Spin-torque switching and control using chirped oscillating currents

We propose to use oscillating spin currents with slowly varying frequency (chirp) to manipulate and control the magnetization dynamics in a nanomagnet. By recasting the Landau-Lifshitz-Slonczewski equation in a quantum-like two-level formalism, we show that a chirped spin current polarized in the direction normal to the anisotropy axis can induce a stable precession of the magnetic moment at any angle (up to $90^\circ$) with respect to the anisotropy axis. The drive current can be modest ($10^6\,\rm A/cm^2$ or lower) provided the chirp rate is sufficiently slow. The induced precession is stable against thermal noise, even for small nano-objects at room temperature. Complete reversal of the magnetization can be achieved by adding a small external magnetic field antiparallel to the easy axis. Alternatively, a combination of chirped ac and dc currents with different polarization directions can also be used to trigger the reversal

An Asymptotic Expansion and Recursive Inequalities for the Monomer-Dimer Problem

Let (lambda_d)(p) be the p monomer-dimer entropy on the d-dimensional integer lattice Z^d, where p in [0,1] is the dimer density. We give upper and lower bounds for (lambda_d)(p) in terms of expressions involving (lambda_(d-1))(q). The upper bound is based on a conjecture claiming that the p monomer-dimer entropy of an infinite subset of Z^d is bounded above by (lambda_d)(p). We compute the first three terms in the formal asymptotic expansion of (lambda_d)(p) in powers of 1/d. We prove that the lower asymptotic matching conjecture is satisfied for (lambda_d)(p).Comment: 15 pages, much more about d=1,2,

Asymptotic Expansions for lambda_d of the Dimer and Monomer-Dimer Problems

In the past few years we have derived asymptotic expansions for lambda_d of the dimer problem and lambda_d(p) of the monomer-dimer problem. The many expansions so far computed are collected herein. We shine a light on results in two dimensions inspired by the work of M. E. Fisher. Much of the work reported here was joint with Shmuel Friedland.Comment: 4 page

Transverse "resistance overshoot" in a Si/SiGe two-dimensional electron gas in the quantum Hall effect regime

We investigate the peculiarities of the "overshoot" phenomena in the transverse Hall resistance R_{xy} in Si/SiGe. Near the low magnetic field end of the quantum Hall effect plateaus, when the filling factor \nu approaches an integer i, R_{xy} overshoots the normal plateau value h/ie^2. However, if magnetic field B increases further, R_{xy} decreases to its normal value. It is shown that in the investigated sample n-Si/Si_{0.7}Ge_{0.3}, overshoots exist for almost all \nu. Existence of overshoot in R_{xy} observed in different materials and for different \nu, where splitting of the adjacent Landau bands has different character, hints at the common origin of this effect. Comparison of the experimental curves R_{xy}(\nu) for \nu = 3 and \nu = 5 with and without overshoot showed that this effect exist in the whole interval between plateaus, not only in the region where R_{xy} exceeds the normal plateau value.Comment: 3 pages, 5 EPS figure

Mycobacterium tuberculosis-infected human monocytes down-regulate microglial MMP-2 secretion in CNS tuberculosis via TNFα, NFκB, p38 and caspase 8 dependent pathways

