全原子分子动力学模拟结合核磁共振波谱研究N-甘氨酰甘氨酸水溶液的结构和弱相互作用

采用分子动力学模拟方法结合核磁共振化学位移系统研究了甘氨酰甘氨酸水溶液体系饱和溶解度范围的弱相互作用. 径向分布函数表明体系中不同类型的原子显示出形成氢键的不同能力. 氢键网络分析发现了不同氢键所能形成的分子簇结构. 随温度变化核磁共振化学位移值用于研究形成氢键的变化情况,并和模拟得到的结果进行比较,模拟和实验结果得到了较好的吻合.     

分子动力学模拟研究DMSO-水体系的结构和相互作用

用分子动力学模拟方法结合核磁共振化学位移和红外光谱结果,研究二甲基亚砜DMSO水溶液在全浓度范围内的结构和弱相互作用. 表明径向分布函数分析,DMSO水溶液中既存在着传统的强氢键又存在C—H…O弱相互作用. 氢键网络分析发现DMSO水溶液体系在水富集区域,水分子倾向于自身缔合形成稳定的分子簇结构,而随着DMSO浓度的逐渐增加,水的有序结构受到破坏. DMSO的摩尔分数为0.35是一个特殊点,多种性质偏离理想混合最远. 水分子和DMSO分子发生了交叉缔合作用形成稳定的分子聚集体. 分子动力学统计的平均氢键数与核磁共振化学位移和红外波数变化数据结果进行比较,结果吻合很好.     

Structures and Hydrogen Bonding Interactions in Urea-water System Studied by All-atom MD Simulation and Chemical Shifts in NMR Spectrum

采用分子动力学模拟方法结合核磁共振化学位移和粘度对尿素水溶液在稀浓度范围内的结构和弱相互作用进行研究. 从径向分布函数(RDF)分析看出,尿素水溶液中存在着几种不同类型、不同氢键形成能力的传统氢键. 氢键网络分析发现尿素水溶液体系在水富集区域,水分子倾向于自身缔合形成稳定的分子簇结构,而随着尿素浓度的逐渐增加,水的有序结构受到破坏,水分子和尿素分子发生了交叉缔合作用形成氢键,尿素分子有形成自身缔合的趋势. 分子动力学统计的平均氢键数与核磁共振化学位移和粘度数据结果进行比较,发现它们的变化趋势一致,证明了实验和理论结果有很强的可靠性.     

分子间相互作用对核酸碱基中17O屏蔽张量与四极耦合常数影响的理论计算研究

通过高精度量子化学理论计算的方法研究了分子间弱的非键相互作用对胸腺嘧啶、尿嘧啶、胞嘧啶和鸟嘌呤四种核酸碱基中~(17)O核的屏蔽张量(σO)和四极耦合常数(QCC)的影响.计算结果表明分子间强的氢键作用以及弱的范德华(vd W)相互作用都对~(17)O核的化学位移(δO)具有较大的影响.随着分子间氢键作用的逐渐增强,δO逐渐减小,当采用包含所有弱相互作用的周期性模型进行计算时,理论结果与实验值吻合.进一步的电荷分析显示,~(17)O核化学位移的减小主要是由于分子间氢键作用强度增加导致~(17)O原子的负电荷密度逐渐增加.此外,计算结果表明碱基中分子间氢键网络和弱的范德华作用对碱基~(17)O QCC也具有显著的影响.周期性模型下,碱基上氧原子的局域结构环境得到平衡,~(17)O QCC达到最小值,与实验结果最为接近.以核酸碱基为例,说明了分子间的氢键网络以及分子间弱的相互作用对于准确计算生物样品的核磁共振(NMR)参数非常重要,以小的团簇模型来计算生物体系的核磁参数将会产生较大的偏差.     

