Quadratic programming with transaction costs

We consider the problem of maximizing the mean-variance utility function of n$n$ assets. Associated with a change in an asset's holdings from its current or target value is a transaction cost. These must be accounted for in practical problems. A straightforward way of doing so results in a 3n$3n$-dimensional optimization problem with 3n$3n$ additional constraints. This higher dimensional problem is computationally expensive to solve. We present an algorithm for solving the 3n$3n$-dimensional problem by modifying an active set quadratic programming (QP) algorithm to solve the 3n$3n$-dimensional problem as an n$n$-dimensional problem accounting for the transaction costs implicitly rather than explicitly. The method is based on deriving the optimality conditions for the higher dimensional problem solely in terms of lower dimensional quantities and requires substantially less computational effort than any active set QP algorithm applied directly on a 3n$3n$-dimensional problem.     

Die polymerisation der lactame XI. Die copolymerisation von 6-caprolactam mit 12-laurolactam

The course of the incorporation of 6-caprolactam and 12-laurolactam into polymer chains during the hydrolytic, cationic and anionic copolymerization for an equimolar ratio of the monomers was studied. During the hydrolytic copolymerization 6-caprolactam is incorporated more rapidly at 260, 230 or 200°C at the beginning of the polymerization process; the differences between incorporation rates of the lactams into the copolymer increase with decreasing temperature. During the cationic copolymerization the incorporation of 12-laurolactam is more rapid by orders of magnitude for the above temperatures at the beginning of the process. Changes in the composition of cationic copolymers as compared to the hydrolytic copolymers are independent of the temperature during the copolymerization. The anionic copolymerization is characterized by a more rapid incorporation of 6-caprolactam into the polymer chain. The differences in the polymerization activity of the two lactams decrease with increasing temperature of the anionic copolymerization. The described course of incorporation of individual monomers, with the various mechanisms of the polymerization, also corresponds to melting points of copolymers in accordance with their composition.     

Etching of n-GaN - Important step in device processing

Photo-assisted electrochemical (PEC) and photo-assisted electrodeless (ELPEC) etching of n-doped GaN layers grown on sapphire in a KOH based solution under illumination of Hg arc lamp is demonstrated. Smooth surfaces were obtained for a narrow range of etching conditions. It was found out that this window could be extended by using etching conditions which produced “whiskers”. For ELPEC etching final etched surfaces were much smoother with stirring but showed distinct bar objects. Such objects could be eliminated by chopped irradiation when also the etching rate decreased and smoothing of pyramidal and bar objects in the etched surfaces was observed. This effect is most probably caused by the electron-hole pair recombination suppressed at semiconductor dislocation locations.     

Die Polymerisation von Lactamen. IV. Die anionische Copolymerisation von 6-Caprolactam mit 8-Caprylolactam

Conditions were defined for preparing homogeneous castings based on copolymers of 6-caprolactam and 8-caprylolactam under conditions of the low-temperature adiabatic copolymerization of the two lactams below the melting point of polymeric products (catalyst: sodium salt of lactams, activator: N-acetyl-6-caprolactam). The content of 8-caprylolactam in the copolymer cannot exceed 30 mole-% owing to its high polymerization heat and to the dependence of the copolymer melting point on the concentrations of the two lactams; the homopolymerization of the 8-caprylolactam cannot be accomplished under these conditions. The copolymer melting point exhibits a minimum in the region of the equimolar ratio of the two lactams. Further, the temperature dependence of the 8-caprylolactam specific heat was determined over an interval of 100 to 226°C (C_p = 0.2543 + 0.0007 T). The copolymerization rate of the anionic process increases with increasing content of 8-caprylolactarn, in accordance with differences of several orders existing between homopolymerization rates of the two lactams. The content of water extractable portions in the copolymers drops proportionally to increasing content of 8-caprylolactam, similarly as in equilibrium copolymers prepared by the hydrolytic copolymerization.     

