# JLUdocs

## Dauerhafte URI für den Bereich

JLUdocs ist der Bereich für Open-Access-Publikationen von Mitgliedern und Angehörigen der JLU Gießen.

In JLUdocs können Sie Ihre Textdokumente im Sinne von Open Access frei zugänglich veröffentlichen. Alle Dokumente erhalten einen Digital Object Identifier (DOI) und werden langfristig zugänglich gemacht. Die Dokumente werden zudem in Bibliothekskatalogen und Suchmaschinen nachgewiesen, wodurch sich die Sichtbarkeit Ihrer Publikation deutlich erhöht.

JLUdocs hat die Giessener Elektronische Bibliothek (GEB) abgelöst. Die in GEB publizierten Dokumente finden Sie nun in JLUdocs.

Sie können uns per E-Mail erreichen: jlupub@bibsys.uni-giessen.de

## Stöbern nach

### Auflistung JLUdocs nach Auflistung nach Fachbereich/Einrichtung "FB 07 - Mathematik und Informatik, Physik, Geographie"

Gerade angezeigt 1 - 20 von 992

###### Treffer pro Seite

###### Sortieroptionen

Item 18. Theorietag "Automaten und Formale Sprachen" : Wettenberg-Launsbach bei Gießen 30. September - 2. Oktober 2008(2008)Der Theorietag ist die Jahrestagung der Fachgruppe Automaten und Formale Sprachen der Gesellschaft für Informatik. Er wird seit 1991 von Mitgliedern der Fachgruppe an wechselnden Orten in Deutschland und Österreich veranstaltet. Im Laufe des Theorietags findet auch die jährliche Fachgruppensitzung statt. Seit 1996 wird der Theorietag von einem eintägigen Workshop mit eingeladenen Vorträgen begleitet. Die bisherigen Austragungsorte waren Magdeburg (1991), Kiel (1992), Dagstuhl (1993), Herrsching (1994), Schloß Rauischholzhausen (1995), Cunnersdorf (1996), Barnstorf (1997), Riveris (1998), Schauenburg-Elmshagen (1999), Wien (2000), Wendgräben (2001), Wittenberg (2002), Herrsching (2003), Caputh (2004),Lauterbad (2005), Wien (2006) und Leipzig (2007). Der diesjährige Theorietag wird nach 13 Jahren wieder vom Institut für Informatik der Justus-Liebig-Universität Gießen ausgerichtet. Er findet mit dem vorangestellten Workshop über Selected Topics in Theoretical Computer Science vom 30. September bis zum 2. Oktober 2008 in Wettenberg-Launsbach bei Gießen statt. Teilnehmer aus Belgien, Deutschland, England, Frankreich, Italien, Österreich, Tschechien und Ungarn folgten der Einladung nach Mittelhessen.Item 3D Impedance Modelling of Metal Anodes in Solid-State Batteries − Incompatibility of Pore Formation and Constriction Effect in Physical-Based 1D Circuit Models(2022-09-08) Eckhardt, Janis K.; Fuchs, Till; Burkhardt, Simon; Klar, Peter J.; Janek, Jürgen; Heiliger, ChristianA non-ideal contact at the electrode/solid electrolyte interface of a solid-state battery arising due to pores (voids) or inclusions results in a constriction effect that severely deteriorates the electric transport properties of the battery cell. The lack of understanding of this phenomenon hinders the optimization process of novel components, such as reversible and high-rate metal anodes. Deeper insight into the constriction phenomenon is necessary to correctly monitor interface degradation and to accelerate the successful use of metal anodes in solid-state batteries. Here, we use a 3D electric network model to study the fundamentals of the constriction effect. Our findings suggest that dynamic constriction as a non-local effect cannot be captured by conventional 1D equivalent circuit models and that its electric behavior is not ad hoc predictable. It strongly depends on the interplay of the geometry of the interface causing the constriction and the microscopic transport processes in the adjacent phases. In the presence of constriction, the contribution from the non-ideal (porous) electrode/solid electrolyte interface to the impedance spectrum may exhibit two signals that cannot be explained when the porous interface is described by a physical-based (effective medium theory) 1D equivalent circuit model. In consequence, the widespread assumption of a single interface contribution to the experimental impedance spectrum may be entirely misleading and can cause serious misinterpretation.Item A biologically inspired repair mechanism for neuronal reconstructions with a focus on human dendrites(2024) Groden, Moritz; Moessinger, Hannah M.; Schaffran, Barbara; DeFelipe, Javier; Benavides-Piccione, Ruth; Cuntz, Hermann; Jedlicka, PeterInvestigating and modelling the functionality of human neurons remains challenging due to the technical limitations, resulting in scarce and incomplete 3D anatomical reconstructions. Here we used a morphological modelling approach based on optimal wiring to repair the parts of a dendritic morphology that were lost due to incomplete tissue samples. In Drosophila, where dendritic regrowth has been studied experimentally using laser ablation, we found that modelling the regrowth reproduced a bimodal distribution between regeneration of cut branches and invasion by neighbouring branches. Interestingly, our repair model followed growth rules similar to those for the generation of a new dendritic tree. To generalise the repair algorithm from Drosophila to mammalian neurons, we artificially sectioned reconstructed dendrites from mouse and human hippocampal