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Numrering	Referens	Omslagsbild	Hitta
1.	Abdullaev, Fatkhulla, et al. (författare) Collective dynamics of Fermi-Bose mixtures with an oscillating scattering length 2019 Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 99:3 Tidskriftsartikel (refereegranskat)abstract Collective oscillations of superfluid mixtures of ultra cold fermionic and bosonic atoms are investigated while varying the fermion-boson scattering length. We study the dynamics with respect to excited center of mass modes and breathing modes in the mixture. Parametric resonances are also analyzed when the scattering length varies periodically in time, by comparing partial differential equation (PDE) models and ordinary differential equation (ODE) models for the dynamics. An application to the recent experiment with fermionic Li-6 and bosonic Li-7 atoms, which approximately have the same masses, is discussed.
2.	Abdullaev, Fatkhulla, et al. (författare) Faraday waves in quasi-one-dimensional superfluid Fermi-Bose mixtures 2013 Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 87:2 Tidskriftsartikel (refereegranskat)abstract The generation of Faraday waves in superfluid Fermi-Bose mixtures in elongated traps is investigated. The generation of waves is achieved by periodically changing a parameter of the system in time. Two types of modulations of parameters are considered: a variation of the fermion-boson scattering length and the boson-boson scattering length. We predict the properties of the generated Faraday patterns and study the parameter regions where they can be excited.
3.	Abdullaev, F. Kh., et al. (författare) Management of solitons in medium with competing cubic and quadratic nonlinearities 2023 Ingår i: Optik (Stuttgart). - : Elsevier. - 0030-4026 .- 1618-1336. ; 274 Tidskriftsartikel (refereegranskat)abstract Management of solitons in media with competing quadratic and cubic nonlinearities is investigated. Two schemes, using rapid modulations of a mismatch parameter, and of the Kerr nonlinearity parameter are studied. For both cases, the averaged in time wave equations are derived. In the case of mismatch management, the region of the parameters where stabilization is possible is found. In the case of Kerr nonlinearity management, it is shown that the effective chi(2) nonlinearity depends on the intensity imbalance between fundamental (FH) and second (SH) harmonics. Predictions obtained from the averaged equations are confirmed by numerical simulations of the full PDE’s.
4.	Abdullaev, F. Kh., et al. (författare) Nonlinearity managed vector solitons 2023 Ingår i: Physics Letters A. - : Elsevier. - 0375-9601 .- 1873-2429. ; 491 Tidskriftsartikel (refereegranskat)abstract The evolution of vector solitons under nonlinearity management is studied. The averaged over strong and rapid modulations in time of the inter-species interactions vector Gross-Pitaevskii equation (GPE) is derived. The averaging gives the appearance of the effective nonlinear quantum pressure depending on the population of the other component. Using this system of equations, the existence and stability of the vector solitons under the action of the strong nonlinearity management (NM) is investigated. Using a variational approach the parameters of NM vector solitons are found. The numerical simulations of the full time-dependent coupled GPE confirms the theoretical predictions.
5.	Abdullaev, Fatkhulla, et al. (författare) Matter waves in atomic-molecular condensates with Feshbach resonance management 2021 Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - : American Physical Society. - 1063-651X .- 1095-3787. ; 104:2 Tidskriftsartikel (refereegranskat)abstract The dynamics of matter waves in the atomic to molecular condensate transition with a time-modulated atomic scattering length is investigated. Both the cases of rapid and slow modulations are studied. In the case of rapid modulations, the average over oscillations for the system is derived. The corresponding conditions for dynamical suppression of the association of atoms into the molecular field, or of second-harmonic generation in nonlinear optical systems, are obtained. For the case of slow modulations, we find resonant enhancement in the molecular field. We then illustrate chaos in the atomic-molecular BEC system. We suggest a sequential application of the two types of modulations, slow and rapid, when producing molecules.
6.	Abdullaev, Farakhulla, et al. (författare) Zeno effect and switching of solitons in nonlinear couplers 2011 Ingår i: Optics Letters. - : Optical Society of America. - 0146-9592 .- 1539-4794. ; 36:23, s. 4566-4568 Tidskriftsartikel (refereegranskat)abstract The Zeno effect is investigated for soliton type pulses in a nonlinear directional coupler with dissipation. The effect consists in increase of the coupler transparency with increase of the dissipative losses in one of the arms. It is shown that localized dissipation can lead to switching of solitons between the arms. Power losses accompanying the switching can be fully compensated by using a combination of dissipative and active (in particular, parity-time-symmetric) segments.
