Effect of viscous dissipation on the mixed convection heat transfer from an exponentially stretching surface

The mixed convection flow and heat transfer from an exponentially stretching vertical surface in a quiescent fluid is analyzed using similarity solution technique. Wall temperature and stretching velocity are assumed to have specific exponential function forms. The influence of buoyancy along with viscous dissipation on the convective transport in the boundary layer region is analyzed in both aiding and opposing flow situations. The flow is governed by the mixed convection parameter Gr/Re². The velocity and temperature inside the boundary layer are observed to be influenced by the parameters like Prandtl number Pr, Gebhart number Gb. Significant changes are observed in non-dimensional skin friction and heat transfer coefficients due to viscous dissipation in the medium. The flow and temperature distributions inside the boundary layer are analyzed and the results for non-dimensional skin friction and heat transfer coefficients are discussed through computer generated plots.     

Radical polymerization as an indicator reaction for determination of organic compounds

Polymerization of methyl methacrylate (MMA) and 4-vinylpyridine (VP) has been carried out in an aqueous solution in the presence of the initiating system persulfate-tetramethylethylenediamine. The reaction rate has been monitored by measuring the light absorbance of the suspension of the resulting polymer. The effect of 26 model organic compounds on the polymerization rate has been studied. It has been shown that the VP polymerization is inhibited by a smaller number compounds (9 compounds) than the MMA polymerization (22 compounds), which indicates that the former reaction has better selectivity, whereas the determination of model compounds using the MMA polymerization reaction is more sensitive. This is explained by the lower chain growth rate constant for VP vs. MMA and different stationary concentrations of radicals in the systems. The use of these indicator polymerization reactions makes it possible to distinguish some closely related compounds, e.g., 1,4-benzoquinone and 9,10-anthraquinone (MMA reaction) or dinitrophenol and 4-nitrophenol or phenol (VP reaction). Determination of ascorbic acid in a pharmaceutical formulation has been carried out.     

Adsorption–Catalytic Test Methods

In the development of a new hybrid adsorption–catalytic method it was shown that the selective adsorption isolation of components can be combined with their catalytic determination directly on the adsorbent. To provide theoretical grounds and find fields of the application of the new method, the effect of the support matrix on the rate of catalytic (enzymatic and indicator) reactions was studied. The changes in the performance characteristics of procedures for determining inorganic and organic substances directly on the adsorbent with respect to those of procedures for determining in solutions were analyzed. It was proved that the development of catalytic test procedures with the visual detection of the analytical signal is expedient.     

Sorption-catalytic determination of cadmium using bromobenzothiazo noncovalently bound to silica and paper

Cadmium (along with Fe(II), Co(II), Zn(II), and Pb(II) ions) decreases the rate of oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) with KIO4 conducted either without or with Mn(II) as a catalyst. Cadmium(II) is preconcentrated from aqueous solutions on silica plates or paper filters physically modified with a reagent for selective determination of Cd(II), namely 1-[(6-bromo-2-benzothiazolyl)azo]-2-naphthol (bromobenzothiazo, or BBT). The modifier is strongly retained on the both supports at pH 6-10 and does not affect the inhibiting effect of Cd(II) in the indicator reaction. Cadmium is determined by its inhibiting action directly on the sorbents by measuring transmittance (BBT/paper) or reflectance (BBT/silica) with limits of detection of 2 x 10(-4) and 0.03 mg/L, respectively. The proposed hybrid combination of sorption with catalytic detection on the sorbent allows to increase the selectivity factors several times (up to 2 orders) relatively to the determination in solution. Tap water samples and soil extracts were analyzed.     

Kinetic methods for determining water-soluble polymers

The effect of synthetic water-soluble polymers on the reactions of hydroquinone or 3,3′,5,5′-tetramethylbenzidine periodate oxidation with hydrogen peroxide is studied. A polymer solution was introduced into the reaction and a change in its rate was detected by photometry. Possible reasons for the effect of polymers are discussed, the role of the positive and negative charges of the polymeric chain and the nature of the indicator reaction are considered. The possibility of determining polyelectrolytes by their accelerating and inhibiting effect is demonstrated, including that, under the conditions of polyelectrolyte complex formation, and also by binding with a metal ion catalyzing the indicator reaction. Procedures are proposed for the simple and rapid determination of 3,6-ionene, polyanetholesulfonic acid, polyhexamethyleneguanidine (～10^?5 to 10^?4 M, in terms of the monomer), polyethyleneimine and chitosans (～10^?7?10^?6 M in terms of the monomer) in aqueous solutions, and also of polyethyleneimine by carrying out the indicator reaction on a silica surface (4 × 10^?6 to 0.7 M in terms of the monomer).     

Growth morphology of zinc tris(thiourea) sulphate crystals

The growth morphology of crystals of zinc tris(thiourea) sulphate (ZTS) is investigated experimentally, and computed using the Hartman-Perdok approach. Attachment energies of the observed habit faces are calculated for determining their relative morphological importance. A computer code is developed for carrying out these calculations. A special procedure is adopted for computing the cohesive energy of a slice of the structure parallel to any rational crystallographic plane. For estimating the cohesive energies, formal charges on the experimentally determined atomic positions in the molecules of ZTS are calculated by ab initio molecular-orbital computations, with wave functions obtained by the Hartree-Fock procedure. Fairly good agreement with the observed crystal morphology is obtained for a model of growth mechanism in which ZTS is assumed to exist in solution sa szinc tris(thiourea) ions and sulphate ions.