基于时间连续性及季节周期性的风速短期组合预测方法

根据风电机组功率曲线,可由风速计算出风电机组出力,因此,风电功率预测问题可转化为风速预测问题。基于风电场气象及风速数据的时间连续性及季节周期性,提出了一种风速短期组合预测模型。该模型采用模式识别技术分别提取时间连续性的样本及季节周期性的样本,以反向传播(BP)神经网络作为预测模型,得到风速横向预测值和纵向预测值,最后再通过BP神经网络进行组合预测。对国内某风电场的风速预测结果表明,所提出的风速预测模型可行、有效,具有较好的预测精度。

季节周期性Elman网络的网络流量分析与应用

针对静态前馈网络和Elman网络在网络流量预测中的不足,建立了一个基于改进Elman神经网络的流量模型,并提出了一种基于季节周期性学习方法,根据实际网络中测量得到的网络流量数据,对网络流量进行预测。实验结果表明,该模型具有良好的预测效果,相对于传统线性模型、BP神经网络模型及标准Elman神经网络模型具有更高的预测精度和更好的自适应性,应用于网络流量预测是可行、有效的。

发电量季节周期性预测模型的探讨

分析了广东省发电量数据特点 ,应用中位移动平均法 ,将其分解成趋势项和周期项 ,提出了乘法模型。预测结果显示此方法简单有效 ,对于季节时间序列的辨识、预测有实用价值。

财务柔性与短期融资需求——基于沪深A股季节周期性企业的研究

季节周期性企业是国民经济的重要组成部分,然而其财务决策研究相对匮乏。对季节周期性企业财务决策的研究可以深入探讨企业如何运用不同的融资渠道来满足短期融资需求。采用季度时间序列数据,以2002—2017年沪深A股企业为样本划分公司季节周期性,以此确定企业季节周期性最大财季,探讨季节周期性企业在短期融资需求时财务决策的最佳方式。结果表明:相较于非季节周期性企业,季节周期性企业实施较为稳健的财务决策,且主要通过信息不对称程度较低的短期负债,尤其是以商业信用来保持短期财务柔性。此外,季节周期性企业持有超额现金的成本高于私人债务成本,持有超额现金储备并非季节周期性企业保持短期财务柔性的主要渠道。

草原风电场气象与时间纵横组合的风速预测

该研究提出的风速预测模型以气象因子作为特征输入矢量,并利用带加权的欧氏距离在时间纵横方向上寻找待测日的相似矢量,通过RBF神经网络进行风速预测。结果表明:所研究风速预测模型预测精度高,预测结果的全年总平均相对偏差和均方差最小,是一种有效的草原风电场风速预测方法。

基于时间序列和主成分分析的订购运输规划研究

在实际生产中,不同供货商和转运商在不同时间对于原材料的供应和转运情况有所差异。为减少资源消耗并满足生产需求,采用时间序列和主成分分析法对某企业的材料订购与运输规划进行研究。将该企业5年内每周订货量、402家供应商供货量、8家转运商运输损耗率数据作为研究对象,对其供应商和转运商进行综合评价和量化分析,给出具体排名。根据该排名,通过季节周期性时间预测和目标规划,制订出未来24周该企业的原材料订购和转运规划策略。该策略不仅能提高企业原材料订购与运输效率,还能改善生产效益。

Reproductive Cycle and Seasonal Variations in Lipid Content and Fatty Acid Composition in Gonad of the Cockle Fulvia mutica in Relation to Temperature and Food

From March 2004 to February 2005,seasonal variations in lipid content and fatty acid composition of gonad of the cockle Fulvia mutica(Reeve) were studied on the eastern coast of China in relation to the reproductive cycle and environment conditions(e.g.,temperature and food availability).Histological analysis as well as lipid and fatty acid analyses were performed on neutral and polar lipids of the gonad.Results showed that gametogenesis occurred in winter and spring at the expense of lipids previously accumulated in summer and autumn,whereas spawning occurred in summer(20.4-24.6℃).The seasonal variation in lipid content was similar to that of the mean oocyte diameter.In both neutral and polar lipids,the 20:5n-3 and 22:6n-3 levels were relatively higher than saturated fatty acids,and polyunsaturated fatty acids were abundant,with series n-3 as the predominant component.Seasonal variations in the 20:5n-3 and 22:6n-3 levels and the principal n-3 fatty acids were clearly related to the reproductive cycle.The ∑(n-3) and ∑(n-6) values were relatively high during January-May,and the associated unsaturation index was significantly higher than that in other months.The results suggest that fatty acids play an important role in the gametogenesis of F.mutica.

