598 research outputs found
Revisiting the luminosity function of single halo white dwarfs
White dwarfs are the fossils left by the evolution of low-and
intermediate-mass stars, and have very long evolutionary timescales. This
allows us to use them to explore the properties of old populations, like the
Galactic halo. We present a population synthesis study of the luminosity
function of halo white dwarfs, aimed at investigating which information can be
derived from the currently available observed data. We employ an up-to-date
population synthesis code based on Monte Carlo techniques, that incorporates
the most recent and reliable cooling sequences for metal poor progenitors as
well as an accurate modeling of the observational biases. We find that because
the observed sample of halo white dwarfs is restricted to the brightest stars
only the hot branch of the white dwarf luminosity function can be used for such
purposes, and that its shape function is almost insensitive to the most
relevant inputs, like the adopted cooling sequences, the initial mass function,
the density profile of the stellar spheroid, or the adopted fraction of
unresolved binaries. Moreover, since the cut-off of the observed luminosity has
not been yet determined only lower limits to the age of the halo population can
be placed. We conclude that the current observed sample of the halo white dwarf
population is still too small to obtain definite conclusions about the
properties of the stellar halo, and the recently computed white dwarf cooling
sequences which incorporate residual hydrogen burning should be assessed using
metal-poor globular clusters.Comment: 9 pages, 9 figures, accepted for publication in A&
Green's function of a finite chain and the discrete Fourier transform
A new expression for the Green's function of a finite one-dimensional lattice
with nearest neighbor interaction is derived via discrete Fourier transform.
Solution of the Heisenberg spin chain with periodic and open boundary
conditions is considered as an example. Comparison to Bethe ansatz clarifies
the relation between the two approaches.Comment: preprint of the paper published in Int. J. Modern Physics B Vol. 20,
No. 5 (2006) 593-60
Optimizing omnidirectional reflection by multilayer mirrors
Periodic layered media can reflect strongly for all incident angles and
polarizations in a given frequency range. Quarter-wave stacks at normal
incidence are commonplace in the design of such omnidirectional reflectors. We
discuss alternative design criteria to optimize these systems.Comment: 9 pages, 6 figures. To be published in J. Opt. A: Pure and Applied
Optic
Amicable pairs and aliquot cycles for elliptic curves
An amicable pair for an elliptic curve E/Q is a pair of primes (p,q) of good
reduction for E satisfying #E(F_p) = q and #E(F_q) = p. In this paper we study
elliptic amicable pairs and analogously defined longer elliptic aliquot cycles.
We show that there exist elliptic curves with arbitrarily long aliqout cycles,
but that CM elliptic curves (with j not 0) have no aliqout cycles of length
greater than two. We give conjectural formulas for the frequency of amicable
pairs. For CM curves, the derivation of precise conjectural formulas involves a
detailed analysis of the values of the Grossencharacter evaluated at a prime
ideal P in End(E) having the property that #E(F_P) is prime. This is especially
intricate for the family of curves with j = 0.Comment: 53 page
Optimization of organized silicon nanowires growth inside porous anodic alumina template using hot wire chemical vapor deposition process
International audienceA Hot Wire assisted Chemical Vapor Deposition (HWCVD) process has been developed for producing highdensity arrays of parallel, straight and organized silicon nanowires (SiNWs) inside vertical Porous Anodic Alumina (PAA) templates, exploring temperatures ranging from 430 °C to 600 °C, and pressures varying between 2.5 and 7.5 mbar. In order to prevent parasitic amorphous silicon (a-Si) deposit and to promote the crystalline SiNWs growth, we used a tungsten hot wire to partially crack H2 into atomic hydrogen, which acts like a selective etchant regarding a-Si. Here we describe the optimization route we followed to limit the deposit of a-Si onto the surface of the porous membrane and on the walls of the pores, which led to the possibility to grow SiNWs inside the PAA membranes. Such an approach has high potentialities for device realization, like PIN junctions, FETs or electrodes for Li-ion batteries
Finance, distribution and the economic objective of cooperative financial institutions
This paper proposes a model where the structure rather than the size of the financial sector explains its influence on income distribution. Because of information asymmetries, a financial sector dominated solely by profit‐maximizing financial intermediaries will increase income and wealth inequality as it gives preferential access to credit for high‐income agents, whereas a diversified inclusive financial sector with alternative models of finance, like cooperatives, will reduce the inequality gap. No full convergence in income distribution can be realized through finance only and there is still a need for redistribution policies. Accordingly, an objective function for cooperative financial institutions should define a desired pricing behaviour that can increase the income of members at a rate higher than the average growth rate of the economy
13-Series resolvins mediate the leukocyte-platelet actions of atorvastatin and pravastatin in inflammatory arthritis
This work was supported by funding from the European Research Council under the European Union’s Horizon 2020 research and innovation program (Grant 677542), a Sir Henry Dale Fellowship jointly funded by the Wellcome Trust and the Royal Society (Grant 107613/Z/15/Z), and the Barts Charity (Grant MGU0343). This work was also funded, in part, by Medical Research Council Advance Course Masters (Grant MR/J015741/1). The authors declare no conflicts of interest
Acute respiratory distress syndrome in children with bilateral postviral pneumonia. Case report
USMF „Nicolae Testemițanu”, Catedra Anesteziologie și Reanimatologie, IMSP SCMC „V. Ignatenco”SDRA reprezintă cea mai severă manifestare
dintr-un spectru de răspunsuri apărute la
diverse leziuni pulmonare acute. Prezentăm
un caz clinic de tratament cu succes al
unui copil de 1 an si 6 luni, cu sindromul
de detresă respiratorie acută. Ca rezultat
pozitiv se conclude ca diagnosticarea cât
mai precoce a ARDS, urmată de instituirea
unui tratament eficace, măresc șansele de
recuperare a bolnavilor.ARDS represents the most rigorous
manifestation from large variety of acute
pulmonary lesions. We present a case
report of success treatment of a 1 year
and 6 months child with Acute respiratory
detress syndrome. As a positive
result we conclude that early diagnostic
and treatment in ARDS major the optimistic
chances in the recovering of the
patients
Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC
The uncertainty on the calorimeter energy response to jets of particles is
derived for the ATLAS experiment at the Large Hadron Collider (LHC). First, the
calorimeter response to single isolated charged hadrons is measured and
compared to the Monte Carlo simulation using proton-proton collisions at
centre-of-mass energies of sqrt(s) = 900 GeV and 7 TeV collected during 2009
and 2010. Then, using the decay of K_s and Lambda particles, the calorimeter
response to specific types of particles (positively and negatively charged
pions, protons, and anti-protons) is measured and compared to the Monte Carlo
predictions. Finally, the jet energy scale uncertainty is determined by
propagating the response uncertainty for single charged and neutral particles
to jets. The response uncertainty is 2-5% for central isolated hadrons and 1-3%
for the final calorimeter jet energy scale.Comment: 24 pages plus author list (36 pages total), 23 figures, 1 table,
submitted to European Physical Journal
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