Results for "Dirk Honecker"

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Theory of magnetic small-angle neutron scattering of two-phase ferromagnetsApr 11 2013Based on micromagnetic theory we have derived analytical expressions for the magnetic small-angle neutron scattering (SANS) cross section of a two-phase particle-matrix-type ferromagnet. The approach---valid close to magnetic saturation---provides access ... More
Probing the stability and magnetic properties of magnetosome chains in freeze-dried magnetotactic bacteriaApr 24 2019\textit{Magnetospirillum gryphiswaldense} contain typically 15-30 magnetite nanoparticles, i.e. magnetosomes, with diameters of around 40\,nm. They are arranged in linear chains inside the bacteria, which makes them a paradigm of 1D magnetic nanostructures. ... More
A Comparative Study of the Magnetization Process of Two-Dimensional AntiferromagnetsFeb 11 1999Plateaux in the magnetization curves of the square, triangular and hexagonal lattice spin-1/2 XXZ antiferromagnet are investigated. One finds a zero magnetization plateau (corresponding to a spin-gap) on the square and hexagonal lattice with Ising-like ... More
The magnetic structure factor of correlated nanoparticle moments in small-angle neutron scatteringApr 12 2019Here, we derive expressions for the magnetic small-angle neutron scattering (SANS) cross section of magnetic nanoparticle ensembles under consideration of a magnetic structure factor. We show that for structurally disordered ensembles with correlated ... More
Rigid D6-branes on T6/[Z(2)xZ(2M)xOmegaR] with discrete torsionOct 28 2010Jan 05 2011We give a complete classification of T6/[Z(2)xZ(2M)xOmegaR] orientifolds on factorisable tori and rigid D6-branes on them. The analysis includes the supersymmetry, RR tadpole cancellation and K-theory conditions and complete massless open and closed string ... More
On axionic dark matter in Type IIA string theoryDec 16 2013Dec 18 2013We investigate viable scenarios with various axions in the context of supersymmetric field theory and in globally consistent D-brane models. The Peccei-Quinn symmetry is associated with an anomalous U(1) symmetry, which acquires mass at the string scale ... More
Complete Gauge Threshold Corrections for Intersecting Fractional D6-Branes: The Z6 and Z6' Standard ModelsOct 06 2009Dec 11 2009We perform a complete analysis of one-loop threshold corrections to the gauge couplings of fractional D6-branes. This includes besides SU(N) also symplectic, orthogonal and massless Abelian gauge factors and the full computation of contributions from ... More
Towards the field theory of the Standard Model on fractional D6-branes on T6/Z6': Yukawa couplings and massesJan 27 2012We present the perturbative Yukawa couplings of the Standard Model on fractional intersecting D6-branes on T6/Z6' and discuss two mechanisms of creating mass terms for the vector-like particles in the matter spectrum, through perturbative three-point ... More
D6-Brane Model Building and Discrete Symmetries on T6/Z(2)xZ(6')xOR with Discrete TorsionMar 27 2013We review several geometric aspects and properties of the orbifold T6/Z(2)xZ(6')xOR with discrete torsion, that are crucial with respect to global model building and the search for discrete gauge symmetries in the context of intersecting D6-brane models. ... More
Discrete Abelian gauge symmetries and axionsFeb 03 2015We combine two popular extensions of beyond the Standard Model physics within the framework of intersecting D6-brane models: discrete Zn symmetries and Peccei-Quinn axions. The underlying natural connection between both extensions is formed by the presence ... More
To Tilt or Not To Tilt: Discrete Gauge Symmetries in Global Intersecting D-Brane ModelsMar 18 2013Sep 25 2013Discrete gauge symmetries in global intersecting D-brane models constrain the exact form of the perturbative as well as non-perturbative superpotential. We derive the complete set of conditions on the existence of discrete Zn gauge symmetries on toroidal ... More
Comment on "Origin of Surface Canting within $\mathrm{Fe}_3\mathrm{O}_4$ Nanoparticles"Nov 20 2014We comment on the Letter "Origin of surface canting within $\mathrm{Fe}_3\mathrm{O}_4$ nanoparticles" by K.L. Krycka et al. [Phys. Rev. Lett. $\bf 113$, 147203 (2014)].
