IEEE 802.11g标准的物理层采用了扩频技术，工作在（）频段。

事故经过：1992年10月15日某市日用化工厂一台泡花碱转体锅投入试运行。上午8时50分工人投料完毕，检查转体锅盖封盖无误之后，向锅内输入蒸汽，11时30分，压力指示为0.41～0.42MPa，设备运行正常，11时40分，在正常压力下运行的转体锅锅盖突然失去控制，沿车间厂房东北方向45°飞出，锅内约7000kg的泡花碱随蒸汽倾泻而出，致使在车间内的操作者一人重度烧伤，一人中度烧伤，二人轻度烧伤。此次事故造成直接原料损失1800元，医疗费30000元。事故原因分析：（1）事故发生的直接原因是由于转体锅盖压臂断裂。爆炸的转体锅是由甘肃某厂提供图纸，某市日化厂委托外厂加工制造的。转体锅罐体和锅盖压臂分别由两家工厂制造。由于压臂设计不当，制造时使用的材料又不符合图纸要求，使压臂能承受的作用力成倍降低，发生断裂，造成锅盖飞出。事故发生后，经过对压力臂断裂面的观察及对材料进行的化学成分分析和力学性能试验，发现钢材本身存在裂纹，各项指标不符合要求。（2）各级领导对转体锅压臂等部件同属压力容器承压部件认识不清，认为罐体已进行过强度试验，而忽视了设备的整体试验。在设备安全状况不明的情况下，盲目将具有先天缺陷的设备投入运行。事故责任者的处理：（1）厂长对压力容器的安全认识不足，缺乏有关的基本知识，自行套用他厂图纸委托外厂加工。加工厂家又使用不符合要求的材料制造设备部件，设备本身也带有先天性缺陷，存在事故隐患，将此设备投入试生产，必然会发生爆炸事故。因此厂长对这次事故负有主要领导管理责任，给予罚款300元的处理。（2）生产副厂长作为分管生产安全的负责人对这次事故负有重要领导管理责任，给予罚款150元处理。（3）设备主管、安全员在设备没有进行有关安全检验的情况下，允许车间投料生产，对这次事故负有直接管理责任，给予罚款100元的处理。（4）生产科长对安全检查不力，负有管理责任，给予罚款100元的处理。防止同类事故的措施：（1）压力容器的设计、制造要符合国家的规定，要由具有相应设计资格的单位进行设计和制造，不要套用他厂图纸委托无制造资格的工厂代为加工，以保证压力容器在投入使用前不存在先天性缺陷和事故隐患。（2）从工厂领导到车间工人都应该学习有关压力容器安全的基础知识和常识，提高管理水平和安全操作水平。问题：请简述安全生产责任制的主要内容。 点击查看答案

Archimedes was a famous Greek mathematician and scientist. He was born around 287 BC and he died in the year 212 BC. Archimedes is most well-known for one specific idea that he came up with. 'Archimede's Principle' states that a solid object which is immersed in a liquid is pushed up by a force which is equal to the weight of the water that the object moves. For example, if you put a piece of wood and a piece of gold the same size in water, only the wood will float. Both the wood and gold move the same amount of water, but the wood weighs less than this water, while the gold weighs more. It is believed that Archimedes discovered this principle when the king of Syracuse asked him to solve a problem. The king wanted to know if his crown was pure gold or a mixture of gold and silver. The king, of course, did not melt his crown to find out. The idea came to Archimedes as he lowered himself into his bath. He noticed how the water spilled out of the tub. He decided to use the same idea for the crown. He knew that a gold crown immersed in water would weigh more than one made of silver. The experiment was done and the goldsmith was proved guilty of trying to cheat the king.A good title for the selection is ______.A．ArchimedesB．Archimedes' PrincipleC．A gold and silver crownD．The king of Syracuse

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A．Archimedes
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