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991.
Xiaosheng Gao Tingting ZhangJun Zhou Stephen M. GrahamMatthew Hayden Charles Roe 《International Journal of Plasticity》2011,27(2):217-231
It has been shown that the plastic response of many materials, including some metallic alloys, depends on the stress state. In this paper, we describe a plasticity model for isotropic materials, which is a function of the hydrostatic stress as well as the second and third invariants of the stress deviator, and present its finite element implementation, including integration of the constitutive equations using the backward Euler method and formulation of the consistent tangent moduli. Special attention is paid for the adoption of the non-associated flow rule. As an application, this model is calibrated and verified for a 5083 aluminum alloy. Furthermore, the Gurson-Tvergaard-Needleman porous plasticity model, which is widely used to simulate the void growth process of ductile fracture, is extended to include the effects of hydrostatic stress and the third invariant of stress deviator on the matrix material. 相似文献
992.
John S. Caughman Charles L. Dunn Nancy Ann Neudauer Colin L. Starr 《Discrete Mathematics》2011,(16):1803
Lattice chains and Delannoy paths represent two different ways to progress through a lattice. We use elementary combinatorial arguments to derive new expressions for the number of chains and the number of Delannoy paths in a lattice of arbitrary finite dimension. Specifically, fix nonnegative integers n1,…,nd, and let L denote the lattice of points (a1,…,ad)∈Zd that satisfy 0≤ai≤ni for 1≤i≤d. We prove that the number of chains in L is given by where . We also show that the number of Delannoy paths in L equals Setting ni=n (for all i) in these expressions yields a new proof of a recent result of Duchi and Sulanke [9] relating the total number of chains to the central Delannoy numbers. We also give a novel derivation of the generating functions for these numbers in arbitrary dimension. 相似文献
993.
994.
This study examined whether secondary students in an urban school district perceived racial differences in opportunity to be successful in mathematics, whether those perceptions differed between students of color and white students, and the relation of those perceptions to teachers’ choice and implementation of mathematical tasks. The results of multi-level regression models based on student survey and teacher observation data revealed two primary findings: (a) students of color were more likely to perceive opportunity differences than were white students; and (b) this difference was greater in classrooms in which teachers attempted to use cognitively demanding tasks but allowed the cognitive demand to decline during the lesson. Implications for both future research and mathematics teacher education are discussed. 相似文献
995.
Sun Yunwei Carrigan Charles Cassata William Hao Yue Ezzedine Souheil Antoun Tarabay 《Transport in Porous Media》2021,139(1):131-153
Transport in Porous Media - Isotopic ratios of radioactive xenons sampled in the subsurface and atmosphere can be used to detect underground nuclear explosions (UNEs) and civilian nuclear reactors.... 相似文献
996.
This paper discusses the role of the level shift operator in vibronically mixed molecular resonances. The effect of this operator on the shapes of resonances is particularly important when the resonances contain resolved structure. 相似文献
997.
Single crystals of pure, Ca2+ and Sr2+ doped NH4Sb3F10 are grown by slow evaporation technique. The effect of dopants on the growth and physicochemical properties also have been investigated and reported for the first time. The grown crystals are characterized with the aid of single crystal X-ray diffractometry to confirm the crystal structure. EDAX studies are done to confirm the presence of dopants in the crystal lattice. The vibrational frequencies of various group ligands in the crystals have been derived from the Fourier transform infrared (FT-IR) spectrum. From the optical absorption spectrum the band gap energy was calculated and it was found to be 5.76, 6.29 and 6.35 eV for pure, Ca2+ and Sr2+ doped NH4Sb3F10 crystals respectively. Thermal stability of the sample has been analysed using TG-DTA analysis. The activation energy of pure, Ca2+ and Sr2+ doped NH4Sb3F10 crystals were calculated from the dc conductivity measurements and it is found to be 0.2728, 0.2816 and 0.3622 eV Experimental results shows improved physicochemical properties when the dopant is added to the pure material. 相似文献
998.
Farouk S. El-feraly Moshera M. El-sherei Charles D. Hufford Edward M. Croom Jr. Thomas J. Mahier 《光谱学快报》2013,46(10):843-849
The 13C nmr assignments for all carbons except the methylene groups were made for artemisinin (1), artemether (2) and desoxyartemisinin (3). The assignments were based on chemical shift theory and confirmed by selective band decoupling experiments. 相似文献
999.
J. P. B. Silva K. C. Sekhar A. Almeida J. Agostinho Moreira M. Pereira M. J. M. Gomes 《Applied Physics A: Materials Science & Processing》2013,113(2):379-384
BaTiO3 thin films were deposited by pulsed laser deposition on Pt–Si at different laser pulse repetition frequencies. X-ray diffraction spectra show that preferred oriented films can be grown by adjusting the pulse repetition frequency. Enhanced dielectric and ferroelectric properties obtained in films deposited at 1 Hz is attributed to preferred orientation, low strain and homogeneous grain distribution. The films deposited at 1 Hz show an impressive remanent polarization of 21.4 μC/cm2 with a coercive field of 70.0 kV/cm. The shift in Curie temperature, which stems from changing the laser pulse repetition frequency, is associated with the strain state in the film. 相似文献
1000.
Charles V. Shank 《Applied physics. B, Lasers and optics》1989,49(1):A6-A6
Ultrashort Light Pulses 相似文献