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Transient ischemic attack (TIA) is defined as "an episode of focal loss of brain function attributed to ischemia that lasts less than 24 hours, is localized to a portion of the brain supplied by one vascular system, has no persistent deficit, and is not attributable to any other cause." Most TIAs are caused by small thromboemboli that originate in atheromatous areas in neck vessels or the heart. Other mechanisms include nonatherosclerotic vascular diseases, mitral valve prolapse, hematologic diseases, and abnormal blood pressure fluctuations. Even in series of fully investigated cases, there remains a group in which no cause can be found. The great majority of TIAs are extremely brief. In one series, 24% ended within 5 minutes, 39% in 15 minutes, 50% in 30 minutes, and 60% in 1 hour.  相似文献   
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Poverty,population and environmental degradation in China   总被引:7,自引:0,他引:7  
Rozelle S  Huang J  Zhang L 《Food Policy》1997,22(3):229-251
This article examines the relationship between poverty, population, and environmental degradation in China. Environmental conditions include water pollution, deforestation, destruction of grasslands, soil erosion, and salinization. The authors review China's success in controlling environmental degradation through leadership, environmental policies, and institutional capacity. Findings suggest that environmental progress is best achieved indirectly by poverty alleviation, market integration, and population control. Government policies were not very effective. Degradation occurs due to limited financial resources, poorly trained personnel, and political factors. Control of water pollution was instituted since the 1980s. The levels of pollutants have been reduced, but the type of pollutant determines the seriousness of impact. Water pollution is due to industrial wastes, agricultural run-off, and soil erosion. Since the 1970s, reforestation targets have not been met. Technical extension and monitoring of planting is not available in most areas, and private, profit seeking interests control acreage. Grassland destruction is due to deforestation, agricultural expansion, and overgrazing. Independent regional authorities have successfully managed pasture programs. Erosion is the most serious in Loess Plateau, the Red Soils area, the Northeast China Plain, and the Northwest Grasslands, which comprise 70% of total land area. In 1990, erosion control was practiced in 39% of eroded land area. Salinization has remained fairly constant. Environmental controls (direct regulation, planned recovery, and state-mandated technological improvements) are uneven. The main tool for environmental management is the State Environmental Protection Commission and its executive unit, SEPA. Problems stem from vague laws, lack of means of enforcement, lack of coordination of laws, and lack of standards, schedules, and other provisions in ordinances.  相似文献   
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Peak performance is often the beginning of failure. The process of continuously creating peak-to-peak performance defines the Genesis Enterprise. There will always be more problems than there are solutions. We need to install a process that anticipates and solves problems before they are problems and to continuously transform our organization into a championship organization that is nevertheless the underdog.  相似文献   
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