Impurity and soliton dynamics in a Fermi gas with nearest-neighbor interactions

We study spinless fermions with repulsive nearest-neighbor interactions perturbed by an impurity particle or a local potential quench. Using the numerical time-evolving block decimation method and a simplified analytic model, we show that the pertubations create a soliton-antisoliton pair. If solitons are already present in the bath, the two excitations have a drastically different dynamics: The antisoliton does not annihilate with the solitons and is therefore confined close to its origin while the soliton excitation propagates. We discuss the consequences for experiments with ultracold gases.Comment: 12 pages, 16 figure

Preface to the Proceedings of the 5th European Academic Symposium on EAF Steelmaking

Abstract The European Academic Symposium on EAF Steelmaking (EASES) is a series of events targeted at researchers and doctoral candidates working with different aspects of electric arc furnace (EAF) steelmaking. Previously, four events were organised in 2015, 2016, 2018, and 2021 in Aachen, Germany. The 5th European Academic Symposium on EAF Steelmaking (EASES 2023) was organised jointly by the RWTH Aachen University (Department for Industrial Furnaces and Heat Engineering) and University of Oulu (Process Metallurgy Research Unit) and held at the University of Oulu in Oulu, Finland on 5-7 June 2023. A total of 29 presentations were held at the event, out of which 13 featured an accompanying full paper. After the symposium, the authors of the full papers were invited to submit their manuscripts to be included in the proceedings. The proceedings consist of a total of 12 peer-reviewed papers published in the IOP Conference Series: Materials Science and Engineering. Based on the presentations, the development of modelling and monitoring tools for process optimization, the use of biochar to replace fossil carbon for slag foaming, and the use of hydrogen as an alternative burner fuel were identified as current hot topics. In the future, the importance of the EAF process is expected to increase further due to the increasing availability of scrap and plans for ore-based production routes based on hydrogen direct reduction.Abstract The European Academic Symposium on EAF Steelmaking (EASES) is a series of events targeted at researchers and doctoral candidates working with different aspects of electric arc furnace (EAF) steelmaking. Previously, four events were organised in 2015, 2016, 2018, and 2021 in Aachen, Germany. The 5th European Academic Symposium on EAF Steelmaking (EASES 2023) was organised jointly by the RWTH Aachen University (Department for Industrial Furnaces and Heat Engineering) and University of Oulu (Process Metallurgy Research Unit) and held at the University of Oulu in Oulu, Finland on 5-7 June 2023. A total of 29 presentations were held at the event, out of which 13 featured an accompanying full paper. After the symposium, the authors of the full papers were invited to submit their manuscripts to be included in the proceedings. The proceedings consist of a total of 12 peer-reviewed papers published in the IOP Conference Series: Materials Science and Engineering. Based on the presentations, the development of modelling and monitoring tools for process optimization, the use of biochar to replace fossil carbon for slag foaming, and the use of hydrogen as an alternative burner fuel were identified as current hot topics. In the future, the importance of the EAF process is expected to increase further due to the increasing availability of scrap and plans for ore-based production routes based on hydrogen direct reduction

Robust high-dimensional precision matrix estimation

The dependency structure of multivariate data can be analyzed using the covariance matrix $\Sigma$. In many fields the precision matrix $\Sigma^{-1}$ is even more informative. As the sample covariance estimator is singular in high-dimensions, it cannot be used to obtain a precision matrix estimator. A popular high-dimensional estimator is the graphical lasso, but it lacks robustness. We consider the high-dimensional independent contamination model. Here, even a small percentage of contaminated cells in the data matrix may lead to a high percentage of contaminated rows. Downweighting entire observations, which is done by traditional robust procedures, would then results in a loss of information. In this paper, we formally prove that replacing the sample covariance matrix in the graphical lasso with an elementwise robust covariance matrix leads to an elementwise robust, sparse precision matrix estimator computable in high-dimensions. Examples of such elementwise robust covariance estimators are given. The final precision matrix estimator is positive definite, has a high breakdown point under elementwise contamination and can be computed fast

Nonlinear transport in the presence of a local dissipation

We characterize the particle transport, particle loss, and nonequilibrium steady states in a dissipative one-dimensional lattice connected to reservoirs at both ends. The free-fermion reservoirs are fixed at different chemical potentials, giving rise to particle transport. The dissipation is due to a local particle loss acting on the center site. We compute the conserved current and loss current as functions of voltage in the nonlinear regime using a Keldysh description. The currents show step-like features which are affected differently by the local loss: The steps are either smoothened, nearly unaffected, or even enhanced, depending on the spatial symmetry of the single-particle eigenstate giving rise to the step. Additionally, we compute the particle density and momentum distributions in the chain. At a finite voltage, two Fermi momenta can occur, connected to different wavelengths of Friedel oscillations on either side of the lossy site. We find that the wavelengths are determined by the chemical potentials in the reservoirs rather than the average density in the lattice.Comment: 19 pages, 19 figure

