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Mariusz Doszy 《Journal of forecasting》2019,38(5):459-469
Forecasting methods are often valued by means of simulation studies. For intermittent demand items there are often very few non–zero observations, so it is hard to check any assumptions, because statistical information is often too weak to determine, for example, distribution of a variable. Therefore, it seems important to verify the forecasting methods on the basis of real data. The main aim of the article is an empirical verification of several forecasting methods applicable in case of intermittent demand. Some items are sold only in specific subperiods (in given month in each year, for example), but most forecasting methods (such as Croston's method) give non–zero forecasts for all periods. For example, summer work clothes should have non–zero forecasts only for summer months and many methods will usually provide non–zero forecasts for all months under consideration. This was the motivation for proposing and testing a new forecasting technique which can be applicable to seasonal items. In the article six methods were applied to construct separate forecasting systems: Croston's, SBA (Syntetos–Boylan Approximation), TSB (Teunter, Syntetos, Babai), MA (Moving Average), SES (Simple Exponential Smoothing) and SESAP (Simple Exponential Smoothing for Analogous subPeriods). The latter method (SESAP) is an author's proposal dedicated for companies facing the problem of seasonal items. By analogous subperiods the same subperiods in each year are understood, for example, the same months in each year. A data set from the real company was used to apply all the above forecasting procedures. That data set contained monthly time series for about nine thousand products. The forecasts accuracy was tested by means of both parametric and non–parametric measures. The scaled mean and the scaled root mean squared error were used to check biasedness and efficiency. Also, the mean absolute scaled error and the shares of best forecasts were estimated. The general conclusion is that in the analyzed company a forecasting system should be based on two forecasting methods: TSB and SESAP, but the latter method should be applied only to seasonal items (products sold only in specific subperiods). It also turned out that Croston's and SBA methods work worse than much simpler methods, such as SES or MA. The presented analysis might be helpful for enterprises facing the problem of forecasting intermittent items (and seasonal intermittent items as well). 相似文献
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以一种典型的产品生命周期管理(PLM)软件--SmarTeam为例,研究了基于仿真的采办(SBA)中PLM的应用.PLM用于管理SBA中的不同资源,共享产品数据.此外,从三个方面扩展了PLM:首先,使用PLM的开发接口和ActiveX技术将PLM与Matlab集成,使用户可以在PLM中浏览Matlab生成的控制系统文件;其次,使用PLM的工具以及PLM和MS Project的开发接口将PLM与Project集成,提高了PLM的项目管理功能;最后,使用PLM工具并设置SBA资源建立SBA权限控制模型,使PLM可以管理SBA系统的所有权限.PLM的应用及扩展使其可以更好的支撑SBA系统,同时解决了SBA复杂权限管理的问题. 相似文献
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利用介孔材料孔径和生物大分子的尺寸相当的特点,采用有序介孔分子筛SBA-15为载体实现对血红蛋白(Hb)和葡萄糖氧化酶(GOx)的固载,并考察其生物活性.紫外可见光谱和红外吸收光谱表明:以介孔分子筛SBA-15作为固定载体可以有效地吸附血红蛋白和葡萄糖氧化酶,且在吸附过程中很好的保持了蛋白质的天然二级结构. 相似文献
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介孔分子筛SBA-15中表面羟基及模板剂去除的1H核磁共振研究 总被引:1,自引:0,他引:1
^1H超高速魔角旋转固体核磁共振技术可直接和定量地检测SBA-15表面存在的3种硅羟基,即单羟基(Hs),氢键羟基(Hh)和双羟基(Hg)。此方法可用于准确跟踪介孔分子筛的嫁接和改性过程。^1H核磁共振亦发现,在不同的萃取条件下,多种有机溶剂不能完全除去模板剂,焙烧是在嫁接前除去模板剂的有效方法。 相似文献
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以聚氧乙烯-聚氧丙烯-聚氧乙烯(P123)嵌段共聚物表面活性剂为模板剂,正硅酸乙酯(TEOS)为硅源,Fe( NO3)3·9H2O为铁源在酸性条件下合成Fe-SBA-15介孔分子筛.通过XRD,N2吸附-脱附,红外等分析手段对样品进行了表征.结果表明合成的样品具有有序的六方介孔结构.铁含量的不同对SBA-15的孔径及其比表面积均有影响.所合成的材料在苯羟基化反应中表现出良好的催化活性,最高转化率可达32.16%. 相似文献
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SBA支撑环境技术的研究 总被引:32,自引:12,他引:20
介绍了具有我国自主知识产权的SBA支撑环境项目的阶段研究成果,包括给出自行开发成功并初步应用的多学科复杂产品虚拟样机工程支撑平台的体系结构、新技术特点、协同仿真平台系统组成结构、多学科虚拟样机协同仿真平台、多学科虚拟样机协同CAX/DFX工具集及全生命周期虚拟产品数据管理PLM等;研究了“仿真网格”的内涵、功能与体系结构,进而提出一种基于“仿真网格”的SBA支撑环境体系结构及其相关关键技术等。最后,展望了进一步的研究工作。 相似文献
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小企业投资公司计划——美国政府发展风险投资的方法 总被引:2,自引:0,他引:2
美国是风险投资发展最早,也是最完善的国家之一,在风险投资的发展历史中,美国政府一直扮演着重要的角色,其主要方法是实施小企业投资公司计划,并成立美国小企业管理局专门负责该项计划的实施。文章介绍了小企业投资公司计划的资金来源、申请加入程序及投资运作方式等内容,并介绍了小企业管理局的管理与监督职能。 相似文献
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以SBA15分子筛为载体,添加Ni-Mo活性组分作为催化剂,在Parr高温高压反应釜中,采用加氢脱硫(HDS)方法脱除噻吩类中的硫物质。通过XRD,TEM以及孔结构分析,研究掺杂Ti原子对SBA15基催化剂的形貌、比表面积和孔径等的影响,并考察一系列的不同硅、钛摩尔比(n(Si)/n(Ti)分别为∞,10,30和60)对催化剂加氢脱硫活性的影响。研究结果表明:经过改性后的SBA15的结构没有改变,但影响了载体的比表面积,改性后的比表面积有所降低;Ni和Mo活性相以NiMoO4和MoO3物相存在;Ti原子的加入有利于苯并噻吩(BT)和二苯并噻吩(DBT)中硫的脱除,并且不同硅钛摩尔比的催化剂呈现不同的脱硫率;当n(Si)/n(Ti)=30时,脱硫率最高。 相似文献