Equatorial and related non-equilibrium states in magnetization dynamics of ferromagnets: Generalization of Suhl's spin-wave instabilities

We investigate the nonlinear dynamics underlying the evolution of a 2-D nanoscale ferromagnetic film with uniaxial anisotropy in the presence of perpendicular pumping. Considering the associated Landau-Lifshitz spin evolution equation with Gilbert damping together with Maxwell equation for the demagnetization field, we study the dynamics in terms of the stereographic variable. We identify several new fixed points for suitable choice of external field in a rotating frame of reference. In particular, we identify explicit equatorial and related fixed points of the spin vector in the plane transverse to the anisotropy axis when the pumping frequency coincides with the amplitude of the static parallel field. We then study the linear stability of these novel fixed points under homogeneous and spin wave perturbations and obtain a generalized Suhl's instability criterion, giving the condition for exponential growth of P-modes under spin wave perturbations. Two parameter phase diagrams (in terms of amplitudes of static parallel and oscillatory perpendicular magnetic fields) for stability are obtained, which differ qualitatively from those for the conventional ferromagnetic resonance near thermal equilibrium and are amenable to experimental tests.Comment: 23 pages, 5 figures, To appear in Physica

Origin of four-fold anisotropy in square lattices of circular ferromagnetic dots

We discuss the four-fold anisotropy of in-plane ferromagnetic resonance (FMR) field $H_r$, found in a square lattice of circular Permalloy dots when the interdot distance $a$ gets comparable to the dot diameter $d$. The minimum $H_r$, along the lattice $$axes, and the maximum, along the$$ axes, differ by $\sim$ 50 Oe at $a/d$ = 1.1. This anisotropy, not expected in uniformly magnetized dots, is explained by a non-uniform magnetization \bm(\br) in a dot in response to dipolar forces in the patterned magnetic structure. It is well described by an iterative solution of a continuous variational procedure.Comment: 4 pages, 3 figures, revtex, details of analytic calculation and new references are adde

Bias with respect to socioeconomic status: A closer look at zip code matching in a pneumococcal vaccine effectiveness study

In 2010, 13-valent pneumococcal conjugate vaccine (PCV13) was introduced in the US for prevention of invasive pneumococcal disease in children. Individual-level socioeconomic status (SES) is a potential confounder of the estimated effectiveness of PCV13 and is often controlled for in observational studies using zip code as a proxy. We assessed the utility of zip code matching for control of SES in a post-licensure evaluation of the effectiveness of PCV13 (calculated as [1-matched odds ratio]*100). We used a directed acyclic graph to identify subsets of confounders and collected SES variables from birth certificates, geocoding, a parent interview, and follow-up with medical providers. Cases tended to be more affluent than eligible controls (for example, 48.3% of cases had private insurance vs. 44.6% of eligible controls), but less affluent than enrolled controls (52.9% of whom had private insurance). Control of confounding subsets, however, did not result in a meaningful change in estimated vaccine effectiveness (original estimate: 85.1%, 95% CI 74.8–91.9%; adjusted estimate: 82.5%, 95% CI 65.6–91.1%). In the context of a post-licensure vaccine effectiveness study, zip code appears to be an adequate, though not perfect, proxy for individual SES

Probing domain wall structures in Co(0001) thin films using ferromagnetic resonance

By exploiting different pumping field configurations in ferromagnetic resonance (FMR) experiments, four new modes are found in the FMR excitation spectrum for the magnetic stripe domain structure in epitaxial Co(0001) thin films. These modes provide evidence for the two-dimensional domain wall profile consisting of Bloch wall sections in the film center as well as large flux closure caps at the film surface

Controlled phase shifts in interlayer magnetic coupling with the doping of the magnetic layer

We report the first observation of a strong change in the phase (up to 360 degrees) of the interlayer magnetic exchange coupling in Co/Ru/Co and Co/Cu/Co trilayer system which is controlled by the addition of small amounts of Ag (up to 8%) to the Co layers. The phase shifts may be due to modifications of magnetic-film spin-dependent potentials which control conduction electron contributions to the interlayer coupling. In addition, a strong additive antiparallel bias to the interlayer magnetic exchange coupling in Co/Ru/Co trilayers is observed, indicating a possible additive superexchange interaction

THE EFFECTS OF GRUNTING ON VERTICAL JUMP IN RECREATIONAL BASKETBALL PLAYERS

K. Bryson, C. Peach, W. Wigen, S. Cool, W.M. Silvers Whitworth University, Spokane, WA Grunting effects on muscle force output (MFO) has been examined for sports, such as tennis, mixed martial arts (MMA), and powerlifting. Grunting may increase vertical jump (VJ) height, which is a standard measurement of MFO for the lower extremities. Grunting during a VJ may benefit the overall performance of recreational basketball players. PURPOSE: The purpose of this research study was to investigate the effects of grunting on VJ height in recreational basketball players. METHODS: Twenty-eight healthy male and female collegiate recreational basketball players, aged 18-25 yr (nm = 22, nf = 6; height: 177.46 ± 3.31 cm, weight: 74.77 ± 12.17 kg, age: 20.85 ± 0.65 yr), participated in the research study. Participants performed two countermovement jump (CMJ) trials, with and without grunting, to measure VJ height. The highest jump was recorded for analysis. Participants warmed up with a dynamic warm-up protocol prior to each trial and rested for 10 min between trials. A dependent groups t-test (significance level p ≤ 0.05) was utilized to determine the existence of significant differences between experimental conditions for all dependent variables. RESULTS: No statistical differences were observed between grunting and non-grunting conditions (55.93 ± 14.36 cm v. 55.65 ± 14.34 cm; p = 0.48) for VJ height. Therefore, the research hypothesis that grunting would positively impact VJ was rejected. CONCLUSION: Under these research conditions, grunting did not improve VJ height performance. The primary explanations for the observed results were the inability to distinguish between grunting and non-grunting breathing techniques and the small sample size utilized in the study. No learning effect was evident because the a follow up dependent groups t-test revealed no statistically significant difference between the first and second trial (p = 0.48). Participants should have been grouped by athletic performance because recreational status may have been too broad of a population, as skill level and experience appeared to vary. Future researchers should investigate the effects of grunting with a larger sample size, alternative breathing technique, and standardization of ability between participants