Modelling of artefacts in estimations of particle size of needle-like particles from laser diffraction measurements

Manufacturing of particulate products across many industries relies on accurate measurements of particle size distributions in dispersions or powders. Laser diffraction (or small angle light scattering) is commonly used, usually off-line, for particle size measurements. The estimation of particle sizes by this method requires the solution of an inverse problem using a suitable scattering model that takes into account size, shape and optical properties of the particles. However, laser diffraction instruments are usually accompanied by software that employs a default scattering model for spherical particles, which is then used to solve the inverse problem even though a significant number of particulate products occur in strongly non-spherical shapes such as needles. In this work, we demonstrate that using the spherical model for the estimation of sizes of needle-like particles can lead to the appearance of artefacts in the form of multimodal populations of particles with size modes much smaller than those actually present in the sample. This effect can result in a significant under-estimation of the mean particle size and in false modes in estimated particles size distributions.Comment: 28 pages 8 figures accepted in the journal of Chemical Engineering Scienc

The Impact of Making Reading Heavenly Instruction on Fluency and Accuracy

The purpose of this action research project was to determine if using the systematic phonics program Making Reading Heavenly would have an impact on student fluency and accuracy in reading. For five weeks, the researcher introduced a new phonics lesson each day, where students learn and practice a new skill. With each new lesson, students continued to practice skills learned in previous lessons. Each Monday, the teacher-researcher assessed student fluency and accuracy using reading passages from a benchmark leveling kit. Analysis of the data shows that overall, the majority of students made progress between the pre-test and post-test assessments, increasing their fluency and accuracy

Crystal templating through liquid–liquid phase separation

Controlled induction of crystal nucleation is a highly desirable but elusive goal. Attempts to speed up crystallization, such as high super saturation or working near a liquid–liquid critical point, always led to irregular and uncontrollable crystal growth. Here, we show that under highly nonequilibrium conditions of spinodal decomposition, water crystals grow as thin wires in a template-less formation of “Haareis”. This suggests that such nonequilibrium conditions may be employed more widely as mechanisms for crystal growth control

Validity of particle size analysis techniques for measurement of the attrition that occurs during vacuum agitated powder drying of needle-shaped particles

Analysis of needle-shaped particles of cellobiose octaacetate (COA) obtained from vacuum agitated drying experiments was performed using three particle size analysis techniques: laser diffraction (LD), focused beam reflectance measurements (FBRM) and dynamic image analysis. Comparative measurements were also made for various size fractions of granular particles of microcrystalline cellulose. The study demonstrated that the light scattering particle size methods (LD and FBRM) can be used qualitatively to study the attrition that occurs during drying of needle-shaped particles, however, for full quantitative analysis, image analysis is required. The algorithm used in analysis of LD data assumes the scattering particles are spherical regardless of the actual shape of the particles under evaluation. FBRM measures a chord length distribution (CLD) rather than the particle size distribution (PSD), which in the case of needles is weighted towards the needle width rather than their length. Dynamic image analysis allowed evaluation of the particles based on attributes of the needles such as length (e.g. the maximum Feret diameter) or width (e.g. the minimum Feret diameter) and as such, was the most informative of the techniques for the analysis of attrition that occurred during drying

Formation of valine microcrystals through rapid antisolvent precipitation

In this work we have experimentally studied concentration effects on antisolvent precipitation of valine (an amino acid) from aqueous isopropanol solutions. Our experiments showed that the valine precipitation is very sensitive to both the supersaturation and to the water content in the final solution. Results from spectrophotometric measurements and supersaturation analysis showed that the crystal formation kinetics are strongly dependent on both mixing and concentration profiles in the early stages of the process, even though no visible change in the systems occurs immediately upon mixing with the antisolvent or subsequent dilution. Results from small-angle static light scattering measurements showed that the first visible crystals are of micron size and they grow only little over time, while their number increases gradually. Taken together, these experiments point to intermediate phase separation of (possible amorphous) precursors, being either very small nanoparticles or droplets with their refractive index closely matching that of the continuous phase, which subsequently assemble into micron size valine crystals

Dynamic response studies on aggregation and breakage dynamics of colloidal dispersions in stirred tanks

Aggregation and breakage of aggregates of fully destabilized polystyrene latex particles in turbulent flow was studied experimentally in both batch and continuous stirred tanks using small-angle static light scattering. It was found that the steady-state values of the root-mean-square radius of gyration are fully reversible upon changes of stirring speed as well as solid volume fraction. Steady-state values of the root-mean-square radius of gyration were decreasing with decreasing solid volume fraction as well as with increasing stirring speed. Moreover, it was found that the steady-state structure and shape of the aggregates is not influenced by the applied stirring speed

Effects of temperature and concentration on mechanism and kinetics of thermally induced deposition from coffee extracts

Production of soluble (instant) coffee powders typically involves extraction of roasted coffee by water followed by evaporation in order to concentrate extracts before spray or freeze drying to produce dry coffee powder. In the course of evaporation, deposition of dissolved material from coffee extracts is a major cause of fouling at the heat exchange surfaces of evaporators. Therefore, in order to improve the design and optimization of evaporation processes of coffee extracts, better understanding of the deposition mechanism and kinetics is needed. In this study, optical waveguide lightmode spectroscopy (OWLS) was used to monitor the initial formation of nanometer scale deposits on surfaces exposed to coffee extracts. OWLS measurements were complemented by light scattering from extract solutions, gravimetry of macroscopic deposits, and scanning electron microscopy imaging of deposited layers. Primary molecular-scale layers of about 1 mg m^−2 were rapidly formed in the first stage of deposition, even at ambient temperature, followed by the secondary deposition with kinetics strongly dependent on temperature. Secondary deposition rates were low and largely independent of the extract concentration at ambient temperature, but became strongly dependent on the extract concentration at elevated temperatures. In particular, activation energies for the deposition between 25◦C and 70◦C were much higher for the original extract (13.3 mass %, solids) than for diluted extracts (up to 1.3 mass %, solids). Furthermore, heating of the original extracts above 60◦C resulted in rapid aggregation of suspended macromolecules into large clusters, while only gradual aggregation was observed in diluted extracts

Closely Held Firms As Going Concerns

This current GAAP determination of a going concern is shortsighted for two important reasons. The most important deals with creditors and other stakeholders involved with the business. Do they enter into contracts with the business or with the individual owner/manager? Currently, they contract with both since, in reality, they make no determination whether a separate firm (entity) exists. The second deals with valuing a business. If the business is not really a separate going concern, it would typically be valued as the sum of its individual assets instead of the present value of its future cash flows. Many times when buying a business, the acquirer is really just buying the assets to start his own business. This is particularly true in most service businesses. The purpose of this paper is to advocate reintroducing a qualification to the going concern audit opinion when an entity separate from its owner/manager does not exist. Criteria for determination are also proposed. Arguably, this will make audited accounting statements more meaningful for closely-held firms. More important, this should produce information useful for potential creditors and outside owners. Traditionally, banks have extended loans to small, closely-held firms with only compiled statements; there was no need to provide audited statements. However, the process of lending is changing from a direct, face-to-face process between borrower and lender to an indirect one where credit scoring systems are used. Audited statements can provide better, higher quality information to lenders extending credit