39,942 research outputs found
Efficient configurational-bias Monte-Carlo simulations of chain molecules with `swarms' of trial configurations
Proposed here is a dynamic Monte-Carlo algorithm that is efficient in
simulating dense systems of long flexible chain molecules. It expands on the
configurational-bias Monte-Carlo method through the simultaneous generation of
a large set of trial configurations. This process is directed by attempting to
terminate unfinished chains with a low statistical weight, and replacing these
chains with clones (enrichments) of stronger chains. The efficiency of the
resulting method is explored by simulating dense polymer brushes. A gain in
efficiency of at least three orders of magnitude is observed with respect to
the configurational-bias approach, and almost one order of magnitude with
respect to recoil-growth Monte-Carlo. Furthermore, the inclusion of `waste
recycling' is observed to be a powerful method for extracting meaningful
statistics from the discarded configurations
Electron lithography STAR design guidelines. Part 1: The STAR user design manual
The STAR system developed by NASA enables any user with a logic diagram to design a semicustom digital MOS integrated circuit. The system is comprised of a library of standard logic cells and computer programs to place, route, and display designs implemented with cells from the library. Library cells of the CMOS metal gate and CMOS silicon gate technologies were simulated using SPICE, and the results are shown and compared
Threshold effects for two pathogens spreading on a network
Diseases spread through host populations over the networks of contacts
between individuals, and a number of results about this process have been
derived in recent years by exploiting connections between epidemic processes
and bond percolation on networks. Here we investigate the case of two pathogens
in a single population, which has been the subject of recent interest among
epidemiologists. We demonstrate that two pathogens competing for the same hosts
can both spread through a population only for intermediate values of the bond
occupation probability that lie above the classic epidemic threshold and below
a second higher value, which we call the coexistence threshold, corresponding
to a distinct topological phase transition in networked systems.Comment: 5 pages, 2 figure
Random graphs with clustering
We offer a solution to a long-standing problem in the physics of networks,
the creation of a plausible, solvable model of a network that displays
clustering or transitivity -- the propensity for two neighbors of a network
node also to be neighbors of one another. We show how standard random graph
models can be generalized to incorporate clustering and give exact solutions
for various properties of the resulting networks, including sizes of network
components, size of the giant component if there is one, position of the phase
transition at which the giant component forms, and position of the phase
transition for percolation on the network.Comment: 5 pages, 2 figure
Mean-field solution of the small-world network model
The small-world network model is a simple model of the structure of social
networks, which simultaneously possesses characteristics of both regular
lattices and random graphs. The model consists of a one-dimensional lattice
with a low density of shortcuts added between randomly selected pairs of
points. These shortcuts greatly reduce the typical path length between any two
points on the lattice. We present a mean-field solution for the average path
length and for the distribution of path lengths in the model. This solution is
exact in the limit of large system size and either large or small number of
shortcuts.Comment: 14 pages, 2 postscript figure
Percolation in the Sherrington-Kirkpatrick Spin Glass
We present extended versions and give detailed proofs of results concerning
percolation (using various sets of two-replica bond occupation variables) in
Sherrington-Kirkpatrick spin glasses (with zero external field) that were first
given in an earlier paper by the same authors. We also explain how
ultrametricity is manifested by the densities of large percolating clusters.
Our main theorems concern the connection between these densities and the usual
spin overlap distribution. Their corollaries are that the ordered spin glass
phase is characterized by a unique percolating cluster of maximal density
(normally coexisting with a second cluster of nonzero but lower density). The
proofs involve comparison inequalities between SK multireplica bond occupation
variables and the independent variables of standard Erdos-Renyi random graphs.Comment: 18 page
Nature vs. Nurture: Predictability in Low-Temperature Ising Dynamics
Consider a dynamical many-body system with a random initial state
subsequently evolving through stochastic dynamics. What is the relative
importance of the initial state ("nature") vs. the realization of the
stochastic dynamics ("nurture") in predicting the final state? We examined this
question for the two-dimensional Ising ferromagnet following an initial deep
quench from to . We performed Monte Carlo studies on the
overlap between "identical twins" raised in independent dynamical environments,
up to size . Our results suggest an overlap decaying with time as
with ; the same exponent holds for a
quench to low but nonzero temperature. This "heritability exponent" may equal
the persistence exponent for the 2D Ising ferromagnet, but the two differ more
generally.Comment: 5 pages, 3 figures; new version includes results for nonzero
temperatur
Identity and Search in Social Networks
Social networks have the surprising property of being "searchable": Ordinary
people are capable of directing messages through their network of acquaintances
to reach a specific but distant target person in only a few steps. We present a
model that offers an explanation of social network searchability in terms of
recognizable personal identities: sets of characteristics measured along a
number of social dimensions. Our model defines a class of searchable networks
and a method for searching them that may be applicable to many network search
problems, including the location of data files in peer-to-peer networks, pages
on the World Wide Web, and information in distributed databases.Comment: 4 page, 3 figures, revte
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