37,460 research outputs found

    Multi-Objective Trust-Region Filter Method for Nonlinear Constraints using Inexact Gradients

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    In this article, we build on previous work to present an optimization algorithm for nonlinearly constrained multi-objective optimization problems. The algorithm combines a surrogate-assisted derivative-free trust-region approach with the filter method known from single-objective optimization. Instead of the true objective and constraint functions, so-called fully linear models are employed, and we show how to deal with the gradient inexactness in the composite step setting, adapted from single-objective optimization as well. Under standard assumptions, we prove convergence of a subset of iterates to a quasi-stationary point and if constraint qualifications hold, then the limit point is also a KKT-point of the multi-objective problem

    Testing the nomological network for the Personal Engagement Model

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    The study of employee engagement has been a key focus of management for over three decades. The academic literature on engagement has generated multiple definitions but there are two primary models of engagement: the Personal Engagement Model of Kahn (1990), and the Work Engagement Model (WEM) of Schaufeli et al., (2002). While the former is cited by most authors as the seminal work on engagement, research has tended to focus on elements of the model and most theoretical work on engagement has predominantly used the WEM to consider the topic. The purpose of this study was to test all the elements of the nomological network of the PEM to determine whether the complete model of personal engagement is viable. This was done using data from a large, complex public sector workforce. Survey questions were designed to test each element of the PEM and administered to a sample of the workforce (n = 3,103). The scales were tested and refined using confirmatory factor analysis and then the model was tested determine the structure of the nomological network. This was validated and the generalisability of the final model was tested across different work and organisational types. The results showed that the PEM is viable but there were differences from what was originally proposed by Kahn (1990). Specifically, of the three psychological conditions deemed necessary for engagement to occur, meaningfulness, safety, and availability, only meaningfulness was found to contribute to employee engagement. The model demonstrated that employees experience meaningfulness through both the nature of the work that they do and the organisation within which they do their work. Finally, the findings were replicated across employees in different work types and different organisational types. This thesis makes five contributions to the engagement paradigm. It advances engagement theory by testing the PEM and showing that it is an adequate representation of engagement. A model for testing the causal mechanism for engagement has been articulated, demonstrating that meaningfulness in work is a primary mechanism for engagement. The research has shown the key aspects of the workplace in which employees experience meaningfulness, the nature of the work that they do and the organisation within which they do it. It has demonstrated that this is consistent across organisations and the type of work. Finally, it has developed a reliable measure of the different elements of the PEM which will support future research in this area

    Adjacent LSTM-Based Page Scheduling for Hybrid DRAM/NVM Memory Systems

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    Recent advances in memory technologies have led to the rapid growth of hybrid systems that combine traditional DRAM and Non Volatile Memory (NVM) technologies, as the latter provide lower cost per byte, low leakage power and larger capacities than DRAM, while they can guarantee comparable access latency. Such kind of heterogeneous memory systems impose new challenges in terms of page placement and migration among the alternative technologies of the heterogeneous memory system. In this paper, we present a novel approach for efficient page placement on heterogeneous DRAM/NVM systems. We design an adjacent LSTM-based approach for page placement, which strongly relies on page accesses prediction, while sharing knowledge among pages with behavioral similarity. The proposed approach leads up to 65.5% optimized performance compared to existing approaches, while achieving near-optimal results and saving 20.2% energy consumption on average. Moreover, we propose a new page replacement policy, namely clustered-LRU, achieving up to 8.1% optimized performance, compared to the default Least Recently Used (LRU) policy

    Exact methods for defects in conformal field theory

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    The defect operators admitted by a given quantum field theory (QFT) contain crucial information. E.g in 4d gauge theories some defects play the role of order parameters, classifying phases of the theory. Defects are also omnipresent in real-world laboratories. E.g. real systems typically have impurities and defects, which may change their properties. Since QFT can be used to describe such systems in the continuum limit, it is essential to systematically understand defects in QFT. This thesis explores defects in d-dimensional conformal field theories (CFT). CFTs arise naturally at fixed points of renormalisation group (RG) flows and describe real physical systems at criticality. We focus on p-dimensional defects, with p ≤ d-1, that preserve some of the system's conformal invariance. Conformal defects give rise to defect-localised contributions to the CFT's Weyl anomaly. Their coefficients are often called defect central charges. They control many physical observables, and obey interesting bounds, constraints, and relations, partially characterising the defect. We report novel and original results about conformal defects and their central charges across dimensions. Our results are exact and apply to large classes of defects. Firstly, we determine the form of the defect Weyl anomaly of a p=4 conformal defect in a CFT of arbitrary co-dimension q=d-4. We show how some of the new defect central charges appear in physical observables, and discuss bounds that they need to obey. We then illustrate these results with a set of simple, yet non-trivial, examples of defects in free CFTs. Using existing methods available in free field theories, we compute various correlation functions exactly for arbitrary p, and demonstrate how to extract defect central charges when p=2 and p=4. Moreover, we study novel defect RG flows which are found to obey monotonicity theorems. Finally, we develop novel techniques to compute central charges for superconformal defects in a large class of interacting superconformal field theories. Our methods rely on supersymmetric localisation, and thus are non-perturbative in the coupling constants. We illustrate our techniques in numerous examples

    The stumbling block in ‘the race of our lives’: transition-critical materials, financial risks and the NGFS climate scenarios

