二维相关振动光谱技术

从发展历史、计算方程、性质规则等方面系统地介绍了近年来发展起来的二维相关光谱技术.结合各种常见的一维振动光谱, 如红外、拉曼、荧光、近红外-红外等光谱举例阐述了二维振动光谱的优势及其普适性.介绍了在广义二维相关光谱理论上最新延伸发展起来的二维样品-样品相关技术和二维杂化相关技术的基本理论, 并将之与传统的二维变量-变量相关技术(广义二维相关光谱)进行了比较.     

移动窗口二维相关光谱技术

移动窗口二维相关光谱是一种新的二维相关分析方法,它将移动窗口的概念和二维相关分析方法有效地结合在了一起,利用移动窗口将庞大的光谱数据按矩阵分割成若干个便于操作的子矩阵,用二维相关光谱分别处理,将得到的结果综合分析,用以光谱变量和扰动变量为坐标的等高图表现出来,从中可以非常直观地观察出光谱强度在扰动变量方向上的变化,进而找出引起光谱强度突变的特征扰动点。本文主要介绍了移动窗口二维相关光谱的计算方法、基本特征、影响因素和实际应用,同时还详细介绍了以它为基础改进得到的扰动相关移动窗口二维相关光谱。扰动相关移动窗口二维相关光谱包括同步图和异步图,它不仅能很好地反映出引起光谱强度突变的特征扰动,还能详尽地描述出光谱强度在扰动过程中的变化情况。     

数字图像相关技术在应力应变测量中的发展与最新应用

在现代材料的应力应变测量中,数字图像相关测量法具有非接触、全场性、对实验条件要求低、精度高等优点,是一种有效、实用的应力应变测量方法,被广泛的应用于实验力学及其他学科领域。本文综述了数字图像相关技术在材料应力应变方面的发展;将数字图像相关技术与其它测量技术进行了比较;介绍了数字图像相关技术的系统结构与相关算法、搜索方法;最后列举了数字图像相关技术在材料应力应变中的最新应用和新产品。     

二维相关荧光光谱技术

从发展历史、计算方程、一般规则和特有性质等方面系统地介绍了近年来在二维相关荧光光谱技术方面的方法探索和应用进展。以不同的外扰方式，如浓度、激发波长、猝灭以及其他如pH等分类，举例阐述了二维荧光相关光谱的可操作性及其应用，并与普通一维荧光光谱比较，说明了二维荧光相关光谱技术的优势。     

二维相关分析光谱技术

给出推导二维相关光谱和推广至普遍意义上的数学过程,其物理含义和二维相关光谱的性质及其解释规则。以应用实例给出了该光谱技术在分析结构、相互作用等相关性方面的独特性质。还给出紫外可见二维相关光谱。     

基于相关因素的遥感影像辐射质量度量模型研究

目前遥感影像辐射质量评价多以目视判读为主,具有很强的主观性。针对如何客观、全面地评价遥感影像辐射质量这一问题,本文研究了一种利用质量相关因素来评价遥感影像辐射质量的度量模型。该模型提取遥感影像的四个因素指标,即亮度、清晰度、信息量和纹理特征,采用相关分析法计算各个因素指标的权值。对于清晰度指标,通过改进梯度函数,研究了新的清晰度提取方法。实验证明,对于多种不同类型的遥感影像,本模型所得的评价结果可较好地符合人眼的视觉感受。该遥感影像辐射质量度量模型能够客观、定量地分析遥感影像辐射质量,同时与主观评价具有一致性。     

成人血清元素相关性及比值分析

用ＩＣＰ－ＭＳ法测定了７９例成人血清１４种元素水平,并进行了相关分析。结果提示,多种元素间存在显著正相关;分析了部分元素的比值,为相关研究提供了参考范围,且对元素比值的离散程度进行分析,为多元素关系研究提供了新的线索与依据。     

