Anonymity Analysis of Cryptocurrencies

Cash in the real world allows for parties to exchange currency without the need to go through some sort of central authority. One person, Alice, can simply hand cash over to another person, Bob. In this transaction the only two people that have knowledge of this exchange are Alice and Bob. Until recently there was no electronic equivalent to this exchange. In 1982 David Chaum proposed a system of anonymous electronic cash based on blind signatures, and in 1990 founded DigiCash as an electronic cash company. There were a few banks that implemented electronic cash systems, but these banks and DigiCash ultimately went bankrupt in 1997 and 1998 despite the enthusiasm surrounding anonymous electronic cash. Between 1998 and 2008 there were no successful implementations of electronic cash that offer a decentralized, anonymous, and untraceable system. In 2008 a paper was published by Satoshi Nakamoto on the cryptocurrency known as Bitcoin. A cryptocurrency is a form of electronic cash backed by mathematical and cryptographic constructs, unlike traditional currency which was historically backed by gold or silver. Cryptocurrencies have seen rising popularity in recent years due to their decentralized, distributed, peer-to-peer protocols. Part of this rising popularity is also attributable to the supposed anonymity of these protocols; however, due to the public transaction history required for these protocols and the fact that transactions are pseudonymous and not purely anonymous, this supposed anonymity does not exist. While the systems may achieve the goal of decentralized currency it does not achieve the goal of untraceability. In this thesis we analyze the technical implementations of Bitcoin and other cryptocurrencies to determine the level of anonymity provided by these protocols. We also analyze proposed improvements for their feasibility

State Sponsored Health Insurance and State Economic and Employment Growth

While there is a clear relationship between better health and better economic outcomes, the effects of increasing health insurance on the economy remain understudied. We employ two datasets, one on health insurance coverage in the contiguous 48 U.S. states and one for countries in the Organisation for Economic Co-operation and Development, to model the effect of expanding health insurance on state and country economic and employment growth over the last two decades. We find that increased health insurance coverage of the working age population, especially through government programs like Medicaid, is associated with faster gross domestic product and employment growth. However, we also find that these results may be contingent on controlling the per-enrollee cost of these programs. These findings are informative for future health insurance reforms both federally and in the U.S. states

Mechanisms of high frequency activity in epileptic foci

High frequency activity (HFA) is oscillatory brain activity faster than ~100 Hz. It is subdivided into physiological ripples (~100-250 Hz) and pathological fast ripples (~250-500 Hz). Ripples in the hippocampus are paced by recurrent inhibition from interneurons. The mechanism for pathological HFA is unknown, but may be the same as for ripples and could provide new insight into the pathological nature of epileptic tissue. HFA was induced using the high potassium (${in vitro}$) and tetanus neurotoxin (${ex vivo}$) models of epilepsy. Field HFA was recorded simultaneously with action potentials from visually targeted interneurons, made possible using VGAT-Venus A rats and a membrane chamber. The phase relationship between HFA and interneuron firing was examined. In both models, HFA frequency was normally distributed between 100-300 Hz. Interneurons increased their firing rate during epileptiform bursts and were subdivided into four groups based on their firing patterns. The most pertinent group fired at >100 Hz throughout epileptiform bursts and were candidates to pace HFA. Of this group, significant phase relationships were seen in four interneurons using high potassium and one interneuron with tetanus neurotoxin. These interneurons were compatible with the hypothesis that they pace HFA, but blockade of GABAergic signalling using bicuculline did not abolish HFA, suggesting a modulatory rather than causative role for interneurons

Is threat in the way they move? Influences of static and gait information on threat judgments of unknown people

Recognising intraspecies threat is essential for survival. However, this needs to be balanced against the undue avoidance of unknown others who may be useful to us. Research has shown that judgments of ‘aggression’ and ‘threat’ posed by an unknown person can accurately reflect that person’s general aggressive tendencies. To date, there has not been a within-sample comparison of the informativeness of static and walking stimuli for threat judgments. In this study, 193 participants rated the threat posed by 23 target people presented as both simplified gait presentations (point-light walkers) and still images. We analysed how threat judgments made by participants were predicted by the target’s self-reported aggression (accuracy), the sex of the targets and the medium of target presentation (point-light vs. still image). Our results showed that participants’ threat judgments accurately predicted targets’ aggression. Male targets received higher threat ratings than female targets and point-light displays were rated as more threatening than still images. There were no effects of target sex and presentation medium on accuracy of threat perception and no sex by medium interactions on judgments themselves. Overall, this study provides further evidence of the accuracy of threat judgments at detecting trait aggression. However, further research is needed to explain what features of the target people are enabling the accurate judgments of aggression