Evidence for the formation of nanoprecipitates with magnetically disordered regions in bulk $\mathrm{Ni}_{50}\mathrm{Mn}_{45}\mathrm{In}_{5}$ Heusler alloysMar 11 2019Shell ferromagnetism is a new functional property of certain Heusler alloys which has been recently observed in $\mathrm{Ni}_{50}\mathrm{Mn}_{45}\mathrm{In}_{5}$. We report the results of a comparative study of the magnetic microstructure of bulk $\mathrm{Ni}_{50}\mathrm{Mn}_{45}\mathrm{In}_{5}$ ... More
Effect of Dzyaloshinski-Moriya interaction on spin-polarized neutron scatteringMay 27 2016For magnetic materials containing many lattice imperfections (e.g., nanocrystalline magnets), the relativistic Dzyaloshinski-Moriya (DM) interaction may result in nonuniform spin textures due to the lack of inversion symmetry at interfaces. Within the ... More
Excitation Spectrum and Correlation Functions of the Z_3-Chiral Potts Quantum Spin ChainSep 28 1994We study the excitation spectrum and the correlation functions of the Z_3- chiral Potts model in the massive high-temperature phase using perturbation expansions and numerical diagonalization. We are mainly interested in results for general chiral angles ... More
The sawtooth chain: From Heisenberg spins to Hubbard electronsJun 05 2008Nov 13 2008We report on recent studies of the spin-half Heisenberg and the Hubbard model on the sawtooth chain. For both models we construct a class of exact eigenstates which are localized due to the frustrating geometry of the lattice for a certain relation of ... More
Analysis of magnetic neutron-scattering data of two-phase ferromagnetsJul 16 2013We have analyzed magnetic-field-dependent small-angle neutron scattering (SANS) data of soft magnetic two-phase nanocomposite ferromagnets in terms of a recent micromagnetic theory for the magnetic SANS cross section [D. Honecker and A. Michels, Phys. ... More
The Importance of Being Rigid: D6-Brane Model Building on T6/Z2xZ6' with Discrete TorsionSep 13 2012Nov 13 2012Model building with rigid D6-branes on the Type IIA orientifold on T6/Z2xZ6' with discrete torsion is considered. The systematic search for models of particle physics is significantly reduced by proving new symmetries among different lattice orientations. ... More
Using the singular value decomposition to extract 2D correlation functions from scattering patternsMar 26 2019We apply the truncated singular value decomposition (SVD) to extract the underlying 2D correlation functions from small-angle scattering patterns. We test the approach by transforming the simulated data of ellipsoidal particles and show that also in case ... More
Magnetization Plateaux in N-Leg Spin LaddersFeb 03 1998Jun 30 1998In this paper we continue and extend a systematic study of plateaux in magnetization curves of antiferromagnetic Heisenberg spin-1/2 ladders. We first review a bosonic field-theoretical formulation of a single XXZ-chain in the presence of a magnetic field, ... More
Transport in quasi one-dimensional spin-1/2 systemsJan 08 2008We present numerical results for the spin and thermal conductivity of one-dimensional (1D) quantum spin systems. We contrast the properties of integrable models such as the spin-1/2 XXZ chain against nonintegrable ones such as frustrated and dimerized ... More
Jordan-Wigner approach to the frustrated spin one-half XXZ chainMay 26 2005Jan 17 2006The Jordan-Wigner transformation is applied to study the ground state properties and dimerization transition in the $J_1-J_2$ $XXZ$ chain. We consider different solutions of the mean-field approximation for the transformed Hamiltonian. Ground state energy ... More
Magnetization Curves of Antiferromagnetic Heisenberg Spin-1/2 LaddersJul 09 1997Nov 06 1997Magnetization processes of spin-1/2 Heisenberg ladders are studied using strong-coupling expansions, numerical diagonalization of finite systems and a bosonization approach. We find that the magnetization exhibits plateaux as a function of the applied ... More
D6-Brane Model Building on Z(2)xZ(6): MSSM-like and Left-Right Symmetric ModelsAug 31 2015We perform a systematic search for globally defined MSSM-like and left-right symmetric models on D6-branes on the T6/Z(2)xZ(6)xOR orientifold with discrete torsion. Our search is exhaustive for models that are independent of the value of the one free ... More
Deformations, Moduli Stabilisation and Gauge Couplings at One-LoopFeb 27 2017We investigate deformations of $\mathbb{Z}_2$ orbifold singularities on the toroidal orbifold $T^6/(\mathbb{Z}_2\times\mathbb{Z}_6)$ with discrete torsion in the framework of Type IIA orientifold model building with intersecting D6-branes wrapping special ... More
