8,403 research outputs found

    Countermeasures for the majority attack in blockchain distributed systems

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    La tecnología Blockchain es considerada como uno de los paradigmas informáticos más importantes posterior al Internet; en función a sus características únicas que la hacen ideal para registrar, verificar y administrar información de diferentes transacciones. A pesar de esto, Blockchain se enfrenta a diferentes problemas de seguridad, siendo el ataque del 51% o ataque mayoritario uno de los más importantes. Este consiste en que uno o más mineros tomen el control de al menos el 51% del Hash extraído o del cómputo en una red; de modo que un minero puede manipular y modificar arbitrariamente la información registrada en esta tecnología. Este trabajo se enfocó en diseñar e implementar estrategias de detección y mitigación de ataques mayoritarios (51% de ataque) en un sistema distribuido Blockchain, a partir de la caracterización del comportamiento de los mineros. Para lograr esto, se analizó y evaluó el Hash Rate / Share de los mineros de Bitcoin y Crypto Ethereum, seguido del diseño e implementación de un protocolo de consenso para controlar el poder de cómputo de los mineros. Posteriormente, se realizó la exploración y evaluación de modelos de Machine Learning para detectar software malicioso de tipo Cryptojacking.DoctoradoDoctor en Ingeniería de Sistemas y Computació

    Consent and the Construction of the Volunteer: Institutional Settings of Experimental Research on Human Beings in Britain during the Cold War

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    This study challenges the primacy of consent in the history of human experimentation and argues that privileging the cultural frameworks adds nuance to our understanding of the construction of the volunteer in the period 1945 to 1970. Historians and bio-ethicists have argued that medical ethics codes have marked out the parameters of using people as subjects in medical scientific research and that the consent of the subjects was fundamental to their status as volunteers. However, the temporality of the creation of medical ethics codes means that they need to be understood within their historical context. That medical ethics codes arose from a specific historical context rather than a concerted and conscious determination to safeguard the well-being of subjects needs to be acknowledged. The British context of human experimentation is under-researched and there has been even less focus on the cultural frameworks within which experiments took place. This study demonstrates, through a close analysis of the Medical Research Council's Common Cold Research Unit (CCRU) and the government's military research facility, the Chemical Defence Experimental Establishment, Porton Down (Porton), that the `volunteer' in human experiments was a subjective entity whose identity was specific to the institution which recruited and made use of the subject. By examining representations of volunteers in the British press, the rhetoric of the government's collectivist agenda becomes evident and this fed into the institutional construction of the volunteer at the CCRU. In contrast, discussions between Porton scientists, staff members, and government officials demonstrate that the use of military personnel in secret chemical warfare experiments was far more complex. Conflicting interests of the military, the government and the scientific imperative affected how the military volunteer was perceived

    DIN Spec 91345 RAMI 4.0 compliant data pipelining: An approach to support data understanding and data acquisition in smart manufacturing environments

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    Today, data scientists in the manufacturing domain are confronted with a set of challenges associated to data acquisition as well as data processing including the extraction of valuable in-formation to support both, the work of the manufacturing equipment as well as the manufacturing processes behind it. One essential aspect related to data acquisition is the pipelining, including various commu-nication standards, protocols and technologies to save and transfer heterogenous data. These circumstances make it hard to understand, find, access and extract data from the sources depend-ing on use cases and applications. In order to support this data pipelining process, this thesis proposes the use of the semantic model. The selected semantic model should be able to describe smart manufacturing assets them-selves as well as to access their data along their life-cycle. As a matter of fact, there are many research contributions in smart manufacturing, which already came out with reference architectures or standards for semantic-based meta data descrip-tion or asset classification. This research builds upon these outcomes and introduces a novel se-mantic model-based data pipelining approach using as a basis the Reference Architecture Model for Industry 4.0 (RAMI 4.0).Hoje em dia, os cientistas de dados no domínio da manufatura são confrontados com várias normas, protocolos e tecnologias de comunicação para gravar, processar e transferir vários tipos de dados. Estas circunstâncias tornam difícil compreender, encontrar, aceder e extrair dados necessários para aplicações dependentes de casos de utilização, desde os equipamentos aos respectivos processos de manufatura. Um aspecto essencial poderia ser um processo de canalisação de dados incluindo vários normas de comunicação, protocolos e tecnologias para gravar e transferir dados. Uma solução para suporte deste processo, proposto por esta tese, é a aplicação de um modelo semântico que descreva os próprios recursos de manufactura inteligente e o acesso aos seus dados ao longo do seu ciclo de vida. Muitas das contribuições de investigação em manufatura inteligente já produziram arquitecturas de referência como a RAMI 4.0 ou normas para a descrição semântica de meta dados ou classificação de recursos. Esta investigação baseia-se nestas fontes externas e introduz um novo modelo semântico baseado no Modelo de Arquitectura de Referência para Indústria 4.0 (RAMI 4.0), em conformidade com a abordagem de canalisação de dados no domínio da produção inteligente como caso exemplar de utilização para permitir uma fácil exploração, compreensão, descoberta, selecção e extracção de dados

