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排序方式: 共有94条查询结果,搜索用时 15 毫秒
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2.
U. Dahmen 《Metallurgical and Materials Transactions A》1994,25(9):1857-1863
The connection between the optimum shape and orientation relationship of precipitates in a solid is examined. Three simple
criteria for precipitate morphology are compared and illustrated schematically: the principle that precipitate dimensions
tend to be inverse to the magnitude of the transformation strain; the postulate that precipitates are bounded by unrotated
planes (eigenplanes); and the proposal that interfaces are parallel to the planes of three independent dislocation loop arrays
necessary to accommodate the transformation strain completely. These principles are illustrated for different orientation
relationships, and it is shown that special features are displayed by invariant-line precipitates. The implications of these
criteria for experimental studies of precipitate morphologies are discussed and their predictions compared with results from
a recent study of lath-shaped precipitates in Cu-Cr alloys.
This article is based on a presentation made at the Pacific Rim Conference on the “Roles of Shear and Diffusion in the Formation
of Plate-Shaped Transformation Products,” held December 18-22, 1992, in Kona, Hawaii, under the auspices of ASM INTERNATIONAL’S
Phase Transformations Committee. 相似文献
3.
This article describes a novel software tool, the KSpaceNavigator, which combines sample stage and crystallographic coordinates in a control sphere. It also provides simulated kinematic diffraction spot patterns, Kikuchi line patterns and a unit cell view in real time, thus allowing intuitive and transparent navigation in reciprocal space. By the overlay of experimental data with the simulations and some interactive alignment algorithms, zone axis orientations of the sample can be accessed quickly and with great ease. The software can be configured to work with any double-tilt or tilt–rotation stage and overcomes nonlinearities in existing goniometers by lookup tables. A subroutine for matching the polyhedral shape of a nanoparticle assists with 3D analysis and modeling. The new possibilities are demonstrated with the case of a faceted BaTiO3 nanoparticle, which is tilted into three low-index zone axes using the piezo-controlled TEAM stage, and with a multiply twinned tetrahedral Ge precipitate in Al, which is tilted into four equivalent zone axes using a conventional double-tilt stage. Applications to other experimental scenarios are also outlined. 相似文献
4.
This work investigates the mechanism and dynamics of grain boundary migration driven by capillary forces via in situ electron microscopy, complemented by molecular-dynamics simulations. Using thin films of Au with the mazed bicrystal geometry, the shrinkage of island grains with 90°〈1 1 0〉 tilt grain boundaries was observed by diffraction contrast and high-resolution imaging. The grains remained cylindrical throughout the shrinkage, and there was no measurable grain rotation even at very small sizes. The rate of shrinkage was found to be erratic and inconsistent with parabolic kinetics, accelerating before complete disappearance. Residual defects were found immediately after complete shrinkage, although the type and magnitude of the defects varied from grain to grain. Measurement of the grain boundary shape anisotropy showed a preference for facets on low-index planes of the crystals, including the mirror-symmetry planes of the bicrystal. These facets were also found directly on individual images extracted from high-resolution video recordings of shrinking grains at ~300 °C. The dynamics of boundary motion were found to be limited by nucleation and propagation of steps on these facets. The cylindrical geometry and size of the experimentally observed island grains allow direct comparison with molecular-dynamics simulations on the same length scale, which reproduced many of the experimentally observed features, including non-parabolic shrinkage, absence of systematic grain rotation, step-controlled migration and dislocation debris after complete grain shrinkage. Differences between model and experiment are discussed in terms of the possible role of impurities, surfaces and interfacial steps. 相似文献
5.
Joseph Dahmen 《Journal of Architectural Education》2017,71(1):57-64
Three recent projects fabricated from living mushroom bricks that create a visceral experience of mycelium biocomposites are described as a natural example of a “soft system.” The move toward soft, regenerative systems has important implications for the way we approach the production of architectural materials and environments in the Anthropocene. Collectively, the projects suggest a future in which dynamic materials that contribute to local ecosystems are grown rather than manufactured and engage with temporality in new and productive ways. 相似文献
6.
