PREDATOR–PREY DYNAMICS WITH SEASONAL WATER-LEVEL FLUCTUATIONS

Water level in rivers, lakes and reservoirs has great influence on the interactions between prey and predator fish. Indeed, the increase of the water volume hinders the capture of the prey by the predator. The same reasoning applies when there is a decrease in the volume of water, favoring the capture of the prey by the predator. In this paper, we consider a seasonally varying predator–prey model to study the influence of water-level variations on the interaction between two species of fishes in an artificial lake. A seasonal variation of the water-level is introduced in the predation rate taking into account two values, leading to a general switched system. Permanence, stability and existence of an invariant domain containing at least one periodic solution are established. Our theoretical results confirm the assumption that the water exerts a strong influence on the interaction between fishes

Synthesis and characterization of a composite organic semiconductor (curcumin-paracetamol/TiO2)

The aim of this work is to study some physical and chemical properties of an organic semiconductor (OSc)/x%titanium dioxide (TiO2) heterosystem (with 0 ≤ x ≤ 20%) (OScs/x%TiO2). The OSc is obtained from pure curcumin and paracetamol as starting molecules. The synthesis methodology of the mixtures of OScs/x%TiO2 heterosystem involves a microwave-assisted multicomponent reaction using curcumin, paracetamol, and TiO2 as a heterogeneous solution. All mixtures were analyzed by Fourier-transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis/differential thermal analysis, X-ray diffraction, ultraviolet–visible spectroscopy, and scanning electron microscopy. The results obtained show a new nanocomposite with interesting pharmaceutical, optical, electronic, and structural properties, which can be used in the fields of energy production, water purification, and air purification, as a biomaterial and for electronic applications

An investigation of crystal structure, surface area and surface chemistry of strontium niobate and their influence on photocatalytic performance

Sr1−xNbO3 is an unusual material that displays both metallic type conduction and photocatalytic activity, despite being an NbIV oxide, and it sustains photo-oxidation without degradation. The influence of crystal structure, surface area and surface chemistry on the photocatalytic activity of strontium niobate has been investigated. The crystal structure of strontium niobate depends on the Sr content of the A site, with cubic symmetry for Sr ≤ 0.92 and orthorhombic symmetry for 0.92 < Sr ≤ 0.97. The change of crystal structure from cubic to orthorhombic symmetry seems to have a negative effect on the photocatalytic activity, as the NbO6 octahedra become distorted and unfavourable for d-orbital overlapping. The photocatalytic activity increased significantly by enlarging the surface area through ball milling, nevertheless, a clear trend for the surface area effect on activity is not obtained among samples with different Sr content. An enrichment of Sr on the surface of strontium niobate was observed by XPS, which seems to be a governing factor for improving stability.PostprintPeer reviewe