Dynamical process of photoinduced polarization reversion in polymers

In polymeric molecules, the self-trapping associated with the photoinduced polarization reversion (PPR) produces bond distortion and creates gap states. The relaxation processes of the bond distortion and the gap states are revealed by studying the dynamics of the photoexcitation. The switching speed associated with the PPR can be determined from the relaxation process.     

Dynamical aspects of the photoinduced phase transition in spin-crossover complexes

We report a dynamical study on the photoinduced cooperative changes of the spin configurations in single crystals of the organometal spin-crossover complex. In the photoswitching process between low- and high-spin states, nonlinear characteristics such as thresholdlike behavior, incubation period, and phase separation have been observed. These results demonstrate that the cooperative intersystem crossing mediated by spin-lattice interaction plays a key role in the driving process of a new class of nonequilibrium phenomena so called photoinduced phase transition.     

Dynamical XPS measurements for probing photoinduced voltage changes

Photoillumination with 405 nm laser causes shifts in XPS peaks of n-Si(100), and CdS. To distinguish between surface photovoltage (SPV), and charging, dynamical measurements are performed, while sample is subjected to square wave pulses of ± 10.00 V amplitude, and 10^?3–10⁵ Hz frequency. For n-Si, Si2p peaks are twinned at + 10.00 and ?10.00, yielding always 20.00 eV difference. Photoillumination shifts the twinned peaks to higher energies, but the difference is always 20.00 eV. However, for CdS, the measured binding difference of Cd3d peaks exhibits strong frequency dependence due to charging, which indicates that both fast SPV and slow charging effects are operative.     

Theory for photoinduced structural phase transitions

A general concept for photoinduced structural phase transitions is developed in terms of the hidden multistability of the ground state and the proliferations of optically excited states. Taking the ionic→neutral (I - N) phase transition in the organic charge transfer crystal, TTF—CA, as a typical example for this type of transition, we, at first, theoretically show an adiabatic path of this transition, which starts from a single charge transfer exciton in the ionic phase, but finally reaches a neutral domain with a macroscopic size. In connection with this I—N transition, the concept of the initial condition sensitivity is also developed so as to clarify experimentally observed nonlinear characteristics of this material. In the next, using a more simplified model for the many-exciton system, we theoretically study the early time quantum dynamics of the exciton proliferation, which finally results in the domain formation of a large number of ex-citons. For this purpose, we derive a stepwise iterative equation to describe the exciton proliferation, and clarify the origin of the initial condition sensitivity.     

Stochastic and deterministic domino processes in photoinduced structural changes

The photoinduced structural change is discussed theoretically using a one-dimensional model, which is composed of localized electrons and lattices. We clarify the condition for the adiabatic and/or diabatic approximations. The global structural change by one-site excitation is possible in both cases. Under the adiabatic picture, the domain wall between the two phases moves at constant velocity, and the structural change in each site occurs nonradiatively within the time order of the lattice vibration. On the contrary, under the diabatic picture, the motion of the domain wall becomes a stochastic process because the structural change in each site occurs via the radiative transition, which takes a longer time than the lattice vibration.     

修正屏蔽库仑势下二维尘埃等离子体的动力学和结构特性

本文考虑等离子体密度分布变化, 得到了修正屏蔽库仑势的解析解. 数值分析以及分子动力学模拟表明, 在常见实验室参数情况下, 等离子体密度分布变化引起的屏蔽库仑势修正对二维尘埃等离 子体系统的动力学和结构特性影响很小. 在极限参数情况下, 本模型的计算结果表明二维尘埃等离子体系统的扩散能力明显降低, 并且系统组态呈圆形分布. 此外, 本文还研究了实验室常见大小磁场对二维尘埃等离子体系统的影响. 关键词： 修正屏蔽库仑势 二维尘埃等离子体 分子动力学模拟     

Theory for pattern formation dynamics in photoinduced structural phase transitions

We theoretically study formation dynamics of exciton domain patterns organized in optically excited 2-dimensional many-exciton system which is strongly coupled with an Einstein-phonon, and also immersed in a reservoir. It is shown that the exciton may proliferate quite rapidly by several successive photon-pulse excitation, and the resultant pattern becomes something like a fjord structure. Furthermore, the further proliferation can be occurred by filling up this structure even when the excitation is already turned off. We also investigate the effect of anisotropy of inter-exciton interaction on the efficiency of the proliferation. Consequently, we conclude that the strong anisotropy leads to the very efficient proliferation and makes the resultant photoinduced structural phase transition vast and successful, as compared with isotropic cases.     

