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Cernuda C.,Johannes Kepler University | Lughofer E.,Johannes Kepler University | Hintenaus P.,University of Salzburg | Marzinger W.,I RED Infrarot Systeme GmbH | And 3 more authors.
Chemometrics and Intelligent Laboratory Systems | Year: 2013

In melamine resin production process, it is essential to supervise the condensation process. Monitoring the value of the cloud point indicates the best point of time to stop the condensation. Currently, the supervision is conducted manually by operators, which from time to time need to draw and analyze samples from the production process. In order to increase efficiency and to improve quantification quality, in this paper we investigate the usage of non-linear chemometric models, which are calibrated based on near infrared (FTNIR) process spectrum measurements. They rely on fuzzy systems model architecture and are able to incrementally adapt themselves during the on-line process, resolving dynamic process changes which may appear on-line over time due to long-term fluctuations (e.g., caused by dirt) and changes in the composition of the educt, often leading to severe error drifts of static models. Extracting the most informative wavebands prior to model training is essential to avoid a curse of dimensionality; this is achieved by a new extended variant of forward selection, termed as forward selection with bands (. FSB). Furthermore, variants of how to integrate auxiliary sensor information (temperature, pH value, pressure) together with the FTNIR spectra are presented (. hybridity). A specific ensemble strategy is developed which is able to properly compensate noise in repeated spectrum measurements. Results on high-dimensional data from four independent types of melamine resin show that 1) our non-linear modeling methodology can outperform state-of-the-art linear and non-linear chemometric modeling methods in terms of validation error, 2) the ensemble strategy is able to improve the performance of models without ensembling significantly and 3) incremental model updates are necessary in order to keep the predictive quality of the models high by preventing drifting residuals. © 2013 Elsevier B.V.


Katletz S.,Recendt GmbH | Pfleger M.,Recendt GmbH | Puhringer H.,Recendt GmbH | Mikulics M.,Jülich Research Center | And 6 more authors.
Optics Express | Year: 2012

We present a practicable way to take advantage of the spectral information contained in a broadband terahertz pulse for the determination of birefringence and orientation of the optical axis in a glass fiber reinforced polymer with a single measurement. Our setup employs circularly polarized terahertz waves and a polarization-sensitive detector to measure both components of the electromagnetic field simultaneously. The anisotropic optical parameters are obtained from an analysis of the phase and frequency resolved components of the terahertz field. This method shows a high tolerance against the skew of the detection axes and is also independent of a reference measurement. © 2012 Optical Society of America.


Katletz S.,Recendt GmbH | Pfleger M.,Recendt GmbH | Puhringer H.,Recendt GmbH | Vieweg N.,TU Braunschweig | And 7 more authors.
Optics Express | Year: 2011

In this work, we develop a pulsed terahertz imaging system in reflection geometry, where due to scanning of the terahertz beam neither the sample nor the emitter and detector have to be moved. We use a two mirror galvanoscanner for deflecting the beam, in combination with a single rotationally symmetric focusing lens. In order to efficiently image planar structures, we develop an advanced scanning routine that resolves all bending effects of the imaging plane already during measurement. Thus, the measurement time is reduced, and efficient imaging of surfaces and interfaces becomes possible. We demonstrate the potential of this method in particular for a plastic-metal composite sample, for which non-destructive evaluation of an interface is performed. © 2011 Optical Society of America.


PubMed | Johannes Kepler University, RECENDT GmbH, Basque Center for Applied Mathematics and BrauUnion GmbH
Type: Journal Article | Journal: Analytical and bioanalytical chemistry | Year: 2016

