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31.
Y Kigami I Yamamoto H Ohnishi H Miura Y Ohnaka T Ota I Yuu K Masuda R Morita 《Canadian Metallurgical Quarterly》1996,37(5):815-818
To understand age-related changes of whole-body and regional skeletal metabolism, it is important to investigate the mechanisms of age-related bone loss and to develop suitable treatments for it. Bone biopsies show metabolism of the particular site examined while biochemical markers for bone metabolism reflect total skeletal metabolism. Bone scintigraphy is a convenient and simple way to analyze whole-body and regional skeletal metabolism. We attempted to study and understand age-related changes in bone metabolism by quantifying the bone scan and correlating it with biochemical bone metabolic markers. METHODS: The whole-body skeletal uptake (WBSU) and tracer distribution pattern were studied in men and women by bone scintigraphy using 99mTc-hydroxy-methane-diphosphonate (HMDP). Bone scans were performed using a standard protocol and quantified by setting regions of interest (ROIs) on selected regions. WBSU and the skeletal distribution pattern were compared with simultaneously obtained serum biochemical markers. RESULTS: WBSU showed an increase with age in both sexes, but in women, uptake in the head and legs increased more relatively than in the thoracic region, while in men no such tendency was observed. Increase of WBSU and relative increase of uptakes in the head demonstrated a weak correlation with the serum levels of alkaline phosphatase and type 1 collagen metabolites. CONCLUSION: These results show an age-related increase of skeletal turnover and sex-dependent regional skeletal metabolism. The age-related changes seen in bone scintigrams might be a sign of progressive bone loss, reflecting changes in local bone metabolism. 相似文献
32.
Structure defect prediction of single crystal turbine blade by dendrite envelope tracking model 总被引:1,自引:0,他引:1
The structure defects such as stray grains during unidirectional solidification can severely reduce the performance of single crystal turbine blades. A dendrite envelope tracking model is developed for predicting the structure defects of unidirectional solidification turbine blade. The normal vector of dendrite envelope is estimated by the gradient of dendrite volume fraction, and the growth velocity of the dendrite envelope (dendrite tips) is calculated with considering the anisotropy of grain growth. The solute redistribution at dendrite envelope is calculated by introducing an effective solute partition coefficient. Simulation tests show that the solute-build-up due to the rejection at envelope greatly affects grain competition and consequently solidification structure. The model is applied to predict the structure defects (e.g. stray grain) of single crystal turbine blade during unidirectional solidification. The results show that the developed model is reliable and has the following abilities: reproduce the growth competition among the different-preferential-direction grains; predict the stray grain formation; simulate the structure evolution (single crystal or dendrite grains). 相似文献
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The spaces (voids) available for cations in the five exchange resins with varying exchange capacities and cross-linking degrees were estimated, on the basis of the additivity of molar volumes of the constituents. Tetraalkylammonium ions (NR(4)(+); R: Me, Et, Pr) may completely exchange potassium ion on the resin having a larger void radius. In contrast, the ratio of saturated adsorption capacity to exchange capacity of the resin having a smaller void radius decreased with an increase in size of NR(4)(+) ions, due to the interionic contacts. Alkali metal ions could be exchanged quantitatively. While the hydration numbers of K(+), Rb(+), and Cs(+) were independent of the void radius, those of Li(+) and Na(+), especially Na(+), decreased with a decrease in void radius. Interionic contacts between the hydrated ions enhance the dehydration. Multivalent metal ions have the hydration numbers, comparable to or rather greater than those in water. A greater void volume available due to exchange stoichiometry released the interionic contacts and occasionally promoted the involvement of water molecules other than directly bound molecules. The close proximity between ions in the conventional ion-exchange resins having higher exchange capacities may induce varying interactions. 相似文献
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The addition of a small amount of Cu is effective in accelerating the + Si eutectoid decomposition. Some elements (Pd, Pt, Ag and Au) that are expected to have similar chemical properties were added to an Fe2Si5 based alloys up to 1.0 at.% to examine whether a similar effect could be revealed. The microstructures, X-ray diffraction and differential thermal analysis (DTA) of slowly solidified or heat treated specimens were investigated in detail. The solubility of all containing elements into the phase was less than 0.2 at.% for the slowly solidified specimen. The excess of the additive solidified as a phase of a eutectic with the Si phase. On the other hand, the solubility of these additives in the phase was classified into two groups. The first group had higher solubility in the phase than that in the phase. The solubility of the other group was as low as that in the phase. Pd and Au belonged to the former and Pt and Ag belonged to the later. The acceleration of the eutectoid decomposition was only observed in the former group but it was negligible in the later group. The existence of the eutectic melt at the annealing temperature was effective on the coarsening of the eutectoid structure but not essential for the acceleration. The eutectoid decomposition strongly depended on the solubility of these elements into the phase. 相似文献
37.
It was unknown whether or not the class of sets of square tapes accepted by nondeterministic two-dimensional finite automata is closed under cyclic closure. This short paper solves this problem, and shows that the class is not closed under row or column cyclic closure. 相似文献
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This paper introduces a new type of automata on a two-dimensional tape, which decides acceptance or rejection of an input tape x by scanning the tape x from various sides by various automata. The accepting power of such an automaton is investigated. This paper mainly concentrates on investigating the accepting power of two-dimensional automata which consist of four parallel/sequential array automata, say M1, M2, M3, and M4, and which accept an input tape x if and only if x, xR, (xR)R, and ((xR)R)R are accepted by M1, M2, M3, and M4, respectively, where for any tape y, yR is the tape obtained by rotating y clockwise 90°. 相似文献
40.
In this paper, we first investigate the relationship between the accepting powers of four-way two-dimensional finite automata and deterministic three-way tape-bounded two-dimensional Turing machines whose input tapes are restricted to square ones. The second part of this paper solves several open problems concerning closure properties of deterministic three-way tape-bounded two-dimensional Turing machines. 相似文献