12,952 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

    Factors that affect English proficiency in students of advanced English courses of the undergraduate program in English at Universidad Nacional Abierta y a Distancia (UNAD)

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    Se anexan tablas de análisis de datos, graficas de encuestas y cuestionarios, consentimiento informado, cuestionario sociodemográfica y encuesta de caracterización.El propósito de este estudio de investigación se centró en establecer y analizar la relación entre diferentes variables en cuanto a la adquisición del inglés como lengua extranjera para los estudiantes de pregrado en lenguas extranjeras de los cursos avanzados de inglés de la UNAD. Este estudio de investigación reunió como participantes a estudiantes activos de los cursos de inglés del último periodo académico que voluntariamente formaron parte del mismo, el análisis de datos de este estudio se basó en información cuantitativa y cualitativa obtenida a través de dos instrumentos creados específicamente para la población objeto, e implementados durante el desarrollo de este estudio de investigación, los datos cuantitativos fueron recolectados mediante el instrumento "Cuestionario Socioeconómico" y se utilizó el Cambridge English Placement test (CEPTO) para analizar el nivel de inglés de los estudiantes, mientras que los datos cualitativos se obtuvieron a través de una encuesta de caracterización, como resultado del análisis de datos mencionado anteriormente se identificaron tres (3) categorías, estratificación socioeconómica, estudios de Pregrado en línea y antecedentes económicos del hogar, las observaciones y conclusiones logradas durante este proceso abren un espacio de reflexión frente a la posibilidad de implementar estrategias de cara a las necesidades de la población especifica de la UNAD concerniente al aprendizaje del inglés como lengua extranjera.This paper establishes and analyzes the relationship between different variables related to English as a foreign language learning for undergraduate students of the Bachelor in English program from the advanced English courses at UNAD. It has been observed that for some students of the undergraduate program the low language performance is related to their socioeconomic context, as well as engagement. This research study invited students enrolled in the advanced English courses at UNAD to participate, the data analysis of this study is based on quantitative and qualitative information obtained through means of two instruments specifically created for the target population, and implemented during the development of this research study, quantitative data was gathered by the instrument “Socioeconomic Questionnaire” and the Cambridge English Placement test (CEPTO) was used to analyze the English level of the students, while qualitative data was obtained through a characterization survey, after thorough analysis it was found that the learners´ socioeconomic status is a fundamental factor that contributes to English acquisition in the target population and has correlation with their language performance, it was also found that although their level of engagement was high the majority did not obtain the B2 English level expected to graduate in the program. The angles explored were: students’ financial status, parents’ background, English language performance, and engagement towards the language. It is expected that the findings of this study can pave the way for other researchers to undertake further investigations and find solutions on the basis of the discerned results

    Annual SHOT Report 2018

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    SHOT is affiliated to the Royal College of PathologistsAll NHS organisations must move away from a blame culture towards a just and learning culture. All clinical and laboratory staff should be encouraged to become familiar with human factors and ergonomics concepts. All transfusion decisions must be made after carefully assessing the risks and benefits of transfusion therapy. Collaboration and co-ordination among staff is vital

    Bridging technology and educational psychology: an exploration of individual differences in technology-assisted language learning within an Algerian EFL setting

