摘要:

An apparatus is described which permits the accurate determination of the volume of solids by helium expansion. The apparatus consists of a differential micromanometer whose two arms are connected to a pair of sample and reference burets of nearly equal volume for helium expansion into sample and reference cells also of nearly equal volume. The volume of solids of 20 cm3or smaller can be measured with an accuracy on the order of 0.0005 cm3.

ISSN:0034-6748    

DOI:10.1063/1.1137477

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Electrode configurations are described that can be used in measuring the electrical conductivity of a core sample from a borehole in ground. The use of these configurations is warranted for laboratory measurements simulating the pressure and fluid flow conditions encountered at depth within the earth. Three particular electrode configurations are illustrated with numerical results depicting their relative merits.

ISSN:0034-6748    

DOI:10.1063/1.1137478

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A new system has been developed for determining the writing speed of sweeping image cameras. In this system the time intervals between light pulses from the image of a small objective slit as seen by a photomultiplier tube through a pair of slits at the object plane are measured by a time interval meter. Several features of this system allow the writing speed of an individual measurement to be determined to better than a tenth of a percent so that very precise corrections can be determined for nonideal behavior of the camera’s optical system.

ISSN:0034-6748    

DOI:10.1063/1.1137479

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The optimal dimensions of thin coil systems of three and four square coils for producing uniform magnetic fields are calculated. We find that for three square coils, of sidedand separationsbetween the outer coils, the most uniform field distribution occurs withs/d=0.821 116 and withI′/I=0.512 797.I′/Iis the ratio of the currents in the center coil to that of the outer coils. With four square coils, the best uniformity is obtained whena/d=0.128 106 andb/d=0.505 492, whereais the distance from the center to the inner coils andbis the distance from the center to the outer coils. The ratio of the current in the inner pair of coils to that in the outer pair must beI′/I=0.423 514. We compare the uniformity of the field produced by these coil systems with each other and with Rubens’ five‐coil system, both on and off axis. It is shown that the optimal four‐coil design is superior to the three‐ and five‐coil systems. The sensitivity of the uniformity to the precision of construction is discussed. Dimensions of regions around the center of the coil systems, uniform to 1 part in 106to 1 part in 102, are given.

ISSN:0034-6748    

DOI:10.1063/1.1137480

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A system is described that records digital data onto video cassettes and writes the data to a computer tape for subsequent processing. The system is capable of recording and playing back 172 800 bytes/s. This corresponds to the maximum rate achievable with a nine‐track computer tape drive writing 1600 bits per inch at 125 ips. A standard two‐hour cassette has a capacity of 1.2 Gbytes. Six checkbits are written with each 16‐bit word to facilitate error detection and correction. Upon playback, the data are written via DMA into a computer and then to a nine‐track computer tape. Error rates of less than 1 word in 300 000 have been achieved with an off‐the‐shelf portable video recorder and commercially available tape. The system comprises a low‐cost solution to the problem of high‐volume, fast data recording at remote locations when a small error rate can be tolerated.

ISSN:0034-6748    

DOI:10.1063/1.1137481

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A Josephson‐junction noise thermometer produces a sequence of frequency readings from whose variations the temperature of the thermometer may be calculated. A preprocessor system has been constructed to collect the frequency readings delivered to an IEEE 488 bus by an ordinary counter operating at up to 1000 readings per second, perform the required calculations, and send summary information to a desk calculator or minicomputer on another 488 bus at a more convenient rate.

ISSN:0034-6748    

DOI:10.1063/1.1137482

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The Wheatstone bridge of a Pirani gauge has been made self‐balancing, and the gauge thermostatic, using a simple but novel dual op‐amp circuit. The system retains the electrical and pneumatic robustness, and the atmospheric to high‐vacuum pressure range, characteristic of conductance‐type gauges. Without recourse to ultrathin material for the temperature‐dependent resistor, response time constants (dependent on bridge setting) of <30 ms in high vacuum have been demonstrated. At total pressures <0.1 Pa, the system can detect pressure change, sustained for >0.1 s, of 2.5 mPa; or an impulse of pressure change, occurring within 50 ms, of 0.25 mPa s. The circuit described is also applicable to bolometric power measurement, where fast response is required.

ISSN:0034-6748    

DOI:10.1063/1.1137492

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A simple technique is described which allows a reservoir‐type liquid‐nitrogen trap to be converted to continuous operation with a closed‐cycle mechanical refrigeration system. The conversion requires no internal modification to the trap and uses only standard commercial refrigeration components. Using 502 refrigerant as the working fluid, temperatures of −52 °C are readily achieved in a trap operating above a 6‐in. water‐cooled baffle and oil diffusion pump.

ISSN:0034-6748    

DOI:10.1063/1.1137493

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Large capacitor banks, as used in many pulsed plasma experiments, are subject to catastrophic failure in the event of a short in the output or in an individual capacitor. Methods are described for minimizing the damage and down time caused by such a failure.

ISSN:0034-6748    

DOI:10.1063/1.1137494

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An attachment which may be fitted to a standard crystallographic goniometer head for the purpose of taking x‐ray section topographs is described and its application in synchrotron x‐ray topography is illustrated. A collar attached below the arcs and translation slides of the goniometer head provides a bearing for a rotatable sleeve, concentric with the goniometer axis. The sleeve carries a removable x‐ray entrance slit and a removable mirror used for angular setting by optical means. The device is easily transferable between topograph cameras at conventional x‐ray sources and synchrotron radiation sources. It can be rapidly aligned at either source.

ISSN:0034-6748    

DOI:10.1063/1.1137495

出版商:AIP    

年代:1983

数据来源: AIP