Fourier Analysis of Serial Dependence Measures

Classical spectral analysis is based on the discrete Fourier transform of the autocovariances. In this article we investigate the asymptotic properties of new frequency‐domain methods where the autocovariances in the spectral density are replaced by alternative dependence measures that can be estimated by U‐statistics. An interesting example is given by Kendall's τ, for which the limiting variance exhibits a surprising behavior.     

Bridging the critical interface: Ambidextrous innovation for water provision in Nairobi's informal settlements

This article examines innovation activities in water infrastructure in Nairobi, Kenya. The focus is on efforts by Nairobi City Water and Sewerage Corporation (NCWSC) to provide water services to the inhabitants in the informal areas of the city using an automated vending machine, or Pre-Paid Dispenser (PPD). In this study, we investigate what happens when a regime actor like NCWSC tries to implement an ambidextrous (two-handed) strategy: managing the existing system according to conventional practice and at the same time innovate in new technical solutions and business models to cater for unconnected users.Besides presenting our results, our aim in this article is also to introduce a research strategy for innovation studies in infrastructural systems in low-income urban areas. Three interconnected parts stand out as our contribution:First, we present a novel conceptual framework, by adding ideas from innovation studies to the Large Technical Systems approach. We investigate how regime actors can innovate to provide water to unconnected users, without expanding the system in a traditional way.Second, we propose a novel method for analysing and understanding innovation on the margins of the infrastructural system, or in our terms, innovation in the critical interface. Central to our method is, through empirical observation, to identify misalignment between the innovation (PPD) and contextual factors at the local level, where the innovation is implemented (interface misalignment), and misalignment between the innovation and the existing water regime (internal misalignment). We use a qualitative method and results forms as a basis for further research and starting point for regime actors in search of an improved ambidextrous strategy.Third, we analyse the innovation process per se. In the Nairobi case, we assess the ambidextrous innovation strategy, and claim that the PPD functions as an adapter in the critical interface, enabling the regime actors to operate in an environment of misalignment.     

柱塞副微观表面对间隙油膜压力的影响

根据分形理论中的W-M函数建立柱塞与缸体孔表面三维形貌数学模型,并利用MATLAB软件编写程序,分析分形维数对表面微观形貌的影响。将柱塞副间隙油膜沿轴向展成平面,建立油膜厚度及压力分布计算模型,采用有限体积法求解二维雷诺方程,分析粗糙度对柱塞副间隙油膜压力分布的影响。结果表明:随着分形维数的增加,柱塞表面粗糙度呈增加趋势,且表面粗糙度越大,压力峰值越大。     

甲烷在钯基催化剂上脱氢的分子模拟

为探明甲烷在钯基二聚体催化剂上脱氢反应过程的微观机理,对甲烷燃烧催化剂的设计与使用提供指导。在M06L/6-311++G(d,p)+SDD//M06L/6-311G(d,p)+LANL2DZ基组水平上,采用密度泛函理论(DFT)对甲烷在钯基二聚体催化剂(Pd_2、PdPt和PdNi)上的脱氢过程进行了研究。对比了甲烷在催化剂Pd_2、PdPt和PdNi上反应的能垒(E_b)、活化能(E_a)及反应速率常数(k),结果表明:CH_2→CH是甲烷在二聚体Pd_2反应的速率控制步骤(RDS),而CH_3→CH_2是催化剂PdPt和PdNi反应的RDS;钯基二聚体催化剂对甲烷脱氢的催化活性顺序为PdPtPd_2PdNi;抗积炭性能顺序为PdNiPd_2PdPt。PdPt适用于要求催化效率较高的项目,而抗积炭性能较好的PdNi催化剂可用于大型工业催化。     

A variational approach for free vibrating micro-rods with classical and non-classical new boundary conditions accounting for nonlocal strengthening and temperature effects

