A new family of BiO(ClxBr1 − x) visible light sensitive photocatalysts

A new family of BiO(Cl_xBr_1 − x) photocatalysts have been synthesized by a hydrothermal method. The photocatalytic activity of the new material was measured on the degradation of Rhodamine B (RhB) and Acetophenone (AP) and photooxidation of potassium iodide in water under UV–vis and visible light (λ ≥ 420 nm) irradiations. In comparison to Degussa P25, the new photoactive material with x = 0.5 demonstrated 3 times higher rate in removing aqueous RhB under visible light irradiation. A morphology, chemical composition and crystalline structure of BiO(Cl_xBr_1 − x) were characterized using scanning electron microscopy and powder X-ray diffraction. The values of their unit cell parameters depend on Cl/Br ratio and they change according to the Vegard's law.     

Design of X-ray supermirrors

A new approach is proposed for the design of wide band-pass multilayer optical elements operating in the hard X-ray spectral region. The method, based on the combination of analytical and numerical methods, solves the inverse problem consisting of inferring the composition profile of a depth-graded multilayer coating. The key feature of our approach consists in using an analytical expression for the depth-distribution of the period as initial solution for direct computer calculations. This allows a global minimization of the merit function and a many-fold decrease of the computer run time. Simulations of two particular cases are presented: a constant reflectivity over a wide spectral range and a complicated reflectivity profile. The best choice of material pairs for composing a depth-graded multilayer structure is discussed from the viewpoint of maximum achievable reflectivity and least number of bi-layers. Features of depth-graded multilayer mirrors, which are distinctive from conventional periodic mirrors, are examined. The factors influencing the optical quality of broad-band multilayers are also considered.     

Elasticity Theories with Higher-order Gradients of Inertia and Stiffness for the Modelling of Wave Dispersion in Laminates

Dispersive wave propagation is simulated with a continuum elasticity theory that incorporates gradients of strain and inertia. The additional parameters are the Representative Volume Element (RVE) sizes in statics and dynamics, respectively. For the special case of a periodic laminate, expressions for these two RVE sizes can be provided based on the properties of the two components. The fourth-order governing equations are rewritten in two sets of coupled second-order equations, whereby the two sets of unknowns are the macroscopic displacements and the microscopic displacements. The resulting formulation is thus a true multi-scale continuum. In a numerical wave propagation example it is shown that the higher-order continuum model provides an excellent approximation of an explicit model of the heterogeneous laminate.     

An efficient algorithm for the minimal unsatisfiability problem for a subclass of CNF

We consider the minimal unsatisfiability problem for propositional formulas over n variables with n+k clauses for fixedk. We will show that in case of at most n clauses no formula is minimal unsatisfiable. For n+1 clauses the minimal unsatisfiability problem is solvable in quadratic time. Further, we present a characterization of minimal unsatisfiable formulas with n+1clauses in terms of a certain form of matrices. This revised version was published online in June 2006 with corrections to the Cover Date.     

AROMATIZATION OF PROPYLENE OVER HZSM-5: A DESIGN OF EXPERIMENTS (DOE) APPROACH

Aromatization of propylene was performed in a continuous reactor over HZSM-5 catalysts. A full-factorial design of experiments (DOE) methodology identified the effects of temperature (400°–500°C), Si:Al ratio (50–80), propylene feed concentration (8.9–12.5 mol.%), and catalyst amount (0.2–1.0 g) on propylene conversion as well as the yields of benzene, toluene, p-xylene, o-xylene (BTX), and total BTX. The Si:Al ratio and amount of the HZSM-5 catalyst influenced all of the responses, while temperature affected all the responses except the yield of p-xylene. An increase in feed concentration significantly increased the yields of benzene, toluene, and total BTX. An interaction between propylene feed concentration and catalyst amount influenced the yields of benzene, toluene, and total BTX. This interaction indicated that a higher feed concentration promotes aromatization at higher catalyst concentrations. By contrast, the interaction of Si:Al ratio with propylene feed concentration was found significant for p-xylene and o-xylene yields, but not for benzene and toluene, suggesting that xylenes are synthesized on different sites than those for benzene and toluene. These interaction effects demonstrate how the use of DOE can uncover significant information generally missed using traditional experimental strategies.     

Skim acidic milk whey cryoconcentration and assessment of its functional properties: Impact of processing conditions

In the present research two objectives were studied. The first was aimed to optimize whey cryoconcentration process by minimizing the amount of the dry matter entrapped in the ice fraction. This was possible by recycling the ice fraction. It was possible to concentrate acidic whey from 5.71 ± 0.01% (w/w) up to 24.68 ±0.03% (w/w) total dry matter using three cryoconcentration cycles and one recycling ice cycle. The second objective was to study the emulsifying and foaming properties of the concentrated whey as function of the cryoconcentration cycle. Results showed that emulsion stability index (ESI) of the cryoconcentrated whey increased by increasing the cryoconcentration cycle whereas the emulsion activity index (EAI) decreased. Foaming ability expressed as nitrogen volume needed to get foam volume three times higher than the initial volume increased by increasing cryoconcentration cycle and foam stability decreased by increasing the cryoconcentration cycle.Industrial relevanceSeveral efforts and studies have been made to increase the use of milk whey, a valuable by-product of cheese processing, especially for human nutrition. In the present work, cryoconcentration technology was used for whey recovery and valorisation as promising ingredient in the food industry.