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  • 1. Aaboud, M
    et al.
    Kastanas, Konstatinos A.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Sidebo, P. Edvin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Jet reconstruction and performance using particle flow with the ATLAS Detector2017Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 77, nr 7, artikel-id 466Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper describes the implementation and performance of a particle flow algorithm applied to 20.2 fb- 1 of ATLAS data from 8 TeV proton–proton collisions in Run 1 of the LHC. The algorithm removes calorimeter energy deposits due to charged hadrons from consideration during jet reconstruction, instead using measurements of their momenta from the inner tracker. This improves the accuracy of the charged-hadron measurement, while retaining the calorimeter measurements of neutral-particle energies. The paper places emphasis on how this is achieved, while minimising double-counting of charged-hadron signals between the inner tracker and calorimeter. The performance of particle flow jets, formed from the ensemble of signals from the calorimeter and the inner tracker, is compared to that of jets reconstructed from calorimeter energy deposits alone, demonstrating improvements in resolution and pile-up stability.

  • 2.
    Björk, Gunnar
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Information gain when measuring an unknown qubit2018Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 39, nr 1, artikel-id 015403Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In quantum information the fundamental information-containing system is the qubit. A measurement of a single qubit can at most yield one classical bit. However, a dichotomous measurement of an unknown qubit will yield much less information about the qubit state. We use Bayesian inference to compute how much information one progressively gets by making sucessive, individual measurements on an ensemble of identically prepared qubits. Perhaps surprisingly, even if the measurements are arranged so that each measurement yields one classical bit, that is, the two possible measurement outcomes are a priori equiprobable, it takes almost a handful of measurements before one has gained one bit of information about the gradually concentrated qubit probability density. We also show that by following a strategy that reaps the maximum information per measurement, we are led to a mutually unbiased basis as our measurement bases. This is a pleasing, although not entirely surprising, result.

  • 3.
    Dunnett, K.
    et al.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Gorman, M. N.
    Aberystwyth Univ, Dept Phys, Aberystwyth SY23 3BZ, Ceredigion, Wales..
    Bartlett, P. A.
    UCL, Dept Phys & Astron, Gower St, London WC1E 6BT, England..
    Assessing first-year undergraduate physics students' laboratory practices: seeking to encourage research behaviours2019Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 40, nr 1, artikel-id 015702Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Encouraging positive inquiry-focused behaviours within the constraints of a physics teaching laboratory environment can be challenging. Here, we report on an implementation, the 'working grade' ( w-grade), designed to directly assess aspects of students' laboratory practice with the aim of encouraging first-year undergraduate students to look beyond the concept of a correct outcome' to a physics experiment. The w-grade is composed of the five aspects of group work, querying, exploration, attitude and progress which are each marked on a 0, 1, 2, 3 scale. The initial implementation is presented in full as well as a second, simpler variant. The w-grade emphasises and directly rewards inquiry behaviours and students were much more willing to explore the experiments than in previous years.

  • 4.
    Essen, Hanno
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Sten, Johan C-E
    A new look at the pushing force of an electromagnetic wave on a classical charged particle2015Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 36, nr 5, artikel-id 055029Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The interaction between a plane wave and a classical charged particle is reviewed in this paper. A matrix formulation is used to derive the relativistic motion of the particle due to the Lorentz force of a spatially homogeneous time-harmonic radiation field. The Landau-Lifshitz approach to the radiation damping force is then investigated for the same field. In conclusion only the radiation damping accelerates the particle in the direction of the Poynting vector for this type of field. The Lorentz force only leads to an extra constant drift velocity, plus oscillations with the frequency of the field.

