3,022 research outputs found

    The manifold rheology of fluidized granular media

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    Fluidized granular media have a rich rheology: measuring shear stress σ\sigma as a function of shear rate γ˙\dot\gamma, they exhibit Newtonian behavior σ∼γ˙\sigma\sim\dot\gamma for low densities and shear rates, develop a yield stress for intermediate shear rates and densities approaching the granular glass transition, and finally, cross over to shear-thickening Bagnold scaling, σ∼γ˙2\sigma\sim\dot\gamma^2. This wealth of flow-behaviors makes fluidized beds a fascinating material, but also one that is challenging to encompass into a global theory, despite its relevance for optimizing industrial processes and predicting natural hazards. We provide careful measurements spanning eight orders of magnitude in shear rate, and show that all these rheological regimes can be described qualitatively and quantitatively using the granular integration through transient formalism, a theory for glassy dynamics under shear adapted to granular fluids

    The input reduction principle of agroecology is wrong when it comes to mineral fertilizer use in sub-Saharan Africa

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    Can farmers in sub-Saharan Africa (SSA) boost crop yields and improve food availability without using more mineral fertilizer? This question has been at the center of lively debates among the civil society, policy-makers, and in academic editorials. Proponents of the “yes” answer have put forward the “input reduction” principle of agroecology, i.e. by relying on agrobiodiversity, recycling and better efficiency, agroecological practices such as the use of legumes and manure can increase crop productivity without the need for more mineral fertilizer. We reviewed decades of scientific literature on nutrient balances in SSA, biological nitrogen fixation of tropical legumes, manure production and use in smallholder farming systems, and the environmental impact of mineral fertilizer. Our analyses show that more mineral fertilizer is needed in SSA for five reasons: (i) the starting point in SSA is that agricultural production is “agroecological” by default, that is, very low mineral fertilizer use, widespread mixed crop-livestock systems and large crop diversity including legumes, but leading to poor soil fertility as a result of widespread soil nutrient mining, (ii) the nitrogen needs of crops cannot be adequately met solely through biological nitrogen fixation by legumes and recycling of animal manure, (iii) other nutrients like phosphorus and potassium need to be replaced continuously, (iv) mineral fertilizers, if used appropriately, cause little harm to the environment, and (v) reducing the use of mineral fertilizers would hamper productivity gains and contribute indirectly to agricultural expansion and to deforestation. Yet, the agroecological principles directly related to soil fertility—recycling, efficiency, diversity—remain key in improving soil health and nutrient-use efficiency, and are critical to sustaining crop productivity in the long run. We argue for a nuanced position that acknowledges the critical need for more mineral fertilizers in SSA, in combination with the use of agroecological practices and adequate policy support

    The ethics and politics of deportation in Europe

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    Defence date: 19 February 2019Examining Board: Professor Rainer Bauböck, European University Institute (Supervisor); Professor Matthew Gibney, University of Oxford; Professor Iseult Honohan, University College Dublin; Professor Jennifer Welsh, McGill University (formerly European University Institute)This thesis explores key empirical and normative questions prompted by deportation policies and practices in the contemporary European context. The core empirical research question the thesis seeks to address is: what explains the shape of deportation regimes in European liberal democracies? The core normative research question is: how should we evaluate these deportation regimes morally? The two parts of the thesis address each of these questions in turn. To explain contemporary European deportation regimes, the four chapters of the first part of the thesis investigate them from a historical and multilevel perspective. (“Expulsion Old and New”) starts by comparing contemporary deportation practices to earlier forms of forced removal such as criminal banishment, political exile, poor law expulsion, and collective expulsions on a religious or ethnic basis, highlighting how contemporary deportation echoes some of the purposes of these earlier forms of expulsion. (“Divergences in Deportation”) looks at some major differences between European countries in how, and how much, deportation is used as a policy instrument today, concluding that they can be roughly grouped into four regime types, namely lenient, selective, symbolically strict and coercively strict. The next two chapters investigate how non-national levels of government are involved in shaping deportation in the European context. (“Europeanising Expulsion”) traces how the institutions of the European Union have come to both restrain and facilitate or incentivise member states’ deportation practices in fundamental ways. (“Localities of Belonging”) describes how provincial and municipal governments are increasingly assertive in frustrating deportations, effectively shielding individuals or entire categories of people from the reach of national deportation efforts, while in other cases local governments pressure the national level into instigating deportation proceedings against unwanted residents. The chapters argue that such efforts on both the supranational and local levels must be explained with reference to supranational and local conceptions of membership that are part of a multilevel citizenship structure yet can, and often do, come apart from the national conception of belonging. The second part of the thesis addresses the second research question by discussing the normative issues deportation gives rise to. (“Deportability, Domicile and the Human Right to Stay”) argues that a moral and legal status of non-deportability should be extended beyond citizenship to all those who have established effective domicile, or long-term and permanent residence, in the national territory. (“Deportation without Domination?”) argues that deportation can and should be applied in a way that does not dominate those it subjects by ensuring its non-arbitrary application through a limiting of executive discretion and by establishing proportionality testing in deportation procedures. (“Resisting Unjust Deportation”) investigates what can and should be done in the face of unjust national deportation regimes, proposing that a normative framework for morally justified antideportation resistance must start by differentiating between the various individual and institutional agents of resistance before specifying how their right or duty to resist a particular deportation depends on motivational, epistemic and relational conditions

