Determination of oscillator strengths from the self-absorption of resonance radiation in rare gases

A method is presented which determines directly oscillator strengths for rare gas atoms from the selfabsorption of resonance radiation. It is shown that under suitable experimental conditions the oscillator strength can be derived from the selfabsorption by a simple formalism. Some problems concerning this method are treated in detail, such as reemission of absorbed radiation and the presence of more than one isotope. A value of 0.262±0.018 was obtained for the oscillator strength of the He(1¹S→2¹P) resonance transition. Preliminary data were also obtained for some resonance transitions in neon, using neon gas with a natural abundance of the isotopes.     

Oscillations due to two-electron exchange during He-Ne collisions

Ne (-)(1s(2)2s(2)2p(5)3s(2)) and He (-)(1s2s(2)) autodetachment peaks in electron spectra arising from He-Ne collisions at energies ranging from 350 eV to 6 keV have been measured. The areas of these two peaks are found to oscillate approximately in antiphase, with a constant wavelength, on a (velocity)(-1) scale. It is shown that this behavior can be explained by the "quasiresonance" situation for the separating particles in the channels Ne (-)-He (+) and He (-)-Ne (+). This explanation implies that the oscillations can be understood as being due to the simultaneous "hopping" of two electrons.     

MRI hippocampal volume and neuropsychology in epilepsy surgery

A review is provided of recent findings on relationships between neurocognitive test data and magnetic resonance imaging (MRI)-determined hippocampal volumes in nonlesional temporal lobectomy patients. The difference between the right and left hippocampal volumes is correlated with postoperative verbal memory in left temporal lobectomy patients who do not have lesional pathology. MRI hippocampal volume data are not associated with measures of executive functioning or naming. Sex differences have been found for verbal memory outcome as women have better verbal memory following left temporal lobectomy. Sex differences have also been found in the relationships between verbal and visual memory, and hippocampal volume data. The systematic combination of MRI-acquired morphological data and neuropsychological test data may further our understanding of neurocognitive function, and provide clinically useful data for counseling epilepsy surgery patients. The current data are promising with regard to prediction of memory outcome following temporal lobectomy, but they do not yet allow for prediction of specific individual patient outcomes. Rather, the currently available data support counseling patients based on the memory outcome of others with similar characteristics.     

Quasi-Norm interpolation error estimates for the piecewise linear finite element approximation of p-Laplacian problems

Summary. In this work, new interpolation error estimates have been derived for some well-known interpolators in the quasi-norms. The estimates are found to be essential to obtain the optimal a priori error bounds under the weakened regularity conditions for the piecewise linear finite element approximation of a class of degenerate equations. In particular, by using these estimates, we can close the existing gap between the regularity required for deriving the optimal error bounds and the regularity achievable for the smooth data for the 2-d and 3-d p-Laplacian.Mathematics Subject Classification (1991): 65N30     

Determination of oscillator strengths from the self-absorption of resonance radiation in rare gases—II. Neon and argon

A previously developed method, based on the self-absorption of resonance radiation, is used to derive oscillator strengths for fourteen resonance transitions of neon and argon. Electron beam excitation of the atoms is used to produce the resonance radiation, which is partly absorbed in the gas between the beam and the spectrometer. A v.u.v. spectrometer is employed to record the radiation intensities as a function of gas pressure. Oscillator strengths are derived from the measurements by using a simple formalism. The influence of recoil effects (as a consequence of the excitation process) on the shape of the spectral emission lines and thereby on the transmission is checked by detailed numerical calculations. Special attention is paid to the determination of the quantities relevant in absorption measurements, i.e. the temperature, the absorption length and the number density of the atoms. The oscillator strengths obtained are compared with results from other experiments of various types (particularly forward inelastic electron scattering, for which on the whole good agreement with the present results exists) and from theoretical calculations.     

S,O-ligand-promoted palladium-catalyzed C–H olefination of arenes with allylic substrates

An efficient catalytic system for the C–H olefination of arenes with different allylic substrates is reported. The catalytic system is based on Pd(OAc)₂ and a readily accessible bidentate S,O-ligand. The methodology shows high activity with a wide range of arenes, including bulky and, electron-rich and -poor arenes. The applicability of this catalyst is demonstrated in the late-stage functionalization of the complex molecule O-methylestrone.