Diversity and spatial distribution of Opuntia spp. in the Mediterranean Basin     

P. Erre  I. Chessa  G. Nieddu  P.G. Jones   《Journal of Arid Environments》2009,73(12):1058-1066

This work offers a methodology based on statistical tools and GIS applications in a study of the adaptability of Opuntia to the environment, applied on the Mediterranean island of Sardinia. Detailed surveys of habitats containing naturalized populations of Opuntia spp. were made in order to select study sites. The topographic, soil and climatic features of these are described. The local biotypes are ascribed mainly to the spineless Opuntia ficus–indica (L.) Mill. and to the spiny Opuntia amyclaea Ten. Although introduced at different times, for different uses, they have adapted to the Sardinian environment and established in the wild. The distributions of the two species differed. The FloraMap^® modelling approach was used to simulate Opuntia distribution as a function of the island's climate and produced individual distribution maps using the accession points for the two species. Our analysis showed that environmental conditions at elevations above 800 m are the main limiting factors for the presence and abundance of Opuntia in Sardinia. Spatial representation developed by GIS software indicated temperatures below 2 °C as the threshold impairing the species naturalized distribution. The statistic results also show that variation in rainfall does not affect Opuntia spatial distribution in Sardinia.  相似文献   

试用三维地形模式计算茂密林区火险等级   总被引：2，自引：0，他引：2  

钱锦霞  张洪涛 《山西气象》2001,(3):15-17

本文用考虑森林植被的三维地形模式，对1972年4月15日神逐架林区森林火灾发生期间的风场、温度场和相对湿度场等进行了模拟，并在此基础上计算森林火险等级。结果表明，采用数值模拟方法可以得到无测站地区的气象要素，为进行森林火险等级预报奠定了基础。  相似文献   

测井评价稠油层等级的新方法   总被引：1，自引：0，他引：1       下载免费PDF全文

谭廷栋 《地球物理学报》1992,35(6):781-789

从测井信息中提取油和水的重量百分比,最能反映稠油层质量的特征.用油和水的重量百分比评价稠油层等级,是一种新概念.测井评价稠油层等级的新方法,就是根据这一新概念建立的.本文论述了新方法的物理基础,建立了测井评价稠油层等级的数学公式,并且给出了评价法则和应用范例.  相似文献   

模式识别与成矿预测Ⅳ——Isokid模式识别方法及其在矿产预测中的应用     

张景廉  叶伟龙 《铀矿地质》1990,(2)

在Isodata、Isomix等方法的基础上,笔者提出一个新的非监督模式识别方法即Isokid算法,该法还吸取了Cora-3、Hamming等监督模式识别方法的一些特点,使它具有很多优点:(1) 简化了初始聚类中心的计算;(2) 利用信息量计算法给特征加权;(3) 采用了删除特征试验;(4) 适用于多类分类识别。本文以广东花岗岩型铀矿床的识别预测和对赣中南产铀、产钨岩体的识别为例,介绍了本方法的使用情况和特点。结果表明,本方法识别结果可靠稳定,是目前模式识别中较好的方法,除应用于地质找矿外,还可应用于其它领域。  相似文献   

固态毫米波雷达探测模式的对比评估与分析   总被引：1，自引：1，他引：0  

武静雅  刘黎平  郑佳锋 《气象》2016,42(7):790-798

利用2014年广东阳江和青藏高原外场观测中多种探测仪器的观测资料,对比了灾害天气国家重点实验室与航天科工23所联合研制的固态毫米波雷达三种探测模式最小可测回波强度、可测液态水(冰水)含量、观测同一目标时回波强度的差异以及与K波段微降水雷达回波强度的差异等。结果表明:(1)毫米波雷达不同模式最小可测回波强度差异与理论差异一致,边界层模式和降水模式能观测近地面全部层云和积云,卷云能观测5km高度冰水含量在0.0007 g·m~(-3)以上的卷云,随着高度上升探测能力有所下降;(2)毫米波雷达使用不同模式观测同一目标时,不同观测模式宏观回波强度一致,大部分差异不超过3.5 dB;(3)K波段微降水雷达和Pasivel2激光雨滴谱仪的近地面回波强度一致,毫米波雷达与K波段微降水雷达存在系统差异。  相似文献   

Bipolar molecular outflows     

R. Bachiller  J. Gómez-González 《Astronomy and Astrophysics Review》1992,3(3-4):257-287

Summary Bipolar molecular outflows are a ubiquitous phenomenon in the process of star formation. We review the main observational properties of the outflows around young stellar objects, highlighting the recent wealth of information provided by the new generation of large radiotelescopes operating at millimeter wavelengths (in particular the IRAM 30-m, the NRO 45-m, and the JCMT 15-m dishes). The observations of outflows containing molecular, jet-like flows and bullets are discussed in detail, as they provide key information for understanding origin and evolution of the outflows. We also discuss a number of closely related issues: the evidence for dense shocked gas associated with the flows, the interaction of the outflows with the ambient dense cores, the evolutionary status of the sources driving the outflows, the properties of circumstellar disks, and theoretical models of the origin of the neutral winds. All these areas are important for developing a plausible scenario for the formation and evolution of the bipolar molecular outflows.This article was processed by the author using the Springer-Verlag T_EX AAR macro package 1991.  相似文献   

