Comparison of four QHR systems within one month using a temperatureand pressure stabilized 100-Ω resistor

We have carried out a resistance comparison of four QHR systems using a 100-Ω resistor in a temperature-controlled and hermetically sealed enclosure, the comparison was performed in November and December 1998, the participants were Bureau International des Poids et Mesures (BIPM), Bureau National de Metrology-Laboratoire Central des Industries Electroniques (BNM-LCIE) France, Physikalisch-Technische Bundesanstalt (PTB) Germany, and Valtion Teknillinen Tutkimuskeskus (VTT Automation) Finland, acting as a pilot laboratory. The comparison results agree within 3 parts in 10⁹ with a relative combined standard uncertainty of ±1×10^-8     

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     

Kinetically Controlled Synthesis of Hexagonally Close‐Packed Cobalt Nanorods with High Magnetic Coercivity

High‐quality monodisperse metallic cobalt nanorods are obtained by the reduction of carboxylate salts of Co^II in 1,2‐butanediol using a rapid, simple, and solid‐template‐free procedure. In this polyol process, particle shape can be controlled via the growth rate, which depends on three parameters: i) the nature of the cobalt carboxylate, ii) the temperature ramp, and iii) the basicity of the medium. Cobalt in the hexagonally close‐packed phase favored the growth of anisotropic particles. Magnetic measurements of the cobalt nanorods indicate they are ferromagnetic at room temperature. They have a very high coercivity of 9.0 kOe at 140 K, much higher than that observed for wires prepared with solid templates. This can be attributed to their small mean diameter and high crystallinity.     

Rapid synthesis of cryptomelane-type manganese oxide under ultrasonic process

Cryptomelane-type manganese oxide (OMS-2) was rapidly prepared under ultrasonic irradiation in short time. Characterization results using X-ray powder diffraction (XRD), surface area analyzer, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), oxygen temperature-programmed desorption (O₂-TPD) revealed that ultrasonic irradiation has tremendous effect on the surface area, morphology, surface defects, and redox properties of the OMS-2 materials. The OMS-2 prepared via ultrasonic irradiation shows nanoneedle morphology with smaller crystallite size, larger surface area (120.4 m²/g), more surface defects, and higher oxygen mobility, thus it demonstrates excellent activity in the catalytic combustion of dimethyl ether with a start-off temperature of 160 °C and a complete combustion temperature of 172 °C.     

Synthesis and Characterization of Highly Dispersed Molybdenum Carbides in Mesoporous Silica

Highly dispersed molybdenum carbides in MCM-41 mesoporous silica are synthesized by temperature-programmed carburization and are characterized. Two methods of preparation are examined: (i) insertion of molybdenum during the synthesis of the MCM-41 silica and (ii) postsynthesis incorporation into a MCM-41 silica matrix by the incipient wetness method. Propene transformation (hydrogenation and metathesis) was used as a probe reaction; the observed catalytic behavior can be explained as a result of the preparation method, i.e., of the relative strength of interaction between the molybdenum oxide precursor and the support.     

Development and application of thermo-oxidation laboratory tests. Correlations with engine lubricant specifications

Laboratory simulation tests are an important stage in the selection of engine lubricants. Where these tests are brief and repeatable, they allow numerous studies and can provide a wide range of information. They are all the more valuable if they have a close degree of correlation with a specification test. The IIID high temperature oxidation test, the ME 1517 oxidation laboratory test and the Renault 30 diesel engine test are examples of specifications for the formulation of engine lubricants. The aim of the present study has been to find or develop a brief, repeatable laboratory test for these specifications and to establish a correlation between the test and the specification. Data obtained show satisfactory correlations between the TFOUT (Thin Film Oxygen Uptake Test) and the IIID sequence, the open oxidation laboratory test COST (24 h) and ME 1517 (192 h), and the ELF/ECL microcoking test and the Renault 30 turbo diesel test.     

Measurements of single electron transistor devices combined with aCCC: progress report

The BNM-LCIE is developing a current standard based on single electron transistor (SET) pumps. This paper gives an overview of the experimental set-up. It includes the circuit details, in particular the combination of miniature filters and homemade lines giving high attenuation in a wide frequency band, and a cryogenic current comparator (CCC) with winding ratio of 10000:1 for high accuracy amplification of the current. The results of the testing of the circuit and CCC are presented, together with the first measurements of the current through a SET carried out by means of a CCC. Coulomb blockade oscillations with an amplitude less than 200 fA have been observed with a signal to noise ratio approaching 100 and at bias voltages as small as a 100 nV