During the production process of beer, it is of utmost importance to guarantee a high consistency of the beer quality. For instance, the bitterness is an essential quality parameter which has to be controlled within the specifications at the beginning of the production process in the unfermented beer (wort) as well as in final products such as beer and beer mix beverages. Nowadays, analytical techniques for quality control in beer production are mainly based on manual supervision, i.e., samples are taken from the process and analyzed in the laboratory. This typically requires significant lab technicians efforts for only a small fraction of samples to be analyzed, which leads to significant costs for beer breweries and companies. Fourier transform mid-infrared (FT-MIR) spectroscopy was used in combination with nonlinear multivariate calibration techniques to overcome (i) the time consuming off-line analyses in beer production and (ii) already known limitations of standard linear chemometric methods, like partial least squares (PLS), for important quality parameters Speers et al. (J I Brewing. 2003;109(3):229-235), Zhang et al. (J I Brewing. 2012;118(4):361-367) such as bitterness, citric acid, total acids, free amino nitrogen, final attenuation, or foam stability. The calibration models are established with enhanced nonlinear techniques based (i) on a new piece-wise linear version of PLS by employing fuzzy rules for local partitioning the latent variable space and (ii) on extensions of support vector regression variants (-PLSSVR and -PLSSVR), for overcoming high computation times in high-dimensional problems and time-intensive and inappropriate settings of the kernel parameters. Furthermore, we introduce a new model selection scheme based on bagged ensembles in order to improve robustness and thus predictive quality of the final models. The approaches are tested on real-world calibration data sets for wort and beer mix beverages, and successfully compared to linear methods, showing a clear out-performance in most cases and being able to meet the model quality requirements defined by the experts at the beer company. Figure Workflow for calibration of non-Linear model ensembles from FT-MIR spectra in beer production.


Ramer G.,Vienna University of Technology | Kasberger J.,RECENDT GmbH | Brandstetter M.,Vienna University of Technology | Saeed A.,Johannes Kepler University | And 2 more authors.
Applied Physics B: Lasers and Optics | Year: 2014

We present the design and fabrication of a single-mode slab waveguide structure for mid-infrared spectroscopy optimized for broadband coupling. The sensor uses grating couplers for robust off-axis coupling and a silicon nitride guiding layer for mechanical robustness. An external cavity quantum cascade laser-based transmission method is introduced for characterizing the structure's broadband coupling behavior. Light from an external cavity quantum cascade laser with a spectral range of 0.5 μm around 6 μm was coupled into the waveguide without the need for moving parts. First spectra taken with this sensor are presented. © 2013 Springer-Verlag Berlin Heidelberg.


Cernuda C.,Johannes Kepler University | Lughofer E.,Johannes Kepler University | Marzinger Wolfgang W.,I RED Infrarot Systeme GmbH | Kasberger J.,Recendt GmbH
Chemometrics and Intelligent Laboratory Systems | Year: 2011

In polyetheracrylat (PEA) production, it is important to monitor three process parameters in order to assure a high quality of the final product: hydroxyl (OH) number, viscosity and acidity (acid number). Due to the high resolution and high sensitivity, it has been shown in the past that the Fourier transform near infrared (FTNIR) process spectrum measurements can be used to obtain spectra with precise content information about these process parameters. In order to perform an automatic supervision and to reduce the (off-line, laboratory) analysis effort of experts and operators of these substances, chemometric quantification models have to be used. In this paper, we investigate the usage of a specific type of fuzzy systems, so-called Takagi-Sugeno fuzzy systems, for calibrating the chemometric models. This type of model architecture supports the usage of piecewise local linear predictors, being able to model flexibly different degrees of non-linearities implicitly contained in the mapping between NIR spectra and reference values. The training of these models is conducted by an evolving clustering method (adding new local linear models on demand) and a local (weighted) least squares estimation of the consequent parameters, and connected with a wavelength (dimensionality) reduction mechanism. Results on a concrete data set show that it can outperform state-of-the-art calibration methods as well as support vector regression as alternative non-linear model. © 2011 Elsevier B.V.


