Simulated convergence rates with application to an intractable α-stable inference problem

© 2017 IEEE. We report the results of a series of numerical studies examining the convergence rate for some approximate representations of α-stable distributions, which are a highly intractable class of distributions for inference purposes. Our proposed representation turns the intractable inference for an infinite-dimensional series of parameters into an (approximately) conditionally Gaussian representation, to which standard inference procedures such as Expectation-Maximization (EM), Markov chain Monte Carlo (MCMC) and Particle Filtering can be readily applied. While we have previously proved the asymptotic convergence of this representation, here we study the rate of this convergence for finite values of a truncation parameter, c. This allows the selection of appropriate truncations for different parameter configurations and for the accuracy required for the model. The convergence is examined directly in terms of cumulative distribution functions and densities, through the application of the Berry theorems and Parseval theorems. Our results indicate that the behaviour of our representations is significantly superior to that of representations that simply truncate the series with no Gaussian residual term

Deposit shape control for local repair and welding by cold spray

Cold spray (CS) has proven to be a versatile deposition method with considerable capabilities in multiple fields including coating, additive manufacturing, and repair. Despite the significant progress in new applications of cold spray, there are still several challenges associated with controlling the shape of cold spray deposits that consequently affect their range of application and functionality. In this study, we discuss and demonstrate a new application of CS to connect adjoining edges along with repair local damages, focusing on deposit shape prediction. To do so, we start by proposing a numerical model that can predict the CS deposit geometry, by providing specific input parameters for a given set of particle and substrate properties, substrate geometry and nozzle position. Then we employ this numerical method to design the toolpath required for filling the artificial local damages and/or the welding grooves with controlled geometries. Through comparing the predictions with the shape of experimentally obtained depositions, we propose some corrections for the model. In both local repair and welding cases, the experimental results show a great resemblance to the predicted deposit profile and after applying the corrective measures, to the deposit height

Corporate governance performance ratings with machine learning

We use machine learning with a cross-sectional research design to predict governance controversies and to develop a measure of the governance component of the environmental, social, governance (ESG) metrics. Based on comprehensive governance data from 2,517 companies over a period of 10 years and investigating nine machine-learning algorithms, we find that governance controversies can be predicted with high predictive performance. Our proposed governance rating methodology has two unique advantages compared with traditional ESG ratings: it rates companies' compliance with governance responsibilities and it has predictive validity. Our study demonstrates a solution to what is likely the greatest challenge for the finance industry today: how to assess a company's sustainability with validity and accuracy. Prior to this study, the ESG rating industry and the literature have not provided evidence that widely adopted governance ratings are valid. This study describes the only methodology for developing governance performance ratings based on companies' compliance with governance responsibilities and for which there is evidence of predictive validity

Сравнительный анализ показателей качества авиационных керосинов, биотоплив и их смесей

Modern trends of civil aviation development indicate the need to improve fuel efficiency and environmental friendliness of the utilized fuels. The use of conventional jet fuel is meeting to a lesser degree the promising requirements concerning environmental friendliness at a constantly rising price for it. Apart from that, oil reserves are limited. According to many experts, the solution to the growing problems with oil fuels can be application of alternative types of aviation fuel. A number of companies around the world, together with aircraft manufacturers under the significant state support, are actively developing new types of fuel. At the moment the most widespread biofuels consisting of bioethanol are obtained from various plant and animal sources. Alternative fuels should not be inferior to petroleum fuels in its operational properties. A possible transition to them should not require significant costs for the modernization of aircraft and facilities of ground aviation fuel supply. Therefore, an urgent task is to compare the main indicators of the quality of oil fuels, biofuels and their mixtures to assess the possibility of using biofuels on aircraft. A comparative analysis was carried out on some quality indicators. Afterwards the comments were given on the impact of changes of these quality indicators on the performance properties of the fuels. It is shown that according to some quality indicators, biofuels under research have the advantages over oil ones. The relevance of comprehensive study of the performance properties of biofuels is obvious. The improvement of oil fuels and their comprehensive study have been under way for more than 60 years. Biofuels are just beginning their life, so it is reasonable to conduct thorough research on their use in aviation.Современные тенденции развития гражданской авиации указывают на необходимость повышения топливной эффективности и экологичности применяемых топлив. Применение традиционного авиакеросина все в меньшей степени удовлетворяет перспективным требованиям по экологичности при постоянно растущей на него цене. Кроме того, запасы нефти не безграничны. По мнению многих специалистов, решением нарастающих проблем с нефтяными топливами может быть использование альтернативных видов авиационного топлива. Ряд компаний в разных странах мира совместно с производителями авиационной техники при весомой государственной поддержке активно разрабатывают новые виды топлива. Наиболее распространены на данный момент биотоплива, состоящие из биоэтанола, полученные из различных растительных и животных источников. Альтернативные виды топлив по своим эксплуатационным свойствам не должны уступать нефтяным топливам. Возможный переход на них не должен требовать значительных затрат на модернизацию воздушных судов и средств наземного авиатопливообеспечения. Поэтому актуальной задачей является проведение сравнения основных показателей качества нефтяных топлив, биотоплив и их смесей для оценки возможности применения биотоплив на воздушных судах. Сравнительный анализ проводился по некоторым показателям качества, после чего были даны комментарии по влиянию изменений этих показателей качества на эксплуатационные свойства топлив. Показано, что по некоторым показателям качества исследуемые биотоплива имеют преимущества перед нефтяными. Очевидна актуальность проведения полных и всесторонних изучений эксплуатационных свойств биотоплив. Совершенствование нефтяных топлив и их всестороннее изучение продолжается уже более 60 лет, биотоплива только начинают свой жизненный путь, поэтому целесообразно проведение всесторонних исследований по их применению в авиации