    Downconversion of Phonons to Suppress Correlated Errors in Superconducting Qubit Arrays

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    Quantum computers have the potential to solve critical problems that are intractable on conventional processors, with applications in a wide range of areas. The operation of a fault-tolerant quantum processor requires the use of quantum error correction, which involves encoding logical qubits across a large array of physical qubits. One promising system for implementing physical qubits is based on superconducting circuits, such as the transmon. For superconducting qubits, recent research have demonstrated that one source of decoherence comes from high-energy particles, such as gamma rays from background radioactivity and cosmic ray muons. When these particles hit the device substrate, they produce a burst of energetic phonons that travel throughout the chip. Upon hitting the device layer, these phonons generate dissipative excitations, which are quasiparticles, in the superconducting films that make up the qubit, thus causing an error in the qubit. Because the phonons from a single particle impact spread throughout the chip, a single impact event can cause correlated errors across the qubit array, which cannot be mitigated by conventional quantum error correction. In this thesis, we demonstrate a scheme to downconvert pair-breaking phonon energy by fabricating normal metal reservoirs on the back side of our qubit chip. We utilize voltage-biased Josephson junctions around the perimeter of our qubit chip to inject pair-breaking phonons into the substrate, allowing us to quantify our phonon downconversion efficiency. We investigate two devices, one with and one without normal metal reservoirs, that are measured in the same low-temperature environment. For the device with back-side metallization, we observe a reduction in the flux of injected pair-breaking phonons reaching the qubit by more than an order of magnitude. We also measured the quasiparticle charge parity switching rate on multiple qubits in the array, and observed a reduction in the two-fold and three-fold correlated switching rates by two orders of magnitude for the device with the normal metal reservoirs. This work thus provides a practical phonon downconversion technique that suppresses two-fold correlated errors in qubit arrays below the threshold required for running quantum error correction in the presence of background radioactivity

    The link between lithospheric scale deformations and deep fluid emanations: Inferences from the Southeastern Carpathians, Romania

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    Understanding the formation, migration and emanation of deep CO2, H2O and noble gases (He–Ne) in deep-seated deformation settings is crucial to understand the complex relationship between deep-originated fluids and lithospheric deformation. To gain a better insight into these phenomena, we studied the origin of H2O, CO2 and noble gases of gas-rich springs found in the Târgu Secuiesc Basin located in the southeasternmost part of the Carpathian-Pannonian region of Europe. This study area is one of the best natural examples to understand the connection between the deep sources of gas emanations and deep-seated deformation zones, providing an excellent analogue for regions worldwide with similar tectonic settings and fluid emanation properties. We studied the δ2H and δ18O stable isotopic ratios of the spring waters, and the δ13C, He and Ne stable isotopic ratio of the emanating CO2-rich gases dissolved in the mineral spring waters in Covasna town and its vicinity. Based on the δ2H, δ13C, δ18O stable isotopic ratios, the spring waters and the majority of the gases are released through two consecutive fluid infiltration events. The preservation of the metamorphic signal of the upwelling H2O is linked to the local groundwater flow and fault abundancy. Furthermore, the noble gas isotopic ratios show a high degree of atmospheric contamination in the dissolved water gasses that is most likely related to the local hydrogeology. Nevertheless, the elevated corrected helium stable isotopic ratios (Rc/Ra) of our filtered data suggest that part of the emanating gases have a potential upper mantle source component. Beneath the Southeastern Carpathians, mantle fluids can have multiple origin including the dehydration of the sinking slab hosting the Vrancea seismogenic zone, the local asthenospheric upwelling and the lithospheric mantle itself. The flux of the mantle fluids is enhanced by lithospheric scale deformation zones that also support the fluid inflow from the upper mantle into the lower crust. The upwelling CO2–H2O mantle fluids may induce the release of crustal fluids by shifting the pore fluid composition (X(CO2)) and, consequently, initiating decarbonisation and devolatilization metamorphic reactions as a result of carbonate and hydrous mineral destabilisation in the crust. Based on the p-T-X(CO2) conditions of calc-silicates and the local low geotherm, we emphasise the importance of the upwelling fluids in the release and upward migration of further H2O and CO2 in the shallower lower and upper crust. Our observations in the Southeastern Carpathians show a strong similarity to other deep-seated deformation zones worldwide (e.g., Himalayas, Alps, San Andreas Fault). We infer that migration of deep fluids may also play an important role in addition to temperature control on the generation of crustal fluids in deep-seated deformation zones

