3,559 research outputs found
Current Induced Order Parameter Dynamics: Microscopic Theory Applied to Co/Cu/Co spin valves
Transport currents can alter alter order parameter dynamics and change steady
states in superconductors, in ferromagnets, and in hybrid systems. In this
article we present a scheme for fully microscopic evaluation of order parameter
dynamics that is intended for application to nanoscale systems. The approach
relies on time-dependent mean-field-theory, on an adiabatic approximation, and
on the use of non-equilibrium Greens function (NEGF) theory to calculate the
influence of a bias voltage across a system on its steady-state density matrix.
We apply this scheme to examine the spin-transfer torques which drive
magnetization dynamics in Co/Cu/Co spin-valve structures. Our microscopic
torques are peaked near Co/Cu interfaces, in agreement with most previous
pictures, but suprisingly act mainly on Co transition metal -orbitals rather
than on -orbitals as generally supposed.Comment: 9 pages, 5 figure
Ab-initio GMR and current-induced torques in Au/Cr multilayers
We report on an {\em ab-initio} study of giant magnetoresistance (GMR) and
current-induced-torques (CITs) in Cr/Au multilayers that is based on
non-equilibrium Green's functions and spin density functional theory. We find
substantial GMR due primarily to a spin-dependent resonance centered at the
Cr/Au interface and predict that the CITs are strong enough to switch the
antiferromagnetic order parameter at current-densities times smaller
than typical ferromagnetic metal circuit switching densities.Comment: 8 pages, 6 figure
New approaches for estimating risk from exposure to diethylstilbestrol.
A subgroup from a National Institute of Environmental Health Sciences, workshop concerned with characterizing the effects of endocrine disruptors on human health at environmental exposure levels considered the question, If diethylstilbestrol (DES) were introduced into the market for human use today and likely to result in low-dose exposure of the human fetus, what would be required to assess risk? On the basis of an analysis of the quality of data on human DES exposure, the critical times and doses for inducing genital tract malformations and cancer must be determined. This would be facilitated through analysis of the ontogeny of estrogen receptor expression in the developing human genital tract. Models of low-dose estrogenic effects will have to be developed for human and rodent genital tract development. Mouse models offer many advantages over other potential animal models because of the wealth of the earlier literature, the availability of sensitive end points, the availability of mutant lines, and the possibility of generating genetically engineered model systems. Through multidisciplinary approaches, it should be possible to elucidate the cellular and molecular mechanisms of endocrine disruption elicited by estrogens during development and facilitate an assessment of risk to humans
Ovarian Transcriptomic Analyses in the Urban Human Health Pest, the Western Black Widow Spider
Due to their abundance and ability to invade diverse environments, many arthropods have become pests of economic and health concern, especially in urban areas. Transcriptomic analyses of arthropod ovaries have provided insight into life history variation and fecundity, yet there are few studies in spiders despite their diversity within arthropods. Here, we generated a de novo ovarian transcriptome from 10 individuals of the western black widow spider (Latrodectus hesperus), a human health pest of high abundance in urban areas, to conduct comparative ovarian transcriptomic analyses. Biological processes enriched for metabolism—specifically purine, and thiamine metabolic pathways linked to oocyte development—were significantly abundant in L. hesperus. Functional and pathway annotations revealed overlap among diverse arachnid ovarian transcriptomes for highly-conserved genes and those linked to fecundity, such as oocyte maturation in vitellogenin and vitelline membrane outer layer proteins, hormones, and hormone receptors required for ovary development, and regulation of fertility-related genes. Comparative studies across arachnids are greatly needed to understand the evolutionary similarities of the spider ovary, and here, the identification of ovarian proteins in L. hesperus provides potential for understanding how increased fecundity is linked to the success of this urban pest
Professionalism, golf coaching and a master of science degree
A distinction can be made between 'professionalisation', which is concerned with occupational status and standing, and 'professionalism,' which refers to matters of quality and standards of practice (especially specialized knowledge, ethics and altruism). The purpose of this stimulus article is to present key features of contemporary medical professionalism as a basis for critically reflecting on discourse associated with Tiger Woods' current coach, Sean Foley. It is suggested that that provision of a Master of Science degree in golf teaching/coaching would facilitate the development of 'professionalism' in golf coaches
