Use of a range scaling method to determine alanine/water stopping power ratios

A phantom composed of alanine dosimeter material has been constructed and depth–dose measurements made in a 10 MeV electron beam. The results have demonstrated the feasibility of using relative depth–dose measurements to determine stopping power ratios in materials of dosimetric interest. Experimental stopping power ratios for alanine dosimeter material and water agreed with the data of ICRU Report 37 within the uncertainty of the experiment (±1.2% at a 95% confidence level).     

The cyclodimerisation of 3-methyl-2-butenenitrile

3-Methyl-2-butenenitrile (1) cyclodimerised on treatment with lithium diisopropylamide in dimethoxyethane at temperatures between ?78°C and 0°C to 3-amino-4-cyano-1,5,5-trimethyl-1,3-cyclohexadiene (2) the structure of which was established by acid hydrolysis to the known 4-cyano-1,5,5-trimethyl-1-cyclohexene-3-one (3).     

Nature of the Arsonium-Ylide Ph3As=CH2 and a Uranium(IV) Arsonium–Carbene Complex

Treatment of [Ph₃EMe][I] with [Na{N(SiMe₃)₂}] affords the ylides [Ph₃E=CH₂] (E=As, 1As ; P, 1P ). For 1As this overcomes prior difficulties in the synthesis of this classical arsonium-ylide that have historically impeded its wider study. The structure of 1As has now been determined, 45 years after it was first convincingly isolated, and compared to 1P , confirming the long-proposed hypothesis of increasing pyramidalisation of the ylide-carbon, highlighting the increasing dominance of E⁺−C⁻ dipolar resonance form (sp³-C) over the E=C ene π-bonded form (sp²-C), as group 15 is descended. The uranium(IV)–cyclometallate complex [U{N(CH₂CH₂NSiPrⁱ₃)₂(CH₂CH₂SiPrⁱ₂CH(Me)CH₂)}] reacts with 1As and 1P by α-proton abstraction to give [U(Tren^TIPS)(CHEPh₃)] (Tren^TIPS=N(CH₂CH₂NSiPrⁱ₃)₃; E=As, 2As ; P, 2P ), where 2As is an unprecedented structurally characterised arsonium-carbene complex. The short U−C distances and obtuse U-C-E angles suggest significant U=C double bond character. A shorter U−C distance is found for 2As than 2P , consistent with increased uranium- and reduced pnictonium-stabilisation of the carbene as group 15 is descended, which is supported by quantum chemical calculations.     

Real-time, whole-field speckle photography using a bistable optically addressed spatial light modulator

The application of a bistable optically addressed spatial light modulator for real-time visualization of solid-body displacement fields is described. Double-exposure speckle patterns are recorded on the spatial light modulator and a whole-field filtering technique is used to generate fringes of constant displacement.     

Temperature-dependent infrared absorption cross sections of methyl cyanide (acetonitrile)

Pressure broadened (1 atm. N₂) absorption cross sections and integrated band intensities have been derived from laboratory spectra of CH₃CN, recorded at 276, 298, and 323 K, covering 600-. The spectra were recorded at a resolution of using a commercial Fourier transform spectrometer and a custom flowing sample delivery system. We report integrated absorption cross sections for intervals corresponding to the most prominent bands, compare the results with previously reported values, and discuss error sources, which are estimated as ∼7% with systematic error the largest error source.     

Optical frequency conversion by a rotating molecular wave plate

We demonstrate efficient four-wave mixing in low-pressure molecular deuterium without the need for phase matching. We use two laser fields with opposite circular polarizations to produce a strong excitation of a rovibrational transition at a frequency of 3167 cm(-1) . The coherent molecular motion, in turn, modulates a third laser field (also circularly polarized) and results in highly efficient single-sideband conversion.