Discrete radiation boundary conditions for a semi-infinite layer of fluid

The paper deals with the discrete formulation of radiation boundary conditions for a layer of fluid. The problem is examined with the help of the finite difference method. The proposed radiation boundary enables us to replace an infinite layer by a finite domain. The conditions ensure near equivalence between the infinite layer and the proposed finite model. The method is consistent itself and operates on a finite number of points. The results of numerical solutions are in good agreement with the results of analytical solutions of the problem.     

Determination of surface tension coefficient of liquid metals and alloys using the phenomenon of capillary wave formation

A possibility of determining the surface tension coefficient of 6H13 liquid steel and of technically pure iron (ArmcoFe) has been presented. In the investigation the phenomenon of ring structure formation (capillary waves) on the surface of a molten metal affected by light pulses of a glass neodymium laser (λ = 1,06 μm, τ_i ≈ 1 ms, E_i ≈ 6J) has been considered. The values obtained for the surface tension coefficient are in good agreement with those determined by other methods (for liquid metals in the temperature range 2000K – 5000K).     

Multi-stage activation of brown-coal chars with oxygen

Activation of xylitic brown-coal coke XBC 900 with water vapour and carbon dioxide, when modified by partial replacement of the basic activating agent with 10% oxygen at a lower temperature, results in products with an increased microporosity. Thus, oxygen as activating agent for xylitic coke develops, preferentially, micropores, and this property is more strongly pronounced for oxygen than for the carbon dioxide and water vapour. A drawback to the process of activation with oxygen, i.e. blockage of initially formed micropores by chemisorbed oxygen, can be eliminated by removal of the chemisorbed oxygen by heat treatment in argon (multi-stage oxygen activation). This increases the micropore volume of the xylitic brown-coal coke XBC 900 activated with oxygen to 70% total burnoff, from about 0.2 cm³ g^?1 to almost 0.5 cm³ g^?1. The increase of the total adsorptive volume (micropores and mesopores) of these samples is from 0.45 cm³ g^?1 to over 0.6 cm³ g^?1 and the surface area S_BET in benzene increases from 650 m² g^?1 to over 1200 m² g^?1. These last values are close to the limiting conditions for 70% activation obtainable for this material. Temperature of carbonization of the brown-coal char has a strong effect on the possibility of pore development through further activation. Multi-stage oxygen activation of xylitic brown-coal semicoke XBC 500 produces a material with a smaller micropore volume and a lower surface area than that of xylitic brown-coal coke XBC 900 similarly activated.     

Canonical structures of DC-AC thyristor converters

Realizability conditions of periodic waveforms in passive switched circuits are presented. Formulae for an identification of state matrices in switched circuits are derived. As input data, time functions of excitation and response are chosen. Six general transformer structures of 1-port thyristor converters have been obtained as a result of the synthesis method. The synthesis methods presented can be applied to create new thyristor and transistor arrangements, particularly thyristor compensators.     

Spectrophotometric assay for copper and iron in transformer oil using partial least squares regression (PLS2)

A simple and low cost spectrophotometric assay is proposed in this work for simultaneous determination of copper and iron levels in insulating oils. The procedure requires minimum sample volume (250 muL), it is carried out in disposable micro tubes (1.5 mL) and aqueous standards are used for calibration. In brief, after dilution with n-propanol, the wear metals are extracted with hydrochloric acid and, after neutralization, the analytes are reduced to the oxidation states Cu(I) and Fe(II) respectively. Finally, the mixture of bathocuproine-disulfonic acid and bathophenantroline-disulfonic acid is added for selective formation of copper and iron complexes. Then, chloroform and methanol are added, the sample is centrifuged and absorption spectra are registered in the upper-aqueous layer (470-550 nm). Multivariate calibration, covering concentration range 0-4 mug/mL of each analyte in oil is performed using partial least squares regression. The test solutions are prepared by spiking the aqueous standards of copper and iron to metal-free oil diluted with n-propanol (1:1). The prediction results were in agreement with those obtained using univariate spectrophotometric assay (one ligand) and those obtained by electrothermal atomic absorption spectrometry (after dissolution of wear metals and dilution with n-propanol)     

Selective derivatization of cytosine and methylcytosine moieties with 2-bromoacetophenone for submicrogram DNA methylation analysis by reversed phase HPLC with spectrofluorimetric detection

In eukaryotes, actual DNA methylation patterns provide biologically important information, for which both, genome-wide and locus-specific methylation at cytosine residues have been extensively studied. The original contribution of this work relies on the selective derivatization of cytosine moieties with 2-bromoacetophenone for the determination of global DNA methylation by reversed phase high performance liquid chromatography with spectrofluorimetric detection. The important features of the proposed procedure are as follows: (1) no need for the elimination of RNA, (2) detection limits for cytidine, 2'-deoxycytidine, 5-methylcytidine, and 5-methyl-2'-deoxycytidine in the range of 14.4-22.7 fmol, (3) feasibility for the detection of 0.06% of methylation in a low amount of DNA (80 ng), (4) potential viability for the evaluation of RNA methylation, and (5) relative simplicity in terms of analytical instrumentation and personnel training. The results obtained in the analysis of salmon testes DNA and nucleic acids from plant, human blood, and earthworms demonstrate the utility of the proposed procedure in biological studies and, in particular, for evaluation of the potential effect of environmental factors on actual DNA methylation in different types of living organisms.