直流微电网建模与稳定性分析

针对直流微电网的稳定性问题,采用状态空间法建立了直流微电网中多种变流装置及其控制系统的平均模型,并在此基础上对直流微电网进行了小扰动稳定性分析,得出了随着变流器控制参数变化的系统特征值轨迹。分析表明,当变流器的控制系数增大到一定数值时,将会出现实部为正的系统特征值,即系统不稳定。为了验证这一分析方法的可行性,又对所研究的直流微电网进行了时域仿真,得出负荷突增时不同控制系数下的时域电压曲线。仿真结果一方面验证了稳定性分析的结果,另一方面也表明,当控制系数在稳定范围内时,系数越大,则电压控制的效果也越好。由此可见,合理选择变流器的控制参数能够很好地保证直流微电网的电压稳定性。     

路易斯·康的话语方式和修辞策略

以路易斯·康的论文《Order Is》为例,对法则问题及其研究方法的未来走向进行了思考。     

The Ergonomics Society Annual Conference 1977 Abstracts of Papers

In multi-disciplinary design projects (e.g. the design of traffic-control rooms) it can be difficult for the applied ergonomist to emphasize the human factor. A workshop with all the members of the project team in an early stage of the project has been shown to improve the cohesiveness in the team during the process. The applied ergonomist should uphold ('market') his ergonomic contributions to those from other disciplines in this workshop. In other stages of the process, the applied ergonomist can act as an intermediary between divergent disciplines, due to his multi-disciplinary approach and know-how. Presentation of concepts and solutions to the client and the end-users should be done in a professional way. This improves feedback and effects a more positive attitude towards the final solution.     

Body composition and self-perceived health and fitness among indoor sports participants

Abstract

This paper examines (1) the responses of participants in specific indoor sports to questions regarding their self-perceived health and fitness, and (2) the relation betweeen these responses and body composition. A representative sample of indoor sports participants (n = 4308; 2938 male and 1370 female) from six cities in the United Kingdom responded to a questionnaire concerned with their self-perception of health and fitness. Height and weight was established from self-report and a body mass index (BMI) was calculated. Seventy eight percent of males and 85% of females reported their health as ‘good’ or ‘excellent’. Less than 2% of the sample reported their health as ‘poor’ or ‘very poor’. However, only 67% of males and 67% of females reported their fitness as ‘good’ or ‘excellent’. Again, the proportion of the sample reporting ‘poor’ or ‘very poor’ fitness was low; less than 4%. The question on health was compared with a recent general population survey and this yielded markedly more ‘unfavourable’ results; only 72% of males and 70% of females reported their health as being ‘good’ or ‘excellent’. A comparison of the response category groups for BMI showed significant differences between the ‘poor’ and ‘fair’ groups but not between the ‘good’ and ‘excellent’ groups.

It is concluded that: (1) indoor sports participants regard their health and fitness highly, but their fitness less so than their health; (2) adiposity tends to be associated with poorer perceptions of health and fitness; (3) women sports participants perceive their health more highly than others of the same age compared with men, yet the reverse is true of fitness.     

High pressure organic colloid method for the preparation of high performance carbon nanotube-supported Pt and PtRu catalysts for fuel cell applications

Highly dispersed,high performance Pt and PtRu catalysts,supported on multiwalled carbon nanotubes(CNTs),were prepared by a high pressure organic colloid method.The particle sizes of the active components were as small as 1.2 nm for Pt and 1.1 nm for PtRu,and the active Pt surface areas were 295 and 395 m2/g,respectively.The catalysts showed very high activities toward the anodic oxidation of methanol,evaluated by cyclic voltammetry,being up to 4 times higher than that of commercial Johnson Matthey Hispec 20...     

弹道方程边值问题中的直射弹道公式

本文探求了属于微分方程边值问题的直射弹道公式,以形简、意明、精确度高、研究方法的多样性和事物规律的不同表现形式为特征。在直射弹道的定义和数学描述之后,先从它的微分方程出发推导出了公式;再从方程的数字解出发探寻并确立了其规律性。     

基于直接转矩控制的高性能磁链观测与速度观测

提出了一种高性能的定子磁链和转子磁链的观测方法，并在转子磁链的基础上估算出电机转速，最后将结合磁链观测的速度估计器应用到无速度传感器直接转矩控制系统中。仿真和实验结果表明，这种观测方法能够提高速度的观测精度，增强系统的鲁棒性，并使直接转矩控制系统的低速性能得到较大提高。     

Parametric macromodeling based on amplitude and frequency scaled systems with guaranteed passivity

We propose a novel parametric macromodeling method for systems described by scattering parameters, which depend on multiple design variables such as geometrical layout or substrate features. It is able to build accurate multivariate macromodels that are stable and passive over the entire design space. Poles and residues are parameterized indirectly. The proposed method is based on an efficient and reliable combination of rational identification, a procedure to find amplitude and frequency scaling system coefficients and positive interpolation schemes. Pertinent numerical examples validate the proposed parametric macromodeling technique. Copyright © 2011 John Wiley & Sons, Ltd.     

Multiphoton Lithography as a Promising Tool for Biomedical Applications

Multiphoton lithography (MPL) is a powerful and useful structuring tool capable of generating 2D and 3D arbitrary micro- and nanometer features of various materials with high spatial resolution down to nm-scale. This technology has received tremendous interest in tissue engineering and medical device manufacturing, due to its ability to print sophisticated structures, which is difficult to achieve through traditional printing methods. Thorough consideration of two-photon photoinitiators (PIs) and photoreactive biomaterials is key to the fabrication of such complex 3D micro- and nanostructures. In the current review, different types of two-photon PIs are discussed for their use in biomedical applications. Next, an overview of biomaterials (both natural and synthetic polymers) along with their crosslinking mechanisms is provided. Finally, biomedical applications exploiting MPL are presented, including photocleaving and photopatterning strategies, biomedical devices, tissue engineering, organoids, organ-on-chip, and photodynamic therapy. This review offers a helicopter view on the use of MPL technology in the biomedical field and defines the necessary considerations toward selection or design of PIs and photoreactive biomaterials to serve a multitude of biomedical applications.