Quasi Two-dimensional Transfer of Elastic Waves

A theory for multiple scattering of elastic waves is presented in a random medium bounded by two ideal free surfaces, whose horizontal size is infinite and whose transverse size is smaller than the mean free path of the waves. This geometry is relevant for seismic wave propagation in the Earth crust. We derive a time-dependent, quasi-2D radiative transfer equation, that describes the coupling of the eigenmodes of the layer (surface Rayleigh waves, SH waves, and Lamb waves). Expressions are found that relate the small-scale fluctuations to the life time of the modes and to their coupling rates. We discuss a diffusion approximation that simplifies the mathematics of this model significantly, and which should apply at large lapse times. Finally, coherent backscattering is studied within the quasi-2D radiative transfer equation for different source and detection configurations.Comment: REVTeX, 36 pages with 10 figures. Submitted to Phys. Rev.

University of Colorado 1974 Field Season in Eastern Baffin Island

The summer of 1974 saw one of the largest research parties the University of Colorado has been able to mount operating along the eastern coast of Baffin Island. The early and widespread break-up of sea ice greatly assisted in the completion of the field programme in which a total of sixteen persons were involved. In addition to members of the University staff, the following individuals from other institutions also participated. In the programme: a member of the Department of Micropalaeontology of the University of Aarhus, Denmark; a soil scientist from the University of Pennsylvania, U.S.A.; a Quaternary geologist from Brock University, Ontario, Canada; and a Quaternary geologist from Grand Valley State College, Michigan, U.S.A. ... Raised marine sediments and tills were investigated on Broughton Island and northwards along the coast to Quajon Fiord. Specific attention was focused on collecting samples for micro-faunal analysis and delimiting different marine episodes. In addition, a number of sites were revisited on Broughton Island and northwards along the coast to Kivitoo and Quajon Fiord. Large (1000-g and over) samples of marine shells were collected from sites previously given dates of over 30,000 years BP. ... One field party mapped the southern part of the Baffin Island National Park, giving particular attention to (a) the delimitation of glacial periods on the basis of surface weathering of boulders, and (b) determining the elevation of local marine limits and lower strandlines. The latter research was concentrated on the mapping of the southern shore of Cumberland Peninsula, from outer Kingnait Fiord westward to the head of Cumberland Sound. ... Soil scientists established a soil chronosequence, and investigated the range of soil types existing within the southern part of Cumberland Peninsula. They sent samples south from laboratory analysis. Plant collection: Specimens of vascular plants, mosses and lichens were collected from Broughton Island and from the head of Maktak Fiord, and sent to the University of Colorado Museum. By December 1974, a total of 86 vascular plants had been identified. Climatological studies in relation to fast ice: Work done during the summer of 1974 concludes the field-measurement phase of the University of Colorado's study of the surface energy budgets of fast ice at Broughton Island. A micrometeorological station was operated at a site approximately one kilometre south of Broughton settlement, from late May until local break-up in early July. The programme of observation consisted of the periodic taking of profiles of wind, temperature and relative humidity; the continuous measurement of temperature at two metres, and net radiation over both saturated and unsaturated surfaces; and transects of surface short-wave albedo. Salinity and temperature profiles in the ice and water were taken every 304 days. Comparative analysis of the data for 1972-74 is now in progress in relation to the observed ice regime. The 1974 data should provide better estimates of the turbulent flux components of the energy budget than it was possible to make in previous summers. Meteorological observations were continued near the base of the Broughton Island operations through mid-August. Results are now available of four summers and two winters of standard meteorological observations, and global solar and net radiation measurements as well. The Atmospheric Environment Service Cooperative Observer station, with its twice-daily measurements of maximum and minimum temperatures and of precipitation, is now into its fourth calendar year of operation. The summer of 1974 was unusually mild. The mean ablation seasonal temperature was 3.9°C at the Broughton DEW line weather station. In contrast, 1972 was the coldest (-1.2 C°). The early part of June 1974 was dominated by anticyclonic synoptic weather patterns which greatly accelerated the fast ice ablation rate to give the earliest break-up in five years. Satellite-observed conce ntrations of pack ice in Davis Strait in late May were less than at the same time in 1973. With the resurvey of the "Boas" Glacier (67 35 N, 65 16 W) in August 1974, the mass balance measurements were extended to five balance years. Accurate measurements were not possible, because most ablation poles melted out during the warm summer of 1974. However, it is estimated that the net specific balance for the 1973-74 budget year was approximately -0.5 m water equivalent (w.e.). ... Analysis of the past five budget years shows that (a) the "Boas" Glacier exhibited a two-year alternation of large mass gains and losses during the first four years, and (b) the estimated net specific mass balance for the five-year period was -0.16 m w.e., in spite of the total net mass gains of 0.38 m w.e. during the first four years. ..