pyramidal cell morphologies, and showed that the regrown dendrites were morphologically similar to the original ones. Furthermore, we were able to restore their electrophysiological functionality, as evidenced by the recovery of their firing behaviour. Importantly, we show that such repairs also apply to other neuron types including hippocampal granule cells and cerebellar Purkinje cells. We then extrapolated the repair to incomplete human CA1 pyramidal neurons, where the anatomical boundaries of the particular brain areas innervated by the neurons in question were known. Interestingly, the repair of incomplete human dendrites helped to simulate the recently observed increased synaptic thresholds for dendritic NMDA spikes in human versus mouse dendrites. To make the repair tool available to the neuroscience community, we have developed an intuitive and simple graphical user interface (GUI), which is available in the TREES toolbox (www.treestoolbox.org).Item A differential delay equation with a planar attractor(1991) Walther, Hans-OttoItem A Dry-Processed Al2O3/LiAlO2 Coating for Stabilizing the Cathode/Electrolyte Interface in High-Ni NCM-Based All-Solid-State Batteries(2022) Negi, Rajendra S.; Yusim, Yuriy; Pan, Ruijun; Ahmed, Shamail; Volz, Kerstin; Takata, Ryo; Schmidt, Franz; Henss, Anja; Elm, Matthias T.Item A first-order representation of stable models(1998) Eiter, Thomas; Lu, James; Subrahmanian, V.STuri (1991) introduced the important notion of a constrained atom: an atom with associated equality and disequality constraints on its arguments. A set of constrained atoms is a constrained interpretation. We investigate how nonground representations of both the stable model semantics and the wellfounded semantics may be obtained through Turi's approach. The practical implication of this is that the wellfounded model (or the set of stable models) may be partially precomputed at compiletime, resulting in the association of each predicate symbol in the program to a constrained atom. Algorithms to create such models are presented, both for the well founded case, and the case of stable models. Query processing reduces to checking whether each atom in the query is true in a stable model (resp. wellfounded model). This amounts to showing the atom is an instance of one of some constrained atom whose associated constraint is solvable. Various related complexity results are explored, and the impacts of these results are discussed from the point of view of implementing systems that incorporate the stable and wellfounded semantics.Item A fundamental problem of hypothesis testing with finite inventory in e-commerce(2020) Bohle, Dennis; Marynych, Alexander; Meiners, MatthiasItem A kinetic Fokker-Planck algorithm for simulating multiscale gas flows(2022) Hepp, ChristianNumerical, aerodynamic analysis of spacecraft requires the modeling of rarefied hypersonic flows. Such flow regimes are usually dominated by broad shock waves and strong expansion flows. In such areas of the flow the gas is far from its equilibrium state and therefore conventional modeling approaches such as the Euler or Navier-Stokes equations cannot be used. Instead, non-equilibrium modeling approaches must be applied. While most non-equilibrium flow solvers are computationally expensive, a recently introduced kinetic Fokker-Planck (FP) method shows the potential of describing non-equilibrium flows with satisfactory accuracy and, at the same time, significantly reducing computational costs. However, the application of kinetic FP solvers was so far still limited to simple, single species gases. The aim of this study is to extend the capabilities of the kinetic FP approach for describing complex gas flows. Particular attention is paid to the modeling of non-equilibrium aerodynamics, as it is relevant for describing spacecraft related gas flows. Methods for describing polyatomic species as well as gas mixtures within the kinetic FP framework are constructed. All models are intensively validated by comparison to already established numerical methods, as well as in comparison to experimental studies. Excited energy states are modeled by a stochastic jump process described by a master equation. This approach allows the description of both continuous and discrete energy levels. Gas mixtures are modeled based on the hard-sphere and variable hard-sphere collision potentials. For both cases, FP models are constructed for an arbitrary number of species. The efficiency of the described models is investigated and different strategies are proposed to use kinetic FP methods efficiently. The expansion of synthetic air from an axially symmetric orifice is numerically reproduced using the developed models and results are compared with experimental measurements. Although the numerical simulations capture several magnitudes of Knudsen numbers, from the continuum flow in the reservoir up to the free-molecular far field, good agreement between simulation and experiment is seen.Item A Sensitivity Assessment of COSMO-CLM to Different Land Cover Schemes in Convection-Permitting Climate Simulations over Europe(2021) Zhang, Mingyue; Tölle, Merja