基于微柱状电极生长ZnO纳米线的研究

利用自己开发的硅衬底电极无催化剂制备横向 ZnO 纳米线网的技术,实现了二维氧化锌纳米线网电路的制备。本论文涉及的技术一方面可以为突破纳电子器件制备极限提供新技术参考。另一方面,去除了纳米线生长过程中的金催化剂污染,降低成本,简化工艺。     

建筑排水立管内微生物组成及特性分析

排水立管肩负输送、排放污废水的功能,与我们的生活密切相关。但排水管道内壁易附着污物,滋生细菌,产生生物膜,生物膜可能包含各式各样的微生物,有些微生物在排水管道中会产生臭气甚至有毒有害气体,这些气体若进入室内则会污染室内环境卫生,危害人体健康。本文通过实地采集了排水立管内的生物膜,研究了其生物相及采用菌种分离的方法培养确定了常见建筑排水立管内微生物的种类及数量,同时分析排水立管内的生物相及可能产生的危害,为室内环境的保护提供基础数据和针对性的改善措施。     

Effect of Solidifcation Rate on Grain Structure Evolution During Directional Solidifcation of a Ni-based Superalloy

The effect of solidification rate on grain structure evolution during directional solidification(DS) of a Ni-based superalloy was explored.It was found that a high solidification rate led to sharper <001> texture and smaller grain size in the DS samples.One of the most important findings in this work was that such result was not in accordance with the general concept,and the sharper <001> texture was accompanied by the larger grain size.To explain the contradiction,the modeling samples with five grains were produced and the effect of solidification rate on the evolution of grain texture was illustrated based on the modeling samples.     

Application of energy density theory on finite cracked bodies

Abstract

A new concept of the energy release rate of a finite cracked body is proposed. Considering the global view of the strain energy density field, the new fracture parameter presented here is different from the conventional energy release rate that only depends on the stress field around the crack tip but neglects the influences induced by the boundary conditions on the far field. Based on the hypothesis of the energy density theory, fracture initiation and termination, respectively can be predicted by the local and global relative minima of the strain energy density function. The new energy release rate is then defined as the integration of the strain energy density along the fracture trajectory from the initiation point to the destination point. The results show that the difference between the new and the conventional energy release rate becomes more pronounced if the material has a large core region (or the material is more ductile) and if the height‐width ratio of a finite cracked plate is comparatively small.     

An arrayed uniform eddy current probe design for crack monitoring and sizing of surface breaking cracks with the aid of a computational inversion technique

This study demonstrates that eddy current testing can be an effective method for monitoring the growth of surface breaking cracks with the aid of computational inversion techniques. A uniform eddy current probe with 23 arrayed detectors was designed, and pseudo monitoring tests were carried out to measure signals due to six mechanical fatigue cracks introduced into type 316L austenitic stainless steel plates. In the test the position of the probe was fixed to simulate monitoring. The depths of the cracks were evaluated using a computational inversion method developed on the basis of k-nearest neighbor algorithm. The depths of the mechanical fatigue cracks whose actual depths were 1.1, 2.1, 3.1, 5.5, 6.7, and 8.5 mm were evaluated to be 0.9, 1.9, 3.8, 4.3, 7.0, and 5.7 mm, respectively. Additional simulations were conducted to demonstrate the stability of the method.     

Oxygen-related photoluminescence quenching in selectively grown GaN nanocolumns: Dependence on diameter

This work reports on the effects of air exposure on the photoluminescence intensity of GaN nanocolumns, with diameters ranging from below 40 nm up to around 230 nm, grown selectively on GaN/sapphire and GaN/Si(111). The high control of dimensions provided by selective area growth epitaxy allowed for a better study of the relationship between the observed phenomena, namely the photoluminescence intensity quenching due to oxygen photo-adsorption, and the nanocolumns properties (morphology and dimensions). For nanocolumns with diameters below 120 nm and lengths of about 300 nm, photoluminescence intensity dropped by more than 90% of the initial value, while for shorter nanocolumns a reduced drop value was found.     

Estimating cost of equity in project discount rates using the capital asset pricing model and Gordon’s wealth growth model

Since the 2008 global financial crisis, mining projects have to invariably compete for scarce capital under depressed market conditions. The discounted cash flow analysis commonly used for the valuation of mining projects relies on using a discount rate. However, an appropriate discount rate is sometimes the subject of contestation since factors such as the stage of development of the mineral project affect the rate. This paper independently tests the reliability of capital asset pricing model and Gordon’s wealth growth model estimates of cost of equity in discount rates and concludes that Gordon’s wealth growth model provides better estimates under depressed market conditions.     

现浇钢筋混凝土楼板裂缝控制措施及修复方法

对某工程钢筋混凝土楼板产生的几类裂缝进行了原因分析,阐明了裂缝对结构的危害性,提出了该工程相应的裂缝修复处理方法,并从施工方面提出了针对性的预防和控制措施,为解决相同类型的工程问题积累了经验。     

Nonlocal criterion of bridged cracks growth: Weak interface

A nonlocal fracture criterion with accounting of the work during bonds deformation at a fracture process zone has been implemented analytically for analysis of quasistatic cracks growth along a weak interface. The criterion consists of two clauses: (1) the necessary energy condition of the crack tip limit equilibrium which takes into account the energy release rate to the crack tip and the rate of the deformation energy consumed by bonds in the crack process zone; (2) the sufficient condition is the equality of the crack opening at the process zone trailing edge to the bond limit stretching. Subcritical and quasi-statical regimes of cracks growth are analyzed for the case of a homogeneous plate with internal straight bridged crack and bonds traction which is constant and independent of the external loading. The critical fracture stress and the crack bridged zone size in the limit equilibrium state have been determined and analyzed. The limit case of a crack which is filled with bonds is considered as a weak interface model.     

The effect of homogeneously dispersed few-layer graphene on microstructure and mechanical properties of Al2O3 nanocomposites

Fully dense few-layer graphene (FG)/Al₂O₃ nanocomposites with homogeneously dispersed FG in matrix are prepared by using a heteroaggregation method followed by spark plasma sintering. It is found that the two dimensional FG has great ability to restrain grain growth in comparison to other inclusions. In addition, the morphology of grain in composite is modified by the addition of FG during densification process compared with monolithic alumina. Thanks to the greatly decreased grain size, the composites are almost as hard as monolithic alumina at low sintering temperature (1573 K) even if graphene content is as high as 1.2 vol.%. However, at higher sintering temperature (1673 K), the hardness of composites decreases further but the change in elastic modulus is very limited. The decline of hardness and elastic modulus mainly arises from the sliding feature of FG, low modulus of reduced graphene oxide in both in-plane and out-of-plane directions.