Rubber friction: role of the flash temperature
When a rubber block is sliding on a hard rough substrate, the substrate
asperities will exert time-dependent deformations of the rubber surface
resulting in viscoelastic energy dissipation in the rubber, which gives a
contribution to the sliding friction. Most surfaces of solids have roughness on
many different length scales, and when calculating the friction force it is
necessary to include the viscoelastic deformations on all length scales. The
energy dissipation will result in local heating of the rubber. Since the
viscoelastic properties of rubber-like materials are extremely strongly
temperature dependent, it is necessary to include the local temperature
increase in the analysis. At very low sliding velocity the temperature increase
is negligible because of heat diffusion, but already for velocities of order
0.01 m/s the local heating may be very important. Here I study the influence of
the local heating on the rubber friction, and I show that in a typical case the
temperature increase results in a decrease in rubber friction with increasing
sliding velocity for v > 0.01 m/s. This may result in stick-slip instabilities,
and is of crucial importance in many practical applications, e.g., for the
tire-road friction, and in particular for ABS-breaking systems.Comment: 22 pages, 27 figure
Causes and Mitigation of Fuel Pilot Operated Valve Pilot Seal Extrusion in Space Shuttle Orbiter Primary RCS Thrusters
Extrusion of a polytetrafluoroethylene (PTFE) pilot seal located in the Space Shuttle Orbiter Primary Reaction Control Subsystem (PRCS) thruster fuel valve has been implicated in 68 ground and on-orbit fuel valve failures. A rash of six extrusion-related in-flight anomalies over a six-mission span from December 2001 to October 2002 led to heightened activity at various NASA centers, and the formation of a multidisciplinary team to solve the problem. Empirical and theoretical approaches were used. For example, thermomechanical analysis (TMA) and exposure tests showed that some extrusion is produced by thermal cycling; however, a review of thruster service histories did not reveal a strong link between thermal cycling and extrusion. Calculations showed that the amount of observed extrusion often exceeded the amount allowed by thermally-induced stress relief. Failure analysis of failed hardware also revealed the presence of fuel-oxidizer reaction product (FORP) inside the fuel valve pilot seal cavity, and differential scanning calorimetry (DSC) showed that the FORP was intimately associated with the pilot seal material. Component-level exposure tests showed that FORP of similar composition could be produced by adjacent oxidizer valve leakage in the absence of thruster firing. Specific gravity data showed that extruded fuel valve pilot seals were less dense than new pilot seals or oxidizer valve pilot seals, indicating permanent modification of the PTFE occurred during service. It is concluded that some thermally-induced extrusion is unavoidable; however, oxidizer leakage-induced extrusion is mostly avoidable and can be mitigated. Several engineering level mitigation strategies are discussed
Progress in Absorber R&D for Muon Cooling
A stored-muon-beam neutrino factory may require transverse ionization cooling
of the muon beam. We describe recent progress in research and development on
energy absorbers for muon-beam cooling carried out by a collaboration of
university and laboratory groups.Comment: 7 pages, 1 figure, presented at the 3rd International Workshop on
Neutrino Factory Based on Muon Storage Rings (NuFACT'01), May 24-30, 2001,
Tsukuba, Japa
Spin transfer in an antiferromagnet
An electrical current can transfer spin angular momentum to a ferromagnet.
This novel physical phenomenon, called spin transfer, offers unprecedented
spatial and temporal control over the magnetic state of a ferromagnet and has
tremendous potential in a broad range of technologies, including magnetic
memory and recording. Recently, it has been predicted that spin transfer is not
limited to ferromagnets, but can also occur in antiferromagnetic materials and
even be stronger under some conditions. In this paper we demonstrate transfer
of spin angular momentum across an interface between ferromagnetic and
antiferromagnetic metals. The spin transfer is mediated by an electrical
current of high density (~10^12 A/m^2) and revealed by variation in the
exchange bias at the ferromagnet/antiferromagnet interface. We find that,
depending on the polarity of the electrical current flowing across the
interface, the strength of the exchange bias can either increase or decrease.
This finding is explained by the theoretical prediction that a spin polarized
current generates a torque on magnetic moments in the antiferromagnet.
Current-mediated variation of exchange bias can be used to control the magnetic
state of spin-valve devices, e.g., in magnetic memory applications.Comment: 5 pages, 3 figure
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