7.	Abrahamsson, Johan, 1977-, et al. (författare) A Fully Levitated Cone-Shaped Lorentz-Type Self-Bearing Machine With Skewed Windings 2014 Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 50:9 Tidskriftsartikel (refereegranskat)abstract Brushless dc coreless electric machines with double-rotor and single-stator configuration have very low losses, since the return path of the magnetic flux rotates with the permanent magnets. The eddy-current loss in the stator is additionally very small due to the lack of iron, making it ideal for kinetic energy storage. This paper presents a design for self-bearing rotor suspension, achieved by placing the stator windings skewed on a conical surface. A mathematical analysis of the force from a skewed winding confined to the surface of a cone was found. The parametric analytical expressions of the magnitude and direction of force and torque were verified by finite-element method simulations for one specific geometry. A dynamic model using proportional-integral-differential control was implemented in MATLAB/Simulink, and the currents needed for the self-bearing effect were found by solving an underdetermined system of linear equations. External forces, calculated from acceleration measurements from a bus in urban traffic, were added to simulate the dynamic environment of an electrical vehicle.
8.	Brack, M., et al. (författare) Uniform semiclassical trace formula for U(3) → SO(3) symmetry breaking 2005 Ingår i: Journal of Physics A. - : Institute of Physics (IOP). - 0305-4470 .- 1361-6447. ; 38:46, s. 9941-9967 Tidskriftsartikel (refereegranskat)abstract We develop a uniform semiclassical trace formula for the density of states of a three-dimensional isotropic harmonic oscillator (HO), perturbed by a term . This term breaks the U(3) symmetry of the HO, resulting in a spherical system with SO(3) symmetry. We first treat the anharmonic term for small ε in semiclassical perturbation theory by integration of the action of the perturbed periodic HO orbit families over the manifold which is covered by the parameters describing their four-fold degeneracy. Then, we obtain an analytical uniform trace formula for arbitrary ε which in the limit of strong perturbations (or high energy) asymptotically goes over into the correct trace formula of the full anharmonic system with SO(3) symmetry, and in the limit ε (or energy) →0 restores the HO trace formula with U(3) symmetry. We demonstrate that the gross-shell structure of this anharmonically perturbed system is dominated by the two-fold degenerate diameter and circular orbits, and not by the orbits with the largest classical degeneracy, which are the three-fold degenerate tori with rational ratios ωr:ωφ ≤ N:M of radial and angular frequencies. The same holds also for the limit of a purely quartic spherical potential V(r) ∝ r4.
9.	Carlsen, Martin, et al. (författare) Efficiency of a gyroscopic device for conversion of mechanical wave energy to electric energy : Technical report from ESGI-83 workshop in industrial mathematics 2011 2011 Rapport (övrigt vetenskapligt/konstnärligt)abstract We consider a recently proposed gyroscopic device for conversion of mechanical ocean wave energy to electrical energy. Two models of the device derived from standard engineering mechanics from the literature are analysed, and a model is derived from analytical mechanics considerations. From these models, estimates of the power production, efficiency, forces and moments are made. We find that it is possible to extract a significant amount of energy from an ocean wave using the described device. Further studies are required for a full treatment of the device.
10.	Corboz, Philippe, et al. (författare) Phase-space methods for fermions 2013 Ingår i: Quantum Gases. - London : Imperial College Press. - 1848168101 ; , s. 407-416 Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract We review phase-space simulation techniques for fermions, showing how a Gaussian operator basis leads to exact calculations of the evolution of a many-body quantum system in both real and imaginary time. We apply such techniques to the Hubbard model and to the problem of molecular dissociation of bosonic molecules into pairs of fermionic atoms.
11.	Edström, Daniel, 1986-, et al. (författare) Forces on parallel three-phase AC-conductors during a phase to ground fault 2019 Konferensbidrag (refereegranskat)abstract We consider the problem of calculating forces on high current solid conductors, as is present in various types of electrical installations e.g. in substations [1]. An example of such an installation with three parallel conductors is shown in Figure 1. The conductor forces are important for the design of the station, in particular for the conductor geometry and mechanical support.
12.	Gulliksson, Mårten, 1963-, et al. (författare) Damped Dynamical Systems for Solving Equations and Optimization Problems 2019 Ingår i: Handbook of the Mathematics of the Arts and Sciences. - Cham : Springer. - 9783319706580 Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract We present an approach for solving optimization problems with or without constrains which we call Dynamical Functional Particle Method (DFMP). The method consists of formulating the optimization problem as a second order damped dynamical system and then applying symplectic method to solve it numerically. In the first part of the chapter, we give an overview of the method and provide necessary mathematical background. We show that DFPM is a stable, efficient, and given the optimal choice of parameters, competitive method. Optimal parameters are derived for linear systems of equations, linear least squares, and linear eigenvalue problems. A framework for solving nonlinear problems is developed and numerically tested. In the second part, we adopt the method to several important applications such as image analysis, inverse problems for partial differential equations, and quantum physics. At the end, we present open problems and share some ideas of future work on generalized (nonlinear) eigenvalue problems, handling constraints with reflection, global optimization, and nonlinear ill-posed problems.
