大视觉智能巡线车控制系统开发

针对常规的智能车传感器固定,视觉范围小,影响智能车的运行速度和准确性问题,提出了基于双舵机的大视觉智能巡线车控制系统。采用激光传感器、将路径识别传感器安装在车架上随动舵机的轮盘上,MCU通过控制随动摆头舵机来带动传感器的运动,使智能车的路径识别角度范围增大。经试验证明,此控制系统紧密结合双舵机的特点,充分发挥装在车架上的随动舵机带动路径识别传感器的优势,增大了智能车巡线过程中能识别到的路径范围,使智能车模实现高速稳定行驶。在不"丢线"的情况下,速度得到较大的提升,能适应各种赛道。     

Recent change in summer chlorophyll a dynamics of southeastern Lake Michigan

Six offshore stations in southeastern Lake Michigan were sampled during a pre quagga mussel Dreissena rostriformis bugensis period (1995–2000) and a post quagga mussel period (2007–2011). Chlorophyll a fluorescence profiles were used to characterize chlorophyll a concentrations during early (June–July) and late (August–September) summer stratification. During the early summer period the average whole water column chlorophyll a, the deep chlorophyll maximum, and the size of deep chlorophyll layer decreased 50%, 55%, and 92%, respectively, between 1995–2000 and 2007–2011. By contrast, in late summer there were no changes in these metrics between periods. Surface mixed layer chlorophyll a in early and late summer did not differ between time periods. On the other hand, chlorophyll a in the near bottom zone (bottom 20 m) declined 63% and 54% between 1995–2000 and 2007–2011 in early and late summer respectively. Changes in total phosphorus between 1995–2000 and 2007–2011 were less dramatic, with declines of 22–27% in early summer and 11–30% in late summer. Changes in the chlorophyll a conditions were attributed to dreissenid mussels which reduced material available from the spring bloom and disrupted the horizontal transport of nutrients to the offshore. Although light availability increased (i.e., increased secchi depths), reduced nutrient availability and spring diatom abundance resulted in a much smaller deep chlorophyll layer in 2007–2011.     

The Great Lakes Region and Bulk Water Exports

Abstract

The article provides an overview of the latest developments in the debate concerning the bulk water export of Great Lakes water. It examines the policy and legal dimensions of this new debate. The policy dimension focuses on the public attention and concern, in Canada, regarding bulk water removals from the Great Lakes basin. This concern has triggered the new Canadian federal legislation banning water exports from the region (Bill C-15). Is this a sign that the Canadian government now embraces a water conservation ethic? Is its position in line with the recent recommendations on the issue of the International Joint Commission (IJC), the joint body created by the United States and Canada to manage its shared waters? The attempt by investors to export water from the Great Lakes basin raises issues regarding Canada's obligations under international and regional trade agreements, most notably the General Agreement on Tariffs and Trade (GATT) and the North American Free Trade Agreement (NAFTA). The article examines the provisions of those two trade agreements in the context of the water export debate in Canada and concludes that increased clarity on Canada/US transboundary water issues is required.     

AMPHIBIAN OCCUPANCY IN FLOOD‐CREATED AND EXISTING WETLANDS OF THE LOWER MISSOURI RIVER ALLUVIAL VALLEY

During the previous century, the wetland area in the lower Missouri River alluvial valley was reduced by 39% because of river channelization and bank stabilization projects. The Great Flood of 1993 reversed the trend of wetland loss by creating 466 new wetlands in the alluvial valley between Kansas City and St. Louis, Missouri. We estimated amphibian occupancy, detection probability and number of species exhibiting evidence of reproduction in eight flood‐created and 16 pre‐flood existing wetlands from 1996 through 1998. We also evaluated whether hydroperiod (the number of days any water was present in a wetland from 20 February through 31 August) and distance to river predicted those values. Detection probabilities for adult amphibian species were relatively constant across years and ranged from 0.013 [Great Plains toad (Anaxyrus cognatus)] to 0.280 [Woodhouse's toad (Anaxyrus woodhousii woodhousii)]. Occupancy of adult amphibians differed across years and was not correlated with habitat features. Estimated occupancy probabilities for amphibian species ranged from 0.126 [Plains spadefoot (Spea bombifrons)] to 0.896 [boreal chorus frog (Pseudacris maculata)]. Almost double the number of amphibian species showed evidence of reproduction in existing wetlands (wetlands created before the Great Flood of 1993) when compared with that in flood‐created wetlands. Similarly, temporary wetlands had nearly double the number of amphibian species showing evidence of reproduction when compared with permanent wetlands. Finally, the highest number of species showed evidence of reproduction in wetlands with spring–summer hydroperiods between 135 and 140 days. All these relationships suggest that the invasion and persistence of predators in wetlands negatively influence amphibian reproduction. If the Missouri River is allowed to reconnect with the alluvial valley, more predators may be introduced into wetlands, leading to reduced amphibian occupancy and reproduction. However, this connection will not likely occur over the entire alluvial valley and, therefore, should not adversely impact amphibians that find refuge in higher‐elevation, non‐connected regions of the alluvial valley. Copyright © 2011 John Wiley & Sons, Ltd.     

