Calculation of separation columns by nonlinear block successive relaxation methods

A novel technique: nonlinear block successive relaxation (NBSR) method, is proposed to solve the steady-state balance equations describing separation columns. The NBSR methods are a generalization of point relaxation methods frequently used towards solution of elliptic partial differential equations. Aspects of partitioning of the original set of equations into blocks as well as ordering of blocks is discussed. Problems arising in construction of a universal program based on the NBSR methods are presented. A new procedure making use of grouping of equations according to the set of trays is proposed. Aspects of calculation of separation equipments by this procedure is discussed. It is shown that overlapping blocks may essentially improve the convergence properties of the algorithm. The procedure is very simple and can be easily used towards calculation of large separation problems on a small computer. The method described is illustrated on calculation of an absorption column. Application of the NBSR methods to solution of a complex plant is suggested.     

Emission Spectra of a Two-level Atom in a Kerr-like Medium

Abstract

We have investigated the spectrum of light emitted by a single atom interacting with a single mode of the radiation field in an ideal cavity filled with a Kerr-like medium. It is shown that owing to the Kerr-like nonlinearity in the system the spectrum of the emitted light exhibits a single-peaked structure for sufficiently high intensities of the initial coherent field instead of the triplet structure in the case of the standard Jaynes-Cummings model.     

Antibacterial poly(vinyl alcohol) film containing silver nanoparticles: Preparation and characterization

The importance of antibacterial materials for biomedical applications is growing nowadays. The presented article deals with the characterization of structural, mechanical and thermal properties and of antibacterial polymeric films based on polyvinyl alcohol (PVA) and silver nitrate, which can find their applicability in wound dressing components and protective coating. The methods of transmission electron microscopy, UV–vis and XRD spectroscopy, optical microscopy, differential scanning calorimetry, stress–strain analysis, and agar diffusion test were used to characterize the polymer films prepared. The results showed strong antibacterial activity against Escherichia coli and Staphylococcus aureus already at the lowest addition level of silver nitrate. An improvement of mechanical properties (Young's modulus) was also noticed due to a modification of PVA with silver nitrate up to 1 wt. % of silver content. Furthermore, the results show a strong effect of the thermal history of the sample preparation on the degree of silver‐ion reduction and formation of nanoparticles. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Melectin: a novel antimicrobial peptide from the venom of the cleptoparasitic bee Melecta albifrons

A novel antimicrobial peptide designated melectin was isolated from the venom of the cleptoparasitic bee Melecta albifrons. Its primary sequence was established as H-Gly-Phe-Leu-Ser-Ile-Leu-Lys-Lys-Val-Leu-Pro-Lys-Val-Met-Ala-His-Met-Lys-NH(2) by Edman degradation and ESI-QTOF mass spectrometry. Synthetic melectin exhibited antimicrobial activity against both gram-positive and -negative bacteria and it degranulated rat peritoneal mast cells, but its hemolytic activity was low. The CD spectra of melectin measured in the presence of trifluoroethanol and sodium dodecyl sulfate showed a high content alpha-helices, which indicates that melectin can adopt an amphipathic alpha-helical secondary structure in an anisotropic environment such as the bacterial cell membrane. To envisage the role of the proline residue located in the middle of the peptide chain on biological activity and secondary structure, we prepared several melectin analogues in which the Pro11 residue was either replaced by other amino acid residues or was omitted. The results of biological testing suggest that a Pro kink in the alpha-helical structure of melectin plays an important role in selectivity for bacterial cells. In addition, a series of N- and C-terminal-shortened analogues was synthesized to examine which region of the peptide is related to antimicrobial activity.     