Rigour and Rigidity: Systematics on particle physics D6-brane models on Z(2)xZ(6)Sep 03 2014Sep 10 2014We launch a systematic search for phenomenologically appealing string vacua with intersecting D-branes on the promising T6/Z(2)xZ(6)xOR orientifold with discrete torsion. The number of independent background lattices is reduced from six to two by new ... More
Massless Spectra and Gauge Couplings at One-Loop on Non-Factorisable Toroidal OrientifoldsSep 22 2017Nov 14 2017So-called `non-factorisable' toroidal orbifolds can be rewritten in a factorised form as a product of three two-tori by imposing an additional shift symmetry. This finding of Blaszczyk et al., arXiv:1111.5852, provides a new avenue to Conformal Field ... More
An elementary approach to the Daugavet equationDec 12 1994Let $T\dopu C(S)\to C(S)$ be a bounded linear operator. We present a necessary and sufficient condition for the so-called Daugavet equation $$ \|\Id+T\| = 1+\|T\| $$ to hold, and we apply it to weakly compact operators and to operators factoring through ... More
Using Search Engine Technology to Improve Library CatalogsNov 18 2015This chapter outlines how search engine technology can be used in online public access library catalogs (OPACs) to help improve users experiences, to identify users intentions, and to indicate how it can be applied in the library context, along with how ... More
Investigating the X-ray Emission from the Galactic TeV Gamma-ray Source MGRO J1908+06Dec 26 2015MGRO J1908+06 is a bright, extended TeV gamma-ray source located near the Galactic plane. The TeV emission has previously been attributed to the pulsar wind nebula of the radio-faint gamma-ray pulsar PSR J1907+0602 discovered with Fermi. However, studies ... More
AR-Components of domestic finite group schemes: McKay-Quivers and RamificationDec 15 2015For a domestic finite group scheme, we give a direct description of the Euclidean components in its Auslander-Reiten quiver via the McKay-quiver of a finite linearly reductive subgroup scheme of $SL(2)$. Moreover, for a normal subgroup scheme $\mathcal{N}$ ... More
The Influence of Commercial Intent of Search Results on Their Perceived RelevanceNov 18 2015We carried out a retrieval effectiveness test on the three major web search engines (i.e., Google, Microsoft and Yahoo). In addition to relevance judgments, we classified the results according to their commercial intent and whether or not they carried ... More
Google Scholar as a tool for discovering journal articles in library and information scienceNov 18 2015Purpose: The purpose of this paper is to measure the coverage of Google Scholar for the Library and Information Science (LIS) journal literature as identified by a list of core LIS journals from a study by Schloegl and Petschnig (2005). Methods: We checked ... More
Classification of indecomposable modules for finite group schemes of domestic representation typeSep 17 2015Apr 01 2016We investigate the representation theory of domestic group schemes $\mathcal{G}$ over an algebraically closed field of characteristic $p > 2$. We present results about filtrations of induced modules, actions on support varieties, Clifford theory for certain ... More
Existence of localised normal modes in nonlinear latticesJun 25 2015Jul 13 2016We prove the existence of exponentially localised and time-periodic solutions in general nonlinear Hamiltonian lattice systems. Like normal modes, these localised solutions are characterised by collective oscillations at the lattice sites with a uniform ... More
Societal, Economic, Ethical and Legal Challenges of the Digital Revolution: From Big Data to Deep Learning, Artificial Intelligence, and Manipulative TechnologiesApr 15 2015In the wake of the on-going digital revolution, we will see a dramatic transformation of our economy and most of our societal institutions. While the benefits of this transformation can be massive, there are also tremendous risks to our society. After ... More
What can we learn from Knizhnik--Zamolodchikov Equations?Jul 19 2014We discuss structural similarities between Knizhnik--Zamolodchikov equations (in fact, their simplest version needed to introduce the Drinfeld associator) and Dyson--Schwinger equations. We emphasize that the latter allow for a filtration by co-radical ... More
Some mathematical properties of the Bartlett chi ratioOct 17 2013Based on artistic interpretations, art professor Christopher Bartlett (Towson University, USA) suggested introducing a new mathematical constant related to the golden ratio. He called it the chi ratio, as chi follows phi in the Greek alphabet. Without ... More
On the Maxwell Inequalities for Bounded and Convex DomainsNov 09 2013Jul 23 2014For a bounded and convex domain in three dimensions we show that the Maxwell constants are bounded from below and above by Friedrichs' and Poincare's constants.
