有限深两层流体中内孤立波造波实验及其理论模型

将置于大尺度密度分层水槽上下层流体中的两块垂直板反方向平推, 以基于 Miyata-Choi-Camassa (MCC)理论解的内孤立波诱导上下层流体中的层平均水平速度作为其运动速度, 发展了一种振幅可控的双推板内孤立波实验室造波方法. 在此基础上, 针对有限深两层流体中定态内孤立波 Korteweg-de Vries (KdV), 扩展KdV (eKdV), MCC和修改的Kdv (mKdV)理论的适用性条件等问题, 开展了系列实验研究.结果表明, 对以水深为基准定义的非线性参数ε 和色散参数μ, 存在一个临界色散参数μ₀, 当μ < μ₀ 时, KdV理论适用于ε ≤μ 的情况, eKdV理论适用于μ < ε ≤√μ 的情况, 而MCC理论适用于ε > √μ 的情况, 而且当μ ≥μ₀ 时MCC理论也是适用的.结果进一步表明, 当上下层流体深度比并不接近其临界值时, mKdV理论主要适用于内孤立波振幅接近其理论极限振幅的情况, 但这时MCC理论同样适用.本项研究定量地表征了四类内孤立波理论的适用性条件, 为采用何种理论来表征实际海洋中的内孤立波特征提供了理论依据. 关键词： 两层流体 内孤立波 双板造波 临界色散参数     

Al纳米线不同晶向力学行为和变形机制的模拟

采用分子动力学模拟计算方法,考察具有较高层错能的Al纳米线沿不同晶向的力学行为和变形机制。在相同计算条件下与具有较低层错能的Ni、Cu、Au和Ag等FCC金属纳米线进行比较。结果表明：在力学行为方面,Al纳米线的弹性模量呈现明显的结构各向异性,满足E_[111] > E_[110] > E_[100]的关系,这一关系在FCC金属纳米线中普遍成立;Al纳米线的屈服应力随晶向呈现σ_y[100] > σ_y[111] > σ_y[110]的关系,这一关系在具有较低层错能的FCC金属纳米线中不具有普遍性,这与体系中位错形成机制密切相关。根据拉伸变形过程微观结构的演变规律,阐明Al纳米线不同晶向的变形机制,并与具有较低层错能的Ni、Cu、Au和Ag等FCC金属纳米线的变形机制进行比较。结果表明,对于尺度较小的高层错能Al纳米线,Schmid因子和广义层错能均难以准确预测其变形机制。     

Dielectric and piezoelectric properties of(110) oriented Pb(Zr_(1-x)Ti_x)O_3 thin films

A phenomenological Landau–Devonshire theory is developed to investigate the ferroelectric, dielectric, and piezoelectric properties of(110) oriented Pb(Zr_(1-x)Ti_x)O_3(x = 0.4, 0.5, 0.6, and 0.7) thin films. At room temperature, the tetragonal a_1 phase, the orthorhombic a_2c phase, the triclinic γ_1 phase, and the triclinic γ_2 phase are stable. The appearance of the negative polarization component P_2 in the a_2c phase and the γ_1 phase is attributed to the nonlinear coupling terms in the thermodynamic potential. The γ phase of the Pb(Zr_(1-x)Ti_x)O_3 thin films has better dielectric and piezoelectric properties than the a_2c phase and the a_1 phase. The largest dielectric and piezoelectric coefficients are obtained in the Pb(Zr_(0.5)Ti_(0.5))O_3 thin film. The piezoelectric coefficient of 110–150 pm/V is obtained in the(110) oriented Pb(Zr_(0.5)Ti_(0.5))O_3 thin film, and the Pb(Zr_(0.3)Ti_(0.7))O_3 thin film has the remnant polarization and relative dielectric constant of 50 μC/cm~2 and 100, respectively,which are in agreement with the experimental measurements reported in the literature.     

SeN_2自由基解析势能函数的耦合簇理论研究

利用单双迭代耦合簇理论CCSD结合相关一致四重基组cc-pVQZ对SeN2基态的平衡结构和谐振频率进行了优化计算.计算结果表明:基态SeN2自由基分子稳定态为C2v构型,基态电子组态为X1A1,平衡核间距RSe-N=0.1691 nm,RN-N=0.1970 nm,αN-Se-N=71.289?,离解能De=4.78 eV.基态简正振动频率分别为:ν1=326.9288 cm-1,ν2=808.0161 cm-1以及ν3=948.3430 cm-1.对SeN基态和N2基态采用上述相同方法进行几何构型与谐振频率的计算并进行单点能扫描,使用Murrell-Sorbie函数进行最小二乘拟合得到其势能函数和光谱常数,通过和其他理论值以及实验值做比较,显示本文的计算工作达到了很高的精度.应用多体项展式理论导出了基态SeN2的全空间解析势能函数,其势能函数等值势能图准确再现了SeN2分子的结构特征和能量变化.     

