高指数稳定硅表面的低能电子衍射图分析

报道了在系统搜寻稳定硅表面的过程中对四个稳定高指数表面Si(1，1，11)，(1，0，8)，(2，1，2)和(15，1，17)的低能电子衍射(LEED)图进行的分析和结果.这些表面经充分退火后都能给出属于各自表面的LEED图，而不是小面化的，说明它们都是稳定的.从它们的LEED斑点强度分布特征不仅可以推断(15，1，17)是主稳定表面，而(1，1，11)，(1，0，8)和(2，1，2)则是副稳定表面，还能知道这些副稳定表面的原胞结构特征，甚至许多重要细节.从原胞结构特征来看，这些副稳定表面有可能用作生长周期量子线的模板.     

胸腺嘧啶在改进银溶胶溶液中的表面增强拉曼散射光谱信号与浓度的定量关系

尝试使用高分子材料作为银溶胶的稳定剂,以吡啶作为内标化合物研究胸腺嘧啶浓度与其SERS信号强度的关系。在胸腺嘧啶的浓度为2×10-4～1×10-3 mol·L-1的范围内,谱峰强度之比与胸腺嘧啶的浓度之间呈现良好的线性关系,线性回归方程为y=3.143x+0.348 7, 线性相关系数R2=0.975 4。     

Direct transition from a stable equilibrium to quasiperiodicity in non-smooth systems

The purpose of this Letter is to show how a border-collision bifurcation in a piecewise-smooth dynamical system can produce a direct transition from a stable equilibrium point to a two-dimensional invariant torus. Considering a system of nonautonomous differential equations describing the behavior of a power electronic DC/DC converter, we first determine the chart of dynamical modes and show that there is a region of parameter space in which the system has a single stable equilibrium point. Under variation of the parameters, this equilibrium may collide with a discontinuity boundary between two smooth regions in phase space. When this happens, one can observe a number of different bifurcation scenarios. One scenario is the continuous transformation of the stable equilibrium into a stable period-1 cycle. Another is the transformation of the stable equilibrium into an unstable period-1 cycle with complex conjugate multipliers, and the associated formation of a two-dimensional (ergodic or resonant) torus.     

Small-scale instabilities in dynamical systems with sliding

We demonstrate with a minimal example that in Filippov systems (dynamical systems governed by discontinuous but piecewise smooth vector fields) stable periodic motion with sliding is not robust with respect to stable singular perturbations. We consider a simple dynamical system that we assume to be a quasi-static approximation of a higher-dimensional system containing a fast stable subsystem. We tune a system parameter such that a stable periodic orbit of the simple system touches the discontinuity surface: this is the so-called grazing-sliding bifurcation. The periodic orbit remains stable, and its local return map becomes piecewise linear. However, when we take into account the fast dynamics the local return map of the periodic orbit changes qualitatively, giving rise to, for example, period-adding cascades or small-scale chaos.     

金属稳定同位素标记生物分析进展

细胞和组织的很多特定功能都由其在不同的生理条件下的生物分子含量决定,极少数分子的改变就有可能影响细胞生物功能并触发疾病生理过程,因此高灵敏的生物分子检测技术在疾病机理研究和疾病早期诊断方面具有重要作用。金属稳定同位素和放射同位素化学性质相近,借鉴放射同位素标记的成功经验,通过金属稳定同位素标记多组分生物分子,可以用原子质谱高灵敏地检测多组分生物分子。作为灵敏准确的金属元素检测工具,电感耦合等离子体质谱检出限低、基体效应低、线性范围广、同位素谱线分辨率高,因此适用于金属元素标记生物分子检测。金属稳定同位素标记已经被广泛应用到蛋白质、核酸、酶活性、生物小分子、甚至单个细胞的检测中,取得了一些可喜的进展,并展现了广阔未来应用前景。金属稳定同位素标记生物分析方法有三个特性：高灵敏度-大多数金属的稳定同位素有较高的标记灵敏度,并且可以通过纳米材料标记等方法实现信号放大;多组分同时分析-质谱仪同位素谱线高分辨率提供了多组分分析能力;高准确度-同位素稀释法提供了可溯源到SI国际单位制的高准确度检测结果。为了更好的推动相关研究,简要介绍金属稳定同位素标记生物分析的进展,主要内容包括以下几个部分：金属稳定同位素检测工具-无机质谱、金属稳定同位素标记高灵敏度分析、金属稳定同位素标记多组分同时分析、金属稳定同位素标记高准确度分析、金属稳定同位素标记单细胞分析的进展。     