H.; Hartmann, Eva; Xoplaki, Eleni; Luterbacher, JürgItem A Short Comment on Controlled Context-Free Grammar Derivations(2024-07-04) Holzer, MarkusWe prove that the family of languages generated by regularly controlled grammars with control languages accepted by ordered automata is equal to the family of languages generated by matrix grammars. To our knowledge, this equivalence has been overlooked in the literature.Item A surface-enhanced Raman-spectroscopic study: Verification of the interparticle gap dependence of field enhancement by triangulation of spherical gold nanoparticle trimers(2019) Dort, Katharina; Kroth, Kathrin; Klar, Peter J.Item A theorem on the amplitudes of periodic solutions of delay equations, with an application to bifurcation(1978) Walther, Hans-OttoItem A Time Hierarchy for Bounded One-Way Cellular Automata(2001) Klein, Andreas; Kutrib, MartinItem A uniqueness problem for a nonlinear differential delay equation(1985) Walther, Hans-OttoItem An ab initio approach to spin transport in magnetic tunnel junctions with disorder(2015) Franz, ChristianIn this work we investigate the spin(-dependent) transport in FeCo/MgO/FeCo magnetic tunnel junctions (MTJ) using advanced ab initio methods. Here, a special focus lies on the impact of the disordered alloy leads with varying Co concentration.The central effect in these MTJs is the dependence of the tunneling probability of the conduction electrons on their symmetry character (symmetry selection); this is a result of the epitaxial MgO barrier. In combination with the band structure of the ferromagnetic leads, this leads to a giant tunnel magnetoresistance (TMR) and highly spin-polarized currents. The latter are beneficial for the efficient generation of spin-transfer torque (STT) and other applications. These effects are illustrated in detail for the system with pure iron leads. We also discuss other effects that are important, e.g. the interface resonance states. The discussion is then extended to FeCo leads using a realistic description of the disordered alloys, which includes the effects of disorder scattering. We discuss the interplay of the coherent tunneling and the disorder scattering in the leads and also the effects of the band filling and their impact on the (spin) transport. The TMR and STT are investigated in the full concentration range and for a large range of bias voltages. Here, the consistent study of the MTJ with iron leads provides a starting point and a solid basis for the profound understanding of the observed dependencies. These are traced back to the underlying physical effects and contributing states using a combination of advanced techniques.The theoretical prediction of the giant TMR (Butler 2001), i.e. a large increase in the resistance when switching the alignment of the magnetizations in the ferromagnetic leads from parallel to anti-parallel, has inspired a large interest in coherent MTJs. They are now widely used as magnetic field sensors, e.g. in the read heads of hard disk drives. MTJs are also used in MRAM, where the STT provides an efficient switching mechanism. Further, magnetic tunnel contacts are an important element in many proposed spintronic devices. While experiments usually consider FeCo alloys as lead material, the theoretical investigations so far only considered ordered materials.Here, we discuss the impact of the disordered leads of the MTJs based on ab initio calculations. The transport is described using non-equilibrium Green´s functions. For the disordered leads we use the coherent potential approximation, which provides an efficient and accurate description of the alloys including the effects of disorder scattering. These methods (including the necessary vertex corrections for transport calculations and the restricted alloy averages) are derived and discussed in this work. They provide a detailed picture of the transport processes in the presence of disorder.This shows that the disorder scattering interferes with the symmetry selection in the barrier leading to a reduction of the TMR. However, a detailed investigation reveals that the concentration dependence of the TMR (at zero bias voltage) is controlled by a combination of several effects including also band filling and interface resonance states. At higher bias voltages the TMR is increasingly influenced by minority states above the Fermi-energy with a high tunneling probability. For Co leads these lead to a fast decrease of the TMR with increasing bias voltage.The STT is a torque exerted on the magnetizations by electrons which cross the barrier at non-collinear alignment. The component of the STT in the plane spanned by the magnetizations is most important for the switching and can be accurately described by a model in terms of spin currents. This allows us to understand the concentration and bias dependence in terms of effects which are also observed for the TMR. In particular, this explains the observed linear bias dependence at low bias, which is independent of the concentration, and also the strong asymmetric deviations at large bias and high Co concentrations. The