13.	Gulliksson, Mårten, 1963-, et al. (författare) Dynamical representations of constrained multicomponent nonlinear Schrödinger equations in arbitrary dimensions 2021 Ingår i: Journal of Physics A: Mathematical and Theoretical. - : IOP Publishing. - 1751-8113 .- 1751-8121. ; 54:27 Tidskriftsartikel (refereegranskat)abstract We present new approaches for solving constrained multicomponent nonlinear Schrödinger equations in arbitrary dimensions. The idea is to introduce an artificial time and solve an extended damped second order dynamic system whose stationary solution is the solution to the time-independent nonlinear Schrödinger equation. Constraints are often considered by projection onto the constraint set, here we include them explicitly into the dynamical system. We show the applicability and efficiency of the methods on examples of relevance in modern physics applications.
14.	Jarodzka, Halszka, et al. (författare) There's more to multimedia than meets the eye : is seeing pictures believing? 2013 Ingår i: 17th European Conference on Eye Movements. - : European Group for Eye Movement Research. ; , s. 211-211 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract Cognitive theories on learning with multimedia recommend combining different presentation formats (e.g., text and pictures) in teaching. However, recent research showed that pictures lurk people into trusting the accompanying text, instead of critically studying it. To investigate this we asked 36 physics students to solve mathematical problems, which consisted of a text describing the problem and a statement about the problem that had to be confirmed or rejected (control). The multimedia condition additionally received graphs displaying the same information as the text. Results revealed a bias to confirm statements that were accompanied by a graph irrespective of their correctness. Eye tracking showed that students looked less at the text and the problem statement when a graph was present. The more students looked at the statement and the more transitions they made between the statement and the graph, the better they performed. Verbal data showed that students heavily relied on the graphs: when the graph itself was correct, but the statement was not, students judged the statement as correct referring to the graph. Thus, the mere presence of pictures is not sufficient. Instead, they need to be carefully integrated with the problem statement to improve performance.
15.	Kavoulakis, Georgios, et al. (författare) Superfluidity in a gas of strongly interacting bosons 2006 Ingår i: Europhysics letters. - : Institute of Physics (IOP). - 0295-5075 .- 1286-4854. ; 76:2, s. 215-221 Tidskriftsartikel (refereegranskat)abstract We consider small systems of bosonic atoms rotating in a toroidal trap. Using the method of exact numerical diagonalization of the many-body Hamiltonian, we examine the transition from the Bose-Einstein condensed state to the Tonks-Girardeau state. The system supports persistent currents in a wide range between the two limits, even in the absence of Bose-Einstein condensation.
16.	Lockby, Andreas, et al. (författare) Finding Stationary Solutions of PDEs with Constraints using Damped Dynamical Systems 2016 Ingår i: Comsol Conference 2016. Konferensbidrag (refereegranskat)abstract The dynamical functional particle method(DFPM) is a method for solving equations, e.g. PDEs, using a second order damped dynamical system. We show how the method can be extended to include constraints both explicitly as global constraints and adding the constraints as additional damped dynamical equations. These methods are implemented in Comsol and we show numerical tests for finding the stationary solution of a nonlinear heat equation with and without constraints (global and dynamical). The results show that DFPM is a very general and robust way of solving PDEs and it should be of interest to implement the approach more generally in Comsol.
17.	Møller-Andersen, Jakob, et al. (författare) Perturbative semiclassical trace formulae for harmonic oscillators 2015 Ingår i: Reports on mathematical physics. - 0034-4877 .- 1879-0674. ; 75:3, s. 359-382 Tidskriftsartikel (refereegranskat)abstract In this article we extend previous semiclassical studies by including more general perturbative potentials of the harmonic oscillator in arbitrary spatial dimensions. Our starting point is a radial harmonic potential with an arbitrary even monomial perturbation, which we use to study the resulting U(D) to O(D) symmetry breaking. We derive the gross structure of the semiclassical spectrum from periodic orbit theory, in the form of a perturbative (ħ → 0) trace formula. We then show how to apply the results to even-order polynomial potentials, possibly including mean-field terms. We have drawn the conclusion that the gross structure of the quantum spectrum is determined from only classical circular and diameter orbits for this class of systems.
