旋转方形散射体对三角晶格磁振子晶体带结构的优化

用改进的平面波展开法数值计算了正方形散射体三角排列的二维磁振子晶体当散射体旋转时的带结构. 结果显示, 同样的填充率下, 旋转正方柱散射体可以在新的频率范围内打开更多的带隙, 或者使低频带隙加宽. 说明旋转散射体可以有效地优化带隙.     

Approximate wø ∽ Ωø Relations in Quintessence Models

Quintessence field is a widely-studied candidate of dark energy. There is ``tracker solution' in quintessence models, in which evolution of the field ø at present times is not sensitive to its initial conditions. When the energy density of dark energy is neglectable (Ω<sub>ø</sub><< 1), evolution of the tracker solutioncan be well analysed from ``tracker equation'. In this paper, we try tostudy evolution of the quintessence field from ``full tracker equation',which is valid for all spans of Ω<sub>ø.</sub> We get stable fixed points of w<sub>ø</sub> and Ω<sub>ø</sub> (noted as \hat{w}<sub>ø</sub> and \hat{Ω}<sub>ø</sub>) from the ``full tracker equation', i.e., w_ø and Ω_ø will always approach \hat{w}_ø and \hat{Ω}_ø respectively. Since \hat{w}_ø and \hat{Ω}_ø are analytic functions of ø, analytic relation of \hat{w}_ø ~ \hat{Ω}_ø can be obtained, which is a good approximation for the w_ø ~ Ω_ø relation and can be obtained for the most type of quintessence potentials. By using this approximation, we find that inequalities \hat{w}_ø < w_ø and \hat{Ω}_ø < Ω_ø are statisfied if the w_ø (or \hat{w}_ø) decreases with time. In this way, the potential U(ø) can be constrained directly from observations, by no need of solving the equations of motion numerically.     

On the density fluctuations of the superconducting state

The fluctuations of the number of particles in a subvolumeΩ′≦Ω in the superconducting state are investigated in the framework of the strong coupling limit of the BCS-theory. It is shown for values ofΩ′?Ω these fluctuations are proportional to the subvolumeΩ′ and agree for theseΩ′-values with the density fluctuations of the quasivacuum state.     

Light mixing induced by the giant two-photon absorption of excitonic molecules in CuCl

Three-wave mixing of light has been observed in connection with a giant two-photon absorption generating excitonic molecules. The efficiency of mixing of light for energies 2Ω₁ - Ω₂ and 2Ω₂ - Ω₁ is enhanced remarkably when Ω₁ and/or Ω₂ is varied across the giant two-photon absorption band-region. Moreover, the mixed lights with energies 3Ω₁ - 2Ω₂ and 4Ω₁ - 3Ω₂ have also been detected.     

Ω＋Ω→（ΩΩ）Jπ=0＋＋X Cross section Calculation

The cross sections of Ω+Ω→(ΩΩ)_J^π=0⁺+X are studied by using an effective Hamiltonian method. The results are σ_{Ω+Ω→(ΩΩ)0⁺+γ}=0.03～0.16×10^-29 cm² for p_Ω=100～400 MeV, and the cross sections of η production are about 10^-28 cm² for p_Ω > 880 MeV.     

Parity effects in radiative Ω−-decays

It is shown that, for values of theΩ ^? magnetic moment near that predicted bySU(6), parity effects in radiativeΩ ^?-decays are expected to be small and, contrary to the situation in hyperon decays, more pronounced in decays with heavy charged particles. They depend, however, sensitively on the magnetic moment ofΩ ^? and are insensitive to the hyperon moments. This is due to the dominance of a “contact” term which has to be introduced in the amplitude in order to ensure gauge invariance.     

Geometry of generalised nonlinear Schrödinger and Heisenberg ferromagnetic spin equations with linearly x-dependent coefficients

The integrable generalised nonlinear Schrödinger equation with linearly x-dependent coefficients is shown to be equivalent to the equation of motion of a generalised Heisenberg ferromagnet in the continuum limit. This is represented by the motion of a nonlinear string thereby clarifying its geometric structure. An (L?, Â) pair is constructed for this string and the eigenvalues have a simple time evolution. Although these flows are not isospectral they all satisfy the vanishing curvature condition $\text{Θ≡dΩ?Ω∧Ω=0}$.     

Tunable spectral switching in the far field with a chirped cosh-Gaussian pulse

We have shown the possibility of tunable spectral switching in the far field with an apertured chirped cosh-Gaussian pulse by varying its cosh parameter (Ω). We have also shown that the switching frequency and both blue and red shifted frequencies can be also tuned by varying Ω. Possible application of our results in optical space communications has been highlighted.     

