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268 results on '"Yu, R.C."'

30. High-pressure synthesis of the cubic perovskite BaRu[O.sub.3] and evolution of ferromagnetism in ARu[O.sub.3] (A - Ca, Sr, Ba) ruthenates

Author

Jin, C.-Q., Zhou, J.-S., Goodenough, J.B., Liu, Q.Q., Zhao, J.G., Yang, L.X., Yu, Y., Yu, R.C., Katsura, T., Shatskiy, A., and Ito, E.

Subjects
Perovskite -- Magnetic properties, Ferromagnetism -- Evaluation, Materials at high pressures -- Evaluation, Geological research, Science and technology
Abstract

The cubic perovskite BaRu[O.sub.3] has been synthesized under 18 GPa at 1,000[degrees]C. Rietveld refinement indicates that the new compound has a stretched Ru-O bond. The cubic perovskite BaRu[O.sub.3] remains metallic to 4 K and exhibits a ferromagnetic transition at [T.sub.c] = 60 K, which is significantly lower than the [T.sub.c] [approximately equal to] 160 K for SrRu[O.sub.3]. The availability of cubic perovskite BaRu[O.sub.3] not only makes it possible to map out the evolution of magnetism in the whole series of ARu[O.sub.3] (A = Ca, Sr, Ba) as a function of the ionic size of the A-site [r.sub.A], but also completes the polytypes of BaRu[O.sub.3]. Extension of the plot of [T.sub.c] versus [r.sub.A] in perovskites ARu[O.sub.3] (A = Ca, Sr, Ba) shows that [T.sub.c] does not increase as the cubic structure is approached, but has a maximum for orthorhombic SrRu[O.sub.3]. Suppressing [T.sub.c] by Ca and Ba doping in SrRu[O.sub.3] is distinguished by sharply different magnetic susceptibilities [sub.x](T) of the paramagnetic phase. This distinction has been interpreted in the context of a Griffiths' phase on the (Ca Sr)Ru[O.sub.3] side and bandwidth broadening on the (Sr,Ba)Ru[O.sub.3] side. magnetism | compounds | Ruthenate

Published
2008

50. Evolution of the fracture process zone in high-strength concrete under different loading rates

Author

Cámara M., Tarifa M., Ruiz G., Zhang X., and Yu R.C.

Subjects
Physics, QC1-999
Abstract

For cementitious materials, the inelastic zone around a crack tip is termed as fracture process zone (FPZ) and dominated by complicated mechanism, such as microcracking, crack deflection, bridging, crack face friction, crack tip blunting by voids, crack branching, and so on. Due to the length of the FPZ is related with the characteristic length of the cementitious materials, the size, extent and location of the FPZ has been the object of countless research efforts for several decades. For instance, Cedolin et al. [1] have used an optical method based on the moiré interferometry to determine FPZ in concrete. Castro-Montero et al. [2] have applied the method of holographic interferometry to mortar to study the extension of the FPZ. The advantage of the interferometry method is that the complete FPZ can be directly observed on the surface of the sample. Swartz et al. [3] has adopted the dye penetration technique to illustrate the changing patterns observed as the crack progress from the tensile side to the compression side of the beam. Moreover, acoustic emission (AE) is also an experimental technique well suited for monitoring fracture process. Haidar et al. [4] and Maji et al. [5] have studied the relation between acoustic emission characteristics and the properties of the FPZ. Compared with the extensive research on properties of the FPZ under quasi-static loading conditions, much less information is available on its dynamic characterization, especially for high-strength concrete (HSC). This paper presents the very recent results of an experimental program aimed at disclosing the loading rate effect on the size and velocity of the (FPZ) in HSC. Eighteen three-point bending specimens were conducted under a wide range of loading rates from from 10-4 mm/s to 103 mm/s using either a servo-hydraulic machine or a self-designed drop-weight impact device. The beam dimensions were 100 mm 100 mm in cross section, and 420 mm in length. The initial notch-depth ratio was approximately 0.5, and the span was fixed at 300 mm during the tests. Four strain gauges mounted along the ligament of the specimen were used to measure the FPZ size. Surprisingly, the FPZ size remains almost constant (around 20 mm) when the loading rate varies seven orders of magnitude. This is clearly different from NSC, in which the FPZ size actually decreased with loading rate.

Published
2010
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