out-of-plane component is an even function of the bias voltage and shows a weak concentration dependence.Item Ab initio calculations of conduction band effective mass parameters of thermoelectric Mg2X1-xYx (X, Y = Si, Ge, Sn) alloys(2020) Guerra-Castro, Juan Manuel; Mahr, Carsten; Giar, Marcel; Czerner, Michael; Heiliger, ChristianItem Ab initio description of disorder effects in layered cathode active materials by the coherent potential approximation(2022) Eckhardt, Janis K; Risius, Philipp E; Czerner, Michael; Heiliger, ChristianDisorder effects in alloys are usually modeled by averaging various supercell calculations considering different positions of the alloy atoms. This approach, however, is only possible as long as the portion of the individual components of the alloy is sufficiently large. Herein, we present an ab initio study considering the lithium insertion material Li1−x[Ni0.33Co0.33Mn0.33]O2 as model system to demonstrate the power of the coherent potential approximation within the Korringa–Kohn–Rostoker Green's function method. This approach enables the description of disorder effects within alloy systems of any composition. It is applied in this study to describe the (de-)intercalation of arbitrary amounts of lithium from the cathode active material. Moreover, we highlight that using either fully optimized structures or experimental lattice parameters and atomic positions both lead to comparable results. Our findings suggest that this approach is also suitable for modeling the electronic structure of state-of-the-art materials such as high-nickel alloys.Item Ab initio description of lattice dynamics in oxide semiconductors(2017) Giar, MarcelAs non-toxic and sustainable materials the system of binary oxide semiconductors Cu2O, Cu4O3, and CuO is in the focus of current research, e.g., for solar-cell applications. The objective of this work is to analyse the vibrational and Raman spectroscopic properties of these binary semiconductors using ab initio methods (density functional theory).The phonon dispersions of polar semiconductors display a splitting in frequency of the longitudinal optical (LO) and transversal optical (TO) infrared active modes (LO-TO splitting) in the limit of vanishing phonon wave vector. This traces back to long-ranged dipole-dipole interactions present in these crystals. The theoretical treatment of these interactions requires the usage of certain correction schemes for the dynamical matrices. Two methods implementing these corrections [Phys. Rev. B 55, 10355 (1997) (Gonze s method); J. Phys.: Condens. Matter 22, 202201 (2010) (Wang s method)] are employed. Gonze s method, which is traditionally in the framework of density function perturbation theory, is shown to be applicable together with the real space method. Both correction schemes are compared using the insulator CaF2 as test system. The evolution of the phonon frequencies of the modes showing LO-TO splitting close to the Brillouin zone centre in many cases is better described by Gonze s method. Wang s method, on the contrary, can introduce artificial features in the phonon dispersion.The phonon dispersion and derived quantities of all three copper oxide phases are calculated and compared to experiment. It becomes particularly clear that the corrections following Gonze s method are necessary to obtain agreement with experimentally determined phonon dispersions. Good agreement with experiment is obtained for the vibrational contributions to the specific heat and the entropy. Based on Gonze s method the velocities of sound are calculated along several directions also yielding good accordance with experiment.The focus of the Raman spectroscopy investigations is on Cu4O3 and CuO. Cu4O3 is not too extensively studied theoretically as well as experimentally, and for CuO different crystal structures must be considered for room temperature (RT) and low temperatures (LT) (below 213 K). While group theory predicts three Raman active modes for CuO at RT additional modes appear in the experimental LT Raman spectrum [Phys. Rev. B 52, R13130 (1995)]. The appearance of the extra Raman active modes can be explained by a local symmetry lowering of the atomic positions compared to the RT structure owing to a change in the antiferromagnetic ordering. Additional measured Raman active modes can be identified in the calculations; more extra modes are calculated than measured, while each of those not visible in experiment shows a small intensity in the calculated Raman spectrum. Additionally, a rather different behaviour of the Raman intensities of the modes common to both the RT and the LT structures as a function of the laser energy is found. For Cu4O3 the dependence of the Raman intensities on the crystal orientation and the chosen polarisations are investigated in detail. Particularly, the totally symmetric A1g mode has noteworthy angular intensity dependence since it depends on the relative phase of the complex-valued Raman tensor elements. The effect of hydrostatic pressure is also studied showing that the frequencies of the Raman active modes are very sensitive to the exerted pressure.