Fourier space for accurate ab initio RHF band structure calculations on chainlike systems

Minimal basis-set (STO-3G) direct and Fourier space restricted Hartree-Fock (RHF) calculations on the infinite regular (metallic) and alternating chains of lithium molecules, (-Li₂-)_x, are reported to illustrate two advantages of the Fourier representation method: accurate calculation of all lattice summations and faithful reproduction of the genuine features of the RHF approach for metallic cases. © 1996 John Wiley & Sons, Inc.     

A basic property of dye lasers: Spectral evolution

We have derived an analytical equation which is found to be useful in understanding injection locking, progressive narrowing, enhancement of intracavity absorption and amplification, dual-wavelength dye lasers, broad band shift and coupled cavities. The basic property of the dye laser emission, i.e. the spectral evolution, is described without explicit reference to the molecular populations and the excitation time shape. The concept of spectral evolution is expressed in terms of new parameters such as the evolution length of the amplifier and the evolution time of the oscillator.     

Remote sensing of high temperature H2O-CO2-CO mixture with a correlated k-distribution fictitious gas method and the single-mixture gas assumption

Infrared spectra of high temperature H₂O-CO₂-CO mixtures are calculated using narrow band models in order to simulate hot jet signature at long distance. The correlated k-distribution with fictitious gas (CKFG) approach generally gives accurate data in such situations (especially for long atmospheric paths) but results in long computation time in cases involving mixtures of gases. This time may be reduced if the mixture is treated as a single gas (single-mixture gas assumption, SMG). Thus the lines of the single-mixture gas are assigned to the fictitious gases. In this study, the accuracy of two narrow band models is evaluated. The first narrow band model considers one single-mixture gas and no fictitious gas (CK-SMG) whereas the second model accounts for one single-mixture gas and three fictitious gases (CKFG-SMG). Both narrow band models are compared with reference spectra calculated with a line-by-line (LBL) approach. As expected, the narrow band accuracy is improved by the fictitious gas (FG) assumption particularly when long atmospheric paths are involved. Concerning the SMG assumption, it may lead to an underestimation of about 10% depending on the variation of the gas mixture composition ratio. Nevertheless, in most of realistic situations the SMG assumption results in negligible errors and may be used for remote sensing of plume signature.     

Influence of the Electromagnetic Forces on Momentum and Heat Transfer in a 3-Phase ac Plasma Reactor

A new 3-phase ac plasma reactor has been developed within the framework of research on hydrocarbon cracking for the production of carbon black and hydrogen. ^(1,2) One of the main characteristics of the system is related to the 3-phase, 50 Hz ac current plasma generator which induces a very particular arc motion affecting the heat and mass transfer inside the reactor. In a first step, the general flow inside the reactor in the absence of hydrocarbon injection has been studied. A simplified approach to characterize the heat and mass transfer inside the reactor is presented in this paper. The arc zone analysis is carried out simultaneously by a theoretical analysis of the electromagnetic forces and by an ultrahigh-speed cine-camera analysis. The flow in the reactor is modeled with a CFD commercial code. Results are compared with experimental temperature measurements.     

Temperature Distribution in a Pilot Plasma Tundish: Comparison Between Plasma Torch and Graphite Electrode Systems

Arc, bath, and refractory wall temperatures are measured in a pilot transferred-arc plasma furnace by atomic emission spectroscopy (AES) and multiwavelength pyrometry. Argon plasma torch and graphite electrode with nitrogen as plasma gas are both examined and compared using the steel bath as anode. With argon, a two-slope characteristic curve is measured for arc temperature, which ranges from 9000 to 25,000 K. Another trend is observed with nitrogen for temperatures in the range 8000–12,000 K. In this latter case, the bath temperature is very sensitive to arc length: more than 100 K increase results in arc length rise from 50 to 150 mm. Experimental data shows the variation of heat transfer efficiency between the two configurations, which is supported by results about surface emissivity in the spectral domain 1–15 m.     

Separation of Gold from Sulfide Using a Plasma Arc Fuming Process

Transferred-arc plasma treatment of iron sulfides containing gold is examined from both thermodynamic and experimental points of view. Three cases are analyzed: argon plasma with sulfide, argon plasma with a carbon–sulfide mixture, and argon–methane plasma with sulfide. The carboreduction of the materials appears to be well adapted for gold separation by fuming, but experimentally the process is limited by the poor mixing of graphite with molten material. The reduction with a CH₄ (10%) plasma is a proved alternative to the aforementioned process. A gold extraction efficiency of 90% is achieved for batch smelting operations.     

Rate equations for dye lasers: Comments on the spiking phenomenon

The rate equations generally used for dye lasers necessitate a number of assumptions. The assumptions are tested in the case of pulsed dye oscillator. It is shown that the assumptions break down during the laser onset. The main result is this: the spikes computed for the excited state population and for laser photon flux cannot be given a physical meaning and cannot be used to explain the properties of pulsed dye lasers.     

Study of stimulated emission in attenuating and amplifying dye solutions

Steady state transmission measurements are made in flashpumped attenuating or amplifying solutions of fluorescein, 2, 7 dichlorofluorescein and rhodamine 6G in aerated ethanol. Stimulated emission and transient absorption are studied by varying the input signal intensity. It is shown that the presence of stimulated emission can be demonstrated in attenuating solutions also. Results are interpreted with the aid of the steady-state gain theory.