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1.
Acoustic emission, dilatometry, and optical microscopy were used to study the polarization of PKR-70 PbTiO3 ferroceramic samples. It was established that in an electric field higher than 2.5 kV/mm the piezoeffect in the samples acquires an infinite anisotropy, accompanied by acoustic-emission and dilatometric anomalies. It is shown that this anisotropy of the piezoeffect is caused by microcracking of the samples in the direction of the polarizing field. Pis’ma Zh. Tekh. Fiz. 25, 21–25 (November 26, 1999)  相似文献   
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The present results show that the sense of the stress-induced irreversible changes in the unstressed magnetization is not always towards the anhysteretic. Examples where the change is away from the anhysteretic are shown, as well as cases where the cyclic uniaxial stress does not cause an irreversible change in the sample's unstressed magnetization when that magnetization does not coincide with a point along the anhysteretic curve. Examination of the magnetization changes with cyclic stress along the upper or lower branches of a minor hysteresis loop suggests that the distance along that branch from the previous turning point is the most important factor in determining the sense of the stress-induced changes in magnetization. Initially the stress-induced changes in the unstressed magnetization occur in the same sense as they would have before the turning point, but the interaction between the domain walls and the pinning sites in the sample as the applied magnetic field changes after the turning point causes this stress-induced change to decrease in value and then reverse in sign. This suggests that the isofield cyclic stress-induced changes in the magnetization should be considered to be towards a local equilibrium condition rather than a global equilibrium condition (the anhysteretic curve)  相似文献   
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Growth of Cement Hydration Products on Single-Walled Carbon Nanotubes   总被引:2,自引:0,他引:2  
Single-walled carbon nanotubes (SWCNT) were distributed on the surface of ordinary Portland cement (OPC) grains. The OPC/SWCNT composite was then hydrated at a 0.5 w/c ratio. The effects of the SWCNT on the early hydration process were studied using isothermal conduction calorimetry, high-resolution scanning electron microscopy and thermogravimetric analysis. The observed behavior of the composite samples was compared with both OPC sonicated without SWCNT and previously published data on as-delivered OPC. The SWCNT were found to accelerate the hydration reaction of the C3S in the OPC. The morphology of both the initial C3A and the C3S hydration products were found to be affected by the presence of the SWCNT. In particular, the nanotubes appeared to act as nucleating sites for the C3S hydration products, with the nanotubes becoming rapidly coated with C–S–H. The resulting structures remained on the surface of the cement grains while those in the sonicated and as-delivered OPC samples grew out from the grain surfaces to form typical C–S–H clusters. Classical evidence of reinforcing behavior, in the form of fiber pullout of the SWCNT bundles, was observed by 24 h of hydration.  相似文献   
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Problems related to neutral particle flux measurements on the ITER tokamak reactor under intense plasma background radiation conditions are considered. The results of measuring a background sensitivity with respect to neutron and γ-radiation for the scintillation detector, which is based on three different crystals (CsI (Tl), ZnO(Ga), and YAG(Ce)), are presented. The scintillators are compared and conclusions about the possibility of their applications in detectors of neutral particle analyzers currently created at the Ioffe Institute for the ITER tokamak reactor, are drawn.  相似文献   
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BACKGROUND: The current classification dividing patients with functional gastrointestinal symptoms into subgroups remains controversial. AIMS: To determine whether distinct symptom groupings exist in the community. METHODS: A random sample of Sydney residents in Penrith, Australia was mailed a validated self report questionnaire. Gastrointestinal symptoms including the Rome criteria for irritable bowel syndrome (IBS) and dyspepsia were measured. RESULTS: Among 730 respondents, the 12 month age and gender adjusted prevalence (adjusted to the Australian population) of IBS, dyspepsia, and gastro-oesophageal reflux were 11.8% (95% confidence interval (CI) 9.3 to 14.3%), 11.5% (95% CI 9.6 to 14.6%), and 17.5% (95% CI 14.2 to 19.9%), respectively. In total, 60% of the population reported four or more gastrointestinal symptoms. There was considerable overlap of IBS with dyspepsia and among the dyspepsia subgroups by application of the Rome criteria. Independently, 10 symptom groupings were identified by factor analysis. The underlying constructs measured by these factors were generally the major abdominal syndromes recognised by the Rome classification: dyspepsia, IBS, reflux, painless constipation, painless diarrhoea, and bloating, in addition to a number of more specific symptom groupings. CONCLUSION: Gastrointestinal symptoms are common and overlap in the community, but distinct upper and lower abdominal symptom groupings can be identified.  相似文献   
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