Experimental Study of Heat Transfer Enhancement in Solar Tower Receiver Using Internal Fins

The receiver is an important element in solar energy plants. The principal receiver’s tubes in power plants are devised to work under extremely severe conditions, including excessive heat fluxes. Half of the tube’s circumference is heated whilst the other half is insulated. This study aims to improve the heat transfer process and reinforce the tubes’ structure by designing a new receiver; by including longitudinal fins of triangular, circular and square shapes. The research is conducted experimentally using Reynolds numbers ranging from 28,000 to 78,000. Triangular fins have demonstrated the best improvement for heat transfer. For Reynolds number value near 43,000 Nusselt number (Nu) is higher by 3.5% and 7.5%, sequentially, compared to circular and square tube fins, but varies up to 6.5% near Re = 61000. The lowest friction factor is seen in a triangular fin receiver; where it deviates from circular fins by 4.6%, and square fin tubes by 3.2%. Adding fins makes the temperature decrease gradually, and in the case of no fins, the temperature gradient between the hot tube and water drops sharply in the planed tube by 7%.     

Drying-induced changes in the structure of alkali-activated pastes

Drying of cement paste, mortar, or concrete specimens is usually required as a pre-conditioning step prior to the determination of permeability-related properties according to standard testing methods. The reaction process, and consequently the structure, of an alkali-activated slag or slag/fly ash blend geopolymer binder differs from that of Portland cement, and therefore there is little understanding of the effects of conventional drying methods (as applied to Portland cements) on the structure of the geopolymer binders. Here, oven drying (60 °C), acetone treatment, and desiccator/vacuum drying are applied to sodium silicate-activated slag and slag/fly ash geopolymer pastes after 40 days of curing. Structural characterization via X-ray diffraction, infrared spectroscopy, thermogravimetry, and nitrogen sorption shows that the acetone treatment best preserves the microstructure of the samples, while oven drying modifies the structure of the binding gels, especially in alkali-activated slag paste where it notably changes the pore structure of the binder. This suggests that the pre-conditioned drying of alkali activation-based materials strongly affects their microstructural properties, providing potentially misleading permeability and durability parameters for these materials when pre-conditioned specimens are used during standardized testing.     

Design and In Vitro Evaluation of Polymeric Formulae of Simvastatin for Local Bone Induction

ABSTRACT

Simvastatin (SVS), a cholesterol-lowering drug, has been shown to stimulate bone formation. This study deals with the design and in vitro evaluation of local delivery systems for simvastatin. They are intended to treat bony defects resulting from periodontitis or to induce osteogenesis around the titanium implants. Granules and gels were formulated using bioerodible/biocompatible polymers, namely hydroxypropylmethyl cellulose (H), sodium carboxymethyl cellulose (C), and chitosan (Ch). The in vitro release profiles and kinetics were evaluated and the swelling and/or erosion was monitored. Differential scanning calorimetry (DSC) and infrared (IR) were used to detect any SVS/polymer interactions that may affect drug release. The results revealed variable extents of controlled drug release from the designed formulae depending on the polymer nature. About 50% cumulative SVS was released from both H granules and gel formulae within 24 h and ～66% and ～88% from C granules and gel, respectively. Ch formulae exhibited ～50% release from granules and ～30% from gel.     

Material screening and choosing methods – A review

The selection of a material for a specific engineering purpose is a lengthy and expensive process. Approximately always more than one material is suitable for an engineering application, and the final selection is a compromise that brings some advantages as well as disadvantages. One of the issues that emerges from this review is that regardless of the relation of design stages and process selection with material selection, screening and ranking are two vital steps in the material selection. A variety of quantitative selection procedures have been developed to solve this issue, so that a systematic evaluation can be made. This paper seeks to address the following questions: (1) what is the contribution of the literature in the field of screening and choosing the materials? (2) What are the methodologies/systems/tools for material selection of engineering components? (3) Which approaches were prevalently applied? (4) Is there any inadequacy of the approaches? This research not only provides evidence that the multi-criteria decision making approaches has the potential to greatly improve the material selection methodology, but also aids the researchers and decision makers in applying the approaches effectively.     

Enzyme-linked amperometric electrochemical genosensor assay for the detection of PCR amplicons on a streptavidin-treated screen-printed carbon electrode

A general purpose enzyme-based amperometric electrochemical genosensor assay was developed wherein polymerase chain reaction (PCR) amplicons labeled with both biotin and fluorescein were detected with peroxidase-conjugated antifluorescein antibody on a screen-printed carbon electrode (SPCE). As a proof of principle, the response selectivity of the genosensor was evaluated using PCR amplicons derived from lolB gene of Vibrio cholerae. Factors affecting immobilization, hybridization, and nonspecific binding were optimized to maximize sensitivity and reduce assay time. On the basis of the background amperometry signals obtained from nonspecific organisms and positive signals obtained from known V. cholerae, a threshold point of 4.20 microA signal was determined as positive. Under the optimum conditions, the limit of detection (LOD) of the assay was 10 CFU/mL of V. cholerae. The overall precision of this assay was good, with the coefficient of variation (CV) being 3.7% using SPCE and intermittent pulse amperometry (IPA) as an electrochemical technique. The assay is sensitive, safe, and cost-effective when compared to conventional agarose gel electrophoresis, real-time PCR, and other enzyme-linked assays for the detection of PCR amplicons. Furthermore, the use of a hand-held portable reader makes it suitable for use in the field.     