Mo-SiO2-C3H6催化反应体系的ESR动态表征

文章考察了Mo-SiO₂催化剂体系在丙烯歧化反应过程中的动态ESR波谱,发现在催化歧化反应过程中有两种Mo⁵⁺顺磁中心,一种为扰动八面体配位,g_||=1.89,g_⊥=1.94;另一种为扰动四棱锥配位,g_||=1.86,g_⊥=1.95。测得同位素^95,97Mo⁵⁺的各向异性超精细耦合常数A_||=90.3×10^-4cm^-1,A_⊥=44.8×10^-4cm^-1;观测到反应产生的积炭信号,g≈2.0O₂;氧阴离子自由基信号g₁=2.018,g₂=2.011,g₃=2.005。用LCAO-MO理论对上述Mo⁵⁺的ESR波谱进行计算,求得分子轨道系数,发现并总结出△g_||/△g_⊥与△g成直线关系,并建议用△g_||/△g_⊥=4(△E(B₂→E))/(△E(B₂→B₁)(β₁/ε)²之比值作为衡量C_4v扰动程度的尺度。     

Infrared fluorescence from exciting the v1 and v8 modes of CF2Cl2 with a TEA CO2 laser

Infrared fluorescence from CF₂Cl₂ molecules excited with a TEA CO₂ laser below dissociation threshold, is time resolved with a HgCdTe detector without spectral resolution in the range 1100-700 cm^-1. The signal fits well to a sum of three exponentials, which are interpreted as a bulk vibration-vibration (V-V) energy transfer between the fraction of highly excited and non-excited molecules in the irradiated volume, vibro-translation (V-T) deactivation and diffusional heat and mass transport to the surrounding. The measured V-V and V-T rates increase with vibrational excitation and the V-T deactivation is independent on the observed modes (v₁/v₆ or v₈) if v₈ or v₁ are excited respectively.     

Two-loop renormalization of tanβ and its gauge dependence

Renormalization of two-loop divergent corrections to the vacuum expectation values (v₁,v₂) of the two Higgs doublets in the minimal supersymmetric standard model, and their ratio tanβ=v₂/v₁, is discussed for general R_ξ gauge fixings. When the renormalized (v₁,v₂) are defined to give the minimum of the loop-corrected effective potential, it is shown that, beyond the one-loop level, the dimensionful parameters in the R_ξ gauge fixing term generate gauge dependence of the renormalized tanβ. Additional shifts of the Higgs fields are necessary to realize the gauge-independent renormalization of tanβ.     

光解苯半醌自由基的CIDEP谱

用高时间分辨ESR谱仪实验给出了光解对苯醌产生的苯半醌自由基的CIDEP发射谱.用三重态机理,同时考虑了自由基对机理的影响,从理论上分析了极化强度,计算出了增强因子V(Ⅰ)=-0.66,V(R)=0.2,一级反应速率k_1,A=0.05/μs,二级反应速率β=0.02/μs,横向和纵向弛豫时间T₁≈T₂=2.3μs.     

Dynamic behaviors of water contained in calcium-silicate-hydrate gel at different temperatures studied by quasi-elastic neutron scattering spectroscopy

The dynamic behaviors of water contained in calcium-silicate-hydrate(C-S-H) gel with different water content values from 10%to 30%(by weight),are studied by using an empirical diffusion model(EDM) to analyze the experimental data of quasi-elastic neutron scattering(QENS) spectra at measured temperatures ranging from 230 K to 280 K.In the study,the experimental QENS spectra with the whole Q-range are considered.Several important parameters including the bound/immobile water elastic coefficient A,the bound water index BWI,the Lorentzian with a half-width at half-maximum(HWHM) Γ_1(Q) and Γ_2(Q),the self-diffusion coefficients D_(t1) and D_(t2) of water molecules,the average residence times τ_(01)and τ_(02),and the proton mean squared displacement(MSD)(u~2) are obtained.The results show that the QENS spectra can be fitted very well not only for small Q(≤1 A~1) but also for large Q.The bound/immobile water fraction in a C-S-H gel sample can be shown by the fitted BWI.The distinction between bound/immobile and mobile water,which includes confined water and ultra-confined water,can be seen by the fitted MSD.All the MSD tend to be the smallest value below 0.25 A~2(the MSD of bound/immobile water) as the Q increases to 1.9 A~1 no matter what the temperature and water content are.Furthermore,by the abrupt changes of the fitted values of D_(t1),τ_(01),and Γ_1(Q),a crossover temperature at 250 K,namely the liquid-to-crystal-like transition temperature,can be identified for confined water in large gel pores(LGPs) and/or small gel pores(SGPs) contained in the C-S-H gel sample with 30% water content.     

