TY - JOUR A1 - Schlappa, Stephanie A1 - Brenker, Lee Josephine A1 - Bressel, Lena A1 - Hass, Roland A1 - Münzberg, Marvin T1 - Process characterization of polyvinyl acetate emulsions applying inline photon density wave spectroscopy at high solid contents JF - Polymers / Molecular Diversity Preservation International N2 - The high solids semicontinuous emulsion polymerization of polyvinyl acetate using poly (vinyl alcohol-co-vinyl acetate) as protective colloid is investigated by optical spectroscopy. The suitability of Photon Density Wave (PDW) spectroscopy as inline Process Analytical Technology (PAT) for emulsion polymerization processes at high solid contents (>40% (w/w)) is studied and evaluated. Inline data on absorption and scattering in the dispersion is obtained in real-time. The radical polymerization of vinyl acetate to polyvinyl acetate using ascorbic acid and sodium persulfate as redox initiator system and poly (vinyl alcohol-co-vinyl acetate) as protective colloid is investigated. Starved-feed radical emulsion polymerization yielded particle sizes in the nanometer size regime. PDW spectroscopy is used to monitor the progress of polymerization by studying the absorption and scattering properties during the synthesis of dispersions with increasing monomer amount and correspondingly decreasing feed rate of protective colloid. Results are compared to particle sizes determined with offline dynamic light scattering (DLS) and static light scattering (SLS) during the synthesis. KW - photon density wave spectroscopy KW - multiple light scattering KW - emulsion KW - polymerization KW - process analytical technology KW - polyvinyl acetate Y1 - 2021 U6 - https://doi.org/10.3390/polym13040669 SN - 2073-4360 VL - 13 IS - 4 PB - MDPI CY - Basel ER - TY - JOUR A1 - Sandmann, Michael A1 - Münzberg, Marvin A1 - Bressel, Lena A1 - Reich, Oliver A1 - Hass, Roland T1 - Inline monitoring of high cell density cultivation of Scenedesmus rubescens in a mesh ultra-thin layer photobioreactor by photon density wave spectroscopy JF - BMC Research Notes / Biomed Central N2 - Objective Due to multiple light scattering that occurs inside and between cells, quantitative optical spectroscopy in turbid biological suspensions is still a major challenge. This includes also optical inline determination of biomass in bioprocessing. Photon Density Wave (PDW) spectroscopy, a technique based on multiple light scattering, enables the independent and absolute determination of optical key parameters of concentrated cell suspensions, which allow to determine biomass during cultivation. Results A unique reactor type, called "mesh ultra-thin layer photobioreactor" was used to create a highly concentrated algal suspension. PDW spectroscopy measurements were carried out continuously in the reactor without any need of sampling or sample preparation, over 3 weeks, and with 10-min time resolution. Conventional dry matter content and coulter counter measurements have been employed as established offline reference analysis. The PBR allowed peak cell dry weight (CDW) of 33.4 g L-1. It is shown that the reduced scattering coefficient determined by PDW spectroscopy is strongly correlated with the biomass concentration in suspension and is thus suitable for process understanding. The reactor in combination with the fiber-optical measurement approach will lead to a better process management. KW - Photon density wave spectroscopy KW - Multiple light scattering KW - Process KW - analytical technology KW - Fiber-optical spectroscopy KW - Mesh ultra-thin layer KW - photobioreactor Y1 - 2022 U6 - https://doi.org/10.1186/s13104-022-05943-2 SN - 1756-0500 VL - 15 IS - 1 PB - Biomed Central (London) CY - London ER - TY - JOUR A1 - Mink, Albert A1 - McHardy, Christopher A1 - Bressel, Lena A1 - Rauh, Cornelia A1 - Krause, Mathias J. T1 - Radiative transfer lattice Boltzmann methods BT - 3D models and their performance in different regimes of radiative transfer JF - Journal of quantitative spectroscopy & radiative transfer N2 - The numerical prediction of radiative transport is a