Progress in the Realization of the Units of Capacitance, Resistance, and Inductance at the National Physical Laboratory, India

This paper describes the progress made at the National Physical Laboratory (NPL), New Delhi, India, in the realization of the units of capacitance and resistance based on a calculable crosscapacitor. The realization of the unit of inductance in terms of capacitance using the Maxwell-Wein bridge and resonance techniques has also been described.     

Upgradation of a spectral irradiance measurement facility at National Physical Laboratory,India

This report describes the details of a recently upgraded spectral irradiance measurement facility in optical radiation standards at National Physical Laboratory, India. This facility provides the calibration of spectral irradiance in the wavelength range 280 nm – 2500 nm. PTB, Braunschweig, Germany calibrated five numbers of 1000 W quartz halogen lamps, which are used as reference standards for spectral irradiance scale. In addition to providing the details of instruments, the procedure of calibration and evaluation of uncertainties is also described. For checking the fidelity, repeatability and reproducibility of the upgraded system, calibration of one of the PTB calibrated lamps, was done against the other four PTB calibrated lamps. These measurements not only provide confidence on the upgraded system but also verify the retention of the PTB certificate values after a lapse of two years after their calibration.     

The National High Magnetic Field Laboratory at Los Alamos National Laboratory

Los Alamos National Laboratory (LANL) is the home institution of the Pulsed Field Facility of the National High Magnetic Field Laboratory (NHMFL). The NHMFL laboratories are the only facilities in the US (among a few world-wide) to host qualified users while running strong in-house science programs related to high magnetic field research. At Los Alamos, the NHMFL advances the frontiers of condensed matter physics at extreme conditions of high magnetic field, low temperature and pressure, utilizing start-of-the-art pulsed magnets and unique experimental capabilities. This paper will describe the current and future plans of pulsed magnet technology and science at the NHMFL Pulsed Field Facility at LANL.     

Improvements in Atomic Cesium Beam Frequency Standards at the National Bureau of Standards

The National Bureau of Standards Frequency Standard, NBS-III, a cesium beam with a 3.66-meter interaction region, has been in operation since 1963. The last published (1966) accuracy capability for NBS-III was 1.1 ? 10-12(l?). Recently, several new solid-state broad-band frequency-multiplier chains have been constructed. Reduction of the random phase noise by more than 20 dB compared to the previous state of the art has been obtained consistently. In addition, a solid-state servo system has been installed to control the frequency of the 5-MHz slave oscillator. Comparisons were made between NBS-III and one of the commercial cesium standards in the NBS clock ensemble. The relative fractional frequency stability ?(N = 2, T = 7 days, ? = 1 day) = 1 ? 10-13 was observed for nine weekly comparisons. The very-long-term frequency stability for this recently improved NBS-III system has not been evaluated fully. Due to the improvements both in electronic systems and evaluative techniques, however, an accuracy of 5 ? 10-13(1?) for a single evaluative experiment is reported. Substantial effort is being expended toward improvement of the accuracy and figure of merit (presently 10) of the NBS cesium standard. The modified system, to be called NBS-5, is expected to be in operation in the latter half of 1970 and to exhibit a figure of merit in excess of 500.     

The Performance and Capability of Cesium Beam Frequency Standards at the National Bureau of Standards

NBS II, the older of the two cesium atomic beam frequency standards which are used alternatively as the United States Frequency Standard, has been operating for more than five years. The contribution to inaccuracy produced by uncertainties in the C field has been reduced by a factor of 30 to ±2 × 10-13. The average precision of measurement (standard deviation of the mean) has been demonstrated to be 1 × 10-12 for averaging times of 1 hour and 2 × 10-13 for 12 hours. The overall accuracy is considered to be ±8 × 10-123?. A new cesium standard, NBS III with an interaction length of 3.66 meters is in operation and has demonstrated an improved precision of 1 × 10-13 over 2 hours and an accuracy of ±5 × 10-123?. The C field contributions to inaccuracy in this machine have been reduced to ±1 × 10-13. Considerable effort has been devoted to the detection and elimination of small frequency shifts produced by various electronic components of the excitation systems. In spite of the various improvements effected, a small unexplained difference in frequency of about 1 × 10-12 continues to exist between the standards. The extremely high stability of the difference frequency, however, suggests that resolution of the difficulties should result in an accuracy capability of perhaps ±1 × 10-123?.     