Flow Diagnostics and the Acoustic Behavior of a Fan-and-Coil Assembly

Project 84 concentrated on understanding the noise generating mechanisms of axial-flow fans with the intent of proposing methods of component design and system assembly by which noise generation is reduced or minimized. The project focused on the fan-coil unit typical to room air conditioners and many split-system applications. This report presents the accomplishments of the project, including the design, construction, and qualification of an anechoic chamber, the acquisition of acoustic, flow, and pressure data within a fan-coil unit over a typical operating range, and the development of an understanding of the flow-structure interactions responsible for noise generation in the fan-coil unit. This report focuses on the investigation of a method for measuring the dynamic axial force generated by a fan operating in a steady but spatially non-uniform flow field. Several variations of a measurement system that uses a cantilever beam were tested. Experimental results indicated, in all designs, that the measurement system introduced additional sources of axial motion, occurring at the frequencies of interest and at amplitudes much larger than the one to be measured. Recommendations for future work are given.Air Conditioning and Refrigeration Project 8

High-frequency dynamics of wave localisation

We study the effect of localisation on the propagation of a pulse through a multi-mode disordered waveguide. The correlator of the transmitted wave amplitude u at two frequencies differing by delta_omega has for large delta_omega the stretched exponential tail ~exp(-sqrt{tau_D delta_omega/2}). The time constant tau_D=L^2/D is given by the diffusion coefficient D, even if the length L of the waveguide is much greater than the localisation length xi. Localisation has the effect of multiplying the correlator by a frequency-independent factor exp(-L/2xi), which disappears upon breaking time-reversal symmetry.Comment: 3 pages, 1 figur

Bedside theatre performance and its effects on hospitalised children's well-being

This article reports on practice-based pilot research being undertaken at Birmingham Children's Hospital in England on the impact of bedside theatre performance on hospitalised children's well-being. It discusses the process of creating theatre for sick children, connecting with the hospital and working within the hospital tight routines, dealing with ethics, working with theatre artists and performing to children bedside. It also reports on evidence collected by questionnaire and interviews about the perceived benefits of bedside theatre by children and their parent/carers. This emphasis on the process is appropriate for theatre practitioners, arts therapists and clinical staff who work with hospitalised children

Level statistics and eigenfunctions of pseudointegrable systems: dependence on energy and genus number

We study the level statistics (second half moment $I_0$ and rigidity $\Delta_3$) and the eigenfunctions of pseudointegrable systems with rough boundaries of different genus numbers $g$. We find that the levels form energy intervals with a characteristic behavior of the level statistics and the eigenfunctions in each interval. At low enough energies, the boundary roughness is not resolved and accordingly, the eigenfunctions are quite regular functions and the level statistics shows Poisson-like behavior. At higher energies, the level statistics of most systems moves from Poisson-like towards Wigner-like behavior with increasing $g$. Investigating the wavefunctions, we find many chaotic functions that can be described as a random superposition of regular wavefunctions. The amplitude distribution $P(\psi)$ of these chaotic functions was found to be Gaussian with the typical value of the localization volume $V_{\rm{loc}}\approx 0.33$. For systems with periodic boundaries we find several additional energy regimes, where $I_0$ is relatively close to the Poisson-limit. In these regimes, the eigenfunctions are either regular or localized functions, where $P(\psi)$ is close to the distribution of a sine or cosine function in the first case and strongly peaked in the second case. Also an interesting intermediate case between chaotic and localized eigenfunctions appears

Scattering of elastic waves by periodic arrays of spherical bodies

We develop a formalism for the calculation of the frequency band structure of a phononic crystal consisting of non-overlapping elastic spheres, characterized by Lam\'e coefficients which may be complex and frequency dependent, arranged periodically in a host medium with different mass density and Lam\'e coefficients. We view the crystal as a sequence of planes of spheres, parallel to and having the two dimensional periodicity of a given crystallographic plane, and obtain the complex band structure of the infinite crystal associated with this plane. The method allows one to calculate, also, the transmission, reflection, and absorption coefficients for an elastic wave (longitudinal or transverse) incident, at any angle, on a slab of the crystal of finite thickness. We demonstrate the efficiency of the method by applying it to a specific example.Comment: 19 pages, 5 figures, Phys. Rev. B (in press

Universal behavior of localization of residue fluctuations in globular proteins

Localization properties of residue fluctuations in globular proteins are studied theoretically by using the Gaussian network model. Participation ratio for each residue fluctuation mode is calculated. It is found that the relationship between participation ratio and frequency is similar for all globular proteins, indicating a universal behavior in spite of their different size, shape, and architecture.Comment: 4 pages, 3 figures. To appear in Phys. Rev.

Green functions for generalized point interactions in 1D: A scattering approach

Recently, general point interactions in one dimension has been used to model a large number of different phenomena in quantum mechanics. Such potentials, however, requires some sort of regularization to lead to meaningful results. The usual ways to do so rely on technicalities which may hide important physical aspects of the problem. In this work we present a new method to calculate the exact Green functions for general point interactions in 1D. Our approach differs from previous ones because it is based only on physical quantities, namely, the scattering coefficients, $R$ and $T$, to construct $G$. Renormalization or particular mathematical prescriptions are not invoked. The simple formulation of the method makes it easy to extend to more general contexts, such as for lattices of $N$ general point interactions; on a line; on a half-line; under periodic boundary conditions; and confined in a box.Comment: Revtex, 9 pages, 3 EPS figures. To be published in PR