摘要:

A 10‐GHz superconducting niobium re‐entrant cavity parametric transducer was developed for use in a cryogenic 1.5‐tonne Nb resonant bar gravitational radiation antenna. The transducer has a very high electricalQ(6×105at 4.2 K), and was operated at high cavity fields without degrading theQ. A very high electromechanical coupling between the antenna and the transducer was therefore achieved. The highest coupling attained, constrained by the available pump power, was 0.11. If the transducer were to be operated in conjunction with a wideband impedance matching element, an antenna bandwidth comparable to the frequency of the antenna would be attained. The temperature dependence of theQof the transducer was in good agreement with theory. At temperatures above about 6 K theQwas degraded by the increase in the BCS surface resistance, while at lower temperatures theQwas limited by radiative losses.

ISSN:0034-6748    

DOI:10.1063/1.1143227

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We developed a system for localizing orthogonal triplets of small magnetic dipoles with an array of magnetometers. These triplets can be used to measure, in quasi‐real time, the position of an object. This system is particularly useful when used with superconducting biomagnetic multichannel detectors. We present here a complete numerical simulation of the system performances and the first experimental tests with a biomagnetic detector (an array of 37 superconducting magnetometers). This system can be operated at frequencies outside the range of interest for biomagnetic measurements (that is typically 10−2–103Hz). It features an accuracy of ±0.3 cm driving the triplet at a field intensity ≊10−12T. The speed of the algorithm allows for quasi‐real‐time operation (t∼ 10−1s).

ISSN:0034-6748    

DOI:10.1063/1.1143228

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A micronic‐size hot wire anemometer operating at cryogenic temperatures (4 K) has been developed; using superconducting and resistive thin films, its electrical resistance is very sensitive to the velocity of a gaseous4He subsonic jet. The fabrication procedure is described and the measured characteristics are compared with a simple thermal equilibrium model.

ISSN:0034-6748    

DOI:10.1063/1.1143229

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We examine the causes of spacing dependence of the nulling bias voltage in the vibrating capacitor contact potential measurement technique. In addition to effects already recognized in the literature, namely, nonuniform work functions, nonparallel surfaces, fringe fields, and capacitive coupling to distant surfaces, we investigate the effects of finite gain and spurious signals in feedback loop systems. We argue that much of the spacing dependence reported in the literature may be due to microphonic signals, which are very difficult to eliminate. We also discuss the means by which existing spacing dependence can be minimized.

ISSN:0034-6748    

DOI:10.1063/1.1143230

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An experimental technique for absolute measurement of ultrasonic wave particle displacement amplitudes in liquids is reported. The technique is capable of measurements over a frequency range of two decades with a sensitivity less than one angstrom. The technique utilizes a previously reported submersible electrostatic acoustic transducer (ESAT) [Rev. Sci. Instrum.50, 31 (1979)] featuring a conductive membrane stretched over a recessed electrode. An uncertainty analysis shows that the displacement amplitude of an ultrasonic plane wave incident on the ESAT can be experimentally determined to better than 2.3%–4%, depending on frequency, in the frequency range of 0.5–15 MHz. Membranes with lower and more uniform areal densities can improve the accuracy and extend the operation to higher frequencies.

ISSN:0034-6748    

DOI:10.1063/1.1143231

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A fast method for extracting the interface trap density profile of the semiconductor‐insulator interface in metal‐insulator‐semiconductor structures is proposed. The method is based on the well known conductance technique and extracts the interface state density profile from the maximums of the parallel conductance versus applied gate bias curves,Gp(Va). In addition, this method is directly applicable to fully automated experimental setups available in industrial environments.

ISSN:0034-6748    

DOI:10.1063/1.1143232

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A continuous bubble‐rise‐velocity (BRV) viscometry method was developed for Newtonian fluids which is based upon the remote determination of the rise velocity of a helium bubble. The bubble rise velocity was remotely determined by using a helium‐leak detector to measure the rise time of a bubble passing through a constant distance. The density of the fluid was simultaneously obtained from differential pressure measurements in the bubble launch tubes. Empirical equations were developed which allow for calculation of the absolute viscosity and density from several remotely measurable variables: helium gas pressures in the bubble generation and launching system, liquid temperature, and helium concentrations at the liquid/air interface as a function of time. BRV viscometry results for highly viscous liquids (1 Pa s<viscosity <40 Pa s) correlated within ±10% with data obtained with capillary or rotational viscometers. An integrated probe was conceived for the on‐line monitoring of viscosity, density, temperature, and liquid level, especially in a hostile environment.

ISSN:0034-6748    

DOI:10.1063/1.1143233

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A novel version of the capillary method for viscosity measurements of liquids is presented. Viscosity data can be deduced in a straightforward way from mass transfer data obtained by differential weighing during the gravity‐induced flow of the liquid between two cylindrical chambers. Tests of this technique with water, carbon tetrachloride, and ethanol suggest that this arrangement provides an accuracy of about ±1%. The technique facilitates operation under sealed, isothermal conditions and, thus can readily be applied to reactive and/or high vapor pressure liquids.

ISSN:0034-6748    

DOI:10.1063/1.1143234

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The falling needle viscometer is a particularly useful instrument for measuring the shear viscosity when small sample volumes are necessitated. Under some conditions this instrument can exhibit bimodal terminal velocity observations which precludes a straightforward analysis to obtain the viscosity. This phenomenon is explained via an analysis for the fluid mechanics and associated entropy production of a needle falling asymmetrically with respect to the centerline of the instrument. This analysis provides a rationale for using only the smaller terminal velocities, thereby permitting an unambiguous data analysis.

ISSN:0034-6748    

DOI:10.1063/1.1143235

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

In multiwavelength pyrometry it is very difficult to represent the wavelength variation of emissivity so that a ‘‘correct’’ blackbody temperatureT0is obtained. On the other hand, use ofTr’s, the radiance temperature, permits the calculation of the blackbody temperatureT0. In all cases studied up to now, in the wavelength range 0.4–4 &mgr;m, we have a linear relationship betweenTrandL, the wavelength,Tr=Tlin−hL, whereTlinis the calculated blackbody temperature.

ISSN:0034-6748    

DOI:10.1063/1.1143236

出版商:AIP    

年代:1992

数据来源: AIP