PLEPS: Pulsed low energy positron system

PLEPS, operated by the Universität der Bundeswehr München, located at NEPOMUC, is a unique tool for depth profiling of defects with positron annihilation lifetime spectroscopy using a pulsed positron beam of variable energy

Cultivation of CHO Cells in Thomson Optimum Growth™ Shake Flasks and Scale-up

In biotechnology, the usage of shaking flasks in upstream processing is widely common due to the easy handling. Frequent applications are process screening and optimization. Thereby, the focus lies mostly on a homogeneous and fast distribution of substrates and gases whilst power consumption and shearing force are meant to be kept low, which ideally results in high biomass concentrations and product titers. For characterization purposes, the mixing time and the oxygen mass transfer coefficient (kLa) were measured in 5 L and 500 mL Thomson Optimal Growth™ shaking flasks, using the de-colorization or the dynamic gassing-out method, respectively. Those geometrical optimized bioreactors are promising higher space-time yields compared to the predominant Erlenmeyer-shake flask design. According to the results of the procedural experiments, CHO (Chinese hamster ovary) cells were cultivated at selected, auspicious parameter combinations. The effectiveness of the predetermined parameters was evaluated and a scale-up method elaborated. The results can be summarized as follows: The key parameter for all experimental setups is the shaking rate. In contrast, the filling volume showed to have a more ambiguous role. Modeling results in the 500 mL flasks showed no significant influence of the filling volume to the maximal cell density, in contrast to the 5L flask (both shaken at 50 mm throw). The highest viable cell density (up to 4.8∙10⁶ cells mL⁻¹) was reached using the 500 mL flask with high shaking rates at 50 mm shaking diameter. Thereby, a µmax of 0.038 h-1 was achieved that correlates with a td of less than 19 h. All in all, the highest µmax of 0.055 h⁻¹ was reached during the scale-up process, whereby higher viable cell densities were reached compared to the batch cultivations using the same parameter settings. In addition to the experiments performed to date, simulations with computational fluid dynamics and experimental determination of specific power consumption rates are already in progress, increasing the range of applicability and the validity of the proposed model correlations

A combined experimental and theoretical study of small and large vacancy clusters in tungsten

Publisher Copyright: © 2022 The AuthorsTungsten is considered to be used in the future fusion reactors as plasma-facing material. In such ex-treme environments, defects are induced in materials that modify their macroscopic properties such as the mechanical ones. It is of paramount importance to be able to determine concentration and size of the vacancy defects, from the mono vacancy to the large cavities, to validate the models developed to predict the evolution of the microstructure of irradiated materials. Positrons are very useful non-destructive probes that can characterize vacancy-type defects in materials. We present a combined ex-perimental and theoretical study on detecting and estimating the sizes of vacancy clusters that are invis-ible with electron microscopy in tungsten, using positron annihilation spectroscopy. We here model the positron annihilation in the tungsten lattice and in vacancy-type defects using state-of-the-art first prin-ciples methodology. The Doppler broadening spectra and positron lifetimes in tungsten are calculated with two-component density functional theory with local density approximation and weighted density approximation. Our calculations are in excellent agreement with our experimental results. We show that the sizes of vacancy clusters in tungsten can be well estimated by combining both positron lifetimes and Doppler broadening spectra. We also determine the limit of validity of the canonical calculation method, which here is shown to fail when the vacancy clusters grow beyond their nucleation stage. This work is a first step needed to better interpret the measured positron annihilation characteristics (Doppler and lifetime) in tungsten and then extract quantitative data on small vacancy defects required to improve the understanding of early-stage vacancy defect evolution in tungsten. The method used in this paper could be used to study other metallic materials.(c) 2022 The Authors. Published by Elsevier B.V.This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )Peer reviewe

Identification of lead vacancy defects in lead halide perovskites

Perovskite photovoltaics advance rapidly, but questions remain regarding point defects: while experiments have detected the presence of electrically active defects no experimentally confirmed microscopic identifications have been reported. Here we identify lead monovacancy (VPb) defects in MAPbI3 (MA = CH3NH3+) using positron annihilation lifetime spectroscopy with the aid of density functional theory. Experiments on thin film and single crystal samples all exhibited dominant positron trapping to lead vacancy defects, and a minimum defect density of ~3 7 1015 cm−3 was determined. There was also evidence of trapping at the vacancy complex (VPbVI)− in a minority of samples, but no trapping to MA-ion vacancies was observed. Our experimental results support the predictions of other first-principles studies that deep level, hole trapping, VPb2−, point defects are one of the most stable defects in MAPbI3. This direct detection and identification of a deep level native defect in a halide perovskite, at technologically relevant concentrations, will enable further investigation of defect driven mechanisms

Non-steady diffusion and adsorption of organic micropollutants in ion-exchange membranes : effect of the membrane thickness