First evidence of ψ(2S)→Ω-Ω+

The decay ψ(2S)→Ω^-Ω⁺ is analyzed using 14×10⁶ ψ(2S) events recorded by the Beijing Spectrometer Ⅱ (BESⅡ) at the Beijing Electron Positron Collider (BEPC). Based upon events with no missing charged tracks and a satisfactory four-constraint kinematic t, we determine the upper limit for the branching fraction of ψ(2S)→Ω^-Ω⁺ to be 1.5×10⁴ at a 90% confidence level. By including events with one missing charged track, we are able to report the first evidence of an Ω⁺ signal with a statistical signi cance of 3.1|σ. The branching fraction of ψ(2S)Ω⁺ is determined to be (4.80±1.56(stat)±1.30(sys))10⁵.     

Detecting the optimal number of communities in complex networks

To obtain the optimal number of communities is an important problem in detecting community structures. In this paper, we use the extended measurement of community detecting algorithms to find the optimal community number. Based on the normalized mutual information index, which has been used as a measure for similarity of communities, a statistic Ω(c) is proposed to detect the optimal number of communities. In general, when Ω(c) reaches its local maximum, especially the first one, the corresponding number of communities c is likely to be optimal in community detection. Moreover, the statistic Ω(c) can also measure the significance of community structures in complex networks, which has been paid more attention recently. Numerical and empirical results show that the index Ω(c) is effective in both artificial and real world networks.     

Electric field induced phase transition in first order ferroelectrics with large zero point energy

An electric field induced phase transition in first order ferroelectrics with very large zero point energy is studied on the framework of the effective field approach. It is well known that when the zero point energy of a system is relatively large, the ferroelectric behaviour is depressed and no phase transition can be observed. The critical value Ω_cf of zero point energy for whom the phase transition disappears turns out to be dependant on the order of transition. For zero point energies larger than this critical value, a phase transition may be induced applying an external electric field. This temperature dependence of the induced polarization shows a discontinuous step when the applied electric field is weak, but becoming a continuous one at a strong applied electric field. Another critical value of zero point energy Ω_cp>Ω_cf is deduced for which no phase transition at all can be attained.     

实现大气压负直流辉光放电的针-柱电极结构设计与实验

为了实现大气压环境下稳定的辉光放电,设计了一种新型的针-柱电极结构放电装置。采用针尖直径为56.4 μm的不锈钢针作为放电阴极,直径为4 mm的紫铜圆柱作为放电阳极,两者通过精密机械结构保持平行。当针-柱之间间距为2 mm、镇流电阻10 MΩ,放电电阻10 MΩ,测试电阻1 kΩ、放电电压-2 740 V、大气压环境、室温、无外部通入气流时,针-柱之间实现了稳定的辉光放电。示波器存储的放电波形和数码相机记录的放电图像验证了从电晕放电到辉光放电,再到火花放电的三种放电模式。该针-柱结构易于用MEMS工艺加工制作,可应用于便携式分析仪器中作为离子源使用。     

周期力调制噪声驱动下单模激光系统的多重随机共振

在周期力调制噪声驱动下单模激光系统的光强方程中加入调幅波, 用线性化近似方法计算了系统的光强关联函数和输出信噪比, 并对信噪比进行数值计算和分析, 发现低频调制频率Ω、高频载波频率ω和周期力频率Ω_λ对系统的输出信噪比有很大的影响. 具体表现为信噪比R 随低频调制频率Ω 的变化过程中出现了多重随机共振和极强的单峰共振, 当Ω << ω 时, 系统出现的是多峰共振, 且随着Ω_λ 增加, 共振峰间的距离增大, 峰值位置不变; 当Ω → ω 时, 输出信噪比R迅速增大, 而Ω_λ 的影响被削弱甚至可以忽略, 多峰共振消失; 当Ω = ω 时, 系统出现了极强的单峰共振. 此外, 信噪比随周期力频率的变化呈现振幅减小的多重随机共振, 而随载流频率的变化出现单峰随机共振.     

Horizon problem in a closed universe dominated by fluid with negative pressure

We discuss the horizon problem in a universe dominated by fluid with negative pressure. We show that for generally accepted value of nonrelativistic matter energy density parameter Ω_m0 < 1, the horizon problem can be solved only if the fluid influencing negative pressure (the so-called “X” component) violates the point-wise strong energy condition and if its energy density is sufficiently large (Ω_X0 > 1). The calculated value of the Ω_X0 parameter allowing for the solution of the horizon problem is confronted with some recent observational data. Assuming that p_X/ρ_X < —0.6 we find that the required amount of the “X” component is not ruled out by the supernova limits. Since the value of energy density parameter Ω_v0 for cosmological constant larger than 1 is excluded by gravitational lensing observations the value of the ratio p_X/ρ_X should lie between the values —1 and —0.6 if the model has to be free of the horizon problem beeing at the same time consistent with observations. The value of Ω_X0 + Ω_m0 in the model is consistent with the constraints 0.2 < Ω_tot < 1.5 following from cosmic microwave background observations provided that Ω_m0 is low (<0.2).     

