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Julich, Germany

Forschungszentrum Jülich GmbH is a member of the Helmholtz Association of German Research Centres and is one of the largest interdisciplinary research centres in Europe. It was founded on 11 December 1956 by the state of North Rhine-Westphalia as a registered association, before it became "Kernforschungsanlage Jülich GmbH" or Nuclear Research Centre Jülich in 1967. In 1990, the name of the association was changed to "Forschungszentrum Jülich GmbH". It has close collaborations with RWTH Aachen in the form of Jülich-Aachen Research Alliance . Wikipedia.

Weber K.,EnBW | Martinsen D.,Julich Research Center
Fuzzy Sets and Systems | Year: 2013

The transformation of existing energy systems into sustainable energy systems is a task which is related to several of the most urgent global problems, e.g. security of energy supply, shortage of resources, and climate change. Energy system modeling has played an important role in the computation of optimal possible future energy systems. In particular, technology oriented bottom-up energy system models have given insight into the required evolution of the energy technology mix. In face of the discussion about climate change, energy systems analysis has focused on the calculation of cost minimal energy futures subject to greenhouse gas mitigation paths, especially CO2 mitigation paths. IKARUS-LP is a model of the German energy system which has been used for optimization tasks of this type. As CO2 mitigation covers only one facet of sustainability, IKARUS-LP has been enhanced to optimize the German energy system for various sustainability targets specified by energy indicators for sustainable development. The resulting model is a fuzzy linear program, IKARUS-FLP. It computes an optimal compromise between the partly contradictory sustainability targets and system cost minimization. In this paper we introduce this model. Emphasis is given to the derivation of the crisp equivalent of the fuzzy problem. We show that a context-based semantics of fuzzy constraints is not adequate and found our semantics on the fuzzy extension principle. In a real-world case study for a time horizon until 2030 the mitigation path approach of IKARUS-LP and the sustainability optimization approach of IKARUS-FLP are compared. The results prove the feasibility of our new approach and its usefulness. © 2012 Elsevier B.V.

Lohse M.,Max Planck Institute of Molecular Plant Physiology | Bolger A.M.,Max Planck Institute of Molecular Plant Physiology | Nagel A.,Max Planck Institute of Molecular Plant Physiology | Fernie A.R.,Max Planck Institute of Molecular Plant Physiology | And 5 more authors.
Nucleic Acids Research | Year: 2012

Recent rapid advances in next generation RNA sequencing (RNA-Seq)-based provide researchers with unprecedentedly large data sets and open new perspectives in transcriptomics. Furthermore, RNA-Seq-based transcript profiling can be applied to non-model and newly discovered organisms because it does not require a predefined measuring platform (like e.g. microarrays). However, these novel technologies pose new challenges: the raw data need to be rigorously quality checked and filtered prior to analysis, and proper statistical methods have to be applied to extract biologically relevant information. Given the sheer volume of data, this is no trivial task and requires a combination of considerable technical resources along with bioinformatics expertise. To aid the individual researcher, we have developed RobiNA as an integrated solution that consolidates all steps of RNA-Seq-based differential gene-expression analysis in one user-friendly cross-platform application featuring a rich graphical user interface. RobiNA accepts raw FastQ files, SAM/BAM alignment files and counts tables as input. It supports quality checking, flexible filtering and statistical analysis of differential gene expression based on state-of-the art biostatistical methods developed in the R/Bioconductor projects. In-line help and a step-by-step manual guide users through the analysis. Installer packages for Mac OS X, Windows and Linux are available under the LGPL licence from http://mapman.gabipd.org/web/guest/robin. © 2012 The Author(s).

Haidenbauer J.,Julich Research Center
Nuclear Physics A | Year: 2013

Results from an ongoing study of baryon-baryon systems with strangeness S = - 1 and -2 within chiral effective field theory are reported. The investigations are based on the scheme proposed by Weinberg which has been applied rather successfully to the nucleon-nucleon interaction in the past. Results for the hyperon-nucleon and hyperon-hyperon interactions obtained to leading order are reviewed. Specifically, the issue of extrapolating the binding energy of the H-dibaryon, extracted from recent lattice QCD simulations, to the physical point is addressed. Furthermore, first results for the hyperon-nucleon interaction at next-to-leading order are presented and discussed. © 2013 Elsevier B.V.

Hoffmann L.,Julich Research Center | Xue X.,Anhui University of Science and Technology | Alexander M.J.,NorthWest Research Inc
Journal of Geophysical Research: Atmospheres | Year: 2013

The main aim of this study is to find and classify hotspots of stratospheric gravity waves on a global scale. The analysis is based on a 9 year record (2003 to 2011) of radiance measurements by the Atmospheric Infrared Sounder (AIRS) aboard NASA's Aqua satellite. We detect gravity waves based on 4.3 mm brightness temperature variances. Our method focuses on peak events, i.e., strong gravity wave events for which the local variance considerably exceeds background levels. We estimate the occurrence frequencies of these peak events for different seasons and time of day and use the results to find local maxima or "hotspots." In addition, we use AIRS radiances at 8.1 mm to simultaneously detect convective events, including deep convection in the tropics and mesoscale convective systems at middle latitudes. We classify the gravity wave sources based on seasonal occurrence frequencies for convection, but also by means of time series analyses and topographic data. Our study reproduces well-known hotspots of gravity waves, e.g., the Andes and the Antarctic Peninsula. However, the high horizontal resolution of the AIRS observations also allows us to locate numerous mesoscale hotspots, which are partly unknown or poorly studied so far. Most of these mesoscale hotspots are found near orographic features like mountain ranges, coasts, lakes, deserts, or isolated islands. This study will help to select promising regions and seasons for future case studies of gravity waves. © 2012. American Geophysical Union.

