Influence of Poloxamer 407 on Surface Properties of Aqueous Solutions of Polysorbate Surfactants

Owing to their ability to adsorb at interfaces, polysorbates have an important role in pharmaceutical formulations. Because surfactant mixtures can have improved properties, it was hypothesized in this work that introduction of poloxamer 407 to aqueous solutions of polysorbates (polysorbate 60, polysorbate 80 and polysorbate 85) might improve their surface properties. Nonideal behavior of surfactant mixtures at the air/water interface was investigated using Rosen's model and recently introduced method for the determination and quantification of nonideal behavior regarding surface tension reduction and adsorption effectiveness. Although nonideal behavior was noticed in all mixed monolayers, it was shown that the structure of the hydrophobic domain of the polysorbates and the conformation of poloxamer 407 at the interface have strong influence on the nonideality.     

Improved Thermoelectric Characteristics of Si-Doped Misfit-Layered Cobaltite

The cobaltite Ca₃Co₄O_9+δ has shown large thermopower and is considered to be a good candidate for use as a thermoelectric material. The composition of Ca₃Co₄O_9+δ is better expressed as [Ca₂CoO₃][CoO₂] _b1/b2 with the misfit-layered structure featuring different periodicities along the b axis, with b ₁ referring to the b-axis length of the NaCl-type [Ca₂CoO₃] sublattice and b ₂ referring to the b-axis length of the [CoO₂] sublattice. The crystal structure of Ca₃Co₄O_9+δ can be viewed as being of two subsystems, i.e., the distorted NaCl-type [Ca₂CoO₃] sublattice and the CdI₂-type [CoO₂] sublattice, alternately stacked along the c-axis. In this paper, we report measurements of the electrical resistivity and Seebeck coefficient for a series of misfit-layered oxides Ca₃Co_4−x Si _x O_9+δ prepared by solid-state reaction. Structural parameters are refined with the superspace group X2/m(0β0)s0 using powder x-ray diffraction data. With partial substitution of Si⁴⁺ for Co³⁺, the resistivity decreases, while the thermopower increases simultaneously. These results indicate that partial substitution of Si⁴⁺ improves the thermoelectric characteristics of Ca₃Co₄O_9+δ .     

Comparative analysisof grounding systems formed by MV cable lines with either uninsulated or insulated metal sheath(s)

It is well known that medium-voltage (MV) paper-insulated cables essentially reduce the potentials appearing during a ground fault in substations located in urban surroundings. This is explained by the fact that these cables usually (normally) have an uncoated metallic sheath. Due to this, MV cable lines leaving a high-voltage/middle-voltage (HV/MV) substation act as long external grounding electrodes and spontaneously form one very large and complex grounding system around this substation. Cables with an insulated metallic sheath however, are progressively being more applied in contemporary power distribution practice. Consequently, the following quite logical question arises: how will a cable with such constructive characteristic influence the general conditions for solving the grounding problem of distribution substations, especially of those working in high-voltage (HV) networks with directly grounded neutral(s)? The analysis performed in this paper shows that, when applied these cables spontaneously form a grounding system which also exhibits excellent grounding performances.     

Serbian energy development based on lignite production

Lignite, as an energy resource, is a mainstay of electricity generation in the Republic of Serbia. Installed capacity of lignite power plants represents 68% of the total installed capacity of Electric Power Industry of Serbia, the only company in Serbia, which manages electricity generation. In the future, with the increase in demand for electricity, both in Serbia and in Europe, we should expect more extensive and effective utilization of lignite as the main energy potential. In addition, due to increased emissions of CO₂, NO_X and other pollutants, the Republic of Serbia must accelerate the implementation of flexible mechanisms of Kyoto Protocol and the guidelines set by the European Union. Lignite in the future will retain its existential importance in the electricity generation in the Republic of Serbia.     

Comparative cavitation erosion test on steels produced by ESR and AOD refining

Cavitation erosion studies of steels produced by Electroslag Refining (ESR) and Argon Oxygen Decarburization (AOD refining) have been carried out. The experiments were conducted using the modified ultrasonically induced cavitation test method. Erosion rates were measured and the morphology of damages under cavitation action was studied by scanning electron microscopy and optical microscopy techniques. The present work is aimed at understanding the cavitation erosion behaviour of electroslag refined steel (ESR) compared with the steel produced by Argon Oxygen Decarburization (AOD refining), commonly used in the production of hydraulic machinery parts (Pelton blades). The results exhibited lower cavitation rate of ESR steel compared with AOD steel, as a consequence of its better mechanical properties and homogeneous and fine-grained microstructure.