Max Planck Institute for Mathematics in the Sciences

Leipzig, Germany

Max Planck Institute for Mathematics in the Sciences

Leipzig, Germany

The Max Planck Institute for Mathematics in the science in Leipzig was founded on March 1, 1996.At the institute scientists work on projects which apply mathematics in various areas of natural science, in particular physics, biology, chemistry and material science.Main research areas are Scientific computing , Pattern formation, energy landscapes and scaling laws Riemannian, Kählerian and algebraic geometry , neuronal networks ,The institute has an extensive visitors programme which had made Leipzig a main place for research in applied mathematics. Wikipedia.

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Neukamm S.,Max Planck Institute for Mathematics in the Sciences
Archive for Rational Mechanics and Analysis | Year: 2012

We present a rigorous derivation of a homogenized, bending-torsion theory for inextensible rods from three-dimensional nonlinear elasticity in the spirit of Γ -convergence. We start with the elastic energy functional associated with a nonlinear composite material, which in a stress-free reference configuration occupies a thin cylindrical domain with thickness h ≪ 1. We consider composite materials that feature a periodic microstructure with period ε ≪ 1. We study the behavior as ε and h simultaneously converge to zero and prove that the energy (scaled by h -4) Γ -converges towards a non-convex, singular energy functional. The energy is finite only for configurations that correspond to pure bending and twisting of the rod. In this case, the energy is quadratic in curvature and torsion. Our derivation leads to a new relaxation formula that uniquely determines the homogenized coefficients. It turns out that their precise structure additionally depends on the ratio h/ε and, in particular, different relaxation formulas arise for h ≪ ε, ε ~ h and ε ≪ h. Although the initial elastic energy functional and the limiting functional are nonconvex, our analysis leads to a relaxation formula that is quadratic and involves only relaxation over a single cell. Moreover, we derive an explicit formula for isotropic materials in the cases h ≪ ε and h ≫ ε, and prove that the Γ -limits associated with homogenization and dimension reduction in general do not commute. © 2012 Springer-Verlag.

Oikonomou V.K.,Max Planck Institute for Mathematics in the Sciences
Nuclear Physics B | Year: 2013

We study N=2 supersymmetric Chern-Simons Higgs models in (2+1)-dimensions and the existence of extended underlying supersymmetric quantum mechanics algebras. Our findings indicate that the fermionic zero modes quantum system in conjunction with the system of zero modes corresponding to bosonic fluctuations, are related to an N=4 extended 1-dimensional supersymmetric algebra with central charge, a result closely connected to the N=2 spacetime supersymmetry of the total system. We also add soft supersymmetric terms to the fermionic sector in order to examine how this affects the index of the corresponding Dirac operator, with the latter characterizing the degeneracy of the solitonic solutions. In addition, we analyze the impact of the underlying supersymmetric quantum algebras to the zero mode bosonic fluctuations. This is relevant to the quantum theory of self-dual vortices and particularly for the symmetries of the metric of the space of vortices solutions and also for the non-zero mode states of bosonic fluctuations. © 2013 Elsevier B.V.

Oikonomou V.K.,Max Planck Institute for Mathematics in the Sciences
General Relativity and Gravitation | Year: 2013

We present an exponential F(R) modified gravity model in the Jordan and the Einstein frame. We use a general approach in order to investigate and demonstrate the viability of the model. Apart from the general features that this model has, which actually render it viable at a first step, we address the issues of finite time singularities, Newton's law corrections and the scalaron mass. As we will evince, the model passes these latter two tests successfully and also has no finite time singularities, a feature inherent to other well studied exponential models. © 2013 Springer Science+Business Media New York.

