Globally stable adaptive robust tracking control using RBF neural networks as feedforward compensators

In previous adaptive neural network control schemes, neural networks are usually used as feedback compensators. So, only semi-globally uniformly ultimate boundedness of closed-loop systems can be guaranteed, and no methods are given to determine the neural network approximation domain. However, in this paper, it is showed that if neural networks are used as feedforward compensators instead of feedback ones, then we can ensure the globally uniformly ultimate boundedness of closed-loop systems and determine the neural network approximation domain via the bound of known reference signals. It should be pointed out that this domain is very important for designing the neural network structure, for example, it directly determines the choice of the centers of radial basis function neural networks. Simulation examples are given to illustrate the effectiveness of the proposed control approaches.     

Conceptualising improvisation in information systems security

Information Systems Security (ISS) has constantly been ranked as a key concern for Information Systems (IS) managers. Research in the field has largely assumed rational choice (functional) approaches to managing ISS. Such approaches do not give due recognition to the role of improvisation in ISS work. Empirical evidence in organisations suggests that in the context of dynamic, volatile and uncertain environments practitioners are both rational and adaptive (a manifestation of improvisation). In this paper, we conceptualise and demonstrate the manifestation of improvisation in ISS. In order to develop a better understanding of improvisation in ISS activities, hermeneutical and exegetical techniques were employed. Empirical data were collected through in-depth interviews in a single case study. The data obtained were analysed and interpreted hermeneutically. Generally it was found that improvisation is manifested in ISS activities. Implications of these and other findings for the scholarly community and for practical use are discussed.     

Microstructure and refining performance of an Al−5Ti−0.25C refiner before and after equal-channel angular pressing

Refining experiments were conducted to evaluate the grain refining performance of an Al−5Ti−0.25C refiner before and after equal-channel angular pressing (ECAP) with the use of a high-purity Al. The results show that the Al−5Ti−0.25C refiner has remarkable and stable grain refining performance when the holding times are within 5 to 30 minutes and the melt temperatures are within 1003 to 1073 K. Furthermore, some Al−5Ti−0.25C refiner samples were subjected to severe plastic deformation by using the ECAP technique at 298 K. It was found that Al₃Ti and TiC particles were significantly fragmented and their mean sizes were decreased to 10 and 1.08 μm, respectively, and the Al−5Ti−0.25C refiner appeared to have a double grain refining effect in comparison with that of before ECAP. It is also testified that the Vickers microhardness (Hv) value of the pure Al samples refined by the Al−5Ti−0.25C refiner after ECAP processing has a significant increment than that of before ECAP processing. It is concluded that the Al−5Ti−0.25C refiner with ECAP technique has a very useful practical application in refining industrial Al alloys. ZUOGUI ZHANG, formerly Master's Student, the Key Laboratory of Liquid Structure and Heredity of Material, Ministry of Education, Shandong University, Jinan 250061, People's Republic of China     

The share of items of highly productive sources as a function of the size of the system

Summary The research in this paper is based on the paper of D.W. Aksnes & G. Sivertsen: The effect of highly cited papers on national citation indicators, Scientometrics 59 (2) (2004), 213-224, where one states that “the few highly cited papers account for the highest share of the citations in the smallest fields”. This, at first sight, evident property is examined in the theoretical models that exist in the literature. We first define exactly what we mean by “size of a field” (i.e. when is a field “smaller” or “larger” than another one). We show that there are two, non-equivalent possible definitions. Next we define exactly the possible property under study. This leads us again to two possible, non-equivalent formulations. Hence, in total, there are four different formulations to consider. We show, by giving counterexamples, that none of these four formulations are true in general. We also express conditions (in Lotkaian and Zipfian informetrics), under which the property of Aksnes and Sivertsen is true. All these results are not only valid in the papers-citations relationships but in any informetric source-item relationship. In this connection we present formulae describing the share of items of highly productive sources as a function of the parameters of the system (e.g. the size of the system).     

