Sulfonic acid coating of refractory sand for three-dimensional printing applications

Abstract: Rapid sand casting processes by additive manufacturing are predominantly based on furfuryl alcohol resin bonded sand catalysed with sulfonic acid. The prior coating of the refractory sand with sulfonic acid is a crucial process to ensure the suitability of the sand for threedimensional printing applications. The present paper investigated the sulfonic acid coating process of a local silica sand, which was found to have potential for three-dimensional printing applications in previous studies. Experimental conditions included sulfonic acid catalyst addition and mixing time. Coated sand was assessed for flowability and mechanical properties of test specimens produced by three-dimensional printing using a Voxeljet VX 1000. The optimum catalyst addition ranged between 0.3 and 0.6% yielding to transverse strength in the order of 110 to 165 KN/m2 and tensile strength ranging from 710 to 770 KN/m2

Customer satisfaction, trust and commitment as predictors of customer loyalty within an optometric practice environment

Optometric businesses need to adopt strategies to enhance loyalty, as customer satisfaction is not enough to ensure loyalty and customer retention. It has been stated that 85% of patients in the optometric industry who defect to other service providers were satisfied with the service received just before defecting. Consequently, to assist optometric practices in South Africa with their customer loyalty strategies, the purpose of the research conducted for this article was to develop an understanding of theinfluence of the independent variables of customer satisfaction, trust and commitment on customer loyalty within an optometric practice. The methodological approach followed was exploratory and quantitative in nature. The sample consisted of 357 patients who had visited the practice twice or more within the past six years. A structured questionnaire, with a five-point Likert scale, was used. A descriptive and multiple regression analysis approach was used to analyse the results. The main conclusion is that customer satisfaction had the highest correlation with customer loyalty, but the other independent variables also significantly influence customer loyalty within an optometric practice environment. The implication is that optometric practices need to focus on customer satisfaction, trustand commitment in order to improve customer loyalty.Key words: optometric practice, customer loyalty, customer retention, customer satisfaction, customer relationship managemen

The superfield quantisation of a superparticle action with an extended line element

A massive superparticle action based on the generalised line element in N = 1 global superspace is quantised canonically. A previous method of quantising this action, based on a Fock space analysis, showed that states existed in three supersymmetric multiplets, each of a different mass. The quantisation procedure presented uses the single first class constraint as an operator condition on a general N = 1 superwavefunction. The constraint produces coupled equations of motion for the component wavefunctions. Transformations of the component wavefunctions are derived that decouple the equations of motion and partition the resulting wavefunctions into three separate supermultiplets. Unlike previous quantisations of superparticle actions in N = 1 global superspace, the spinor wavefunctions satisfy the Dirac equation and the vector wavefunctions satisfy the Proca equation. The off-shell closure of the commutators of the supersymmetry transformations, that include mass parameters, are derived by the introduction of auxiliary wavefunctions. To avoid the ghosts arising in a previous Fock space quantisation an alternative conjugation is used in the definition of the current, based on a Krein space approach

The relationship between key variables and customer loyalty within the independent financial advisor environment

Research is required to determine the key variables that have a positive relationship with customer loyalty in the independent financial adviser environment. Knowledge of the factors that could assist in fostering customer loyalty might help independent financial advisers firstly in maintaining their client base, and then secondly, to strategise with them over the long term to behave more financially responsible, achieve their saving goals, and become financially independent. Therefore, the primary aim of this article is to explore the relationship between key variables and customer loyalty within the independent financial adviser environment in Gauteng. The population was defined as all the clients of independent financial advisers in the Gauteng region. A convenience non-probability sampling technique was applied and self-administered questionnaires were distributed to the clients in Gauteng who matched the sampling frame. A total of 123 questionnaires were completed and could be used in the analysis. Descriptive and standard multiple regression analysis as well as the one-way analysis of variance (ANOVA) technique was used to analyse the results. Trust and commitment can be viewed as predictors of customer loyalty within the independent financial adviser environment in Gauteng and must form part of the core of the financial adviser’s relationship building strategies. It is therefore important for independent financial advisers to ensure that their clients have confidence in their ability to provide sound financial advice. Clients must be convinced that financial advisers have their best interest at heart and as such, should remain committed to their practices

Limitations of the 3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyl-2H-tetrazolium bromide (MTT) assay when compared to three commonly used cell enumeration assays

BACKGROUND : The tetrazolium-based MTT assay has long been regarded as the gold standard of cytotoxicity assays as it is highly sensitive and has been miniaturised for use as a high-throughput screening assay. However, various reports refer to interference by different test compounds, including the glycolysis inhibitor 3-bromopyruvate, with the conversion of the dye to coloured formazan crystals. This study assessed the linear range and reproducibility of three commonly used cell enumeration assays; the neutral red uptake (NRU), resazurin reduction (RES) and sulforhodamine B (SRB) assays, in comparison to the MTT assay. Interference between the MTT assay and three glycolysis inhibitors, 2-deoxyglucose, 3-bromopyruvate and lonidamine, was investigated. RESULTS : Data indicate that the NRU, RES and SRB assays showed the smallest variability across the linear range, while the largest variation was observed for the MTT assay. This implies that these assays would more accurately detect small changes in cell number than the MTT assay. The SRB assay provided the most reproducible results as indicated by the coefficient of determination after a limited number of experiments. The SRB assay also produced the lowest variance in the derived 50% inhibitory concentration (IC50), while IC50 concentrations of 3-bromopyruvate could not be detected using either the MTT or RES assays after 24 hours incubation. Interference in the MTT assay was observed for all three tested glycolysis inhibitors in a cell-free environment. No interferences were observed for the NRU, SRB or RES assays. CONCLUSIONS : This study demonstrated that the MTT assay was not the best assay in a number of parameters that must be considered when a cell enumeration assay is selected: the MTT assay was less accurate in detecting changes in cell number as indicated by the variation observed in the linear range, had the highest variation when the IC50 concentrations of the glycolysis inhibitors were determined, and interference between the MTT assay and all the glycolysis inhibitors tested were observed. The SRB assay performed best overall considering all of the parameters, suggesting that it is the most suitable assay for use in preclinical screening of novel therapeutic compounds with oxido-reductive potential.Additional file 1: The IC50 concentrations of 3-bromopyruvate calculated for MCF-7 cells after 24 or 72 hour incubation calculated per experimental repeat. Results are indicated as IC50 ± SEM. Where no values are given these could not be calculated as the assay reported relative cell survival of greater than 50% at the tested concentrations (n = 4).Additional file 2: Interference of three glycolysis inhibitors with the NRU, RES and SRB assays in cell-free systems (n = 3).The National Research Foundation of South Africa (TTK1207072152)http://www.biomedcentral.com/bmcpublichealtham201