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    The implementation of technology in language learning and teaching has a great influence onthe teaching and learning process as a whole and its impact on the learners’ psychological state seems of paramount significance, since it could be either an aid or a barrier to students’ academic performance. This thesis therefore explores individual learner differences in technology-assisted language learning (TALL) and when using educational technologies in higher education within an Algerian English as a Foreign Language (EFL) setting. Although I initially intended to investigate the relationship between TALL and certain affective variables mainly motivation, anxiety, self-confidence, and learning styles inside the classroom, the collection and analysis of data shifted my focus to a holistic view of individual learner differences in TALL environments and when using educational technologies within and beyond the classroom. In an attempt to bridge technology and educational psychology, this ethnographic case study considers the nature of the impact of technology integration in language teaching and learning on the psychology of individual language learners inside and outside the classroom. The study considers the reality constructed by participants and reveals multiple and distinctive views about the relationship between the use of educational technologies in higher education and individual learner differences. It took place in a university in the north-west of Algeria and involved 27 main and secondary student and teacher participants. It consisted of focus-group discussions, follow-up discussions, teachers’ interviews, learners’ diaries, observation, and field notes. It was initially conducted within the classroom but gradually expanded to other settings outside the classroom depending on the availability of participants, their actions, and activities. The study indicates that the impact of technology integration in EFL learning on individual learner differences is both complex and dynamic. It is complex in the sense that it is shown in multiple aspects and reflected on the students and their differences. In addition to various positive and different negative influences of different technology uses and the different psychological reactions among students to the same technology scenario, the study reveals the unrecognised different manifestations of similar psychological traits in the same ELT technology scenario. It is also dynamic since it is characterised by constant change according to contextual approaches to and practical realities of technology integration in language teaching and learning in the setting, including discrepancies between students’ attitudes and teacher’ actions, mismatches between technological experiences inside and outside the classroom, local concerns and generalised beliefs about TALL in the context, and the rapid and unplanned shift to online educational delivery during the Covid-19 pandemic situation. The study may therefore be of interest, not only to Algerian teachers and students, but also to academics and institutions in other contexts through considering the complex and dynamic impact of TALL and technology integration at higher education on individual differences, and to academics in similar low-resource contexts by undertaking a context approach to technology integration

    A Decision Support System for Economic Viability and Environmental Impact Assessment of Vertical Farms

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    Vertical farming (VF) is the practice of growing crops or animals using the vertical dimension via multi-tier racks or vertically inclined surfaces. In this thesis, I focus on the emerging industry of plant-specific VF. Vertical plant farming (VPF) is a promising and relatively novel practice that can be conducted in buildings with environmental control and artificial lighting. However, the nascent sector has experienced challenges in economic viability, standardisation, and environmental sustainability. Practitioners and academics call for a comprehensive financial analysis of VPF, but efforts are stifled by a lack of valid and available data. A review of economic estimation and horticultural software identifies a need for a decision support system (DSS) that facilitates risk-empowered business planning for vertical farmers. This thesis proposes an open-source DSS framework to evaluate business sustainability through financial risk and environmental impact assessments. Data from the literature, alongside lessons learned from industry practitioners, would be centralised in the proposed DSS using imprecise data techniques. These techniques have been applied in engineering but are seldom used in financial forecasting. This could benefit complex sectors which only have scarce data to predict business viability. To begin the execution of the DSS framework, VPF practitioners were interviewed using a mixed-methods approach. Learnings from over 19 shuttered and operational VPF projects provide insights into the barriers inhibiting scalability and identifying risks to form a risk taxonomy. Labour was the most commonly reported top challenge. Therefore, research was conducted to explore lean principles to improve productivity. A probabilistic model representing a spectrum of variables and their associated uncertainty was built according to the DSS framework to evaluate the financial risk for VF projects. This enabled flexible computation without precise production or financial data to improve economic estimation accuracy. The model assessed two VPF cases (one in the UK and another in Japan), demonstrating the first risk and uncertainty quantification of VPF business models in the literature. The results highlighted measures to improve economic viability and the viability of the UK and Japan case. The environmental impact assessment model was developed, allowing VPF operators to evaluate their carbon footprint compared to traditional agriculture using life-cycle assessment. I explore strategies for net-zero carbon production through sensitivity analysis. Renewable energies, especially solar, geothermal, and tidal power, show promise for reducing the carbon emissions of indoor VPF. Results show that renewably-powered VPF can reduce carbon emissions compared to field-based agriculture when considering the land-use change. The drivers for DSS adoption have been researched, showing a pathway of compliance and design thinking to overcome the ‘problem of implementation’ and enable commercialisation. Further work is suggested to standardise VF equipment, collect benchmarking data, and characterise risks. This work will reduce risk and uncertainty and accelerate the sector’s emergence

    Security of Scottish electricity supply: gauging the perceptions of industry stakeholders