challenging task due to the complexity of the radiative transport equation. We apply the lattice Boltzmann method (LBM), originally developed for fluid flow problems, to solve the radiative transport in volume. One model (meso RTLBM) is derived directly from a discretization of the radiative transport equation, yielding in a precise but numerical costly scheme. The second model (macro RTLBM) solves the Helmholtz equation, which is a proper approximation for highly scattering volumes. Both numerical algorithms are validated against Monte-Carlo data for a set of 35 optical parameters, which correspond to radiative transport ranging from ballistic to diffuse regimes. Together with a set of four benchmark simulations, the comprehensive validation concludes the overall quality and detects asymptotic trends for radiative transport LBM. Furthermore, an accuracy map is presented, which summarizes the error for all parameters. This graph allows to determine the validity range for both radiative transport LBM at a glance. Finally, comprehensive guidelines are formulated to facilitate the choice of the radiative transport LBM model. KW - Radiative transport KW - Lattice Boltzmann methods KW - Monte-Carlo KW - Analysis scattering kernel KW - Optical parameter set Y1 - 2019 U6 - https://doi.org/10.1016/j.jqsrt.2019.106810 SN - 0022-4073 SN - 1879-1352 VL - 243 PB - Pergamon Press CY - Oxford ER - TY - JOUR A1 - Hille, Carsten A1 - Berg, Maik A1 - Bressel, Lena A1 - Munzke, Dorit A1 - Primus, Philipp A1 - Löhmannsröben, Hans-Gerd A1 - Dosche, Carsten T1 - Time-domain fluorescence lifetime imaging for intracellular pH sensing in living tissues N2 - pH sensing in living cells represents one of the most prominent topics in biochemistry and physiology. In this study we performed one-photon and two-photon time-domain fluorescence lifetime imaging with a laser-scanning microscope using the time-correlated single-photon counting technique for imaging intracellular pH levels. The suitability of different commercial fluorescence dyes for lifetime-based pH sensing is discussed on the basis of in vitro as well of in situ measurements. Although the tested dyes are suitable for intensity-based ratiometric measurements, for lifetime- based techniques in the time-domain so far only BCECF seems to meet the requirements of reliable intracellular pH recordings in living cells. Y1 - 2008 U6 - https://doi.org/10.1007/s00216-008-2147-0 ER - TY - JOUR A1 - Hass, Roland A1 - Münzberg, Marvin A1 - Bressel, Lena A1 - Reich, Oliver T1 - Industrial applications of photon density wave spectroscopy for in-line particle sizing [Invited] JF - Applied optics N2 - Optical spectroscopy in highly turbid liquid material is often restricted by simultaneous occurrence of absorption and scattering of light. Photon Density Wave (PDW) spectroscopy is one of the very few, yet widely unknown, technologies for the independent quantification of these two optical processes. Here, a concise overview about modern PDW spectroscopy is given, including all necessary equations concerning the optical description of the investigated material, dependent light scattering, particle sizing, and PDW spectroscopy itself. Additionally, it is shown how the ambiguity in particle sizing, arising from Mie theory, can be correctly solved. Due to its high temporal resolution, its applicability to highest particle concentrations, and its purely fiber-optical probe, PDW spectroscopy possesses all fundamental characteristics for optical in-line process analysis. Several application examples from the chemical industry are presented. (C) 2013 Optical Society of America Y1 - 2013 U6 - https://doi.org/10.1364/AO.52.001423 SN - 1559-128X SN - 2155-3165 VL - 52 IS - 7 SP - 1423 EP - 1431 PB - Optical Society of America CY - Washington ER - TY - JOUR A1 - Bressel, Lena A1 - Reich, Oliver T1 - Theoretical and experimental study of the diffuse transmission of light through highly concentrated absorbing and scattering materials Part I: Monte-Carlo simulations JF - Journal of quantitative spectroscopy & radiative transfer N2 - In