摘要:

We describe a supersonic molecular‐beam source that can be heated to over 2300 K. Our design employs a commercially available tungsten tube which is resistively heated by passage of current along its length between two water‐cooled copper clamps. The clamps are supported so as to minimize bending stresses on the tube while allowing for thermal expansion. Gas is supplied to the tube at one end using an o‐ring connection and emerges from an orifice drilled about halfway along the length. The other end of the tube is welded closed. Temperature is measured by a thermocouple spot‐welded adjacent to the orifice. The entire tube is surrounded by two tantalum heat shields which are split lengthwise for convenient assembly. These have large holes aligned with the beam axis. We present details of the design, assembly, and characterization of this source.

ISSN:0034-6748    

DOI:10.1063/1.1143242

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A high‐resolution, high‐sensitivity, automated ac calorimeter capable of heat capacity measurements on very small samples (m<20 mg) with a temperature resolution of a few mK in the ac mode is described. This calorimeter also can be operated in the relaxation mode to provide absolute heat capacity values with precision and accuracy of around 2%. A microprocessor was employed to generate a stable oscillatory heating signal and to control the heater power, in order to improve the sensitivity of the measurement over other designs. A new very sensitive and miniature temperature probe (a film flake of a thermistor material), which increased measurement resolution and minimized the heat contribution of the addenda, also was used. This calorimeter was tested by measuring the heat capacity of gadolinium over its ferromagnetic phase transition. The results agree well with the literature data giving, however, substantially better resolution of the heat capacity in the critical region.

ISSN:0034-6748    

DOI:10.1063/1.1143243

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A sinusoi¨dal temperature modulation method has been developed to provide direct access to the derivative of the resistance with respect to temperaturedR/dT. This quantity is of a high physical interest since it gives information on the critical behavior of the specific heat of magnetic materials near the critical points. The original aspect of such an experimental device is the high sensitivity of its detection. Indeed it provides a resolution &Dgr;R/Rof 10−9withR=3 m&OHgr;. Finally, we demonstrate the high accuracy of this technique with experimental measurements ofdR/dTof a rare‐earth single crystal.

ISSN:0034-6748    

DOI:10.1063/1.1143244

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

In this paper we describe how multivariate calibration techniques including experimental design and partial least‐squares regression, PLS, can be used to determine thermal diffusivity from mirage data. In order to illustrate the utility of the theory a case study is presented where photothermal mirage data were simulated for a series of polymeric film samples. A PLS model was calculated that predicts thermal diffusivity with high precision.

ISSN:0034-6748    

DOI:10.1063/1.1143245

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The transient hot‐strip (THS) method has been modified to measure thermal conductivity of small test specimens. The conventional metal strip used simultaneously as the heater and the temperature sensor was substituted with a 50‐&OHgr; commercial temperature sensor (grid 5.85 mm×6.35 mm). The short transient hot‐strip (STHS) method was tested on Pyrex 7740, stainless steel (NIST 1462 standard reference material), and aluminum to cover more than two orders of magnitude in thermal conductivity. The STHS method agreed with conventional measurement techniques within 3% in the thermal conductivity range 1–200 W m−1 K−1.

ISSN:0034-6748    

DOI:10.1063/1.1143246

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A method to measure the absolute intensity of a weak magnetic field is described. This method uses patterned superconducting strip lines as a spatial modulator of the field and detects the magnetic field distribution over them as a function of applied magnetic fields. The field distribution change measured by an rf SQUID system is proportional to the component of the absolute intensity of the magnetic field at the specimen that is parallel with the pick‐up coil axis. The magnetic field intensity can be determined absolutely from about 1 &mgr;G by this method. A spatial resolution of the field as good as a few millimeters is obtained. Some practical limitations of this method and possible ways for improving are also discussed.

ISSN:0034-6748    

DOI:10.1063/1.1143247

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Calculations are described of the elastic stress, strain, and surface displacement for a high‐pressure optical window consisting of a transparent cylinder which is supported on a flat seat with an axial hole (Poulter window). Under pressure the window is compressed, and its outside surface bulges through the hole in the support. The net optical effect is to create a weak positive lens and to increase the axial optical thickness of the window.

ISSN:0034-6748    

DOI:10.1063/1.1143248

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A free deforming‐cylinder pressure transducer with bonded strain gauges is presented for pressure measurements in liquid media up to 0.5 GPa. Description is given of its operating principle and of its main metrological properties; the overall accuracy of this prototype pressure transducer is inside ±0.25 MPa.

ISSN:0034-6748    

DOI:10.1063/1.1143249

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The velocity of a steady, low‐pressure (≊0.1 Torr) plasma jet is measured by analyzing the local response of the medium to the action of an external magnetic field set up by two Helmholtz coils placed at the edge of the jet, yielding a field of 0.92 G/A. The induced electric field is measured by two floating‐potential electrostatic probes. The mean velocity of the electrons (between 1000 and 5000 m s−1) is found from the generalized Ohm’s law.

ISSN:0034-6748    

DOI:10.1063/1.1143250

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A synchronous detector electronics package with self‐contained oscillator is described. It uses only three integrated circuits, all of which contain operational amplifiers. The performance of the detector was evaluated with a capacitance sensor. Linearity and stability were found to compare favorably with general purpose commercial systems costing hundreds to thousands of dollars. Although the noise performance was less impressive, the dynamic range was still in excess of 90 db, permitting better than 100 &mgr;rad resolution over a range of nearly 3 rad. As presently configured, the detector is compatible only with high impedance sensors such as the capacitance type; however, coupling the oscillator output through a power amplifier would permit its use with LVDTs.

ISSN:0034-6748    

DOI:10.1063/1.1143251

出版商:AIP    

年代:1992

数据来源: AIP