摘要:

A potentiometric technique for accurately determining a fixed voltage ratio has been developed which employs a voltbox subdivided for optimum self‐calibration. The calibration procedure minimizes the effects of resistor self‐heating and interconnection resistances which are commonly limiting factors. The basic theory of the technique and the design and construction of an instrument to compare a Josephson device (10 mV) and a standard cell (1 V) are described. This cascaded‐interchange comparator (CIC) was evaluated in conjunction with another instrument, based on the double series‐parallel exchange technique, in a series of 2 e/h measurements and direct instrument comparisons. The over‐all uncertainty for the CIC was about 3 parts in 108(1&sgr;) and the direct comparisons between the two instruments agreed to within their combined uncertainty of 4 parts in 108. The cascaded‐interchange technique should also be useful for the accurate measurement of high voltages.

ISSN:0034-6748    

DOI:10.1063/1.1686725

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A completely automatic chemiluminescent instrument has been developed forin situmeasurements of NO in the stratosphere. Signal intensity is linear in NO. Typical responsivity at 21.3 km is 1860 counts/sec ppbv. With a 1 sec measuring time constant, the detection limit as determined by noise is 0.03 ppbv. The instrument has been flown from balloon platforms to 30.8 km and from aircraft platforms between 12.2. and 18.3 km.

ISSN:0034-6748    

DOI:10.1063/1.1686726

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A new technique has been developed for detecting critical loads when using the scratch test to determine the adhesion of deposited thin films. In this technique, a 2&mgr; diam 15 keV electron beam impinges upon the sample and the intensity of the induced x‐radiation emission from the film and the substrate are monitored simultaneously and used to determine the applied normal load necessary to cause a diamond probe to cleanly strip off the film. Preliminary results are discussed using this technique to study the adhesion of rf sputtered TiC films on high speed steel substrates. Preheating of the substrate prior to deposition was shown to significantly increase the film adhesion.

ISSN:0034-6748    

DOI:10.1063/1.1686727

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A continuous wave photofragment spectrometer is described which can investigate photodissociative reactions by measuring angular dependent mass spectra of the recoiling photofragments. The three‐state differentially pumped vacuum system consists of three mutually orthogonal axes: a polarized light axis (high pressure Hg&sngbnd;Xe), a molecular beam axis, and a quadrupole mass filter axis. The electric vector of the polarized light is rotated by a stepper motor (1‐rpm). The photofragment signal from the tuned amplifier is lock‐in detected and displayed on a strip chart recorder. Various inorganic filter solutions are employed in order to suitably excite the desired transitions of molecules with favorable absorption coefficients (∼100 1 mole−1cm−1) in the spectral range of the excitation source. Signal averaging is accomplished using long lock‐in amplifier time constants as well as multichannel scaling. The relative merits of cw photofragment spectroscopy are also discussed with particular reference to the photodissociation of large aromatic molecules. From the angular data, the polarization of the transition dipole relative to the detector axis, the lifetime of the excited molecular state, and the relative ease of fragmentation into different channels can be determined.

ISSN:0034-6748    

DOI:10.1063/1.1686728

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Standard procedures employed in the use and calibration of vibrating sample magnetometers rely upon the sample being a pure dipole. We have measured deviations from pure dipole behavior in right circular cylinders having a diameter to length ratio of ∼1 to 5. The nature of these deviations and their relation to coil geometry is discussed.

ISSN:0034-6748    

DOI:10.1063/1.1686729

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The distinctive features of the tuned spin‐echo spectrometer described here are high sensitivity, high resolution, simple operation, and a frequency variation throughout the range 170–1700 MHz. In addition to magnetic structure and hyperfine interaction studies this apparatus is capable of detecting very small concentration of impurities in ferromagnetic compounds.

ISSN:0034-6748    

DOI:10.1063/1.1686730

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

An apparatus is described for measuring thermal and magnetization dynamics during thermomagnetic writing of information onto magneto‐optic films. By probing various regions of the reversed spot, the spatial dynamics of bit formation can be reconstructed. The spatial resolution of the measurement is better than 1 &mgr; and the intrinsic temporal resolution is 10 nsec. Representative results obtained with a ferrimagnetic and a ferromagnetic sample are included.

ISSN:0034-6748    

DOI:10.1063/1.1686731

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Techniques are described which have been found adequate for operating a HCN laser with stable cw action at wavelengths of 337 and 311 &mgr;; the fluctuation of output power is about ±2% without intentional stabilization by retuning for over 10 h. The main features of the design are: (i) a mixture of CH4, N2, and He gases is used as the flowing gas with a mixing ratio of 1:1:2 by volume; total pressure of 1.6 Torr and gas flowrate of 6∼8 liter Torr/min; (ii) the fluctuation of gas pressure is kept within 0.01 Torr; (iii) the cathode is not grounded but negatively charged about 10% of the dc source voltage. Some of these techniques are applicable to other HCN lasers.

ISSN:0034-6748    

DOI:10.1063/1.1686732

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A new method for confining a metal vapor at a pressure of about 10−3Torr, with extremely low loss of metal into the vacuum chamber surrounding the metal cell, has been demonstrated; it consists in recycling the metal, condensed in the liquid state; its return to the high pressure region is ensured by capillarity. Two versions of the new cell, built for different applications, are described: a heat pipe heated lithium cell, characterized by a high uniformity of temperature, and a cesium cell, equipped with a surface ionization gauge for cesium pressure measurement, and a LiF window. Measurements carried out with the surface ionization gauge in the cesium cell led to a ratio 103between the cesium atom flux at the center of the canal and at its port. The contribution of direct metal loss from the hot central region of the canal and that due to desorption from the canal ports is discussed.

ISSN:0034-6748    

DOI:10.1063/1.1686733

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A fast photodiode recording system is described for use in a shock tube laser schlieren system. This device is relatively inexpensive, has a superior signal‐to‐noise ratio, is insensitive to ripple in the light source, and provides a convenient calibration correction for long term variations in laser intensity. Measurements of both relaxation and dissociation behind shock waves have been carried out using this device.

ISSN:0034-6748    

DOI:10.1063/1.1686734

出版商:AIP    

年代:1974

数据来源: AIP