4,274 research outputs found
Higher Order Effects in the Dielectric Constant of Percolative Metal-Insulator Systems above the Critical Point
The dielectric constant of a conductor-insulator mixture shows a pronounced
maximum above the critical volume concentration. Further experimental evidence
is presented as well as a theoretical consideration based on a phenomenological
equation. Explicit expressions are given for the position of the maximum in
terms of scaling parameters and the (complex) conductances of the conductor and
insulator. In order to fit some of the data, a volume fraction dependent
expression for the conductivity of the more highly conductive component is
introduced.Comment: 4 pages, Latex, 4 postscript (*.epsi) files submitted to Phys Rev.
Population structure of invasive Streptococcus pneumoniae in The Netherlands in the pre-vaccination era assessed by MLVA and capsular sequence typing
Alterations in fuel homeostasis in adult male rats by perinatal poly-unsaturated fatty acid supplementation are insulin-dependent
Risk factors for leaving employment due to multiple sclerosis and changes in risk over the past decades: using competing risk survival analysis
Background: No studies have assessed changes in employment survival in multiple sclerosis (MS) populations over recent decades, including the introduction of disease-modifying therapies (DMTs). Objectives: To evaluate factors associated with leaving employment due to MS; to assess whether the risk of leaving employment has changed over recent decades in Australia, stratified by MS phenotype. Methods: We included 1240 participants who were working before MS diagnosis. Information on employment status, reasons for leaving employment and year of leaving were collected. Data were analysed using competing risk survival analysis. Results: Males, progressive MS, lower education level and older age at diagnosis were associated with a higher sub-distribution hazard of leaving employment. Compared to the period before 2010, the sub-distribution hazard during 2010-2016 for relapsing-remitting multiple sclerosis (RRMS) was reduced by 43% (sub-distribution hazard ratio (sHR) 0.67, 95% confidence interval (CI): 0.50 to 0.90), while no significant reduction was seen for primary-progressive multiple sclerosis (PPMS) (sHR 1.25, 95% CI: 0.72 to 2.16) or secondary-progressive multiple sclerosis (SPMS) (sHR 1.37, 95% CI: 0.84 to 2.25). Conclusion: Males, people with progressive MS and those of lower education level were at higher risk of leaving employment. The differential changed risk of leaving employment between people with different MS phenotype after 2010 coincides with the increased usage of high-efficacy DMTs for RRMS
Numerical description of discharge characteristics of the plasma needle
The plasma needle is a small atmospheric, nonthermal, radio-frequency discharge, generated at the tip of a needle, which can be used for localized disinfection of biological tissues. Although several experiments have characterized various qualities of the plasma needle, discharge characteristics and electrical properties are still not well known. In order to provide initial estimates on electrical properties and quantities such as particle densities, we employed a two-dimensional, time-dependent fluid model to describe the plasma needle. In this model the balance equation is solved in the drift-diffusion approach for various species and the electron energy, as well as Poisson's equation. We found that the plasma production occurs in the sheath region and results in a steady flux of reactive species outwards. Even at small (< 0.1%) admixtures of N-2 to the He background, N-2(+) is the dominant ion. The electron density is typically 10(11) cm(-3) and the dissipated power is in the order of 10 mW. These results are consistent with the experimental data available and can give direction to the practical development of the plasma needle. (c) 2005 American Institute of Physics
Minimal Model for Sand Dunes
We propose a minimal model for aeolian sand dunes. It combines an analytical
description of the turbulent wind velocity field above the dune with a
continuum saltation model that allows for saturation transients in the sand
flux. The model provides a qualitative understanding of important features of
real dunes, such as their longitudinal shape and aspect ratio, the formation of
a slip face, the breaking of scale invariance, and the existence of a minimum
dune size.Comment: 4 pages, 4 figures, replaced with publishd versio
Tracking poverty using satellite imagery and big data
Despite recent improvements in the availability and quality of socioeconomic data from developing countries, there are still persistent data gaps that are preventing comprehensive monitoring and evaluation of targets and indicators of the Sustainable Development Goals. Approaches are hampered by the inconsistent spatial and temporal coverage of census data and Demographic and Health Surveys, which serve as the primary source for population-level statistics in most developing countries. Traditional censuses are too expensive to be implemented in remote areas where population density is low and road networks are poor. However, the recent and rapid diffusion of high-resolution satellite imagery offers a new wealth of relatively untapped information that can be used to gain in-depth information on groups that have historically been left out by traditional surveys. Moreover, there are new data streams such as call detail records from mobile phone data networks can help to derive behavioral indicators and improve tracking of expenditure and wealth. This exploratory research conflates various data streams to derive spatially explicit poverty indicators for Senegal with immense scaling potential to other regions
Coupled calcium and inorganic carbon uptake suggested by magnesium and sulfur incorporation in foraminiferal calcite
Shell chemistry of foraminiferal carbonate proves to be
useful in reconstructing past ocean conditions. A new addition to the proxy
toolbox is the ratio of sulfur (S) to calcium (Ca) in foraminiferal shells,
reflecting the ratio of SO42- to CO32- in seawater. When
comparing species, the amount of SO42- incorporated, and therefore
the S∕Ca of the shell, increases with increasing magnesium (Mg) content. The
uptake of SO42- in foraminiferal calcite is likely connected to
carbon uptake, while the incorporation of Mg is more likely related to Ca
uptake since this element substitutes for Ca in the crystal lattice. The
relation between S and Mg incorporation in foraminiferal calcite therefore
offers the opportunity to investigate the timing of processes involved in Ca
and carbon uptake. To understand how foraminiferal S∕Ca is related to Mg∕Ca,
we analyzed the concentration and within-shell distribution of S∕Ca of three
benthic species with different shell chemistry: Ammonia tepida, Bulimina marginata and Amphistegina lessonii. Furthermore, we
investigated the link between Mg∕Ca and S∕Ca across species and the
potential influence of temperature on foraminiferal S∕Ca. We observed that
S∕Ca is positively correlated with Mg∕Ca on a microscale within specimens, as
well as between and within species. In contrast, when shell Mg∕Ca increases
with temperature, foraminiferal S∕Ca values remain similar. We evaluate our
findings in the light of previously proposed biomineralization models and
abiological processes involved during calcite precipitation. Although all
kinds of processes, including crystal lattice distortion and element
speciation at the site of calcification, may contribute to changes in either
the amount of S or Mg that is ultimately incorporated in foraminiferal
calcite, these processes do not explain the covariation between Mg∕Ca and
S∕Ca values within specimens and between species. We observe that groups of
foraminifera with different calcification pathways, e.g., hyaline versus
porcelaneous species, show characteristic values for S∕Ca and Mg∕Ca, which
might be linked to a different calcium and carbon uptake mechanism in
porcelaneous and hyaline foraminifera. Whereas Mg incorporation might be
controlled by Ca dilution at the site of calcification due to Ca pumping, S
is linked to carbonate ion concentration via proton pumping. The fact that
we observe a covariation of S and Mg within specimens and between species
suggests that proton pumping and Ca pumping are intrinsically coupled across
multiple scales.</p
- …