Species Richness and Trophic Diversity Increase Decomposition in a Co-Evolved Food Web

Ecological communities show great variation in species richness, composition and food web structure across similar and diverse ecosystems. Knowledge of how this biodiversity relates to ecosystem functioning is important for understanding the maintenance of diversity and the potential effects of species losses and gains on ecosystems. While research often focuses on how variation in species richness influences ecosystem processes, assessing species richness in a food web context can provide further insight into the relationship between diversity and ecosystem functioning and elucidate potential mechanisms underpinning this relationship. Here, we assessed how species richness and trophic diversity affect decomposition rates in a complete aquatic food web: the five trophic level web that occurs within water-filled leaves of the northern pitcher plant, Sarracenia purpurea. We identified a trophic cascade in which top-predators — larvae of the pitcher-plant mosquito — indirectly increased bacterial decomposition by preying on bactivorous protozoa. Our data also revealed a facultative relationship in which larvae of the pitcher-plant midge increased bacterial decomposition by shredding detritus. These important interactions occur only in food webs with high trophic diversity, which in turn only occur in food webs with high species richness. We show that species richness and trophic diversity underlie strong linkages between food web structure and dynamics that influence ecosystem functioning. The importance of trophic diversity and species interactions in determining how biodiversity relates to ecosystem functioning suggests that simply focusing on species richness does not give a complete picture as to how ecosystems may change with the loss or gain of species

Exploring preference homogeneity and heterogeneity for proximity to urban public services

© 2018 Elsevier Ltd Given that the majority of the world's population lives in urban places, the quality of the urban environment has emerged as an issue of fundamental concern for citizens, academic researchers, and policy makers. This study explores residents’ preferences and valuation of living in proximity to urban amenities in the built environment. The study demonstrates that environmental evaluation techniques can be used as a tool to help relevant decision makers (e.g., urban managers, developers, city officials, planners, realtors and researchers) with policy making, effective decision making and efficient city management procedures. The models indicate how household preference for proximity to urban amenities change as a function of the cost of provision as exemplified by a change (increase or decrease) in annual property tax. The study reports the results for two different models: one which assumes preference homogeneity and the other preference heterogeneity in the sampled population. The results show that older residents and higher educated people are more likely to be willing to pay a higher property tax for having proximity to parks. Middle and low income residents prefer close proximity to bus stops and local shopping centres. This research suggests that a win-win strategy for residents and local government lies in increasing and maintaining residents’ accessibility to urban amenities, and in increasing an urban area's sustainability

Conservation or deterioration in heritage sites? Estimating willingness to pay for preservation

A significant part of the United Nations World Heritage Sites (WHSs) islocated in developing countries. These sites attract an increasing number oftourist and income to these countries. Unfortunately, many of these WHSs are ina poor condition due to climatic and environmental impacts; war and tourismpressure, requiring the urgent need for restoration and preservation (Tuan &Navrud, 2007). In this study, we characterise residents from Shiraz city(visitors and non-visitors) willingness to invest in the management of theheritage sites through models for the preservation of heritage and developmentof tourism as a local resource. The research looks at different categories ofheritage sites within Shiraz city, Iran. The measurement instrument is a statedpreference referendum task administered state-wide to a sample of 489respondents, with the payment mechanism defined as a purpose-specificincremental levy of a fixed amount over a set period of years. A Latent ClassBinary Logit model, using parametric constraints is used innovatively to dealwith any strategic voting such as Yea-sayers and Nay-sayers, as well asrevealing the latent heterogeneity among sample members. Results indicate thatalmost 14% of the sampled population is unwilling to be levied any amount(Nay-sayers) to preserve any heritage sites. Not recognizing the presence ofnay-sayers in the data or recognizing them but eliminating them from theestimation will result in biased Willingness to Pay (WTP) results and,consequently, biased policy propositions by authorities. Moreover, it is foundthat the type of heritage site is a driver of WTP. The results from this studyprovide insights into the WTP of heritage site visitors and non-visitors withrespect to avoiding the impacts of future erosion and destruction andcontributing to heritage management and maintenance policies

Convergence results for tractable inference in α-stable stochastic processes

The α-stable distribution is highly intractable for inference because of the lack of a closed form density function in the general case. However, it is well-established that the α-stable distribution admits a Poisson series representation (PSR) in which the terms of the series are a function of the arrival times of a unit rate Poisson process. In our previous work, we have shown how to carry out inference for regression models using this series representation, which leads to a very convenient conditionally Gaussian framework, amenable to tractable Gaussian inference procedures. The PSR has to be truncated to a finite number of terms for practical purposes. The residual error terms have been approximated in our previous work by a Gaussian distribution, and we have recently shown that this approximation can be justified through a Central Limit Theorem (CLT). In this paper we present a new and exact characterisation of the first and second moments of the residual series over finite time intervals for the unit rate Poisson process, correcting a previous version that was only true in the infinite time limit. This enables us to test through simulation the rapid convergence of the residual terms to a Gaussian distribution of the Poisson series residual. We test this convergence using both Q-Q plots and the classical Kolmogorov-Smirnov test of Gaussianity