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    Efforts to reduce greenhouse gas (GHG) emissions together with the increase in electricity generated from renewable energy are dramatically changing the electricity supply landscape. This document reports and reviews the opinions of industry experts and stakeholders regarding security of electricity supply in Scotland, collected in May 2021 via an online survey and subsequent discussions in a roundtable event in July 2021.https://www.climatexchange.org.uk/media/5118/cxc-security-of-scottish-electricity-supply-gauging-the-perceptions-of-industry-stakeholders-september-2021.pd

    Unresolved taxonomy confounds invasive species identification: the Lysmata vittata Stimpson, 1860 (Decapoda: Caridea: Lysmatidae) species complex and recent introduction of Lysmata vittata sensu stricto in the western Atlantic

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    Peppermint shrimp resembling Lysmata vittata Stimpson, 1860, a species native to the Indo- West Pacific, were found in the lower Chesapeake Bay and adjacent coastal embayments in 2013, representing the first recorded introduction of this species in the northwestern Atlantic. Conflicting morphological descriptions, inconsistent morphological terminology, and limited molecular data (i.e., unresolved taxonomy), as well as the destruction of the type material of L. vittata, created uncertainty regarding proper identification. We provide the first phylogeny incorporating individuals from across the presumed native and introduced range of L. vittata. Morphological and phylogenetic analyses clearly indicate L. vittata represents a species complex of two widely divergent groups: 1) “Bruce Type” with a uniramous dorsal antennule that agrees with A.J. Bruce’s 1990 redescription of L. vittata, and 2) “Rauli Type” with a one-article accessory branch on the dorsal antennule that agrees most closely with the junior synonym L. rauli Laubenheimer & Rhyne, 2010. Given the taxonomic ambiguity surrounding L. vittata, we designate the individual used by A.J. Bruce to redescribe L. vittata and incorporated in our analyses as a neotype to fix the identity of this species. We therefore identify introduced North American and New Zealand populations as L. vittata sensu stricto and postulate that the native range spans temperate/subtropical East Asia. These data suggest that L. rauli is a valid species, which includes a possible undescribed sister species. We confirm the presence of L. californica Stimpson, 1866 in New Zealand, the first non-native record for this species. We also provide data suggesting L. dispar Hayashi, 2007 may be more widespread in the Indo-West Pacific than currently known and consider L. lipkei Okuno & Fiedler, 2010 to be a likely junior synonym

    On the Mechanism of Building Core Competencies: a Study of Chinese Multinational Port Enterprises

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    This study aims to explore how Chinese multinational port enterprises (MNPEs) build their core competencies. Core competencies are firms’special capabilities and sources to gain sustainable competitive advantage (SCA) in marketplace, and the concept led to extensive research and debates. However, few studies include inquiries about the mechanisms of building core competencies in the context of Chinese MNPEs. Accordingly, answers were sought to three research questions: 1. What are the core competencies of the Chinese MNPEs? 2. What are the mechanisms that the Chinese MNPEs use to build their core competencies? 3. What are the paths that the Chinese MNPEs pursue to build their resources bases? The study adopted a multiple-case study design, focusing on building mechanism of core competencies with RBV. It selected purposively five Chinese leading MNPEs and three industry associations as Case Companies. The study revealed three main findings. First, it identified three generic core competencies possessed by Case Companies, i.e., innovation in business models and operations, utilisation of technologies, and acquisition of strategic resources. Second, it developed the conceptual framework of the Mechanism of Building Core Competencies (MBCC), which is a process of change of collective learning in effective and efficient utilization of resources of a firm in response to critical events. Third, it proposed three paths to build core competencies, i.e., enhancing collective learning, selecting sustainable processes, and building resource base. The study contributes to the knowledge of core competencies and RBV in three ways: (1) presenting three generic core competencies of the Chinese MNPEs, (2) proposing a new conceptual framework to explain how Chinese MNPEs build their core competencies, (3) suggesting a solid anchor point (MBCC) to explain the links among resources, core competencies, and SCA. The findings set benchmarks for Chinese logistics industry and provide guidelines to build core competencies
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