Theoretical and experimental analysis of the core sampling method: Reducing diffusional losses in aerosol sampling line

Core sampling method (extracting a portion of a flow from the core of the flow) will reduce diffusional losses of highly diffusive species (e.g., aerosol nanoparticles, ions, and gases) when transporting them through a sampling tube. Revealing parameters governing the sampling efficiency of a core sampling system, η_sam, helps to design the apparatus and to optimize its performance. In this study, we report an analytical solution for quantifying the η_sam by solving the convection diffusion equation of laminar flow field. The analytical results were experimentally evaluated using 1–5?nm tungsten oxide nanoparticles. η_sam is governed by a dimensionless loss parameter and the transport-to-sample flow ratio. Theoretically predicted values for η_sam agree with experimental results, e.g., the relative deviation is within 5% when the value for the loss parameter is less than 0.1. The core sampling method is recommended to work at the loss parameter less than 0.1 such that η_sam is equal or close to the maximum value of unity and is also insensitive to variations in sampling conditions. In this study, how to apply the findings in designing and optimizing a core sampling system was discussed. A core sampling apparatus was then designed and experimentally evaluated. Its sampling efficiency was shown to be significantly higher than those of a tee, a cross fitting, and a Y fitting when the same sampling conditions were used.

Copyright © 2019 American Association for Aerosol Research     

Microbial exposures in moisture-damaged schools and associations with respiratory symptoms in students: A multi-country environmental exposure study

Moisture-damaged buildings are associated with respiratory symptoms and underlying diseases among building occupants, but the causative agent(s) remain a mystery. We first identified specific fungal and bacterial taxa in classrooms with moisture damage in Finnish and Dutch primary schools. We then investigated associations of the identified moisture damage indicators with respiratory symptoms in more than 2700 students. Finally, we explored whether exposure to specific taxa within the indoor microbiota may explain the association between moisture damage and respiratory health. Schools were assessed for moisture damage through detailed inspections, and the microbial composition of settled dust in electrostatic dustfall collectors was determined using marker-gene analysis. In Finland, there were several positive associations between particular microbial indicators (diversity, richness, individual taxa) and a respiratory symptom score, while in the Netherlands, the associations tended to be mostly inverse and statistically non-significant. In Finland, abundance of the Sphingomonas bacterial genus and endotoxin levels partially explained the associations between moisture damage and symptom score. A few microbial taxa explained part of the associations with health, but overall, the observed associations between damage-associated individual taxa and respiratory health were limited.     

A method to measure the fusion strength between expanded polystyrene (EPS) beads

Cellular polystyrene (EPS) is the most commonly used cellular thermoplast whose main applications are insulation and packages. One of its new applications is core material in building elements, and this poses higher requirements for strength. This is particularly evident in self-supporting roof elements. This study presents a method for determining the fusion strength between beads in cellular polystyrene and the dependence of this strength on processing. This method has also enabled us to determine the adhesion of cellular polystyrene beads to other materials, such as glass fibre, and it allows measurement of the fusion strength between EPS beads without the influence of porosity. Fusion strength was found to have a characteristic behaviour. It has an absolute upper limit, and fusion forces approximate this limit asymptotically as heating time is prolonged (this increase is dependent on the energy content of the steam).     

The active site of Trichoderma reesei cellobiohydrolase II: the role of tyrosine 169

Trichoderma reesei cellobiohydrolase II (CBHII) is an exoglucanasecleaving primarily cellobiose units from the non-reducing endof cellulose chains. The ß-l,4 glycosidic bond iscleaved by acid catalysis with an aspartic acid, D221, as thelikely proton donor, and another aspartate, D175, probably ensuringits protonation and stabilizing charged reaction intermediates.The catalytic base has not yet been identified experimentally.The refined crystal structure of CBHII also shows a tyrosineresidue, Y169, located close enough to the scissile bond tobe involved in catalysis. The role of this residue has beenstudied by introducing a mutation Y169F, and analysing the kineticand binding behaviour of the mutated CBHII. The crystal structureof the mutated enzyme was determined to 2.0 Å resolutionshowing no changes when compared with the structure of nativeCBHII. However, the association constants of the mutant enzymefor cellobiose and cellotriose are increased threefold and for4-methylumbelliferyl cellobioside over 50-fold. The catalyticconstants towards cellotriose and cellotetraose are four timeslower for the mutant. These data suggest that Y169, on interactingwith a glucose ring entering the second subsite in a narrowtunnel, helps to distort the glucose ring into a more reactiveconformation. In addition, a change in the pH activity profilewas observed. This indicates that Y169 may have asecond rolein the catalysis, namely to affect the protonation state ofthe active site carboxylates, D175 and D221.     

