四轮独立驱动高地隙无人喷雾机轨迹跟踪自适应控制

针对高地隙喷雾机在自主导航作业中因侧滑影响而导致轨迹跟踪精度降低的问题,提出一种基于四轮独立驱动(4WID)高地隙无人喷雾机的自适应控制方法。首先,建立4WID高地隙喷雾机的运动学模型;然后基于运动学几何约束和速度约束,引入两个表征侧滑效应的参数构建改进位姿误差模型;最后将参数自适应与反步控制方法结合,设计自适应控制律实时估计并补偿侧滑效应。以典型的U形作业路径为例,在考虑和不考虑侧滑的情况下分别进行了仿真和试验验证。仿真结果表明：本文提出的控制算法在喷雾机出现侧滑的情况下可以保证较高的轨迹跟踪精度;水田试验表明,当喷雾机在常规作业速度3.6km/h时,与不考虑侧滑的轨迹跟踪控制算法相比,喷雾机轨迹跟踪的横向平均绝对误差减小至0.041m,标准差减小至0.059m;纵向平均绝对误差减小至0.018m,标准差减小至0.015m;航向平均绝对误差减小至2.56°,标准差减小至3.57°。     

From small-scale habitat loopholes to decadal cycles: a habitat-based hypothesis explaining fluctuation in pelagic fish populations off Peru

The Peru‐Humboldt Current system (HCS) supports the world's largest pelagic fisheries. Among the world's eastern boundary current systems, it is the most exposed to high climatic stress and is directly affected by El Niño and La Niña events. In this volatile ecosystem, fish have been led to develop adaptive strategies in space and time. In this paper, we attempt to understand the mechanisms underlying such strategies, focusing on the El Niño 1997–98 in Peru from which an extensive set of hydrographic, capture and acoustic survey data are available. An integrated analysis of the data is crucial, as each has substantial shortcomings individually; for example, both catch data and acoustic surveys may easily lead to wrong conclusions. Existing hypotheses on anchovy and sardine alternations lead us to a ‘habitat‐based’ synthetic hypothesis. Using our data, an integrated approach evaluated how fish responded to habitat variation, and determined the consequences in terms of fish‐population variability. Various factors occurring at a range of different spatio‐temporal scales were considered: interdecadal regime (warm ‘El Viejo’/cool ‘La Vieja’ decadal scale); strength and the duration of the El Niño Southern Oscillation event (interannual scale); population condition before the event (interannual scale); fishing pressure and other predation (annual scale); changes in reproductive behaviour (intra‐annual scale); presence of local upwelling (local scale). During El Niño 1997–98, anchovy was able to exploit a small‐scale temporal and spatial ‘loophole’ inside the general unfavourable conditions. Moreover, sardine did not do better than anchovy during this El Niño and was not able to take advantage of the ‘loophole’ opened by this short‐term event. Our results question the traditional view that El Niño is bad for anchovy and good for sardine.     

运输应激对比格犬血常规及生化指标的影响

为了研究运输应激伴随的冷应激、驱赶、捕捉及饲料改变等多重应激对比格犬血常规和血液临床生化指标造成的影响,并且评估1周适应性饲养时间的合理性。以30只比格犬作为试验对象,对其适应性饲养前后的血常规和血液临床生化指标进行检查,并对数据进行分析发现,适应性饲养前犬的血常规和生化指标都有显著变化,1周的常规适应性饲养后,犬应激症状消失,血常规和生化检查指标均回复正常;这说明应激对比格犬造成了显著的影响,1周的适应性饲养是合理且必须的。     

The mbuna cichlids of Lake Malawi: a model for rapid speciation and adaptive radiation

Mbuna, the dominant fishes on the rocky shores of Lake Malawi, have become a major ‘model system’ for the study of rapid speciation and adaptive radiation. At least 295 putative species are known, of which more than 200 remain undescribed. There is no good evidence for monophyly in the mbuna, rather mitochondrial DNA phylogenies indicate that they are polyphlyetic with respect to benthic feeding cichlids of the genera Aulonocara, Alticorpus and some species of Lethrinops. Male mbuna hold territories for 18 months or more and breed year‐round. All species are maternal mouthbrooders, but females do not guard free‐swimming young. Mbuna are polygamous (both sexes). There is sexual dimorphism in size, colour and fin length, and many species show within‐population colour polymorphism. Mbuna genera are largely differentiated on the basis of head, jaw and tooth morphology, but congeneric species are generally distinguished by male colour. Many morphologically specialized forms have broad diets and often feed on common easily obtainable resources. While it is likely that dietary and habitat niche partitioning contributes to species coexistence, this has never clearly been demonstrated under experimental conditions. Populations on spatially separated habitat patches are often genetically differentiated, probably because most species are specialized for life on rocky shores, and lack a dispersal phase in their life histories. Males seem to disperse more than females, but are able to home several kilometres back to their territories. Some closely related ecologically equivalent allopatric populations are differentiated in male colour. Those tested have been shown to mate at least partially assortatively. Sexual selection acting on male colour seems the most plausible mechanism for initial species divergence. The same colour forms seem to have arisen several times, suggesting frequent parallel evolution. The main conservation threat to mbuna at present seems to be translocation of species within the lake as a result of the aquarium trade. However, deleterious effects on indigenous populations are not documented. In the long run, sedimentation, pollution, introduction of alien species and the development of targeted food fisheries could be more serious threats.     