Semantics of a Typed Algebraic Lambda-Calculus

Algebraic lambda-calculi have been studied in various ways, but their semantics remain mostly untouched. In this paper we propose a semantic analysis of a general simply-typed lambda-calculus endowed with a structure of vector space. We sketch the relation with two established vectorial lambda-calculi. Then we study the problems arising from the addition of a fixed point combinator and how to modify the equational theory to solve them. We sketch an algebraic vectorial PCF and its possible denotational interpretations

Extending scientific computing system with structural quantum programming capabilities

We present a basic high-level structures used for developing quantum programming languages. The presented structures are commonly used in many existing quantum programming languages and we use quantum pseudo-code based on QCL quantum programming language to describe them. We also present the implementation of introduced structures in GNU Octave language for scientific computing. Procedures used in the implementation are available as a package quantum-octave, providing a library of functions, which facilitates the simulation of quantum computing. This package allows also to incorporate high-level programming concepts into the simulation in GNU Octave and Matlab. As such it connects features unique for high-level quantum programming languages, with the full palette of efficient computational routines commonly available in modern scientific computing systems. To present the major features of the described package we provide the implementation of selected quantum algorithms. We also show how quantum errors can be taken into account during the simulation of quantum algorithms using quantum-octave package. This is possible thanks to the ability to operate on density matrices

Antigenic diversity is generated by distinct evolutionary mechanisms in African trypanosome species

Antigenic variation enables pathogens to avoid the host immune response by continual switching of surface proteins. The protozoan blood parasite Trypanosoma brucei causes human African trypanosomiasis ("sleeping sickness") across sub-Saharan Africa and is a model system for antigenic variation, surviving by periodically replacing a monolayer of variant surface glycoproteins (VSG) that covers its cell surface. We compared the genome of Trypanosoma brucei with two closely related parasites Trypanosoma congolense and Trypanosoma vivax, to reveal how the variant antigen repertoire has evolved and how it might affect contemporary antigenic diversity. We reconstruct VSG diversification showing that Trypanosoma congolense uses variant antigens derived from multiple ancestral VSG lineages, whereas in Trypanosoma brucei VSG have recent origins, and ancestral gene lineages have been repeatedly co-opted to novel functions. These historical differences are reflected in fundamental differences between species in the scale and mechanism of recombination. Using phylogenetic incompatibility as a metric for genetic exchange, we show that the frequency of recombination is comparable between Trypanosoma congolense and Trypanosoma brucei but is much lower in Trypanosoma vivax. Furthermore, in showing that the C-terminal domain of Trypanosoma brucei VSG plays a crucial role in facilitating exchange, we reveal substantial species differences in the mechanism of VSG diversification. Our results demonstrate how past VSG evolution indirectly determines the ability of contemporary parasites to generate novel variant antigens through recombination and suggest that the current model for antigenic variation in Trypanosoma brucei is only one means by which these parasites maintain chronic infections

A cost effective public transport management system for go!durban

The eThekwini Transport Authority (ETA) is implementing an Integrated Public Transport Network (Go!Durban) which is essentially a traditional BRT system. Go!Durban requires a Public Transport Management System (PTMS) in order to monitor the performance and compliance of the BRT operator and provide real time information on the BRT system. In 2014, the ETA advertised a tender for an Advanced PTMS. The lowest tender to specification was priced at around R350 million. This was deemed too expensive, and the tender was not awarded. Subsequent to this, in 2018 the ETA commenced discussions with Netstar, the current eThekwini fleet management contractor, to extend their fleet management system to include compliance monitoring, thus meeting the core functionality of a PTMS. The Go!Durban team developed a minimum User Requirements Specification (URS), based on the original ETA APTMS specification, which Netstar then used to map their proposal and cost estimate to develop the system. The system is being developed in two phases with a Proof of Concept or Pilot phase, building on their existing system functionality, followed by a Phase 2 to address the gaps in the APTMS minimum URS – essentially functionality that required further development. Based on the Netstar fleet management system, the ETA has thus developed a cost-effective PTMS to support the operations of the Go! Durban Integrated Public Transport Network (IPTN). This PTMS Lite system provides the essential functionality of the traditional PTMS at a fraction of the cost. The ETA PTM Lite System is a tool to manage bus movements against a static timetable on the Go!Durban corridors and provide appropriate reporting and bus communication for the Transport Operator. In order to drive down operational costs (and therefore subsidies) ITS practitioners have a significant role to play in looking for cost effective solutions. The Netstar system presented here offers significant cost savings for capital and operating budgets. It offers an application centric solution for passenger information and provides all the essential functionality of a traditional APTMS at around a tenth of the cost. This should assist planners in their quest for a more financially sustainable public transport system.Papers presented virtually at the 39th International Southern African Transport Conference on 05 -07 July 202