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1. chinaXiv:201911.00097 [pdf]

Review of Machine-Vision-Based Plant Detection Technologies for Robotic Weeding

Li,Nan; Zhang, Xiaoguang ; Zhang, Chunlong; Ge, Luzhen; He, Yong; Wu,Xinyu
Subjects: Computer Science >> Computer Application Technology

Controlling weeds with reduced reliance on herbicides is one of the main challenges to move toward a more sustainable agriculture. Robotic weeding is a thought to be a viable way to reduce the environmental loading of agrochemicals while keeping the operation efficiency high. One of the key technologies for performing robotic weeding is automatic detection of crops and weeds in fields. This paper presents an overview on various methods for detecting plants based on machine vision, mainly concentrating on two main challenges: dealing with changing light and crop/weed discrimination. To overcome the first challenge, both physical and algorithmic methods have been proposed. Physical methods can result in a more cumbersome machine while algorithmic methods are less robust. For crop/weed discrimination, deep-learning-based methods have shown obvious advantages over traditional methods based on hand-crafted features. However, traditional methods still hold some merits that can be leveraged to deep-learning-based methods. With the fast development of hardware technologies, researchers should take full advantage of advanced hardware to ease the algorithm design. In the future, the identification of crops and weeds can be more accurate and fine-grained with the support of online databases and computing resources based on the advances in artificial intelligence and communication technologies.

submitted time 2019-11-23 Hits22849Downloads1411 Comment 0

2. chinaXiv:201803.00957 [pdf]

Crop positioning for robotic intra-row weeding based on machine vision

Li, Nan; Zhang,Chunlong; Chen, Ziwen; Ma, Zenghong; Sun, Zhe; Yuan,Ting; Li, Wei; Zhang, Junxiong
Subjects: Mechanical Engineering >> Mechanical Manufacture and Automation

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.

submitted time 2018-03-16 Hits1804Downloads1079 Comment 0

3. chinaXiv:201605.01360 [pdf]

Increased Sensitivity of DNA Damage Response-Deficient Cells to Stimulated Microgravity-Induced DNA Lesions

Li, Nan; An, Lili; Hang, Haiying; Li, Nan
Subjects: Biology >> Biophysics

Microgravity is a major stress factor that astronauts have to face in space. In the past, the effects of microgravity on genomic DNA damage were studied, and it seems that the effect on genomic DNA depends on cell types and the length of exposure time to microgravity or simulated microgravity (SMG). In this study we used mouse embryonic stem (MES) and mouse embryonic fibroblast (MEF) cells to assess the effects of SMG on DNA lesions. To acquire the insight into potential mechanisms by which cells resist and/or adapt to SMG, we also included Rad9-deleted MES and Mdc1-deleted MEF cells in addition to wild type cells in this study. We observed significant SMG-induced DNA double strand breaks (DSBs) in Rad9(-/-) MES and Mdc1(-/-) MEF cells but not in their corresponding wild type cells. A similar pattern of DNA single strand break or modifications was also observed in Rad9(-/-) MES. As the exposure to SMG was prolonged, Rad9(-/-) MES cells adapted to the SMG disturbance by reducing the induced DNA lesions. The induced DNA lesions in Rad9(-/-) MES were due to SMG-induced reactive oxygen species (ROS). Interestingly, Mdc1(-/-) MEF cells were only partially adapted to the SMG disturbance. That is, the induced DNA lesions were reduced over time, but did not return to the control level while ROS returned to a control level. In addition, ROS was only partially responsible for the induced DNA lesions in Mdc1(-/-) MEF cells. Taken together, these data suggest that SMG is a weak genomic DNA stress and can aggravate genomic instability in cells with DNA damage response (DDR) defects.

submitted time 2016-05-11 Hits1694Downloads833 Comment 0

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