雨水入渗对非饱和土坡稳定性影响的参数研究

很多国家和地区的斜坡失稳与雨水入渗有密切关系。通过参数分析研究可以深化对这种关系的认识和理解,因而对滑坡灾害的预测和预防有重要意义。针对香港地区一种典型非饱和土斜坡,用有限元法模拟雨水入渗引起的暂态渗流场,然后将计算得到的暂态孔隙水压力分布用于斜坡的极限平衡分析。计算中采用延伸的摩尔－库伦破坏准则以便考虑基质吸力对抗剪强度的贡献,研究了降雨特征、水文地质条件及坡面防渗处理等因素对暂态渗流场和斜坡安全因数的影响。数值模拟结果表明：降雨强度、降雨历时和雨型对暂态渗流场及斜坡稳定性有明显的影响;土体的渗透系数,尤其是渗透系数各向异性的影响特别显著;斜坡中相对隔水层的存在以及斜坡防渗护面的效果等因素的影响均不容忽视。     

Dust-acoustic wave modulation in the presence of q-nonextensive electrons and/or ions in dusty plasma

A study is presented of the nonlinear self-modulation of low-frequency electrostatic dust acoustic waves (DAWs) propagating in a dusty plasma, within the theoretical framework of the nonextensive statistics proposed by Tsallis. Using the reductive perturbation method (RPM), the nonlinear Schrödinger equation (NLSE) which governs the modulational instability (MI) of the DAWs is obtained. The presence of the nonextensive electron/ion distribution is shown to influence the MI of the waves. Furthermore it is observed that nonextensive distributed ions has more effect on the MI of the DAW than electrons.     

Quantitative urban climate mapping based on a geographical database: A simulation approach using Hong Kong as a case study

The urban environment has been dramatically changed by artificial constructions. How the modified urban geometry affects the urban climate and therefore human thermal comfort has become a primary concern for urban planners. The present study takes a simulation approach to analyze the influence of urban geometry on the urban climate and maps this climatic understanding from a quantitative perspective. A geographical building database is used to characterize two widely discussed aspects: urban heat island effect (UHI) and wind dynamics. The parameters of the sky view factor (SVF) and the frontal area density (FAD) are simulated using ArcGIS-embedded computer programs to link urban geometry with the UHI and wind dynamic conditions. The simulated results are synergized and classified to evaluate different urban climatic conditions based on thermal comfort consideration. A climatic map is then generated implementing the classification. The climatic map shows reasonable agreement with thermal comfort understanding, as indicated by the biometeorological index of the physiological equivalent temperature (PET) obtained in an earlier study. The proposed climate mapping approach can provide both quantitative and visual evaluation of the urban environment for urban planners with climatic concerns. The map could be used as a decision support tool in planning and policy-making processes. An urban area in Hong Kong is used as a case study.     

Professionalization of the shipping industry via postgraduate education

The paper investigates the roles and nature of postgraduate education on the professionalization of the shipping industry. The recent growth of postgraduate education is marked by the massive expansion of professional programmes on disciplines which traditionally emphasized non-academic, apprentice-style learning approach, including shipping business and management. The reasons behind such growth of demands, however, have remained scarce and empirically under-researched. Understanding this deficiency, in this study, we have undertaken a questionnaire survey completed by students/graduates who are pursuing/have recently pursued masters' programmes in shipping-related business and management offered by six Asian and European universities. Specifically, we analyze student motivations, considerations, and sources of information before enrolling such programmes, the extent that the shipping industry or other forces act as driving forces towards such enrollment, as well as students' evaluation of the postgraduate programmes that they are pursing/have pursued. Integrated in these discussions are comparative analyses of the data provided by different student groups based on their professional experiences and cultural backgrounds. We believe that this study has provided the lacking empirical inputs essential for achieving the sustainable development of postgraduate education in shipping business and management.     

Dynamics of an elastically moored floating body by the three-dimensional infinite element method

The three-dimensional problem of the dynamics of a moored floating object under the action of regular waves is solved numerically as a boundary value problem by use of the finite-infinite element method. The cross-sectional shape of the floating body and the mooring arrangements may all be arbitrary. The mathematical formulations of the problem and procedures of the numerical method are presented in this paper. A corresponding computer program WALOAD has been developed, which is capable of computing wave forces on fixed and floating structures. Numerical computations using this program could give very accurate results, even though rather coarse meshes were used. The program is easy to use and is readily applicable in many practical situations.     

The state‐of‐the‐art in marine navigation

Tide gauges distributed all over the world provide valuable information for monitoring mean sea level changes. The statistical models used in estimating sea level change from the tide gauge data assume implicitly that the random model components are stationary in variance. We show that for a large number of global tide gauge data this is not the case for the seasonal part using a variate-differencing algorithm. This finding is important for assessing the reliability of the present estimates of mean sea level changes because nonstationarity of the data may have marked impact on the sea level rate estimates, especially, for the data from short records.     

Field Test Research on Embankment Supported by Plastic Tube Cast-in-place Concrete Piles

The plastic tube cast-in-place concrete pile (TC pile) with a small diameter consists of pre-driven plastic tube filled with concrete. Based on the case of TC pile-reinforced embankment on soft ground, and according to the monitoring data of the TC pile-reinforced embankment system, the treatment effect and reinforcement characteristics for this system were analyzed. The field monitoring results indicates that the critical height of embankment is about 1.1 times the pile net spacing, and the small-spacing arranged TC piles can be applied to low embankment engineering; the load share rate can reflect the degree of soil arching more better and steadily and exceeds 70 % at the end of monitoring period; the settlements of pile cap and soil between piles mainly occurs in the embankment construction period; the different settlement between pile cap and soil approaches the maximum and then reduces gradually when the embankment height is about 2.2 times the pile net spacing. The variation of layered settlement and pore water pressure illustrates that the embankment settlement is mainly caused by the compression of soils within pile length, which is about 90 % of the total settlement; the influence depth of pore water pressure is about 1/3 pile length.     

Development of a diatom-based specific conductivity model for the glacio-isostatic lakes of Truelove Lowland: implications for paleoconductivity and paleoenvironmental reconstructions in Devon Island lakes, N.W.T., Canada

Diatoms are identified and enumerated from the surface sediments of 100 lakes of Truelove Lowland, Devon Island, N.W.T., Canada. These lakes range from large oligotrophic lakes, to small tundra ponds, to coastal marine lagoons which are diverse in terms of ionic concentration and composition. The relationship between diatoms and 15 limnological variables is examined using Canonical Correspondence Analysis (CCA). Specific conductivity is identified as the most important variable influencing the distribution of diatoms in the Truelove lakes. A Weighted Averaging (WA) calibration model is developed to predict diatom-inferred specific conductivity. The reliability of the model is tested by evaluating the correlation between observed and diatom-inferred values and determining the error of prediction by bootstrapping. The applicability of the predictive conductivity equation is demonstrated by reconstructing the paleoconductivity history of Fish Lake.