简介:目前众多的矢量数据压缩算法存在提高压缩曲线精度的同时牺牲压缩效率的问题。为此,文章提出一种以带有径向约束的Douglas—Peucker算法为基础来调整曲线局部形态特征点位置的矢量数据压缩算法。首先,通过带有径向约束的Douglas—Peucker算法提取曲线的特征点;其次,筛选出各个局部曲线段的重要形态特征点;最终,通过重要形态特征点对曲线进行局部调整,以提高曲线整体精度。实验表明,该方法一方面保证了压缩效率不变,另一方面能够有效降低局部位移偏差和面积偏差,从而提高曲线的压缩精度。
简介:把科技进步等生产的内涵性因素引入C-D函数,并计量分析了这些因素对推进产出增长所起的作用,介绍的实例说明了这种分析的有效性。
简介:Background:Volumeandtaperequationsareessentialforobtainingestimatesoftotalandmerchantablestemvolume.Taperfunctionsprovideadvantagestomerchantablevolumeequationsbecausetheyestimatediameterinsideoroutsidebarkatspecificheightsonthestem,enablingtheestimationoftotalandmerchantablestemvolume,volumeofindividuallogs,andaheightatagivendiameter.Methods:Usingdatacollectedfrom1218trees(1093Douglas-fir(Pseudotsugamenziesii(Mirbel)Franco)and125westernhemlock(Tsugaheterophylla)),weevaluatedtheperformanceofonesimplepolynomialfunctionandfourvariable-exponenttaperfunctionsinpredictingupperstemdiameter.SampletreeswerecollectedfromdifferentpartsofthestatesofOregon,Washington,andCalifornia.Wecomparedinside-barkvolumeestimatesobtainedfromtheselectedtaperequationwithestimatesobtainedfromasimplelogarithmicvolumeequationforthedataobtainedinthisstudyandtheequationsusedbytheForestInventoryandAnalysisprograminthePacificNorthwest(FIA-PNW)inthestateofCaliforniaandwesternhalfofthestatesofOregonandWashington.Results:Variableexponenttaperequationsweregenerallybetterthanthesimplepolynomialtaperequations.TheFIA-PNWvolumeequationsperformedfairlywellbutvolumeequationswithfewerparametersfittedinthisstudyprovidedcomparableresults.TheRMSEobtainedfromtaper-basedvolumeestimateswerealsocomparablewiththeRMSEoftheFIA-PNWvolumeequationsforDouglas-firandwesternhemlocktreesrespectively.Conclusions:ThetaperequationsfittedinthisstudyprovideaddedbenefittotheusersovertheFIA-PNWvolumeequationsbyenablingtheuserstopredictdiameteratanyheight,heighttoagivendiameter,andmerchantablevolumeinadditiontocubicvolumeincludingtopandstump(CVTS)ofDouglas-firandwesternhemlocktreesinthePacificNorthwest.ThefindingsofthisstudyalsogivemoreconfidencetotheusersofFIA-PNWvolumeequations.
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简介:摘要:数据结构作为计算机科学的核心,已经成为人们必须掌握的一切信息知识。作为经典的最短路径算法,Dijkstra算法数据结构被在生活中的各方面都有所体现。本文从数据结构和最短路径算法的定义入手,介绍了Dijkstra算法的算法优缺点和算法实例,最后阐述了最短路径算法在现实生活中的作用,说明该算法的重要意义。
简介:在HITS算法的基础上应用蚁群算法的主要思想,对网页按关键字搜索后被点击的次数进行统计,结合相关内容提出了一种新的搜索算法—基于蚁群算法的改进HITS算法.实验表明,该算法在使得返回结果中相关度较高的网页通过人们的自主选择获得了不同程度的加权,使得其在查准率及解决HITS算法的主题漂移方面都优于传统HITS算法.
简介:EctomycorrhizalfungusLaccariabicolorS238N,isolatedfromaforestsoilincentralFrancein1990s,hasdemonstratedunequivocallyandabilitytopromotepinegrowth.Inthepresentnurserybedexperiment,theabilityofthisectomycorrhizalfungustoincreasegrowthandPandKuptakeofDouglasFirseedlings(Zone22)wasexamined.Growthofinoculatedseedlingswasovertwice(plantheight)andthreetimes(biomass)thatofnon-inoculatedones.Similarly,boththeconcentrationsandtheamountsofPandKuptakebyseedlingsweresignificantlyincreasedbyfungalinoculation,indicatingtheimprovementofPandKnutritioninmycorrhizalseedlings.Incontrast,Al-Pinthesoilswasdecreasedobviouslybyplants,especiallybymycorrhizas,suggestingutilizationofthissoilPpoolbyplantsandmoreefficientAl-Pmobilizationbymycorrhizasthanbynomycorrhizas.Moreover,Kextractedby1mol/LHClfollowingconsecutiveextractionofH2OandCH3COONH4,whichmaynotbeplantavailable,couldbeutilizedbyfunguscoloniedroots.ThiscouldbeexplainedbythereleaseofprotonsandoxalatebyhypaewhichleadstoreplacementofinterlayerKinnonexpanded2:1claymineralsandbio-weatheringofphyllosilicates.