基于决策树的羽流追踪机器人自主决策方法研究

针对无法获得可靠羽流流向信息不利于实现羽流追踪的问题，提出了一种基于决策树的羽流追踪移动机器人自主决策方法。该方法通过移动机器人两侧的浓度传感器采集到的浓度信息，利用追踪的行为规则建立决策树模型，获得行为决策信息，使机器人高效地追踪到羽流并精确地定位。由于浓度变化关系蕴含了羽流的流向及流速信息，从而取代了传统方法中流向及流速传感器。在扩散环境下，通过移动机器人羽流追踪实验，实现了良好的源定位效果。     

Beam and image experiment of beam deflection electron gun for distributed X-ray sources

Distributed X-ray sources comprise a single vacuum chamber containing multiple X-ray sources that are triggered and emit X-rays at a specific time and location. This process facilitates an application for innovative system concepts in X-ray and computer tomography. This paper proposes a novel electron beam focusing, shaping,and deflection electron gun for distributed X-ray sources.The electron gun uses a dispenser cathode as an electron emitter, a mesh grid to control emission current, and two electrostatic lenses for beam shaping, focusing, and deflection. Novel focusing and deflecting electrodes were designed to increase the number of focal spots in the distributed source. Two identical half-rectangle opening electrodes are controlled by adjusting the potential of the two electrodes to control the electron beam trajectory, and then, multifocal spots are obtained on the anode target. The electron gun can increase the spatial density of the distributed X-ray sources, thereby improving the image quality. The beam experimental results show that the focal spot sizes of the deflected(deflected amplitude 10.5 mm)and non-deflected electron beams at full width at half maximum are 0.80 mm 90.50 mm and 0.55 mm 90.40 mm, respectively(anode voltage 160 kV; beam current 30 mA). The imaging experimental results demonstrate the excellent spatial resolution and time resolution of an imaging system built with the sources, which has an excellent imaging effect on a field-programmable gate array chip and a rotating metal disk.     

Optimal parameter choice of CR–RC~m digital filter in nuclear pulse processing

CR–RC~m filters are widely used in nuclear energy spectrum measurement systems. The choice of parameters of a CR–RC~m digital filter directly affects its performance in terms of energy resolution and pulse count rate in digital nuclear spectrometer systems. A numerical recursive model of a CR differential circuit and RC integration circuit is derived, which shows that the shaping result of CR–RC~m is determined by the adjustment parameter(k, it determines the shaping time of the shaper)and the integral number(m). Furthermore, the amplitude–frequency response of CR–RC~m is analyzed, which shows that it is a bandpass filter; the larger the shaping parameters(k and m), the narrower is the frequency band. CR–RC~m digital Gaussian shaping is performed on the actual sampled nuclear pulse signal under different shaping parameters. The energy spectrum of ~(137)Cs is measured based on the LaBr_3(Ce) detector under different parameters. The results show that the larger the shaping parameters(m and k), the closer the shaping result is to Gaussian shape, the wider is the shaped pulse, the higher is the energy resolution, and the lower is the pulse count rate. For the same batch of pulse signals, the energy resolution is increased from 3.8 to 3.5%, and the full energy peak area is reduced from 7815 to 6503. Thus, the optimal shaping parameters are m=3 and k=0:95. These research results can provide a design reference for the development of digital nuclear spectrometer measurement systems.     

Reference Point Based Multi-Objective Optimization of Reservoir Operation: a Comparison of Three Algorithms

Traditional multi-objective evolutionary algorithms treat each objective equally and search randomly in all solution spaces without using preference information. This might reduce the search efficiency and quality of solutions preferred by decision makers, especially when solving problems with complicated properties or many objectives. Three reference point based algorithms which adopt preference information in optimization progress, e.g., R-NSGA-II, r-NSGA-II and g-NSGA-II, have been shown to be effective in finding more preferred solutions in theoretical test problems. However, more efforts are needed to test their effectiveness in real-world problems. This study conducts a comparison of the above three algorithms with a standard algorithm NSGA-II on a reservoir operation problem to demonstrate their performance in improving the search efficiency and quality of preferred solutions. Under the same calculation times of the objective functions, Pareto optimal solutions of the four algorithms are used in the empirical comparison in terms of the approximation to the preferred solutions. Three performance indicators are then adopted for further comparison. Results show that R-NSGA-II and r-NSGA-II can improve the search efficiency and quality of preferred solutions. The convergence and diversity of their solutions in the concerned region are better than NSGA-II, and the closeness degree to the reference point can be increased by 42.8%, and moreover the number of preferred solutions can be increased by more than 3 times when part of objectives are preferred. By contrast, g-NSGA-II shows worse performance. This study exhibits the performance of three reference point based algorithms and provides insights in algorithm selection for multi-objective reservoir optimization problems.