National and international university departmental Web site interlinking

Although many link patterns have been identified at the university level, departmental interlinking has been relatively ignored. Universities are multidisciplinary by nature and various disciplines may employ the Web differently, thus patterns identified at the university level may hide subject differences. Departments are typically subject-oriented, and departmental interlinking may therefore illustrate interesting disciplinary linking patterns, perhaps relating to informal scholarly communication. The aim of this paper is to identify whether and how link patterns differ along country and disciplinary lines between similar disciplines and similar countries. Physics, Chemistry and Biology departments in Australia, Canada and the UK have been chosen. In order to get a holistic picture of departments' Web use profiles and link patterns, five different perspectives are identified and compared for each set of departments. Differences in link patterns are identified along both national and disciplinary lines, and are found to reflect offline phenomena. Along national lines, a likely explanation for the difference is that countries with better research performances make more general use of the Web; and, with respect to international peer interlinking, countries that share more scholarly communication tend to interlink more with each other. Along disciplinary lines, it seems that departments from disciplines which are more willing to distribute their research outputs tend to make more general use of the Web, and also interlink more with their national and international peers.     

Modification of High Performances of Polymer Cement Concrete

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UV-vis and photoluminescent spectra of TiO<Subscript>2</Subscript> films

TiO₂ fims have been deposited on glass substrates using DC reactive magnetron sputtering at different oxygen partial pressures from 0. 10 Pa.to 0.65 Pa. The transmittance (UV-vis) and photoluminescence (PL) spectra of the films were recorded. The results of the UV-vis spectra show that the deposition rate of the films decreased at oxygen partial pressure P(O₂)≥0.15 Pa, the band gap increased from 3.48 eV to 3.68eV for direct transition and from 3.27 eV to 3.34 eV for indirect transition with increasing the oxygen partial pressure. The PL spectra show convincingly that the transition for films was indirect, and there were some oxygen defect energy levels at the band gap of the films. With increasing the O₂ partial pressure, the defect energy levels decreased. For the films sputtered at 0.35 and 0.65 Pa there were two defect energy levels at 2.63 eV and 2.41 eV, corresponding to 0.72 eV and 0.94 eV below the conduction band for a band gap of 3.35 eV, respectively. For the films sputtered at 0.10 Pa and 0.15 Pa, there was an energy band formed between 3.12 eV and 2.06 eV, corresponding to 0.23 eV and 1.29 eV below the conduction band. ZHAO Qing-nan : Born in 1963 Funded by Natural Science Foundation of Hubei Province, China.     

Development of a measure for the information technology infrastructure construct

The goal of this research was to operationalize the information technology infrastructure (ITI) concept by identifying its underlying dimensions and establishing a valid and reliable measure for the construct. In order to accomplish this task with the highest degree of certainty, two approaches were sequentially applied: exploratory factor analysis and confirmatory factor analysis. In evaluating the confirmatory factor model, a step-by-step process was employed, assessing unidimensionality, reliability, discriminant validity, and nomological validity. The dimensions of ITI were determined to be: Chief Information Officer, IT Planning, IT Security, Technology Integration, Advisory Committee, Enterprise Model, and Data Administration. Researchers may now make use of this validated ITI measure to conduct investigations of ITI and other organizational measures. Implications of the ITI measure with other organizational initiatives such as electronic commerce and knowledge management are explored.     

A comparative study of exchange and aggregation models in the B2B e-marketplace

This research seeks to provide an economic framework for understanding two major forms of e-marketplaces: aggregation-oriented vs. exchange-oriented e-marketplaces. By analyzing the marginal benefit per transaction in alternative models, we are able to determine the most suitable B2B e-marketplace for a wide variety of product categories, market conditions, and procurement methods. For example, when companies sell commodities in a fragmented market, the aggregation model is suitable for spot purchasing, and the exchange model works best for systematic purchasing. In addition, the effect of supplier consolidation and information technology-enabled cost reduction on model selection is discussed.