409 research outputs found
Surface Induced Order in Liquid Metals and Binary Alloys
Measurements of the surface x-ray scattering from several pure liquid metals
(Hg, Ga, and In) and from three alloys (Ga-Bi, Bi-In, and K-Na) with different
heteroatomic chemical interactions in the bulk phase are reviewed.
Surface-induced layering is found for each elemental liquid metal. The surface
structure of the K-Na alloy resembles that of an elemental liquid metal. Bi-In
displays pair formation at the surface. Surface segregation and a wetting film
are found for Ga-Bi.Comment: 10 pages, 3 fig, published in Journal of Physics: Condensed Matte
Wetting Phase Transition at the Surface of Liquid Ga-Bi alloys: An X-ray Reflectivity Study
X-ray reflectivity measurements of the binary liquid Ga-Bi alloy reveal a
dramatically different surface structure above and below the monotectic
temperature C.
A Gibbs-adsorbed Bi monolayer resides at the surface at both regimes.
However, a 30 {\AA} thick, Bi-rich wetting film intrudes between the Bi
monolayer and the Ga-rich bulk for .
The internal structure of the wetting film is determined with {\AA}
resolution, showing a theoretically unexpected concentration gradient and a
highly diffuse interface with the bulk phase.Comment: 5 RevTex pages, 3 figures, Phys. Rev. Let
X-ray study of the liquid potassium surface: structure and capillary wave excitations
We present x-ray reflectivity and diffuse scattering measurements from the
liquid surface of pure potassium. They strongly suggest the existence of atomic
layering at the free surface of a pure liquid metal with low surface tension.
Prior to this study, layering was observed only for metals like Ga, In and Hg,
the surface tensions of which are 5-7 fold higher than that of potassium, and
hence closer to inducing an ideal "hard wall" boundary condition. The
experimental result requires quantitative analysis of the contribution to the
surface scattering from thermally excited capillary waves. Our measurements
confirm the predicted form for the differential cross section for diffuse
scattering, where , over a range of and that is larger than
any previous measurement. The partial measure of the surface structure factor
that we obtained agrees with computer simulations and theoretical predictions.Comment: 7 pages, 7 figures; published in Phys. Rev.
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.
Tracking sickness through social networks - the practical use of social network mapping in supporting the management of an E. coli O157 outbreak in a primary school in London.
This paper describes the practical use of social network diagrams in the management of an outbreak of Escherichia coli O157 (VTEC) in a primary school in London. The diagrams were created during the outbreak to establish the extent and nature of person-to-person transmission in the cases and their contacts. The diagrams supported a tailored public health action, and hence aided in the control of the outbreak. We conclude that for selected infectious diseases, social network diagrams can provide a valuable tool in the management of an outbreak
Recommended from our members
Competition between Surface Layering and Surface Phase Formation in Dilute Liquid Hg−Au Alloys
We present temperature-dependent X-ray reflectivity measurements of liquid Hg alloyed with 0.06−0.20 atom % Au. At low Au concentrations, we find temperature-dependent surface-induced layering similar to that observed in pure Hg, except that the presence of Au reduces the layering amplitude. Upon approaching the solubility limit of Au in Hg, a new surface phase forms which is 1−2 atomic diameters thick and has a density of about half that of bulk Hg. We present a surface phase diagram, summarizing the evolution of this unexpected surface structure upon varying composition and temperature. Such surface modifications may account for the variations observed in catalytic and electrochemical reactions at liquid metal surfaces upon alloying.Engineering and Applied Science
Surface layering of liquids: The role of surface tension
Recent measurements show that the free surfaces of liquid metals and alloys
are always layered, regardless of composition and surface tension; a result
supported by three decades of simulations and theory. Recent theoretical work
claims, however, that at low enough temperatures the free surfaces of all
liquids should become layered, unless preempted by bulk freezing. Using x-ray
reflectivity and diffuse scattering measurements we show that there is no
observable surface-induced layering in water at T=298 K, thus highlighting a
fundamental difference between dielectric and metallic liquids. The
implications of this result for the question in the title are discussed.Comment: 5 pages, 4 figures, to appear in Phys. Rev. B. 69 (2004
- …