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.     

Synthesis and antioxidant activity of selected 4-methylcoumarins

A series of selected 4-methylcoumarins (4-methyl-2H-1-benzopyran-2-ones) were synthesised and tested for radical-scavenging ability using the stable 1,1-diphenyl-2-picrylhydrazyl radical, and for reducing power ability with a test based on the reduction of ferric to ferrous cation. All studied compounds showed activity comparable to Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), an already known antioxidant, which is used as standard in most of the testing methods. Observations from the study were made with regard to structural features that regulated the behaviour of the compounds. The antioxidant activity of some 4-methylcoumarin representatives is presented here for the first time and extends our knowledge of the range of valuable biological activities and possible roles in therapy and for food preservation associated with this group of compounds.     

Tuning of BiFeO3 multiferroic properties by light doping with Nb

Bulk ceramic samples of BiFeO₃ were light doped (up to 1%) with Nb⁵⁺ in the place of Fe³⁺ (B-site doping) and their multiferroic properties were investigated using XRD, SEM, polarization (PMTS) and magnetization (SQUID) techniques. It is shown that even the small percentages of doping can notably change electric and magnetic behavior. Electric conductivity differs by two orders of magnitude between samples doped with 0.2% and 1% Nb. The ferroelectric behavior strongly depended on conduction mechanism, and transition from space-charge-limited current (SCLC) conduction to trap-filled limited (TFL) conduction regime reflected on a change in hysteresis patterns, particularly for the samples with 0.2% and 0.5% Nb. Separation of ZFC-FC magnetization curves occurred for all Nb concentrations and increased with Nb doping. Weak ferromagnetic behavior and the increase of remnant magnetization with Nb concentration was observed from the hysteresis measurements. Coercive field changed drastically compared to the pure BiFeO₃, namely, the sample with 1% Nb exhibited very high coercive magnetic field of ~ 10?kOe.     

Improving Heat Transfer with Pool Boiling by Covering of Heating Surface with Metallic Spheres

Abstract

Boiling heat transfer (BHT) was investigated experimentally. Smooth copper walls were covered with single sphere layer and corresponding temperature difference and heat flux were measured. The results were compared with published data for several types of heating surfaces. Comparative analysis shows that surfaces covered with spheres have characteristics as good as the other systems, if not better.     

1D linear-phase band-pass multiplierless FIR Hilbert transformers and filters

An original analytical method, based on modified Christoffel–Darboux formula, is used in the paper in order to synthesise a linear-phase band-pass finite impulse response (FIR) filter function that can have an effect of Hilbert transformer. New structure of the band-pass FIR filter in recursive realisation, together with the corresponding difference equation, is presented providing the efficient filter solution without multipliers. Several examples of filter types for different parity of two real free integer parameters, including a particular solution of Hilbert transformer, are considered in terms of required number of adders and values of cut-off frequencies of the pass and stop bands. A comparison of the proposed band-pass filter characteristics with those of a classical filter solution is provided in the paper.     

Nutritional and therapeutic value of fermented caprine milk

Caprine milk is a nutritional and therapeutic food. The unique and beneficial characteristics of caprine milk that are superior to bovine milk include: better digestibility; greater buffering capacity; fat globules that are smaller in diameter and better distributed in the milk emulsion; higher content of short‐chain fatty acids in the milk fat; higher content of zinc, iron and magnesium; stronger lactoperoxidase (antimicrobial) system as well as better immunological and antibacterial characteristics. The larger amounts of some minerals, such as calcium, zinc and magnesium, in caprine milk may influence the growth of lactic acid bacteria since they are a normal part of some enzymatic complexes involved in lactose fermentation. The higher whey protein content could also be significant because Lactobacillus acidophilus and bifidobacteria grow better in the presence of higher levels of some amino acids (valine, glycine, hystidine). The use of caprine and ovine milk in cheesemaking is well known, but the production of fermented caprine milk via probiotics has not yet been developed, although many studies have highlighted the requirements for production of that kind of healthy food. During fermentation caprine milk loses its characteristic ‘goaty’ taste, which is unacceptable to many consumers. Moreover, the nutritive value of caprine milk increases during fermentation. The rise in the number of goat farms in Croatia has created the need to find other products that can be produced using caprine milk. According to the present situation in Croatia, there is no real possibility of producing fermented caprine milk for the global market, but many studies of fermented caprine milk have been performed.     

Evaluation of the antioxidant activity of a series of 4-methylcoumarins using different testing methods

Continuing our research on oxidation reactions of 4-methylcoumarins (4-methyl-2H-1-benzopyran-2-ones), this study presents evaluation of the antioxidant activity of 23 4-methylcoumarin derivatives, using different spectrophotometric and spectrofluorimetric radical testing methods. All studied compounds showed activity comparable to Trolox, an already known antioxidant, which is used as a standard in most testing methods. Observations from the study were made with regard to structural features that regulated the behaviour of the compounds. This paper extends our knowledge of the range of valuable biological activities and possible roles in medicinal therapy associated with this group of compounds.     

Calculation of steady-state load flows incorporating system control effects and consumer self-regulation characteristics

In standard methods for the calculation of steady-state load flows, based on the swing-bus concept, the effects of automatic generation control, static response of prime movers, consumer self-regulation characteristics and load-shedding action are neglected. Calculations of line flows and bus voltages are unrealistic, particularly in the case of large generation/load disturbances, when both the system frequency and tieline loads deviate from their scheduled values. To overcome this shortcoming, a load-flow model without a swing bus is proposed which takes into account all the relevant actions mentioned above that have been neglected so far. The model is used for load-flow calculations by applying the standard Newton-Raphson iterative procedure for the solution of nonlinear problems, as well as the technique of sparse matrices employed in the solution of a system of linear equations. The method is proved on a sample system of 43 buses and 53 branches of a 220 kV and 400 kV network in the Republic of Serbia. The results obtained from this example justify the use of such a non-standard load-flow model, particularly for security analysis following large generator and tieline outages.