  • 5.
    Essén, Hanno
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    An exact formula for electromagnetic momentum in terms of the charge density and the Coulomb gauge vector potential2018Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 39, nr 2, artikel-id 025202Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electromagnetic momentum p=1(4 pi c) integral E x BdV is sometimes approximated by p(0)=(1/c) integral rho AdV, where rho is the charge density and A is the Coulomb gauge vector potential. Here, we show that p(0) is the first term in an exact two-term expression p = p(0)+p(1) where the second term refers to radiation. When the charge density is zero, p = p(1) is the momentum of fields propagating in vacuum. In the presence of charged particles, however, p(0) normally dominates. We argue that p(0) is the natural formula for the electromagnetic momentum when radiation can be neglected. It is shown that this term may in fact be much larger than the purely mechanical contribution from mass times velocity.

  • 6.
    Essén, Hanno
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Comment on 'Modeling the magnetic dipole'2016Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 37, nr 5, artikel-id 058001Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    The model which Seleznyova et al (2016 Eur. J. Phys. 37 025203) claim to consist of two oppositely charged magnetic monopoles is in fact a model of an infinitely thin solenoid.

  • 7.
    Essén, Hanno
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Electrodynamic model connecting superconductor response to magnetic field and to rotation2005Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 26, nr 2, s. 279-285Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Theory and experiment on the London moment is reviewed. A simple mathematical model is motivated and then used to study the responses of a spherical superconductor to an external field and to rotation. It reveals a connection between perfect diamagnetism (Meissner effect) and the London moment. In the model neither of these are exact but the deviation from B = 0 internal field in the former and from B = (2mc/e)Omega in the latter case is described by the same dimensionless parameter. Apart from its pedagogical value the model might throw some light on the controversy surrounding the correction to the London moment.

  • 8.
    Essén, Hanno
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Teoretisk och tillämpad mekanik.
    From least action in electrodynamics to magnetomechanical energy-a review2009Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 30, nr 3, s. 515-539Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    The equations of motion for electromechanical systems are traced back to the fundamental Lagrangian of particles and electromagnetic fields, via the Darwin Lagrangian. When dissipative forces can be neglected the systems are conservative and one can study them in a Hamiltonian formalism. The central concepts of generalized capacitance and inductance coefficients are introduced and explained. The problem of gauge independence of self-inductance is considered. Our main interest is in magnetomechanics, i.e. the study of systems where there is exchange between mechanical and magnetic energy. This throws light on the concept of magnetic energy, which according to the literature has confusing and peculiar properties. We apply the theory to a few simple examples: the extension of a circular current loop, the force between parallel wires, interacting circular current loops and the rail gun. These show that the Hamiltonian, phase space, form of magnetic energy has the usual property that an equilibrium configuration corresponds to an energy minimum.

  • 9.
    Essén, Hanno
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Gravitationally bound ideal gas sphere in Newtonian and in Einsteinian gravity2014Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 35, nr 6, s. 065003-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The gravitational hydrostatic equilibrium of an isothermal ideal gas with pressure proportional to density is investigated. The system is known from the literature as the singular isothermal sphere since it has infinite central density and infinite total mass. In spite of these unphysical features the system is of pedagogical interest since it allows exact mathematical treatment both within Newtonian gravity and within general relativity. The difference between these two theories is nicely illustrated.

  • 10.
    Essén, Hanno
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Teoretisk och tillämpad mekanik.
    Mechanics, cosmology and Mach's principle2013Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 34, nr 1, s. 139-145Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is pointed out that recent cosmological findings seem to support the view that the mass/energy distribution of the universe defines the Newtonian inertial frames, as originally suggested by Mach. The background concepts of inertial frame, Newton's second law and fictitious forces are clarified. A precise definition of Mach's principle is suggested. Then, an approximation to general relativity discovered by Einstein, Infeld and Hoffmann is used and it is found that this precise formulation of Mach's principle is realized provided the mass/energy density of the universe has a specific value. This value turns out to be twice the critical density. The implications of this approximate result are put into context.