Nogga A.,Julich Research Center
Nuclear Physics A | Year: 2013

We present binding energies and properties of wave functions for the light hypernuclei HΛ3, HΛ4, and HeΛ4 based on realistic hyperon-nucleon and nucleon-nucleon interactions including Λ-σ conversion. For the solution, the non-relativistic Schrödinger equation is rewritten into Faddeev or Yakubovsky equations which are solved in momentum space. The accuracy of the numerical calculations is discussed. Based on first leading and next-to-leading order chiral interactions, we discuss the possibility to constrain the hyperon-nucleon interactions by hypernuclear binding energies. Finally, we predict the charge-symmetry breaking of the Λ separation energies of HΛ4/. HeΛ4. © 2013 Elsevier B.V.

Mai M.,University of Bonn | Meissner U.-G.,University of Bonn | Meissner U.-G.,Julich Research Center
Nuclear Physics A | Year: 2013

We perform a combined analysis of antikaon-nucleon scattering cross sections and the recent SIDDHARTA kaonic hydrogen data in the framework of a K̄N-. πY coupled-channel Bethe-Salpeter approach at next-to-leading order in the chiral expansion of the effective potential. We find a precise description of the antikaon-proton scattering amplitudes and are able to extract accurate values of the scattering lengths, a0=-1.81-0.28+0.30+i0.92-0.23+0.29fm and a1=+0.48-0.11+0.12+i0.87-0.20+0.26fm. We also discuss the two-pole structure of the Λ(1405). © 2013 Elsevier B.V.

Kogerler P.,RWTH Aachen | Kogerler P.,Julich Research Center | Tsukerblat B.,Ben - Gurion University of the Negev | Muller A.,Bielefeld University
Dalton Transactions | Year: 2010

The structural versatility characterizing polyoxometalate chemistry, in combination with the option to deliberately use well-defined building blocks, serves as the foundation for the generation of a large family of magnetic clusters, frequently comprising highly symmetric spin arrays. If the spin centers are coupled by antiferromagnetic exchange, some of these systems exhibit spin frustration, which can result in novel magnetic properties of purely molecular origins. We discuss here the magnetic properties of selected nanosized polyoxometalate clusters featuring spin triangles as their magnetic 'building blocks' or fragments. This includes unique porous Keplerate clusters of the type {(Mo)Mo5}12M30 (M = FeIII, Cr III, VIV) with the spin centers defining a regular icosidodecahedron and the {V15As6}-type cluster sphere containing a single equilateral spin triangle; these species are widely discussed and studied in the literature for their role in materials science as molecular representations of Kagomé lattices and in relation to quantum computing, respectively. Exhibiting fascinating and unique structural features, these magnetic molecules allow the study of the implications of frustrated spin ordering. Furthermore, this perspective covers the impact of spin frustration on the degeneracy of the ground state and related problems, namely strong magnetic anisotropy and the interplay of antisymmetric exchange and structural Jahn-Teller effects. © The Royal Society of Chemistry 2010.

Aslam M.N.,COMSATS Institute of Information Technology | Qaim S.M.,Julich Research Center
Applied Radiation and Isotopes | Year: 2014

Excitation functions of the 61Ni(p,n)61Cu, 62Ni(p,2n)61Cu, 60Ni(d,n)61Cu and 58Ni(α,p)61Cu reactions were analyzed with respect to the production of 61Cu (T1/2=3.33h), a promising radionuclide for PET imaging. The nuclear model codes EMPIRE and TALYS reproduced the experimental data of all reactions well, except those for the (d,n) process. The fitted excitation functions were employed to calculate the integral yield of 61Cu in all reactions. The amounts of the possible impurities 62Cu and 60Cu were assessed. A validation of the evaluated (p,xn) data was attempted. © 2014 Elsevier Ltd.

Li L.,Polytechnic University of Valencia | Zhou H.,Polytechnic University of Valencia | Gomez-Hernandez J.J.,Polytechnic University of Valencia | Hendricks Franssen H.-J.,Julich Research Center
Journal of Hydrology | Year: 2012

Real-time data from on-line sensors offer the possibility to update environmental simulation models in real-time. Information from on-line sensors concerning contaminant concentrations in groundwater allow for the real-time characterization and control of a contaminant plume. In this paper it is proposed to use the CPU-efficient Ensemble Kalman Filter (EnKF) method, a data assimilation algorithm, for jointly updating the flow and transport parameters (hydraulic conductivity and porosity) and state variables (piezometric head and concentration) of a groundwater flow and contaminant transport problem. A synthetic experiment is used to demonstrate the capability of the EnKF to estimate hydraulic conductivity and porosity by assimilating dynamic head and multiple concentration data in a transient flow and transport model. In this work the worth of hydraulic conductivity, porosity, piezometric head, and concentration data is analyzed in the context of aquifer characterization and prediction uncertainty reduction. The results indicate that the characterization of the hydraulic conductivity and porosity fields is continuously improved as more data are assimilated. Also, groundwater flow and mass transport predictions are improved as more and different types of data are assimilated. The beneficial impact of accounting for multiple concentration data is patent. © 2012 Elsevier B.V.

Malzbender J.,Julich Research Center
Ceramics International | Year: 2016

Interest in ceramic transport membrane materials has increased significantly leading also to questions with respect to mechanical reliability and robustness, hence, requiring knowledge of the mechanical properties. The current review focuses on the mechanical properties of such ceramics, emphasizing in particular relationships between mechanical properties, non-elastic effects, phase changes and materials' stability. Room and elevated temperature application is considered with a main emphasis on elastic and creep deformation as well as fracture. Consideration is given to dense membranes as well as porous substrate materials for advanced asymmetric concepts. Properties are summarized for selected oxygen and proton conductors. Furthermore, mechanical properties of some selected porous ceramic and metallic substrate materials are given. In addition to the failure probability associated with the Weibull distribution of fracture stresses, creep rupture of dense materials and enhanced creep deformation of porous materials are aspects that need special consideration in the application of these materials in gas separation systems. © 2016 Elsevier Ltd and Techna Group S.r.l.