Cernuda C.,Johannes Kepler University | Lughofer E.,Johannes Kepler University | Suppan L.,Kompetenzzentrum Holz GmbH | Roder T.,Lenzing AG | And 4 more authors.
Analytica Chimica Acta | Year: 2012

In viscose production, it is important to monitor three process parameters in order to assure a high quality of the final product: the concentrations of H 2SO 4, Na 2SO 4 and Z nSO 4. During on-line production these process parameters usually show a quite high dynamics depending on the fiber type that is produced. Thus, conventional chemometric models, which are trained based on collected calibration spectra from Fourier transform near infrared (FT-NIR) measurements and kept fixed during the whole life-time of the on-line process, show a quite imprecise and unreliable behavior when predicting the concentrations of new on-line data. In this paper, we are demonstrating evolving chemometric models which are able to adapt automatically to varying process dynamics by updating their inner structures and parameters in a single-pass incremental manner. These models exploit the Takagi-Sugeno fuzzy model architecture, being able to model flexibly different degrees of non-linearities implicitly contained in the mapping between near infrared spectra (NIR) and reference values. Updating the inner structures is achieved by moving the position of already existing local regions and by evolving (increasing non-linearity) or merging (decreasing non-linearity) new local linear predictors on demand, which are guided by distance-based and similarity criteria. Gradual forgetting mechanisms may be integrated in order to out-date older learned relations and to account for more flexibility of the models. The results show that our approach is able to overcome the huge prediction errors produced by various state-of-the-art chemometric models. It achieves a high correlation between observed and predicted target values in the range of [0.95,0.98] over a 3 months period while keeping the relative error below the reference error value of 3%. In contrast, the off-line techniques achieved correlations below 0.5, ten times higher error rates and the more deteriorate, the more time passes by. © 2012 Elsevier B.V.


Passler K.,University of Graz | Nuster R.,University of Graz | Gratt S.,University of Graz | Burgholzer P.,Recendt GmbH | And 2 more authors.
Biomedical Optics Express | Year: 2010

A dual mode scanning acoustic microscope is investigated, yielding simultaneously images with optical and acoustical contrast. Short laser pulses are used to excite acoustic waves in a sample for the photoacoustic imaging mode. At the same time the pulses irradiate a conical target generating limited diffraction acoustic waves (X-waves) for large depth of field ultrasound imaging. For photoacoustic as well as for ultrasound imaging a focusing, ring shaped detector is applied. First phantom experiments demonstrate the possibility to acquire data for both imaging modes in a single scan, by separating images due to their different time of flight. © 2010 Optical Society of America.


Grun H.,RECENDT GmbH | Berer T.,RECENDT GmbH | Burgholzer P.,RECENDT GmbH | Nuster R.,University of Graz | Paltauf G.,University of Graz
Journal of Biomedical Optics | Year: 2010

For photoacoustic imaging, usually point-like detectors are used. As a special sensing technology for photoacoustic imaging, integrating detectors have been investigated that integrate the acoustic pressure over an area or line that is larger than the imaged object. Different kinds of optical fiber-based detectors are compared regarding their sensitivity and resolution in three-dimensional photoacoustic tomography. In the same type of interferometer, polymer optical fibers yielded much higher sensitivity than glass fibers. Fabry-Pérot glassfiber interferometers in turn gave higher sensitivity than Mach-Zehnder-type interferometers. Regarding imaging resolution, the single-mode glass fiber showed the best performance. Last, three-dimensional images of phantoms and insects using a glass-fiber-based Fabry-Pérot interferometer as integrating line detector are presented. © 2010 Society of Photo-Optical Instrumentation Engineers.


Grun H.,RECENDT GmbH
Journal of biomedical optics | Year: 2010

For photoacoustic imaging, usually point-like detectors are used. As a special sensing technology for photoacoustic imaging, integrating detectors have been investigated that integrate the acoustic pressure over an area or line that is larger than the imaged object. Different kinds of optical fiber-based detectors are compared regarding their sensitivity and resolution in three-dimensional photoacoustic tomography. In the same type of interferometer, polymer optical fibers yielded much higher sensitivity than glass fibers. Fabry-Perot glass-fiber interferometers in turn gave higher sensitivity than Mach-Zehnder-type interferometers. Regarding imaging resolution, the single-mode glass fiber showed the best performance. Last, three-dimensional images of phantoms and insects using a glass-fiber-based Fabry-Perot interferometer as integrating line detector are presented.

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