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Carrier mobility in crystalline germanium at high injection: experimental characterization of carrier-carrier scattering
No full textThe decay of the sum of electron and hole mobilities, µs = µn+µp, due to carrier-carrier scattering was experimentally investigated in crystalline germanium (Ge) at high-injection conditions. Contactless measurements of the mobility sum as a function of the excess carrier density (¿n) in Ge were obtained using photoconductance decay methods. First, the measurement method was revised and improvements were introduced to ensure that µs(¿n) could be obtained for independent samples with improved accuracy. This method is successfully validated with crystalline silicon and, then, applied to Ge samples of different doping types and resistivity. The analysis of the data suggests that the mobility decay at high injection levels cannot be properly explained with the usual assumption of equal cross section for carrier-carrier and carrier-ion scattering events. Instead, we find the mobility sum due to carrier-carrier scattering to be inversely proportional to ¿n according to the expression 8 × 1020·¿n-1 cm2V-1s-1. The limitations and potential error sources of the measurement method are discussed and, finally, the mobility model is used to improve lifetime analysis at high injection, allowing to estimate the ambipolar Auger recombination coefficient at Camb = 7 × 10-31 cm6s-1.Postprint (published version
The recent evolution of energy performance premiums in Barcelona
No full textDecarbonization of buildings is a key step in curbing global Greenhouse Gas (GHG) emissions. In Europe such a goal has envisaged several policies including the creation of market incentives to foster energy retrofits and the construction of efficient homes. Energy Performance Certificates aimed to reduce information asymmetries may help to create market premiums for efficient dwellings. While extant research has focused in proving the existence of such premiums little attention has been paid to learn on their evolution. The events occurred in 2020–2023 period represent an exceptional opportunity to explore whether a better understanding of home deficiencies due to the COVID-19 lockdown and the boom of energy prices produced by Ukraine invasion have affected the marginal price of energy efficiency. In doing so a set of hedonic models have been calibrated using selling apartments in Metropolitan Barcelona. Results suggest that the market premiums have unevenly arose in the different housing segments, being sharper in that targeted to low-income population. By creating brown discounts for the main assets of lest affluent population socioeconomic gaps are being enlarged. Such findings have relevant implications in critically assessing energy and housing policies.Peer ReviewedPostprint (published version
Performance analysis of macroscale concentrated photovoltaic thermal receivers
No full textEffective heat dissipation is a key factor governing the conversion efficiency of high-concentration photovoltaic cells. This study compares several macroscale receiver geometries for concentrated photovoltaicthermal systems—circular, square, rectangular, and Quarter cut pipes—with and without finned heat sinks. A three-dimensional conservative transient conjugate heat transfer model, incorporating radiative effects, was developed in OpenFOAM to simulate the coupled fluid–solid thermal behavior. The model was validated using reported experimental data, showing excellent agreement with a maximum temperature deviation below 1.4 ¿C. The numerical results indicate that the Quarter cut tube with a 7-fin heat sink achieves the best performance, reaching 70.7% thermal efficiency, 4% electrical efficiency, and an overall efficiency of 74.7% at a high flow rate. The system exhibits a fast thermal response of 4.9 s at high flow rates and 20.7 s at low flow rates, confirming its low thermal inertia. The novelty of this work lies in the application of a conservative 3D modeling framework to macroscale receivers, enabling quantitative evaluation and comparison of alternative designs using a consistent numerical approach, and identifying the 7-fin Quarter cut receiver, usually regarded as inferior to the rectangular pipe, as the most efficient configuration.This work is supported by the SIMEX project (PID2022-142174OBI00) of Ministerio de Ciencia e Innovación, Spain, and by the Solar Cofund 2 Joint Call - Economic COgeneration by Efficiently COncentrated SUNlight (JTC-2_2019_024). D. Santos acknowledges a FI AGAURGeneralitat de Catalunya fellowship (2022FI_B_00173), extended and financed by Universitat Politècnica de Catalunya and Banc Santander.Postprint (published version
A checkerboard-free, symmetry-preserving, conservative method for magnetohydrodynamics