胃癌与七种元素关系的分析

57例胃癌癌灶内锌值为(13.740±4.150)×10~(-6),低于癌边缘组织(15.677±4.567)×10~(-6)(P<0.01),亦低于正常组织(15.897±3.580)×10~(-6)(P<0.01)。癌灶铜值为(7.91±6.19)×10~(-6),高于正常组织(5.62±12.01)×10~(-6)(P<0.05),癌灶铜/锌比值亦高于正常组织(P<0.01),但与边缘组织无显著性差异。分化较好的胃腺癌与未分化癌间七种微量元素含量均无显著性差异。这些结果提示,胃癌组织中锌值的降低与铜/锌比值的升高可作为胃癌的辅助诊断指标,而且锌值的检测更具意义。但与分化程度无关。     

色谱流动相的相关系数法聚类分析

１引言在色谱分离工作中，为了更好地选择溶剂以达到分离相似组分的目的，需要对溶剂进行分类。这方面，Ｓｎｙｄｅｒ的工作比较出色，但仅仅考虑了ｘｅ、ｘｄ、ｘｎ３个选择性参数。有人根据原始数据运用Ｆｕｚｚｙ聚类分析法计算了８１种溶剂的选择性参数，并考虑了另外两个选择性参数：ｘｔ和ｘｍ。本文运用相关系数法，对８１种溶剂重新进行了计算，分类结果直观，合理，并发现了一类特殊性质的溶剂。２理论部分２．１溶剂的选择性参数　溶剂的极性参数Ｐ’定义为：式中，Ｋ”ｇ为极性分配参数。若定义：　则有：它们分别表示了接受质子…     

HX体系电子对内、对间相关研究

在6-311+G^*基组水平上用CISD（configurationinteractionwithsinglyanddoublyexcitedconfigurations)方法研究HX(X=Li-F,HBe)体系电子对内、对间的相关能。计算结果表明不同元素形成的HX(X=Li-F,HBe^+,HBe)体系,其价层电子对内、对间相关能的变化较大,它们之间存在着轨道差别,不宜将其相关贡献归为简单的常数。在使用相同理论方法和相同质量基组的前提下,电子数将直接影响到电子对间相关能的大小。对于多电子体系,电子对间相关在总相关中占有优势,若将其忽略会引起较大误差。     

Effects of Pressure and pH on the Physical Stability of an I-Motif DNA Structure

The thermodynamic stability of a cytosine(C)-rich i-motif tract of DNA, which features pH-sensitive [C..H..C]⁺ moieties, has been studied as function of both pressure (0.1–200 MPa) and pH (3.7–6.2). Careful attention was paid to correcting citrate buffer pH for known variations that stem from changes in pressure. Once pH-corrected, (i) at pH >4.6 the i-motif becomes less stable as pressure is increased (K_D decreases), giving a small negative volume change for dissociation (Δ_DV°) of the i-motif – a conclusion opposite to that which would be drawn if the buffer pH was not corrected for the effects of pressure; (ii) the i-motif's melting temperature increases by more than 30 K between pH 6.5 and 4.5, the consequence of an enthalpy for dissociation (Δ_DH°) of 77(3) and 90(3) kJ (mol H⁺)⁻¹ at 0.1 and 200 MPa, respectively; (iii) below pH 4.6 at 0.1 MPa (pH 4.3 at 200 MPa) the melting temperature decreases as a result of double protonation of cytosine pairs, and Δ_DH° and Δ_DV° change signs; and (iv) the combination of Δ_DH° and Δ_DV° lead to the melting temperature at pH 4.3 being 3 K higher at 200 MPa than at 0.1 MPa.     

