946 research outputs found
Local Simulation Algorithms for Coulombic Interactions
We consider dynamically constrained Monte-Carlo dynamics and show that this
leads to the generation of long ranged effective interactions. This allows us
to construct a local algorithm for the simulation of charged systems without
ever having to evaluate pair potentials or solve the Poisson equation. We
discuss a simple implementation of a charged lattice gas as well as more
elaborate off-lattice versions of the algorithm. There are analogies between
our formulation of electrostatics and the bosonic Hubbard model in the phase
approximation. Cluster methods developed for this model further improve the
efficiency of the electrostatics algorithm.Comment: Proceedings Statphys22 10 page
Early life mental health and problematic drinking in mid-adulthood: evidence from two British birth cohorts
PURPOSE: Accumulating evidence suggests that externalising problems are consistently associated with alcohol use behaviours, but findings are inconsistent regarding the role of internalising problems. We investigate whether externalising and internalising problems are associated with problematic drinking in mid-adulthood, and whether potential associations are modified by age, sex and cohort. METHODS: The National Child Development Study (NCDS58, n = 17,633) and 1970 British Cohort Study (BCS70, n = 17,568) recruited new-borns in Great Britain in a single week in 1958 and 1970. Mental health was assessed with the Rutter Behaviour Questionnaire at ages 7, 11, and 16 in NCDS58 and ages 5, 10 and 16 in BCS70. Problematic drinking was measured with the CAGE questionnaire at age 33 in NCDS58 and age 34 in BCS70, and the AUDIT scale at age 44/45 in NCDS58 and age 46 in BCS70. Latent scores of externalising and internalising problems were added chronologically into lagged logistic regression models. RESULTS: Externalising and internalising problems were associated in opposite directions with problematic drinking in mid-adulthood. Externalising was a risk factor (OR [95% CI] ranging from 1.06 [1.03, 1.10] to 1.11 [1.07, 1.15] for different ages), and internalising was a protective factor (OR [95% CI] ranging from 0.95 [0.92, 0.99] to 0.90 [0.86, 0.94] for different ages). Associations between early life mental health and mid-adulthood problematic drinking did not differ by developmental timing but were stronger in males. CONCLUSION: Our study provides new insights on links of externalising and internalising difficulties with alcohol use and has implications for public policy in the UK
Morphological evolution and classification of the red algal order Ceramiales inferred using plastid phylogenomics.
The order Ceramiales contains about one third of red algal diversity and it was classically classified into four families according to morphology. The first phylogenies based on one or two molecular markers were poorly supported and failed to resolve these families as monophyletic. Nine families are currently recognized, but relationships within and among them are poorly understood. We produced a well-resolved phylogeny for the Ceramiales using plastid genomes for 80 (28 newly sequenced) representative species of the major lineages. Three of the previously recognized families were resolved as independent monophyletic lineages: Ceramiaceae, Wrangeliaceae and Rhodomelaceae. By contrast, our results indicated that the other six families require reclassification. We propose the new order Inkyuleeales, a new circumscription of the Callithamniaceae to include the Spyridiaceae, and a new concept of the Delesseriaceae that includes the Sarcomeniaceae and the Dasyaceae. We also investigated the evolution of the thallus structure, which has been important in the classical delineation of families. The ancestor of the Ceramiales was a monosiphonous filament that evolved into more complex morphologies several times independently during the evolutionary history of this hyperdiverse lineage
cISP: A Speed-of-Light Internet Service Provider
Low latency is a requirement for a variety of interactive network
applications. The Internet, however, is not optimized for latency. We thus
explore the design of cost-effective wide-area networks that move data over
paths very close to great-circle paths, at speeds very close to the speed of
light in vacuum. Our cISP design augments the Internet's fiber with free-space
wireless connectivity. cISP addresses the fundamental challenge of
simultaneously providing low latency and scalable bandwidth, while accounting
for numerous practical factors ranging from transmission tower availability to
packet queuing. We show that instantiations of cISP across the contiguous
United States and Europe would achieve mean latencies within 5% of that
achievable using great-circle paths at the speed of light, over medium and long
distances. Further, we estimate that the economic value from such networks
would substantially exceed their expense
Simulation of a semiflexible polymer in a narrow cylindrical pore
The probability that a randomly accelerated particle in two dimensions has
not yet left a simply connected domain after a time decays as
for long times. The same quantity also determines the
confinement free energy per unit length of a
semiflexible polymer in a narrow cylindrical pore with cross section . From simulations of a randomly accelerated particle we estimate the
universal amplitude of for both circular and rectangular cross
sections.Comment: 10 pages, 2 eps figure
Writhing Photons and Berry Phases in Diffusive Wave Scattering
We study theoretically the polarization state of light in multiple scattering
media in the limit of weak gradients in refractive index. Linearly polarized
photons are randomly rotated due to the Berry phase associated with the
scattering path. For circularly polarized light independent speckle patterns
are found for the two helical states. The statistics of the geometric phase is
related to the writhe distribution of semiflexible polymers such as DNA.Comment: 4 pages, 1 figur
Elastic fluctuations as observed in a confocal slice
Recent confocal experiments on colloidal solids motivate a fuller study of
the projection of three-dimensional fluctuations onto a two-dimensional
confocal slice. We show that the effective theory of a projected crystal
displays several exceptional features, such as non-standard exponents in the
dispersion relations. We provide analytic expressions for the effective
two-dimensional elastic properties which allow one to work back from sliced
experimental observations to three-dimensional elastic constants.Comment: 5 pages, 2 figure
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