Iterated discriminants

It is shown that the discriminant of the discriminant of a multivariate polynomial has the same irreducible factors as the product of seven polynomials each of which is defined as the GCD of the generators of an elimination ideal. Under relatively mild conditions of genericity, three of these polynomials are irreducible and generate the corresponding elimination ideals, while the other four are equal to one. Moreover the irreducible factors of two of these polynomials have multiplicity at least two in the iterated discriminant and the irreducible factors of two others of the seven polynomials have multiplicity at least three.     

Optimisation of a continuous flash fermentation for butanol production using the response surface methodology

Factorial design and response surface techniques were used in combination with mathematical modelling and computational simulation to optimise an innovative industrial bioprocess, the production of biobutanol employing the flash fermentation technology. A parametric analysis performed by means of a full factorial design at two levels determined the influence of operating variables on butanol yield and productivity. A second set of simulations were carried out based on the central composite rotatable design. This procedure generated simplified statistical models that describe butanol yield and productivity as functions of the significant operating variables. From these models, response surfaces were obtained and used to optimise the process. For a range of substrate concentration from 130 to 180 g/l, the optimum operating ranges ensure butanol productivity between 7.0 and 8.0 g/l h, butanol yield between 19 and 22%, substrate conversion above 90% and final butanol concentration around 25 g/l.     

Priorities in environmental health Part 2

Continuing the format of the inventory, as introduced and outlined in Part 1 (of Priorities in Environmental Health) Part 2 lists the two remaining categories of environmental health hazards. The first category Involves man's indirect rote as the transmitter of the impediment. The second category concerns hazards which occur when man is neither the aetiological agent or the transmitter.     

Hydrogen evolution by templated cadmium indate nanoparticles under natural sunlight illumination

Carbon-doped cadmium indate (CdIn₂O₄) nanoparticles were synthesized by a sol–gel templating method using the block co-polymer surfactant Pluronic F127 and evaluated for hydrogen generation activity under artificial and natural solar illumination. Each catalyst powder was loaded with platinum as a cocatalyst in order to promote charge carrier separation. BET surface area measurements indicated an increase in surface area with F127 introduction of up to 5 times the area of the non-templated sample. Natural sunlight illumination experiments showed the hydrogen evolution rate of CdIn₂O₄ was 17 μmol h⁻¹ as compared to 2.1 μmol h⁻¹ for the Pt:TiO₂ reference material. The H₂ rate was determined to be similar under both stirring and non-stirring conditions for the CdIn₂O₄ catalyst, which resulted from 10 min irradiation exposure times. Laboratory experiments confirmed this effect and showed that at longer, out to 60 min, irradiation times the evolution rate was 3 times greater for stirred over non-stirred samples. The templated nanoparticle CdIn₂O₄ catalysts are promising for solar hydrogen conversion.     

Properties of purified direct steam grown silicon thermal oxides

Thermal silicon oxides are known to very effectively passivate silicon surfaces. Choosing a water vapor ambient instead of a dry oxygen atmosphere increases the oxidation rate by about one order of magnitude and considerably reduces process time and costs. State of the art pyrox systems produce steam by pyrolysis of hydrogen and oxygen gas. A new approach is the purification of vaporized deionized (DI) water. In this work we present a direct comparison of both steam generation systems, which are connected to the same quartz tube of an industrial high quality tube furnace. The higher steam saturation of the direct steam process enhances the growth rate by about 20% compared to a pyrolytic steam based process. On low-resistivity p-type substrates, excellent surface recombination velocities of around 25 cm/s are found for both systems after a forming gas anneal. Detailed characterization shows similar physical properties of the oxide layers grown by either steam from pyrolysis or purified steam. Moreover, thermal oxide rear surface passivated silicon solar cells show similar high efficiencies exceeding 18.0% irrespective of the applied steam generation technology.     

SEM study of the morphology of asymmetric cellulose acetate membranes produced from recycled agro-industrial residues: sugarcane bagasse and mango seeds

Cellulose, obtained both from sugarcane bagasse and mango seeds, was used for synthesizing cellulose acetate in order to produce asymmetric membranes. These were compared to membranes of commercial cellulose acetate (Rhodia). All produced membranes were asymmetric, characterized by the presence of a dense skin and a porous support. Differences regarding the morphology of the surfaces as well as of the porous support can be noticed. Scanning Electron Microscopy (SEM) showed that the morphology of the superficial layer, responsible for transport, depends on the different lignin content of the starting material and also on the viscosity average molecular weight of the cellulose acetates produced from sugarcane bagasse, mango seed, and Rhodia’s commercial cellulose acetate.     

Asymmetric buckling of shell-stiffened annular plates

The present study is devoted to some stability problems of annular plates with shell-stiffening. The plate is simply supported, or clamped, or elastic restrains are applied on the boundaries of the plate. Though the load is axisymmetric we shall assume that the deformations are not necessarily axisymmetric. The displacement fields in the plate and the shell are expanded into Fourier series. For the shell all physical quantities are derived from an appropriately chosen Galerkin function. The main goal is to clarify the effect of a stiffening shell on the buckling load. Hence the field equations together with the boundary- and continuity conditions are clarified. These provide the eigenvalue problem from which the critical load can be calculated. In order to solve the eigenvalue problem we have established, appropriate numerical methods are used.