Chemical actinometry at 147.0 nm

Hexafluoroacetone (HFA) and O₂ were photolyzed at 147.0 nm to investigate their use in chemical actinometry. The products, CO for the former and O₃ in the latter case, were monitored. For accurate comparison, both of these substances were irradiated by a single light source with two identical reaction cells at 180° to each other. The light intensities I were measured under the same integrated as well as instantaneous photon flux based on ? and ?_CO (quantum yield) as 2 and 1, respectively. Optimum conditions for maximum product yield were 5.0 torr HFA pressure and an O₂ flow rate of 200 ml/min at 1 atm pressure for a 20-minute photolysis period. For light intensity variations between 1.09 × 10¹⁴ and 2.10 × 10¹⁵ photons absorbed/sec, the ratio I/I_HFA was found to be unity. Calibration with the commonly used N₂O actinometer for a ? value of 1.41 showed that I/I_HFA and I/I are unity. Both HFA and O₂ are suitable chemical actinometers at 147.0 nm with ?_CO and ? of 1 and 2, respectively. The light intensity determination in the first case involves the measurement of only one product which is noncondensible at 77°K, whereas wet analysis for O₃, the only product, in the second actinometer is necessary. Both of these determinations are quite simple and are preferable over product analysis in N₂O actiometry, wherein N₂ separation from other noncondensibles at 77°K is required.     

Updating conjugate directions by the BFGS formula

Many iterative algorithms for optimization calculations form positive definite second derivative approximations,B say, automatically, butB is not stored explicitly because of the need to solve equations of the formBd--g. We consider working with matricesZ, whose columns satisfy the conjugacy conditionsZ ¹ BZ=1. Particular attention is given to updatingZ in a way that corresponds to revisingB by the BFGS formula. A procedure is proposed that seems to be much more stable than the direct use of a product formula [1]. An extension to this procedure provides some automatic rescaling of the columns ofZ, which avoids some inefficiencies due to a poor choice of the initial second derivative approximation. Our work is also relevant to active set methods for linear inequality constraints, to updating the Cholesky factorization ofB, and to explaining some properties of the BFGS algorithm. Dedicated to Martin Beale, whose achievements, advice and encouragement were of great value to my research, especially in the field of conjugate direction methods.     

Temperature dependent peaks in secondary electron emission spectra

Peaks in the secondary emission spectra not associated with Auger effects have been observed in various metals (particularly copper and cobalt). These peaks are suppressed at elevated temperature and appear to have amplitudes which are unique functions of temperature. They are characteristic of well ordered, and, particularly, clean surfaces, and are interpreted in terms of the diffraction of the emitted secondary electrons.     

The microwave spectrum,force field and dipole moment of CF2

Measurements of the microwave spectrum of CF₂ have been extended to include transitions up to J = 40. Using these extended measurements, a centrifugal distortion analysis has been performed and from the distortion constants, the force field, infrared spectrum, average structure, Coriolis coupling constants, and inertial defect have been calculated. The original assignment of the infrared spectrum has been confirmed. An improved value for the dipole moment, 0.469 ± 0.026 D, has been obtained.     

A note on the limitations in the use of the impulse precision sound level meter

The limitations in the use of the Impulse Precision Sound Level Meter for the assessment of the sound energy of recurrent impact noise have been investigated. For repetition rates above 30 impacts per second the meter reading and level predicted by an energy law agree to within ±2 dB. Below 30 impacts per second, for pulses with decay times in the range 2 to 28 msec, a simple empirical correction applied to the meter reading will produce results that follow the energy law. For decay times in excess of 28 msec simple corrections are not adequate and therefore the Impulse Sound Level Meter cannot be used in practice.     

Halogen assisted volatilization in electrothermal atomic absorption spectroscopy: reduction of memory effects from refractory carbides

Memory (carry-over) effects associated with electrothermal atomic absorption spectroscopic (ETAAS) analysis of metals which form refractory carbides can be overcome by a halogen (Cl₂) purging process. Residual carbides are removed from the graphite or pyrolytic graphite-coated furnaces after each analysis, or group of analyses, by injection of Cl₂ into the heated furnace. Alternatively, Cl₂ may be injected during the atomization step immediately after maximum absorption is observed, thus avoiding a separate heating/purging cycle. The application of this method to the determination of V and Cr is reported. Optimum temperatures were established for volatilization of residual refractory carbides prepared in situ. The results are supported by thermodynamic calculations.     

Stimulated acceleration and confinement of deuterons in focuseddischarges. II

For pt.I see ibid., vol.16, no.3, p.368-73, June 1988. Methods of increasing, by a factor greater than five, the neutron yield/short Y _n from D-D fusion reactions in a plasma focus (PF) enhance both the D⁺-ion acceleration to energy values E _d>1-8 MeV and the ion confinement in the pinch region. Nuclear activation of C and N in the (doped) filling gas of the discharge chamber and of solid targets of C and BN bombarded by the ion beam in the direction of the electrode axis (0°) confirms earlier determination of the energy spectrum of the trapped ions (dφ_t/dE∝φ_0tE ^-m) and of the ejected beam (dφ_b/dE∝φ_0bE _d^-m, m=2.5±0.5 for 0.1 MeV≲E≲3 MeV). A Thomson (parabola) spectrometer with nanosecond time resolution determines the time of emission t( E) of the beam at 0°. Ion acceleration and trapping occur within the small (filamentary) elements of the magnetic fine structure of the pinch, which can be dispersed on a relatively large confinement volume after the pinch disintegration. It has been found that φ_t/φ_b≳10-10³ for E_d≳1 MeV, depending on Y_n     

Bound water fractions from quasi-elastic neutron scattering

Quasi-elastic neutron scattering measurements of AlCl₃ aqueous solution are analysed to derived the ratio of bound to solvent water molecules. We find that the ratio depends on the nature of the binding of the water molecules in the hydration shell and in the solvent. If the details of the binding are not known it is shown that such measurements must be carried out at small neutron wavevector transfers to obtain quantitative results.     

Restricted recourse strategies for bounding the expected network recourse function

This paper presents bounds for the expected recourse function for stochastic programs with network recourse. Cyclic recourse, a concept introduced by Wallace [18], allows the approximation of the recourse problem by restricting the optimal flows on a set of cycles and by augmenting the original network to induce separability. We introduce a new procedure that uses again a set of cycles but does not approximate the problem; instead it solves it heuristically without altering the original network or requiring separability. The method produces tighter bounds and is computationally feasible for large networks. Numerical experiments with selected networks illustrate the effectiveness of the approach.