雷诺数是一个无因次数群,无论采用何种单位制,只要数群中各物理量的单位一致,算出的雷诺数相等。
参考答案:对
下列有关文学常识的表述,不正确的一项是( )
A.先秦两汉历史散文内容丰富,形式多样。有编年体的《左传》,有国别体的《国语》《战国策》,有纪传体的《史记》和《汉书》等。
B.盛唐出现了两大诗歌流派:以高适、岑参为代表的边塞诗派,以王维、谢灵运为代表的山水田园诗派。其中王维的诗被誉为“诗中有画,画中有诗”。
C.《欧也妮•葛朗台》是法国批判现实主义作家巴尔扎克的小说,它塑造了“守财奴”老葛朗台这一经典的形象,揭露了资本主义的罪恶。
D.创作于三十年代的《边城》、《竹林的故事》均是我国 “乡土文学”的优秀作品。其作者分别是沈从文、废名。
In meditation (冥想), people sit quietly and focus their attention on their breath. As they breathe in and out, they attend to their feelings. As thoughts go through their minds, they let them go. Breathe. Let go. Breathe. Let go. According to a recent study at the Insight Meditation Society in Barre, Massachusetts, three months of training in this kind of meditation causes a marked change in how the brain allocates (分配) attention. It appears that the ability to let go thoughts that come into mind frees the brain to attend to more rapidly changing things and events in the outside world. Expert mediators are better than other people at catching such fast-changing stimuli(刺激), like facial-expressions. The study provides evidence for changes in the workings of the brain with mental training. People can learn and improve abilities of all sorts with practice, everything from driving to playing the piano. The study has shown that meditation is good for the brain. It appears to reduce pressure and promote a sense of well-being. In an experiment, 17 volunteers with no meditation experience in the experimental group spent three months meditating 10 to 12 hours a day. A control group also with no meditation experience meditated for 20 minutes a day over the same period. Both groups were then given the tests with two numbers in a group of letters. As both groups looked for the numbers, their brain activity was recorded. Everyone could catch the first number. But the brain recordings showed that the less experienced mediators tended to grasp the first number and hang onto it, so they missed the second number. Those with more experience gave less attention to the first number, as if letting it go, which led to an increased ability to grasp the second number. This shows that attention can change with practice. Just ask Daniel Levision, who meditated for three months as part of the study. "I am a much better listener," he said, "I do not get lost in my own personal reaction to what people are saying. \
Meditators manage their daily tasks better because they ______.
A.are given less pressure
B.allocate their attention better
C.have more stimuli for life
D.practice them more frequently