Search for a spin glass phase in Mn0.22Zn0.78F2

No spin glass behaviour has been found in Mn_0.22Zn_0.78F₂ which is close to the antiferromagnetic critical concentration. Bulk magnetic measurements show no cusp above 1.7 K, no remanent moment after cooling in a field, and no difference between field cooled and zero field cooled susceptibilities. The infinite time susceptibility derived from diffuse neutron scattering measurements is also in good agreement with the bulk measurement, indicating no frozen component of the bulk susceptibility. The temperature dependence of the susceptibility is explained with a simple paramagnetic model.     

Substructure search systems for large chemical data bases

The substructure search systems, S⁴, DARC, HTSS and MACCS are briefly reviewed. The performance of the different systems are compared and evaluated in terms of accuracy and search time. The results show that the accuracy of all four systems is excellent and that S⁴ has by far the best search-time performance. The successful implementation of S^r4 for use with CD-ROMs is also demonstrated.     

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.