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46. A very common operation in industry is that of pick and place. This would be typified by a packing operation, such as that shown in the figure, where items are taken from a conveyor and placed into a pallet. The position of the item on the conveyor and the pallet position provide constraints on the endpoints of the trajectory of the item, but it does not matter from a functional point of view what path is taken by the robot. In practice, the path which gives the shortest time to perform the task will be the best. Note, however, that it will be desirable to constrain the robot to avoid collisions. Thus, once it has gripped the object it should move upwards from the conveyor, then move across to a position over the pallet, and then move downwards before releasing the object. VII. Read the following passage, and then fill in the table with the information based on the passage. (10%) What Could Possibly Go Wrong: Genetically-Modified Mosquitoes As carriers for diseases such as malaria, dengue fever and yellow fever, mosquitoes are the deadliest creatures on the planet, responsible for millions of human deaths every year. And as the planet warms, the insects are broadly expanding their turf and bringing their diseases with them; thousands of cases of dengue, a tropical disease, have appeared in the U.S. in the past five years. DDT was long used to control the mosquito population, but it is now widely banned, and in any case, many scientists believe that mosquitoes quickly build up a resistance to the insecticide. That, in part, is why the battle against mosquitoes has gone genetic. Generally speaking, the goal of gene-based mosquito-control projects is either to kill the insects or make them benign. Researchers at Johns Hopkins University, for example, are studying mosquitoes that were made malaria-resistant through the activation of a gene responsible for a protein that blocks the infection. And the British company Oxitec has engineered a strain of mosquito that cannot survive without regular doses of tetracycline; in the wild, these mosquitoes would survive just long enough to mate and pass on their tetracycline-junkie genes to their doomed offspring. In a trial in the Cayman Islands last year, Oxitec-modified mosquitoes were able to cut the overall population by 80 percent in just six months. But the problem is that we don’t fully understand how mosquitoes and the diseases they carry would adapt in response to such experiments. New strains of malaria and other diseases could emerge. Jo Lines, a malaria expert at the London School of Hygiene and Tropical Medicine has described the process as “a series of arms races that the [malaria] parasite has consistently won.” Three percent of the offspring from Oxitec’s tetracycline-dependent mosquitoes survive-what happens if those bugs breed with wild mosquitoes? It’s even possible that the changes we induce in mosquitoes could move into other animals. Horizontal gene transfer could result in midges, gnats and black flies developing the same mutations, including the unfortunate characteristic of dying shortly after hatching-and a mass die-off of insects that provide sustenance to birds, bats, frogs and fish would be a food-chain disaster. Genetically-Modified Mosquitoes | Why Genetically Modified | | Mosquitoes quickly build up a resistance to traditional ___47___. | | Goal of Gene-based Mosquito-control Projects | | To ___48___. | To ___49___. | | Possible Wrong Results | | New diseases ___50___. | Changes induced in mosquitoes ___51___. |
VIII. Directions: Write a passage (150-200 words) in English on the following title. Develop the ideas according to the Chinese outline given below. (15%) 52. School Education and Self-taught Learning (1)学校教育与自学的关系； (2)各自利弊； (3)你更喜欢哪种方式。
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