溴代1-己基-3-甲基咪唑离子液体与丙酮的相互作用

运用核磁共振氢谱和碳谱手段,研究了室温离了液体溴代1-己基-3-甲基咪唑([C6mim]Br)在不同浓度的离子液体/丙酮混合体系中的1H和13C化学位移．实验结果表明,离了液体[C6mim]Br的阴离子与丙酮甲基上的氢原子相互作用并形成了氢键．量子化学计算结果与核磁共振实验结果一致．     

全原子分子动力学模拟研究丙氨酸二肽水溶液的结构和氢键作用

采用全原子分子动力学模拟研究了丙氨酸二肽分子在水溶液中的结构和氢键作用。径向分布函数和氢键统计用于分子动力学模拟的分析。从径向分布函数（RDF）发现不同类型的强氢键显示出不同的形成能力,而体系中的C−H•••O弱相互作用较为明显,也不能忽略。氢键统计分析的结果也证实了这一点。分子内距离、回转半径和骨架二面角用于表征丙氨酸二肽分子在水溶液中的构象变化。丙氨酸二肽分子在水溶液中的柔顺性较好,构象在折叠和伸展之间相互转换。     

三种二元水溶液体系中氢键对拉曼线宽的影响

采用显微共聚焦拉曼光谱对三种二元水溶液(乙腈/水、二甲基亚砜(DMSO)/水和丙酮/水)进行测量,得到含有氢键作用的水溶液体系拉曼频移和线宽随浓度的变化规律。应用混合模型和相互作用体系的线宽经验公式对实验结果进行了分析。结果表明,含有氢键作用的水溶液体系中,氢键作用越强线宽越大,并且线宽随单位浓度变化率大;同种氢键体系中,线宽不仅受浓度浮动的影响,氢键作用也是一个重要的影响因素,定量分析证明线宽与浓度、氢键作用关系很好地符合Ojha等提出的线宽公式。     

PAMAM树状大分子与5-氟尿嘧啶相互作用的NMR研究

本文利用多种核磁共振（NMR）技术研究了聚酰胺-胺树状大分子（PAMAM）与5-氟尿嘧啶（5-FU）在水溶液中的相互作用.¹H NMR化学位移滴定结果表明5-FU分子结合在PAMAM分子表面,¹³C NMR化学位移滴定分析结果表明5-FU分子通过氢键或疏水间相互作用进入到PAMAM的内部疏水空腔.¹H核和¹⁹F核自旋-晶格弛豫时间（T₁）的测定结果也说明了二者之间存在相互作用.NOESY实验进一步验证了5-FU分子进入到PAMAM分子的内部空腔.本研究为研究树状大分子和药物小分子的相互作用提供了系统的NMR分析方法.     

在晶体和溶液中氟离子的核磁共振化学位移的研究

本文简单地描述了一种具有中等分辨本领的核磁共振波谱仪及测量固体中共振讯号化学位移的方法。对周期表中第一、二两族元素的氟化物晶体的F¹⁹共振的化学位移(δ)作了研究,发现除LiF以外,δ随着金属元素原子序数的增加而减少。用Yosida和Moriya的部分共价性理论以及Kondo和Yamashita电子壳层重迭理论讨论了实验结果,计算了碱金属氟化物相邻离子的重迭积分,用Kondo和Yamashita公式得到了与实验基本相符的磁屏蔽常数。根据这个符合,估计了氟的核磁屏蔽常数的绝对值σ,得到了合理的结果。研究了NH₄F盐类水溶液中F¹⁹共振位移的浓度效应,发现δ随浓度的增加而直线下降。把δ值和浓度关系的曲线外推到固体的克分子浓度值时,得到与直接测得的δ值相符的结果。其他碱金属氟化物水溶液的化学位移也有类似行为,表明溶液中离子间的相互作用对离子的电子结构的影响与固体中基本相同酸性氟化物盐类水溶液的研究确定了HF和HF₂^-的δ值。     

