Network Transitivity and Matrix Models

This paper is a step towards a systematic theory of the transitivity (clustering) phenomenon in random networks. A static framework is used, with adjacency matrix playing the role of the dynamical variable. Hence, our model is a matrix model, where matrices are random, but their elements take values 0 and 1 only. Confusion present in some papers where earlier attempts to incorporate transitivity in a similar framework have been made is hopefully dissipated. Inspired by more conventional matrix models, new analytic techniques to develop a static model with non-trivial clustering are introduced. Computer simulations complete the analytic discussion.Comment: 11 pages, 7 eps figures, 2-column revtex format, print bug correcte

Evolution of dosage compensation under sexual selection differs between X and Z chromosomes.

Complete sex chromosome dosage compensation has more often been observed in XY than ZW species. In this study, using a population genetic model and the chicken transcriptome, we assess whether sexual conflict can account for this difference. Sexual conflict over expression is inevitable when mutation effects are correlated across the sexes, as compensatory mutations in the heterogametic sex lead to hyperexpression in the homogametic sex. Coupled with stronger selection and greater reproductive variance in males, this results in slower and less complete evolution of Z compared with X dosage compensation. Using expression variance as a measure of selection strength, we find that, as predicted by the model, dosage compensation in the chicken is most pronounced in genes that are under strong selection biased towards females. Our study explains the pattern of weak dosage compensation in ZW systems, and suggests that sexual selection plays a major role in shaping sex chromosome dosage compensation

Evolution of Cooperation in Public Goods Games with Stochastic Opting-Out

This paper investigates the evolution of strategic play where players drawn from a finite well-mixed population are offered the opportunity to play in a public goods game. All players accept the offer. However, due to the possibility of unforeseen circumstances, each player has a fixed probability of being unable to participate in the game, unlike similar models which assume voluntary participation. We first study how prescribed stochastic opting-out affects cooperation in finite populations. Moreover, in the model, cooperation is favored by natural selection over both neutral drift and defection if return on investment exceeds a threshold value defined solely by the population size, game size, and a player's probability of opting-out. Ultimately, increasing the probability that each player is unable to fulfill her promise of participating in the public goods game facilitates natural selection of cooperators. We also use adaptive dynamics to study the coevolution of cooperation and opting-out behavior. However, given rare mutations minutely different from the original population, an analysis based on adaptive dynamics suggests that the over time the population will tend towards complete defection and non-participation, and subsequently, from there, participating cooperators will stand a chance to emerge by neutral drift. Nevertheless, increasing the probability of non-participation decreases the rate at which the population tends towards defection when participating. Our work sheds light on understanding how stochastic opting-out emerges in the first place and its role in the evolution of cooperation.Comment: 30 pages, 4 figures. This is one of the student project papers arsing from the Mathematics REU program at Dartmouth 2017 Summer. See https://math.dartmouth.edu/~reu/ for more info. Comments are always welcom

Comparative analyses between the zero-inertia and fully dynamic models of the shallow water equations for unsteady overland flow propagation

The shallow water equations are a mathematical tool widely applied for the simulation of flow routing in rivers and floodplains, as well as for flood inundation mapping. The interest of many researchers has been focused on the study of simplified forms of the original set of equations. One of the most commonly applied simplifications consists in neglecting the inertial terms. The effects of such a choice on the outputs of the simulations of flooding events are controversial and are an important topic of debate. In the present paper, two numerical models recently proposed for the solution of the complete and zero-inertia forms of the shallow water equations, are applied to several unsteady flow routing scenarios. We simulate synthetic and laboratory scenarios of unsteady flow routing, starting from very simple geometries and gradually moving towards complex topographies. Unlike the studies of the range of validity of the zero-inertia model, based on a small perturbation of the linearized flow model, in unsteady flow propagation over irregular topographies, it is more difficult to specify criteria for the applicability of the simplified set of equations. Analyzing the role of the terms in the momentum equations, we try to understand the effect of neglecting the inertial terms in the zero-inertia formulation. We also analyze the computational costs

Project FATIMA Final Report: Part 1.

