Ab initio studies of the spin-transfer torque in tunnel junctions

We calculate the spin-transfer torque in Fe/MgO/Fe tunnel junctions and compare the results to those for all-metallic junctions. We show that the spin-transfer torque is interfacial in the ferromagnetic layer to a greater degree than in all-metallic junctions. This result originates in the half metallic behavior of Fe for the $\Delta_1$ states at the Brillouin zone center; in contrast to all-metallic structures, dephasing does not play an important role. We further show that it is possible to get a component of the torque that is out of the plane of the magnetizations and that is linear in the bias. However, observation of such a torque requires highly ideal samples. In samples with typical interfacial roughness, the torque is similar to that in all-metallic multilayers, although for different reasons.Comment: 5 pages, 4 figure

Beowulf 33a and Hapax Legomena

It is pointed out that ūtfūs in line 33a of the Old English poem Beowulf is not a hapax legomenon, as it appears in two late Middle English verse texts. It is also argued that the first word of the half line, manuscript īsiġ, is a hapax legomenon in English, if emendation to īliġ is accepted. The distribution of this latter adjective in West Germanic and its meaning are discussed

Winter Conditions Influence Biological Responses of Migrating Hummingbirds

Conserving biological diversity given ongoing environmental changes requires the knowledge of how organisms respond biologically to these changes; however, we rarely have this information. This data deficiency can be addressed with coordinated monitoring programs that provide field data across temporal and spatial scales and with process-based models, which provide a method for predicting how species, in particular migrating species that face different conditions across their range, will respond to climate change. We evaluate whether environmental conditions in the wintering grounds of broad-tailed hummingbirds influence physiological and behavioral attributes of their migration. To quantify winter ground conditions, we used operative temperature as a proxy for physiological constraint, and precipitation and the normalized difference vegetation index (NDVI) as surrogates of resource availability. We measured four biological response variables: molt stage, timing of arrival at stopover sites, body mass, and fat. Consistent with our predictions, we found that birds migrating north were in earlier stages of molt and arrived at stopover sites later when NDVI was low. These results indicate that wintering conditions impact the timing and condition of birds as they migrate north. In addition, our results suggest that biologically informed environmental surrogates provide a valuable tool for predicting how climate variability across years influences the animal populations

The movement for increased street railway fares

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Spin transfer torque in continuous textures: semiclassical Boltzmann approach

We consider a microscopic model of itinerant electrons coupled via ferromagnetic exchange to a local magnetization whose direction vector n(r,t) varies in space and time. We assume that to first order in the spatial gradient and time derivative of n(r,t) the magnetization distribution function f(p,r,t) of itinerant electrons has the Ansatz form: f(p,r,t)=f_{parallel}(p)n(r,t)+ f_{1 r}(p) n ^ nabla_{r} n+f_{2 r}(p) nabla_{r} n+ f_{1 t}(p) n ^ partial_t n+f_{2 t}(p) partial_t n. Using then the Landau-Sillin equations of motion approach we derive explicit forms for the components f_{parallel}(p), f_{1 r}(p), f_{2 r}(p), f_{1 t}(p) and f_{2 t}(p) in "equilibrum" and in out of equilibrum situations for: (i) no scattering by impurities, (ii) spin conserving scattering and (iii) spin non-conserving scattering. The back action on the localized electron magnetization from the out of equilibrum part of the two components f_{1 r}, f_{2 r} constitutes the two spin transfer torque terms.Comment: Revised version accepted for publication, 12 pages, one figur