Extremal dynamics of the generalized Hutchinson equation

A scalar nonlinear differential-difference equation with two delays that generalizes Hutchinson’s equation is considered. The bifurcation of self-oscillations of this equation from the zero equilibrium is studied in the extremal situation when one delay is asymptotically large while the other parameters are on the order of unity. Analytical methods combined with numerical techniques are used to show that the well-known buffer phenomenon occurs in the equation in this case. This means that an arbitrary finite number of different attractors coexist in the phase space of the equation with suitably chosen parameters.     

光伏碲镉汞探测器在波段内连续激光辐照下的非线性响应机理研究

利用波段内连续激光, 辐照禁带宽度为0.33 eV的中波光伏碲镉汞探测器. 实验结果表明, 随着辐照激光光强的逐渐增大, 探测器从线性响应过渡为非线性响应. 当探测器进入非线性状态, 探测器的开路电压随激光光强的增大而减小, 且在激光开启辐照时开路电压信号迅速下跳, 在激光停止辐照时开路电压信号迅速上跳. 通过考虑激光辐照下探测器的温度场分布以及温度对p-n结内建电场的影响, 结合考虑机械快门在开启和关闭时对激光光强变化的影响, 建立了光伏探测器在波段内连续激光辐照下的解析模型, 模型计算结果与实验结果吻合得较好. 研究表明, 激光辐照过程中的非线性响应, 主要由温度对p-n结内建电场的影响决定, 激光开启和关闭时的开路电压的幅值是由光强和温度共同决定.     

加长棒脉冲钕玻璃激光器异常实验现象理论研究

以激光原理为基础, 以大量精确的实验数据为依据;考虑被忽略的自发辐射的影响, 对加长到抽运腔外的钕玻璃棒, 未受到抽运, 反而产生光放大异常实验现象的机理进行了理论研究.理论研究结果与实验结果基本相符.     

Critical behavior in Co-doped manganites La0.67Pb0.33Mn1−xCoxO3 (0≤x≤0.08)

The critical properties of perovskite manganite La_0.67Pb_0.33Mn_1−xCo_xO₃ (0≤x≤0.08) around the paramagnetic-ferromagnetic phase transition are investigated through various techniques such as the modified Arrott plot, Kouvel-Fisher method and critical isotherm analysis. Though the nature of this transition was found to be in second order, the estimated critical exponents β (0.233≤β≤0.368), γ (1.03≤γ≤1.40) and δ (4.32≤δ≤5.54) are in between the theoretically predicted values for three-dimensional Heisenberg and tricritical mean-field model. This model suggests the coexistence of the short-range and long-range ferromagnetic orders around the critical temperature. The values of the critical exponents obtained from different methods and the well-obeyed scaling behavior confirm that the calculated exponents are unambiguous and purely intrinsic to the system.     

Spherulites: How Do They Emerge at an Onset of Nonequilibrium Kinetic-Thermodynamic and Structural Singularity Addressing Conditions?

This communication addresses the question of the far-from-equilibrium growth of spherulites with different growing modes. The growth occurs in defects containing and condensed matter addressing environments of (bio)polymeric and biominerals involving outcomes. It turns out that it is possible to anticipate that, according to our considerations, there is a chance of spherulites’ emergence prior to a pure diffusion-controlled (poly)crystal growth. Specifically, we have shown that the emergence factors of the two different evolution types of spherulitic growth modes, namely, diffusion-controlled growth and mass convection-controlled growth, appear. As named by us, the unimodal crystalline Mullins–Sekerka type mode of growth, characteristic of local curvatures’ presence, seems to be more entropy-productive in its emerging (structural) nature than the so-named bimodal or Goldenfeld type mode of growth. In the latter, the local curvatures do not play any crucial roles. In turn, a liaison of amorphous and crystalline phases makes the system far better compromised to the thermodynamic-kinetic conditions it actually, and concurrently, follows. The dimensionless character of the modeling suggests that the system does not directly depend upon experimental details, manifesting somehow its quasi-universal, i.e., scaling addressing character.     

聚电解质PDDA/PSS层层自组装膜的渗透汽化性能

采用聚电解质层层自组装(LbL)技术, 在不同盐浓度下制备了聚(二烯丙基二甲基氯化铵)/聚苯乙烯磺酸钠(PDDA/PSS) 多层自组装膜, 并用于渗透汽化性能的研究. 重点考察了组装溶液中NaCl的浓度、组装层数及操作温度对自组装膜的异丙醇脱水性能的影响. 同时, 用扫描电镜观测了不同条件下制备膜的表面形貌. 结果表明, 在高NaCl含量的聚电解质溶液中只需组装几个双层的LbL膜, 即能获得较高的分离因子和较大的通量, 并解释了该LbL膜呈现反“trade-off”现象的原因.     

First Digits’ Shannon Entropy

Related to the letters of an alphabet, entropy means the average number of binary digits required for the transmission of one character. Checking tables of statistical data, one finds that, in the first position of the numbers, the digits 1 to 9 occur with different frequencies. Correspondingly, from these probabilities, a value for the Shannon entropy H can be determined as well. Although in many cases, the Newcomb–Benford Law applies, distributions have been found where the 1 in the first position occurs up to more than 40 times as frequently as the 9. In this case, the probability of the occurrence of a particular first digit can be derived from a power function with a negative exponent p > 1. While the entropy of the first digits following an NB distribution amounts to H = 2.88, for other data distributions (diameters of craters on Venus or the weight of fragments of crushed minerals), entropy values of 2.76 and 2.04 bits per digit have been found.     

时空克莱因瓶上的热力学——从二维生物的奇妙旅行到共形量子态的路径积分

在克莱因瓶和莫比乌斯带上环游世界的二维生物会经历有趣的手征变换,这可归因于这些不可定向曲面的独特拓扑性质。作者最近在研究中发现,让共形场论中的量子态在这些曲面上做“时空旅行”(路径积分),也会得到新奇而普适的热力学性质。例如,克莱因瓶上的二维共形场论的自由能中包含一项普适的克莱因瓶熵。它仅依赖于共形场论的一些基本特征。利用克莱因瓶熵,可以精确地找到量子相变点,并刻画其普适类。更一般地,不可定向曲面上的普适热力学数据不仅对于研究凝聚态和统计物理中的临界现象有意义,对于其他领域,比如全息黑洞热力学等也有启发。     

有限长正方形棱柱绕流的双稳态现象

运用大涡模拟(large eddy simulation, LES) 方法对有限长正方形棱柱绕流进行了研究. 棱柱高宽比为5,一端固定于平板上,另一端为自由端. 平板表面边界层厚度可忽略不计. 基于自由流速度和棱柱宽度的雷诺数为3 900. 由计算结果发现,有限长棱柱的尾流在自由端后下扫流的作用下具有显著的三维性. 尾流中会交替出现两种典型的流动状态:一种是柱体两侧所脱落的涡在尾流中形成类似卡门涡街的交错排列状态;另一种是柱体尾流中涡团对称分布且无明显的周期性. 两种典型流动状态的交替出现,对有限长棱柱气动力特性有直接的影响.     

过渡金属化合物中的竞争序与多体合作现象

文章简要介绍了过渡金属化合物所体现的层展现象和近几年作者所在研究组在几个不同过渡金属化合物系统开展的部分研究工作.