UTILIZATION OF ALUMINA RED MUD FOR SYNTHESIS OF INORGANIC POLYMERIC MATERIALS

Red mud is a residue coming from the metallurgical treatment of bauxite with the Bayer process. Million of tons of red mud are produced annually worldwide and disposed of on land, degrading vast areas. Therefore, red mud utilization is a first-priority issue for any alumina plant. In the present work, the potential use of red mud for synthesis of inorganic polymeric materials through geopolymerization process was studied. The main focus was the production of inorganic polymeric materials that could be used in the construction sector as artificial structural elements such as massive bricks. The geopolymerization process involves a chemical reaction between red mud and alkali metal silicate solution under highly alkaline conditions. The product of this reaction is an amorphous to semi-crystalline polymeric structure, which binds the individual particles of red mud transforming the initial granular material to a compact and strong one. The effect of main synthesis parameters—like solid-to-liquid ratio, caustic soda as well as soluble silica concentrations, and metakaolin addition—on the properties of red mud-based inorganic polymeric materials was investigated. The results showed that the produced materials have high compressive strength, very low water absorption, satisfactory apparent density, and excellent fire resistance. Therefore, this work proved that the red mud-based inorganic polymeric materials have promising properties and have the potential to be used as artificial structural elements in the construction sector.     

Reactivity of Valganciclovir in Aqueous Solution

The rates of hydrolysis of valganciclovir to ganciclovir and L-valine and isomerization of the R and S diastereomers of valganciclovir in aqueous buffer solution from pH 3.8 to 11.5 were determined at 37°C. The kinetics of hydrolysis were first order for at least two half-lives in neutral and basic solutions. In acidic solutions where less than 10% degradation occurred, the rate of hydrolysis was determined assuming a first-order loss in drug. At 37°C and pH 7.08, the half life is 11 h. The maximum stability at the pH values studied occurred at pH 3.81 with a half life of 220 days. The kinetics of the approach to equilibrium for the isomerization were first order and the ratio of the R:S isomer at equilibrium was 52:48. Isomerization was approximately 10 fold faster than hydrolysis over the pH range studied with a half-life at pH 7.01 of 1 h. The maximum stability toward isomerization (t_1/2 > 533 h) occurs at a pH below 3.8. The pH-rate profile for the hydrolysis and the isomerization reaction are best described by hydroxide ion catalyzed mechanisms. In acidic and neutral solutions, the hydroxide reacts with the protonated form of the drug, while in basic solutions, the hydroxide reacts with the neutral form of the drug.     

Prospects and Challenges of Graphene in Biomedical Applications

Graphene materials have entered a phase of maturity in their development that is characterized by their explorative utilization in various types of applications and fields from electronics to biomedicine. Herein, we describe the recent advances made with graphene‐related materials in the biomedical field and the challenges facing these exciting new tools both in terms of biological activity and toxicological profiling in vitro and in vivo. Graphene materials today have mainly been explored as components of biosensors and for construction of matrices in tissue engineering. Their antimicrobial activity and their capacity to act as drug delivery platforms have also been reported, however, not as coherently. This report will attempt to offer some perspective as to which areas of biomedical applications can expect graphene‐related materials to constitute a tool offering improved functionality and previously unavailable options.     

Dyadic Green's function of a sphere with an eccentric spherical inclusion

An exact, analytical solution to the problem of point-source radiation in the presence of a sphere with an eccentric spherical inclusion has been obtained by combined use of the dyadic Green's function formalism and the indirect mode-matching technique. The end result of the analysis is a set of linear equations for the vector wave amplitudes of the electric Green's dyad. The point source can be anywhere, even within the aforesaid nonspherical body, and there is no restriction with regard to the electrical properties in any part of space. Several checks confirm that this solution obeys the energy conservation and reciprocity principles. Numerical results are presented for an electric Hertz dipole radiating from within an acrylic sphere, which contains an eccentric spherical cavity.     

Digital clubbing as an unusual complication associated with severe secondary hyperparathyroidism: report of two cases

Digital clubbing due to secondary hyperparathyroidism has been described as an unusual complication among patients with chronic kidney disease undergoing maintenance hemodialysis therapy. Although the pathogenesis of digital clubbing is unknown, certain growth factors such as platelet-derived growth factor and hepatocyte growth factor have been associated with this clinical syndrome. Two patients of our renal unit population presented this unique clinical feature bilaterally, among the other clinical findings of severe secondary hyperparathyroidism. Both patients were subjected to parathyroidectomy. Histological examination revealed diffuse hyperplasia of parathyroid glands. Despite the improvement of clinical symptoms and laboratory findings of secondary hyperparathyroism after parathyroidectomy, digital clubbing remained unchanged.     