  • 11.
    Essén, Hanno
    KTH, Tidigare Institutioner                               , Mekanik.
    Note on the relativistic elastic head-on collision2002Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 23, nr 5, s. 565-568Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A short, elegant, instructive, and explicit solution for the relativistic elastic head-on collision is presented. It uses the invariance of the relative speed and a suitable Lorentz transformation of the total momentum four-vector before and after the collision.

  • 12.
    Essén, Hanno
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Apazidis, Nicholas
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Turning points of the spherical pendulum and the golden ratio2009Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 30, nr 2, s. 427-432Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the turning point problem of a spherical pendulum. The special cases of the simple pendulum and the conical pendulum are noted. For simple initial conditions the solution to this problem involves the golden ratio, also called the golden section, or the golden number. This number often appears in mathematics where you least expect it. To put our result in perspective we briefly discuss its relevance in physics.

  • 13.
    Essén, Hanno
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Nordmark, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    A simple model for the falling cat problem2018Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 39, nr 3, artikel-id 035004Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We introduce a specific four-particle, four degree-of-freedom model and calculate the rotation that can be achieved by purely internal torques and forces, keeping the total angular momentum zero. We argue that the model qualitatively explains much of the ability of a cat to land on its feet even though released from rest upside down.

  • 14.
    Essén, Hanno
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Teoretisk och tillämpad mekanik.
    Nordmark, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Static deformation of a heavy spring due to gravity and centrifugal force2010Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 31, nr 3, s. 603-609Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The static equilibrium deformation of a heavy spring due to its own weight is calculated for two cases: first for a spring hanging in a constant gravitational field, and then for a spring which is at rest in a rotating system where it is stretched by the centrifugal force. Two different models are considered: first a discrete model assuming a finite number of point masses connected by springs of negligible weight, and then the continuum limit of this model. In the second case, the differential equation for the deformation is obtained by demanding that the potential energy is minimized. In this way a simple application of the variational calculus is obtained.

  • 15.
    Essén, Hanno
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Nordmark, Arne B.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Relativistic version of the Feynman-Dyson-Hughes derivation of the Lorentz force law and Maxwell's homogeneous equations2016Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 37, nr 5, artikel-id 055201Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The canonical Poisson bracket algebra of four-dimensional relativistic mechanics is used to derive the equation of motion for a charged particle, with the Lorentz force, and the homogeneous Maxwell equations.

  • 16. Fannon, James
    et al.
    Loiseau, Jean-Christophe
    Valluri, Prashant
    Bethune, Iain
    Naraigh, Lennon O.
    High-performance computational fluid dynamics: a custom-code approach2016Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 37, nr 4, artikel-id 045001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We introduce a modified and simplified version of the pre-existing fully parallelized three-dimensional Navier-Stokes flow solver known as TPLS. We demonstrate how the simplified version can be used as a pedagogical tool for the study of computational fluid dynamics (CFDs) and parallel computing. TPLS is at its heart a two-phase flow solver, and uses calls to a range of external libraries to accelerate its performance. However, in the present context we narrow the focus of the study to basic hydrodynamics and parallel computing techniques, and the code is therefore simplified and modified to simulate pressure-driven single-phase flow in a channel, using only relatively simple Fortran 90 code with MPI parallelization, but no calls to any other external libraries. The modified code is analysed in order to both validate its accuracy and investigate its scalability up to 1000 CPU cores. Simulations are performed for several benchmark cases in pressure-driven channel flow, including a turbulent simulation, wherein the turbulence is incorporated via the large-eddy simulation technique. The work may be of use to advanced undergraduate and graduate students as an introductory study in CFDs, while also providing insight for those interested in more general aspects of high-performance computing.