18.	Nepal, Surendra, et al. (författare) Random walks and moving boundaries : Estimating the penetration of diffusants into dense rubbers 2023 Ingår i: Probabilistic Engineering Mechanics. - : Elsevier. - 0266-8920 .- 1878-4275. ; 74 Tidskriftsartikel (refereegranskat)abstract For certain materials science scenarios arising in rubber technology, one-dimensional moving boundary problems with kinetic boundary conditions are capable of unveiling the large-time behavior of the diffusants penetration front, giving a direct estimate on the service life of the material. Driven by our interest in estimating how a finite number of diffusant molecules penetrate through a dense rubber, we propose a random walk algorithm to approximate numerically both the concentration profile and the location of the sharp penetration front. The proposed scheme decouples the target evolution system in two steps: (i) the ordinary differential equation corresponding to the evaluation of the speed of the moving boundary is solved via an explicit Euler method, and (ii) the associated diffusion problem is solved by a random walk method. To verify the correctness of our random walk algorithm we compare the resulting approximations to computational results based on a suitable finite element approach with a controlled convergence rate. Our numerical results recover well penetration depth measurements of a controlled experiment designed specifically for this setting.
19.	Nikolaou, S., et al. (författare) Rotating quantum droplets confined in a harmonic potential 2023 Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society. - 2469-9926 .- 2469-9934. ; 108:5 Tidskriftsartikel (refereegranskat)abstract We investigate the rotational properties of a two-component, two-dimensional self-bound quantum droplet, which is confined in a harmonic potential and compare them with the well-known problem of a single-component atomic gas with contact interactions. For a fixed value of the trap frequency, choosing some representative values of the atom number, we determine the lowest-energy state, as the angular momentum increases. For a sufficiently small number of atoms, the angular momentum is carried via center-of-mass excitation. For larger values, when the angular momentum is sufficiently small, we observe vortex excitation instead. Depending on the actual atom number, one or more vortices enter the droplet. Beyond some critical value of the angular momentum, however, the droplet does not accommodate more vortices and the additional angular momentum is carried via center-of-mass excitation in a "mixed" state. Finally, the excitation spectrum is also briefly discussed.
20.	Nikolaou, S., et al. (författare) Rotating quantum droplets confined in an anharmonic potential 2024 Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society. - 2469-9926 .- 2469-9934. ; 109 Tidskriftsartikel (refereegranskat)abstract We investigate the rotational properties of quantum droplets, which form in a mixture of two Bose-Einstein condensates, in the presence of an anharmonic trapping potential. We identify various phases as the atom number and the angular momentum or angular velocity of the trap vary. These phases include center-of-mass–like excitation (without or with vortices), vortices of single and multiple quantization, etc. Finally, we compare our results with those of the single-component problem.
21.	Nyström, Marcus, et al. (författare) A pilot study of problem solving in vector calculus using eye-tracking 2011 Ingår i: Utvecklingskonferens 11 LU. - : Lund University. - 9789197797467 ; , s. 118-123 Konferensbidrag (refereegranskat)
22.	Nyström, Marcus, et al. (författare) How illustrations influence performance and eye movement behaviour when solving problems in vector calculus 2012 Ingår i: Conference on Teaching and Learning 2012. - : Lund University. Konferensbidrag (refereegranskat)abstract Mathematical formulas in vector calculus often have direct visual representations, which in form of illustrations are used extensively during teaching and when assessing students’ levels of understanding. However, there is very little, if any, empirical evidence of how the illustrations are utilized during problem solving and whether they are beneficial to comprehension. In this paper we collect eye movements and performance scores (true or false answers) from students while solving eight problems in vector calculus; 20 students solve illustrated problems whereas 16 students solve the same problems, but without the illustrations. Results show no overall performance benefit for illustrated problems even though they are clearly visually attended. Surprisingly, we found a significant effect of whether the answer to the problem was true of false; students were more likely to answer that the question was true given an illustrated problem. We interpret this finding as if the illustrations persuade the students that the answer is true, irrespective of whether or not it in fact is. These results may question the tacit consensus among teachers of vector calculus that illustrations are generally beneficial for comprehending a problem.
23.	Rousse, François, 1989-, et al. (författare) Correlated quantum dynamics of graphene clusters 2023 Ingår i: Physical Review B. - : American Physiological Society. - 2469-9950 .- 2469-9969. ; 107:13 Tidskriftsartikel (refereegranskat)abstract Phase-space representations are a family of methods for dynamics of both bosonic , fermionic systems, that work by mapping the system's density matrix to a quasiprobability density and the Liouville-von Neumann equation of the Hamiltonian to a corresponding density differential equation for the probability. We investigate here the accuracy and the computational efficiency of one approximate phase-space representation, called the fermionic truncated Wigner approximation (fTWA), applied to the Fermi-Hubbard model. On a many-body 2D system, with hopping strength and Coulomb U tuned to represent the electronic structure of graphene, the method is found to be able to capture the time evolution of first-order (site occupation) and second-order (correlation functions) moments significantly better than the mean-field, Hartree-Fock method. The fTWA was also compared to results from the exact diagonalization method for smaller systems , in general the agreement was found to be good. The fully parallel computational requirement of fTWA scales in the same order as the Hartree-Fock method, and the largest system considered here contained 198 lattice sites.