The projected electrostatic potential is reconstructed from a high-resolution exit wave function through a maximum-likelihood refinement algorithm. The theory of an already existing algorithm [1] is extended to include the effects of phenomenological absorption. Various tests with a simulated exit wave function of YBa2Cu3O7 in [100] orientation used as a source show that the reconstruction is successful, regardless of the strongly differing scattering power of atomic columns, even for the case of strong dynamical diffraction. Object thickness, the amount of absorption, and a residual defocus aberration of the wave function-parameters often unknown or difficult to measure in experiments-can be determined accurately with the aid of the refinement algorithm in a self-consistent way. For the next generation of instruments, with information limits of 0.05nm and better, reconstruction accuracies of better than 2% can be expected, which is sufficient to measure and display the structural and chemical information with the aid of an accurate projected potential map. © 2009 Elsevier B.V.

Hoffmann L.,Julich Research Center | Alexander M.J.,NorthWest Research Associates, Inc.
Journal of Geophysical Research: Atmospheres | Year: 2010

Convective gravity waves are an important driver of the equator-to-pole circulation in the stratospheric summer hemisphere, but their nature is not well known. Previous studies showing tight relationships between deep convection and convective waves mainly focus on tropical latitudes. For midlatitudes most analyses are based on case studies. Here we present a new multiyear occurrence frequency analysis of convective waves at midlatitudes. The study is based on radiance measurements made by the Atmospheric Infrared Sounder (AIRS) satellite experiment during the North American thunderstorm season, May to August, in the years 2003-2008. For this study we optimized an existing algorithm to detect deep convection in AIRS data to be applicable at midlatitudes. We also present a new detection algorithm for gravity waves in AIRS data based on a variance filter approach for 4.3 m brightness temperatures. The new algorithm can detect plane wave perturbations in the altitude range from 20 to 65 km with vertical wavelengths larger than 15 km and horizontal wavelengths from 50 to 1000 km. By analyzing spatial and temporal correlations of the individual AIRS observations, it can be shown that more than 95% of the observed gravity waves in a core region over the North American Great Plains are related to deep convective clouds, i.e., are likely being classified appropriately as convective waves. We conclude that the core region is a good location to observe and characterize the properties of convective waves at midlatitudes. The statistical analyses presented here are also valuable to validate parameterization schemes for convective gravity waves. For completeness, it should be mentioned that our analyses cover not only the U.S. Midwest but the North American continent as well as the surrounding ocean regions in general. Our analysis also reveals interesting details about tropical convection and related gravity wave activity, as well as the capability of the AIRS instrument to observe these. Copyright © 2010 by the American Geophysical Union.

Persson B.N.J.,Julich Research Center | Persson B.N.J.,Tel Aviv University
European Physical Journal E | Year: 2010

We calculate the friction force acting on a hard cylinder or spherical ball rolling on a flat surface of a viscoelastic solid. The rolling-friction coefficient depends non-linearly on the normal load and the rolling velocity. For a cylinder rolling on a viscoelastic solid characterized by a single relaxation time Hunter has obtained an exact result for the rolling friction, and our result is in very good agreement with his result for this limiting case. The theoretical results are also in good agreement with experiments of Greenwood and Tabor. We suggest that measurements of rolling friction over a wide range of rolling velocities and temperatures may constitute a useful way to determine the viscoelastic modulus of rubber-like materials. © 2010 EDP Sciences / Societá Italiana di Fisica / Springer-Verlag.

Strodel B.,Julich Research Center | Lee J.W.L.,University of Cambridge | Whittleston C.S.,University of Cambridge | Wales D.J.,University of Cambridge
Journal of the American Chemical Society | Year: 2010

We model oligomers of the Alzheimer's amyloid β-peptide Aβ1-42 in an implicit membrane to obtain insight into the mechanism of amyloid toxicity. It has been suggested that Aβ oligomers are the toxic species, causing membrane disruption in neuronal cells due to pore formation. We use basin-hopping global optimization to identify the most stable structures for the Aβ1-42 peptide monomer and small oligomers up to the octamer inserted into a lipid bilayer. To improve the efficacy of the basin-hopping approach, we introduce a basin-hopping parallel tempering scheme and an oligomer generation procedure. The most stable membrane-spanning structure for the monomer is identified as a β-sheet, which exhibits the typical strand-turn-strand motif observed in NMR experiments. We find ordered β-sheets for the dimer to the hexamer, whereas for the octamer, we observe that the ordered structures separate into distinct tetrameric units that are rotated or shifted with respect to each other. This effect leads to an increase in favorable peptide-peptide interactions, thereby stabilizing the membrane-inserted octamer. On the basis of these results, we suggest that Aβ pores may consist of tetrameric and hexameric β-sheet subunits. These Aβ pore models are consistent with the results of biophysical and biochemical experiments. © 2010 American Chemical Society.

Cooper D.,CEA Grenoble | Dunin-Borkowski R.E.,Julich Research Center
Journal of Electron Microscopy | Year: 2013

An approach is presented that allows independent determination of the mean inner potential contribution to a phase image of a highly doped layer in a semiconductor measured using off-axis electron holography, in order to quantify the contribution to the recorded phase from the dopant potential alone. The method takes into account the possible presence of both substitutional and interstitial dopant atoms and is used here to analyse an experimental phase image of 12 delta-doped B layers in Si that are separated from each other by <6 nm. © 2013 The Author. Published by Oxford University Press [on behalf of The Japanese Society of Microscopy]. All rights reserved.

