Planar Polymer Optical Waveguide with Metal-Organic Framework Coating for Carbon Dioxide Sensing

An easily fabricated gas sensor based on planar polymer optical waveguides with an integrated zeolite imidazole framework-8 (ZIF-8) thin film is presented for carbon dioxide detection and sensing. The planar optical waveguides are made of polymethylmethacrylate and fabricated by hot embossing, which makes it flexible and cost-efficient. Thin ZIF-8 films are uniformly grown on the waveguides surface through a simple solution method, which is crucial for the envisioned production of metal organic framework-based sensing devices on a large scale. Experimental results show that the produced optical elements exhibit a sensitivity of ≈2.5 μW/5 vol% toward carbon dioxide (CO2) with very rapid response time (≈6 s) and excellent reversibility of adsorption and desorption of the gas molecules. The demonstrated planar polymer sensing devices provide the potential to develop flexible on-chip gas sensors in an inexpensive and reproducible way

Electrical and optical properties linked to laser damage behavior in conductive thin film materials

Epsilon-near-zero-materials (ENZ-materials) and their unique properties are key to the successful integration and miniaturization of optical components. Novel concepts, which promise significant progress in this field of research, such as optical switches and thin film electrooptical modulators, are possible when the electrical and optical properties of ENZ-materials are carefully exploited. To achieve a greater understanding of these properties, in this paper the electrical conductivity, optical transmittance, as well as absorption of thin indium tin oxide films, are investigated and linked to their laser-induced damage threshold in the ultra-short pulse regime. To the best of the authors’ knowledge, this is the first concise study linking the electrical properties of indium tin oxide to its properties regarding high-power laser applications. © 2020. All Rights Reserved

A systematic study of the residence time of flour in a vibrating apparatus used for thermal processing

AbstractThe dry heat treatment of flour is well established for the production of cake flour for high ratio cakes. This study investigates a new tubular apparatus in which flour is conveyed by vibrations through a helical pipe. Residence time distributions (RTDs) of flour were characterised for various processing conditions and the development of the residence time in extended operation was analysed.A method was developed to accurately determine the RTDs, which could be approximated by normal distributions. The width of the distributions is a critical factor for the accuracy of a thermal process and was identified for different processing conditions. The distributions were narrow, with variations of ±1% at most.In some cases, the residence time increased over 3.5h of machine run-time by 7.7%–13.9%. To explain this phenomenon, several hypotheses have been tested. The machine performance was constant with time and no influence of ambient temperature or humidity could be found. It was furthermore shown that changes in the bulk material passing through the apparatus were not the cause of the increase. However, electrostatic charging of the material was observed.Two things led to a reduction in residence time: i) cleaning the pipe with a cleaning pig and water and ii) time, during which the machine is not running. It was suggested that a thin layer of particles inside the pipe in combination with electrostatics effects could be the reason for the residence time increase. Frequent cleaning can therefore allow relatively uniform behaviour and control of residence time.Industrial relevanceThis work investigates the potential application of a novel, vibrating device for the dry heat treatment of flour as a replacement for chlorination in the production of cake flour. Since chlorination was banned in the EU in the year 2000, there is an industrial interest for alternative treatments and equipment to produce flour for high ratio cakes

Processing of barley grains in a continuous vibrating conveyor

AbstractA novel tubular industrial apparatus for the surface pasteurization of particles has been studied. Particles are conveyed through a helical pipe by vibrations created by off-balance motors. The residence time of barley grains was characterized. The behaviour of the system was a function of motor angle and motor speed. The residence time could vary up to 21% during one experiment of 2 h (20°, 740 rpm). However, ranges of processing conditions were identified that produce stable operation and thus effective pasteurization of product. In some cases, residence time increased by up to 7% of the initial value over consecutive experiments (40°, 710 rpm). Some reasons for this phenomenon have been proposed and tested. The formation of a powder layer inside the pipe has been proven to affect the residence time of barley grains. A simple model for pasteurization of particles has been developed to characterise the impact of variation in residence time on microbial inactivation

Seeding Layer Approach for the Synthesis of Co-ZIF-90 Thin Films of Optical Quality