An empirical analysis of spreadsheet calculation

Spreadsheet calculation is a powerful tool in simple administrative data processing. Formulae in spreadsheets have similar forms to expressions in traditional programming languages, but the implementation of control structures is totally different. This paper contains an analysis of 101 spreadsheets made and used in business and government. The analysis concerns general properties, such as cell contents and referencing, the role of input, output and computation, and the different ways iteration is implemented. Finally some effects of expertise are studied. The results show that less than half of the available functions are really used, only one cell in 25 contains computation, and iteration is implemented in at least four different ways. Formulae are found to differ in their contents from expressions of programming languages, as control structures are implemented differently in these systems. Summation with a constant skip is suggested to be included in the set of functions of spreadsheet calculation.     

On the time response determination of condensation particle counters

Condensation particle counter (CPC) technology has continued to evolve, with the introduction of several new instruments over the last several years. An important aspect in the characterization of these instruments is the measurement of their time response. Yet there is no standardly accepted approach for this measurement. Here we evaluate different classically used methods for determining CPC time response, and present the potential pitfalls associated with these approaches. Further, we introduce a new simple definition for the term response time, ?, which is based on the first-order systems response, while providing a practical definition by corresponding to ～95% change in concentration. We also present results for various commonly used CPCs, and for the Airmodus A11 nano Condensation Nucleus Counter (nCNC) system, the TSI 3777+3772 Nano Enhancer system, and Aerosol Dynamics Inc.'s (ADI) new versatile water condensation particle counter.

Copyright © 2018 American Association for Aerosol Research     

Microstructural Studies of Cold Sprayed Copper,Nickel, and Nickel-30% Copper Coatings

Cold spraying enables to produce metallic coatings with low porosity level and low oxygen content. Several material properties such as electrical conductivity and corrosion resistance rely on these properties. Aim of this study was to characterize microstructural properties of cold sprayed copper, nickel, and nickel-30%copper coatings. Microstructures, denseness, and deformation of particles were investigated. SEM analysis and corrosion tests were done to get information of through-porosity. Open porosity has an important role on protectiveness of anodically protective coatings, such coating materials like copper and nickel. In this study, cold-sprayed Cu coating was fully dense. However, cold-sprayed Ni and Ni-30%Cu coatings seemed to be microstructurally dense but some porosity in some areas of the coatings especially in some parts of particle boundaries was noticed after corrosion tests. Furthermore, effect of annealing to microstructure and corrosion test behavior was studied. Cold sprayed Ni coating became denser during heat treatment.     

MRI quality assurance based on 3D FLAIR brain images

Objective

Quality assurance (QA) of magnetic resonance imaging (MRI) often relies on imaging phantoms with suitable structures and uniform regions. However, the connection between phantom measurements and actual clinical image quality is ambiguous. Thus, it is desirable to measure objective image quality directly from clinical images.

Materials and methods

In this work, four measurements suitable for clinical image QA were presented: image resolution, contrast-to-noise ratio, quality index and bias index. The methods were applied to a large cohort of clinical 3D FLAIR volumes over a test period of 9.5 months. The results were compared with phantom QA. Additionally, the effect of patient movement on the presented measures was studied.

Results

A connection between the presented clinical QA methods and scanner performance was observed: the values reacted to MRI equipment breakdowns that occurred during the study period. No apparent correlation with phantom QA results was found. The patient movement was found to have a significant effect on the resolution and contrast-to-noise ratio values.

Discussion

QA based on clinical images provides a direct method for following MRI scanner performance. The methods could be used to detect problems, and potentially reduce scanner downtime. Furthermore, with the presented methodologies comparisons could be made between different sequences and imaging settings. In the future, an online QA system could recognize insufficient image quality and suggest an immediate re-scan.

     

Aerosol analysis of residual and nanoparticle fractions from spray pyrolysis of poorly volatile precursors

The quality of aerosol‐produced nanopowders can be impaired by micron‐sized particles formed due to non‐uniform process conditions. Methods to evaluate the quality reliably and fast, preferably on‐line, are important at industrial scales. Here, aerosol analysis methods are used to determine the fractions of nanoparticles and micron‐sized residuals from poorly volatile precursors. This is accomplished using aerosol instruments to measure the number and mass size distributions of Liquid Flame Spray‐generated alumina and silver particles produced from metal nitrates dissolved in ethanol and 2‐ethylhexanoic acid (EHA). The addition of EHA had no effect on silver, whereas, 5% EHA concentration was enough to shift the alumina mass from the residuals to nanoparticles. The size‐resolved aerosol analysis proved to be an effective method for determining the product quality. Moreover, the used on‐line techniques alone can be used to evaluate the process output when producing nanopowders, reducing the need for tedious off‐line analyses. © 2016 American Institute of Chemical Engineers AIChE J, 63: 881–892, 2017