共查询到20条相似文献，搜索用时 62 毫秒
1.
王宝琪 《小学生之友(智力探索版)》2002,(Z1)
船速一定的轮船往返于上、下游两个码头之间一趟,和在静水中往返同样距离所花的时间一样吗?假如问起这个问题,也许有人会这样回答,这两次往返所费的时间是一样的。因为在河水中,轮船去时遇到逆流,速度虽然减小了,但回来时就是顺流,速度增加,轮船去时多用的时间,被回来时少花的时间一抵消,岂不是跟在静水中往返一次花费一样的时间吗?”其实,这种说法是似是而非的。 相似文献
2.
孙昆峰 《河北能源职业技术学院学报》2006,6(3):51-54
利用自然对流物理模型,采用SIMPLE算法,对流扩散项采用二阶迎风格式.计算研究了有水平等温阻流件的二维封闭方腔中空气的自然对流换热.得出了在一定的Ra下,具有不同长度的阻流件的平均Nu数.有水平阻流件的封闭方腔与无阻流件时相比,相同条件下自然对流的换热系数随阻流件长度的增加先略减少,然后增加.而且随着阻流件长度变化,在方腔内的环流由一个增加到两个和三个.同时阻流件布置在不同壁面上的布置方式对换热强度也有一定影响. 相似文献
3.
本文研究了各种型式肋片在辐射—对流—导热联合作用和变热特性参数条件下,稳态和非稳态传热时的通用数学物理模型和数值计算方法．为编制通用程序奠定了基础。 相似文献
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在有效场理论和切断近似的框架内,研究了二模磁场中随机晶场作用的混合自旋横向Ising模型的临界行为.在T-h相图中,晶场浓度对有序相的影响需要将二模磁场分段考虑;大的晶场和适当的晶场浓度有利于二级重入相变现象;但横场对三临界点的作用值得更多研究.在T-D相图中,负晶场比例较大降低有序相,正晶场比例较大增大有序相;强二模磁场和横场都抑制有序相,但强二模磁场有利于三临界点的出现,而横场抑制三临界点.在T-Ω相图中,晶场和晶场浓度对有序相范围有显著影响. 相似文献
5.
《浙江大学学报(A卷英文版)》2016,(8)
目的:为更好地评价填埋场覆盖层系统的闭气性能,建立水气耦合条件下的覆盖层中气体运移模型。在此基础上分析大气压强波动、渗透系数变化和对流扩散等因素耦合作用下填埋气在覆盖层中的运移规律。创新点:建立水气耦合条件下填埋气在覆盖层中的运移模型,分析多种因素耦合作用下填埋气的运移过程,并比较对流运移和扩散运移的相对重要性。方法:1.通过理论分析,建立考虑压强、对流、扩散和非饱和情况的填埋气耦合运移模型;2.通过试验拟合,得到大气压强波动的拟合经验公式(公式(22)),构建考虑压强波动下填埋气多场耦合运移模型;3.通过仿真模拟,验证所建模型的可行性和正确性(图2),并分析包含大气压强波动和渗透率等影响因素作用下填埋气的运移规律(图6~8)。结论:1.覆盖层厚度从1米变化到2米,覆盖层中填埋气的浓度变化可达31%;2.对于受大气压强波动影响较大的覆盖层系统(如1×103 Pa),不能忽略压强波动对填埋气运移的影响;3.气体渗透系数在初期对气体运移有较大影响,随运移时间增加直至气体运移达到稳定状态,渗透率的影响可以忽略(仅3%)。 相似文献
6.
《实验室研究与探索》2016,(1)
为了进一步研究不同地震破坏程度后黄土的变形特性及稳态强度,通过MTS土动三轴仪进行了不同围压(100、150、200 k Pa)、不同动应变(0,1%、2%、3%)条件下的饱和黄土静力剪切试验。结果表明:在相同试样条件下,应力路径对稳态强度影响极小,不同震动破坏程度的试样在试验结束后的残余强度几乎相等;黄土液化后的稳态强度随着初始孔隙比的减小而增加;饱和度主要对黄土的黏聚力产生影响;初始有效固结压力与稳态强度有良好的拟合关系。比较震后斜坡重力驱动剪应力与稳态强度的关系,可判断斜坡会否发生破坏。 相似文献
7.
采用动电位扫描结合SEM和XRD等技术研究先进电子制造封装过程中Sb掺杂对64Sn-35Bi-1Ag钎焊料在3%（wt.）NaCl溶液中腐蚀和电化学迁移行为影响。结果显示：Sb掺杂前后腐蚀电流密度（Icorr）随着Sb含量增加而有较显著的变化。其中当Sb含量小于1%时,随着Sb含量增加,其腐蚀电流密度（Icorr）减小。当Sb含量大于1%时,其腐蚀电流密度（Icorr）随着Sb含量的增大而增大;不论掺杂多少量,Sb掺杂后,钎料的腐蚀速率显著的增大,说明Sb掺杂后64Sn-35Bi-1Ag更易被腐蚀。电化学迁移结果显示,Sb掺杂前后,枝晶生长的速率显著不同,且枝晶成份有较大差异,掺杂后大于掺杂前,说明Sb掺杂不利于先进电子制造和封装技术。 相似文献
8.
