摘要:

An imaging instrument that can replace mechanically scanning photometers in ground based auroral photometry has been developed. The instrument utilizes a Reticon photodiode array, 1*1024 pixels, coupled with fiber optics to a second generation image intensifier. The optics are a telecentric design allowing for 170° field of view (FoV) with narrow‐band interference filters. Peltier element cooling is found to be sufficient to neglect dark current noise for 1‐s integration time. The whole system is controlled by a computer via the IEEE‐488 bus. Initial results and instrument performance are reported.

ISSN:0034-6748    

DOI:10.1063/1.1138473

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A diamond anvil cell and cryostat suitable for optical studies from 1.1 K to room temperature at ultrahigh pressures is described. Special provisions and techniques for loading condensable gases (cryogases) are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1138514

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A device for applying compressive uniaxial stress has been developed to fit within the pickup coils of a SQUID magnetometer. Forces of up to 300 N may be applied from liquid‐helium temperature up to room temperature. Strain gauges provide a voltage output proportional to stress that is linear and reproducible to within 3% of full scale. Combined with a SQUID moment sensitivity of 1.2×10−8G cm3, detailed studies of the stress dependence of the magnetization are possible. Stress‐induced shifts in magnetic, superconducting, and other types of transition temperatures can also be observed easily.

ISSN:0034-6748    

DOI:10.1063/1.1138479

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Using a recently published paper as a basis, the magnetic field produced by steel bars inserted in a superconducting NMR imaging magnet is analyzed in a spherically harmonic basis set. A description is then given of how such bars were used to improve the homogeneity of the field within the magnet’s imaging volume from 1.2 parts per thousand to about 10 ppm. The poor homogeneity was caused by the magnet’s being placed in a steel‐laden environment, a situation normally shunned by investigators, and it is the author’s contention that the results obtained abrogate the main objection to NMR equipment’s being installed in an ordinary hospital building. To facilitate the latter, the equations developed may also be used to estimate, prior to installation, the effects of the proposed environment on field homogeneity.

ISSN:0034-6748    

DOI:10.1063/1.1138480

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A new device measuring Hall voltages down to 5 nV in fields up to 7 T is presented. The setup uses the double‐ac method and works at temperatures ranging from 450 to 4.2 K. As a convenience, manual or automatic field sweeps can be chosen.

ISSN:0034-6748    

DOI:10.1063/1.1138532

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

As active magnetic bearings and suspensions are position servomechanisms, accurate measurement of the position of the suspended rotor is very important. The various position sensing devices that have been in use are: optical, inductance, capacitance, and eddy current transducers. In this paper the optical measurement technique is revived using modern, solid‐state infrared devices. In general, this method results in simplicity of sensor interface, adequate sensitivity and linearity, and cost effectiveness. This article describes the mechanical design feature of the electro‐optics, the sensor circuitry, and the transfer characteristics of the sensor subsystem. Results of actual performance of the sensor in an electromagnetic bearing are also given.

ISSN:0034-6748    

DOI:10.1063/1.1138481

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A solid‐state alpha dosimeter has been designed and tested suitable for personal and environmental radon/thoron monitoring. The dosimeter basically consists of an electrostatic collector and an alpha‐particle counting system with spectroscopy capabilities. The sensitive volume (∼20 cm3) of the electrostatic collector consists of a cylindrically shaped metal wire screen and a diffused‐junction silicon alpha‐detector covered with a thin aluminized Mylar sheet. A dc voltage (∼500 V) is applied between the wire screen and the Mylar sheet, with the latter held at negative potential relative to the former. Data can be retrieved during or after sampling by means of a microcomputer (Epson HX20) via a RS–232 communication interface unit. The dosimeter has been calibrated in a large (26 m3) radon/thoron test facility. A linear relationship was found between the dosimeter’s alpha‐count and both radon gas concentration and radon daughter working level. The dosimeter is mounted on top of an ordinary miner’s cap lamp battery and is ideally suited for personal monitoring in underground uranium mines and other working areas. The dosimeter presented here is a considerably improved version of an earlier prototype.

ISSN:0034-6748    

DOI:10.1063/1.1138482

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A complete system performing data acquisition as well as process control is presented. This apparatus is based on a commercially available microcomputer coupled with a quite simple hardware environment. The high versatility of the device is obtained through a more elaborate software whose main ideas are detailed. Two typical applications in the atomic physics field are described.

ISSN:0034-6748    

DOI:10.1063/1.1138458

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The IQS 401 spectrum analyzer, a commercial addition to the Apple II and III personal computers, can be modified for low‐cost power spectrum measurements of random noise signals and similar waveforms. The IQSbasiccontrol program is changed to perform low‐frequency sampling, spectral averaging, and spectrum scaling. External analog filtering must be provided on the lowest sampling rates; however, no change is made to the original IQS hardware. Resolution of 0.5 dB is obtainable from 10−4Hz to 20 kHz.

ISSN:0034-6748    

DOI:10.1063/1.1138459

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A simple method is proposed to detect a gel structure using a light‐scattering technique. A sample in a cylindrical cell was rotated in a typical dynamic light‐scattering setup. The measurements were made on a solution of gelatin in which polystyrene latex spheres were added as the light‐scattering probes. When the solution became a gel state, the light intensity observed at a fixed scattering angle showed a large fluctuation during rotation of the sample. The amplitude of the fluctuation was found to be a good measure of the gel structure.

ISSN:0034-6748    

DOI:10.1063/1.1138460

出版商:AIP    

年代:1985

数据来源: AIP