结合静电喷雾技术与浸渍法制备的固体氧化物燃料电池阴极

使用浸渍法制备具有纳米催化粒子的固体氧化物燃料电池电极可以提高电池性能。结合静电喷雾技术以及浸渍法制备的Sm0.2Ce0.8O2-δ（SDC）La0.6Sr0.4Co0.2Fe0.8O3-δ（LSCF）浸渍阴极。对于静电喷雾技术中沉积温度对于薄膜形貌的影响做了讨论。阻抗谱研究表明,以300℃下沉积制得的薄膜为骨架的阴极具有最小的极化阻抗,在650、700、750、800℃分别为0.484、0.077、0.034、0.022Ω.cm2。以这种电极为阴极并以稳定的氧化锆为电解质的单电池在750℃时最大功率密度为254mW/cm。     

Spectroscopic studies of Nd and Er in KGd(WO4)2 single crystals

Single crystals of KGd(WO₄)₂ doped with Nd³⁺ and Er³⁺ ions were grown by the top seeded solution growth method. Detailed analysis of the room-temperature absorption spectra was performed using the conventional Judd-Ofelt theory and actual dependence of the refractive index on the wavelength. In addition to the intensity parameters Ω_2,Ω_4,Ω₆, the branching ratios and radiative lifetimes were estimated for all possible transitions in the studied spectral region. Those transitions which can be potentially used for laser applications have been identified for both ions.     

Lattice dynamics of an isotopic defect

Using a spectrum ～Ω ²√Ω _m ² ?Ω ² for the frequenciesΩ of the ideal crystal simple analytic expressions are derived for the response function, phonon scattering cross section and related quantities. The interpretation of resonances and localized vibrations as damped and undamped harmonic oscillators is discussed in detail.     

Asymptotic power laws for hadron calorimeter experiments

This is a study of asymptotic QCD predictions for collisions in which a finite fraction of the available energy is carried by hadrons into an angular region $\text{Ω}$ whose complement is $\text{Ω}{}_{\mathrm{<mtext>a</mtext>}}$ or $\text{Ω}{}_{\mathrm{<mtext>b</mtext>}}$ or $\text{Ω}{}_{\mathrm{<mtext>a</mtext>}}\text{UΩ}{}_{\mathrm{<mtext>b</mtext>}}\text{, Ω}{}_{\mathrm{<mtext>a</mtext>}}$ being fixed cones about the directions of motion of the initial particles. Apart from slow (logarithmic) corrections the asymptotic power laws derived from the covariant parton model appear to be justified provided certain conditions on $\text{Ω}{}_{\mathrm{<mtext>a</mtext>}}$ and/or $\text{Ω}{}_{\mathrm{<mtext>b</mtext>}}$ and the energy deposited in them are met.     

LiNbO3和LiTaO3晶体Er3+/Yb3+掺杂水热外延层室温吸收光谱分析

本文引入与浓度和厚度有关的k_NL待定参数, 在J-O理论基础上, 对Er³⁺/Yb³⁺掺杂的LiNbO₃和LiTaO₃单晶衬底上 的多晶水热外延样品进行了基于吸收光谱的拟合计算. LiNbO₃:Ω₂=2.34× 10^-20 cm², Ω₄=0.77× 10^-20 cm², Ω₆=0.31×10^-20 cm², k_NL=4.32× 10^-2 mol·m^-2. LiTaO₃:Ω₂=1.68×10^-20 cm², Ω₄=0.84×10^-20 cm², Ω₆=0.45×10^-20 cm², k_NL=9.17×10^-3 mol· m^-2. 该方法可尝试推广到粉体或胶体等难以直接获得浓度和厚度数据的体系. 经上转换发光测试及光谱参数计分析认为Er³⁺/Yb³⁺离子的掺杂浓度比为1:1的情况下, 样品呈现绿色上转换发光光谱; 可尝试以降低基质声子能量的方法提高⁴I_13/2能级 对²H_11/2和⁴S_3/2能级的量子剪裁效率.     

Angular momentum transport in turbulent flow between independently rotating cylinders

We present measurements of the angular momentum flux (torque) in Taylor-Couette flow of water between independently rotating cylinders for all regions of the (Ω1, Ω2) parameter space at high Reynolds numbers, where Ω1 (Ω2) is the inner (outer) cylinder angular velocity. We find that the Rossby number Ro = (Ω1 - Ω2)/Ω2 fully determines the state and torque G as compared to G(Ro = ∞) ≡ G∞. The ratio G/G∞ is a linear function of Ro(-1) in four sections of the parameter space. For flows with radially increasing angular momentum, our measured torques greatly exceed those of previous experiments [Ji et al., Nature (London), 444, 343 (2006)], but agree with the analysis of Richard and Zahn [Astron. Astrophys. 347, 734 (1999)].