Theoretical studies of intramolecular electron transfer reactions: Distance and free energy dependences

Electron tunneling through a square potential energy barrier is used to calculate the distance-dependent factors of electron transfer (ET) processes in metal-monolayer-metal junctions, donors and acceptors dispersed in rigid organic glasses, intramolecular ET in rigid donorbridge—acceptor species in solution and redox centers attached to electrodes through adsorbed monolayers. This tunneling model of distancedependent non-adiabatic factors is incorporated in the intersecting state model (ISM). The result is a simple semiclassical theory which is used to calculate the rates of non-adiabatic ET reactions. When the electron is originally located in a π* molecular orbital of the donor and the reaction free energy is no lower than approximately −50 kJ mol⁻¹, no adjustable parameters are necessary to calculate the intramolecular ET rates from a donor, through a rigid bridge, to an acceptor. Such calculated rates are within an order of magnitude of the experimental values. The model can also account for the ET rates of more exothermic reactions provided that the value of an empirical parameter, which is constant for structurally related reactants and solvents of similar polarity, is estimated. The physical meaning of this parameter is related to the dynamics of the reactions. The profiles of the distance and free energy dependences of photoinduced ET rates are closely reproduced. The occurrence of distance-dependent non-adiabatic factors in intermolecular σ*-d ETs is rationalized.     

Effects of stress ratio on fatigue crack growth of thermoset epoxy resin

The influences of stress ratio (R) on fatigue crack growth (FCG) of thermoset epoxy resin with polyamine hardener were investigated. The FCG growth rates (da/dN) have been correlated by the linear-elastic fracture mechanics parameters (ΔK and K_max), and nonlinear-elastic fracture mechanics parameter (ΔJ). The effects of R on FCG were observed when the ΔK and ΔJ were used as fracture mechanics parameters for FCG. However, the K_max successfully characterized FCG under cyclic-dependent condition (FCGs at R = 0.1 and 0.4); but it failed to characterize the FCG under time-dependent condition (FCG at R = 0.7). As a time-dependent fracture mechanics parameter, C* was applied to correlate the time-dependent FCG rate (da/dt). A reasonable agreement was obtained between time-dependent FCG (R = 0.7) and creep crack growth (CCG) results.     

Dosimetric properties of commercial grade plexiglas as a possible routine dosimeter for radiation processing

Dyed and undyed polymethylmethacrylate (PMMA) are commercially available for high dose dosimetry in radiation processing applications. In order to investigate the properties of the locally available clear perspex as a subsitute routine dosimeter, we have looked into the optical and dosimetric properties of clear perspex sheets with a thickness of 2 mm.

The selected wavelength used for read out was 314 nm. Absorption spectra obtained showed a sharp cutoff at 260 nm wavelength. Post-irradiation studies at different doses indicate that the optical density decrease with storage time. No significant dose rate dependence in the range of 1.1 to 11 kGy/hr has been observed. The temperature response of the said clear perspex in the range of 0–30°C during irradiation has also been determined.

Comparison of the optical density versus dose for the local clear perspex against that of red perspex from Harwell, at an absorbed dose of 25 kGy, as obtained in our gamma irradiator, IR-136, showed a difference of 3%. The reproducibility of the local clear PMMA has been observed to be also less than 3% in an absorbed dose range of 5 to 50 kGy.     

Temperature and frequency dependencies of the complex dielectric constant of poly(ethylene oxide) under hydrostatic pressure

Electrical impedance measurements have been made in the frequency range 5 Hz to 10 MHz in pure poly(ethylene oxide) having a molecular weight of 600,000 from 12 K nearly up to the melting point of the crystalline phase (about 330 K). A pronounced relaxation peak in the dielectric loss and a corresponding step in the dielectric constant have been observed at about 240 K, which can be readily related to the glass-rubber transition in the amorphous region of the polymer. As the temperature approaches the melting point there are large increases in the real ϵ′ and imaginary e′ parts of the dielectric constant. The frequency dependence of ϵ′ is characterized by a primary relaxation process, whose frequency increases with increasing temperature as a consequence of decrease of the average structural relaxation time. There is strong evidence that this low-frequency dispersion arises mainly from the diffusive transport of ionic charge carriers rather than a purely orientation relaxation process. In addition, the effects of hydrostatic pressures (0–0.25 GPa) on the frequency dependencies of the real ϵ′ and imaginary ϵ′ parts of the dielectric constant have been measured in the temperature range from 254 to 329 K. An advantage of applying pressure is that it shifts the α_𝒶 relaxation peak into an experimentally accessible frequency window of the equipment; the lowering of frequency results from a decrease in the relaxation volume and a consequent reduction in the mobility of the molecular units. Results are discussed in terms of theoretical models of the effect of pressure on the glass transition, providing information on the cooperative dynamics. © 1996 John Wiley & Sons, Inc.     