回归传统价值:《了不起的盖茨比》的救赎之路

《了不起的盖茨比》生动地描述了二十世纪二十时代的美国社会丰裕物质生活与精神荒原的冲突。美国梦的幻灭、道德和宗教信仰体系的坍塌引发了菲茨杰拉德对美国精神和传统价值观的思索,呼吁回归传统价值观,重塑道德体系。     

Sediment Resuspension and Hydrodynamics in Lake Okeechobee during the Late Summer

In this study, in order to better understand the mechanisms affecting sediment resuspension, extensive data sets were collected in September and October of 2002 including wind velocity, wave, current velocity, water temperature, total suspended solid, suspended sediment concentration, and total phosphorus. Analyses of these data indicate that waves are the dominant factors in sediment resuspension while wind-induced currents are the primary forces to transport suspended sediments. Surface and bottom currents frequently flow in opposite directions, forming a stratified water column. A time lag exists between currents near lake bottom and wind forcing at the surface. The diurnal thermal stratification occurs in the deep region of the lake. A time lag is also found between suspended sediment concentration and wind speed. The study provides valuable storm-event data and mechanism analyses, which can improve our understanding of the lake circulation, wave dynamics, and their impact on sediment resuspension and vertical mixing in Lake Okeechobee. The data resulting from this study will be used to validate the Lake Okeechobee Environment Model which is used to predict the impacts of different management scenarios on lake activities.     

Local demand shocks and firms' survival: An application to the Italian economy during the Great Recession

The Italian economy is characterised by a large number of micro-firms and small firms and by a long-lasting gap between North and South Italy. Therefore, global shocks – such as the Great Recession – have had a heterogeneous impact at the local level: the collapse in private demand was unequally distributed across different products, services and regions. The aim of this paper, therefore, is to evaluate the impact of the Great Recession on firm's survival for the universe of Italian firms in the light of two relevant indicators: local exposure to crisis and local demand shocks. The results suggest a strong negative impact of local demand shocks on the survival of firms, whereas the degree of exposure to the crisis generally has a weak effect.     

A tale of two Great Lakes conferences: Urging global collaboration on our largest freshwater resources

Scientific meetings and conferences are a part of the scientific process, and can facilitate collaboration, idea-sharing, and harmonization of research and management. The success of a conference can be measured using many criteria, including consistency and reoccurrence of the meetings, credibility by participation of reputable professionals, and attendance by a diverse community. In the interest of increasing the success of large-lake, freshwater science, policy, and management, this comment focuses on two recent conferences attended by the authors: the 60th annual meeting of the International Association for Great Lakes Research, in Detroit, U.S.A., and the African Great Lakes Conference, in Entebbe, Uganda. By our measures of success, we suggest that to make a larger impact on research, policy, and management of global, large, freshwater lakes that each conference can improve, either through greater diversity of experts from the global freshwater research community, or by consistently reoccurring on a regular basis.     

Relative contributions of nearshore and wetland habitats to coastal food webs in the Great Lakes

Hydrologic linkages among coastal wetland and nearshore areas allow coastal fish to move among the habitats, which has led to a variety of habitat use patterns. We determined nutritional support of coastal fishes from 12 wetland-nearshore habitat pairs using stable isotope analyses, which revealed differences among species and systems in multi-habitat use. Substantial (proportions?>?0.30) nutrition often came from the habitat other than that in which fish were captured. Nearshore subsidies to coastal wetlands indicate wetlands are not exclusively exporters of energy and materials; rather, there is reciprocity in the mutual energetic support of nearshore and wetland food webs. Coastal wetland hydrogeomorphology influenced the amount of multi-habitat use by coastal fishes. Fishes from systems with relatively open interfaces between wetland and nearshore habitats exhibited less nutritional reliance on the habitat in which they were captured, and higher use of resources from the adjacent habitat. Comparisons of stable isotope analyses of nutrition with otolith analyses of occupancy indicated nutritional sources often corresponded with habitat occupancy; however, disparities among place of capture, otolith analyses, and nutritional analyses indicated differences in the types of support those analyses inform. Disparities between occupancy information and nutritional information can stem from movements for support functions other than foraging. Together, occupancy information from otolith microchemistry and nutritional information from stable isotope analyses provide complementary measures of the use of multiple habitats by mobile consumers. This work underscores the importance of protecting or restoring a diversity of coastal habitats and the hydrologic linkages among them.