Solvothermal synthesis of nanocrystalline zinc oxide doped with Mn2+, Ni2+, Co2+ and Cr3+ ions

ZnO nanopowders doped with Mn²⁺, Ni²⁺, Co²⁺ and Cr³⁺ ions have been synthesised for the first time using a solvothermal reaction with microwave heating. The nanopowders were produced from a solution of zinc acetate and manganese (II), chromium (III), nickel (II) and cobalt (II) acetates, using ethylene glycol as a solvent. The content of Ni²⁺, Co²⁺ and Cr³⁺ ions in the solution and in the solid phase were close to each other up to 5 mol%. The doping level of Mn²⁺ ions in the solid is about 50% of that in the solution. No phases or compounds other than ZnO were detected by X-ray diffraction with Mn²⁺, Co²⁺ and Ni²⁺ doping. With Cr³⁺ ions a small amount of chromium oxide was found. None of the powders displayed any luminescence after doping. The Mn²⁺-doped powder displayed a paramagnetic behaviour. ESR and magnetisation investigations have revealed that no clustering of Mn²⁺ ions occurred up to a doping level of 3.9 mol%. The average grain size of powders doped with Ni²⁺, Cr³⁺, Co²⁺ and Mn²⁺ for a 10 mol% ion content in the solution was about 20 nm and the grain size dispersion 30%. With increasing dopant content the grain size decreased. It appears that the solvothermal process employed allows relatively high doping levels of the transition metal ions to be achieved without any dopant clustering or oxide precipitation.     

On the problem of vacuum energy in brane theories

We point out that modern brane theories suffer from a severe vacuum energy problem. To be specific, the Casimir energy associated with the matter fields confined to the brane, is stemming from the one and the same localization mechanism which forms the brane itself, and is thus generically unavoidable. Possible practical solutions are discussed, including in particular spontaneously broken supersymmetry, and quantum mechanically induced brane tension.     

Inhibition of energy transfer between conjugated polymer chains in host/guest nanocomposites generates white photo- and electroluminescence

The generation of white light requires the combination of two or more chromophores that emit simultaneously. The observed color of a mixture of light-emitting molecules, however, originates generally only from the lowest band-gap species because of efficient energy transfer between the chromophores which is difficult to avoid. Here we report on a nanocomposite material designed to yield pure and stable white photo- and electroluminescence. In this material, red, green, and blue emitting conjugated polymers are confined within the galleries of a layered semiconducting host matrix. The host hinders polymer pi-pi interactions which are responsible for the energy transfer between polymer chains, consequently, emission from the three chromophores is observed simultaneously resulting in white photoluminescence. The efficacy of the nanocomposites is demonstrated in simple single-layer white-emitting polymer diodes. The mechanism suggested here for white light generation, supported by extensive luminescence measurements, is in contrast to that previously reported in white-emitting polymer diodes where efficient energy transfer between polymer chains was essential for obtaining white light.     

Effect of sonochemistry: Li- and Mn-rich layered high specific capacity cathode materials for Li-ion batteries

Li- and Mn-rich layered Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ cathode material was synthesized using sonochemical method followed by annealing at 700, 800, and 900 °C for 10 h. The material was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and electrochemical techniques. Its performance as a cathode material for Li-ion batteries was examined. With the sample annealed at 900 °C, an initial specific capacity of 240 mAh g^?1 was obtained, which decreased to 215 mAh g^?1 after 80 cycles, thus retaining about 90 % of its initial capacity. In contrast, samples annealed at lower temperatures exhibited lower capacity retention upon cycling. Thus, the final annealing temperature was found to have a significant effect on the electrochemical stability of this material in terms of capacity, average voltage, and rate capability. The advantage of this synthesis, which includes a sonochemical stage, compared with a conventional co-precipitation synthesis, was also confirmed.     

