收入冲击、偏好冲击与中国经济波动——基于DSGE方法的数值分析

文章基于包含消费习惯与借贷约束的rbC模型,尝试将收入冲击与偏好冲击纳入到该模型中,并采用随机动态一般均衡(dSgE)方法解释中国经济波动。研究发现:(1)模型能够解释实际产出、消费、投资与资本波动的92.6%、77.8%、84.5%、87.6%。(2)收入冲击与偏好冲击对我国实际产出、投资、就业和资本的影响均有明显的持续性,而对消费的影响均表现为短期性。(3)收入冲击对消费的影响较小,而对就业有较大影响;消费偏好冲击对两者的影响与收入冲击恰恰相反。国家社科基金项目(项目号:12CTJ018); 国家教育部人文社会科学研究青年基金项目(项目号:12YJC910013); 国家统计科学研究项目(项目号:2013353); 国家博士后科学基金项目(项目号:2013M531544

A Review on Heterogeneous Nanostructures: A Strategy for Superior Mechanical Properties in Metals

Generally, strength and ductility are mutually exclusive in homogeneous metals. Nanostructured metals can have much higher strength when compared to their coarse-grained counterparts, while simple microstructure refinement to nanoscale generally results in poor strain hardening and limited ductility. In recent years, heterogeneous nanostructures in metals have been proven to be a new strategy to achieve unprecedented mechanical properties that are not accessible to their homogeneous counterparts. Here, we review recent advances in overcoming this strength-ductility trade-off by the designs of several heterogeneous nanostructures in metals: heterogeneous grain/lamellar/phase structures, gradient structure, nanotwinned structure and structure with nanoprecipitates. These structural heterogeneities can induce stress/strain partitioning between domains with dramatically different strengths, strain gradients and geometrically necessary dislocations near domain interfaces, and back-stress strengthening/hardening for high strength and large ductility. This review also provides the guideline for optimizing the mechanical properties in heterogeneous nanostructures by highlighting future challenges and opportunities

Extraordinary strain hardening by gradient structure

Gradient structures have evolved over millions of years through natural selection and optimization in many biological systems such as bones and plant stems, where the structures change gradually from the surface to interior. The advantage of gradient structures is their maximization of physical and mechanical performance while minimizing material cost. Here we report that the gradient structure in engineering materials such as metals renders a unique extra strain hardening, which leads to high ductility. The grain-size gradient under uniaxial tension induces a macroscopic strain gradient and converts the applied uniaxial stress to multiaxial stresses due to the evolution of incompatible deformation along the gradient depth. Thereby the accumulation and interaction of dislocations are promoted, resulting in an extra strain hardening and an obvious strain hardening rate up-turn. Such extraordinary strain hardening, which is inherent to gradient structures and does not exist in homogeneous materials, provides a hitherto unknown strategy to develop strong and ductile materials by architecting heterogeneous nanostructures.</p

Effect of local damages on the buckling behaviour of pyramidal truss core sandwich panels

Truss core sandwich panels have been widely investigated due to their superior mechanical performances. However, local defects or damages during preparation and service may reduce the strength significantly. The objective of this paper is to examine the imperfection sensitive of this kind of structures under in-plane compression. The elastic and plastic buckling behaviour of pyramidal truss core sandwich panels with local damages under in-plane compression are studied experimentally and numerically. Local damages including unbound nodes between lattice truss and the facesheet, missing lattice cells and holes in the facesheet are considered. In-plane compression tests of truss core sandwich panels with prefabricated local damages are conducted, and then a finite element model in conjunction with random number is developed to simulate the buckling behaviour of the panel with randomly distributed damages in a specific region. Experimental and numerical results show that, besides the damage extent, the location of unbound nodes and missing lattice cells have significant effect on the buckling strength of the pyramidal truss core sandwich panel. In addition, the local damage sensitiveness of sandwich panel with round holes in the facesheet is lower than that with square holes. (C) 2016 Published by Elsevier Ltd.</p

Baseline-free damage identification of metallic sandwich panels with truss core based on vibration characteristics

A baseline-free damage identification method is proposed to identify damages in metallic sandwich panels with truss core in the article. The method is based on flexibility matrix and gapped smoothing method, with damage index defined DIm. The weight coefficient m is introduced to consider the effect of damages on both low-order modes and high-order modes. Numerical simulations and experiments are conducted to evaluate the present method. Besides, damage index DIm* is also defined by processing DIm with Teager energy operator, and comparisons between DIm and DIm* are also carried out. Results show that the proposed method is effective in detecting single damage and multiple damages of the same or different extent. The weight coefficient m plays a very important role in identification of multiple damages of different styles. When comparing with DIm*, it is found that the present index DIm is better at suppressing the singularity caused by contact nodes and detecting of multiple damages which contain small or slight damages.</p

Enhanced Cytotoxic Effects of Arenite in Combination with Active Bufadienolide Compounds against Human Glioblastoma Cell Line U-87

