摘要:

The reported nearly constant temperature sensitivity of appropriately annealed polycrystalline AuxGe1−xthin films at cryogenic temperatures would appear to make them promising materials for low mass, rapid thermal response resistive thermometers, but their adoption has been limited by difficulties in fabrication and uncertainties in annealing. In this work, we present a method of fabrication and annealing which allows control of the two most important parameters for these films: the room-temperature resistivity&rgr;RTand the temperature sensitivity&eegr;(T), where&eegr;≡−d ln R/d ln T. We find that the dependence of&rgr;RTon total anneal durationtforx≈0.18is given by&rgr;RT=&rgr;∞[1−Aexp(−t/&tgr;)], where the limiting room-temperature resistivity&rgr;∞,the annealing coefficientA,and relaxation time&tgr;are annealing temperature dependent parameters. The dependence of&rgr;RTand temperature calibration&rgr;(T)on anneal duration can be minimized by annealing above 250 °C. Like&rgr;RT, the sensitivity&eegr;(T)also depends on annealing temperature, with higher annealing temperatures corresponding to lower cryogenic sensitivities. In all cases&eegr;(T)can be well described by a polynomial expansion inln Tfrom room temperature down to at least 2 K. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148488

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A detailed investigation of the practical spectroscopic features and the effect of prolonged exposure to elevated temperatures of an intrinsic Nd:doped fiber optic thermometer probe using the fluorescence decay time technique has been carried out. Results have shown the optimum length for the doped fiber and a maximum operating temperature of 750 °C, beyond which a range of high-temperature “annealing” effects are seen. These are discussed in light of the operation of the thermometers over the range from−196to 750 °C and potentially above. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148489

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The use of multiple material fluorescence-based sensors, where each is optimized to a particular temperature range yet is pumped by the same light source, emitting over the same spectral region, makes for a very simple, convenient and promising optical arrangement which can be applied in real-time, quasidistributed temperature sensor systems. The fluorescence lifetime approach, which is an important technique to enable fluorescence emission to be exploited for thermometry, is adopted in the system discussed. An analysis scheme using Prony’s method has been reported which enables exponential decays from either single-material or two material and quasidistributed sensors to be deconvolved and thus data and associated measurand information encoded in each individual signal to be recovered. In this work, in the development of quasidistributed temperature sensor algorithms based on Prony’s method are used for the estimation of exponential time constants of a convolved triple exponential fluorescence decay, each corresponding to a different-point temperature. Experimental results obtained are presented to justify their use in practical multiexponential fluorescence decay analysis and show a comparison of the Prony method to the Marquardt nonlinear least-squares approximation algorithm to achieve the deconvolution. The computational time for Prony’s approach is approximately one-thousandth that of the Marquardt technique while the accuracy achieved using Prony’s method is still high enough for practical use. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148520

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We describe the design and measured electrical performance of the first electrical substitution radiometer based on superconducting thermometers. Prospective applications emphasize high precision measurement of low power, mid- and far-IR blackbody radiation. The minimum noise floor for a single measurement of substitution power was 2 pW for an integration time of 2.7 s. For an extended series of experiments covering a range of substitution power from 0.5 nW to 5 &mgr;W, the noise floor can be roughly approximated as 4 pW plus7×10−6times the measured power. Analysis of the results indicates the precision is limited by a combination of thermal parasitics and electronic noise contributions.

ISSN:0034-6748    

DOI:10.1063/1.1148522

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A new, simple, and low cost apparatus was developed to control the temperature in the very low-temperature region (0.3–3.3 K) using a3Herefrigerator. A low temperature was obtained by controlling the3Hevapor pressure. The apparatus consists of a set of valves, an automated microvalve, a manually operated auxiliary valve, a controller including a one-board microcomputer, and a set of pressure transducers. The temperature was easily controlled by this apparatus. The temperature stability was 0.95&percent; at 1.04 K bycontrolling the3Hevapor pressure. The temperature drift was typically 0.02 K at 0.85 K. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148490

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A new method for measuring heat capacities that makes the calibration of thermometers obsolete is presented. The particularity of the principle, based on the ac steady-state method, is the insertion of a reference mass with a heater between the ensemblesubstrate+sample+thermometer+heater,and the bath. The method could find a broad application in calorimetric devices where the thermometer must often be recalibrated due to, e.g., a drift of the thermometer’s characteristics with thermal cycles or magnetic field. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148491

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A high-resolution computerized calorimeter capable of fully automatic operation in either ac or relaxation modes is described. Emphasis is given to a new version of the relaxation technique in which the heater power is ramped linearly in time. This improvement results in superior performance and convenience in studying both first- and second-order phase transitions and allows quantitative evaluation of latent heats as well as pretransitional heat capacity variations. Examples are given for the use of this calorimeter in the study of liquid crystal phase transitions. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148492

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have developed a top-loading type adiabatic calorimeter which works in the temperature range 13–375 K. This calorimeter drastically reduces the time required for the sample setup (to ∼10 min) and enables us to set up samples at liquid nitrogen temperature (77 K). The heat capacity of an empty cell was measured in a test experiment. The imprecision of the heat capacity measurement was±0.2&percent;at 13–30 K,±0.1&percent;at 30–50 K, and±0.02&percent;at above 50 K. These are as good as the performance of any of the traditional adiabatic calorimeters. The heat capacity of(1,3-propanediol)0.5(1,2-propanediamine)0.5was measured in the temperature range 20–290 K and the enthalpy relaxation in its glassy state was also measured nearTg(=178 K).Because of the top-loading feature, fast-quenched samples prepared at 77 K outside the cryostat could be set up without ever undergoing a temperature above 100 K. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148493

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A novel adiabatic calorimeter was constructed for simultaneous measurement of enthalpy and volume under high pressure. The calorimeter works under constant pressure up to 100 MPa and in the temperature range 80–380 K. The sample is pressurized hydrostatically by using a liquid pressure transmitting medium. The sample volume is measured with a new type of dilatometer using bellows installed in the cell. The dilatometer has two resolution modes (high and low) with different scanning range. As the calibration and test experiments, the heat capacities and volumes of toluene and water were measured at 0.1 and 50.1 MPa in the temperature range between 275 and 380 K. In the low resolution mode, the accuracies of heat capacity and volume were±0.2&percent;and 20 ppm of total, respectively. The test of the volume measurement in the high resolution mode showed that the resolution was±0.1 ppmof total sample volume, which is ∼ ten times better than that of the previous best dilatometer. To demonstrate the performance of the present apparatus, the enthalpy and volume changes due to the structural relaxation of glassy polystyrene were measured simultaneously. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148494

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We describe an experimental method to measure the water density of a plume created from a shallow underwater explosion. Our approach is based on the attenuation characteristics of a microwave signal propagated through the plume. A unique correlation exists between the amount of attenuation and macroscopic quantities including the volume fraction of water in air. In this article, both the theory required for data analysis and the experimental arrangement used for measuring the highly attenuated microwave signal are discussed. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148525

出版商:AIP    

年代:1998

数据来源: AIP