Abstract

Transverse vibration of a circular cross sectional micro-rod subjected to a new kind of boundary constraints with elastic torsional springs is presented based on nonlocal elasticity. A nonlocal strengthening beam model is utilized and the effect of temperature changing is taken into consideration. The variational method and Hamilton’s principle are applied to derive the governing equation of motion and corresponding boundary conditions. A higher-order partial differential equation that is a typical characteristic of nonlocal strengthening model is developed, and the boundary conditions contain not only classical conditions but also non-classical higher-order conditions. Unlike previous studies which were only concerned with some conventional boundary constraints, we consider more general boundary conditions named elastic torsional spring supports. Such boundary conditions are between the simply supported and clamped ones, and they are closer to the actual constraints of existing engineering structures. Natural frequencies of micro-rods with new boundary constraints are determined via an eigenvalue method and compared with other results in the literature. It is shown that the nonlocal scale factor, thermal parameter, rigidity parameter and torsional spring coefficient play significant roles in free vibration of micro-rods. The research can provide a reference for a large class of boundary conditions ranging from simply supported to clamped micro-rods.     

考虑速度滑移的多孔质静压气体轴承静特性

对于多孔质材料内的气体流动,基于Darcy定律建立其理论模型,并建立气膜间隙流场的雷诺方程,考虑速度滑移修正方程;将上述2个区域的压力分布方程进行耦合,通过有限元方法对耦合后的压力分布方程进行离散化,用超松弛迭代求解出气膜内各节点的压力分布,分析速度滑移对多孔质静压气体轴承静特性的影响。结果表明,考虑速度滑移所计算的气膜压力分布变化平稳过渡,没有较大的突变。计算轴承的承载力及刚度,结果显示在气密间隙小于15μm时,随着气膜厚度的增大偏心导致的压差增大使承载力不断增大;且当速度滑移系数小于0.1时,速度滑移对轴承承载力及刚度有较大的影响。     

A novel methodology for forecasting gas supply reliability of natural gas pipeline systems

In this paper, a novel systematic and integrated methodology to assess gas supply reliability is proposed based on the Monte Carlo method, statistical analysis, mathematical-probabilistic analysis, and hydraulic simulation. The method proposed has two stages. In the first stage, typical scenarios are determined. In the second stage, hydraulic simulation is conducted to calculate the flow rate in each typical scenario. The result of the gas pipeline system calculated is the average gas supply reliability in each typical scenario. To verify the feasibility, the method proposed is applied for a real natural gas pipelines network system. The comparison of the results calculated and the actual gas supply reliability based on the filed data in the evaluation period suggests the assessment results of the method proposed agree well with the filed data. Besides, the effect of different components on gas supply reliability is investigated, and the most critical component is identified. For example, the 48th unit is the most critical component for the SH terminal station, while the 119th typical scenario results in the most severe consequence which causes the loss of 175.61×10⁴ m³ gas when the 119th scenario happens. This paper provides a set of scientific and reasonable gas supply reliability indexes which can evaluate the gas supply reliability from two dimensions of quantity and time.     

A framework for understanding institutional factors affecting the success and failure of offshoring models in India

The objective of this paper is to identify and analyse the factors that influence offshore location decisions from an institutional theory perspective. In the years, emerging economies have shown great growth potential and have attracted significant foreign direct investment, especially from companies willing to set up operations. Despite such a seemingly favourable trade environment, not all companies that entered an emerging economy have been successful. Thus, there is a need to understand the factors that influence the success of any offshore location decision. It is also important to understand the relative importance of these factors, in order to develop novel insights useful to practitioners. There is a lack of literature addressing this issue, which this study aims to fill. We conducted a multi-case analysis with examples of European companies entering India. The findings indicate that successful companies employed locally focused business strategies that enabled them to acquire important relationships and knowledge, and also to adapt to formal institutions, including governmental and regulatory procedures. It was found that, irrespective of size, disregarding collaborative strategies was the main reason for exiting India. These findings are highly relevant for managers and policy makers.     

Component spectroscopic properties of light-harvesting complexes with DFT calculations

Photosynthesis is a fundamental process in biosciences and biotechnology that influences profoundly the research in other disciplines. In this paper, we focus on the characterization of fundamental components, present in pigment-protein complexes, in terms of their spectroscopic properties such as infrared spectra, nuclear magnetic resonance, as well as nuclear quadrupole resonance, which are of critical importance for many applications. Such components include chlorophylls and bacteriochlorophylls. Based on the density functional theory method, we calculate the main spectroscopic characteristics of these components for the Fenna-Matthews-Olson light-harvesting complex, analyze them and compare them with available experimental results. Future outlook is discussed in the context of current and potential applications of the presented results.