Parametric study of the flow and temperature fields in an inductively coupled r.f. plasma torch

A theoretical investigation of the effect of different parameters on the flow and the temperature fields in a radiofrequency inductively coupled plasma is carried out. The parameters studied are: central injection gas flow rate, total gas flow rate, input power, and the type of plasma gas. The results obtained for argon and nitrogen plasmas at atmospheric pressure indicate that the flow and the temperature fields in the coil region, as well as the heat flux to the wall of the plasma confinement tube, are considerably altered by the changes in the torch operating conditions.     

Effect of the Coil Angle in an Inductively Coupled Plasma Torch: A Novel Two-Dimensional Model

A two-dimensional model has been developed for the calculation of the electromagnetic (EM) fields generated by spiral coil currents, in order to obtain a better representation of the actual configuration used in a typical inductively coupled plasma (ICP) torch. In order to obtain the EM fields in a two-dimensional model, the change of EM field in tangential direction is neglected and the coil is assumed to be a concentric cylinder. In order to justify our assumption, the EM, flow and temperature fields resulting from five-ring coil and concentric cylinder coil are compared and the results are almost the same except for the EM field in the vicinity of the coil. In the case of the spiral coil, the coil current is inclined with respect to the horizontal plane. Therefore current in the cylinder coil is assumed to have the same inclined angle, which is split into tangential and axial components. The axial electric field and hence an axial current in plasma is induced by the axial component of the spiral coil current. Charge density is accumulated in the plasma, since the axial current cannot form a loop. In order to obtain the EM field and the charge distribution in the plasma generated by the spiral coil, the equations of axial vector potential and electrostatic potential have been derived. Due to the swirling Lorentz force (J_z×B_r) an axisymmetrical swirling fluid model is used to simulate the plasma flow in an axisymetrical configuration. With an inclined angle of the coil current being 3.7° and the frequency being 3 MHz, computational results show that the swirling Lorentz force causes plasma swirling with a maximum speed of 3.41 m/s near the plasma center when the injected sheath gas and central gas are not swirling. In these conditions, the real and imaginary parts of the maximum electrostatic potential are 0.95 V and 1.66 V, respectively. When the electrostatic field is neglected, the swirling velocity of the plasma is 3.95 m/s.     

Automated analysis of geosmin, 2-methyl-isoborneol, 2-isopropyl-3-methoxypyrazine, 2-isobutyl-3-methoxypyrazine and 2,4,6-trichloroanisole in water by SPME-GC-ITDMS/MS

This paper describes a method of determining the following compounds in water characterised by complex matrices (raw waters and drinking waters): geosmin, 2-methylisoborneol (2-MIB), 2-isobutyl-3-methoxypyrazine (IBM), 2-isopropyl-3-methoxypyrazine (IPM) and 2,4,6-trichloroanisole (TCA). The method is carried out using headspace solid-phase microextraction (HS-SPME) combined with gas chromatography (GC) and ion trap mass spectrometry (ITMS). Several parameters of extraction and desorption were optimised through the use of a Combi PAL autosampler to automate various tasks (temperature extraction, extraction time, stir speed). Quantities of NaCl and the liquid volume/total volume ratio were also optimised. Double fragmentation (tandem MS/MS) was optimised on the target compounds. The method resulted in good linearity obtained for concentrations of 1 to 100?ng?L^?1 and provided detection limits of approximately below 1?ng?L^?1. Good precision (1–8%) was obtained. This method was successfully applied to the analysis of earthy and musty odours in municipal raw source waters with high concentrations of natural organic matter and in the corresponding treated waters. This is the first time MS/MS has been used to analyse odorous compounds in waters destined for human consumption. In addition, the method as developed is simple to use and lends itself to easy interpretation of chromatograms.     

Description of the response of a fiber optic velocity sensor applied to capillary gas chromatography

This paper explores the response of a novel fiber optics sensor allowing real-time determination of the migration rate of vapor zones in capillary gas chromatography. The sensitivity is related to the gradient of the vapor zone distribution in the capillary and it is highest when vapor zones show steep variations in concentration. The expected linearity between the height of the velocity peaks and the response of a thermal conductivity detector is demonstrated experimentally. The sensor can be used to infer an approximate value of the analyte diffusion coefficient from the time response. Finally, the time evolution of the envelope of the optical signal is explained with experimental evidences.     

On the genus of five- and six-regular graphs

This paper shows how to construct infinitely many regular graphs of degrees five and six having given genus γ > 0, which settles favorably Conjecture 1 stated by T. W. Tucker. Tucker has shown that there are infinitely many regular graphs of degrees four and three of arbitrary given genus (Theorem 1). He also proved that the number of regular graphs of degree greater than six embeddable in a given surface is finite (Corollary to Proposition 1). The case of the regular graphs of degrees six and five was left unanswered (Conjecture 1). This paper also shows a new way of constructing infinitely many regular graphs of degrees three and four of arbitrary genus γ > 0.     

Influence of particle size and mineral phase in the analysis of iron ore slurries by Laser-Induced Breakdown Spectroscopy

Laser-Induced Breakdown Spectroscopy (LIBS) was applied to the analysis of iron ore concentrates. The objective was to determine the influence of particle size and mineral phase on the LIBS signal. The LIBS spectra of hematite and magnetite ore concentrates were qualitatively indistinguishable from each other but magnetite yielded systematically less than hematite. This behavior could be set into an empirical equation to correct the iron peak intensities according to the level of magnetite in the analyzed sample. Similarly, an increase of the LIBS signal was observed as the particle size of the ore samples decreased. Again, an equation could be written down to correct the intensity of either iron or silicon in response to a variation of the average particle size of the ore concentrate. Using these corrections, proper response of the silicon signal against the concentration of silica in the samples was restored. The observed dependence of the strength of the iron signal upon the mineral phase is attributed to oxidation of magnetite into hematite.     

Focal points and bargaining

This is a contribution to the growing experimental literature on how trial-and-error adjustment processes can establish a convention for coordination on an equilibrium in a game. A simple bargaining game introduced by Nash is used for this purpose. Subjects are conditioned in different treatments to use four different bargaining solutions. The stability of the conditioning is then studied as the bargaining game is played over an extended period. The data obtained is unusually sharp. In the long run, the median subject behaves as though optimizing often down to a fraction of a penny. The results are therefore not supportive of the view that strategic considerations in such situations can be neglected in favor of a study of fairness norms. Indeed, the equilibrium actually achieved in a session turns out to be a very good predictor of what the median subject says is fair in the game after play is over.We are grateful to the National Science Foundation for funding the experiments reported in this paper under Grant NSF-SES-8821521. We also gratefully acknowledge funding from the University of Michigan to set up the Michigan Economics Laboratory, where the experiments were conducted. We would also like to thank Richard Stallman and the Free Software Foundation for developing EMACS, Luke Tierney for developing LISPSTAT, and Hal Varian for showing us how to use both.