摘要:

The pressure loss in a high pressure vessel of a piston‐cylinder press has been studied at the bismuth (I‐II) and (II‐III) transitions. This was accomplished by measuring the abrupt diminution of volume of bismuth, which was surrounded by a solid pressure transmitting medium, at the pressure‐induced phase transitions. The study of pressure loss has been made by measuring three pressure losses which are defined as follows: (1) Pressure loss I is due to the interfacial friction between the cylinder and the piston. (2) Pressure loss II is due to the interfacial friction between the cylinder and the solid pressure transmitting medium which separates the piston and bismuth. (3) Pressure loss III originates within ``the sample‐containing cross section of the cylinder'' and is due to the internal friction of the medium. Experiment showed that the pressure loss III is the largest among the pressure losses. The difference between the true pressure on the bottom of a sample and the average pressure on the top of the piston due to pressure loss III has been formulated. This pressure loss study has been applied to the pressure calibration of a high pressure furnace containing a sample under investigation and also to the drawing of a diagram of pressure distribution in the furnace.

ISSN:0034-6748    

DOI:10.1063/1.1720958

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The design and performance of a large area, low voltage device for controllably subliming metals or nonmetals at temperatures up to 1400°C is described. The sublimator consists of a BeO ceramic core internally heated by six resistive elements connected in parallel to eliminate hot spot and instability problems. The material to be sublimed is affixed to the core as a split tube, sheet, strip, wire, or powder slurry and is heated uniformly by thermal conduction. Problems of heat flow, thermal runaway, and high temperature chemical reactivity of adjacent sublimator elements are considered together with solutions obtained. Performance data are presented for a titanium sublimation application in which sublimation rates of 6.8×10−7g/sec at 450 W increasing to 8.3×10−5g/sec at 950 W were obtained. Usable lifetimes in excess of 30 000 h of continuous operation are possible.

ISSN:0034-6748    

DOI:10.1063/1.1720959

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

This paper describes the instrumentation and in‐flight performance of the rubidium vapor magnetometers being flown by the National Aeronautics and Space Administration on the POGO satellites. An optically pumped, self‐oscillating rubidium magnetometer was selected as being most compatible with the objectives of the study and with the spacecraft capabilities. A four absorption cell configuration is used to reduce the effect of the null zones inherent in these instruments and to obtain accuracies compatible with the scientific objectives of the program. Scalar magnetic field data are obtained in both digital (PCM) and analog (frequency multiplex) form. Instrument performance parameters are monitored through both main frame and subcommutated PCM data. The first instrument orbited was aboard OGO‐II which was launched on 14 October 1965. This instrument has returned a large quantity of data, and is still operating when sufficient spacecraft power is available. The accuracy of the data is determined, apart from orbit accuracy, by spurious phase shifts within the instrument. These arise from such sources as optical axis misalignment, electronic nonlinearities and frequency dependence, and propagation delay over the long cables connecting sensor and electronics. The magnitude of the resulting error is inversely proportional to the phase slope of the dual cell absorption line. The total effect in the POGO instrument of these sources of error is an accuracy of better than 1.5&ggr; over the entire instrument range of 15 000 to 64 000&ggr;.

ISSN:0034-6748    

DOI:10.1063/1.1720960

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The optical Faraday effect hysteresigraph is an instrument for measuring the static thermomagneto‐optic properties of thin transparent magnetic film samples. Via an oscilloscope, it displays 60 Hz magnetic hysteresis loops of the samples over a temperature range of 20°C±40°, with peak magnetic fields of 2600 Oe. Its use of thermoelectric elements results in a compact package, highly effective for rapid change and accurate control of sample temperature.

ISSN:0034-6748    

DOI:10.1063/1.1720961

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Three pressure transducers that can be used in high temperature gas dynamic studies are described and their performance discussed. It is shown that the Baganoff gauge can be usefully employed to study high temperature and pressure gaseous detonation wave phenomena, provided the gauge is constructed from glass. This modification results in greatly reduced sensitivity, but preserves the high frequency response and over‐all characteristics of the original gauge. A second gauge, using the pressure bar principle, is shown to have wide application in studies of high temperature shock waves in the presence of large magnetic and electric fields, provided the pressure bar is constructed from a nonconductor having appropriate properties. The results of experiments with this gauge indicate that, even with poor acoustic matching of the gauge elements, it is possible to obtain an accurate estimate of the pressure behind a shock or blast wave with a time resolution of about 2 &mgr;sec. The third device described is designed for use where only the accurate arrival time of a pressure pulse is desired and has been used extensively at this Laboratory for plotting shock trajectories in magnetic shock tubes.