二芳基乙烯光致各向异性动态特性研究

建立了光致变色二芳基乙烯样品光致各向异性动力学的理论模型.计算了在线偏振光激发下,二芳基乙烯分子数密度、光致二向色性和光致双折射随时间(曝光量)的动态变化曲线.结果表明,随着激发曝光量的增加,二芳基乙烯呈色态分子数密度不断下降直至饱和,光致各向异性随曝光量增加先增加,达到最大之后开始下降,最佳曝光量为260J/cm².利用正交偏振检测方法测量了反映材料各向异性的探测光透过率动力学曲线,并与理论计算结果进行了比较,二者基本相符. 关键词： 光致各向异性 二芳基乙烯 动态特性 最佳曝光量     

Photoelectric properties and photoinduced changes in ann-GaAs-glass-metal structure

A study is made of the photoelectric properties of metal-insulator-semiconductor (MIS) structures ofn-GaAs with a V₂O₅−B₂O₃−CaO insulating layer before and after illumination with subthreshold radiation. It is suggested that these properties are formed on account of the combined action of the barrier photo-emf and the Dember photo-emf dominating at low and high frequencies. The changes discovered in the photoelectric and noise properties of the structures are explained by the occurrence of photoinduced transformations in the ensemble of semiconductor defects. This is confirmed by a metallographic investigation. It is noted that the characteristics of photoinduced changes in crystalline and amorphous systems have common features. State Academy of Control and Radioelectronic Systems, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 6–12, August, 1996.     

Composition dependence of the photoinduced refractive-index change in lead silicate glasses

A large photoinduced refractive-index change (as great as Dn=0.21+/-0.04) is obtained in lead silicate glasses by irradiation with the frequency-quadrupled output of a Q -switched YAG laser (266 nm). An approximately exponential relationship is found between the photoinduced refractive-index change and the lead cation mole fraction over the composition range from 18.7% to 57%. The induced refractive-index change is permanent and shows no decay after heating to 360 degrees C during 1 h. Dispersion of the refractive-index change suggests that the photosensitivity is associated with changes in the intrinsic glass absorption edge.     

Dynamical properties of constrained drops

In this communication we analyze the behavior of excited drops contained in spherical volumes. We study different properties of the dynamical systems, i.e. the maximum Lyapunov exponent MLE, the asymptotic distance in momentum space d _∞ and the normalized variance of the maximum fragment. It is shown that the constrained system behaves as undergoing a first-order phase transition at low densities while as a second-order one at high densities. The transition from liquid-like to vapor-like behavior is signaled both by the caloric curves, the thermal response functions and the MLE. The relationship between the MLE, d _∞, and the caloric curve is explored. Received: 28 March 2002 / Accepted: 17 May 2002     

Dynamical properties of superconducting nanowires

The dynamical properties of thin superconducting wires (nanowires) are studied using numerical simulations based on a one-dimensional time-dependent Ginzburg-Landau equation, which is modified by introducing an order parameter u characterizing the “purity” of the superconductor material. It is established that relatively long nanowires (with lengths much greater than the coherence length) made of a “pure” superconductor (u > 1) are characterized by two critical current density values: j _c1 and j _c2. For j < j _c1, the total current is entirely superconducting, whereas for j > j _c2, the current is purely normal. In the intermediate region of current densities, j _c1 < j < j _c2, the total current contains both superconducting and normal components (mixed state) and the nanowire exhibits the generation of high-frequency electromagnetic waves. The current-voltage characteristics are constructed and the radiation spectrum is obtained. The properties of short superconducting nanowires (with lengths on the order of the coherence length) coincide with those of the Josephson junction. In the case of an “impure” superconductor (u < 1), the nanowire is characterized by a single critical current density.     

Transport and photoinduced properties in highly Sr-deficient manganite films

We used the method of finite-difference time domain (FDTD) to study the characteristics of the patch antenna based on a novel periodic structure, and the theory of photonic crystal structure (also photonic band gap [PBG]) structure was introduced. The results obtained show that the surface waves propagating along the substrate surface can be suppressed by the periodic structure due to the influence of its forbidden band, and the energy of the electromagnetic waves is concentrated mainly in the substrate. As a result, the patch antenna based on the periodic structure has a wider bandwidth in comparison with the conventional patch antennae; and a higher gain is reached, so the patch antenna’s performance is improved. Due to such the advantages, the application of patch antennae can be extended in such fields as mobile communication, satellite communication, aviation, etc.     

酵母蛋白质网络的动力学性质

蛋白质-蛋白质、蛋白质-DNA相互作用网络决定了细胞中各种关键功能的执行．基于芽殖酵母(budding yeast saccharomyces cerevisiae)的蛋白质-蛋白质相互作用网络数据和相关的实验文献，我们建立了调控细胞周期和生命周期(cell cycle and life cycle)的蛋白质网络，并利用离散模型研究了该网络的动力学性质，研究表明：细胞周期网络的动力学性质具有很强的稳定性，约94％的蛋白质初态将演化到对应于生物学G1基态的稳定态，使其成为惟一的全局吸引点；同时，绝大多数的初态的演化路径都通过由G1激发态到G1基态的细胞周期演化路径，使细胞周期路径成为全局性的“吸引”路径。     

Dynamical properties of water in living cells

With the aim of studying the effect of water dynamics on the properties of biological systems, in this paper, we present a quasi-elastic neutron scattering study on three different types of living cells, differing both in their morphological and tumor properties. The measured scattering signal, which essentially originates from hydrogen atoms present in the investigated systems, has been analyzed using a global fitting strategy using an optimized theoretical model that considers various classes of hydrogen atoms and allows disentangling diffusive and rotational motions. The approach has been carefully validated by checking the reliability of the calculation of parameters and their 99% confidence intervals. We demonstrate that quasi-elastic neutron scattering is a suitable experimental technique to characterize the dynamics of intracellular water in the angstrom/picosecond space/time scale and to investigate the effect of water dynamics on cellular biodiversity.