Insights into the sonochemical decomposition of Fe(CO)5: theoretical and experimental understanding of the role of molar concentration and power density on the reaction yield

The present work analyses, in detail, the optimization of a sonochemical process with respect to concentration of precursor and power supplied in a system. This is due to that even a small change in power dramatically changes the high-energy conditions created with the bubble collapse. A model reaction that has been considered for this purpose involves the decomposition of Fe(CO)₅ in decalin solvent as this reaction is strongly influenced by the cavitation conditions. Sonochemical treatment of this carbonyl results in the formation of amorphous Fe₂O₃, which on heat treatment gives nanocrystalline Fe₂O₃. It has been observed that concentration and power density parameters play an important role to obtain higher decomposition of Fe(CO)₅ and hence higher yield of the amorphous Fe₂O₃ product. Also, using the experimentally observed results, a correlation (polynomial) has been developed.     

Fragrance release profile from sonochemically prepared protein microsphere containers

Protein microspheres have been prepared by sonicating a mixture of pure fragrant oil (amyl acetate (AA)) with an aqueous protein (bovine serum albumin) solution. The prepared protein spheres are nano- to micrometer sized with an encapsulation efficiency of approx. 97% for the AA present on the surface and inside the BSA capsule. Containers were found stable for more than 6 months when stored sealed at 4 °C and 20 °C. For the release profile measurements, we used a simple, automated and direct method. We continuously weighed the encapsulated microspheres and measured the evaporation rates. The release profiles at 15 °C and 25 °C display two different evaporation rates. The higher rate is the sum of a few evaporation rates, including water molecules, while the slower rate is due to the evaporation of pure AA. The changes in the evaporation rates occur upon the collapse of the container. This event coincides with the full evaporation of water. For morphological characterization we dyed the AA with Nile red, and used SEM, ESEM, Cryo-SEM, light microscopy, and confocal laser scanning microscopy measurements.     

Programming scale-free optics in disordered ferroelectrics

Using the history dependence of a dipolar glass hosted in a compositionally disordered lithium-enriched potassium tantalate niobate (KTN:Li) crystal, we demonstrate scale-free optical propagation at tunable temperatures. The operating equilibration temperature is determined by previous crystal spiralling in the temperature/cooling-rate phase space.     

Sonochemical coating of cotton and polyester fabrics with "antibacterial" BSA and casein spheres

A novel antibacterial coating for cotton and polyester fabrics has been developed by using drug-loaded proteinaceous microspheres made of bovine serum albumin and casein proteins. The microbubbles were created and anchored onto the fabrics (see figure) in a one-step reaction that lasts 3 min. The sonochemically produced "antibacterial fabrics" have been characterized. The efficiency of the sonochemical process in converting the native proteins into microspheres, encapsulating the drug, and coating the fabric has also been studied.     

The second law of thermodynamics revisited I. The absolute zero of potential and the general expression for the efficiency of universal reversible cycle

The fundamental equation of thermodynamics expresses the internal energy of a system as a function of all the extensive parameters of the system. The differential form of this equation is referred to as the Gibbs equation. We have integrated this equation and have used it to derive an expression characterising the efficiency of a system for any kind of cyclical process by which work is produced. This system has access to two reservoirs at low and high thermodynamics potential respectively. It is claimed that all thermodynamic potentials (temprature, chemical potential, hydrostatic pressure, electric potential, etc) can have an absolute value of zero which we defined as the value of the potential in the lower reservoir when the efficiency of the cycle is 1. It is also shown that the classical Carnot machine, in which heat is converted into mechanical work, is an example of the general expression.     

Hidden convexity in some nonconvex quadratically constrained quadratic programming

We consider the problem of minimizing an indefinite quadratic objective function subject to twosided indefinite quadratic constraints. Under a suitable simultaneous diagonalization assumption (which trivially holds for trust region type problems), we prove that the original problem is equivalent to a convex minimization problem with simple linear constraints. We then consider a special problem of minimizing a concave quadratic function subject to finitely many convex quadratic constraints, which is also shown to be equivalent to a minimax convex problem. In both cases we derive the explicit nonlinear transformations which allow for recovering the optimal solution of the nonconvex problems via their equivalent convex counterparts. Special cases and applications are also discussed. We outline interior-point polynomial-time algorithms for the solution of the equivalent convex programs. This author's work was partially supported by GIF, the German-Israeli Foundation for Scientific Research and Development and by the Binational Science Foundation. This author's work was partially supported by National Science Foundation Grants DMS-9201297 and DMS-9401871.