摘要:

A new method of measuring low magnetic fields accurately by employing a nuclear quadrupole resonance (NQR) technique in which a hexamethylene–tetramine [(CH2)6N4] crystal is used as the detector is proposed here. By applying the magnetic field (B0) along theZaxis of the electric field gradient tensor at14N in this crystal (&eegr;=0), one14N NQR line (&ngr;0) splits into two lines (&ngr;+and &ngr;−). The difference of these two lines (&dgr;&ngr;=&ngr;+−&ngr;−) is proportional to the applied low magnetic field. Consequently, the magnetic field can be measured with this frequency difference in terms of the nuclear magnetic moment of the14N nucleus. The accuracy, advantages, and limitations of this technique are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1144856

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The model of the perfect continuous counterflow heat exchanger introduced by Frossatietal. to describe the performance of dilution refrigerators is solved rigorously with the proper boundary condition. Unlike the original solution by Frossatietal., the present solution gives the refrigerator cooling power which is in good agreement with experimental data over the entire temperature range. The analysis of the cooling power using the present result allows more detailed evaluation of the refrigerator performance than has been possible with the analysis of the base temperature. An approximate expression for the cooling power is discussed which simplifies the prediction of the cooling rate of a large thermal load such as a copper nuclear‐demagnetization stage.

ISSN:0034-6748    

DOI:10.1063/1.1144857

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A new enclosed injector system for low temperature kinetic studies is described. This system offers a number of advantages over more conventional designs of moveable inlet injectors. The enclosed injector prevents the introduction of contaminants into the flow reactor. In conventional designs, ambient contaminants adsorbed onto the outside of the injector could be transported into the flow reactor. The enclosed injector exposes the reactant gas to the same length of inlet tubing at a uniform temperature regardless of the injector position. In addition, the enclosed injector minimizes temperature gradients in the flow reactor caused by heat transfer along the injector. This is a particular problem when the flow reactor is operated near atmospheric pressure at reduced temperatures. Finally, this design is significantly more compact than conventional injector designs. This system has been successfully employed in studies of the heterogeneous reaction of N2O5with sulfuric acid aerosols over the temperature range 225–293 K.  

ISSN:0034-6748    

DOI:10.1063/1.1144858

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Instead of the fixed pulse durations in conventional differential normal pulse voltammetry, a PC‐based instrument using adaptable pulse duration vectors for background current correction has been proposed and implemented. With this PC‐based instrument, a sequence of pulse duration vectors is determined in an initial blank solution voltammetry by assigning a decay percentage constant to the charging current. These vectors are then used in the subsequent test solution in order to obtain a pure oxidation current response in a resulting voltammogram with its corresponding features. Experimental results are presented to show the effectiveness and advantages of the PC‐based instrument for the measurements of dopamine in a phosphate buffered solution.

ISSN:0034-6748    

DOI:10.1063/1.1144859

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A laser system for high accuracy positioning, either on‐axis or off‐axis, over distances up to 50 m along the beam path is described. A beam delivery system with four degrees of freedom is used for initial alignment to an accuracy of 1 &mgr;m. Proper processing of the signals from a semiconductor quadrant detector reduces the measurement uncertainties and provides real‐time response. Theoretical consideration of the beam propagation characteristics is included. Laboratory and field test results show the system gives uncertainties of less than 1% for off‐axis positions up to 1 mm.

ISSN:0034-6748    

DOI:10.1063/1.1144860

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We describe a new laser‐based hygrometer for ambient water vapor monitoring which uses a fiber‐optic coupled, near‐infrared diode laser in conjunction with high frequency wavelength modulation spectroscopy. The instrument operates unattended, uses little power, can be extremely compact, and exhibits high detection sensitivity. This instrument was flown on a KC‐135 aircraft for a period of six months and measured frost points at altitudes between 10 000 and 40 000 ft. The water detection sensitivity corresponds to a volume mixing ratio of 8 ppm V. Further improvements including the use of newly designed near‐infrared lasers are expected to realize frost points below −100 °C.

ISSN:0034-6748    

DOI:10.1063/1.1144861

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A prototype single‐mode fiber‐based ultrahigh pressure remote sensor based upon a Fizeau cavity using a dual‐wavelength coherence reading technique with built‐in temperature compensation has been constructed capable of remote operation at distances up to 10 km. A separate fiber‐based temperature sensor with similar cavity length was incorporated into the pressure probe to allow the pressure measurement to be corrected for the temperature dependence of the pressure sensor. A range to resolution of ∼1.67×104:1 and an overall measurement accuracy of ∼±0.69% over a pressure range of ∼1000 bar have been achieved. This system represents a practical approach for industrial applications, such as measuring the pressure of an oil well.

ISSN:0034-6748    

DOI:10.1063/1.1144862

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A new magnetostrictive force sensor is presented and its operation is verified experimentally. The sensor has a single excitation coil and a single detection coil, which utilize the magnetostrictive effect. The cores of the coils function as ‘‘spring elements’’ of the sensor, and are linked together by rigid end plates. The magnetostrictive force sensor is compensated for asymmetric magnetostrictive behavior, and measures both tensile and compressive forces. Force sensitivity increases with excitation current and coil turns, but is less influenced by excitation frequency.  

ISSN:0034-6748    

DOI:10.1063/1.1144863

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

An examination of the results of the accuracy measurements of a bench top audio‐frequency selective voltmeter, based on the superheterodyne principle, showed that an accuracy of the order of only 10% of measured values could be achieved if no internal error correction procedure in the measurements had been used. The temperature variations of the parameters of the quartz band‐pass filter have been identified as the main source of the measurement error. An application of the internal reference signal from a relatively simple and inexpensive source improved the overall accuracy up to the order of 3%. Finally, it was shown that by combining the wide band and selective measurements of the signals from the built‐in tracking generator further improved the overall accuracy to better than 1% and eliminated altogether the need for using any separate source of internal reference signals.

ISSN:0034-6748    

DOI:10.1063/1.1145212

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The Quadrumafios electron cyclotron resonance ion source (ECRIS) has been especially designed to permit physical studies of the plasma; this paper describes the source itself (which has been operated at 10 GHz in a first step), its preliminary performances, and the different diagnostics involved, which mainly concern the electron population (ECE, x rays, diamagnetism, microwave interferometer, and electron analyzer). The results are presented and discussed: There is of course a close relationship between the parameters of the plasma and the performances of the source; this point will be discussed in the article.

ISSN:0034-6748    

DOI:10.1063/1.1144864

出版商:AIP    

年代:1994

数据来源: AIP