离散正交法(DOM)离散点的正交分析与程序设计

对能够求解一系列线性常微分方程组边值问题的数值计算方法--离散正交法(DOM)进行了离散点的正交分析,给出了计算机实现数值计算的程序设计原理与计算流程图,指出了该方法能够克服传统计算方法由于所求函数的快速增长所引起的边界效应和局部效应的缺点,给出了得到稳定计算过程的可能性.为了推广应用,文中介绍了离散正交法的基本原理、实现方法和求解过程,讨论了采用离散正交法来求解非线性问题的处理方法.并且以承受均布载荷的环形板为例,将采用离散正交法的计算结果与经典解作了对比.

基于DOM解析器的XML编辑器研究

DOM是一种独立于语言和平台的XML解析模型。给出了支持DOM核心模型和多种DOM扩展规范的XML编辑器ONCEXMLEditor的实现。ONCEXMLEditor具有高效的XML验证和序列化性能,同时提供给用户多种功能,包括按需遍历文档、提供上下文感知的编写环境、实时纠错、灵活的装载和序列化机制等。描述了ONCEXMLEditor的体系结构及其实现核心算法,同时给出了XML文档有效性验证和装载及序列化的性能优化策略。

高效DOM实现的技术研究

DOM是目前为止唯一成为W3C正式标准的XML解析模型。本文充分考虑了DOM模型的特点,设计并实现了一个高性能的支持DOM的XML解析器OnceDOMParser。为了提高DOM实现的性能,我们采用用户堆提高对象管理的效率,减少对象在JVM中创建的数量,并采取了数据的延迟装载策略。OnceDOMParser经过了严格的XML兼容性测试和DOM API兼容性测试,多方面的性能测试表明OnceDOMParser性能优越,其平均吞吐量比目前最流行的XML解析器Xerces高43.7%左右。

Shallow gas in the muddy sediments of Eckernförde Bay, Germany

The seafloor of central Eckernförde Bay is characterised by soft muddy sediments that contain free methane gas. Bubbles of free gas cause acoustic turbidity which is observed with acoustic remote sensing systems. Repeated surveys with subbottom profiler and side scan sonar revealed an annual period both of depth of the acoustic turbidity and backscatter strength. The effects are delayed by 3–4 months relative to the atmospheric temperature cycle. In addition, prominent pockmarks, partly related to gas seepage, were detected with the acoustic systems. In a direct approach gas concentrations were measured from cores using the gas chromatography technique. From different tests it is concluded that subsampling of a core should start at its base and should be completed as soon as possible, at least within 35 min after core recovery. Comparison of methane concentrations of summer and winter cores revealed no significant seasonal variation. Thus, it is concluded that the temperature and pressure influences upon solubility control the depth variability of acoustic turbidity which is observed with acoustic remote sensing systems. The delay relative to the atmospheric temperature cycle is caused by slow heat transfer through the water column. The atmospheric temperature cycle as ‘exiting function’ for variable gas solubility offers an opportunity for modelling and predicting the depth of the acoustic turbidity. In practice, however, small-scale variations of, e.g., salinity, or gas concentration profile in the sediment impose limits to predictions. In addition, oceanographic influences as mixing in the water column, variable water inflow, etc. are further complications that reduce the reliability of predictions.

Characterization of stable isotope fractionation during methane production in the sediment of a eutrophic lake,lake dagow,germany

We measured delta C-13 of CO2, CH4, and acetate-methyl in profundal sediment of eutrophic Lake Dagow by incubation experiments in the presence and absence of methanogenic inhibitors chloroform, bromoethane sulfonate (BES), and methyl fluoride, which have different specificities. Methyl fluoride predominantly inhibits acetoclastic methanogenesis and affects hydrogenotrophic methanogenesis relatively little. Optimization of methyl fluoride concentrations resulted in complete inhibition of acetoclastic methanogenesis. Methane was then exclusively produced by hydrogenotrophic methanogenesis and thus allowed determination of the fractionation factors specific for this methanogenic pathway. Acetate, which was then no longer consumed, accumulated and allowed determination of the isotopic signatures of the fermentatively produced acetate. BES and chloroform also inhibited CH4 production and resulted in accumulation of acetate. The fractionation factor for hydrogenotrophic methanogenesis exhibited variability, e. g., it changed with sediment depth. The delta C-13 of the methyl group of the accumulated acetate was similar to the delta C-13 of sedimentary organic carbon, while that of the carboxyl group was by about 12 parts per thousand higher. However, the delta C-13 of the acetate was by about 5 parts per thousand lower in samples with uninhibited compared with inhibited acetoclastic methanogenesis, indicating unusual isotopic fractionation. The isotope data were used for calculation of the relative contribution of hydrogenotrophic vs. acetoclastic methanogenesis to total CH4 production. Contribution of hydrogenotrophic methanogenesis increased with sediment depth from about 35% to 60%, indicating that organic matter was only partially oxidized in deeper sediment layers.