This review article examines past and current research on the application of near-infrared (NIR) reflectance/transmittance spectroscopy (NIRS) for real-time monitoring of moisture content and density of solid wood. Most of the applications of NIRS on solid wood have focussed on the application of multivariate statistics as exploratory tools for the prediction of physical, chemical and mechanical properties, such as moisture content, density, stiffness, cellulose and lignin content. However, very few studies on the development of optical models and the use of NIRS transmittance techniques on solid wood have been reported. NIRS technology has the potential to be used as a rapid tool that could be employed for at-line measurement and monitoring of wood properties in the forest products industry.Keywords: wood properties, near-infrared spectroscopy, multivariate statistics, optical model, transmittance, reflectance résumé Cet article de revue examine la recherche passée et actuelle sur l'application de la spectroscopie proche infra-rouge en mode réflectance/transmittance pour le suivi en temps réel de la teneur en eau et de la densité du bois solide. La plupart des applications de la spectroscopie proche infra-rouge sur le bois solide ont porté sur l'application des méthodes statistiques multi-variées pour l' estimation des propriétés physiques, chimiques et mécaniques, telles que la teneur en eau, la densité, la dureté, le contenu en cellulose et en lignine. Cependant, peu d' études ont porté sur le développement de modèles optiques et sur l'utilisation de la spectroscopie proche infra-rouge en mode transmittance pour le bois solide. La spectroscopie proche infra-rouge a le potentiel d' être utilisée comme un outil rapide de mesure et suivi en temps réel des propriétés du bois dans l'industrie des produits forestiers.
b appalachian Hardwood center, West Virginia university, Morgantown, WV 26506-6125. uSa In this study, a method suitable for online rapid classification and separation of red oak and white oak wood species has been developed with the use of near infrared (NIR) spectroscopy and soft independent modeling of class analogies (SIMCA). The spectra of 10 wood specimens of each species were collected over wavelength window of 800-200 nm. The raw spectra and spectra pre-treated by first derivative and standard normal variate (SNV) transformation were used to develop calibration models using the wavelength ranges 800-200 nm, 1100-2200 nm and 1400-1900 nm by the SIMCA method. Principal component analysis (PCA) models were made for each class from the calibration set consisting of 100 specimens of red oak and white oak, respectively, and specimens not present in the calibration set (Testing set) consisting of 100 specimens were tested for classification according to the SIMCA method at the % and 2% significance level. Type I error (rejection of true member) associated with the models developed ranged from 2% to 20% and from 1% to %, respectively, for % and 2% significance level, while type II error (acceptance of a false member) was 0% for all models developed. There was no significant improvement in models developed with spectra pre-treated with first derivative or standard normal variate transformation over models developed with raw spectra. The full NIR spectral region of 800-200 nm provided the most useful information for distinguishing between the two species. The results of this study showed that NIR spectroscopy coupled with the SIMCA method of multivariate data analysis could be used to reliably separate and sort wood of red oak and white oak.
Background
Adherence is critical for successful topical, vaginally delivered anti-retroviral (ARV)-based HIV pre-exposure prophylaxis (PrEP). Quantitating systemic or tissue ARV levels through LC–MS/MS is currently viewed as the most reliable measure of adherence. However, for placebo-controlled trials, this is a high cost analysis that measures adherence only in the drug treatment group. A desirable marker of adherence is one that is measured in both placebo and drug treatment groups using a simple on-site clinical laboratory test, which allows necessary interventions for supporting participant adherence. Our objective was to develop adherence markers for four vaginal placebo products currently used as microbicide delivery systems: gel, film, insert, and intravaginal ring. Excipient and spectroscopy-based approaches were used for preclinical development of the placebo markers and subsequently validated by the CONRAD 135 study. The study collected vaginal swabs collected each day for 1 week post vaginal application of gel, film, or insert in the clinic with or without sex. Intravaginal rings were collected after 1 day, 7, and 30 days of use.
Results
Placebo gel, film, and insert in vaginal swabs were successfully detected by specific excipient colorimetric or probe-based assays for hydroxyethylcellulose, glycerin, and sorbitol respectively, as well as spectroscopy-based prediction models. The range of detection for gel, film, and insert in swabs collected up to 16 h post vaginal application was 70-100% of the total swabs per time point, with some markers showing potential for longer duration. Decreasing residual glycerin levels and increasing bioanalyte penetration of vaginally used intravaginal rings showed significant changes between 1 and 30 days of use.
Conclusions
We demonstrated clinical proof-of-concept that adherence markers for placebo product can be measured using simple, lower cost approaches. Measuring adherence in both placebo and drug arms of a HIV PrEP study would better inform future trial designs.
Electronic supplementary material
The online version of this article (10.1186/s40169-018-0213-6) contains supplementary material, which is available to authorized users.
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