The electrical properties of ceramic BaTiO3 were investigated by ac impedance spectroscopy over the ranges 25°-330°C and 0.03 Hz-1 MHz. Results are compared with those obtained from fixed-frequency measurements, at 1 kHz and 100 kHz. Fixed-frequency Curie-Weiss plots show deviations from linearity at temperatures well above t c. The ac measurements show that grain boundary impedances influence Curie-Weiss plots in two ways: at high temperatures, they increasingly dominate the fixed-frequency permittivities; at lower temperatures, closer to T c, the high-frequency permittivity contains a contribution from grain boundary effects. Methods for extraction of bulk and grain boundary capacitances from permittivity and electric modulus complex plane plots are discussed. The importance of selecting the appropriate equivalent circuit to model the impedance response is stressed. A constriction impedance model for the grain boundary in BaTiO3 ceramics is proposed: the grain boundary capacitance is neither temperature-independent, nor shows Curie-Weiss behavior. The grain boundary is ferroelectric, similar to the grains, but its impedance is modified by either air gaps or high-impedance electrical inhomogeneity in the region of the necks between grains; the activation energy of the constriction grain boundary impedance differs from that of the bulk, suggesting differences in defect states or impurity levels. 相似文献
Texture and grain size distribution of the austenite phase at high temperature have distinct effects on the subsequent transformed microstructure and mechanical properties of steel alloys at room temperature. Measurement of austenite at high temperature is not, however, a trivial task especially if orientation maps are desired. Therefore, a technique for determining austenite texture and grain size that was present at high temperature is highly desirable. In this work, we review several pipe samples intended for use as well casing with large variations in toughness and martensitic microstructures at room temperature. Microstructural analysis of the martensite structures could not easily explain these differences due to how martensite forms from austenite. An algorithm was developed to reconstruct the parent austenite at high temperature from martensite microstructure at room temperature. This technique successfully reconstructed orientation maps for the prior austenite in these samples, demonstrating differences in texture, grain orientation spread, and austenite grain size that could account for the differences in mechanical properties. 相似文献
As building information modelling (BIM) software becomes ever more powerful, how will the architect's role be affected? Ian Keough and Anthony Hauck of the AEC Generative Design group at leading software corporation Autodesk present their vision. They argue that the value of building professionals' expertise in advising clients on priorities and choices has never been higher. BIM offers greater guarantees of structural integrity and constructional feasibility, and scalable cloud computing allows numerous factors to be explored simultaneously; but success is only assured if the right parameters are set. 相似文献
Experimental observations have been made of the fringe contrast which appears at the terminating edges of thin objects in defocused, scanning-transmission electron micrographs. In general only a single bright fringe is present and the displacement and width of this fringe was found to vary linearly with defocus, indicating the contrast does not result from simple-Fresnel diffraction. A model for this contrast, based on the refraction of incident electrons by the object edge, is shown to explain the observed results. 相似文献
World landings of fish and shellfish are approaching 100 million metric tons (MMT) annually. Of this total, around 28% is
processed into fish meal and oil. Economic pressures due to poor landings, low prices in traditional markets and high fuel
costs have forced the industry to seek new markets and products that can take advantage of the unique properties of fish proteins
and oils.
Fish meal processing continues to evolve. Fresh raw materials and new, low-temperature processing techniques lead to products
with excellent nutritional value. These new, special meals are finding uses in feeding farmed fish, early-weaned pigs, ruminants
and pets.
Fish oils, whether present as fat in the fish meal or as separated oil, are rich in ω3 fatty acids. When fed to food animals,
these ω3 fatty acids deposit in the meat and depot fat. Concepts for poultry with an equivalent amount of ω3 fatty acids to
lean fish are being developed. Eggs with a high ω3 fatty acid content and good functionality and flavor are under evaluation.
Catfish with shelf-stable flavors and high ω3 fatty acids are also under study. ω3 Fatty acids may affect the immune function
of livestock. Future research will evaluate the overall immune function of animals, including resistance to disease, survival
under stress and hatchability. 相似文献
A normal-phase high-pressure liquid chromatography technique has been elaborated for the separation of quaternary ammonium
surfactants. The separation was achieved on a bonded polyphenol silica gel column with gradient elution and evaporative light-scattering
(ELS) detection. The proposed method has been applied to the quantitative determination of low levels of monoalkyltrimethylammonium
and trialkylmethylammonium chlorides in dialkyldimethylammonium chloride. 相似文献
The rising level of atmospheric CO2 has stimulated several recent studies attempting to predict the effects of increased CO2 on ecological communities. However, most of these studies have been conducted in the benign conditions of the laboratory and in the absence of herbivores. In the current study, we utilized large octagonal chambers, which enclosed portions of an intact scrub-oak community to investigate the interactive effects of CO2 and insect herbivory on myrtle oak, Quercus myrtifolia. Specifically, we assessed the effects of ambient and elevated CO2 (2x current concentrations) on percent foliar nitrogen, C:N ratio, total relative foliar tannin content, and the presence of leaf damage caused by leaf mining and leaf chewing insects that feed on myrtle oak. Total foliar N declined and C:N ratios increased significantly in oaks in elevated CO2 chambers. The percentages of leaves damaged by either leafminers or leaf chewers tended to be lower in elevated compared to ambient chambers, but they co-occurred on leaves less than expected, regardless of CO2 treatment. Leaves that had been either mined or chewed exhibited a similar wounding or defensive response; they had an average of 25 and 21% higher protein binding ability, which is correlated with tannin concentration, compared to nondamaged control leaves, respectively. While the protein-binding ability (expressed as total percent tannin) of leaves from elevated CO2 was slightly higher than from leaves grown in ambient chambers, this difference was not significant. 相似文献
A new type of mesoporous silica has been prepared which showed 780 m2/g of BET surface area and 0.6 ml/g of primary mesopores narrowly distributed around 4.2 nm. More importantly however, is that it showed short-range zeolite crystallinity as demonstrated by FTIR and XRD analysis, and hydrophobicity as demonstrated by water and n-hexane adsorption.
This material was synthesized via a dual-template, three-step hydrothermal–flocculation–steaming synthesis procedure developed by us recently. Briefly, MFI nanoprecursors (NPs) were first prepared by a low-temperature hydrothermal step using TPAOH as template for zeolite structure, and then flocculated using a surfactant that served as the template for the mesopores. The collected NPs are mesoporous silica exhibiting short-range MFI domains when directly calcined. However, the steaming step promoted the crystallization of the NPs and created uniform mesopores. It was found that almost every detail in these procedures affected the properties of the final product. The most important variables, however, were identified as the duration the flocculants were kept in contact with the liquid phase, and the humidity under which the steaming was conducted. By properly adjusting the procedures, the said mesoporous silica, as well as nanocrystals having high external surface area, could be produced at will. 相似文献