130,937 research outputs found
Enhanced spin transfer torque effect for transverse domain walls in cylindrical nanowires
No full textRecent studies have predicted extraordinary properties for transverse domain walls in cylindrical nanowires: zero depinning current, the absence of the Walker breakdown, and applications as domain wall oscillators. In order to reliably control the domain wall motion, it is important to understand how they interact with pinning centers, which may be engineered, for example, through modulations in the nanowire geometry (such as notches or extrusions) or in the magnetic properties of the material. In this paper we study the motion and depinning of transverse domain walls through pinning centers in ferromagnetic cylindrical nanowires. We use (i) magnetic fields and (ii) spin-polarized currents to drive the domain walls along the wire. The pinning centers are modelled as a section of the nanowire which exhibits a uniaxial crystal anisotropy where the anisotropy easy axis and the wire axis enclose a variable angle ?P. Using (i) magnetic fields, we find that the minimum and the maximum fields required to push the domain wall through the pinning center differ by 30%. On the contrary, using (ii) spin-polarized currents, we find variations of a factor 130 between the minimum value of the depinning current density (observed for ?P=0?, i.e., anisotropy axis pointing parallel to the wire axis) and the maximum value (for ?P=90?, i.e., anisotropy axis perpendicular to the wire axis). We study the depinning current density as a function of the height of the energy barrier of the pinning center using numerical and analytical methods. We find that for an industry standard energy barrier of 40 kBT, a depinning current of about 5 ?A (corresponding to a current density of 6×1010 A/m2 in a nanowire of 10 nm diameter) is sufficient to depin the domain wall. We reveal and explain the mechanism that leads to these unusually low depinning currents. One requirement for this depinning mechanism is for the domain wall to be able to rotate around its own axis. With the right barrier design, the spin torque transfer term is acting exactly against the damping in the micromagnetic system, and thus the low current density is sufficient to accumulate enough energy quickly. These key insights may be crucial in furthering the development of novel memory technologies, such as the racetrack memory, that can be controlled through low current densities.<br/
EFFECTIVENESS OF TIAMULIN IN DRINKING WATER FOR TREATMENT AND CONTROL OF PORCINE PROLIFERATIVE ENTEROPATHY (ILEITIS) DUE TO LAWSONIA INTRACELLULARlS INFECTION
No full textWalter, D.; Knittel, J.; Schwartz, K.; Kroll, J.; Roof, M.. (2000). EFFECTIVENESS OF TIAMULIN IN DRINKING WATER FOR TREATMENT AND CONTROL OF PORCINE PROLIFERATIVE ENTEROPATHY (ILEITIS) DUE TO LAWSONIA INTRACELLULARlS INFECTION. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/161156
Participation of Rotational Motion in Vibrational Relaxation of Molecules in Condensed Media
No full textReducing Petroleum Consumption from Transportation
No full texthttp://web.mit.edu/ceepr/www/publications/workingpapers.htmlThe United States consumed more petroleum-based liquid fuel per capita than any other OECD- high-income country- 30 percent more than the second-highest country (Canada) and 40 percent more than the third-highest (Luxemburg). This paper examines the main channels through which reductions in U.S. oil consumption might take place: (a) increased fuel economy of existing vehicles, (b) increased use of non-petroleum-based low-carbon fuels, (c) alternatives to the internal combustion engine, and (d) reduced vehicles miles travelled. I then discuss how the policies for reducing petroleum consumption used in the US compare with the standard economics prescription for using a Pigouvian tax to deal with externalities. Taking into account that energy taxes are a political hot button in the United States, and also considering some evidence that consumers may not correctly value fuel economy, I offer some thoughts about the margins on which policy aimed at reducing petroleum consumption might usefully proceed
Micromagnetic studies of three-dimensional pyramidal shell-structures
Get PDFIn this article we present a systematic, numerical analysis of the magnetic properties of pyramidal-shaped core-shell structures in a size range below 400nm.These are three dimensional structures consisting of a ferromagnetic shell which is grown on top of a non-magnetic core. The standard micromagnetic model without themagnetocrystalline anisotropy term is used to describe the properties of the shell. We vary the thickness of the shell between the limiting cases of an ultra thin shell and a conventional pyramid and delineate different stable magnetic configurations. We find different kinds of single domain states, which predominantly occur at smaller systemsizes. In analogy to equivalent states in thin square films we term these onion, flower, C, and S state. At larger system sizes we also observe two types of vortex states, which we refer to as symmetric and asymmetric vortex state. For a classification of the observed states, we derive a phase diagram which specifies the magnetic ground state as a function of structure size and shell thickness. The transitions between different ground states can be understood qualitatively. We address the issue ofmetastability by investigating the stability of all occurring configurations for different shell thicknesses. For selected geometries and directions hysteresis measurements are analysed and discussed. We observe that the magnetic behaviour changes distinctively in the limit of ultra-thin shells. The study has been motivated by the recent progress made in the growth of faceted core-shell structures
Effect of Temperature and Quencher Concentration on Vibrational Relaxation in Condensed Media
No full textMeSH term explosion and author rank improve expert recommendations
Get PDFInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
Get PDFBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
- …
