Piezoelectric Disk Resonators Based on Epitaxial AlGaAs Films

A new design for anisotropic piezoelectric disk resonators is demonstrated using single-crystal Al_0.3Ga_0.7As films. The shape of the disk resonator is based on the velocity propagation profile of the elastic wave in the plane of the piezoelectric film, with lateral dimensions scaled to the half wavelength of the desired resonance frequency. The resonators are designed with supports which emulate free-free boundary conditions. Prototype resonators are fabricated using a three-layer Al_0.3Ga_0.7As heterostructure containing silicon-doped electrodes and an undoped piezoelectric Al_0.3Ga _0.7As layer. Quality factors as high as 11 200 are measured in air for a 23.25 MHz fundamental resonant mode, with a corresponding motional resistance of 1.67 kOmega. A finite-element model for the resonator design is also described. Simulation results agree well with both theoretical calculations and experimental data     

接触式点样机器人及相关技术研究进展

分模块对现有接触式点样机器人中的机械手布局、接触式点样、点样针清洗和干燥、环境控制及防挥发等技术进行了总结和分析．针对现有仪器中待解决的问题及发展方向提出了几点看法．     

异步采样有功功率表

介绍了一种以异步采样方式工作的有功功率数字表。与同步采样方式不同，这里采样频率不必满足同步采样条件，而只须根据Nyquist定理和被测信号中的谐波次数来确定。工作中该表对一个周波进行多点采样，然后根据改进的有功功率计算式算出该周波的有功功率值。该表能对被测信号的每个周波的有功功率进行测量，测量过程简单，且响应十分快速。     

Stability and control of dynamic walking for a five-link planar biped robot with feet

During dynamic walking of biped robots, the underactuated rotating degree of freedom (DOF) emerges between the support foot and the ground, which makes the biped model hybrid and dimension-variant.This paper addresses the asymptotic orbit stability for criterion for DVHS is also presented, and the result is then used to study dynamic walking for a five-link planar biped robot with feet. Time-invariant gait planning and nonlinear control strategy for dynamic walking with flat feet is also introduced. Simulation results indicate that an asymptotically stable limit cycle of dynamic walking is achieved by the proposed method.     

Considering Context: A Study of First‐Year Engineering Students

High‐quality engineering design requires an understanding of how the resulting engineered artifact interacts with society, the natural environment, and other aspects of context. This study examines how first‐year engineering undergraduates approached two engineering design tasks. We focused on how much students considered contextual factors during problem‐scoping, a critical part of the design process. As part of a larger, longitudinal study, we collected data from 160 students at four U.S. institutions. Students varied in their consideration of each design task's context, and women's responses were more likely to be context‐oriented than men's. Overall, context‐orientation was positively correlated between the two design tasks, despite differences in data collection and analysis. Having found that beginning engineering students, particularly women, are sensitive to important contextual factors, we suggest that efforts to broaden participation in engineering should consider legitimizing and fostering context‐oriented approaches to engineering earlier in the curriculum.     

Study on underground thermal characteristics by using digital national land information, and its application for energy utilization

This paper describes a method for evaluating characteristics of underground thermal properties and groundwater, whose evaluation is essential for designing systems of underground thermal energy utilization. First, the systems using underground thermal energy are classified into two categories: borehole system with indirect heat exchange, and aquifer system with direct use of underground water. These systems are also divided into thermal storage systems and heat source/sink systems. Second, the characteristics of the underground in Japan are analyzed by using a geographical information system (GIS) and hydrogeological information. Regulations on environmental protection, such as those relating to national parks for instance, and the distribution of thermal energy demand eliminate 77% of Japan from consideration for underground thermal energy utilization. Areas limited to borehole thermal energy utilization account for 17% of areas where underground thermal energy can be used, with the remaining 74% suitable for both boreholes and aquifers. Finally, we estimate the thickness of aquifer and groundwater velocity in Sapporo. We find that most parts of Sapporo are suitable for aquifer thermal energy storage (ATES).     

Identification of amino acids involved in protein structural uniqueness: implication for de novo protein design

Structural uniqueness is characteristic of native proteins andis essential to express their biological functions. The majorfactors that bring about the uniqueness are specific interactionsbetween hydrophobic residues and their unique packing in theprotein core. To find the origin of the uniqueness in theiramino acid sequences, we analyzed the distribution of the sidechain rotational isomers (rotamers) of hydrophobic amino acidsin protein tertiary structures and derived     

Brittle fracture initiation associated with the strain localization in a heat-affected zone of a low carbon steel

Brittle fracture initiation in the ductile-brittle fracture transition region in the heat-affected zone (HAZ) of weldments of a low carbon steel has been investigated. Consistent with the previous results from blunt notch Charpy tests, brittle fracture initiation was observed in the case of J-integral tests to take place at the intersection of small bainitic ferrite grains of different orientations within a mixed area of bainitic ferrite and quasipolygonal ferrite in proximity to the boundary between a coarse bainitic ferrite. Partial load drop during loading, pop-in phenomena, in fracture mechanics tests in the low-temperature region is caused by essentially the same mechanism as for unstable brittle fracture initiation. Inhomogeneous microstructure in the HAZ gives rise to intense strain localizations in the mixed area of bainitic ferrite and quasipolygonal ferrite due to the constraint of plastic deformation therein and may produce accumulated defects that form an incipient crack for the brittle fracture. Partial load drop proceeds in association with repetitive initiations of brittle facets and their ductile linking. The strong temperature dependence of the magnitude of partial load drop is likely to show that the temperature dependence of the brittle fracture initiation is controlled by the first initiation of a brittle facet and the ductile linking with the following induced facets. Existence of coarse bainitic ferrite grains is a prerequisite for the extension of an incipient crack.     

Subjective contours at line terminations depend on scene layout analysis, not image processing.

Subjective contours at abutting lines, commonly attributed to levels of the visual system where image properties are directly encoded, are shown to require an explanation at the level of visual surface understanding. By the use of stereoscopic displays, subjective contours could either be abolished where they were monocularly strong or be created where they were monocularly nonexistent. Furthermore, it was shown that subjective contours are determined by the boundaries of occluded rather than occluding regions. The results cannot be accounted for by adding a stereo component to existing image-based theories, such as those based on end-stopped cells. Instead, any plausible process must explicitly determine the position of bounding surface contours in the scene. Minimum requirements of such a process are given. (PsycINFO Database Record (c) 2010 APA, all rights reserved)