基于FFT的循环自相关函数算法在滚动轴承故障诊断中的应用

根据循环自相关函数等于两个移频形式的互相关及循环自相关函数的周期性特征,提出基于FFT及IFFT的循环自相关函数算法,该算法将周期函数的互相关快速算法引入循环自相关函数的计算中,相对直接按公式的计算大大提高了速度.由该算法得到的循环自相关函数进行谱分析及平方谱分析,进一步证明了该算法的正确性.最后将该算法应用于滚动轴承故障诊断中,通过对滚动轴承内圈故障及外圈故障信号的分析,证明该算法的实用性.     

直升机数字化多点协调加载系统设计研究

多点协调加载技术是直升机静力试验和疲劳试验的关键技术,对试件是否同步平衡加载直接影响到施加载荷的精度和测量数据的准确性。 多点协调加载是多输入——多输出力系统,通道间存在着相互的耦合,如何减少耦合也成为协调加载技术的一个重要难题。 为了更好的解决直升机协调加载中的技术难题,在跟踪国内外发展动态和充分消化理解静力、疲劳试验的基础上：针对直升机静力、疲劳试验的特点,提出了系统的总体需求目标和技术指标;对系统进行了总体设计,系统总体上采用3级分布式结构;开发了适用于直升机强度试验的控制补偿算法,对减少通道间的相互耦合具有明显的效果;开发出了强大的试验控制软件包;通过试验验证了系统的功能和技术指标;验证了不同补偿控制算法的有效性。     

锦屏二级水电站引水隧洞围岩岩爆特性研究

为了解锦屏二级水电站引水隧洞围岩岩爆特性,对该工程区典型岩爆岩样系统地开展了岩石力学特性试验研究。试验结果表明岩样较完整坚硬、抗压强度高,主要以脆性破坏形式为主;典型地层试样的岩爆倾向性指数平均值W_et均大于2.0,当地处高应力区时,岩爆特征明显;岩样卸围压破坏过程中变形特征规律为初始卸载围压越大,岩石的扩容效应越显著,与常规三轴压缩试验相比,岩样卸荷破坏的峰后应力跌落时的轴向应变变化较小,初始围压越大脆性破坏特征越明显;CT扫描断面与图像重组手段分析表明,试样在卸荷试验过程中,首先经历压密阶段,然后进入扩容状态直至破坏,破坏后存在“密度回弹”现象。卸围压试验中,试样瞬间发生破坏,多数伴有破裂响声,多数产生“双剪”破坏;利用岩体基本质量指标来描述岩石坚硬程度和岩体完整程度,提出了一种新的岩爆判据形式与分级标准,利用试验成果对提出的岩爆判据与分级进行了验证,结论与锦屏二级水电站辅助洞岩爆实际情况相符。     

高职教育工学结合实践教学模式的构建

工学结合是高等职业教育内涵建设的一个重要内容,如何开展工学结合并在实践中解决比较突出的工学矛盾,已成为高等职业院校实践教学中的一个十分重要的工作内容。文中根据工学结合的职业能力目标体系,构建了工学结合的实践教学体系,并在强化实践教学环节方面提出了的建议。     

Mapping review networks: Exploring research community roles and contributions

In this paper we investigate the position of a review network within a research specialty; the network of scholars who write reviews of their colleagues’ work. This is one of the voluntary activities that researchers perform as a prerequisite for the functioning of the invisible college. We compare this network to other networks within the specialty, and this allows us to distinguish various roles: stars, influentials, members, reviewers and juniors. As scholars are characterized by different role-configurations, the invisible college becomes stratified. We discuss the implications for the development of a referee factor and review factor, norms for refereeing and reviewing, and the development of systems-based research evaluations.     

Estimation of Small Reservoir Storage Capacities with Remote Sensing in the Brazilian Savannah Region

Small reservoirs play an important role in supporting the local economy in the savannah areas of Brazil and are primarily used for the provision of water for irrigation and watering livestock. Hundreds of small reservoirs have been built in the last few decades in the Preto River Basin, but efficient water management and sound planning are hindered by inadequate knowledge of the number, storage capacity and spatial distribution of reservoirs in the basin. The main reason for the lack of this information is that current methodologies for quantifying the physical parameters of reservoirs are laborious, time consuming and costly. To address this lack of data, a simple method to estimate reservoir storage volumes based on remotely sensed reservoir surface area measured with LANDSAT was developed. The method was validated with a subset of reservoirs in the Preto River Basin for which surface areas, shapes and depths were determined with ground-based survey measurements. The agreement between measured and the remotely sensed reservoir volumes was satisfactory, indicating that remotely-sensed images can be used for improved management of water in the Brazilian Savannah region. With the newly developed methods we found that the Preto River Basin’s 147 small reservoirs can store 19 × 10⁶ m³ of water at full capacity.     

