基于双树复小波包变换能量泄漏特性分析的齿轮故障诊断

为有效利用双树复小波包变换提取齿轮故障特征信息,提出基于双树复小波包能量泄漏特性分析的故障诊断方法。首先根据高斯白噪声频率充满整个频带的特性,通过双树复小波包变换对高斯白噪声进行分解,利用频带能量泄漏的定量分析方法,验证了双树复小波包变换具有较低的频带能量泄漏特性;其次利用双树复小波包变换逐层分解信号,对每层分解所得分量求其FFT谱的峭度,得到基于双树复小波包变换的谱峭度图,根据图中峭度最大的原则,可以自动准确的选择信号分解最佳层数和最佳分量;最后将基于双树复小波包变换的谱峭度图的故障诊断方法应用于实际工程中,对齿轮故障振动信号进行分析,选择最佳分解层数和分量后利用希尔伯特包络解调,有效准确地提取了故障特征信息,验证了方法的可行性和有效性。该研究可为旋转机械设备中齿轮箱故障诊断的故障特征提取提供参考。     

基于小波和径向基函数神经网络的滚动轴承故障模式识别

利用振动信号对滚动轴承的状态监测和故障诊断是工程中面临的难题之一，传统的基于平稳信号假设的方法不适于故障轴承的非平稳信号，有效提取故障轴承的故障特征和将故障特征准确分类是解决问题的两个关键。小波分析具有良好的时-频局部化特征，因而非常适于对瞬态或时变信号进行分类, 而人工神经网络可完成非线性系统辨识和模式分类。利用上述原理根据滚动轴承振动信号的频域变化特征，首先采用小波包分析对其建立频域能量特征向量，然后利用径向基函数神经网络完成滚动轴承故障模式的识别。试验结果表明，系统不仅能够检测到轴承故障的存在，而且能够比较准确地识别轴承的内外环故障模式，可以满足工程中的需要。     

一种适用于非平稳、非线性振动信号分析方法研究

Hilbert-Huang变换(HHT)被认为近年来信号分析领域的一大突破。适用于非平稳、非线性信号分析。从往复机械上得到的振动信号往往具有非平稳、非线性特征,因此采用HHT方法分析是一种较佳的选择。然而,该方法提出不久,并不能用一个解析公式表示,影响了对其理论分析及性能评价。建立一多分量仿真信号,并应用HHT、傅里叶变换、小波变换、时频分布对其分析比较,证明它具有较高的分解效率及准确地刻画信号的能力,并由此发展了能消除多分量信号交叉干扰项的时频分析方法。应用HHT对内燃机敲缸信号进行分析,有效地提取故障的特征信息,为往复机械的状态监测及故障诊断提供了一条有效途径。     

基于经验小波变换的复杂强噪声背景下弱故障检测方法

针对复杂强噪声背景下的非平稳振动信号的弱故障和复合故障检测的难题,引入经验小波变换(empirical wavelet transform,EWT)以提高故障确诊率,并提出一种基于EWT的复杂强噪声背景下弱故障的检测方法。EWT能够通过完全自适应小波基提取信号的固有模式,与经典小波变换一样具有完备的理论基础。通过对含有复杂强噪声的仿真信号和实际信号进行EWT分析,并对比经验模态分解,验证了基于EWT的复杂强噪声背景下弱故障检测的可行性和有效性。该研究可为复杂工况下机械设备的弱故障和复合故障检测以及故障特征提取提供参考。     

综合模式分量能量及时频域特征的柴油机故障诊断

柴油机缸盖振动信号中包含着丰富的柴油机工作状态信息,利用缸盖振动信号诊断柴油机工作状态是一种有效方法。鉴于缸盖振动信号非平稳性的特点,该文提出用经验模式分解方法对获取的信号进行分解,选取前三阶的模式分量近似代替原信号,用模式分量的能量百分比、重心频率和重心幅值、偏度、峭度、方差等构成柴油机工作状态特征向量,基于支持向量机对实测的柴油机故障进行诊断分类,诊断的正确率达到92%以上,验证了方法的可行性。该研究也可为其他机械设备的故障诊断提供参考。     

