12,435 research outputs found
On the Evolution, Numbers, and Characteristics of Close-Binary Supersoft Sources
The ability to perform detailed evolutionary calculations is essential to the
development of a well-defined and testable binary model. Unfortunately,
traditional evolutionary calculations cannot be used to follow a significant
fraction of possible close-binary supersoft sources (CBSSs). It is therefore
important to examine the input physics carefully, to be sure that all relevant
and potentially important physical processes are included. In this paper we
continue a line of research begun last year, and explore the role that winds
are expected to play in the evolution of CBSSs. We find that at least a subset
of the systems that seemed to be candidates for common envelope evolution may
survive, if radiation emitted by white dwarf drives winds from the system. We
study the effects of winds on the binary evolution of CBSSs, and compute the
number and characteristics of CBSSs expected to be presently active in galaxies
such as our own or M31.Comment: 13 pages; figures included in 0.33 M postscript file; in Supersoft
X-ray Sources, ed. J. Greiner (Springer-Verlag: Berlin) (1996
The Progenitors of Type Ia Supernovae: II. Are they Double-Degenerate Binaries? The Symbiotic Channel
In order for a white dwarf (WD) to achieve the Chandrasekhar mass, M_C, and
explode as a Type Ia supernova (SNIa), it must interact with another star,
either accreting matter from or merging with it. The failure to identify the
types of binaries which produce SNeIa is the "progenitor problem". Its solution
is required if we are to utilize the full potential of SNeIa to elucidate basic
cosmological and physical principles. In single-degenerate models, a WD
accretes and burns matter at high rates. Nuclear-burning WDs (NBWDs) with mass
close to M_C are hot and luminous, potentially detectable as supersoft x-ray
sources (SSSs). In previous work we showed that > 90-99% of the required number
of progenitors do not appear as SSSs during most of the crucial phase of mass
increase. The obvious implication is that double-degenerate (DD) binaries form
the main class of progenitors. We show in this paper, however, that many
binaries that later become DDs must pass through a long-lived NBWD phase during
which they are potentially detectable as SSSs. The paucity of SSSs is therefore
not a strong argument in favor of DD models. Those NBWDs that are the
progenitors of DD binaries are likely to appear as symbiotic binaries for
intervals > 10^6 years. In fact, symbiotic pre-DDs should be common, whether or
not the WDs eventually produce SNeIa. The key to solving the progenitor problem
lies in understanding the appearance of NBWDs. Most do not appear as SSSs most
of the time. We therefore consider the evolution of NBWDs to address the
question of what their appearance may be and how we can hope to detect them.Comment: 24 pages; 5 figures; submitted to Ap
Entropy of Folding of the Triangular Lattice
The problem of counting the different ways of folding the planar triangular
lattice is shown to be equivalent to that of counting the possible 3-colorings
of its bonds, a dual version of the 3-coloring problem of the hexagonal lattice
solved by Baxter. The folding entropy Log q per triangle is thus given by
Baxter's formula q=sqrt(3)(Gamma[1/3])^(3/2)/2pi =1.2087...Comment: 9 pages, harvmac, epsf, uuencoded, 5 figures included, Saclay
preprint T/9401
Paving the way for future labour migration: A Belgian-Tunisian Skills Mobility Partnership. CEPS Policy Insight 28 Sep 2020.
Since September 2017, the European Commission has been encouraging the use of new approaches to broaden labour migration to the EU. In response to this call, several pilots for skill mobility partnerships are being tested by partner countries with, for example, different target groups (e.g. recent graduates or young professionals), types of contract (e.g. internship or work) or duration.
The IOM skills mobility partnership between Belgium and Tunisia highlights the importance of multidimensional cooperation between different stakeholders from both countries (e.g. immigration office, public employment services, employers’ associations) throughout the implementation of the project (e.g. in assessing labour market needs, streamlining procedures, selecting candidates). Throughout this pilot project, IOM improved its understanding of the private sector’s interest in international hiring and the difficulties faced by companies with this issue, while companies became acquainted with different aspects of international labour migration such as ethical recruitment practices and skills recognition.