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    Several ‘critical’ raw materials, including metals, minerals and Rare Earth Elements (REEs), play a central role in the low-carbon transition and are needed to expand the deployment of low-carbon technologies. The reliable and affordable supply of these resources is subject to supply-side risks and demand-induced pressures. This paper empirically estimates the material demand requirements for ‘Transition-Critical Materials’ (TCMs) implied under two NGFS Climate Scenarios, namely the ‘Net Zero by 2050’ and ‘Delayed Transition’ scenarios. We apply material intensity estimates to the underlying assumptions on the deployment of low-carbon technologies to determine the implied material demand between 2021 and 2040 for nine TCMs. We find several materials to be subject to significant demand-induced pressures under both scenarios. Subsequently, the paper examines the possible emergence of material bottlenecks for three materials, namely copper, lithium and nickel. The results indicate possible substantial mismatches between supply and demand, which would be further exacerbated if the transition is delayed rather than realised immediately. We discuss these findings in the context of different possible transmission channels through which these bottlenecks could affect financial and price stability, and propose avenues for future research

    Comedians without a Cause: The Politics and Aesthetics of Humour in Dutch Cabaret (1966-2020)

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    Comedians play an important role in society and public debate. While comedians have been considered important cultural critics for quite some time, comedy has acquired a new social and political significance in recent years, with humour taking centre stage in political and social debates around issues of identity, social justice, and freedom of speech. To understand the shifting meanings and political implications of humour within a Dutch context, this PhD thesis examines the political and aesthetic workings of humour in the highly popular Dutch cabaret genre, focusing on cabaret performances from the 1960s to the present. The central questions of the thesis are: how do comedians use humour to deliver social critique, and how does their humour resonate with political ideologies? These questions are answered by adopting a cultural studies approach to humour, which is used to analyse Dutch cabaret performances, and by studying related materials such as reviews and media interviews with comedians. This thesis shows that, from the 1960s onwards, Dutch comedians have been considered ‘progressive rebels’ – politically engaged, subversive, and carrying a left-wing political agenda – but that this image is in need of correction. While we tend to look for progressive political messages in the work of comedians who present themselves as being anti-establishment rebels – such as Youp van ‘t Hek, Hans Teeuwen, and Theo Maassen – this thesis demonstrates that their transgressive and provocative humour tends to protect social hierarchies and relationships of power. Moreover, it shows that, paradoxically, both the deliberately moderate and nuanced humour of Wim Kan and Claudia de Breij, and the seemingly past-oriented nostalgia of Alex Klaasen, are more radical and progressive than the transgressive humour of van ‘t Hek, Teeuwen and Maassen. Finally, comedians who present absurdist or deconstructionist forms of humour, such as the early student cabarets, Freek de Jonge, and Micha Wertheim, tend to disassociate themselves from an explicit political engagement. By challenging the dominant image of the Dutch comedian as a ‘progressive rebel,’ this thesis contributes to a better understanding of humour in the present cultural moment, in which humour is often either not taken seriously, or one-sidedly celebrated as being merely pleasurable, innocent, or progressively liberating. In so doing, this thesis concludes, the ‘dark’ and more conservative sides of humour tend to get obscured

    Experimental Evidence of Accelerated Seismic Release without Critical Failure in Acoustic Emissions of Compressed Nanoporous Materials

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    The total energy of acoustic emission (AE) events in externally stressed materials diverges when approaching macroscopic failure. Numerical and conceptual models explain this accelerated seismic release (ASR) as the approach to a critical point that coincides with ultimate failure. Here, we report ASR during soft uniaxial compression of three silica-based ( SiO2) nanoporous materials. Instead of a singular critical point, the distribution of AE energies is stationary, and variations in the activity rate are sufficient to explain the presence of multiple periods of ASR leading to distinct brittle failure events. We propose that critical failure is suppressed in the AE statistics by mechanisms of transient hardening. Some of the critical exponents estimated from the experiments are compatible with mean field models, while others are still open to interpretation in terms of the solution of frictional and fracture avalanche models

    Graph-based identification of critical elements in urban water infrastructure

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    The purpose of this thesis was to develop and demonstrate methods for determining the criticality of elements in networks. The impact failures could have on the network performance was its primary focus. A second objective was to determine whether the developed method could be applied successfully based on network characteristics. To achieve these goals, research was conducted on factors that influence the criticality of an element, on the possibilities of applying simplified hydrodynamic processes in the determination of criticality and on the contribution of different model components to the functioning of water network models.Sanitary Engineerin

    Indigenous Wāhine Talking Critically in the Museum Space

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    As greater numbers of community groups experience social disconnect, museums need to find better methods of engagement in order to remain relevant. We know that museums are no longer neutral spaces; in fact, they have a role to play in activism, which means they can shift their mission to support local communities celebrate and protect their Indigenous heritage (Drubay and Singhal 2020; Message 2018; Shelton 2013). What follows is a meditation by researchers in Aotearoa New Zealand who engage with Pacific-Indigenous concepts and museum practice in unique ways. Our big idea is to see “Oceania through Indigenous eyes” (Lagi-Maama 2019: 291) and, in particular, the eyes of Nālani Wilson-Hokowhitu with mo‘okū‘auhau to Kalapana, Hawai‘i, and Moloka‘i Nui a Hina; Maree Mills with whakapapa to Tongariro, Taupō, and Ngāti Tūwharetoa; and Rachel Yates, who hails from Vaisala, Sāmoa. As a collective, their curatorial talano kaōrero/mo‘olelo/stories connect to current debates in the museum world where local problems need local solutions. In this instance, Wilson-Hokowhitu and Mills share the ideas that shaped their mahi at Waikato Museum Te Whare Taonga o Waikato in Hamilton, and Yates has just finished a COVID-19 project as Curator of Pacific Cultures at the Museum of New Zealand Te Papa Tongarewa in Wellington.</jats:p
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