Tuberculosis (TB) of the central nervous system (CNS) is a deadly disease characterized by extensive tissue destruction, driven by molecules such as Matrix Metalloproteinase-2 (MMP-2) which targets CNS-specific substrates. In a simplified cellular model of CNS TB, we demonstrated that conditioned medium from Mycobacterium tuberculosis-infected primary human monocytes (CoMTb), but not direct infection, unexpectedly down-regulates constitutive microglial MMP-2 gene expression and secretion by 72.8% at 24 hours, sustained up to 96 hours (P < 0.01), dependent upon TNF-α. In human CNS TB brain biopsies but not controls the p38 pathway was activated in microglia/macrophages. Inhibition of the p38 MAP kinase pathway resulted in a 228% increase in MMP-2 secretion (P < 0.01). In contrast ERK MAP kinase inhibition further decreased MMP-2 secretion by 76.6% (P < 0.05). Inhibition of the NFκB pathway resulted in 301% higher MMP-2 secretion than CoMTb alone (P < 0.01). Caspase 8 restored MMP-2 secretion to basal levels. However, this caspase-dependent regulation of MMP-2 was independent of p38 and NFκB pathways; p38 phosphorylation was increased and p50/p65 NFκB nuclear trafficking unaffected by caspase 8 inhibition. In summary, suppression of microglial MMP-2 secretion by M.tb-infected monocyte-dependent networks paradoxically involves the pro-inflammatory mediators TNF-α, p38 MAP kinase and NFκB in addition to a novel caspase 8-dependent pathway

Sexual Risk Behaviour among HIV-Positive Individuals in Clinical Care in Urban KwaZulu-Natal, South Africa

Objectives: To assess the prevalence and predictors of unprotected sex among HIV+ individuals in clinical care in urban KwaZulu-Natal, South Africa. Design: Cross-sectional survey of 152 HIV+ individuals attending a hospital-based HIV-clinic. Methods: Structured interviews were conducted by bilingual interviewers. Sexual risk behaviour in the preceding 3 months was assessed via event counts. Results: In one of the first studies of its kind in South Africa we found that nearly half of the sample reported vaginal or anal sex during the preceding 3 months, and 30% of these patients reported unprotected vaginal or anal sex. Among sexually active patients, a total of 171 unprotected sex events were reported, 40% of which were with partners perceived to be HIV negative or HIV-status unknown. Nine such partners were potentially exposed to HIV. Alcohol use during sex, being forced to have sex, sex with a perceived HIV+ partner, and sex with a casual partner predicted more unprotected sex, whereas HIV-status disclosure was related to less unprotected sex. Conclusions: HIV+ individuals in clinical care in South Africa may engage in unprotected sex that place others at risk of HIV infection and themselves at risk for infection with STIs. With a national ARV rollout currently underway in South Africa, increasing numbers of HIV+ individuals are entering care. This affords a crucial opportunity to link HIV prevention with HIV care, an approach that aims to reduce transmission risk behaviour among HIV+ individuals and is consistent with international agencies’ current prevention priorities

A Second Giant Planet in 3:2 Mean-Motion Resonance in the HD 204313 System

We present 8 years of high-precision radial velocity (RV) data for HD 204313 from the 2.7 m Harlan J. Smith Telescope at McDonald Observatory. The star is known to have a giant planet (M sin i = 3.5 M_J) on a ~1900-day orbit, and a Neptune-mass planet at 0.2 AU. Using our own data in combination with the published CORALIE RVs of Segransan et al. (2010), we discover an outer Jovian (M sin i = 1.6 M_J) planet with P ~ 2800 days. Our orbital fit suggests the planets are in a 3:2 mean motion resonance, which would potentially affect their stability. We perform a detailed stability analysis, and verify the planets must be in resonance.Comment: Accepted for publication in Ap

Evaluation of the informed consent process for male circumcision scale-up in Zambia

This report evaluates the informed consent process for male circumcision conducted through the Male Circumcision Partnership for Zambia, led by Population Services International (Society for Family Health, Zambia), in partnership with Jhpiego, Marie Stopes International, and the Population Council. The objectives of the study were to assess male circumcision clients\u27 comprehension of the informed consent process, examine social norms and practices regarding informed consent for adolescents, compare clients\u27 expectations and experiences, and make additional recommendations for improving the informed consent process

Evaluation of the informed consent process for male circumcision scale-up in Swaziland

This report evaluates the informed consent process for male circumcision conducted through the Male Circumcision Partnership for Swaziland, led by Population Services International, in partnership with Jhpiego, Marie Stopes International, and the Population Council. The study assesses participants\u27 comprehension of the circumcision process, the informed consent process, as well as the affect of male circumcision counseling on their experience