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51.
H. D. Espinosa B. C. Prorok B. Peng K. H. Kim N. Moldovan O. Auciello J. A. Carlisle D. M. Gruen D. C. Mancini 《Experimental Mechanics》2003,43(3):256-268
The mechanical properties of ultrananocrystalline diamond (UNCD) thin films were measured using microcantilever deflection
and membrane deflection techniques. Bending tests on several free-standing UNCD cantilevers, 0.5 μm thick, 20 μm wide and
80 μm long, yielded elastic modulus values of 916–959 GPa. The tests showed good reproducibility by repeated testing on the
same cantilever and by testing several cantilevers of different lengths. The largest source of error in the method was accurate
measurement of film thickness. Elastic modulus measurements performed with the novel membrane deflection experiment (MDE),
developed by Espinosa and co-workers, gave results similar to those from the microcantilever-based tests. Tests were performed
on UNCD specimens grown by both micro and nano wafer-seeding techniques. The elastic modulus was measured to be between 930–970
GPa for the microseeding and between 945–963 GPa for the nanoseeding technique. The MDE test also provided the fracture strength,
which for UNCD was found to vary from 0.89 to 2.42 GPa for the microseeded samples and from 3.95 to 5.03 for the nanoseeded
samples. The narrowing of the elastic modulus variation and major increase in fracture strength is believed to result from
a reduction in surface roughness, less stress concentration, when employing the nanoseeding technique. Although both methods
yielded reliable values of elastic modulus, the MDE was found to be more versatile since it yielded additional information
about the structure and material properties, such as strength and initial stress state. 相似文献
52.
IA Simpson R Bol ID Bull RP Evershed K Petzke SJ Dockrill 《Rapid communications in mass spectrometry : RCM》1999,13(13):1315-1319
Compound specific stable isotope analyses of managed soils using isotope ratio mass spectrometry have been undertaken as a means of determining early land use practices. delta (15)N amino acid signals demonstrate differences between manured grassland, unmanured grassland and continuous cereal cultivation under long-term experimental land use control conditions, with delta (15)N in hydrophobic amino acids providing the most distinctive signals. Analysis of early modern/medieval and of Bronze age anthropogenic soils from Orkney demonstrates that such signals are retained in archaeological contexts. delta (13)C analyses of n- alkanoic acid components of the fossil, Bronze Age, anthropogenic soils suggest a major terrestrial input to these soils, with uniform composition of formation materials. Surficial soils demonstrate the assimilation of isotopically lighter carbon, providing a means of assessing the mobility of the n- alkanoic acids within soils and sediments. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
53.
Casey TC Carlisle J Tisselli P Male L Spencer N Grainger RS 《The Journal of organic chemistry》2010,75(21):7461-7464
Pyrrolidine enamines derived from three 1,3-dioxan-5-ones undergo α,α'-annelation reactions with methyl α-(bromomethyl)acrylate to produce bridged 2,4-dioxabicyclo[3.3.1]nonane ring systems with complete stereocontrol. Stereochemical outcomes have been rationalized based on steric and stereoelectronic interactions in intermediate boat-like conformations of the 1,3-dioxane ring and subsequent kinetic protonation to set an axial ester group on the cyclohexanone ring. Base-mediated ester epimerization provides the stereochemical array found in the highly oxygenated cyclohexane ring of phyllaemblic acid and glochicoccins B and D. 相似文献
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55.
We have performed extensive small-angle neutron scattering (SANS) diffraction studies of the vortex lattice in single crystal
YNi2B2C for B‖c. High-resolution SANS, combined with a field-oscillation vortex lattice preparation technique, allows us to separate Bragg
scattered intensities from two orthogonal domains and accurately determine the unit cell angle, β. The data suggest that upon increasing field there is a finite transition width where both low- and high-field distorted
hexagonal vortex lattice phases, mutually rotated by 45°, coexist. The smooth variation of diffracted intensity from each
phase through the transition corresponds to a redistribution of populations between the two types of domains. 相似文献
56.
57.
New first- and high-order centred methods for conservation lawsare presented. Convenient TVD conditions for constructing centredTVD schemes are then formulated and some useful results areproved. Two families of centred TVD schemes are constructedand extended to nonlinear systems. Some numerical results arealso presented. 相似文献
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Enantiomerically enriched C2-symmetric tetrols were synthesised by a route involving a 'self-metathesis' reaction with Grubbs' second-generation ruthenium catalyst; these tetrols produced interesting bicyclic products when rearranged under acidic conditions. 相似文献