Homogeneous Gold Catalysis through Relativistic Effects: Addition of Water to Propyne

In the catalytic addition of water to propyne the Au(III) catalyst is not stable under non-relativistic conditions and dissociates into a Au(I) compound and Cl2. This implies that one link in the chain of events in the catalytic cycle is broken and relativity may well be seen as the reason why Au(III) compounds are effective catalysts.Comment: 12 pages, 3 figures, 1 tabl

Electrical performance of zinc oxide varistor using powders processed by different latex binders

The critical electrical parameters such as I-V characteristics, watt-loss and energy absorption capability etc. are the determinants for performance evaluation of ZnO varistors. In this regard there are a large number of contributing variables. Selection of proper binder in the processing of electro-ceramic powder is also a crucial factor. It imparts green strength, enhances compressibility and reduces density gradient within the green discs. Grain growth during sintering and subsequent microstructure of the varistor is also highly influenced by the binder system. It is envisaged that a disc with higher mechanical strength could be capable of withstanding more thermal stress due to temperature gradients. The energy absorption capability as well as high current performance can thus be enhanced. It was possible to generate varistor discs from the powder processed by the latex binder with better electrical performance than that of the powder processed with conventional binder of polyvinyl alcohol. Factorial analysis showed that the level of binder and solid concentration in the slurry had great influence on the energy absorption capability of ZnO varistor

Fast upsetting of circular cylinders of aluminium metal matrix composites: experimental results and numerical analysis

Cylindrical specimens of Al/Cu and Al/Li metal matrix composite (MMC) were subjected to dynamic compression at room temperature using an experimental drop hammer. Force-time and displacement-time traces were recorded. The experimental results are compared with theoretical results obtained using finite-difference analysis proposed in a previous paper by the authors [1]. The computational results obtained for the force-time histories agree reasonably with the experimental observation. Effect of strain rate and thermal softening on the mechanical behaviour of Al/Cu MMC and Al/Li MMC were examined

Design and Characterization of a Flexible Wideband Antenna Using Polydimethylsiloxane Composite Substrate

The design and characterization of a simple, flexible wideband antenna using polydimethylsiloxane (PDMS) composite are presented. Conductive fibers are used to construct the metallic parts on a PDMS composite. To characterize the performance, two identical antennas are designed, one using the PDMS composite while the other on conventional dielectric materials. It was observed that both antennas behave well in terms of the matched bandwidth; however, the radiation towards the broadside direction is reduced when using the PDMS composite as substrate, particularly at higher frequencies. The antenna exhibits a matched bandwidth of 59.9%, ranging from 3.43 to 11.1 GHz. Moreover, the bending analysis carried out for different scenarios show that the wideband behavior of the antenna is well preserved and the variation reaches a maximum of 1% variation

Design and Characterization of a Flexible Wideband Antenna Using Polydimethylsiloxane Composite Substrate

The design and characterization of a simple, flexible wideband antenna using polydimethylsiloxane (PDMS) composite are presented. Conductive fibers are used to construct the metallic parts on a PDMS composite. To characterize the performance, two identical antennas are designed, one using the PDMS composite while the other on conventional dielectric materials. It was observed that both antennas behave well in terms of the matched bandwidth; however, the radiation towards the broadside direction is reduced when using the PDMS composite as substrate, particularly at higher frequencies. The antenna exhibits a matched bandwidth of 59.9%, ranging from 3.43 to 11.1 GHz. Moreover, the bending analysis carried out for different scenarios show that the wideband behavior of the antenna is well preserved and the variation reaches a maximum of 1% variation

Climatic variability and periodicity for upstream sub-basins of the Yangtze river, China

