Effects of Transverse Magnetic Field with Different Alternating Currents on Heat Flux Density Distributions of Plasma Arc
An external transverse-alternating magnetic field with sinusoidal and triangular alternating currents was applied to a combined plasma arc to create a plasma arc for expanding the cross section of arc column and flatting the distributions of arc temperature. Two mathematical models were developed to describe the heat flux density distributions of the combined plasma arc driven by a transverse-alternating magnetic field with sinusoidal and triangular alternating currents. The behavior of plasma arc under the external transverse-alternating magnetic field imposed perpendicular to the plasma current was discussed theoretically and experimentally by changing various parameters such as working gas flux, arc current, magnetic flux density including its wave form and the standoff from the nozzle to the workpiece. The analytical results show that it is feasible to adjust the shape and heat flux density of the combined plasma arc by the transverse- alternating magnetic field, which expands the region of combined plasma arc thermal treatment and uniforms the heat flux density upon the workpiece. Changing the waveform of the alternating current can also control the heat flux density distribution. As well as, calculated heat flux density distributions of combined plasma arc driven by the external transverse-alternating magnetic field show a good agreement with experimental data. The magnetic field with triangular alternating current can flat the heat flux density distribution on the anode rather than sinusoidal one. This approach to flat the heat flux density distribution on the anode surface will give an effective controllability to the combined plasma arc application.
Radial distribution of the heat-flux density in the bearing spot of a plasma cutting arc
The results are reported from an experimental study of the laws governing the variation of the heat-flux density in the bearing spot of a cutting arc as a function of the arc polarity as well as the design and operating parameters of the plasmatron.
What is an archival education?1
This article introduces the approach to Master's level archival education adopted at the University of Manitoba. It is intended as a contribution to the recently renewed discussion of graduate archival education in the UK and Ireland. The author maintains that recent major developments in the accessibility, uses, and very conception of archives powerfully underscore the distinctiveness of archival work. These developments foster continued collaboration between archivists and those in related professions such as records management, but, more importantly, reinforce their longstanding distinctiveness. The article discusses why and how the University of Manitoba has responded to the increasingly complex challenges facing archivists and archival educators in this evolving setting with an archival, conceptual, historical, and research-oriented curriculum.