摘要:

The principle of inertial sliding of a platform on a periodically accelerated support is exploited for the design of a piezoelectric fine‐positioning device. The device provides step sizes of 0.04–0.2 &mgr;, speeds of up to 0.2 mm/s, and practically unlimited translation range. It is powered by a sawtooth electric waveform of 60–300‐V amplitude and useable for loads of up to 1 kg and probably even more. Mechanical parts and driver electronics are extremely simple, reliable, and easy to operate.

ISSN:0034-6748    

DOI:10.1063/1.1139566

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

High‐power rf radiation with a frequency of 800 MHz was extracted from a modulated intense relativistic electron beam into a rectangular waveguide. The rf extraction was limited to a rf power below 500 MW. Problems which prevent generation of higher power were identified and solutions offered.

ISSN:0034-6748    

DOI:10.1063/1.1139567

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A new approach to the design of a fiber‐optic interface that links a commercial sampling head to its matching time‐domain reflectometer (TDR)/sampler oscilloscope plug‐in unit is reported. Three fiber‐optic links replace the wired signal paths of the original design that convey the vertical error signal, the feedback signal, and the horizontal sampling command signal between the sampling head and the oscilloscope sampling plug‐in. The dielectric fiber pigtails allow the use of the sampling head inside objects that need to be electromagnetically insulated from the instrumentation system. Low‐frequency analog links are used to convey the error and feedback signals. The sampling command signal is conveyed via a link where a powerful, fast‐rise infrared laser pulse is generated. The laser pulse is used to trigger an avalanche transistor in the strobe generator circuit of the sampling head by directly coupling the optical energy to the transistor chip. This direct method of detection minimizes the time jitter introduced to the strobe signal, resulting in a bandwidth of 4 GHz. Some of the results of the tests which were carried out on the system are reported.

ISSN:0034-6748    

DOI:10.1063/1.1139514

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A thermometer is described which employs luminescence emitting molecular sensors to measure temperatures in the cryogenic range below 20 K. Upon photoexcitation, the molecular sensor emits luminescence from an excited spin state having two optically resolved sublevels. The sublevels are in thermal equilibrium due to rapid spin‐lattice relaxation and thus act as a two‐level radiator whose relative luminescence intensities vary with temperature according to the Boltzmann population equation. A device is described which employs photon‐counting techniques to measure the intensity ratio of the luminescence originating from these two levels and then uses this ratio to calculate the temperature of the sensor and thereby of its surroundings. The device employs remote fiber‐optic sensing and is independent of fluctuations in the excitation source or in the detection system efficiency since it monitors the intensity ratio of two emission bands. Since this temperature measurement technique is based on photophysical and thermodynamic properties of a well‐defined system, the molecular sensors employed need not be individually calibrated, only the response curve of the device needs to be determined.

ISSN:0034-6748    

DOI:10.1063/1.1139515

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Detailed calculations of the output signal‐to‐noise ratio for correlators with a linear averaging and an arbitrarily chosen weighting function are presented. Analytical relationships are derived for three mathematical models of white noise. Finally, a comparison of obtained results is made.

ISSN:0034-6748    

DOI:10.1063/1.1139517

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

This paper describes a real‐time speckle interferometer specially designed to measure the thermal expansion of a large class of intermetallic compounds for which surface optical treatments are difficult or even impossible. The instruments’ 5% accuracy, experimentally checked over the range 300–900 K, makes it a more accurate and cheaper alternative to the x‐ray devices commonly used for the above‐mentioned compounds. Moreover, the extreme simplicity of the optical setup allows an almost immediate alignment procedure and therefore makes the instrument suitable for routine measurements. The advantages of simultaneous measurements in different spots of the sample surface are also outlined. A comparison with standards, together with the measured expansion anomaly of an intermetallic compound (Ce24Co11) are presented.

ISSN:0034-6748    

DOI:10.1063/1.1139518

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

This paper describes the use of a thermal conductivity cell to measure the para hydrogen concentration in a mixture of para and ortho hydrogen gas. The device was calibrated over its entire range and the output compared with the theoretically expected form. The output of this device had been previously assumed to be linear, this assumption can lead to systematic errors of up to 5.6% in the determination of the para hydrogen concentration. A simple calibration procedure is described.

ISSN:0034-6748    

DOI:10.1063/1.1139519

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A thermocouple‐type radiometer is constructed by mounting a blackened thin‐foil heat‐flux sensor on a reflective heat‐sink block. Either the sensor alone or the completed assembly is calibrated in a thermal conductivity apparatus. The device measures total hemispheric radiation and is estimated to be accurate to within 2%. Simplicity and ruggedness make the radiometer well suited for measuring output of radiant heaters in hostile factory environments.

ISSN:0034-6748    

DOI:10.1063/1.1139520

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

An infrared scanning system was used along with inverse heat conduction methods in IR computerized axial tomography (IR CAT scan). The method consists of scanning the exposed surfaces of an object with an unknown inner boundary geometry and reconstructing section views of the object using the surface temperature data and the boundary condition prescribed along the inner boundary as input in an analysis. The mathematical theory and operational procedures of IR CAT scan are developed, and they are applied to the successful reconstruction of a section of a test model with a Dirichlet condition prescribed along the inner boundary. The sensitivity of the method to erroneous input temperature data is discussed. The mathematical theory of the IR CAT scan method developed in this paper is general and can be applied to other situations when Neumann or Robin conditions are prescribed along the inner boundary.

ISSN:0034-6748    

DOI:10.1063/1.1139521

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The medical x‐ray computerized tomography (CT) scanner has proved to be a useful tool for studies of fluid flow in porous media, with particular applications in reservoir engineering and enhanced oil recovery. This paper explains how CT is used to measure the volume fraction of pore space occupied by up to three discrete phases, such as oil, water, and gas. The image processing system, x‐ray transparent high‐pressure flow equipment, choice of fluid dopants, and x‐ray energies are described for scanning of core flood experiments. Examples are given of tertiary miscible carbon dioxide displacements in Berea sandstone.

ISSN:0034-6748    

DOI:10.1063/1.1139522

出版商:AIP    

年代:1987

数据来源: AIP