二甲基亚砜水溶液表面张力及粘度与氢键的拉曼光谱研究

利用ZL-10型全自动界面张力仪(柏金环法)和NDJ-5S型数显粘度计测量体积分数为5%～100%的二甲基亚砜(DMSO)水溶液及超纯水,得到表面张力和粘度的变化规律。用拉曼光谱仪测量不同浓度DMSO水溶液的拉曼光谱,得到体系中含氢键作用的拉曼频移变化规律。实验结果表明,DMSO水溶液的表面张力随浓度的变化受DMSO水溶液中氢键作用的影响,且与氢键强度成反相关。DMSO与水的氢键作用对粘度的影响较表面张力更为复杂,粘度随浓度的变化呈二次函数的反常现象,影响因素包含氢键强度,氢键网络结构和空间方向性多个方面。该研究探索一种利用拉曼光谱研究水溶液微观结构与宏观物理性质关系的实验方法。     

Self-organization of five species in a cyclic competition game

Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity.     

Experimental study on downstep in Chinese intonation

Downstep in pitch contour of Chinese Putonghua is examined using subtly designed sentences by controlling tone combinations. The results show both automatic and nonautomatic downstep phenomena exist in Chinese. In non-automatic downstep, low tones compress downwards the pitch range of the following syllables. and the main influence of downstep is on topline. Low tone not only lower the topline behind it, but also raise the high tones before it, the effects are compatible with each other. In automatic downstep, the topline of pitch contour in intonational phrase is presented as a linear downtrend, but it differs among speakers due to the effect of personal stress practice. In comparison with downstep phenomenon in other tone or non-tone languages, the downstep ratio in Chinese is not constant, and the domain of downstep is not limited within the adjacent tones.     

Contrastive analysis on tone between Putonghua and Taiwan Mandarin

The differences of the pitch and duration of Chinese syllables between Putonghua （PTH） and Taiwan Mandarin （TM） were studied. The speech materials to be used are not only isolated syllables, but also sentences. The results reveal that： For the isolated syllables, T1 and T2 in TM are influenced by Minnan dialect, therefore their pitch are lower than those in PTH. T3 is fall-rise in PTH, while it is fall in TM. Moreover, the syllable duration sequence for different tone is T3〉T2〉T1〉T4 in PTH, while it is T1〉T2〉T3〉T4 in TM. For the syllables in sentences, T2 is mid-rise in PTH, while it is mid-level in TM. And the T3 is longer than T4 but shorter than T1 or T2 in PTH, while it is the shortest in TM. Furthermore the effects of prosodic phrase boundary on duration for different tones are almost the same in PTH, but the lengthening part of T1 or T2 is longer than that of T3 or T4 in TM.     

Abelian-Higgs phase of SU(2) QCD and glueball energy

It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1].     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.     

Real-time restoration of rotational blurred image using gradient-loading

The key to the restoration of rotational motion blurred image is how to restore the image under a low cost and to correct the irreversibility of the degradation function matrix.Based on the special qualities of degradation function matrix and precise deduction in space-domain, we present a new approach using gradient-loading for restoration of rotational blurred image.By easily adding a gradient operator, the irreversibility of the original matrix is corrected and can be applied for inverse filtering then.Gradientloading is the optimized approach which combines the advantages of both the approaches using constrained least square filtering and traditional diagonal-loading.Compared with the approach using least square filtering, its peak signal-to-noise ratio (PSNR) is improved from 3.18 to 6.46dB, while the computing time is reduced to 1/2-1/3.Experimental results demonstrate the effectiveness, noise-resistibility, robustness, and low complexity of this approach, which make it more suitable for real-time environment.     

All-Optical Logic Device Using Bent Nonlinear Tapered Y-Junction Waveguide Structure

We propose an all-optical logic device made of a bent tapered Y-junction waveguide with a Kerr-type nonlinear interface. It could provide an AND gate, OR gate, and exclusive-OR (XOR) gate. We could obtain different transmission results by adjusting the bending angle. The numerical simulation results show that the device functions as AND, OR, and XOR gates.