China Science

Different iron–chromium alloys (4, 8, 13 and 20 wt.%Cr) were nitrided in a NH3/H2 gas mixture at 580 °C for various times. The nitrided microstructure was characterized by X-ray diffraction, light microscopy and hardness measurements. Composition depth profiles of the nitrided zone were determined by electron-probe microanalysis. Residual stress–depth profiles of the nitrided specimens were measured using the (X-ray) diffraction sin2 ? method in combination with cumulative sublayer removals and correction for corresponding stress relaxations. Unusual, nonmonotonous changes of stress with depth could be related to the microstructure of the nitrided zone. A model description of the evolution of the residual stress as function of depth and nitriding time was given.

N.E. Vives Díaza?R.E. Schacherlb Email:r.schacherl@mf.mpg.de?L.F. Zagonela?E.J. Mittemeijera
[a]Max Planck Institute for Metals Research, Heisenbergstrasse 3, D-70569 Stuttgart, Germany;[b]Institute for Physical Metallurgy, University of Stuttgart, Germany ;[1] On leave from: Instituto de Física “Gleb Wataghin”, Universidade Estadual de Campinas, Unicamp, P.O. Box 6165 Campinas, SP, 13083-970, Brazil; Present address: CEA-DSM/DRECAM-SPCSI, CEA-Saclay, 91191, Gif-sur-Yvette, France.

A trace (0.1 at.%) addition of Ge to a base Al–1.7Cu–0.3Mg alloy resulted in considerable refinement of the ?? (Al2Cu) precipitate dispersion as well as stimulating the formation of 0 0 1 lath-shaped precipitates in a fine and uniform distribution. These precipitates contain mainly Ge and Mg. The formation of the S(Al2CuMg) and ?(Al5Cu6Mg2) phases was suppressed, presumably due to the stronger interaction between Ge and Mg over Cu and Mg. Significantly, the trace addition of Ge produced an internal structure within the ?? precipitate phase with its habit plane parallel to the {1 0 1}?? planes. Our investigations reveal that this unusual internal structure is secondary precipitation within ?? precipitation of a Mg–Ge rich phase thought to be an allomorph of Mg2Ge, and this influences both the nucleation and growth of ?? precipitates. This internal structure is designated as K phase, possessing a close packed hexagonal structure (a = 0.405 nm, c = 0.607 nm) and oriented such that, (0 0 0 1)K//(1 0 1)?? and ]K//[1 0 0]??. Prolonged ageing at 200 °C led to replacement of the 0 0 1 lath-shaped precipitates through their dissolution and reprecipitation of a more stable form of Mg2Ge (face-centred cubic, Fmm, a = 0.638 nm).

S.P. RingeraEmail:s.ringer@usyd.edu.au?K.S. Prasada?G.C. Quanc
[a]Australian Key Centre for Microscopy; Microanalysis, The University of Sydney, Madsen Building F09, Sydney, NSW 2006, Australia;[b]ARC Centre of Excellence for Design in Light Metals, The University of Sydney, NSW 2006, Australia;[c]Wescast Industries Inc., Brantford, ON, N3T 5L8, Canada

Sequestration of CO2 into deep, unminable coal seams is an attractive option to reduce atmospheric emissions. However, coal seams commonly have low initial permeability, and CO2 adsorption causes the coal matrix to swell, which further reduces the permeability and may result in inefficient injection. We investigate numerically the impacts of coal swelling on coal permeability and, thus, CO2 injection efficiency with constraints determined by experimental adsorption-associated volumetric strain measurements on three western Canadian coals. Our results show that injecting pure CO2 markedly reduces permeability through time to the extent that it is not a feasible sequestration technology for almost all coals. However, injection of a gas mixture of N2 and CO2 (flue gas) markedly improved CO2 injection efficiency while mildly reducing CO2 sequestration capacity. The study also suggests that different geological settings and mechanical properties of specific coal seams strongly control coal seam permeability during gas injection and, thus, viability of CO2 sequestration.

R. Marc Bustin?Xiaojun Cui?Laxmi Chikatamarla
Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, British Columbia, Canada V6T 1Z4

Differentiation of microbial versus thermogenic methane in coalbed and black shale accumulations can affect strategies for exploration and may influence the total gas content in a given area. Early identification of these processes from crushed core materials, even before formation fluids and produced gas samples are available, could permit a more efficient and cost-effective exploration. Total gas contents and compositional and isotopic data from New Albany Shale core materials are presented, which delineate regional occurrence of microbial, thermogenic, and mixed gas generation in the Illinois Basin. These trends are consistent with those identified from detailed prior studies of produced gas and water chemistry from the same locations. The most useful markers for microbial gas in crushed core gases are elevated CO2 contents characterized by high ?~(13)C_(CO2) values (> 5 per thousand). Core gas analyses from wells in which microbial gas is identified commonly have significantly more total gas absorbed than do core samples from wells producing gases solely of thermogenic origin. These observations are independent of variations in sample depth and organic carbon content in a given core. Thus, this integrated case study of core and produced gases in the Illinois Basin illustrates that the areas containing microbial gas, in addition to early thermogenic gas, may be more productive than pure thermogenic zones for these early to immature unconventional gas deposits.

Anna M. Martini?Lynn M. Walter?Jennifer C. Mcintosh
Department of Geology, Amherst College, Amherst, Massachusetts 01002; Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109; Department of Hydrology and Water Resources, University of Arizona, Tucson, Arizona 85716

In this paper, I highlight how popular understandings of neoinstitutionalism as a theory of isomorphism need to be revised as institutionalists have shifted attention towards the study of organizational heterogeneity. As part of this shift, old emphases on arational mimicry and stability have been replaced with new emphases on institutional rationality and ongoing struggle and change. I discuss these new directions and the implications for the study of accounting practice. I argue that given recent efforts by institutionalists to account for actors and practice diversity, there is an important opportunity for dialogue with practice theorists, such as those drawing on Actor Network Theory, and the creation of a more comprehensive approach to the study of practice that attends to both institutional and micro-processual dynamics.

Michael Lounsbury aEmail:ml37@ualberta.ca
[a]University of Alberta School of Business; National Institute for Nanotechnology, 4-30E Business Building, Edmonton, Alberta, Canada T6G 2E7

Sequestration of CO2 into deep, unminable coal seams is an attractive option to reduce atmospheric emissions. However, coal seams commonly have low initial permeability, and CO2 adsorption causes the coal matrix to swell, which further reduces the permeability and may result in inefficient injection. We investigate numerically the impacts of coal swelling on coal permeability and, thus, CO2 injection efficiency with constraints determined by experimental adsorption-associated volumetric strain measurements on three western Canadian coals. Our results show that injecting pure CO2 markedly reduces permeability through time to the extent that it is not a feasible sequestration technology for almost all coals. (more…)

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BackgroundThe compliance review (CR) is a federal program monitoring motor carrier safety performance and regulatory compliance. This study sought to assess the impact of CRs on reviewed trucking companies in reducing truck crashes.MethodsData was from the Motor Carrier Management Information System. Study subjects were trucking companies established during 1990–1995, had at least one truck, and remained active until April 2004. (more…)

ObjectiveTo analyse international variation in clinical injury incidence, and explore the performance of different injury indicators in cross-country comparisons.MethodsHospital discharge data of seven European countries (Austria, Denmark, Ireland, Netherlands, Norway, England and Wales) were analysed. (more…)