     

六盘水市煤炭行业竞争战略分析

我国是富煤贫油少气的国家，煤炭是我国最重要的一次能源。但从能源激烈的竞争市场环境而言，当前我国煤炭行业发展出现了困境。为了更好地发展六盘水地区的煤炭行业，结合竞争战略理论和六盘水市的煤炭行业发展状况，运用PEST分析法和波特五力模型对六盘水市煤炭行业进行分析，得出整合资源，结合自身优势大力吸引人才，最终达到产业转型的生态化煤炭发展战略模型。分析结果可为提高六盘水煤炭行业竞争力提供理论支持。     

Physicochemical,textural and volatile characteristics of fermented milk co-cultured with Streptococcus thermophilus,Bifidobacterium animalis or Lactobacillus plantarum

Fermented milks were prepared with various culture combinations of Lactobacillus plantarum or Bifidobacterium animalis with Streptococcus thermophilus, and the impact of microbes combinations on acidification, proteolysis, lipolysis, texture, volatiles and sensory quality of fermented milk was investigated during 21-day storage at 4 °C. The results showed that products from the co-cultures displayed higher titratable acidity, more peptides, higher proteolytic activity and lipolysis capacity compared with that from the pure strains of S. thermophilus. When L. plantarum and B. animalis combined in a ratio of 2:1 with S. thermophilus, the products maintained relatively more viable cell counts of the 3 strains, strong proteolysis ability and lipolysis capacity during the storage. Milk fermented by co-cultures of the 3 strains exhibited higher cohesiveness, more volatiles and better sensory quality compared with these fermented by S. thermophilus only or in co-cultures with either B. animalis or L. plantarum based on principal component analysis.     

Oxygen reduction reaction and hydrogen evolution reaction catalyzed by carbon-supported molybdenum-coated palladium nanocubes

Oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) are two important processes for electrochemical energy storage and conversion. Herein, we describe the preparation of carbon-supported Pd nanocubes@Mo core@shell nanostructures as efficient dual catalysts for both ORR and HER. The core@shell structure was manifested by high-resolution transmission electron microscopy measurements, including high angle-angular dark field-scanning transmission electron microscopy and elemental mapping analysis. Further structural insights were obtained in X-ray diffraction and X-ray photoelectron spectroscopy measurements. The nanostructures exhibited apparent electrocatalytic activity toward both ORR and HER, and the performances were markedly higher than those without the deposition of a Mo overlayer. In ORR, the activity was even better than that of commercial Pt/C within the context of onset potential, specific and mass activities; whereas in HER, the performance of Pd nanocubes@Mo core@shell nanostructures remained subpar as compared to that of Pt/C in terms of the overpotential to reach the current density of 10 mA cm^?2, the Tafel slope was comparable and the stability was excellent. The excellent electrocatalytic performance can be attributed to the Pd-Mo synergistic effects imparted from the core-shell structure.     

风电机组传动链典型故障特征提取方法

为解决风电机组传动链易发生故障的问题,文章阐述了风电机组齿轮箱特征频率的计算方法和基于振动信号分析的故障特征提取方法。结合实际情况,以行星级齿轮磨损、中间轴小齿轮崩齿、高速轴齿轮崩齿和发电机轴承电腐蚀等典型故障为例,通过齿轮箱特征频率和传动链典型故障振动信号基本特征分析,可较好地完成故障识别。结果表明,采用经典信号处理方法能对上述典型故障进行特征提取,验证了经典方法对单一、明显故障特征提取的有效性,为深入开展传动链故障特征提取方法研究奠定了基础,为风电机组故障检修维护提供了技术支撑。