“海上虚拟人口”假说及其应用探索

为解决海洋社会经济数据难以获取的问题,促进海洋空间评价的科学化和标准化,文章提出"海上虚拟人口"假说,并对其应用进行探索。研究结果表明:"海上虚拟人口"不是海上实际常住人口,而是对陆上人口数据进行插值后所形成的虚拟人口分布;某一海域的虚拟人口一般按照该海域与海岸线的距离进行插值,距海岸线近的数量多,距海岸线远的数量少;"海上虚拟人口"是海洋社会经济数据的载体之一,其数量可间接反映海洋开发利用水平和海洋社会经济状况;应用步骤包括确定海岸线形状、划分网格单元、修正原始数据和插值计算4个部分。目前"海上虚拟人口"假说及其应用仍处于探索阶段,需在实践中不断检验和完善。     

Effects of sample size on numerical estimates of diel prey consumption in a fish population

Numerical data based on stomach content analysis of the zooplanktivorous freshwater fish, Retropinna semoni, were used to examine the effect of fish sample size on mean counts of dominant prey items. Fifty adult R. semoni were collected from throughout the open‐water of Lake Benanee, Australia at each of five times over a diel period. Bootstrapping was used to generate confidence intervals around sample means, and markedly more accurate means were obtained from samples collected in the day than the night. High variation in night samples was the by‐product of a diurnal feeding regime. Traditional sample sizes of 10 to 15 stomachs resulted in reasonable confidence intervals of sample means derived from collections on the first day, corresponding to uniform feeding patterns in the population. However, increased sample sizes were required to describe more complex feeding behaviour on the second day, when a proportion of the population switched to an alternative prey source.     

Influence of mesh size and core penetration on estimates of deep-sea nematode abundance,biomass, and diversity

It is essential to maximize the information that can be gathered in deep-sea studies by thoroughly assessing sample processing methods. Nematodes are commonly used for the study and monitoring of deep-sea floor habitats, but the potential effects of different methods on the quantification of community attributes remain to be quantified. Here, we consider key methodological elements by comparing the effect of sediment depth and mesh size (63, 45, and 32 μm) on: (1) estimates of nematode community attributes, and (2) the sampling effort required to detect changes in these attributes at a bathyal site on the Chatham Rise, south-west Pacific Ocean. The 63 μm mesh retained most (95%) of the nematode biomass but a lower proportion (53–71%) of the nematode abundance. Retention efficiency of common species on this mesh ranged from 12 (Hapalomus sp.) to >88% (Comesomatidae spp.). The 63 μm mesh yielded significantly lower diversity estimates than the finer meshes, and failed to detect differences in community structure observed using the 45 and 32 μm mesh sizes. Sediment depth had a substantial effect on all measured community attributes, highlighting the importance of sufficient core penetration into the sediment (≥5 cm) for adequately characterizing nematode distribution. Power analysis showed that using a 32 μm mesh and deepest core penetration led to relatively few (3–8) samples being required to detect significant changes in nematode diversity indices relative to coarser mesh sizes. Characterization of nematode diversity and community structure using appropriate and robust methods of sampling is suggested as a sensitive and efficient tool for the assessment of anthropogenic impacts on deep-sea ecosystems.     

Flocculation and phytoplankton cell size can alter Th-based estimates of the vertical flux of particulate organic carbon in the sea

The deficit of ²³⁴Th relative to its radioactive parent ²³⁸U in the surface ocean can yield reliable estimates of vertical Particulate Organic Carbon (POC) fluxes to deeper waters, but only when coupled with an accurate ratio of POC concentration to activity of ²³⁴Th on sinking matter. Assuming a simple partitioning of suspended phytoplankton mass between single cells and flocs, we calculate the ratio of the POC flux estimated from ²³⁴Th deficit to the actual POC flux (p ratio, Smith, J.N., Moran, S.B., Speicher, E.A., in press. The p-ratio: a new diagnostic for evaluating the accuracy of upper ocean particulate organic carbon export fluxes estimated from ²³⁴Th/²³⁸U disequilibrium. Deep-Sea Research I.). The p ratios are calculated under the assumption that particle surface area is correlated with ²³⁴Th activity and particle volume is correlated with POC concentration. The value of the p ratio depends on the relative contributions of single cells and flocs to the vertical flux. When large single cells make up a significant fraction of the vertical flux, p ratios are less than one, meaning POC fluxes estimated from ²³⁴Th deficits underestimate actual POC fluxes. When large single cells are abundant but do not sink fast enough to contribute to vertical POC flux, p ratios are greater than one (up to 3 × overestimate). Factor analysis of the model indicates that altering the extent of flocculation in suspension and changing the density and maximum size of phytoplankton cells have the greatest effects on the p ratio. Failure to measure the properties of flocs when characterizing the ratio of POC to thorium on sinking matter potentially leads to large overestimation of the POC flux (over 20 ×). Failure to characterize the POC to thorium ratio of large particles, by, for example, destruction of phytoplankton cells in pumps, can lead to underestimation of POC flux. Estimates of POC flux should be most reliable in highly flocculated suspensions populated by small cells and rapidly sinking flocs. These conditions are often associated with intense phytoplankton blooms.     

