摘要:

An 8085‐based microprocessor system was developed to monitor and control the magnetic field in a three‐axis, Helmholtz‐coil cage for an electron energy‐loss apparatus. The nulling field produced by the coils is monitored by three RFL Industries Model 101 magnetometers, and the coil current is provided by three Kepco PCX21‐1MAT power supplies. The computer reads the magnetometers and provides the appropriate reference voltage to each supply to null the field in each direction. The static field is typically nulled to 5 &mgr;G with this system.

ISSN:0034-6748    

DOI:10.1063/1.1137219

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The Bureau of Mines has developed a system for the rapid grab sampling of heterogeneous mixtures of gases and dusts during the preignition and postignition stages of dust explosions. The combustion chamber in which the explosion occurs is first fitted with a hypodermic sampling needle with its inlet end at the desired sampling point within the chamber and its sharp, injecting end protruding outside of the chamber. Rapid sampling (approximately 25 to 50 ms) is achieved with a double‐acting, air‐pressure‐actuated cylinder. The forward stroke of the cylinder thrusts the rubber septum seal of an evacuated glass sampling tube onto the protruding needle which punctures the septum, filling the tube with gas and dust from the combustion chamber. The return stroke of the cylinder reseals the sampling tube by returning the mechanism to its original position. The initial time of sampling and the duration of sampling are independently variable and controlled by a microprocessor. Results obtained with a trimodal distribution of coal dust show no significant size discrimination at least up to 70 &mgr;m. Data obtained from laboratory‐scale coal dust explosion tests are also presented. Such data provide valuable insights into the basic phenomena involved in explosions.

ISSN:0034-6748    

DOI:10.1063/1.1137220

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

We demonstrate a new technique for localized melting and boring of materials using discharges guided by laser induced breakdown of atmospheric pressure air. This technique has important applications to a novel method for machining and welding materials, since the melting location can be controlled by adjusting the path of the focused laser beam. These experiments have demonstrated several features of localized metallic melting by laser guided discharges: (1) the melted spot can be scanned by changing only the position of the laser focal spot on the metal sample; (2) the melted spot diameter and profile depend upon the relative timing of the laser pulse and the discharge; (3) defocusing the laser beam has an effect upon the melted spot pattern; and (4) hole boring has been accomplished in aluminum foils which cover the stainless‐steel electrode.

ISSN:0034-6748    

DOI:10.1063/1.1137221

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

We developed a special laser system for two pulse (about 100 ms interval) and multiple position (10 different points) Thomson scattering. A special feature of this laser system is that the beam quality is improved by adjusting the condition of the cavity wall. For two pulses, the power supplies are doubled and thyristor switches are used.

ISSN:0034-6748    

DOI:10.1063/1.1137222

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A very simple welded double diaphragm press has been constructed and tested. It is suitable for providing the forces and displacements for operation of a diamond anvil cell and requires only a small capillary connecting a helium gas pressure source and the diamond anvil cell.

ISSN:0034-6748    

DOI:10.1063/1.1137223

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An absorption cell for use with 10‐&mgr;m radiation has been designed and tested. The cell is capable of operation to 400 °C and to pressures of at least 15 atm.

ISSN:0034-6748    

DOI:10.1063/1.1137224

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A single‐photon timing system is described which is capable of extracting fluorescence lifetimes as short as 25 ps. The system is an improved version of an earlier apparatus. The new system uses a synchronously pumped, mode‐locked dye laser with 10‐ps pulses operating at 82‐MHz repetition rate. A fast photodetector and a leading‐edge discriminator were developed to use with this light source. Also, a special rate reduction circuit was built to eliminate large oscillations in fluorescence decay spectra due to the excessive stop rates that overload commercial time‐to‐amplitude converters.

ISSN:0034-6748    

DOI:10.1063/1.1137225

出版商:AIP    

年代:1983

数据来源: AIP