-R×S~n中具常平均曲率的类空超曲面

我们讨论-R×Sn中具有常平均曲率的类空超曲面,利用Omori-Yau广义极大原理得到关于Lorentzian乘积空间-R×Sn中具有常平均曲率的类空超曲面的Bernstein-type结果.     

关于矩阵值Lipschitz映射空间的若干研究

引入并研究了由紧的距离空间(K,d)到Mm,n(F)中的Lipschitz-α映射构成的空间Lα(K,Mm,n(F))和lα(K,Mm,n(F));并证明了它们关于范数‖f‖α=‖f‖∞ Lα(f)是Lipschitz空间;得到了lα(K,Mm,n(F))是Lα(K,Mm,n(F))的闭子空间;当0<α≤β≤1时,Lβ(K,Mm,n(F))是Lα(K,Mm,n(F))的闭子空间.     

形如Cn=(an+b)qn的数列快速求和

数列求和一直是高考的热点,因此,正确快速求和就显得尤为重要.对于一般的等差乘等比数列常用错位相减法来求和. 例 求Cn=(2n-1)2n的前n项和. 解:由Sn=1×2+3×22+5×23+…+(2n-1)·2n,得2Sn=1×22+3×23+5×24+…+(2n-1)·2n+1. 两式项减得:-Sn=2+2×22+2×23+…+2×2n-(2n-1)·2n+1.     

不同退火条件下Sn掺杂浓度对ZnO薄膜性能影响

采用溶胶-凝胶法提拉镀膜制备Sn掺杂ZnO薄膜,研究了空气退火、高真空退火(10-2Pa)、低真空退火(1 Pa)和循环退火四种条件下Sn掺杂浓度对SZO薄膜光电性能的影响。结果表明:四种退火条件下不同Sn掺杂浓度时制备的SZO薄膜均为纤锌矿结构且具有C轴择优取向生长特性,当Sn掺杂浓度为5 at.%时SZO薄膜的结晶生长最好。高真空退火条件下Sn掺杂浓度为3 at.%时,电学性能最优,其电阻率可达到5.4×10^(-2)Ω·cm。当Sn掺杂浓度小于3 at.%时,薄膜的可见光区平均透过率均大于85%,当掺杂浓度高于3 at.%时,薄膜的透过率随着掺杂浓度的增大而降低。     

错在哪里

1.数列{an}(n∈N*)的首项为14,前n项的和为Sn,点(an,an+1)在直线x-y-2=0上,则Sn的最大值为＿＿.错解:由题意得an-an+1-2=0,则an+1-an=-2,即数列{an}是等差数列,且其首项为14,公差为-2,故Sn=14n+n(n-1)/2×(-2)=-(n-15/2)2+225/4,从而Sn的最大值为225/4.     

对称群Sn的极小生成集

本文给出了Sn的几个子集，并证明了它们均可极小生成Sn。     

好题三解集锦

例1 在等差数列{an}中,a1=13,试求Sn的最大值. 解法1:由S3=S11得3a1 3×2/2d=11a1 11×10/2d,又a1=13, 所以8a1 52d=0,d=-2, 所以an=13 (n-1)×(-2)=15-2n. 令an≥0,即15-2n≥0,所以n≤7.5. 故当n=7时,Sn最大,且S7=49. 解法2:(同解法1)d=-2,     

等比数列和“和”性质与试题多解

设等比数列{an}的首项为a1，公比为q，前n项和为Sn，当q≠1时，除了课本中介绍的两个前n项和Sn公式，即Sn=a1(1-q^n)/1-q和Sn=a1-anq/1-q，及在数列中都有an=sn-sn-1，n≥2，S1，n=1，还可得到关于Sn的下列几个常见性质。     

等差数列“和”性质与试题多解

设等差数列{an}的首项为a1，公差为d，前n项和为Sn，除了课本中介绍前n项和Sn的两个公式，即Sn=(n(a1 an))/2和Sn=na1 (n(n-1)d)/2，以及在所有数列中都有an={Sn-Sn-1,n≥2, S1,n=1， 还可得到关于Sn的下列几个常见性质。     

公式Sn=A&#183;q^nA的一些应用

我们已经知道等比数列前n项和Sn(q≠1)公式为Sn=(a1(1-q^n))/1-q.在这个公式中若令a1/1-q=-A即可得Sn=Aq^n-A(A≠0，q≠1)．由此可得一个非常数的等比数列其前n项和具有Sn=Aq^n-A这样的特征．这个公式形式简洁，其应用较广．下面是这个公式的一些简单应用．     

卡思卡特城堡

It is worthy of noting that, whilst Crookston Castle witnessed the earlier and happier portion of Mary's variegated life,     

不同的吃喝玩乐

一、吃和喝吃苹果 eat an apple, 吃药 take medicine,吃糖 have some sweets,吃饭 have one's meals,吃馆子 dine out,吃惊 be surprised/     

漏洞百出的教育

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?     

只要努力,不要后悔

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.     

浅谈移民问题

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.     

Sister Carrie, an Adherent of Desires

Sister Carrie is one of the most controversial characters in American literature.Thought as a "fallen woman" firstly,she was defined as a "new woman" by some critics later. However, by digging into the motivaton behind the whole process of Carrie's "success", the relationship between Carrie and her creator (the author), the social conditions of then American, it can be found that Carrie has never been free-standing on her thought and she has never found her real-sdf even after becoming a famous actress. In a society dominated by mass consumerism Carrie is only an adherent of her own desires. She also is a representative of all those country girls flooded into cities, a symbol and a sacrifice of the urbanization of America in a time countryside was overcome by cities.     

Improvement of one-cycle controller by use of proportional integral differential controller

1.IntroductionOne-cyclecontrolmethod,whichwasproposedaboutonedecadeago[1],hasbecomeanattractivemethodinspecialfieldssuchaspowerfactorcorrection[2-6],switchingamplifiers[7,8],etc.Themainideaofthiscontrollerisbasedonintegrationofdiodevoltageinone-cycleandforcesittobeexactlyequaltothereferencevalue.Themainadvantageofthiscontrollerisitsrealtimeabilitytorejectthevariationofinputvoltage[1].Despitethisgreatability,ithasnogoodperformancesinrejectingofloaddisturbanceandfollowingreferencecommands.Espec…     

库克斯顿城堡

城堡, 是欧洲典型的建筑之一, 每个城堡都有一个美丽的传说或是一段历史。从本期开始, 我们将推出“城堡之旅”, 带各位读者去浏览、观赏欧洲各地的城堡, 开始一段文化与历史的旅途!     

胡主席在印度,我却在中国

Today, Sunday morning, I sit thinking and typing at my computer. My thoughts are in my homeland, India and my body is in China. The body is here and mind there for a good reason. Mr. Hu is president and I am resident and both are in each other's countries (what a difference the absence of one small letter makes!). Mr. Hu will return in a few days and I will stay on longer.