摘要:

A hot‐wire anemometer probe with a circular shape has been developed in order to measure the magnitude of the instantaneous velocity vector. The theoretical cooling law and calibration curves show that a ring wire is less sensitive to the lateral components of the velocity, i.e., less sensitive to positioning errors than straight wires. The theoretical considerations agree rather well with experimental data.

ISSN:0034-6748    

DOI:10.1063/1.1139481

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The ring wire, a circular hot‐wire anemometer probe, orientated normal to the flow, is useful to measure turbulent scales in the dissipative range. It is less sensitive to angular positioning errors than straight wire sensors. Following the rationale of Wyngaard [J. Phys. E. 52,1, 1105 (1968)], theoretical expressions are derived for the high wave number attenuation due to spatial resolution (line averaging). The expressions are applied to the estimation of longitudinal velocity spectrum and dissipation rate. The ring wire is shown to present much smaller attenuations than the straight wire of the same length or, inversely, to have a much higher sensitivity and frequency response than the straight wire of similar spatial resolution. The theoretical results are confirmed by experimental data.

ISSN:0034-6748    

DOI:10.1063/1.1139482

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A new method for accurate measurements of resonant frequency is described here, which uses a phase‐modulated locked loop to avoid errors due to unknown phase shifts or to synchronous pickup noise.

ISSN:0034-6748    

DOI:10.1063/1.1139483

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Detailed calculations of the root‐mean‐square value of the output noise of correlators with an exponentially weighted average and an arbitrarily chosen weighting function for three commonly used mathematical models of white noise are derived. A comparative analysis has been made of noise properties of correlators with exponentially weighted average and true average based on two figures of merits: the output signal‐to‐noise ratio and the signal‐to‐noise improvement ratio. An analysis of noise properties of a boxcar averager for any gate width is performed. Expressions for the output signal‐to‐noise ratio and the signal‐to‐noise improvement ratio of a boxcar averager are derived.

ISSN:0034-6748    

DOI:10.1063/1.1139484

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A low‐power persistent switch module for a superconducting magnet in an adiabatic demagnetization experiment is presented. It performs with heater power as low as 25 mW and has a small decay rate 1.1 ppm/h when the persistent current is 60 A.

ISSN:0034-6748    

DOI:10.1063/1.1139485

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The thermal expansion of the ceramic piezoelectric material PZT Channel 5800 between 2 and 300 K is found to be anisotropic, being negative parallel to the poling direction and positive normal to this direction. The piezoelectric response is temperature dependent, decreasing significantly as the temperature is reduced.

ISSN:0034-6748    

DOI:10.1063/1.1139486

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Data are presented showing that thick scattering foils (or solid targets) can be used in retarding‐potential Mott polarimeters without degrading their performance. Use of thick foils can simplify the design and operation of such polarimeters. A straightforward calibration procedure is described.

ISSN:0034-6748    

DOI:10.1063/1.1139324

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The recently observed in‐flight capture of keV antiprotons and protons in a Penning trap requires that the −3‐kV potentials on electrodes of a Penning trap near 4.2 K be switched on and off with switching times less than 20 ns. These rapidly switched potentials are applied via transmission lines which are not terminated at the trap, thereby avoiding unacceptable heat load on the helium Dewar. Simple high‐voltage switching circuits are constructed using krytrons and reed relays. A krytron provides the rapid switching and stays on just long enough for a reed relay to kick in and maintain the switched state indefinitely.

ISSN:0034-6748    

DOI:10.1063/1.1139325

出版商:AIP    

年代:1987

数据来源: AIP