掺稀土元素(Y，La)的γ-Si3N4的电子结构和光学性质

采用基于密度泛函的平面赝势方法(PWP)和广义梯度近似(GGA)，计算了未掺杂和掺杂稀土(Y，La)的γ-Si₃N₄中N-Y(La)键的布居值和它们的键长、掺杂后能带结构和态密度.发现掺杂后的带隙要减小，并且可能形成新的半导体，这将为找到新的半导体提供一个方向.还进一步研究了掺杂稀土(Y，La)后的光学性质，掺杂后有更高的静态介电常数，可以作为新的介电材料和好的折射材料，这对于一定的光学元件有潜在的应用前景.     

Heusler合金Li2AlX(X=Ga，In)的晶格动力学和电子特性

本文计算了Heusler合金Li₂AlGa和Li₂AlIn的晶格参数、体积模量、体积模量的一阶导数、 电子能带结构、声子色散曲线和声子态密度,并与密度泛函理论中的广义梯度近似计算结果进行比较. 计算的晶格参数与文献有很好的一致性. 两个Heusler合金的电子能带结构表明它们是半金属结构. 并利用声子色散曲线和声子密度图研究Heusler合金晶格动力学. Li₂AlGa和Li₂AlIn Heusler合金在基态呈现动力学稳定.     

n型透明导电薄膜CdIn2O4电学性质的研究和大面积制备的最佳条件

在Ar+O2₂气氛中，采用射频反应溅射Cd-In靶制备CdIn2₂O4₄ 薄膜.制得的薄膜经x射线衍射（XRD）检测为CdIn2₂O4₄和CdO相组成的多晶.从理论上分析了热 处理前后氧空位、掺杂点缺陷和富氧电子陷阱在影响膜的载流子浓度和电子散射中所起的重要作用.同时，对样品 进行Hall效应、Seebeck效应测试并得出不同载流子浓度下的迁移率、有效质量、弛豫时间以及它们之间的相互关系，特别强调     

Density Functional Theory Study on Electronic and Magnetic Properties of Mn-doped (MgO)n (n=2～10) Clusters

利用密度泛函理论方法优化了纯的和M_n原子掺杂的(MgO)_n (n=2～10)团簇的几何结构. 在Mn原子掺杂的氧化镁结构中, 获得了一系列的同分异构体和与之相对应的总能量.MnMg_n-1O_n(n=2～10)的几何构型显示Mn原子优先取代低配位的Mg原子. 结构稳定性分析表明,除了(MgO)₁₀团簇外,其它纯的和掺杂结构的平均结合能均随着团簇的增大而增强. MnMg_n-1O_n团簇的二阶能量差结果表明MnMg₅O₆和MnMg₈O₉比相邻的团簇表现出更高的相对稳定性. 除了MnMgO₂团簇的磁矩为3.00 μB外,其它掺杂结构的磁矩均为5 μB左右. 它们的磁性主要受电荷转移大小、原子在结构中的位置以及结构尺寸所影响.     

AdS5\otimes S1, AdS5\otimes S5和AdS2\otimes S2超弦模型的一种KRR参数化新方法

给出了3种典型超弦模型AdS₅\otimes S¹, AdS₅\otimes S⁵和AdS₂\otimes S²的一种简单的KRR参数化新方法, 并结合这些超弦模型所具有的κ对称性给出了它们的卡当1-form, Maurer-Cartan方程, 作用量和运动方程.     

掺杂质子化石墨相氮化碳增强碳基太阳能电池中钙钛矿的结晶

钙钛矿层的品质极大影响钙钛矿太阳能电池性能. 然而,在溶液法生成多晶钙钛矿膜过程中会不可避免地形成缺陷和陷阱位. 通过在钙钛矿层中嵌入添加物改善钙钛矿晶化,用于减少和钝化缺陷是非常重要的. 本文合成一种环境友好的二维纳米材料质子化石墨相氮化碳(p-g-C₃N₄),并掺杂于碳基钙太阳能电池的钙钛矿层中. 实验证明,在钙钛矿前驱体溶液中添加p-g-C₃N₄不仅能调解碘铅甲胺(MAPbI₃)结晶的成核和生长速率,获得大晶粒尺寸的平滑表面,还能减少钙钛矿层的本征缺陷. 质子化过程在氮化碳表面引入活性基团-NH₂/-NH₃,它们和钙钛矿晶体表面N-H键发生强化学作用,有效地钝化电子陷阱,提高钙钛矿结晶质量. 结果表明,与不掺杂的对照电池(效率为4.48%)和掺杂石墨相氮化碳(g-C₃N₄)电池(效率为5.93%)相比,掺杂质子化石墨相氮化碳(p-g-C₃N₄)的电池获得了6.61%的较高效率. 本工作展示了一种通过掺杂改性添加物改善钙钛矿膜的简单方法,为碳基钙钛矿太阳能电池的低成本制备提供了建议.     

