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.     

Mechanism of electrodimerization of retinal and cinnamaldehyde

Electrochemical reduction of either cinnamaldehyde or retinal in acetonitrile containing 0.5 M. TBAP and water or phenol leads to a mixture of dimeric products. However, electroreduction of either of these aldehydes in the presence of the carbon acid, diethyl malonate, leads to increased yield of pinacol formation. The mechanism of these electrodimerization reactions has been discerned using cyclic voltammetry-variations in peak potential as a function of scan rate, proton donor concentration and concentration of aldehyde have been compared to published diagnostic criteria. Retinal and cinnamaldehyde form dimeric products in a radical-radical coupling pathway. The major mechanistic feature that correlates with product distribution is the association (solvation) of oxygen acids, phenol and water with the radical anion. In contrast, diethyl malonate reacts with the radical anion of either cinnamaldehyde or retinal by a direct proton transfer.     

Characterization and optimization of HPIC for on-line preconcentration of trace metals with detection by ICP-mass spectrometry

The objective of this study was to investigate the feasibility of using a commercially available cation-exchange column for trace metal preconcentration. In addition, the advantages of interfacing the column to a highly sensitive element-selective detector were examined. A high-performance ion-chromatograph (HPIC) with a high-pressure pump and valve system was used to aid loading and delivery of the mobile phase. An inductively coupled plasma mass spectrometer combination (ICP-MS) was used as a detection device, with interfacing by means of a small diameter liquid-transport tube. The performance of the HPIC/ICP-MS combination was optimized by varying the concentration and flow-rate of two eluents (nitric acid and hydrochloric acid). The effects of varying the sample pH were assessed and the column capacity was determined by "breakthrough" tests. The elements copper, cadmium, mercury and lead were studied; the detection capability was dependent upon the sample volume loaded onto the column. The accuracy of the method was assessed by analysis of an "in house" reference standard.     

Incident-energy dependence of 3p electron energy-loss spectra of nickel

The intensities of two features in the 3p electron energy-loss spectrum of nickel, a dip prior to the threshold and a satellite ～ 12 eV above the threshold, are observed to systematically decrease as the incident electron energy is lowered from 1000 to 150 eV. These intensity changes indicate a dependence of the matrix elements for each excitation on momentum transfer as the incident energy is decreased, in part through changes in the strength of Fano interference near threshold.