Effect of temperature on the evolution of bright and dark screening—photovoltaic spatial solitons

We investigate theoretically the temperature effects on the evolution of both bright and dark screening-photovoltaic optical spatial solitons in biased photovoltaic-photocefractive crystals in the case of neglecting the diffusion process.For a stable bright or dark screening-photovoltaic soliton originally formed in a crystal at a given temperature,when the crystal temperature changes,it will evolve into another stable screening-photovoltaic soliton if the change is quite small,whereas it will become unstable or break down if the temperature change is large enough.The spatial shape of a stable screening-photovoltaic soliton can be reshaped by appropriately adjusting the crystal temperature.     

Controlling the bonding and band gaps of solid carbon monoxide with pressure

We use a combination of a searching method and first-principles electronic structure calculations to predict novel structures of carbon monoxide (CO) which are energetically more stable than the known structures. The most stable forms of CO at zero pressure consist of metallic polycarbonyl chains with single and double bonds, rather than the familiar triply bonded insulating CO molecules. At pressures >2 GPa the most stable phases are semiconducting and insulating singly bonded three-dimensional framework and layered structures. We also find a molecular Pbcm structure which is more stable than the R3c structure proposed previously for the observed ? phase.     

Generators of quasiperiodic oscillations with three-dimensional phase space

Considering a family of three-dimensional oscillators originating in the field of radio-engineering, the paper describes three different mechanisms of torus formation. Particular emphasis is paid to a process in which a saddle-node bifurcation eliminates a stable cycle and leaves the system to find a stationary state between a saddle cycle and a pair of equilibrium points of unstable focus/stable node and unstable node/stable focus type.     

A simple two-component reaction-diffusion system showing rich dynamic behavior: spatially homogeneous aspects and selected bifurcation scenarios

We present a simple reaction-diffusion model for two variables. The model was originally designed to have a stable localized solution for a range of parameters as a consequence of the coexistence of a stable limit cycle and a stable fixed point. We classify the spatially homogeneous solutions of the model. In addition we describe several bifurcation scenarios for particle-like solutions as a function of two of the parameters.     

应用级联倍频方法提高倍频系统输出稳定性研究

提出应用级联倍频方法提高倍频系统输出稳定性,并就该方法的有效性进行了理论分析和模拟计算.分析和计算结果不但证明级联倍频方法能实现倍频系统稳定输出,而且还表明可以通过仔细调节第一块倍频晶体中波矢方向 k 与光轴间夹角、两块倍频晶体间的间隔,能调节改变实现倍频系统最稳输出时所需第二块晶体的理论计算长度,使之与第二块倍频晶体的实际加工长度一致,最终实现系统稳定倍频输出.级联倍频方法在实现高输出稳定性的同时能实现高的倍频转换效率,对应用于光参量啁啾脉冲放大系统的高稳定抽运源系统的设计建造具有重要参考意义. 关键词： 级联倍频 稳定倍频输出 光参量啁啾脉冲放大     

乘性和加性α稳定噪声环境下的过阻尼单稳随机共振现象

本文将α稳定噪声与单稳随机共振系统相结合,研究了乘性和加性α稳定噪声环境下的过阻尼单稳随机共振现象,探究了α稳定噪声特征指数α(0α2)、对称参数β(-1β1),单稳系统参数a及乘性α稳定噪声放大系数D对共振输出效应的作用规律.研究结果表明,在不同分布的α稳定噪声环境下,在一定范围内通过调节a或D均可诱导随机共振来实现单个或多个高、低频微弱信号的检测,且a和D分别存在一个最优值可使系统产生最佳的随机共振效应;不同α或β均可对系统共振输出效应产生规律性的影响,且α或β在高、低频微弱信号检测中的作用规律相同;在研究α稳定噪声环境下单、多频单稳随机共振现象时所得结论是相同的.本研究结果可为实现α稳定噪声环境下单稳随机共振系统参数的自适应调节奠定基础.     

