人肠道微生物对海带岩藻聚糖硫酸酯及其寡糖的降解利用

采用人肠道微生物体外厌氧发酵技术,研究人肠道微生物对不同分子量岩藻聚糖硫酸酯的降解利用。分别将五个志愿者的肠道微生物接种到以高分子量和低分子量岩藻聚糖硫酸酯为唯一碳源的培养基中,酵解48h后,采用TLC和PAGE分析分子量变化,PMP-HPLC分析单糖组成变化,GC分析短链脂肪酸的生成情况。结果发现:在人肠道微生物体外降解岩藻聚糖硫酸酯的体系中,岩藻聚糖硫酸酯寡糖和低分子量组分(10—20k Da)含量显著降低,而且酵解产物的单糖组成没有变化,说明被人肠道微生物彻底降解利用;而人肠道微生物对高分子量岩藻聚糖硫酸酯(20k Da)的降解和利用度很低,产物的半乳糖和甘露糖的比例明显下降。低分子量和高分子量岩藻聚糖硫酸酯在酵解后均生成短链脂肪酸乙酸、丙酸和丁酸,但在高分子量岩藻聚糖硫酸酯发酵液中还生成了支链脂肪酸(异丁酸、异戊酸)和戊酸。研究结果表明,人肠道微生物能够彻底降解利用复杂的海带岩藻聚糖硫酸酯寡糖和低分子量组分,但是对高分子量岩藻聚糖硫酸酯的降解率很低。单糖分析说明人肠道微生物能够降解和利用多糖中的所有单糖,产生有利于肠道健康的短链脂肪酸,但是只有低分子量岩藻聚糖硫酸酯能够抑制支链脂肪酸生成。     

吉林省雾的气候特征及变化成因分析

利用1961~2010年吉林省雾日统计资料,对吉林省雾日的时空分布特征、变化趋势进行了详细分析,并分析了雾日变化的原因。结果表明：近50 a来,吉林省年和四季雾日的空间分布均呈东南部地区多、西部地区少的分布特征;雾日季节变化特征表现为8~9月多,10月至次年5月少,西部和中部地区雾日数月季变化呈现双峰型,东南部和东部地区呈现单峰型;雾大多数开始于夜间21时至次日早晨09时,结束于夜间22时至次日午后13时,持续时间多在6 h以下。近50 a来,除了春季雾日没有明显变化外,全省平均及各区域年和四季雾日均呈减少趋势;在2000年前后雾日数发生了一次明显的突变。雾日空间分布与海拔高度有密切关系;雾日趋于减少有人类活动导致的“热岛效应”、“干岛效应”、气溶胶密度加大等原因,也有气候趋于暖干化的自然原因。     

Simulating stiffness degradation and damping in soils via a simple visco-elastic–plastic model

Stiffness degradation and damping represent some of the most well-known aspects of cyclic soil behavior. While standard equivalent linear approaches reproduce these features by (separately) prescribing stiffness reduction and damping curves, in this paper a multiaxial, 3D, viscoelastic – plastic model is developed for the simultaneous simulation of both cyclic curves over a wide cyclic shear strain range.The proposed constitutive relationship is based on two parallel resisting/dissipative mechanisms, purely frictional (elastic–plastic) and viscous. The frictional mechanism is formulated as a bounding surface plasticity model with vanishing elastic domain, including pressure-sensitive failure locus and non-associative plastic flow – which are essential for effective stress analysis. At the same time, the use of the parallel viscous mechanism is shown to be especially beneficial to improve the simulation of the overall dissipative performance.In order to enable model calibration from stiffness degradation ($G/G_{\mathit{max}}$) and damping curves, the constitutive equations are purposely kept as simple as possible with a low number of material parameters. Although the model performance is here explored with reference to pure shear cyclic tests, the 3D, multiaxial formulation is appropriate for general loading conditions.     

Inelastic seismic behavior of soil–pile raft–structure system under bi-directional ground motion

Performance based design of structure requires a reasonably accurate prediction of displacement or ductility demand. Generally, displacement demand of structure is estimated assuming fixity at base and considering base motion in one direction. In reality, ground motions occur in two orthogonal directions simultaneously resulting in bidirectional interaction in inelastic range, and soil–structure interaction (SSI) may change structural response too. Present study is an attempt to develop insight on the influence of bi-directional interaction and soil–pile raft–structure interaction for predicting the inelastic response of soil–pile raft–structure system in a more reasonably accurate manner. A recently developed hysteresis model capable to simulate biaxial interaction between deformations in two principal directions of any structural member under two orthogonal components of ground motion has been used. This study primarily shows that a considerable change may occur in inelastic demand of structures due to the combined effect of such phenomena.     

上边界条件对多年冻土地温场数值模拟结果的影响分析

以玛多地区多年冻土为背景,建立多年冻土地温场的数值计算模型,以不同的方式考虑近 60 a 来的气温变化构成不同的上边界条件,通过模型计算分析不同上边界条件下的不同时期温度场、未来冻土退化特征.结果表明：在上边界条件中采用气象站实测近60 a波动温度值和采用近60 a平均恒定值时,浅层冻土地温差异明显,且越浅层地温与越近时间的上边界条件相关.预测未来100 a冻土地温变化趋势发现,相同升温速率和升温初始温度条件下,上边界采用实测60 a波动温度值对冻土退化过程影响较小;升温初始温度值提高到与趋势线衔接后,冻土退化起始时间从约第45年提前到约第20年;60 a实测温度和升温初始温度值均提高到与其初始温度场上边界条件衔接后,冻土退化起始时间从约第20年提前到约第15年;冻土退化从开始到完全退化经历时间为25 a左右.     

