Highly conductive nb-doped BaTiO3 epitaxial thin films grown by laser molecular beam epitaxy

于2010-11-23批量导入

Regioselective Bis-Selenation of Allenes Catalyzed by Palladium Complexes: A Theoretical Study

The reaction mechanism of Pd(O)-catalyzed allene bis-selenation reactions is investigated by using density functional methods. The overall reaction mechanism has been examined. It is found that with the bulkier PMe3 ligand, the rate-determining step is the reductive elimination process, while allene insertion and reductive elimination processes are competitive for the rate-determining step with the PH3 ligand, indicating the importance of the ligand effect. For both cis and trans palladium complexes, allene insertion into the Pd-Se bond of the trans palladium complex using the internal carbon atom attached to the selenyl group is prefer-red among the four pathways of allene insertion processes. The formation of sigma-allyl and pi-allyl palladium complexes is favored over that of the sigma-vinyl palladium species. By using methylallene, the regioselectivity of monosubstituted allene insertion into the Pd-Se bond is analyzed.

机器人逆动力学简化实时快速算法

本文基于机器人动力学模型，通过引入相对误差准则，提出一种计算机器人逆动力学的简化实时快速算法．该算法，根据动力学模型中各元素在期望工作轨迹上的变化速率不同，运用相对误差准则确定出它们的实时计算周期，达到减少单位控制周期内计算动力学模型的操作数，文中给出了计算实例。

岩溶地区土状堆积物物质来源判别的实用指标—粒度分布特征

选择湘西吉首完整的炭岩风化壳，首次利用粒度参数并结合巳有的矿物学、地球化学的研究成果，为湘西和贵州地区的碳酸盐岩上覆土状堆积物的歼积成因提供了有力的佐证。粒度分析研究结果表明，湘西吉首灰岩风化壳基岩酸不溶物及其上覆半风化带粒度频率分布曲线形态的一致性和渐变性，指示了风化壳对基岩的继承和演化；砂-粉砂-粘粒含量、中值粒径和平均粒径在剖面上的演化趋势，反映了一个标准残积风化壳的发育规律；频率曲线众数峰含量随深度的变化，不担指示了化学风化趋势，而且反映了风化程度的变化梯度。

Learning World Models in Environments with Manifest Causal Structure

This thesis examines the problem of an autonomous agent learning a causal world model of its environment. Previous approaches to learning causal world models have concentrated on environments that are too "easy" (deterministic finite state machines) or too "hard" (containing much hidden state). We describe a new domain --- environments with manifest causal structure --- for learning. In such environments the agent has an abundance of perceptions of its environment. Specifically, it perceives almost all the relevant information it needs to understand the environment. Many environments of interest have manifest causal structure and we show that an agent can learn the manifest aspects of these environments quickly using straightforward learning techniques. We present a new algorithm to learn a rule-based causal world model from observations in the environment. The learning algorithm includes (1) a low level rule-learning algorithm that converges on a good set of specific rules, (2) a concept learning algorithm that learns concepts by finding completely correlated perceptions, and (3) an algorithm that learns general rules. In addition this thesis examines the problem of finding a good expert from a sequence of experts. Each expert has an "error rate"; we wish to find an expert with a low error rate. However, each expert's error rate and the distribution of error rates are unknown. A new expert-finding algorithm is presented and an upper bound on the expected error rate of the expert is derived.

Stochastic Refinement of the Visual Hull to Satisfy Photometric and Silhouette Consistency Constraints

An iterative method for reconstructing a 3D polygonal mesh and color texture map from multiple views of an object is presented. In each iteration, the method first estimates a texture map given the current shape estimate. The texture map and its associated residual error image are obtained via maximum a posteriori estimation and reprojection of the multiple views into texture space. Next, the surface shape is adjusted to minimize residual error in texture space. The surface is deformed towards a photometrically-consistent solution via a series of 1D epipolar searches at randomly selected surface points. The texture space formulation has improved computational complexity over standard image-based error approaches, and allows computation of the reprojection error and uncertainty for any point on the surface. Moreover, shape adjustments can be constrained such that the recovered model's silhouette matches those of the input images. Experiments with real world imagery demonstrate the validity of the approach.