24.	Rousse, François, 1989-, et al. (författare) Simulations of quantum dynamics with fermionic phase-space representations using numerical matrix factorizations as stochastic gauges 2024 Ingår i: Journal of Physics A. - : Institute of Physics (IOP). - 1751-8113 .- 1751-8121. ; 57:1 Tidskriftsartikel (refereegranskat)abstract The Gaussian phase-space representation can be used to implement quantum dynamics for fermionic particles numerically. To improve numerical results, we explore the use of dynamical diffusion gauges in such implementations. This is achieved by benchmarking quantum dynamics of few-body systems against independent exact solutions. A diffusion gauge is implemented here as a so-called noise-matrix, which satisfies a matrix equation defined by the corresponding Fokker-Planck equation of the phase-space representation. For the physical systems with fermionic particles considered here, the numerical evaluation of the new diffusion gauges allows us to double the practical simulation time, compared with hitherto known analytic noise-matrices. This development may have far reaching consequences for future quantum dynamical simulations of many-body systems.
25.	Rousse, François, 1989-, et al. (författare) The role of super-spreaders in modeling of SARS-CoV-2 2022 Ingår i: Infectious Disease Modelling. - : KeAi Publishing Communications Ltd.. - 2468-0427. ; 7:4, s. 778-794 Tidskriftsartikel (refereegranskat)abstract In stochastic modeling of infectious diseases, it has been established that variations in infectivity affect the probability of a major outbreak, but not the shape of the curves during a major outbreak, which is predicted by deterministic models (Diekmann et al., 2012). However, such conclusions are derived under idealized assumptions such as the population size tending to infinity, and the individual degree of infectivity only depending on variations in the infectiousness period. In this paper we show that the same conclusions hold true in a finite population representing a medium size city, where the degree of infectivity is determined by the offspring distribution, which we try to make as realistic as possible for SARS-CoV-2. In particular, we consider distributions with fat tails, to incorporate the existence of super-spreaders. We also provide new theoretical results on convergence of stochastic models which allows to incorporate any offspring distribution with a finite moment.
26.	Roussou, Alexandra, et al. (författare) Excitation spectrum of a mixture of two Bose gases confined in a ring potential with interaction asymmetry 2018 Ingår i: New Journal of Physics. - : Institute of Physics (IOP). - 1367-2630. ; 20 Tidskriftsartikel (refereegranskat)abstract We study the rotational properties of a two-component Bose-Einstein condensed gas of distinguishable atoms which are confined in a ring potential using both the mean-field approximation, as well as the method of diagonalization of the many-body Hamiltonian. We demonstrate that the angular momentum may be given to the system either via single-particle, or "collective" excitation. Furthermore, despite the complexity of this problem, under rather typical conditions the dispersion relation takes a remarkably simple and regular form. Finally, we argue that under certain conditions the dispersion relation is determined via collective excitation. The corresponding many-body state, which, in addition to the interaction energy minimizes also the kinetic energy, is dictated by elementary number theory.
27.	Sandin, Patrik, 1980-, et al. (författare) Dimensional reduction in Bose-Einstein condensed clouds of atoms confined in tight potentials of any geometry and any interaction strength 2017 Ingår i: Physical Review E. - : American Physical Society. - 2470-0045 .- 2470-0053. ; 95:1 Tidskriftsartikel (refereegranskat)abstract Motivated by numerous experiments on Bose-Einstein condensed atoms which have been performed in tight trapping potentials of various geometries (elongated and/or toroidal/annular), we develop a general method which allows us to reduce the corresponding three-dimensional Gross-Pitaevskii equation for the order parameter into an effectively one-dimensional equation, taking into account the interactions (i.e., treating the width of the transverse profile variationally) and the curvature of the trapping potential. As an application of our model we consider atoms which rotate in a toroidal trapping potential. We evaluate the state of lowest energy for a fixed value of the angular momentum within various approximations of the effectively one-dimensional model and compare our results with the full solution of the three-dimensional problem, thus getting evidence for the accuracy of our model.
28.	Sandin, Patrik, 1980-, et al. (författare) Numerical solution of the stationary multicomponent nonlinear Schrodinger equation with a constraint on the angular momentum 2016 Ingår i: Physical Review E. - : American Physical Society. - 2470-0045. ; 93:3 Tidskriftsartikel (refereegranskat)abstract We formulate a damped oscillating particle method to solve the stationary nonlinear Schrodinger equation (NLSE). The ground-state solutions are found by a converging damped oscillating evolution equation that can be discretized with symplectic numerical techniques. The method is demonstrated for three different cases: for the single-component NLSE with an attractive self-interaction, for the single-component NLSE with a repulsive self-interaction and a constraint on the angular momentum, and for the two-component NLSE with a constraint on the total angular momentum. We reproduce the so-called yrast curve for the single-component case, described in [A. D. Jackson et al., Europhys. Lett. 95, 30002 (2011)], and produce for the first time an analogous curve for the two-component NLSE. The numerical results are compared with analytic solutions and competing numerical methods. Our method is well suited to handle a large class of equations and can easily be adapted to further constraints and components.
