Diffusive benefits of cylinders in front of a Schroeder diffuser

A numerical investigation is performed into the diffusive effects of cylinders positioned in front of a Schroeder diffuser. A regular line of cylinders is shown to offer notable improvements to diffusion from a periodic Schroeder device, provided lateral cylinder spacing is incommensurable with the Schroeder period width. Further investigation considers angular dependence and low frequency results in greater detail, as well as the effects on narrowband and modulated Schroeder devices. An optimization procedure is subsequently performed to investigate the effects of an irregular cylinder arrangement, which provides further diffusive benefits. (C) 2010 Acoustical Society of America

Volumetric diffusers : pseudorandom cylinder arrays on a periodic lattice

Most conventional diffusers take the form of a surface based treatment, and as a result can only operate in hemispherical space. Placing a diffuser in the volume of a room might provide greater efficiency by allowing scattering into the whole space. A periodic cylinder array (or sonic crystal) produces periodicity lobes and uneven scattering. Introducing defects into an array, by removing or varying the size of some of the cylinders, can enhance their diffusing abilities. This paper applies number theoretic concepts to create cylinder arrays that have more even scattering. Predictions using a Boundary Element Method are compared to measurements to verify the model, and suitable metrics are adopted to evaluate performance. Arrangements with good aperiodic autocorrelation properties tend to produce the best results. At low frequency power is controlled by object size and at high frequency diffusion is dominated by lattice spacing and structural similarity. Consequently the operational bandwidth is rather small. By using sparse arrays and varying cylinder sizes, a wider bandwidth can be achieved

Cu-Ni-PGE mineralisation at the Aurora Project and potential for a new PGE province in the Northern Bushveld Main Zone

This is the final version of the article. Available from Elsevier via the DOI in this record.he Aurora Project is a Cu-Ni-PGE magmatic sulphide deposit in the northern limb of the Bushveld Complex of South Africa. Since 1992 mining in the northern limb has focussed on the Platreef deposit, located along the margin of the complex. Aurora has previously been suggested to represent a far-northern facies of the Platreef located along the basal margin of the complex and this study provides new data with which to test this assertion. In contrast to the Platreef, the base metal sulphide mineralisation at Aurora is both Cu-rich (Ni/Cu 50,000) reflecting the preferential removal of Pd over Cu in the sulphides below. Similarly high Cu/Pd ratios characterise the Upper Main Zone in the northern limb above the pigeonite + orthopyroxene interval and suggest that Aurora-style sulphide mineralisation may be developed here as well. The same mineralogy and geochemical features also appear to be present in the T Zone of the Waterberg PGE deposit, located under younger cover rocks to the north of Aurora. If these links are proved they indicate the potential for a previously unsuspected zone of Cu-Ni-PGE mineralisation extending for over 40 km along strike through the Upper Main Zone of the northern Bushveld.Sulphur isotope analyses were carried out by Alison MacDonald at the Scottish Universities Environmental Research Centre as part of NERC Isotope Geoscience Facilities Committee award IP/909/0506. HSRH is sponsored by the Claude Leon Foundation

Volume diffusers for architectural acoustics

Most conventional diffusers are used on room surfaces, and consequently can only operate on a hemispherical area. Placing a diffuser in the volume of a room may provide greater efficiency by allowing scattering into the whole space. There are very few examples of volume diffusers and they tend to be limited in design; subsequently a suitable method for their development is lacking.2D volumetric diffusers are investigated, considering a number of design concepts; namely arrays of slats, percolation structures and cylinder arrays. An experimental technique is adapted for their measurement, and the results are used to verify prediction models for each type. Diffusive efficacy is assessed through a new metric based on an existing surface diffuser coefficient and a measure of scattered power requiring half of the energy to be back-scattered.Single layer slat arrays are formed from optimal aperiodic sequences, though due to the directional scattering from individual slats at higher frequencies, performance is heavily dependent on line-of-sight through the array. This limits the operational bandwidth to approximately 1.5 octaves. Multi-layer structures offer improvements by allowing cancellation of the back-scattered lobe, though at high frequency the specular reflection from an individual slat still dominates. Percolation fractals use slats orientated in multiple directions and by scattering laterally can channel sound and diffuse at lower frequencies. Low frequency diffusion however is limited and the best structures are those which provide a broad range of geometric reflection paths.Through application of number theoretic concepts, arrangements of cylinders are shown to offer more enhanced diffusing abilities than slat and percolation structures. At low frequency scattered power is controlled by cylinder size and at high frequency diffusion is dominated by their spacing. By minimising structural similarity and including cylinders with circumference comparable to wavelength, significant diffusion is achieved over an approximate 5 octave bandwidth