Stabilization in the ZaP Flow Z-Pinch

The ZaP flow Z-pinch experiment at the University of Washington investigates the innovative plasma confinement concept of using sheared flows to stabilize an otherwise unstable configuration. The ZaP experiment generates an axially flowing Z-pinch that is 1 m long with a 1 cm radius with a coaxial accelerator coupled to a pinch assembly chamber. Magnetic probes measure the fluctuation levels of the azimuthal modes m = 1, 2, and 3. After assembly, the plasma is magnetically confined for an extended quiescent period where the mode activity is significantly reduced. Experimental measurements show a sheared flow profile that is coincident with the low magnetic fluctuations during the quiescent period. Recent experimental modifications produce more energetic Z-pinch plasmas that exhibit the same general behavior. The plasma equilibrium is characterized with a suite of diagnostics that measure the plasma density, magnetic field, ion and electron temperatures, in addition to plasma flow. The equilibrium is shown to satisfy radial force balance.     

Ferroelectric SrBi 2 Nb 2 O 9 Thin Films by Aqueous Chemical Solution Deposition

SrBi 2 Nb 2 O 9 (SBN) thin films on a Pt/Ti/SiO 2 /Si substrate were prepared by aqueous chemical solution deposition. The precursor solution was synthesized by means of an 'aqueous solution-gel method', starting with stable, inexpensive and easily available inorganic salts which are dissolved in an aqueous solution of chelating or coordinating ligands (acetates and citrates). Afterwards the synthesized precursor was spin-coated. However, problems arose as a consequence of insufficient 'wetting' of the substrate surface by the aqueous solution (poor film-substrate adhesion). Instead of improving surface adhesion by the addition of a surface-wetting reagent, a new strategy was developed: prior to spin-coating the platinum surface characteristics were modified using a UV/ozone technique. In this way the precursor solution was not chemically changed. Wetting/wettability was verified by means of contact angle measurements. A uniform, three-layer thin film with a total thickness of about 200 nm was obtained after thermal treatment, as could be verified using SEM and XRD.     

Forgetting Exceptions is Harmful in Language Learning

We show that in language learning, contrary to received wisdom, keeping exceptional training instances in memory can be beneficial for generalization accuracy. We investigate this phenomenon empirically on a selection of benchmark natural language processing tasks: grapheme-to-phoneme conversion, part-of-speech tagging, prepositional-phrase attachment, and base noun phrase chunking. In a first series of experiments we combine memory-based learning with training set editing techniques, in which instances are edited based on their typicality and class prediction strength. Results show that editing exceptional instances (with low typicality or low class prediction strength) tends to harm generalization accuracy. In a second series of experiments we compare memory-based learning and decision-tree learning methods on the same selection of tasks, and find that decision-tree learning often performs worse than memory-based learning. Moreover, the decrease in performance can be linked to the degree of abstraction from exceptions (i.e., pruning or eagerness). We provide explanations for both results in terms of the properties of the natural language processing tasks and the learning algorithms.     

Effects of relative humidity,temperature, and population density on production of cuticular hydrocarbons in housefly Musca domestica L

The production of cuticular hydrocarbons by both males and females of Musca domestica L. under very wet conditions (90% relative humidity) compared to the production at 50 and 20% relative humidity is delayed up to at least 3 days after emergence from the pupae. Eight days after emergence, however, males contain the same amounts of hydrocarbons at 90, 50, and 20% relative humidity, whereas females at 90% still possess less of these substances than at 50 and 20%. It is suggested that this is due to the fact that males, being more active than females, need more cuticular hydrocarbons to prevent water loss. No indication is found that relative humidity has a different effect on the production of the sex pheromone, muscalure [(Z)-9-tricosene] by females than on the production of the other hydrocarbons. Male and female flies produce more hydrocarbons at 35°C than at 20°C. On females, the relative amounts of nonacosane and methyl- and dimethylnonacosanes are significantly higher at 35°C than at 20°C. Female flies produce some (Z)-9-tricosene after eight generations at low population density in contrast to females at high population density, which did not produce muscalure. We suggest that because of the relatively large contribution to the total population, the properties of a small number of females are likely to be expressed sooner in the next generations of small populations than in those of large populations.