New Ways to Promote Sustainability and Social Well-Being in a Complex, Strongly Interdependent World: The FuturICT ApproachOct 13 2013FuturICT is one of six proposals currently being considered for support within the European Commission's Flagship Initiative (see Box 1). The vision of the FuturICT project is to develop new science and new information and communication systems that will ... More
A New Kind of Economy is Born - Social Decision-Makers Beat the "Homo Economicus"Sep 28 2013The Internet and Social Media change our way of decision-making. We are no longer the independent decision makers we used to be. Instead, we have become networked minds, social decision-makers, more than ever before. This has several fundamental implications. ... More
Number Series of Atoms, Interatomic Bonds and Interface Bonds Defining Zinc-Blende Nanocrystals as Function of Size, Shape and Surface Orientation: Analytic Tools to Interpret Solid State Spectroscopy DataJul 21 2016Semiconductor nanocrystals (NCs) experience stress and charge transfer by embedding materials or ligands and impurity atoms. In return, the environment of NCs experiences a NC stress response which may lead to matrix deformation and propagated strain. ... More
Observations about Leonardo's drawings for Luca PacioliNov 12 2013Three versions of Luca Pacioli's 'De Dvina Proportione' remain: a manuscript held in Milan, another in Geneva and a printed version edited in Venice. A recent book, 'Antologia della Divina Proporzione', has all three in one volume, allowing an easy comparison ... More
FuturICT - New Science and Technology to Manage Our Complex, Strongly Connected WorldAug 31 2011Oct 03 2011We have built particle accelerators to understand the forces that make up our physical world. But we still don't understand the principles underlying our strongly connected, techno-socio-economic systems. To fill the knowledge gaps and keep up with the ... More
Accelerating Scientific Discovery by Formulating Grand Scientific ChallengesAug 19 2012One important question for science and society is how to best promote scientific progress. Inspired by the great success of Hilbert's famous set of problems, the FuturICT project tries to stimulate and focus the efforts of many scientists by formulating ... More
Directed transient long-range transport in a slowly driven Hamiltonian system of interacting particlesAug 14 2008We study the Hamiltonian dynamics of a one-dimensional chain of linearly coupled particles in a spatially periodic potential which is subjected to a time-periodic mono-frequency external field. The average over time and space of the related force vanishes ... More
SupersymmetryJun 25 2009The determination of supersymmetric parameters at the LHC in favorable as well as difficult scenarios is presented. If discovered and measured at the LHC and the ILC, supersymmetry may provide a link between collider physics and cosmology.
Extraction of SUSY Parameters from Collider DataAug 26 2008Aug 28 2008The extraction of the parameters of the supersymmetric Lagrangian is discusse d. Particular emphasis is put on the rigorous treatment of experimental and theo retical errors. While the LHC can provide a valuable first estimate of the parameters, the combination ... More
Extracting the fundamental parametersSep 30 2009If supersymmetry is discovered at the LHC, the extraction of the fundamental parameters will be a formidable task. In such a system where measurements depend on different combinations of the parameters in a highly correlated system, the identification ... More
The residues of quantum field theory - numbers we should knowApr 13 2004Apr 23 2004We discuss in an introductory manner structural similarities between the polylogarithm and Green functions in quantum field theory.
New mathematical structures in renormalizable quantum field theoriesNov 14 2002Nov 26 2002Computations in renormalizable perturbative quantum field theories reveal mathematical structures which go way beyond the formal structure which is usually taken as underlying quantum field theory. We review these new structures and the role they can ... More
How useful can knot and number theory be for loop calculations?Jul 17 1998We summarize recent results connecting multiloop Feynman diagram calculations to different parts of mathematics, with special attention given to the Hopf algebra structure of renormalization.
Factorization in quantum field theory: an exercise in Hopf algebras and local singularitiesJun 03 2003Jun 10 2003I discuss the role of Hochschild cohomology in Quantum Field Theory with particular emphasis on Dyson--Schwinger equations.
