Environmental changes and the responses of the ecosystems of the Yellow Sea during 1976–2000

The changes in the environmental features of the Yellow Sea during the last 25 years of the 20th century were studied using a set of seasonally monitored data along a transect (at 36°N) maintained by the State Oceanic Administration of China. The data included the ocean temperature (T), salinity (S) and biogenic elements, such as dissolved oxygen (DO), phosphorus (PO₄-P), silicon (SiO₃-Si) and dissolved inorganic nitrogen (DIN).The seasonal (summer and winter) values and the annual mean of these elements showed significant changes during the monitored period. Time series of T, S, DIN and N:P ratios exhibited positive trends, while those of DO, P and Si exhibited negative trends. During this period, the annual mean of T and DIN in the Yellow Sea increased by 1.7 °C and 2.95 μmol L⁻¹, respectively, while those of DO, P and Si decreased by 59.1, 0.1 and 3.93 μmol L⁻¹, respectively. In the 1980s, particularly in between 1985 and 1989, concentrations of P and Si dropped to near the ecological threshold for growth of diatoms. The N:P ratio increased from 4 in 1984 to over 16 in 2000. The climate trend coefficients, R_xt, for these time series are all above 0.43 with significance levels of 95%, except for salinity. The increases in T were consistent with the recent climate warming in northern China and the adjacent seas, i.e. the Bohai Sea and the East China Sea. The reduction of DO was probably attributable to the increase in T and decrease in primary production in these regions. The positive trend of DIN was mainly attributable to precipitation and partly to Changjiang River discharge. The negative concentration trends of P and Si were due to the decreases in their concentrations in seawater that flowed to the Yellow Sea from the Bohai Sea. As a result, N:P ratios greatly increased in the seawater of the Yellow Sea.Moreover, some important responses of the Yellow Sea ecosystems to the changes in physical variables and chemical biogenic elements were obviously displayed. These responses include strengthening nutrient limitation, decreasing chlorophyll a, primary production and phytoplankton abundance, succession of dominant phytoplankton species from diatoms to non-diatoms, changes in fish community structure and species diversity.     

Spatial and temporal variation of bacterioplankton in a sub-Antarctic coastal area (Kerguelen Archipelago)

Bacterial abundance and production were measured monthly for one year along cross-shore transects in 3 sub-Antarctic fjords of the Kerguelen Archipelago (seven stations each). Mean values of the 3 most coastal (inside) and most offshore (outside) stations were used to describe the relationship between temperature, phytoplankton biomass, bacterial abundance and bacterial production over a one year annual cycle. The entire sampling protocol was repeated twice during each cruise: once at noon and once at midnight. Over the whole sampling period, the temperature ranged from 2.1 to 7.4 °C, while chlorophyll a concentrations varied by a factor of 10, and bacterial abundance and production varied by factors of 12 and 30, respectively. Within one day, all of these parameters sometimes varied by a factor of 4 between noon and midnight. A clear seasonality was observed for all of the parameters. However, while variations of phytoplankton and bacterial production paralleled those of temperature, bacterial abundance was low in midsummer and maximum in autumn. While no general pattern could be observed from the total data set, spatial gradients could interfere strongly with temporal changes.     

Contribution of supposed wave condition on the long-term distribution of a wave-induced load

This report is concerned with the statistical analysis of the long-term distribution of a wave-induced load, and examines which factors influence the long-term distribution of the load level, e.g., the significant wave height, the mean wave period of the supposed wave condition, and the relative angle between the ship's course and the wave direction. The long-term distribution is broken down into these factors, and a contribution rate analysis method for each factor in each load level in the long-term distribution is introduced. Based on the method used, the contribution rate of a specific mean wave period and a wave angle encountered is clarified, when the long-term distribution is larger than other wave periods and wave angles. The specific mean wave period and wave angle encountered are defined as the wave condition which governs the long-term distribution. The maximum wave-induced load in the vicinity of a probability of exceedance of around 10⁻⁸ in the long-term distribution is decided by the most severe short-term wave condition which has the largest significant wave height with a specific mean wave period. Based on S–N curves and Miner's rule, the relation between the fatigue damage and the supposed wave condition is examined. The contribution rate analysis method for fatigue damage is introduced. The governing wave condition and the most severe short-term wave condition also have an important effect on the fatigue damage. A simple estimation method for the long-term distribution, described by the Weibull distribution from the statistical properties of the most severe short-term wave condition, is introduced. Several examples show the applicability of the estimation method. Received: November 22, 2001 / Accepted: January 9, 2002     

EP 信号潜伏期变化的自适应相位谱估计方法

研究了诱发电位（ＥＰ）信号潜伏期变化的检测与估计问题．传统的时域平均ＥＰ信号检测方法不能跟踪潜伏期的时变特性，基于相关计算的ＥＰ信号检测方法在存在外界周期性干扰的条件下是很不可靠的．本文提出一种自适应相位谱时间延迟估计方法，用于在低信噪比和低信扰比条件下检测和估计诱发电位信号潜伏期的变化．实验和计算机模拟表明，在信噪比和信扰比均低至－５ｄＢ时，本文方法仍能有效地跟踪ＥＰ信号潜伏期的变化，给出正确的估计结果．这种方法也可以用于时实ＥＰ信号的分析和处理．     

