摘要:

The shock loading and the unloading behavior of piezoresistive carbon gauges was investigated by means of impact experiments performed with a smooth bore gas gun. Experiments in the range 0.291–5.485 GPa provided shock stress‐time profiles. Up to about 2 GPa the shock loading data were fitted with a least square polynomial in good agreement with other published date. Over 2 GPa the carbon presents a strongly scattering behavior. The unloading response in the reliable loading behavior range (0–2 GPa), exhibits an important hysteresis phenomena which could be imputed to the presence of pores in the carbon strip.

ISSN:0034-6748    

DOI:10.1063/1.1136339

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

An electronic instrumentation for heterodyne evaluation of holographic interferograms by accurate phase‐measurements is described. It allows to achieve an overall interpolation accuracy of 1/1000 of a fringe. The specifications for the electronic circuitry are derived from the conditions in the optical experiment. To improve the SNR, a narrow‐band signal‐filtering is needed; an AGC circuit has to adapt the gain in the signal channel to various experimental conditions. Special measures for reduction of phase errors due to these circuits are discussed. The phase meter with an accuracy of 0.1 deg is described in detail. It counts continuously the multiples of &pgr;’s as obtained when the detectors are crossing fringes in the image plane of a reconstructed interferogram. The total measuring range for phase is given by the capacity of the up‐down counter, and thus practically unlimited.

ISSN:0034-6748    

DOI:10.1063/1.1136340

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Graphite–halogen (Br2, ICl) residue compounds have been found to be convenient temperature calibration standards for transmission electron microscopy in the medium temperature range. Due to the order–disorder transformation associated with the intralayer intercalate ordering in these intercalation compounds, the observation of the disappearance of the superlattice diffraction spots as the sample temperature is raised serves to calibrate the temperature. The transformation occurs at 100±1 °C in graphite–Br2and 41±1 °C in graphite–ICl. The simplicity of specimen preparation gives added attraction to the use of graphite–halogens as temperature calibration standards.

ISSN:0034-6748    

DOI:10.1063/1.1136341

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A technique for measuring directly the angular distributions, and consequently the absolute differential cross sections, for positron‐ and electron‐atom elastic scattering is described. By exploiting time‐of‐flight spectrometry, simultaneous measurement over a wide range of forward angles is achieved. The structure and performance of the components of the experimental system are described in detail, and the reliability of the apparatus in the measurement of positron‐atom cross sections is tested by using the same spectrometer to study electron scattering. Results are presented for elastic electron‐argon scattering at energies between 5 and 20 eV which are in reasonable agreement with other recent results. Systematic effects on the measurements are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1136342

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The trochoidal electron monochromator employs an axial magnetic field and a transverse electric field. Many aspects of its performance can be described by electron trajectory equations which include the voltage drop across the entrance aperture. A beam shear is predicted, which is a function of a parameter tan&Vthgr;. Optimum performance is achieved by matching the exit aperture to the sheared beam. tan&Vthgr; establishes a relationship between the field magnitudes and the dimensions of the monochromator. Estimates of appropriate values for these parameters can be made, with the final optimum values being determined by a combination of practical and empirical considerations. Finally, the use of the instrument as an energy analyzer is described.

ISSN:0034-6748    

DOI:10.1063/1.1136332

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

An efficient photon correlator has been developed for the measurements of the temporal change of a very weak fluorescence. It was designed by using a TTL integrated circuit which is standard and easily available. Data acquired by an electric circuit were processed and accumulated in the memory of a computer. The system operates in a delayed counting mode and its temporal resolution is 25 ns.

ISSN:0034-6748    

DOI:10.1063/1.1136343

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

An automatic digitizer has been developed that employs a microcomputer‐controlled photosensor to detect and digitize analog curves from strip‐chart paper, drawings, photographs of oscilloscope traces, negatives, etc. The control and data acquisition programs are coded in BASIC enabling real‐time interactive control of the system. Movement of the photosensor is accomplished under program control and is selectable in either a curve‐follower or raster‐scan mode. Use of visible‐LED photodetectors permits curves drawn with different colored inks to be discriminated and separately digitized. The system is simple to use and highly versatile with capabilities that extended beyond curve digitization. In the raster‐scan mode, operation of the apparatus as an optical densitometer is possible enabling detailed image analysis and digital image reconstruction to be performed (e.g., quantitative measurement of intensity distribution and mode structure from photographs of laser output beams.)

ISSN:0034-6748    

DOI:10.1063/1.1136353

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The melting curves of indium and bismuth were determined in a piston‐cylinder device. A comparison of the results obtained by differential thermal analysis and volumetric techniques confirms the existence of an asymmetric friction component. Transition pressures are overestimated if allowance is not made for asymmetric friction. The application of Mirwald’s ’’zero friction’’ technique for talc and NaCl assemblies indicated that only symmetrical and not asymmetrical friction is eliminated.

ISSN:0034-6748    

DOI:10.1063/1.1136354

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A high pressure differential scanning calorimeter for low temperature investigations is described. It allows the measurement of thermodynamic properties of substances over wide ranges of temperature and pressure, e.g., between 100 and 450 K at normal pressure and between 100 and 300 K at 4 kbar. Up to now the calorimeter has been used for the determination of transition enthalpies and transition temperatures of some plastic crystals up to 1500 bar from which other properties, e.g., transition entropies and transition volumes, can be calculated.

ISSN:0034-6748    

DOI:10.1063/1.1136355

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A wavelength‐scan and intensity‐control system for a widely‐used, high‐intensity monochromator is described. The wavelength scan is bidirectional and variable speed, and may be controlled manually or by TTL logic from a computer. The intensity control is effected by use of a programmable dc power supply and D–A converter. Various filters are described which allow an intensity of up to 2×1014photons/cm2s to be achieved in a 1 cm×3 cm area over a wavelength range 0.76–2.50 &mgr;m, at 0.07 &mgr;m bandwidth, with a single grating. (A lesser intensity is available to 3.4 &mgr;m.) This wide range is made possible by the use of second‐order light from 0.76–1.00 &mgr;m. Photoconductivity data in GaAs:Cr and InP:Fe are presented, as an example.

ISSN:0034-6748    

DOI:10.1063/1.1136356

出版商:AIP    

年代:1980

数据来源: AIP