Electron paramagnetic resonance spectroscopy as a novel approach to measure macromolecule–surface interactions and activities of extracellular enzymes

The dynamics of high molecular weight organic matter in marine systems are influenced by molecular conformation, interactions with surfaces and susceptibility to enzymatic hydrolysis, parameters that are difficult to observe experimentally. Here we use electron paramagnetic resonance spectroscopy (EPR) and spin-labeled (SL-) polysaccharides to monitor the sorption of SL-polysaccharides to natural sediment surfaces and to montmorillonite and to observe decreases in polysaccharide size due to enzymatic hydrolysis. SL-pullulan, SL-xylan and SL-maltoheptaose all sorbed rapidly to muddy sediments but not to sandy sediments. SL-pullulan and SL-maltoheptaose also both sorbed to montmorillonite; however, SL-pullulan reached substantially greater final surface loadings than did SL-maltoheptaose. Using EPR has the advantages of being rapid (spectra can be acquired in 100 seconds), non-destructive and functional in complex media, including sediment slurries, muddy water or other optically opaque samples, permitting investigation of the interactions between biomacromolecules, extracellular enzymes and mineral surfaces in aquatic environments.     

Influence of non-linearities on the limits of stability of ships rolling in head seas

The present paper describes an investigation on parametric resonance in head seas in which a new third-order coupled mathematical model is considered. The restored modes of heave, roll and pitch are contemplated. The discussion is illustrated for the case of a transom stern fishing vessel at different speeds. It is pointed out that numerical simulations employing the new model are successfully compared to experimental results previously obtained for the vessel.Considering that analyticity is an important tool when handling complex stability issues, some theoretical dynamic characteristics of the equations are discussed. By means of the analysis of the coupled linear variational equation derived from an extended third-order model, the appearance of super-harmonics and increased rigidity proportional to wave amplitude squared due to third-order terms is demonstrated.In the present paper, an important tool is explored, that is the analysis of the limits of stability obtained from the new model. Limits of stability are a well-known and practical way of looking into the problem of parametric resonance. New limits of stability are derived and compared to the more conventional Strut diagram. Dynamic characteristics associated with the new limits of stability are discussed. The influence of different parameters is investigated, including vessel speed, damping and tuning. Consistent and revealing results are obtained through the analysis of the new limits of stability for different speeds and damping.     

长江三峡工程的地质构造环境及地球动力学演变分析

根据卫星遥感影像特征和区域地质调查与地球应力分析的综合材料,运用遥感地质学和地球动力学及地质环境演变的分析方法,对长江三峡工程的背景构造(区域构造)-岩块构造(体域构造)-坝区构造(局域构造)进行了多层次的系统研究,查清了地质构造环境演变过程及其变化规律,发现了多级构造序次及多级构造应力场之间的相互转变关系,提出区域应力场与库区荷载应力场和周边采矿卸载应力场的共振效应,是对工程安全运行和长周期工程寿命的最大潜在威胁,为大型工程优化管理和工程灾害风险预防及国家建设合理决策等方面提供科学依据。     

多离子成分空间等离子体中斜传播波的混杂共振：（Ⅱ）实验观测与波模识别

在分析ＡＲＣＳ３探空火箭记录到的由人工离子束激发的低频等离子波的特征和激发机制的过程中，提出了多离子成分冷等离子体中的一般混杂共振和一般混杂波的概念，给出了斜向传播冷等离子体波的混杂共振条件．在上述理论的基础上，考虑了电子、氧离子、氦离子和人工氩离子束的贡献，计算出ＡＲＣＳ３实验条件下的等离子体介电函数，并用等离子体波模识别的方法，识别出频率在１８０Ｈｚ。附近的最强波峰乃是Ｏ＋－Ｈｅ＋双离子混杂波．     

MR成像中脂肪抑制技术的应用

本文措施了磁共振成像中的几种脂肪抑制技术，包括相位对比，短ＴＩ反转恢复和脂肪饱合技术，介绍了脂肪抑制的磁共振扫描床适应症，指出脂肪抑制磁共振扫描可对脂肪来源病变作出特征诊断，还可增加ＴＩ加权成像中造影剂增强效果。     

Mn~(2+)在方解石中的零场分裂

本文采用高阶微扰的方法,对3d~5电子组态的离子在D_(3d)对称晶场下的零场分裂进行了计算,推导出了高达八阶微扰的零场分裂常数D的公式。作为公式的应用,本文利用Mn~(2+)的SCF-d轨道,计算了菱锰矿(MnCO_3)的晶场吸收谱和Mn~(2+)掺入方解石(CaCO_3)中的零场分裂常数D。计算结果与实验观察符合较好。     

Numerical analysis of ESR spectra from atmospheric samples

Improvements of the matrix isolation/electron spin resonance technique for the measurement of NO₂, NO₃, and RO₂ radicals in the atmosphere are described. The use of D₂O instead of H₂O as the matrix yields a better spectral resolution and, as a consequence, larger a signal-to-noise ratio as well as better identification of the different species. Reference spectra of the different radicals in H₂O and D₂O matrices are compared. While a large degree of correlation exists amongst the spectra of the different (unsubstituted and substituted) alkylperoxy radicals, the spectra of HO₂, CH₃C(O)O₂, and NO₃ show significant differences that allow their distinction in atmospheric samples.A numerical procedure for the analysis of the composite ESR spectra obtained from atmospheric samples was developed. Subtraction of the dominant NO₂ signal is performed by matching a reference NO₂ spectrum with respect to amplitude, spectral position, and line width to the sample spectrum. The manipulations are performed with the virtually noise-free reference spectrum and are based on physical information. The residual spectrum is then analyzed for RO₂ (and/or NO₃) by simultaneously fitting up to six different reference spectra.The method was applied to laboratory samples as well as to atmospheric samples in order to demonstrate the ability of retrieving small amounts of HO₂ in the presence of large amounts of NO₂ and other peroxy radicals. The new algorithm allowed, for the first time, the identification of the HO₂ and CH₃C(O)O₂ radical in tropospheric air at concentrations ranging up to 40 ppt.     

Response of a harbour opened to a sea of variable depth

Wave-induced oscillations in a circular harbour with protruding breakwaters and narrow mouth are analytically investigated by using a variational method. The effects of the bottom topography of the contiguous external sea are studied, especially as far as Helmholtz resonance is concerned; it has been found that the amplitude of the resonance peak is quite sensitive to the depth variation, while the related resonance wavenumber is more stable.     

含铬明矾局部压缩率的研究

本文运用晶体场理论计算了几种含铬明矾的自旋-晶格耦合系数G_(44)在此基础上,求得了它们的零场劈裂对键角的变化率。根据单轴压力下的EPR谱数据,获得了在这几种明矾中的(T~(3+)·6H_2O)~(3+)基团的局部压缩率,这些值都明显地小于明矾晶体的压缩率。在本文中,我们讨论了产生这种现象的原因并论证了这些局部值的合理性。由此可以看出,压力下的EPR谱是研究含顺磁离子矿物的局部结构和局部压缩率的有效手段。