354 research outputs found
Empirical description of beta-delayed fission partial half-lives
Background: The process of beta-delayed fission (bDF) provides a versatile
tool to study low-energy fission in nuclei far away from the beta-stability
line, especially for nuclei which do not fission spontaneously. Purpose: The
aim of this paper is to investigate systematic trends in bDF partial
half-lives. Method: A semi-phenomenological framework was developed to
systematically account for the behavior of bDF partial half-lives. Results: The
bDF partial half-life appears to exponentially depend on the difference between
the Q value for beta decay of the parent nucleus and the fission-barrier energy
of the daughter (after beta decay) product. Such dependence was found to arise
naturally from some simple theoretical considerations. Conclusions: This
systematic trend was confirmed for experimental bDF partial half-lives spanning
over 7 orders of magnitudes when using fission barriers calculated from either
the Thomas-Fermi or the liquid-drop fission model. The same dependence was also
observed, although less pronounced, when comparing to fission barriers from the
finite-range liquid-drop model or the Thomas-Fermi plus Strutinsky Integral
method.Comment: accepted for publication in Phys. Rev.
The chameleon groups of Richard J. Thompson: automorphisms and dynamics
The automorphism groups of several of Thompson's countable groups of
piecewise linear homeomorphisms of the line and circle are computed and it is
shown that the outer automorphism groups of these groups are relatively small.
These results can be interpreted as stability results for certain structures of
PL functions on the circle. Machinery is developed to relate the structures on
the circle to corresponding structures on the line
Entropy of geometric structures
We give a notion of entropy for general gemetric structures, which
generalizes well-known notions of topological entropy of vector fields and
geometric entropy of foliations, and which can also be applied to singular
objects, e.g. singular foliations, singular distributions, and Poisson
structures. We show some basic properties for this entropy, including the
\emph{additivity property}, analogous to the additivity of Clausius--Boltzmann
entropy in physics. In the case of Poisson structures, entropy is a new
invariant of dynamical nature, which is related to the transverse structure of
the characteristic foliation by symplectic leaves.Comment: The results of this paper were announced in a talk last year in IMPA,
Rio (Poisson 2010
Black Hole Entropy, Topological Entropy and the Baum-Connes Conjecture in K-Theory
We shall try to exhibit a relation between black hole entropy and topological
entropy using the famous Baum-Connes conjecture for foliated manifolds which
are particular examples of noncommutative spaces. Our argument is qualitative
and it is based on the microscopic origin of the Beckenstein-Hawking
area-entropy formula for black holes, provided by superstring theory, in the
more general noncommutative geometric context of M-Theory following the Connes-
Douglas-Schwarz article.Comment: 17 pages, Latex, contains an important paragraph in section 2 which
gives a better understandin
What is required to end the AIDS epidemic as a public health threat by 2030? The cost and impact of the fast-track approach
In 2011 a new Investment Framework was proposed that described how the scale-up of key HIV interventions could dramatically reduce new HIV infections and AIDS-related deaths in low and middle income countries by 2015. This framework included ambitious coverage goals for prevention and treatment services for 2015, resulting in a reduction of new HIV infections by more than half, in line with the goals of the declaration of the UN High Level Meeting in June 2011. However, the approach suggested a leveling in the number of new infections at about 1 million annually-far from the UNAIDS goal of ending AIDS by 2030. In response, UNAIDS has developed the Fast-Track approach that is intended to provide a roadmap to the actions required to achieve this goal. The Fast-Track approach is predicated on a rapid scale-up of focused, effective prevention and treatment services over the next 5 years and then maintaining a high level of programme implementation until 2030. Fast-Track aims to reduce new infections and AIDS-related deaths by 90% from 2010 to 2030 and proposes a set of biomedical, behavioral and enabling intervention targets for 2020 and 2030 to achieve that goal, including the rapid scale-up initiative for antiretroviral treatment known as 90-90-90. Compared to a counterfactual scenario of constant coverage for all services at early-2015 levels, the Fast-Track approach would avert 18 million HIV infections and 11 million deaths from 2016 to 2030 globally. This paper describes the analysis that produced these targets and the estimated resources needed to achieve them in low- and middle-income countries. It indicates that it is possible to achieve these goals with a significant push to achieve rapid scale-up of key interventions between now and 2020. The annual resources required from all sources would rise to US8.2Bn in lower middle-income countries and US$10.5Bn in upper-middle-income-countries by 2020 before declining approximately 9% by 2030
Upper bound on the density of Ruelle resonances for Anosov flows
Using a semiclassical approach we show that the spectrum of a smooth Anosov
vector field V on a compact manifold is discrete (in suitable anisotropic
Sobolev spaces) and then we provide an upper bound for the density of
eigenvalues of the operator (-i)V, called Ruelle resonances, close to the real
axis and for large real parts.Comment: 57 page
Boundaries of Siegel Disks: Numerical Studies of their Dynamics and Regularity
Siegel disks are domains around fixed points of holomorphic maps in which the maps are locally linearizable (i.e., become a rotation under an appropriate change of coordinates which is analytic in a neighborhood of the origin). The dynamical behavior of the iterates of the map on the boundary of the Siegel disk exhibits strong scaling properties which have been intensively studied in the physical and mathematical literature. In the cases we study, the boundary of the Siegel disk is a Jordan curve containing a critical point of the map (we consider critical maps of different orders), and there exists a natural parametrization which transforms the dynamics on the boundary into a rotation. We compute numerically this parameterization and use methods of harmonic analysis to compute the global Holder regularity of the parametrization for different maps and rotation numbers. We obtain that the regularity of the boundaries and the scaling exponents are universal numbers in the sense of renormalization theory (i.e., they do not depend on the map when the map ranges in an open set), and only depend on the order of the critical point of the map in the boundary of the Siegel disk and the tail of the continued function expansion of the rotation number. We also discuss some possible relations between the regularity of the parametrization of the boundaries and the corresponding scaling exponents. (C) 2008 American Institute of Physics.NSFMathematic
Broadband vehicle-to-vehicle communication using an extended autonomous cruise control sensor
For several years road vehicle autonomous cruise control (ACC) systems as well as anti-collision radar have been developed. Several manufacturers currently sell this equipment. The current generation of ACC sensors only track the first preceding vehicle to deduce its speed and position. These data are then used to compute, manage and optimize a safety distance between vehicles, thus providing some assistance to car drivers. However, in real conditions, to elaborate and update a real time driving solution, car drivers use information about speed and position of preceding and following vehicles. This information is essentially perceived using the driver's eyes, binocular stereoscopic vision performed through the windscreens and rear-view mirrors. Furthermore, within a line of vehicles, the frontal road perception of the first vehicle is very particular and highly significant. Currently, all these available data remain strictly on-board the vehicle that has captured the perception information and performed these measurements. To get the maximum effectiveness of all these approaches, we propose that this information be shared in real time with the following vehicles, within the convoy. On the basis of these considerations, this paper technically explores a cost-effective solution to extend the basic ACC sensor function in order to simultaneously provide a vehicle-to-vehicle radio link. This millimetre wave radio link transmits relevant broadband perception data (video, localization...) to following vehicles, along the line of vehicles. The propagation path between the vehicles uses essentially grazing angles of incidence of signals over the road surface including millimetre wave paths beneath the cars
Entropy production in Gaussian thermostats
We show that an arbitrary Anosov Gaussian thermostat on a surface is
dissipative unless the external field has a global potential
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