Simulation of glassy state relaxations in polymers: A static analysis of methyl group and methoxy group rotation in poly(vinyl methyl ether)

We show that the simple quasi-static technique, also called the adiabatic mapping technique, can be used to determine the energetics of rotation of methyl and methoxy groups in amorphous poly(vinyl methyl ether) even though the latter process is too slow to be amenable to direct molecular dynamics simulation. For the methyl group rotation, we find that the mean and standard deviation of the simulated rotational barrier heights agree well with experimental data from quasi-elastic neutron scattering. In the case of the methoxy groups we find that just 4% of the groups contribute more than 90% of the observed dielectric relaxation strength. The groups which make the most contribution are those which, by virtue of their particular conformation and local environment, have two alternative positions of similar energy.

Comparative gene expression analysis of NKT cell subpopulations

Natural killer T (NKT) cells are a lymphocyte lineage, which has diverse immune regulatory activities in many disease settings. Most previous studies have investigated the functions of this family of cells as a single entity, but more recent evidence highlights the distinct functional and phenotypic properties of NKT cell subpopulations. It is likely that the diverse functions of NKT cells are regulated and coordinated by these different NKT subsets. Little is known about how NKT subsets differ in their interactions with the host. We have undertaken the first microarray analysis comparing the gene expression profiles of activated human NKT cell subpopulations, including CD8(+) NKT cells, which have often been overlooked. We describe the significant gene expression differences among NKT cell subpopulations and some of the molecules likely to confer their distinct functional roles. Several genes not associated previously with NKT cells were shown to be expressed differentially in specific NKT cell subpopulations. Our findings provide new insights into the NKT cell family, which may direct further research toward better manipulation of NKT cells for therapeutic applications.

Multidimensional analysis of perceived risk in commercial air travel

This study attempts to assess the role of perceived risk in air passenger behaviour. A survey of 889 respondents is used to investigate a multidimensional concept of perceived risk and to analyse the differences between socio-demographic characteristics regarding passengers' risk assessment. The results indicate that financial risk and temporal risk are the most important in the context of commercial air travel. All perceived risk dimensions differ according gender, age, cultural background, income, previous experience, and reason for travelling. (C) 2006 Elsevier Ltd. All rights reserved.

Formal analysis of human-computer interaction using model checking

Experiments with simulators allow psychologists to better understand the causes of human errors and build models of cognitive processes to be used in human reliability assessment (HRA). This paper investigates an approach to task failure analysis based on patterns of behaviour, by contrast to more traditional event-based approaches. It considers, as a case study, a formal model of an air traffic control (ATC) system which incorporates controller behaviour. The cognitive model is formalised in the CSP process algebra. Patterns of behaviour are expressed as temporal logic properties. Then a model-checking technique is used to verify whether the decomposition of the operator's behaviour into patterns is sound and complete with respect to the cognitive model. The decomposition is shown to be incomplete and a new behavioural pattern is identified, which appears to have been overlooked in the analysis of the data provided by the experiments with the simulator. This illustrates how formal analysis of operator models can yield fresh insights into how failures may arise in interactive systems.

Bifurcation analysis of a dynamic power system with SVC devices

Bifurcation analysis is a very useful tool for power system stability assessment. In this paper, detailed investigation of power system bifurcation behaviour is presented. One and two parameter bifurcation analysis are conducted on a 3-bus power system. We also examined the impact of FACTS devices on power system stability through Hopf bifurcation analysis by taking static Var compensator (SVC) as an example. A simplified first-order model of the SVC device is included in the 3-bus sample system. Real and reactive powers are used as bifurcation parameter in the analysis to compare the system oscillatory properties with and without SVC. The simulation results indicate that the linearized system model with SVC enlarge the voltage stability boundary by moving Hopf bifurcation point to higher level of loading conditions. The installation of SVC increases the dynamic stability range of the system, however complicates the Hopf bifurcation behavior of the system

A mathematical modelling technique for the analysis of the dynamics of a simple continuous EDA

This paper presents some initial attempts to mathematically model the dynamics of a continuous estimation of distribution algorithm (EDA) based on a Gaussian distribution and truncation selection. Case studies are conducted on both unimodal and multimodal problems to highlight the effectiveness of the proposed technique and explore some important properties of the EDA. With some general assumptions, we show that, for ID unimodal problems and with the (mu, lambda) scheme: (1). The behaviour of the EDA is dependent only on the general shape of the test function, rather than its specific form; (2). When initialized far from the global optimum, the EDA has a tendency to converge prematurely; (3). Given a certain selection pressure, there is a unique value for the proposed amplification parameter that could help the EDA achieve desirable performance; for ID multimodal problems: (1). The EDA could get stuck with the (mu, lambda) scheme; (2). The EDA will never get stuck with the (mu, lambda) scheme.

Consumer search of the web: An exploratory analysis of antecedents of web search satisfaction

This article explores consumer Web-search satisfaction. It commences with a brief overview of the concepts consumer information search and consumer satisfaction. Consumer Web adoption issues are then briefly discussed and the importance of consumer search satisfaction is highlighted in relation to the adoption of the Web as an additional source of consumer information. Research hypotheses are developed and the methodology of a large scale consumer experiment to record consumer Web search behaviour is described. The hypotheses are tested and the data explored in relation to post-Web-search satisfaction. The results suggest that consumer post-Web-search satisfaction judgments may be derived from subconscious judgments of Web search efficiency, an empirical calculation of which is problematic in unlimited information environments such as the Web. The results are discussed and a future research agenda is briefly outlined.

