Phase boundaries near the bicritical point of MnF2

Phase boundaries near the bicritical point (T_b = 64.74 ± 0.01 K, H_b = 118.45 ± 0.4 kOe) of the uniaxial antiferromagnet MnF₂ were redetermined with higher precision from ultrasonic attenuation measurements. The results are compared with recent theories of Fisher et al.     

Search for resonances in 12C(9Be, α)17O

Excitation functions at 7° (lab) have been measured from E_c.m. = 5.1 to 11.4 MeV in approximately 114 keV steps for 15 groups of final states in ¹⁷O populated by the ¹²C(⁹Be, α) reaction. Statistical tests have been used to locate possible non-statistical structure in the excitation functions. Possible anomalies were found near E_c.m. = 6.3, 7.5, 8.9 and 9.7 MeV. Angular distributions were measured at E_c.m. = 9.20, 9.71 and 10.23 MeV for the three lowest excited states in ¹⁷O. The data have been compared with Hauser-Feshbach calculations in addition to the following reaction mechanisms: compound plus a single resonance, compound plus interfering resonances and compound plus direct reactions.     

The reactions of combined organocuprate-chlorotrimethylsilane reagents with conjugated carbonyl compounds

Organocuprates and chlorotrimethylsilane are compatible as separate species in THF or ether solution at ?50 to ?78°, and in combination can both accelerate and improve 1,4-addition reactions with conjugated carbonyl compounds.     

Cyclodextrin complexes of polyaromatic hydrocarbons in the presence of aliphatic alcohols

Pyrene, as a fluorescence probe, has been used to study the cyclodextrin complexation process in the presence of different alcohols. The complex formation as well as the hydrophobicity of the cyclodextrin interior can be significantly influenced by the introduction of alcohols. The alcoholic alkyl group and the primary and secondary hydroxyl groups of the cyclodextrin proved to be the determining factors in the complex formation.     

Exchange energy for conduction electrons in (ZnMn)Se derived from spin-flip Raman scattering and magnetization

Spin-flip Raman scattering, magnetization, and susceptibility data for Zn_0.97Mn_0.03Se are reported. The exchange energy N_oα = 243 ± 10 meV for the conduction electrons is obtained from an analysis of the Raman and magnetization data. At large magnetic fields (H > 60 kOe), the spin-flip energy ΔE saturates at 14 meV. At low fields ΔE does not extrapolate to zero as H → 0, which is characteristic of scattering from donor-bound electrons. The low temperature magnetization curves are fit to a modified Brillouin function. The fit gives $\text{x}\text{?}\text{/x}\text{= 0.67}$ as the fraction of active magnetic ions, and an effective temperature T_eff = T + T_o with T_o = 1.1 K. The magnetic susceptibility follows a Curie-Weiss law between T = 150 and 280 K with a Curie-Weiss temperature θ = ?33 K.     

Dispersion of inert solutes in spatially periodic,two-dimensional model porous media

Taylor dispersion of a passive solute within a fluid flowing through a porous medium is characterized by an effective or Darcy scale, transversely isotropic dispersitivity , which depends upon the geometrical microstructure, mean fluid velocity, and physicochemical properties of the system. The longitudinal, and lateral, dispersivity components for two-dimensional, spatially periodic arrays of circular cylinders are here calculated by finite element techniques. The effects of bed voidage, packing arrangement, and microscale Péclet and Reynolds numbers upon these dispersivities are systematically investigated.The longitudinal dispersivity component is found to increase with the microscale Péclet number at a rate less than Pe². This accords with previous calculations by Eidsath et al. (1983), although the latter calculations were found to yield significantly lower longitudinal dispersivities than those obtained with the present numerical scheme. With increasing Péclet number, a Pe² dependence is, however, approached asymptotically, particularly for square cylindrical arrays - owing to the creation of a linear streamline zone between cylinders.     

Evidence for a reversible d, π-complexation, β-cupration sequence in the conjugate addition reaction of Gilman reagents with α,β-enones.

$\text{In situ}$ trapping of reaction intermediates combined with stereochemical studies of the reaction of lithium dimethylcuprate with enones provides evidence for a pathway involving d,π-cuprate-enone and copper(III) β-adducts as important intermediates in cuprate-mediated conjugate addition of carbon.