Impacts of Seasonal Fossil and Ocean Emissions on the Seasonal Cycle of Atmospheric CO_2

The seasonal cycle of atmospheric CO2 at surface observation stations in the northern hemisphere is driven primarily by net ecosystem production (NEP) fluxes from terrestrial ecosystems. In addition to NEP from terrestrial ecosystems, surface fluxes from fossil fuel combustion and ocean exchange also contribute to the seasonal cycle of atmospheric CO2. Here the authors use the Goddard Earth Observing System-Chemistry (GEOS-Chem) model (version 8-02-01), with modifications, to assess the impact of these fluxes on the seasonal cycle of atmospheric CO2 in 2005. Modifications include monthly fossil and ocean emission inventories. CO2 simulations with monthly varying and annual emission inventories were carried out separately. The sources and sinks of monthly averaged net surface flux are different from those of annual emission inventories for every month. Results indicate that changes in monthly averaged net surface flux have a greater impact on the average concentration of atmospheric CO2 in the northern hemisphere than on the average concentration for latitudes 30-90°S in July. The concentration values differ little between both emission inventories over the latitudinal range from the equator to 30°S in January and July. The accumulated impacts of the monthly averaged fossil and ocean emissions contribute to an increase of the total global monthly average of CO2 from May to December.An apparent discrepancy for global average CO2 concentration between model results and observation was because the observation stations were not sufficiently representative. More accurate values for monthly varying net surface flux will be necessary in future to run the CO2 simulation.

Gametogenic Cycle, the Spawning Season, First Sexual Maturity, and the Biological Minimum Size in Male Ruditapes philippinarum （Bivalvia： Veneridae） in Western Korea

The male gametogenic cycle, spawning season, first sexual maturity, and the biological minimum size in male Ruditapes philippinarum were investigated by qualitative and quantitative reproductive analyses. In the study of the male gametogenic cycle by qualitative histological analysis, the gametogenic cycle in male individuals can be classified into five successive stages： （1） early active stage, （2） late active stage, （3） ripe stage, （4） partially spawned stage, and （5） spent and inactive stage. Monthly changes in the gonad index in males measured by qualitative analysis showed a similar pattern to the male gametogenic cycle. In the study of the male gametogenic cycle by quantitative statistical analysis, monthly changes in the portions （%） of areas occupied by the testis areas to total tissue areas showed a rapid increase in March, and reached the maximum in May-June. And also monthly changes in the portions （%） of areas occupied by the spermatogenic stages to the testis area showed a maximum in May and gradually decreased from June to October. Therefore, this species showed a unimodal gametogenic cycle during the year, and the number of spawning seasons occurred once per year, from June to October, with a peak spawning between July and August. The percentage at the first sexual maturity of male clams ranging from 15.1-20.0 mm in shell length was 64.7%, and that of all individuals ranging from over 25.1 mm in shell length was 100%. The biological minimum size （shell lengths at 50% of sexual maturity （RMs0）） of male mature clams that was fitted to an exponential equation was 17.16 mm （considered to be 1 year old）. Because harvesting clams less than 17.16 mm in shell length could potentially cause a drastic reduction in recruitment, a measure indicating a prohibitory fishing size should be enacted for adequate fisheries management.

The seasonal cycle of redistribution of atmospheric mass between continent and ocean in the Northern Hemisphere

Using NCEP/NCAR and ERA-40 reanalyses,we studied the seasonal cycle of redistribution of air mass between continents and oceans over the Northern Hemisphere.Our results demonstrate that air mass in the Northern Hemisphere shifts clearly between continents and oceans when the season cycles.In July,the air mass reaches its lowest over Eurasia and its highest over the Pacific,and the opposite occurs in January.However,a different scenario is observed over the north Atlantic;the accumulated air mass reaches its maximum there in May.The maintenance of the accumulation or loss of air mass in a region is found to be related to the areal mean air mass flux divergence and the difference between precipitation and evaporation in an air column.The zonal-vertical circulations change with season,with the air ascent and decent reversed between land and sea.Besides,there also exists a noticeable difference of water vapor content of the air between continents and oceans,and this difference is season-dependent.Physically,the vapor content is able to significantly affect the atmosphere in absorbing solar short-and earth’s long-wave radiations,hence influencing atmospheric thermal conditions.The land-sea thermal contrasts inclusive of the diabatic heating rate changes their signs with season going on,resulting in the reversal of orientations of the temperature gradient.These thermal forcings not only facilitate the formation of the monsoons but also indirectly induce the seasonal cycle of the air mass exchanging over regions between continents and oceans.

Ionospheric absorption and planetary wave activity in East Asia sector

In this paper, we focus on ionospheric absorption in the East Asia sector, and look for manifestations of atmospheric influences in this area. First, a 4-year historical record of absorption measurement at Beijing is presented. This record was obtained by a sweep frequency technique, in which 27-days periodic variation of the absorption level was found to be dominant, appearing in most seasons except winters. Instead, unusual enhancements of the absorption level appeared in winters (winter anomaly), at the meantime the level varied with periods mainly in the range of 8-12 days. Comparing to 27-days period from the Sun, the shorter period oscillations should be related to planetary wave activities in lower atmosphere. Second, fmin data from 5 mid-latitude ionosondes in Japan were used as an indirect but long-term measurement. With the fmin data covering two solar cycles, disturbances with various periods were found to be active around solar maximum years, but the 8-12 days oscillations always existed in winter, showing seasonal dependence instead of connection to solar activity. These results given in this paper demonstrate seasonal and solar cycle-dependent features of the ionospheric absorption in East Asia sector, and confirm the existence of influence from atmosphere-ionosphere coupling in this area, as well as the relationship between ionospheric winter anomaly and planetary wave activity.