No full textMany industrial applications, such as nuclear fusion reactor design and aeronautics, require accurate numerical simulation tools, that conserve physical properties, for magnetohydrodynamic (MHD) flows at low magnetic Reynolds numbers. The interaction between the magnetic field and the conductive fluid often results in complex flow phenomena, which require conservative discretisation schemes. These schemes minimise numerical dissipation to improve accuracy, but can lead to the checkerboard problem if applied on collocated grid arrangements, which are necessary in complex geometries. An algorithm is constructed to simulate MHD flows, which relies on the symmetry-preserving discretisation to allow minimal numerical dissipation. Moreover, it quantifies the checkerboard problem, to dynamically balance it with numerical dissipation, only when necessary. Results for a laminar MHD Taylor-Green vortex case show the importance of the symmetry-preserving discretisation, for which the face-to-cell interpolation method is highlighted. Moreover, it is shown that the solver is virtually free from numerical dissipation on uniform meshes, and effectively counter-acts checkerboarding on skew meshes, where other solvers encounter difficulties. Turbulent MHD duct flow cases show the ability of the solver to generate accurate flow statistics and turbulent kinetic energy (TKE) budgets, while mitigating checkerboarding which lead to flow laminarisation in a comparative solver. These findings establish the presented framework as a reliable and efficient approach for MHD simulations at low magnetic Reynolds numbers, particularly where collocated grid arrangements and low numerical dissipation are required.This work is supported by the SIMEX project (PID2022-142174OB-I00) of Ministerio de Ciencia e Innovación and the RIS3CATFEDER, FusionCAT project (001-P-001722) of Generalitat de Catalunya, Spain. J.A.H. is supported by FI AGAUR-Generalitat de Catalunya fellowship (2023 FI_B1 00204), financed and extended by Universitat Politècnica de Catalunya and Banc Santander. The numerical experiments have been conducted on the MareNostrum5 supercomputer at the Barcelona Supercomputing Center under the project IM-2024-3-0019. The authors thankfully acknowledge these institutions.Peer ReviewedPostprint (published version
A novel approach to forecasting product end-of-life circularity from material compositions using a hybrid autoencoder-predictor model
No full textConstruction and demolition activities are a major source of industrial waste, yet material end-of-life circularity and traceability remain poorly understood. This study addresses the challenge of forecasting end-of-life pathways from building material compositions by introducing a hybrid autoencoder–predictor model. The approach encodes material profiles into continuous embeddings and considers additional design parameters to predict probable end-of-life scenarios. Trained on 8,680 environmental product declaration-derived samples, the model achieved a mean error of 0.01%, MAE of 3.3%, RMSE of 6.2%, and R² = 0.82. Results identify key materials that enable recycling and highlight the importance of design-for-disassembly and recycled content in guiding end-of- life decisions. Besides, findings also reveal that end-of-life reporting practices are somewhat inconsistent, especially for reuse, filling, reconditioning, and composting, highlighting opportunities for policy and reporting standard enhancements. By enabling probabilistic forecasting of end-of-life outcomes, this tool supports transparent material traceability and informs procurement, policy development, and sustainable design.This research was supported by the Catalan agency AGAUR through its Industrial Doctorate support program (2023 DI 00037), as well as its research group support program (2021 SGR 00341). The authors would like to express their gratitude to Grupo Construcía for supporting this research, and to its consulting firm, Eco Intelligent Growth, for providing the necessary guidance to conduct it. Special thanks are extended to Roberto Ordoyo Romero, Director of Innovation at Grupo Construcía, for overseeing and guiding the objectives of the project on behalf of the company.Peer ReviewedPostprint (published version
Design of Ni-promoted Ca2Fe2O5/modified ceria as oxygen carrier for fast and carbon-resistant chemical-looping steam methane reforming
