摘要:

An improved oscillator system is described for use in high‐frequency polarization modulation experiments. The improvement provides constant polarization modulation even when the resonant Q of the modulator crystal varies. A scanning split‐beam spectrophotometer providing digital output of optical density has been developed which is readily interchangeable with other applications of the system.

ISSN:0034-6748    

DOI:10.1063/1.1686248

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A new dynamic bridge for measuring the capacitance of lossy loads has been designed and constructed. Initial testing has demonstrated 10% accuracy over a range of frequencies from 1 to 105Hz in loads having loss tangents which can exceed 104.

ISSN:0034-6748    

DOI:10.1063/1.1686249

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A simple, inexpensive apparatus is described for the generation of particulate aerosols of known identity with aerodynamic size distributions characteristic of urban atmospheres. Means for using this system for the exposure of plants to selected lead aerosols are described. The design offers improvements over other systems used for similar purposes.

ISSN:0034-6748    

DOI:10.1063/1.1686250

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A high temperature thermal cavity system, designed for material and material‐environment studies, is described. A cylindrical cavity (17.4 mm diam and 25.4 mm long) is formed by a 2 mm thick vitreous carbon tube and two vitreous carbon end plugs. Provisions were made on the vitreous carbon tube and end plugs for temperature and mass spectrometric measurements and for admittance of environmental gases. The thermal cavity is resistively heated to 2000 K at an input power level of 2.5 kW with a partially open, four‐layer molybdenum heat shield. Higher temperatures are obtained with a smaller cavity. The design of the thermal cavity, the temperature performance of the cavity, the change in electrical resistance of the vitreous carbon at high temperatures, and the mass spectrometric analysis of vitreous carbon‐oxygen reaction are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1686251

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A new differential technique to measure the ratio of specific heats of two samples (and their addenda) to 0.25% or better is described. The technique has been used in the temperature range 1.5–400 K to give specific heats to an accuracy of 0.50%. The unique feature of the technique is a heat link placed between the samples as an aid in maintaining them in a near‐equilibrium state.

ISSN:0034-6748    

DOI:10.1063/1.1686252

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A biaxial split Hopkinson bar which operates in simultaneous compression and torsion is described. The device utilizes torsional stress waves generated by release of a stored torque and compressive waves generated by mechanical impact of a long rod onto a loading bar. The torque is released by capacitive discharge explosion of a thin foil in a holding adhesive joint. The two stress waves travel in opposite directions toward a specimen sandwiched between two rods, arriving at the specimen within 10 &mgr;sec of each other. The machine is used on specimens of compact bone, and it is found that plastic deformation without fracture can be achieved under the combined dynamic torsion and compression, whereas it seldom occurs under either of these loading modes alone.

ISSN:0034-6748    

DOI:10.1063/1.1686253

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A system employing a small digital computer and a multichannel tape recorder produces a set of signals simulating those obtained from the elements of an array when a source moves through its field of view. Source and array may be two‐dimensional, the source may move in real time and a change in the array or source characteristics is simply a program change. The principles of operation and two test simulations are described.

ISSN:0034-6748    

DOI:10.1063/1.1686254

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A system for measuring small specific heats of samples with low thermal diffusivity is described. A simple method for treating data obtained using discontinuous heating when temperature drifts and thermal nonequilibrium are large is introduced. The measurements on a copper sample deliberately in poor thermal contact with a calorimeter provided a test of the system and data handling.

ISSN:0034-6748    

DOI:10.1063/1.1686255

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A new analog‐to‐digital method of monitoring and recording transient electrical resistance vs time data is described, together with its application to kinetic studies of gas/metal reactions at filament temperatures above 1000 K. Resistance measurements with a precision of 0.02% are recorded at up to 40/sec on paper tape to facilitate digital computer data processing. Owing to its speed and accuracy, the method is shown to permit reaction rate determinations during transient temperature operation; allowing a portion of the Arrhenius diagram to be obtained in a single experiment, and experiments through or up to phase transformation temperatures (e.g., filament melting). Illustrative results are presented and discussed for the F‐atom/platinum reaction, which exhibits a reaction rate maximum at a temperature well below the Pt melting point.

ISSN:0034-6748    

DOI:10.1063/1.1686256

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A method is presented to observe surface species subject to electron‐induced desorption by Auger electron spectroscopy. The surface to be examined is moved under the electron beam at constant velocity, establishing a time‐independent condition and eliminating the time response of the electron spectrometer as a limiting factor. The dependence of the Auger signal on the sample velocity, incident electron current, beam diameter, and desorption cross section is analyzed. It is shown that it is advantageous to analyze the moving sample with a high beam current, in contrast to the usual practice of using a low beam current to minimize desorption from a stationary sample. The method is illustrated by the analysis of a friction transfer film of PTFE, in which the fluorine is removed by electron‐induced desorption. The method is relevant to surface studies in the field of lubrication and catalysis.

ISSN:0034-6748    

DOI:10.1063/1.1686257

出版商:AIP    

年代:1973

数据来源: AIP