Investigations on the gas phase crystal growth of hematite

The optimum conditions of transport of hematite with chlorine were been studied theoretically. Using computed data on the partial pressures of the components in the transport system, the dependencies of the change in conversion degree of the transport reaction and of the super-saturation upon the temperature in the crystallization zone were plotted with various temperature gradients and carrier concentrations. On the basis of these dependencies, conclusions about the appropriate crystallization temperatures and chlorine concentrations were drawn. Experimental resulta qualitatively confirmed these conclusions. Homogeneous stoichiometric crystals of hematite with maximum dimensions of 5 – 6 mm were obtained.     

Growth of ZnCr2O4 single crystals by chemical transport

The preparation of spinel zinc chromite, ZnCr₂O₄, single crystals by close-spaced chemical transport with Cl₂ as a transport agent has been studied. The composittion of the gas phase at temperatures ranging from 800 to 1500 K and a total pressure of 0, 1, 0, 5, 1, 2, 3, 5 and 8 atm, respectively, was calculated using available thermodynamic data. The temperature dependence of the solubility of ZnCr₂O₄ in the gas phase was obtained at the same total pressure and on this basis the efficiency of the transport was estimated. Single crystals of spinel zinc chromite in the form of octahedra with maximum edge length of 10 mm were obtained.     

On the preparation of nickel ferrite single crystals by chemical transport

A thermodynamic study of the process of close-spaced chemical transport of nickel ferrite with tellurium tetrachloride has been carried out. On the basis of computed data on the partial pressures of the species in the transport system, the temperature dependence of the change in the conversion degree of the transport reaction and of the supersaturation in the crystallization zone were plotted and used to determine the optimum experimental conditions. Stoichiometric nickel ferrite crystals with maximum edge dimensions of 5 mm were obtained.     

Oil-in-oil emulsions: a unique tool for the formation of polymer nanoparticles

Polymer latex particles are nanofunctional materials with widespread applications including electronics, pharmaceuticals, photonics, cosmetics, and coatings. These materials are typically prepared using waterborne heterogeneous systems such as emulsion, miniemulsion, and suspension polymerization. However, all of these processes are limited to water-stable catalysts and monomers mainly polymerizable via radical polymerization. In this Account, we describe a method to overcome this limitation: nonaqueous emulsions can serve as a versatile tool for the synthesis of new types of polymer nanoparticles. To form these emulsions, we first needed to find two nonmiscible nonpolar/polar aprotic organic solvents. We used solvent mixtures of either DMF or acetonitrile in alkanes and carefully designed amphiphilic block and statistical copolymers, such as polyisoprene- b-poly(methyl methacrylate) (PI- b-PMMA), as additives to stabilize these emulsions. Unlike aqueous emulsions, these new emulsion systems allowed the use of water-sensitive monomers and catalysts. Although polyaddition and polycondensation reactions usually lead to a large number of side products and only to oligomers in the aqueous phase, these new conditions resulted in high-molecular-weight, defect-free polymers. Furthermore, conducting nanoparticles were produced by the iron(III)-induced synthesis of poly(ethylenedioxythiophene) (PEDOT) in an emulsion of acetonitrile in cyclohexane. Because metallocenes are sensitive to nitrile and carbonyl groups, the acetonitrile and DMF emulsions were not suitable for carrying out metallocene-catalyzed olefin polymerization. Instead, we developed a second system, which consists of alkanes dispersed in perfluoroalkanes. In this case, we designed a new amphipolar polymeric emulsifier with fluorous and aliphatic side chains to stabilize the emulsions. Such heterogeneous mixtures facilitated the catalytic polymerization of ethylene or propylene to give spherical nanoparticles of high molecular weight polyolefins. These nonaqueous systems also allow for the combination of different polymerization techniques to obtain complex architectures such as core-shell structures. Previously, such structures primarily used vinylic monomers, which greatly limited the number of polymer combinations. We have demonstrated how nonaqueous emulsions allow the use of a broad variety of hydrolyzable monomers and sensitive catalysts to yield polyester, polyurethane, polyamide, conducting polymers, and polyolefin latex particles in one step under ambient reaction conditions. This nonpolar emulsion strategy dramatically increases the chemical palette of polymers that can form nanoparticles via emulsion polymerization.     

Nonlinear exchange of mass between a gas and a liquid runoff film. 2. Asymptotic analysis

We propose an asymptotic method for the solution of the problem concerned with the determination of the rate of nonlinear mass exchange between a gas and a runoff fluid film, when the process is limited to the transport of mass in the gaseous phase. We have derived equations for the distributions of velocities and concentrations both in the liquid and the gas. The results from asymptotic theory are compared with the results of numerical analysis and against the experimental data.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 59, No. 2, pp. 277–286, August, 1990.     

Shape-Based Object Detection via Boundary Structure Segmentation

We address the problem of object detection and segmentation using global holistic properties of object shape. Global shape representations are highly susceptible to clutter inevitably present in realistic images, and thus can be applied robustly only using a precise segmentation of the object. To this end, we propose a figure/ground segmentation method for extraction of image regions that resemble the global properties of a model boundary structure and are perceptually salient. Our shape representation, called the chordiogram, is based on geometric relationships of object boundary edges, while the perceptual saliency cues we use favor coherent regions distinct from the background. We formulate the segmentation problem as an integer quadratic program and use a semidefinite programming relaxation to solve it. The obtained solutions provide a segmentation of the object as well as a detection score used for object recognition. Our single-step approach achieves state-of-the-art performance on several object detection and segmentation benchmarks.