29.	Schindler, Maike, 1983-, et al. (författare) Creativity in the eye of the student : Refining investigations of mathematical creativity using eye-tracking goggles 2016 Ingår i: Proceedings of the 40th Conference of the International Group for the Psychology of Mathematics Education (PME). Konferensbidrag (refereegranskat)abstract Mathematical creativity is increasingly important for improved innovation and problem-solving. In this paper, we address the question of how to best investigate mathematical creativity and critically discuss dichotomous creativity scoring schemes. In order to gain deeper insights into creative problem-solving processes, we suggest the use of mobile, unobtrusive eye-trackers for evaluating students’ creativity in the context of Multiple Solution Tasks (MSTs). We present first results with inexpensive eye-tracking goggles that reveal the added value of evaluating students’ eye movements when investigating mathematical creativity—compared to an analysis of written/drawn solutions as well as compared to an analysis of simple videos.
30.	Sørensen, Mads Peter, et al. (författare) The dynamics of magnetic vortices in type II superconductors with pinning sites studied by the time dependent Ginzburg–Landau model 2017 Ingår i: Physica. C, Superconductivity. - Amsterdam : Elsevier. - 0921-4534 .- 1873-2143. ; 533, s. 40-43 Tidskriftsartikel (refereegranskat)abstract We investigate the dynamics of magnetic vortices in type II superconductors with normal state pinning sites using the Ginzburg–Landau equations. Simulation results demonstrate hopping of vortices between pinning sites, influenced by external magnetic fields and external currents. The system is highly nonlinear and the vortices show complex nonlinear dynamical behaviour.
31.	Yu, Yongle, et al. (författare) Supershell structure in trapped dilute Fermi gases 2005 Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 72:5 Tidskriftsartikel (refereegranskat)abstract We show that a dilute harmonically trapped two-component gas of fermionic atoms with a weak repulsive interaction has a pronounced super-shell structure: The shell fillings due to the spherical harmonic trapping potential are modulated by a beat mode. This changes the "magic numbers" occurring between the beat nodes by half a period. The length and amplitude of this beating mode depend on the strength of the interaction. We give a simple interpretation of the beat structure in terms of a semiclassical trace formula for the symmetry breaking U(3)→SO(3).
32.	Ögren, Magnus, 1977-, et al. (författare) A numerical damped oscillator approach to constrained Schrödinger equations 2020 Ingår i: European journal of physics. - : Institute of Physics (IOP). - 0143-0807 .- 1361-6404. ; 41:6 Tidskriftsartikel (refereegranskat)abstract This article explains and illustrates the use of a set of coupled dynamical equations, second order in a fictitious time, which converges to solutions of stationary Schrödinger equations with additional constraints. In fact, the method is general and can solve constrained minimization problems in many fields. We present the method for introductory applications in quantum mechanics including three qualitative different numerical examples: the radial Schrödinger equation for the hydrogen atom; the two-dimensional harmonic oscillator with degenerate excited states; and a non-linear Schrödinger equation for rotating states. The presented method is intuitive, with analogies in classical mechanics for damped oscillators, and easy to implement, either in own coding, or with software for dynamical systems. Hence, we find it suitable to introduce it in a continuation course in quantum mechanics or generally in applied mathematics courses which contain computational parts. The undergraduate student can for example use our derived results and the code (supplemental material) to study the Schrödinger equation in 1D for any potential. The graduate student and the general physicist can work from our three examples to derive their own results for other models including other global constraints.
33.	Ögren, Magnus, 1977-, et al. (författare) An exact lower energy bound for the infinite square well potential 2011 Ingår i: European journal of physics. - : Institute of Physics (IOP). - 0143-0807 .- 1361-6404. ; 32:2, s. L3-L6 Tidskriftsartikel (refereegranskat)abstract We give a lower bound for the energy of a quantum particle in the infinite square well. We show that the bound is exact and identify the well-known element that fulfils the equality. Our approach is not directly dependent on the Schrödinger equation and illustrates an example where the wavefunction is obtained directly by energy minimization. The derivation presented can serve as an example of a variational method in an undergraduate level university course in quantum mechanics.
34.	Ögren, Magnus, 1977-, et al. (författare) Atom-atom correlations in colliding Bose-Einstein condensates 2009 Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 79:2 Tidskriftsartikel (refereegranskat)abstract We analyze atom-atom correlations in the s -wave scattering halo of two colliding condensates. By developing a simple perturbative approach, we obtain explicit analytic results for the collinear (CL) and back-to-back (BB) correlations corresponding to realistic density profiles of the colliding condensates with interactions. The results in the short-time limit are in agreement with the first-principles simulations using the positive- P representation and provide analytic insights into the experimental observations of Perrin [Phys. Rev. Lett. 99, 150405 (2007)]. For long collision durations, we predict that the BB correlation becomes broader than the CL correlation.