Marx M.,Julich Research Center
Cerebral cortex (New York, N.Y. : 1991) | Year: 2013

Neocortical lamina 6B (L6B) is a largely unexplored layer with a very heterogeneous cellular composition. To date, only little is known about L6B neurons on a systematic and quantitative basis. We investigated the morphological and electrophysiological properties of excitatory L6B neurons in the rat somatosensory barrel cortex using whole-cell patch-clamp recordings and simultaneous biocytin fillings. Subsequent histological processing and computer-assisted 3D reconstructions provided the basis for a classification of excitatory L6B neurons according to their structural and functional characteristics. Three distinct clusters of excitatory L6B neurons were identified: (C1) pyramidal neurons with an apical dendrite pointing towards the pial surface, (C2) neurons with a prominent, "apical"-like dendrite not oriented towards the pia, and (C3) multipolar spiny neurons without any preferential dendritic orientation. The second group could be further subdivided into three categories termed inverted, "tangentially" oriented and "horizontally" oriented neurons. Furthermore, based on the axonal domain two subcategories of L6B pyramidal cells were identified that had either a more barrel-column confined or an extended axonal field. The classification of excitatory L6B neurons provided here may serve as a basis for future studies on the structure, function, and synaptic connectivity of L6B neurons.

Haidenbauer J.,Julich Research Center
Few-Body Systems | Year: 2013

Current activities in the description of baryon-baryon systems with strangeness S = -1 and -2 within chiral effective field theory are reviewed. In particular, results for the hyperon-nucleon and hyperon-hyperon interactions obtained to leading order are presented. Preliminary results for Λ N and Σ N scattering at next-to-leading order are discussed. Some comments on the H dibaryon are made. © 2012 Springer-Verlag.

A stochastic differential equation for intermittent plasma density dynamics in magnetic fusion edge plasma is derived, which is consistent with the experimentally measured gamma distribution and the theoretically expected quadratic nonlinearity. The plasma density is driven by a multiplicative Wiener process and evolves on the turbulence correlation time scale, while the linear growth is quadratically damped by the fluctuation level. The sensitivity of intermittency to the nonlinear dynamics is investigated by analyzing the nonlinear Langevin representation of the beta process, which leads to a root-square nonlinearity. © 2013 American Institute of Physics.

Hammer H.-W.,University of Bonn | Nogga A.,Julich Research Center | Schwenk A.,TU Darmstadt | Schwenk A.,Helmholtz Center for Heavy Ion Research
Reviews of Modern Physics | Year: 2013

It is often assumed that few- and many-body systems can be accurately described by considering only pairwise two-body interactions of the constituents. We illustrate that three- and higher-body forces enter naturally in effective field theories and are especially prominent in strongly interacting quantum systems. We focus on three-body forces and discuss examples from atomic and nuclear physics. In particular, the importance and the challenges of three-nucleon forces for nuclear structure and reactions, including applications to astrophysics and fundamental symmetries, are highlighted. © 2013 American Physical Society.

Jonsson S.A.,Lund University | Mohanty S.,Julich Research Center | Irback A.,Lund University
Proteins: Structure, Function and Bioinformatics | Year: 2012

The α-synuclein protein (αS), implicated in Parkinson's disease, shows conformational versatility. It aggregates into β-sheet-rich fibrils, occurs in helical membrane-bound forms, is disordered as a free monomer, and has recently been suggested to have a folded helical tetramer as its main physiological form. Here, we use implicit solvent all-atom Monte Carlo methods to explore the conformational ensemble sampled by the free αS monomer. We analyze secondary structure propensities, size, and topological properties and compare with existing experimental data. Our study suggests that free αS has two distinct phases. One phase has the expected disordered character. The other phase also shows large conformational variability. However, in this phase, the β-strand content is substantial, and the backbone fold shows statistical similarities with that in αS fibrils. Presence of this phase is consistent with data from low-temperature experiments. Conversion of disordered αS to this fibril-like form requires the crossing of a rather large apparent free-energy barrier. © 2012 Wiley Periodicals, Inc.

Peksen M.,Julich Research Center
International Journal of Hydrogen Energy | Year: 2014

Full commercialisation of the solid oxide fuel cell (SOFC) technology faces many technological challenges that prevent the incorporation of the technology into the global energy sector. The effort to increase the transient thermomechanical reliability of the interacting fuel cell components and the associated fuel cell system requires a comprehensive understanding of the complex multiphysics, occurring within the system. State of the art dynamic fuel cell system modelling comprises sub-models of the assembly, or is based on empirical nature. The present study introduces a transient, coupled 3D computational fluid dynamics/computational solid mechanics model of a complete solid oxide fuel cell system and its experimental validation. The model includes all system components; namely the fuel cell stack, afterburner, pre-reformer, air pre-heater and the auxiliary components. All components are presented in their real geometrical resolution. The capabilities of the 3D system level model are demonstrated by simulating the heating-up process and the critical system locations susceptible to thermomechanically induced stress, over time. © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 37.

Heinrichs H.,Julich Research Center | Jochem P.,Karlsruhe Institute of Technology | Fichtner W.,Karlsruhe Institute of Technology
Energy | Year: 2014

The EU ETS (European Emissions Trading System) is being enlarged stepwise to cover an increasing amount of overall European CO2 emissions. However, one of the largest and still growing CO2-emitting sector, the transport sector, and particularly road transport, has not yet been included in the EU ETS. Against this background, the question arises whether integrating the road transport sector in the EU ETS represents a cost-efficient CO2 reduction strategy. For this reason, the consequences of this integration are analysed with a focus on Germany. To do so we utilise a model-based approach. In order to account for both sectors simultaneously, we couple an electricity system model, PERSEUS-EU (Package for Emission Reduction Strategies in Energy Use and Supply in Europe), with a road transport model, COMIT (CO2 emission Mitigation in the Transport sector). The time horizon we consider ranges from 2010 to 2030. In our analysis, we differentiate our scenarios according to commodity prices, share of renewable energies in electricity generation and share of electric vehicles. The results show that the enlargement of the EU ETS to include road transport leads to a reduction of overall CO2 emissions, but equally reduces the mitigation efforts in the road transport sector. Simultaneously, the German electricity sector is mainly influenced according to the certificate demand or supply of the road transport sector. © 2014 Elsevier Ltd.

