Modeling entangled dynamics: comparison between stochastic single-chain and multichain models

To test the effectiveness of stochastic single-chain models in describing the dynamics of entangled polymers, we systematically compare one such model; the slip-spring model; to a multichain model solved using stochastic molecular dynamics(MD) simulations (the Kremer-Grest model). The comparison involves investigating if the single-chain model can adequately describe both a microscopic dynamical and a macroscopic rheological quantity for a range of chain lengths. Choosing a particular chain length in the slip-spring model, the parameter values that best reproduce the mean-square displacement of a group of monomers is determined by fitting toMDdata. Using the same set of parameters we then test if the predictions of the mean-square displacements for other chain lengths agree with the MD calculations. We followed this by a comparison of the time dependent stress relaxation moduli obtained from the two models for a range of chain lengths. After identifying a limitation of the original slip-spring model in describing the static structure of the polymer chain as seen in MD, we remedy this by introducing a pairwise repulsive potential between the monomers in the chains. Poor agreement of the mean-square monomer displacements at short times can be rectified by the use of generalized Langevin equations for the dynamics and resulted in significantly improved agreement.

Infrared absorption spectra, radiative efficiencies, and global warming potentials of perfluorocarbons: Comparison between experiment and theory

Experimentally and theoretically determined infrared spectra are reported for a series of straight-chain perfluorocarbons: C2F6, C3F8, C4F10, C5F12, C6F14, and C8F18. Theoretical spectra were determined using both density functional (DFT) and ab initio methods. Radiative efficiencies (REs) were determined using the method of Pinnock et al. (1995) and combined with atmospheric lifetimes from the literature to determine global warming potentials (GWPs). Theoretically determined absorption cross sections were within 10% of experimentally determined values. Despite being much less computationally expensive, DFT calculations were generally found to perform better than ab initio methods. There is a strong wavenumber dependence of radiative forcing in the region of the fundamental C-F vibration, and small differences in wavelength between band positions determined by theory and experiment have a significant impact on the REs. We apply an empirical correction to the theoretical spectra and then test this correction on a number of branched chain and cyclic perfluoroalkanes. We then compute absorption cross sections, REs, and GWPs for an additional set of perfluoroalkenes.

First-order turbulence closure for modelling complex canopy flows

Simple first-order closure remains an attractive way of formulating equations for complex canopy flows when the aim is to find analytic or simple numerical solutions to illustrate fundamental physical processes. Nevertheless, the limitations of such closures must be understood if the resulting models are to illuminate rather than mislead. We propose five conditions that first-order closures must satisfy then test two widely used closures against them. The first is the eddy diffusivity based on a mixing length. We discuss the origins of this approach, its use in simple canopy flows and extensions to more complex flows. We find that it satisfies most of the conditions and, because the reasons for its failures are well understood, it is a reliable methodology. The second is the velocity-squared closure that relates shear stress to the square of mean velocity. Again we discuss the origins of this closure and show that it is based on incorrect physical principles and fails to satisfy any of the five conditions in complex canopy flows; consequently its use can lead to actively misleading conclusions.

Microarray data classification using automatic SVM kernel selection

Microarray data classification is one of the most important emerging clinical applications in the medical community. Machine learning algorithms are most frequently used to complete this task. We selected one of the state-of-the-art kernel-based algorithms, the support vector machine (SVM), to classify microarray data. As a large number of kernels are available, a significant research question is what is the best kernel for patient diagnosis based on microarray data classification using SVM? We first suggest three solutions based on data visualization and quantitative measures. Different types of microarray problems then test the proposed solutions. Finally, we found that the rule-based approach is most useful for automatic kernel selection for SVM to classify microarray data.

Do entrepreneurship programs matter? An analysis of North American university innovation systems

Are there differences in commercialization outcomes between universities in Canada and the USA? If so, why? We first examine the commercialization performance of universities on both sides of the 49th parallel through indicators of university spinouts generated. Secondly, we measure the presence and growth in numbers of entrepreneurship centers to determine if there are any parallels or discernable patterns that may be related to spinout performance. Based upon theories that suggest entrepreneurial culture plays a significant role in the spinout process, we then test the hypothesis that entrepreneurship education programs play a significant role in determining spinout performance. Our model assumes that the level and intensity of an academic entrepreneurship program/center is a valid indicator of “entrepreneurial culture” that may impact upon a universities propensity to spinout new knowledge intensive firms. Our results find that there is indeed a correlation between intensity of entrepreneurship program and commercialization outcomes.

