摘要:

A winding geometry for the construction of coreless transformers has been devised. The geometry can be employed for the construction of transformers with both a high turn ratio and high coupling factor. If made with superconductors, the transformers could find applications for matching the input coil of a SQUID to a high impedance source. A turn ratio of 1500 with a coupling factork=0.91 has been obtained experimentally using commercial wire. The high power superconducting version of this transformer could also find application at advanced energy distribution sites. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145602

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A resonant optoacoustic technique is described using continuous wave laser excitation and piezoelectric detection of overtone absorptions of liquefied gases at cryogenic temperatures. This technique uses a piezoelectric detector directly attached to a low temperature cell inside a cryostat. The liquefied sample inside the cell is vibrationally excited in the visible region with a continuous wave dye laser. The laser is modulated around 100 kHz with an acousto‐optic modulator. The modulation frequency corresponds to an acoustic resonance frequency of the cylindrical cell which increases the sensitivity of the detection system. The pressure wave detected by the piezoelectric transducer is sent to a lock‐in amplifier and processed with a microcomputer. This sensitive technique is used to obtain the visible spectra of pure liquid methane and ethane. Spectra of the fourth overtone of the C‐H stretch vibration of methane, in solution with liquid argon at 94 K, and in solution with liquid nitrogen at 84 K, are also reported. Comparison is made with nonresonant and pulsed acoustic techniques. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145603

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The physical properties of polymer fibers are directly related to the development of orientation in the draw zone under extensional conditions. Although the final properties and microstructure of fibers can be evaluated after processing is completed, it is desirable to understand the development of orientation during drawing independently from the effects superimposed by subsequent unit operations.Insitux‐ray scattering measurements of the extrudate in the draw zone provide an ideal means of accomplishing this goal. Depending on the polymeric system to be studied, rotating anode or synchrotron‐based x‐ray sources may be required, making portability of the fiber drawing device highly desirable. This paper describes an easily transportableinsitux‐ray filament drawing device, and discusses typical data obtained using the device to produce filaments from a liquid crystalline nematic solution of poly(cis‐benzoxazole) in polyphosphoric acid. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145604

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An automatic tracking of the angular alignment position of mask with respect to the wafer in a photolithographic mask aligner is reported. It is demonstrated that automatic dynamic control with very high accuracy and stability of the angular alignment position is practically possible. The moire´ interference fringe method is employed for the present experiments. The alignment marks are used in the form of 25 &mgr;m pitch Ronchi ruling gratings. The best angular alignment accuracy obtained with the present experimental conditions is of the order of 2×10−7rad. An alignment accuracy up to ±3×10−7rad is reported for more than 30 min which enables the present technique to be used for the real photolithographic mask aligner. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145605

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report on the design and performance of a low‐temperature sample manipulator for ultrahigh‐vacuum surface studies. The arrangement consists essentially of modified commercial sample manipulator coupled to a closed‐cycle helium refrigerator. The device allows a metal sample or a substrate, which is electrically isolated, to be cooled down to 16 K and heated up to 1100 K for cleaning and annealing purposes. Besides, the sample can be translated by ±0.5 cm in three perpendicular directions (X,Y, andZaxes), rotated by ±100° azimuthally along the main shaft (Zaxis), and flipped over a range of 50° about an axis perpendicular to the main shaft. The sample holder, which includes the rotation supports, is sufficiently compact to be manipulated without hindrance as close as 1.4 cm from a given instrumentation. A simple mathematical model is developed to predict the cooling capacity of the present design or that of similarly constructed devices. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145606

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A simple event‐counting technique is considered that can be implemented on detector systems with adjustable exposure times. A single measurement cycle has two steps: exposure and readout. During readout a threshold is used to discriminate against background noise, making it impossible to differentiate between single or multiple events. The actual event rate can be estimated by accumulating the results of repeated measurement cycles, and applying a correction based on the probability for multiple events to occur. By considering the uncertainty in the estimation of the event rate, and assuming a Poisson process, it is shown that optimum exposure requires an average event count per exposure of roughly 1.7. The technique is applied to a high‐energy electron‐counting system based on a linear CCD photodetector. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145607

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A wideband (dc to 500 Hz) low noise accelerometer has been developed. It makes use of a suspended mass whose displacement relative to the supporting structure is sensed by a linear variable differential transformer. It works both in horizontal and in vertical direction. The electronics is connected to the mechanical structure through 12 m long cables. The spectral sensitivity is 7×10−10(m/s2)/&sqrt;Hz below 6 Hz. The accelerometer will be used to perform an inertial damping of the resonances of the suspension of the mirrors in VIRGO, an interferometric antenna for gravitational waves detection. ©1995 American Institute of Physics. 

ISSN:0034-6748    

DOI:10.1063/1.1145608

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The development of a portable gamma ray spectrometer based on a CsI(Tl) scintillator (1.8 cm×1.8 cm×4 cm) with integralp‐i‐ndiode (1.8 cm×4 cm) is described. A single board computer containing the MC68HC11 microcontroller, a single‐chip self‐contained computer system, is used for system control. The total size of the instrument is only 12 in×7 in. including the spectrometer and power supply. The system provides a low cost, low power gamma ray spectrometer as compared to the more common PMT‐based devices. Spectra can be collected in daily intervals for up to 1 week. Special software which monitors the proper working of the spectrometer insures long term stability. This spectrometer can be used for routine monitoring and detection of gamma ray emitting radio nuclides. Performance of the spectrometer as well as gamma ray spectra are presented. The qualitative and quantitative reliability have shown its potential as a stand alone field monitoring instrument due to its low power consumption and intelligence. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145609

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

This paper describes an optoelectronic system suitable for road surface tests. Its purpose is to detect the presence of ice, water, or mud on road surfaces. The system uses backscattered and reflected light information. A considerable amount of the work was done to investigate scattered light patterns as they relate to asphalt conditions. Results from a laboratory prototype are presented for four asphalt conditions. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145610

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

This paper reports an automatic instrument developed for characterization of optical waveguides. A specially designed waveguide excitation unit offers a flexible platform for measurement of optical waveguide characteristics like number of propagating modes, mode field intensity distribution, the refractive index profiles, waveguide geometry, attenuation, and dispersion. Further, the availability of attachments like filters, polarizers, chopper, intensity profiler, and CCD camera make the instrument flexible enough for a variety of other experiments also. The instrument is PC controlled and assisted by user friendly menu‐driven software. A large number of waveguides have been analyzed using the setup. These results are also presented in the paper. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145611

出版商:AIP    

年代:1995

数据来源: AIP