浙江沿岸春季上升流的数值研究

采用三维斜压非线性数值模式ROMS(Regional Ocean Modeling System),在浙江沿岸特殊地形的基础上综合考虑风场、台湾暖流、潮流以及长江径流等可变因子,对春季浙江沿岸上升流进行了数值研究。研究结果表明,浙江沿岸春季存在上升流,且上升流以带状分布在浙江近岸海域,在渔山列岛附近(28.40°N,122.00°E)以及舟山群岛附近(30.70°N,122.60°~123.00°E)存在2个上升流中心。风、台湾暖流和潮动力是影响浙江沿岸春季上升流的重要因子,其中风和台湾暖流对浙江沿岸整条上升流带均有影响;潮动力仅对28.60°N 纬度线以北至舟山群岛附近的上升流以及2个上升流中心的强度存在影响;长江径流对2个上升流中心、舟山群岛及长江口附近的上升流有一定影响。通过对浙江沿岸海域流场的分析可以发现,舟山群岛附近底层各等深线上水体向岸运动的速度比周围海域的大,跨越底层各等深线向上涌升的趋势更明显,间接反映了舟山群岛附近的上升流强度相对较强。对于舟山群岛附近的上升流而言,30 m深度以浅的海域,科氏力、水平平流作用与垂直粘性力是上升流形成的主要动力, 30 m深度以深的海域,上升流形成的主要动力为科氏力与压强梯度力,此时水平平流作用和垂直粘性力对上升流的影响较弱。     

Mapping vertical profile of discontinuous permafrost with ground penetrating radar at Nalaikh depression,Mongolia

Ground-penetrating radar (GPR) has become an important geophysical tool which can provide a wealth of interpretive information about the vertical profile of discontinuous permafrost. A GPR investigation was conducted in October 2006 at the Nalaikh site at the southern boundary of the Siberian discontinuous permafrost region in Mongolia. GPR data were collected along four 100-m-long profiles to identify the location of the permafrost body, which included an in situ drilling borehole and analysis of temperature observations and soil water content measurements from boreholes. The GPR interpretation results indicated that the thickness of discontinuous permafrost at the study site was only 1.9–3.0 m and the permafrost is vulnerable to climate change. The soil temperature and soil water content data demonstrate the precision of GPR image interpretation. This case demonstrated that GPR is well suited for mapping the internal structure of discontinuous permafrost with relatively low soil water content.     

Monitoring and methods to analyse the groundwater quality degradation risk in coastal karstic aquifers (Apulia,Southern Italy)

A multi-methodological approach based on monitoring and spatio-temporal analysis of groundwater quality changes is proposed. The presented tools are simple, quick and cost-effective to give service to all sorts of users. The chief purpose of the monitoring network is the detection of the piezometric or potenziometric level in the aquifer. The spatial and multi-temporal analysis of usual chemical and physical data provides both an assessment of the spatial vulnerability of the aquifer to seawater intrusion, defining a salinity threshold between fresh groundwater and brackish groundwater and of the water quality trend in terms of salinity. The evaluation of the salinity trend or of salinity-correlated parameters highlights the effects of groundwater mismanagement. The multiparameter logging provides a rapid groundwater quality classification for each well. The whole approach allows evaluating the effects of current management criteria and designing more appropriate management targets. The Apulian karstic coastal aquifers have been selected as a case study (Southern Italy). Three types of aquifer zones can be distinguished: (1) areas with low vulnerability to seawater intrusion, (2) areas with high vulnerability and (3) areas with variable vulnerability in which the salt degradation largely depends on the ability to manage the well discharge. The water quality degradation caused by seawater intrusion appears to be a combined effect of an anomalous succession of drought periods observed from about 1980 onwards and increased groundwater pumping, particularly during drought periods. A management criterion based on aquifer zones is proposed.     

Influences of alpine ecosystem degradation on soil temperature in the freezing-thawing process on Qinghai–Tibet Plateau

The alpine ecosystem is very sensitive to environmental change due to global and local disturbances. The alpine ecosystem degradation, characterized by reducing vegetation coverage or biomass, has been occurring in the Qinghai–Tibet Plateau, which alters local energy balance, and water and biochemical cycles. However, detailed characterization of the ecosystem degradation effect is lack in literature. In this study, the impact of alpine ecosystem degradation on soil temperature for seasonal frozen soil and permafrost are examined. The vegetation coverage is used to indicate the degree of ecosystems degradation. Daily soil temperature is monitored at different depths for different vegetation coverage, for both permafrost and seasonal frozen soils. Results show that under the insulating effort of the vegetation, the freezing and thawing process become quicker and steeper, and the start of the freezing and thawing process moves up due to the insulating effort of the vegetation. The influence of vegetation coverage on the freezing process is more evident than the thawing process; with the decrease of vegetation coverage, the integral of frozen depth increases for seasonal frozen soil, but is vice versa for permafrost.     

断层崖演化与古地震研究

从断层崖演化模型及其理论分析入手 ,给出了模型的数学分析解 ,导出了一次突发事件和蠕动成因断层崖演化的等时地形 (地层 )线、最大坡度和崖下堆积体截面积的精确表达式 ,据此分析了可能造成的几何与沉积构造特征。根据野外观察、实验分析及理论研究 ,探讨了断层崖演化及其古地震学研究的一些重要问题 ,提出了与断层崖相关的古地震几何形态、沉积结构和实验分析的综合标志 ,并具体研究和确定了与红果子贺兰山东麓断层崖和孟家湾F2 0 1断层崖相关的 8次古地震事件及其近地表特征和复发周期 ,前者为 2 .0～ 3.0ka,平均 2 .4ka ,后者为 3.3～ 4 .0ka ,平均 3.6ka