457 research outputs found
Population synthesis of DA white dwarfs: constraints on soft X-ray spectra evolution
Extending the population synthesis method to isolated young cooling white
dwarfs we are able to confront our model assumptions with observations made in
ROSAT All-Sky Survey (Fleming et al., 1996). This allows us to check model
parameters such as evolution of spectra and separation of heavy elements in DA
WD envelopes. It seems like X-ray spectrum temperature of these objects is
given by the formula T_{X-ray} = min(T_eff, T_max). We have obtained DA WD's
birth rate and upper limit of the X-ray spectrum temperature: DA birth rate in cubic parsec per year and T_max = 41000 K. These values
are in good correspondence with values obtained by other authors (Liebert et
al., 2004; Wolff et al., 1996). From this fact we also conclude that our
population synthesis method is applicable to the population of close-by
isolated cooling white dwarfs as well as to the population of the isolated
cooling neutron stars.Comment: 4 pages, 3 figures, conference "European White Dwarf Workshop, 2010",
Tubingen, German
Extensive population synthesis of isolated neutron stars with field decay
We perform population synthesis studies of different types of neutron stars
taking into account the magnetic field decay. For the first time, we confront
our results with observations using {\it simultaneously} the Log N -- Log S
distribution for nearby isolated neutron stars, the Log N -- Log L distribution
for magnetars, and the distribution of radio pulsars in the --
diagram. We find that our theoretical model is consistent with all sets of data
if the initial magnetic field distribution function follows a log-normal law
with and . The
typical scenario includes about 10% of neutron stars born as magnetars,
significant magnetic field decay during the first million years of a NS life.
Evolutionary links between different subclasses may exist, although robust
conclusions are not yet possible.
We apply the obtained field distribution and the model of decay to study
long-term evolution of neuton stars till the stage of accretion from the
interstellar medium. It is shown that though the subsonic propeller stage can
be relatively long, initially highly magnetized neutron stars ( G) reach the accretion regime within the Galactic lifetime if their
kick velocities are not too large. The fact that in previous studies made 10
years ago, such objects were not considered results in a slight increase of the
Accretor fraction in comparison with earlier conclusions. Most of the neutron
stars similar to the Magnificent seven are expected to become accreting from
the interstellar medium after few billion years of their evolution. They are
the main predecestors of accreting isolated neutron stars.Comment: 4 pages, conference "Astrophysics of Neutron Stars - 2010" in honor
of M. Ali Alpar, Izmir, Turke
Sustained expression of microRNA-155 in hematopoietic stem cells causes a myeloproliferative disorder
Mammalian microRNAs are emerging as key regulators of the development and function of the immune system. Here, we report a strong but transient induction of miR-155 in mouse bone marrow after injection of bacterial lipopolysaccharide (LPS) correlated with granulocyte/monocyte (GM) expansion. Demonstrating the sufficiency of miR-155 to drive GM expansion, enforced expression in mouse bone marrow cells caused GM proliferation in a manner reminiscent of LPS treatment. However, the miR-155–induced GM populations displayed pathological features characteristic of myeloid neoplasia. Of possible relevance to human disease, miR-155 was found to be overexpressed in the bone marrow of patients with certain subtypes of acute myeloid leukemia (AML). Furthermore, miR-155 repressed a subset of genes implicated in hematopoietic development and disease. These data implicate miR-155 as a contributor to physiological GM expansion during inflammation and to certain pathological features associated with AML, emphasizing the importance of proper miR-155 regulation in developing myeloid cells during times of inflammatory stress
Hyper-complex four-manifolds from the Tzitz\'eica equation
It is shown how solutions to the Tzitz\'eica equation can be used to
construct a family of (pseudo) hyper-complex metrics in four dimensions.Comment: To be published in J.Math.Phy
The technologies of using generating gas in cogeneration installations
The paper discusses the experimental setup of gas generation from wood waste. The obtained experimental dependence of the composition of the generator gas temperature at the exit of the gasifier.В работе рассмотрена экспериментальная установка генерации газа из древесных отходов. Получены экспериментальные зависимости состава генераторного газа от температуры на выходе из газогенератора
Strominger--Yau--Zaslow geometry, Affine Spheres and Painlev\'e III
We give a gauge invariant characterisation of the elliptic affine sphere
equation and the closely related Tzitz\'eica equation as reductions of real
forms of SL(3, \C) anti--self--dual Yang--Mills equations by two
translations, or equivalently as a special case of the Hitchin equation.
We use the Loftin--Yau--Zaslow construction to give an explicit expression
for a six--real dimensional semi--flat Calabi--Yau metric in terms of a
solution to the affine-sphere equation and show how a subclass of such metrics
arises from 3rd Painlev\'e transcendents.Comment: 38 pages. Final version. To appear in Communications in Mathematical
Physic
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