The headwaters of the Yangtze River are located on the Qinghai Tibetan Plateau, which is affected by climate change. Here, treamflow trends for Tuotuohe and Zhimenda sub-basins and relations to temperature and precipitation trends during 1961–2015 were investigated. The modified Mann–Kendall trend test, Pettitt test, wavelet analysis, and multivariate correlation analysis was deployed for this purpose. The temperature and precipitation significantly increased for each sub-basin, and the temperature increase was more significant in Tuotuohe sub-basin as compared to the Zhimenda sub-basin. A statistically significant periodicity of 2–4 years was observed for both sub-basins in different time spans. Higher flow periodicities for Tuotuohe and Zhimenda sub-basin were found after 1991 and 2004, respectively, which indicates that these are the change years of trends in streamflows. The influence of temperature on streamflow is more substantial in Tuotuohe sub-basin, which will ultimately impact the melting of glaciers and snowmelt runoff in this sub-basin. Precipitation plays a more critical role in the Zhimenda streamflow. Precipitation and temperature changes in the headwaters of the Yangtze River will change the streamflow variability, which will ultimately impact the hydropower supply and water resources of the Yangtze Basin. This study contributes to the understanding of the dynamics of the hydrological cycle and may lead to better hydrologic system modeling for downstream water resource developments

Role of the dielectric constant of ferroelectric ceramic in enhancing the ionic conductivity of a polymer electrolyte composite

The dispersal of high dielectric constant ferroelectric ceramic material Ba(0.7)Sr(0.3)TiO(3) (Tc~30 C) and Ba(0.88)Sr(0.12)TiO(3) (Tc~90 C) in an ion conducting polymer electrolyte (PEO:NH4I) is reported to result in an increase in the room temperature ionic conductivity by two orders of magnitude. The conductivity enhancememt "peaks" as we approach the dielectric phase transition of the dispersed ferroelectric material where the dielectric constant changes from ~ 2000 to 4000. This establishes the role of dielectric constant of the dispersoid in enhancing the ionic conductivity of the polymeric composites.Comment: 10 pages, 2 figure

Performance evaluation of zinc oxide varistor produced from powder under different spray drying conditions

I-V characteristics, wattloss behavior and energy absorption capability etc. are the critical characteristics for performance evaluation of ZnO varistors. In the long processing steps of this electro-ceramic with a considerable number of contributing variables, the preparation of pressing grade electro-ceramic materials is very important. It demands powders with high degree of compositional and microstructural homogeneity, high purity and reliability, proper shape and proper size and distribution. This kind of ceramic powder can be generated by spray drying. Apart from affecting the physical properties of varistor discs, the powder characteristics influence the grain growth and microstructure which are anticipated to affect the electrical behavior of the discs. To investigate this, varistor powder was produced from standard slurry under different spray drying conditions in pilot scale. Feed flow rate, atomizing air pressure and outlet drying air temperature were considered as input variables and nominal voltage, wattloss, clamp ratio, non-linear co-efficient and energy absorption capability were considered as response. It was found that nominal voltage, wattloss and energy absorption capability was highly influenced by spray drying variables but no significant influence was observed on clamp ratio and nonlinear co-efficient for both the pre-breakdown and breakdown region. Not only high but consistent energy absorption capability was achieved by optimizing spray drying conditions. Thus optimization of spray drying variables could help securing desirable varistor characteristics and enhanced reliability of the electrical system

A Detailed Cloud Fraction Climatology of the Upper Indus Basin and Its Implications for Near-Surface Air Temperature*

implications for near surface air temperature. Journal of Climate 2015, 28(9)

Cracks, microcracks, and fracture toughness of polymer composites: formation, testing method, nondestructive detection, and modifications

Polymer matrix composite consists of polymeric matrix and fiber as reinforcement. The properties of the matrices and fibers are usually opposite to each other. Where the matrix is soft, the fibers are rigid. This is how they complement each other since the main purpose of the rigid fiber addition was to increase the strength of the soft polymer matrix. However, because of these differences, the microcrack and crack formation and propagation in polymer composite become a complicated topic to be studied since it involves the interaction between the different type of materials. Example of factors that influence the formation of cracks as discussed in the chapter were type and dimensions of the fiber material used, compatibility between the matrix and fiber material, manufacturing process methodology, and application environment. After the cracks or microcracks formed, the next step is the propagation of the cracks. This progress was also influenced by these parameters and the type of composite configuration. The objective of this chapter is to review the different effects of the factors that influence the formation and propagation of cracks and microcracks in polymer composite. Following the discussion about the formation of microcracks, a step-by step method on how to detect and measure the cracks and microcracks, fracture mechanics, and the nondestructive testing available related to it is discussed in detail. Finally, based on knowledge of composite materials, two methods that have been studied and show promising results to improve fracture toughness in polymer composite material