分类： 其他 >> 综合 提交时间： 2018-03-16 合作期刊: 《中国科学院院刊》
分类： 机械工程 >> 机械制造自动化 提交时间： 2018-03-16
摘要： 根据移栽蔬菜田间锄草作业工况和要求，基于视觉伺服控制技术，设计了电驱锄草机器人系统。该系统以中小功率拖拉机为配套动力，由伺服电动机驱动月牙形锄草刀护苗锄草和对行，减少了能耗与污染物排放，提高了系统伺服特性。机器视觉系统实时采集田间图像并处理，对作物进行识别与定位。控制器结合视觉系统获取的刀苗距、锄草机器人前进速度、锄刀相位角度及机器人横向偏差信息，利用智能伺服驱动器精确控制锄草刀避苗和对行。试验表明，在前进速度不高于1.5km/h、作物株距不小于0.35m工况下，伤苗率小于10%，田间杂草锄净率约为90%。
分类： 机械工程 >> 机械制造自动化 提交时间： 2018-03-16
摘要： A machine-vision-based method of locating crops is described in this research. This method was used to provide real-time positional information of crop plants for a mechanical intra-row weeding robot. Within the normalized red, green, and blue chromatic coordinates (rgb), a modified excess green feature (g-r>T & g-b>T) was used to segment plant material from back ground in color images. The threshold T was automatically selected by the maximum variance (OTSU) algorithm to cope with variable natural light. Taking into account the geometry of the camera arrangement and the crop row spacing, the target regions covering the crop rows were defined based on a pinhole camera model. According to the statistical variation in the pixel histogram in each target region, locations of the crop plants were initially estimated. To obtain the accurate locations of crops, median filtering was conducted locally in the bounding boxes of the crops close to the bottom of the images. For the lateral guidance of the robot, a novel method of calculating lateral offset was proposed based on a simplified match between a template and the detected crops. Field experiments were conducted under three different illumination conditions. The results showed that the accurate identification rates on lettuce, cauliflower and maize were all above 95%. The positional error as within ±15 mm, and the average processing time for a 640×480 image was 31 ms. The method was adequate to meet the technical requirement of the weeding robot, and laid a foundation for robotic weeding in commercial production system.
分类： 生物学 >> 遗传学 提交时间： 2018-03-16
摘要： Mutations in PI3K and/or AKT have been reported in a variety of cancers. This indicates that the two pathways interact to cause cancer. We have therefore investigated their roles in gastric cancer (GC) in China. In our study, exons 9, 18 and 20 of PIK3CA gene and exons 6~14 of AKT2 gene were screened in 10 GC cell lines and 100 advanced primary GC together with matched normal tissues. Denaturing high performance liquid chromatography (DHPLC) and DNA sequencing were used to analyze the mutations in the two genes. Two point mutations in the PIK3CA gene were identified in 4 of 10 GC cell lines and in 4 of 100 GC primary tumors. Two polymorphisms in AKT2 were detected in 19 of 100 GC primary tumors. One point mutation in AKT2 was detected in 1 of 10 GC cell lines and 3 of 100 GC primary tumors, and no hot spot variation was detected. Our results indicate that PIK3CA and AKT2 mutations are found in GC, although not a common event, therefore they might still play an important role in mediating kinase activities towards gastric carcinogenesis.
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