The measurement of beta asymmetries at UNISOR/NOF using external plastic scintillator detectors

The performance of two external plastic scintillator detectors has been tested in an off-line mode using a source of¹⁰⁶RuFe at UNISOR/NOF. The measurement of beta asymmetries at various temperatures has resulted in the reproduction of the previously-determined magnetic dipole moment for the 1⁺ ground state of¹⁰⁶Rh and in addition the conclusion that the sign of this moment is positive.     

Comparison of short range interactions in nematic liquid crystals A 2H-NMR study of 5CB-d19 as a solute

Previous studies using dideuterium as a solute have demonstrated the importance for orientation of the interaction between the solute molecular quadrupole moment and the average electric field gradient present in liquid crystals. With the aim of learning about additional orientational mechanisms, we have studied the temperature dependence of the ²H-NMR spectra of the liquid crystal 5CB-d₁₉ as the solute in three liquid crystal mixtures: 55 wt % 1132/EBBA, 56·5 wt % 1132/EBBA and 70 wt % 5CB/EBBA. In these mixtures, the contribution from the environment to the average electric field gradient at the ²H nucleus of dideuterium is zero. The spectra of 5CB-d₁₉ in the mixtures 55 wt % 1132/EBBA and 56·5 wt % 1132/EBBA are equivalent, but are different from those in 70 wt % 5CB/EBBA. The spectra of 5CB in 55 wt % 1132/EBBA and 70 wt % 5CB/EBBA are analysed using two different models for the short range potential, and param eters of the models are used to compare the potentials in the different mixtures. For a given spectral splitting of the chain C₁ deuteron, the reduced short range potential is the same in all three mixtures studied. The spectral differences observed are a consequence of different nematic-isotropic phase transition temperatures combined with the effect of trans/gauche-isomerization in the hydrocarbon chain.     

Solution and crystal lattice effects on the photochemistry of 6-substituted cyclohexenones(1)(,)(2)

The photochemistry of 13 4,4-diphenylcyclohexenones, substituted at carbon-6, was investigated in solution and in the crystalline state. The stereoselectivity was of particular interest. In the solution photochemistry of C-6 monosubstituted enones in benzene, there was a unique preference for migration of the cis-phenyl group with formation of bicyclo[3.1.0]hexanone photoproducts, with the original 6-substituent having an endo configuration at carbon-3 of the product. In methanol the reaction was diverted to afford 3,4-diphenylcyclohex-2-enes understood as arising from a hydrogen-bonded zwitterionic intermediate. The solid-state photochemistry was also investigated. There was a dramatic absence of the 3,4-diphenylcyclohex-2-ene products in accord with the absence of the hydrogen bonding encountered in methanol. Further, the solid-state reactivity correlated with a vector analysis using X-ray atomic coordinates. This established that the migrating phenyl group required an orientation facing the enone beta-carbon. While the interesting preference for the cis-endo migration was not intuitively predicted, ab initio computations on the alternative phenyl-bridged triplet intermediates did lead to an understanding of the selectivity.     

Synthesis and in Vitro Evaluation of N-[[4-[2-(Carboxyl)-1-Cycloalken-1-yl]Phenyl]Methyl]Imidazoles as Nonpeptide Angiotensin II Receptor Antagonists

A series of nonpeptide angiotensin II receptor antagonists was synthesized via palladium-assisted cross coupling of aryl stannane and cycloalkenyl triflates and subsequent alkylation of silyl-protected imidazole. Our compounds, which have a terminal five- to seven-membered cycloalkenyl ring, are compared to DuPont EXP7711, an N-[(2′-carboxybiphenylyl)methyl]imidazole, which has a terminal phenyl moiety. Physicochemical properties of the compounds, such as lipophilicity, steric bulk, conformation, and the relative spatial proximity of the 2-carboxyl and the middle phenyl, are quantitated by computational chemistry. Potency in terms of binding affinity to AT₁ receptors in rat adrenal glomerulosa and rabbit aorta is maximized when the terminal ring is aromatic.     