云底高度的地基毫米波云雷达观测及其对比   总被引：4，自引：2，他引：2       下载免费PDF全文

唐英杰  马舒庆  杨玲  陶法  李思腾  谢成华  唐凡洁 《应用气象学报》2015,26(6):680-687

对2014年11月20日—12月31日中国气象局大气探测综合试验基地Ka波段毫米波云雷达、Vaisala CL51激光云高仪、L波段高空探测系统观测的云底高度进行对比分析。结果表明:在低能见度条件下,毫米波云雷达对云的探测能力明显优于激光云高仪,随着能见度的增加,两设备云探测能力差距在减小;毫米波云雷达与激光云高仪同时观测到有云时,二者观测的云底高度相关系数为0.92;毫米波云雷达与探空观测云底、云顶高度的相关系数分别为0.93和0.78;云雷达观测的云底高度均略低于激光云高仪和探空,云雷达观测的云顶高度略高于探空。  相似文献   

图像预处理对人脸识别系统性能影响研究     

金欣  文成玉  杜鸿 《成都信息工程学院学报》2015,30(2)

目前多数工程化人脸识别系统是基于子空间算法的,针对子空间算法识别系统中稳定性和抗干扰性不高的问题,从图像预处理的角度出发,通过Matlab仿真Eigenface和Fisherface两种算法识别过程,建立起图像差值模型,同时引入不同预处理方法进行比较,根据类间距离和类内距离的变化,从中确定出最优的预处理方法,改善算法识别率和效率,实验结果表明,加入合适的图像预处理可以增强识别系统的强壮性.  相似文献   

Perihelion motion of small irregular dust particles due to radiation forces     

J. Kla?ka  F. Kundracík 《Planetary and Space Science》2006,54(4):379-393

Perihelion motion, i.e. a secular change of longitude of perihelion, of interplanetary dust particles is investigated under the action of solar gravity and solar electromagnetic radiation. As for spherical particle [Kla?ka, J., 2004. Electromagnetic radiation and motion of a particle. Cel. Mech. Dynam. Astron. 89, 1-61]: (i) perihelion motion is of the order ( is heliocentric velocity of the meteoroid and c is the speed of light in vacuum), if a component of electromagnetic radiation acceleration is considered as a part of central acceleration; (ii) perihelion motion is of the first order in if the total electromagnetic radiation force is considered as a disturbing force. The new facts presented in this paper concern irregular dust particles. Detailed numerical calculations were performed for the grains ejected at aphelion of comet Encke. Perihelion motion for irregular interplanetary dust particles exists already in the first order in for both cases of central accelerations. Moreover, perihelion motion of irregular particles exhibits both positive and negative directions during the particle orbital motion. Irregularity of the grains causes not only perihelion motion, but also dispersion of the dust in various directions, also normal to the orbital plane of the parent body.  相似文献   

Equilibrium trading of climate and weather risk and numerical simulation in a Markovian framework   总被引：3，自引：3，他引：0  

Sébastien Chaumont  Peter Imkeller  Matthias Müller 《Stochastic Environmental Research and Risk Assessment (SERRA)》2006,20(3):184-205

We consider financial markets with agents exposed to external sources of risk caused, for example, by short-term climate events such as the South Pacific sea surface temperature anomalies widely known by the name El Nino. Since such risks cannot be hedged through investments on the capital market alone, we face a typical example of an incomplete financial market. In order to make this risk tradable, we use a financial market model in which an additional insurance asset provides another possibility of investment besides the usual capital market. Given one of the many possible market prices of risk, each agent can maximize his individual exponential utility from his income obtained from trading in the capital market, the additional security, and his risk-exposure function. Under the equilibrium market-clearing condition for the insurance security the market price of risk is uniquely determined by a backward stochastic differential equation. We translate these stochastic equations via the Feynman–Kac formalism into semi-linear parabolic partial differential equations. Numerical schemes are available by which these semilinear pde can be simulated. We choose two simple qualitatively interesting models to describe sea surface temperature, and with an ENSO risk exposed fisher and farmer and a climate risk neutral bank three model agents with simple risk exposure functions. By simulating the expected appreciation price of risk trading, the optimal utility of the agents as a function of temperature, and their optimal investment into the risk trading security we obtain first insight into the dynamics of such a market in simple situations.

Peter ImkellerEmail:

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