| 1. |
- Abrahamsson, Christoffer, et al.
(författare)
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Scatter correction of transmission NIR spectra by photon migration data - Quantitative analysis of solids
- 2005
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 6009, s. 60090-60090
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Konferensbidrag (refereegranskat)abstract
- The scope of this presentation is a new methodology to correct conventional NIR data for scattering effects. The technique aims at measuring the absorption coefficient of the samples rather than the total attenuation, measured by 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 measurements in this work were made using a novel system for time-resolved measurements, based on short light continuum pulses generated in an index-guided crystal fibre and a spectrometer-equipped streak camera. The system enables spectral recordings in the wavelength range 500 - 1200 nm with a spectral resolution of 5 nm and a temporal resolution of 30 ps. The evaluation scheme is based on modeling of light transport by diffusion theory, that provides an independent measure of the scattering properties of the samples, that later is used to correct conventional NIR data. This yields a clear advantage over other pre-processing techniques, where scattering effects are estimated and corrected for by using the shape of the measured spectrum only. PLS calibration models shows that, by using the proposed evaluation scheme, the predictive ability is improved by 50% as compared to models based on conventional NIR data. The method also makes it possible to predict the concentration of active substance in samples with physical properties different from those of the samples included in the calibration model.
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| 2. |
- Bergenholtz, Johan, 1964, et al.
(författare)
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On-off dissociation dynamics of colloidal doublets
- 2013
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 104:1
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Tidskriftsartikel (refereegranskat)abstract
- First-passage time theory is used to analyze the dissociation behavior of doublets of colloidal particles. The first-passage time distribution for particles interacting via a DLVO potential is determined numerically. For strongly attractive particles the distribution becomes broad such that the mean first-passage time becomes a poor measure of the dynamics. In spite of this, use can be made of the mean in a matching condition, which allows for reproducing distributions for strongly attractive doublets by a semi-analytical solution for particles interacting only through surface adhesion. The smallest eigenvalue in the analytical solution, which governs the long-time asymptotic behavior of the first-passage time distribution, is identified analytically for strongly attractive pairs of particles. In addition, in this limit the distribution is shown to asymptote to an exponential distribution, which means that the dissociation process can be simply captured by an on-off model, without sacrificing the effect of the surface chemistry, with a constant probability for dissociation. This probability is simply related to the surface-adhesive parameter and the separation distance at which the pair of particles ceases to be considered a doublet.
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| 3. |
- Bonmann, Marlene, 1988, et al.
(författare)
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Terahertz radar observes powder dynamics for pharmaceutical manufacturing
- 2024
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Ingår i: IEEE Sensors Journal. - 1558-1748 .- 1530-437X. ; 24:13, s. 20512-20522
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Tidskriftsartikel (refereegranskat)abstract
- The optical opaqueness of powders has precluded the observation of powder flow dynamics in processing tubes, with important implications, for example, in the pharmaceutical industry, where non-destructive monitoring during the manufacturing process is essential to ensure the quality of the final product and the effectiveness of the process. Taking advantage of the high penetration of terahertz electromagnetic waves in powders and its wavelength-to-particle size ratio, we demonstrate that a submillimeter-wave pulse-Doppler radar can overcome the present challenges and characterize powder flow dynamics in pharmaceutical manufacturing processes. Mimicking typical vessel shapes in pharmaceutical operations, we were able to characterize falling powder streams in a tube with a sample volume resolution of a few cubic centimeters and a range resolution of about 5 mm. We successfully monitored particle velocity, particle distribution within the tube, and mass flow rate in real-time. This remote sensing method, based on advanced terahertz electronics, opens up the possibility to study and monitor powder dynamics in a wide range of applications.
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| 4. |
- Brülls, Mikael, et al.
(författare)
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Applying spectral peak area analysis in near-infrared spectroscopy moisture assays
- 2007
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Ingår i: Journal of Pharmaceutical and Biomedical Analysis. - : Elsevier BV. - 0731-7085. ; 44:1, s. 127-136
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Tidskriftsartikel (refereegranskat)abstract
- Spectral peak area analysis has in this study been shown to be a viable method in near-infrared spectroscopy (NIRS) moisture assays. The study also shows that the required number of calibration samples can be minimized, and the method is, therefore, especially suitable for moisture assays in early formulation development and in-situ process monitoring.Diffuse NIRS was utilized in the development of moisture assays for the model compounds polyvinylpyrrolidone and hydroxypropyl-beta-cyclodextrin and also for a lyophilized formulation. Reference data were obtained using coulometric Karl Fischer titration. The NIRS measurements were performed through the bottoms of the sample vials using either a Fourier Transform-Near-infrared (FT-NIR) spectrometer fitted with a diffuse reflectance probe or a dispersive single beam spectrometer. The ratios of the peak areas of a water peak at 5200 cm(-1) and a reference peak were evaluated using linear regression analysis. The spectral peak area analysis method was compared with a conventional partial least squares regression method. The moisture assays were verified using independent test sets. The investigated moisture range was 0-22% for the samples of PVP, 0-8.5% for the samples of hydroxypropyl-beta-cyclodextrin and 0.5-8.5% for the samples of the lyophilized formulation.The results of the spectral peak area analysis and the conventional partial least squares regression were similar, but the peak area method was more robust and could also make accurate predictions for lyophilized PVP samples, although the calibration set consisted of non-lyophilized samples. The peak area method required fewer calibration samples than the conventional partial least squares regression method.