高能反应机制与自旋效应

高能强子一强子反应实验中发现一系列引人注目的自旋效应,这些效应出现的机理一直是人们关注的热门课题之一.近几年,在实验及理论家共同的努力下,虽仍有许多不清楚的问题,但已取得一些突破.结果表明,不仅对这些现象产生机理研究能为强子结构及强子反应机制提供信息,而且这些现象本身也用作探索强子反应机制的工具.例如用它们来研究小x_B光子与强子反应的性质.本报告将首先简单总结这些现象及其产生机理研究的结论,然后介绍该例的主要思想及结果.     

双参数变形多模玻色算符的代数结构及其应用(Ⅲ)

构造了双参数变形多模玻色算符高次幂的本征态,发现它们构成完备Hilbert空间,另外,还给出了双参数变形量子代数SL_q,s(3)的数学结构、玻色实现以及Sl_q,s(2)的阶类张量算符,指出将SL_q,s(3)的上述结果推广到多模情况是容易的.     

C掺杂锐钛矿相TiO2吸收光谱的第一性原理研究

运用第一性原理,对C掺杂锐钛矿相TiO₂的电子结构进行了研究,从能带结构理论解释了C掺杂TiO₂吸收光谱的一些实验现象.发现在C掺杂后的锐钛矿相TiO₂的禁带宽度增大,并且在带隙中出现了杂质能级,这些杂质能级主要是由C 2p轨道上的电子构成的,它们之间是独立的,正是这些独立的杂质能级使TiO₂掺杂后可以发生可见光响应.价带上的电子可以吸收一定能量的光子跃迁到杂质能级,而杂质能级上的电子也可以吸收一定能量的光子跃迁到导带,所以从理论上可以计算出掺杂后的TiO₂在可见光范围内存在两个吸收边,与实验中所得到的现象相一致.     

FC(O)O2的结构及其自由基与NO反应的微观机理研究

用密度泛函理论(DFT)和哈特里-福克(HF)从头计算方法和半经验势方法等研究了FC(O)O₂ 的结构和振动性质.在DFT中采用B3LYP方法,在6-311G(d)基组上对FC(O)O₂自由基与NO反应的微观过程进行了分析.首先给出了各反应物、中间体、过渡态和生成物的几何构型,然后计算了它们的能量和频率,通过频谱分析得到反应的中间体和过渡态信息,即FC(O)O₂与NO反应为多反应通道,势垒高度和反应速度给出主要通道是FC(O)O₂     

Dynamic structure factor of vibrating fractals

Motivated by novel experimental work and the lack of an adequate theory, we study the dynamic structure factor S(k,t) of large vibrating fractal networks at large wave numbers k. We show that the decay of S(k,t) is dominated by the spatially averaged mean square displacement of a network node, which evolves subdiffusively in time, ((u[over →](i)(t)-u[over →](i)(0))(2))～t(ν), where ν depends on the spectral dimension d(s) and fractal dimension d(f). As a result, S(k,t) decays as a stretched exponential S(k,t)≈S(k)e(-(Γ(k)t)(ν)) with Γ(k)～k(2/ν). Applications to a variety of fractal-like systems are elucidated.     

一类本征态迭加的高次压缩特性

对一类光子消灭算符aN的正交归一本征态的迭加态的振幅k次方压缩特性进行研究,结果表明一类aN的正交归一本征态的迭加态的振幅k次方压缩特性明显地区别于aN的正交归一本征态k次方压缩.无论N取奇数还是偶数迭加态均存在振幅k(k=Nt或Nt/2)次方压缩,当位相差δ=2mπ/t(m为整数)时迭加态不存在振幅k次方压缩;当δ=π时,只有N和t同时为奇数才有可能存在k次方压缩;当δ=π/2时,对应t≠4m的不同取值迭加态存在k次方压缩;因而参量的位相对振幅的k次方压缩起着关键性的作用.     

