Synthesis and characterization of cobalt ferrite nanoparticles in hybrid micelles of poly[styrene-<Emphasis Type="Italic">block</Emphasis>-(ethylene oxide)] and sodium dodecyl sulfate

Cobalt ferrite nanoparticles are synthesized in hybrid micelles of poly[styrene-block-(ethylene oxide)] and sodium dodecyl sulfate in water at room temperature. The nanoparticles are prepared by the chemical precipitation method via the exchange reaction between iron and cobalt salts with sodium dodecyl sulfate and the redox reaction under the action of an aqueous solution of methylamine. As evidenced by small-angle X-ray scattering, transmission electron microscopy, and ferromagnetic resonance examination, cobalt ferrite nanoparticles occurring in hybrid micelles of the block copolymer and sodium dodecyl sulfate are polydisperse (their size is 0.3–50 nm) and ferromagnetic.     

On the disconnection of a discrete cylinder by a random walk

We investigate the large N behavior of the time the simple random walk on the discrete cylinder needs to disconnect the discrete cylinder. We show that when d≥2, this time is roughly of order N ^{2 d} and comparable to the cover time of the slice , but substantially larger than the cover timer of the base by the projection of the walk. Further we show that by the time disconnection occurs, a massive ``clogging' typically takes place in the truncated cylinders of height . These mechanisms are in contrast with what happens when d=1.     

Structure of composites prepared via polypyrrole synthesis in supercritical CO2 on microporous polyethylene

The synthesis of polypyrrole in supercritical carbon dioxide in the presence of the microporous polyethylene has been studied. Formation of polymer composites based on polypyrrole and polyethylene has been demonstrated. The structure of the test samples has been investigated by vibrational spectroscopy, SAXS, and atomic force and scanning electron microscopy. It has been discovered that the oxidized structure of polypyrrole forms during the synthesis under supercritical conditions.     

Effect of polymer charge density and ionic strength on the formation of complexes between sodium arylamido-2-methyl-1-propane-sulfonate-co-acrylamide gels and cetylpyridinium chloride

The effects of sodium chloride on the composition and structure of polyelectrolyte gel-surfactant complexes (PSCs) formed by the sodium salt of acrylamide-2-methyl-1-propane-sulfonic acid-co-acrylamide gels and cetylpyridinium chloride have been studied. At a low ionic strength of the solution, the composition of all the complexes is close to stoichiometric by charge. In the presence of 0.3 M sodium chloride, the composition of the complexes formed by the gel with 99 mol % charged groups is close to stoichiometric, while for the gel with 33 mol % charged monomer units, a nonstoichiometric complex with a high excess of the surfactant is formed. Further decrease of the charge density up to 10 mol % leads to partial or complete dissociation of the PSCs. The study of PSCs by the method of small-angle X-ray scattering (SAXS) shows that the complexes formed by the gels with high and intermediate charge densities are highly ordered. The decrease of the charge density of the swollen networks at first leads to a change in symmetry of the ordered domains in the PSCs and then to their disordering. The formation of nonstoichiometric PSCs at a high enough concentration of salt is explained by the effect of fitting, when the packing of the surfactant and polymer components in the PSCs is improved due to the inclusion of extra surfactant molecules together with their counterions in the ordered domains.     

Aging for interacting diffusion processes

We study the aging phenomenon for a class of interacting diffusion processes {Xt(i),i∈Zd}. In this framework we see the effect of the lattice dimension d on aging, as well as that of the class of test functions f(Xt) considered. We further note the sensitivity of aging to specific details, when degenerate diffusions (such as super random walk, or parabolic Anderson model), are considered. We complement our study of systems on the infinite lattice, with that of their restriction to finite boxes. In the latter setting we consider different regimes in terms of box size scaling with time, as well as the effect that the choice of boundary conditions has on aging. The key tool for our analysis is the random walk representation for such diffusions.     

Truncated-newtono algorithms for large-scale unconstrained optimization

We present an algorithm for large-scale unconstrained optimization based onNewton's method. In large-scale optimization, solving the Newton equations at each iteration can be expensive and may not be justified when far from a solution. Instead, an inaccurate solution to the Newton equations is computed using a conjugate gradient method. The resulting algorithm is shown to have strong convergence properties and has the unusual feature that the asymptotic convergence rate is a user specified parameter which can be set to anything between linear and quadratic convergence. Some numerical results on a 916 vriable test problem are given. Finally, we contrast the computational behavior of our algorithm with Newton's method and that of a nonlinear conjugate gradient algorithm. This research was supported in part by DOT Grant CT-06-0011, NSF Grant ENG-78-21615 and grants from the Norwegian Research Council for Sciences and the Humanities and the Norway-American Association. This paper was originally presented at the TIMS-ORSA Joint National Meeting, Washington, DC, May 1980.     

Optimal design of a membrane separation process using signomial programming

A multistage membrane separation process for hydrogen recovery is described and formulated as a signomial programming problem. Two different configurations are examined. A 3-stage and a 5-stage process design problem are solved. The optimal solution to these programs is computed from an initial point that does not satisfy the mass balance or transport constraints of the process, using a primal-based geometric programming code. Also examined is the sensitivity of the optimal solution to changes in purity requirements. In all cases, computation times are very reasonable ranging from 2 to 4 seconds of IBM 370/165 CPU time.     

Investigation into the structure of Langmuir-Blodgett films prepared from salts of acetylenic acids

Langmuir-Blodgett films are prepared from lead, cadmium, and copper salts of carboxylic acids, namely, 23-tetracosynoic acid HC≡C(CH₂)₂₁COOH (with the terminal triple bond) and 2-docosynoic acid CH₃(CH₂)₁₈C≡CCOOH (with the internal triple bond). The structural transformations in the films during polymerization under exposure to UV radiation are investigated using X-ray reflectomertry. It is found that the X-ray reflectograms of the initial films prepared from salts of both acids exhibit no less than four or five pronounced intense Bragg reflections. This suggests that the initial films have good layer ordering. The bilayer periods for all the films are determined, and the influence of the salt type on the bilayer period is analyzed. It is established that, under exposure to UV radiation, the structural transformations in the films prepared from the salts of 23-tetracosynoic acid occur without substantial disturbances and defects, as can be judged from the absence of significant changes in the location and intensity of the Bragg reflections. An increase in the time of irradiation of the films prepared from the salts of 2-docosynoic acid leads to an increase in the bilayer period. This effect is especially pronounced for the lead and copper salts. However, upon long-term exposure to UV radiation, the salts undergo photolysis, the bilayer period decreases, and the structure of the film begins to break down.