many technical materials and commercial products like sunscreen or paint high particle and absorber concentrations are present. An important parameter for slabs of these materials is the diffuse transmission of light, which quantifies the total amount of directly and diffusely transmitted light. Due to the high content of scattering particles not only multiple scattering but also additional dependent scattering occurs. Hence, simple analytical models cannot be applied to calculate the diffuse transmission. In this work a Monte-Carlo program for the calculation of the diffuse transmission of light through dispersions in slab-like geometry containing high concentrations of scattering particles and absorbers is presented and discussed in detail. Mie theory is applied for the calculation of the scattering properties of the samples. Additionally, dependent scattering is considered in two different models, the well-known hard sphere model in the Percus-Yevick approximation (HSPYA) and the Yukawa model in the Mean Spherical Approximation (YMSA). Comparative experiments will show the accurateness of the program as well as its applicability to real samples [1]. (C) 2014 Elsevier Ltd. All rights reserved. KW - Monte-Carlo simulations KW - Multiple light scattering KW - Dependent light scattering KW - Hard sphere model in the Percus-Yevick Approximation KW - Yukawa model in the Mean Spherical Approximation KW - Polymer dispersions Y1 - 2014 U6 - https://doi.org/10.1016/j.jqsrt.2014.01.007 SN - 0022-4073 SN - 1879-1352 VL - 146 SP - 190 EP - 198 PB - Elsevier CY - Oxford ER - TY - GEN A1 - Bressel, Lena A1 - Herzog, Bernd A1 - Reich, Oliver T1 - Monte-Carlo simulations of light transport in dense materials BT - dependent scattering and influence on sunscreen formulations T2 - Diffuse Optical Spectroscopy and Imaging N2 - Monte-Carlo calculations are carried out to simulate the light transport in dense materials. Focus lies on the calculation of diffuse light transmission through films of scattering and absorbing media considering additionally the effect of dependent scattering. Different influences like interaction type between particles, particle size, composition etc. can be studied by this program. Simulations in this study show major influences on the diffuse transmission. Further simulations are carried out to model a sunscreen film and study best compositions of this film and will be presented. KW - Monte-Carlo simulations KW - dependent scattering KW - sunscreen KW - light scattering KW - high concentrations Y1 - 2019 SN - 978-1-5106-2841-0 SN - 978-1-5106-2842-7 U6 - https://doi.org/10.1117/12.2527076 SN - 0277-786X SN - 1996-756X VL - 11074 PB - SPIE CY - Bellingham ER - TY - JOUR A1 - Bressel, Lena A1 - Hass, Roland A1 - Reich, O. T1 - Particle sizing in highly turbid dispersions by Photon Density Wave spectroscopy JF - JOURNAL OF QUANTITATIVE SPECTROSCOPY & RADIATIVE TRANSFER N2 - Photon Density Wave (PDW) spectroscopy is presented as a fascinating technology for the independent determination of scattering (mu(s)’ and absorption (ita) properties of highly turbid liquid dispersions. The theory is reviewed introducing new expressions for the PDW coefficients k(I) and k(Phi). Furthermore, two models for dependent scattering, namely the hard sphere model in the Percus-Yevick Approximation (HSPYA) and the Yukawa model in the Mean Spherical Approximation (YMSA), are experimentally examined. On the basis of the HSPYA particle sizing is feasible in dispersions of high ionic strength. It is furthermore shown that in dialyzed dispersions or in technical copolymers with high particle charge only the YMSA allows for correct dilution-free particle sizing. (C) 2013 Elsevier Ltd. All rights reserved. KW - Photon Density Wave spectroscopy KW - Multiple light scattering KW - Dependent light scattering KW - Percus-Yevick model KW - Yukawa model KW - Particle sizing KW - Polymer dispersions Y1 - 2013 U6 - https://doi.org/10.1016/j.jqsrt.2012.11.031 SN - 0022-4073 VL - 126 IS - 1 SP - 122 EP - 129 PB - PERGAMON-ELSEVIER SCIENCE LTD CY - OXFORD ER -