超声导波技术在海上管道检测中的应用

介绍采用超声导波技术对近海管道进行检测。该技术可检测,导柱底部或水下管道关键区域。利用专门研制的机械系统可检测海平面下深达500 m的管道。讨论了导波技术检测水下管道及导柱底部的优势及局限性,给出了检测结果。     

Infrared and millimeter-wave sensors for military special operations and law enforcement applications

We consider the application of infrared and millimeter-wave sensors, developed for the most part during the Cold War, to the solution of problems encountered by military special operations units and law enforcement personnel. These problems include detection of weapons concealed beneath clothing, through-the-wall surveillance, and wide-area surveillance under poor lighting conditions. Key sensors used in these applications are infrared cameras, millimeter-wave passive and active cameras, and millimeter-wave real-aperture and holographic radars. This paper discusses each type of sensor, describes its operation, and gives an example of its output, except in those cases where the device is early in its development phase and thus no outputs are available. All of these sensors form images, but the images are of varying quality. We conclude with a brief discussion of methods of using multiple sensors to improve performance.     

Characterization of Nanostructured SilicaCat Pd0

Abstract  

Structural investigation on nanostructured SiliaCat Pd⁰ palladium catalyst sheds light into the origins of the remarkable activity of these new catalytic materials.     

The reflection of guided waves from notches in pipes: a guide for interpreting corrosion measurements

Ultrasonic guided waves are used for the rapid screening of pipelines in service and simple, standard testing procedures are already defined. The implementation of the method enables the localization of the defects along the length of the pipe and offers a rough estimate of defect size. In this article we present a systematic analysis of the effect of pipe size, defect size, guided wave mode and frequency on the reflection from notches. The maximum and minimum value of the reflection coefficient at varying axial extent are identified and used for the purpose of defect sizing. Maps of reflection coefficient as a function of the circumferential extent and depth of the defect are presented for a 3 in. schedule 40 steel pipe. An approximate formula, which allows these results to be extrapolated to other pipe sizes, is proposed and evaluated.     

Catalysis with Doped Sol‐Gel Silicates

Silicates doped with catalytic species have only been slowly adopted by the fine chemicals and pharmaceutical industries, in spite of their remarkable and unique properties such as pronounced physical and chemical stability; high (enantio)selective activity and ease of materials production and application. This is now changing thanks to stricter safety regulations and to concomitant success of the first commercial catalysts. In this account we tell the story of these materials and identify some deficiencies in the innovation process that may serve as lesson in guiding the future management of innovation in these relevant industries.     

Emulator of first- and second-order polarization-mode dispersion

Contrary to approaches which try to mimic a standard fiber as closely as possible, the emulator presented here gives constant (but user adjustable) values for differential group delay (DGD) and ratio of first- to second-order polarization-mode dispersion (PMD). Once it is set, the ratio is conserved while the DGD can be easily varied within a range of 0-300 ps. This allows to investigate the low-probability events of large DGD and second-order PMD important for system outage     

Thermal transitions in cold-crystallized blends of isotactic and static polystyrene

Solution-cast blends of isotactic and atactic polystyrene were stripped of casting solvent and heated above the glass transition temperature to temperatures below the equilibrium melting point of the respective blends to induce the development of crystallinity of the isotactic polystyrene. The samples, maintained at these crystallization temperatures for various times, were subsequently characterized by differential scanning calorimetry. The amount of crystallinity, the crystalline melting point, and the rate of crystallization were determined for each of the blends from the d.s.c. scans. The development of crystallinity, characterized by increased melting points, resulted from annealing at progressively higher temperatures. The maximum rate of crystallization for each of the blends was observed at a temperature corresponding closely to $\text{8}\text{9}$ of the absolute equilibrium melting temperature. The decrease in the melting point of the isotactic polymer, crystallized in the presence of atactic diluent, resulted primarily from weak enthalpic interactions between isotactic and atactic polystyrene homopolymers. Scanning electron photomicroscopy revealed that atactic-rich blends, immersed in n-hexane at 40°C, developed a non-intercommunicating network of microvoids. Similar solvent treatment of isotactic rich blends had little effect on the samples. D.s.c. measurements confirmed recently published results which indicated that n-hexane, at modest temperatures, does not induce the development of crystallinity in isotactic polystyrene.     

Thermal and swelling properties of polystyrene-polyolefin blends

Model blends of glassy amorphous polystyrene and each of four different crystallizable and rubbery polyolefins of varying side-chain molecular weight (polyethylene, polypropylene, poly(1-butene), poly (4-methyl-1-pentene)) have been prepared by melt extrusion of the polymeric components. Density measurements, differential scanning calorimetry (DSC), swelling measurements, and X-ray diffraction have been performed on the extruded fibers. In all cases, over the entire range of blend composition, the polymeric blends are immiscible and incompatible. The DSC measurements indicated that the polystyrene T_g was not decreased after blending and that the small reductions in the crystallinity and melting point of the respective polyolefins was best explained by thermal and kinetic interference with homo-crystallization of the respective polyolefins in the blends. The volumetric swelling and gravimetric sorption of n-hexane in the various blends increased monotonically with polystyrene content. The companion experiments, relating axial swelling with polystyrene content, indicated that this particular mode of distension actually decreased with increasing polystyrene content. The composite results, including DSC, X-ray, density, volumetric swelling and axial swelling suggest that the polystyrene phase is essentially microfibrillar and oriented in the direction of extrusion.