Showing papers by "Peter R. Griffiths published in 2001"

Raman Spectroscopy and Genetic Algorithms for the Classification of Wood Types

Abstract: Raman spectroscopy and pattern recognition techniques are used to develop a potential method to characterize wood by type. The test data consists of 98 Raman spectra of temperate softwoods and hardwoods, and Brazilian and Honduran tropical woods. A genetic algorithm (GA) is used to extract features (i.e., line intensities at specific wavelengths) characteristic of the Raman profile of each wood-type. The spectral features identified by the pattern recognition GA allow the wood samples to cluster by type in a plot of the two largest principal components of the data. Because principal components maximize variance, the bulk of the information encoded by these spectral features is about differences between wood types. The predictive ability of the descriptors identified by the pattern recognition GA and the principal component map associated with them is validated using an external prediction set consisting of tropical woods and temperate hard and softwoods.

Instrumentation for far infrared spectroscopy.

Abstract: Fourier transform spectrometers developed in three distinct spectral regions in the early 1960s. Pierre Connes and his coworkers in France developed remarkably sophisticated step-scan interferometers that permitted near-infrared spectra to be measured with a resolution of better than 0.0 1 cm{sup {minus}1}. These instruments may be considered the forerunners of the step-scan interferometers made by Bruker, Bio-Rad (Cambridge, MA, USA) and Nicolet although their principal application was in the field of astronomy. Low-resolution rapid-scanning interferometers were developed by Larry Mertz and his colleagues at Block Engineering (Cambridge, MA, USA) for remote sensing. Nonetheless, the FT-IR spectrometers that are so prevalent in chemical laboratories today are direct descendants of these instruments. The interferometers that were developed for far-infrared spectrometry in Gebbie's laboratory ,have had no commercial counterparts for at least 15 years. However, it could be argued that these instruments did as much to demonstrate the power of Fourier transform spectroscopy to the chemical community as any of the instruments developed for mid- and near-infrared spectrometry. Their performance was every bit as good as today's rapid-scanning interferometers. However, the market for these instruments is so small today that it has proved more lucrative to modify rapid-scanning interferometers that were originally designed for mid-infrared spectrometry than to compete with these instruments with slow continuous scan or step-scan interferometers.

Generation of front-surface low-mass epoxy-composite mirrors by spin-casting

Abstract: Spin-casting liquid mixtures followed by in situ polymerization offers an elegant and inexpensive method of generating front surface paraboloidal mirrors of almost any focal length, aperture, and on- or off-axis character, requiring no post polishing. Mirrors have been made from a variety of substrates including epoxy-composite mixtures, with focal lengths ranging from 2 to 80 m, and apertures from 5 to 76 cm. The goal of this project was to make spin-cast mirrors for use as reflectors, telescopes, and cat’s-eye retroreflectors in open path Fourier transform infrared (OP/FT-IR) spectrometry. These mirrors were designed for portable outdoor use, and thus have been optimized for maximum ruggedness and mechanical strength, and minimal mass, coefficient of thermal expansion, and cost. After spin-casting, the only preparation prior to silvering is a thermal post-cure. Results are presented giving details of the materials, hardware, and procedures used to spin-cast paraboloidal mirrors.