基于小波分析的车辆变速箱故障检测的研究

利用离散正交小波变换，把车辆变速箱的振动信号进行多层小波分解，使其突变信号和非平稳信号与平稳周期性信号分开，并进行图形显示，为车辆变速箱故障检测提供理论依据。     

基于LMD和MED的滚动轴承故障特征提取方法

机械系统所拾取的振动信号包含着许多复杂的信息成分,微弱故障信号的提取往往会受到这些成分的影响,故障识别非常困难,尤其是滚动体故障识别,往往比内圈和外圈故障识别更困难。提出局域均值分解(local mean decomposition,LMD)与最小熵反褶积(minimum entropy deconvolution,MED)结合的方式,提取强噪声、强确定性成分下微弱故障信号的特征。先用LMD对信号做预处理,自适应地分解为若干个乘积函数(product function,PF)分量,再对前4个PF分量做MED处理以放大故障脉冲特征,最后对MED处理后的信号进行包络分析。通过对强噪声背景下滚动轴承滚动体的故障实例分析,该方法得到的输出频谱故障特征频率处峰值与200 Hz内所有峰值均值的比值较原信号的增加了96.4%,同时信噪比提高了18.3%,成功地提取了故障特征,取得了良好的效果,该研究可为强噪声环境下轴承故障识别和诊断提供参考。     

基于小波包原理的蚕茧无损检测研究

提出了基于声学的蚕茧无损检测新方法，研究了利用小波包原理提取噪声信号的特征值的方法。噪声信号经过小波包分解后，得到各频段内的信号，将各频段内信号的能量谱作为识别蚕蛹质量的特征值。结果表明，通过小波包原理提取的能量谱特征值能有效地识别出蚕蛹的质量，解决了蚕茧无损检测过程中难找出与蚕蛹质量有关的信号特征值的难题。     

油松单根抗拉试验数据的降噪分析

林木单根抗拉试验数据经常受到试验环境背景、仪器随机误差、人为操作等各类噪声污染,对根系抗拉力学特性的分析结果影响很大。为了提高根系抗拉力学特性的分析精度,需要对试验数据进行预处理。尽管小波降噪理论日渐成熟,但其在林业根系固土机制研究方面的应用并未得到推广。应用小波变换对油松250标距的单根抗拉试验数据进行降噪研究,分别采用到的降噪研究方法有:3～31点平滑法、非线性小波硬阈值(Hard)法、固定阈值(Fixed)法、最大最小阈值(Mini-max)法及Rig.Sure阈值(sure)法。结果表明:各种窗口宽度的平滑法中,9点平滑法被证明降噪效果更为显著;而基于小波变换的Rig.Sure阈值法能够更为有效地降低试验数据中的噪声信号,保留有效信息,提高试验数据的质量及分析能力。     

自适应最大相关峭度反褶积方法诊断齿轮轴承复合故障

为了解决传统最大相关峭度反褶积(maximum correlated kurtosis deconvolution,MCKD)在故障诊断中容易出现因参数选择不当而影响诊断效果的问题,该文提出了一种基于量子遗传算法(quantum genetic algorithm,QGA)的自适应最大相关峭度反褶积方法(maximum correlated kurtosis deconvolution with quantum genetic algorithm,QMCKD)用于齿轮和轴承复合故障诊断。通过量子遗传算法自适应选择最大相关峭度反褶积的2个关键参数滤波器长度(L)和反褶积周期(T)。使用QMCKD处理原始振动信号,提取复合故障信号中的所有单个故障信号,分别对单个故障信号进行频谱分析从而识别故障特征。在对齿面磨损-滚动轴承外圈损伤复合故障诊断中,QMCKD能够识别齿轮故障频率及其2~4倍频,识别轴承故障频率及其2~6倍频,且主要频率成分周围干扰谱线很少,故障类型容易识别。与直接频谱分析和变分模态分解(variational mode decomposition,VMD)相比,该方法在诊断效果上具有优越性。在对齿根裂纹-轴承滚动体损伤复合故障诊断中,QMCKD能够突出齿轮故障频率及其2~5倍频,突出轴承故障频率及其2~8倍频,齿轮和轴承故障特征明显,验证了方法的稳定性。试验结果表明QMCKD能够有效识别复合故障中齿轮和轴承的故障特征,可用于齿轮箱的齿轮、轴承复合故障诊断。     

