共查询到20条相似文献，搜索用时 187 毫秒
1.
Morse势阱中三次谐波产生的研究 总被引：1，自引：0，他引：1
利用量子力学中的密度矩阵算符理论,推导在具有多频率的复光场作用下线性和非线性极化率的一般表达式,然后利用图形技术,即利用费曼(Feynman)图方法来考虑三阶非线性过程,得到三次谐波系数的解析表达式.并以典型的GaAs/AlGaAs Morse势阱为例引入参数进行数值计算.结果表明,在该系统中得到了比体材料大的三次谐波系数,并适当增大势阱参数a可以获得较大的三次谐波系数;三次谐波系数随着弛豫常数hГ减小而增大. 相似文献
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分别求出了一类平面三次系统q=p=0型奇点结构的两种相关判定量的前9个和前6个量,并证明当这些量都为0时后面的量将均为0;然后根据这些判定量具体分析出这类系统原点为中心或焦点的所有可能情形,并给出了应用实例. 相似文献
3.
王庚运 《湖南农业大学学报(自然科学版)》1981,8(1)
本文从理论上研究了自控系统对单位阶跃的响应时正确使用FFT的途径和方法.对单位阶跃U(t)进行FFT时,由于取样范围T有限,频谱渗漏效应使得频率域的点ω_n=2nπ/T的频谱U(jω_n)=0.对U(t)的连续频谱U(jω)进行离散采样,将其和系统的传递函数对应相乘,再对积进行逆FFT,就求出系统的响应C(K△t),等距值△t和系统响应的带宽互为倒数关系,根据系统参数和给定的过渡过程时间指标确定带宽,由它确定△t值,把频谱混迭效应形成的误差限制在给定的精度之内. 相似文献
4.
邓远北 《湖南农业大学学报(自然科学版)》1984,11(3)
在本文中我们证明了,若f(z)为单叶函数族K内的一函数,(w)为其逆并且(w)=w sum from n=1 to ∞ r_nw~n,则当n=8时,|r_n|1,等号成立仅当f(z)为f_0(z)=z/1-z及其族转的情形。在此之前,Libera,R.J.和Zlotkiewicz,E.J.考察了1n7时的情形。 相似文献
5.
泰勒(Taylor)中值定理是微分学中1个重要的定理之一,在一般的数学分析或高等数学教材中,该定理的证明是先构造函数的n次泰勒(Taylor)多项式,然后再给出证明.本文给出1个别于传统的证明.教学实践表明,这种证明学生易于掌握. 相似文献
7.
本文所讨论的是载有集中质量的梁的振动频率.假设粱的一端由恒定刚度的弹簧铰定,另一端是自由的.通过频率方程求解,发现了极值频率定理.理论证明:如果集中质量很小(对梁的质量而言),当集中质量的位置改变,位于无载梁的某次简正振动的节点(腹点),振动频率具有极大(极小)值.极大频率就是梁在该次的简正振动的频率,与集中质量的大小无关;极小频率却与质量有关.最后在改变边界条件的情况下,梁振动的极值频率定理也被研究是成立的.所以本定理具有普遍意义. 相似文献
8.
为减少白菜冷库贮藏期间由于微生物活动所造成的损失,以细菌和霉菌为指示性微生物,研究不同臭氧浓度、处理时间和处理频率对白菜表面细菌和霉菌的抑菌效果,并以霉菌抑菌率为响应指标,利用响应面法优化臭氧处理技术参数,结果确定臭氧处理白菜的最佳条件为:臭氧浓度13.91mg.m-3,臭氧处理时间30min,处理频率1d.次-1。试验证明冷库贮藏白菜采用臭氧处理效果明显,方法可行。 相似文献
9.
提出了一个全差分式电流控制电流传输器电路(FDCCCII),分析了其工作原理. 该全差分式电路具有电流控制功能,并能抑制偶次谐波和共模干扰. 仿真结果表明,在0～30 MHz的频率范围内,提出的电路满足FDCCCII理想端口特性. 当偏置电流IB=1.3 μA时, FDCCCII电路的功耗为5.69×10-5 W. 据此电路设计了一个差分式电流控制电流模式滤波器,仿真结果证明该滤波器是可行的. 相似文献
10.
针对小型船舶电力推进系统产生的谐波对船舶电网电能质量的影响,建立了谐波分析模型,研究变频驱动产生的输入侧电流谐波在不同工作状态下谐波分布情况,并分析了电力推进系统的动、静态特性对系统产生谐波分布的影响,研究结果表明,谐波电流的大小主要由负载的大小决定,在特殊工况下,系统频率的变化及系统阻抗的变化对谐波分布产生较大影响. 相似文献
11.
