Key comparisons of the VNIIM and BIPM voltage standards

The results of key comparisons of the national primary standard of Russia for the unit of electrical voltage, the volt, at the Mendeleev Institute of Metrology (VNIIM) with the Josephson effect voltage standard at the BIPM are reported. For these measurements, VNIIM provided a voltage measure based on the Josephson effect with a nominal output voltage of 10 V. Measurements were made with apparatus from the BIPM voltage standard. The VNIIM voltage measure is planned for use as a transfer standard for comparison with national standards for the volt. The comparisons indicate a high degree of equivalence of the compared VNIIM and BIPM primary standards with a relative combined standard uncertainty of 2·10–10 at 10 V.     

Recent developments in the PTB RF standard attenuation measuringequipment

Developments in standard equipment for precise attenuation measurements are described. The frequency range of the RF standard attenuation measuring equipment at the Physikalisch-Technische Bundesanstalt (PTB), Germany, has been extended up to 40 GHz in the waveguide bands R 220 and R 320. The total uncertainty of the system is estimated to be equal to or smaller than 0.002 dB for a 30-dB attenuation step     

Recent developments in anionic polymerization

The past year witnessed very significant advances in the living anionic polymerization of (meth)acrylate monomers, particularly in hydrocarbons at or below 0°C. Block polymerization of alkyl methacrylates with primary alkyl acrylates, although somewhat improved, remains a challenge. Anionic polymerization of styrene, diene and its derivatives was carried out with the aim of synthesizing functional polymers and block copolymers of various architectures. There has been a trend towards combining different living techniques in order to design polymers of unique architectures and properties     

Recent developments in detector research

Recently developed methods of cryogenic particle detection and potential applications will be introduced. The main part of this article focuses on our experimental results on two different approaches of detecting nuclear radiation with superconducting tunnel junctions. The best energy resolution is obtained when the junction itself serves as absorber. Using Sn/SnO_x/Sn tunnel junctions we obtained an energy resolution of about 90 eV for 6 keV X-rays up to now. The processes limiting the resolution of the present devices will be discussed. Larger absorber masses and position resolution are realized by an entirely new type of particle detector based on the detection of nonthermal phonons which are generated by the absorption of radiation within a single-crystalline absorber of dielectric material. We report on experimental tests of a detector composed of a silicon single crystal (size: 10 × 20 × 3 mm³) and of an array of superconducting Al/Al₂O₃/Al tunnel junctions evaporated onto the surface of the crystal, serving as phonon detectors. Pulse height analysis and the investigation of time differences between pulse onsets in different junctions are shown to yield information about the absorption point of -particles.     

Recent developments in explosive welding

Explosion welding (EXW) is one of the joining methods consisting of a solid state welding process in which controlled explosive detonation on the surface of a metal. During the collision, a high velocity jet is produced to remove away the impurities on the metal surfaces. Flyer plate collides with base plate resulting in a bonding at the interface of metals. The metal plates are joined at an internal point under the influence of a very high pressure and causes considerable local plastic deformation at the interface in which metallurgical bonding occurs in nature and even stronger than the parent metals. Similar and dissimilar materials can be joined by explosive welding. In this paper, after detection the theories of welding and wave formation, experimental research and numerical studies on explosive welding are reviewed for the last four decades. Also, future developments in explosive welding are predicted and criticized in an outlook.     

Recent developments in ultrasonic fatigue

The recently increased interest in very high cycle fatigue properties of materials has led to extended use and further development of the ultrasonic fatigue testing technique. Specimens are stimulated to resonance vibrations at ultrasonic frequency, where the high frequency allows collecting lifetime data of up to 10¹⁰ cycles and measuring crack propagation rates down to 10^?12 m per cycle within reasonable testing times. New capabilities and methods of ultrasonic testing and outstanding results obtained since the year 1999 are reviewed. Ultrasonic tests at load ratios other than R = ?1, variable amplitude tests, cyclic torsion tests and methods for in situ observation of fatigue damage are described. Advances in testing at very high temperatures or in corrosive environments and experiments with other than bulk metallic materials are summarized. Fundamental studies with copper and duplex steel became possible and allowed new insights into the process of very high cycle fatigue damage. Higher cyclic strength of mild steels measured at ultrasonic frequency because of plastic strain rate effects are described. High‐strength steels and high‐alloy steels are less prone to frequency influences. Environmental effects that can lead to prolonged lifetimes in some aluminium alloys and possible frequency effects in titanium and nickel and their alloys are reviewed.     

Recent developments in plasma technology

This report looks at the use of the plasma state of matter and how it can be put to good use in metal cutting and metal extraction.     

Recent developments in carbon nanotubes

Unique and interesting nanotube properties directly result from their special topologies. Intrinsic electronic and transport properties are only now starting to be understood and demonstrate a wide variety of geometrical structure-dependent behaviors. High-temperature Aharonov-Bohm oscillations have been observed and exceptionally high current densities have been attained. Nanotube transistors and flat panel displays have been demonstrated. These recent discoveries point towards important applications and new insights into nanotube properties.     

