牙科用氧化锆陶瓷材料的着色研究

采用粉体混合和预烧体浸泡两种方法对牙科用氧化锆陶瓷材料进行着色,并比较了着色效果及力学性能.结果表明,二者三点弯曲强度均在1000 MPa以上,能满足牙科修复材料的要求.添加Fe_2O_3的氧化锆陶瓷呈黄色,且颜色均匀,正反面色差小;浸泡VITA染色液的氧化锆样品着色不均匀,出现斑点,正反面色差较大,说明其着色的效果与预烧体的显微结构密切相关.用粉体混合的方法进行着色比染色液浸泡法更容易得到均匀、稳定的着色效果.     

局部遮阴下基于改进AVOA的光伏多峰MPPT控制

光伏阵列受部分遮阴影响，其功率-电压特性曲线呈多峰状，导致传统最大功率点跟踪（MPPT）算法失效，因此提出了一种改进的非洲秃鹫优化算法（AVOA）运用于光伏的MPPT控制。首先，引入Tent混沌映射使种群位置更具多样性，避免过早收敛。然后，优化算法在探索和开发阶段的更新策略，减少计算力的浪费，提高寻优速率。最后，在MATLAB 2022b/Simulink环境下，应用所提算法对不同辐照情况的3组工况进行仿真。实验结果表明，在多峰MPPT控制中，该算法具有寻优效率高、收敛速度快等特点，能有效地提升复杂遮阴环境下光伏能源的利用率。     

基于粒子群遗传算法的光伏MPPT控制研究

局部阴影条件下,光伏阵列的功率特性曲线会出现多个峰值,传统的MPPT跟踪算法容易陷入局部极值点,无法准确地跟踪到最大功率点。粒子群算法具有很强的全局搜索能力,可以有效解决多峰寻优问题,但是普通粒子群算法容易出现收敛速度慢、早熟现象。提出一种改进的粒子群遗传（IPSO-GA）算法,该算法的惯性权重与学习因子随着迭代次数不断改变,可以同时兼顾算法的局部搜索与全局寻优能力,并且引进遗传算法的交叉、变异操作以增加种群多样性。仿真结果表明,改进算法在多峰最大功率跟踪过程中,具有良好的跟踪速度与寻优精度。     

局部遮挡条件下的光伏阵列防逆流措施选择

对于光伏发电单元,阴影的遮挡可能导致有逆流通过光伏组件,使组件发热损坏。为了防止逆流的产生,通常的做法是在组件回路设置防反二极管。而设置防反二极管可能导致设备体积增大、工程造价增加、汇流设备温度升高等问题。是否设置防反二极管以及防反二极管的设置位置是工程设计中的重点问题。本文以光伏组件的工程应用模型为基础,给出了在局部遮挡条件下逆流的计算方法,包括不设置防反二极管以及防反二极管设置在直流配电柜的逆流计算方法,根据计算结果以及生产厂商提供的光伏组件的参数,来配置防反二极管,优化设备选型。     

一种光伏系统的多峰值最大功率点跟踪策略

局部阴影条件下,光伏阵列的输出功率-电压(P-U)特性曲线存在多个局部峰值(LMPP)。传统的最大功率点跟踪(MPPT)法可能使系统工作于LMPP,错失真正的全局最大功率点(GMPP)。通过分析局部阴影条件下光伏阵列的输出电流-电压(I-U)特性曲线,提出了将电流控制和扰动观察法(PO)结合的MPPT策略,实现了跟踪GMPP的目标。仿真结果表明该算法比扫描整条P-U曲线法节省了50%的时间,实验验证了其易用性。     

半透明效果在RenderMan中的实现

在RenderMan中,运用其Shading Language编写半透明材质实现了半透明效果,并和在Mental Ray中实现的半透明材质的效果作比较,得出其优劣及其原因.     

Real time discrete shading

A shading technique for voxel-based images, termedcongradient shading, is presented. As the surface information is not available in voxel representation, the surface normal must be recovered from the 3D discrete voxel map itself. The technique defines the normal as one of a finite set of neighborhood-estimated gradients and can thus employ precalculated look-up tables. Furthermore, a table-driven mechanism permits changing the light source parameters by merely redefining the look-up table. The technique uses only simple arithmetic operations and is thus suitable for hardware implementation. Since it has been implemented not as a post-processor, but as part of the projection pipeline of the cube architecture, congradient shading can be executed in real time. Two versions of the technique in real time. Two versions of the technique have been conceived and implemented:unidirectional shading, in which the gradient is estimated only from neighborhoods along the scan-lines;bidirectional shading, in which both horizontal and vertical components of the gradient are considered. In spite of the simplicity of the technique, the results are practically indistinguishable from images generated by conventional techniques.This work was supported by the National Science Foundation under grants DCR 8603603, CCR 8743478, CCR 8717016, and MIP 8805130     

Effect of edge shading on the performance of silicon solar cell

Non-uniform solar radiation incident on solar cells is of significant concern in cell performance. It may result in non-uniform cell local heating and borders de-activation. Edge shading is a problem occurring in photovoltaic concentrator systems, due to tracking low accuracy and misalignment. An increase in both open circuit voltage and fill factor resulted from shading the edges of the cell by opaque frames of different widths. On the contrary, short circuit current density showed a drop by introducing such frames, illustrating that cell shading is responsible for the formation of series and parallel sub-cells operating at different operating conditions.     

Efficient region segmentation on compressed gray images using quadtree and shading representation

Image segmentation, which partitions the image into homogeneous regions, is a fundamental operation in image processing. Suppose the input gray image with size N×N has been compressed into the compressed image via quadtree and shading representation. Assume that the number of blocks in the representation is B, commonly B<N² due to the compression effect. This paper first derives some closed forms for computing the mean/variance of any block and for calculating the two statistical measures of any merged region in O(1) time. It then presents an efficient O(Bα(B))-time algorithm for performing region segmentation on the compressed image directly where α(B) is the inverse of the Ackerman's function and is a very slowly growing function. With the same time complexity, our results extend the pioneering results by Dillencourt and Samet from the map image to the gray image. In addition, with four real images, experimental results show that our proposed algorithm has about 55.4% execution time improvement ratio when compared to the previous fastest region-segmentation algorithm by Fiorio and Gustedt whose O(N²)-time algorithm is run on the original N×N gray image.