Scatter correction of transmission near-infrared spectra by photon migration data: Quantitative analysis of solids

The scope of this work is a new methodology to correct conventional near-infrared (NIR) data for scattering effects. The technique aims at measuring the absorption coefficient of the samples rather than the total attenuation measured in conventional NIR spectroscopy. The main advantage of this is that the absorption coefficient is independent of the path length of the light inside the sample and therefore independent of the scattering effects. The method is based on time-resolved spectroscopy and modeling of light transport by diffusion theory. This provides an independent measure of the scattering properties of the samples and therefore of the path length of light. This yields a clear advantage over other preprocessing techniques, where scattering effects are estimated and corrected for by using the shape of the measured spectrum only. Partial least squares (PLS) calibration models show that, by using the proposed evaluation scheme, the predictive ability is improved by 50% as compared to a model based on conventional NIR data alone. The method also makes it possible to predict the concentration of active substance in samples with other physical properties than the samples included in the calibration model

Time-resolved NIR/Vis spectroscopy for analysis of solids: Pharmaceutical tablets

Time-resolved spectroscopy in the visible and near-infrared (NIR) regions was used in a feasibility study for analysis of solid pharmaceuticals. The objective of the experiments was to study the interaction of light with pharmaceutical solids and to investigate the usefulness of the method as an analytical toot for spectroscopic analysis. In these experiments, a pulsed Ti:sapphire laser and white light generation in water was utilized to form a pulsed light source in the visible/NIR region. The light was focused onto the surface of tablets, and the transmitted light was detected by a time-resolving streak camera. Two types of measurements were performed. First, a spectrometer was put in front of the streak camera for spectral resolution. Secondly, the signal originating from different locations of the sample was collected. Time-resolved and wavelength/spatially resolved data were generated and compared for a number of different samples. The most striking result from the experiments is that the typical optical path length through a 3.5-mm-thick tablet is about 20-25 cm. This indicates very strong multiple scattering in these samples. Monte Carlo simulations and comparison with experimental data support very high scattering coefficients on the order of 500 cm(-1). Furthermore, the data evaluation shows that photons with a particular propagation time through the sample contain a higher chemical contrast than other propagation times or than steady-state information. In conclusion, time-resolved NIR spectroscopy yields more information about solid pharmaceutical samples than conventional steady-state spectroscopy

Global monitoring of fluidized-bed processes by means of microwave cavity resonances

We present an electromagnetic measurement system for monitoring of the effective permittivity in closed metal vessels, which are commonly used in the process industry. The measurement system exploits the process vessel as a microwave cavity resonator and the relative change in its complex resonance frequencies is related to the complex effective permittivity inside the vessel. Also, thermal expansion of the process vessel is taken into account and we compensate for its influence on the resonance frequencies by means of a priori information derived from a set of temperature measurements. The sensitivities, that relate the process state to the measured resonance frequencies, are computed by means of a detailed finite element model. The usefulness of the proposed measurement system is successfully demonstrated for a pharmaceutical fluidized-bed process, where the water and solid contents inside the process vessel is of interest

Pericytes contribute to airway remodeling in a mouse model of chronic allergic asthma

Myofibroblast accumulation, subepithelial fibrosis, and vascular remodeling are complicating features of chronic asthma, but the mechanisms are not clear. Platelet-derived growth factors (PDGFs) regulate the fate and function of various mesenchymal cells and have been implicated as mediators of lung fibrosis. However, it is not known whether PDGF-BB signaling via PDGFRβ, which is critical for the recruitment of pericytes to blood vessels, plays a role in airway remodeling in chronic asthma. In the present study, we used a selective PDGFRβ inhibitor (CP-673451) to investigate the role of PDGFRβ signaling in the development of airway remodeling and lung dysfunction in an established mouse model of house dust mite-induced chronic allergic asthma. Unexpectedly, we found that pharmacological inhibition of PDGFRβ signaling in the context of chronic aeroallergen exposure led to exacerbated lung dysfunction and airway smooth muscle thickening. Further studies revealed that the inflammatory response to aeroallergen challenge in mice was associated with decreased PDGF-BB expression and the loss of pericytes from the airway microvasculature. In parallel, cells positive for pericyte markers accumulated in the subepithelial region of chronically inflamed airways. This process was exacerbated in animals treated with CP-673451. The results indicate that perturbed PDGF-BB/PDGFRβ signaling and pericyte accumulation in the airway wall may contribute to airway remodeling in chronic allergic asthma

Residence time distributions of different size particles in the spray zone of a Wurster fluid bed studied using DEM-CFD

Particle cycle and residence time distributions in different regions, particularly in the spray zone, play an important role in fluid bed coating. In this study, a DEM-CFD (discrete element method, computational fluid dynamics) model is employed to determine particle cycle and residence time distributions in a laboratory-scale Wurster fluid bed coater. The calculations show good agreement with data obtained using the positron emission particle tracking (PEPT) technique. The DEM-CFD simulations of different size particles show that large particles spend a longer time in the spray zone and in the Wurster tube than small particles. In addition, large particles are found on average to move closer to the spray nozzle than small particles, which implies that the large particles could shield small particles from the spray droplets. Both of these effects suggest that large particles receive a greater amount of coating solution per unit area per cycle than small particles. However, the simulations in combination with the PEPT experiments show that this is partly compensated for by a longer cycle time for large particles. Large particles thus receive more coating per unit area per pass through the spray zone, but also travel through the spray zone less frequently than small particles