Performance Evaluation of an Edge Computing Implementation of Hyperledger Sawtooth for IoT Data Security

Blockchain offers a potential solution to some of the security challenges faced by the internet-of-things (IoT) by using its practically immutable ledger to store data transactions. However, past applications of blockchain in IoT encountered limitations in the rate at which transactions were committed to the chain as new blocks. These limitations were often the result of the time-consuming and computationally expensive consensus mechanisms found in public blockchains. Hyperledger Sawtooth is an open-source private blockchain platform that offers an efficient proof-of-elapsed-time (PoET) consensus mechanism. Sawtooth has performed well in benchmarks against other blockchains. However, a performance evaluation for a practical application of Sawtooth for IoT data security using real data was found to be lacking in the literature. To address this gap, an experiment was designed to evaluate the performance of an edge computing implementation of Sawtooth to store temperature data from a physical IoT device. Experiments were then performed for a range of input transaction rates to evaluate performance under different workloads. The results of the experiments indicate that Sawtooth can store transactions at a rate of at least 10 transactions per second in the edge computing implementation that was evaluated. The implementation was highly reliable in terms of transactions submitted versus transactions committed. The experiment also demonstrates that blockchain applications for IoT data security can be extended to any environment that has access to relatively low specification hardware and Wi-Fi internet connectivity. Some limitations were encountered during the experiments, particularly in relation to the amount of variance in the rate at which transactions were committed to the blockchain. This could have implications for some use cases at the business solution layer that depend on stable and consistent performance

Process-based models of species distributions and the mid-domain effect

Null models that place species ranges at random within a bounded geographical domain produce hump-shaped species richness gradients (the “Mid-Domain Effect”, or MDE). However, there is debate about the extent to which these models are a suitable null expectation for effects of environmental gradients on species richness. Here, I present a process-based framework for modeling species distributions within a bounded geographical domain. Analysis of null models consistent with the mid-domain hypothesis shows that MDEs are indeed likely to be ubiquitous consequences of geographical domain boundaries. Comparing the probability distributions of range locations for the process-based and randomization-based models reveals that randomization models probably overestimate the contribution of MDEs to empirical patterns of species richness, but it also indicates that other, testable predictions from randomization models are likely to be robust. I also show how this process-based framework can be extended beyond null models, to incorporate effects of environmental gradients within the domain. This study provides a first step towards an ecological theory of species distributions in geographical space that can incorporate both “geometric constraints” and effects of environmental gradients, and shows how such a theory can inform our understanding of species richness gradients in nature

Review of Michèle H. Richman, Sacred Revolutions: Durkheim and the College of Sociology.

Michèle H. Richman, Sacred Revolutions: Durkheim and the College of Sociology. Minneapolis: University of Minnesota Press, 2002. 248 pp. ISBN 0816639744 (paper)

Detonation Physics-Based Modelling & Design of a Rotating Detonation Engine

A rotating detonation engine (RDE) is a new, more thermodynamically efficient, propulsion concept that replaces the traditional constant pressure combustion mechanism found in all currently used rockets and power generation devices. The constant pressure combustion is replaced by a detonation wave: a coupled shock-flame complex propagating at speeds of up to 2-3 km/s and generating combustion products at pressures 5-10 times the initial reactant pressure. This pressure gain through the combustion process leads to more compact, simpler devices that no longer require (or depend less upon) initial reactant precompression. Detonation-based cycles also have the added advantage of being theoretically more thermodynamically efficient than their constant pressure combustion counterparts. As such, RDEs have become increasingly popular in the propulsion research community, although there is still a lack of understanding in the underlying physics which govern their operability, though the existence of a minimum mass flow rate limit for stable operation has been observed. To help engineers and researchers design an RDE, a model was developed which combines geometric properties, 1D isentropic flow, and detonation physics to predict the stable operating bounds of an RDE. An engine testing facility was also constructed in collaboration with McGill University to test RDEs and confirm the performance of the prediction model developed

Synthesizing Larval Competence Dynamics and Reef-Scale Retention Reveals a High Potential for Self-recruitment in Corals

Many organisms have a complex life-cycle in which dispersal occurs at the propagule stage. For marine environments, there is growing evidence that high levels of recruitment back to the natal population (self-recruitment) are common in many marine organisms. For fish, swimming behavior is frequently invoked as a key mechanism allowing high self-recruitment. For organisms with weak-swimming larvae, such as many marine invertebrates, the mechanisms behind self-recruitment are less clear. Here, we assessed whether the combination of passive retention of larvae due to re-circulation processes near reefs, and the dynamics of settlement competence, can produce the high levels of self-recruitment previously estimated by population genetic studies for reef-building corals. Additionally, we investigated whether time to motility, which is more readily measurable than competence parameters, can explain the between-species variation in self-recruitment. We measured the larval competence dynamics of broadcast-spawning and brooding corals and incorporated these in a model of larval retention around reefs to estimate the potential for self-recruitment and assess its variation among species and reefs. Our results suggest that the larvae of many corals, even those with an obligate planktonic phase, develop with sufficient rapidity to allow high levels of self-recruitment, particularly for reefs with long water retention times. Time to motility explained 77–86% of the between-species variation in potential self-recruitment in scenarios with a realistic range of retention times. Among broadcast spawners, time to motility was strongly and positively correlated with egg size, i.e., broadcast spawner species with small eggs developed more rapidly and exhibited greater potential for self-recruitment. These findings suggest that, along with water retention estimates, easy-to-measure species traits, such as egg size and time to motility, may be good predictors of potential self-recruitment, and therefore may be used to characterize the spectrum of self-recruitment in corals

