Processes during the electrorefining and electrowinning of lead

The anodic and cathodic processes in the fluorosilicate electrolytes during galvanostatic deposition under (DC) and polarity reversal current (PRC) regimes were investigated. It was established that, during the process of lead electrorefining from concentrated electrolyte without applying PRC, at c.d. i = 300 A/m² (3 A/dm²), after 60–80 h of the 95 h operation cycle, a limiting anodic polarization barrier value (Δ?_Acr = 200 mV) is attained. In this case bismuth and antimony start to dissolve actively from the anodes and are deposited onto the cathode, while under PRC conditions Δ?_Acr is not reached even after 95 h. The cathodic deposits are rounded crystal grains and display pronounced epitaxial growth. Spectral analysis shows that Sb is the main impurity of cathodic lead instead of Bi.During the electrowinning of the lead, without using H₃PO₄ as an inhibitor of β-PbO₂ parasitic deposition onto the inert graphite anodes, it was established that a critical value of the anodic potential ?_Acr = 1430–1500 mV/SCE) exists, under which β-PbO₂ is not deposited. If H₃PO₄ is present, β-PbO₂ is not deposited onto the graphite anodes at any values of the anodic potential.     

Calibrating SECCM measurements by means of a nanoelectrode ruler.The intrinsic oxygen reduction activity of PtNi catalyst nanoparticles

Scanning electrochemical cell microscopy(SECCM)is increasingly applied to determine the intrinsic catalytic activity of single electrocatalyst particle.This is especially feasible if the catalyst nanoparticles are large enough that they can be found and counted in post-SECCM scanning electron microscopy images.Evidently,this becomes impossible for very small nanoparticles and hence,a catalytic current measured in one landing zone of the SECCM droplet cannot be correlated to the exact number of catalyst particles.We show,that by introducing a ruler method employing a carbon nanoelectrode decorated with a countable number of the same catalyst particles from which the catalytic activity can be determined,the activity determined using SECCM from many spots can be converted in the intrinsic catalytic activity of a certain number of catalyst nanoparticles.     

Determination of energy and spatial distribution of oxide border traps in In0.53Ga0.47As MOS capacitors from capacitance–voltage characteristics measured at various temperatures

In this work, we have systematically studied the frequency dispersion of the capacitance–voltage (C–V) characteristics of In_0.53Ga_0.47As metal–oxide-semiconductor (MOS) capacitors in accumulation region at various temperatures based on a distributed border traps model. An empirical method to evaluate the frequency and temperature dependent response of the border traps distributed along the depth from the interface into the oxide is established. While the frequency dependent response results from the dependence of the time constant of the border traps on their depths, the temperature dependent response is ascribed to the thermal activated capture cross-section of the border traps due to the phonon-related inelastic capturing process. Consequently, it is revealed that the frequency dispersion behaviors of the accumulation capacitance at different temperatures actually reflect the spatial distribution of the border traps. On this basis, we propose a methodology to extract the border trap distribution in energy and space with emphasis on analyzing the C–V characteristics measured from low to high temperatures in sequence.     

Stability and dynamics of isothermal CMSMPR crystallizers

Detailed analysis of stability and bifurcation properties and of the dynamic behaviour of isothermal continuous mixed suspension, mixed product removal (CMSMPR) crystallizers is presented using the moment equation model. It is shown that isothermal CMSMPR crystallizers may exhibit not only limit cycle oscillations but, in the case of magma-dependent nucleation, also saddle point instabilities. Applying the Mikhailov stability criterion, two equivalent sets of necessary and sufficient conditions are derived for checking the stability of steady states.Stability maps are presented in the planes of different pairs of system parameters. It is shown that saddle node and boundary bifurcation, as well as bifurcation at infinity may arise in the case of magma-dependent secondary nucleation. Oscillations of the population density and distribution functions are also presented and analysed, approximating the size distribution by gamma distribution. In dynamic states, the crystal size distribution may differ significantly from the exponential one, while the mean values of oscillations of supersaturation are lower than the corresponding steady state values. A causal loop diagram between the variables reveals that instabilities are created by the interactions of the autoinhibition generated negative feedback and a positive feedback between the four leading moments of crystal size.     

Chitosan/poly(lactic acid) blends as drug delivery systems

Abstract

The immobilization and controlled release of salicylic acid (SA) in chitosan/poly(lactic acid) (Ch/LA) blends were studied in the present work. The Ch/PLA bland’s morphology was studied by SEM. FT-IR and DSC were used to investigate the interactions between the polymer matrix and the SA. The SA release kinetics was interpreted by the Weibull and Higuchi models. The SA release was the fastest in Ch/PLA systems with inhomogeneous and porous structure. It was slower in neat PLA matrix due to its dense structure and hydrophobic behavior, and in neat chitosan matrix, because of specific electrostatic chitosan/SA interactions and complex formation.     

Matrix of small-radius radio-frequency discharges as a volume-production based source of negative hydrogen ions

Based on experience from a work--both theoretical and experimental one--on negative hydrogen ion beam sources studied regarding fusion applications, a novel design of a rf source with volume production of the ions is proposed. The suggestion is for a source constructed as a matrix of small-radius tandem discharges (with magnetic filters largely extended over the discharge length), inductively driven (by a single coil, for the whole matrix) and with a single aperture extraction from each of them.     

Introducing DInaMo: A Package for Calculating Protein Circular Dichroism Using Classical Electromagnetic Theory

The dipole interaction model is a classical electromagnetic theory for calculating circular dichroism (CD) resulting from the π-π* transitions of amides. The theoretical model, pioneered by J. Applequist, is assembled into a package, DInaMo, written in Fortran allowing for treatment of proteins. DInaMo reads Protein Data Bank formatted files of structures generated by molecular mechanics or reconstructed secondary structures. Crystal structures cannot be used directly with DInaMo; they either need to be rebuilt with idealized bond angles and lengths, or they need to be energy minimized to adjust bond lengths and bond angles because it is common for crystal structure geometries to have slightly short bond lengths, and DInaMo is sensitive to this. DInaMo reduces all the amide chromophores to points with anisotropic polarizability and all nonchromophoric aliphatic atoms including hydrogens to points with isotropic polarizability; all other atoms are ignored. By determining the interactions among the chromophoric and nonchromophoric parts of the molecule using empirically derived polarizabilities, the rotational and dipole strengths are determined leading to the calculation of CD. Furthermore, ignoring hydrogens bound to methyl groups is initially explored and proves to be a good approximation. Theoretical calculations on 24 proteins agree with experiment showing bands with similar morphology and maxima.     

Artisanal cheeses relying on spontaneous fermentation as sources of unusual microbiota – The example of the Bulgarian ‘mehovo sirene’ skin bag cheese

The Bulgarian ‘mehovo sirene’ cheese is a type of regional artisanal cheese prepared from raw ewe milk in a skin bag relying on spontaneous fermentation. A metagenomics study revealed an unusual microbiome comprising beneficial bacteria such as Staphylococcus equorum, Lactococcus lactis, Streptococcus thermophilus, Lactobacillus delbrueckii, Lactobacillus kefiranofaciens, Lactococcus raffinolactis, Lactiplantibacillus plantarum, Limosilactobacillus fermentum and Loigolactobacillus coryniformis. Our findings suggest that ‘mehovo sirene’ could have some functional food properties and is a source of beneficial microorganisms.