Determination of porous glass surface free energy components from contact angles

The contact angles of water drops and diiodomethane drops on pellets made of controlled porosity glasses have been measured. The surface of the glasses was modified by thermal treatment at 873 K which led to an increase in the surface concentration of boron atoms. Glass modified with Carbowax 20M (polyethylene glycol) and fully hydroxylated glass have also been studied. Using the measured contact angles and modified Young equation, the dispersion and nondispersion components of the glass surface free energy have been calculated. The values show that with increasing heating time (increasing surface density of boron atoms) an increase in the surface polarity takes place. However, the polarity of the same samples decreases after treatment with Carbowax, increasingly so with higher boron atom concentrations.     

Fusion and protein-mediated phospholipid exchange studied with single bilayer phosphatidylcholine vesicles of different density

A novel method has been developed for the study of phospholipid exchange and fusion of phospholipid vesicles. Two homogeneous populations of single bilayer phosphatidylcholine vesicles of similar size but markedly different density have been prepared. "Dense" vesicles were made from brominated dioleoyl phosphatidylcholine. "Light" vesicles were prepared from dioleoyl phosphatidylcholine. The two populations were easily separated by density gradient centrifugation. Phosphatidylcholine exchange protein from beef liver was used to promote lecithin exchange between the vesicle populations. Only the lecithin of the external monolayers of the vesicles was available for exchange by exchange protein, implying that flip-flop of vesicle phosphatidylcholine did not take place at a detectable frequency. No spontaneous intervesicle phosphatidylcholine exchange was observed. However, the dense and light vesicles did spontaneously fuse, over several hours, to produce particles of hybrid density.     

Evaluation of a pressure head and pressure zones in water distribution systems by artificial neural networks

Neural Computing and Applications - Water distribution system design is inherently associated with hydraulic calculations that require thorough evaluation of obtained results and accuracy of the...     

Properties of thermally modified controlled porous glasses (CPG) I. Influence of additional thermal treatment of CPG on adsorption processes on its surface

Controlled porous glasses (CPG) are the sorbents and supports of chemically bonded phases very widely applied in chromatographic columns for the separation of polymers and biopolymers by means of gel permeation and affinity chromatography. The chemical structure of CPG surface can easily be changed by additional heating of porous glass. Such thermal modification leads to the enrichment of the surface in boron atoms. In consequence, the the prepared materials possess specific surface properties. In this paper some adsorption isotherms obtained for chemically different compounds on the CPG surfaces thermally treated in various ways are presented.     

The antioxidant properties of alcoholic extracts from Sambucus nigra L. (antioxidant properties of extracts)

The antioxidant properties of alcoholic extracts from the leaves, berries and flowers of Sambucus nigra L. are estimated by means of DPPH and β-carotene/linoleic acid methods, and considered in relation to the extraction temperature (in the range 20-200 °C) and to the level of flavonoids most representative for this plant. The extracts of S. nigra act as antioxidants neutralizing the activities of free radicals and inhibiting the co-oxidation reactions of linoleic acid and β-carotene. There is no direct correlation between the level of flavonoids in the extracts and their antioxidant activity. The data presented show that the extraction temperature strongly influences the antioxidant properties of the extracts, especially in the case of leaves.     

Heat transfer and pressure drop during flow boiling of pure refrigerants and refrigerant/oil mixtures in tube with porous coating

The experimental stand and procedure for flow boiling investigations are described. Experimental data for pure R22, R134a, R407C and their mixtures with polyester oil FUCHS Reniso/Triton SEZ 32 in a tube with porous coating and smooth, stainless steel reference tube are presented. Mass fraction of oil was equal to 1% or 5%. During the tests inlet vapour quality was set at 0 and outlet quality at 0.7. Mass velocity varied from about 250 to 500 kg/m²s. The experiments have been conducted for average saturation temperature 0 °C. In the case of flow boiling of pure refrigerants, the application of a porous coating on inner surface of a tube results in higher average heat transfer coefficient and simultaneously in lower pressure drop in comparison with the flow boiling in a smooth tube for the same mass velocity. Correlation equation for heat transfer coefficient calculation during the flow boiling of pure refrigerants inside a tube with porous coating has been proposed.     

Computer analysis of nystagmus

An algorithm for the computer analysis of nystagmus is described in this paper. This algorhythms was based on digital differentiator, which monitors the eye position. The computed eye velocity is next used as an input to the fast phase detector. Several procedures, including minimum velocity test, slope sense test, SPV and FPV relationship test are invoked to extract the fast phases from the recorded signal. Based on three-years experience (approx. 3000 examinations) using the ENG-PC System in clinical practice we can conclude, that application of the nystagmus detector was useful in most cases. In our opinion, despite from system imperfection which is observed during the analysis of recording disturbed by artifacts, this system has unquestionable advantage over the traditional technique.     

Antioxidant properties of BHT estimated by ABTS assay in systems differing in pH or metal ion or water concentration

Antioxidant activity (capacity or potential) is widely used as parameter to characterize different substances and mixtures, which is able to scavenge or neutralize free radicals. Recently, ABTS assay has been the most widely employed method for estimating antioxidant activity. The method is based on the spectrophotometric measurement of ABTS cation radical (ABTS^•+) concentration changes resulting from the ABTS^•+ reaction with antioxidants. Yet little is known about factors influencing the kinetics that reaction i.e., about factors affecting the estimation of antioxidant activity of examined compounds’. The paper shows that metal ion type and concentration, water content and pH of the measuring system all significantly influence the estimation of antioxidant activity in ABTS assay and thus make the estimation of correct antioxidant properties of plant and food extracts difficult. Butylhydroxytoluene (BHT) was used as standard antioxidant in the performed experiments. The relationships discussed in this paper indicate the necessity of standardizing the ABTS method and reveal the complexity of estimating adequate antioxidant activity of examined substances.     

The importance of solvent type in estimating antioxidant properties of phenolic compounds by ABTS assay

ABTS assay belongs to the most popular methods employed for estimating antioxidant activity. However, researchers seldom pay attention to specific factors influencing the determination of antioxidant activity of the examined compounds and mixtures. The paper shows that the type of alcohol used significantly influences the estimation of antioxidant activity of phenolic compounds in ABTS assay, namely that their antioxidant activity increase with the lengthening of the aliphatic chain in alcohol. It results rather from the changes in ABTS ^?+ solvatation energy by the employed alcohols than from dissociation variations of phenolic compounds. The obtained results point to the difficulties in the correct estimation of the real antioxidant properties of plant and food extracts by ABTS assay. The presented results have also an ecological implication as they refer to the difference in estimation of antioxidant properties of compounds resulting from the replacement of toxic methanol by GRAS (Generally-Recognized-As Safe) solvents, ethanol and propanol.