Community succession along a chronosequence of vegetation restoration on sand dunes in Horqin Sandy Land

Species diversity influences plant community structure and function. This paper examines the patterns and dynamics of species diversity along a chronosequence of vegetation recovery on sand dunes in a semi-arid region to assess the probability of vegetation recovery via succession, and provides some implications for revegetation practices in this region. Species richness and diversity indices gradually increased with succession, except for a decline in the community of 18 years, which is attributed to the strong dominance of Artemisia halodendron. In each stage of the restoration process, there was a dominant species with particular life history traits which contribute to the dominance of this species. Species replacement and habitat changes were the main drivers Of Succession, while plant species and Community succession drove the process of vegetation recovery. Results showed,that restoration via succession holds promise for vegetation recovery and desertification control within protected, fenced enclosures. (c) 2005 Elsevier Ltd. All rights reserved

A FLUOROMETRIC METHOD FOR THE DETERMINATION OF CYANIDE WITH FLUORESCEIN AND IODINE

A rapid, simple and sensitive fluorimetric method has been developed for the determination of cyanide with fluorescein as fluorogenic reagent (lambda(ex) = 494 nM, lambda(em) = 514 nm) at pH 6.0-7.0. A linear calibration curve was obtained in the range 0.004-2.0 mu g CN-/25 ml. The detection limit is 0.004 mu g CN-/25 ml. The method was successfully applied to the determination of cyanide in waste water

Synthesis, characterization and antitumor activity of benzaldehyde nitrogen mustard picolinoyl hydrazone complexes

Cu-II, Ni-II, Co-II, Zn-II and Cd-II complexes of picolin-amido-4-bis(2-chloroethyl)aminobenzaldimine (PBAB) have been synthesized and characterized by elemental analysis, conductivity, i.r. u.v.-vis. and e.p.r. spectra. The results suggest a square planar structure for the Cu-II complex, a tetrahedral geometry for the Zn-II and Cd-II complexes and an octahedral structure for the Co-II and Ni-II complexes. The complexes have been screened for antitumor activity against SMMC-7721 human liver cancer cell line; all of them exhibit biological activity at high concentrations for the cell line studied and a synergic effect between Cu-II and PBAB is evident

Extracting and Stabilizing the Unstable State of Hysteresis Loop

A novel perturbation method for the stabilization of unstable intermediate states of hysteresis loop (i.e. S-shaped curve) is proposed. This method only needs output signals of the system to construct the perturbation form without delay-coordinate embedding technique, it is more practical for real-world systems. Stabilizing and tracking the unstable intermediate branch are demonstrated through the examples of a bistable laser system and delay feedback system. All the numerical results are obtained by simulating each of the real experimential conditions.Comment: 6 pages, REVTEX, 4 ps figure

Self-similarity in a system with short-time delayed feedback

Using the Poincar\'{e} section technique, we study in detail the dynamical behaviors of delay differential system and find a new type of solutions $S_i$ in short-time delay feedback. Our numerical results remind us to deny the opinion that there are no complex phenomena in short-time delay case. Many similarities between foundamental solution and the new type of solutions are found. We demonstrate that the scales of $S_i$ increase with exponential growth via $i$ in the direction of $\mu$, while decrease with exponential decays in the direction of $x$ or delay time $t_R$.Comment: 4 pages, REVTEX, 4 ps figures, to be published in Phys. Lett.

Designing asymmetric neural networks with associative memory

A strategy for designing asymmetric neural networks of associative memory with controllable degree of symmetry and controllable basins of attraction is presented. It is shown that the performance of the networks depends on the degree of the symmetry, and by adjusting the degree of the symmetry the spurious memories or unwanted attractors can be suppressed completely

长短期记忆网络预测混沌时间序列

近年来,深度学习技术的快速发展推动了机器学习的广泛应用.其中,储备池计算(Reservoir Computing)方法由于在混沌时间序列预测方面的卓越效果而受到了越来越多的重视,形成了一个新的研究热点.本文以传统的长短期记忆网络(LSTM)和全连接层作为模型的基础,构建了基于循环神经网络的LSTM学习机.在仿真实验中,我们以平均有效预测时间作为度量指标,使用模型对洛伦兹系统的状态变量进行预测,并针对混沌系统特殊的动力学性质,为模型搭配了四项策略来辅助预测.结果表明, LSTM学习机搭配合适的组合策略,其预测能力也能达到与储备池计算相比拟的效果,且模型复杂度更低.因此,储备池计算并没有超越于传统方法的绝对优势,这启发我们通过进一步研究学习机预测时间序列的机制和方法,寻找更加有效的时间序列预测学习机.国家自然科学基金(编号:11335006)资助项

Extended pole placement technique and its applications for targeting unstable periodic orbit

In this paper we extend the pole placement technique in the case of one adjustable system parameter. The extended technique allows a more general choice of feedback forms, so it can improve the performance of the control system in many aspects. As an example of the application, we show how to target the unstable orbit from the corresponding stable one in the vicinity of a tangential bifurcation paint without the need of knowing the location of the unstable orbit in advance. This technique can be used to obtain the unstable output related to bistability from an experimental device

机器学习在座逾渗相变问题中的应用

机器学习理论区别于传统方法,因其在对于复杂的数据集识别、分类的准确性和高效性而被广泛应用于各个领域.识别相变是机器学习和统计物理领域相结合的最有代表性的工作.到目前为止,机器学习完成的相变识别几乎都是基于具有动力学演化过程的自旋模型,如Ising模型等,而其在另一类不具有动力学演化过程而完全由系统结构特征决定的相变模型,如逾渗模型等,仍未有细致研究.本文结合现有的机器学习技术,卷积神经网络和一般向量机,对二维方格子上的座逾渗问题进行了研究,发现能以高正确率对不同相的构型进行识别,证明了机器学习在这类问题上研究的可行性.通过已完成训练的学习机对不同参数下构型预测的正确率计算,发现正确率在相变点附近会出现急剧衰减,与系统参数呈幂律衰减.这与传统相变理论一致.通过定量计算,还发现2种学习机的正确率衰减规律都满足同一个幂律指数.这不仅进一步从全新的角度揭示了相变的普适性,而且为找寻相变点提供了新的方法.国家自然科学基金重点项目(11335006

Heat conduction in graphene flakes with inhomogeneous mass interface

National Natural Science Foundation of China [10775115, 10925525]Using nonequilibrium molecular dynamics simulations, we study the heat conduction in graphene flakes composed by two regions. One region is mass-loaded and the other one is intact. It is found that the mass interface between the two regions greatly decreases the thermal conductivity, but it would not bring about a thermal rectification effect. The dependence of thermal conductivity upon the heat flux and the mass difference ratio is studied to confirm the generality of the result. The interfacial scattering of solitons is studied to explain the absence of the rectification effect