Investigation of the curing kinetics of alkyd–melamine–epoxy resin system

Properties of coatings based on alkyd resin can be improved via blending with other suitable resins. Recent studies assessed that many properties could be improved by blending with epoxy resins as well as with melamine resins. The aim of this work was to investigate the effect of epoxy resin content on the curing process in alkyd–melamine–epoxy three component blends. The coatings with two mixing ratios of alkyd/melamine (70:30 and 80:20) were formulated. They were made into baking enamels by blending with 3 and 5 wt% of epoxy resin on total resin solid. Curring kinetics was investigated by differential scanning calorimetry (DSC) and application of Ozawa isoconversional method. Fourier transform infrared spectroscopy (FTIR) was used to follow major curing reactions. The absorbance of –OH and –N–CH₂R, showed significant reduction and confirmed that the epoxy resin reacts and inserts in enamel structure. It was found that resin system with alkyd/melamine ratio of 70:30 and 3 wt% of epoxy resin has the lowest apparent activation energy of 141.5 kJ mol⁻¹ and needs the shortest time of 34.2 min to reach final apparent degree of cure. Isothermal DSC experiments have confirmed these findings. The samples with 30 wt% of melamine resin had higher hardness of baked enamels then samples with 20 wt%. They also showed an increase of hardness with the increase of epoxy resin content.     

Gamma irradiation aging of NBR/CSM rubber nanocomposites

The effect of gamma-irradiation on the acrylonitrile butadiene/chlorosulphonated polyethylene rubber blends (NBR/CSM) based nanocomposites containing carbon black (CB) and silica filler (Si) were investigated by TG-DTG and ATR-FTIR techniques. The silica (with primary particle size of 22 nm) was added in content of 0, 10, 20 and 30 phr and carbon black (with primary particle size 40–48 nm) was added in content of 30 phr and rubber blend compounds were prepared. The obtained elastomeric materials were aging to different γ-irradiation doses (100, 200 and 400 kGy). The cure and mechanical properties of obtained nanocomposites were determined. Incorporating 20 phr of silica to the control NBR/CSM rubber blends containing 30 phr CB resulted 152% increase in tensile strength, 116%, in elongation at break and 142% modulus at 100% elongation, according to synergistic effect between the fillers. FTIR measurements of aged samples estimated the formation of alcohols, ethers and small amounts of lactones, anhydrides, esters and carboxylic acids after exposure to lower doses of γ-radiation (100 kGy). On the basis of the obtained spectra the formation of shorter polyene sequences and aromatic rings in aged elastomeric samples are assumed. The results show that 30 phr of carbon black (CB) and 20 phr of silica are needed for the best gamma aging resistance of NBR/CSM rubber nanocomposites. The result of radiation exposure is decrease in mechanical properties. The dose at which ultimate mechanical properties decreased was at 200 kGy. TG-DTG measurements estimated decrease in thermal stability of gamma-irradiated NBR/CSM rubber blend based nanocomposites. Silica reinforced NBR/CSM rubber blend had better radiation resistant than carbon black. Rough and heterogeneity of fracture surfaces has been observed for NBR/CSM rubber blends filled with silica. More uniform morphology of fracture surfaces according to high polymer–filler interaction and low filler–filler interaction has been observed for CB/Si filled NBR/CSM rubber blend.     

A simple and rapid method for histamine determination in fermented sausages by mediated chronopotentiometry

In order to provide the basis for the development of an inexpensive, sensitive, and reliable method for histamine determination in foods, the electrochemical behavior of histamine at planar gold disc electrode was investigated by chronopotentiometry. In solutions with sufficient chloride content dual oxidative mechanism of histamine was observed and included catalytic effect of electrogenerated chlorine. Well defined signal observed at +1.15 V in 0.0025 mol/l hydrochloric acid demonstrated sensitive changes with histamine content and was attributed to histamine. Electrogenerated chlorine facilitated charge transfer between histamine and the gold electrode resulting in enhancement of sensitivity. The effects of the most important experimental parameters of the chlorine-mediated chronopotentiometric analysis, such as the type and concentration of supporting electrolyte, initial potential and oxidation current were optimised. Under optimal experimental conditions, linear response of histamine was observed in the range 2–100 mg/l with achieved limit of detection for 0.27 mg/l of histamine. Developed method was applied for histamine determination in fermented sausages.