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Surface Layering in Liquid Gallium: An X-Ray Reflectivity Study
Surface-induced atomic layering in liquid gallium has been observed using x-ray reflectivity, ultrahigh vacuum conditions, and sputtered clean surfaces. Reflectivity data, collected on a supercooled liquid sample to momentum transfers as large as = 3.0 Ã…, exhibit a strong maximum near 2.4 Ã… indicating a layer spacing that is comparable to its atomic dimensions. The amplitude of the electron density oscillations decays with a characteristic length of 6 Ã…. This is unexpectedly twice that of recent results for Hg, and the difference may be related to covalent bonding or supercooling.Engineering and Applied Science
Microscopic Surface Structure of Liquid Alkali Metals
We report an x-ray scattering study of the microscopic structure of the
surface of a liquid alkali metal. The bulk liquid structure factor of the
eutectic K67Na33 alloy is characteristic of an ideal mixture, and so shares the
properties of an elemental liquid alkali metal. Analysis of off-specular
diffuse scattering and specular x-ray reflectivity shows that the surface
roughness of the K-Na alloy follows simple capillary wave behavior with a
surface structure factor indicative of surface induced layering. Comparison of
thelow-angle tail of the K67Na33 surface structure factor with the one measured
for liquid Ga and In previously suggests that layering is less pronounced in
alkali metals. Controlled exposure of the liquid to H2 and O2 gas does not
affect the surface structure, indicating that oxide and hydride are not stable
at the liquid surface under these experimental conditions.Comment: 12 pages, 3 figures, published in Phys. Rev.
Rapid clearance of Schistosoma mansoni circulating cathodic antigen after treatment shown by urine strip tests in a Ugandan fishing community - Relevance for monitoring treatment efficacy and re-infection.
UNLABELLED: Schistosomiasis control and elimination has priority in public health agendas in several sub-Saharan countries. However, achieving these goals remains a substantial challenge. In order to assess progress of interventions and treatment efficacy it is pertinent to have accurate, feasible and affordable diagnostic tools. Detection of Schistosoma mansoni infection by circulating cathodic antigen (CCA) in urine is an attractive option as this measure describes live worm infection noninvasively. In order to interpret treatment efficacy and re-infection levels, knowledge about clearance of this antigen is necessary. The current study aims to investigate, whether antigen clearance as a proxy for decreasing worm numbers is reflected in decreasing CCA levels in urine shortly after praziquantel treatment. Here CCA levels are measured 24 hours post treatment in response to both a single and two treatments. The study was designed as a series of cross-sectional urine and stool sample collections from 446 individuals nested in a two-arm randomised single blinded longitudinal clinical trial cohort matched by gender and age (ClinicalTrials.gov Identifier: NCT00215267) receiving one or two praziquantel treatments. CCA levels in urine were determined by carbon-conjugated monoclonal antibody lateral flow strip assay and eggs per gram faeces for S. mansoni and soil-transmitted helminths by Kato-Katz. Significant correlations between CCA levels and S. mansoni egg count at every measured time point were found and confirmed the added beneficial effect of a second treatment at two weeks after baseline. Furthermore, presence of hookworm was found not to be a confounder for CCA test specificity. Twenty-four hours post treatment measures of mean CCA scores showed significant reductions. In conclusion, removal of CCA in response to treatment is detectable as a decline in CCA in urine already after 24 hours. This has relevance for use and interpretation of laboratory based and point-of-care CCA tests in terms of treatment efficacy and re-infection proportions as this measure provides information on the presence of all actively feeding stages of S. mansoni, which conventional faecal microscopy methods do not accurately reflect. TRIAL REGISTRATION: ClinicalTrials.gov NCT00215267
Cumulative dyslipidemia with arterial stiffness and carotid IMT progression in asymptomatic adolescents: A simulated intervention longitudinal study using temporal inverse allocation model
