摘要:

We measured the vibrational transfer function of a newly proposed crossed wire pendulum in the frequency range 0.03–3 Hz. We confirmed that it behaves as a much longer simple pendulum of the same period as far as one dimensional movement of its center of mass is concerned. We conclude that the pendulum shows promise as a component in an ultra‐low frequency anti‐vibration system. ©1994 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145202

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The application of hydrogenated amorphous silicon (a–Si:H) to optoelectronic devices are now well established as a viable low cost technology and is presently receiving much interest. Taking advantage of the properties of a–Si:H based devices, single and dual axis large area (up to 80×80 mm2) thin film position sensitive detectors (TFPSD) based on a–Si:Hp–i–ndiodes have been developed, produced by plasma enhanced chemical vapor deposition. In this study, the main optoelectronic properties presented by the TFPSD as well as their behavior under operation conditions, concerning its linearity and signal to noise ratio, are reported. ©1994 American Institute of Physics.  

ISSN:0034-6748    

DOI:10.1063/1.1144507

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A detailed description is given of a new facility for transmission57Fe Mo¨ssbauer spectroscopy (MS) studies on absorbers in a miniature diamond‐anvil cell in the temperature range 10–300 K and pressure range 0–45 GPa. Spectra with an adequate signal‐to‐noise ratio for a reliable analysis to be made have each been measured in 20–30 h of data accumulation time. This has been accomplished in spite of the severe constraints imposed by both the minute sample area and the high attenuation of the 14.4 keV probing radiation by the diamond anvils compared with the experimental conditions of conventional MS experiments. A custom‐made Rh(57Co) ‘‘point’’ source with a high specific activity has been used in conjunction with absorbers that have an optimal enrichment (10%–20%) of57Fe. The successful implementation of57Fe Mo¨ssbauer spectroscopy at very high pressures and variable cryogenic temperatures has been accomplished by making relatively simple refinements to existing elements of high‐pressure MS methodology. ©1994 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1144508

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We describe a highly sensitive new type of calorimeter based on the deflection of a ‘‘bimetallic’’ micromechanical sensor as a function of temperature. The temperature changes can be due to ambient changes, giving a temperature sensor or, more importantly, due to the heat absorbed by a coating on the sensor, giving a heat sensor. As an example we show the results of using the sensor as a photothermal spectrometer. The small dimensions and low thermal mass of the sensor make it highly sensitive and we demonstrate a sensitivity of roughly 100 pW. By applying a simple model of the system the ultimate sensitivity is expected to be of the order of 10 pW. The thermal response time of the cantilever can also be determined, giving an estimate of the minimum detectable energy of the sensor. This we find to be 150 fJ and again from our model, expect a minimum value of the order of 20 fJ.

ISSN:0034-6748    

DOI:10.1063/1.1144509

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Diamond film thermistors were fabricated from polycrystalline diamond films grown on sintered Si3N4by microwave plasma chemical vapor deposition. An undoped diamond layer and a zigzag or rectangular pattern of B‐doped semiconducting diamond were successively deposited by a selected‐area deposition technique. For ohmic electrodes, a Ti/Au bilayer was used. The resistance‐temperature characteristics were measured from room temperature to 300 °C. It was found that the temperature coefficient of a diamond film thermistor with a B‐doped diamond layer grown using 0.1 ppm B2H6as dopant gas was higher than those of platinum resistive temperature detectors and SiC film thermistors. ©1994 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1144510

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The long‐term time‐dependent relaxation of the electrical resistance in several carbon and RuO2based temperature sensors at helium temperatures was investigated. The relative change of the resistance at fixed low temperature, measured immediately after sufficiently rapid cooldown has been found to be always logarithmic with time. In the helium temperature range, the spurious temperature drift associated with this effect for Allen–Bradley and Matsushita carbon radio resistors and for Philips RuO2based thick film sensors reaches about 1 mK per time decade, while for Rivac carbon film sensors it is an order of magnitude higher. The theoretical model explaining this relaxation based on the variable range hopping conductivity mechanism and the standard levels AHV theory of glasses at low temperatures was developed. ©1994 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145168

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A prototype three‐axis magnetometer has been developed, intended for geophysical applications, involving high‐transition temperature dc superconducting quantum interference devices (SQUIDs). Each SQUID was fabricated from a thin film of YBa2Cu3O7−xdeposited on a SrTiO3bicrystal to form two Josephson junctions, and was directly coupled to a single‐turn pickup loop patterned in the same film. The three orthogonally mounted sensors were immersed in liquid nitrogen in a fiberglass Dewar and operated in separate flux‐locked loops. In nominally zero ambient magnetic field, the best magnetic field resolution was 170 fT Hz−1/2in the white noise, increasing to 225 fT Hz−1/2at 1 Hz. The dynamic range was ±1.6×106Hz1/2in the white noise, and the highest slew rate achieved was 1.6 mT s−1, at 900 Hz. The 3 dB point in the frequency response was about 90 kHz. The three channels were mutually orthogonal to about 1%. The three‐axis magnetometer was also operated outside the laboratory in the presence of 60 Hz and radio‐frequency noise. ©1994 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145169

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A new type of SQUID gradiometer, a direct‐feedback gradiometer, is introduced in this paper. It is an axial gradiometer made of thin superconductive films. It consists of two magnetometers: a ‘‘cancellation magnetometer’’ and a ‘‘sensing magnetometer.’’ The feedback flux of the cancellation magnetometer is applied to both pickup coils of these magnetometers by connecting their feedback coils in a series. Environmental magnetic noise applied to the sensing magnetometer is cancelled by the magnetic flux measured by the cancellation magnetometer, when the two magnetometers are connected with normal conductive wires. The gradiometer has been fabricated and operated in a moderate magnetically shielded room. The capability to reduce environmental noise and thus to measure auditory evoked fields from the human brain has been confirmed. ©1994 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145170

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A modified Kra¨tschmer–Huffman reactor for the mass production of fullerenes is presented. Fullerene mass production is fundamental for the synthesis of higher and endohedral fullerenes. The reactor employs mechanisms for continuous graphite‐rod feeding andinsituslag removal. Soot collects into a Soxhlet extraction thimble which serves as a fore‐line vacuum pump filter, thereby easing fullerene separation from soot. Thermal gravimetric analysis (TGA) for yield determination is reported. This TGA method is faster and uses smaller samples than Soxhlet extraction methods which rely on aromatic solvents. Production of 10 g of soot per hour is readily achieved utilizing this reactor. Fullerene yields of 20% are attained routinely. ©1994 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145171

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A centrifuge ball viscometer was developed for fluids with a wide viscosity range. The viscosity &eegr; could be obtained from an empirically derived relationshipac=b(&eegr;V∞)c, whereacis the applied acceleration,bandcare empirically determined parameters, andV∞is the terminal velocity. The key features of this viscometer are as follows. (1) A wide range of viscosities can be accommodated: about 10−1to 105Pa s with 1010Pa s achievable, in principle, for about a one‐data point per day measurement. (2) A computer controlled motion controller allows rotation speed of the motor varying over a speed of 1 to 5000 (±0.01) RPM (revolutions per minute). Thus, measurements at different low shear rates can be accomplished. (3) About 0.5 ml of sample volume is needed for the present setup. (4) The temperature can be maintained from ambient to over 400 °C (±0.05 °C). (5) The samples are isolated by sealing them in glass tubes, a potential advantage when dealing with polymer solutions, polymer melts, and/or those systems subject to oxidative degradation. ©1994 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145172

出版商:AIP    

年代:1994

数据来源: AIP