单轴压缩下含预制孔洞板状花岗岩试样力学响应的试验和数值研究

 利用挪威Iddefjord花岗岩试样加工制备含双侧预制方形孔洞的板状试样,并在Instron液压伺服控制试验机上开展单轴压缩试验,监测试样的应力、应变、声发射信号特征及试样破坏过程。研究发现,随着轴向应力的增大,试样在平行于孔洞竖直方向的位置相继出现劈裂裂纹并逐渐贯通,孔洞周边岩体出现块体弹射、片帮等应变型岩爆特征。试验研究表明,含孔洞花岗岩试样在单轴压缩下总是从孔洞周边的劈裂破坏开始,试样的声发射曲线比完整岩样存在更多的跳跃突变点。在此基础上,利用FLAC3D对室内试验进行数值模拟,通过线弹性模型分析含孔洞岩石材料的应力分布特性,通过应变软化莫尔–库仑准则模拟岩样的破坏过程,监测各计算时步下单元拉伸和剪切破坏特性;发现单轴压缩下含孔洞岩样的塑形破坏单元以拉伸破坏为主,拉伸破坏单元沿孔洞竖向边界贯通形成劈裂破坏面,这和室内试验观测结果是一致的。研究结果在一定程度上揭示了深部硬岩洞室开挖后,在高地应力作用下总是产生平行于洞室开挖边界面的板裂、片帮破坏现象。     

基于DSC的全数字控制高频开关电源整体解决方案

数字控制由于高集成度带来的低成本、设计沿继性、控制灵活等优点而应用逐渐广泛,本文利用Freescale半导体公司新型号数字信号控制器(DSC)－MC56F8323的高性能特性,提供了基于DSC数字控制的高频开关电源的完整解决方案,给出了全数字控制的软开关数字功率因数校正和全数字控制的带同步整流的软开关移相全桥直直变换器两个子系统的详细设计,最后用一台500W实验样机验证了基于数字控制的完整开关电源系统的优良系统性能。     

Polyaniline-related ion-barrier anticorrosion coatings: I. Ionic permeability of polyaniline,cationic, and bipolar films

Ionic permeabilities of coating films were studied with a variety of experimental methods including measurements of membrane potential, salt diffusion, and electron spectroscopy for chemical analysis (ESCA). The results show that polyaniline (PAn) allows diffusion of anions (if PAn is dispersed in a cationic polymer matrix, the resulting film may have cationic defects that allow the passage of cations), a cationic film is permeable to cations, and the combination of a PAn containing primer with the cationic topcoat is an ion-barrier which delays penetration of both anions and cations.     

Optimal fitting of strain-controlled flattenable mesh surfaces

In this paper, an eye-in-hand vision-based robotic bin-picking system is proposed. The system can identify the pose of a plumbing part from a pile and grip it correctly. A monocular eye-in-hand camera and a laser projector are employed to reconstruct the 3-D point cloud of plumbing parts stacked together. The projection direction of the laser line projector is controlled to change in order to scan the pile of objects while the camera is observing. 3-D points can then be determined by the a priori known geometry between the camera and the laser line projector. To estimate the pose of an object, the iterative closest point (ICP) is employed to match the point clouds of the object and the model. The transformation between the object and the model can thus be determined. A computed closer point (CCP) approach is proposed to estimate the pose of an object since the deviation from the object to the model is initially large in nature. The proposed CCP approach combining with the ICP algorithm can improve the success rate and accuracy of point cloud matching. The proposed system has been validated by experiments with potential applications in production lines.     

Discussions on rockburst and dynamic ground support in deep mines

The paper is a summary of discussions on four topics in rockburst and dynamic ground support.Topic1 is the mechanisms of rockburst.Rockburst events are classified into two categories in accordance with the triggering mechanisms,i.e.strain burst and fault-slip burst.Strain burst occurs on rock surfaces when the tangential stress exceeds the rock strength in hard and brittle rocks.Fault-slip burst is triggered by fault-slip induced seismicity.Topic 2 is prediction and forecasting of rockburst events.Prediction for a rockburst event must tell the location,timing and magnitude of the event.Forecasting could simply foresee the probability of some of the three parameters.It is extremely challenging to predict rockbursts and large seismic events with current knowledge and technologies,but forecasting is possible,for example the possible locations of strain burst in an underground opening.At present,the approach using seismic monitoring and numerical modelling is a promising forecasting method.Topic 3 is preconditioning methods.The current preconditioning methods are blasting,relief-hole drilling and hydrofracturing.Defusing fault-slip seismicity is difficult and challenging but has been achieved.In very deep locations(3000 m),the fracturing could extend from the excavation face to a deep location ahead of the face and therefore preconditioning is usually not required.Topic 4 is dynamic ground support against rockburst.Dynamic ground support requires that the support system be strong enough to sustain the momentum of the ejecting rock on one hand and tough enough on the other hand to absorb the strain and seismic energies released from the rock mass.The current dynamic support systems in underground mining are composed of yielding tendons and flexible surface retaining elements like mesh/screen and straps.Yielding props and engineered timber props are also used for dynamic support.     