Over 10 million seawater temperature records for the United Kingdom Continental Shelf between 1880 and 2014 from 17 Cefas (United Kingdom government) marine data systems

The datasets described here bring together quality-controlled seawater temperature measurements from over 130 years of departmental government-funded marine science investigations in the UK (United Kingdom). Since before the foundation of a Marine Biological Association fisheries laboratory in 1902 and through subsequent evolutions as the Directorate of Fisheries Research and the current Centre for Environment Fisheries & Aquaculture Science, UK government marine scientists and observers have been collecting seawater temperature data as part of oceanographic, chemical, biological, radiological, and other policy-driven research and observation programmes in UK waters. These datasets start with a few tens of records per year, rise to hundreds from the early 1900s, thousands by 1959, and hundreds of thousands by the 1980s, peaking with  >  1 million for some years from 2000 onwards. The data source systems vary from time series at coastal monitoring stations or offshore platforms (buoys), through repeated research cruises or opportunistic sampling from ferry routes, to temperature extracts from CTD (conductivity, temperature, depth) profiles, oceanographic, fishery and plankton tows, and data collected from recreational scuba divers or electronic devices attached to marine animals. The datasets described have not been included in previous seawater temperature collation exercises (e.g. International Comprehensive Ocean–Atmosphere Data Set, Met Office Hadley Centre sea surface temperature data set, the centennial in situ observation-based estimates of sea surface temperatures), although some summary data reside in the British Oceanographic Data Centre (BODC) archive, the Marine Environment Monitoring and Assessment National (MERMAN) database and the International Council for the Exploration of the Sea (ICES) data centre. We envisage the data primarily providing a biologically and ecosystem-relevant context for regional assessments of changing hydrological conditions around the British Isles, although cross-matching with satellite-derived data for surface temperatures at specific times and in specific areas is another area in which the data could be of value (see e.g. Smit et al., 2013). Maps are provided indicating geographical coverage, which is generally within and around the UK Continental Shelf area, but occasionally extends north from Labrador and Greenland to east of Svalbard and southward to the Bay of Biscay. Example potential uses of the data are described using plots of data in four selected groups of four ICES rectangles covering areas of particular fisheries interest. The full dataset enables extensive data synthesis, for example in the southern North Sea where issues of spatial and numerical bias from a data source are explored. The full dataset also facilitates the construction of long-term temperature time series and an examination of changes in the phenology (seasonal timing) of ecosystem processes. This is done for a wide geographic area with an exploration of the limitations of data coverage over long periods. Throughout, we highlight and explore potential issues around the simple combination of data from the diverse and disparate sources collated here. The datasets are available on the Cefas Data Hub (https://www.cefas.co.uk/cefas-data-hub/). The referenced data sources are listed in Sect. 5

The impact of peer pressure: extending Axelrod’s model on cultural polarisation

Culture represents the broad range of things over which people influence each other, and frequently contributes to the behaviour, interaction and outlook of groups. Although it has been studied in the context of humans, it is also relevant to future intelligent cognitive systems, that could have the capability to update their disposition and strategy based on the influence of others. In this work we transfer concepts from social sciences to the computing sciences and examine the effect of peer influence on culture. We consider the notion of “peer pressure”, being the combined effect from all an individual’s neighbours exerting influence at the same time, and also through influence flowing from indirect sources. This approach is derived using Social Impact Theory. We benchmark this against the cultural polarisation model from Axelrod, which involves influence being restricted to dyadic interactions between agents. We find that peer pressure provides complex contagion with a significant impact on cultural evolution. Greater cultural diversity is maintained, with indirect paths mitigating this by effectively forming disruptive weak links. This reaffirms that maintaining diversity in social ties, as well as a wide breadth, supports the mitigation of cultural isolation and polarisation. The model provides a platform to explore culture in a wide range of further scenarios, including electronic, coalition and organisational contexts

