Forecasting item-level demands: an analytical evaluation of top-down versus bottom-up forecasting in a production-planning framework

Rajesh Piplani School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798, Republic of Singapore Email: vish{at}pmail.ntu.edu.sg Received on 12 January 2007. Accepted on 19 November 2007. We compare the performance of top–down (TD) and bottom–up(BU) strategies for forecasting the demand of an item that belongsto a product family. The TD strategy forecasts the sum of theitem demands and distributes it to the individual item basedupon the historical demand proportion of each item in the family.The BU strategy forecasts each item demand individually usingthe historical demand data for the particular item. All theitem demands, which may be correlated with each other, are assumedto follow a first-order univariate moving average process. Asis common in a production-planning environment, the forecastingunder both strategies is carried out using the exponential smoothingtechnique. We show that the performance of the two forecastingstrategies is nearly identical, regardless of the coefficientof correlation between the item demands, the items' proportionin the family and the coefficient of the serial correlationterm of the demand process. We further investigate the relativeperformance of the two strategies when a fixed (rather thanthe optimal) smoothing constant is used for forecasting thedemand under both strategies.     

人造细胞的化学构建及其生物医学应用研究

人造细胞是模拟生物细胞结构,人工构建的与细胞功能相近的微米囊泡。人造细胞的构建主要有两种模式:自上而下模式主要利用生物学方法对生物基因序列进行重新设计,获得具有细胞类似结构功能的人造细胞;自下而上模式主要利用化学方法采用非生命物质构筑简化的细胞结构模型。自下而上化学模式构建的人造细胞大多只包含执行所需功能的最小单元,具有简单的细胞仿生的结构与功能。本文详细综述了人造细胞的构建模式以及化学构建人造细胞的常见类型,包括脂质囊泡、蛋白体囊泡、聚合物囊泡、凝集体液滴和胶体囊泡等,总结了人造细胞在分析传感、细胞结构与功能模拟、生物载体转运、微纳米反应器、疾病诊疗方面的生物医学应用现状。     

Identification evidence unraveled by strict proteomics rules toward forensic samples

Snake venom is a complex mixture of proteins and peptides secreted by venomous snakes from their poison glands. Although proteomics for snake venom composition, interspecific differences, and developmental evolution has been developed for a decade, current diagnosis or identification techniques of snake venom in clinical intoxication and forensic science applications are mainly dependent on morphological and immunoassay. It could be expected that the proteomics techniques directly offer great help. This work applied a bottom-up proteomics method to identify proteins’ types and species attribution in suspected snake venom samples using ultrahigh-performance liquid chromatography–quadrupole-electrostatic field Orbitrap tandem mass spectrometric technique, and cytotoxicity assay was amended to provide a direct evidence of toxicity. Toward the suspicious samples seized in the security control, sample pretreatment (in-sol and in-gel digestion) and data acquisition (nontargeted and targeted screening) modes complemented and validated each other. We have implemented two consequent approaches in identifying the species source of proteins in the samples via the points of venom proteomics and strict forensic identification. First, we completed a workflow consisting of a proteomics database match toward an entire SWISS-PROT (date 2018-11-22) database and a result-directed specific taxonomy database. The latter was a helpful hint to compare master protein kinds and reveal the insufficiency of specific venom proteomics characterization rules. Second, we suggested strict rules for protein identification to meet the requirements of forensic science on improved identification correctness, that is, (1) peptide spectrum matches confidence, peptide confidence, and protein confidence were both high (with the false-discovery ratio less than 1%); (2) the number of unique peptides was more than or equal to two in one protein, and (3) within unique peptides, which at least 75% of the ∆m/z of the matched y and b ions were less than 5 ppm. We identified these samples as cobra venom containing 10 highly abundant proteins (P00597, P82463, P60770, Q9YGI4, P62375, P49123, P80245, P60302, P01442, and P60304) from two snake venom protein families (acid phospholipase A2 and three-finger toxins), and the most abundant proteins were cytotoxins.     