  • 17.
    Nordmark, Arne B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Teoretisk och tillämpad mekanik.
    Essen, Hanno
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Teoretisk och tillämpad mekanik.
    The comfortable roller coaster-on the shape of tracks with a constant normal force2010Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 31, nr 6, s. 1307-1317Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A particle that moves along a smooth track in a vertical plane is influenced by two forces: gravity and normal force. The force experienced by roller coaster riders is the normal force, so a natural question to ask is, what shape of the track gives a normal force of constant magnitude? Here we solve this problem. It turns out that the solution is related to the Kepler problem; the trajectories in velocity space are conic sections.

  • 18.
    Nordmark, Arne B.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Biomekanik.
    Essén, Hanno
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    The skipping rope curve2007Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 28, nr 2, s. 241-247Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The equilibrium of a flexible inextensible string, or chain, in the centrifugal force field of a rotating reference frame is investigated. It is assumed that the end points are fixed on the rotation axis. The shape of the curve, the skipping rope curve or troposkien, is given by the Jacobi elliptic function sn.

  • 19.
    Nordmark, Arne
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Essén, Hanno
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    An impacting linear three body system2018Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 39, nr 1, artikel-id 015001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study a system of three identical bodies that can move freely on a horizontal track. Initially one body moves and two are at rest. The moving body impacts with one of the resting bodies which then impacts with the third and so on. The impacts are assumed to be characterised by a coefficient of restitution. We investigate the total number of impacts, the final velocities of the bodies, and the final energy of the system in terms of the initial velocity and the coefficient of restitution. The problem, which originates from mechanics textbooks, can be analysed as a discrete dynamical system with three degrees of freedom. The full solution is more subtle that one might expect.

  • 20.
    Nordmark, Arne
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Essén, Hanno
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Reply to Comment on 'An impacting linear three body system'2018Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 39, nr 3, artikel-id 038002Artikel i tidskrift (Övrigt vetenskapligt)
  • 21.
    Sten, Johan C-E
    et al.
    Univ Helsinki, Dept Math & Stat, Helsinki, Finland..
    Essén, Hanno
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    On a tendency of the magnetic field to maximise its energy2019Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 40, nr 3, artikel-id 035202Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We show that a system of movable conductors in which constant currents are maintained will tend to maximise its magnetic energy. Even if it is not a new discovery, very few textbooks present this somewhat counterintuitive result. We outline the underlying theory using the basic laws of electrodynamics and discuss some illuminating examples, among them the law of attraction of parallel currents.

  • 22. Sun, Fei
    et al.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. Zhejiang University, China.
    Reversing the direction of space and inverse Doppler effect in positive refraction index media2017Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 38, nr 1, artikel-id 014003Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A negative refractive index medium, in which all spatial coordinates are reversed (i.e. a left-hand triplet is formed) by a spatial folding transformation, can create many novel electromagnetic phenomena, e.g. backward wave propagation, and inversed Doppler effect (IDE). In this study, we use coordinate rotation transformation to reverse only two spatial coordinates (e.g. x' and y'), while keeping z' unchanged. In this case, some novel phenomena, e.g. radiation-direction-reversing illusions and IDE, can be achieved in a free space region wrapped by the proposed shell without any negative refractive index medium, which is easier for experimental realization and future applications.

  • 23.
    Wang, Wenlong
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Diaz-Mendez, Rogelio
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Capdevila, Raudys
    Univ Politecn Valencia, Dept Appl Math, E-46022 Valencia, Spain..
    Solving the one-dimensional Ising chain via mathematical induction: an intuitive approach to the transfer matrix2019Ingår i: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 40, nr 6, artikel-id 065102Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of this work is to present a formulation to solve the one-dimensional Ising model using the elementary technique of mathematical induction. This formulation is physically clear and leads to the same partition function form as the transfer matrix method, which is a common subject in the introductory courses of statistical mechanics. In this way our formulation is a useful tool to complement the traditional more abstract transfer matrix method. The method can be straightforwardly generalised to other short-range chains, coupled chains and is also computationally friendly. These two approaches provide a more complete understanding of the system, and therefore our work can be of broad interest for undergraduate teaching in statistical mechanics.

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