Scalar BEKK and indirect DCC

The paper derives the scalar special case of the well‐known BEKK multivariate GARCH model using a multivariate extension of the random coefficient autoregressive (RCA) model. This representation establishes the relevant structural and asymptotic properties of the scalar BEKK model using the theoretical results available in the literature for general multivariate GARCH. Sufficient conditions for the (direct) DCC model to be consistent with a scalar BEKK representation are established. Moreover, an indirect DCC model that is consistent with the scalar BEKK representation is obtained, and is compared with the direct DCC model using an empirical example. The paper shows, within an asset allocation and risk measurement framework, that the two models are similar in terms of providing parameter estimates and forecasting value‐at‐risk thresholds for equally weighted and minimum variance portfolios. Copyright © 2008 John Wiley & Sons, Ltd.     

超材料混凝土抗冲击效应数值研究

作为一种广泛应用的工程材料,混凝土材料抗拉强度低的缺点限制了其应用.当高速冲击荷载作用在混凝土结构上时,由于混凝土的脆性和较低的抗拉强度,结构后部的混凝土通常会产生严重的层裂破坏.因此,有效降低混凝土的层裂破坏对于提高结构性能很重要.近些年学者提出了局域共振超材料,它利用人造微结构的存在能使该超材料呈现出天然材料所不具备的超常物理性质.本文借鉴局域共振超材料的工作原理,通过将混凝土中的部分天然骨料替换为人工骨料超材料来降低冲击荷载下的层裂破坏.通过LS-DYNA,建立考虑随机分布的砂浆、天然骨料和人工骨料的超材料混凝土三维细观模型来进行层裂实验的数值模拟.研究超材料混凝土在冲击荷载作用下的材料性能以及人工骨料的材料属性和几何属性对超材料混凝土动态性能的影响.     

Scepticism,relativism and the argument from the criterion

This article explores the relationship between epistemic relativism and Pyrrhonian scepticism. It is argued that a fundamental argument for contemporary epistemic relativism derives from the Pyrrhonian problem of the criterion. Pyrrhonian scepticism is compared and contrasted with Cartesian scepticism about the external world and Humean scepticism about induction. Epistemic relativism is characterized as relativism due to the variation of epistemic norms, and is contrasted with other forms of cognitive relativism, such as truth relativism, conceptual relativism and ontological relativism. An argument from the Pyrrhonian problem of the criterion to epistemic relativism is presented, and is contrasted with three other arguments for epistemic relativism. It is argued that the argument from the criterion is the most fundamental argument for epistemic relativism. Finally, it is noted how the argument of the present paper fits with the author’s previous suggestion that a particularist response to the Pyrrhonian sceptic may be combined with a naturalistic view of epistemic warrant to meet the challenge of epistemic relativism.     

非资源消费型野生动物旅游者的环境态度研究——以澳大利亚海豚探索中心为例

通过对前往澳大利亚班布里海豚探索中心的访客进行调研, 使用新生态范式量表, 运用K-means聚类分析、方差分析等定量方法, 探析游客对在野外生境中接触海豚的环境态度及差异性, 主要结论如下。首先, 受访者样本总体环境态度分为三类: 近人类中心主义、近生态中心主义和立场中立者, 样本总体的环境态度归属近生态中心主义。其次, 不同环境态度群组的人口社会学特征具有差异性。人口社会学特征中, 性别和学历在环境态度存在显著性差异(p≤0.05)。不同年龄、收入和家庭状况对环境态度无显著性差异(p≤0.05)。最后, 旅游行为中旅游经历、信息来源途径对环境态度具有显著差异, 旅行同伴、消费额和停留时间对环境态度无显著性差异; 重游意愿对风险感知具有显著性差异, 满意度无显著性差异。研究结果有助于理解野生动物旅游者特征和理解人与野生动物接触的复杂过程, 对野生动物旅游目的地管理具有重要意义。     

Molecular compounds without chemical bonding

Zusammenfassung Die Infrarotspektren der Einschlussverbindungen [Ni(CN)₂(NH₃)(C₆H₆)] und [Ni(CN)₂(NH₃)C₄H₅N] wurden untersucht und mit den Spektren von gasförmigen und flüssigen C₆H₆ bzw. C₄H₆N verglichen.

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Clathrate work was carried out under a research grant by University of Western Australia. Nickel cyanide-ammonia clathrates were further investigated by the author at the Punjab University (Chandigarh, India), University of Rome (Rome, Italy) and Fisk University (Nashville, Tennessee, USA).     

Growth and the average duration of larval life in the southern hemisphere lamprey,Geotria australis Gray

Summary The average duration of larval life in the anadromous lamprey,Geotria australis (the sole representative of the Geotriidae) is estimated as 41/4 years. Compared with other lampreys, the ammocoetes ofG. australis have a slow growth rate, increase in length during the year preceding metamorphosis and typically enter metamorphosis at a small mean length (<100 mm) and weight (<1.2 g).     

Advances in electrocatalysts for oxygen evolution reaction of water electrolysis-from metal oxides to carbon nanotubes

The water electrolysis for hydrogen production is constrained by the thermodynamically unfavorable oxygen evolution reaction(OER),which requires input of a large amount of energy to drive the reaction.One of the key challenges to increase the efficiency of the water electrolysis system is to develop highly effective and robust electrocatalysts for the OER.In the past 20–30 years,significant progresses have been made in the development of efficient electrocatalysts,including metal oxides,metal oxide-carbon nanotubes(CNTs) hybrid and metal-free CNTs based materials for the OER.In this critical review,the overall progress of metal oxides catalysts and the role of CNTs in the development of OER catalyst are summarized,and the latest development of new metal free CNTs-based OER catalyst is discussed.