AC measurements of the minimum longitudinal resistance of a QHEsample from 10 Hz to 10 kHz

AC measurements of the longitudinal resistance, R_xx, of a quantum Hall effect (QHE) sample have been made in a frequency range from 10 Hz to 10 kHz. The results show no frequency effect on the minimum value of R_xx corresponding to the quantum numbers i=2 and i=4, within the measurement resolution of 0.5 mΩ. Therefore, the influence of frequency on the value of the quantized Hall resistance, R_H, should not exceed a few parts in 10⁹ . Some unwanted effects detected during the development of the resistance bridge have been pointed out     

Limitations of a relaxation oscillator in capacitance measurements

Oscillation periods of a relaxation oscillator consisting of an op-amp-based integrator and a comparator are measured over a wide range of RC integration constants, and the results are compared with theoretical values derived in terms of the finite gain-bandwidth (GB) product and the slew rate of an op-amp and the response delay of a comparator. The comparison validates the theoretical derivation which gives the design criteria of a relaxation oscillator for capacitance measurements and sensor signal processing     

Precise measurements of holes with diameters of 0.05 to 200 mm

Conclusions Engineering enterprises which require precision measurements of holes in mass production can be guided by the following arrangement for transferring dimensions from the initial measures to the product. Reference rings made with the maximum possible precision should be certified on the BV-2007 instrument. Horizontal interferometers in conjunction with these rings should be used for certifying adjusting rings used in setting pneumatic measuring machines to size for testing holes in components. The adjusting rings for setting inside gauges are certified on horizontal optimeters. If it is necessary to raise the precision of certification, the optimeters should be set by means of reference rings certified on the horizontal interferometer. Rings intended for testing high-precision inside gauges should be certified on the horizontal interferometer by means of block gauges.Translated from Izmeritel'naya Tekhnika, No. 1, pp. 81–84, January, 1970.     

Work function measurements for gas detection using tin oxide layers with a thickness between 1 and 200 nm

Tin oxide films, 1, 2, 20, 50, 80 and 200 nm thick, were deposited on platinum and titanium/tungsten surfaces by reactive sputter deposition. The structure and composition of tin oxide as well as the film homogeneity were investigated by scanning electron microscopy, Auger electron spectroscopy, Rutherford backscattering spectrometry and atomic force microscopy.

The 200 nm SnO₂ films are polycrystalline, with a grain size between 40 and 80 nm. For layers between 20 and 200 nm the composition is characteristic for stoichiometric SnO₂. The 1 and 2 nm layers show a homogeneous coverage of the metal. For all sensitive systems gas measurements were carried out with a Kelvin probe. Testing gases were humidity (40% r.h.), carbon monoxide (1000 ppm), hydrogen (100 ppm), nitrogen dioxide (8 ppm) and ammonia (10 ppm).

For thinner SnO₂ adlayers only surface-related processes contribute to the response, which is still material specific. It turns out that the thin layers are more stable.     

Improved entrance optic for global irradiance measurements with a Brewer spectrophotometer

A new entrance optic for a Brewer spectrophotometer has been designed and tested both in the laboratory and during solar measurements. The integrated cosine response deviates by 2.4% from the ideal, with an uncertainty of +/- 1%. The systematic uncertainties of global solar irradiance measurements with this new entrance optic are considerably reduced compared with measurements with the traditional design. Simultaneous solar irradiance measurements between the Brewer spectrophotometer and a spectroradiometer equipped with a state-of-the-art shaped diffuser agreed to within +/- 2% during a five-day measurement period.     

Vibration spectrum of a pulse-tube cryostat from 1 Hz to 20 kHz

The vibrations of the cold finger of a low-vibration helium pulse-tube cryostat are measured from 1 Hz to 20 kHz using an optical interferometer specially designed to measure small amplitude vibrations at high frequencies in the presence of large vibrations at lower frequencies. While the vibrational amplitude is dominated by the contribution at the fundamental compressor frequency of 1.4 Hz, the pulse tube contributes mechanical noise at frequencies up to 15 kHz, where the spectral density is measured to be 4 × 10⁻¹² m/Hz^1/2. Root-mean-squared vibration amplitudes of 5.2 μm and 3 μm are measured along perpendicular axes in the horizontal plane, and 1.0 μm in the vertical direction. The effect of a suspended sample holder for the purpose of attenuating high-frequency vibrations is evaluated. Finally, the cryostat is shown to be considerably noisier than typical laboratory floors.     

