Thermal stability of ion-implanted ZnO

Zinc oxide single crystals implanted at room temperature with high-dose (1.4x10(17) cm(-2)) 300 keV As+ ions are annealed at 1000-1200 degrees C. Damage recovery is studied by a combination of Rutherford backscattering/channeling spectrometry (RBS/C), cross-sectional transmission electron microscopy (XTEM), and atomic force microscopy. Results show that such a thermal treatment leads to the decomposition and evaporation of the heavily damaged layer instead of apparent defect recovery and recrystallization that could be inferred from RBS/C and XTEM data alone. This study shows that heavily damaged ZnO has relatively poor thermal stability compared to as-grown ZnO which is a significant result and has implications for understanding results on thermal annealing of ion-implanted ZnO. (c) 2005 Americian Institute of Physics.

Las estatuas-menhir noroccidentales en contexto: conectividad y conexiones materiales durante el Bronce Tardío/Final

Este artículo analiza las estatuas-menhir noroccidentales que se distribuyen en el área comprendida entre los valles del río Duero y el río Miño, pero que descubrimientos recientes han extendido a regiones fuera de este área nuclear. Partiendo de tres aspectos claves para su interpretación (la cronología, su relación con el paisaje y su sentido iconográfico), se examinan las relaciones entre estas formas materiales y un paisaje socio-material de acción específico (las formas socio-materiales de interacción propias del Bronce final atlántico). Para ello, se tiene en cuenta diferentes conexiones materiales (presencia, encuentro, coexistencia, hibridación, etc.) que permiten contextualizar las estatuasmenhir dentro de un proceso histórico particular: la integración del noroeste de la península Ibérica en un contexto de relaciones mediterráneo-atlánticas, en la segunda mitad del II milenio a.C.

Melting of metasomatized peridotite at 4–6 GPa and up to 1200 °C: an experimental approach

The phase assemblages and compositions in a K-bearing lherzolite + H2O system are determined between 4 and 6 GPa and 850–1200 °C, and the melting reactions occurring at subarc depth in subduction zones are constrained. Experiments were performed on a rocking multi-anvil apparatus. The experiments had around 16 wt% water content, and hydrous melt or aqueous fluid was segregated and trapped in a diamond aggregate layer. The compositions of the aqueous fluid and hydrous melt phases were measured using the cryogenic LA-ICP-MS technique. The residual lherzolite consists of olivine, orthopyroxene, clinopyroxene, and garnet, while diamond (C) is assumed to be inert. Hydrous and alkali-rich minerals were absent from the run products due to preferred dissolution of K2O (and Na2O) to the aqueous fluid/hydrous melt phases. The role of phlogopite in melting relations is, thus, controlled by the water content in the system: at the water content of around 16 wt% used here, phlogopite is unstable and thus does not participate in melting reactions. The water-saturated solidus, i.e., the first appearance of hydrous melt in the K–lherzolite composition, is located between 900 and 1000 °C at 4 GPa and between 1000 and 1100 °C at 5 and 6 GPa. Compositional jumps between hydrous melt and aqueous fluid at the solidus include a significant increase in the total dissolved solids load. All melts/fluids are peralkaline and calcium-rich. The melting reactions at the solidus are peritectic, as olivine, clinopyroxene, garnet, and H2O are consumed to generate hydrous melt plus orthopyroxene. Our fluid/melt compositional data demonstrate that the water-saturated hybrid peridotite solidus lies above 1000 °C at depths greater than 150 km and that the second critical endpoint is not reached at 6 GPa for a K2O–Na2O–CaO–FeO–MgO–Al2O3–SiO2–H2O–Cr2O3(–TiO2) peridotite composition.

EPICA Dome C carbon dioxide concentrations from 650 to 391 kyr BP

A record of atmospheric carbon dioxide (CO2) concentrations measured on the EPICA (European Project for Ice Coring in Antarctica) Dome Concordia ice core extends the Vostok CO2 record back to 650,000 years before the present (yr B.P.). Before 430,000 yr B.P., partial pressure of atmospheric CO2 lies within the range of 260 and 180 parts per million by volume. This range is almost 30% smaller than that of the last four glacial cycles; however, the apparent sensitivity between deuterium and CO2 remains stable throughout the six glacial cycles, suggesting that the relationship between CO2 and Antarctic climate remained rather constant over this interval.

Histoire des paysans, depuis la fin du moyen âge jusqu'à nos jours, 1200-1850 : précédée d'une introduction, an 50 avant J.-C.-1200 après J.-C. /

Mode of access: Internet.

Impulse-response studies on tracer doses of [C-14]lignocaine and its multiple metabolites in the perfused rat liver

The outflow-concentration-time profiles for lignocaine (lidocaine) and its metabolites have been measured after bolus impulse administration of [C-14]lignocaine into the perfused rat liver. Livers from female Sprague-Dawley rats were perfused in a once-through fashion with red-blood-cell-free Krebs-Henseleit buffer containing 0 or 2% bovine serum albumin. Perfusate flow rates of 20 and 30 mL min(-1) were used and both normal and retrograde flow directions were employed. Significant amounts of metabolite were detected in the effluent perfusate soon after lignocaine injection. The early appearance of metabolite contributed to bimodal outflow profiles observed for total C-14 radioactivity. The lignocaine outflow profiles were well characterized by the two-compartment dispersion model, with efflux rate << influx rate. The profiles for lignocaine metabolites were also characterized in terms of a simplified two-compartment dispersion model. Lignocaine was found to be extensively metabolized under the experimental conditions with the hepatic availability ranging between 0.09 and 0.18. Generally lignocaine and metabolite availability showed no significant change with alterations in perfusate flow rate from 20 to 30 mt min(-1) or protein content from 0 to 2%. A significant increase in lignocaine availability occurred when 1200 mu M unlabelled lignocaine was added to the perfusate. Solute mean transit times generally decreased with increasing flow rate and with increasing perfusate protein content. The results confirm that lignocaine pharmacokinetics in the liver closely follow the predictions of the well-stirred model. The increase in lignocaine availability when 1200 mu M unlabelled lignocaine was added to the perfusate is consistent with saturation of the hydroxylation metabolic pathways of lignocaine metabolism.