低氮和干旱胁迫对富士和秦冠生长及氮素利用的影响

【目的】以富士（Fuji）、 秦冠（Qinguan）嫁接在平邑甜茶（Malus hupehensis Rehd.）上的当年生盆栽苗为试验材料,采用砂培方法,研究了缺氮胁迫和干旱对富士和秦冠生长情况、 光合参数、 植株各部位氮磷钾含量及氮素利用效率的影响,分析比较了低氮干旱条件下富士和秦冠生长及氮素利用的差异,以期为果树生产高效肥水利用提供理论指导。【方法】试验共设四个处理: 正常氮正常水（ZZ）、 低氮正常水（DZ）、 正常氮干旱（ZG）、 低氮干旱（DG）。氮素和水分均设置两个水平,分别为正常氮（6 mmol/L NO-3-N）、 低氮（0.3 mmol/LNO-3-N）、 正常供水（保持盆中砂子相对含水量为饱和含水量的80%~85%）、 干旱处理（保持盆中砂子相对含水量为饱和含水量的60%~65%）。【结果】富士和秦冠的生物量（茎和叶）、 株高茎粗等生长指标以及光合速率、 气孔导度、 蒸腾速率均为正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）,并且相对应处理下秦冠的以上指标均高于富士;正常供水下,缺氮处理使富士、 秦冠的根冠比比正常氮处理均有所增加,富士提高了2.05%,秦冠提高了22.40%。富士和秦冠的氮、 磷、 钾含量均表现出正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）; 氮、 钾元素含量在植株各部位的分布顺序依次是叶＞根＞茎,磷元素则是根＞叶＞茎;光合氮素利用效率（PNUE）和氮素利用效率表现为秦冠处理之间差异极显著,富士处理之间差异不显著;秦冠的PNUE和NUE明显高于富士,在低氮正常水（DZ）处理下,秦冠氮肥利用率比富士高42.07%,在低氮干旱（DG）处理下高64.14%;低氮胁迫下富士和秦冠的NUE显著提高,并且秦冠提高的幅度高于富士。【结论】施用氮肥能够显著提高富士与秦冠的干物质量,同等水肥条件下,秦冠生长优于富士;水分亏缺会减少叶片对氮的吸收,干旱条件下适度增施氮肥,可提高果树的抗旱能力;低氮干旱胁迫下秦冠的生长指标、 光合指标及氮素利用效率指标均优于富士,表现出较强的抗低氮干旱胁迫的能力。     

Pasture Vegetation Elemental Analysis by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a new technique for the analysis of plant material. This study investigates the application of LIBS to pasture-based plant samples. The LIBS measurements were obtained from pelletized pasture samples (100 samples) that had been also analyzed by inductively coupled plasma–optical emission spectroscopy (ICP-OES) following microwave digestion for calibration and comparison purposes. Comparisons for elements sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), boron (B), phosphorus (P), and sulfur (S) showed that LIBS could be used for almost all the standard profile total elements with concentrations down to low mg/kg levels (observed error of Na: 0.024 percent, K: 0.18 percent, Mg: 0.016 percent, Ca: 0.073 percent, P: 0.017 percent, Mn: 31 mg/kg, Fe: 150 mg/kg, Zn: 6.6 mg/kg, and B: 1.1 mg/kg). Elemental analysis at less than mg/kg levels was not possible using LIBS. The elements S and Cu were particularly difficult to analyze with reliability using LIBS at the concentration levels found in the plant samples. Replacing microwave digestion and subsequent ICP analysis with a direct analysis of dried plant samples using LIBS has the potential to improve the productivity and reduce the cost of testing.     