The growth of zeolitic imidazolate framework (ZIF) thin films is an interesting topic, since ZIFs have a high thermal and chemical stability compared to many other MOFs. A variety of functionalities can be introduced via the imidazole linker molecule. Here, we report on a new approach for the preparation of thin films of a novel ZIF material: Co-ZIF-90. The preparation of thin films is possible on silicon or glass when ZIF-8 seeding layers are deposited first. The resulting constructions are effectively MOF-on-MOF layer systems. The synthesis procedure has been optimized with regard to obtaining high-quality thin films of Co-ZIF-90 on ZIF-8 for optical applications. Notably, the preparation of Co-ZIF-90 thin films is possible only by using a mixture of two different cobalt precursor salts (acetate and nitrate). The thin films are characterized in detail. With regard to the use as an optical material, UV-vis absorption spectra of the MOF-on-MOF constructs were measured and the refractive index of Co-ZIF-90 was determined using ellipsometry. Furthermore, the refractive index of the Co-ZIF-90 film can be modulated reversibly by the adsorption and desorption of water via the gas phase. The kinetics of this fast process are on the time scale of 1 s. In addition to the preparation of thin films, we obtained Co-ZIF-90 as a powder sample and basically characterized the powder. The approach to use an easy-to-crystallize ZIF-8 film as a seeding layer for the growth of films of other ZIFs may be extended as a general concept for the deposition of crystalline ZIF layers in such cases, where a direct deposition is difficult or not possible

A fast and sensitive method for the continuous in situ determination of dissolved methane and its d13C-isotope ratio in surface waters

A fast and sensitive method for the continuous determination of methane (CH4) and its stable carbon isotopic values (d13C-CH4) in surface waters was developed by applying a vacuum to a gas/liquid exchange membrane and measuring the extracted gases by a portable cavity ring-down spectroscopy analyser (M-CRDS). The M-CRDS was calibrated and characterized for CH4 concentration and d13C-CH4 with synthetic water standards. The detection limit of the M-CRDS for the simultaneous determination of CH4 and d13CCH4 is 3.6 nmol L21 CH4. A measurement precision of CH4 concentrations and d13C-CH4 in the range of 1.1%, respectively, 1.7& (1r) and accuracy (1.3%, respectively, 0.8& [1r]) was achieved for single measurements and averaging times of 10 min. The response time s of 5765 s allow determination of d13C-CH4 values more than twice as fast than other methods. The demonstrated M-CRDS method was applied and tested for Lake Stechlin (Germany) and compared with the headspace-gas chromatography and fast membrane CH4 concentration methods. Maximum CH4 concentrations (577 nmol L21) and lightest d13C-CH4 (235.2&) were found around the thermocline in depth profile measurements. The M-CRDS-method was in good agreement with other methods. Temporal variations in CH4 concentration and d13C-CH4 obtained in 24 h measurements indicate either local methane production/oxidation or physical variations in the thermocline. Therefore, these results illustrate the need of fast and sensitive analyses to achieve a better understanding of different mechanisms and pathways of CH4 formation in aquatic environments

Persistence of functional memory B cells recognizing SARS-CoV-2 variants despite loss of specific IgG

Although some COVID-19 patients maintain SARS-CoV-2-specific serum immunoglobulin G (IgG) for more than 6 months postinfection, others eventually lose IgG levels. We assessed the persistence of SARS-CoV-2-specific B cells in 17 patients, 5 of whom had lost specific IgGs after 5–8 months. Differentiation of blood-derived B cells in vitro revealed persistent SARS-CoV-2-specific IgG B cells in all patients, whereas IgA B cells were maintained in 11. Antibodies derived from cultured B cells blocked binding of viral receptor-binding domain (RBD) to the cellular receptor ACE-2, had neutralizing activity to authentic virus, and recognized the RBD of the variant of concern Alpha similarly to the wild type, whereas reactivity to Beta and Gamma were decreased. Thus, differentiation of memory B cells could be more sensitive for detecting previous infection than measuring serum antibodies. Understanding the persistence of SARS-CoV-2-specific B cells even in the absence of specific serum IgG will help to promote long-term immunity