Generic dissipation of entanglement

We find states for a multi-level system which are stable under a very general model of dissipation, one which is governed simply by generic rate parameters; in general such stable states are not entangled. We exhibit such a state explicitly for a two-qubit system. We then specialize to a more physical model of dissipation, one which is governed by pure dephasing. In such a case it is possible, by choice of the dephasing rates, to have a stable, and limiting, entangled state under the evolution governed by the free hamiltonian and pure decoherence. We exhibit such a choice explicitly which has a stable and limiting two-qubit state of maximum entanglement (Bell state).     

One family of 13315 stable periodic orbits of non-hierarchical unequal-mass triple systems

The three-body problem can be traced back to Newton in 1687,but it is still an open question today.Note that only a few periodic orbits of three-body systems were found in 300 years after Newton mentioned this famous problem.Although triple systems are common in astronomy,practically all observed periodic triple systems are hierarchical(similar to the Sun,Earth and Moon).It has traditionally been believed that non-hierarchical triple systems would be unstable and thus should disintegrate into a stable binary system and a single star,and consequently stable periodic orbits of non-hierarchical triple systems have been expected to be rather scarce.However,we report here one family of 135445 periodic orbits of non-hierarchical triple systems with unequal masses;13315 among them are stable.Compared with the narrow mass range(only 10-5)in which stable"Figure-eight"periodic orbits of three-body systems exist,our newly found stable periodic orbits have fairly large mass region.We find that many of these numerically found stable non-hierarchical periodic orbits have mass ratios close to those of hierarchical triple systems that have been measured with astronomical observations.This implies that these stable periodic orbits of non-hierarchical triple systems with distinctly unequal masses quite possibly can be observed in practice.Our investigation also suggests that there should exist an infinite number of stable periodic orbits of non-hierarchical triple systems with distinctly unequal masses.Note that our approach has general meaning:in a similar way,every known family of periodic orbits of three-body systems with two or three equal masses can be used as a starting point to generate thousands of new periodic orbits of triple systems with distinctly unequal masses.     

Stable vortex tori in the three-dimensional cubic-quintic Ginzburg-Landau equation

We demonstrate the existence of stable toroidal dissipative solitons with the inner phase field in the form of rotating spirals, corresponding to vorticity S=0, 1, and 2, in the complex Ginzburg-Landau equation with the cubic-quintic nonlinearity. The stable solitons easily self-trap from pulses with embedded vorticity. The stability is corroborated by accurate computation of growth rates for perturbation eigenmodes. The results provide the first example of stable vortex tori in a 3D dissipative medium, as well as the first example of higher-order tori (with S=2) in any nonlinear medium. It is found that all stable vortical solitons coexist in a large domain of the parameter space; in smaller regions, there coexist stable solitons with either S=0 and S=1, or S=1 and S=2.     

α稳定噪声环境下多频微弱信号检测的参数诱导随机共振现象

本文将α稳定噪声与双稳随机共振系统相结合, 研究了不同α稳定噪声环境下高低频(均为多频)微弱信号检测的参数诱导随机共振现象, 探究了α稳定噪声的特征指数α(0 < α ≤ 2)和对称参数β (-1≤ β ≤ 1)及随机共振系统参数a, b对共振输出效应的作用规律. 研究结果表明, 在不同分布的α稳定噪声环境下, 通过调节系统参数a和b均可诱导随机共振来实现多个高、低频微弱信号的检测, 且存在多个a, b参数区间均可诱导随机共振, 这些区间不随α或β的变化而变化; 在高、低频微弱信号检测中, α或β对随机共振输出效应的作用规律相同. 本研究结果将有助于α稳定噪声环境下参数诱导随机共振现象中系统参数的合理选取, 进而可为实现基于随机共振的多频微弱信号检测方法的工程应用奠定基础. 关键词： 随机共振 α稳定噪声')" href="#">α稳定噪声 多频微弱信号检测 平均信噪比增益     

AN INVESTIGATION OF STABILITY IN THE LARGE BEHAVIOUR OF A CONTROL SURFACE WITH STRUCTURAL NON-LINEARITIES IN SUPERSONIC FLOW