Determinants of self‐employment among commuters and non‐commuters

We analyse the determinants of self‐employment and focus on the contextual environment. By distinguishing between commuters and non‐commuters we are able to analyse the influence from the work and home environment, respectively. Our results indicate a significant difference between non‐commuters and commuters in terms of the role of networks for becoming self‐employed. Our results indicate that it is the business networks where people work, rather than where they live that exerts a positive influence on the probability of becoming self‐employed. These effects are further robust over educational and occupational categories.     

Feature based 3D garment design through 2D sketches

This paper presents a new approach for intuitively modeling a three-dimensional (3D) garment around a 3D human model by two-dimensional (2D) sketches input. Our approach is feature based—every human model has pre-defined features, and the constructed garments are related to the features on human models. Firstly, a feature template for creating a customized 3D garment is defined according to the features on a human model; secondly, the profiles of the 3D garment are specified through 2D sketches; finally, a smooth mesh surface interpolating the specified profiles is constructed by a modified variational subdivision scheme. The resulting mesh surface can be cut and flattened into 2D patterns to be manufactured. Our approach provides a 3D design tool to create garment patterns directly in the 3D space through 2D strokes, which is a characteristic not available in other computer aided garment design systems. The constructed garment patterns are related to the features on a human model, so the patterns can be regenerated automatically when creating the same style of garment for other human models. Our technique can greatly improve the efficiency and the quality of pattern making in the garment industry.     

Orthogonal Array Sampling for Monte Carlo Rendering

We generalize N‐rooks, jittered, and (correlated) multi‐jittered sampling to higher dimensions by importing and improving upon a class of techniques called orthogonal arrays from the statistics literature. Renderers typically combine or “pad” a collection of lower‐dimensional (e.g. 2D and 1D) stratified patterns to form higher‐dimensional samples for integration. This maintains stratification in the original dimension pairs, but looses it for all other dimension pairs. For truly multi‐dimensional integrands like those in rendering, this increases variance and deteriorates its rate of convergence to that of pure random sampling. Care must therefore be taken to assign the primary dimension pairs to the dimensions with most integrand variation, but this complicates implementations. We tackle this problem by developing a collection of practical, in‐place multi‐dimensional sample generation routines that stratify points on all t‐dimensional and 1‐dimensional projections simultaneously. For instance, when t=2, any 2D projection of our samples is a (correlated) multi‐jittered point set. This property not only reduces variance, but also simplifies implementations since sample dimensions can now be assigned to integrand dimensions arbitrarily while maintaining the same level of stratification. Our techniques reduce variance compared to traditional 2D padding approaches like PBRT's (0,2) and Stratified samplers, and provide quality nearly equal to state‐of‐the‐art QMC samplers like Sobol and Halton while avoiding their structured artifacts as commonly seen when using a single sample set to cover an entire image. While in this work we focus on constructing finite sampling point sets, we also discuss potential avenues for extending our work to progressive sequences (more suitable for incremental rendering) in the future.     

Exemplar-based statistical model for semantic parametric design of human body

This paper presents an exemplar-based method to provide intuitive way for users to generate 3D human body shape from semantic parameters. In our approach, human models and their semantic parameters are correlated as a single linear system of equations. When users input a new set of semantic parameters, a new 3D human body will be synthesized from the exemplar human bodies in the database. This approach involves simpler computation compared to non-linear methods while maintaining quality outputs. A semantic parametric design in interactive speed can be implemented easily. Furthermore, a new method is developed to quickly predict whether the parameter values is reasonable or not, with the training models in the human body database. The reconstructed human bodies in this way will all have the same topology (i.e., mesh connectivity), which facilitates the freeform design automation of human-centric products.