Effect of rosemary extract, chitosan and α-tocopherol on lipid oxidation and colour stability during frozen storage of beef burgers

The effect of rosemary extract, chitosan and α-tocopherol, added individually or in combination, on lipid oxidation and colour stability of frozen (−18 °C) beef burgers stored for 180 days was investigated. The burgers’ lipid oxidation and appearance were evaluated through measurement of primary (conjugated dienes and peroxide value) and secondary (malondialdehyde) oxidation products, together with visual assessment and instrumental measurement of colour. Chitosan alone and in combination with either rosemary or α-tocopherol had the best antioxidative effect (P ? 0.05) compared to individual use of rosemary or α-tocopherol, while the best results were obtained with the combination of chitosan and rosemary. The differences of antioxidative effects, however, between individual use of rosemary or α-tocopherol as compared to the controls were also significant (P ? 0.05). Chitosan added individually or in combination with either rosemary or α-tocopherol had also a noteworthy effect on the burgers’ appearance as it contributed to red colour retention for a much longer period (P ? 0.05) compared all other treatments and the controls. In conclusion, the best antioxidative effects were obtained with the combination of chitosan and rosemary extract.     

Resilient Security Mechanism for Wireless Ad hoc Network

A wireless multihop network is emerging as one of the most important technologies in the field of ubiquitous networking. However, a number of formidable challenges remain, several of the most crucial been associated with robustness and network security. In this paper, we introduce a comprehensive resilient security framework for wireless ad hoc networks that are using multipath routing. It deploys an integrated multisignatures scheme and uses a self-certified public keying technique to ensure secure route discovery. In addition, it uses the Schnorr signature scheme along with an information dispersal algorithm to ensure secure data transfer. We provide security analysis of the proposed approach and compare it with several existing popular schemes. It can be seen that the proposed approach is more secure than other existing schemes. We also evaluated the proposed approach by means of computer simulation and compared its performance to that of the existing popular schemes. The results are in favor of the proposed technique in terms of efficiency and effectiveness.     

Fluorescence anisotropy based single liposome assay to measure molecule-membrane interactions

Nanometer-scaled liposomes are used frequently for research, therapeutic, and analytical applications as carriers for water-soluble molecules. Recent technical advances allow the monitoring of single liposomes, which provides information on heterogeneous properties that were otherwise hidden due to ensemble averaging. Recent observations demonstrated that the efficiency of entrapping water-soluble molecules increases with decreasing vesicle size. The molecular mechanism behind this observation is not clear, but enhanced molecule-membrane interactions due to the increase of the surface area-to-volume ratio could play an important role. To investigate this hypothesis, we extended our single liposome assay based on confocal fluorescence imaging by implementation of fluorescence anisotropy. This combination has not been widely exploited, and confocal fluorescence anisotropy imaging in particular has seldom been used. We investigated different small dye molecules and were able to determine if these molecules interact or not with the liposome membrane. We confirm the liposome size-dependent entrapment of molecules whereas the molecule-membrane interactions appear to be independent of liposome size. Our fluorescence anisotropy assay can be used as a general method to investigate molecule-membrane interactions or molecule-molecule interactions in a high-throughput manner in nanometer-scaled containers like liposomes.     

Material Interactions in a Novel Pinless Tool Approach to Friction Stir Spot Welding Thin Aluminum Sheet

The requirement for a probe, or pin, in friction stir spot welding (FSSW) leads to an undesirable keyhole and “hooking,” which can influence the fracture path and weld strength. Furthermore, the full weld cycle for FSSW is typically longer than ideal for the automotive industry, being 2 to 5 seconds. Here, it is shown that using a novel pinless tool design it is possible to achieve high lap shear strength (~3.4 kN) in thin aluminum sheet (~1 mm thick), with short weld cycle times (<1 second). Several techniques have been exploited to study the material flow and mechanisms of weld formation in pinless FSSW, including high-resolution X-ray tomography, to understand the role of the tool design and weld parameters. Despite the “simple” nature of a pinless tool, material flow in the weld zone was found to be surprisingly complex and strongly influenced by surface features on the tool, which greatly increased the penetration of the plastic zone into the bottom sheet. Because of the rapid thermal cycle and high level of grain refinement, the weld zone was found to develop a higher strength than the parent material with little evidence of a heat affected zone (HAZ) after postweld natural aging.