Enhancing student engagement to positively impact mathematics anxiety, confidence and achievement for interdisciplinary science subjects

Contemporary science educators must equip their students with the knowledge and practical know-how to connect multiple disciplines like mathematics, computing and the natural sciences to gain a richer and deeper understanding of a scientific problem. However, many biology and earth science students are prejudiced against mathematics due to negative emotions like high mathematical anxiety and low mathematical confidence. Here, we present a theoretical framework that investigates linkages between student engagement, mathematical anxiety, mathematical confidence, student achievement and subject mastery. We implement this framework in a large, first-year interdisciplinary science subject and monitor its impact over several years from 2010 to 2015. The implementation of the framework coincided with an easing of anxiety and enhanced confidence, as well as higher student satisfaction, retention and achievement. The framework offers interdisciplinary science educators greater flexibility and confidence in their approach to designing and delivering subjects that rely on mathematical concepts and practices

The Reality of Knowing: The Status of Ideas in Aquinas and Reid

Thesis advisor: Ronald TacelliThomas Aquinas and Thomas Reid are philosophers who, while writing from very different historical and intellectual contexts, both share a common conviction as epistemological realists. This paper will argue that, despite any initial appearances of conflict, their arguments and conclusions are both compatible and complementary, and that through such an agreement we can come to a richer understanding of the realist tradition. At the heart of this unity lie the shared principles that: * Knowledge involves a direct apprehension of things themselves. * Ideas are not themselves objects or intermediaries, but the active means by which the intellect understands. * The relationship between the mind and its object is not one of a material likeness, but of a formal likeness. * The existence of external objects of knowledge is not demonstrable, but is a self-evident first principle.Thesis (PhD) — Boston College, 2009.Submitted to: Boston College. Graduate School of Arts and Sciences.Discipline: Philosophy

Benthic composition changes on coral reefs at global scales

Globally, ecosystems are being reconfigured by a range of intensifying human-induced stressors. Coral reefs are at the forefront of this environmental transformation, and if we are to secure their key ecosystem functions and services, it is important to understand the likely configuration of future reefs. However, the composition and trajectory of global coral reef benthic communities is currently unclear. Here our global dataset of 24,468 observations spanning 22 years (1997–2018) revealed that particularly marked declines in coral cover occurred in the Western Atlantic and Central Pacific. The data also suggest that high macroalgal cover, widely regarded as the major degraded state on coral reefs, is a phenomenon largely restricted to the Western Atlantic. At a global scale, the raw data suggest decreased average (± standard error of the mean) hard coral cover from 36 ± 1.4% to 19 ± 0.4% (during a period delineated by the first global coral bleaching event (1998) until the end of the most recent event (2017)) was largely associated with increased low-lying algal cover such as algal turfs and crustose coralline algae. Enhanced understanding of reef change, typified by decreased hard coral cover and increased cover of low-lying algal communities, will be key to managing Anthropocene coral reefs

A unified model explains commonness and rarity on coral reefs

Abundance patterns in ecological communities have important implications for biodiversity maintenance and ecosystem functioning. However, ecological theory has been largely unsuccessful at capturing multiple macroecological abundance patterns simultaneously. Here, we propose a parsimonious model that unifies widespread ecological relationships involving local aggregation, species-abundance distributions, and species associations, and we test this model against the metacommunity structure of reef-building corals and coral reef fishes across the western and central Pacific. For both corals and fishes, the unified model simultaneously captures extremely well local species-abundance distributions, interspecific variation in the strength of spatial aggregation, patterns of community similarity, species accumulation, and regional species richness, performing far better than alternative models also examined here and in previous work on coral reefs. Our approach contributes to the development of synthetic theory for large-scale patterns of community structure in nature, and to addressing ongoing challenges in biodiversity conservation at macroecological scales

Indo-Pacific biodiversity of coral Rreefs: deviations from a mid-domain model

Understanding the nature and causes of global gradients in species richness is a perennial ecological problem, and recent work has highlighted the need to assess these gradients relative to an appropriate statistical expectation. This paper examines latitudinal and longitudinal gradients in species richnesses of corals and reef fishes in the Indo-Pacific domain and compares them with gradients predicted by a mid-domain model in which geographic domains are located at random between the latitudinal and longitudinal boundaries of this region. We test for significant differences between observed and predicted species-richness patterns, and we identify regions that are enriched or depauperate in species, relative to expectation. In addition, we move beyond previous mid-domain analyses by directly comparing observed spatial distributions of geographic ranges with those predicted by a mid-domain model. This comparison indicates precisely how species-richness anomalies are produced by nonrandomness in the distribution of species ranges. For both corals and fishes, large and statistically significant differences exist between observed latitudinal and longitudinal species-richness gradients and those predicted by mid-domain models. Longitudinally, species richness is markedly higher than predicted along the African coast and, to a lesser extent, within the Indo-Australian Archipelago (IAA), and it is markedly lower than expected in the eastern Pacific. Latitudinally, species richness becomes increasingly higher than predicted as one moves from the equator to the tropical margins; then it becomes sharply lower than predicted beyond the tropics. Unexpectedly, differences between observed and predicted spatial distributions of range endpoints and midpoints reveal a pattern of nonrandomness that is highly congruent with the hypothesis that gyres in the Indian and Pacific Oceans, with the IAA forming a porous boundary between them, have a major influence on Indo-Pacific species-richness patterns. Our analyses indicate that the perspective offered by a focus on explaining nonrandomness in the location of geographic ranges (rather than explaining why species numbers vary in space) is likely to dramatically alter our assessments of alternative explanations for global species-richness gradients