Forecasting and the Social Sciences

Journal of the Operational Research Society -     

Surfactant-free "emulsions" generated by freeze-thaw

The stability ofsurfactantless dispersions of surface chemically pure alkanes was studied in the presence and absence of dissolved gas. It was found that simply freezing and thawing a sample of oil and water results in a dispersion. A mechanism based on fingering of the insoluble oil into the aqueous phase, due to local surface tension gradients, followed by separation and nucleation into droplets, is proposed to account for this observation.     

Electron hopping conductivity and vapor sensing properties of flexible network polymer films of metal nanoparticles

Films of monolayer protected Au clusters (MPCs) with mixed alkanethiolate and omega-carboxylate alkanethiolate monolayers, linked together in a network polymer by carboxylate-Cu2+-carboxylate bridges, exhibit electronic conductivities (sigma(EL)) that vary with both the numbers of methylene segments in the ligands and the bathing medium (N2, liquid or vapor). A chainlength-dependent swelling/contraction of the film's internal structure is shown to account for changes in sigma(EL). The linker chains appear to have sufficient flexibility to collapse and fold with varied degrees of film swelling or dryness. Conductivity is most influenced (exponentially dependent) by the chainlength of the nonlinker (alkanethiolate) ligands, a result consistent with electron tunneling through the alkanethiolate chains and nonbonded contacts between those chains on individual, adjacent MPCs. The sigma(EL) results concur with the behavior of UV-vis surface plasmon adsorption bands, which are enhanced for short nonlinker ligands and when the films are dry. The film conductivities respond to exposure to organic vapors, decreasing in electronic conductivity and increasing in mass (quartz crystal microgravimetry, QCM). In the presence of organic vapor, the flexible network of linked nanoparticles allows for a swelling-induced alteration in either length or chemical nature of electron tunneling pathways or both.     

Ultrafast dynamic compression technique to study the kinetics of phase transformations in bismuth

Preheated Bi (296-532 K) was ramp compressed with 15-35 ns rise times to a peak stress of approximately 11 GPa to explore structural phase-transformation kinetics under dynamic loading conditions. At high strain rates, epsilon[over ]>5 x 10;{6} s;{-1}, deviation from equilibrium phase boundaries suggests that compression time scales are comparable to the new phase incubation period. The dependence of DeltaP/kT on epsilon[over ] is consistent with a thermally activated transformation.     

The Photoaddition of Aldehydes to Enones: A Direct Route to 1,4-Diketones

Recent work in this² and other³ laboratories has shown that the photochemically-induced addition of oxy-carbinyl species to enones provides a simple and effective method of carbon-carbon bond formation. Thus addition of alcohols^2C,3,4 and acetals^2a to enones (e. g. 1 or 4) affords keto-alcohols (e. g. 2 or 5) and keto-ketals (e. g. 6), the synthetic value of which are enhanced by the fact that the functionalities are conveniently differentiated, thereby facilitating selective manipulation.⁵     

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Hydrogen adsorption on the indium-rich indium phosphide (001) surface: a novel way to produce bridging In-H-In bonds

The indium phosphide (001) surface provides a unique chemical environment for studying the reactivity of hydrogen toward the electron-deficient group IIIA element, indium. Hydrogen adsorption on the In-rich delta(2 x 4) reconstruction produced a neutral, covalently bound bridging indium hydride. Using vibrational spectroscopy and ab initio cluster calculations, two types of bridging hydrides were identified, a (mu-H)In(2) and a (mu-H)(2)In(3) "butterfly-like" structure. These structures were formed owing to the large thermodynamic driving force for adsorption of H atoms on solid-state indium dimers.