EXECUTIVE SUMMARY This Final Report covers the results of the EU-funded research project FATIMA (Financial Assistance for Transport Integration in Metropolitan Areas) which had the following objectives: (i) to identify the benefits to the private sector of optimal urban transport strategies, and the potential for obtaining private sector funding to reflect those benefits; (ii) to determine the differences between strategies optimised using public funds and those optimised within the constraints imposed by private funding initiatives; (iii) to propose mechanisms by which private sector funding can be provided so as to achieve appropriately optimal transport strategies while maintaining quality of operation; and (iv) to use the results to provide more general guidance on the role of private sector funding for urban transport in the EU. The project adopted an approach which involved the application of the same study method to nine cities, chosen to reflect a range of urban transport policy contexts in Europe: Edinburgh, Eisenstadt, Helsinki, Merseyside, Oslo, Salerno, Torino, Tromsø and Vienna. This method involved specifying appropriate policy objective functions against which transport strategies could be assessed, and finding the specific strategy that optimised each of these functions. The objective functions covered a range of differing regimes with respect to constraints on public finance and the involvement of the private sector. It was found that, in a majority of the case study cities, optimal socio-economic policies could be funded by road pricing or increased parking charges, considered over a 30 year time horizon. Such measures would typically be used to make it feasible to increase public transport frequency levels or decrease public transport fares. In general it was found to be important that the city transport planning authority had complete control over all transport measures, affecting both private and public transport. However, such strategies are likely to require significant levels of investment and, given current attitudes towards constraints on public spending, it might be politically awkward for the public sector to raise such finance. There is thus a potentially useful role for private finance to be used to help overcome such (short term) financing problems. However, it must be appreciated that the private sector will expect to make a profit on such investment. In cities where optimal policies are funded by travellers, the private sector can be reimbursed by travellers. In cities where it is unfeasible for travellers to fund all the costs of optimal policies, it will be necessary for the private sector to be reimbursed from public funds (raised from taxes). An important issue here is that the use of private finance should not be allowed to replace optimal policies with sub-optimal policies. Whether or not the private sector is involved in financing a strategy, there may be interest in private sector operation of the public transport service. However, evidence on the scale of benefits or losses from such operation is unclear. If, though, a city authority decides that private operation is beneficial, it should use, where legally possible, a franchising model in which it specifies optimal public transport service levels and fares. On the other hand, if a deregulation model is required (in order to comply with national law), private operators should not be given complete freedom to determine the operating conditions which meet their profitability target, even if the level of profitability is itself constrained as a result. There are typically a number of combinations (e.g. of fares and frequency) which achieve a given level of profitability, and not all will be equally effective in terms of public policy objectives

An investigation of theories of focusing

This thesis investigates the proposals of a number of psychological and computational accounts of focusing and pronoun interpretation in view of obtaining experimental evidence for the questions raised by the accounts. Four distinct but related studies were conducted with the aim of bringing together various frameworks as a step towards developing an integrated model of the processes of comprehension. Experiments 1-3 in Chapter 2 show that thematic role and surface position focusing take precedence over the salience from naming, but that naming effects are seen in the absence of thematic role focusing. Experiments 4-5 in Chapter 3 show the effect of clause subordination in certain complex sentences, with main clauses being more prominent than subordinate ones. Experiments 6-8 in Chapter 3 show that this effect may not be generalised to different types of complex sentences, however. Experiments 9-18 in Chapter 4 show that animacy has a strong effect on prominence, overriding thematic role and surface position effects. The presence of these latter two effects is crucially dependent on the pattern of animacy. Experiments 19-21 in Chapter 5 show the effects of grammatical parallelism, in which the features of both the anaphor and the antecedent have an influence, which overlays structural focusing. These results show that a variety of constraints can complete in determining the accessibility of discourse referents. The structural, semantic, and pragmatic discourse context in which referents are introduced and the attributes of the cue used to re-access them have a role. The findings are discussed in terms of an activation-based framework, whereby pronoun resolution is determined by the relative activation of the potential antecedents in the mental representation of the discourse. They suggest a dynamic model of focusing in which an antecedent’s features establish and update the focus, and in which certain linguistic elements may trigger the current focus to be modified

Rethinking How Establishment Skills Surveys Can More Effectively Identify Workforce Skills Gaps

Through a multicountry, practice-based review of establishment skills surveys, this article identifies conceptual issues with defining and measuring skills gaps. By harmonizing divergent conceptualizations, an operational definition of skills gaps as a situation in which current employees lack the skills to perform their jobs which results in the compromised ability of a firm to meet business objectives is proposed. This operationalization of the concept offers a more complete answer to how firms are impacted by workforce deficiencies in achieving business objectives implying that understanding job proficiency without assessing the organizational context in which workforce skills are deployed towards market objectives is insufficient. By addressing measurement issues, an alternative approach to establishment skills surveys is advanced that can play a more effective role in determining how workforce skills influence achievement of firm business objectives. The open systems model of the firm is used to explain how skills gaps serve as a bottleneck to the overall functioning of the firm and to demonstrate that firm mitigation strategies are subject to managerial perceptions which can influence the effectiveness and level at which strategies are targeted. A typology of the causes of skills gaps is also proposed as a starting point for government intervention.