Time-dependent master equation simulation of complex elementary reactions in combustion: Application to the reaction of (CH2)-C-1 with C2H2 from 300-2000 K

Computational simulations of the title reaction are presented, covering a temperature range from 300 to 2000 K. At lower temperatures we find that initial formation of the cyclopropene complex by addition of methylene to acetylene is irreversible, as is the stabilisation process via collisional energy transfer. Product branching between propargyl and the stable isomers is predicted at 300 K as a function of pressure for the first time. At intermediate temperatures (1200 K), complex temporal evolution involving multiple steady states begins to emerge. At high temperatures (2000 K) the timescale for subsequent unimolecular decay of thermalized intermediates begins to impinge on the timescale for reaction of methylene, such that the rate of formation of propargyl product does not admit a simple analysis in terms of a single time-independent rate constant until the methylene supply becomes depleted. Likewise, at the elevated temperatures the thermalized intermediates cannot be regarded as irreversible product channels. Our solution algorithm involves spectral propagation of a symmetrised version of the discretized master equation matrix, and is implemented in a high precision environment which makes hitherto unachievable low-temperature modelling a reality.

Microstructural evolution of the Serido Belt, NE-Brazil: the effect of two tectonic events on development of c-axis preferred orientation in quartz

The polyphase evolution of the Serido Belt (NE-Brazil) includes D, crust formation at 2.3-2.1 Ga, D-2 thrust tectonics at 1.9 Ga and crustal reworking by D-3 strike-slip shear zones at 600 Ma. Microstructural investigations within mylonites associated with D-2 and D-3 events were used to constrain the tectono-thermal evolution of the belt. D-2 shear zones commenced at deeper crustal levels and high amphibolite facies conditions (600-650 degreesC) through grain boundary migration, subgrain rotation and operation of quartz Q-prism slip. Continued shearing and exhumation of the terrain forced the re-equilibration of high-T fabrics and the switching of slip systems from (c)-prism to positive and negative (a)-rhombs. During D-3, enhancement of ductility by dissipation of heat that came from syn-D-3 granites developed wide belts of amphibolite facies mylonites. Continued shearing, uplift and cooling of the region induced D-3 shear zones to act in ductile-brittle regimes, marked by fracturing and development of thinner belts of greenschist facies mylonites. During this event, switching from (a)-prism to a basal slip indicates a thermal path from 600 to 350 degreesC. Therefore, microstructures and quartz c-axis fabrics in polydeformed rocks from the Serido Belt preserve the record of two major events, which includes contrasting deformation mechanisms and thermal paths. (C) 2003 Elsevier Ltd. All rights reserved.

Exposition au VIH, à l'hépatite B et C au cabinet médical et à l'hôpital. Prévention et prophylaxie postexpositionnelle [Exposure to HIV, hepatitis B and C in office practice and hospital. Prevention and post-exposure prophylaxis]

Suite à un accident exposant à du sang (piqûre; coupure), provenant d'un patient infecté, le risque d'infection par VIH est d'environ 0,3% et par le virus de l'hépatite C (VHC) d'environ 0,5%. Chez les personnes vaccinées avec une réponse immunitaire adéquate (titre d'anticorps HBs >100 mUI/ml), aucune infection professionnelle par hépatite B n'a été reconnue en Suisse. La plupart des infections par VIH et VHB peuvent être prévenues par un traitement d'urgence et une prophylaxie postexpositionnelle (PEP). Il n'y a actuellement aucune prophylaxie postexpositionnelle pour le VHC. En cas de transmission de VHC, un traitement rapide par peginterféron et ribavirine est à envisager. Chaque hôpital et cabinet médical doivent mettre sur pied un système pour assurer une prise en charge optimale et en urgence des blessures par piqûres ou coupures. Lors de blessures accidentelles avec du sang de patients séropositifs pour le VIH et dans des situations complexes, il est recommandé de consulter un médecin du personnel ou un infectiologue expérimenté. The risk of infection after an occupational needle stick injury with blood from an infected source patient is approximately 0.3% for HIV and 0.5% for hepatitis C virus (HCV). In Switzerland no cases of occupational HBV infection have been recorded in fully vaccinated persons with a documented adequate vaccine response (HBsantibody titer >100 mIU/mL). Most occupational HIV und HBV infections can be prevented by appropriate emergency measures and post-exposure prophylaxis (PEP). No HCV-PEP is currently available. Early therapy with peginterferon and ribavirin should be considered in cases of occupational HCV seroconversion. Every hospital and office practice should establish a system for 24 h/24 h emergency management of occupational needle stick injuries. In the setting of an HIV-seropositive source patient and in complex situations, early consultation with a specialist in occupational medicine or infectious diseases should be considered.