Computational Gains Using RPVM on a Beowulf Cluster

The Beowulf cluster Becker et al. (1995); Scyld ComputingCorporation (1998) is a recent advance incomputing technology that harnesses the power ofa network of desktop computers using communicationsoftware such as PVM Geist et al. (1994) and MPIMessage Passing Interface Forum (1997). Whilst thepotential of a computing cluster is obvious, expertisein programming is still developing in the statisticalcommunity.Recent articles in R-news Li and Rossini (2001)and Yu (2002) entice statistical programmers to considerwhether their solutions could be effectively calculatedin parallel. Another R package, SNOW Tierney(2002); Rossini et al. (2003) aims to skillfullyprovide a wrapper interface to these packages, independentof the underlying cluster communicationmethod used in parallel computing. This article concentrateson RPVM and wishes to build upon the contributionof Li and Rossini (2001) by taking an examplewith obvious orthogonal components and detailingthe R code necessary to allocate the computationsto each node of the cluster. The statistical techniqueused to motivate our RPVM application is the geneshavingalgorithm Hastie et al. (2000b,a) for whichS-PLUS code has been written by Do andWen (2002)to perform the calculations serially.The first section is a brief description of the Beowulfcluster used to run the R programs discussedin this paper. This is followed by an explanation ofthe gene-shaving algorithm, identifying the opportunitiesfor parallel computing of bootstrap estimatesof the "strength" of a cluster and the rendering ofeach matrix row orthogonal to the "eigen-gene". Thecode for spawning child processes is then explainedcomprehensively and the conclusion compares thespeed of RPVM on the Beowulf to serial computing

Wavelet-based feature extraction applied to small-angle x-ray scattering patterns from breast tissue: a tool for differentiating between tissue types

This paper reports on the application of wavelet decomposition to small-angle x-ray scattering (SAXS) patterns from human breast tissue produced by a synchrotron source. The pixel intensities of SAXS patterns of normal, benign and malignant tissue types were transformed into wavelet coefficients. Statistical analysis found significant differences between the wavelet coefficients describing the patterns produced by different tissue types. These differences were then correlated with position in the image and have been linked to the supra-molecular structural changes that occur in breast tissue in the presence of disease. Specifically, results indicate that there are significant differences between healthy and diseased tissues in the wavelet coefficients that describe the peaks produced by the axial d-spacing of collagen. These differences suggest that a useful classification tool could be based upon the spectral information within the axial peaks

Evaluation of an enclosed portable chamber to measure crop and pasture actual evapotranspiration at small scale

An enclosed portable chamber was constructed and calibrated to measure actual evapotranspiration (ET) from crop and pasture and then evaluated against established methods that are used to determine evapotranspiration. The chamber was equipped with variable speed electric fans to mix the air within the chamber during each ET measurement. The most appropriate fan speed was investigated.Pasture ET measured using the enclosed portable chamber compared well with predicted water loss using the water balance method for a 6-day period during winter 1997 in Armidale (NSW, Australia). Mean cumulative pasture ET for the 6-day period was 5.8 and 5.9 mm measured with the enclosed portable chamber and water balance method, respectively.Wheat crop ET measured using the enclosed portable chamber was compared with that estimated by the Bowen ratio (BR) method for a 2-day period in the early growth stages of the crop. Mean ET using the enclosed portable chamber was 2.4 mm per day compared with 2.3 mm per day using the BR method.Results from the enclosed portable chamber method showed sensitivity to the choice of fan speed. A slow fan speed that produced an air velocity of 2.7 km/h, gave the closest agreement with the Bowen ratio method (2.3 mm per day versus 2.2 mm per day) for the wheat crop.The main attractions of the enclosed portable chamber method include: (1) its suitability for ET measurement within small areas

Wavelet Based UXO Detection

The detection and classification of Unexploded Ordnance (UXO) is considered a multi-dimensional pattern recognition problem. Standard techniques in solving multi-dimensional detection and classification problems involve using large sets of templates or libraries. This paper shows that by using Wavelet Transformation a single library will allow a particular class of ordnance to be classified over a range of depths