Gundacker C Komarnicki G Jagiello P Gencikova A Dahmen N Wittmann KJ Gencik M 《The Science of the total environment》2007,385(1-3):37-47
BACKGROUND: Detoxification is an essential process in all living organisms. Humans accumulate heavy metals primarily as a result of lifestyle and environmental contamination. However, not all humans experience the estimated individual exposure. This suggests the presence of genetic regulatory mechanisms. OBJECTIVE: In order to identify genetic factors underlying the inter-individual variance in detoxification capacity for the heavy metal mercury, 192 students were investigated. We focused on the relationship between polymorphisms in glutathione-S-transferase (GST) genes and mercury concentrations in blood, urine, and hair. The correlation between blood mercury levels, GSTT1 and GSTM1 polymorphism, and gene expression of certain metallothionein subgroups (MT1, MT3) was evaluated in a further group of students (N=30). METHODS: Mercury levels in acid digested samples were measured by cold vapor AAS. Genotyping of the GSTT1 and GSTM1-gene deletion polymorphism was performed by means of PCR. Gene expression of several MT genes was analyzed in lymphocytes from fresh peripheral blood by semiquantitative RT-PCR. RESULTS: The following was noted: a) hair mercury concentrations are significantly increased in persons with the double deleted genotype (GSTT1-/- and GSTM1-/-) as compared to persons with the intact genotype, and b) MT1X expression is higher in persons with the intact genotype (GSTT1+/+ and GSTM1+/+). CONCLUSIONS: We conclude that the epistatic effect of the GSTT1 and the GSTM1 deletion polymorphism is a risk factor for increased susceptibility to mercury exposure. The relationship between MT gene expression and GST gene polymorphisms needs further investigation. If MT expression depends on GST polymorphisms it would have important implications on the overall metal detoxification capability of the human organism. 相似文献
7.
Optimisation of the critical medium components for better growth of Picochlorum sp. and the role of stressful environments for higher lipid production 下载免费PDF全文
8.
David Mitlin V. Radmilovic J. W. Morris U. Dahmen 《Metallurgical and Materials Transactions A》2003,34(13):735-742
Al−Cu−Si−Ge alloys display a unique combination of ultrarapid aging response, high peak hardness, and extended-aging microstructural
stability. The purpose of this work is to explain these properties in terms of the role that the Si−Ge additions have on modifying
the conventional Al−Cu aging sequence. In both AlCu and AlCuSiGe, the room-temperature microstructure consists of both Guinier-Preston
(GP) zones and ϕ″ precipitates. Upon aging at 190°C, Al−Cu displays the well-known precipitation sequence: the slow dissolution
of GP zones and ϕ″ and the gradual formation of ϕ′. In the quaternary alloy, Si−Ge particles quickly nucleate and grow during
elevated-temperature aging (they are detected after as little as 30 minutes at 190 °C). The Si−Ge particles then act as nucleation
sites for ϕ′ precipitates, resulting in a peak-aged microstructure consisting of a dense distribution of ϕ′ attached to Si−Ge.
DAVID MITLIN, Postdoctoral Fellow, formerly with the Materials Science Department, University of California-Berkeley and the
Lawrence Berkeley National Laboratory. 相似文献
9.
Spencer L. Tomarken Daniel M. Silevitch Gabriel Aeppli Braden A.W. Brinkman Jian Xu Karin A. Dahmen Thomas F. Rosenbaum 《Advanced functional materials》2014,24(20):2986-2992
Random magnetic fields, varying from site to site in a magnetic material, are a form of disorder that can determine the local architecture and stability of the magnetic state. In a ferromagnet, the application of an external magnetic field can amplify the effects of the internal random fields and, in principle, harden a magnetic domain, without changing temperature and only for as long as the external field is present. Here, the rare‐earth compound Nd2Fe14B, formed with a granular morphology of random‐packed, elongated grains, is an experimental realization of the Random Field Ising Model in a room temperature ferromagnet. The application of magnetic fields transverse to the easy axis tunes the coupling between the structural disorder and the magnetic pinning properties. This material both illuminates the intricacies of tunable disorder and serves as a guidepost along the way to developing increased‐density magnetic storage media. 相似文献
10.
A new cofactor related cDNA in the bony fish Paralablax nebulifer, (barred sand bass) was isolated from a sand bass liver cDNA library. The clone (c71) is 1040 bp in size and the predicted translation product of 204 amino acids contains a hydrophobic signal peptide, which is followed by a region of three short consensus repeats (SCRs). The three SCRs display high homology to SCRs of the 110 kDa chain of the sand bass plasma cofactor protein, and to a lesser degree to human complement factor H related protein 3 (FHR-3) and to human factor H. Recombinant expression of the c71 cDNA in the baculovirus system shows a product of an apparent molecular mass of 27 kDa, which is secreted and glycosylated. It also contains a His-tag for purification purposes. Removal of the His-tag yields a 24 kDa protein, and deglycosylation further reduces the molecular mass to 21 kDa. This size is in agreement with the calculated molecular mass based on amino acid composition. The sand bass SBCFR-1 protein is immunologically related to the human complement proteins, factor H and factor H-related protein 3. The recombinantly expressed protein reacted with antisera against the human FHR-3 protein and SCRs 19-20 of human factor H. The presence of SCR-containing proteins in sand bass plasma and their structural and immunological homology to human FHR-3 and factor H suggests for a common function between these evolutionary related proteins. 相似文献