基于服务最大化的果蔬品配送中心选址问题

针对果蔬品具有易腐、消耗快等特点,建立基于服务最大化的果蔬品区域配送中心选址的数学模型,并运用遗传算法求解该模型。最后通过实例研究验证该模型的有效性。     

农产品配送中心选址模型研究

针对农产品物流配送的实际情况,选取交通情况、经济因素、环境因素和其他因素构建了农产品配送中心选址的评价指标体系;采用层次分析法计算农产品配送中心选址评价指标权重,然后在评价信息为区间数的情况下,用不确定性多属性决策方法建立了农产品配送中心选址模型;以某市为例,探讨了该模型在农产品配送中心选址上的应用。实例分析结果表明,构建的模型充分考虑了评价过程中的随机性和不确定性,可以使得评价结果更客观,更结合实际,所以评价效果应该较以往的实数评价标度更好。     

国际金融危机对云南 －东盟贸易影响和自贸区的机遇

运用引力模型对云南 －东盟双边贸易进行数量考察,计量分析了国际金融危机对双边贸易的影响。主要结论有：国际金融危机的影响是暂时的,双方贸易是自主的。阐述了中国 －东盟自由贸易区对云南经济发展的重要意义。最后,针对云南特点对抓住自贸区机遇、促进双边贸易给出若干建议。     

基于动量定理的汽车碰撞模型的同一性研究

为了研究基于动量定理的汽车碰撞模型的同一性,分析了2种典型模型建模坐标系的差别.应用理论和实车碰撞试验相结合的方法,对2种模型的同一性进行了研究.在上述研究的基础上,应用2种模型对同一起汽车碰撞事故进行了分析,结果表明：合理选择力学参数能够保证2种模型计算结果相同,从而研究验证了以质心为坐标原点和以碰撞点为坐标原点建立的汽车碰撞模型的同一性,可为应用同类模型得到的汽车碰撞事故分析结果的相互验证提供依据.     

水稻高产群体质量栽培技术研究与应用

以上海长江、跃进农场4000hm~2水稻田为研究对象,应用水稻高产群体质量栽培技术,建立水稻高产示范基地。2006-2008年累计实施面积9196.13hm~2,平均产量11136.6kg/hm~2,经济效益显著。     

浅谈重力滴灌技术的设计及注意事项

文章主要针对广西坡地上运用重力滴灌技术,从水源、管网布设及轮灌区划分等方面进行了概述。     

高活性谷氨酰胺酶豆豉芽孢杆菌的筛选及glsA基因的克隆

为筛选获得高活性谷氨酰胺酶豆豉芽孢杆菌菌株,提高谷氨酸的含量,试验通过康维皿弥散法对525株芽孢杆菌进行酶活检测,获得一株产谷氨酰胺酶活力为68.407 mg NH3/(g曲·h·37℃)的B.subtilis GA317菌株,其酶活力较B.subtilis BJ3-2高5.59倍.对2个菌株谷氨酰胺酶编码基因glsA...     

Detecting amphibian population cycles: The importance of appropriate statistical analyses

Amphibian populations are declining worldwide and understanding their temporal dynamics should be important to separate declines from natural fluctuations. In this study sixteen long-term amphibian time series, lasting 15 years or more, were analysed by means of conventional methods of time series analysis to evaluate the relative importance of exogenous and endogenous factors controlling population dynamics, and in particular to assess the existence of population cycles. There was significant autocorrelation in seven time series, and the autocorrelation function showed no signs of statistical cyclicity, but in one case there was some evidence for weak periodicity. In 12 populations the partial rate correlation function suggested the presence of direct density dependence, while there was no evidence for delayed density dependent regulation. In all time series the global Lyapunov exponent, a statistic that characterises the predictability of a dynamic system, indicated that the population trajectories had a tendency to converge towards a stable dynamics. These results may have conservation implications, because populations with direct density dependence possess high capacity of returning to equilibrium after a perturbation and therefore are less likely to go extinct. In the future, I encourage ecologists to increase the use of statistical time series methods and autoregressive modelling to analyse amphibian population dynamics in the framework of local and global climate variability.     

Counting elusive animals: Comparing field and genetic census of the entire mountain gorilla population of Bwindi Impenetrable National Park, Uganda

Accurate population size estimates are an essential part of every effective management plan for conserving endangered species. However, censusing rare and elusive wild animals is challenging and often relies on counting indirect signs, such as nests or feces. Despite widespread use, the accuracy of such estimates has rarely been evaluated. Here we compare an estimate of population size derived solely from field data with that obtained from a combination of field and genetic data for the critically endangered population of mountain gorillas (Gorilla beringei beringei) in Bwindi Impenetrable National Park, Uganda. After genotyping DNA from 384 fecal samples at 16 microsatellite loci, the population size estimate was reduced by 10.1% to 302 individuals, compared with 336 gorillas estimated using the traditional nest-count based method alone. We found that both groups and lone silverbacks were double-counted in the field and that individuals constructed multiple nests with an overall rate of 7.8%, resulting in the overestimation of the population size in the absence of genetic data. Since the error associated with the traditional field method exceeded the estimated population growth of 5% in the last 4 years, future genetic censusing will be needed to determine how the population size is changing. This study illustrates that newly improved molecular methods allow fast, efficient and relatively affordable genotyping of several hundred samples, suggesting that genetic censusing can be widely applied to provide accurate and reliable population size estimates for a wide variety of species.     

Dragon’s blood tree - Threatened by overmaturity, not by extinction: Dynamics of a Dracaena cinnabari woodland in the mountains of Soqotra

Age determination of tropical trees, and monocotyledons in general, is not an easy task. Representatives of the Dracaena genus have survived in woodlands on dry margins of the Tethys tropical forest since the Tertiary Period. Here we present analyses of Dracaena cinnabari (DC) stand dynamics via direct and indirect methods of age determination. The direct method has taken advantage of historical photographs of DC mountain woodlands from Soqotra during an Austrian scientific expedition in 1899 by comparing these with the woodland stage in 2004. A decline in the number of tree individuals is obvious, but considering the little that is known about dynamics of DC woodland, one cannot simply state that such decline means forest destruction. The results from this direct method are compared to an indirect mathematical method of age determination using data from 2003. Indirect age determination values differed only about 6.5% from those obtained with the direct method, indicating that the indirect methodology is quite precise.