1,165 research outputs found
Calculations of the Local Density of States for some Simple Systems
A recently proposed convolution technique for the calculation of local
density of states is described more thouroughly and new results of its
application are presented. For separable systems the exposed method allows to
construct the ldos for a higher dimensionality out of lower dimensional parts.
Some practical and theoretical aspects of this approach are also discussed.Comment: 5 pages, 3 figure
Evidence for density dependent population regulation in southern elephant seals in the southern Indian Ocean
The means by which populations are regulated form a central theme in conservation biology, and much debate has revolved around density dependence as a mechanism driving population change. Marion Island (46o54'S, 37o45'E) is host to a relatively small breeding population of southern elephant seals, which like its counterparts in the southern Indian and southern Pacific Oceans, have declined precipitously over the past few decades. An intensive mark-recapture study, which commenced in 1983, has yielded a long time-series of resight data on this population. We used the program MARK to estimate adult female survival in this population from resight data collected over the period 1986-1999. Including concurrent population counts as covariates significantly improved our mark-recapture models and suggests density dependent population regulation to be operational in the population. Although predation may have been involved, it is far more likely that density dependent regulation has been based on a limited food supply. A significant increase in adult female survival was evident which is likely to have given rise to recent changes in population growth
Constraints on massive gravity theory from big bang nucleosynthesis
The massive gravity cosmology is studied in the scenario of big bang
nucleosynthesis. By making use of current bounds on the deviation from the
fractional mass, we derive the constraints on the free parameters of the
theory. The cosmological consequences of the model are also discussed in the
framework of the PAMELA experiment.Comment: 5 page
Seasonal variation of ozone deposition to a tropical rain forest in southwest Amazonia
International audienceWithin the project EUropean Studies on Trace gases and Atmospheric CHemistry as a contribution to Large-scale Biosphere-atmosphere experiment in Amazonia (LBA-EUSTACH), we performed tower-based eddy covariance measurements of O3 flux above an Amazonian primary rain forest at the end of the wet and dry season. Ozone deposition revealed distinct seasonal differences in the magnitude and diel variation. In the wet season, the rain forest was an effective O3 sink with a mean daytime (midday) maximum deposition velocity of 2.3 cm s?1, and a corresponding O3 flux of ?11 nmol m?2 s?1. At the end of the dry season, the ozone mixing ratio was about four times higher (up to maximum values of 80 ppb) than in the wet season, as a consequence of strong regional biomass burning activity. However, the typical maximum daytime deposition flux was very similar to the wet season. This results from a strong limitation of daytime O3 deposition due to reduced plant stomatal aperture as a response to large values of the specific humidity deficit. As a result, the average midday deposition velocity in the dry burning season was only 0.5 cm s?1. The large diel ozone variation caused large canopy storage effects that masked the true diel variation of ozone deposition mechanisms in the measured eddy covariance flux, and for which corrections had to be made. In general, stomatal aperture was sufficient to explain the largest part of daytime ozone deposition. However, during nighttime, chemical reaction with nitrogen monoxide (NO) was found to contribute substantially to the O3 sink in the rain forest canopy. Further contributions were from non-stomatal plant uptake and other processes that could not be clearly identified. Measurements, made simultaneously on a 22 years old cattle pasture enabled the spatially and temporally direct comparison of O3 dry deposition values from this site with typical vegetation cover of deforested land in southwest Amazonia to the results from the primary rain forest. The mean ozone deposition to the pasture was found to be systematically lower than that to the forest by 30% in the wet and 18% in the dry season
Dynamical approach to chains of scatterers
Linear chains of quantum scatterers are studied in the process of
lengthening, which is treated and analysed as a discrete dynamical system
defined over the manifold of scattering matrices. Elementary properties of such
dynamics relate the transport through the chain to the spectral properties of
individual scatterers. For a single-scattering channel case some new light is
shed on known transport properties of disordered and noisy chains, whereas
translationally invariant case can be studied analytically in terms of a simple
deterministic dynamical map. The many-channel case was studied numerically by
examining the statistical properties of scatterers that correspond to a certain
type of transport of the chain i.e. ballistic or (partially) localised.Comment: 16 pages, 7 figure
FIBONACCI SUPERLATTICES OF NARROW-GAP III-V SEMICONDUCTORS
We report theoretical electronic structure of Fibonacci superlattices of
narrow-gap III-V semiconductors. Electron dynamics is accurately described
within the envelope-function approximation in a two-band model.