ISSN:0034-6748    

DOI:10.1063/1.1720962

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

It is the purpose of this paper to establish a new series development representing the solid angle subtended by a circular disk at a point situated directly above and in the immediate vicinity of the periphery. After having recalled Masket's series expansion which is applicable only for distances larger than the diameter of the disk, a few initial terms of the new series expansion are deduced starting from an integral representation of the solid angle and applying some formulas from the theory of Legendre's complete elliptic integrals. In this way, it is shown that the series must contain logarithmic terms besides integer powers of the distance variable. Then, after having transformed the problem under study into an equivalent problem of electrostatics, the complete infinite series representation of the solid angle is deduced from its expression as a Fourier integral by applying a new expansion theorem to the latter. The paper ends with an interesting verification of the obtained result.

ISSN:0034-6748    

DOI:10.1063/1.1720963

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Tungsten‐rhenium thermocouple systems were evaluated for use in measuring temperatures between 1600 and 3000°C. Temperature‐millivolt relationships were extended from 2300 to 3000°C for bare‐wire W3Re/W25Re and W5Re/W26Re thermocouples in vacuum. The performance of W26Re sheathed, high‐fired beryllia‐insulated thermocouples was limited only by the melting point of the beryllia insulation (∼2550°C). The thermoelectric output of high‐fired thoria‐insulated thermocouples sheathed in W26Re was determined and found to be reliable up to at least 2850°C, when corrected for electrical shunting through the insulation. Stability of high temperature thermocouples using thoria insulation was within ±0.3 mV (±40°C) when held at 2425°C for 148 h.

ISSN:0034-6748    

DOI:10.1063/1.1720964

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Techniques have been developed for conducting shock tube experiments on mixtures of fine solid particles and gases. Particles with diameters of 1 &mgr; and smaller are prepared by grinding in a dry atmosphere. The powdered material is injected into the shock tube test section by opening a valve connecting the evacuated shock tube with a tank containing gas into which the powder has been previously suspended by a pressurized injection. The axial distribution of powder in the shock tube has been measured both by determining the weight of powder which has settled out on small stainless steel slides placed in the shock tube and by observing the optical absorption from a long‐life reaction product of the shock‐heated powder‐gas mixture as the mixture sweeps by an observation port. Typical operating results are presented, including particle size distribution of a solid material after grinding, powder distribution along the shock tube axis after injection, and oscilloscope records of absorption at 2536 Å by the CF2formed from Teflon decomposition behind the incident shock wave.

ISSN:0034-6748    

DOI:10.1063/1.1720965

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A versatile instrument code named SPECS (for Switched Proton Electron Channeltron Spectrometer) has been developed for measurement of charged particles in space. Particles entering the device pass between a pair of deflection plates across which is established a voltage Vi. Particles of a given charge and different energies are then deflected into a set of five channeltron devices located on one side of the deflection plates, while particles of the opposite polarity but comparable energies are deflected into a funneltron located on the opposite side of the plates. Thus, electrons and protons are detected simultaneously in a total of six differential energy intervals. The voltage Viis then changed over six steps: ±35 V, ±350 V, and ±3500 V. In this way electrons are measured over an energy range of about 50 electron volts (eV) to about 100 000 eV. Protons are measured over the same energy range, with the lowest detectable energy set by the intrinsic channeltron efficiency of detection of positive ions at some hundreds of electronvolts. The thirty‐six energy channels can be measured in an adjustable cycle time as short as 1 sec. Stepping can be internally or externally synchronized. Different versions of the device have been built for numerous rocket and satellite applications, with weight between 900 and 1600 g, and power less than 1.5 W. Five small units have been flown to date on Javelin rockets, and the larger will be put into orbit in the satellites code‐named Owls 1 and 2 and Aurora 1, while another set will be deployed by the astronauts on the lunar surface. The scientific advantages and flexibility of the units are described.

ISSN:0034-6748    

DOI:10.1063/1.1720966

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A method of making ceramic‐to‐metal seals is described. The technique is based on a nickel‐titanium intermetallic compound which is ductile and has a wide composition range. The compound is used as a braze which wets ceramics, such as sapphire, very easily to form hermetic seals. The braze may be made in an argon stream and does not rely on a vacuum. The seals can be made quickly and easily and are very stable towards the liquid metal cesium, and may be used in air up to 800°C for extended periods of time.

ISSN:0034-6748    

DOI:10.1063/1.1720967

出版商:AIP    

年代:1967

数据来源: AIP