46 research outputs found
Current and State of Charge Estimation of Lithium-Ion Battery Packs Using Distributed Fractional Extended Kalman Filters
In this paper, a method for current and state of charge estimation of lithium-ion battery packs is proposed. On the basis of a fractional 1-RQ equivalent circuit cell model, a string model containing cells in serial connection, and a pack model containing strings in parallel connection is built up. In order to reduce computational costs, the model is distributed string-wise into subsystems. An algorithm using distributed fractional extended Kalman filters is applied to estimate the state of charge of all cells of each string, locally. To avoid costly measurements of numerous currents, a model based calculation is proposed which describes how the total battery current is split up between the strings. The algorithm is tested and validated using measurement data
Phase Structure of Z(3)-Polyakov-Loop Models
We study effective lattice actions describing the Polyakov loop dynamics
originating from finite-temperature Yang-Mills theory. Starting with a
strong-coupling expansion the effective action is obtained as a series of
Z(3)-invariant operators involving higher and higher powers of the Polyakov
loop, each with its own coupling. Truncating to a subclass with two couplings
we perform a detailed analysis of the statistical mechanics involved. To this
end we employ a modified mean field approximation and Monte Carlo simulations
based on a novel cluster algorithm. We find excellent agreement of both
approaches concerning the phase structure of the theories. The phase diagram
exhibits both first and second order transitions between symmetric,
ferromagnetic and anti-ferromagnetic phases with phase boundaries merging at
three tricritical points. The critical exponents nu and gamma at the continuous
transition between symmetric and anti-ferromagnetic phases are the same as for
the 3-state Potts model.Comment: 20 pages, 22 figure
Staggered fermions, zero modes, and flavor-singlet mesons
We examine the taste structure of eigenvectors of the staggered-fermion Dirac
operator. We derive a set of conditions on the eigenvectors of modes with small
eigenvalues (near-zero modes), such that staggered fermions reproduce the 't
Hooft vertex in the continuum limit. We also show that, assuming these
conditions, the correlators of flavor-singlet mesons are free of contributions
singular in , where is the quark mass. This conclusion holds also when
a single flavor of sea quark is represented by the fourth root of the
staggered-fermion determinant. We then test numerically, using the HISQ action,
whether these conditions hold on realistic lattice gauge fields. We find that
the needed structure does indeed emerge.Comment: 24 pages, 21 figures, v2 clarifies a dependence and matches published
versio
Supersymmetry Breaking in Low Dimensional Models
We analyse supersymmetric models that show supersymmetry breaking in one and
two dimensions using lattice methods. Starting from supersymmetric quantum
mechanics we explain the fundamental principles and problems that arise in
putting supersymmetric models onto the lattice. We compare our lattice results
(built upon the non-local SLAC derivative) with numerically exact results
obtained within the Hamiltonian approach. A particular emphasis is put on the
discussion of boundary conditions. We investigate the ground state structure,
mass spectrum, effective potential and Ward identities and conclude that
lattice methods are suitable to derive the physical properties of
supersymmetric quantum mechanics, even with broken supersymmetry. Based on this
result we analyse the two dimensional N=1 Wess-Zumino model with spontaneous
supersymmetry breaking. First we show that (in agreement with earlier
analytical and numerical studies) the SLAC derivative is a sensible choice in
the quenched model, which is nothing but the two dimensional phi^4 model. Then,
we present the very first computation of a renormalised critical coupling for
the complete supersymmetric model. This calculation makes use of Binder
cumulants and is supported by a direct comparison to Ward identity results,
both in the continuum and infinite volume limit. The physical picture is
completed by masses at two selected couplings, one in the supersymmetric phase
and one in the supersymmetry broken phase. Signatures of the Goldstino in the
fermionic correlator are clearly visible in the broken case.Comment: 33 pages, 28 figure
Fermi-Einstein condensation in dense QCD-like theories
While pure Yang-Mills theory feature the centre symmetry, this symmetry is
explicitly broken by the presence of dynamical matter. We study the impact of
the centre symmetry in such QCD-like theories. In the analytically solvable
Schwinger model, centre transitions take place even under extreme conditions,
temperature and/or density, and we show that they are key to the solution of