No full textChemical looping steam methane reforming enables the production of high-purity syngas and hydrogen while eliminating the energy-intensive downstream separation steps typically required by conventional technologies. Ca2Fe2O5 is a promising oxygen carrier thanks to its high redox stability and low equilibrium pO2. However, its practical application is hindered by sluggish reduction kinetics. Here, we have overcome this limitation by preparing nickel-promoted composite oxygen carriers (OC) through the physical mixing of Ca2Fe2O5 and modified CeO2. The selective deposition of Ni on the surface of the CeO2-based phase significantly increases the OC reduction rate, outperforming samples in which Ni is in close contact with Ca2Fe2O5 (either on the surface or within the lattice). SiO2 modified ceria was found to be more effective than CeO2-Al2O3 and Ce0.8Zr0.2O2 in promoting the microstructural stability of CeO2 within the composite, ensuring consistent performance over multiple redox cycles. The co-presence of Ca2Fe2O5 and the catalyst in the same reactive bed effectively limits carbon formation at a low OC conversion degree. In situ synchrotron X-ray diffraction and isothermal packed-bed tests revealed a gas-mediated synergistic mechanism whereby carbon deposition was inhibited by H2O and CO2 generated locally from the reduction of Ca2Fe2O5. This led to fast oxygen exchange and stable syngas production. After 50 reaction cycles, the composite OC produced 13.0¿mmol/g of syngas in the reduction step with 88¿% CH4 conversion, and 6.8¿mmol/g of H2 in the water splitting step with >¿99¿% purity, demonstrating the potential of this OC design strategy.Postprint (published version
Optical and radio characterization of continuing current lightning with ASIM, GLM and ELF sensors
No full textLightning with continuing current is a special type of cloud-to-ground flash that can damage electrical systems and cause forest fires, with implications to air quality. Therefore, their precise characterization and early detection are crucial. Here we use a combination of space-based (Atmosphere–Space Interaction Monitor and Geostationary Lightning Mapper) and ground-based (Earth Networks Total Lightning Network and Extreme Low Frequency magnetic field antenna) instruments to systematically identify continuing current lightning between June 1, 2018 and December 31, 2021 in the Contiguous United States. Matched flashes are analyzed using two approaches. In the first, we classify the flashes according to the approximate models of Fairman and Bitzer (2022) as either having continuing current or not. In the second approach, we classify cloud-to-ground flashes reported by the Earth Networks Total Lightning Network using ¿B, a sensitive magnitude derived from Extreme Low Frequency magnetic signals. ¿B quantifies the difference in the average magnetic field signal during the 20 ms before and after the return stroke. A threshold of 0.15 pT was established based on simultaneous observations of a continuing current flash on April 22, 2017, recorded by an Extreme Low Frequency magnetic antenna in Cabo Verde and the Huntsville, Alabama Marx Meter Array. Significant differences were observed in the dual-wavelength (337.0 nm and 777.4 nm) light curves recorded by the Atmosphere–Space Interaction Monitor for flashes with and without continuing current, suggesting its potential for identifying this type of lightning based on spectral emission.This work was supported by the Spanish Ministry of Science and Innovation under project PID2022-136348NB-C31 and the FEDER programme. PACF acknowledges a PhD research contract through the project PID2022-136348-C31. FJPI acknowledges the sponsorship provided by a fellowship (LCF/BQ/PI22/11910026) from the La Caixa Foundation (ID 100010434). In addition, FJPI acknowledges the fellowship RYC2022-035821-I, funded by MCIN/AEI/10.13039/501100011033 and FSE+. Additionally, FJPI, FJGV and PACF acknowledge support from the Severo Ochoa grant CEX2021-001131-S funded by MCIN/AEI/ 10.13039/501100011033. ASIM is a mission of the European Space Agency (ESA) and is funded by the European Space Agency and by national grants of Denmark, Norway and Spain. The UPC work was supported by research grants from the Spanish Ministry (MCIN/AEI/10.13039/501100011033) PID2019-109269RB-C42, PID2022-136348NB-C32, and EQC2021-006957-P.Peer ReviewedPostprint (published version
Membrane effects in reinforced concrete: From experimental evidence to numerical and analytical modelling
No full textThe development of membrane effects in reinforced concrete structures allows for significant enhancements in the resistance provided that lateral movements of a structure or sub-assemblage are restricted. First, the restrained dilation of flexural cracking allows developing axial compressive forces, which increase the resistance with respect to an unconfined response, called Compressive Membrane Action (CMA) or Arching Action when referring to linear members. CMA is significant for low levels of displacements and its effect is considered in some design codes (e.g. punching resistance in EN1992–1–1:2023). For higher levels of displacement, the member elongates and the compressive forces reduce, becoming eventually in tension and activating the so-called Tensile Membrane Action (TMA). TMA has traditionally been widely considered for robustness considerations (response after accidental actions such as column removal). In this paper, a consistent treatment of CMA and TMA on reinforced concrete sub-assemblages of linear members is presented. First, a database of 56 tests is compiled, filtered and digitalized in terms of the load-displacement curve (covering a wide range of