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1.
方庆清  焦永芳  李锐  汪金芝  陈辉 《物理学报》2005,54(4):1826-1830
采用溶胶-凝胶法制备了单轴M型锶铁氧体SrFe12-x12-xCrxxO 1919(x=0—1)超细晶粒.实验结果表明, 随掺杂量x的增大,质量饱和磁化强 度σss在x≤04范围内增大,在x=02附近达到极大值.矫顽力Hcc在x<05的范围 内单调降低,这对于用作高密度磁记录材料非常有利.当x≤04时,样品是单相结构, 在 x=06以后出现非磁性相α-Fe22O3< 关键词: 锶铁氧体 3+')" href="#">Cr3+3+ 结构 磁性  相似文献   

2.
采用高温固相法,通过阳离子替代的实验策略,制备出系列窄带发射且颜色可由深黄色调至绿色的K2-xNaxZn0.94SiO4∶0.06Mn2+(0≤x≤2)荧光粉。用X射线粉末衍射仪对样品的物相进行表征,通过扫描电子显微镜和能量色散谱测试对样品的形貌和元素分布进行分析。结果表明,成功地合成了纯相且元素分布均匀的K2-xNaxZn0.94SiO4∶0.06Mn2+(0≤x≤2)荧光粉。在蓝光激发下,随着Na+离子逐渐代替K+离子,K2-xNaxZn0.94SiO4∶0.06Mn2+(0≤x≤2)荧光粉的发光强度逐渐增强,原荧光粉的发光强度得到有效提高的同时发光颜色由深黄色调至绿色。在427 nm激光的激发下:当x=0.8时,...  相似文献   

3.
可兴奋性细胞混沌放电区间的识别机理   总被引:6,自引:2,他引:4       下载免费PDF全文
在神经起步点记录到加周期分岔过程的生理实验数据,在对此分岔过程中位于周期n爆发 和周期(n+1)爆发之间的混沌的峰峰间期数据检测不稳定的周期轨道时,发现从靠近周期 n爆发的混沌的峰峰间期数据中,可以检测出不稳定的周期n轨道;而从靠近周期(n+1)爆 发的混沌的峰峰间期数据中,不仅可以检测出不稳定的周期(n+1)轨道,还可以检测出不稳 定的周期n轨道.针对该现象,借助于Sherman建议的胰腺β细胞模型,从非线性动力 学角度给出了理论解释.指明了由鞍结分岔和倍周期分岔分别产生第一类阵发和第三类阵发 为出现该 关键词: 峰峰间期 不稳定的周期轨道 鞍结分岔 倍周期分岔  相似文献   

4.
基于多组态Dirac-Fock理论方法,利用GRASP92和RATIP以及在此基础上最新发展的RERR06程序,对类氢U91+(1s)离子的辐射复合截面以及辐射退激发过程进行了详细的理论研究.系统地计算了具有确定能量的连续电子被处于基态的类氢U91+(1s)离子俘获到nl (1≤n≤8, 0≤l≤6)轨道形成类氦U90+(1snl)离子的辐射复合截面,并研究了这辐射复合末态退激发谱的相对强度.研究发现,类氢U91+(1s)离子辐射复合到不同轨道的截面随其主量子数的增大而显著减小;同时,辐射复合末态的退激发对Kα谱线的相对强度有重要影响. 关键词: 辐射复合 多组态Dirac-Fock理论方法 辐射退激发  相似文献   

5.
对称混沌系统的非线性动力学行为及控制   总被引:6,自引:0,他引:6       下载免费PDF全文
于津江  张明轩  徐海波 《物理学报》2004,53(11):3701-3705
基于线性反馈控制思想,提出了一种对称动力学系统及其控制混沌的方法,给出了预期各周期轨道反馈系数的选择原则,适当选择反馈系数,即可得到不同的周期轨道.将此方法应用 到Logistic映射中,取得了良好的控制效果. 关键词: 反馈控制 周期转道 对称系统  相似文献   

6.
胡妮  刘雍  程莉  石兢  熊锐 《物理学报》2011,60(1):17503-017503
利用固相反应法制备了Mn位Fe3+和Cr3+掺杂的系列锰氧化物La0.4Ca0.6(Mn1-x(y)Bx(y))O3 (B=Fe3+ (0≤x≤0.1); Cr3+ (0≤y≤0.1)) 多晶样品,研究了掺杂对样品输运性质的影响.实验结果表明两种离子具有截 关键词: 锰氧化物 反铁磁 磁电阻效应  相似文献   

7.
应用三进制方法,分别在初始值x0取有限位小数、任意循环小数、任意不循环小数等3种情况重点讨论xn在区间[0,1]之内的帐棚映射的动力学特性.帐棚映射的归宿随初始值x0的不同而呈现多样性,有的趋于0,有的趋于-∞,有的在区间[0,1]内的周期轨道上,还有的在区间[0,1]内的混沌轨道上.  相似文献   

8.
田顺宝  林祖纕 《物理学报》1986,35(8):1108-1114
用固相反应、X射线衍射、金相显微镜观察、测定比热和复平面阻抗谱的方法研究了Na3Zr2-xInxSi2-xP1+xO12系统。在此系统中存在两种固溶体:单斜固溶体(0≤x<0.8)和三方固溶体(0.8≤x≤1.8)。即从x=0.8的组成开始,NASICON型Na3Zr2-xInxSi2-x 关键词:  相似文献   

9.
制备了Gd3(Fe1-xCox)25Cr4(0≤x≤0.6)和Gd3Fe29-yCry(3.5≤x≤5.0)化合物,通过X射线衍射和磁性测量手段研究了它们的结构和磁性.实验表明这些化合物都属于A2/m空间群.Cr含量增加导致居里温度下降,饱和磁化强度降低,磁晶各向异性场下降.Co替代Fe导致单胞体积收缩,居里温度升高,5K的饱和磁化强度在x=0.3左右达到极大值,磁晶各向异性在x=0.4附近由易面转变为易轴. 关键词:  相似文献   