It is well known that the presence of non-linearities may significantly affect the aeroelastic response of an aerospace vehicle structure. In this paper, the aeroelastic behaviour at high Mach numbers of an all-moving control surface with a non-linearity in the root support is investigated. Very often, a stable equilibrium point, corresponding to zero displacement of the structure, together with an unstable limit cycle arising from a sub-critical Hopf bifurcation results from the presence of the non-linearity. The stable equilibrium point will then possess a domain of attraction. In this paper, this situation is investigated by first applying the averaging method to obtain a new set of aeroelastic equations in which the limit cycle is replaced by an unstable equilibrium point. A fourth order power series approximation to the stable manifold in the neighbourhood of this equilibrium point is then determined. From the stable manifold, predictions of the domain of attraction of the stable equilibrium point may then be made. The method is applied to two examples in which the non-linearity in the root support was due to either a cubic hardening restoring moment or the presence of freeplay. The approximation to the stable manifold was sufficient to enable significant information about the domain of attraction of the stable equilibrium point of the control surface to be obtained; agreement with predictions from numerical integration of the aeroelastic equations in the time domain was shown to be generally good in the cases considered, though outside the region of validity of the stable manifold expansion, discrepancies will occur. The averaging method was shown to be sufficiently accurate for this analysis even when the non-linearities could not be considered as weak.     

基于2008年1月中国南方低温雨雪冰冻事件10-30天延伸期稳定分量的研究

对北半球1978-2007年1月6日-2月4日逐日500 hPa高度场资料带通滤波,得到10-30 d 时间尺度分量,结合经验正交函数分解方法(empirical orthogonal function, EOF)提取出气候态基底.同样滤波北半球2008年1月冰冻雨雪事件的逐日实况资料,并将其投影到气候态基底上,利用各贡献率作为考察该EOF分量对原场的影响指标. 从10-30 d延伸期预报的角度提取稳定分量进行诊断分析,探讨影响此次天气过程的主要因素.通过贡献率分析方法把10-30 d延伸期稳定分量划分为气候态稳定分量和异常型稳定分量两个部分.结果表明:气候态稳定分量在我国南方2008年1月冰冻雨雪事件中占主体地位,异常型稳定分量相当于在气候态稳定分量的基础上叠加的扰动值, 但异常型稳定分量在本次过程中的作用不能忽视,甚至起到关键性的作用, 并且与实况距平在太平洋地区整体环流形势有较好的对应.这些结论加深了对10-30 d 时间尺度可预报性的认识,为10-30 d延伸期预报提供了一种新的思路和解决问题的途径.     

Numerical Study of the Magnetic Phase Diagram of Perovskite Mn Oxides at Low Temperatures

We obtain the magnetic phase diagram of perovskite Mn oxides at low tempera tures. Our results show that when temperature T→0 a spiral state is stable in a lower doping concentration, a canted state is stable in a higher doping concentration and a ferromagnetic (FM) state becomes stable in the intermediate doping concentration. With temperature increasing, a paramagnetic (PM) state appears at the higher doping concentration and then the canted state disappears.     

Stability in linear response and clustering properties

We derive a necessary and sufficient asymptotic condition assuring that a quantum dynamical system in equilibrium is stable in linear response. We prove, in particular, that if the Hamiltonian has no singular-continuous spectrum and zero is the only eigenvalue, the dynamical system is stable. Finally we prove that a dynamical system is strongly clustering, if and only if, it is weakly clustering and stable in linear response.     

Microwave spectrum of the complex of 3,3,3-trifluoro-2-(trifluoromethyl)propanoic acid and formic acid

ABSTRACT

We report the first high resolution spectroscopic observation of the complex of 3,3,3-trifluoro-2-(trifluoromethyl)propanoic acid (TTPA) and formic acid. The rotational spectra were measured using a broadband chirped pulse and a narrow band cavity-based Fourier transform microwave spectrometer in the 8–10?GHz range. The conformational landscape of the TTPA-formic acid complex was explored at several levels of theory. The two most stable TTPA-formic acid conformers are of similar stability and feature the usual cyclic carboxylic double hydrogen bonded ring. Based on the broadband spectra obtained, only one stable heterodimer conformer was observed. We explain the absence of the second conformer to be a result of a double hydrogen tunnelling motion which converts the less stable heterodimer to the one observed in the jet expansion. Further CCSD(T) relative energy calculations confirm that the heterodimer conformer detected contains the most stable TTPA monomeric subunit. It is interesting to note that hydrogen bonding with formic acid offers a new path to effectively convert the less stable TTPA subunit to the most stable one in the jet expansion, while both TTPA monomeric conformers were detected in the same experiment.