Intermittent demand forecasting in the Enterprise: Empirical verification

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).     

纯黏土与砂-黏土混合物渗透特性差异及机理分析

根据重塑纯黏土和砂-黏土混合物试样的室内固结试验结果,反演了渗透系数,探讨了纯黏土和砂-黏土混合物的渗透特性差异.试验结果表明:常用于评价纯黏土渗透性状的归一化指标e/eL(孔隙比与液限状态孔隙比的比值)能拓展运用于砂-黏土混合物中,但e/eL与渗透系数之间呈现非线性关系,这显著不同于纯黏土的线性关系,其本质原因在于混合物在压缩过程中形成了砂骨架.骨架形成前,纯黏土和砂-黏土混合物的e/eL与渗透系数的2条关系曲线吻合良好,而在骨架形成后,两者的关系曲线存在明显的差异;引入砂-黏土混合物四相体系,从黏土孔隙比和砂孔隙比的角度阐述了砂骨架的形成机制,且对两者渗透性状的差异性进行了详细的机理解释;最后给出了一种可以预测纯黏土和砂-黏土混合物渗透系数的经验公式.     

关于高校图书馆书库管理的思考

书库是一个图书馆的中心，高质量的书库管理工作直接决定了整个图书馆的服务质量。针对图书馆书库管理中存在的问题，提出了提高书库管理工作质量的措施，使书库能更高效地为读者服务。     

选材引起测量金属丝杨氏模量的误差分析

杨氏模量的测量是大学物理中重要的力学实验之一。我们对不同直径、不同长度的钢丝进行了杨氏模量测定,分析了选材对实验结果的影响。研究结果表明,在仪器允许的测量范围内,直径越小、长度越长的材料,其杨氏模量的相对合成标准不确定度越小。     

海岛旅游者生态旅游行为浅析--以湄洲岛为例

随着生态旅游的兴起，生态旅游行为内涵不断地得到丰富.文章以深层生态学为基础，设计海岛生态旅游行为调查问卷，探索旅游型海岛游客生态旅游行为的特征和影响因素.运用SPSS19.0数据平台，分析了旅游者的人口社会学属性和生活经历对生态旅游行为的影响及影响强度.分析结果表明，我国旅游者比较缺乏深层生态旅游行为的品质，社会属性中的受教育程度是影响旅游者旅游行为的重要因素.同时，旅游者平时的环保习惯与旅行过程中的环保行为表现出一致的现象.     

住宅中儿童活动空间设计方法

住宅发展致力于解决住户最基本的生活问题,直到近年来住宅多样化,才出现儿童房等功能分区。然而,儿童活动空间仍未得到住户与设计者足够的重视。由此,试图通过分析儿童在住宅内的行为习惯与设计存在的问题,归纳其需求。在此基础上,研究文献,结合实际提出儿童活动空间的位置选择,家具布置方法,提出可持续设计建议。     

大型结构件——连续采煤机主机架的制造工艺研究

为控制大型结构件——连续采煤机主机架的生产质量,除精选必要的制造设备外,工艺工装的设计也起着举足轻重的作用。从下料、焊接、时效去应力、组焊件检查等方面,对大型结构件——连续采煤机主机架的制造工艺进行了研究。     

北京高校学生生活垃圾源头分类行为及其影响因素研究

生活垃圾源头分类制度的推广受到了社会的广泛关注。结合计划行为理论及相关文献提出5个研究假设,根据对北京市10所大学500余名在校大学生问卷调查的统计结果,分析了影响高校学生进行生活垃圾源头分类的因素,从政策制定、宣传教育、基础设施建设及创新体制机制等方面提出对策建议。     

Rediscovery of Disepyris semiruber (Kieffer) (Hymenoptera: Bethylidae) in Southern Africa,with first description of the male

Holepyris semiruber Kieffer is redescribed and illustrated based on freshly collected specimens. Holepyris semiruber var. striatipleura Kieffer is considered a colour variant of this species and therefore a junior synonym of H. semiruber syn. nov. This species is transferred to Disepyris, D. semiruber (Kieffer) comb. nov., based on the possession of a short 2r-rs&Rs vein in the fore wing and presence of long flat spine-shaped setae on the outer (posterior) surface of the protarsi. The male is described for the first time from new specimens collected in South Africa. This species is recorded for the first time from Namibia and Zimbabwe. All photographs are available on www.waspweb.org.     

热输入对Q460钢焊接接头组织及拉伸变形行为的影响

以Q460钢为对象，研究了埋弧焊热输入对其接头组织及其拉伸变形行为的作用规律与机理.结果表明:接头HAZ宽度随热输入增加而增大，同时FZ柱状晶比例也增加，FZ靠近熔合线的组织明显细化，且FZ的软化得到改善.热输入对接头整体强度无明显影响，而断裂延伸率呈增加趋势.19.0kJ/cm下焊接接头FZ与HAZ界面的变形不协调，导致过早发生断裂.随热输入的增加，FZ组织细化，缓解了FZ与HAZ界面硬度差，提高了接头的塑性变形能力，拉伸断裂位置由FZ转移至BM.