Norwich Near Infrared Consultancy

Cringleford, United Kingdom

Norwich Near Infrared Consultancy

Cringleford, United Kingdom
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Norris K.H.,11204 Montgomery Road | Davies A.M.C.,Norwich Near Infrared Consultancy
Spectroscopy Europe | Year: 2012

The article examines diffuse reflection and transmission spectra more thoroughly. The first set of spectra was collected more than 20 years ago to study the effect of temperature on the near infrared (NIR) spectra of starch: They include transmission spectra of the sample. In the original study the spectra of a mixture of water and glass heads were measured to observe the effect of freezing on the spectra of water. As reported, the water with the glass beads showed a band at 2005 nm for temperatures below zero. Another set of old data is that of 198 wheat samples representing most of the wheat samples from all of the wheat- production areas of the US. These data have been used in several research reports.


Davies A.M.C.,Norwich Near Infrared Consultancy | Fearn T.,University College London
Spectroscopy Europe | Year: 2010

Classical Least Square (CLS) can be easily extended to cope with variable linear baselines. There is no requirement that peaks should not overlap, they overlap considerably in the example, to the extent that we only see two peaks in the mixture, merely that each pair of pure spectra must differ somewhere. In fact we do not need the entire spectrum for this calculation. The spectra can be reduced to three spectral points, so long as the three reduced spectra still satisfy the condition of having no linear dependence between them. If the system behaves as assumed, and there is no noise anywhere, the equation recovers the exact proportions in the mixture. How good an estimate it is will depend on the amount of noise, and also on how distinct are the three pure spectra.


Davies A.M.C.,Norwich Near Infrared Consultancy | Fearn T.,University College London
Spectroscopy Europe | Year: 2013

Powered partial least squares (PPLS) is a modification of the NIPALS algorithm, which was one of the earliest of the many algorithms that now exist for PLS. The modification concerns the computation of the loading weights, which determine the contributions of the original variables to each factor. In the standard algorithm these loading weights are proportional to the covariances between the dependent variable y and the predictors. PPLS gives more weight to the correlations, with an extra tuning parameter to control this weight. The influence of a variable on the prediction result depends on the size of the coefficient computed by PLS. If the coefficient is very small then it will have very little effect on the result except that every variable will add a small noise component. Thus predictions produced by PLS calibrations must have more than the minimum of added noise. If it was possible to include variables in PLS only when they made a useful contribution to the precision of the predicted result then some of this noise could be excluded.


Davies A.M.C.,Norwich Near Infrared Consultancy
Spectroscopy Europe | Year: 2014

A vast hall full of white-bearded mathematicians working with slide rules that the film explained would be required to compute an MLR computation, while the computer would take only a few hours. Several techniques have been introduced which were all tackling the problems of collinearity. The most important are principal components regression (PCR) and partial least-squares (PLS). The critical advantages of PCA are that the data are considerably compressed and they are orthogonal. Typically 700 NIR wavelength variables can be compressed into 20 PCs. The fact that PCA scores are orthogonal means that they are uncorelated so the collinearity problem is removed. PLS can most easily be understood by considering it as a modification of PCR.


Davies A.M.C.,Norwich Near Infrared Consultancy
Spectroscopy Europe | Year: 2011

A. M. C. Davies discusses how low noise level is one of the essential characteristics of MR spectrometers. Moreover, instrument manufacturers provide programs to check that the spectrometer is operating within the specified limits. In 1985 there was a very active UK NIR User Group and for one of the meetings Ian Cowe organized a principal component study of the spectrometers. Temperature control was achieved by switching the refrigerant pump on or off. When we recorded the temperature of the laboratory air we found that that the temperature cycle time was around two minutes which was slightly greater than the time required to measure and record a spectrum. The question of the importance of this noise and how to minimize it is not relevant to this column but anyone interested can find some additional information in the references. It may have been known for some time but it is still a current problem.


Davies A.M.C.,Norwich Near Infrared Consultancy
Spectroscopy Europe | Year: 2011

GrainSpec™ used a tungsten halogen bulb as the energy source. NIR wavelengths were selected by use of a blocking filter to exclude visible radiation and then narrow bands of NIR wavelengths were selected by 11 interference filters held on a rotating wheel which brought each filter in turn into the optical path. The wavelengths selected by interference filters depend on the construction of the filter and the angle of the incident beam on the filter, thus varying the angle of the filter to the radiation will produce a range of output wavelengths. The wavelengths selected by interference filters depend on the construction of the filter and the angle of the incident beam on the filter, thus varying the angle of the filter to the radiation will produce a range of output wavelengths. A collimated band of energy that passed through the blocking filter illuminated a tuning wheel. Tests of the technique on sets of sub-samples gave an eight to ten fold reduction in the variability of sub-samples and it was agreed that this processing should become part of GS.


Davies A.M.C.,Norwich Near Infrared Consultancy
Spectroscopy Europe | Year: 2013

A.M.C. Davies shares his knowledge and experience about principal component analysis (PCA). In 1989, Ian Michael invited Davies to write about chemometrics in the new publication Spectroscopy World, which became Spectroscopy Europe in 1992. The first column was a gentle introduction to chemometrics but the second was about the idea of computing new variables, as happens in PCA. Davies' first article that was directly about PCA was the last in Spectroscopy World and the first TD column in Spectroscopy Europe. In 2004 Tom Fearn and Davies wrote the first of the 'Back to Basics' columns with the same title as that first column. It was about PCA and Davies does not think he can improve on it. PCA is a very useful tool but it will not solve all the problems. PCA is good at showing the groups that some samples naturally form, but this is not the same as forming the groups one would like to see. Sometimes it will work and other times something more specific is required.


Johansson P.,Chalmers University of Technology | Dauies A.M.C.,Norwich Near Infrared Consultancy
Spectroscopy Europe | Year: 2010

A study was conducted to interpret infrared and Raman spectra assisted by computational chemistry. The Raman spectrum of the room temperature ionic liquid 1-butyl-3-methyl-imidazolium tetra-fluoroborate [BMI][BF4] was shown and the task of band assignment for the experimental spectrum was simple. The computational chemistry was found to be helpful in creating a set of models, including atomic coordinates for the cation in different conformational states. Each vibrational mode was considered to be completely decoupled from all other modes and each movement from the equilibrium atomic distances to be harmonic to prevent the computational chemistry from becoming complex.


Davies A.M.C.,Norwich Near Infrared Consultancy
Spectroscopy Europe | Year: 2012

Chemometrics is concerned with the application of mathematical and statistical techniques to extract chemical and physical information from complex data, as defined by Svente Wold. Ian Cowe offered a different perspective, according to which, a Chemometrician brings knowledge of the chemical and sometimes the instrumental influences, which affect the data. People consider that there is a need for programs that education in chemometrics has been slow to develop and is still very unevenly available. ICNIRS (the international body for NIR spectroscopy) has been trying to develop a program of lectures for several years. Another recent addition to this area of on line education is from Eigenvector Research which is a well-respected chemometric company who has many years of experience in chemometric training in addition to their development of chemometric software.

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