35.	Ögren, Magnus, 1977-, et al. (författare) Blick för bättre läromedel? 2012 Ingår i: Manus. - Stockholm : Läromedelsförfattarnas förening. - 2000-4028. ; :2, s. 6-6 Forskningsöversikt (populärvet., debatt m.m.)
36.	Ögren, Magnus, 1977- (författare) ESGI-88 (European Study Group with Industry) workshop on industrial mathematics : Report 2012 Rapport (övrigt vetenskapligt/konstnärligt)
37.	Ögren, Magnus, 1977-, et al. (författare) First-principles quantum dynamics for fermions : Application to molecular dissociation 2010 Ingår i: Europhysics letters. - : European Physical Society. - 0295-5075 .- 1286-4854. ; 92:3 Tidskriftsartikel (refereegranskat)abstract We demonstrate that the quantum dynamics of a many-body Fermi-Bose system can be simulated using a Gaussian phase-space representation method. In particular, we consider the application of the mixed fermion-boson model to ultracold quantum gases and simulate the dynamics of dissociation of a Bose-Einstein condensate of bosonic dimers into pairs of fermionic atoms. We quantify deviations of atom-atom pair correlations from Wick's factorization scheme, and show that atom-molecule and molecule-molecule correlations grow with time, in clear departures from pairing mean-field theories. As a first-principles approach, the method provides benchmarking of approximate approaches and can be used to validate dynamical probes for characterizing strongly correlated phases of fermionic systems.
38.	Ögren, Magnus, 1977- (författare) Klassisk mekanik vs kvantmekanik 2010 Ingår i: Forskning. - Göteborg : Forskningsförlaget. - 1654-8876. ; :3-4, s. 50-54 Forskningsöversikt (populärvet., debatt m.m.)
39.	Ögren, Magnus, 1977- (författare) Local boundary conditions for NMR-relaxation in digitized porous media 2014 Ingår i: The European Physical Journal B. - : Springer Berlin/Heidelberg. - 1434-6028 .- 1434-6036. ; 87:11, s. 255- Tidskriftsartikel (refereegranskat)abstract We narrow the gap between simulations of nuclear magnetic resonance dynamics on digital domains (such as CT-images) and measurements in D-dimensional porous media. We point out with two basic domains, the ball and the cube in D dimensions, that due to a digital uncertainty in representing the real pore surfaces of dimension D − 1, there is a systematic error in simulated dynamics. We then reduce this error by introducing local Robin boundary conditions.
40.	Ögren, Magnus, 1977- (författare) Lärarhandledning [Teacher's manual] till : Kvantvärldens fenomen: teori och begrepp 2006 Bok (övrigt vetenskapligt/konstnärligt)
41.	Ögren, Magnus, 1977-, et al. (författare) Med blick på vektoranalys : Ögonrörelsemätning vid problemlösning 2011 Ingår i: Lärande i LTH. - Lund : Lund Institute of Technology. ; 15, s. 6-7 Forskningsöversikt (populärvet., debatt m.m.)
42.	Ögren, Magnus, 1977-, et al. (författare) Numerical simulations of NMR relaxation in chalk using local Robin boundary conditions 2019 Ingår i: Journal of magnetic resonance. - : Elsevier. - 1090-7807 .- 1096-0856. ; 308 Tidskriftsartikel (refereegranskat)abstract The interpretation of nuclear magnetic resonance (NMR) data is of interest in a number of fields. In Ögren [Eur. Phys. J. B (2014) 87: 255] local boundary conditions for random walk simulations of NMR relaxation in digital domains were presented. Here, we have applied those boundary conditions to large, three-dimensional (3D) porous media samples. We compared the random walk results with known solutions and then applied them to highly structured 3D domains, from images derived using synchrotron radiation CT scanning of North Sea chalk samples. As expected, there were systematic errors caused by digitalization of the pore surfaces so we quantified those errors, and by using linear local boundary conditions, we were able to significantly improve the output. We also present a technique for treating numerical data prior to input into the ESPRIT algorithm for retrieving Laplace components of time series from NMR data (commonly called T-inversion).