Hupkes J.,Julich Research Center
Physica Status Solidi (A) Applications and Materials Science | Year: 2016

We report on electrical properties and corrosion of ZnO:Al thin films on glass after damp heat treatments under various atmospheric conditions. The ZnO:Al films were prepared by in-line magnetron sputtering onto glass substrates. Damp heat treatments took place at 90°C in various humid atmospheres including air, nitrogen, and mixtures of argon and carbon dioxide. Dry heat did not affect the properties of ZnO:Al films. Humidity, however, led to a significant increase in resistivity depending on preparation conditions of the ZnO:Al and the composition of the atmosphere. Additionally, humid CO2 levels exceeding 5% significantly etched the ZnO:Al films with resistance increase by orders of magnitude. The only exception from degradation exhibited the damp heat stable ZnO:Al that had experienced the so-called high-mobility annealing under the protective layer before degradation. This unique behavior was related to bulk properties of the ZnO:Al rather than a barrier effect at the film surface. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Feldmeyer D.,Julich Research Center | Feldmeyer D.,RWTH Aachen
Frontiers in Neuroanatomy | Year: 2012

Neocortical areas are believed to be organized into vertical modules, the cortical columns, and the horizontal layers 1-6. In the somatosensory barrel cortex these columns are defined by the readily discernible barrel structure in layer 4. Information processing in the neocortex occurs along vertical and horizontal axes, thereby linking individual barrel-related columns via axons running through the different cortical layers of the barrel cortex. Long-range signaling occurs within the neocortical layers but also through axons projecting through the white matter to other neocortical areas and subcortical brain regions. Because of the ease of identification of barrel-related columns, the rodent barrel cortex has become a prototypical system to study the interactions between different neuronal connections within a sensory cortical area and between this area and other cortical as well subcortical regions. Such interactions will be discussed specifically for the feed-forward and feedback loops between the somatosensory and the somatomotor cortices as well as the different thalamic nuclei. In addition, recent advances concerning the morphological characteristics of excitatory neurons and their impact on the synaptic connectivity patterns and signaling properties of neuronal microcircuits in the whisker-related somatosensory cortex will be reviewed. In this context, their relationship between the structural properties of barrel-related columns and their function as a module in vertical synaptic signaling in the whisker-related cortical areas will be discussed. © 2012 Feldmeyer.

Butz M.,Julich Research Center | van Ooyen A.,VU University Amsterdam
PLoS Computational Biology | Year: 2013

Lasting alterations in sensory input trigger massive structural and functional adaptations in cortical networks. The principles governing these experience-dependent changes are, however, poorly understood. Here, we examine whether a simple rule based on the neurons' need for homeostasis in electrical activity may serve as driving force for cortical reorganization. According to this rule, a neuron creates new spines and boutons when its level of electrical activity is below a homeostatic set-point and decreases the number of spines and boutons when its activity exceeds this set-point. In addition, neurons need a minimum level of activity to form spines and boutons. Spine and bouton formation depends solely on the neuron's own activity level, and synapses are formed by merging spines and boutons independently of activity. Using a novel computational model, we show that this simple growth rule produces neuron and network changes as observed in the visual cortex after focal retinal lesions. In the model, as in the cortex, the turnover of dendritic spines was increased strongest in the center of the lesion projection zone, while axonal boutons displayed a marked overshoot followed by pruning. Moreover, the decrease in external input was compensated for by the formation of new horizontal connections, which caused a retinotopic remapping. Homeostatic regulation may provide a unifying framework for understanding cortical reorganization, including network repair in degenerative diseases or following focal stroke. © 2013 Butz, van Ooyen.

Doring M.,University of Bonn | Meissner U.-G.,University of Bonn | Meissner U.-G.,Julich Research Center
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011

We analyse the impact of the recent measurement of kaonic hydrogen X rays by the SIDDHARTA collaboration on the allowed ranges for the kaon-deuteron scattering length in the framework of non-relativistic effective field theory. Based on data from K-N scattering only, we predict the kaon-deuteron scattering length AKd=(-1.46+i1.08) fm, with an estimated uncertainty of about 25% in both the real and the imaginary part. © 2011 Elsevier B.V.

Abdullaev S.S.,Julich Research Center
Physics of Plasmas | Year: 2011

Universal and generic features of poloidal spectra of external magnetic perturbations created by a set of saddle coils in tokamak plasmas are studied in a vacuum approximation. It is found that the poloidal mode spectra with high-accuracy are described by a linear combination of three universal asymptotical formulas which depend only on the safety factor of the equilibrium plasma and the geometry of perturbation coils. The validity of these formulas is confirmed by numerical calculations of the mode spectra in the DIII-D plasma [G. L. Jackson, Europhys. Conf. Abstr. 27A, P-4.47 (2007)] and a spherical tokamak, National Spherical Tokamak Experiment [D. A. Gates, Nucl. Fusion 49, 104016 (2009)], plasmas perturbed by external control coils. © 2011 American Institute of Physics.

Qaim S.M.,Julich Research Center
Journal of the Korean Physical Society | Year: 2011

Nuclear procedures play an important role in medicine, both in diagnosis and therapy. The status of nuclear data relevant to production and application of standard diagnostic and therapeutic radionuclides is discussed. Some of the recent advances in nuclear data research are outlined and the new trends are described. They pertain to development of non-standard longer lived positron emitters and novel soft-radiation emitting therapeutic radionuclides. The formation of activation products in the human tissue under proton therapy conditions is discussed.