    Active Curation: algorithmic awareness for cultural commentary on social media platforms

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    This thesis examines how everyday social media users engage in curation practices to influence what news and information they see on their social feeds. It finds that cultural commentary content can act as a proxy for news on these platforms, contributing to public debate and the fifth estate. While much research has explored the implications of algorithmically driven recommender systems for content personalisation and news visibility, this thesis investigates a gap in our understanding of how social media users understand and respond to algorithmic processes, customising their feed in their day-to-day curation practices on these platforms. It explores how a group of Australians aged 18–30 respond to algorithmic recommender systems and how effective their practices are in shaping their social feeds. The study used a mixed methods approach that included a digital ethnography of social media use and a comparative content analysis of social media news exposure and topics in the legacy news cycle. This study develops a taxonomy of consumptive curation practices that users can engage in to influence their personalised social feeds. The study also examines users’ motivations for this curation and how effective these are in filtering news and ‘cultural commentary’ content into or out of their feed. The findings demonstrate that algorithmic literacy is a driver of active curation practices, where users consciously engage in practices designed to influence recommender processes that customise their social feed. They also demonstrate the prevalence of non-journalistic news-related content or ‘cultural commentary’ on social media platforms in the form of hot takes, memes, and satire, and how this cultural commentary can act as a proxy for the news, even for users who are news avoidant. These findings address gaps in our understanding of news discovery and consumption on social media platforms, with implications for how news businesses can reach emerging news audiences

    Automatic Generation of Personalized Recommendations in eCoaching

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    Denne avhandlingen omhandler eCoaching for personlig livsstilsstøtte i sanntid ved bruk av informasjons- og kommunikasjonsteknologi. Utfordringen er ü designe, utvikle og teknisk evaluere en prototyp av en intelligent eCoach som automatisk genererer personlige og evidensbaserte anbefalinger til en bedre livsstil. Den utviklede løsningen er fokusert pü forbedring av fysisk aktivitet. Prototypen bruker bÌrbare medisinske aktivitetssensorer. De innsamlede data blir semantisk representert og kunstig intelligente algoritmer genererer automatisk meningsfulle, personlige og kontekstbaserte anbefalinger for mindre stillesittende tid. Oppgaven bruker den veletablerte designvitenskapelige forskningsmetodikken for ü utvikle teoretiske grunnlag og praktiske implementeringer. Samlet sett fokuserer denne forskningen pü teknologisk verifisering snarere enn klinisk evaluering.publishedVersio

    Concurrent Product and Supply Chain Architecture Design Considering Modularity and Sustainability

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    Since sustainability is a growing concern, businesses aim to integrate sustainability principles and practices into product and supply chain (SC) architecture (SCA) design. Modular product architecture (MPA) is essential for meeting sustainability demands, as it defines detachable modules by selecting appropriate components from various potential combinations. However, the prevailing practice of MPA emphasizes architectural aspects over interface complexity and design production processes for the structural dimension, potentially impending manufacturing, assembly/disassembly, and recovery efficiency. Most MPA has been developed assuming equal and/or fixed relations among modules rather than configuring for SC effectiveness. Therefore, such methods cannot offer guidance on modular granularity and its impact on product and SCA sustainability. Additionally, there is no comparative assessment of MPA to determine whether the components within the configured modules could share multiple facilities to achieve economic benefits and be effective for modular manufacture and upgrade. Therefore, existing modular configuration fails to link modularization drivers and metrics with SCA, hampering economic design, modular recycling, and efficient assembly/disassembly for enhancing sustainability. This study focuses on the study of design fundamentals and implementation of sustainable modular drivers in coordination with SCA by developing a mathematical model. Here, the architectural and interface relations between components are quantified and captured in a decision structure matrix which acts as the foundation of modular clustering for MPA. Again, unlike previous design approaches focused only on cost, the proposed work considers facility sharing through a competitive analysis of commonality and cost. It also evaluates MPA's ease of disassembly and upgradeability by a comparative assessment of different MPA to enhance SCA sustainability. The primary focus is concurrently managing the interdependency between MPA and SCA by developing mathematical models. Consistent with the mathematical model, this thesis also proposes better solution approaches. In summary, the proposed methods provide a foundation for modeling the link between product design and SC to 1) demonstrate how sustainable modular drivers affect the sustainability performance, 2) evaluate the contribution of modularity to the reduction of assembly/disassembly complexity and cost, 3) develop MPA in coordination with SC modularity by trading off modular granularity, commonality, and cost, and 4) identify a sustainable product family for combined modularity considering the similarity of operations, ease of disassembly and upgradability in SCA. Using metaheuristic algorithms, case studies on refrigerators showed that MPA and its methodology profoundly impact SCA sustainability. It reveals that interactions between components with levels based on sustainable modular drivers should be linked with modular granularity for SCA sustainability. Another key takeaway is that instead of solely focusing on cost, facility sharing and ensuring ease of disassembly and upgradeability can help to reap sustainability benefits
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