Quasiperiodicity is introduced by considering two different III-V semiconductor
layers and arranging them according to the Fibonacci series along the growth
direction. The resulting energy spectrum is then found by solving exactly the
corresponding effective-mass (Dirac-like) wave equation using tranfer-matrix
techniques. We find that a self-similar electronic spectrum can be seen in the
band structure. Electronic transport properties of samples are also studied and
related to the degree of spatial localization of electronic envelope-functions
via Landauer resistance and Lyapunov coefficient. As a working example, we
consider type II InAs/GaSb superlattices and discuss in detail our results in
this system.Comment: REVTeX 3.0, 16 pages, 8 figures available upon request. To appear in
Semiconductor Science and Technolog
Suppression of Persistent Currents in 1-D Disordered Rings by Coulomb Interaction
Effects of Coulomb interaction on persistent currents in disordered
one-dimensional rings are numerically investigated. First of all effectiveness
of the Hartree-Fock approximation is established on small systems. Then the
calculations are done for systems with 40 electrons in 100 sites. It is found
that the amplitude of the average persistent current in the diffusive regime is
suppressed as the strength of the Coulomb interaction increases. The
suppression of the current is stronger in larger rings than in smaller ones.
The enhancement of the current by the electron-electron interaction was not
observed in the diffusive regime.Comment: 9 pages (RevTeX), 4 figures available upon request
([email protected]), KCMG-preprint-HK
Collective decision-making on triadic graphs
Many real-world networks exhibit community structures and non-trivial clustering associated with the occurrence of a considerable number of triangular subgraphs known as triadic motifs. Triads are a set of distinct triangles that do not share an edge with any other triangle in the network. Network motifs are subgraphs that occur significantly more often compared to random topologies. Two prominent examples, the feedforward loop and the feedback loop, occur in various real-world networks such as gene-regulatory networks, food webs or neuronal networks. However, as triangular connections are also prevalent in communication topologies of complex collective systems, it is worthwhile investigating the influence of triadic motifs on the collective decision-making dynamics. To this end, we generate networks called Triadic Graphs (TGs) exclusively from distinct triadic motifs. We then apply TGs as underlying topologies of systems with collective dynamics inspired from locust marching bands. We demonstrate that the motif type constituting the networks can have a paramount influence on group decision-making that cannot be explained solely in terms of the degree distribution. We find that, in contrast to the feedback loop, when the feedforward loop is the dominant subgraph, the resulting network is hierarchical and inhibits coherent behavior
Prosocial video game as an intimate partner violence prevention tool among youth: A randomised controlled trial
Evidence demonstrates that exposure to prosocial video games can increase players’ prosocial behaviour, prosocial thoughts, and empathic responses. Prosocial gaming has also been used to reduce gender-based violence among young people, but the use of video games to this end as well as evaluations of their effectiveness are rare. The objective of this study was to assess the effectiveness of a context-specific, prosocial video game, Jesse, in increasing affective and cognitive responsiveness (empathy) towards victims of intimate partner violence (IPV) among children and adolescents (N = 172, age range 9 – 17 years, M = 12.27, SD = 2.26). A randomised controlled trial was conducted in seven schools in Barbados. Participants were randomly assigned to an experimental (prosocial video game) or control (standard school curriculum) condition. Experimental and control group enrolled 86 participants each. Girls and boys in the experimental condition, but not their counterparts in the control condition, recorded a significant increase in affective responsiveness after intervention. This change was sustained one week after game exposure. No significant effects were recorded for cognitive responsiveness. Findings suggest that Jesse is a promising new IPV prevention tool among girls and boys, which can be used in educational settings
Black Holes in Magnetic Monopoles
We study magnetically charged classical solutions of a spontaneously broken
gauge theory interacting with gravity. We show that nonsingular monopole
solutions exist only if the Higgs vacuum expectation value is less than or
equal to a critical value , which is of the order of the Planck mass.
In the limiting case the monopole becomes a black hole, with the region outside
the horizon described by the critical Reissner-Nordstrom solution. For
, we find additional solutions which are singular at , but which
have this singularity hidden within a horizon. These have nontrivial matter
fields outside the horizon, and may be interpreted as small black holes lying
within a magnetic monopole. The nature of these solutions as a function of
and of the total mass and their relation to the Reissner-Nordstrom
solutions is discussed.Comment: (28 pages
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