Internet resources for agent-based modelling

The use of agent-based models (ABMs) is steadily increasing in all the disciplines including environmental chemistry and toxicology. This growth is mainly driven by their ability to address problems that conventional modelling techniques cannot, such as the change of scale or the emergence of unanticipated phenomena resulting from interactions between their constitutive goal-directed agents. After a brief introduction on the basic principles of agent-based modelling and the presentation of selected case studies, the main software resources available on the Internet are presented. An attempt is made to estimate the complexity of these tools versus their potentialities and flexibility.     

多维高效液相色谱技术在蛋白质分离研究中的进展

蛋白质组学出现之后,多维高效液相色谱(multidimensional HPLC,MD-HPLC)系统以其快速、高效、自动化程度高以及容易与质谱等其他技术联用等优势而成为蛋白质组学相关分析技术中研究应用的热点。本文主要以本实验室在蛋白质组学研究中的技术进展为主线,介绍了多维高效液相色谱技术的发展,包括经典的“bottom-up”技术和“top-down”式的多维高效液相色谱技术路线,以及为了提高系统的分离通量而自行设计搭建的阵列式多维高效液相色谱平台,这些技术路线在蛋白质组学研究中有着极大的潜在应用价值。     

Enhanced Photocurrent Generation in Self-Assembled Monolayers Formed at Plasmonic Gold Nanostructures

The effect of localized surface plasmon resonance (SPR) appearing at the surfaces of gold nanoparticles (AuPs) was successfully applied for the enhancement of photocurrents from porphyrin ( Po ) immobilized on AuPs. The electrode consisting of AuPs with different sizes (∼15 or ∼35 nm) was prepared using the AuP film formed at the liquid/liquid interface, and then Po was self-assembled on the gold surface. The SPR effect for the AuP film was verified from the attenuated total reflection SPR and absorption measurements. Photocurrents from the modified electrodes were compared with the corresponding planar electrode. Appreciable enhancement of photocurrents was observed.     

表面合成异质原子掺杂的石墨烯纳米带

超高真空环境下,通过自下而上的方法原子级精确合成石墨烯纳米带是打开石墨烯带隙的重要方法。合理地设计带有异质原子(如硼、氮、氧等)的前驱体分子可以合成异质原子掺杂的石墨烯纳米带。掺杂的异质原子可以显著地调制石墨烯纳米带的电学、磁学等物理化学性质,并且调控的效果与异质原子的种类、位置、密度等密切相关。本文综述了近些年来利用分子束外延方法,在表面上合成异质原子掺杂的石墨烯纳米带的研究进展,同时对掺杂石墨烯纳米带的应用前景进行了展望。     

在云母晶面上应用“自下而上”和“自上而下”两种途径制造胶原蛋白纳米线阵列

以云母晶体的（001）晶面为基质,以天然Ⅰ型鼠尾胶原蛋白单体溶液为原料,分别考察了蛋白单体受基质规导进行“自下而上”的自组装过程,以及原子力显微镜探针对吸附在基质表面的蛋白膜层进行“自上而下”加工过程：（1） 两种制备途径均能 加工出结构精确可控的胶原蛋白纳米线阵列;（2） “自下而上”制备途径利用了蛋白单体和基质晶体在界面上互相识别并规范的“反相生物矿化”原理;（3） “自上而下”的加工利用了原子力显微镜接触模式下探针的“分子扫帚”机理。     

Construction and Application of a UHV Compatible Cluster Deposition System

The design and operation of a new UHV-compatible atomic cluster deposition system is described. The design is optimised for high cluster fluxes and for the production of cluster-assembled nano-devices. One key feature of the system is a high degree of flexibility, including interchangeable sputtering and inert gas aggregation sources, and two kinds of mass spectrometer, which allow both characterisation of the cluster size distribution and deposition of mass-selected clusters. Another key feature is that clusters are deposited onto electrically contacted lithographically defined devices mounted on an UHV-compatible cryostat cold finger, allowing deposition at room temperature as well as cryogenic and elevated temperatures. In-situ electrical characterisation of cluster-assembled devices can then be performed in the temperature range 1.2--75 K.