Statistical mechanics analysis of LDPC coding in MIMO Gaussian channels

Using analytical methods of statistical mechanics, we analyse the typical behaviour of a multiple-input multiple-output (MIMO) Gaussian channel with binary inputs under low-density parity-check (LDPC) network coding and joint decoding. The saddle point equations for the replica symmetric solution are found in particular realizations of this channel, including a small and large number of transmitters and receivers. In particular, we examine the cases of a single transmitter, a single receiver and symmetric and asymmetric interference. Both dynamical and thermodynamical transitions from the ferromagnetic solution of perfect decoding to a non-ferromagnetic solution are identified for the cases considered, marking the practical and theoretical limits of the system under the current coding scheme. Numerical results are provided, showing the typical level of improvement/deterioration achieved with respect to the single transmitter/receiver result, for the various cases. © 2007 IOP Publishing Ltd.

An introduction to analysis of variance (ANOVA) with special reference to data from clinical experiments in optometry

This article is aimed primarily at eye care practitioners who are undertaking advanced clinical research, and who wish to apply analysis of variance (ANOVA) to their data. ANOVA is a data analysis method of great utility and flexibility. This article describes why and how ANOVA was developed, the basic logic which underlies the method and the assumptions that the method makes for it to be validly applied to data from clinical experiments in optometry. The application of the method to the analysis of a simple data set is then described. In addition, the methods available for making planned comparisons between treatment means and for making post hoc tests are evaluated. The problem of determining the number of replicates or patients required in a given experimental situation is also discussed. Copyright (C) 2000 The College of Optometrists.

A comparative analysis of cultural value orientations of Indians and migrant Indians in the USA

Understanding the cultural value systems of nations is a key factor in anticipating the behaviour of business managers and employees in a specific business environment. Many research studies have acknowledged the impact of culture on communication across nations and its impact on business operations, however no study has attempted to measure and quantify the cultural orientations of people originating from one nation, but working in two different national settings. This study adopted Kluckhohn and Strodtbeck's framework to examine cultural dimensions of a total of 580 Indian respondents comprising two groups: 429 Indian natives living and working in India and 151 Indian migrants living and working in the USA. It initially compares the cultural orientations of the total population of each of the two groups and then examines cultural differences in the same based on demographic characteristics consisting of occupation, gender, age, and level of education. The study found significant cultural value differences between the two groups on both levels of analysis. The theoretical and practical implications of these findings are discussed in detail.

Technology sourcing versus technology exploitation:An analysis of US foreign direct investment flows

The traditional paradigm of foreign direct investment (FDI) suggests that FDI is undertaken principally to exploit some firm-specific advantage in a foreign country which provides a locational advantage to the investor. However, recent theoretical work suggests a model of FDI in which the motivation is not to exploit existing technological advantages in a foreign country, but to access such technology and transfer it from the host economy to the investing multinational corporation via spillover effects. This paper tests the technology sourcing versus technology exploiting hypotheses for a panel of sectoral FDI flows between the United States and major OECD nations over a 15 year period. The research makes use of Patel and Vega's (Research Policy, 28, 145-55, 1999) taxonomy of sectors which are likely a priori to exhibit technology sourcing and exploiting behaviour respectively. While there is evidence that FDI flows into the United States are attracted to R and D intensive sectors, very little support is found for the technology sourcing hypothesis either for inward or outward FDI flows. The results suggest that, in aggregate, firm-specific 'ownership' effects remain powerful determinants of FDI flows.

Impaired balance in developmental dyslexia? A meta-analysis of the contending evidence

Background: Developmental dyslexia is typically defined by deficits in phonological skills, but it is also associated with anomalous performance on measures of balance. Although balance assessments are included in several screening batteries for dyslexia, the association between impairments in literacy and deficits in postural stability could be due to the high co-occurrence of dyslexia with other developmental disorders in which impairments of motor behaviour are also prevalent. Methods: We identified 17 published studies that compared balance function between dyslexia and control samples and obtained effect-sizes for each. Contrast and association analyses were used to quantify the influence of hypothesised moderator variables on differences in effects across studies. Results: The mean effect-size of the balance deficit in dyslexia was .64 (95% CI = .44-.78) with heterogeneous findings across the population of studies. Probable co-occurrence of other developmental disorders and variability in intelligence scores in the dyslexia samples were the strongest moderator variables of effect-size. Conclusions: Balance deficits are associated with dyslexia, but these effects are apparently more strongly related to third variables other than to reading ability. Deficits of balance may indicate increased risk of developmental disorder, but are unlikely to be uniquely associated with dyslexia.

Statnote 23: Non-parametric analysis of variance (ANOVA)

To carry out an analysis of variance, several assumptions are made about the nature of the experimental data which have to be at least approximately true for the tests to be valid. One of the most important of these assumptions is that a measured quantity must be a parametric variable, i.e., a member of a normally distributed population. If the data are not normally distributed, then one method of approach is to transform the data to a different scale so that the new variable is more likely to be normally distributed. An alternative method, however, is to use a non-parametric analysis of variance. There are a limited number of such tests available but two useful tests are described in this Statnote, viz., the Kruskal-Wallis test and Friedmann’s analysis of variance.