83,959 research outputs found
Invariance of density correlations with charge density in polyelectrolyte solutions
We present a theory for the equilibrium structure of polyelectrolyte
solutions. The main element is a simple, new optimization scheme that allows
theories such as the random phase approximation (RPA) to handle the harsh
repulsive forces present in such systems. Comparison is made with data from
recent neutron scattering experiments of randomly charged, hydrophilic polymers
in salt-free, semi-dilute solution at various charge densities. Models with
varying degrees of realism are examined. The usual explanation of the
invariance observed at high charge density has been counterion condensation.
However, when polymer-polymer correlations are treated properly, we find that
modeling polymer-counterion correlations at the level of Debye-Huckel theory is
sufficient.Comment: 4 pages, 2 figure
Interdot Coulomb repulsion effect on the charge transport of parallel double single electron transistors
The charge transport behaviors of parallel double single electron transistors
(SETs) are investigated by the Anderson model with two impurity levels. The
nonequilibrium Keldysh Green's technique is used to calculate the
current-voltage characteristics of system. For SETs implemented by quantum dots
(QDs) embedded into a thin layer, the interdot Coulomb repulsion is
more important than the interdot electron hopping as a result of high potential
barrier height between QDs and . We found that the interdot Coulomb
repulsion not onlyleads to new resonant levels, but also creates negative
differential conductances.Comment: 12 pages, 7 figure
Characterizing heterogeneous dynamics at hydrated electrode surfaces
In models of Pt 111 and Pt 100 surfaces in water, motions of molecules in the
first hydration layer are spatially and temporally correlated. To interpret
these collective motions, we apply quantitative measures of dynamic
heterogeneity that are standard tools for considering glassy systems.
Specifically, we carry out an analysis in terms of mobility fields and
distributions of persistence times and exchange times. In so doing, we show
that dynamics in these systems is facilitated by transient disorder in
frustrated two-dimensional hydrogen bonding networks. The frustration is the
result of unfavorable geometry imposed by strong metal-water bonding. The
geometry depends upon the structure of the underlying metal surface. Dynamic
heterogeneity of water on the Pt 111 surface is therefore qualitatively
different than that for water on the Pt 100 surface. In both cases, statistics
of this adlayer dynamic heterogeneity responds asymmetrically to applied
voltage.Comment: 6 page, 4 figure
Preformed metal crowns for decayed primary molar teeth
BackgroundPreformed metal crowns (PMCs) are recommended by the British Society of Paediatric Dentistry (BSPD) for restoring badly broken down primary molar teeth. However, few dental practitioners adopt this technique in clinical practice, citing cost and clinical difficulty as reasons for this. Whilst there is a subjective impression by clinical academics that PMCs provide a more durable restoration than filling materials, there appears to be little evidence within the literature to support this.ObjectivesThe primary aim of this systematic review was to compare clinical outcomes for primary molar teeth restored using PMCs compared to those restored with filling materials.Search methodsThe literature was searched using: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2005, Issue 3); MEDLINE (1966 to August 2005); EMBASE (1980 to August 2005); System for Information on Grey Literature in Europe (SIGLE) (1976 to August 2005). Relevant publications' reference lists were reviewed for relevant articles. The most recent search was carried out on 24 August 2005.Selection criteriaRandomised controlled trials (RCTs) that assessed the effectiveness of PMCs compared with filling materials or where there had been no treatment in children with untreated tooth decay in one or more primary molar teeth.Data collection and analysisTwo review authors independently assessed the title and abstracts for each article from the search results to decide whether it was likely to be relevant. Full papers were obtained for relevant articles and all three review authors studied these.Main resultsFortyâseven records were retrieved by the search strategies of which some were duplicates. Of these, 14 studies were scrutinised. No studies met the inclusion criteria and six studies were excluded from the review as they were either retrospective in design or reported as prospective outcomes but not randomised. No data were available for extraction and analysis and therefore, no conclusion could be made as to whether PMCs were more successful than filling materials for restoring primary molar teeth.Authors' conclusionsNo RCTs were available for appraisal. Whilst this technique is recommended by the BSPD for use in clinical practice, the evidence to support this is not strong, consisting mainly of case reports and uncontrolled studies. It is important that the absence of evidence for PMCs is not misinterpreted as evidence for their lack of efficacy.There is a strong need for prospective RCTs comparing PMCs and fillings for managing decayed primary molar teeth. The lower levels of evidence that have been produced, however, have strength in that the clinical outcomes are consistently in favour of PMCs, despite many of the studies placing PMCs on the most damaged of the pair of teeth being analysed
Spatio-Temporal Wildland Arson Crime Functions
Wildland arson creates damages to structures and timber and affects the health and safety of people living in rural and wildland urban interface areas. We develop a model that incorporates temporal autocorrelations and spatial correlations in wildland arson ignitions in Florida. A Poisson autoregressive model of order p, or PAR(p) model, is estimated for six high arson Census tracts in the state for the period 1994-2001. Spatio-temporal lags of wildland arson ignitions are introduced as dummy variables indicating the presence of an ignition in previous days in surrounding Census tracts and counties. Temporal lags of ignition activity within the Census tract are shown to be statistically significant and larger than previously reported for non-spatial variants of the PAR(p) model. Spatio-temporal lagged relationships with current arson that were statistically significant show that arson activity up to a county away explains arson patterns, and spatio-temporal lags longer than two days were not significant. Other variables showing significance include weather and wildfire activity in the previous six years, but prescribed fire and several variables that provide evidence that such activity is consistent with an economic model of crime were less commonly significant.Resource /Energy Economics and Policy,
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