heights (90–660 mm), reinforcement ratios (0.31–1.3 %) and slenderness ratios (4¿ 27)). By analysis of the test results and interpretation using refined finite element simulations, the phenomena underlying the activation of CMA and TMA are investigated and quantified. On this basis, a general approach grounded on limit analysis is presented, both for CMA and TMA, and providing sound and consistent agreement to the test results. This approach enables simple analytical expressions for design, covering different ranges of displacement and thus providing a consistent transition from CMA to TMA. Its predictions show in addition low scatter when compared to test results, smaller than several other approaches currently available in the literature.Peer ReviewedPostprint (published version
Numerical study of wave-structure interactions with porous artificial reefs using smoothed particle hydrodynamics
No full textPorous artificial reefs are increasingly being used for nature-based coastal protection, given their ability to attenuate waves while providing habitat for marine species. The wave attenuation and ecological functions of porous artificial reefs depend on how wave-driven flows interact with the porous interior structure of a reef; however, these hydrodynamic processes are still relatively poorly understood. To overcome the challenges with resolving the detailed flow-structure interactions within porous artificial reefs at fine (order mm) spatial resolution, this study utilized a mesh-free Computational Fluid Dynamics modelling approach based on Smoothed Particle Hydrodynamics (SPH) using the DualSPHysics solver. The capability of the SPH model to accurately reproduce the reef hydrodynamics (including wave transformation, hydrodynamic forces acting on the structure, and drag and inertia coefficients) was first validated against three independent experimental datasets of wave-structure interactions. The model was then used in a two-dimensional (2D) numerical investigation of wave-structure interactions with porous artificial reefs, where the 3D geometric parameters of the reef structure were adjusted within the 2D model to properly account for the hydrodynamic forces within the reef (i.e., using a quasi-3D approach). The results reveal how the porous reefs modify the dynamics of wave-induced oscillatory flows within the reef structure that are responsible for generating horizontal and vertical drag forces, wave dissipation, turbulent kinetic energy, and mean currents. Drag coefficients decreased with the Keulegan-Carpenter number, with vertical drag coefficients typically larger than horizontal values. Wave dissipation across the porous reefs was due to a combination of horizontal drag forces and wave breaking, with vertical drag forces playing only a secondary role. Compared to less porous structures, the enhanced drag dissipation in porous artificial reefs enables them to attenuate waves more effectively over a greater range of water levels. Finally, the findings of this study underscore the potential for SPH models to be used as a cost-effective tool to support the design of porous artificial reefs for coastal protection.This project forms part of the Ph.D. study of J. Huang at The University of Western Australia which is supported by the China Scholarship Council and The University of Western Australia Joint Scholarship (202006710182), and funding from an ARC Linkage Project Grant (LP31000800) to R. J. Lowe, M. Ghisalberti, and J. E. Hansen. C. Altomare acknowledges funding from Spanish government and the European Social Found (ESF) under the programme ‘Ramon ´ y Cajal 2020’ (RYC2020-030197-I/AEI/10.13039/501100011033). The numerical modelling work was supported by resources from both the Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia, and the Australian Research Data Commons (ARDC) Nectar Research Cloud funded through the National Collaborative Research Infrastructure Strategy (NCRIS).Peer ReviewedPostprint (published version
Spatial decay in mixtures of heat conductive rigid solids as an evolutive problem
No full textThe objective of this article is to study the spatial behavior of solutions in the case of heat conduction in a static cylinder for a mixture of rigid solids. Although this question is an ill-posed problem in the Hadamard sense, since there is no uniqueness of solutions nor continuous dependence on initial data, we focus on the study of decaying solutions. When we restrict to this class of functions, we obtain a well-posed problem. We will show that we can see the solutions through an analytic semigroup structure, for which the long variable acts as the evolution variable. Therefore, we can apply the properties of these semigroups. Finally, we also consider the case in which a certain type of supply terms is introduced, and the solutions are obtained with the help of semigroups theory. A few comments for alternative boundary conditions are also considered.Peer ReviewedPostprint (published version