摘要:

A circuit has been developed for the generation of isolated currents having precisely defined ratios. It can be used to compare resistances with accuracies up to 0.03 ppm and with sensitivities as low as 1 nV. When comparisons are made using low frequency currents, thermal emf's are eliminated. Several variations of the circuit which can be made easily in the laboratory are described.

ISSN:0034-6748    

DOI:10.1063/1.1684561

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A direct coupled function generator has been developed which provides a fourth degree polynomial function in times of the order of 100 nsec. Analog multipliers utilizing field effect transistors are used. A unique circuit configuration allows the generation of a fourth degree polynomial having individually adjustable coefficients with only two multipliers. The instrument, operating at 5 V input and output levels, achieves an accuracy of 1% for the lower order terms and 2% for the higher order terms.

ISSN:0034-6748    

DOI:10.1063/1.1684562

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Problems arising when averaging fast signals random in shape and occurrence time are systematically examined. A setup is described, comprising a sampling oscilloscope and a memory unit, allowing high speed random operation. The system logic, which insures one‐to‐one delay‐channel correspondence under the most stringent conditions, allows averaging signals satisfying various specified conditions and optimizes the statistical accuracy of the results. An add‐subtract method allows elimination of synchronous transient noise, either external or arising from the sampling unit itself. Signals of 30 &mgr;V were averaged out in this way with a 0.1 nsec instrumental risetime. Applications are shown to a broad range of problems which include fast signal enhancement, optical signal measurements, photomultiplier single electron response studies, illumination function measurements for fast organic and slow scintillators, and semiconductor detector risetime observation. Two‐dimensional representation of random signal properties is also shown. It allows, for example, time jitter determinations with some tens of picosecond precision. The setup allows direct measurement of noise correlation and cross correlation functions.

ISSN:0034-6748    

DOI:10.1063/1.1684563

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

In the presence of an electrical current through the bathing medium, the measurement of electrical potentials in solution with glass micropipettes is characterized by an error. This error is very troublesome when glass microelectrodes are used to sense the membrane potential during voltage clamping. The source of the error is identified and discussed. The construction of a microelectrode that minimizes the error is described in detail.

ISSN:0034-6748    

DOI:10.1063/1.1684564

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The quality of transmission diffraction topographs is strongly dependent on many experimental factors. Among them the fixed screen is one of the more important elements. A new design of a good performing screen manipulator is described and its practical application to the ``parallel section'' x‐ray topography is discussed.

ISSN:0034-6748    

DOI:10.1063/1.1684565

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

In the design of high speed piezoelectric pressure probes the criterion of matching the acoustic impedance of elements in the stress transmission system composed of piezoelement and backing rod is found to be inconsequential. Analysis and empirical evaluation of a typical probe configuration indicate that optimum probe performance can be achieved by utilizing backing rod material with minimum lateral strain (&ngr;/E) characteristics so as to serve effectively to damp induced radial stress oscillations in the piezoelement.

ISSN:0034-6748    

DOI:10.1063/1.1684566

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

An apparatus is described for the measurement of temperature near the interface of bodies sliding in a vacuum. The rotating element or slider is electromagnetically suspended inside the vacuum system and rotated with an induction motor positioned outside the vacuum system. Because of the suspension system, the only contacts in the apparatus are the stationary elements or riders acting on the slider. The temperatures measured near the sliding interface can be used in analysis as boundary points to provide the temperature and temperature gradient at the interface of each element. The juncture condition of continuity of temperature and its gradient can then be checked. To avoid unnecessary contacts in the system, the temperatures on the slider are telemetered out of the vacuum system by transmitters located on the slider. Thermocouples are used to measure temperature on the rider. The vacuum system is hermetically sealed, with suspension and rotation being affected from outside the vacuum system. The torque in the system and the normal load of the rider are also measured. The maximum sliding speed is 39 cm/sec and a vacuum of the order of 10−3Torr was used. Results are given for Teflon sliding on steel.

ISSN:0034-6748    

DOI:10.1063/1.1684567

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The paper describes a highly stable ac mutual inductance bridge suitable for low temperature use. The application of the bridge to magnetic thermometry below 3 K is discussed.

ISSN:0034-6748    

DOI:10.1063/1.1684568

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

An automatic ellipsometer based on the principle of measurement of intensities is described. Use is made of a rotating analyzer with a three‐channel strobing voltmeter to read the photomultiplier output at chosen analyzer angles. The outputs are recorded in digital form, and the time for one optical measurement is 150 msec. Sources of error and ways of eliminating noise from the signal are discussed. The system incorporates a cell specially engineered for electrochemical investigations, and its performance is illustrated with results from an experiment on the electrochemical formation of a thin oxide layer on platinum.

ISSN:0034-6748    

DOI:10.1063/1.1684569

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Short duration pressure pulses generated by impacting samples with thin plastic sheets, or flyers, are being widely used to investigate dynamic materials properties. Peak pulse pressures are directly dependent upon impact velocity. Two types of exploding foil launchers are currently available that can produce flyer velocities of 0–0.4 and 0.8–4.0 mm/&mgr;sec. A ``velocity gap'' has existed between 0.4 and 0.8 mm/&mgr;sec which has limited the usefulness of the over‐all technique. A third launcher design has been developed that can accelerate flyers to velocities between 0.4 and 0.8 mm/&mgr;sec. The new design uses a free expansion gas chamber to moderate the performance of the older high velocity launcher. This design produces flyers with planarities usually less than 0.4 mm.

ISSN:0034-6748    

DOI:10.1063/1.1684570

出版商:AIP    

年代:1970

数据来源: AIP