Rauh J.,Max Planck Institute for Mathematics in the Sciences
IEEE Transactions on Information Theory | Year: 2011

This paper investigates maximizers of the information divergence from an exponential family E. It is shown that the rI-projection of a maximizer P to E is a convex combination of P and a probability measure P- with disjoint support and the same value of the sufficient statistics A. This observation can be used to transform the original problem of maximizing D(·∥E) over the set of all probability measures into the maximization of a function Dr over a convex subset of ker A. The global maximizers of both problems correspond to each other. Furthermore, finding all local maximizers of D̄r yields all local maximizers of D(·∥E). This paper also proposes two algorithms to find the maximizers of D̄r and applies them to two examples, where the maximizers of D(·∥E) were not known before. © 2011 IEEE.

Bacak M.,Max Planck Institute for Mathematics in the Sciences
SIAM Journal on Optimization | Year: 2014

The geometric median as well as the Fréchet mean of points in a Hadamard space are important in both theory and applications. Surprisingly, no algorithms for their computation are hitherto known. To address this issue, we use a splitting version of the proximal point algorithm for minimizing a sum of convex functions and prove that this algorithm produces a sequence converging to a minimizer of the objective function, which extends a recent result of Bertsekas [Math. Program., 129(2011), pp. 163-195] into Hadamard spaces. The method is quite robust, and not only does it yield algorithms for the median and the mean, but also it applies to various other optimization problems. We, moreover, show that another algorithm for computing the Fréchet mean can be derived from the law of large numbers due to Sturm [Ann. Probab., 30(2002), pp. 1195-1222]. In applications, computing medians and means is probably most needed in tree space, which is an instance of a Hadamard space, invented by Billera, Holmes, and Vogtmann [Adv. in Appl. Math., 27(2001), pp. 733-767] as a tool for averaging phylogenetic trees. Since there now exists a polynomialtime algorithm for computing geodesics in tree space due to Owen and Provan [IEEE/ACM Trans. Comput. Biol. Bioinform., 8(2011), pp. 2-13], we obtain efficient algorithms for computing medians and means of trees, which can be directly used in practice. © 2014 Societ y for Industrial and Applied Mathematics.

Background: In visual psychophysics, precise display timing, particularly for brief stimulus presentations, is often required. The aim of this study was to systematically review the commonly applied methods for the computation of stimulus durations in psychophysical experiments and to contrast them with the true luminance signals of stimuli on computer displays. Methodology/Principal Findings: In a first step, we systematically scanned the citation index Web of Science for studies with experiments with stimulus presentations for brief durations. Articles which appeared between 2003 and 2009 in three different journals were taken into account if they contained experiments with stimuli presented for less than 50 milliseconds. The 79 articles that matched these criteria were reviewed for their method of calculating stimulus durations. For those 75 studies where the method was either given or could be inferred, stimulus durations were calculated by the sum of frames (SOF) method. In a second step, we describe the luminance signal properties of the two monitor technologies which were used in the reviewed studies, namely cathode ray tube (CRT) and liquid crystal display (LCD) monitors. We show that SOF is inappropriate for brief stimulus presentations on both of these technologies. In extreme cases, SOF specifications and true stimulus durations are even unrelated. Furthermore, the luminance signals of the two monitor technologies are so fundamentally different that the duration of briefly presented stimuli cannot be calculated by a single method for both technologies. Statistics over stimulus durations given in the reviewed studies are discussed with respect to different duration calculation methods. Conclusions/Significance: The SOF method for duration specification which was clearly dominating in the reviewed studies leads to serious misspecifications particularly for brief stimulus presentations. We strongly discourage its use for brief stimulus presentations on CRT and LCD monitors. © 2010 Tobias Elze.

Mlynarski W.,Max Planck Institute for Mathematics in the Sciences
PLoS Computational Biology | Year: 2015