Karevski D.,CNRS Jean Lamour Institute | Popkov V.,University of Florence | Popkov V.,Max Planck Institute for Complex Systems | Schutz G.M.,Julich Research Center
Physical Review Letters | Year: 2013

We demonstrate that the exact nonequilibrium steady state of the one-dimensional Heisenberg XXZ spin chain driven by boundary Lindblad operators can be constructed explicitly with a matrix product ansatz for the nonequilibrium density matrix where the matrices satisfy a quadratic algebra. This algebra turns out to be related to the quantum algebra U q[SU(2)]. Coherent state techniques are introduced for the exact solution of the isotropic Heisenberg chain with and without quantum boundary fields and Lindblad terms that correspond to two different completely polarized boundary states. We show that this boundary twist leads to nonvanishing stationary currents of all spin components. Our results suggest that the matrix product ansatz can be extended to more general quantum systems kept far from equilibrium by Lindblad boundary terms. © 2013 American Physical Society.

Kowalski P.M.,German Research Center for Geosciences | Kowalski P.M.,Julich Research Center | Wunder B.,German Research Center for Geosciences | Jahn S.,German Research Center for Geosciences
Geochimica et Cosmochimica Acta | Year: 2013

Over the last decade experimental studies have shown a large B isotope fractionation between materials carrying boron incorporated in trigonally and tetrahedrally coordinated sites, but the mechanisms responsible for producing the observed isotopic signatures are poorly known. In order to understand the boron isotope fractionation processes and to obtain a better interpretation of the experimental data and isotopic signatures observed in natural samples, we use first principles calculations based on density functional theory in conjunction with ab initio molecular dynamics and a new pseudofrequency analysis method to investigate the B isotope fractionation between B-bearing minerals (such as tourmaline and micas) and aqueous fluids containing H3BO3 and H4BO4- species. We confirm the experimental finding that the isotope fractionation is mainly driven by the coordination of the fractionating boron atoms and have found in addition that the strength of the produced isotopic signature is strongly correlated with the B. O bond length. We also demonstrate the ability of our computational scheme to predict the isotopic signatures of fluids at extreme pressures by showing the consistency of computed pressure-dependent β factors with the measured pressure shifts of the B. O vibrational frequencies of H3BO3 and H4BO4- in aqueous fluid. The comparison of the predicted with measured fractionation factors between boromuscovite and neutral fluid confirms the existence of the admixture of tetrahedral boron species in neutral fluid at high P and T found experimentally, which also explains the inconsistency between the various measurements on the tourmaline-mica system reported in the literature. Our investigation shows that the calculated equilibrium isotope fractionation factors have an accuracy comparable to the experiments and give unique and valuable insight into the processes governing the isotope fractionation mechanisms on the atomic scale. © 2012 Elsevier Ltd.

Misiorny M.,Julich Research Center | Misiorny M.,Adam Mickiewicz University | Barnaa J.,Adam Mickiewicz University | Barnaa J.,Polish Academy of Sciences
Physical Review Letters | Year: 2013

Spin-polarized transport through bistable magnetic adatoms or single-molecule magnets (SMMs), which exhibit both uniaxial and transverse magnetic anisotropy, is considered theoretically. The main focus is on the impact of transverse anisotropy on transport characteristics and the adatom's or SMM's spin. In particular, we analyze the role of quantum tunneling of magnetization (QTM) in the mechanism of the current-induced spin switching, and show that the QTM phenomenon becomes revealed as resonant peaks in the average values of the molecule's spin and in the charge current. These features appear at some resonant fields and are observable when at least one of the electrodes is ferromagnetic. © 2013 American Physical Society.

Guo X.,Huazhong University of Science and Technology | Guo X.,Julich Research Center
Physical Chemistry Chemical Physics | Year: 2014

As a classic dielectric material, BaTiO3 is one of the most important materials used in electronic applications. In this work, highly dense BaTiO3 ceramics with an average grain size of 35 nm were prepared, and dielectric and electrical properties were investigated. Microcrystalline BaTiO3 is an insulator at low temperatures; however, nanocrystalline BaTiO3 shows considerable semiconductivity with an activation energy of only 0.27 eV at temperatures ≤200 °C. At room temperature, the conductivity of nanocrystalline BaTiO3 is about fourteen orders of magnitude higher than that of the microcrystalline counterpart. Only by decreasing the grain size, one can transform BaTiO3 from an insulator to a semiconductor. © the Owner Societies 2014.

Armbruster M.,Max Planck Institute for Chemical Physics of Solids | Wowsnick G.,Max Planck Institute for Chemical Physics of Solids | Friedrich M.,Max Planck Institute for Chemical Physics of Solids | Heggen M.,Julich Research Center | Cardoso-Gil R.,Max Planck Institute for Chemical Physics of Solids
Journal of the American Chemical Society | Year: 2011

A two-step synthesis for the preparation of single-phase and nanoparticulate GaPd and GaPd2 by coreduction of ionic metal-precursors with LiHBEt3 in THF without additional stabilizers is described. The coreduction leads initially to the formation of Pd nanoparticles followed by a Pd-mediated reduction of Ga3+ on their surfaces, requiring an additional annealing step. The majority of the intermetallic particles have diameters of 3 and 7 nm for GaPd and GaPd 2, respectively, and unexpected narrow size distributions as determined by disk centrifuge measurements. The nanoparticles have been characterized by XRD, TEM, and chemical analysis to ensure the formation of the intermetallic compounds. Unsupported nanoparticles possess high catalytic activity while maintaining the excellent selectivity of the ground bulk materials in the semihydrogenation of acetylene. The activity could be further increased by depositing the particles on α-Al2O3. © 2011 American Chemical Society.

Galanakis I.,University of Patras | Ozdogan K.,Yildiz Technical University | Sasoglu E.,Julich Research Center | Sasoglu E.,Fatih University
Applied Physics Letters | Year: 2013

Using ab-initio electronic structure calculations, we propose an alternative class of spin filter materials (SFMs) based on the quaternary Heusler compounds CoVXAl (X Ti, Zr, Hf). We show that the p-d hybridization leads to the formation of the ferromagnetic band gap with a moderate exchange splitting Δ E ex and a Curie temperature TC well above the room temperature. We find that all three compounds are thermodynamically and magnetically stable. Combination of high TC value together with moderate exchange splitting, as well as crystal structures compatible to the existing semiconductors and metals, makes these compounds promising candidates to find applications as SFMs in spintronics devices. © 2013 AIP Publishing LLC.