Using New Submillimetre Surveys to Identify the Evolutionary Status of High-z Galaxies

This paper describes a key submillimetre survey which we are currently conducting to address some of the outstanding questions in cosmology - how, at what epoch and over what period of time did massive galaxies form at high redshift? A summary of the technical feasibility of future submillimetre observations with new ground-based, airborne and satellite telescopes is also presented.Comment: 6 pages, 3 postscript figures, LaTex uses Kluwer book style file crckapb10.sty, to appear in "Observational Cosmology with the New Radio Surveys", 13-15 January 1997, Puerto de la Cruz, Tenerife, M.Bremer, N.Jackson, I.Perez-Fournon (eds.), Kluwe

Object-based reverberation for spatial audio

Object-based audio is gaining momentum as a means for future audio content to be more immersive, interactive, and accessible. Recent standardization developments make recommendations for object formats; however, the capture, production, and reproduction of reverberation is an open issue. In this paper parametric approaches for capturing, representing, editing, and rendering reverberation over a 3D spatial audio system are reviewed. A framework is proposed for a Reverberant Spatial Audio Object (RSAO), which synthesizes reverberation inside an audio object renderer. An implementation example of an object scheme utilizing the RSAO framework is provided, and supported with listening test results, showing that: the approach correctly retains the sense of room size compared to a convolved reference; editing RSAO parameters can alter the perceived room size and source distance; and, format-agnostic rendering can be exploited to alter listener envelopment

The Hindered M1 Radiative Decay Υ(2S) → ηb(1S)γ from Lattice NRQCD

We present a calculation of the hindered M$1$ $\Upsilon(2S) \to \eta_b(1S) \gamma$ decay rate using lattice non-relativistic QCD. The calculation includes spin-dependent relativistic corrections to the NRQCD action through $\mathcal{O}(v^6)$ in the quark's relative velocity, relativistic corrections to the leading order current which mediates the transition through the quark's magnetic moment, radiative corrections to the leading spin-magnetic coupling and for the first time a full error budget. We also use gluon field ensembles at multiple lattice spacing values, all of which include $u$, $d$, $s$ and $c$ quark vacuum polarisation. Our result for the branching fraction is $\mathcal{B}(\Upsilon(2S)\to\eta_b(1S)\gamma) = 5.4(1.8)\times 10^{-4}$, which agrees with the current experimental value.This is the author accepted manuscript. The final version is available from APS via http://dx.doi.org/10.1103/PhysRevD.92.09450

Cardiovascular Risk Factors from Early Life Predict Future Adult Cardiac Structural and Functional Abnormalities: A Systematic Review of the Published Literature

Background: Clinical practice evaluates cardiovascular risk based on current risk factor (RF) levels [Blood pressure (BP), body mass index (BMI) and glycaemic control] largely disregarding previous risk-factor history over the totality of the life course. RFs are related to contemporaneous echocardiographic measures of cardiac structure and function which in turn are independently related to cardiovascular morbidity and mortality in cross-sectional studies. However, the effect of lifetime or earlier RF history on future echocardiographic changes has never been systematically examined. Methods: A systematic review of the published literature identified 24 studies relating either earlier BP, BMI, glycaemic control or a combination to future cardiac structure and/or function. Results: The majority of studies showed that elevated BP and BMI in earlier life and greater cumulative burden of these factors resulted in worse cardiac structure up to 24 years later. Studies examining glycaemic control as a RF were few, but poorer glycaemic control in young adults was associated with increased future left ventricular mass. While only 5 papers related RFs to future cardiac function, all RFs were positively associated with worse future diastolic function. Conclusions: BP, BMI and glycaemic control measures in childhood, adolescence and early adulthood and subsequent longitudinal trajectories of BP and BMI are predictive of future abnormalities in cardiac structure and function. Lifetime RF history should be used to inform clinical practice. Further research is required to enable the identification of any sensitive periods in the life course to enable prevention when it is most likely to be effective