4,057 research outputs found
Tuning surface metallicity and ferromagnetism by hydrogen adsorption at the polar ZnO(0001) surface
The adsorption of hydrogen on the polar Zn-ended ZnO(0001) surface has been
investigated by density functional {\it ab-initio} calculations. An on top
H(1x1) ordered overlayer with genuine H-Zn chemical bonds is shown to be
energetically favorable. The H covered surface is metallic and spin-polarized,
with a noticeable magnetic moment at the surface region. Lower hydrogen
coverages lead to strengthening of the H-Zn bonds, corrugation of the surface
layer and to an insulating surface. Our results explain experimental
observations of hydrogen adsorption on this surface, and not only predict a
metal-insulator transition, but primarily provide a method to reversible switch
surface magnetism by varying the hydrogen density on the surface.Comment: 4 pages, 3 figure
Reversible enhancement of the magnetism of ultrathin Co films by H adsorption
By means of ab initio calculations, we have investigated the effect of H
adsorption in the structural, electronic and magnetic properties of ultrathin
Co films on Ru(0001). Our calculations predict that H occupies hollow sites
preserving the two-dimensional 3-fold symmetry. The formation of a complete H
overlayer leads to a very stable surface with strong H-Co bonds. H tends to
suppress surface features, in particular, the enhancement of the magnetic
moments of the bare film. The H-induced effects are mostly confined to the Co
atoms bonded to H, independent of the H coverage or of the thickness and the
structure of the Co film. However, for partial H coverages a significant
increase occurs in the magnetic moment for the surface Co atoms not bonded to
H, leading to a net enhancement of surface magnetism.Comment: 6 pages, 4 figures, 3 table
Palenque de San Basilio in Colombia: genetic data support an oral history of a paternal ancestry in Congo
The Palenque, a black community in rural Colombia, have an oral history of fugitive African slaves founding a free village near Cartagena in the seventeenth century. Recently, linguists have identified some 200 words in regular use that originate in a Kikongo language, with Yombe, mainly spoken in the Congo region, being the most likely source. The non-recombining portion of the Y chromosome (NRY) and mitochondrial DNA were analysed to establish whether there was greater similarity between present-day members of the Palenque and Yombe than between the Palenque and 42 other African groups (for all individuals,n= 2799) from which forced slaves might have been taken. NRY data are consistent with the linguistic evidence that Yombe is the most likely group from which the original male settlers of Palenque came. Mitochondrial DNA data suggested substantial maternal sub-Saharan African ancestry and a strong founder effect but did not associate Palenque with any particular African group. In addition, based on cultural data including inhabitants' claims of linguistic differences, it has been hypothesized that the two districts of the village (Abajo and Arriba) have different origins, with Arriba founded by men originating in Congo and Abajo by those born in Colombia. Although significant genetic structuring distinguished the two from each other, no supporting evidence for this hypothesis was found
Nuevo material compuesto de matriz geopolimérica activado con ceniza de cascarilla de arroz y KOH: Desempeño a alta temperatura
Geopolymers were produced using an environmentally friendly alkali activator (based on Rice Husk Ash and potassium hydroxide). Aluminosilicates particles, carbon and ceramic fibres were used as reinforcement materials. The effects of reinforcement materials on the flexural strength, linear-shrinkage, thermophysical properties and microstructure of the geopolymers at room and high temperature (1200 ÅãC) were studied. The results indicated that the toughness of the composites is increased 110.4% for geopolymer reinforced by ceramic fibres (G-AF) at room temperature. The presence of particles improved the flexural behaviour 265% for geopolymer reinforced by carbon fibres and particles after exposure to 1200 .C. Linear-shrinkage for geopolymer reinforced by ceramic fibres and particles and the geopolymer G-AF compared