Influence Of Current Leads On Critical Current For Spin Precession In Magnetic Multilayers

In magnetic multilayers, a dc current induces a spin precession above a certain critical current. Drive torques responsible for this can be calculated from the spin accumulation $\bar{\Delta\mu}$. Existing calculations of $\bar{\Delta\mu}$ assume a uniform cross section of conductors. But most multilayer samples are pillars with current leads flaring out immediately to a much wider cross-section area than that of the pillar itself. We write spin-diffusion equations of a form valid for variable cross section, and solve the case of flat electrodes with radial current distribution perpendicular to the axis of the pillar. Because of the increased volume available for conduction-electron spin relaxation in such leads, $\bar{\Delta\mu}$ is reduced in the pillar by at least a factor of 2 below its value for uniform cross section, for given current density in the pillar. Also, $\bar{\Delta\mu}$ and the critical current density for spin precession become nearly independent of the thickness of the pinned magnetic layer, and more dependent on the thickness of the spacer, in better agreement with measurements by Albert et al. (2002).Comment: To appear in J. Magn. Magn. Mate

Extended direct lysis method for virus detection on berries including droplet digital RT-PCR or real time RT-PCR with reduced influence from inhibitors

Detection of viruses on berries is a challenging task, often hampered by the presence of RT-qPCR inhibiting substances from berry juice. A direct extraction method for virus detection (murine norovirus and GA phage) on frozen raspberries was previously published. We expanded (different types of berries and viruses) and improved the method using MobiSpin S400 columns that filter nucleic acids based on size-exclusion chromatography. While no inhibition was detected in filtered RNA, unfiltered RNA needed from 1:2 to more than 1:8 dilution in order to remove inhibition. The modified method gave recoveries of bovine norovirus around 40.8 ± 4.5% (40.0 ± 7.0%), 48.0 ± 26.0% (50.5 ± 7.8%), 28.3 ± 2.6% (45.8 ± 6.6%) from frozen (fresh) raspberries, strawberries and blueberries, respectively. For the same samples, recoveries of hepatitis A virus were 34.0 ± 5.9% (34.0 ± 6.0%), 40.0 ± 13.3% (34.2 ± 10.5%) and 23.0 ± 6.8% (31.5 ± 7.9%). For adenovirus40 (DNA virus), recoveries were 21.2 ± 8.6%, 16.0 ± 3.2% and 5.7 ± 0.2% from fresh raspberries, strawberries and blueberries respectively and column filtration did not add any improved effect. The modified method is effective and timesaving for detection of viral RNA from both fresh and frozen berries. As an emerging detection and direct quantification method, droplet digital RT-PCR was compared to RT-qPCR and was much less influenced by inhibitors when detecting mengovirus in unfiltered RNA from berries. However, for low levels of pure RNA, RT-qPCR showed slightly higher sensitivity and more stable results

Spin transfer switching of spin valve nanopillars using nanosecond pulsed currents

Spin valve nanopillars are reversed via the mechanism of spin momentum transfer using current pulses applied perpendicular to the film plane of the device. The applied pulses were varied in amplitude from 1.8 mA to 7.8 mA, and varied in duration within the range of 100 ps to 200 ns. The probability of device reversal is measured as a function of the pulse duration for each pulse amplitude. The reciprocal pulse duration required for 95% reversal probability is linearly related to the pulse current amplitude for currents exceeding 1.9 mA. For this device, 1.9 mA marks the crossover between dynamic reversal at larger currents and reversal by thermal activation for smaller currents

Raw fabric hardware implementation and characterization

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (p. 109-110).The Raw architecture is scalable, improving performance not by pushing the limits of clock frequency, but by spreading computation across numerous simple, replicated tiles. The first Raw processors fabricated have 16 RISC processor tiles that share the workload. The Raw Fabric system extends Raw's scalability by weaving together multiple 16-tile Raw processors. The Raw Fabric is a modular and scalable system comprised of two board types: one to house 4 Raw processors (Processor board) and one to handle communications (I/O board). The design is modular because it breaks down the system into smaller parts, and it is scalable because these modules may be combined to create large Fabrics. The ultimate goal is to produce a Raw Fabric with 16 Processor boards (equivalently, 64 Raw processors or 1024 tiles), though the current largest Fabric system includes one Processor board and 3 I/O boards. This thesis walks through the important design and implementation challenges and documents how they were solved. The most basic challenge faced was to design a system flexible enough to accommodate a variety of Fabric sizes.(cont.) Next, the distribution of vital signals such as power and clock provides a problem unique to the Fabric system because of the possible size of the final product. Finally, the astounding number of signal wires running between boards presents a unique challenge in finding parts and designing the mechanical aspects. The intent of this thesis is to provide the reader with an idea of the considerations necessary for designing and implementing a system of this magnitude and level of flexibility.by Albert Sun.M.Eng

Current-driven excitations in magnetic multilayers: a brief review

In 1996, Berger and Slonczewski independently predicted that a large enough spin-polarized dc current density sent perpendicularly through a ferromagnetic layer could produce magnetic excitations (spin-waves) or reversal of magnetization (switching). In the past few years, both current-driven switching and current-driven excitation of spin-waves have been observed. The switching is of potential technological interest for direct 'writing' of magnetic random access memory (MRAM) or magnetic media. The spin-wave generation could provide a new source of dc generated microwave radiation. We describe what has been learned experimentally about these two related phenomena, and some models being tested to explain these observations.Comment: 5 pages, 7 figures, expected to appear in conf. proceeding

