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&

Resonant, broadband and highly efficient optical frequency conversion in semiconductor nanowire gratings at visible and UV wavelengths

Using a hydrodynamic approach we examine bulk- and surface-induced second and third harmonic generation from semiconductor nanowire gratings having a resonant nonlinearity in the absorption region. We demonstrate resonant, broadband and highly efficient optical frequency conversion: contrary to conventional wisdom, we show that harmonic generation can take full advantage of resonant nonlinearities in a spectral range where nonlinear optical coefficients are boosted well beyond what is achievable in the transparent, long-wavelength, non-resonant regime. Using femtosecond pulses with approximately 500 MW/cm2 peak power density, we predict third harmonic conversion efficiencies of approximately 1% in a silicon nanowire array, at nearly any desired UV or visible wavelength, including the range of negative dielectric constant. We also predict surface second harmonic conversion efficiencies of order 0.01%, depending on the electronic effective mass, bistable behavior of the signals as a result of a reshaped resonance, and the onset fifth order nonlinear effects. These remarkable findings, arising from the combined effects of nonlinear resonance dispersion, field localization, and phase-locking, could significantly extend the operational spectral bandwidth of silicon photonics, and strongly suggest that neither linear absorption nor skin depth should be motivating factors to exclude either semiconductors or metals from the list of useful or practical nonlinear materials in any spectral range.Comment: 12 pages, 4 figure

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

Catalyst faceting during graphene layer crystallization in the course of carbon nanofiber growth

International audienceThe low temperature catalytic growth of multiwall carbon nanotubes (MWCNTs) rests on the continuous nucleation and growth of graphene layers at the surface of crystalline catalystparticles. Here, we study the atomic mechanisms at work in this phenomenon, by observing the growth of such layers in situ in the transmission electron microscope, in the case of iron-based catalysts. Graphene layers, parallel to the catalyst surface, appear by a mechanism of step flow, where the atomic layers of catalyst are "replaced" by graphene planes. Quite remarkably, catalyst facets systematically develop while this mechanism is at work. We discuss the origin of faceting in terms of equilibrium particle shape and graphene layer nucleation. Step bunching due to impeded step migration, in certain growth conditions, yields characteristic catalyst nail-head shapes. Mastering themechanisms of faceting and step bunching could open up the way to tailoring the structure of low temperature-grown MWCNTs, e.g. with highly parallel carbon walls and, ultimately, with controlled structure and chirality

Оценка гемодинамического эффекта Левосимендана у пациентов с острым инфарктом миокарда осложненным кардиогенным шоком

Department of Anaesthesia and Intensive Care, Department of Internal Medicine, Discipline of Cardiology, Medical Clinic No 3, Nicolae Testemitanu State Medical and Pharmaceutical University, Congresul III al Medicilor de Familie din Republica Moldova, 17–18 mai, 2012, Chişinău, Republica Moldova, Conferinţa Naţională „Maladii bronhoobstructive la copii”, consacrată profesorului universitar, doctor habilitat Victor Gheţeul, 27 aprilie, Chişinău, Republica MoldovaCardiogene shock (CS) is a syndrome caused by the incapacity of the heart to assure an appropriate tissular perfusion for the methabolic needs, having as consequences an accentuated decrease of the cardiac flow and tissular hipoxy. The level of the mortality in CS is high and varies between 35% and 73% of the cases. The majority of the deceased patients are detected during the first 24 hours from hospitalization, a fact that suggests the need of starting an appropriate intensive treatment of the patient associated with improvement of clinical symptoms, starting a good diuresis, and vessel dilation, the lack of proarhytmogen activity, and no interference with other treatments of the heart failure, this way decreasing and the duration of hospitalization. The intensive treatment with Levosimendan represents an effective therapy in decompensated heart failure. Administering LSMD in patients with AMI complicated with cardiogene shock determined the increase of the ejection fraction between 31, 6% and 42.7% of the cases, increase of the beat volume from 48 ± 3ml to 59 ± 6 ml (p < 0.03), and the increase of the cardiac index from 2.2 l/minute (initial) until at 3.1 l/minute at 72 h (p < 0.01). The initial administration of LSMD in these patients also reduced the pressure at the level of the pulmonary capillaries from 22 ± 1 mm Hg, to 16 ± 3 mm Hg (p < 0.03), and significantly decreased the systemic vascular resistence from 214 ± 276 to 932 ± 282 dyne.sec.cm (-4), p < 0,01). In the patients included in this study, during the first five days of treatment with LSVD (lot No I) was noticed: the improvement of the clinic health status, the significant decrease of the values of BNP, and also a significant decrease of the number of deceased patients comparing with the number of the deceased ones that were treated with Dubutamine (lot No II).Кардиогенный шок (КШ) это клинический синдром, характеризующийся гипоперфузией тканей из-за сердечной недостаточности (СН), которая сохраняется после коррекции преднагрузки. Уровень смертности при КШ высокая и составляет от 35% до 73 %, большинство пациентов умирают в течение первых 24 часов от госпитализации, что свидетельствует в пользу необходимости своевременного экстренного начала лечения для максимально быстрой стабилизации гемодинамики и уменьшения клинических симптомов острой сердечной недостаточности (ОСН). Несвоевременное и неадекватное лечение неминуемо ведет к смерти. Интенсивное лечение Левосименданом приводит к положительному инотропному действию, обеспечивая повышение чувствительности сократительных белков кардиомиоцитов к кальцию, и активацию калиевых каналов в гладкой мускулатуре, что приводит к вазодилатации. Левосимендан показан при ОСН с низким сердечным выбросом у больных с систолической дисфункцией левого желудочка (низкой фракцией выброса) при отсутствии тяжелой артериальной гипотонии (систолическое АД < 85 мм рт.ст.). Применение Левосимендана в лечении больных с острым инфарктом миокарда, осложнённым кардиогенным шоком способствовало увеличению фракции выброса ЛЖ от 31,6% и 42,7% случаев повышению сердечного объёма от 48 ± 3ml до 59 ± 6 ml (p < 0,03), увеличению сердечного индекса от 2,2 l/min. в начале лечения до 3,1 l/min после 72 часов (p < 0,01), снижению давления в легочных капиллярах от 22 ± 1 mm Hg до 16 ± 3 mm Hg (p < 0,03), значительному снижению системного сосудистого сопротивления от 1214 ± 276 до 932 ± 282 dyne. sec. cm (-4), p < 0,01). У пациентов, включённых в данное исследование, в первые пять дней лечения Левосименданом (I группа) было замечено: улучшение клинического состояния, значительное снижение натридиуретического гормона (НДГ), уменьшение смертности по сравнению с пациентами II группы, которые лечились Добутамином

The Philia project – for the successful integration of the young through their empowerment and social network development

The Philia+ project has been approved for funding within the Erasmus + Programme. Several partners from Belgium, France, Germany, Portugal and Romania (from higher education and social work institutions) have worked to support the academic success and social inclusion of (pre)adolescents aged 13-18 in foster care, and to enhance, preserve and develop their support networks. Training programmes were held for teachers, trainers and researchers involved in the project, as well as for students and social work professionals and young people in difficulty in the care of associations and organizations providing them social and psychological support. The aim has always been to change their position according to the theoretical DPAPC (empowerment of individuals and communities) framework and to the methodological RAC (collaborative research-action) framework, in order to enable them to understand the mechanism of the social determinism of success and failure and to enhance their support networks. We managed to create two training modules, teasers of experienced testimonies (focus groups, comprehensive conversations), educational films for the two modules, educational films on accompanying Roma and unaccompanied minors.info:eu-repo/semantics/publishedVersio

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