Varian Associates

About: Varian Associates is a based out in . It is known for research contribution in the topics: Beam (structure) & Amplifier. The organization has 2160 authors who have published 2591 publications receiving 46002 citations.

Ball-type vacuum valve for leak detection apparatus

Abstract: In a system for leak detection having many valves, it is desirable to have high vacuum valves operated by solenoids at opposite ends of a diffusion pump in order to isolate the diffusion pump during powr failure or during an intentional shutdown. A valve having a hard spherical ball fitting a vacuum seal and having a spring means to bias the ball in a closed position will close during a power failure. A bell-shaped actuator connected to a solenoid can be used to open the valve with built-in mechanical advantage. A circuit means can be used to supply high starting voltage to the solenoid and then lower voltage to hold the valve open.

The role of intruder dislocations in modifying the misfit dislocation structures and growth kinetics of precipitate plates

Abstract: Intruder dislocations formed at θ’ and η plates in Al-4 pet Cu and Al-0.2 pct Au alloys respectively by a small plastic strain partially compensate the misfit by single arrays ; the Burgers vector of the dislocations has a component normal to the plate interfaces. On subsequently aging such deformed microstructures, little change takes place in θ’ where the misfit is low. In η, on the other hand, the large misfit is sufficient to nucleate other compensatory arrays which interact with the intruder dislocations to form the lowest energy dislocation network and to annihilate the Burgers vector component directed normal to the plates. The lengthening kinetics of θ’ plates are unaffected by the intruder dislocations, but the thickening kinetics are briefly accelerated, probably by means of vacancy-enhanced diffusion associated with the plastic deformation. The thickening enhancement later falls off as the defects are annealed. In Al-Au, an interesting morphological instability develops and leads to the formation of elongated plates. These we believe are caused by a mechanism of sympathetic nucleation.

Thermal barrier for variable temperature nmr

Abstract: An NMR system for obtaining high resolution spectroscopic measurements at a selected temperature includes gradient correcting means (40) disposed in proximity to an NMR probe (32), for imposing desired gradients on the volume occupied by the sample (35) within the probe (32). A heat exchange gas is impelled through a heat exchanger (33) and then surrounds the sample (35) to bring the sample (35) to the desired temperature. A thermal barrier (72), innocuous to RF excitation and of relatively low magnetic susceptibility protects the gradient correcting means (40) from drift due to heat exchange with the heat exchanging gas.

HTS coils for high resolution nuclear magnetic resonance spectroscopy

Abstract: Low noise detectors offer improved performance in low-signal-level nuclear-magnetic-resonance (NMR) spectroscopy and imaging (MRI) applications. High temperature superconducting coils, fabricated with YBa2Cu3O7-δ thin films, were developed for high resolution NMR spectroscopy. Quality factors exceeding 104 have been achieved in a 9.4 T magnet. Current handling and magnetization of the coils approach the desired requirements. High resolution NMR spectra have been successfully obtained with these coils. A signal-to-noise ratio improvement over conventional technology of more than a factor of 4 was realized.

Pulse width modulator for AM-RF transmitter

Abstract: An RF-AM transmitter of the type including a power pulse amplifier driving an RF amplifier with a modulating voltage via a low pass filter includes a pulse width modulator for deriving variable frequency pulses having a frequency that is a direct function of an RMS like function of the amplitude and frequency of an information source; the width of the pulses is determined by the instantaneous amplitude of the information signal source. The pulse width modulator includes a constant amplitude, variable frequency triangular wave voltage controlled oscillator responsive to a DC signal representing the frequency and amplitude of the information source. In response to amplitude crossovers between the variable frequency triangular wave and the information source, transitions in the pulse width modulated wave are derived.