The Earth's Gamma-ray Albedo as observed by EGRETOct 20 2004The Earth's high energy gamma-ray emission is caused by cosmic ray interactions with the atmosphere. The EGRET detector on-board the CGRO satellite is only the second experiment (after SAS-2) to provide a suitable dataset for the comprehensive study of ... More
Faster Background Determination - a method for gaining time coverage and flux measurement accuracy with Cherenkov telescopesApr 28 2003An improved way of taking off-source data for background determination in Cherenkov telescope observations is proposed. Generalizing the traditional concept of taking on-source/off-source observations of equal duration (e.g. 30 minutes ON followed by ... More
Validation of internal rating systems and PD estimatesJun 07 2006This paper elaborates on the validation requirements for rating systems and probabilities of default (PDs) which were introduced with the New Capital Standards (Basel II). We start in Section 2 with some introductory remarks on the topics and approaches ... More
Modeling and Simulation of Multi-Lane Traffic FlowJun 09 1998A most important aspect in the field of traffic modeling is the simulation of bottleneck situations. For their realistic description a macroscopic multi-lane model for uni-directional freeways including acceleration, deceleration, velocity fluctuations, ... More
Empirical Traffic Data and Their Implications for Traffic ModelingJun 04 1998From single vehicle data a number of new empirical results about the temporal evolution, correlation, and density-dependence of macroscopic traffic quantities have been determined. These have relevant implications for traffic modeling and allow to test ... More
Derivation of a Fundamental Diagram for Urban Traffic FlowJul 11 2008Feb 04 2009Despite the importance of urban traffic flows, there are only a few theoretical approaches to determine fundamental relationships between macroscopic traffic variables such as the traffic density, the utilization, the average velocity, and the travel ... More
Production, Supply, and Traffic Systems: A Unified DescriptionJan 23 2004The transport of products between different suppliers or production units can be described similarly to driven many-particle and traffic systems. We introduce equations for the flow of goods in supply networks and the adaptation of production speeds. ... More
A Section-Based Queueing-Theoretical Traffic Model for Congestion and Travel Time Analysis in NetworksJul 01 2003Dec 14 2003While many classical traffic models treat the spatial extension of streets continuously or by discretization into cells of a certain length, we will subdivide roads into comparatively long homogeneous road sections of constant capacity with an inhomogeneity ... More
Modeling Supply Chains and Business Cycles as Unstable Transport PhenomenaJan 13 2003Physical concepts developed to describe instabilities in traffic flows can be generalized in a way that allows one to understand the well-known instability of supply chains (the so-called ``bullwhip effect''). That is, small variations in the consumption ... More
Structure and Instability of High-Density Equations for Traffic FlowJun 10 1998Similar to the treatment of dense gases, fluid-dynamic equations for the dynamics of congested vehicular traffic are derived from Enskog-like kinetic equations. These contain additional terms due to the anisotropic vehicle interactions. The calculations ... More
A stochastic behavioral model and a `microscopic' foundation of evolutionary game theoryMay 26 1998A stochastic model for behavioral changes by imitative pair interactions of individuals is developed. `Microscopic' assumptions on the specific form of the imitative processes lead to a stochastic version of the game dynamical equations. That means, the ... More
Injective Spaces via AdjunctionApr 02 2008Our work over the past years shows that not only the collection of (for instance) all topological spaces gives rise to a category, but also each topological space can be seen individually as a category by interpreting the convergence relation $\mathfrak{x}\to ... More
Chen's Iterated Integral represents the Operator Product ExpansionJan 21 1999Sep 18 1999The recently discovered formalism underlying renormalization theory, the Hopf algebra of rooted trees, allows to generalize Chen's lemma. In its generalized form it describes the change of a scale in Green functions, and hence relates to the operator ... More
Analysing the Robustness of Evolutionary Algorithms to Noise: Refined Runtime Bounds and an Example Where Noise is BeneficialDec 03 2018We analyse the performance of well-known evolutionary algorithms (1+1)EA and (1+$\lambda$)EA in the prior noise model, where in each fitness evaluation the search point is altered before evaluation with probability $p$. We present refined results for ... More
Parallel Focal Structure and Singular Riemannian FoliationsMar 02 2004Jun 15 2004We prove that a submanifold with parallel focal structure, which is a generalization of isoparametric and equifocal submanifolds, induces a singular Riemannian foliation of the ambient space by its parallel and focal manifolds.
