Structural and Luminescence Properties of ZnO Nanoparticles Synthesized by Mixture of Fuel Approach in Solution Combustion Method

Zinc oxide has been used for many applications, for example optoelectronic devices, ceramics, catalysts, pigments, varistors and many other important applications. In this study, ZnO nanoparticles were synthesized by mixture of fuel approach in solution combustion method. Mixtures of urea, glycine and citric acid were mixed at room temperature with Zinc nitrates as fuels resulting in spontaneous ignition resulting in production of ZnO nanopowder. The crystal structure and size of the synthesized powder were determined by X-ray diffractometer (XRD), which revealed that the synthesized ZnO nanopowder has the pure wurtzite structure having crystallite size 26–40 nm. Optical studies of nanomaterial were examined by FTIR and UV-Visible absorption spectrum. The luminescence studies also investigated in the visible region 360–800 nm with excitation 325 nm laser. These nanomaterials may be used in solid-state lightening devices

A lower bound on the eccentric connectivity index of a graph

AbstractIn pharmaceutical drug design, an important tool is the prediction of physicochemical, pharmacological and toxicological properties of compounds directly from their structure. In this regard, the Wiener index, first defined in 1947, has been widely researched, both for its chemical applications and mathematical properties. Many other indices have since been considered, and in 1997, Sharma, Goswami and Madan introduced the eccentric connectivity index, which has been identified to give a high degree of predictability. If G is a connected graph with vertex set V, then the eccentric connectivity index of G, ξC(G), is defined as ∑v∈Vdeg(v)ec(v), where deg(v) is the degree of vertex v and ec(v) is its eccentricity. Several authors have determined extremal graphs, for various classes of graphs, for this index. We show that a known tight lower bound on the eccentric connectivity index for a tree T, in terms of order and diameter, is also valid for a general graph G, of given order and diameter

UV-Vis-NIR quantum cutting suitable for c-Si solar cell application

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.The possibility of using the broad band spectra of Eu2+ to improve the absorption of the Pr3+-Yb3+ quantum cutting couple was investigated. The energy transfer mechanisms between Eu2+ and Pr3+ in the SrF2 host are briefly discussed in order to evaluate the potential of Eu2+ as a sensitizer for the Pr3+-Yb3+ couple. The results showed that Eu2+ could be a good sensitizer for the absorption of UV photons and efficiently enhancing the Pr3+ emission, and hence improving the near infrared emission. The investigated system can therefore enable the c-Si solar cell to utilize the solar spectrum more efficiently in the broad wavelength region where c-Si shows a weak response.cf201

A conservation model for black rhino

Over the past thirty years the black rhinoceros (Diceros bicornis) population in Africa has declined from about 65 000 to 3 500. In contrast the South African and Namibian population has increased four-fold to 1 000 over the same period. The recently developed national conservation strategy for black rhino has as its main goal a further four-fold increase in the current population in as short a period as possible. To achieve this, the growth rate of the population as a whole will have to be maximised. This involves removing animals from areas where the population is approaching the ecological carrying capacity and establishing new viable populations in other suitable reserves. A model incorporating what is known about the population biology of black rhino, was developed to give guidance to managers on the most appropirate harvesting strategy to adopt for their populations; in particular, to determine the rate of removals and the age and sex of individuals to be removed to attain the conservation goal as soon as possible