Background and aimsWe aimed to examine the longitudinal associations of total cholesterol (TC), non–high-density lipoprotein cholesterol (non–HDL-C), high-density lipoprotein cholesterol (HDL-C), triglyceride, and low-density lipoprotein cholesterol (LDL-C) with carotid-femoral pulse wave velocity (cfPWV) and carotid intima-media thickness (cIMT) progression.MethodsWe studied 1779, 15-year-old participants from the Avon Longitudinal Study of Parents and Children, UK birth cohort, followed up for 9 years. Fasting TC, non–HDL-C, HDL-C, triglyceride, and LDL-C were measured at 15, 17, and 24 years and age-categorized as normal, elevated, and dyslipidemia based on National Heart, Lung, and Blood Institute lipid guidelines. cfPWV and cIMT were measured at 17 and 24 years. Associations were examined using linear mixed-effect models. To simulate the treatment of dyslipidemia we conducted temporal inverse allocation model analyses.ResultsAmong 1779 [49.9% female] participants, mean lipid levels and proportions at elevated or dyslipidemia categories increased from ages 15 through 24 years. Persistently elevated TC: effect estimate 0.026 mm; [95% CI 0.004 to 0.049; p = 0.024], elevated non–HDL-C, and elevated LDL-C were cumulatively associated with cIMT progression. Persistent borderline-low HDL-C: −0.027 mm; [-0.050 to −0.005; p = 0.019] and very-low HDL-C −0.035 mm; [-0.057 to −0.013; p = 0.002] levels were associated with cIMT progression. A temporal inverse allocation of elevated and dyslipidemic levels with normal lipid levels at age 17 years attenuated the associations of cumulative elevated TC, non–HDL-C, LDL-C, and low HDL-C with cIMT progression. Cumulative elevated lipids or dyslipidemia were not associated with cfPWV progression.ConclusionsLate adolescence is key to preventing, halting, and reversing dyslipidemic-related preclinical atherosclerosis progression, warranting universal lipid screening in the general pediatric population.</p
Surface Structure of Liquid Metals and the Effect of Capillary Waves: X-ray Studies on Liquid Indium
We report x-ray reflectivity (XR) and small angle off-specular diffuse
scattering (DS) measurements from the surface of liquid Indium close to its
melting point of C. From the XR measurements we extract the surface
structure factor convolved with fluctuations in the height of the liquid
surface. We present a model to describe DS that takes into account the surface
structure factor, thermally excited capillary waves and the experimental
resolution. The experimentally determined DS follows this model with no
adjustable parameters, allowing the surface structure factor to be deconvolved
from the thermally excited height fluctuations. The resulting local electron
density profile displays exponentially decaying surface induced layering
similar to that previously reported for Ga and Hg. We compare the details of
the local electron density profiles of liquid In, which is a nearly free
electron metal, and liquid Ga, which is considerably more covalent and shows
directional bonding in the melt. The oscillatory density profiles have
comparable amplitudes in both metals, but surface layering decays over a length
scale of \AA for In and \AA for Ga. Upon controlled
exposure to oxygen, no oxide monolayer is formed on the liquid In surface,
unlike the passivating film formed on liquid Gallium.Comment: 9 pages, 5 figures; submitted to Phys. Rev.
Surface Screening Charge and Effective Charge
The charge on an atom at a metallic surface in an electric field is defined
as the field-derivative of the force on the atom, and this is consistent with
definitions of effective charge and screening charge. This charge can be found
from the shift in the potential outside the surface when the atoms are moved.
This is used to study forces and screening on surface atoms of Ag(001)
c -- Xe as a function of external field. It is found that at low
positive (outward) fields, the Xe with a negative effective charge of -0.093
is pushed into the surface. At a field of 2.3 V \AA the charge
changes sign, and for fields greater than 4.1 V \AA the Xe experiences
an outward force. Field desorption and the Eigler switch are discussed in terms
of these results.Comment: 4 pages, 1 figure, RevTex (accepted by PRL
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