The art of probability-of-default curve calibrationDec 15 2012Nov 26 2013PD curve calibration refers to the transformation of a set of rating grade level probabilities of default (PDs) to another average PD level that is determined by a change of the underlying portfolio-wide PD. This paper presents a framework that allows ... More
Conditional Expectation as Quantile DerivativeApr 19 2001For a linear combination of random variables, fix some confidence level and consider the quantile of the combination at this level. We are interested in the partial derivatives of the quantile with respect to the weights of the random variables in the ... More
Algebraic Structures in local QFTJul 02 2010A review of the Hodge and Hopf-algebraic approach to QFT.
The dissipation distance for a 2D single crystal with two symmetric slip systemsJul 22 2002We solve a model problem from single crystal plasticity.We consider 4 slip systems in the plane with orthogonal slip-directions and equal slip rates, forward as well as backwards. We compute the associated dissipation distance by solving an optimal control ... More
Bounded solutions to backward SDE's with jumps for utility optimization and indifference hedgingFeb 14 2007We prove results on bounded solutions to backward stochastic equations driven by random measures. Those bounded BSDE solutions are then applied to solve different stochastic optimization problems with exponential utility in models where the underlying ... More
Parameter curves for the regular representations of tame bimodulesDec 19 2007Jun 16 2008We present results and examples which show that the consideration of a certain tubular mutation is advantageous in the study of noncommutative curves which parametrize the simple regular representations of a tame bimodule. We classify all tame bimodules ... More
Some integral representations and limits for (products of) the parabolic cylinder functionMay 08 2015May 26 2015Veestraeten [1] recently derived inverse Laplace transforms for Laplace transforms that contain products of two parabolic cylinder functions by exploiting the link between the parabolic cylinder function and the transition density and distribution functions ... More
Nigel Kalton's work in isometrical Banach space theoryMar 16 2011This paper surveys some of the late Nigel Kalton's contributions to Banach space theory. The paper is written for the Nigel Kalton Memorial Website, which is scheduled to go online in summer 2011.
Capital allocation for credit portfolios with kernel estimatorsDec 16 2006May 11 2008Determining contributions by sub-portfolios or single exposures to portfolio-wide economic capital for credit risk is an important risk measurement task. Often economic capital is measured as Value-at-Risk (VaR) of the portfolio loss distribution. For ... More
Locality, QED and Classical ElectrodynamicsOct 05 1998We report on some conceptual changes in our present understanding of Quantum Field Theory and muse about possible consequences for the understanding of $v>c$ signals.
Three Etudes in QFTSep 24 2009We review QFT from the algebraic structure of its perturbative expansion and point out three new results.
The core Hopf algebraFeb 07 2009We study the core Hopf algebra underlying the renormalization Hopf algebra.
Anatomy of a gauge theorySep 17 2005Feb 08 2006We exhibit the role of Hochschild cohomology in quantum field theory with particular emphasis on gauge theory and Dyson--Schwinger equations, the quantum equations of motion. These equations emerge from Hopf- and Lie algebra theory and free quantum field ... More
What is the trouble with Dyson--Schwinger equations?Jul 02 2004We discuss similarities and differences between Green Functions in Quantum Field Theory and polylogarithms. Both can be obtained as solutions of fixpoint equations which originate from an underlying Hopf algebra structure. Typically, the equation is linear ... More
Feynman Diagram Calculations - From finite Integral Representations to knotted InfinitiesMay 05 1995May 07 1995Work is reported on finite integral representations for 2-loop massive 2-, 3- and 4-point functions, using orthogonal and parallel space variables. It is shown that this can be utilized to cover particles with arbitrary spin (tensor integrals), and that ... More
Threshold corrections to the gamma t anti-t vertex at O(alpha alpha(s))Feb 18 2009In these proceedings a recent calculation of the last missing piece of the two-loop O(alpha alpha(s)) corrections to gamma t anti-t vertex at the t anti-t threshold due to the exchange of a W boson and a gluon is summarised. The calculation constitutes ... More
Statistical Properties of Narrow-Line Seyfert 1 galaxiesMay 08 2000The number of publications considering Narrow-Line Seyfert 1 galaxies has increased dramatically in recent years. Especially after the launch of the X-ray missions ROSAT and ASCA, Narrow-Line Seyfert 1s have become very popular. In these proceedings I ... More
