Pore growth during the initial stages of sintering ceramics

Mercury porosimetry was used to measure changes in pore size distribution during initial stage sintering of compacts of submicron size particles of several oxides. Pore growth was observed in MgO and Fe₂O₃, and in Al₂O₃ under certain conditions. Pores can grow by these mechanisms: surface diffusion, particle size distribution effects, particle coalescence, phase transformation, and evaporation/condensation. Surface diffusion may be the mechanism in the case of an alpha alumina. Phase transformation was shown to be the cause when sintering gamma alumina. In the case of magnesia and ferric oxide, particle coalescence appears to be operating. Since pore growth competes with densification for the use of surface energy, it is an important sintering process.     

Catabolism of lipid-free recombinant apolipoprotein serum amyloid A by mouse macrophages in vitro results in removal of the amyloid fibril-forming amino terminus

A series of 101 consecutive patients undergoing pancreatic resection for cancer was retrospectively analyzed to define factors that may affect the immediate postoperative outcome. Overall morbidity and mortality were 28.7% and 10.9%, respectively, although these figures were greatly reduced during the last years; the complication rate dropped from 55.6% (1981-1987) to 20.0% (1993-1995) and the mortality from 16.7% to 6.7%. At univariate statistical analysis the patient characteristics (sex, age, American Society of Anesthesiologists [ASA] class, nutritional status, jaundice), tumor characteristics (site, size, TNM stage, and grading), and type of surgery were found not to affect postoperative morbidity and mortality. In contrast, a significantly lower rate of complications was observed in patients not undergoing gastric resection, in those who received 3 units or less of blood intraoperatively, and in subjects operated more recently (after 1990). At multivariate analysis the period when the operation was performed was the only independent variable that affected the immediate postoperative outcome. Among the examined factors, only the experience acquired over time regarding the intra- and perioperative treatment of these patients seems able to lower the rate of postoperative complications.     

The acute phase response in apolipoprotein A-1 knockout mice: apolipoprotein serum amyloid A and lipid distribution in plasma high density lipoproteins

In plasma, the bulk of apoSAA, a positive acute phase reactant protein, is transported in high density lipoproteins (HDL), especially HDLH (apoA1-rich HDL). In this study we tested whether apoA1 deficiency would adversely affect apoSAA concentration and lipid distribution in mouse plasma lipoproteins. Acute phase response (APR) was induced in C57BL/6J (apoA1+/+) and apoA1-knockout mice (apoA1-/-) by a subcutaneous injection of silver nitrate. The APR increased cholesterol concentrations in LDL of apoA1-/- mice and apoA1+/+ mice in a like manner. In contrast to apoA1+/+ mice, concentrations of cholesterol, phospholipids and proteins in both HDLL (1.063相似文献   

Investigating the Social Dimensions of Transport Disadvantage—I. Towards New Concepts and Methods1

This article is the first of two papers that engage critically and productively with the relationship between the socio-economic transformations of cities, the differentiation of vulnerable groups within urban space and the distribution of transport services. This article undertakes a comprehensive review of the major conceptual and methodological approaches by which scholars and policy researchers have sought to address the connection between social disadvantage and access to transport. The article critically assesses the relative merits of various spatial analytical methodologies in illuminating social–transport links. The study finds that there is a need for greater sophistication in the use of analytical methods in transport research as well as an imperative for greater sensitivity to social differentiation within urban areas and relative to infrastructure and services. The article concludes by developing a method for combining spatial social and transport service data that is then deployed in the empirical case study reported in the second paper.     

A new property evaluation scheme for mass transfer analysis in fire problems

A simple scheme for the estimation of average thermo-physical properties has been presented. Properties such as thermal conductivity and specific heat have been calculated at suitable temperatures, which are functions of the ambient and the adiabatic flame temperatures. These have been successfully employed in the empirical correlations available in standard combustion text books for the estimation of burning rate constants and flame stand-off distances in the combustion of liquid and solid fuels. The average thermal conductivity is estimated as the thermal conductivity of standard air calculated at a temperature given as one-third of the sum of ambient and the adiabatic flame temperatures. The average specific heat is calculated as the specific heat of standard air at the adiabatic flame temperature itself. Extensive validation of the scheme with the experimental data is presented employing several liquid fuels and a solid fuel.     

Theory of relativistic optical harmonic generation

We present a theoretical model of optical harmonic generation excited by laser beams sufficiently intense that relativistic effects are important. This model shows that, under relativistic conditions, third-harmonic generation can be excited with comparable efficiency by either linear or circularly polarized light. This result is to be contrasted with experience from traditional (nonrelativistic) nonlinear optics, where group-theoretical arguments show that third-harmonic emission cannot occur under circularly polarized excitation. These results are in good agreement with the observed polarization dependence of the third-harmonic emission reported recently in an experiment conducted under conditions such that relativistic effects are important. Our theoretical model also predicts that all even and odd harmonies of the fundamental laser frequency are emitted in the near-forward direction with an intensity that increases with that of the incident laser field     

Natural amenities and regional tourism employment: A spatial analysis

This research examines the spatial linkages between natural amenities and tourism employment spillovers under alternative neighbourhood structures. A main contribution is to contrast models where economic distance defines neighbouring regions with a model where the spatial structure is defined by geographical proximity. Significant spillovers are found not only between geographical neighbours, but also between economic neighbours with important implications for policy design. Internet, population, regional parks and state forests and World Heritage Areas are found to be important drivers of regional spillovers. This study uses data for Queensland, Australia, however the approach and conclusions can be extrapolated to similar economies.