Dynamical causes of asymmetry in the arrangement of gaps in the asteroid belt

The centers of the gaps observed in the asteroid belt are displaced toward Jupiter from their positions that correspond to the exact commensurability between the mean motions of an asteroid and Jupiter. Using the current theory of stability and nonlinear oscillations of Hamiltonian systems, we point out the dynamical causes of this asymmetry. Our analysis is performed in terms of the plane circular restricted three-body problem. The orbits that correspond to Poincaré periodic solutions of the first kind are taken as unperturbed asteroid orbits.     

近地小行星轨道演化的研究

主要阐述近年来在近地小行星轨道演化研究工作中所获得的一些基本结果，即合理的力学模型和相应的有效算法，并以实际预报算例（近地小行星与地球的交会状态）与有关权威性的结果作了比较，证实这些研究结果确实是可信的。在给出的力学模型中，考虑了所有可能影响近地小行星运动的力学因素，包括各大天体和较大的主带小行星的引力作用、有关天体的扁率影响以及源于太阳引力的后牛顿效应。而在计算方法中，合理地处理了变步长问题和月球位置量这种相对而言的快变化问题，使得数值求解一个高维方程组时，对各天体而言，可采用同一步长进行 积分，避免了求解过程中的复杂性。     

ESR dating of optically bleached quartz grains from Plio-Pleistocene to Holocene coastal dune deposits (Wilderness-Knysna area,South Africa): a comparison with luminescence

Five Plio-Pleistocene to Holocene aeolian quartz samples from the coastal dune deposits of the Wilderness-Knysna area (South Africa) previously dated by OSL were selected for ESR dating. Samples were processed following the Multiple Centre approach and using the Multiple Aliquot Additive dose method. Aluminium (Al) and Titanium (Ti) signals were systematically measured in all samples.Our study shows that ESR results obtained for Middle Pleistocene to Holocene samples may be strongly impacted by (i) the presence of a significant high frequency noise in the ESR spectra acquired for the Ti signals and (ii) the choice of the fitting function employed. In particular, if not taken into account, very noisy spectra can lead to a significant overestimation of the true ESR intensity measured for the Ti–H signal. These sources of uncertainty are however not sufficient to remove the ESR age overestimations. Consequently, our results indicate that the Al and Ti ESR signals of these quartz samples have not been fully reset during their aeolian transport.While this work contributes to improve our understanding of the ESR method applied to quartz grains, and especially of the potential and limitations of the Ti signals, it also provides additional baseline data to illustrate the existing variability among quartz samples of different origins or sedimentary context. Our results are consistent with previous studies by confirming that the Ti–H signal shows the best potential for the evaluation of low dose values (<100 Gy for these samples), whereas it becomes inappropriate for the higher dose range, and the Ti–Li–H (option D sensu Duval and Guilarte, 2015) should be used instead.Beyond the methodological outcome, this ESR dating study also provides a useful addition to the existing chronology of the aeolian deposits in this region. In particular, new (and possibly) finite numerical age results were obtained for the two oldest samples, constraining the aeolianite landward barrier dune and the coversand formations to the MIS 10-8 and Pliocene, respectively.     

磁共振探测估算含水层渗透系数的原位试验研究

通过一个完整的磁共振探测（MRS）、钻探、抽水试验过程,开展了MRS估算含水层渗透系数的原位试验研究。在分析MRS估算渗透系数准确性的基础上,系统剖析了引起准确性差异的主要因素,并对进一步提高估算效果提出了建议。结果显示：（1）采用现阶段常用的参数设置,与抽水试验计算值相比,MRS估算渗透系数的差值为抽水试验计算值的17.59%。（2）MRS推断的含水层顶板、底板埋深与钻孔揭示的信息相比,差值分别为4.11m、1.03m,表明其对估算渗透系数准确性的影响较小。（3）CP值是影响估算准确性的重要因素,其值为10-9数量级符合大多数地层的特点。另外,通过在已知渗透系数的钻孔附近进行MRS,从而获取CP参考值,应用该值估算的渗透系数准确性高于常用的参数设置。（4）指数a、b设置方面,应用Seevers公式（a=1、b=2）的估算效果优于Kenyon公式（a=4、b=2）。本成果有助于提高MRS估算渗透系数方法在野外条件下的适用性。     

Diagenesis of organic matter in a 400 m organic rich sediment core from offshore Namibia using solid state 13C NMR and FTIR

Although rates and mechanisms of early diagenesis have been well studied, the effects of microbial metabolism on the molecular composition of the sedimentary organic matter (SOM) over long periods of time need more investigation. In this study, we characterize the early diagenesis of marine SOM from organic rich sediments of the Ocean Drilling Program site 1082 located off Namibia, in the vicinity of the Benguela coastal upwelling system. We used both Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (¹³C NMR) to assess the quantitative partitioning of the organic carbon into major compound classes (aliphatic, aromatic, ester, carboxylic, amide and carbons from carbohydrates). Then, we calculate the SOM composition in the main biomolecules (proteins, carbohydrates, lipids and lignin) on the basis of previous ¹³C NMR based estimates of the molecular composition of the organic mixtures. Results show that the SOM is still labile at 7 m below the seafloor (mbsf) and composed of about 25% proteins and 15% carbohydrates. With increasing depth, the protein content exponentially decreases to 13% at 367 mbsf, whereas the carbohydrate content decreases linearly to 11%. The lignin and lipid content consistently represent around 10% and 40% of the SOM, respectively, and show an increase with depth, due mostly to selective enrichment as the more labile components are lost by degradation. Thus, these components of the SOM are considered refractory at the depth scale considered. The calculated remineralization rates are extremely slow ranging from 5.6 mol C m⁻³ ky⁻¹ at the top of the core to 0.2 mol C m⁻³ ky⁻¹ according to the organic carbon flux to the seafloor. Knowing the labile carbon losses, we propose a method to calculate the initial TOC before the diagenesis took place.     

