A novel soft hydrothermal (SHY) route to crystalline PbS and CdS nanoparticles exhibiting diverse morphologies

We report a simple and rapid aqueous route to crystalline nanoparticles of PbS and CdS using single-source precursors and a conventional household pressure cooker.     

Anti-Diabetic Potential of Plant-Based Pentacyclic Triterpene Derivatives: Progress Made to Improve Efficacy and Bioavailability

Diabetes mellitus (DM) results from the inability of the pancreas to produce sufficient insulin or weakened cellular response to the insulin produced, which leads to hyperglycemia. Current treatments of DM focus on the use of oral hypoglycemic drugs such as acarbose, alpha-glucose inhibitors, sulphonylureas, thiazolidinediones, and biguanides to control blood glucose levels. However, these medications are known to have various side effects in addition to their bioavailability, efficacy, and safety concerns. These drawbacks have increased interest in the anti-diabetic potential of plant-derived bioactive compounds such as oleanolic and maslinic acids. Although their efficacy in ameliorating blood glucose levels has been reported in several studies, their bioavailability and efficacy remain of concern. The current review examines the anti-diabetic effects of oleanolic, maslinic, asiatic, ursolic, and corosolic acids and their derivatives, as well as the progress made thus far to enhance their bioavailability and efficacy. The literature for the current review was gathered from leading academic databases—including Google Scholar and PubMed—the key words listed below were used. The literature was searched as widely and comprehensively as possible without a defined range of dates.     

Phosphine-Free Tetradentate Salicylaldimine Ligand Complexed with Palladium: First Application in Heck Reactions

Heck reactions were carried out using phosphine-free tetradentate salicylaldimine ligand complexed with PdCl₂ under mild reaction conditions, short reaction time, and low palladium loading. All aryl iodides underwent coupling reactions with olefins, giving corresponding trans-products, with good to excellent yields, whereas aryl bromides gave very poor yields and aryl chlorides failed to react.     

Novel tetrahydroisoquinoline based organocatalysts for asymmetric Diels–Alder reactions: insight into the catalytic mode using ROESY NMR and DFT studies

For the first time an organocatalyst bearing a secondary nitrogen within a cyclohexane ring has been evaluated in the asymmetric Diels–Alder reaction. This organocatalyst is also the first of its kind based on a (1R,3S)-6,7-dimethoxy-1-phenyl-1,2,3,4-tetrahydroisoquinoline backbone. These catalysts were tested over a range of dienes and dienophiles and displayed promising chemical conversions of up to 100% with up to 64% ee with triflic acid as the cocatalyst. Density functional theory computational studies and 2D NMR spectroscopy were used to determine the structure of the intermediate iminium ion formed between the most efficient catalyst and cinnamaldehyde. The reaction profile for each of the four possibilities in this reaction were calculated and it was found that the iminium intermediate leading to the major product is higher in energy but kinetically preferred. The activation energies of all possible reaction paths were calculated and the results correlated with the observed products. These experiments revealed that the presence of both (E)- and (Z)-isomers of the cinnamaldehyde were contributing factors for the low enantioselectivity of the reaction products.     

Mineral associations in coal and their transformation during gasification

The principle aim of this investigation was to determine the effect that minerals and mineral associations in dense medium coal fractions have on the ash fusion temperature (AFT) of coal, where the mineral matter associated with coal undergoes transformations during gasification. Samples from three coal sources used by Sasol for gasification were acquired and a comprehensive characterisation on all dense medium fractions was conducted, including proximate analyses, AFT, ash oxide analyses, XRD and Mössbauer spectroscopy. From the proximate analyses, the ash content was the highest for the higher density fractions, with an accompanying decrease in fixed carbon content, consistent with the XRD and Mössbauer analyses. From the ash oxide analyses, it was evident that at higher relative densities more Fe₂O₃ and SiO₂ were present than in the lower density samples. From XRD analyses, the low density fractions contained calcite and dolomite. Pyrite and quartz were found in the higher density fractions whereas kaolinite occurred in all density separated fractions. From the different techniques it follows that with the Fe-content high in high density fractions, the AFT was low. When Ca and other basic oxide levels were abundant in low density fractions, the AFT was low and when the SiO₂/Al₂O₃ ratio was high in high density fractions the AFT increased.     

Causal Heat Transport in Inhomogeneous Cosmologies

We investigate the effect of heat dissipation in inhomogeneous cosmologies by invoking the full causal theory of heat transport within the framework of extended irreversible thermodynamics. This work extends earlier results which were obtained using the truncated causal heat transport equation. In particular, we show that the truncation of the heat transport equation implicitly defines a temperature law which leads to pathological behaviour in the temperature of the evolving cosmic fluid.     

D.C. conductivity of transparent conductive ZnO:Al films in the temperature range 80–360 K

An experimental study of the temperature dependence of the d.c. conductivity σ as a function of temperature T in the range from 80–360 K on nanocrystalline ZnO:Al films (Al³⁺ 2%) of thickness 500 nm prepared on glass microscope slides by a dip — coating method is presented. The electrical conductivity σ, which at room temperature varied between 0.1 to 2.7 S/cm, increased almost linearly with T for all the samples. Measurements of the Hall coefficient at room temperature and in a magnetic field of 1.2 T, gave R_H=0.53 cm³C⁻¹, from which a carrier concentration of n=1.18×10¹⁹ cm⁻³ and a carrier mobility of μ=1.40 cm²/Vs were deduced. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14–18, 2004.     

Generating physically realizable stellar structures via embedding

In this work we present an exact solution of the Einstein–Maxwell field equations describing compact charged objects within the framework of classical general relativity. Our model is constructed by embedding a four-dimensional spherically symmetric static metric into a five-dimensional flat metric. The source term for the matter field is composed of a perfect fluid distribution with charge. We show that our model obeys all the physical requirements and stability conditions necessary for a realistic stellar model. Our theoretical model approximates observations of neutron stars and pulsars to a very good degree of accuracy.     

Coriolis Effect on Convection in a Rotating Porous Layer Subjected to Variable Gravity

We consider the effects of rotation in a porous layer heated from below and subjected to a variable gravity field. The study is presented for large Vadasz numbers where no oscillatory convection is possible. It is demonstrated that the Coriolis acceleration stabilizes the convection in a variable gravity field, whilst the effect of gravity parameter stabilses the convection when reduced and destabilizes the convection when increased.     

An analogy between a gravity modulated porous layer heated from below and the inverted pendulum with an oscillating pivot point

The governing equations for the inverted pendulum is developed and shown to be analogous to the gravity modulated porous layer heated from below. In particular the temperature in a gravity modulated porous layer heated from below (R>0-unstable) is likened to the motion of an inverted pendulum (unstable). As gravity modulation stabilizes convection, Transport Porous Med. 57 (2004), 113, it is found that oscillating the pivot point of an unstable, inverted pendulum stabilizes the motion.