12,672 research outputs found
Fluid-solid transition in hard hyper-sphere systems
In this work we present a numerical study, based on molecular dynamics
simulations, to estimate the freezing point of hard spheres and hypersphere
systems in dimension D = 4, 5, 6 and 7. We have studied the changes of the
Radial Distribution Function (RDF) as a function of density in the coexistence
region. We started our simulations from crystalline states with densities above
the melting point, and moved down to densities in the liquid state below the
freezing point. For all the examined dimensions (including D = 3) it was
observed that the height of the first minimum of the RDF changes in an almost
continuous way around the freezing density and resembles a second order phase
transition. With these results we propose a numerical method to estimate the
freezing point as a function of the dimension D using numerical fits and
semiempirical approaches. We find that the estimated values of the freezing
point are very close to previously reported values from simulations and
theoretical approaches up to D = 6 reinforcing the validity of the proposed
method. This was also applied to numerical simulations for D = 7 giving new
estimations of the freezing point for this dimensionality.Comment: 13 pages, 10 figure
GTI-space : the space of generalized topological indices
A new extension of the generalized topological indices (GTI) approach is carried out torepresent 'simple' and 'composite' topological indices (TIs) in an unified way. Thisapproach defines a GTI-space from which both simple and composite TIs represent particular subspaces. Accordingly, simple TIs such as Wiener, Balaban, Zagreb, Harary and Randićconnectivity indices are expressed by means of the same GTI representation introduced for composite TIs such as hyper-Wiener, molecular topological index (MTI), Gutman index andreverse MTI. Using GTI-space approach we easily identify mathematical relations between some composite and simple indices, such as the relationship between hyper-Wiener and Wiener index and the relation between MTI and first Zagreb index. The relation of the GTI space with the sub-structural cluster expansion of property/activity is also analysed and some routes for the applications of this approach to QSPR/QSAR are also given
Influence of the absorber dimensions on wavefront shaping based on volumetric optoacoustic feedback
The recently demonstrated control over light distribution through turbid
media based on real-time three-dimensional optoacoustic feedback has offered
promising prospects to interferometrically focus light within scattering
objects. Nevertheless, the focusing capacity of the feedback-based approach is
strongly conditioned by the number of effectively resolvable optical modes
(speckles). In this letter, we experimentally tested the light intensity
enhancement achieved with optoacoustic feedback measurements from different
sizes of absorbing microparticles. The importance of the obtained results is
discussed in the context of potential signal enhancement at deep locations
within a scattering medium where the effective speckle sizes approach the
minimum values dictated by optical diffraction
Sweetened beverages, snacks and overweight: findings from the Young Lives cohort study in Peru
OBJECTIVE: To determine the association between consumption of snacks and sweetened beverages and risk of overweight among children. DESIGN: Secondary analysis of the Young Lives cohort study in Peru. SETTING: Twenty sentinel sites from a total of 1818 districts available in Peru. SUBJECTS: Children in the younger cohort of the Young Lives study in Peru, specifically those included in the third (2009) and the fourth (2013) rounds. RESULTS: A total of 1813 children were evaluated at baseline; 49·2 % girls and mean age 8·0 (sd 0·3) years. At baseline, 3·3 (95 % CI 2·5, 4·2) % reported daily sweetened beverage consumption, while this proportion was 3·9 (95 % CI 3·1, 4·9) % for snacks. Baseline prevalence of overweight was 22·0 (95 % CI 20·1, 23·9) %. Only 1414 children were followed for 4·0 (sd 0·1) years, with an overweight incidence of 3·6 (95 % CI 3·1, 4·1) per 100 person-years. In multivariable analysis, children who consumed sweetened beverages and snacks daily had an average weight increase of 2·29 (95 % CI 0·62, 3·96) and 2·04 (95 % CI 0·48, 3·60) kg more, respectively, than those who never consumed these products, in approximately 4 years of follow-up. Moreover, there was evidence of an association between daily consumption of sweetened beverages and risk of overweight (relative risk=2·12; 95 % CI 1·05, 4·28). CONCLUSIONS: Daily consumption of sweetened beverages and snacks was associated with increased weight gain v. never consuming these products; and in the case of sweetened beverages, with higher risk of developing overweight
