19,867 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
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Small smooth units (‘young’ lavas?) abutting lobate scarps on Mercury
We have identified small units abutting, and so stratigraphy younger than, lobate scarps. This post dates the end of large scale smooth plains formation at the onset of global contraction. This elaborates the history of volcanism on Mercury
Potential Identification of sublimation-driven downslope mass movement on Mercury
We have identified a further example of mass movement, in addition to the previously identified example in the pyroclastic vent NE of Rachmaninoff. Both examples show evidence of hollow sublimation being a cause of the mass movements
1:3M Geological Mapping of the Derain (H-10) Quadrangle of Mercury
We are making a high resolution geological map of the Derain quadrangle of Mercury. This is part of a coordinated project to create a global set of geological maps for BepiColombo
Risk factors for house-entry by malaria vectors in a rural town and satellite villages in The Gambia.
Background:
In the pre-intervention year of a randomized controlled trial investigating the protective effects of house screening against malaria-transmitting vectors, a multi-factorial risk factor analysis study was used to identify factors that influence mosquito house entry.
Methods:
Mosquitoes were sampled using CDC light traps in 976 houses, each on one night, in Farafenni town and surrounding villages during the malaria-transmission season in The Gambia. Catches from individual houses were both (a) left unadjusted and (b) adjusted relative to the number of mosquitoes caught in four sentinel houses that were operated nightly throughout the period, to allow for night-to-night variation. Houses were characterized by location, architecture, human occupancy and their mosquito control activities, and the number and type of domestic animals within the compound.
Results:
106,536 mosquitoes were caught, of which 55% were Anopheles gambiae sensu lato, the major malaria vectors in the region. There were seven fold higher numbers of An. gambiae s.l. in the villages (geometric mean per trap night = 43.7, 95% confidence intervals, CIs = 39.5–48.4) than in Farafenni town (6.3, 5.7–7.2) and significant variation between residential blocks (p < 0.001). A negative binomial multivariate model performed equally well using unadjusted or adjusted trap data. Using the unadjusted data the presence of nuisance mosquitoes was reduced if the house was located in the town (odds ratio, OR = 0.11, 95% CIs = 0.09–0.13), the eaves were closed (OR = 0.71, 0.60–0.85), a horse was tethered near the house (OR = 0.77, 0.73–0.82), and churai, a local incense, was burned in the room at night (OR = 0.56, 0.47–0.66). Mosquito numbers increased per additional person in the house (OR = 1.04, 1.02–1.06) or trapping room (OR = 1.19, 1.13–1.25) and when the walls were made of mud blocks compared with concrete (OR = 1.44, 1.10–1.87).
Conclusion:
This study demonstrates that the risk of malaria transmission is greatest in rural areas, where large numbers of people sleep in houses made of mud blocks, where the eaves are open, horses are not tethered nearby and where churai is not burnt at night. These factors need to be considered in the design and analysis of intervention studies designed to reduce malaria transmission in The Gambia and other parts of sub-Saharan Africa
Random template banks and relaxed lattice coverings
Template-based searches for gravitational waves are often limited by the
computational cost associated with searching large parameter spaces. The study
of efficient template banks, in the sense of using the smallest number of
templates, is therefore of great practical interest. The "traditional" approach
to template-bank construction requires every point in parameter space to be
covered by at least one template, which rapidly becomes inefficient at higher
dimensions. Here we study an alternative approach, where any point in parameter
space is covered only with a given probability < 1. We find that by giving up
complete coverage in this way, large reductions in the number of templates are
possible, especially at higher dimensions. The prime examples studied here are
"random template banks", in which templates are placed randomly with uniform
probability over the parameter space. In addition to its obvious simplicity,
this method turns out to be surprisingly efficient. We analyze the statistical
properties of such random template banks, and compare their efficiency to
traditional lattice coverings. We further study "relaxed" lattice coverings
(using Zn and An* lattices), which similarly cover any signal location only
with probability < 1. The relaxed An* lattice is found to yield the most
efficient template banks at low dimensions (n < 10), while random template
banks increasingly outperform any other method at higher dimensions.Comment: 13 pages, 10 figures, submitted to PR
Direct observation of voids in the vacancy excess region of ion bombarded silicon
The results reported in this letter indicate that the spatial separation of the vacancy and interstitial excesses which result from ion bombardment gives rise to stable voids upon annealing at 850 °C even for implants where the projected ion range is only of the order of a few thousand Ångstrom. Such voids have been observed directly by transmission electron microscopy. Furthermore, in cases where both voids and interstitial-based defects are present at different depths, it is found that Au has a strong preference for decorating void surfaces and hence Au can, indeed, be used as a selective detector of open volume defects in Si.One of the authors ~J.W.-L.!
acknowledges the Australian Research Council for financial
support
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Icelandic debris flow and their relationship to martian gullies
Abstract not available
Entropy and Entanglement in Quantum Ground States
We consider the relationship between correlations and entanglement in gapped
quantum systems, with application to matrix product state representations. We
prove that there exist gapped one-dimensional local Hamiltonians such that the
entropy is exponentially large in the correlation length, and we present strong
evidence supporting a conjecture that there exist such systems with arbitrarily
large entropy. However, we then show that, under an assumption on the density
of states which is believed to be satisfied by many physical systems such as
the fractional quantum Hall effect, that an efficient matrix product state
representation of the ground state exists in any dimension. Finally, we comment
on the implications for numerical simulation.Comment: 7 pages, no figure
Shorebird Breeding Biology in Wetlands of the Playa Lakes, Texas, USA
Wetlands in the Playa Lakes Region of Texas are important habitats for North American wintering waterfowl and migrant shorebirds. However, shorebird breeding biology has been overlooked in characterizing the region’s ecological importance. In 1998 and 1999, American Avocet (Recurvirostra americana), Black-necked Stilt ( Himantopus mexicanus ), Killdeer (Charadrius vociferous), and Snowy Plover (C. alexandrinus) breeding ecology were studied in playas, saline lakes, and riparian wetlands in the Playa Lakes Region of Texas. Chronology of nest initiation, clutch sizes, and hatching success for 298 Snowy Plover, 111 American Avocet, 43 Killdeer, and 26 Blacknecked Stilt clutches were measured. All four species nested in saline lakes, American Avocet and Killdeer also nested in playas, and Snowy Plover nested on riparian wetlands. American Avocet had higher hatching success in 1999 (52%) than 1998 (8%), because of more suitable hydrological conditions and lower predation. Hatching success was higher in 1998 than 1999 for Killdeer (1998, 63%; 1999, 21%) and Snowy Plover (1998, 47%; 1999, 33%) due to failures caused by flooding and hail in 1999. In other regions, clutch predation limits shorebird productivity, but hatching success in the Playa Lakes Region appears to be limited by unpredictable precipitation patterns and wetland hydroperiod. As such, breeding shorebird conservation and management should focus upon maintaining wetland hydrological integrity
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