High-Speed Photography in Aerodynamic Research at the National Physical Laboratory

A brief account is given of some of the applications of high-speed photography and optical methods of flow-visualization to recent work in the wind-tunnels and shock-tubes of the Aerodynamics Division of the National Physical Laboratory. The examples shown are a simulated boiler-tube experiment, an aileron-buzz experiment, colour-schlieren and polarization-interferometer photography of transonic flows, photography of direct luminosity of flows in shock-tubes, and a multiple-spark camera for shock-tube applications.     

Evaluation of a Thallium Atomic Beam Frequency Standard at the National Bureau of Standards

The original NBS cesium standard (NBS I) has been converted to a thallium standard and was operated for one and one-half years with a typical precision of 2 × 10-12 and an accuracy of 1 × 10-11. Experiments are described which were performed to establish these precision and accuracy estimates. These results, which are comparable to those obtained with longer cesium standards, are considered sufficiently encouraging to justify the conversion of a longer cesium standard to thallium for a more thorough evaluation.     

Pressure-Drop Considerations in the Characterization of Dew-Point Transfer Standards at High Temperatures

During calibration of precision optical dew-point hygrometers (DPHs), it is usually necessary to take into account the pressure drop induced by the gas flow between the “point of reference” and the “point of use” (mirror or measuring head of the DPH) either as a correction of the reference dew-point temperature or as part of the uncertainty estimation. At dew-point temperatures in the range of ambient temperature and below, it is sufficient to determine the pressure drop for the required gas flow, and to keep the volumetric flow constant during the measurements. In this case, it is feasible to keep the dry-gas flow into the dew-point generator constant or to measure the flow downstream the DPH at ambient temperature. In normal operation, at least one DPH in addition to the monitoring DPH are used, and this operation has to be applied to each instrument. The situation is different at high dew-point temperatures up to 95 °C, the currently achievable upper limit reported in this paper. With increasing dew-point temperatures, the reference gas contains increasing amounts of water vapour and a constant dry-gas flow will lead to a significant enhanced volume flow at the conditions at the point of use, and therefore, to a significantly varying pressure drop depending on the applied dew-point temperature. At dew-point temperatures above ambient temperature, it is also necessary to heat the reference gas and the mirror head of the DPH sufficiently to avoid condensation which will additionally increase the volume flow and the pressure drop. In this paper, a method is provided to calculate the dry-gas flow rate needed to maintain a known wet-gas flow rate through a chilled mirror for a range of temperature and pressures.     

Primary Atomic Frequency Standards at NIST

The development of atomic frequency standards at NIST is discussed and three of the key frequency-standard technologies of the current era are described. For each of these technologies, the most recent NIST implementation of the particular type of standard is described in greater detail. The best relative standard uncertainty achieved to date for a NIST frequency standard is 1.5×10⁻¹⁵. The uncertainties of the most recent NIST standards are displayed relative to the uncertainties of atomic frequency standards of several other countries.     

The National High Magnetic Field Laboratory

The National High Magnetic Field Laboratory (NHMFL) is a collaboration between Florida State University, the University of Florida, and the Los Alamos National Laboratory. The DC Field Facilities are located at the main campus for the NHMFL in Tallahassee, Florida and are described in this paper. The DC Field Facility has a variety of resistive and superconducting magnets. The DC Field Facility infrastructure, the most powerful in the world, is able to provide 57 MW of continuous low noise DC power. Constant magnetic fields of up to 45 tesla in a 32 mm bore and 20 tesla in 195 mm bore are available at no charge to the user community. The users of the facility are selected by a peer reviewed process. Roughly 400 research groups visit the lab to conduct experiments each year. Experimental capabilities provided by the NHMFL are magneto-optics, millimeter wave spectroscopy, magnetization, dilatometry, specific heat, electrical transport, ultrasound, low to medium resolution NMR, EMR, and materials processing. Measurements of properties can be made on samples at temperatures from 20 mK to 1000 K, pressures from ambient to 10 GPa, orientation and currents from 1 pA to 10 kA.     