高价钼络合物化学——(Ⅱ) ESR和磁化率研究五价钼半胱氨酸体系的酸解反应

本文利用ESR和磁化率为手段研究了二钼半胱氨酯系列化合物,Na₂Mo₂(μ₂-X)(μ₂-Y)-O₂(cyst)₂(X=Y=O,(Ⅰ);X=O,Y=S,(Ⅱ);X=Y=S,(Ⅲ)),在不同浓度的盐酸溶液中离解的机制,并讨论了不同桥原子对该系列化合物化学稳定性的影响。     

二维圆盘颗粒体系声学行为的数值研究

数值测量了卸载过程中二维单分散圆盘颗粒系统的横波、纵波声速、声衰减系数、非线性系数随压强的变化以及声衰减系数随频率的变化.结果表明,二维(2D)圆盘颗粒体系的横波、纵波声速均随压强呈分段幂律标度:当压强P10~(-4)时,横波、纵波声速随压强的增大而减小;当P10~(-4)时,有v_t~P~(0.202),v_l~P~(0.338).进一步得到其剪切模量和体积模量的比值G/B也随压强呈幂律标度,G/B~P~(-0.502),暗示在低压强下,与三维(3D)球形颗粒体系类似,2D圆盘颗粒体系也处于L玻璃态.水平激励和垂直激励下2D圆盘颗粒系统的衰减系数随频率变化也呈现分段行为:当频率f0.05时,衰减系数不随f变化;当f0.05时,横波纵波的衰减系数α~f;当f0.35时,横波衰减系数α_T~f~2,纵波衰减系数α_L~f~(1.5).此外,竖直水平激励下的2D圆盘颗粒系统的非线性系数和衰减系数随压强也呈现与声速类似的分段规律:当P10~(-4)时,横波非线性系数β_T~P~(-0.230),其余都不随压强变化.当P10~(-4)时,两者均随压强增大呈幂律减小:β_T~P~(-0.703),β_L~P~(-0.684),α_T~P~(-0.099),α_L~P~(-0.105).进而得到2D圆盘颗粒系统中散射相关的特征长度?~*随压强呈幂律标度,当P10~(-4)时,?~*~P~(-0.595);当P10~(-4)时,?~*~P~(0.236).     

定向凝固单晶冰的取向确定与选晶

基于六方冰晶偏振光学特性,定义了用于确定冰晶晶体取向的三个参数:光轴倾角α,消光角β和与冰晶基面(0001)面内晶体学择优方向1120与温度梯度的夹角γ,提出了定量判定冰晶晶体取向的理论基础,并在定向凝固平台上采用偏光显微镜成功实现了冰晶晶体取向的精确主动控制,获得了任意取向的单晶冰.本文成功解决了冰晶的定向凝固晶体取向确定和选择的难题,为冰晶生长过程中相关理论问题的研究提供了有效的途径.     

反应物NO的振动激发对反应C(3P)+NO(X2Π)→CO(X1Σ+)+N(2D)立体动力学性质的影响

采用准经典轨线方法研究碰撞能为0.23 eV时,反应物分子NO在不同初始振动态（v=0~3）下发生在两个电子态（²A″和²A'）势能面上反应C（³P）+NO（X²Π）→CO（X¹Σ⁺）+N（²D）的立体动力学性质。计算反应产物的转动角动量矢量分布（P（θ_r）和P（φ_r））以及微分散射截面（P₀₀（ω_t）,P₂₀（ω_t））。结果表明：反应物的振动激发对发生在²A'势能面上的反应立体动力学性质影响显著,而对发生在²A″势能面上的反应立体动力学性质影响较小,这可能与两个势能面的构型有关。在两个电子态势能面上发生的反应均受内平面反应机理支配。     

