A microcontroller system for investigating the catch effect: Functional electrical stimulation of the common peroneal nerve

Correction of drop foot in hemiplegic gait is achieved by electrical stimulation of the common peroneal nerve with a series of pulses at a fixed frequency. However, during normal gait, the electromyographic signals from the tibialis anterior muscle indicate that muscle force is not constant but varies during the swing phase. The application of double pulses for the correction of drop foot may enhance the gait by generating greater torque at the ankle and thereby increase the efficiency of the stimulation with reduced fatigue. A flexible controller has been designed around the Odstock Drop Foot Stimulator to deliver different profiles of pulses implementing doublets and optimum series. A peripheral interface controller (PIC) microcontroller with some external circuits has been designed and tested to accommodate six profiles. Preliminary results of the measurements from a normal subject seated in a multi-moment chair (an isometric torque measurement device) indicate that profiles containing doublets and optimum spaced pulses look favourable for clinical use

Measuring dark energy properties with 3D cosmic shear

We present parameter estimation forecasts for present and future 3D cosmic shear surveys. We demonstrate that, in conjunction with results from cosmic microwave background (CMB) experiments, the properties of dark energy can be estimated with very high precision with large-scale, fully 3D weak lensing surveys. In particular, a 5-band, 10,000 square degree ground-based survey to a median redshift of zm=0.7 could achieve 1-$\sigma$ marginal statistical errors, in combination with the constraints expected from the CMB Planck Surveyor, of $\Delta$w0=0.108 and $\Delta$wa=0.099 where we parameterize w by w(a)=w0+wa(1-a) where a is the scale factor. Such a survey is achievable with a wide-field camera on a 4 metre class telescope. The error on the value of w at an intermediate pivot redshift of z=0.368 is constrained to $\Delta$w(z=0.368)=0.0175. We compare and combine the 3D weak lensing constraints with the cosmological and dark energy parameters measured from planned Baryon Acoustic Oscillation (BAO) and supernova Type Ia experiments, and find that 3D weak lensing significantly improves the marginalized errors. A combination of 3D weak lensing, CMB and BAO experiments could achieve $\Delta$w0=0.037 and $\Delta$wa=0.099. Fully 3D weak shear analysis avoids the loss of information inherent in tomographic binning, and we show that the sensitivity to systematic errors is much less. In conjunction with the fact that the physics of lensing is very soundly based, this analysis demonstrates that deep, wide-angle 3D weak lensing surveys are extremely promising for measuring dark energy properties.Comment: 18 pages, 16 figures. Accepted to MNRAS. Figures now in grayscale. Further discussions on non-Gaussianity and photometric redshift errors. Some references adde

Consideration of probability of bacterial growth for Jovian planets and their satellites

Environmental parameters affecting growth of bacteria are compared with current atmospheric models for Jupiter and Saturn, and with the available physical data for their satellites. Different zones of relative probability of growth are identified for Jupiter and Saturn. Of the more than two dozen satellites, only the largest (Io, Europa, Ganymede, Callisto, and Titan) are found to be interesting biologically. Titan's atmosphere may produce a substantial greenhouse effect providing increased surface temperatures. Models predicting a dense atmosphere are compatible with microbial growth for a range of pressures at Titan's surface. For Titan's surface the probability of growth would be enhanced if: (1) the surface is entirely or partially liquid; (2) volcanism is present; or (3) access to internal heat sources is significant

Weak Gravitational Flexion

Flexion is the significant third-order weak gravitational lensing effect responsible for the weakly skewed and arc-like appearance of lensed galaxies. Here we demonstrate how flexion measurements can be used to measure galaxy halo density profiles and large-scale structure on non-linear scales, via galaxy-galaxy lensing, dark matter mapping and cosmic flexion correlation functions. We describe the origin of gravitational flexion, and discuss its four components, two of which are first described here. We also introduce an efficient complex formalism for all orders of lensing distortion. We proceed to examine the flexion predictions for galaxy-galaxy lensing, examining isothermal sphere and Navarro, Frenk & White (NFW) profiles and both circularly symmetric and elliptical cases. We show that in combination with shear we can precisely measure galaxy masses and NFW halo concentrations. We also show how flexion measurements can be used to reconstruct mass maps in 2-D projection on the sky, and in 3-D in combination with redshift data. Finally, we examine the predictions for cosmic flexion, including convergence-flexion cross-correlations, and find that the signal is an effective probe of structure on non-linear scales.Comment: 17 pages, including 12 figures, submitted to MNRA

Dynamic performance of squeeze-film bearings

Earlier work has shown that oil-film forces can be modelled by linear coefficients. Identification techniques were used to generate numerical values for these coefficients. This paper has shown the invalidity of applying the perturbation techniques normally used in bearing studies to derive expressions for linearized coefficients to represent a cavitated oil-film. An alternative approach was developed based upon energy techniques to obtain estimates for linearized coefficients. Some current work being undertaken suggests that an alternative analytical approach is possible. These results will be reported in due course

Magnetic exchange interaction between rare-earth and Mn ions in multiferroic hexagonal manganites

We report a study of magnetic dynamics in multiferroic hexagonal manganite HoMnO3 by far-infrared spectroscopy. Low-temperature magnetic excitation spectrum of HoMnO3 consists of magnetic-dipole transitions of Ho ions within the crystal-field split J=8 manifold and of the triangular antiferromagnetic resonance of Mn ions. We determine the effective spin Hamiltonian for the Ho ion ground state. The magnetic-field splitting of the Mn antiferromagnetic resonance allows us to measure the magnetic exchange coupling between the rare-earth and Mn ions.Comment: accepted for publication in Physical Review Letter

Non-local 2D Generalized Yang-Mills theories on arbitrary surfaces with boundary

The non-local generalized two dimensional Yang Mills theories on an arbitrary orientable and non-orientable surfaces with boundaries is studied. We obtain the effective action of these theories for the case which the gauge group is near the identity, $U\simeq I$. Furthermore, by obtaining the effective action at the large-N limit, it is shown that the phase structure of these theories is the same as that obtain for these theories on orientable and non-orientable surface without boundaries. It is seen that the $\phi^2$ model of these theories on an arbitrary orientable and non-orientable surfaces with boundaries have third order phase transition only on $g=0$ and $r=1$ surfaces, with modified area $\tilde{A}+{\cal A}/2$ for orientable and $\bar{A}+\mathcal{A}$ for non-orientable surfaces respectivly.Comment: 10 pages, no figures, late