Exact Activation Energy of Magnetic Single Domain Particles

I present the exact analytical expression for the activation energy as a function of externally applied magnetic fields for a single--domain magnetic particle with uniaxial anisotropy (Stoner--Wohlfahrt model), and investigate the scaling behavior of the activation energy close to the switching boundary.Comment: published in 2004, posted here for general accessabilit

Diffuse neutral hydrogen in the HI Parkes All Sky Survey

Observations of neutral hydrogen can provide a wealth of information about the distribution and kinematics of galaxies. To detect HI beyond the ionisation edge of galaxy disks, column density sensitivities have to be achieved that probe the regime of Lyman limit systems. Typically HI observations are limited to a brightness sensitivity of NHI~10^19 cm-2 but this has to be improved by at least an order of magnitude. In this paper, reprocessed data is presented that was originally observed for the HI Parkes All Sky Survey (HIPASS). HIPASS provides complete coverage of the region that has been observed for the Westerbork Virgo Filament HI Survey (WVFS), presented in accompanying papers, and thus is an excellent product for data comparison. The region of interest extends from 8 to 17 hours in right ascension and from -1 to 10 degrees in declination. Although the original HIPASS product already has good flux sensitivity, the sensitivity and noise characteristics can be significantly improved with a different processing method. The newly processed data has an 1sigma RMS flux sensitivity of ~10 mJy beam-1 over 26 km s-1, corresponding to a column density sensitivity of ~3\cdot10^17 cm-2. While the RMS sensitivity is improved by only a modest 20%, the more substantial benefit is in the reduction of spectral artefacts near bright sources by more than an order of magnitude. In the reprocessed region we confirm all previously catalogued HIPASS sources and have identified 29 additional sources of which 14 are completely new HI detections. Extended emission or companions were sought in the nearby environment of each discrete detection. With the improved sensitivity after reprocessing and its large sky coverage, the HIPASS data is a valuable resource for detection of faint HI emission.(Abridged)Comment: 22 pages plus appendix, 6 figures, appendix will only appear in online format. Accepted for publication in A&

Are Newly Discovered HI High Velocity Clouds Minihalos in the Local Group?

A set of HI sources extracted from the north Galactic polar region by the ongoing ALFALFA survey has properties that are consistent with the interpretation that they are associated with isolated minihalos in the outskirts of the Local Group (LG). Unlike objects detected by previous surveys, such as the Compact High Velocity Clouds of Braun & Burton (1999), the HI clouds found by ALFALFA do not violate any structural requirements or halo scaling laws of the LambdaCDM structure paradigm, nor would they have been detected by extant HI surveys of nearby galaxy groups other than the LG. At a distance of d Mpc, their HI masses range between $5 x 10^4 d^2 and 10^6 d^2 solar and their HI radii between <0.4d and 1.6 d kpc. If they are parts of gravitationally bound halos, the total masses would be on order of 10^8--10^9 solar, their baryonic content would be signifcantly smaller than the cosmic fraction of 0.16 and present in a ionized gas phase of mass well exceeding that of the neutral phase. This study does not however prove that the minihalo interpretation is unique. Among possible alternatives would be that the clouds are shreds of the Leading Arm of the Magellanic Stream.Comment: 4 pages, 3 figures, 1 table; to appear Ap.J. Letter

Fatigue and Recovery from Dynamic Contractions in Men and Women Differ for Arm and Leg Muscles

Introduction: Whether there is a gender difference in fatigue and recovery from maximal velocity fatiguing contractions and across muscles is not understood. Methods: Sixteen men and 19 women performed 90 isotonic contractions at maximal voluntary shortening velocity (maximal velocity concentric contractions, MVCC) with the elbow flexor and knee extensor muscles (separate days) at a load equivalent to 20% maximal voluntary isometric contraction (MVIC). Results: Power (from MVCCs) decreased similarly for men and women for both muscles (P \u3e 0.05). Men and women had similar declines in MVIC of elbow flexors, but men had greater reductions in knee extensor MVIC force and MVIC electromyogram activity than women (P \u3c 0.05). The decline in MVIC and power was greater, and force recovery was slower for the elbow flexors compared with knee extensors. Conclusions: The gender difference in muscle fatigue often observed during isometric tasks was diminished during fast dynamic contractions for upper and lower limb muscles

