Standstill Conditions Research Articles

Bathymetric change during Early Cretaceous intracratonic marine transgression across the northeastern Eromanga Basin, Australia

Bathymetric change is investigated within the transgressive phase of an extensive Early Cretaceous (Aptian-Albian) marine flooding of the Australian continent. Lithofacies and biofacies associations, found in nine outcrop sections and four continuously cored bore sections in the northeastern Eromanga Basin, are used to reconstruct depositional environments and to determine palaeobathymetry. Shoreface (c . 0–2m water depth), transitional (c . <10m), upper offshore (c . <50m), and lower offshore (c . 50–100m) facies are distinguished. Curves showing bathymetric changes are constructed for each stratigraphic section, and are placed in a time framework by biozones and compared across the region. Three depositional cycles are tentatively recognized during the transgressive phase. The first depositional cycle includes the Gilbert River Formation and the lower part of the Doncaster Member, and ranged from early Aptian (or late Barremian) to within the late Aptian. During maximum flooding, water depth was greatest in the southwest of the study area. Most sediment accumulation occurred under standstill conditions, and a fall in relative sea level occurred at the end of the cycle in all areas within the study region. The second cycle, during the later part of the late Aptian, includes the upper Doncaster Member and the Jones Valley Member. Most sediment accumulation occurred under fluctuating water depths, but a fall in relative sea level ends the cycle in all areas. The third depositional cycle includes the Ranmoor Member, and was represented by a significant late Early Albian transgressive pulse, recognized in age-equivalent formations from widely separated basins in Australia. At maximum flooding, the sea-floor was deepest in the northeast and shallowest in the southwest of the study area. The reversal in the direction of the bathymetric gradient between cycle 1 and cycle 3 in the region is probably related to tectonism along the eastern Australian margin. The apparent lack of correspondence between the Australian Albian record and the global sea-level curve suggests that continental-wide tectonism was an important influence in determining Australian sea levels during this time.

Analysis of a Half-Cycle-Response Magnetic Amplifier with Resistance or A-C Servomotor Load

Half-cycle-response magnetic amplifiers suitable for controlling 2-phase servomotors have been studied by many authors. In particular, Geyger and Kallander suggested a full-wave push-pull circuit which resulted in superposing the fundamental frequency voltage on unidirectional voltage across the control winding, helping to stabilize those servomotors which have a low ratio of effective viscous friction to inertia. This paper considers a modification of these circuits for both resistance and motor loading. The modification results in an improved amplification factor and the motor loaded circuit is analyzed for both stand-still and running conditions, taking into account the generated voltage of the motor and variable extinction angle. Analysis is then verified by experimental data.

Small Two-Phase Induction Motor

A SPECIALLY small motor, developed in the Admiralty Compass Department for use in applying torques for controlling the precession of the gyros of the Admiralty Gy Transmission Unit Mk. II, has now been described. The motor is totally enclosed and has an alluminium alloy shell and end shield. The rotor is mounted in ball bearings and the weight of the complete motor is 5½ oz. It is suitable for use in typical countries. The stator core consists of radiometal laminations 0.010 in. thick. The stator windings are of the double-layer concentrated type, the individual coils being preformed and inserted in the 12-slot core to form a 2-phase 6-pole system. The squirrel-cage rotor is formed by copper strips secured in narrow slots in the laminations ; the twenty-one slots are skewed by one slot pitch to eliminate cogging. The shaft is of stainless steel. The deep narrow rotor bars and open-ended slots assist in providing a relatively flat speed-torque characteristic, since at high slip frequencies the current in the bars is concentrated towards the outer edge giving effectively greater rotor resistance at low rotor speeds. As a torque motor, the machine was required to operate on 333 c./s. and works continuously under standstill conditions, with a temperature rise at 20 volts/phase of about 30° C. As a follow-up motor, at a frequency of 400 c./s., one phase is constantly energized, while the second phase is supplied from the output of a valve amplifier in proportion to the misalignment of following. Under these conditions a fixed phase voltage of 30 volts gives a temperature rise of about 30° C. in normal operation.