摘要:

The dynamic response of the platinum thin‐film thermometer has been investigated. Our experimental results indicate that details of the probe form significantly affect the velocity scaling relationship for these probes. In particular, the theoretical relationship appears appropriate for probes with hemispherical tips with the thin film in the stagnation region, whereas the conical‐tip probes in common usage deviate from the theory and require an empirical scaling relationship.

ISSN:0034-6748    

DOI:10.1063/1.1139550

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A technique has been developed to measure the linear mass density of fibers and ribbons, and adapted to the study of stress/strain coupled diffusion in polymeric materials. The technique overcomes the limitations of sensitivity and range, typical of traditional diffusion measurement techniques, and can be used for a wide range of fiber densities. It is also possible to monitor stress or strain within the fiber while measuring the change in mass, without requiring the fiber to be at equilibrium or interrupting the experiment. Estimates of material property changes, as exemplified by tensile modulus changes, can also be made during the course of the experiment. The mass per unit length, at any given time, of polymer fibers or ribbons under known stresses and strains can be determined by this technique. From this it is possible to estimate the gain or loss in weight in the sample due to permeants diffusion. Some preliminary result of constant strain and constant stress experiments on ribbons of polycarbonate, polyimide, and precured epoxy, and KevlarRmonofilaments, are discussed and the scope and resolution of the apparatus are indicated.

ISSN:0034-6748    

DOI:10.1063/1.1139551

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We describe a very simple method for making measurements of the isotropic and anisotropic static magnetization of small samples which is especially useful in the limit of very low temperatures and high magnetic fields. The sensitivity of this technique can surpass that of commercial superconducting magnetometers in the high magnetic field limit. Methods for calibration are presented and magnetization measurements on several materials are shown to demonstrate the technique.

ISSN:0034-6748    

DOI:10.1063/1.1139552

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Knowledge of the temperature of a junction is very useful for experimenters or technologists. We propose here an easy but accurate method to measure it for any type of junction, isolated or in a device. The method is based on a numerical analysis of a transient signal, provided by the change of capacitance of the space‐charge region of the junction due to the emission of majority carriers from a trap. This method has been tested on different junctions made onn‐GaAs with traps introduced by electron irradiation or originating from the technology. Here we provide, for illustration, results showing the variation of a junction temperature as a function of the injected current density.

ISSN:0034-6748    

DOI:10.1063/1.1139553

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A novel two‐dimensional position‐sensitive detection system has been designed, built, and tested. It has a relatively short processing time (900 ns) which enables countrates up to 105–106/s. The detector has a ring‐shaped geometry. Both polar coordinates can be determined with an accuracy better than 1%. Although intended for use in an ion scattering spectrometer, the system can also be used for detection of other atomic particles or photons.

ISSN:0034-6748    

DOI:10.1063/1.1139554

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We report a sample support rod for use in a vibrating sample magnetometer which includes means for thermal contact and for temperature control. The magnetic susceptibility of the unit is 10−6cgs (which corresponds to 0.01 emu at 10 kG).

ISSN:0034-6748    

DOI:10.1063/1.1139555

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

ReactiveQswitching of a CO2laser by means of a piezoelectrically actuated end reflector is reported. The high‐frequency response of the piezoelectric transducer was maintained by optically polishing the transducer’s surface directly instead of employing a separate mirror. Submicrosecond pulses at rates in excess of 100 kHz were obtained. This technique is especially appropriate for generating high pulse rates in low‐power lasers, as no lossy intracavity elements are required.

ISSN:0034-6748    

DOI:10.1063/1.1139556

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A stable capacitance bridge has been designed to measure changes both in capacitance and in loss of three‐terminal capacitors at temperatures ranging from 0.01 to 100 K. The circuit uses commercially available components, and has a resolution of better than 10−6. Also described is an anomalous voltage dependence present at low temperatures in capacitors which have electrodes applied using an evaporative or similar technique.

ISSN:0034-6748    

DOI:10.1063/1.1139540

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Usually the side walls of a rectangular cavity are less than one skin depth thick at the field‐modulation frequency. Eddy current creates an opposing magnetic field to the incoming modulation field, which tends to reduce the field at the center of the cavity. Moreover if the walls of the cavity are kept thin, interaction of eddy currents and the static magnetic field will create mechanical vibrations that will modulate the microwave frequency, thus generating spurious signals at the output of the amplifier. In this note a cavity forXband (in 9–10 GHz) is described in which the above problems have been overcome by corrugating the cavity walls in a precise manner. In comparison with a thin sidewall, the EMF that drives the eddy currents remains unchanged, but because the resistance increases, the eddy currents decrease.

ISSN:0034-6748    

DOI:10.1063/1.1139541

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We developed a rapid and simple measuring system for contrast thresholds for a human observer, based on simultaneously presenting eight negative, different contrasts against a uniform background on a screen. This experimental method allows: (1) a continuous variation of the presented contrasts and (2) generation of very small chromaticity differences parallel to the luminance differences.

ISSN:0034-6748    

DOI:10.1063/1.1139542

出版商:AIP    

年代:1987

数据来源: AIP