Thermodynamic properties of liquid magnesium-bismuth alloys

Thermodynamic properties of liquid Mg-Bi alloys have been determined, employing galvanic formation and concentration cells. There was a fairly good agreement between data obtained by the two different types of cells. The partial thermodynamic functions exhibit a marked deviation from ideality, which has been interpreted as a consequence of the stable compound Mg₃Bi₂ being formed in the system. The experimental data have been treated according to Krupkowski to give equations for the activity coefficients of magnesium and bismuth. From these equations, together with phase diagram data, the Gibbs free energy of formation of solid Mg₃Bi₂ has been evaluated. A similar treatment also has been applied to literature data for the corresponding Mg-Sb system.     

Toward a theory of fluid mixtures with two-point interactions

We describe a fluid mixture in those situations where the microscopic particles can be considered to interact according to the laws of classical mechanics. It motivates our strong feeling that some essential changes in the form of macroscopic equations governing the behavior of a mixture of fluids are necessary (for the better understanding of the fundamental processes in the system). We provide a clue in the determination of the limits of validity of the Drumheler-Bedford approach [5] to the mixture theory and strongly generalize their main results.     

Investigations of chromium (VI) ion sorption and reduction on strongly basic anion exchanger

Removal of chromium(VI) ions and their reduction were studied on the anion exchanger Dowex PSR-2 in the pH range from 1.5 to 10. The parameters of Cr(VI) sorption process on the anion exchanger were calculated based on the most popular isotherm models such as: Freundlich, Langmuir, Temkin, and Dubinin–Radushkevich (D-R). The Langmuir isotherm was the most appropriate to describe Cr(VI) sorption. The Cr(VI) uptake by Dowex PSR-2 was found to follow the pseudo-second-order rate kinetics. Reduction of chromium(VI) in the pH range 1.5–10 was observed using the HPLC-ICP-MS (high-performance liquid chromatography–inductively coupled plasma-mass spectrometry) method. Oxidation of tri-n-butyl quaternary ammonium groups during the chromate (VI) removal process was observed.     

Magnetic Mixed Matrix Membranes Consisting of PPO Matrix and Magnetic Filler in Gas Separation

Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and magnetic neodymium powder particles MQP-14-12 have been used for the preparation of magnetic mixed matrix membranes. Permeability diffusion and sorption coefficients of O₂, N₂, and synthetic air components were estimated for homogeneous and heterogeneous membranes using the Time Lag method based on dynamic experiments in a constant pressure system. The influence of magnetic field and magnetic powder particles on the gas transport properties of MMMs was studied. The results showed that the membrane permeation properties were improved with the magnetic neodymium particle filling. It was observed that the magnetic ethylcellulose and poly(2,6-dimethyl-1,4-phenylene oxide) membranes showed higher gas permeability, while their permselectivity and solubility were rather maintained or slightly increased. The results also showed that the magnetic powder addition enhanced gas diffusivity significantly in EC and PPO membranes.     

Sorption of Cd(II)-MGDA Complexes on Polyacrylate Anion Exchangers

The possibility of polyacrylic anion exchangers application in the removal of Cd(II) complexes with MGDA (methylglycinediacetic acid) from aqueous solutions was presented. Batch sorption experiments were performed using Amberlite IRA 458 and Amberlite IRA 958. The initial solution pH, the initial concentration of sorbed complexes in the molar ratio M(II)-MGDA = 1:1, the temperature, as well as the contact time were varied. The kinetics of Cd(II) sorption in the presence of MGDA was analyzed. The Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich models were also applied to describe the adsorption isotherm. The values of the thermodynamic parameters (ΔG°, ΔH°, and ΔS°) indicated that in the majority of cases the sorption process was spontaneous and endothermic. From the determined breakthrough curves, the distribution coefficients and the ion exchange capacities were calculated.     

Nitrification process in activated sludge with suspended marble particles

The process of nitrification in activated sludge was investigated. As the solid support for nitrifiers' growth a suspension of marble particles has been used. The results proved the possibility of successful nitrification of 100 mg l^?1 NH₄-N simultaneously with the removal of 600 mg l^?1 COD.     