Long-term correlation structure of wave loads using simulation

This paper proposes a new method for combining the lifetime wave-induced sectional forces and moments that are acting on the ship structure. The method is based on load simulation and can be used to determine the exceedance probabilities of any linear and nonlinear long-term load combination. It can also be used to determine the long-term correlation structure between these loads in the form of the long-term correlation coefficients. They are essential part of the load combination procedures in design and strength evaluations as well as in the fatigue and reliability analysis of ship structures.The simulation method treats the non-stationary wave elevations during the ship’s entire life (long-term) as a sequence of different stationary Gaussian stochastic processes. It uses the rejection sampling technique for the sea state generation, depending on the ship’s current position and the season. Ship’s operational profile is then determined conditional on the current sea state and the ship’s position along its route. The sampling technique significantly reduces the number of sea state-operational profile combinations required for achieving the convergence of the long-term statistical properties of the loads. This technique can even be used in combination with the existing long-term methods in order to reduce the number of required weightings of the short-term CDFs. The simulation method does, however, rely on the assumption that the ship is a linear system, but no assumptions are needed regarding the short-term CDF of the load peaks.The load time series are simulated from the load spectra in each sea state, taking into account the effects of loading condition, heading, speed, seasonality, voluntary as well as involuntary speed reduction in severe sea states and the short-crested nature of the ocean waves. During the simulation procedure, special care has been given to maintaining the correct phase relation between all the loads. Therefore, time series of various load combinations, including the nonlinear ones, can be obtained and their correlation structure examined. The simulation time can be significantly reduced (to the order of minutes rather than hours and days) by introducing the seasonal variations of the ocean waves into a single voyage simulation. The estimate of the long-term correlation coefficient, obtained by simulating only a single voyage with the correct representation of seasonality, approaches the true correlation coefficient in probability. This method can be applied to any ship and any route, or multiple routes as long as the percentage of the ship’s total lifetime spent in each of them is known.A study has been conducted to investigate the effects of ship type, route and the longitudinal position of the loads on the values of the correlation coefficients between six different sectional loads; vertical, horizontal and twisting moments, as well as shear, horizontal and axial forces. Three ocean-going ship types have been considered; bulk carrier, containership and tanker, all navigating on one of the three busy ship routes; North America-Europe, Asia-North America and Asia-Europe. Finally, the correlation coefficient estimates have been calculated for five different positions along the ship’s length to investigate the longitudinal variation of the correlation coefficient.     

围产期心肌病的组织学及亚微结构改变

作者观察1例尸检,2例活检的心肌组织,发现围产期心肌病的组织学改变为灶状肌溶性坏死,病灶呈全心分布,以左室内侧密集且趋向融合,间质未见炎性渗出反应。取右室心肌活检电镜观察,可见心肌细胞有两种变化:一为肌原纤维的灶状溶解脱失,一为肌纤维内絮斑状电子密度物质沉积。闰盘呈各种变异及间隙加宽。作者未发现心肌细胞质内有任何其他沉积物,电镜下也未见任何异常的微丝聚集及高电子密度团块。通过观察,作者同意本病属多因素综合症的说法,其病变可能为机体免疫状态发生变化所导致的变应性心肌病。     

我国城市轨道交通发展的政策变迁

在国家有关文件要求和政策指导下,我国城市轨道交通一直规范有序发展。在当前严控地方债务、防范系统性金融风险的大环境下,城市轨道交通进入新的发展阶段,国办发〔2018〕52号文将在今后一段时期指导和规范我国城市轨道交通健康有序发展。按照缓慢发展、加快发展和快速发展3个阶段,总结梳理了国家有关部门颁布的有关城市轨道交通发展的政策性文件。城市轨道交通发展的政策变迁反映了我国关于城市轨道交通发展总体思路的变化。     

流变效应作用下高地应力铁路软岩隧道衬砌结构长期稳定性研究

高地应力软岩具有变形量大、变形速率快、持续时间长、流变性强等特点,围岩流变性对衬砌结构长期稳定性影响大。以木寨岭铁路隧道为例,结合室内蠕变试验结果,采用Burgers流变模型,分析不同流变周期内支护结构受力随时间变化的规律。结果表明:(1)本文采用的Burgers模型能较好地反映围岩流变特性;(2)目前木寨岭隧道的支护结构形式,已施作的衬砌结构在以后数年发生压溃开裂的风险较大;(3)提高支护结构的长期稳定性及安全性,应从改变围岩流变性的角度出发,降低围岩的流变特性,增强围岩强度。     

基于微观结构变化导致的石灰剂量衰减分析

通过阐述EDTA滴定石灰剂量原理—配位滴定反应,结合电镜下的石灰土微观结构变化,揭示了石灰在土中发生物理化学反应,逐步形成稳定的胶结结构,随时间的推移石灰土中钙离子因浓度减少,导致在EDTA配位滴定反应时,生成稳定的螯合物减少,消耗EDTA配位剂减少,在显色剂指示下到达滴定等量点的时间缩短,滴定试验完成后,在滴定曲线上由EDTA耗量查出的实测石灰剂量随时间增长呈衰减变化的规律。建议工程应用石灰土作路基填筑材料时,在质量控制与验收中,考虑石灰剂量衰减因素。     

岩体裂隙开度变化对浆液扩散规律的影响分析

研究岩体裂隙开度变化对浆液扩散规律的影响。将单一裂隙形状简化为椭圆形和矩形,利用广义柱面坐标、牛顿内摩擦定律、达西定律、渗流微分方程、纳维—斯托克斯(Navier-Stokes)方程和边界条件下的连续性方程,推导牛顿液体在两种裂隙形状中渗透注浆的参数关系,对比研究了裂隙开度不变和变化两种情况下浆液的扩散规律。结果表明,开度变化对扩散距离有较大影响。因此,在进行注浆理论研究中,应该建立反映开度变化的裂隙模型,并研究裂隙开度变化对渗透注浆的影响规律。