Population size of neonate and juvenile dusky sharks Carcharhinus obscurus in the Port of Ngqura,South Africa

Identifying nearshore waters that serve as important habitats for neonate and juvenile sharks is crucial for effective fisheries management. This study examined the abundance of neonate and juvenile dusky sharks Carcharhinus obscurus within the Port of Ngqura, on the south-east coast of South Africa, between September 2006 and August 2007 using a combination of shore-angling catches and mark-recapture data. During this period, the port was non-operational and still undergoing construction. A total of 480 dusky sharks, ranging in size from 50 to 123 cm (precaudal length), was captured. Catch per unit effort was greatest between October and February, peaking in November at 0.51 sharks angler^–1 h^–1. Of the 219 C. obscurus tagged and released during the study period, 37 (16.9%) were recaptured. Sharks were at liberty from 0 to 409 days with the majority (89.2%) recaptured within the port. Using a Jolly-Seber open population model, the abundance of sharks within the port was estimated at 552 (95% CI: 422–765). Annual apparent survival probability was 0.38 (95% CI: 0.30–0.46), with an average annual recapture probability of 0.28 (95% CI: 0.19–0.39). This study demonstrates that the Port of Ngqura is an important summer habitat and core activity zone for both neonate and juvenile dusky sharks.     

岙山成品油码头海底边坡稳定性分析

根据岙山成品油码头工程地质勘察所得的资料,选择边坡较陡的地段,采用折线法、圆弧条分法和总应力极限平衡法,对在自重、地震力和波浪力等因素作用下的边坡稳定性进行验算分析。结果表明,海底边坡较陡地段浅层土体的稳定性较差,土体滑动面可能发生在海底下９～１２．５ｍ处。对地层的作用波浪力较地震力要小,但两者均可能成为边坡土体滑动的诱因。     

虚拟现实技术的发展过程及研究现状

分析了虚拟现实(VR)技术区别于相邻近的技术的重要特征，回顾了虚拟现实技术发展的三个阶段。介绍了虚拟现实技术在美国等国家的研究现状、主要技术及关键技术的开发状况。     

The stability of molecular iodine in seawater

Both theoretical considerations and laboratory studies suggest that molecular iodine undergoes rapid hydrolysis to form hypoiodite when it is added to seawater. Previous experimental designs were not suitable for studying the fate of molecular iodine in seawater.     

The influence of wave-current sea states on the reliability estimates of offshore towers

Since offshore towers are high-cost, high-risk structures, reliability analysis is of great importance in their design. This paper presents a possible practical approach to certify a design through selective critical member reliability estimates. After a brief review of current research in this field, the authors outline a procedure for reliability estimation of structural members in extreme stress and fatigue limit states. A spectral approach for the extreme response statistics with stochastic loading is described. The reliabilities are computed by the Level II first-order second moment (advanced) method. The fatigue reliability is estimated with a narrow-banded stress assumption with discrete, but significant sea states within the life of the structure. Two numerical examples, a three shallow water model and a two-dimensional deep water model are presented along with the influences of stochastic variables (sea state, current, tubular member diameter) on reliabilities (extreme stress and fatigue damage).     

The determination of confidence limits associated with estimates of the spectral peak frequency

A Monte-Carlo simulation technique is used to evaluate the suitability of proposed techniques for the estimation of the spectral peak frequency. Due to the statistical variability of spectral estimates and the discrete frequency resolution of spectra, the calculated values of peak frequency are stochastic variables. The probability density functions for such estimates are functions of the frequency resolution and the number of degrees of freedom of the spectrum from which they are derived as well as the spectral peakedness. The mean values of all techniques are biased high, indicating the derived values of peak frequency are an overestimate of the true value. The probability density functions do not follow an obvious analytical form. Tabular values are, however, presented to enable the determination of confidence limits for estimates of the peak frequency.