The new BIPM 1-V reference standard based on an array of Josephsonjunctions

The authors report the first measurements at the Bureau International des Poids et Mesures (BIPM) with a 1-V reference standard based on an array of Josephson junctions. A novel procedure for standard cell measurements is described. It allows the measurement of a cell electromotive force (EMF) with a random uncertainty of less than 1 nV and a total uncertainty of about 2 nV while avoiding direct connection of the cell to the array. Comparisons with an older Josephson reference standard, which is based on a junction output of 10 mV, were made both indirectly by means of standard cells and directly by connecting the instruments together. The results and the random uncertainties imply that the value assigned to a standard cell using the array minus that given by the older apparatus is -18.8±3.4 nV for the indirect method and -17.1±1.5 nV for the direct method. Taking into account the estimated total uncertainty of 23.5 nV for the old system, the agreement is excellent     

Recent developments in lorentz electron microscopy

Several different methods of obtaining contrast for electron microscopy of magnetic specimens are reviewed. For the investigation of magnetization ripple and the structure of domain walls in magnetic films, two questions must be considered: the correct wave optical interpretation of Lorentz micrographs and the experimental attainment of coherence of the electron beam. Both questions have been sufficiently explored so that experimental results on magnetic film microstructure may be expected in the near future.     

Recent developments in lightwave network analysis

The widespread use of photonic systems having microwave modulation bandwidths, coupled with the inclusion of photonic components in microwave and millimetre-wave systems, is creating a demand for efficient characterization techniques. In particular, new tools will be required for the measurement of fundamental quantities such as the microwave frequency response, bandwidth, gain and return loss of microwave photonic components. However, existing lightwave measurement techniques are primitive when compared with conventional RF and microwave network analysis. This paper provides a review of the theory and techniques used for the small-signal characterization of microwave photonic components. State-of-the-art architectures for lightwave network analysers and the two-port calibration techniques are described     

A new AC voltage standard

An AC voltage standard has been developed for the 10 Hz-1 MHz frequency range with basic accuracy of 37.5 p.p.m. The standard is programmable and twice as accurate as current calibrators. Unique circuitry used to achieve fast response and high frequency, high voltage capability is described. The AC voltage standard incorporates a novel solid-state thermal converter which uses proprietary concepts to speed up AC-DC conversion while maintaining broad bandwidth and high frequency response. Design concepts which reduce maintenance cost, automate calibration, and simplify precise traceable AC voltage measurements are also provided     

A computer-controlled Josephson voltage standard

The characteristics of a computer-controlled Josephson voltage standard developed for routine calibrations of electrochemical cells are described. The device is also suitable for use as a transfer standard. The overall relative uncertainty (1 σ) of the device is less than one part of 10⁸     

聚氨酯基互穿网络聚合物的研究进展

介绍了互穿网络聚合物IPN的分类,重点讨论了聚氨酯基IPN的研究进展,并对聚氨酯互穿网络的发展提出展望.     

热塑性弹性体的研究进展

热塑性弹性体(TPE)兼具塑料和橡胶的特性,是近年来发展较快的一种新型高分子材料.文章介绍了苯乙烯类、聚氨酯类和聚烯烃类3类消耗量最大的热塑性弹性体,并对聚烯烃类热塑性弹性体中采用动态硫化技术制备的热塑性硫化橡胶的国内外研究进展进行了综述.     

声纳换能器的新进展

换能器对整个声纳系统的性能有很大影响。随着科学技术的迅速发展，水声换能器在分析方法、设计理论、材料和制作技术上都有了很大的发展，从而使换能器性能有了很大提高。超磁致伸缩稀土换能器、高性能电致伸缩陶瓷换能器、压电复合材料换能器、矢量水听器、低频大面积PVDF水听器、光纤水听器等是当前换能器研究的热点。文章回顾了20世纪80年代以来，以上几种换能器的最新进展情况。     

Recent developments of fracture mechanics in Greece

To somewhat broaden the scope covered in companion papers of this special issue, which covers fracture research currently being reported in Greece, the author has briefly reviewed associated developments in the region, although rather than being comprehensive, it reflects mainly his own interests. Topics covered include: new trends in the optical method of caustics, kinking and temperature distribution in dynamic crack problems, fatigue crack growth studies, partially bonded inclusions in elastic media, local and global instability in cracked bodies, fracture behavior of composite materials and transient elastodynamic problems.     

Recent developments in modelling preferences under risk

Summary Ever since von Neumann and Morgenstern presented their expected utility theory, the axioms (assumptions) underlying their theory have been intensely debated and tested. Recently, a variety of theories have been presented which model preferences by weakening some of the assumptions of expected utility theory. We describe some of these theories, examine their properties, and provide insights into how they work. Implications for different areas of business research are discussed.

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Zusammenfassung Seit von Neumann und Morgenstern die Erwartungsnutzentheorie vorgestellt haben, werden die dieser Theorie zugrunde liegenden Axiome (Annahmen) intensiv diskutiert. Während man in der Vergangenheit entweder für oder gegen die Theorie war, wurden in letzter Zeit eine Reihe von neuen Ansätzen vorgestellt, die die Erwartungsnutzentheorie durch Abschwächung der ursprünglichen Annahmen erweitern. Nach einer Darstellung der neuen Modelle der erweiterten Erwartungsnutzentheorie werden diese verglichen und bezüglich ihrer Anwendbarkeit in verschiedenen Gebieten der Betriebswirtschaftslehre untersucht.