Two-magnon Raman scattering in insulating cuprates: Modifications of the effective Raman operator

Calculations of Raman scattering intensities in spin 1/2 square-lattice Heisenberg model, using the Fleury-Loudon-Elliott theory, have so far been unable to describe the broad line shape and asymmetry of the two magnon peak found experimentally in the cuprate materials. Even more notably, the polarization selection rules are violated with respect to the Fleury-Loudon-Elliott theory. There is comparable scattering in $B_{1g}$ and $A_{1g}$ geometries, whereas the theory would predict scattering in only $B_{1g}$ geometry. We review various suggestions for this discrepency and suggest that at least part of the problem can be addressed by modifying the effective Raman Hamiltonian, allowing for two-magnon states with arbitrary total momentum. Such an approach based on the Sawatzsky-Lorenzana theory of optical absorption assumes an important role of phonons as momentum sinks. It leaves the low energy physics of the Heisenberg model unchanged but substantially alters the Raman line-shape and selection rules, bringing the results closer to experiments.Comment: 7 pages, 6 figures, revtex. Contains some minor revisions from previous versio

Wings for wildlife: The use of conservation drones, challenges and opportunities

The idea of using low-cost do-it-yourself drones for conservation came in 2011 after two of us (Lian Pin Koh and Serge Wich) discussed the generally high financial and time investments that were made to monitor biodiversity in South East Asia. Particularly when surveying species such as orangutans (Pongo spp), it is costly and time-consuming to cover the entire distribution due to the relatively large geographic extent to which they occur and the fairly inhospitable terrain. Population data therefore rely on estimates, which are obtained by counting the number of nests within a small area and extrapolating these results to estimate the wider population (Ancrenaz et al. 2004; Wich et al. 2008). This means that the extent of data is limited and the frequency at which data are collected limited as well. Because orangutans make a new night nest on every night and these had been observed from manned helicopters and planes (Ancrenaz et al. 2004; Wich, pers. obs) we thought that perhaps drones could be used to obtain images of the forest canopy in which the nests could be detected. Because nobody had tried to take pictures of the canopy from drones to detect orangutan nests before, we were eager to test our idea and started to look for opportunities to obtain a drone that was affordable and could be repaired in the field. We quickly realised that it was best to build our own system based on resources available on the internet and components we could easily order via the internet (details below)

Influence of the amount and morphology of retained austenite on the mechanical properties of an austempered ductile iron

High Si contents in nodular cast irons lead to a significant volume fraction of retained austenite in the material after the austempering treatment. In the present work, the influence of the amount and morphology of this phase on the mechanical properties (proof stress, ultimate tensile strength (UTS), elongation, and toughness) has been analyzed for different austempering conditions. After 300°C isothermal treatments at intermediate times, the austenite is plastically stable at room temperature and contributes, together with the bainitic ferrite, to the proof stress and the toughness of the material. For austenite volume fractions higher than 25 pct, the proof stress is controlled by this phase and the toughness depends mainly on the stability of γ. In these conditions (370°C and 410°C treatments), the present material exhibits a transformation-induced plasticity (TRIP) effect, which leads to an improvement in ductility. It is shown that the strain level necessary to initiate the martensitic transformation induced by deformation depends on the carbon content of the austenite. The martensite formed under TRIP conditions can be of two different types: "autotempered" plate martensite, which forms at room temperature from an austenite with a quasi-coherent epsilon carbide precipitation, and lath martensite nucleated at twin boundaries and twin intersections.Peer reviewe

A systematic survey of floral nectaries

The construction of classifications, as well as the understanding of biological diversity, depends upon a careful comparison of attributes of the organisms studied (Stuessy, 1990). It is widely known that data from diverse sources showing differences from taxon to taxon are of systematic significance. Dur-ing the 20th century, systematists have emphasized that their discipline involves a synthesis of all knowledge (Stevens, 1994) or, in other words, the variation of as many relevant characters as possible should be incorporated into the natural system to be constructed. The extent to which particular characters are constant or labile will determine their usefulness to syste-matics. In general, more conservative characters will be valuable in defining families and orders, whereas more labile characters may be useful at the ge-neric and specific levels (Webb, 1984). There is no doubt that floral characters are among the most used in the classification of flowering plants. At the same time, they constitute essential features in diagnostic keys to taxa in both taxonomic treatments and Floras (Cronquist, 1981, 1988).Fil: Bernardello, Gabriel Luis Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentin

Vorapaxar in the secondary prevention of atherothrombotic events

Item does not contain fulltextBACKGROUND: Thrombin potently activates platelets through the protease-activated receptor PAR-1. Vorapaxar is a novel antiplatelet agent that selectively inhibits the cellular actions of thrombin through antagonism of PAR-1. METHODS: We randomly assigned 26,449 patients who had a history of myocardial infarction, ischemic stroke, or peripheral arterial disease to receive vorapaxar (2.5 mg daily) or matching placebo and followed them for a median of 30 months. The primary efficacy end point was the composite of death from cardiovascular causes, myocardial infarction, or stroke. After 2 years, the data and safety monitoring board recommended discontinuation of the study treatment in patients with a history of stroke owing to the risk of intracranial hemorrhage. RESULTS: At 3 years, the primary end point had occurred in 1028 patients (9.3%) in the vorapaxar group and in 1176 patients (10.5%) in the placebo group (hazard ratio for the vorapaxar group, 0.87; 95% confidence interval [CI], 0.80 to 0.94; P<0.001). Cardiovascular death, myocardial infarction, stroke, or recurrent ischemia leading to revascularization occurred in 1259 patients (11.2%) in the vorapaxar group and 1417 patients (12.4%) in the placebo group (hazard ratio, 0.88; 95% CI, 0.82 to 0.95; P=0.001). Moderate or severe bleeding occurred in 4.2% of patients who received vorapaxar and 2.5% of those who received placebo (hazard ratio, 1.66; 95% CI, 1.43 to 1.93; P<0.001). There was an increase in the rate of intracranial hemorrhage in the vorapaxar group (1.0%, vs. 0.5% in the placebo group; P<0.001). CONCLUSIONS: Inhibition of PAR-1 with vorapaxar reduced the risk of cardiovascular death or ischemic events in patients with stable atherosclerosis who were receiving standard therapy. However, it increased the risk of moderate or severe bleeding, including intracranial hemorrhage. (Funded by Merck; TRA 2P-TIMI 50 ClinicalTrials.gov number, NCT00526474.)