Analysis of order timing tradeoffs in multi-retailer supply systems

We analyse the implications of order timing decisions in multi-retailer supply systems in a single period, newsvendor setting. Specifically, we investigate a supply chain with multiple retailers and a single supplier where one of the retailers is considered a preferred or primary customer of the supplier. In the base model (delayed commitment), customers order after observing demand and the supplier rations its production quantity to retailers according to a generalised uniform allocation rule. In the early-commitment model, the primary retailer commits to an order quantity prior to the selling season and receives her order in full. We compare the expected supplier and retailer profits under each of these strategies and specify conditions under which a particular commitment scheme benefits the supplier, the primary retailer, and the entire system. Our findings indicate that the supplier prefers early commitment under mild conditions, whereas the primary retailer's preference depends on the tradeoff between the supply risk and demand risk. We also compare our findings with a single-retailer system, and observe that both the supplier and the primary retailer benefit from the existence of additional customers under delayed-commitment in many contexts.     

Order timing strategies in a single-supplier,multi-retailer system

The timing of retailer order placement is an important factor in supply chain performance in systems with uncertain end-customer demands. Retailers often prefer short order lead times, which permits the resolution of demand uncertainty prior to order placement, and reduces the risks associated with excess inventory. Suppliers, in contrast, prefer long lead times, in order to match supply output with retailer demand. These conflicting preferences create tension between a supplier and retailers regarding order timing preferences. This paper considers order timing preferences within a strategic framework involving a supplier and one of its retailers in a multiple-retailer system. We identify and explore several mechanisms a supplier can use within this framework to induce early retailer order placement and improve expected cost performance.     

Synergistic evaluation of AgO2 nanoparticles with ceftriaxone against CTXM and blaSHV genes positive ESBL producing clinical strains of Uro‐pathogenic E. coli

The silver oxide nanoparticles (AgO₂ ‐NPs) were synthesised using silver foil as a new precursor in wet chemical method. X‐ray diffraction analysis shows crystallographic structures of AgO₂ ‐NPs with crystallite size of 35.54 nm well‐matched with standard cubic structure. Scanning electron microscopy analysis clearly shows the random distribution of spherical‐shaped nanoparticles. Energy dispersive X‐ray analysis confirmed the purity of the samples as it shows no impurity element. Fourier transforms infra‐red analysis confirmed the formation of AgO₂ ‐NPs with the presence of Ag‐O‐Ag stretching bond. All the techniques also confirmed the loading of ceftriaxone drug on the surface of AgO₂ ‐NPs. This study also described the effect of AgO₂ ‐NPs having synergistic activity with β lactam antibiotic i.e. ceftriaxone against ESBL generating Escherichia coli (E. coli). Among isolated strains of E. coli, 60.0% were found to be ESBL producer. The synergistic activities of AgO₂ ‐NPs with ceftriaxone suggest that these combinations are effective against MDR‐ESBL E. coli strains as evident by increase in zone sizes. The present study observed rise in MDR‐ESBL E. coli with polymorphism of blaCTXM and blaSHV causing UTI infections in Pakistani population. The antibiotic and AgO₂ ‐NPs synergistic effect can be used as an efficient approach to combat uro‐pathogenic infections.Inspec keywords: antibacterial activity, nanofabrication, nanomedicine, drugs, nanoparticles, microorganisms, crystallites, scanning electron microscopy, silver compounds, X‐ray diffraction, X‐ray chemical analysis, Fourier transform infrared spectra, organic compounds, geneticsOther keywords: synergistic evaluation, clinical strains, silver oxide nanoparticles, silver foil, wet chemical method, X‐ray diffraction analysis, crystallographic structures, standard cubic structure, spherical‐shaped nanoparticles, energy dispersive X‐ray analysis, ceftriaxone drug, synergistic activity, ESBL producer, scanning electron microscopy, Fourier transform infrared analysis, Escherichia coli, blaSHV gene positive ESBL, crystallite size, random distribution, β lactam antibiotics, MDR‐ESBL E. coli strains, polymorphism, blaCTXM, uro‐pathogenic infections, uro‐pathogenic E. coli, AgO₂      

Comparison of Oxidation and Thermal Shock Performance of Thermal Barrier Coatings

Operating temperatures in gas turbine engines have reached to 1200°C with the latest developments in coating technology. Thermal shock and furnace oxidation tests are widely used to determine thermal barrier coating (TBC) performance and its durability in aircraft applications. This paper presents the results of thermal shock and furnace oxidation tests, carried out with regard to the microstructure and TGO (thermally grown oxide) growth behavior of TBC systems. Isothermal oxidation behavior of TBCs was evaluated through examination of microstructure, formation, and growth behavior of TGO layers at 1200°C for different time periods in furnace oxidation tests. On the other hand, thermal shock behavior of TBC was evaluated through examination of its durability at 1200°C with thermal shock test, which was carried out until the coating failure became visible. The relationship between the TGO growth and oxidation behavior was discussed using furnace oxidation test results.