试题与答案

某起重机,只有两种交变载荷状态P1和P2(P1>P2),所对应的应力幅分别为σl和σ

题型:问答题

题目:

某起重机,只有两种交变载荷状态P1和P2(P1>P2),所对应的应力幅分别为σl和σ2,已知对应上述两个应力的疲劳破坏循环次数分别为。设计时考虑载荷P1和P2出现的频率分别为20%和80%。每年的载荷循环总次数按2404次/年考虑。试问:

1.该起重机的设计寿命为多少年?

2.该起重机投入使用后,由于工作条件发生变化,年载荷循环总次数比设计时考虑的增加了20%,起吊大载荷的频率也由原来的20%提高到40%。目前该起重机已使用4年。按实际工况,该起重机的总使用寿命为多少年?剩余使用寿命为多少年?注:计算过程中,精确到小数点后第1位。

答案:

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参考答案:C

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题型:完形填空

According to a new study, preschool boys perform better on tests that measure learning and other important skills when they are in classes that have more girls than boys. This doesn’t seem to apply to girls, though. For preschool girls, the presence or absence of boys does not affect learning.

“The study raises questions about having all-boy or all-girl classes for preschool”, says psychologist Arlen Moller, who led the study. She added, “Previous researches have shown that high-school girls may study better in all-g irl schools. In middle school, however, the effects of same-sex schooling are unclear, and even less is known for very young kids.” To find out, researchers studied 70 preschool classes with a total of 806 children who were between 3.5 and 6 years old. For each class, teachers recorded the student’s progress over a 6.5-month school year.

Their data included scores of motor skills, social skills and thinking skills. Researchers found that boys developed each of these skills more quickly when there were more girls in the class than boys.

In majority-girl classrooms, boys developed at the same rate as girls. But in classes where boys were the majority, boys developed more slowly than girls. Girls tended to advance in classrooms which had any combination of boys and girls.

The study is one of the first to look at how the proportion of boys and girls in a class affects learning. Because it’s a new finding, researchers don’t know why this difference exists.

“This is an exciting topic, but it’s too early to draw any conclusion because this area is so under-explored,” says psychologist Lean Malofeeva of the High/Scope Educational Research Foundation in Ypsilanti, Michigan.

81.What is the finding of the researchers led by Arlen Moller? (no more than 15 words)(2 marks)

                                                                       

82.According to the research , what effect does a minority-girl class have on boy’s study?(no more than 8 words)(3 marks)

                                                                       

83.How does Lean Malofeeva find the study of the researchers led by Arlen Moller?(no more than 6 words)(3 marks)

                                                                       

84.List three abilities the researchers focused on. (on more than 7 words)(3 marks)

                                                                       

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