研究了Nd8Fe86B6合金在不同快淬速度下显微组织的变化.当快淬速度为12m/s时,快淬带的组织为纳米晶的Nd2Fe14B相和α-Fe相;当快淬速度增加到15m/s时,快淬带的组织为少量的α-Fe相和大量的非晶相;当快淬速度增加到18m/s时,快淬带的组织为完全非晶相. 相似文献
9.
SH波在正交各向异性功能梯度材料直裂纹处的散射 总被引：2，自引：0，他引：2
研究了正交各向异性功能梯度材料中直裂纹对SH波的散射问题,材料两个方向的剪切模量和密度假定为指数模型,通过积分变换-积分方程方法,建立数学模型,化为对偶积分方程,用Copson方法求解对偶积分方程,最后得到动应力强度因子,并且给出了数值算例,讨论了在SH波作用下,裂纹尖端的动应力强度因子与入射波的频率,入射角的关系． 相似文献
10.
针对DZ125合金通过不同的热处理工艺,及组织形貌的观察,研究不同固溶温度对DZ125合金中碳化物演化规律的影响,结果表明,DZ125合金在不同状态及不同固溶温度下碳化物具有不同的形态.铸态DZ125时合金中为大块的MC碳化物,随着热处理的进行,固溶温度的提高,大块的MC碳化物逐渐分解为沿着晶界不连续析出的粒状M23C6型碳化物,可以抑制晶界滑移,提高合金的强度.经过标准热处理后合金枝晶间γ'相较为粗大,组织并不均匀.但经过高温固溶及时效处理后可消除合金在枝晶间区域存在中的粗大γ'相,使高体积分数细小立方γ'相均匀分布在枝晶间和枝晶干区域. 相似文献
11.
罗艳萍 《读与写:教育教学刊》2008,5(6)
The communication of people partially is the communication of cultures. Culture has a direct effect on international commercial activities in all aspects. Different conceptions about time, space, equality, law and the like, lead people to deal with things in different ways. So to know cultures of the counterpart is to facil-itate our enterprises so as to have a smooth and successful communication in commercial activity. 相似文献
12.
Richard Denner 《海外英语》2007,(4):14-15
Rosco and I wait for the fishermen to return.I sit at a wooden bench near the store at Mt.Baker Resort and watch the clouds change shape. Rosco has my belt around his neck and an eight foot tow chain hooked to a tree. Dogs must be on a leash. Ducks and rabbits are loose. 相似文献
13.
Given a graph G,a subgraph C is called a clique of G if C is a complete subgraph of G maximal under inclusion and |C|≥2. A clique-transversal set S of G is a set of vertices of G such that S meets all cliques of G. The clique-transversal number, denoted as TC (G), is the minimum cardinality of a clique-transversal set in G. The clique-graph of G, denoted as K (G), is the graph obtained by taking the cliques of G as vertices, and two vertices are adjacent if and only if the corresponding cliques in G have nonempty intersection. Let F be a class of graphs G such that F={G|K(G) is a tree}. In this paper the graphs in F having independent clique-transversal sets are shown and thus TC (G)/|G|≤1/2 for all G ∈ F. 相似文献
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《海外英语》2007,(5):10-11
Many college freshmen arrive woefully unprepared to do college work, and as disadvantaged populations continue to grow, the share of the American work force that has made it through college is expected to plummet. Many experts blame that educational failure not just on high schools but also on colleges. School & College, a special report by The Chronicle, looks at efforts to fix the system. What reforms would better prepare students for college? What should schools and colleges be doing differently? How should state and federal officials help? 相似文献
17.
陈美曦 《山东教育学院学报》2008,23(2):103-107
Different nations have different social cultures, and the social culture of every nation is developing with the development of the nation, language is greatly influenced by social culture, which enables language to possess national and historical characteristics. Word is the smallest, independent, meaningful linguistic unit of language. It can well reflect the national and historical characteristics. From synchronic aspect, the social and cultural influence on word meaning is mainly embodied in conceptual and associative meanings of word. The incorrespondence of word meaning is a phenomenon that exists in both conceptual and associative meanings of word among different languages. From diachronic aspect, the development of social culture causes some changes of word meaning to some extent. Therefore, social culture plays a key role in vocabulary learning and mastery of a language. 相似文献
18.
邱崇丙 《唐山师范学院学报》2014,(1):21-23
汉字的六书,《说文》对“转注”一类,语焉不详。后世学者提及转注,也仅限于许慎所举出的例字。《汉字例说》一文,作者从转注的角度综合考虑,对部分现代常用字作了分析,跟传统的解释有所不同。希望能抛砖引玉,互相切磋,以推进学术研究。 相似文献
19.
《海外英语》2007,(4):36
There are numbers of crossroads on our long and unpredictable life journey where we totally have no idea about which direction to choose. No matter what our decision is, we should not turn back, but face the music and go ahead instead. I am this kind of girl who always does try without regretting, one example is how I dealt with my love. 相似文献
20.
Migration occurs behind a variety of reasons and has a great effect on the whole world. People may migrate in order to improve their economic situation, or in order to escape civil strife, persecution, and environmental disasters. The impact of migration is complex, bringing both benefits anddisadvantages. This paper briefly talks about the causes of migration, the allocation of benefits, and the ways in which individual countries and the international community deal with this important subject. 相似文献