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| 5. |
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| 6. |
- Cerullo, Livia, 1982, et al.
(författare)
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Concurrent estimation of space and frequency variation for dielectrics: a microwave tomography system for process sensing applications
- 2011
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Ingår i: Proceedings of the 9th International Conference on Electromagnetic Wave Interaction with Water and Moist Substances, Kansas City, MO USA, May 31 - June 3, 2011. - 9781629934556 ; , s. 177-184
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Konferensbidrag (refereegranskat)abstract
- In many powder processing operations, the effective complex permittivity of the material under processing yields important information concerning the state of the process. This complex permittivity varies in general with respect to both space and frequency. For an accurate estimation of the process material parameters, it is important to be able to incorporate these dependencies in the estimation algorithm. Here, we present a rather general type of parameterization that is tailored for this type of situation. The parameterization is described in terms of a parameterization mesh, which makes it feasible to refine the computational mesh without influencing the number of degrees of freedom in the estimation problem. A test case demonstrates that our approach can yield accurate reconstructions.
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| 7. |
- Cerullo, Livia, 1982, et al.
(författare)
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Inverse scattering for a closed cavity equipped with microwave antenna sensors
- 2012
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Ingår i: AntennEMB, 5-8 March, Stockholm.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Pharmaceutical processes are often hosted by completely closed vessels that are difficult of access by means of measurement equipment. In particular, it is challenging to assess the interior or global process state with sensors placed on the vessel enclosing the process. This information about the process would allow for a better process monitoring and control. Here, a novel application of microwave sensing for process tomography is presented.
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| 8. |
- Cerullo, Livia, 1982, et al.
(författare)
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Microwave measurement system for dispersive dielectric properties of densely packed pellets
- 2017
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Ingår i: Measurement: Journal of the International Measurement Confederation. - : Elsevier BV. - 0263-2241. ; 106, s. 179-189
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Tidskriftsartikel (refereegranskat)abstract
- We present a microwave measurement system that is intended for the estimation of the dispersive dielectric properties for densely packed pellets. In particular, we estimate the Debye parameters for the effective permittivity of a mixture of air and densely packed moist microcrystalline cellulose pellets for the frequency band 2.7–5.1 GHz. The Debye parameters are estimated by means of minimizing the misfit between the measured scattering parameters and the corresponding computed response given a model of the measurement system. This minimization is performed by means of a nonlinear iterative optimization procedure, which is supported by continuum sensitivities, and the optimum is found in 10–60 iterations for the cases presented in this article. We find that increasing moisture content yields an increase in the static permittivity and a decrease in the relaxation time.
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| 9. |
- Cerullo, Livia, 1982, et al.
(författare)
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Microwave Measurements for Metal Vessels
- 2013
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Ingår i: 7th European Conference on Antennas and Propagation, EuCAP 2013, Gothenburg, Sweden, 8-12 April 2013. - 2164-3342. - 9781467321877 ; , s. 3869 - 3873
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Konferensbidrag (refereegranskat)abstract
- We present two different measurement techniques intended for closed metal vessels, where the objective is to measure the permittivity inside the metal vessel. This problem is relevant for many applications found in e.g. process industry. The first approach exploits the measurement of resonance frequencies, where the metal vessel is used as a microwave resonator. In the second approach, we let the boundary of the metal vessel be equipped with aperture antennas, where the aperture antennas are implemented in terms of rectangular waveguides. The waveguide apertures loads the cavity significantly and we exploit the scattering matrix parameters for the solution of the inverse problem.
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| 10. |
- Darelius, Anders, 1977, et al.
(författare)
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A Volume-Based Multi-Dimensional Population Balance Approach for Modelling High Shear Granulation
- 2006
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Ingår i: Chemical Engineering Science. ; 61, s. 2482-2493
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Tidskriftsartikel (refereegranskat)abstract
- A volume-based multi-dimensional population balance model based on the approach used by Verkoeijen et al. (2002) is further developed and applied to a wet granulation process of pharmaceutically relevant material, performed in a high shear mixer. The model is improved by a generalization that accounts for initial non-uniformly distributed liquid and air among the different particle size classes. Only the wet massing period of the granulation process has been modelled and it is experimentally found that the pores in the granules are fully saturated by liquid, i.e. no air is present in the granules during this period. Hence, an alternative model formulation is used as no model for the air in the granules is needed. Particle volume distribution, liquid saturation, liquid to solid ratio and porosity of the granules can all be modelled, as these properties can all be expressed as combinations of three model parameters, i.e. the volume fraction of solid material, total liquid fraction and the liquid fraction inside the granules. The model is also improved by introducing a new coalescence kernel and by increasing the number of size classes used. The simulated results are compared to measurements from a series of five designed experiments where impeller speed and water content are varied. It is found that the evolution of the volume, liquid saturation and porosity distributions could all be explained by fitting the compaction and coalescence rate constants.
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