    Controls on groundwater and surface water salinity in coastal Bangladesh

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    Salinity in surface water and groundwater is a pervasive issue along coastal Bangladesh, a low-lying megadelta where around 35 million people live. A large amount of this land has been reclaimed using a network of low-lying polders. The area is particularly susceptible to flooding from tropical cyclones. Cyclone induced storm surges coupled with the low-lying reclaimed land can breach polder embankments and cause extensive flooding, resulting in excess salinity in soil and surface water. Salinity in drinking water is known to cause adverse effects on human health. It is, therefore, important to identify the controls surface water and groundwater salinity in these coastal areas. A fully coupled surface-subsurface model of a coastal polder by using HydroGeo- Sphere is developed to investigate the impact of storm surge events on groundwater salinity. The hydrological parameters were calibrated from the fieldwork at a field site in the Dacope Upazila, in the southwest coastal region of Bangladesh. The results suggest that sudden salt fluxes in the pond are likely to build up salinity in the underlying sediment. A set of scenarios were considered: a cyclone induced storm surge during both the monsoon and dry seasons, and both with and without remediation. The results show that surge events caused a rise in salinity in drinking water and near-surface groundwater. However, rapid remediation after a surge event could help mitigate the severity of the impact on drinking water. This provides suggestions for water resources management planning. The 2D cross-section model was extended to the 3D model to improve the understanding of the salinity process. Climate change scenarios were then used to evaluate the effects of episodic cyclone surges on shallow groundwater salinity. This study suggests that more frequent cyclones would worsen not only salinity in near-surface groundwater but lateral saltwater intrusion at the shallow or deep aquifers.Open Acces

    The Future of Work and Digital Skills

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    The theme for the events was "The Future of Work and Digital Skills". The 4IR caused a hollowing out of middle-income jobs (Frey & Osborne, 2017) but COVID-19 exposed the digital gap as survival depended mainly on digital infrastructure and connectivity. Almost overnight, organizations that had not invested in a digital strategy suddenly realized the need for such a strategy and the associated digital skills. The effects have been profound for those who struggled to adapt, while those who stepped up have reaped quite the reward.Therefore, there are no longer certainties about what the world will look like in a few years from now. However, there are certain ways to anticipate the changes that are occurring and plan on how to continually adapt to an increasingly changing world. Certain jobs will soon be lost and will not come back; other new jobs will however be created. Using data science and other predictive sciences, it is possible to anticipate, to the extent possible, the rate at which certain jobs will be replaced and new jobs created in different industries. Accordingly, the collocated events sought to bring together government, international organizations, academia, industry, organized labour and civil society to deliberate on how these changes are occurring in South Africa, how fast they are occurring and what needs to change in order to prepare society for the changes.Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) British High Commission (BHC)School of Computin

    Freelance subtitlers in a subtitle production network in the OTT industry in Thailand: a longitudinal study

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    The present study sets out to investigate a subtitle production network in the over-the-top (OTT) industry in Thailand through the perspective of freelance subtitlers. A qualitative longitudinal research design was adopted to gain insights into (1) the way the work practices of freelance subtitlers are influenced by both human and non-human actors in the network, (2) the evolution of the network, and (3) how the freelance subtitlers’ perception of quality is influenced by changes occurring in the network. Eleven subtitlers were interviewed every six months over a period of two years, contributing to over 60 hours of interview data. The data analysis was informed by selected concepts from Actor-Network Theory (ANT) (Law 1992, 2009; Latour 1996, 2005; Mol 2010), and complemented by the three-dimensional quality model proposed by Abdallah (2016, 2017). Reflexive thematic analysis (Braun and Clarke 2019a, 2020b) was used to generate themes and sub-themes which address the research questions and tell compelling stories about the actor-network. It was found that from July 2017 to September 2019, the subtitle production network, which was sustained by complex interrelationships between actors, underwent a number of changes. The changes affected the work practices of freelance subtitlers in a more negative than positive way, demonstrating their precarious position in an industry that has widely adopted the vendor model (Moorkens 2017). Moreover, as perceived by the research participants, under increasingly undesirable working conditions, it became more challenging to maintain a quality process and to produce quality subtitles. Finally, translation technology and tools, including machine translation, were found to be key non-human actors that catalyse the changes in the network under study

    A productive response to legacy system petrification

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    Requirements change. The requirements of a legacy information system change, often in unanticipated ways, and at a more rapid pace than the rate at which the information system itself can be evolved to support them. The capabilities of a legacy system progressively fall further and further behind their evolving requirements, in a degrading process termed petrification. As systems petrify, they deliver diminishing business value, hamper business effectiveness, and drain organisational resources. To address legacy systems, the first challenge is to understand how to shed their resistance to tracking requirements change. The second challenge is to ensure that a newly adaptable system never again petrifies into a change resistant legacy system. This thesis addresses both challenges. The approach outlined herein is underpinned by an agile migration process - termed Productive Migration - that homes in upon the specific causes of petrification within each particular legacy system and provides guidance upon how to address them. That guidance comes in part from a personalised catalogue of petrifying patterns, which capture recurring themes underlying petrification. These steer us to the problems actually present in a given legacy system, and lead us to suitable antidote productive patterns via which we can deal with those problems one by one. To prevent newly adaptable systems from again degrading into legacy systems, we appeal to a follow-on process, termed Productive Evolution, which embraces and keeps pace with change rather than resisting and falling behind it. Productive Evolution teaches us to be vigilant against signs of system petrification and helps us to nip them in the bud. The aim is to nurture systems that remain supportive of the business, that are adaptable in step with ongoing requirements change, and that continue to retain their value as significant business assets
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