Noble Metals

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Noble Metals

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Electron shell contributions to gamma-ray spectra of positron annihilation in noble gases

Gamma-ray positron annihilation spectra of the noble gases are simulated using computational chemistry tools for the bound electron wavefunctions and plane-wave approximation for the low-energy positron. The present annihilation line shapes, i.e. the full width at half maximum, Delta epsilon, of the gamma-ray annihilation spectra for He and Ar (valence) agree well with available independent atomic calculations using a different algorithm. For other noble gases they achieve moderate agreement with the experimental measurements. It is found that the contributions of various atomic electron shells to the spectra depend significantly on their principal quantum number n and orbital angular momentum quantum number l. The present study further reveals that the outermost ns electrons of the noble gases exhibit spectral line shapes in close agreement with those measured, indicating (as expected) that the measurements are not due to a simple sum over the momentum densities for all atomic electrons. The robust nature of the present approach makes it possible for us to proceed to more complex molecular systems using the tools of modern computational chemistry.

Positronium formation from valence and inner shells in noble gas atoms

When recent experimental positronium (Ps) formation cross sections in noble gases have been compared with the most up-to date theoretical studies, the agreement is qualitative, but not quantitative. In this paper we re-examine this process and show that at low energies Ps formation must be treated non-perturbatively. We also look at Ps formation with inner shell electrons.

Harmonic generation by noble-gas atoms in the near-IR regime using ab initio time-dependent R-matrix theory

We demonstrate the capability of ab initio time-dependent R-matrix theory to obtain accurate harmonic generation spectra of noble-gas atoms at near-IR wavelengths between 1200 and 1800 nm and peak intensities up to 1.8 × 10^(14) W/cm^(2). To accommodate the excursion length of the ejected electron, we use an angular-momentum expansion up to Lmax=279. The harmonic spectra show evidence of atomic structure through the presence of a Cooper minimum in harmonic generation for Kr, and of multielectron interaction through the giant resonance for Xe. The theoretical spectra agree well with those obtained experimentally.

Positron scattering and annihilation on noble-gas atoms

Positron scattering and annihilation on noble-gas atoms is studied ab initio using many-body theory methods for positron energies below the positronium formation threshold. We show that in this energy range, the many-body theory yields accurate numerical results and provides a near-complete understanding of the positron–noble-gas atom system. It accounts for positron-atom and electron-positron correlations, including the polarization of the atom by the positron and the nonperturbative effect of virtual positronium formation. These correlations have a large influence on the scattering dynamics and result in a strong enhancement of the annihilation rates compared to the independent-particle mean-field description. Computed elastic scattering cross sections are found to be in good agreement with recent experimental results and Kohn variational and convergent close-coupling calculations. The calculated values of the annihilation rate parameter Zeff (effective number of electrons participating in annihilation) rise steeply along the sequence of noble-gas atoms due to the increasing strength of the correlation effects, and agree well with experimental data.

Noble energy oil & Gas

Equity research report

Livret élégant et consolable autant que spirituel et propre contre la malice de ce temps, à très bon droit appellé la Règle de vie spirituelle, ou le Paradis de l'âme fidèle... par Loys de Blois, et fait françois, par noble homme Charles de Sainsimon, seigneur de Saudricourt avecq deux épitres... par F. G. Dupuyherbault

Comprend : Deux épistre

« Li Abregemens de tres noble homme VEGECE des establissemens apartenans à chevalerie », traduction faite en 1284 pour Jean de Brienne Ier, comte d'Eu, par « JEHAN DE MEUN ».

Commençant par : « Li ancien ont esté coustumier de metre en escript les choses qu'ils penssoient qui fussent bonnes à savoir... » et finissant par : «... car li usages et li hanteis de chascun jour trueve plus de l'art en ces choses que l'ancienne doctrine ne nous en a moustré » .

« L'Abregemens de noble homme VEGECE FLAVE », ou « Des establissemens appartenans à chevalerie », traduction [de JEAN DE MEUNG].

Commençant par : « Les anciens ont esté coustumiers de meitre en escript les choses qu'ilz pensoient qui fussent bonnes à savoir... » et finissant par «... car li usaiges et le hanteis de chascun jour trueuve plus d'art en ces choses que l'ancienne doctrine ne nous en a monstré » .