Sediment trap experiments in the water column off southwestern Taiwan:234Th fluxes

The activity of²³⁴Th (t _1/2=24.1 days) in dissolved, particulate and sediment trap samples was determined in the water column off southwestern Taiwan during 2–4 October, 1993. Vertical²³⁴Th fluxes measured by the free-floating sediment traps ranged from 363 to 2290 dpm m^–2 d^–1 in the upper 450 m. Th-234 fluxes predicted from the irreversible scavenging model concur with those measured by the sediment traps. Comparison of the residence times of particulate²³⁴Th and particulate organic carbon showed that their respective values differ by a factor of approximately 23, which suggests organic carbon is preferentially recycled relative to²³⁴Th in the euphotic zone.     

Role of Siliceous Fossil Dissolution in Downcore Variations of Grain Size and Water Content: Western Margin of Clarion-Clipperton Fracture Zone, NE Equatorial Pacific

Grain size and water content in box-core sediments from the Clarion-Clipperton fracture zone (C-C zone) in the northeast equatorial Pacific were analyzed in detail to understand the downcore variations across a hiatus between Quaternary and Tertiary layers. Grain-size distributions in the topmost core sediments show two modes: a coarse mode (peaked at 50 μm) and a fine mode (at 2-25 μm). The coarse mode disappears gradually with depth accompanied by the dissolution of siliceous fossil tests, whereas the fine mode coarsens due to the formation of authigenic minerals. Water content increases abruptly across a color boundary between an upper pale brown layer and a lower dark brown layer that is the hiatus between Quaternary and Tertiary layers. Abundant smectites and microvoid molds, which are created by the prolonged fossil dissolution in the underlying sediment, are attributed for the abrupt downcore variation of water content. Overall variations in grain size and water content in the topmost core sediments in the western C-C zone are possibly constrained by the dissolution of biogenic siliceous fossils. Variations in geotechnical properties related to these changes must be considered in the design of nodule collectors.     

Fuzzy Risk Analysis of Harbour Engineering Investment by Hierarchy System Approach

The present risk analysis model of engineering investment is built by fuzzy hierarchy approach under the assumption of maximizing the revenues of the project during its whole life cycle of operation. It can reasonably be expressed by a system evaluation analysis. As a matter of fact, the system, aimed by its system goal can be modelled by a set of factors, constitutively structured by certain links between them, to form a factorial network chart, which represents the essentials of the system behaviours, the nodes of which represent the factors concerned. The weight distribution between factors located at the same level can be determined by the eigen-value problem of a "pair comparison" relation matrix. The weight distribution of factors at each level is successively manipulated until the fuzzy synthetic risk assessment. As an example of risk analysis of engineering investment, a harbour construction project is presented for illustration.     

Investigation on the Performance of Articulated Buoys

Articulated buoys become more and more popular by the marine management departments as a new type of aids to navigation, for they possess an excellent hydrodynamic performance with small static heel angle in wind and current and small rolling in wave and accurate position. The structure of articulated buoys and calculation method of their hydrodynamic performance are introduced in this paper. A scries of experiments has been conducted in the State Key Laboratory of Ocean Engineering of China and useful results achieved for providing a design optimization basis.     

Analytical Study on Transmission and Reflection of Non-Linear Shallow Water Waves

The analytical study is made by using the method of matched asymptotic expansions on the transmission and reflection of solitary waves and cnoidal waves on two-dimensional floating bodies. The solutions give explicitly the variation pattern of the transmitted waves and the characteristics of the reflected waves, including the wave profile, amplitude, phase shift and evolution. The effects of the gap between the body and the sea bottom on the transmission and reflection of those waves are also discussed.     

两种不同凝胶柱测定壳聚糖分子量结果的比较

凝胶渗透色谱法测定壳聚糖分子量 ,以葡聚糖为标准品 ,用 2种不同的凝胶柱 (PLaquagel- OH柱和 TSK G4 0 0 0 PWXL柱 )测定 4种样品的分子量及其分布 ,并经过普适标定。比较结果发现 :PL aquagel- OH柱效果稍好于 TSK G4 0 0 0 PWXL柱。两柱所得重均分子量平均偏差为 0 .17%～ 3.38% ,数均分子量的平均偏差为 0 .90 %～ 3.5 7% ,分子量分布宽度指数 1.34～ 1.5 4。     

MICROTOPS II手持式太阳光度计海上测量关键技术

海上的大气参数是卫星遥感器进行大气校正所需的重要参数 ,而手持式太阳光度计的现场测量精度又是能否准确地获得大气参数的重要环节 ,此环节将直接影响大气参数后期数据处理的准确性与可靠性。文章以 MI-CROTOPS II仪器在 2 0 0 2年 6月 HY- 1南海海上试验与 2 0 0 4年 3月天津试验的测量数据为基础 ,针对影响海上测量的一些重要因素与关键技术进行讨论和研究。     

Wavelet and artificial neural network analyses of tide forecasting and supplement of tides around Taiwan and South China Sea

In multi-resolution analysis (MRA) by wavelet function Daubechies (db), we decompose the signal in two parts, the low and high-frequency contents. We remove the high-frequency content and reconstruct a new “de-noise” signal by using inverse wavelet transform. The calculation of tidal constituent phase-lags was made to determine the input and output data patterns used in building network structure of Artificial Neuron-Network (ANN) model. The “de-noise” signal was, then, used as the input data to improve the forecasting accuracy of the ANN model. The wavelet spectrum, conventional energy spectrum (fast Fourier transform, FFT), and harmonic analysis were used to analyze the characteristics of tidal data.Using only a very short-period data as a training data set in Artificial Neuron-Network Back-Propagate (ANN-BP) model, the developed ANN+Wavelet model can accurately predict or supply the missing tide data for a long period (1–5 years). The results also show that the concept of tidal constituent phase-lags can improve ANN model of tidal forecasting and data supplement. The addition of the wavelet analysis to ANN method can prominently improve the prediction quality.     

Trial and Numerical Analysis of Specimen Pipelay

Subsea pipelay has a relatively long history. In recent years, there has been a domestic need for the laying of large diameter thin wall pipes. A land-based trial for the large diameter thin wall specimen pipe is described in this paper. Re-gression analysis is performed for the trial data and the formula derived can express the trial data very well. Numerical analysis is adopted to compute various trial conditions. Then the numerical model is revised with the trial results, which are consistent with each other. After summarization of the results of trial and numerical analysis, the characteristics are described of the spatial configuration during the laying of the pipe and it is concluded that the maximum strain appears around the center of the raised pipeline. In the end, a reference Standard, which limits the maximum stress below the yield stress is provided.