with reference sample (without fibres and particles) is improved by 27.88% and 7.88% respectively at 900 ÅãC. The geopolymer materials developed in this work are porous materials with low thermal conductivity and good mechanical properties with potential thermal insulation applications for building applications.Compuestos geopoliméricos fueron producidos usando un activador alcalino alternativo (basado en ceniza de cascarilla de arroz e hidróxido de potasio), partículas aluminosilicatos, fibras de carbono y cerámicas. Se estudió el efecto de fibras y partículas en la resistencia a la flexión, contracción lineal, propiedades termofísicas y microestructura de los geopolímeros a temperatura ambiente y 1200 °C. Los resultados indican que la tenacidad se incrementó 110.4% para el geopolímero reforzado con fibras cerámicas (G-AF) a temperatura ambiente. La presencia de partículas mejora el comportamiento a la flexión 265% para el geopolímero reforzado con fibras de carbono y partículas después de la exposición a 1200 °C. La contracción lineal para el geopolímero reforzado con fibras cerámicas y partículas y el geopolímero G-AF es mejorada 27.88% y 7.88% respectivamente a 900 ºC con respecto al material sin refuerzo. Los materiales geopoliméricos desarrollados en este estudio son materiales porosos de baja conductividad térmica y buenas propiedades mecánicas con potencial aplicación en la industria de la construcción como aislantes térmicos
Acute febrile illness is associated with Rickettsia spp infection in dogs
BACKGROUND: Rickettsia conorii is transmitted by Rhipicephalus sanguineus ticks and causes Mediterranean Spotted Fever (MSF) in humans. Although dogs are considered the natural host of the vector, the clinical and epidemiological significance of R. conorii infection in dogs remains unclear. The aim of this prospective study was to investigate whether Rickettsia infection causes febrile illness in dogs living in areas endemic for human MSF. METHODS: Dogs from southern Italy with acute fever (n = 99) were compared with case–control dogs with normal body temperatures (n = 72). Serology and real-time PCR were performed for Rickettsia spp., Ehrlichia canis, Anaplasma phagocytophilum/A. platys and Leishmania infantum. Conventional PCR was performed for Babesia spp. and Hepatozoon spp. Acute and convalescent antibodies to R. conorii, E. canis and A. phagocytophilum were determined. RESULTS: The seroprevalence rates at first visit for R. conorii, E. canis, A. phagocytophilum and L. infantum were 44.8%, 48.5%, 37.8% and 17.6%, respectively. The seroconversion rates for R. conorii, E. canis and A. phagocytophilum were 20.7%, 14.3% and 8.8%, respectively. The molecular positive rates at first visit for Rickettsia spp., E. canis, A. phagocytophilum, A. platys, L. infantum, Babesia spp. and Hepatozoon spp. were 1.8%, 4.1%, 0%, 2.3%, 11.1%, 2.3% and 0.6%, respectively. Positive PCR for E. canis (7%), Rickettsia spp. (3%), Babesia spp. (4.0%) and Hepatozoon spp. (1.0%) were found only in febrile dogs. The DNA sequences obtained from Rickettsia and Babesia PCRs positive samples were 100% identical to the R. conorii and Babesia vogeli sequences in GenBank®, respectively. Febrile illness was statistically associated with acute and convalescent positive R. conorii antibodies, seroconversion to R. conorii, E. canis positive PCR, and positivity to any tick pathogen PCRs. Fourteen febrile dogs (31.8%) were diagnosed with Rickettsia spp. infection based on seroconversion and/or PCR while only six afebrile dogs (12.5%) seroconverted (P = 0.0248). The most common clinical findings of dogs with Rickettsia infection diagnosed by seroconversion and/or PCR were fever, myalgia, lameness, elevation of C-reactive protein, thrombocytopenia and hypoalbuminemia. CONCLUSIONS: This study demonstrates acute febrile illness associated with Rickettsia infection in dogs living in endemic areas of human MSF based on seroconversion alone or in combination with PCR
Survey for Emission-Line Galaxies: Universidad Complutense de Madrid List 3
A new low-dispersion objective-prism search for low-redshift (z<0.045)
emission-line galaxies (ELG) has been carried out by the Universidad
Complutense de Madrid with the Schmidt Telescope at the Calar-Alto Observatory.