Seguridad Humana y Derecho Internacional Público
Este estudio sostiene que la seguridad humana guarda una relación conceptual con el derecho internacional público y que además en años recientes se han desarrollado diversas expresiones prácticas de la seguridad humana relevantes para esta rama del derecho que merecen ser estudiadas con mayor detalle. A ese respecto, el enfoque central de este texto no es proporcionar evidencia total de la materialización normativa de la seguridad humana en las fuentes tradicionales del derecho internacional público, sino más bien profundizar en el análisis de las implicaciones normativas de la seguridad humana, especialmente en su simbiosis con los derechos humanos reconocidos por el derecho internacional. Una de las preocupaciones centrales del derecho internacional público contemporáneo es, precisamente, el área del derecho internacional de los derechos humanos. Como tal, se hace referencia a las fuentes del derecho internacional público y se detalla y aclara la manera en que la seguridad humana se relaciona con ellas en el campo concreto de los derechos humanos.This study argues that human security holds a conceptual relationship with public international law and that in recent years several practical expressions of human security have been developed in a manner relevant to this area of the law and, thus, they deserve to be analyzed in further detail. In this respect, the main emphasis of this text is not to provide integral evidence of the normative materialization of human security in the traditional sources of public international law, but rather to deepen in the examination of the normative implications of human security, particularly in its synergies with human rights recognized internationally. One of the main concerns of modern public international law is, precisely, the area of international human rights law. As such, reference is made to the sources of public international law and closer attention is provided to the concrete ways in which human security relates to them in the sphere of human rights
Functional centrality in graphs
In this paper we introduce the functional centrality as a generalization of
the subgraph centrality. We propose a general method for characterizing nodes
in the graph according to the number of closed walks starting and ending at the
node. Closed walks are appropriately weighted according to the topological
features that we need to measure
Surface Vacuum Energy in Cutoff Models: Pressure Anomaly and Distributional Gravitational Limit
Vacuum-energy calculations with ideal reflecting boundaries are plagued by
boundary divergences, which presumably correspond to real (but finite) physical
effects occurring near the boundary. Our working hypothesis is that the stress
tensor for idealized boundary conditions with some finite cutoff should be a
reasonable ad hoc model for the true situation. The theory will have a sensible
renormalized limit when the cutoff is taken away; this requires making sense of
the Einstein equation with a distributional source. Calculations with the
standard ultraviolet cutoff reveal an inconsistency between energy and pressure
similar to the one that arises in noncovariant regularizations of cosmological
vacuum energy. The problem disappears, however, if the cutoff is a spatial
point separation in a "neutral" direction parallel to the boundary. Here we
demonstrate these claims in detail, first for a single flat reflecting wall
intersected by a test boundary, then more rigorously for a region of finite
cross section surrounded by four reflecting walls. We also show how the
moment-expansion theorem can be applied to the distributional limits of the
source and the solution of the Einstein equation, resulting in a mathematically
consistent differential equation where cutoff-dependent coefficients have been
identified as renormalizations of properties of the boundary. A number of
issues surrounding the interpretation of these results are aired.Comment: 22 pages, 2 figures, 1 table; PACS 03.70.+k, 04.20.Cv, 11.10.G
Response of a Fermi gas to time-dependent perturbations: Riemann-Hilbert approach at non-zero temperatures
We provide an exact finite temperature extension to the recently developed
Riemann-Hilbert approach for the calculation of response functions in
nonadiabatically perturbed (multi-channel) Fermi gases. We give a precise
definition of the finite temperature Riemann-Hilbert problem and show that it
is equivalent to a zero temperature problem. Using this equivalence, we discuss
the solution of the nonequilibrium Fermi-edge singularity problem at finite
temperatures.Comment: 10 pages, 2 figures; 2 appendices added, a few modifications in the
text, typos corrected; published in Phys. Rev.
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