17,834 research outputs found
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
Solvation at Aqueous Metal Electrodes
We present a study of the solvation properties of model aqueous electrode
interfaces. The exposed electrodes we study strongly bind water and have closed
packed crystalline surfaces, which template an ordered water adlayer adjacent
to the interface. We find that these ordered water structures facilitate
collective responses in the presence of solutes that are correlated over large
lengthscales and across long timescales. Specifically, we show that the liquid
water adjacent to the ordered adlayers forms a soft, liquid-vapor-like
interface with concomitant manifestations of hydrophobicity. Temporal defects
in the adlayer configurations create a dynamic heterogeneity in the degree to
which different regions of the interface attract hydrophobic species. The
structure and heterogeneous dynamics of the adlayer defects depend upon the
geometry of the underlying ordered metal surface. For both 100 and 111
surfaces, the dynamical heterogeneity relaxes on times longer than nanoseconds.
Along with analyzing time scales associated with these effects, we highlight
implications for electrolysis and the particular catalytic efficiency of
platinum.Comment: 9 pages, 8 figure
Better estimates from binned income data: Interpolated CDFs and mean-matching
Researchers often estimate income statistics from summaries that report the
number of incomes in bins such as \$0-10,000, \$10,001-20,000,...,\$200,000+.
Some analysts assign incomes to bin midpoints, but this treats income as
discrete. Other analysts fit a continuous parametric distribution, but the
distribution may not fit well.
We fit nonparametric continuous distributions that reproduce the bin counts
perfectly by interpolating the cumulative distribution function (CDF). We also
show how both midpoints and interpolated CDFs can be constrained to reproduce
the mean of income when it is known.
We compare the methods' accuracy in estimating the Gini coefficients of all
3,221 US counties. Fitting parametric distributions is very slow. Fitting
interpolated CDFs is much faster and slightly more accurate. Both interpolated
CDFs and midpoints give dramatically better estimates if constrained to match a
known mean.
We have implemented interpolated CDFs in the binsmooth package for R. We have
implemented the midpoint method in the rpme command for Stata. Both
implementations can be constrained to match a known mean.Comment: 20 pages (including Appendix), 3 tables, 2 figures (+2 in Appendix
The Nonprofit Quarterly Study on Nonprofit and Philanthropic Infrastructure
Examines trends in the nonprofit sector's support network and financing system and their capacity to address the impact of the financial crisis on small and midsize nonprofits, share organizational survival strategies, and connect them to resources
Mortality from infectious pneumonia in metal workers: a comparison with deaths from asthma in occupations exposed to respiratory sensitizers
Introduction: national analyses of mortality in England and Wales have repeatedly shown excess
deaths from pneumonia in welders. During 1979-1990 the excess was attributable
largely to deaths from lobar pneumonia and pneumonias other than bronchopneumonia,
limited to working-aged men, and apparent in other metal fume-exposed occupations.
We assessed findings for 1991-2000 and compared the mortality pattern with that from
asthma in occupations exposed to known respiratory sensitizers.Methods: the Office of National Statistics supplied data on deaths by underlying cause among
men aged 16-74 years in England and Wales during 1991-2000, including age and last
held occupation. We abstracted data on pneumonia for occupations with exposure to
metal fume and on asthma for occupations commonly reported to surveillance schemes
as at risk of occupational asthma. We estimated expected numbers of deaths by applying
age-specific proportions of deaths by cause in the population to the total deaths by age in
each occupational group. Observed and expected numbers were compared for each
cause of death.Results: among working-aged men in metal fume-exposed occupations we found excesses of
mortality from pneumococcal and lobar pneumonia (54 deaths vs. 27.3 expected) and
from pneumonias other than bronchopneumonia (71 vs. 52.4), but no excess from these
causes at older ages, or from bronchopneumonia at any age. The attributable mortality
from metal fume (45.3 excess deaths) compared with an estimated 62.6 deaths from
occupational asthma.Conclusion: exposure to metal fume is a material cause of occupational mortality. The hazard
deserves far more attention than it presently receive
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Improving River Flood Extent Delineation From Synthetic Aperture Radar Using Airborne Laser Altimetry
Enhanced recovery after surgery
Enhanced Recovery or Fast Track Recovery after Surgery protocols (ERAS) have significantly changed perioperative care following colorectal surgery and are promoted as reducing the stress response to surgery.
The present systematic review aimed to examine the impact on the magnitude of the systemic inflammatory response (SIR) for each ERAS component following colorectal surgery using objective markers such as C-reactive protein (CRP) and interleukin-6 (IL-6).
A literature search was performed of the US National Library of Medicine (MEDLINE), EMBASE, PubMed, and the Cochrane Database of Systematic Reviews using appropriate keywords and subject headings to February 2015.
Included studies had to assess the impact of the selected ERAS component on the SIR using either CRP or IL-6.
Nineteen studies, including 1898 patients, were included. Fourteen studies (1246 patients) examined the impact of laparoscopic surgery on the postoperative markers of SIR. Ten of these studies (1040 patients) reported that laparoscopic surgery reduced postoperative CRP. One study (53 patients) reported reduced postoperative CRP using opioid-minimising analgesia. One study (142 patients) reported no change in postoperative CRP following preoperative carbohydrate loading. Two studies (108 patients) reported conflicting results with respect to the impact of goal-directed fluid therapy on postoperative IL-6. No studies examined the effect of other ERAS components, including mechanical bowel preparation, antibiotic prophylaxis, thromboprophylaxis, and avoidance of nasogastric tubes and peritoneal drains on markers of the postoperative SIR following colorectal surgery.
The present systematic review shows that, with the exception of laparoscopic surgery, objective evidence of the effect of individual components of ERAS protocols in reducing the stress response following colorectal surgery is limited
Charge fluctuations in nano-scale capacitors
The fluctuations of the charge on an electrode contain information on the
microscopic correlations within the adjacent fluid and their effect on the
electronic properties of the interface. We investigate these fluctuations using
molecular dynamics simulations in a constant-potential ensemble with histogram
reweighting techniques. This approach offers in particular an efficient,
accurate and physically insightful route to the differential capacitance that
is broadly applicable. We demonstrate these methods with three different
capacitors: pure water between platinum electrodes, and a pure as well as a
solvent-based organic electrolyte each between graphite electrodes. The total
charge distributions with the pure solvent and solvent-based electrolytes are
remarkably Gaussian, while in the pure ionic liquid the total charge
distribution displays distinct non-Gaussian features, suggesting significant
potential-driven changes in the organization of the interfacial fluid
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