All participants found a job after their internship in Belgium, the great majority back in Tunisia and some in a subsidiary of the Belgian host company. The project therefore achieved its main objectives of i) providing concrete opportunities for skills mobility to third country nationals while ensuring skills return, ii) meeting the labour market needs in terms of skills, and iii) supporting the private sector’s interest in international hiring. Foreign investment on the part of some of the Belgian host companies was but one positive spillover from this project
A stochastic model for internal HIV dynamics
In this paper we analyse a stochastic model representing HIV internal virus dynamics. The stochasticity in the model is introduced by parameter perturbation which is a standard technique in stochastic population modelling. We show that the model established in this paper possesses non-negative solutions as this is essential in any population dynamics model. We also carry out analysis on the asymptotic behaviour of the model. We approximate one of the variables by a mean reverting process and nd out the mean and variance of this process. Numerical simulations conclude the paper
Improvement of neuropsychological performances and reduction of immune-activation markers after probiotic supplementation and change of life-style in an HIV positive male: targeting the microbiota to act on gut-brain axis
The gut-brain axis is widely in uenced by the intestinal microbiota and dysbiosis is consequently associated with a large dysregulation of its functions. Probiotic supplementation, reducing the harmful effects of dysbiosis, has shown positive effects not only on gut and brain functions, but also on the control of the dangerous effects of immune activation. Mounting evidence has shown that neurocognitive impairment can be a secondary to the impairment of the microbiota-gut-brain axis in HIV positive patients. In this case report we analyzed the im- provement of neurocognitive performances associated with a reduction of levels of peripheral immune-activa- tion, after 6 months of probiotic supplementation. In this case, the achieved result may have been in uenced by a more comprehensive modi cation of the patient’s lifestyle with the introduction of a controlled diet and regular physical activity. Our observations suggest that integrate antiretroviral therapy and non-pharmacological tools into an overall approach, can be a useful strategy to control some non-AIDS related diseases
City of Colton Urban Forest Management Project
As population growth continues in our urban centers, urban forest management becomes an important priority. Trees are an essential component of resilient and healthy urban communities, providing benefits including mediating the urban heat island effect, storm water management, and energy and water efficiency, carbon sequestration, and city beautification. In order to assess the current status of Colton’s urban forest, interdisciplinary teams of students and scientists from the Center for Urban Resilience (CURes) at Loyola Marymount University (LMU) have assisted Jack Sahl & Associates with an extensive inventory of the tree resources within the City. In gathering data describing the size, distribution, age, health, and energy efficiency benefits of the city’s trees, this study seeks to provide recommendations for best management practices of Colton’s urban forest. Colton has strived to engage the public in an open dialogue about this project. Colton is the first city to deal with the task of conducting an inventory of all the trees located within the public domain, in the future the strategies used here will be improved.https://digitalcommons.lmu.edu/cures_posters/1014/thumbnail.jp
Polarizations and differential calculus in affine spaces
Within the framework of mappings between affine spaces, the notion of -th
polarization of a function will lead to an intrinsic characterization of
polynomial functions. We prove that the characteristic features of derivations,
such as linearity, iterability, Leibniz and chain rules, are shared -- at the
finite level -- by the polarization operators. We give these results by means
of explicit general formulae, which are valid at any order , and are based
on combinatorial identities. The infinitesimal limits of the -th
polarizations of a function will yield its -th derivatives (without
resorting to the usual recursive definition), and the above mentioned
properties will be recovered directly in the limit. Polynomial functions will
allow us to produce a coordinate free version of Taylor's formula
Cluster model of glass transition in simple liquids
On the basis of microscopic statistical mechanics of simple liquids the
orientational interaction between clusters consisting of a particle and its
nearest neighbors is estimated. It is shown that there are ranges of density
and temperature where the interaction changes sign as a function of a radius of
a cluster. The model of interacting cubic and icosahedral clusters is proposed
and solved in mean-field replica symmetric approximation. It is shown that the
glass order parameter grows smoothly upon cooling, the transition temperature
being identified with the temperature of the replica symmetry breaking. It is
shown that upon cooling a Lennard-Jones system, cubic clusters freeze first.
The transition temperature for icosahedral clusters is about ten per cent
lower. So the local structure of Lennard-Jones glass in the vicinity of glass
transition should be most probably cubic.Comment: 4 pages, 3 figure
- …