Early stages of growth of gold layers sputter deposited on glass and silicon substrates

Extremely thin gold layers were sputter deposited on glass and silicon substrates, and their thickness and morphology were studied by Rutherford backscattering (RBS) and atomic force microscopy (AFM) methods. The deposited layers change from discontinuous to continuous ones for longer deposition times. While the deposition rate on the silicon substrate is constant, nearly independent on the layer thickness, the rate on the glass substrate increases with increasing layer thickness. The observed dependence can be explained by a simple kinetic model, taking into account different sticking probabilities of gold atoms on a bare glass substrate and regions with gold coverage. Detailed analysis of the shape of the RBS gold signal shows that in the initial stages of the deposition, the gold layers on the glass substrate consist of gold islands with significantly different thicknesses. These findings were confirmed by AFM measurements, too. Gold coverage of the silicon substrate is rather homogeneous, consisting of tiny gold grains, but a pronounced worm-like structure is formed for the layer thickness at electrical continuity threshold. On the glass substrate, the gold clusters of different sizes are clearly observed. For later deposition stages, a clear tendency of the gold atoms to aggregate into larger clusters of approximately the same size is observed. At later deposition stages, gold clusters of up to 100 nm in diameter are formed.     

Possibilities of enhancing the colour of egg yolk

BACKGROUND: This study attempts to compare two possibilities of enhancing the colour of egg yolk. One of them is based on the ecological rearing of laying hens on natural green grass whereas the other uses a feeding dose supplemented with natural pigments in laying hens reared in individual cages. Is it possible to distinguish these two technologies using yolk colour determination in the CIELAB system? RESULTS: Yolk colour parameters such as L*, a*, and b* in the group of grazed hens are significantly different (α = 0.001) from those observed in hens reared in cages. The yolk colour shows a darker, redder and more yellow colour. The greatest difference was seen in the red colour parameter, a*, that increased more than twice. Visually, this means a shift towards a more orange colour. Compared to grazing in the meadow (ΔE* = 13.257), the addition of artificial pigments in the feed resulted in a more significant increase in the parameter ΔE* (CIE total colour difference), with the greatest value of ΔE* being observed with the use of both pigments (ΔE* = 24.265). CONCLUSION: Grazing increases the parameter a* whereas the values of the parameter C*_ab remain relatively low. The parameter ΔE* is significantly lower in the case of grazing as compared to the supplementation of the feed with pigments. However, colourity parameters cannot be used as a specific standard to identify a particular grazing technology as their values vary during the laying period. Copyright © 2011 Society of Chemical Industry     

Support nanostructure boosts oxygen transfer to catalytically active platinum nanoparticles

Interactions of metal particles with oxide supports can radically enhance the performance of supported catalysts. At the microscopic level, the details of such metal-oxide interactions usually remain obscure. This study identifies two types of oxidative metal-oxide interaction on well-defined models of technologically important Pt-ceria catalysts: (1) electron transfer from the Pt nanoparticle to the support, and (2) oxygen transfer from ceria to Pt. The electron transfer is favourable on ceria supports, irrespective of their morphology. Remarkably, the oxygen transfer is shown to require the presence of nanostructured ceria in close contact with Pt and, thus, is inherently a nanoscale effect. Our findings enable us to detail the formation mechanism of the catalytically indispensable Pt-O species on ceria and to elucidate the extraordinary structure-activity dependence of ceria-based catalysts in general.     

The effect of selected hydrocolloids on the rheological properties of processed cheese analogues made with vegetable fats during the cooling phase

The aim of this work was to observe the influence of different hydrocolloids on changes in the rheological properties of processed cheese and their analogues within the process of cooling depending on the type of the fat used (butter, coconut fat and palm oil). κ‐carrageenan, ι‐carrageenan, λ‐carrageenan, arabic gum and locust bean gum were used at a concentration of 1.0% w/w. With the decreasing temperature during the cooling period, an increase in the complex modulus (G*) was observed in all samples tested. Within the cooling period, the sample with the addition of κ‐carrageenan showed both the most significant increase in G* in comparison with the control and the highest values of hardness after a 7‐day storage period regardless of the type of the fat used. The samples with coconut fat were assessed as the hardest. On the other hand, the samples with palm oil showed the lowest hardness (with the same hydrocolloid used). In the gelling hydrocolloids (κ‐ and ι‐carrageenan), only small changes in temperature of coil‐to‐helix transition were observed (in range of 2–7 °C) as a result of the addition of different types of fat.