摘要:

A new wide-annulus Couette-type viscometer/rheometer has been designed, fabricated, and tested with the objective of measuring the shear flow properties of silicate melts and magmatic suspensions containing vapor bubbles and/or solid particles at10−4 GPaand temperatures from 600 to 1500 °C. The goal of this development has been to advance the precision of high-temperature multiphase silicate rheometry in the viscosity regime of104–1010 Pa s,and to attempt experiments on multiphase magmatic mixtures that have heretofore been difficult to perform in the concentric cylinder geometry. With this instrument, fluids with viscosities in the design viscosity range may be tested at shear rates from10−5to 1 s−1, employing a series of interchangeable torque transducers capable of measurements from 0.003 to 3 N m, preserving precision of the stress measurement across the entire dynamic span. A microprocessor-controlled motor drive enables precisely specified rotational motions (position and/or speed of the sample container) for accurate constant-shear-rate or finite-strain experiments. Use of high-purity cast ceramic components rather than platinum alloy for the rotating sample container (cup) and fixed cylindrical bob permit sectioning of the sample following an experiment to inspect and analyze textural characteristics of the magmatic suspensions. Computerized data acquisition is accomplished via a standard microcomputer interface and commercially available software system that allows data to be recorded, visualized, and statistically modeled as an experiment progresses. The instrument has been tested using NIST (NBS) reference material 717 (a borosilicate glass) at viscosities from104to109 Pa s.Value of the standard viscosity has been recovered within the published precision (0.03 log units) at temperatures between 650 and 850 °C. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149106

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Recent advances in high speed photodetector and microwave receiver technology make microwave frequency optical heterodyning an attractive approach for the detection of a number of coherent Raman and Brillouin scattering experiments. We have therefore analyzed the sensitivity of microwave frequency optical heterodyne receivers. Experimental tests on a visible wavelength receiver operating at 13.5 GHz confirm the expectation of shot noise limited sensitivity. The relative merits of microwave frequency optical heterodyne detection and the alternative Fabry–Pe´rot interferometry approach are discussed. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149107

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have developed a method to measure the electric field standing wave distributions in a microwave resonator using a scanned perturbation technique. Fast and reliable solutions to the Helmholtz equation (and to the Schro¨dinger equation for two-dimensional systems) with arbitrarily shaped boundaries are obtained. We use a pin perturbation to image primarily the microwave electric field amplitude, and we demonstrate the ability to image broken time-reversal symmetry standing wave patterns produced with a magnetized ferrite in the cavity. The whole cavity, including areas very close to the walls, can be imaged using this technique with high spatial resolution over a broad range of frequencies. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149108

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

In high resolution continuous-wave nuclear magnetic resonance (NMR) work well-reproducible, linear sweeps of current are needed. We have developed a microcontroller based programmable current supply, tested with superconducting magnets with inductance of 10 mH and 10 H. We achieved a resolution and noise of 4 ppm. The supply has an internal sweep with programmable ramping rate and a possibility for remote operation from a computer with either GPIB or RS232 interface. It is based on an 18-bit D/A converter. The maximum output current is±10 A,the sweep rate can be set between 1 &mgr;A/s–140 mA/s, and the maximum output voltage is±2.5 V.In work at ultralow temperatures, especially in superconducting quantum interference device NMR, all rf interference to the experiment should be avoided. One of the sources of this kind of unwanted input is the digital switching noise of fast logic devices. We discuss this problem in the context of our design. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149109

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A new method of driving miniature fluorescent tubes for liquid crystal display backlighting, with diameters as small as 2 mm, has been devised with the objective of improving the luminance and luminous efficacies of such lamps. The driver voltage wave form consists of high frequency oscillations at the leading and trailing edges of conventional square-wave form voltage pulses of relatively low frequency. The wave form is produced simply by inserting coils between low frequency square-wave pulse generators and the lamp electrodes. A lamp driven in this way operates in a different discharge mode from the conventional glow discharge obtained in the absence of the coils. The twofold intensity increase of visible emission from the positive column region indicates that the vacuum ultraviolet emission increases, enhancing the excitation of the phosphor in the lamp. There is evidence that the luminous efficacy is also increased by a factor of 2 as a result of more efficient use of the input energy. The minimum voltage needed to maintain a discharge is reduced. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149110

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The use of internal ovens is common in high-temperature–high-pressure experiments. Improving the thermal insulation means better efficiency and lower thermal strain on pressure vessels and feedthroughs, but is difficult when using solid media. The addition of a layer of amorphous solid (glass) in the form of a mixed powder is reported to give a significant reduction (20&percent;–50&percent;) in the power dissipated in a high pressure oven. ©1998 American Institute of Physics. 

ISSN:0034-6748    

DOI:10.1063/1.1149111

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

By using a computer automated measurement and control interval counter and a workstation to analyze the data, a system with a Michelson interferometer is used to measure amplitude, frequency, instantaneous speed and other parameters of a mechanical oscillator. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149118

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Negative ions in etching plasma were extracted from a plasma chamber and mass spectra were measured. For the extraction of the negative ions, the plasma sheath was broken by a cone-shaped extractor electrode which had an orifice on the tip. To avoid disturbing the plasma, the tip of the extractor electrode was slightly stuck out of an electrically earthed wall. To remove electrons from the extracted negative charged flux, a magnetic field was applied to the flux. By using the extractor electrode and the magnetic field for the removal of the electrons, the negative ions could be extracted efficiently and the mass spectra could be measured with low noise. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149119

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A heating–pulling device is established for producing the optical fiber probe used in scanning near-field optical microscopy. ACO2laser, the power of which can be adjusted continuously between 0 and 10 W, is used as the heating source. Pulling is done by two identical motors. On the basis of the device, a novel approach different from the conventional heating–pulling method is developed, which eliminates the need for a computer, reflective mirror, and varied force during tip formation. Thus it is simple and easy to use. The cost is reduced greatly. Tips with parabolic taper, short taper region, and a diameter of 65 nm, which are optimal conditions for high transmission efficiency, are obtained. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149112

出版商:AIP    

年代:1998

数据来源: AIP