In mammalian auditory cortex, sound source position is represented by a population of broadly tuned neurons whose firing is modulated by sounds located at all positions surrounding the animal. Peaks of their tuning curves are concentrated at lateral position, while their slopes are steepest at the interaural midline, allowing for the maximum localization accuracy in that area. These experimental observations contradict initial assumptions that the auditory space is represented as a topographic cortical map. It has been suggested that a “panoramic” code has evolved to match specific demands of the sound localization task. This work provides evidence suggesting that properties of spatial auditory neurons identified experimentally follow from a general design principle- learning a sparse, efficient representation of natural stimuli. Natural binaural sounds were recorded and served as input to a hierarchical sparse-coding model. In the first layer, left and right ear sounds were separately encoded by a population of complex-valued basis functions which separated phase and amplitude. Both parameters are known to carry information relevant for spatial hearing. Monaural input converged in the second layer, which learned a joint representation of amplitude and interaural phase difference. Spatial selectivity of each second-layer unit was measured by exposing the model to natural sound sources recorded at different positions. Obtained tuning curves match well tuning characteristics of neurons in the mammalian auditory cortex. This study connects neuronal coding of the auditory space with natural stimulus statistics and generates new experimental predictions. Moreover, results presented here suggest that cortical regions with seemingly different functions may implement the same computational strategy-efficient coding. © 2015 Wiktor Młynarski.

Stephan W.,Max Planck Institute for Mathematics in the Sciences
Communications in Mathematical Physics | Year: 2014

We study the inverse problem of inferring the state of a finite-level quantum system from expected values of a fixed set of observables, by maximizing a continuous ranking function. We have proved earlier that the maximum-entropy inference can be a discontinuous map from the convex set of expected values to the convex set of states because the image contains states of reduced support, while this map restricts to a smooth parametrization of a Gibbsian family of fully supported states. Here we prove for arbitrary ranking functions that the inference is continuous up to boundary points. This follows from a continuity condition in terms of the openness of the restricted linear map from states to their expected values. The openness condition shows also that ranking functions with a discontinuous inference are typical. Moreover it shows that the inference is continuous in the restriction to any polytope which implies that a discontinuity belongs to the quantum domain of non-commutative observables and that a geodesic closure of a Gibbsian family equals the set of maximum-entropy states. We discuss eight descriptions of the set of maximum-entropy states with proofs of accuracy and an analysis of deviations. © 2014 Springer-Verlag Berlin Heidelberg.

Oikonomou V.K.,Max Planck Institute for Mathematics in the Sciences
Classical and Quantum Gravity | Year: 2014

We study fermionic fields localized on topologically unstable domain walls bounded by strings in a grand unified theory theoretical framework. Particularly, we found that the localized fermionic degrees of freedom, which are up and down-quarks as well as charged leptons, are connected to three independent N = 2, d = 1 supersymmetric quantum mechanics algebras. As we demonstrate, these algebras can be combined to form higher order representations of N = 2, d = 1 supersymmetry. Due to the uniform coupling of the domain wall solutions to the down-quarks and leptons, we also show that a higher order N = 2, d = 1 representation of the down-quark-lepton system is invariant under a duality transformation between the couplings. In addition, the two N = 2, d = 1 supersymmetries of the down-quark-lepton system, combine at the coupling unification scale to form an N = 4, d = 1 supersymmetry. Furthermore, we present the various extra geometric and algebraic attributes that the fermionic systems acquire, owing to the underlying N = 2, d = 1 algebras. © 2014 IOP Publishing Ltd.

Khoromskij B.N.,Max Planck Institute for Mathematics in the Sciences
Chemometrics and Intelligent Laboratory Systems | Year: 2012

In the present paper, we give a survey of the recent results and outline future prospects of the tensor-structured numerical methods in applications to multidimensional problems in scientific computing. The guiding principle of the tensor methods is an approximation of multivariate functions and operators relying on a certain separation of variables. Along with the traditional canonical and Tucker models, we focus on the recent quantics-TT tensor approximation method that allows to represent N-d tensors with log-volume complexity, O(d log N). We outline how these methods can be applied in the framework of tensor truncated iteration for the solution of the high-dimensional elliptic/parabolic equations and parametric PDEs. Numerical examples demonstrate that the tensor-structured methods have proved their value in application to various computational problems arising in quantum chemistry and in the multi-dimensional/parametric FEM/BEM modeling-the tool apparently works and gives the promise for future use in challenging high-dimensional applications. © 2011 Elsevier B.V.

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