Special Coils Development at the National High Magnetic Field Laboratory in Toulouse

The Laboratoire National des Champs Magnétiques Intenses (LNCMI) develops different types of coils suited to specific experiments. We present some recent developments on magnet design. Several coils are dedicated to experiments in large scale facilities in France and Switzerland. A 30 T split-pair coil for X-rays diffraction and one 40 T coil for plasma physics at the LULI, two 30 T coils with axial access (one with an conical bore) for X-ray diffraction and absorption experiments. A 40 T wide angle conical access solenoid with a high duty-cycle for neutron scattering at the ILL is being constructed. For use at the installation in Toulouse we have developed, apart from our standard 60 and 70 T coils, several special coils: a coil with a long optical path with 30 T transverse magnetic field and a 90 T long pulse dual coil system.     

Atomic Time and Frequency Standards Development at Shanghai Observatory, China

The performance characteristics of several types of our atomic frequency standards are described. All of these standards are designed, developed, and fabricated in China. The hydrogen maser is the only type developed by the Shanghai Observatory. This paper also describes briefly the basic consideration for system implementation, calculation approach, and experiment results in the generation of the Shanghai Observatory atomic time scale AT(SO). Based on available frequency standards-one prototype laboratory model of cesium clock, three hydrogen clocks, and several (3-6) rubidium clocks-the AT(SO) was established in 1978. The laboratory cesium clock is used to provide the basic calibration reference of the second in 1979, while hydrogen clocks and rubidium clocks are used as the working clocks to ensure the continuity of the time scale.     

LF-VLF Frequency and Time Services of the National Bureau of Standards

The United States Frequency Standard and National Bureau of Standards Time Scale are described, and the techniques by which they are used to control the broadcasts from WWVB and WWVL, Fort Collins, Colo., are presented. A practical method for control of frequency and time broadcasts from WWV, Greenbelt, Md., is described and actual results shown.     

微波低通高阻频率选择复合材料的设计研究

采用数值法设计了8～12GHz(X波段)具有高反射同时2～4GHz(S波段)具有高透射的频率选通复合材料.采用有限元法(FEM)计算了含导电纤维复合材料的传输和反射系数,并用自由空间法对所制备的多层凯夫拉(Kevlar)纤维增强的复合材料样板(424mm× 424mm)进行测量.测量结果与计算结果具有良好的一致性.同时发现复合材料基材的介电特性和所嵌入金属纤维的电导率对材料的传输损耗有很大影响.     

不同“标准水平”国家标准的灰色关联分析

本文运用灰色关联分析方法分析了不同"标准水平"的国家标准与我国国家标准数量的关联情况,得到了不同标准水平国家标准的分布情况和变化趋势,同时也得出了不同标准水平国家标准的关联排序。     

Recent Progress in Cs Beam Frequency Standards at the NRLM

Some causes and cures of frequency uncertainty in the cesium beam frequency standard, NRLM-II, are described. Accuracy reevaluation indicates about 2.2 × 10-13, and the standard frequency is about 8 × 10-14 below that of the International Atomic Time (TAI) scale. The frequency stability is estimated as better than 8 × 10-12 ?-1/2 for short-term and 4 × 10-14 for 1-2 day averages.     

New Methods of Measuring Capacitance and Resistance of Very High Loss Materials at High Frequencies

Two new circuits for the accurate measurement of specimen capacitance and resistive loss are described. The capacitance measurements are unaffected by the specimen resistance when the parallel resistance is greater than 30 ?. The practicality of the circuit is enhanced by its use of coaxial cable to provide both connection to the sample and the inductance required for circuit operation. An important characteristic of the circuit is its ability to measure capacitance and resistance of very high loss specimens accurately.     

Comparison of the National Standards of Russia and China in the Infrasound Frequency Range

The Russian and the Chinese Underwater Pressure National Standards in the frequency range 0.01 Hz to 1 Hz were compared by exchanging hydrophones and the results of calibration. The reproducibility of the calibration results confirmed the high-level metrological characteristics of both standards.