Relationship between Relaxation Internal Friction Peak at about 200℃(f≈1Hz)and Bainitic Transformation In a CuZnAl Alloy

The present investigation showed that the re-laxation peak at about 200℃ (f≈1Hz) was relatedto bainitic transformation in a CuZnAl alloy.Thepeak decreased when bainite precipitated.Theactivation energy of the peak was the same as theapparent activation energy of bainitic transforma-tion.According to the relations between the peakand the bainitic transformation,the mechanism ofthe peak has been discussed.     

PVT measurements of liquid ethanol in the temperature range from 310 to 363 k at pressures up to 200 MPa

Density measurements in the compressed liquid phase for ethanol were performed with a metal-bellows variable volumometer for temperatures between 310 and 363 K at pressures from the vapor pressure to 200 MPa. The results cover the high-density region from 737 to 882 kg m_–3. The experimental uncertainties (total errors) of temperature, pressure, and density were estimated to be no greater than 3 mK, 0.1 %, and 0.1 %, respectively. Measurements of saturated liquid density at temperatures of 310, 340, and 360 K are also reported.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

硝酸氧化改性SBA-15 模板合成的中孔炭电容性能研究

采用有序中孔氧化硅SBA-15为模板，合成了具有高效能量存储的超级电容器电极材料——有序中孔炭材料；以硝酸为氧化剂，分别在26℃、50℃、70℃和100℃下对中孔炭进行了表面官能化处理。结合氮气等温吸附、X射线光电子能谱和热分析方法研究了氧化前后中孔炭孔结构和表面官能团的演化。结果表明：随着氧化温度的升高，比表面积和中孔含量减少，而表面官能团含量增加。电化学测试显示：原始中孔炭的能量密度为3．5Wh／kg，100℃氧化的中孔炭具有最高的能量密度（5．7Wh／kg）。表明硝酸官能化处理可将中孔炭材料应用范围拓展到高能量密度领域。同时初始中孔炭的功率密度为2015W／kg，70℃氧化的中孔炭具有最高的功率密度（3125W／kg）。研究表明能量密度的改善得益于表面官能化对双电层电荷密度的提高和引入了法拉第赝电容反应；而功率密度的提高来自亲水性的官能化炭表面所具有的低离子扩散阻力。     

Morphological stability of a crystal with respect to arbitrary boundary perturbations

The morphological stability of a growing round crystal with respect to harmonic perturbations of arbitrary amplitudes has been studied. The critical crystal size with respect to stable growth decreases with increasing amplitude of perturbations and tends to a value that was previously analytically determined proceeding from the principle of maximum entropy production. This result offers new important evidence for the validity of a hypothesis concerning the possibility of using entropy production instead of a thermodynamic potential in the analysis of nonequilibrium phase transitions.     

Copper and platinum thermal resistance converters for temperature measurements to 200°C

Copper and platinum resistance thermal converters are compared by the criterion of minimum theoretically attainable error when they function as part of transducers with optimized parameters. Translated from Izmeritel'naya Tekhnika, No. 4, pp. 30–32, April, 1997.     

Measurement of Phase Angle Errors of Precision Current Shunts in the Frequency Range From 40 Hz to 200 kHz

This paper describes the measurement techniques and results of the determination of phase angle errors of a set of National Measurement Institute, Australia, precision current shunts, rated from 100 mA to 20 A, in the frequency range from 40 Hz to 200 kHz. The standard uncertainties of the determination range from 1.3 murad at low frequencies to less than 150 murad at 200 kHz     

Charge transport in vacuum-sublimed films of metal-free tetraphenylporphyrin and its relation to capacitance and photocurrent measurements

Drift mobilities (μ) of holes and electrons in vacuum-sublimed films of metal-free tetraphenylporphyrin (H₂TPP) were measured by using a time-of-flight technique with a log-log analysis of photocurrent transients with an electric field (E) and temperature as parameters. Extrapolation of a plot of log μ vs. E^1/2 to E = 0 yielded a very small μ value of the order 10^-16 cm² V^-1 s^-1 for hole and electron transport in the H₂TPP film at 20°C. Field and temperature dependencies of the hole mobilities, analyzed on the basis of the disorder formalism of Bässler and his coworkers, revealed that the extremely slow hole transport in the H₂TPP films was characterized by the largest energetic disorder parameter of 0.22 eV among those reported for other media so far. In addition, measurements of capacitances and photocurrents due to an Al/H₂TPP Schottky junction were carried out with photovoltaic cells of Al/H₂TPP/Au. The lack of dependencies of the capacitances on the frequency and bias voltage was interpreted in terms of the low mobilities of holes in the H₂TPP films. A marked increase of photocurrents with time paralleled a mobility increase, suggesting an important role of carrier mobilities in the mechanism of photocurrent generation in molecular semiconductors.