Chalmers Research
Not a member yet
88095 research outputs found
Sort by
Demonstration of DRL-based intelligent spectrum management over a T-API-enabled optical network digital twin
Get PDFThis demonstration showcases the applicability and benefits of a deep reinforcement learning (DRL) agent for spectrum defragmentation in a realistic deployment. This is achieved by integrating the DRL agent with the operations of a carrier-grade optical network digital twin via standard T-API messages
Timber as a forest-risk commodity: embodied socio-ecological impacts in the Brazilian supply chain
Get PDFThe continued loss and degradation of forest resources is one of the largest sustainability challenges of our time. The past decades rise in global demand for agricultural and forest commodities have created unparalleled pressure on the natural resources, leading to forest destruction and associated loss in carbon stocks, invaluable biodiversity, ecosystems services, livelihoods. Timber and related wood products have long featured among top forest-risk commodities, yet we still lack elementary understanding of this supply chain and how it links consumers across the world to tropical timber extraction and associated socio-ecological impacts. The overarching goal of this research is to advance the understanding of the socio-ecological impacts embodied in the production to consumption of timber originating from Brazilian native forests. It contributes to answering two foundational questions: To what extent can we connect localities of production to consumption? How are the embodied illegality risks of the supply chain distributed? Paper I provides answers to the latter. By adapting environmentally extended input–output modelling to timber originating from Brazilian native forests, we show how distinct illegality risks can be mapped and quantified at species-level across the supply chain to overcome traceability limitations. We focus on high-value ip\uea hardwood from the Amazon state of Par\ue1, a leading timber producer and contested forest frontier. We found less than quarter of all ip\uea entering supply chains between 2009 and 2019 is risk-free, provide insights on the geographical diversification of potential laundering strategies and show how we can use this approach to overcome the lack of traceability. Paper II expands on Paper I in further compiling data on logging permits and timber flows from state- and federal-level transport licenses substantiated by these, and assessing to what extent we can connect forest exploitation to timber flows. We find about 22% of the exploited forests can be associated to authorized areas, whereas the remaining falls within the complex land tenure patchwork of this forest frontier. Next steps include getting closer to answering: How is the embodied forest degradation risk of the supply chain distributed? This thesis may offer important insights toward this end
The Role of Grain Boundary Sites for the Oxidation of Copper Catalysts during the CO Oxidation Reaction
No full textThe oxidation of transition metal surfaces is a process that takes place readily at ambient conditions and that, depending on the specific catalytic reaction at hand, can either boost or hamper activity and selectivity. Cu catalysts are no exception in this respect since they exhibit different oxidation states for which contradicting activities have been reported, as, for example, in the catalytic oxidation of CO. Here, we investigate the impact of low-coordination sites on nanofabricated Cu nanoparticles with engineered grain boundaries on the oxidation of the Cu surface under CO oxidation reaction conditions. Combining multiplexed in situ single particle plasmonic nanoimaging, ex situ transmission electron microscopy imaging, and density functional theory calculations reveals a distinct dependence of particle oxidation rate on grain boundary density. Additionally, we found that the oxide predominantly nucleates at grain boundary-surface intersections, which leads to nonuniform oxide growth that suppresses Kirkendall-void formation. The oxide nucleation rate on Cu metal catalysts was revealed to be an interplay of surface coordination and CO oxidation behavior, with low coordination favoring Cu oxidation and high coordination favoring CO oxidation. These findings explain the observed single particle-specific onset of Cu oxidation as being the consequence of the individual particle grain structure and provide an explanation for widely distributed activity states of particles in catalyst bed ensembles
Tunicate nanocellulose hydrogels for tissue bioengineering: cytotoxicity, inflammation and in vivo biocompatibility assessments
No full textNo abstract availabl
Development of a unified design buckling curve for fibre reinforced polymer plates subjected to in-plane uniaxial and uniform compression
Get PDFPresented are 24 non-dimensional buckling curves to estimate the strengths of Fibre-Reinforced Polymer (FRP) square plates having four simply supported edges and subjected to in-plane uniaxial and uniform in-plane compression. The curves are constructed by the authors from a parametric numerical analysis using ABAQUS\uae software with changing variables for: material properties; initial geometrical imperfections; laminate lay-ups; and plate thicknesses. These strength curves express relationships for the buckling reduction factor with plate slenderness, and account for post-buckling strength. We observe that regardless of the laminate lay-up (except for purely unidirectional), the choice of FRP material and the magnitude of the initial geometrical imperfection the predicted buckling reduction factors display a meaningful correlation with plate slenderness. Presented is a proposed unified buckling design curve, defined as the lower bound to 18 of the 24 ABAQUS\uae-generated buckling curves. This new curve is benchmarked by the authors against experimental test results extracted from the literature and it is found that there is a reasonable agreement. The authors recommend that the proposed buckling design curve has the potential to be introduced into structural design standards as a procedure to design the buckling strengths of FRP plates