Three dimensional anisotropic κ spectra of turbulence at subproton scales in the solar wind

We show the first three dimensional (3D) dispersion relations and k spectra of magnetic turbulence in the solar wind at subproton scales. We used the Cluster data with short separations and applied the k-filtering technique to the frequency range where the transition to subproton scales occurs. We show that the cascade is carried by highly oblique kinetic Alfvén waves with ω(plas) ≤ 0.1ω(ci) down to k(⊥) ρ(i)～2. Each k spectrum in the direction perpendicular to B0 shows two scaling ranges separated by a breakpoint (in the interval [0.4,1]k(⊥)ρ(i): a Kolmogorov scaling k(⊥)?1?? followed by a steeper scaling ～k(⊥)????. We conjecture that the turbulence undergoes a transition range, where part of the energy is dissipated into proton heating via Landau damping and the remaining energy cascades down to electron scales where electron Landau damping may predominate.     

Billiards with a given number of (k,n)-orbits

We consider billiard dynamics inside a smooth strictly convex curve. For each pair of integers (k,n), we focus our attention on the billiard trajectory that traces a closed polygon with n sides and makes k turns inside the billiard table, called a (k,n)-orbit. Birkhoff proved that a strictly convex billiard always has at least two (k,n)-orbits for any relatively prime integers k and n such that 1≤k相似文献   

真空态多光子Jaynes—Cummings模型中场的振幅N次方压缩

本文研究了一初始处于原子相干态的二能级原子与真空态场相互耦合的ｋ光子Ｊａｙｎｅｓ－Ｃｕｍｍｉｎｇｓ模型中场的振幅Ｎ次方程压缩特性。结果表明，场不仅存在振幅Ｎ＝ｋ次方压缩，而且当ｋ为偶数时，还存在振幅Ｎ＝ｋ／２次方压缩。     

Universal order statistics of random walks

We study analytically the order statistics of a time series generated by the positions of a symmetric random walk of n steps with step lengths of finite variance σ(2). We show that the statistics of the gap d(k,n) = M(k,n)-M(k+1,n) between the kth and the (k+1)th maximum of the time series becomes stationary, i.e., independent of n as n → ∞ and exhibits a rich, universal behavior. The mean stationary gap exhibits a universal algebraic decay for large k, ~d(k,∞)-/σ 1/sqrt[2πk], independent of the details of the jump distribution. Moreover, the probability density (pdf) of the stationary gap exhibits scaling, Pr(d(k,∞) = δ) ~/= (sqrt[k]/σ)P(δsqrt[k]/σ), in the regime δ~ (d(k,∞)). The scaling function P(x) is universal and has an unexpected power law tail, P(x) ~ x(-4) for large x. For δ> (d(k,∞)) the scaling breaks down and the pdf gets cut off in a nonuniversal way. Consequently, the moments of the gap exhibit an unusual multiscaling behavior.     

Method for solving moving boundary value problems for linear evolution equations

We introduce a method of solving initial boundary value problems for linear evolution equations in a time-dependent domain, and we apply it to an equation with dispersion relation omega(k), in the domain l(t)相似文献   

Laser interferometry measurements of middle ear fluid and pressure effects on sound transmission

An otitis media with effusion model in human temporal bones with two laser vibrometers was created in this study. By measuring the displacement of the stapes from the medial side of the footplate, the transfer function of the middle ear, which is defined as the displacement transmission ratio (DTR) of the tympanic membrane to footplate, was derived under different middle ear pressure and fluid in the cavity with a correction factor for cochlear load. The results suggest that the DTR increases with increasing frequency up to 4k Hz when the middle ear pressure was changing from 0 to 20 or -20 cm H20 (e.g., +/-196 daPa) and fluid level was increasing from 0 to a full middle ear cavity. The positive and negative pressures show different effects on the DTR. The effect of fluid on DTR varies between three frequency ranges: f < 1k, between 1k and 4k, and f > 4k Hz. These findings show how the efficiency of the middle ear system for sound transmission changes during the presence of fluid in the cavity and variations of middle ear pressure.     

Thermal conductivity of nanoscale colloidal solutions (nanofluids)

Researchers have been perplexed for the past five years with the unusually high thermal conductivity (k) of nanoparticle-laden colloidal solutions (nanofluids). Although various mechanisms and models have been proposed in the literature to explain the high k of these nanofluids, no concrete conclusions have been reached. Through an order-of-magnitude analysis of various possible mechanisms, we show that convection caused by the Brownian movement of these nanoparticles is primarily responsible for the enhancement in k of these colloidal nanofluids.     

原子在双腔场间的共振隧穿

考虑单个二能级原子穿过2个空间分离的单模腔场,研究原子质心运动的动能、腔长与腔间距对原子透射率的影响。结果表明：当原子的动能比较大时,原子有足够的能量穿透腔场对其的阻挡,此时只有腔长的变化对原子的透射有微小的影响而腔间距的作用则可以忽略;当原子的动能较小时,原子本身的能量小于腔场势垒的能量,此时腔长与腔间距对原子透射率的影响极为明显。