This is a continuation of the UCM Survey, which was performed by visual
selection of candidates in photographic plates via the presence of the
Halpha+[NII]6584 blend in emission. In this new list we have applied an
automatic procedure, fully developed by us, for selecting and analyzing the ELG
candidates on the digitized images obtained with the MAMA machine. The analyzed
region of the sky covers 189 square degrees in nine fields near R.A.=14h & 17h,
Dec=25 deg. The final sample contains 113 candidates. Special effort has been
made to obtain a large amount of information directly from our uncalibrated
plates by using several external calibrations. The parameters obtained for the
ELG candidates allow for the study of the statistical properties for the
sample.Comment: 13 pages, 18 PostScript figures, 6 JPEG figures, Table 2 corrected.
Accepted for publication in Astrophysical Journal Supplements, also available
at http://www.ucm.es/info/Astrof/opera/LIST3_ApJS99
A Semi-Empirical Model of the Infra-Red Universe
We present a simple model of the infra-red universe, based as much as
possible on local observations. We model the luminosity and number evolution of
disk and starburst galaxies, including the effects of dust, gas and spectral
evolution. Although simple, our approach is able to reproduce observations of
galaxy number counts and the infra-red and sub-millimeter extra-galactic
backgrounds. It provides a useful probe of galaxy formation and evolution out
to high redshift. The model demonstrates the significant role of the starburst
population and predicts high star formation rates at redshifts 3 to 4,
consistent with recent extinction-corrected observations of Lyman break
galaxies. Starbursting galaxies are predicted to dominate the current SCUBA
surveys. Their star formation is driven predominantly by strong tidal
interactions and mergers of galaxies. This leads to the creation of spheroidal
stellar systems, which may act as the seeds for disk formation as gas infalls.
We predict the present-day baryonic mass in bulges and halos is comparable to
that in disks. From observations of the extra-galactic background, the model
predicts that the vast majority of star formation in the Universe occurs at
z<5.Comment: 23 pages including 9 figures. To appear in ApJ. Model results
available electronically at http://astro.berkeley.edu/~jt/irmodel.htm
The History of Cosmological Star Formation: Three Independent Approaches and a Critical Test Using the Extragalactic Background Light
Taking three independent approaches, we investigate the simultaneous
constraints set on the cosmic star formation history from various observations,
including stellar mass density and extragalactic background light (EBL). We
compare results based on: 1) direct observations of past light-cone, 2) a model
using local fossil evidence constrained by SDSS observations at z~0 (the
`Fossil' model), and 3) theoretical ab initio models from three calculations of
cosmic star formation history: (a) new (1024)^3 Total Variation Diminishing
(TVD) cosmological hydrodynamic simulation, (b) analytic expression of
Hernquist & Springel based on cosmological Smoothed Particle Hydrodynamics
(SPH) simulations, and (c) semi-analytic model of Cole et al. We find good
agreement among the three independent approaches up to the order of
observational errors, except that all the models predict bolometric EBL of
I_tot ~= 37-52 nW m^-2 sr^-1, which is at the lower edge of the the
observational estimate by Hauser & Dwek. We emphasize that the Fossil model
that consists of two components -- spheroids and disks --, when normalized to
the local observations, provides a surprisingly simple but accurate description
of the cosmic star formation history and other observable quantities. Our
analysis suggests that the consensus global parameters at z=0 are: Omega_* =
0.0023+-0.0004, I_EBL = 43+-7 nW m^-2 sr^-1 rho_SFR=(1.06+-0.22)e-2 Msun yr^-1
Mpc^-3, j_bol = (3.1+-0.2)e8 Lsun Mpc^-3.Comment: 40 page, 10 figures. ApJ in press. Matched to the accepted versio
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