Magnetic ordering in U4Cu4P7 single crystal

The magnetic ordering in the tetragonal ternary compound U₄Cu₄P₇ has been studied by neutron diffraction. It orders below T_N = 146 K with an antiferromagnetic structure of wave vector k = (001). The magnetic ordering corresponds to a stacking of ferromagnetic (001) uranium planes according to the sequences m₁, m₁, m₂, -m₂, -m₁, -m₁, -m₂, m₂ where m₁ and m₂ represent the magnetic moment, directed along the tetragonal axis of the two uranium sites U(1) (0,0,± z₁) and U(2) (0,0, ± z₂) respectively. The magnetic moments on these two sites have different temperature dependencies as well as well as they reach the different values of 1.1 and 2.2.μ_B for the U(1) and U(2) sites, respectively.     

Influence of the ferroelastic twin domain structure on the {100} surface morphology of LaAlO3 HTSC substrates

LaAlO₃ crystals have been investigated with differential scanning calorimetry (DSC), high-precision X-ray powder diffraction (XRD) and scanning force microscopy (SFM). The DSC measurements show the second-order phase transition of LaAlO₃ at 544°C, where LaAlO₃ changes its symmetry from the cubic Pm3m high-temperature phase to the pseudocubic rhombohedral low-temperature phase. This paraelastic to improper ferroelastic phase transition causes twinning in the {100} and {110} planes of the pseudocubic lattice. The twin angles between the surface {100}_pseudocubic planes of twin domains were measured by SFM on the surface of a macroscopic (100)_cubic cut crystal plate. The misorientation angle ω₁₀₀ between {100} twins is 0.195(8)°, while {110} twinning gives an angle of ω₁₁₀=0.276(7)°. The two twin kink angles correspond to a rhombohedral angle of the pseudocubic cell of the phase as ₁=90.0973(40)° and ₂=90.0975(30)°, respectively. The XRD result for this rhombohedral angle is =90.096(1)°. The orientation of the misfit steps formed during annealing after mechanical surface polishing depends on the domain orientation and pattern during polishing. Any heating close to or above T_c changes the domain pattern. Footprints of previous domain patterns can thus be found on the surface in the form of surface corrugation and changes in the shape and orientation of misfit steps.     

Electromagnetic coupling reduction in dual-band microstrip antenna array using ultra-compact single-negative electric metamaterials for MIMO application

In this paper, an ultra-compact single negative(SNG) electric waveguided metamaterial(WG-MTM) is first investigated and used to reduce the mutual coupling in E H planes of a dual-band microstrip antenna array. The proposed SNG electric WG-MTM unit cell is designed by etching two different symmetrical spiral lines on the ground, and has two stopbands operating at 1.86 GHz and 2.40 GHz. The circuit size is very compact, which is only λ_0/33.6 ×λ_0/15.1(where λ_0 is the wavelength at 1.86 GHz in free space). Taking advantage of the dual-stopband property of the proposed SNG electric WG-MTM, a dual-band microstrip antenna array operating at 1.86 GHz and 2.40 GHz with very low mutual coupling is designed by embedding a cross shaped array of the proposed SNG electric WG-MTM. The measured and simulated results of the designed dual-band antenna array are in good agreement with each other, indicating that the mutual coupling of the fabricated dual-band antenna array realizes 9.8/11.1 d B reductions in the H plane, 8.5/7.9 d B reductions in the E plane at1.86 GHz and 2.40 GHz, respectively. Besides, the distance of the antenna elements in the array is only 0.35 λ_0(where λ_0 is the wavelength at 1.86 GHz in free space). The proposed strategy is used for the first time to reduce the mutual coupling in E H planes of the dual-band microstrip antenna array by using ultra-compact SNG electric WG-MTM.     

Optical second-harmonic investigations of the isothermal desorption of SiO from the Si(100) and Si(111) surfaces

The isothermal desorption of SiO from the Si(100) and Si(111) surfaces was investigated by means of optical second-harmonic generation (SHG). Due to the high adsorbate sensitivity of this method, desorption rates could be measured over a wide range from 10⁻¹ to 10⁻⁶ ML s⁻¹. From their temperature dependence between 780 and 1000 K, activation energies of E_A=3.4±0.2 eV and E_A=4.0±0.3 eV and pre-exponential factors of ν₀=10^16±1 s⁻¹ and ν₀=10^20±1 s⁻¹ for SiO desorption were obtained for Si(100) and Si(111), respectively. In the case of the Si(100) surface, a pronounced decrease of the first-order rate constants was observed upon increasing the initial coverage from 0.02 to 0.6 ML. The results are interpreted in terms of coverage-dependent oxygen-binding configurations, which influence the stability of the oxide layer.     

