24 resultados para Conventional sintering
em Aston University Research Archive
Resumo:
Grain size effects on the physical properties of polycrystalline ferroelectrics have been extensively studied for decades; however there are still major controversies regarding the dependence of the piezoelectric and ferroelectric properties on the grain size. Dense BaTiO3 ceramics with different grain sizes were fabricated by either conventional sintering or spark plasma sintering using micro- and nano-sized powders. The results show that the grain size effect on the dielectric permittivity is nearly independent of the sintering method and starting powder used. A peak in the permittivity is observed in all the ceramics with a grain size near 1μm and can be attributed to a maximum domain wall density and mobility. The piezoelectric coefficient d33 and remnant polarization Pr show diverse grain size effects depending on the particle size of the starting powder and sintering temperature. This suggests that besides domain wall density, other factors such as back fields and point defects, which influence the domain wall mobility, could be responsible for the different grain size dependence observed in the dielectric and piezoelectric/ferroelectric properties. In cases where point defects are not the dominant contributor, the piezoelectric constant d33 and the remnant polarization Pr increase with increasing grain size.
Resumo:
The paper investigates the efficiency of a sample of Islamic and conventional banks in 10 countries that operate Islamic banking for the period 1996–2002, using an output distance function approach. We obtain measures of efficiency after allowing for environmental influences such as country macroeconomic conditions, accessibility of banking services and bank type. While these factors are assumed to directly influence the shape of the technology, we assume that country dummies and bank size directly influence technical inefficiency. The parameter estimates highlight that during the sample period, Islamic banking appears to be associated with higher input usage. Furthermore, by allowing for bank size and international differences in the underlying inefficiency distributions, we are also able to demonstrate statistically significant differences in inefficiency related to these factors even after controlling for specific environmental characteristics and Islamic banking. Thus, for example, our results suggest that Sudan and Yemen have relatively higher inefficiency while Bahrain and Bangladesh have lower estimated inefficiency. Except for Sudan, where banks exhibits relatively strong returns to scale, most sample banks exhibit very slight returns to scale, although Islamic banks are found to have moderately higher returns to scale than conventional banks. While this suggests that Islamic banks may benefit from increased scale, we would emphasize that our results suggest that identifying and overcoming the factors that cause Islamic banks to have relatively low potential outputs for given input usage levels will be the key challenge for Islamic banking in the coming decades.
Resumo:
The paper investigates the efficiency of a sample of Islamic and conventional banks in 10 countries that operate Islamic banking for the period 1996 to 2002, using an output distance function approach. We obtain measures of efficiency after allowing for environmental influences such as country macroeconomic conditions, accessibility of banking services and bank type. While these factors are assumed to directly influence the shape of the technology, we assume that country dummies directly influence technical inefficiency. The parameter estimates highlight that during the sample period, Islamic banking appear to be associated with higher input usage. Furthermore, by allowing for international differences in the underlying inefficiency distributions, we are also able to demonstrate statistically significant differences in efficiency across countries even after controlling for specific environmental characteristics and Islamic banking. Thus, for example, our results suggest that Sudan and Yemen have relatively higher inefficiency while Iran and Malaysia have lower estimated inefficiency. Except for Sudan, where banks exhibits relatively strong returns to scale, most sample banks exhibit very slight returns to scale, although Islamic banks are found to have moderately higher returns to scale than conventional banks. However while this suggests that Islamic banks may benefit from increased scale, we would emphasize that our results suggest that identifying and overcoming the factors that cause Islamic banks to have relatively high input requirements will be the key challenge for Islamic banking in the coming decades.
Resumo:
Electrical and thermal transport properties of the carbon nanotube bulk material compacted by spark plasma sintering have been investigated. The electrical conductivity of the as-prepared sample shows a lnT dependence from 4 to 50 K, after which the conductivity begins to increase approximately linearly with temperature. A magnetic field applied perpendicularly to the sample increases the electrical conductivity in the range of 0-8T at all testing temperatures, indicating that the sample possesses the two-dimensional weak localization at lower temperatures (?50 K), while behaviors like a semimetal at higher temperatures (?50 K). This material acts like a uniform compact consisting of randomly distributed two dimensional graphene layers. For the same material, the thermal conductivity is found to decrease almost linearly with decreasing temperature, similar to that of a single multi-walled carbon nanotube. Magnetic fields applied perpendicularly to the sample cause the thermal conductivity to decrease significantly, but the influence of the magnetic fields becomes weak when temperature increases.
Resumo:
The surfaces of bulk carbon nanotubes compacted by plasma spark sintering have been modified with polytetrofluorethylene, thereby producing a super-hydrophobic surface with a contact angle above 160°. The surface roughness and air trapped in pores and between the polytetrofluorethylene particles are responsible for the super-hydrophobility. The material can be machined into desired shapes with fine and complex channels, allowing internal surfaces to also be super-hydrophobic.
Resumo:
This study investigates the use of reported loan loss provisions (LLP) by investors in their valuations of banks within the Middle East and North Africa region between the years 2006 and 2011. We decompose LLP into discretionary and non-discretionary components to test for differential valuations in the two banking sectors. We use alternative criteria to define the components of LLP in banks: loan quality/size and earnings management/ manipulation incentives. We employ a price-level valuation model estimated using two-stage analyses. We find that LLP has positive value relevance to investors in both banking sectors. Investors in Islamic banks price the discretionary component relatively lower than their conventional counterparts. We attribute this result to differences in product and governance structures as well as to the religious perception of Islamic banking. In both banking sectors, investors construe an increase in the non-discretionary component as irrelevant valuation information. Our results are relevant to bank regulators in showing the signalling effect of LLP to bank value and stability.
Resumo:
This study investigates the use of reported loan loss provisions (LLP) by investors in their valuations of banks within the Middle East and North Africa region between the years 2006 and 2011. We decompose LLP into discretionary and non-discretionary components to test for differential valuations in the two banking sectors. We use alternative criteria to define the components of LLP in banks: loan quality/size and earnings management/manipulation incentives. We employ a price-level valuation model estimated using two-stage analyses. We find that LLP has positive value relevance to investors in both banking sectors. Investors in Islamic banks price the discretionary component relatively lower than their conventional counterparts. We attribute this result to differences in product and governance structures as well as to the religious perception of Islamic banking. In both banking sectors, investors construe an increase in the non-discretionary component as irrelevant valuation information. Our results are relevant to bank regulators in showing the signalling effect of LLP to bank value and stability. © 2013 Elsevier B.V.
Resumo:
We discuss practical designs of coherent optical fast OFDM, and compare the performance of this scheme to conventional OFDM to identify its suitable application scenarios. © OSA 2013
Resumo:
We experimentally demonstrate 38-Gbit/s offset-16QAM OFDM over 840km without guard interval, and numerically show that 112-Gbit/s PDM offset-QPSK OFDM achieves 23% increase in net capacity over conventional OFDM under the same transmission reach. © 2014 Optical Society of America.