Film audio pace

We explore the concept of film pace expressed through audio to analyse the film at a semantic level. We use domain knowledge to derive a number of measures for film audio pace. We then apply the audio pace to examine two semantic concepts: counterpoint and narrative structure. Counterpoint is a method used to highlight a salient event by contrasting the visual and audio aspects of a film. We divide narrative structure into visual narration, action, and audio narration, plot development. We hypothesise that changes in the narrative structure signal a change in the audio pace. We then test this hypothesis using eight films of varying genres. A pattern was established linking the audio pace features, guided by the properties of the audio energy, to the narrative structure. The method was successful in determining the narrative structure for seven of the films, achieving an overall precision of 76.4% and recall of 80.3%.

Reliability and validity of a new Building Environmental Quality Questionnaire

This study aimed to develop and then test the reliability and validity of a new self-report questionnaire method called the building environmental quality questionnaire (BEQQ) designed to assess the perceived environmental quality in residential apartments in Hong Kong. A total of 108 (46 men and 62 women) Chinese-speaking residents, between 16 and 81 years of age, took part and completed the questionnaire study. The subjects were recruited from 12 different buildings of three distinct quality ratings (low, medium and high) assigned by the building assessment tool called the building health and hygiene index (BHHI). The study was evaluated to determine reliability and this was assessed involving 20 of the participants (18% of the total sample size). The BEQQ was found to have good test-retest reliability, with intra-class correlation coefficient (ICC) values typically around 0.70. The validity testing, also using ICCs, generated moderate to high values for all BEQQ sub-categories (the mean value was around 0.80), indicating a good consistency among residents living within the same building. Finally, the summary BEQQ scores were significantly correlated (—0.68) with the BHHI ratings as the criterion standard. It is concluded that this eight-dimension instrument would provide a short and efficient questionnaire method to obtain self-reported information to determine the perceived residential building quality. The method was shown to yield adequate reliability and has been validated for use in empirical research.

Financial development, shocks, and growth volatility

This paper uses spectral theory to develop the following two testable hypotheses in a unified framework for the predictions of business-cycle and endogenous growth models: (i) financial development affects only business-cycle volatility; and (ii) shocks affect both business-cycle volatility and long-run volatility of GDP growth. In other words, volatility caused by shocks is more persistent than that caused by financial underdevelopment. We decompose the business-cycle and long-run volatility by the spectral method and then test the hypotheses at the cross-country level. Empirical evidence provides support for both hypotheses. Higher private credit, a bank-based measure of financial development, dampens business-cycle volatility but not long-run volatility. Volatility of shocks, as measured by the volatility of changes in the terms of trade, magnifies both business-cycle and long-run volatility. The results are robust to accounting for endogeneity, a market-based measure of financial development, and an alternative method of volatility decomposition.

English and French causal connectives in contrast

Discourse connectives are often said to be language specific, and therefore not easily paired with a translation equivalent in a target language. However, few studies have assessed the magnitude and the causes of these divergences. In this paper, we provide an overview of the similarities and discrepancies between causal connectives in two typologically related languages: English and French. We first discuss two criteria used in the literature to account for these differences: the notion of domains of use and the information status of the cause segment. We then test the validity of these criteria through an empirical contrastive study of causal connectives in English and French, performed on a bidirectional corpus. Our results indicate that French and English connectives have only partially overlapping profiles and that translation equivalents are adequately predicted by these two criteria.

The Devil’s Calculus: Mathematical Models of Civil War

In spite of the movement to turn political science into a real science, various mathematical methods that are now the staples of physics, biology, and even economics are thoroughly uncommon in political science, especially the study of civil war. This study seeks to apply such methods - specifically, ordinary differential equations (ODEs) - to model civil war based on what one might dub the capabilities school of thought, which roughly states that civil wars end only when one side’s ability to make war falls far enough to make peace truly attractive. I construct several different ODE-based models and then test them all to see which best predicts the instantaneous capabilities of both sides of the Sri Lankan civil war in the period from 1990 to 1994 given parameters and initial conditions. The model that the tests declare most accurate gives very accurate predictions of state military capabilities and reasonable short term predictions of cumulative deaths. Analysis of the model reveals the scale of the importance of rebel finances to the sustainability of insurgency, most notably that the number of troops required to put down the Tamil Tigers is reduced by nearly a full order of magnitude when Tiger foreign funding is stopped. The study thus demonstrates that accurate foresight may come of relatively simple dynamical models, and implies the great potential of advanced and currently unconventional non-statistical mathematical methods in political science.