Feeding has the largest effect on the ammonia excretion rate of the southern rock lobster, Jasus edwardsii, and the western rock lobster, Panulirus cygnus

The total ammonia nitrogen (TAN) excretion of spiny lobsters Jasus edwardsii and Panulirus cygnus, was determined in relation to temperature, body weight, emersion, daily rhythm and feeding. Temperature and body weight had large influences on the rate of TAN excretion. Exponential relationships were found between temperature (T) and TAN excretion of both species. These were described by the following equations: J. edwardsii Log₁₀ TAN=0.041T−3.57 (r²=0.979, F=143.2, P=0.001), P. cygnus Log₁₀ TAN=0.057T−3.90 (r²=0.987, F=302.2, P<0.001). TAN excretions of both species were positively correlated to body weight (W), and the relationships were described by the following equations: J. edwardsii Log₁₀ TAN=0.473 log₁₀ W−1.704 (r²=0.42, F=14.05, P=0.001), P. cygnus Log₁₀ TAN=0.499 log₁₀ W−1.346 (r²=0.69, F=44.18, P<0.001). TAN excretion increased significantly when lobsters were re-immersed after a 30 min period of emersion. However, it returned to pre-emersion levels by the second hour of re-immersion. Daily rhythm resulted in a significantly higher nocturnal TAN excretion rate for J. edwardsii; no daily rhythm was observed for P. cygnus. Feeding had the largest influence on TAN excretion, with maximum increases of 6.28 (J. edwardsii) and 5.60 (P. cygnus) times the pre-feeding level. TAN excretion rates remained significantly higher than the pre-feeding levels for an extended period (26 h, J. edwardsii; 30 h, P. cygnus). Implications for the use of purging tanks in lobster holding facilities and for the design of biofiltration systems are discussed.     

植被缓冲带对地表径流阻控效果调查及模拟

为了定量分析和评价植被缓冲带对地表径流的阻控效果,对大沽河流域两岸典型植被进行了现场调查及取样,并利用VFSMOD模型初步探讨了植被缓冲带的作用。根据实地调查,获得了大沽河8个典型位置的缓冲带参数。结果表明:大沽河流域植被缓冲带主要由杨树、松树等高大乔木,罗布麻、碱蓬等灌木植物和结缕草、野艾蒿等草本植物组成; 这些植被对地表覆盖度较高,可有效地拦截泥沙、增加地表粗糙度,对地表径流具有良好的阻控效果。利用VFSMOD模型对北岔河村、仁兆镇拦河闸、程家小里村和后路家村4个缓冲带的地表径流阻控效果进行了模拟,结果表明:4处植被缓冲带分别可以拦截0.8,0.7,0.7,0.4 mm/min以下降雨强度产生的地表径流; 在植被缓冲带宽度和源区宽度同时变化的情况下,4处植被缓冲带宽度分别达到8,20,1,5 m时,对泥沙拦截率达到0.95以上。因此,大沽河两岸现存植被缓冲带可以对泥沙起到较好的阻控作用。     

Forest management and forest state in southern Sweden before and after the impact of storm Gudrun in the winter of 2005

About three times the annual cut in southern Sweden (Götaland) was damaged by the storm Gudrun in January 2005, i.e. almost as much as the normal annual cut for all of Sweden. To establish any differences in forest management and state before and after the storm, measures such as growing stock volume, age-class distribution, and species composition were analyzed within the damaged area. As a reference the situation before and after the storm within the area in Götaland not damaged by the storm was also analyzed. For all analyses, sample plots from the Swedish National Forest Inventory were used. Results based on mean values for the years 2000–2004/2005–2009 showed that the total growing stock for the damaged area decreased by approximately 30 million m³ after the storm. This was mainly caused by a decrease in Norway spruce (Picea abies (L.) H. Karst). Annual growth for pine, spruce, and deciduous trees decreased by 1.8 million m³ in the damaged area. This mainly included stands already thinned and not, as expected, in the stands ready for final felling. Also, the proportional area within each of the age classes 21–40, 41–60, and 61–80 years decreased. The storm led to an increased area in immediate need of precommercial thinning. No changes in choice of species when regenerating could be observed. Furthermore, only marginal adaptation by forest owners to future risk of wind throw could be detected.     

低轨无拖曳卫星的自适应神经网络控制器设计

低轨无拖曳(Drag-free)卫星为相对论的验证、引力波探测以及地球重力场的测量提供了低干扰的试验环境。目前已有的工作主要对无拖曳卫星模型进行线性化,然后进行控制器设计,此种方法忽略了无拖曳卫星控制系统的非线性环节,因此降低了控制器的精度。本文将基于Lyapunov稳定性理论和自适应反步控制,直接针对无拖曳卫星控制系统的非线性模型进行分析,设计一种自适应神经网络控制器。针对系统建模过程中的线性化和未建模动态,利用RBF神经网络对非线性项进行拟合和补偿,建立自适应神经网络权值自适应律,保证闭环系统具有较好的鲁棒稳定性能和抗干扰性能,实现无拖曳卫星控制系统的设计要求。仿真结果表明控制器的有效性,满足了无拖曳卫星的控制精度要求。     

有源电力滤波器数字控制系统设计与数字锁相算法实现

秦典籍少有对圭的形制的描述,后世所见多是历代学者根据典籍及传世品加以想象绘制而成。近代考古学传入中国后,大量出土资料为圭形制的研究提供了科学依据。通过考古研究发现流行于西周的玉柄形器的功能应为某种仪仗类用玉,代表使用者的权力、身份或地位等,应为典籍所载“圭”类瑞玉之一。而盛行于西周的组合玉柄形器无论从尺寸、镶嵌,还是外部鞘饰看都与《考工记·玉人》所记载"命圭"十分吻合。