Bivalent peptides as models for multimeric targets of PDZ domains

PDZ domains are among the most common modules in eukaryotic, including human, genomes. They are found exclusively in large, multidomain cytosolic proteins--often with other domains that belong to a variety of families--and are involved in a plethora of physiological and pathophysiological events. PDZ domains mediate protein-protein interactions by binding to solvent-exposed and extended C-terminal short fragments of membrane-associated proteins, such as receptors and ion channels. Most of what is known about the mechanisms of target binding by PDZ domains is inferred from studies that involve isolated recombinant PDZ domains and short synthetic peptides that represent the targets. These binary systems constitute an obvious oversimplification and disregard factors such as noncanonical modes of binding and enhanced affinity due to multimeric interactions mediated by clusters and oligomers of PDZ-domain-containing proteins. We have tested whether the interaction between a dimeric form of PDZ domain that mimics a functional dimeric guanine nucleotide exchange factor, PDZ-RhoGEF (PDZ-containing RhoA-specific guanine nucleotide exchange factor) or LARG (leukemia-associated RhoA specific guanine nucleotide exchange factor), and a bivalent peptide that mimics the dimer of the plexin B receptor, could enhance the interaction between the two moieties. Peptide dimerization was achieved by cross-linking the N-terminal ends of peptides attached to Wang resin with poly(ethylene glycol) spacers (30-45 Angstroms in length). The interaction of dimeric PDZ domains with dimeric peptides resulted in an up to 20-fold increase in affinity compared to the simple binary system. This is consistent with the notion that multimerization of both receptors and PDZ-containing proteins might constitute an important regulatory mechanism.     

The accuracy of oxygen flux measurements using microelectrodes

An electrochemical analog of a biofilm was constructed to test the accuracy of oxygen flux measurements using microelectrodes. We used a cathodically polarized graphite felt attached to the bottom of a flat plate open channel reactor as the reactive surface consuming oxygen. The oxygen flux to the felt was calculated from the polarization current. Microelectrodes were used to measure the oxygen profiles above and within the graphite felt. From the shape of the oxygen profile we evaluated the oxygen flux to the graphite felt. This provided us with two sets of data, the true oxygen flux, calculated from polarization current, and the oxygen flux estimated from microelectrode measurements. Comparing these two fluxes, for different flow velocities, showed that the fluxes evaluated from the polarization current were different from those evaluated from the oxygen profiles. The differences were likely caused by the presence of the microelectrode in the mass boundary layer and/or by the simplifying assumptions accepted in computational procedures employed to calculate oxygen fluxes. For low flow velocities, between zero and 1.0 cm s⁻¹, the differences were velocity sensitive; the higher the flow velocity, the bigger the difference. For higher flow velocities, between 1 cm s⁻¹ and 3 cm s⁻¹, the flux of oxygen estimated from the microelectrode measurements was consistently approximately 80% higher than the true oxygen flux estimated from the polarization current.     

Influence of sonication on Warner-Bratzler shear force,colour and myoglobin of beef (<Emphasis Type="Italic">m. semimembranosus</Emphasis>)

Research in the past few decades has shown the potential benefits of using ultrasound treatment as a technique to enhance tenderness and sensory properties of meat and its sub-products. The objective of current study was to assess whether the low-frequency, low-intensity ultrasound treatment at 24 h postmortem affects the pH, Warner-Bratzler shear force (WBSF), colour (CIE L^*a^*b^*c^*H°), and relative proportions of myoglobin (Mb) redox forms and total Mb concentration during 96 h of beef (musculus semimembranosus) storage. Muscles were obtained from young bulls (n = 15) of Lowland Black and White breed slaughtered at a live weight of 475 (SD 16.1) kg. Ultrasound treatment did not have a statistically significant (p < 0.05) effect on the pH of meat directly after sonication (24 h postmortem), or at 72 and 96 h postmortem. Sonicated meat sample (S) was characterized by higher, but not statistically significant (p < 0.05), L* coordinate values 24, 48 and 72 h postmortem. During the whole storage period, colour coordinates a*b*c* and H° were not significantly (p < 0.05) affected by sonication. Ultrasound treatment accelerated the total colour change ΔE, limited the formation of MbO₂ and slowed down the formation of MetMb. Measurements carried out 48 and 72 h after slaughter revealed that the ultrasound treatment significantly (p < 0.05) reduced the WBSF. This study demonstrates the potential of low-frequency, low-intensity ultrasound treatment at 24 h postmortem for beef tenderization without detrimental effects on its CIE colour parameters and relative proportions of Mb redox forms.