Spin-orbit coupled spin-polarised hole gas at the CrSe2-terminated surface of AgCrSe2
Get PDFIn half-metallic systems, electronic conduction is mediated by a single spin species, offering enormous potential for spintronic devices. Here, using microscopic-area angle-resolved photoemission, we show that a spin-polarised two-dimensional hole gas is naturally realised in the polar magnetic semiconductor AgCrSe2 by an intrinsic self-doping at its CrSe2-terminated surface. Through comparison with first-principles calculations, we unveil a striking role of spin-orbit coupling for the surface hole gas, unlocked by both bulk and surface inversion symmetry breaking, suggesting routes for stabilising complex magnetic textures in the surface layer of AgCrSe2
The importance of few-nucleon forces in chiral effective field theory
No full textWe study the importance of few-nucleon forces in chiral effective field theory for describing many-nucleon systems. A combinatorial argument suggests that three-nucleon forces-which are conventionally regarded as next-to-next-to-leading order-should accompany the two-nucleon force already at leading order (LO) starting with mass number A≃ 10–20. We find that this promotion enables the first realistic description of the 16 O ground state based on a renormalization-group-invariant LO interaction. We also performed coupled-cluster calculations of the equation of state for symmetric nuclear matter and our results indicate that LO four-nucleon forces could play a crucial role for describing heavy-mass nuclei. The enhancement mechanism we found is very general and could be important also in other many-body problems
Self-stabilizing Byzantine-Tolerant Recycling
No full textNumerous distributed applications, such as cloud computing and distributed ledgers, necessitate the system to invoke asynchronous consensus objects for an unbounded number of times, where the completion of one consensus instance is followed by the invocation of another. With only a constant number of objects available, object reuse becomes vital. We investigate the challenge of object recycling in the presence of Byzantine processes, which can deviate from the algorithm code in any manner. Our solution must also be self-stabilizing, as it is a powerful notion of fault tolerance. Self-stabilizing systems can recover automatically after the occurrence of arbitrary transient-faults, in addition to tolerating communication and (Byzantine or crash) process failures, provided the algorithm code remains intact. We provide a recycling mechanism for asynchronous objects that enables their reuse once their task has ended, and all non-faulty processes have retrieved the decided values. This mechanism relies on synchrony assumptions and builds on a new self-stabilizing Byzantine-tolerant synchronous multivalued consensus algorithm, along with a novel composition of existing techniques
Understanding Problem Solving in\ua0Software Testing: An Exploration of\ua0Tester Routines and\ua0Behavior
No full textSoftware testing is a difficult, intellectual activity performed in a social environment. Naturally, testers use and allocate multiple cognitive resources towards this task. The goal of this study is to understand better the routine and behaviour of human testers and their mental models when performing testing. We investigate this topic by surveying 38 software testers and developers in Sweden. The survey explores testers’ cognitive processes when performing testing by investigating the knowledge they bring, the activities they select and perform, and the challenges they face in their routine. By analyzing the survey results, we provide a characterization of tester practices and identify insights regarding the problem-solving process. We use these descriptions to further enhance a cognitive model of software testing
Sparse Array Beamformer Design via ADMM
No full textIn this paper, we devise a sparse array design algorithm for adaptive beamforming. Our strategy is based on finding a sparse beamformer weight to maximize the output signal-to-interference-plus-noise ratio (SINR). The proposed method utilizes the alternating direction method of multipliers (ADMM), and admits closed-form solutions at each ADMM iteration. The algorithm convergence properties are analyzed by showing the monotonicity and boundedness of the augmented Lagrangian function. In addition, we prove that the proposed algorithm converges to the set of Karush-Kuhn-Tucker stationary points. Numerical results exhibit its excellent performance, which is comparable to that of the exhaustive search approach, slightly better than those of the state-of-the-art solvers, including the semidefinite relaxation (SDR), its variant (SDR-V), and the successive convex approximation (SCA) approaches, and significantly outperforms several other sparse array design strategies, in terms of output SINR. Moreover, the proposed ADMM algorithm outperforms the SDR, SDR-V, and SCA methods, in terms of computational complexity