Effect of signal duration on detection for gated and for continuous noise

Effect of signal duration on detection for gated and continuous nois

Dynamics from diffraction

A model-independent approach for the extraction of detailed lattice dynamical information from neutron powder diffraction data is described. The technique is based on a statistical analysis of atomistic configurations generated using reverse Monte Carlo structural refinement. Phonon dispersion curves extracted in this way are shown to reproduce many of the important features found in those determined independently using neutron triple-axis spectroscopy. The extent to which diffraction data are sensitive to lattice dynamics is explored in a range of materials. The prospect that such detailed dynamical information might be accessible using comparatively facile experiments such as neutron powder diffraction is incredibly valuable when studying systems for which established spectroscopic methods are prohibitive or inappropriate

Design and Development Process for Medical Hardware and Healthcare Monitoring Devices for Spaceflight

No abstract availabl

Twisted Electromagnetic Modes and Sagnac Ring-Lasers

A new approximation scheme, designed to solve the covariant Maxwell equations inside a rotating hollow slender conducting cavity (modelling a ring-laser), is constructed. It is shown that for well-defined conditions there exist TE and TM modes with respect to the longitudinal axis of the cavity. A twisted mode spectrum is found to depend on the integrated Frenet torsion of the cavity and this in turn may affect the Sagnac beat frequency induced by a non-zero rotation of the cavity. The analysis is motivated by attempts to use ring-lasers to measure terrestrial gravito-magnetism or the Lense-Thirring effect produced by the rotation of the Earth.Comment: LaTeX 31 pages, 3 Figure

Phonon broadening from supercell lattice dynamics: random and correlated disorder

We demonstrate how supercell implementations of conventional lattice dynamical calculations can be used to determine the extent and nature of disorder-induced broadening in the phonon dispersion spectrum of disordered crystalline materials. The approach taken relies on band unfolding, and is first benchmarked against virtual crystal approximation phonon calculations. The different effects of mass and interaction disorder on the phonon broadening are then presented, focussing on the example of a simple cubic binary alloy. For the mass disorder example, the effect of introducing correlated disorder is also explored by varying the fraction of homoatomic and heteroatomic neighbours. Systematic progression in the degree of phonon broadening, on the one hand, and the form of the phonon dispersion curves from primitive to face-centered cubic type, on the other hand, is observed as homoatomic neighbours are disfavoured. The implications for rationalising selection rule violations in disordered materials and for using inelastic neutron scattering measurements as a means of characterising disorder are discussed.Comment: 6 pages, 3 figure

The Electrodynamics of Inhomogeneous Rotating Media and the Abraham and Minkowski Tensors II: Applications

Applications of the covariant theory of drive-forms are considered for a class of perfectly insulating media. The distinction between the notions of "classical photons" in homogeneous bounded and unbounded stationary media and in stationary unbounded magneto-electric media is pointed out in the context of the Abraham, Minkowski and symmetrized Minkowski electromagnetic stress-energy-momentum tensors. Such notions have led to intense debate about the role of these (and other) tensors in describing electromagnetic interactions in moving media. In order to address some of these issues for material subject to the Minkowski constitutive relations, the propagation of harmonic waves through homogeneous and inhomogeneous, isotropic plane-faced slabs at rest is first considered. To motivate the subsequent analysis on accelerating media two classes of electromagnetic modes that solve Maxwell's equations for uniformly rotating homogeneous polarizable media are enumerated. Finally it is shown that, under the influence of an incident monochromatic, circularly polarized, plane electromagnetic wave, the Abraham and symmetrized Minkowski tensors induce different time-averaged torques on a uniformly rotating materially inhomogeneous dielectric cylinder. We suggest that this observation may offer new avenues to explore experimentally the covariant electrodynamics of more general accelerating media.Comment: 29 pages, 4 figures. Accepted for publication in Proc. Roy. Soc.

The Luminosity Function of Galaxies in the Las Campanas Redshift Survey

We present the $R$-band luminosity function for a sample of 18678 galaxies, with average redshift $z = 0.1$, from the Las Campanas Redshift Survey. The luminosity function may be fit by a Schechter function with $M^* = -20.29 \pm 0.02 + 5 \log h$, $\alpha = -0.70 \pm 0.05$, and $\phi^* = 0.019 \pm 0.001 \ h^3$~Mpc$^{-3}$, for absolute magnitudes$-23.0 \leq M - 5 \log h \leq -17.5$. We compare our luminosity function to that from other redshift surveys; in particular our normalization is consistent with that of the Stromlo-APM survey, and is therefore a factor of two below that implied by the$b_J \approx 20$bright galaxy counts. Our normalization thus indicates that much more evolution is needed to match the faint galaxy count data, compared to minimal evolution models which normalize at$b_J \approx 20$. Also, we show that our faint-end slope$\alpha = -0.7$, though ``shallower'' than typical previous values$\alpha = -1$, results primarily from fitting the detailed shape of the LCRS luminosity function, rather than from any absence of intrinsically faint galaxies from our survey. Finally, using [OII] 3727 equivalent width$W_{\lambda} = 5$~\AA \ as the dividing line, we find significant differences in the luminosity functions of emission and non-emission galaxies, particularly in their$\alpha$values. Emission galaxies have Schechter parameters$M^* = -20.03 \pm 0.03 + 5 \log h$and$\alpha = -0.9 \pm 0.1$, while non-emission galaxies are described by$M^* = -20.22 \pm 0.02 + 5 \log h$and$\alpha = -0.3 \pm 0.1$. (abridged abstract)Comment: 41 pages, including 13 postscript figures, uses AASTEX v4.0 style files. Important clarification of R-band definition, plus correction of luminosity densities and updated references. Main conclusions unchanged. Final version to appear in Ap