Molecular Dynamics Studies of the Kinetics of Phase Changes in Clusters IV： Crystal Nucleation from Molten （NaCl）256 and （NaCl）500 Clusters

Molecular dynamics computer simulation based on the Born-Mayer-Huggins potential function has been carried out to study the effects of duster size and temperature on the nucleation rate of sodium chloride dusters in the temperature range of 580 K to 630 K. Clusters with 256 and 500 NaCl molecules have been studied and the results have been compared with those obtained from 108 molecule dusters. The melting point (MP) of the clusters were observed to increase with the size of the clusters and can be well described by a linear equation MP =1107(37)-1229(23)N^-1/3(N is the number of molecules in the duster).The nucleation rate was found to decrease with increasing the duster size or temperature. Various nucleation theories have been used to interpret the nucleation rates obtained from this molecular dynamics simulation. It is possible to use a constant diffuse interface thickness to interpret the nucleation rate from the diffuse interface theory in the temperature range of this study. However, the interfacinl free energy estimated from classical nucleation theory and diffuse interface theory increases too fast with increasing the temperature while that from Gran-Gunton theory does not change with changing temperatures.The sizes of critical nuclei estimated from all the theories are smaller than those estimated from our simulations.     

Molecular Dynamics Studies of the Kinetics of Phase Changes in Clusters II: Crystal Nucleation from Molten (RbCl)256 and (RbCl)500 Clusters

Molecular dynamics computer simulations have been carried out to study the effects of cluster size and temperature on the nucleation rate of rubidium chloride clusters in the temperature range of 500-650 K. Clusters with 256 and 500 RbCl molecules have been studied and the results are compared with those obtained from 108 molecule clusters. The melting point (MP) of the clusters was observed to increase with the size of the clusters and can be described by a linear equation MP=997-405 N^−1/3, where N is the number of molecules in the cluster. The nucleation rate is found to decrease with increasing cluster size or increasing nucleation temperature. Both classical nucleation theory and diffuse interface theory are used to interpret our observed results.     

Description of core excitations by time-dependent density functional theory with local density approximation, generalized gradient approximation, meta-generalized gradient approximation, and hybrid functionals

Time-dependent density functional theory (TDDFT) is employed to investigate exchange-correlation-functional dependence of the vertical core-excitation energies of several molecules including H, C, N, O, and F atoms. For the local density approximation (LDA), generalized gradient approximation (GGA), and meta-GGA, the calculated X1s-->pi* excitation energies (X = C, N, O, and F) are severely underestimated by more than 13 eV. On the other hand, time-dependent Hartree-Fock (TDHF) overestimates the excitation energies by more than 6 eV. The hybrid functionals perform better than pure TDDFT because HF exchange remedies the underestimation of pure TDDFT. Among these hybrid functionals, the Becke-Half-and-Half-Lee-Yang-Parr (BHHLYP) functional including 50% HF exchange provides the smallest error for core excitations. We have also discovered the systematic trend that the deviations of TDHF and TDDFT with the LDA, GGA, and meta-GGA functionals show a strong atom-dependence. Namely, their deviations become larger for heavier atoms, while the hybrid functionals are significantly less atom-dependent.