外加电场和Al组分对纤锌矿AlGaN/GaN量子阱中的电子g因子的影响

研究了外加电场和垒层的Al组分对AlGaN/GaN量子阱中的横向和纵向g因子(g⊥和g//)及其各向异性(δg)的影响.纤锌矿体结构的贡献(S_//~(bulk)和g⊥)是构成g⊥=(g//-g_0)=g_//~(bulk)的主要部分,但g_//~(bulk)和g⊥的差值很小且几乎不随外加电场和Al组分改变.当外加电场的方向同极化电场的方向相同(相反)且增加时,g_//~(bulk)和g_⊥~(bulk)的强度同时增加(减小).当外加电场从-1.5×10~8 V·m~(-1)到1.5×10~8 V·m~(-1)变化时,异质结界面对g⊥的贡献(Γ_(Inter))大于0且强度缓慢增加,阱层对g⊥的贡献(Γ_W)小于0且强度也缓慢增加.然而Γ_(Inter)的强度比Γ_w大,且后者的强度随着外加电场的改变增加较快,所以δg0且强度随着外加电场的变化而减小.当垒层的Al组分增加时,如果不考虑应变效应(S_(1,2)=0),g_//~(bulk)和g⊥的强度同时减小,然而考虑应变效应后(S_(1,2)≠0),β_1g⊥和γ1(g_//~(bulk))的强度随着Al组分的增加而增加.随着垒层Al组分的增加,Γ_(Inter)和Γ_w的强度都增加,但Γ_(Inter)的强度较大且增加得较快,所以的的强度缓慢增加.g⊥的强度先随着Al组分的增加而减小,然后又随着Al组分的增加而增加,因为g⊥小于0且强度随着Al组分增加得很快.结果表明,AlGaN/GaN量子阱结构中的电子g因子及其各向异性可以被外加电场、垒层的Al组分、应变效应和量子限制效应共同调制.     

基于ab initio的BD~+离子激光冷却理论研究

基于相关一致基组aug-cc-pV5Z,采用内收缩多参考组态相互作用方法计算了BD~+离子两个最低解离极限B~+(~1Sg)+D(~2Sg)和B+(~3Pu)+D(~2Sg)对应的5个Λ—S态(X~2Σ~+,A~2Π,B~2Σ+,a~4Π和b~4Σ~+)的势能曲线和跃迁偶极矩.根据计算结果,求解核运动的径向薛定谔方程得到相应电子态的振-转光谱常数、Franck-Condon(F-C)因子和振动能级辐射寿命.其中A~2Π—X~2Σ~+的F-C因子(f_(00)=0.923)、辐射寿命(τ=235 ns)满足激光直接冷却的条件.因此,我们基于分子转动跃迁提出了一个可实现Doppler激光冷却的光循环方案:A~2Π_(1/2)(υ′=0)—X~2Σ+(υ′′=0,1),其中υ′=0中包含2个转动能级,υ′′=0和υ′′=1中分别包含6个和4个转动能级.根据方案,模拟了激光冷却过程中的分子布居数动力学变化过程,并计算了初速度为100 m/s的BD~+,历经5.4 ms散射1150个光子可减速到4.6 m/s、温度为13 mK.     

相位角对容性耦合电非对称放电特性的影响

电非对称效应作为一种新兴技术,被广泛用于对离子能量和离子通量的独立调控.此外,在改善等离子体的径向均匀性方面,电非对称效应也发挥了重要作用.本文采用二维流体力学模型,并耦合麦克斯韦方程组,系统地研究了容性耦合氢等离子体中当放电由多谐波叠加驱动时,不同谐波阶数k下的电非对称效应,重点观察了相位角θ_n对自偏压以及等离子体径向均匀性的影响.模拟结果表明：在同一谐波阶数下,自偏压随相位角θ_n的变化趋势不尽相同,且当k增大（k>3）时,自偏压随最高频相位角θ_k的变化范围逐渐减小.此外,通过调节相位角θ_n,可以改变轴向功率密度和径向功率密度的相对关系,进而实现对等离子体径向均匀性的调节.研究结果对于利用电非对称效应优化等离子体工艺过程具有一定的指导意义.