17,907 research outputs found
Spin-transfer-driven nano-oscillators are equivalent to parametric resonators
The equivalence between different physical systems permits us to transfer
knowledge between them and to characterize the universal nature of their
dynamics. We demonstrate that a nanopillar driven by a spin-transfer torque is
equivalent to a rotating magnetic plate, which permits us to consider the
nanopillar as a macroscopic system under a time-modulated injection of energy,
that is, a simple parametric resonator. This equivalence allows us to
characterize the phases diagram and to predict magnetic states and dynamical
behaviors, such as solitons, stationary textures, and oscillatory localized
states, among others. Numerical simulations confirm these predictions.Comment: 8 pages, 7 figure
Spatial Concentration of Institutional Property Ownership: New Wave Atomistic or Traditional Urban Clustering
NCREIF investors acquire property in counties that meet socioeconomic filtering criteria. In contrast to atomistic predictions, these investors acquire their apartment buildings, offices, retail facilities, and warehouses in density clusters. These clusters follow a model of a negative exponential demand curve, a model that previously explained the technologically caused density gradient of urban areas. Institutional investors signal their belief that clustering of properties is a value dimension.
Animal welfare science: recent publication trends and future research priorities
Animal welfare science is a young and thriving field. Over the last two decades, the output of scientific publications on welfare has increased by c. 10-15% annually (tripling as a proportion of all science papers logged by ISI’s Web of Science), with just under half the c. 8500 total being published in the last 4 years. These papers span an incredible 500+ journals, but around three quarters have been in 80 animal science, veterinary, ethology, conservation and specialized welfare publications, and nearly 25% are published in just two: Animal Welfare and Applied Animal Behaviour Science. Farmed animals – especially mammals – have attracted by far the most research. This broadly reflects the vastness of their populations and the degree of public concern they elicit; poultry, however, are under-studied, and farmed fish ever more so: fish have only recently attracted welfare research, and are by far the least studied of all agricultural species, perhaps because of ongoing doubts about their sentience. We predict this farm animal focus will continue in the future, but embracing more farmed fish, reptiles and invertebrates, and placing its findings within broader international contexts such as environmental and food security concerns. Laboratory animals have been consistently well studied, with a shift in recent years away from primates and towards rodents. Pets, the second largest animal sector after farmed animals, have in contrast been little studied considering their huge populations (cats being especially overlooked): we anticipate research on them increasing in the future. Captive wild animals, especially mammals, have attracted a consistent level of welfare research over the last two decades. Given the many thousands of diverse species kept by zoos, this must, and we predict will, increase. Future challenges and opportunities including refining the use of preference tests, stereotypic behaviour, corticosteroid outputs and putative indicators of positive affect, to enable more valid conclusions about welfare; investigating the evolution and functions of affective states; and last but not least, identifying which taxonomic groups and stages of development are actually sentient and so worthy of welfare concern
Winds from Luminous Late-Type Stars: II. Broadband Frequency Distribution of Alfv\'en Waves
We present the numerical simulations of winds from evolved giant stars using
a fully non-linear, time dependent 2.5-dimensional magnetohydrodynamic (MHD)
code. This study extends our previous fully non-linear MHD wind simulations to
include a broadband frequency spectrum of Alfv\'en waves that drive winds from
red giant stars. We calculated four Alfv\'en wind models that cover the whole
range of Alfv\'en wave frequency spectrum to characterize the role of freely
propagated and reflected Alfv\'en waves in the gravitationally stratified
atmosphere of a late-type giant star. Our simulations demonstrate that, unlike
linear Alfv\'en wave-driven wind models, a stellar wind model based on plasma
acceleration due to broadband non-linear Alfv\'en waves, can consistently
reproduce the wide range of observed radial velocity profiles of the winds,
their terminal velocities and the observed mass loss rates. Comparison of the
calculated mass loss rates with the empirically determined mass loss rate for
alpha Tau suggests an anisotropic and time-dependent nature of stellar winds
from evolved giants.Comment: accepted by Ap
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