3,826 research outputs found
Current-induced torques due to compensated antiferromagnets
We analyse the influence of current induced torques on the magnetization
configuration of a ferromagnet in a circuit containing a compensated
antiferromagnet. We argue that these torques are generically non-zero and
support this conclusion with a microscopic NEGF calculation for a circuit
containing antiferromagnetic NiMn and ferromagnetic Co layers. Because of
symmetry dictated differences in the form of the current-induced torque, the
phase diagram which expresses the dependence of ferromagnet configuration on
current and external magnetic field differs qualitatively from its
ferromagnet-only counterpart.Comment: 4 pages, 5 figure
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
Electromagnetic waves in gravitational wave spacetimes
We have considered the propagation of electromagnetic waves in a space-time representing an exact gravitational plane wave and calculated the induced changes on the four-potential field Aμ of a plane electromagnetic wave. By choosing a suitable photon round-trip in a Michelson interferometer, we have been able to identify the physical effects of the exact gravitational wave on the electromagnetic field, i.e. phase shift, change of the polarization vector, angular deflection and delay. These results have been exploited to study the response of an interferometric gravitational wave detector beyond the linear approximation of the general theory of relativity. A much more detailled examination of this problem can be found in our paper recently published in Classical and Quantum Gravity (28 (2011) 235007)
Modeling the impact of zooplankton diel vertical migration on the carbon export flux of the biological pump
Author Posting. © American Geophysical Union, 2010. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 33(2), (2019): 181-199. doi:10.1029/2018GB005983.One pathway of the biological pump that remains largely unquantified in many export models is the active transport of carbon from the surface ocean to the mesopelagic by zooplankton diel vertical migration (DVM). Here, we develop a simple representation of zooplankton DVM and implement it in a global export model as a thought experiment to illustrate the effects of DVM on carbon export and mesopelagic biogeochemistry. The model is driven by diagnostic satellite measurements of net primary production, algal biomass, and phytoplankton size structure. Due to constraints on available satellite data, the results are restricted to the latitude range from 60°N to 60°S. The modeled global export flux from the base of the euphotic zone was 6.5 PgC/year, which represents a 14% increase over the export flux in model runs without DVM. The mean (± standard deviation, SD) proportional contribution of the DVM‐mediated export flux to total carbon export, averaged over the global domain and the climatological seasonal cycle, was 0.16 ± 0.04 and the proportional contribution of DVM activity to total respiration within the twilight zone was 0.16 ± 0.06. Adding DVM activity to the model also resulted in a deep local maximum in the oxygen utilization profile. The model results were most sensitive to the assumptions for the fraction of individuals participating in DVM, the fraction of fecal pellets produced in the euphotic zone, and the fraction of grazed carbon that is metabolized.Support for this work came from the National Science Foundation (OCE‐1434000 and OCE‐1657803) and the National Aeronautics and Space Administration (NASA) as part of the EXport Processes in the global Ocean from RemoTe Sensing (EXPORTS) field campaign (grant 80NSSC17K0692) and the North Atlantic Aerosol and Marine Ecosystems Study (NAAMES, grants NNX15AE72G and 80NSSC18K0018). The satellite data used as drivers for the model are available as supporting information. The World Ocean Atlas data (World Ocean Atlas 2009, Annual Climatology, 1 degree, Temperature, Salinity, Oxygen) containing temperature and oxygen measurements can be downloaded from the ERDAPP data server (https://coastwatch.pfeg.noaa.gov/erddap/index.html).2019-07-1
Control of Silica Dust in Slate Milling Operations
The Mine Safety and Health Administration (MSHA) conducted a study to assess the present state of technology used for controlling employees\u27 respirable silica-bearing dust exposures during dimension slate milling operations. For this study, twelve slate milling operations were visited and various measurements were taken and observations made. These measurements and observations included exhaust and room airflow, types of enclosures, water usage, and building volumes for each of the milling processes. These mills usually employed between five and twenty people. From the study, general guidelines were developed from the best practices observed and can be used at the various sawing, splitting, trimming, and drilling operations throughout the industry
Observation and Modeling of Source Effects in Coda Wave Interferometry at Pavlof Volcano
We examine seismic records of repeating explosions from Pavlof volcano, Alaska, during its 2007 eruption. Repetitive explosions are typical of Strombolian-style eruptions and allow measurement of relative time shifts between similar late-arriving phases using the technique called coda wave interferometry (Snieder et al., 2002). The measurements enable the detection of small changes in the volcanic interior of Pavlof. We are able to resolve an increase in the relative traveltime change of late-arriving seismic waves on the order of 0.3% over the course of two weeks. Based on the spectra of the explosions, their location inside the magma conduit, previous studies of Pavlof volcano, and 3D seismic modeling, we argue the most likely scenario is one in which the velocity and/or the geometry of the conduit changes. This demonstrates the sensitivity of coda wave interferometry to source effects, in addition to path effects, at volcanoes
Sustainable Water Management in the Southwestern United States: Reality or Rhetoric?
Background: While freshwater sustainability is generally defined as the provisioning of water for both people and the environment, in practice it is largely focused only on supplying water to furnish human population growth. Symptomatic of this is the state of Arizona, where rapid growth outside of the metropolitan Phoenix-Tucson corridor relies on the same groundwater that supplies year-round flow in rivers. Using Arizona as a case study, we present the first study in the southwestern United States that evaluates the potential impact of future population growth and water demand on streamflow depletion across multiple watersheds. Methodology/Principal Findings: We modeled population growth and water demand through 2050 and used four scenarios to explore the potential effects of alternative growth and water management strategies on river flows. Under the base population projection, we found that rivers in seven of the 18 study watersheds could be dewatered due to municipal demand. Implementing alternative growth and water management strategies, however, could prevent four of these rivers from being dewatered. Conclusions/Significance: The window of opportunity to implement water management strategies is narrowing. Because impacts from groundwater extraction are cumulative and cannot be immediately reversed, proactive water management strategies should be implemented where groundwater will be used to support new municipal demand. Our approach provides a low-cost method to identify where alternative water and growth management strategies may have the most impact, and demonstrates that such strategies can maintain a continued water supply for both people and the environment
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The quality of political information
The article conceptualizes the quality of political information and shows how the concept can be used for empirical research. I distinguish three aspects of quality (intelligibility, relevance, validity) and use them to judge the constituent foundations of political information, that is component claims (statements of alleged facts) and connection claims (argumentative statements created by causally linking two component claims). The resulting conceptual map thus entails six manifestations of information quality (component claimintelligibility, connection claim intelligibility, component claimrelevance, connection claim relevance, component claim validity, and connection claim validity). I explain how the conceptual map can be used to make sense of the eclectic variety of existing research, and how it can advance new empirical research, as a guide for determining variation in information quality, as a conceptual template for the analysis of different types of political messages and their common quality deficiencies, and as a generator of new research questions and theoretical expectations
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