radiación vía dispersión de Compton. Tal plasma caliente desarrolla inestabilidades mediante la manifiestas en ondas de sonido y rarefacciones. Estas perturbaciones son soportadas hasta cuando el Universo en su expansión se ha enfriado lo suficiente para formar materia neutra. Después de esta recombinación, la radiación se desacopla formando el mar de fotones de CMB. Junto con perturbaciones métricas que aparecen por inflación en el potencial de la materia oscura, las oscilaciones del plasma quedaron impresas tanto en la temperatura de CMB como en el espectro de potencias de materia. Aquí se muestra cómo el lensamiento débil puede ser usado para estudiar estas oscilaciones.
In the current paradigm of cosmology, the ΛCDM model enjoys greater acceptance given the observational evidence. This model is domi-nated mainly by two components of which physics knows very little about them. The dark energy, with a 70% is the main component and caused the rapid universe expansion, while the dark matter, with a 25%, is the major component of the self-gravitantes structures. In less proportion then exists the baryonic component which is the main constituent of stars and there-fore part of the luminous galaxies. Other species in lower proportion are the relativists neutrinos and photons. After the period of rapid expansion, called inflation, the high temperature relativistic plasma was the dominant component in the Universe. This baryonic plasma matter is ionized and is coupled to radiation dispersal via Compton. This hot plasma develops instabilities and trigger sound waves and rarefaction. These disruptions are supported until the universe in its expansion has cooled enough to form a neutral field. After these recombination, radiation was undocked forming the sea of photons of CMB. Along with disturbances metric placed on the potential for inflation of dark matter, plasma oscillations were printed both in the temperature of CMB as in the power spectrum of matter. Here it is shown how Weak Lensing can be used to study these oscillations.
 
Delineating transitions during the evolution of specialised peroxisomes: glycosome formation in kinetoplastid and diplonemid protists
One peculiarity of protists belonging to classes Kinetoplastea and Diplonemea within the phylum Euglenozoa is compartmentalisation of most glycolytic enzymes within peroxisomes that are hence called glycosomes. This pathway is not sequestered in peroxisomes of the third Euglenozoan class, Euglenida. Previous analysis of well-studied kinetoplastids, the ‘TriTryps’ parasites Trypanosoma brucei, Trypanosoma cruzi and Leishmania spp., identified within glycosomes other metabolic processes usually not present in peroxisomes. In addition, trypanosomatid peroxins, i.e. proteins involved in biogenesis of these organelles, are divergent from human and yeast orthologues. In recent years, genomes, transcriptomes and proteomes for a variety of euglenozoans have become available. Here, we track the possible evolution of glycosomes by querying these databases, as well as the genome of Naegleria gruberi, a non-euglenozoan, which belongs to the same protist supergroup Discoba. We searched for orthologues of TriTryps proteins involved in glycosomal metabolism and biogenesis. Predicted cellular location(s) of each metabolic enzyme identified was inferred from presence or absence of peroxisomal-targeting signals. Combined with a survey of relevant literature, we refine extensively our previously postulated hypothesis about glycosome evolution. The data agree glycolysis was compartmentalised in a common ancestor of the kinetoplastids and diplonemids, yet additionally indicates most other processes found in glycosomes of extant trypanosomatids, but not in peroxisomes of other eukaryotes were either sequestered in this ancestor or shortly after separation of the two lineages. In contrast, peroxin divergence is evident in all euglenozoans. Following their gain of pathway complexity, subsequent evolution of peroxisome/glycosome function is complex. We hypothesize compartmentalisation in glycosomes of glycolytic enzymes, their cofactors and subsequently other metabolic enzymes provided selective advantage to kinetoplastids and diplonemids during their evolution in changing marine environments. We contend two specific properties derived from the ancestral peroxisomes were key: existence of nonselective pores for small solutes and the possibility of high turnover by pexophagy. Critically, such pores and pexophagy are characterised in extant trypanosomatids. Increasing amenability of free-living kinetoplastids and recently isolated diplonemids to experimental study means our hypothesis and interpretation of bioinformatic data are suited to experimental interrogation
On the Metric Dimension of Cartesian Products of Graphs
A set S of vertices in a graph G resolves G if every vertex is uniquely
determined by its vector of distances to the vertices in S. The metric
dimension of G is the minimum cardinality of a resolving set of G. This paper
studies the metric dimension of cartesian products G*H. We prove that the
metric dimension of G*G is tied in a strong sense to the minimum order of a
so-called doubly resolving set in G. Using bounds on the order of doubly
resolving sets, we establish bounds on G*H for many examples of G and H. One of
our main results is a family of graphs G with bounded metric dimension for
which the metric dimension of G*G is unbounded
Imprints of galaxy evolution on H ii regions Memory of the past uncovered by the CALIFA survey
H ii regions in galaxies are the sites of star formation and thus particular
places to understand the build-up of stellar mass in the universe. The line
ratios of this ionized gas are frequently used to characterize the ionization
conditions. We use the Hii regions catalogue from the CALIFA survey (~5000 H ii
regions), to explore their distribution across the classical [OIII]/Hbeta vs.
[NII]/Halpha diagnostic diagram, and how it depends on the oxygen abundance,
ionization parameter, electron density, and dust attenuation. We compared the
line ratios with predictions from photoionization models. Finally, we explore
the dependences on the properties of the host galaxies, the location within
those galaxies and the properties of the underlying stellar population. We
found that the location within the BPT diagrams is not totally predicted by
photoionization models. Indeed, it depends on the properties of the host
galaxies, their galactocentric distances and the properties of the underlying
stellar population. These results indicate that although H ii regions are short
lived events, they are affected by the total underlying stellar population. One
may say that H ii regions keep a memory of the stellar evolution and chemical
enrichment that have left an imprint on the both the ionizing stellar
population and the ionized gasComment: 18 pages, 8 figures, accepted for publishing in A&
- …