摘要:

An apparatus incorporating a magnetic suspension technique has been developed for density measurements on liquids and liquid mixtures, particularly at saturation, at temperatures between 90 and 300 K and at pressures to 5 MPa (approximately 50 atm). The feasibility of adapting this method, previously used at room temperature, for low temperature use had been demonstrated in an earlier study with a density measurement on saturated liquid nitrogen near its normal boiling point. The present apparatus, which is significantly improved, and in most respects different from the earlier model, is described in detail. It includes a cryostat for continuous wide‐range temperature control, a windowed equilibrium cell particularly suited for studies of liquid mixtures, and a new electronic servocircuit with a linear differential transformer for position control of the magnetic buoy. Extensive tests and density measurements have been carried out to evaluate the performance of this apparatus. Densities of saturated liquid nitrogen between 95 and 120 K and saturated liquid methane between 105 and 160 K are reported. The estimated standard deviation of a single density measurement is less than 0.02%. The total systematic error in the measurement process from known sources is approximately 0.05%. The total uncertainty of a single density measurement, which is taken as three times the standard deviation plus the systematic error, is approximately 0.1%. Comprehensive comparisons of the present results with previous experimental data are presented.

ISSN:0034-6748    

DOI:10.1063/1.1134519

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

A method is described for determining,insitu, the shapes of nanosecond, positive high‐voltage desorption pulses at the surface of a field‐ion specimen, without the use of waveform‐distorting probes or voltage dividers. In practice, a negative pulse known to be identical in shape to the positive desorption pulse is used to initiate field electron emission from the specimen surface. The resulting time‐varying field emission current is recorded by a detector, and the Fowler–Nordheim equation is iterated to obtain the actual time‐varying specimen potential. The pulse shape obtained can be used to predict accurately the arrival time of unknown surface species in time‐of‐flight atom‐probe instruments, or to monitor the effect of changes in the pulse transmission line to the specimen. When applied to pulsed e‐beam devices and flash x‐ray machines, time‐varying potentials at field‐emission cathodes can be determined with nanosecond resolution.

ISSN:0034-6748    

DOI:10.1063/1.1134520

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The absolute detection efficiency for protons and for hydrogen atoms in the energy range 5–60 keV is determined for a resistance strip magnetic electron multiplier particle‐counting system. Significant history‐dependent gain variations are discussed. The detector system is suitable for use in coincidence experiments requiring particle‐counting rates to 1.0 MHz and timing accuracies of 3.0 nsec.

ISSN:0034-6748    

DOI:10.1063/1.1134521

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

An apparatus has been designed and constructed for the measurement of the optical characteristics of passive displays. It provides isotropic illumination to the top surface of the display and generates data on the contrast ratio of individual segments as they are viewed from any direction above the display. Typical results on the brightness, contrast ratio, and the angle dependence of this contrast ratio are shown for a commercially available LCD.

ISSN:0034-6748    

DOI:10.1063/1.1134522

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Inexpensive large area detonators are described which utilize a mesh of etched copper brigewires to detonate PETN. Breakout simultaneity within 100 nsec is achieved on the surface of a PBX‐9407 booster at discrete initiation points originating from the individual bridgewires. Initiation point densities as high as 3.1×105m−2are achieved by printed circuit manufacturing techniques. Electrical requirements are established from threshold burst current experiments. Two initiators are described; a general purpose 200‐mm diam detonator, employing 750 or 10 000 bridgewires (depending on the mesh pattern used), and a 150×600 mm detonator employing 2300 that was developed for a fast explosive generator. These detonators achieve simultaneous detonation of large surface areas at lower cost and with much less explosive than conventional lens systems. They can also be applied to singly curved surfaces.

ISSN:0034-6748    

DOI:10.1063/1.1134523

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The design of a versatile instrument for aerosol assessment is described. The single stage device incorporates the principal of virtual impaction and a continuously variable slit width to provide for ease of calibration, low internal wall losses, and potential for large‐scale sampling, as well as the option of either fractionating particles into two size classes for mass or chemical analysis or determining entire particle size distributions. Initial tests indicate the efficiency curve of the device is solely a function of particle Stokes number &psgr; for typical geometries and flowrates and is characterized by the cutoff value &psgr;1/250=0.36 ±0.04 and a steepness of &psgr;1/284/&psgr;1/250=1.32±0.06. Moreover, wall losses are shown to peak at less than 15% at the critical Stokes number &psgr;1/250, which is an improvement over existing devices now used for large‐scale sampling.

ISSN:0034-6748    

DOI:10.1063/1.1134504

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

A new type of field ionization source is described. The emitter comprises carbonaceous dendrites grown along the edge of a 20‐&mgr;m‐thick tungsten foil by field ionization of pyridine at 1200 °C. The flow of the material to be ionized is directed to the ionization region by a second foil which defines a slit along the ionizing edge. This field ionization source, which provides a line‐shaped image, has an ionization efficiency comparable to that of a well‐activated multipoint source, and it does not undergo significant deactivation by negative ion bombardment.

ISSN:0034-6748    

DOI:10.1063/1.1134505

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

An apparatus for high pressure x‐ray diffraction at liquid‐He temperature is described that consists of a vessel capable of holding pressure up to 100 kilobar between Bridgman anvils immersed in liquid He in a cryostat. A technique is described for attachment of vacuum‐tight beryllium windows to the cryostat. With this apparatus, the superconducting transition temperature of Pb and its dependence on pressure were measured; the pressure was determined from the lattice parameter of NaCl on the basis of the equation of state for NaCl. The result can be used as a low temperature manometer.

ISSN:0034-6748    

DOI:10.1063/1.1134506

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Modifications to an existing vacuum emissometer are described that allow mathematical elimination of reflection errors of the specimen–window–specimen–detector type. Normal total emittance in the range 20–600 °C can be determined. Successive radiance readingsLsandLs′ are obtained using alternate full‐ and reduced‐size apertures. A separate run on a blackbody crucible allows determination of the correspondingLBBandLBB′ values at the same temperature. The equation for true emittance is shown to be &egr;=Ls−Ls′/LBB−LBB′.

ISSN:0034-6748    

DOI:10.1063/1.1134507

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

A high‐voltage probe measuring system with an overall rise time of less than 50 psec and a peak voltage capability of 20 kV has been developed. Probe perturbations at the 50 &OHgr; impedance level are minimized by maintaining a moderately high input impedance, in conjunction with the absorption of internal reflection waves by means of a lossy distributed transmission line. System long‐term stability and constructional reproducibility have been investigated.

ISSN:0034-6748    

DOI:10.1063/1.1134508

出版商:AIP    

年代:1976

数据来源: AIP