43.	Ögren, Magnus, 1977-, et al. (författare) On the dynamics of the Fermi-Bose model 2013 Ingår i: Journal of Physics A. - : Institute of Physics (IOP). - 1751-8113 .- 1751-8121. ; 46:1 Tidskriftsartikel (refereegranskat)abstract We consider the exponential matrix representing the dynamics of the Fermi-Bose model in an undepleted bosonic field approximation. A recent application of this model is molecular dimers dissociating into its atomic compounds. The problem is solved in D spatial dimensions by dividing the system matrix into blocks with generalizations of Hankel matrices, here referred to as D-block-Hankel matrices. The method is practically useful for treating large systems, i.e. dense computational grids or higher spatial dimensions, either on a single standard computer or a cluster. In particular the results can be used for studies of three-dimensional physical systems of arbitrary geometry. We illustrate the generality of our approach by giving numerical results for the dynamics of Glauber type atomic pair correlation functions for a non-isotropic three-dimensional harmonically trapped molecular Bose-Einstein condensate.
44.	Ögren, Magnus, 1977-, et al. (författare) On the spin asymmetry of ground states in trapped two-component Fermi gases with repulsive interactions 2007 Ingår i: Journal of Physics B. - : Institute of Physics (IOP). - 0953-4075 .- 1361-6455. ; 40:13, s. 2653-2660 Tidskriftsartikel (refereegranskat)abstract We examine the spin asymmetry of ground states for two-dimensional, harmonically trapped two-component gases of fermionic atoms at zero temperature with weakly repulsive short-range interactions. Our main result is that, in contrast to the three-dimensional case, in two dimensions a non-trivial spin-asymmetric phase can only be caused by the shell structure. A simple, qualitative description is given in terms of an approximate single-particle model, comparing well to the standard results of Hartree-Fock or direct diagonalization methods.
45.	Ögren, Magnus, 1977- (författare) Predicting the Petrophysical Parameters from the Nanoscale Properties of Chalk 2013 Rapport (övrigt vetenskapligt/konstnärligt)
46.	Ögren, Magnus, 1977- (författare) Problem med lösningar till kvantmekanik : fördjupningskurs 2006 Bok (övrigt vetenskapligt/konstnärligt)
47.	Ögren, Magnus, 1977-, et al. (författare) Role of spatial inhomogeneity in dissociation of trapped molecular condensates 2010 Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 82:1 Tidskriftsartikel (refereegranskat)abstract We theoretically analyze dissociation of a harmonically trapped Bose-Einstein condensate of molecular dimers and examine how the spatial inhomogeneity of the molecular condensate affects the conversion dynamics and the atom-atom pair correlations in the short-time limit. Both fermionic and bosonic statistics of the constituent atoms are considered. Using the undepleted molecular-field approximation, we obtain explicit analytic results for the asymptotic behavior of the second-order correlation functions and for the relative number squeezing between the dissociated atoms in one, two, and three spatial dimensions. Comparison with the numerical results shows that the analytic approach employed here captures the main underlying physics and provides useful insights into the dynamics of dissociation for conversion efficiencies up to 10%. The results show explicitly how the strength of atom-atom correlations and relative number squeezing degrade with the reduction of the size of the molecular condensate.
48.	Ögren, Magnus, 1977-, et al. (författare) Rotational properties of superfluid Fermi-Bose mixtures in a tight toroidal trap 2020 Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 102:1 Tidskriftsartikel (refereegranskat)abstract We consider a mixture of a Bose-Einstein condensate, with a paired Fermi superfluid, confined in a ring potential. We start with the ground state of the two clouds, identifying the boundary between the regimes of their phase separation and phase coexistence. We then turn to the rotational response of the system. In the phase-separated regime, we have center of mass excitation. When the two species coexist, the spectrum has a rich structure, consisting of continuous and discontinuous phase transitions. Furthermore, for a reasonably large population imbalance it develops a clear quasi- periodic behaviour, in addition to the one due to the periodic boundary conditions. It is then favourable for the one component to reside in a plane-wave state, with a homogeneous density distribution, and the problem resembles that of a single-component system.
49.	Ögren, Magnus, 1977-, et al. (författare) Self-consistent Ginzburg-Landau theory for transport currents in superconductors 2012 Ingår i: Physica. C, Superconductivity. - : Elsevier. - 0921-4534 .- 1873-2143. ; 479, s. 157-159 Tidskriftsartikel (refereegranskat)abstract We elaborate on boundary conditions for Ginzburg-Landau (GL) theory in the case of external currents. We implement a self-consistent theory within the finite element method (FEM) and present numerical results for a two-dimensional rectangular geometry. We emphasize that our approach can in principle also be used for general geometries in three-dimensional superconductors. © 2012 Elsevier B.V. All rights reserved.
50.	Ögren, Magnus, 1977-, et al. (författare) Solitary waves in elongated clouds of strongly interacting bosons 2005 Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 72:2 Tidskriftsartikel (refereegranskat)abstract We examine the propagation of solitary waves in elongated clouds of trapped bosonic atoms as the confinement, the strength of the interatomic interaction, and the atom density are varied. We identify three different physical regimes and develop a general formalism that allows us to interpolate between them. Finally we pay special attention to the transition to the Tonks-Girardeau limit of strongly interacting bosons.

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