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181.
N. E. Whitehead R. G. Ditchburn W. J. McCabe R. Van Der Raaij 《Journal of Radioanalytical and Nuclear Chemistry》1992,160(2):477-485
The electrodeposition of226Ra for -spectrometry was reinvestigated to improve reproducibility and yield. Electrodeposition is from 20 ml of 90% propan-2-ol10% 0.05M HNO3 onto stainless steel disks, using 100 mA at 35 V for 20 minutes and a platinum anode. Half deposition time is 3–4 minutes. The following factors were found important: 1. Maintaining the same anode position. 2. Rotation of cathode. 3. Exclusion of sulphate. 4. Avoiding heating the HNO3/propan-2-ol plating solution. 5. Exclusion of solubilised resin resulting from passage through ion-exchange columns. 6. Maintaining other impurities at less than 10 g. If these precautions are followed yields are greater than 90%. 相似文献
182.
G. Proust G. C. Kaschner I. J. Beyerlein B. Clausen D. W. Brown R. J. McCabe C. N. Tomé 《Experimental Mechanics》2010,50(1):125-133
Twinning is an important deformation mode in hexagonal metals to accommodate deformation along the c-axis. It differs from slip in that it accommodates shear by means of crystallographic reorientation of domains within the
grain. Such reorientation has been shown to be reversible (detwinning) in magnesium alloy aggregates. In this paper we perform
in-situ neutron diffraction reversal experiments on high-purity Zr at room temperature and liquid nitrogen temperature, and follow
the evolution of twin fraction. The experiments were motivated by previous studies done on clock-rolled Zr, subjected to deformation
history changes (direction and temperature), in the quasi-static regime, for temperatures ranging from 76 K to 450 K. We demonstrate
here for the first time that detwinning of { 10[`1] 2 }
á 10[`1][`1]
ñ\left\{ {10\overline 1 2} \right\}\left\langle {10\overline 1 \overline 1 } \right\rangle tensile twins is favored over the activation of a different twin variant in grains of high-purity polycrystalline Zr. A visco-plastic
self-consistent (VPSC) model developed previously, which includes combined slip and twin deformation, was used here to simulate
the reversal behavior of the material and to interpret the experimental results in terms of slip and twinning activities. 相似文献
183.
The Lebesgue constants associated with interpolation at the extrema of the Chebyshev polynomials are investigated. It is shown that these constants are smaller than those associated with the zeros of the Chebyshev polynomials. 相似文献
184.
The critical properties of the three-state Potts model are investigated using Monte Carlo simulations. Special interest is given to the measurement of three-point correlation functions and associated universal objects, i.e., structure constants. The results agree well with predictions coming from conformal field theory, confirming, for this example, the correctness of the Coulomb gas formalism and the bootstrap method. 相似文献
185.
The facile double reduction of bicyclic aromatic sulfonamides was used to synthesize a variety of 2- and 3-aryl-substituted pyrrolidines and 2-phenylpiperidine. The method features a combined nitrogen protection and a traceless tether for the transposition of the aromatic moiety from nitrogen to carbon. 相似文献
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188.
Carbon monoxide adsorption has been studied on a series of presulfided Ni(100) surfaces using vibrational spectroscopy. The sulfided Ni(100) surfaces were characterized using Auger electron spectroscopy and low energy electron diffraction, binding states were isolated by heating CO-dosed surfaces to prescribed temperatures, corresponding to the desorption temperatures of the CO. Adsorption of CO on Ni(100) with a p(2 × 2) array of sulfur lead to CO stretching frequencies of 1740 and 1930 cm?1 corresponding to desorption temperatures of 370 and 290 K, respectively. Adsorption of CO into the c(2 × 2)S structure resulted in a CO stretching frequency of 2115 cm?1 and a desorption peak near 140 K. The binding sites on the p(2 × 2)S structure were interpreted as metal four-fold hollows and bridging sites. The high frequency state was interpreted as weak bonding into the four-fold hollow with back donation into the π1 orbital on CO restricted by stearic hindrance due to adsorbed sulfur. Both the thermal desorption and vibrational results indicated that local CO-sulfur interactions are dominant on the presulfided Ni(100) surface in the coverage range studied. 相似文献
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