SYNTHESIS AND STRUCTURE OF A LINEAR TRIVANADIUM COMPOUND(PH4P)[V3(OC6H4S-o)6]-SIMULATION OF THE VANADIUM SITE OF ALTERNATIVE NITROGENASE

Compound(PH₄P)[V3MP6](MPH₂=o-HOC₆H₄SH)was obtained by reaction of VCl₃ and Na₂MP in ethanol in the presence of PH₄PBr.It is triclinic and crystallizes in space group P1, fw=1237.3, a=14.127(4), b=14.342(4), c=15.878(4)Å;α=65.08(2), β=73.09(2), γ=78.68(2)°;V=2781.3 ų, Z=2, d_c=1.48 g/cm³.Final R factor is 0.063.The three vanadium atoms are linearly arranged and bridged by the oxygen atoms and terminally chelated by the thiolato-atoms of the six MP^2-ligands in pseudo-S₆ symmetry.     

Dual variational principles with deviating argument and discontinuous extremals

We study dual or complementary variational principles for functionals with deviating argument and discontinuous extremals. Local conditions for the existence of a pair of dual extremum principles are given. Results are then applied to the control problem involving linear neutral differential-difference equations.     

Removal and recovery of mercury from aqueous solution using magnetic silica nanocomposites

Thiol-functionalized magnetic silica nanocomposite was synthesized and tested for its mercury pick-up capability in aqueous solution. Magnetic property was to be utilized upon the collection of the adsorbents and the recovery adsorbed Hg by subsequent separation process. Cobalt ferrite nanoparticle, the core of magnetic silica nanocomposite, was synthesized using a thermal decomposition method and grown to a particle having an average size of 13 nm. The dispersed nanoparticles were then further arranged into spherical groups using a nanoemulsion method to enhance the reactivity toward magnets followed by tetraethyl orthosilicate coating using a modified Stöber method. The pore structure was modified by an additional coating of cetyltrimethylammonium bromide and tetraethyl orthosilicate. Finally, the surface of the magnetic silica nanocomposite was functionalized with thiol group. When tested for mercury adsorption capacity, a sufficiently high Hg adsorption capacity of 19.79 mg per g of adsorbent was obtained at room temperature and a pH of 5.5.     

Synthesis of Multifunctional Mn‐Doped CdTe/ZnS Core/Shell Quantum Dots

The synthesis of a novel water‐soluble Mn‐doped CdTe/ZnS core‐shell quantum dots using a proposed ultrasonic assistant method and 3‐mercaptopropionic acid (MPA) as stabilizer is descried. To obtain a high luminescent intensity, post‐preparative treatments, including the pH value, reaction temperature, reflux time and atmosphere, have been investigated. For an excellent fluorescence of Mn‐doped CdTe/ZnS, the optimal conditions were pH 11, reflux temperature 100°C and reflux time 3 h under N₂ atmosphere. While for phosphorescent Mn‐doped CdTe/ZnS QDs, the synthesis at pH 11, reflux temperature 100°C and reflux time 3 h under air atmosphere gave the best strong phosphorescence. The characterizations of Mn‐doped CdTe/ZnS QDs were also identified using AFM, IR, powder XRD and thermogravimetric analysis. The data indicated that the photochemical stability and the photoluminescence of CdTe QDs are greatly enhanced by the outer inorganic ZnS shell, and the doping Mn²⁺ ions in the as‐prepared quantum dots contribute to strong luminescence. The strong luminescence of Mn‐doped CdTe/ZnS QDs reflected that Mn ions act as recombination centers for the excited electron‐hole pairs, attributing to the transition from the triplet state (⁴T₁) to the ground state (⁶A₁) of the Mn²⁺ ions. All the experiments demonstrated that the surface states played important roles in the optical properties of Mn‐doped CdTe/ZnS core‐shell quantum dots.     

Numerical study of the DLC film flow field in the ECR-PECVD reaction chamber

This paper mainly investigates the optimum parameters for the fabrication of uniform diamond-like carbon (DLC) films on the electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) reaction chamber by analyzing the effect of the reacting gas velocity on the film properties. This work makes use of computational fluid dynamics (CFD) approach to model surface chemical reactions, flow and temperature fields, as well as heat and mass transfer phenomena. The simulation has shown that natural convection and mass transfer affect the recirculating flow within the reactor and, therefore, the distribution of material deposition. In other words, as a result of attaching an endplate (baffle) at the top of the substrate, the deposition rate of the substrate is appreciably enhanced. However, the surface uniformity of the substrate is obviously deteriorated.