Establishement of the magnetic flux density standard in the range 100 µT to 1000 µT
The magnetic flux density standard in the range 100 µT to 1000 µT has been established using a standard Helmholtz coil. The ambient magnetic field including earth's magnetic field components inside the room and other noises has been compensated to a level of the order of 100 nT. A circular triaxial Helmholtz coil pair of size nearly 800 mm has been used for compensating the ambient magnetic field. The standard Helmholtz coil of size 300 mm has been placed in the geometrical centre of the triaxial Helmholtz coil pair. The magnetic flux density has been measured using triaxial and single axis fluxgate magnetometers. The coil constant of the standard Helmholtz coil has been found to be 850.6808 ± 0.0036804 µT/A, which is in good agreement with the manufacture's specification viz, 850 µT/A, with an uncertainty of < ± 0.5 %.
Intercomparison of magnetic flux density by means of field coil transfer standard
The coil constant k/sub 0/-i.e. the quotient of magnetic flux density in the coil centre over the coil current-of a Garrett type field coil has been determined in units as maintained by various standard laboratories. Most of the laboratories have also measured the coil constant k(f) as function of frequency up to f=15 kHz.
Persistence and Change in Minkowski Spacetime
There are famously two main metaphysics of persistence, namely three and four-dimensionalism. Both yield a particular solution to the so called puzzle of change. I argue that typical three-dimensionalist solutions to the puzzle face insurmountable difficulties even in the simplest relativistic setting, that of Minkowski spacetime