摘要:

Nuclear magnetic resonance is becoming an important experimental technique to study the behavior of moving granular materials because of its unique ability to measure concentration, velocity, and dissipation within the bulk granular materials rather than only on the surface. Of all the common motions of such assemblies of particles, the most difficult to measure is the vibrating bed because of the unsteady motion. This paper demonstrates a nuclear magnetic resonance imaging method to study highly energetic vibrating granular beds by spatial scanning. In contrast to Fourier imaging, spatial scanning prevents scattering of image intensities caused by unsteady motion. Two-dimensional images of a vibrating bed undergoing period doubling were obtained. A band of high shear was identified by reduced image intensity. It traveled back and forth across the bed with each cycle of up and down motion of the bed. Further studies of vibrating beds with the sequence modified for velocity encoding and velocity compensation should provide additional useful information. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148369

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

While great interest has been focused on low temperature plasma for material processing, the concept of using pulsed high speed and high temperature plasma beam for material surface treatment was put forward. Thus a novel instrument based on Thetatron-Pinch was built up and the plasma beam with a temperature of several hundred eVs and a density up to1016 cm−3was created uniformly over a large cross section. The plasma beam was then accelerated by a sample bias of 0–2.0 kV under a high vacuum circumstance. The energy density exerted on the sample surface is1–20 J/cm2with a duration time of less than 10 &mgr;s, which is comparable to that of laser treatment. Preliminary experiments indicate that this method has the combining feature of laser treatment and ion implantation techniques when it is used for surface modification; moreover, a transient high temperature and high pressure environment exists on the treated surface in this technique and the plasma contains a high concentration of radical particles. Both facts are advantageous to chemical vapor deposition applications. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148335

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A high gravity centrifuge facility in which thin films can be produced, especially from gas phase, was developed. The centrifuge facility allows high gravity materials processing up to100g(gdenotes the terrestrial gravity acceleration). With a minor modification, not only thin films from gas phase but also bulk materials could be produced in the facility. For the first demonstrative attempt in this facility, diamond thin films were grown under high gravity conditions up to100gby means of the direct current-plasma chemical vapor deposition method, in which diamond was deposited on a molybdenum substrate in a moderate pressure condition (27 kPa) of the gas flow of hydrogen-methane mixture (methane 1 vol &percent;). The details of the facility are described, and the preliminary results on the high gravity diamond synthesis are presented. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148336

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new type of apparatus for materials testing in high-pressure hydrogen up to 10 MPa at low temperatures down to 20 K was developed. The apparatus consists of the pressure vessel, cooled by a two-step external cooling method, and the hydraulic loading system. In the first cooling step the specimen in the pressure vessel is cooled to 84 K using a cooling tube between the coolant shroud filled with liquid nitrogen and the pressure vessel. In the second cooling step the specimen is cooled to 20 K using a helium refrigerator. The apparatus is designed to measure the actual load on the specimen with an external load cell irrespective of the axial load caused by high pressure and friction at the sliding seals. As an example of the application of the apparatus, the tensile properties of type 304L stainless steel in 1 MPa hydrogen and helium at low temperature are measured and hydrogen environment embrittlement of the steel is briefly discussed. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148337

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We describe a novel method of obtaining the fuel concentration at various points along the longitudinal axis of a spark ignition engine. This allows us to measure the effect of various engine and fuel parameters on charge stratification in the combustion chamber. The technique is based on sampling the infrared (IR) absorption spectrum through the transparent sapphire engine cylinder. The absorbance is measured at four points down the chamber axis using four IR launching fibers, each of which is matched to a collection fiber. The spectra are simultaneously dispersed and stacked on a diode array detector. We subtract the background from the absorption peak to obtain the absorbance which is shown to be directly proportional to fuel concentration. We find that the axial charge stratification and its evolution during the induction and compression strokes is a sensitive function of injection timing and swirl valve setting. The technique is also applicable to gas phase reactors and any system where spatially homogeneous mixing of reactants is required. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148338

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

This article provides a description of a diagnostic developed to allow spatial and temporal measurements of the average vertical liquid mass flux within a pulsing spray. The diagnostic incorporates a patternator similar to that used in spray research for measuring mass distributions within sprays. For this application, the patternator section consists of a row of sample tubes oriented normal and intersecting the injector axis. However, in addition to the patternator section, the diagnostic incorporates a rotating shutter mechanism, which allows phased or transient sampling of the mass within transient spray plumes. To date, the technique has been successfully applied to a number of pulsing injection systems to produce spatially resolved measurements of transient mass flux. To illustrate the capabilities of this diagnostic, sample mass flux data are provided for a pulsed fuel injector. In this case, mass flux was a strong function of time and space, and measurements were possible for all regions of the spray, independent of spray number density or liquid void fraction. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148339

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Nitrogen dioxide(NO2),an essential gas in atmospheric chemistry, is almost always measured indirectly with just one technique: photolysis ofNO2to NO, followed by detection of resulting NO. However, the photolysis introduces artifact signals that complicate the extraction of theNO2signal at lowNO2volume mixing ratios. A new prototype instrument uses laser induced fluorescence to measure troposphericNO2directly. The atmospheric fluorescence spectra measured with this instrument match the fluorescence spectra ofNO2in a reference cell over the wavelength range 565.1–565.2 nm. This match indicates that fluorescence from other chemical species is not interfering with the measurements. The prototype’s current detection limit is 280 parts per trillion (pptv) in 2.5 min with an absolute uncertainty of±15&percent;(2&sgr; confidence). This detection limit, which can be improved with better optical filtering and more laser power, is currently adequate for urban air conditions. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148384

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We describe an earth’s field nuclear magnetic resonance apparatus which can be used to carry out pulsed gradient spin echo (PGSE) diffusion measurements. The instrument is portable and incorporates automated process control, allowing direct measurement of the Larmor precession. The use of a common clock for pulse sequencing, excitation pulse synthesis, and detection, results in a phase stability sufficient for accurate signal averaging. The analysis of PGSE data under the conditions of a weak detection field is discussed and measurements of diffusion are presented under both New Zealand and Antarctic conditions. The Antarctic results include an example of restricted diffusion of brine water in McMurdo Sound sea ice. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148340

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Monolythic arrays of 12pn-charge coupled devices3×1cm2each, have been developed and produced for the focal plane instrumentation of the high throughput European Photon Imaging Camera on XMM and the German ABRIXAS x-ray satellite mission. The design parameters have been optimized to match the properties of the x-ray imaging optics as well as the x-ray intensity, energy bandwidth, and characteristic time constants of objects to be observed. The pixel size is150×150&mgr;m2;read-out is performed in parallel with 64 channels in each subunit, resulting in a total of 768 channels; low noise, spectroscopic performance is realized by on-chip integrated JFET electronics; high ohmic, ultrapure bulk material allows full depletion and enhances the efficiency for higher energy x-ray detection. The fabrication process, the layout topology, and the operating conditions guarantee ten years operation in space without performance degradation. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148341

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A digital-imaging system based on a personal computer was tested for its ability to track in real time periodic motion with a frequency near 1 Hz. When imaging a vibrationally isolated stationary target, the system displayed a limitation in positional measurement of0.3×10−6 m.Further tests indicate that this limitation arises from environmental vibrations driving the target, even though it is mounted on a vibration-isolation table. This work demonstrates the feasibility of using digital imaging to measure motions other than the (usually very low frequency) torsion motion of a torsion balance, where the ultimate goal is to remove the effects of these motions from the torsion signal of interest. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148385

出版商:AIP    

年代:1997

数据来源: AIP