Faculty positions:Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Macroinvertebrates in North American tallgrass prairie soils: effects of fire, mowing, and fertilization on density and biomass

The responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils.     

Variation in quality parameters between and within 14 Nordic tree fruit and berry species

Abstract

A 3-year study was carried out to investigate quality parameters in 14 tree fruit and berry species grown in southern Norway. The species were blueberry, apple, aronia, sour cherry, sweet cherry, red raspberry, strawberry, blackcurrant, gooseberry, red currant and elderberry, harvested along with wild bilberry, cloudberry and lingonberry. Significant differences between species were identified for all quality parameters. The coefficient of variation between species was lowest for pH (12.5%), dry matter (18.9%) and soluble solids (25.3%), followed by titratable acids (59.3%), total phenolics (83.8%), antioxidant capacity FRAP (85.7%) and antiradical power by the DPPH-assay (97.8%), total monomeric anthocyanins (132%) and ascorbic acid (137%). Average coefficient of variation within species were lower and ranged from 4 (pH) to 62% (ascorbic acid). Only the FRAP values were significantly affected by harvesting year with lower levels in 2004 than in 2005 and 2006. There were significant interactions between species and harvesting year for dry matter, soluble solids, pH, ascorbic acid and FRAP. The results indicate generic ranges in composition within species independent upon growing location and climate, and the composition of the tree fruits and berries is not likely to deviate from these ranges. It is concluded that desirable composition of tree fruits and berries and their products should primarily be achieved by selection among species rather than searching fors broadened variation within individual species.     

Potassium Fixation and Release Characteristics in Rhizosphere and Nonrhizosphere Soils for a Rapeseed–Rice Cropping Sequence

Potassium (K) fixation and release in soil are important factors in the long-term sustainability of a cropping system. Changes in K concentration and characteristics of K fixation and release in rhizosphere and nonrhizosphere soils in the rapeseed (Brassica napus L.)–rice (Oryza sativa L.) rotation were investigated using a rhizobox system. The concentrations of different forms of K in both rhizosphere and nonrhizosphere soils decreased with plants compared to without plants, regardless of K fertilizer application. Potassium uptake by crops mainly came from the rhizosphere soil. In the treatment without K fertilizer (–K), the main form of K supplied by the soil to the crops was 1.0 mol L^?1 nitric acid (HNO₃) nonextractable K, followed by nonexchangeable K, and then exchangeable K. In the treatment with K fertilizer (+K), the main K forms supplied by the soil to the crops were exchangeable K and nonexchangeable K. The amount and rate of K fixation after one cycle of the rapeseed–rice rotation was greater in rhizosphere soil than in nonrhizosphere soil. The amount and rate of K fixation of soil in the +K treatment were significantly less than in the –K treatment. The cumulative amounts of K released with 1.0 mol L^?1 ammonium acetate (NH₄OAc) and 1.0 mol L^?1 HNO₃ extraction increased with the increasing numbers of extractions, but the K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was less in rhizosphere soil than in nonrhizosphere soil. The release of K in the +K treatment was similar to that in the –K treatment in rhizosphere soil, but the K release in nonrhizosphere soil was greater with the +K than the –K treatment. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.     

Electron donor and pH relationships for biologically enhanced dissolution of chlorinated solvent DNAPL in groundwater

Biologically enhanced dissolution offers a method to speed removal of chlorinated solvent dense non-aqueous-phase liquid (DNAPL) sources such as tetrachloroethene (PCE) and trichoroethene (TCE) from aquifers. Bioremediation is accomplished by adding an electron donor to the source zone where fermentation to intermediates leading to acetic acid and hydrogen results. The hydrogen and possibly acetic acid are used by dehalogenating bacteria to convert PCE and TCE to ethene and hydrochloric acid. Reductive dehalogenation is thus an acid forming process, and sufficient alkalinity must be present to maintain a near neutral pH. The bicarbonate alkalinity required to maintain pH above 6.5 is a function of the electron donor: 800 mg/L of bicarbonate alkalinity is sufficient to achieve about 1.2 mM TCE dechlorination with glucose, 1.7 mM with lactate, and a much higher 3.3 mM with formate. Laboratory studies indicate that in mixed culture, formate can be used as an electron donor for complete conversion to ethene, contrary to pure cultures studies indicating it cannot. Various strategies can be used to add electron donor to an aquifer for DNAPL dehalogenation while minimizing pH problems and excessive electron donor usage, including use of injection-extraction wells, dual recirculation wells, and nested injection-extraction wells.     