There is no efficient wastewater treatment solution for removing organic micropollutants ( OMPs), which, therefore, are continuously introduced to the Earth's surface waters. This creates a severe risk to aquatic ecosystems and human health. In emerging water treatment processes based on ion-exchange membranes (IEM), transport of OMPs through membranes remains unknown. We performed a comprehensive investigation of theOMPtransport through a single IEM under non- steady-state conditions. For the first time, positron annihilation lifetime spectroscopy was used to study differences in the free volume element radius between anion- and cation-exchangemembranes, and between their thicknesses. The dynamic diffusion-adsorption model was used to calculate the adsorption and diffusion coefficients ofOMPs. Remarkably, diffusion coefficients increased with the membrane thickness, where its surface resistance was more evident in thinner membranes. Presented results will contribute to the improved design of next-generation IEMs with higher selectivity toward multiple types of organic compounds

Prediction of pregnancy state from milk mid-infrared (MIR) spectroscopy in dairy cows

Submitted 2020-07-14 | Accepted 2020-08-18 | Available 2020-12-01https://doi.org/10.15414/afz.2020.23.mi-fpap.224-232Pregnancy assessment is a very important tool for the reproductive management in efficient and profitable dairy farms. Nowadays, mid-infrared (MIR) spectroscopy is the method of choice in the routine milk recording system for quality control and to determine standard milk components. Since it is well known that there are changes in milk yield and composition during pregnancy, the aim of this study was to develop a discriminant model to predict the pregnancy state from routinely recorded MIR spectral data. The data for this study was from the Austrian milk recording system. Test day records of Fleckvieh, Brown Swiss and Holstein Friesian cows between 3 and 305 days of lactation were included in the study. As predictor variables, the first derivative of 212 selected MIR spectral wavenumbers were used. The data set contained roughly 400,000 records from around 40,000 cows and was randomly split into calibration and validation set by farm. Prediction was done with Partial Least Square Discriminant Analysis. Indicators of model fit were sensitivity, specificity, balanced accuracy and Area Under Receiver Operating Characteristic Curve (AUC). In a first approach, one discriminant model for all cows across the whole lactation and gestation lengths was applied. The sensitivity and specificity of this model in validation were 0.856 and 0.836, respectively. Splitting up the results for different lactation stages showed that the model was not able to predict pregnant cases before the third month of lactation and vice versa not able to predict non-pregnancy after the third month of lactation. Consequently, in the second approach a prediction model for each different (expected) pregnancy stage and lactation stage was developed. Balanced accuracies ranged from 0.523 to 0.918. Whether prediction accuracies from this study are sufficient to provide farmers with an additional tool for fertility management, it needs to be explored in discussions with farmers and breeding organizations.Keywords: MIR spectroscopy, pregnancy prediction, dairy cow, PLSReferencesBalhara, A. K., Gupta, M., Singh, S., Mohanty, A. K., & Singh, I. (2013). Early pregnancy diagnosis in bovines: Current status and future directions. The Scientific World Journal, 2013. hhttps://doi.org/10.1155/2013/958540Bekele, N., Addis, M., Abdela, N., & Ahmed, W. M. (2016). Pregnancy Diagnosis in Cattle for Fertility Management: A Review. Global Veterinaria, 16(4), 355–364. https://doi.org/10.5829/idosi.gv.2016.16.04.103136Benedet, A., Franzoi, M., Penasa, M., Pellattiero, E., & De Marchi, M. (2019). Prediction of blood metabolites from milk mid-infrared spectra in early-lactation cows. Journal of Dairy Science, 102(12), 11298–11307. https://doi.org/10.3168/jds.2019-16937Delhez, P., Ho, P. 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Monitor Pregnancy and Determine the Timing , Frequencies and Sources of Embryonic Mortality in Ruminants. Theriogenology, 56(01), 1417–1433.Kuhn, M. (2008). Building Predictive Models in R Using the caret Package. Journal of Statistical Software, 28(5), 1–26.Lainé, A., Bel Mabrouk, H., Dale, L. M., Bastin, C., & Gengler, N. (2014). How to use mid-infrared spectral information from milk recording system to detect the pregnancy status of dairy cows. Communications in Agricultural and Applied Biological Sciences, 79(1), 33–38.Lainé, A., Bastin, C., Grelet, C., Hammami, H., Colinet, F. G., Dale, L. M., Gillon, A., Vandenplas, J., Deharend, F. & Gengler, N. (2017). Assessing the effect of pregnancy stage on milk composition of dairy cows using mid-infrared spectra. Journal of Dairy Science, 100(4), 2863–2876.https://doi.org/10.3168/jds.2016-11736Lantz, B. (2015). Machine Learning with R. Machine Learning (Second Edi). Packt Publishing Ltd. https://doi.org/10.1002/9781119642183.ch14Mineur, A., Köck, A., Grelet, C., Gengler, N., Egger-Danner, C., & Sölkner, J. (2017). First Results in the Use of Milk Mid-infrared Spectra in the Detection of Lameness in Austrian Dairy Cows Genomic evaluation View project MACSUR View project. Agriculturae Conspectus Scientifi Cus, Vol. 82(No. 2 (163-166)), (163-166). Retrieved from https://www.researchgate.net/publication/325450513Olori, V. E., Brotherstone, S., Hill, W. G., & McGuirk, B. J. (1997). Effect of gestation stage on milk yield and composition in Holstein Friesian dairy cattle. Livestock Production Science, 52(2), 167–176. https://doi.org/10.1016/S0301-6226(97)00126-7Pohler, K. G., Franco, G. A., Reese, S. T., Dantas, F. G., Ellis, M. D., & Payton, R. R. (2016). Past, present and future of pregnancy detection methods. 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Mid-infrared prediction of bovine milk fatty acids across multiple breeds, production systems, and countries. Journal of Dairy Science, 94(4), 1657–1667. https://doi.org/10.3168/jds.2010-3408Soyeurt, H., Bastin, C., Colinet, F. G., Arnould, V. M.-R., Berry, D. P., Wall, E., Dehareng, F., Nguyen, H. N., Pardenne, P., Schefers, J., Vandenplas, J., Weigel, K., Coffey, M., Théron, L., Detilleux, J., Reding, E., Gengler, N. & McParland, S. (2012). Mid-infrared prediction of lactoferrin content in bovine milk: potential indicator of mastitis. Animal, 6(11), 1830–1838. https://doi.org/10.1017/s1751731112000791Toffanin, V., De Marchi, M., Lopez-Villalobos, N., & Cassandro, M. (2015). Effectiveness of mid-infrared spectroscopy for prediction of the contents of calcium and phosphorus, and titratable acidity of milk and their relationship with milk quality and coagulation properties. 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Nature of the positron state in CdSe quantum dots