The electrophoretic mobility of rodlike fd viruses is measured and compared to theory, with the theoretical calculations performed according to Stigter (Stigter, D. Charged Colloidal Cylinder with a Gouy Double-Layer. J. Colloid Interface Sci.1975, 53, 296-306. Stigter, D. Electrophoresis of Highly Charged Colloidal Cylinders in Univalent Salt- Solutions. 1. Mobility in Transverse Field. J. Phys. Chem.1978, 82, 1417-1423. Stigter, D. Electrophoresis of Highly Charged Colloidal Cylinders in Univalent Salt Solutions. 2. Random Orientation in External Field and Application to Polyelectrolytes. J. Phys. Chem.1978, 82, 1424-1429. Stigter, D. Theory of Conductance of Colloidal Electrolytes in Univalent Salt Solutions. J. Phys. Chem.1979, 83, 1663-1670), who describes the electrophoretic mobility of infinite cylinders including relaxation effects. Using the dissociation constants of the ionizable groups on the surfaces of the fd viruses, we can calculate the mobility without any adjustable parameter (apart from the possible Stern layer thickness). In addition, the approximation in the theoretical description of Stigter (and others) of using a model of infinitely long cylinders, which consequently is independent of the aspect ratio, is examined by performing more elaborate numerical calculations for finite cylinders. It is shown that, although the electrophoretic mobility of cylindrical particles in the limit of low ionic strength depends on the aspect ratio much more than "end effects", at moderate and high ionic strengths the finite and infinite cylinder models differ only to a degree that can be attributed to end effects. Furthermore, the range of validity of the Stokes regime is systematically calculated. © 2012 American Chemical Society.

Aeberhard U.,Julich Research Center
Journal of Photonics for Energy | Year: 2014

An optoelectronic device simulation framework valid for arbitrary spatial variation of electronic potentials and optical modes, and for transport regimes ranging from ballistic to diffusive, is used to study the nonlocal photon absorption, photocurrent generation and carrier extraction in ultra-thin film, and nanostructure-based solar cell devices at the radiative limit. Among the effects that are revealed by the microscopic approach and which are inaccessible to macroscopic models is the impact of structure, doping-or bias-induced nanoscale potential variations on the local photogeneration rate and the photocarrier transport regime. © 2014 The Authors.

Kaneko F.,Osaka University | Radulescu A.,Julich Research Center | Ute K.,Tokushima University
Journal of Applied Crystallography | Year: 2014

Syndiotactic polystyrene (sPS) occupies a peculiar position among crystalline polymers: it forms co-crystals with many different kinds of chemical compounds, where the molecules are confined as guests in the regularly arranged cavities surrounded by the side phenyl groups. The guest molecules can be replaced smoothly by exposure to a vapour or a liquid of another compound, keeping the framework of the host polymer crystallites. It has been confirmed that the guest-exchange procedure is an effective way to incorporate a variety of chemical species into the crystalline region of syndiotactic polystyrene. In order to elucidate its characteristics, the guest-exchange process in co-crystals of syndiotactic polystyrene has been studied by in situ time-resolved small-angle neutron scattering measurements, exploiting the scattering length difference between fully protonated and deuterated isotopologues of guest compounds and employing fully deuterated syndiotactic polystyrene as the host matrix to avoid strong incoherent scattering. In this study, the guest-exchange process induced by exposure to the gas of small guest molecules was followed by monitoring of the reflections from crystalline lamellae. The lamellar reflections showed significant variations in intensity during the guest exchange, from which the diffusion coefficients of the guest molecules in the crystalline region could be evaluated. © 2014 International Union of Crystallography.

Berns A.E.,Julich Research Center | Conte P.,University of Palermo
Organic Geochemistry | Year: 2011

Cross polarization (CP) magic angle spinning (MAS) 13C NMR spectroscopy is a solid state NMR technique widely applied to study the chemical composition of natural organic matter. In high magnetic fields (>7T), fast sample spinning is required in order to reduce the influence of spinning sidebands underlying other chemical shift regions. As the spinning speed increases, the Hartmann-Hahn matching profiles break down into a series of narrow matching bands. In order to account for this instability variable amplitude cross polarization techniques (e.g. VACP, ramp-CP) have been developed. In the present study, we experimentally verified the stability of the Hartmann-Hahn condition under two MAS speeds for different samples with known structure and two different humic acids. For a complete restoration of flat matching profiles, large ramp sizes were needed. The matching profiles of the humic acids showed that both samples needed different ramp sizes to restore flat profiles. A set up based on the matching profiles of the commonly used glycine would have led to an insufficient ramp size for one of the humic acids. For the characterization of natural organic matter, we hence recommend to roughly set the matching conditions with a standard and subsequently optimize the matching conditions on a more complex, preferably representative, sample such as a humic acid. We would suggest to either run an array of different ramp sizes until maximum signal intensity is reached for all chemical shift regions or, in the case of unavailable measurement time, to use a ramp size twice the spinning speed. © 2011 Elsevier Ltd.