Luminous and Dark Matter in the Milky Way

(Abridged) Axisymmetric models of the Milky Way exhibit strong interrelations between the Galactic constants (R_0 and T_0), the stellar columndensity (S_*) and the shape of the dark matter (DM) halo. Here we present analytical relations that can be used to investigate the effects of the uncertain gaseous velocity dispersion on the HI flaring constraints. The contribution of cosmic rays and magnetic fields to the pressure gradients is small. A significantly flattened dark matter halo is only possible if R_0 <~ 6.8 kpc. If R_0 is larger than ~7 kpc, or T_0 >~ 170 km/s, we can rule out two DM candidates that require a highly flattened DM halo: 1) decaying massive neutrinos; and 2) a disk of cold molecular hydrogen. It is only possible to construct self-consistent models of the Galaxy based on the IAU-recommended values for the Galactic constants in the unlikely case that the the stellar columndensity is smaller than ~18 M_sun/pc^2. If we assume that the halo is oblate and S_* = 35 +/- 5 M_sun/pc^2, R_0 <~ 8 kpc and T_0 <~ 200 km/s. Combining the best kinematical and star-count estimates of S_*, we conclude that: 25 <~ S_* <~ 45 M_sun/pc^2. Kuijken & Gilmore's (1991) determination of the columndensity of matter with |z|<=1.1 kpc is robust and valid over a wide range of Galactic constants. Our mass models show that the DM density in the Galactic centre is uncertain by a factor 1000. In the Solar neighbourhood we find: rho_DM ~0.42 GeV/c^2/cm^3 or (11 +/- 5) mM_sun/pc^3 -- roughly 15% of rho_tot.Comment: Accepted for publication in MNRA

Neuromuscular responses to mild-muscle damaging eccentric exercise in a low glycogen state.

The aim of this study was to examine the effect of low muscle glycogen on the neuromuscular responses to maximal eccentric contractions. Fourteen healthy men (22±3years) performed single-leg cycling (20min at ∼75% maximal oxygen uptake (V̇O2 max); eight 90 s sprints at a 1:1 work-to-rest ratio (5% decrements from 90% to 55% V̇O2 max until exhaustion) the evening before 100 eccentric (1.57rads(-1)) with reduced (RED) and normal glycogen (NORM). Neuromuscular responses were measured during and up to 48h after with maximal voluntary and involuntary (twitch, 20Hz and 50Hz) isometric contractions. During eccentric contractions, peak torque decreased (RED: -16.1±2.5%; NORM: -6.2±5.1%) and EMG frequency increased according to muscle length. EMG activity decreased for RED only. After eccentric contractions, maximal isometric force was reduced up to 24h for NORM (-13.5±5.8%) and 48h for RED (-7.4±10.9%). Twelve hours after eccentric contractions, twitch force and the 20:50Hz ratio were decreased for RED but not for NORM. Immediate involuntary with prolonged voluntary force loss suggests that reduced glycogen is associated with increased susceptibility to mild muscle-damaging eccentric exercise with contributions of peripheral and central mechanisms to be different during recovery

Muscle Fatigue Analysis Using OpenSim

In this research, attempts are made to conduct concrete muscle fatigue analysis of arbitrary motions on OpenSim, a digital human modeling platform. A plug-in is written on the base of a muscle fatigue model, which makes it possible to calculate the decline of force-output capability of each muscle along time. The plug-in is tested on a three-dimensional, 29 degree-of-freedom human model. Motion data is obtained by motion capturing during an arbitrary running at a speed of 3.96 m/s. Ten muscles are selected for concrete analysis. As a result, the force-output capability of these muscles reduced to 60%-70% after 10 minutes' running, on a general basis. Erector spinae, which loses 39.2% of its maximal capability, is found to be more fatigue-exposed than the others. The influence of subject attributes (fatigability) is evaluated and discussed

Precision near-infrared radial velocity instrumentation II: Non-Circular Core Fiber Scrambler

We have built and commissioned a prototype agitated non-circular core fiber scrambler for precision spectroscopic radial velocity measurements in the near-infrared H band. We have collected the first on-sky performance and modal noise tests of these novel fibers in the near-infrared at H and K bands using the CSHELL spectrograph at the NASA InfraRed Telescope Facility (IRTF). We discuss the design behind our novel reverse injection of a red laser for co-alignment of star-light with the fiber tip via a corner cube and visible camera. We summarize the practical details involved in the construction of the fiber scrambler, and the mechanical agitation of the fiber at the telescope. We present radial velocity measurements of a bright standard star taken with and without the fiber scrambler to quantify the relative improvement in the obtainable blaze function stability, the line spread function stability, and the resulting radial velocity precision. We assess the feasibility of applying this illumination stabilization technique to the next generation of near-infrared spectrographs such as iSHELL on IRTF and an upgraded NIRSPEC at Keck. Our results may also be applied in the visible for smaller core diameter fibers where fiber modal noise is a significant factor, such as behind an adaptive optics system or on a small < 1 meter class telescope such as is being pursued by the MINERVA and LCOGT collaborations.Comment: Proceedings of the SPIE Optics and Photonics Conference "Techniques and Instrumentation for Detection of Exoplanets VI" held in San Diego, CA, August 25-29, 201