Dynamics of coral reef models in the presence of parrotfish

The decline of coral reefs characterized by macroalgae increase has been a global threat. We consider a slightly modified version of an ordinary differential equation (ODE) model proposed in Blackwood, Hastings, and Mumby [Theor. Ecol. 5 (2012), pp. 105–114] that explicitly considers the role of parrotfish grazing on coral reef dynamics. We perform complete stability, bifurcation, and persistence analysis for this model. If the fishing effort (f) is in between two critical values and , then the system has a unique interior equilibrium, which is stable if and unstable if . If is less (more) than these critical values, then the system has up to two (zero) interior equilibria. Also, we develop a more realistic delay differential equation (DDE) model to incorporate the time delay and treating it as the bifurcation parameter, and we prove that Hopf bifurcation about the interior equilibria could occur at critical time delays, which illustrate the potential importance of the inherent time delay in a coral reef ecosystem. Recommendations for Resource Managers

• One serious threat to coral reefs is overfishing of grazing species, including high level of algal abundance. Fishing alters the entire dynamics of a reef (Hughes, Baird, & Bellwood, 2003), for which the coral cover was predicted to decline rapidly (Mumby, 2006). One major issue is to reverse and develop appropriate management to increase or maintain coral resilience.
• We have provided a detailed local and global analysis of model (Blackwood, Hastings, & Mumby, 2012) and obtained an ecologically meaningful attracting region, for which there is a chance of stable coexistence of coral–algal–fish state.
• The healthy reefs switch to unhealthy state, and the macroalgae–parrotfish state becomes stable as the fishing effort increases through some critical values. Also, for some critical time delays, a switch between healthy and unhealthy reef states occurs through a Hopf bifurcation, which can only appear in the delay differential equation (DDE) model. Eventually, for large enough time delay, oscillations appear and an unhealthy state occurs.

     

Diaminobisbenzothiazole chain extended polyurethanes as a novel class of thermoplastic polyurethane elastomers with improved thermal stability and electrical insulation properties

This work was devoted to the development of a new class of modified polyurethane as an electrical insulating material. For this purpose, NCO‐terminated urethane prepolymers at different NCO contents were prepared and chain extended by 6,6′‐oxybis(2‐aminobenzothiazole) (ABT) to produce thermoplastic polyurethane elastomers. All of the polymers were characterized by FTIR and ¹HNMR spectroscopies and examined for their thermal, mechanical, and electrical properties. The dynamic mechanical measurements results showed two glass transitions indicating phase separation. A considerable improvement in the thermal and electrical properties in comparison to common polyurethanes was detected for these polymers. The level of enhancement in the measured properties was related to the polyol molecular weight, hard segment content, and consequently the amount of the introduced urea and benzothiazole moieties. These findings indicated the improved high service temperature performance of these materials as electrical insulator for metallic surfaces. Copyright © 2008 John Wiley & Sons, Ltd.     

Diphenylmethane Oxidation Catalyzed by Mononuclear Mn(III) Complexes

Catalytic property of a series of manganese(III) complexes with tetradentate phenol‐ and pyridinebased ligands on the oxidation of the C‐H bond of diphenylmethane in the presence of hydrogen peroxide as an oxidant at ambient conditions were investigated. In this process, diphenylmethane was oxidized to the corresponding keton and alcohol. The catalytic selectivity of the complexes was evaluated.     

Correlations Between Laser Induced Breakdown Spectroscopy (LIBS) and Dynamical Mechanical Analysis (DMA) for Assessment of Aging Effect on Plastic Bonded Explosives (PBX)

Plastic Bonded Explosives (PBXs) are explosive materials, in which sensitive explosive powders with high detonation performance are bound together in a matrix using small quantities of a synthetic polymer. They provide good thermal stability and improve cook‐off properties with negligible shrinkage. Laser‐induced breakdown spectroscopy (LIBS) has been introduced as a novel method for assessment of thermal aging in PBXs. Thermal aging of fifteen samples of PBXs with the same composition has been studied in two temperatures 60 and 70 °C for 5 period times during 29 d. Dynamical mechanical analysis (DMA) has also been done on different aged samples in order to validate the LIBS results. Among different molecular bands, LIBS data showed that the changes in line intensity in CN and AlO molecular radiations could be used to assess aging effects. Principle component analysis (PCA) chemometric method was also implemented in order to obtain more accurate discrimination between different samples. Since there is a good agreement for the outputs of LIBS data and DMA results, LIBS technique can be introduced a reliable method for assessment of thermal aging of PBXs.     

Nano-Co-[4-chlorophenyl-salicylaldimine-pyranopyrimidine dione]Cl2 as a new Schiff base complex and catalyst for the one-pot synthesis of some 4H-pyrimido[2,1-b]benzazoles

Research on Chemical Intermediates - Nano-Co-[4-clolorophenyl-salsylaldimine-pyranopyrimidine dione]Cl2 {Nano-[Co-4CSP]Cl2} was prepared and fully characterized as a new nano-Schiff base complex....     

An Efficient Method for the Oxidation of Hantzsch 1,4-Dihydropyridines to their Corresponding Pyridine Derivatives Under Mild and Heterogeneous Conditions

A combination of oxalic acid dihydrate and sodium nitrite in the presence of wet SiO₂ was used as an effective oxidizing agent for the oxidation of dihydropyridines to their corresponding pyridine derivatives at room temperature with excellent yields.