Electrical discharges, measurement

Static charge generation causes an ignition hazard only if the accumulated charges create an electric field sufficient to produce an electrical discharge in a flammable atmosphere. In most processes, this means that the electric field intensity at some location must reach the breakdown strength of air (nominally 3 X lO " V/m). The objective of static-control measures is to ensure that electric field intensities cannot reach this value. 

This is a transient discrete electric discharge which takes place between two conductors which are at different potentials, bridging the gap in the form of a single ionization channel (Plate 4). Based on light emission measurements of sparks with symmetrical electrode geometry, the energy is dissipated approximately uniformly along the channel. This is in contrast with asym-... 

The most widespread modem use of mass spectrometers is to identify chemical substances. When a molecule is placed in a mass spectrometer, the electrical discharge strips away one of its electrons. This so-called parent ion has virtually the same mass as the neutral molecule. If the mass of the parent ion is measured with high enough accuracy, the data can provide the molecular formula of the substance. 

The simplest analytical method is direct measurement of arsenic in volatile methylated arsenicals by atomic absorption [ 11 ]. A slightly more complicated system, but one that permits differentiation of the various forms of arsenic, uses reduction of the arsenic compounds to their respective arsines by treatment with sodium borohydride. The arsines are collected in a cold trap (liquid nitrogen), then vaporised separately by slow warming, and the arsenic is measured by monitoring the intensity of an arsenic spectral line, as produced by a direct current electrical discharge [1,12,13]. Essentially the same method was proposed by Talmi and Bostick [10] except that they collected the arsines in cold toluene (-5 °C), separated them on a gas chromatography column, and used a mass spectrometer as the detector. Their method had a sensitivity of 0.25 xg/l for water samples. 

In practice, moderate heating of the emitter at constant current serves to reduce adsorption to its surface during FI measurements. Heating at a constant rate (1-8 mA min ) is frequently employed to enforce desorption of analytes from the emitter in FD-MS. To avoid electric discharges resulting from too massive ion de-... 

Sulfates are precipitated as BaS04, and then reduced with carbon at 1,000°C to produce CO2 and CO. The CO is either measured directly or converted to CO2 by electrical discharge between platinum electrodes (LonginelU and Craig 1967). Total pyrolysis by continuous flow methods has made the analysis of sulfate oxygen more precise and less time-consuming than the off-line methods. Bao and Thiemens (2000) have used a C02-laser fluorination system to liberate oxygen from barium sulfate. 

The antihypertensive activity of clonidine can be ascribed solely to a decrease in the sympathetic activity transmitted from the brain to the peripheral vasculature. After clonidine administration, direct measurements of sympathetic nerve activity show that electrical discharge is reduced in a number of sympathetic nerves, including the cardiac, splanchnic, and cervical nerves. 

The essential advantage of shock tubes over electric discharge devices is the capability of producing a homogeneous gas sample (HGS) with enthalpy and pressure which can be dependably calculated from the measured shock velocity and the conservation laws. 

Observing relaxation. Kinetic measurements over periods of tens of microseconds or less can be made by rapidly inducing a small displacement from the equilibrium position of a reaction (or series of reactions) and observing the rate of return (relaxation) of the system to equilibrium. Best known is the temperature jump method devised by Eigen and associates. Over a period of about 10-6 s a potential difference of -100 kV is applied across the experimental solution. A rapid electrical discharge from a bank of condensers passes... 

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