Bailes M Bates SD Bhalerao V Bhat ND Burgay M Burke-Spolaor S D'Amico N Johnston S Keith MJ Kramer M Kulkarni SR Levin L Lyne AG Milia S Possenti A Spitler L Stappers B van Straten W 《Science (New York, N.Y.)》2011,333(6050):1717-1720
Millisecond pulsars are thought to be neutron stars that have been spun-up by accretion of matter from a binary companion. Although most are in binary systems, some 30% are solitary, and their origin is therefore mysterious. PSR J1719-1438, a 5.7-millisecond pulsar, was detected in a recent survey with the Parkes 64-meter radio telescope. We show that this pulsar is in a binary system with an orbital period of 2.2 hours. The mass of its companion is near that of Jupiter, but its minimum density of 23 grams per cubic centimeter suggests that it may be an ultralow-mass carbon white dwarf. This system may thus have once been an ultracompact low-mass x-ray binary, where the companion narrowly avoided complete destruction. 相似文献
12.
带杠杆千斤顶是基于地震、矿难、车祸等场合的救援或自救而自主研发的一种新型、简便、实用、高效的救援装置。由于其构造简单、携带方便,对于空间狭小且地表复杂的救援非常实用,亦可民用或作为工厂维修工具。本文对设计的原理方案、产品优点及使用进行了系统的说明。 相似文献
13.
Pathways for the reduction of protein disulfide bonds are found in all organisms and are required for the reductive recycling of certain enzymes including the essential protein ribonucleotide reductase. An Escherichia coli strain that lacks both thioredoxin reductase and glutathione reductase grows extremely poorly. Here, we show that a mutation occurring at high frequencies in the gene ahpC, encoding a peroxiredoxin, restores normal growth to this strain. This mutation is the result of a reversible expansion of a triplet nucleotide repeat sequence, leading to the addition of one amino acid that converts the AhpC protein from a peroxidase to a disulfide reductase. The ready mutational interconversion between the two activities could provide an evolutionary advantage to E. coli. 相似文献
14.
在半封闭池塘中混养红鳍东方鲀Fugu rubripes和日本对虾Penaeus japonicus,同时施用复合微生态制剂（每次换水后施用剂量为0.45 g/m3）,对池塘水体中的溶解氧、氨氮、亚硝酸盐氮和化学需氧量进行了监测,并对红鳍东方鲀和日本对虾的成活率和生长情况进行了观察。结果表明：与对照池相比,试验池的溶解氧浓度提高了14.6%,氨氮浓度降低了26.1%,亚硝酸盐氮降低了28.4%,化学需氧量浓度降低了19.8%;与对照池相比,试验池中红鳍东方鲀的体重和成活率分别提高14.3%、6.4%,日本对虾的体长、体重及成活率也分别提高10.3%、15.4%、5.6%。这说明该复合微生态制剂对改善混养池塘水质具有很好的效果,同时对提高红鳍东方鲀和日本对虾的成活率以及促进其生长方面都有很好的作用。 相似文献
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When the sensory fiber of a Pacinian corpuscle (in cat mesentery) is transected (at the inferior mesenteric nerve) transduction fails within 30 hours: the nerve ending produces no generator potentials in response to mechanical stimulation. Electrically elicited nerve impulse conduction continues for at least another 18 hours. A transducer mechanism develops on a regenerating nerve fiber when this fiber enters the denervated corpuscle. Such transducer development takes place on myelinated fibers from the inferior mesenteric nerve, which normally supplies corpuscles, as well as on myelinated hypogastric nerve fibers, which normally do not go to corpuscles, including fibers larger than the original corpuscle afferents. 相似文献
17.
索道承载索张紧度的研究 总被引：3，自引：2，他引：1
本文给出承载索倾斜中央挠度系数即承载索张紧度的概念,并从承载索的安全性和耐久性出发,讨论了张紧度和中央挠度系数允许的范围及其适宜值,所得结果便于承载索的设计、安装架设和检测 相似文献
18.
研究了一类p-Ginzburg-Landau（p〉0）模型的渐近性态.通过局部分析的技巧,推出了泛函的正则性估计.在此基础上,利用Euler方程解的正则性估计及渐近行为,得到了极小元的C1,α收敛. 相似文献
19.
JK Gimzewski C Joachim RR Schlittler V Langlais H Tang I Johannsen 《Science (New York, N.Y.)》1998,281(5376):531-533
Experimental visualization and verification of a single-molecule rotor operating within a supramolecular bearing is reported. Using a scanning tunneling microscope, single molecules were observed to exist in one of two spatially defined states laterally separated by 0.26 nanometers. One was identified as a rotating state and the other as an immobilized state. Calculations of the energy barrier for rotation of these two states show that it is below the thermal energy at room temperature for the rotating state and above it for the immobilized state. 相似文献
20.
CCAAT-enhancer binding protein: a component of a differentiation switch 总被引：95，自引：0，他引：95
The CCAAT-enhancer binding protein (C/EBP) has now been found to promote the terminal differentiation of adipocytes. During the normal course of adipogenesis, C/EBP expression is restricted to a terminal phase wherein proliferative growth is arrested, and specialized cell phenotype is first manifested. A conditional form of C/EBP was developed, making it feasible to test its capacity to regulate the differentiation of cultured adipocytes. Premature expression of C/EBP in adipoblasts caused a direct cessation of mitotic growth. Moreover, when abetted by the effects of three adipogenic hormones, C/EBP promoted terminal cell differentiation. Since C/EBP is expressed in a variety of tissues, it may have a fundamental role in regulating the balance between cell growth and differentiation in higher animals. 相似文献