Market efficiency of commodity futures in India

This paper aims to examine the market efficiency of the commodity futures market in India, which has been growing phenomenally for the last few years. We estimate the long-run equilibrium relationship between the multi-commodity futures and spot prices and then test for market efficiency in a weak form sense by applying both the DOLS and the FMOLS methods. The entire sample period is from 2 January 2006 to 31 March 2011. The results indicate that a cointegrating relationship is found between these indices and that the commodity futures market seems to be efficient only during the more recent sub-sample period since July 2009.

Broader or deeper? Exploring the most effective intervention profile for public small business support

Most advanced economies offer publicly financed advice services to start-up firms and SMEs. In England, local or regional Business Links organisations have provided these services, and divided their support into nonintensive one-off contacts providing information or advice and more intensive support involving a diagnostic process and repeated interaction with firms. A key choice for Business Link managers is how to shape their intervention strategies, balancing resources between intensive and nonintensive support. Drawing on resource dependency theory, we develop a typology of intervention strategies for Business Links in England which reflects differences in the breadth and depth of the support provided. We then test the impacts of these alternative intervention models on client companies using both subjective assessments by firms and econometric treatment models that allow for selection bias. Our key empirical result is that Business Links’ choice of intervention strategy has a significant effect both on actual and on perceived business outcomes, with our results emphasising the value of depth over breadth. The implication is that where additional resources are available for business support these should be used to deepen the assistance provided rather than extend assistance to a wider group of firms.

Measurement of work group diversity

Whilst research on work group diversity has proliferated in recent years, relatively little attention has been paid to the precise definition of diversity or its measurement. One of the few studies to do so is Harrison and Klein’s (2007) typology, which defined three types of diversity – separation, variety and disparity – and suggested possible indices with which they should be measured. However, their typology is limited by its association of diversity types with variable measurement, by a lack of clarity over the meaning of variety, and by the absence of a clear guidance about which diversity index should be employed. In this thesis I develop an extended version of the typology, including four diversity types (separation, range, spread and disparity), and propose specific indices to be used for each type of diversity with each variable type (ratio, interval, ordinal and nominal). Indices are chosen or derived from first principles based on the precise definition of the diversity type. I then test the usefulness of these indices in predicting outcomes of diversity compared with other indices, using both an extensive simulated data set (to estimate the effects of mis-specification of diversity type or index) and eight real data sets (to examine whether the proposed indices produce the strongest relationships with hypothesised outcomes). The analyses lead to the conclusion that the indices proposed in the typology are at least as good as, and usually better than, other indices in terms of both measuring effect sizes and power to find significant results, and thus provide evidence to support the typology. Implications for theory and methodology are discussed.

Exporting and productivity in business services:evidence from the United States

Does exporting make firms more productive, or do more productive firms choose to become exporters? This paper considers the link between exporting and productivity for a sample of firms in US business services. We find that larger, more productive firms are more likely to become exporters, but that these factors do not necessarily influence the extent of exporting. This conforms with previous literature that there is a self-selection effect into exporting. We then test for the effect of exporting on productivity levels after allowing for this selection effect. We model both the relationship between exporting and productivity, and a simultaneous relationship between export intensity and productivity after allowing for selection bias. In both cases we find an association, indicating that productivity is positively linked both to exporting and to increased exposure to international markets.

Exporting and productivity in business services:evidence from the United States

Does exporting make firms more productive, or do more productive firms choose to become exporters? Given the amount of resources devoted by governments to supporting exporters, this is an important question. There are reasons to expect exporting to boost productivity, both through the exposure to foreign competition which exporting brings, and through ‘learning by exporting’. However, the broad thrust of previous research is that more productive firms self-select into export markets, with relatively little evidence that exporting leads to higher productivity thereafter. This paper considers the link between exporting and productivity for a sample of firms in US business services. We find that larger, more productive firms are more likely to become exporters, but that these factors do not necessarily influence the extent of exporting. This conforms with previous literature that there is a self-selection effect into exporting. We then test for the effect of exporting on productivity levels after allowing for this selection effect. We model both the relationship between exporting and productivity, and a simultaneous relationship between export intensity and productivity after allowing for selection bias. In both cases we find a clear association, indicating that productivity is positively linked both to exporting and to increased exposure to international markets.