Many-spinon states and representations of Yangians in the SU(n) Haldane--Shastry modelNov 09 2007Nov 24 2007We study the relation of Yangians and spinons in the SU(n) Haldane--Shastry model. The representation theory of the Yangian is shown to be intimately related to the fractional statistics of the spinons. We construct the spinon Hilbert space from tensor ... More
From Microscopic to Macroscopic Traffic ModelsJun 14 1998The paper presents a systematic derivation of macroscopic equations for freeway traffic flow from an Enskog-like kinetic approach. The resulting fluid-dynamic traffic equations for the spatial density, average velocity, and velocity variance of vehicles ... More
Fundamentals of Traffic FlowJun 05 1998From single vehicle data a number of new empirical results concerning the density-dependence of the velocity distribution and its moments as well as the characteristics of their temporal fluctuations have been determined. These are utilized for the specification ... More
A Mathematical Model for Behavioral Changes by Pair Interactions and Its Relation to Game TheoryMay 08 1998A mathematical model for behavioral changes by pair interactions (i.e. due to direct contact) of individuals is developed. Three kinds of pair interactions can be distinguished: Imitative processes, avoidance processes, and compromising processes. Representative ... More
Modeling Supply Networks and Business Cycles as Unstable Transport PhenomenaJul 15 2003Physical concepts developed to describe instabilities in traffic flows can be generalized in a way that allows one to understand the well-known instability of supply chains (the so-called ``bullwhip effect''). That is, small variations in the consumption ... More
Gas-kinetic derivation of Navier-Stokes-like traffic equationsJun 02 1998Macroscopic traffic models have recently been severely criticized to base on lax analogies only and to have a number of deficiencies. Therefore, this paper shows how to construct a logically consistent fluid-dynamic traffic model from basic laws for the ... More
Stochastic and Boltzmann-like models for behavioral changes, and their relation to game theoryMay 22 1998In the last decade, stochastic models have shown to be very useful for quantitative modelling of social processes. Here, a configurational master equation for the description of behavioral changes by pair interactions of individuals is developed. Three ... More
A Mathematical Model for the Behavior of Individuals in a Social FieldMay 15 1998Related to an idea of Lewin, a mathematical model for behavioral changes under the influence of a social field is developed. The social field reflects public opinion, social norms and trends. It is not only given by external factors (the environment) ... More
A Mathematical Model for Attitude Formation by Pair InteractionsMay 12 1998Two complementary mathematical models for attitude formation are considered: Starting from the model of Weidlich and Haag (1983), which assumes indirect interactions that are mediated by a mean field, a new model is proposed, which is characterized by ... More
Derivation and Empirical Validation of a Refined Traffic Flow ModelMay 12 1998The gas-kinetic foundation of fluid-dynamic traffic equations suggested in previous papers [Physica A 219, 375 and 391 (1995)] is further refined by applying the theory of dense gases and granular materials to the Boltzmann-like traffic model by Paveri-Fontana. ... More
Estimating discriminatory power and PD curves when the number of defaults is smallMay 24 2009Mar 05 2010The intention with this paper is to provide all the estimation concepts and techniques that are needed to implement a two-phases approach to the parametric estimation of probability of default (PD) curves. In the first phase of this approach, a raw PD ... More
Expected Shortfall and BeyondMar 27 2002Oct 20 2002Financial institutions have to allocate so-called "economic capital" in order to guarantee solvency to their clients and counter parties. Mathematically speaking, any methodology of allocating capital is a "risk measure", i.e. a function mapping random ... More
Generation of narrow peaks in charged-particle magnetic spectroscopyAug 12 2015Oct 14 2015In spectroscopy of charged particles, narrow peaks may appear in initially smooth continuous spectra if magnetic transport of the particles is involved. As such unexpected peaks may be misinterpreted as new physics, their generation is investigated for ... More
On the inverse transform of Laplace transforms that contain (products of) the parabolic cylinder functionMay 21 2015The Laplace transforms of the transition probability density and distribution functions for the Ornstein-Uhlenbeck process contain the product of two parabolic cylinder functions, namely D_{v}(x)D_{v}(y) and D_{v}(x)D_{v-1}(y), respectively. The inverse ... More
Responding to complexity in socio-economic systems: How to build a smart and resilient society?Apr 15 2015The world is changing at an ever-increasing pace. And it has changed in a much more fundamental way than one would think, primarily because it has become more connected and interdependent than in our entire history. Every new product, every new invention ... More