Previous studies have shown that positron-annihilation spectroscopy is a highly sensitive probe of the electronic structure and surface composition of ligand-capped semiconductor Quantum Dots (QDs) embedded in thin films. Nature of the associated positron state, however, whether the positron is confined inside the QDs or localized at their surfaces, has so far remained unresolved. Our positron-annihilation lifetime spectroscopy (PALS) studies of CdSe QDs reveal the presence of a strong lifetime component in the narrow range of 358-371 ps, indicating abundant trapping and annihilation of positrons at the surfaces of the QDs. Furthermore, our ab-initio calculations of the positron wave function and lifetime employing a recent formulation of the Weighted Density Approximation (WDA) demonstrate the presence of a positron surface state and predict positron lifetimes close to experimental values. Our study thus resolves the longstanding question regarding the nature of the positron state in semiconductor QDs, and opens the way to extract quantitative information on surface composition and ligand-surface interactions of colloidal semiconductor QDs through highly sensitive positron-annihilation techniques.Comment: 14 pages, 3 figure

Elucidating the Roles of Polyamide Layer Structural Properties in the Permeability–Selectivity Tradeoff Governing Aqueous Separations

A tradeoff relationship between permeability and selectivity of reverse osmosis and nanofiltration aqueous separation membranes is increasingly being documented. However, there is currently no comprehensive mechanistic framework to describe the roles of membrane structural properties in the transport tradeoff. This study investigates two key structural properties of the widely used thin-film composite polyamide (TFC-PA) membranes, namely, the free volume element (FVE) size and the effective transport pathway, and examines their influence on the tradeoff behavior. Permeability and selectivity performance were characterized by challenging chemically modified TFC-PA membranes with two neutral organic tracers. Positron annihilation lifetime spectroscopy (PALS) determined that the FVE diameters slightly increased for more permeable membranes, but the marginal size enlargement cannot fully account for the permeability trend. Instead, analysis using the hindered transport model showed that shortening of the effective transport pathway is identified as having a more significant effect on raising the water permeability. On the other hand, membrane selectivity is found to be dominated by FVE size and is essentially independent of the transport pathway. Lastly, a framework reconciling experimental evidence with transport theory is proposed to relate the influence of membrane structural properties on the permeability–selectivity tradeoff. Findings of this study provide fundamental insights for understanding the transport phenomena in aqueous separation membranes

Aqueous Flow Reactor and Vapour-Assisted Synthesis of Aluminium Dicarboxylate Metal-Organic Frameworks with Tuneable Water Sorption Properties

Energy-efficient indoors temperature and humidity control can be realised by using the reversible adsorption and desorption of water in porous materials. Stable microporous aluminium-based metal-organic frameworks (MOFs) present promising water sorption properties for this goal. The development of synthesis routes that make use of available and affordable building blocks and avoid the use of organic solvents is crucial to advance this field. In this work, two scalable synthesis routes under mild reaction conditions were developed for aluminium-based MOFs: (1) in aqueous solutions using a continuous-flow reactor and (2) through the vapour-assisted conversion of solid precursors. Fumaric acid, its methylated analogue mesaconic acid, as well as mixtures of the two were used as linkers to obtain polymorph materials with tuneable water sorption properties. The synthesis conditions determine the crystal structure and either the MIL-53 or MIL-68 type structure with square-grid or kagome-grid topology, respectively, is formed. Fine-tuning resulted in new MOF materials thus far inaccessible through conventional synthesis routes. Furthermore, by varying the linker ratio, the water sorption properties can be continuously adjusted while retaining the sigmoidal isotherm shape advantageous for heat transformation and room climatisation applications