10.
二维均匀耦合映象格子中的时空周期图案   总被引:1,自引:0,他引:1       下载免费PDF全文
王志斌  胡岗 《物理学报》2001,50(9):1666-1669
目的——构造二维均匀耦合映象格子中的时空周期图案;方法——通过一维耦合映象格子模型的相空间中已知低空间周期轨道,直接构造二维均匀耦合映象格子模型中一系列空间周期轨道,而不必求解其模型方程,并对构造轨道的稳定性进行分析;结果——L2×L2雅可比矩阵可化简为几个2×2矩阵组成的对角矩阵;结论——所构造轨道的稳定性不可能比原来轨道的稳定性高. 关键词: 耦合映象格子 时空周期图案 雅可比矩阵  相似文献   

11.
F.H. Ling 《Physics letters. A》1985,110(3):116-120
A shooting type iterative method for determining bifurcation curves of mappings is developed in this paper. By using this method we are able to calculate bifurcation curves for orbits of periods ≤ 5 of a Hénon-like map in all details. We find an interesting phenomenon that two or more stable periodic orbits of the same or different periods may coexist for some combinations of parameter values. Two stable p5 orbits and their attracting regions are shown for (μ, b) = (1.536, 0.153).  相似文献   

12.
本文研究了标准映象的周期轨道在其余数R=1和R=0附近的行为,对于前者出现倍周期分岔序列,其分岔率δ及标度因子α和β与其它二维保面积映象的结果一致;对于后者发生同周期分岔,这与标准映象的奇对称性有关。文中还计算了混沌轨道的李雅普诺夫指数,发现在倍周期分岔序列的聚点k附近,存在标度关系: λ=λ+A(k—k)+B(k—k)τ, 其中因子τ=0.32。这与理论推断的结果τ=(ln(2))/(l 关键词:  相似文献   

13.
马文聪  金宁德  高忠科 《物理学报》2012,61(17):170510-170510
本文利用动力学变换方法和庞加莱截面方法对两种连续混沌动力学系统进行不稳定周期轨道探测研究, 并对Lorenz系统进行了替代数据法检验.结果表明:基于庞加莱截面的动力学变换改进算法 可有效探测连续混沌动力学系统中的不稳定周期轨道.  相似文献   

14.
We investigate the existence of several families of symmetric periodic solutions as continuation of circular orbits of the Kepler problem for certain symmetric differentiable perturbations using an appropriate set of Poincaré-Delaunay coordinates which are essential in our approach. More precisely, we try separately two situations in an independent way, namely, when the unperturbed part corresponds to a Kepler problem in inertial cartesian coordinates and when it corresponds to a Kepler problem in rotating coordinates on ?3. Moreover, the characteristic multipliers of the symmetric periodic solutions are characterized. The planar case arises as a particular case. Finally, we apply these results to study the existence and stability of periodic orbits of the Matese-Whitman Hamiltonian and the generalized Størmer model.  相似文献   

15.
The unstable periodic orbits of a chaotic system provide an important skeleton of the dynamics in a chaotic system, but they can be difficult to find from an observed time series. We present a global method for finding periodic orbits based on their symbolic dynamics, which is made possible by several recent methods to find good partitions for symbolic dynamics from observed time series. The symbolic dynamics are approximated by a Markov chain estimated from the sequence using information-theoretical concepts. The chain has a probabilistic graph representation, and the cycles of the graph may be exhaustively enumerated with a classical deterministic algorithm, providing a global, comprehensive list of symbolic names for its periodic orbits. Once the symbolic codes of the periodic orbits are found, the partition is used to localize the orbits back in the original state space. Using the periodic orbits found, we can estimate several quantities of the attractor such as the Lyapunov exponent and topological entropy.  相似文献   

16.
Debabrata Biswas 《Pramana》1997,48(2):487-501
We review some properties of periodic orbit families in polygonal billiards and discuss in particular a sum rule that they obey. In addition, we provide algorithms to determine periodic orbit families and present numerical results that shed new light on the proliferation law and its variation with the genus of the invariant surface. Finally, we deal with correlations in the length spectrum and find that long orbits display Poisson fluctuations.  相似文献   

17.
The low temperature specific heat of Bi-2212 and Y-123 is measured for 1.2≤T≤7K and 0≤B≤14 T. We find that the field-induced “linear” term λ*(B)?λ*(0) near 1–3K saturates for B≥8 T, decreases as a function of temeprature, and has nearly the same amplitude for both compounds. This is not easily reconciled with the predicted d-wave contribution C∝γT(B/Bc2)1/2. Oscillations of 2D vortices offer an alternative explanation.  相似文献   

18.
In this paper we analyze the existence of the periodic orbits of the static, spherically symmetric Einstein–Yang–Mills Equations by using the qualitative theory of the ordinary differential equation. We prove that there are no periodic orbits restricted to some invariant set of codimension 1. Furthermore if there is a periodic orbit out of this invariant set, then there must be other periodic orbits, which are symmetric to the first one. We also have results on the non–existence of periodic orbits when the cosmological constant is negative.  相似文献   

19.
Two methods are presented for controlling spatiotemporal chaotic motion in coupled map lattices to a kind of periodic orbit where the dynamical variables of all lattice sites are equal and act periodically as time evolves. Stability analysis of the periodic orbits is presented. We prove that especially the second controlling method can stabilize all the periodic orbits we concern. Basin of attraction and noise problem are discussed.  相似文献   

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