The cytotoxicity of a trivalent arsenic derivative (arsenite, AsIII) combined with arenobufagin or gamabufotalin was evaluated in human U-87 glioblastoma cells. Synergistic cytotoxicity with upregulated intracellular arsenic levels was observed, when treated with AsIII combined with arenobufagin instead of gamabufotalin. Apoptosis and the activation of caspase-9/-8/-3 were induced by AsIII and further strengthened by arenobufagin. The magnitude of increase in the activities of caspase-9/-3 was much greater than that of caspase-8, suggesting that the intrinsic pathway played a much more important role in the apoptosis. An increase in the number of necrotic cells, enhanced LDH leakage, and intensified G2/M phase arrest were observed. A remarkable increase in the expression level of γH2AX, a DNA damage marker, was induced by AsIII+arenobufagin. Concomitantly, the activation of autophagy was observed, suggesting that autophagic cell death associated with DNA damage was partially attributed to the cytotoxicity of AsIII+arenobufagin. Suppression of Notch signaling was confirmed in the combined regimen-treated cells, suggesting that inactivation of Jagged1/Notch signaling would probably contribute to the synergistic cytotoxic effect of AsIII+arenobufagin. Given that both AsIII and arenobufagin are capable of penetrating into the blood–brain barrier, our findings may provide fundamental insight into the clinical application of the combined regimen for glioblastoma.p.21 Article number: 6577 Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/)

Ductility by shear band delocalization in the nano-layer of gradient structure

Nanostructured (NS) metals typically fail soon after yielding, starting with the formation of narrow shear bands. Here we report the observation of shear band delocalization in gradient metals. Shear bands were nucleated and delocalized in the NS layers by propagating along the gage length soon after yielding, converting the shear band into a localized strain zone (LSZ). Synergistic work hardening was developed in the LSZ by regaining dislocation hardening capability, and by back-stress hardening from the strain gradients in the axial and depth directions, which helped with enhancing global ductility. [GRAPHICS

电化学微/纳米加工技术

通讯联系人，E-mail: dpzhan@ xmu． edu． cn介绍电化学微/纳米加工技术,特别是厦门大学电化学微/纳米加工课题组建立起来的约束刻蚀剂层技术,旨在让广大师生了解这一特种加工技术,共同促进我国电化学微/纳米加工技术的研究及产业化进程。国家自然科学基金(No.91023006,91023047,91023043);中央高校基本科研业务费专项资金(No.2010121022

Involvement of restoration of cerebral blood flow and maintenance of eNOS expression in the prophylactic protective effect of a novel ferulic acid derivative FAD012 against ischemia/reperfusion injury in rats

Tissue plasminogen activator, aiming to restore cerebral blood flow (CBF), has been used for acute ischemic strokes in clinics; however, its narrow therapeutic time window remains a serious concern. To develop novel prophylactic drugs to alleviate cerebral ischemia/reperfusion injuries, ferulic acid derivative 012 (FAD012) was synthesized and showed comparable antioxidant properties to ferulic acid (FA) and probably possesses the potent ability to cross the blood–brain barrier. A more potent cytoprotective effect of FAD012 against H2O2-induced cytotoxicity in PC12 cells was also observed. In vivo toxicity was not observed in rats given a long-term oral administration of FAD012, indicating its good tolerability. A one-week-course oral administration of FAD012 significantly alleviated middle cerebral artery occlusion (MCAO)-induced cerebral ischemia/reperfusion injuries in rats, accompanied by the restoration of CBF and endothelial nitrogen oxide synthetase (eNOS) expression. Treatment with FAD012 significantly restored the cell viability and eNOS expression damaged by H2O2, used to mimic MCAO-triggered oxidative stress, in rat brain microvascular endothelial cells. Our findings suggested that FAD012 protected the viability of vascular endothelium and maintained eNOS expression, ultimately contributing to the restoration of CBF, and may provide a rationale for the development of FAD012 into an effective prophylactic drug for patients at high risk of stroke.p.18 Article number: 9663 Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/)

Size effect and boundary type on the strengthening of nanoscale domains in pure nickel

A series of large-scale molecular dynamics simulations were carried out to investigate the interactions between an extended edge dislocation (1/2 (111)) and nanoscale domains in pure nickel. The pinning strength of nano-domains and the corresponding atomistic interaction mechanisms were found to be closely related to the domain boundary type, the domain size and spacing. The pinning strengths were found to be higher for high-angle domains than those for low-angle domains at the same size scale, and increase with increasing domain size and decreasing domain spacing. Unlike the by-pass via interactions between the dislocation and boundaries for high-angle domains (much like the role of hard precipitates in alloys), the dislocation was found to cut partly through the low-angle domains. Thus the dragging force from the boundary segments of the low-angle domains should be smaller when compared to the Orowan's strengthening for "hard particles", such as high-angle domains. The predictions from Ashby's model on Orowan's strengthening are higher than the simulation data for low-angle domains, while agree relatively well with those for high-angle domains. Moreover, a more universal model was proposed to connect the dislocation line shape at the critical shear strain with the pinning strength. (C) 2015 Elsevier B.V. All rights reserved