3,364 research outputs found
Nonequilibrium Phase Transitions in a Driven Sandpile Model
We construct a driven sandpile slope model and study it by numerical
simulations in one dimension. The model is specified by a threshold slope
\sigma_c\/, a parameter \alpha\/, governing the local current-slope
relation (beyond threshold), and , the mean input current of sand.
A nonequilibrium phase diagram is obtained in the \alpha\, -\, j_{\rm in}\/
plane. We find an infinity of phases, characterized by different mean slopes
and separated by continuous or first-order boundaries, some of which we obtain
analytically. Extensions to two dimensions are discussed.Comment: 11 pages, RevTeX (preprint format), 4 figures available upon requs
Spreading and shortest paths in systems with sparse long-range connections
Spreading according to simple rules (e.g. of fire or diseases), and
shortest-path distances are studied on d-dimensional systems with a small
density p per site of long-range connections (``Small-World'' lattices). The
volume V(t) covered by the spreading quantity on an infinite system is exactly
calculated in all dimensions. We find that V(t) grows initially as t^d/d for
t>t^*$,
generalizing a previous result in one dimension. Using the properties of V(t),
the average shortest-path distance \ell(r) can be calculated as a function of
Euclidean distance r. It is found that
\ell(r) = r for r<r_c=(2p \Gamma_d (d-1)!)^{-1/d} log(2p \Gamma_d L^d), and
\ell(r) = r_c for r>r_c.
The characteristic length r_c, which governs the behavior of shortest-path
lengths, diverges with system size for all p>0. Therefore the mean separation s
\sim p^{-1/d} between shortcut-ends is not a relevant internal length-scale for
shortest-path lengths. We notice however that the globally averaged
shortest-path length, divided by L, is a function of L/s only.Comment: 4 pages, 1 eps fig. Uses psfi
Evolution of early continental crust
The present article reviews the evolution of continental crust since the time the earth began to inscribe a permanent history in rocks of the cratonic nuclei. The existence of a sialic crust prior to 4200 Ma ago, soon after the permobile stage of the earth, is documented by detrital zircon in the Precambrian metaconglomerate of Neyerer Complex, Western Australia. The evolution of Archaean crust (> 2500 Ma) is discussed in terms of currently used Nd model-age calculations, based on a depleted mantle evolutionary model. The model fits the generally accepted assumption that LREE depletion of the upper mantle commenced very early in the earth's history and that the present-day MORB is the best representative for the Nd-isotopic composition of today's depleted mantle. Finally, the mechanisms for growth or accretion of the continental crust and the incompatibility of thickened crust during Archaean time are discussed
Independent Domination in Some Wheel Related Graphs
A set S of vertices in a graph G is called an independent dominating set if S is both independent and dominating. The independent domination number of G is the minimum cardinality of an independent dominating set in G . In this paper, we investigate the exact value of independent domination number for some wheel related graphs
Predicting wildlife reservoirs and global vulnerability to zoonotic Flaviviruses.
Flaviviruses continue to cause globally relevant epidemics and have emerged or re-emerged in regions that were previously unaffected. Factors determining emergence of flaviviruses and continuing circulation in sylvatic cycles are incompletely understood. Here we identify potential sylvatic reservoirs of flaviviruses and characterize the macro-ecological traits common to known wildlife hosts to predict the risk of sylvatic flavivirus transmission among wildlife and identify regions that could be vulnerable to outbreaks. We evaluate variability in wildlife hosts for zoonotic flaviviruses and find that flaviviruses group together in distinct clusters with similar hosts. Models incorporating ecological and climatic variables as well as life history traits shared by flaviviruses predict new host species with similar host characteristics. The combination of vector distribution data with models for flavivirus hosts allows for prediction of global vulnerability to flaviviruses and provides potential targets for disease surveillance in animals and humans
Random spread on the family of small-world networks
We present the analytical and numerical results of a random walk on the
family of small-world graphs. The average access time shows a crossover from
the regular to random behavior with increasing distance from the starting point
of the random walk. We introduce an {\em independent step approximation}, which
enables us to obtain analytic results for the average access time. We observe a
scaling relation for the average access time in the degree of the nodes. The
behavior of average access time as a function of , shows striking similarity
with that of the {\em characteristic length} of the graph. This observation may
have important applications in routing and switching in networks with large
number of nodes.Comment: RevTeX4 file with 6 figure
Scaling of the giant dipole resonance widths in hot rotating nuclei from the ground state values
The systematics of the giant dipole resonance (GDR) widths in hot and
rotating nuclei are studied in terms of temperature T, angular momentum J and
mass A. The different experimental data in the temperature range of 1 - 2 MeV
have been compared with the thermal shape fluctuation model (TSFM) in the
liquid drop formalism using a modified approach to estimate the average values
of T, J and A in the decay of the compound nucleus. The values of the ground
state GDR widths have been extracted from the TSFM parametrization in the
liquid drop limit for the corrected T, J and A for a given system and compared
with the corresponding available systematics of the experimentally measured
ground state GDR widths for a range of nuclei from A = 45 to 194. Amazingly,
the nature of the theoretically extracted ground state GDR widths matches
remarkably well, though 1.5 times smaller, with the experimentally measured
ground state GDR widths consistently over a wide range of nuclei.Comment: 15 pages, 4 figures, Accepted for publication in Physical Review
Condensation of Silica Nanoparticles on a Phospholipid Membrane
The structure of the transient layer at the interface between air and the
aqueous solution of silica nanoparticles with the size distribution of
particles that has been determined from small-angle scattering has been studied
by the X-ray reflectometry method. The reconstructed depth profile of the
polarizability of the substance indicates the presence of a structure
consisting of several layers of nanoparticles with the thickness that is more
than twice as large as the thickness of the previously described structure. The
adsorption of 1,2-distearoyl-sn-glycero-3-phosphocholine molecules at the
hydrosol/air interface is accompanied by the condensation of anion silica
nanoparticles at the interface. This phenomenon can be qualitatively explained
by the formation of the positive surface potential due to the penetration and
accumulation of Na+ cations in the phospholipid membrane.Comment: 7 pages, 5 figure
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