the Silver-Blaze problem. We then develop an effective SU(3) quark model which
confines quarks by virtue of centre sector transitions. The phase diagram by
confinement is obtained as a function of the temperature and the chemical
potential. We show that at low temperatures and intermediate values for the
chemical potential the centre dressed quarks undergo condensation due to Bose
like statistics. This is the Fermi Einstein condensation. To corroborate the
existence of centre sector transitions in gauge theories with matter, we study
(at vanishing chemical potential) the interface tension in the
three-dimensional Z2 gauge theory with Ising matter, the distribution of the
Polyakov line in the four-dimensional SU(2)-Higgs model and devise a new type
of order parameter which is designed to detect centre sector transitions. Our
analytical and numerical findings lead us to conjecture a new state of cold,
but dense matter in the hadronic phase for which Fermi Einstein condensation is
realised.Comment: 51 pages, 32 figure
The Fermi energy as common parameter to describe charge compensation mechanisms: A path to Fermi level engineering of oxide electroceramics
Chemical substitution, which can be iso- or heterovalent, is the primary strategy to tailor material properties. There are various ways how a material can react to substitution. Isovalent substitution changes the density of states while heterovalent substitution, i.e. doping, can induce electronic compensation, ionic compensation, valence changes of cations or anions, or result in the segregation or neutralization of the dopant. While all these can, in principle, occur simultaneously, it is often desirable to select a certain mechanism in order to determine material properties. Being able to predict and control the individual compensation mechanism should therefore be a key target of materials science. This contribution outlines the perspective that this could be achieved by taking the Fermi energy as a common descriptor for the different compensation mechanisms. This generalization becomes possible since the formation enthalpies of the defects involved in the various compensation mechanisms do all depend on the Fermi energy. In order to control material properties, it is then necessary to adjust the formation enthalpies and charge transition levels of the involved defects. Understanding how these depend on material composition will open up a new path for the design of materials by Fermi level engineering
Thermodynamics of SU(N) Yang-Mills theories in 2+1 dimensions II - The deconfined phase
We present a non-perturbative study of the equation of state in the
deconfined phase of Yang-Mills theories in D=2+1 dimensions. We introduce a
holographic model, based on the improved holographic QCD model, from which we
derive a non-trivial relation between the order of the deconfinement phase
transition and the behavior of the trace of the energy-momentum tensor as a
function of the temperature T. We compare the theoretical predictions of this
holographic model with a new set of high-precision numerical results from
lattice simulations of SU(N) theories with N=2, 3, 4, 5 and 6 colors. The
latter reveal that, similarly to the D=3+1 case, the bulk equilibrium
thermodynamic quantities (pressure, trace of the energy-momentum tensor, energy
density and entropy density) exhibit nearly perfect proportionality to the
number of gluons, and can be successfully compared with the holographic
predictions in a broad range of temperatures. Finally, we also show that, again
similarly to the D=3+1 case, the trace of the energy-momentum tensor appears to
be proportional to T^2 in a wide temperature range, starting from approximately
1.2 T_c, where T_c denotes the critical deconfinement temperature.Comment: 2+36 pages, 10 figures; v2: comments added, curves showing the
holographic predictions included in the plots of the pressure and energy and
entropy densities, typos corrected: version published in JHE
Infektionsquellensuche bei ambulant erworbenen Fällen von Legionärskrankheit
Bei den meisten Fällen von ambulant erworbener Legionärskrankheit (AE-LK) gelingt es auch in inter¬nationalen Studien nicht, die verantwortliche Infek¬tionsquelle nachzuweisen. Ein Ziel der Berliner LeTriWa-Studie („Legionellen in der Trinkwasser-Installation“) war es, herauszufinden, bei wie vielen Fällen evidenzbasiert eine Infektionsquelle identifi¬ziert werden kann. Dazu wurden im Zeitraum 2016 bis 2020 Fälle von AE-LK und Kontrollpersonen rekrutiert, Urin- und tiefe Atemwegsproben untersucht und Befragungen zu potenziellen Expositionen durchgeführt. Zudem wurden verschiedene häusliche und außerhäusliche Infektionsquellen beprobt. Die Zuordnung der potenziellen Infektionsquelle erfolgte mittels einer eigens entwickelten Evidenz-Matrix. Im vorliegenden Teil 1 des Berichts werden zunächst die Hintergründe, Ziele und Methoden der LeTriWa-Studie vorgestellt.Peer Reviewe