Based on a 5% （mass fraction） Re-containing single crystal nickel-based superalloy with 3% （mass fraction） Cr, the microstructural variation with Cr addition was investigated. The experimental results show that se...Based on a 5% （mass fraction） Re-containing single crystal nickel-based superalloy with 3% （mass fraction） Cr, the microstructural variation with Cr addition was investigated. The experimental results show that segregation of alloying elements was enhanced in as-cast microstructure with Cr addition; and the volume fraction of eutectic is increased. However, the solidus and liquidus temperatures are remarkably reduced. With the increase of Cr content, the average γ＇ size and volume fraction are decreased in the fully heat treated microstructure. X-ray diffraction results indicate that γ/γ＇ lattice misfit becomes more negative. According to the energy dispersive spectroscopy （EDS） results, Cr is mainly distributed in the γ matrix; and more y-forming elements, such as Re and W, enter the γ matrix, while the γ/γ＇ partition ratio of Cr is inversely decreased.展开更多
The present research reports a comparative study on the use of ＂really＂ by Chinese EFL learners. Taking the perspectives colligation and collocation, the study mainly yields the following findings： （1） Compared w...The present research reports a comparative study on the use of ＂really＂ by Chinese EFL learners. Taking the perspectives colligation and collocation, the study mainly yields the following findings： （1） Compared with American native speakers, Chinese EFL learners have different preferences for colligations and collocations of ＂really＂; （2） High achievers and low achievers demonstrate a similar pattern of the ranking order of the colligations, but high achievers are closer to the native speakers in the use of ＂really＂ in terms of collocation; low achievers rely more heavily on ＂very＂ to collocate with adjectives than high achievers.展开更多
Covariance matrix plays an important role in risk management, asset pricing, and portfolio allocation. Covariance matrix estimation becomes challenging when the dimensionality is comparable or much larger than the sam...Covariance matrix plays an important role in risk management, asset pricing, and portfolio allocation. Covariance matrix estimation becomes challenging when the dimensionality is comparable or much larger than the sample size. A widely used approach for reducing dimensionality is based on multi-factor models. Although it has been well studied and quite successful in many applications, the quality of the estimated covariance matrix is often degraded due to a nontrivial amount of missing data in the factor matrix for both technical and cost reasons. Since the factor matrix is only approximately low rank or even has full rank, existing matrix completion algorithms are not applicable. We consider a new matrix completion paradigm using the factor models directly and apply the alternating direction method of multipliers for the recovery. Numerical experiments show that the nuclear-norm matrix completion approaches are not suitable but our proposed models and algorithms are promising.展开更多
基金Projects (2010CB631200, 2010CB631206) supported by the National Basic Research Program of ChinaProject (50931004) supported by the National Natural Science Foundation of China
文摘Based on a 5% （mass fraction） Re-containing single crystal nickel-based superalloy with 3% （mass fraction） Cr, the microstructural variation with Cr addition was investigated. The experimental results show that segregation of alloying elements was enhanced in as-cast microstructure with Cr addition; and the volume fraction of eutectic is increased. However, the solidus and liquidus temperatures are remarkably reduced. With the increase of Cr content, the average γ＇ size and volume fraction are decreased in the fully heat treated microstructure. X-ray diffraction results indicate that γ/γ＇ lattice misfit becomes more negative. According to the energy dispersive spectroscopy （EDS） results, Cr is mainly distributed in the γ matrix; and more y-forming elements, such as Re and W, enter the γ matrix, while the γ/γ＇ partition ratio of Cr is inversely decreased.
文摘The present research reports a comparative study on the use of ＂really＂ by Chinese EFL learners. Taking the perspectives colligation and collocation, the study mainly yields the following findings： （1） Compared with American native speakers, Chinese EFL learners have different preferences for colligations and collocations of ＂really＂; （2） High achievers and low achievers demonstrate a similar pattern of the ranking order of the colligations, but high achievers are closer to the native speakers in the use of ＂really＂ in terms of collocation; low achievers rely more heavily on ＂very＂ to collocate with adjectives than high achievers.
基金supported by National Natural Science Foundation of China(Grant Nos.10971122,11101274 and 11322109)Scientific and Technological Projects of Shandong Province(Grant No.2009GG10001012)Excellent Young Scientist Foundation of Shandong Province(Grant No.BS2012SF025)
文摘Covariance matrix plays an important role in risk management, asset pricing, and portfolio allocation. Covariance matrix estimation becomes challenging when the dimensionality is comparable or much larger than the sample size. A widely used approach for reducing dimensionality is based on multi-factor models. Although it has been well studied and quite successful in many applications, the quality of the estimated covariance matrix is often degraded due to a nontrivial amount of missing data in the factor matrix for both technical and cost reasons. Since the factor matrix is only approximately low rank or even has full rank, existing matrix completion algorithms are not applicable. We consider a new matrix completion paradigm using the factor models directly and apply the alternating direction method of multipliers for the recovery. Numerical experiments show that the nuclear-norm matrix completion approaches are not suitable but our proposed models and algorithms are promising.