The alpha-effect in the stereochemistry of kinetic ketonization of enols

Kinetic control of the stereoselectivity of protonation of enolates and other strongly delocalized anionic species is involved in a large number of organic reactions. Protonation occurring from the less hindered side of the, e.g., enolic system affords the less stable of two diastereomers. However, one apparent discrepancy has been in the synthesis of prostaglandins. The present research deals with the source of this behavior. A curious effect of the substituent at the enolic alpha carbon was uncovered. In certain instances an alpha substituent is forced to twist into a conformation blocking the proton donor from its side, thus reversing the stereochemistry of protonation. In the course of this research, a number of five-ring enols of varying structure were investigated. Finally, the ketonization reaction course has been studied theoretically.     

Influence of solvent polarity upon salt solubilities,II: Solubilities of two potassium carboxylates at 85°C in aqueous 1,4-dioxane

The solubilities of potassium acetate and benzoate in aqueous 1,4-dioxane at a temperature of 85°C are reported together with a quasi-thermodynamic general treatment of the experimental results.This brief contribution is a second report upon the results of systematic solubility measurements, commenced with Ref.¹, which have been performed by Dr.John A. McNaney during his abruptly truncated lifetime.     

Hydraulic conductivity of rock fractures

The flow of a single-phase fluid through a rough-walled rock fracture is discussed within the context of fluid mechanics. The derivation of the cubic law is given as the solution to the Navier-Stokes equations for flow between smooth, parallel plates - the only fracture geometry that is amenable to exact treatment. The various geometric and kinematic conditions that are necessary in order for the Navier-Stokes equations to be replaced by the more tractable lubrication or Hele-Shaw equations are studied and quantified. In general, this requires a sufficiently low flow rate, and some restrictions on the spatial rate of change of the aperture profile. Various analytical and numerical results are reviewed pertaining to the problem of relating the effective hydraulic aperture to the statistics of the aperture distribution. These studies all lead to the conclusion that the effective hydraulic aperture is less than the mean aperture, by a factor that depends on the ratio of the mean value of the aperture to its standard deviation. The tortuosity effect caused by regions where the rock walls are in contact with each other is studied using the Hele-Shaw equations, leading to a simple correction factor that depends on the area fraction occupied by the contact regions. Finally, the predicted hydraulic apertures are compared to measured values for eight data sets from the literature for which aperture and conductivity data were available on the same fracture. It is found that reasonably accurate predictions of hydraulic conductivity can be made based solely on the first two moments of the aperture distribution function, and the proportion of contact area.     

Semiclassical approach to collision-induced emission in the presence of intense laser radiation: An aspect in the study of cooperative chemical and optical pumping

Collion-induced emission in molecular systems in an intense laser field is studied using the semiclassical approach, with a view towards cooperative chemical and optical pumping in laser production. The formalism is developed with the electronic-field representation, which treats collision and radiative interaction on the same footing. Electronic-field surfaces can be regarded as forming spectra for spontaneous emission; and particular emission events can be accounted for by propagating classical trajectories on emission electronic-field surfaces. Pre-emission loss from the excited state is dealt with by propagating classical trajectories on a loss surface along a complex contour of emission branch points. This loss surface is derived on the basis of localized radiative couplings between electronic-field states and provides a framework to treat the general problem of discrete state-continuum interactions. The formalism is applied to a two-state, collinear exponential model to compute S-matrix elements and transition probabilities between asymptotic states.     

Mössbauer effect study of Y(Fe0.022 Co0.978)2 at temperatures between 0.15 and 4.2k

A³He-⁴He dilution refrigerator was constructed to perform Mössbauer measurements well below 4.2K. Results are reported here on the pseudobinary Laves-Phase system Y (Fe_1-x Co_x)₂ for x=0.978. We found that at low temperatures, the Fe ions undergo a disordered magnetic phase transition, with a Curie temperature of approximately 4K and a saturation field of 96K0e. The easy axis of magnetization appears to be the [111] direction. This study is an extension to very low temperatures of previous work on the system with 0X0.978.Supported by the NSF Grant No. DMR 73-07665 AO 3     

Synthesis of hydrocarbons and alcohols from CO and H2 in the presence of CO-Rh catalysts

Catalysts of 4.5% Co- 0.1% Rh- 5:10% Cu/TiO ₂ display high activity in the synthesis from CO and H₂ of a mixture of hydrocarbons and alcohols at 250–300°C and pressures of 0.1–6.0 MPa; these catalysts are more selective than traditional Co catalysts with respect to alcohol formation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1707–1709, August, 1990.