Quantum de Sitter horizon entropy from quasicanonical bulk, edge, sphere and topological string partition functions

Motivated by the prospect of constraining microscopic models, we calculate the exact one-loop corrected de Sitter entropy (the logarithm of the sphere partition function) for every effective field theory of quantum gravity, with particles in arbitrary spin representations. In doing so, we universally relate the sphere partition function to the quotient of a quasi-canonical bulk and a Euclidean edge partition function, given by integrals of characters encoding the bulk and edge spectrum of the observable universe. Expanding the bulk character splits the bulk (entanglement) entropy into quasinormal mode (quasiqubit) contributions. For 3D higher-spin gravity formulated as an sl($n$) Chern-Simons theory, we obtain all-loop exact results. Further to this, we show that the theory has an exponentially large landscape of de Sitter vacua with quantum entropy given by the absolute value squared of a topological string partition function. For generic higher-spin gravity, the formalism succinctly relates dS, AdS$^\pm$ and conformal results. Holography is exhibited in quasi-exact bulk-edge cancelation.Comment: 9 + 47 + N page

Effects of Qigong on Depression: A Systemic Review

Physical exercises and relaxation have been found to be beneficial for depression. However, there is little evidence on the use of Qigong, a mind-body practice integrating gentle exercise and relaxation, in the management of depression. The aim of this paper is to evaluate the effects of Qigong on depression. The paper examined clinical trials measuring the effect of Qigong on depression within six large-scale medical research databases (PubMed, Medline, ProQuest, Science Direct, EMBASE, and PsycInfo) till October 2011. Key words “Qigong,” “depression,” and “mood” were used. Ten studies were identified as original randomized controlled trial (RCT) studies investigating the effect of Qigong on depression as primary (n = 2) or secondary outcome (n = 8). Four studies reported positive results of the Qigong treatment on depression; two reported that Qigong effect on depression was as effective as physical exercise. One study reported that Qigong was comparable to a conventional rehabilitation program, but the remaining three studies found no benefits of Qigong on depression. While the evidence suggests the potential effects of Qigong in the treatment of depression, the review of the literature shows inconclusive results. Further research using rigorous study designs is necessary to investigate the effectiveness of Qigong in depression

Low energy laser light (632.8 nm) suppresses amyloid-β peptide-induced oxidative and inflammatory responses in astrocytes

Oxidative stress and inflammation are important processes in the progression of Alzheimer's disease (AD). Recent studies have implicated the role of amyloid β-peptides (Aβ) in mediating these processes. In astrocytes, oligomeric Aβ induces the assembly of NADPH oxidase complexes resulting in its activation to produce anionic superoxide. Aβ also promotes production of pro-inflammatory factors in astrocytes. Since low energy laser has previously been reported to attenuate oxidative stress and inflammation in biological systems, the objective of this study was to examine whether this type of laser light was able to abrogate the oxidative and inflammatory responses induced by Aβ. Primary rat astrocytes were exposed to Helium-Neon laser (λ=632.8 nm), followed by the treatment with oligomeric Aβ. Primary rat astrocytes were used to measure Aβ-induced production of superoxide anions using fluorescence microscopy of dihydroethidium (DHE), assembly of NADPH oxidase subunits by the colocalization between the cytosolic p47phox subunit and the membrane gp91phox subunit using fluorescent confocal microscopy, phosphorylation of cytosolic phospholipase A2 (cPLA2), and expressions of pro-inflammatory factors including interleukin-1β (IL-1β) and inducible nitric-oxide synthase (iNOS) using Western blot Analysis. Our data showed that laser light at 632.8 nm suppressed Aβ-induced superoxide production, colocalization between NADPH oxidase gp91phox and p47phox subunits, phosphorylation of cPLA2, and the expressions of IL-1β and iNOS in primary astrocytes. We demonstrated for the first time that 632.8 nm laser was capable of suppressing cellular pathways of oxidative stress and inflammatory responses critical in the pathogenesis in AD. This study should prove to provide the groundwork for further investigations for the potential use of laser therapy as a treatment for AD

Magnetization reversal by injection and transfer of spin: experiments and theory

Reversing the magnetization of a ferromagnet by spin transfer from a current, rather than by applying a magnetic field, is the central idea of an extensive current research. After a review of our experiments of current-induced magnetization reversal in Co/Cu/Co trilayered pillars, we present the model we have worked out for the calculation of the current-induced torque and the interpretation of the experiments

Improvement of the robustness on geographical networks by adding shortcuts

In a topological structure affected by geographical constraints on liking, the connectivity is weakened by constructing local stubs with small cycles, a something of randomness to bridge them is crucial for the robust network design. In this paper, we numerically investigate the effects of adding shortcuts on the robustness in geographical scale-free network models under a similar degree distribution to the original one. We show that a small fraction of shortcuts is highly contribute to improve the tolerance of connectivity especially for the intentional attacks on hubs. The improvement is equivalent to the effect by fully rewirings without geographical constraints on linking. Even in the realistic Internet topologies, these effects are virtually examined.Comment: 14 pages, 10 figures, 1 tabl