Biodiversity and ecogeography of wild Lactuca spp. in some European countries

Staff members of the Department of Botany of Palacký University in Olomouc and Gene Bank Department – Workplace Olomouc, Research Institute of Crop Production in Prague, Czech Republic, conducted an expedition in seven European countries (Austria, Czech Republic, France, Germany, Italy, the Netherlands, Switzerland) in August/September 1999 to collect wild Lactuca spp. germplasm and study its geographic distribution, ecology and biodiversity. During the mission, more than 600 locations were visited resulting in the collection of 602 seed samples (accessions) of wild Lactuca species and 13 seed samples of related genera (Chondrilla and Mycelis). Lactuca serriola f. serriola, L. serriola f. integrifolia, L. saligna and L. viminea subsp. chondrilliflora were prevalent in southern Europe (Italy, France), however, only L. serriola was common in central and western Europe (Austria, Czech Republic, Germany, Netherlands, Switzerland). The greatest diversity of Lactuca species was found in France, where also the most seed samples (165) were collected. The most characteristic habitats with a high density of Lactuca spp. populations were observed along roads and highways, grassy ditches, ruderal communities, and dust-heaps. Natural infections by powdery mildew (Erysiphe cichoracearum) and downy mildew (Bremia lactucae) on some wild Lactuca spp. were observed. Recent observations concerning the geographic distribution, population structure, habitats, and natural occurrence of diseases of Lactuca spp. are discussed. This assemblage of genetic resources of Lactuca spp. can serve as the basis of future studies of species diversification, spatial population structure, plant microevolution, domestication processes, and genetic variability of host-parasite interactions.     

Increase in auxiliary photoprotective photosynthetic pigments in wheat seedlings induced by Azospirillum brasilense

Inoculation of wheat seedlings with the plant growth-promoting bacterium Azospirillum brasilense Cd was immobilized in alginate microbeads and, without applying any stress, significantly increased the quantity of several photosynthetic pigments, such as chlorophyll a, chlorophyll b, and the auxiliary photoprotective pigments violaxanthin, zeaxanthin, antheroxanthin, lutein, neoxanthin, and β-carotene. This resulted in greener plants with no apparent visible stress. After monitoring the quantity of photosynthetic pigments for 4 weeks, we observed that inoculated plants had higher quantities of pigments in shoot and stem. The greatest difference in the quantity of all pigments between inoculated and noninoculated plants occurred in the first week of growth. Regardless of treatment, the quantity of pigments in stems was three to four times less than the quantity of these pigments in shoots. Application of Azospirillum, either as liquid inoculant or as alginate microbeads, did not alter the positive effect of the bacteria on pigment production or the positive response of the plants towards A. brasilense Cd inoculation.     

In-situ enrichment and analysis of atrazine-degrading microbial communities using atrazine-containing porous beads

We examined the community composition of microbes that colonized atrazine-containing beads buried in agricultural soils that differed in atrazine treatment history. Bacterial abundance was 5-40-fold greater in atrazine-fortified beads. In beads containing 20 mg atrazine kg⁻¹ buried in soil with a history of atrazine application (conditioned soil), the abundance of Actinobacteria increased approximately 80-fold whereas in control soil, Actinobacteria were enriched only 10-fold and the gamma-Proteobacteria and Planctomycetes increased by 60- and 25-fold, respectively. The gamma-Proteobacteria were enriched by 120- and 230-fold in beads containing 200 mg atrazine kg⁻¹ in conditioned and control soil, respectively. The results demonstrate that BioSep^® beads are a suitable matrix for recruiting a diverse subset of the bacterial community involved in atrazine degradation.