Biochar as a slag foaming agent in EAF – A novel experimental setup

Abstract Slag foaming practice is employed widely in electric arc furnace steelmaking to improve the energy efficiency, protect the furnace structures and reduce noise pollution. Slag foaming is typically launched by injecting fossil-based carbonaceous material (e.g. coke dust) into the melt. In this study, a novel laboratory-scale experimental setup was used for studying the substitution of fossil carbon by biochar as slag foaming agent. The setup was equipped with an injection device for feeding carbon and a camera system for observing the foaming phenomenon and recording the process. A set of experiments was conducted for studying the foaming in slag-carbon systems using two carbonaceous materials: 1) coke dust was used as a reference material and 2) a high-quality biochar was used as a possible replacement. In the experiments, sufficient foaming was achieved with both of the carbonaceous materials. The biochar produced almost equal foaming behavior as coke dust. The results indicate that biochar could be used to substitute carbon for slag foaming in the EAF.Abstract Slag foaming practice is employed widely in electric arc furnace steelmaking to improve the energy efficiency, protect the furnace structures and reduce noise pollution. Slag foaming is typically launched by injecting fossil-based carbonaceous material (e.g. coke dust) into the melt. In this study, a novel laboratory-scale experimental setup was used for studying the substitution of fossil carbon by biochar as slag foaming agent. The setup was equipped with an injection device for feeding carbon and a camera system for observing the foaming phenomenon and recording the process. A set of experiments was conducted for studying the foaming in slag-carbon systems using two carbonaceous materials: 1) coke dust was used as a reference material and 2) a high-quality biochar was used as a possible replacement. In the experiments, sufficient foaming was achieved with both of the carbonaceous materials. The biochar produced almost equal foaming behavior as coke dust. The results indicate that biochar could be used to substitute carbon for slag foaming in the EAF

Coupled dynamic modeling of scrap melting and gas phase reactions in the electric arc furnace process

Abstract Gas phase reactions have a significant effect on the composition and heat content of the off-gas in the electric arc furnace (EAF) process. In this work, a previously developed dynamic scrap melting and heat transfer model was coupled with a gas phase reaction module based on Gibbs energy minimization. The gas phase reaction module retrieves the necessary thermodynamic data from a previously developed thermochemistry module. The gas phase reaction module has been used to improve the description of the gas burners and the freeboard of the EAF. The implementation of the gas phase reaction module has been found to be in good agreement with commercially available software (HSC Sim) for calculations assuming a gas phase equilibrium.Abstract Gas phase reactions have a significant effect on the composition and heat content of the off-gas in the electric arc furnace (EAF) process. In this work, a previously developed dynamic scrap melting and heat transfer model was coupled with a gas phase reaction module based on Gibbs energy minimization. The gas phase reaction module retrieves the necessary thermodynamic data from a previously developed thermochemistry module. The gas phase reaction module has been used to improve the description of the gas burners and the freeboard of the EAF. The implementation of the gas phase reaction module has been found to be in good agreement with commercially available software (HSC Sim) for calculations assuming a gas phase equilibrium

No bias of ignored bilaterality when analysing the revision risk of knee prostheses: Analysis of a population based sample of 44,590 patients with 55,298 knee prostheses from the national Swedish Knee Arthroplasty Register

BACKGROUND: The current practice of the Swedish Knee Register is not to take into consideration if one or both knees in a patient are subject to surgery when evaluating risk of revision after arthroplasty. Risk calculations are typically done by statistical methods, such as Kaplan-Meier analyses and Cox's proportional hazards models, that are based on the assumption that observed events are independent, and this is rarely appreciated. The purpose of this study was to investigate if ignoring bilateral operations when using these methods biases the results. METHODS: The bias of not taking bilateral operations into account was investigated by statistically analysing 55 298 prostheses in 44 590 patients, undergoing knee arthroplasty surgery in Sweden during 1985–1999, using traditional proportional hazards analysis, which assumes that all observations are independent, and a shared gamma frailty model, which allows patients to contribute repeated observations. RESULTS: The effect of neglecting bilateral prostheses is minute, possibly because bilateral prosthesis failure is a rare event. CONCLUSION: We conclude that the revision risk of knee prostheses in general can be analysed without consideration for subject dependency, at least in study populations with a relatively low proportion of subjects having experienced bilateral revisions

Spin transport in a one-dimensional quantum wire

We analyze the spin transport through a finite-size one-dimensional interacting wire connected to noninteracting leads. By combining renormalization-group arguments with other analytic considerations such as the memory function technique and instanton tunneling, we find the temperature dependence of the spin conductance in different parameter regimes in terms of interactions and the wire length. The temperature dependence is found to be nonmonotonic. In particular, the system approaches perfect spin conductance at zero temperature for both attractive and repulsive interactions, in contrast with the static spin conductivity. We discuss the connection of our results to recent experiments with ultracold atoms and compare the theoretical prediction to experimental data in the parameter regime where temperature is the largest energy scale.Comment: 16 pages, 10 figure