Multi-scale variability of water discharge and sediment load into the Bohai Sea from 1950 to 2011

This paper examines the changes in the time series of water discharge and sediment load of the Yellow River into the Bohai Sea. To determine the characteristics of abrupt changes and multi-scale periods of water discharge and sediment load, data from Lijin station were analyzed, and the resonance periods were then calculated. The Mann-Kendall test, order clustering, power-spectrum, and wavelet analysis were used to observe water discharge and sediment load into the sea over the last 62 years. The most significant abrupt change in water discharge into the sea occurred in 1985, and an abrupt change in sediment load happened in the same year. Significant decreases of 64.6% and 73.8% were observed in water discharge and sediment load, respectively, before 1985. More significant abrupt changes in water discharge and sediment load were observed in 1968 and 1996. The characteristics of water discharge and sediment load into the Bohai Sea show periodic oscillation at inter-annual and decadal scales. The main periods of water discharge are 9.14 years and 3.05 years, whereas the main periods of sediment load are 10.67 years, 4.27 years, and 2.78 years. The significant resonance periods between water discharge and sediment load are observed at the following temporal scales: 2.86 years, 4.44 years, and 13.33 years. Water discharge and sediment load started to decrease after 1970 and has decreased significantly since 1985 for several reasons. Firstly, the precipitation of the Yellow River drainage area has reduced since 1970. Secondly, large-scale human activities, such as the building of reservoirs and floodgates, have increased. Thirdly, water and soil conservation have taken effect since 1985.     

A study on resonance Rayleigh scattering spectra of Humic Acid (HA)

This paper deals with the influences of pH, acidity and ionic intensity of the solutions on the resonance Rayleigh scattering spectra and fluorescence spectra of humic acid. When the pH value is low and the acidity and ionic intensity are high, the resonance Rayleigh spectra and fluorescence spectra both show a tendency of increasing, though the former’s intensity is much higher. In combination with the transmission electron microscope data, the factors leading to the occurrence and enhancement of the resonance Rayleigh scattering spectra of humic acid were explored. It is considered that particle enlargement caused by aggregation, the increase of heterogeneity, the increase of hydrophobility, the formation of interface, etc., are the factors leading to the occurrence and enhancement of the resonance Rayleigh scattering spectra of humic acid. As the intensity of the resonance Rayleigh scattering spectra of humic acid is much higher, resonance Rayleigh scattering spectroscopy can be used as a newly developed spectrum technology, which is more sensitive and simpler, to study humic acid and its complicated behaviors.     

采掘坑位置对珊瑚礁海岸波浪传播变形影响试验

为研究珊瑚礁坪上采掘坑位置变化对珊瑚礁海岸波浪传播变形的影响, 本文通过物理模型试验测试了采掘坑在不同位置和无坑情况下一系列不规则波工况的波浪特征。结果表明, 随着采掘坑位置朝岸线附近移动直至无坑时, 岸线附近的短波波高逐渐减小; 采掘坑的存在减弱了岸线附近的低频长波波高, 当采掘坑位于岸线附近时, 长波波高还受到局部水深增加的影响而进一步减弱。采掘坑从礁缘移动至岸线附近直到无坑时, 岸线附近的增水逐渐增大, 这种趋势在礁坪水深较大时更为明显。通过相干函数分析, 证明了礁坪上低频长波是由于短波群破碎点的移动而产生, 采掘坑位置的变化对低频长波的产生无明显影响; 通过传递函数分析, 验证了礁坪上的低频长波存在一阶共振放大效应, 采掘坑的存在减弱了这种放大效应, 当坑位于礁坪中间和岸线附近时, 这种减弱效应更为显著。     

外伤性肝内胆汁瘤的CT与MRI表现

目的:探讨外伤性肝内胆汁瘤的CT与MRI表现特征。方法:回顾性分析10例临床证实的外伤性肝内胆汁瘤的影像资料。结果:全部病例有CT检查资料,2例病程中行MRI检查。全部病例伴肝实质挫裂伤,外伤后短期内CT或MRI检查提示肝内大片状低密度或长T1长T2信号影,随访中很快出现水样密度或信号影。其中囊状单发7例,多发3例。多发者沿胆管树呈囊袋状排列。除7例随访中渐小外,其余3例均经手术或超声或CT引导下引流治愈,其内容物均为胆汁成分。结论:认识外伤性肝内胆汁瘤CT与MRI表现特征对于诊断及进一步治疗具有重要意义。     

CT和MRI对桥脑中央髓鞘溶解症的诊断价值

目的:探讨桥脑中央髓鞘溶解症(CPM)的CT、MRI表现,以提高诊断水平,并评估其在CPM诊断及随访中的价值。方法:回顾性分析8例经我院临床确诊的CPM的临床和影像学资料,总结其影像学特征。结果:4例患者行CT检查,其中阳性2例,阴性2例,阳性病例中桥脑、双侧大脑脚及右侧小脑多发斑片状低密度灶1例,桥脑低密度灶1例;8例患者行MRI检查均有阳性表现,其中桥脑中央病灶8例,对称性分布,边缘清晰,呈圆形、卵圆形或蝶翼状,4例伴桥脑外病变,包括小脑半球、大脑脚、丘脑、基底节及放射冠等区域,病灶在T1WI序列均呈等、低信号,T2WI及T2FLAIR序列呈高信号,DWI序列呈明显高信号,灶周无水肿,增强扫描未见强化。结论:MRI对该病的诊断价值明显优于CT,T2FLAIR及DWI序列对CPM病灶显示敏感,对其诊断、指导临床治疗及评估预后具有较大价值。