Ferrihydrite formation : the role of Fe13 Keggin clusters

Ferrihydrite is the most common iron oxyhydroxide found in soil and is a key sequester of contaminants in the environment. Ferrihydrite formation is also a common component of many treatment processes for clean-up of industrial effluents. Here we characterize ferrihydrite formation during the titration of an acidic ferric nitrate solution with NaOH. In-situ SAXS measurements supported by ex situ TEM indicate that initailly Fe13 Keggin clusters (radius ~0.45 nm) form in solution at pH 0.5 - 1.5, and are persistant for at least 18 days. The Fe13 clusters begin to aggregate above ~ pH 1, initially forming highly linear structures. Above pH ~ 2 densification of the aggregates occurs in conjunction with precipiation of low molecular weight Fe(III) speices (e.g. monomers, dimers) to form mass fractal aggregates of ferrihydrite nanoparticles (~ 3 nm) in which the Fe13 Keggin motif is preserved. SAXS analysis indicates the ferrihydrite particles have a core-shell structure consisting of a Keggin center surrounded by a Fe-depleted shell, supporting the surface depleted model of ferrihydrite. Overall, we present the first direct evidence for the role of Fe13 clusters in the pathway of ferrihydrite formation during base hydrolysis, showing clear structural continuity from isolated Fe13 Keggins to the ferrihydrite particle structure. The results have direct relevance to the fundamental understanding of ferrihydrite formation in environmental, engineered and industrial processes

A computational framework for modelling inter-group behaviour using psychological theory

Psychological theories of inter-group behaviour offer justified representations for interaction, influence, and motivation for coalescence. Agent-based modelling of this behaviour, using evolutionary approaches, further provides a powerful tool to examine the implications of these theories in a dynamic context. In particular, this can enhance our understanding of the escalation of hostility and warfare, and its mitigation, contributing to policy and interventions. In this paper we propose a framework through which social psychology can be embedded in computation for the examination of inter-group behaviour. We examine how various social-psychological theories can be embedded in evolutionary models, and identify ways in which visualisation can support the objective assessment of emergent behaviour. We also discuss how real-world data can be used to parameterise scenarios on which modelling is conducted

Breadth verses depth: the impact of tree structure on cultural influence

Cultural spread in social networks and organisations is an important and longstanding issue. In this paper we assess this role of tree structures in facilitating cultural diversity. Cultural features are represented using abstract traits that are held by individual agents, which may transfer when neighbouring agents interact through the network structure. We use an agent-based model that incorporates both the combined social pressure and influence from an agent's neighbours. We perform a multivariate study where the number of features and traits representing culture are varied, alongside the breadth and depth of the tree. The results reveal interesting findings on cultural diversity. Increasing the number of features promotes strong convergence in flatter trees as compared to narrower and deeper trees. At the same time increasing features causes narrower deeper trees to show greater cultural pluralism while flatter trees instead show greater cultural homogenisation. We also find that in contrast to previous work, the polarisation between nodes does not rise steadily as the number of traits increase but under certain conditions may also fall. The results have implications for organisational structures - in particular for hierarchies where depth supports cultural divergence, while breadth promotes greater homogeneity, but with increased coordination overhead on the root nodes. These observations also support subsidiarity in deep organisational structures - it is not just a case of communication length promoting subsidiarity, but local cultural differences are more likely to be sustained within these structures

Breadth verses depth: the impact of tree structure on cultural influence

Cultural spread in social networks and organisations is an important and longstanding issue. In this paper we assess this role of tree structures in facilitating cultural diversity. Cultural features are represented using abstract traits that are held by individual agents, which may transfer when neighbouring agents interact through the network structure. We use an agent-based model that incorporates both the combined social pressure and influence from an agent's neighbours. We perform a multivariate study where the number of features and traits representing culture are varied, alongside the breadth and depth of the tree. The results reveal interesting findings on cultural diversity. Increasing the number of features promotes strong convergence in flatter trees as compared to narrower and deeper trees. At the same time increasing features causes narrower deeper trees to show greater cultural pluralism while flatter trees instead show greater cultural homogenisation. We also find that in contrast to previous work, the polarisation between nodes does not rise steadily as the number of traits increase but under certain conditions may also fall. The results have implications for organisational structures - in particular for hierarchies where depth supports cultural divergence, while breadth promotes greater homogeneity, but with increased coordination overhead on the root nodes. These observations also support subsidiarity in deep organisational structures - it is not just a case of communication length promoting subsidiarity, but local cultural differences are more likely to be sustained within these structures