2,482 research outputs found
Quantum whistling in superfluid 4He
Fundamental considerations predict that macroscopic quantum systems such as
superfluids and the electrons in superconductors will exhibit oscillatory
motion when pushed through a small constriction. Here we report the observation
of these oscillations between two reservoirs of superfluid 4He partitioned by
an array of nanometer-sized apertures. They obey the Josephson frequency
equation and are coherent amongst all the apertures. This discovery at the
relatively high temperature of 2K (2000 times higher than related phenomena in
3He) may pave the way for a new class of practical rotation sensors of
unprecedented precision.Comment: 6 pages, 3 figures, to be published in Natur
The Analogous Development of the Fair Trade and Tax Limitation Movements
The Fair Trade Act, or resale price maintenance, movement began in 1913. The movement to limit federal income, gift, and estate tax rates to twenty-five per cent in peacetime commenced in 1939. The fair trade act movement was spearheaded by the American Fair Trade League. The federal income, gift, and estate tax rate limitation movement is spearheaded by the Western Tax Council
Brushless DC motor control system responsive to control signals generated by a computer or the like
A control system for a brushless DC motor responsive to digital control signals is disclosed. The motor includes a multiphase wound stator and a permanent magnet rotor. The rotor is arranged so that each phase winding, when energized from a DC source, will drive the rotor through a predetermined angular position or step. A commutation signal generator responsive to the shaft position provides a commutation signal for each winding. A programmable control signal generator such as a computer or microprocessor produces individual digital control signals for each phase winding. The control signals and commutation signals associated with each winding are applied to an AND gate for that phase winding. Each gate controls a switch connected in series with the associated phase winding and the DC source so that each phase winding is energized only when the commutation signal and the control signal associated with that phase winding are present. The motor shaft may be advanced one step at a time to a desired position by applying a predetermined number of control signals in the proper sequence to the AND gates and the torque generated by the motor may be regulated by applying a separate control signal to each AND gate which is pulse width modulated to control the total time that each switch connects its associated winding to the DC source during each commutation period
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