Zahoor A.,Bielefeld University | Otten A.,Julich Research Center | Wendisch V.F.,Bielefeld University
Journal of Biotechnology | Year: 2014

Corynebacterium glutamicum - a well-known industrial amino acid producer - has recently been engineered for the production of a variety of new products including diamines, alcohols, carotenoids and organic acids. Glycolic acid was shown here not to serve as sole or combined carbon source for C. glutamicum. Glycolate affected growth of C. glutamicum only at high concentrations (460 mM) and in a comparable manner as other salts (480 mM potassium chloride and 490 mM sodium chloride). A transcriptome analysis of cells grown in the presence of glycolate or potassium chloride revealed nine glycolate-specific gene expression changes including increased levels of a putative l-lactate permease gene when glycolate was present in medium. Subsequently, glycolate was shown to interfere with l-lactate utilization but not with growth with acetate or pyruvate. Heterologous expression of the glyoxylate reductase gene ycdW from Escherchia coli resulted in a titer of 0.4 g/L glycolate in minimal medium with glucose and acetate. Deletion of the malate synthase gene aceB improved glycolate titer by about tenfold. Reducing isocitrate dehydrogenase activity by replacing the translational start codon (ATG to GTG) further increased glycolate titer by more than 30%. The production of 5.3±0.1 g/L glycolate with a yield of 0.18 g/g and a volumetric productivity of about 0.1 gL-1h-1 is the first report of a C. glutamicum strain capable of glycolate production. © 2014 Elsevier B.V.

Dekens W.,University of Groningen | De Vries J.,University of Groningen | De Vries J.,Julich Research Center
Journal of High Energy Physics | Year: 2013

We perform a systematic study of flavor-diagonal parity- and time-reversal-violating operators of dimension six which could arise from physics beyond the SM. We begin at the unknown high-energy scale where these operators originate. At this scale the operators are constrained by gauge invariance which has important consequences for the form of effective operators at lower energies. In particular for the four-quark operators. We calculate one-loop QCD and, when necessary, electroweak corrections to the operators and evolve them down to the electroweak scale and subsequently to hadronic scales. We find that for most operators QCD corrections are not particularly significant. We derive a set of operators at low energy which is expected to dominate hadronic and nuclear EDMs due to physics beyond the SM and obtain quantitative relations between these operators and the original dimension-six operators at the high-energy scale. We use the limit on the neutron EDM to set bounds on the dimension-six operators. © 2013 SISSA, Trieste, Italy.

Schroder G.F.,Julich Research Center | Schroder G.F.,Heinrich Heine University Dusseldorf | Levitt M.,Stanford University | Brunger A.T.,Stanford University
Acta Crystallographica Section D: Biological Crystallography | Year: 2014

Crystals of membrane proteins and protein complexes often diffract to low resolution owing to their intrinsic molecular flexibility, heterogeneity or the mosaic spread of micro-domains. At low resolution, the building and refinement of atomic models is a more challenging task. The deformable elastic network (DEN) refinement method developed previously has been instrumental in the determinion of several structures at low resolution. Here, DEN refinement is reviewed, recommendations for its optimal usage are provided and its limitations are discussed. Representative examples of the application of DEN refinement to challenging cases of refinement at low resolution are presented. These cases include soluble as well as membrane proteins determined at limiting resolutions ranging from 3 to 7Å. Potential extensions of the DEN refinement technique and future perspectives for the interpretation of low-resolution crystal structures are also discussed. © 2014 International Union of Crystallography.

Huesgen P.F.,Julich Research Center
Nature Methods | Year: 2014

To improve proteome coverage and protein C-terminal identification, we characterized the Methanosarcina acetivorans thermophilic proteinase LysargiNase, which cleaves before lysine and arginine up to 55 °C. Unlike trypsin, LysargiNase-generated peptides had N-terminal lysine or arginine residues and fragmented with b ion–dominated spectra. This improved protein C terminal–peptide identification and several arginine-rich phosphosite assignments. Notably, cleavage also occurred at methylated or dimethylated lysine and arginine, facilitating detection of these epigenetic modifications. © 2014 Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.

Butz M.,Julich Research Center | Steenbuck I.D.,Albert Ludwigs University of Freiburg | Van Ooyen A.,VU University Amsterdam
Frontiers in Synaptic Neuroscience | Year: 2014

In networks with small-world topology, which are characterized by a high clustering coefficient and a short characteristic path length, information can be transmitted efficiently and at relatively low costs. The brain is composed of small-world networks, and evolution may have optimized brain connectivity for efficient information processing. Despite many studies on the impact of topology on information processing in neuronal networks, little is known about the development of network topology and the emergence of efficient small-world networks. We investigated how a simple growth process that favors short-range connections over long-range connections in combination with a synapse formation rule that generates homeostasis in post-synaptic firing rates shapes neuronal network topology. Interestingly, we found that small-world networks benefited from homeostasis by an increase in efficiency, defined as the averaged inverse of the shortest paths through the network. Efficiency particularly increased as small-world networks approached the desired level of electrical activity. Ultimately, homeostatic small-world networks became almost as efficient as random networks. The increase in efficiency was caused by the emergent property of the homeostatic growth process that neurons started forming more long-range connections, albeit at a low rate, when their electrical activity was close to the homeostatic set-point. Although global network topology continued to change when neuronal activities were around the homeostatic equilibrium, the small-world property of the network was maintained over the entire course of development. Our results may help understand how complex systems such as the brain could set up an efficient network topology in a self-organizing manner. Insights from our work may also lead to novel techniques for constructing large-scale neuronal networks by self-organization. © 2014 Butz, Steenbuck and van Ooyen.

Gao S.,Max Delbruck Center for Molecular Medicine | Gao S.,Free University of Berlin | Von der Malsburg A.,Albert Ludwigs University of Freiburg | Dick A.,Max Delbruck Center for Molecular Medicine | And 6 more authors.
Immunity | Year: 2011

Human myxovirus resistance protein 1 (MxA) is an interferon-induced dynamin-like GTPase that acts as a cell-autonomous host restriction factor against many viral pathogens including influenza viruses. To study the molecular principles of its antiviral activity, we determined the crystal structure of nucleotide-free MxA, which showed an extended three-domain architecture. The central bundle signaling element (BSE) connected the amino-terminal GTPase domain with the stalk via two hinge regions. MxA oligomerized in the crystal via the stalk and the BSE, which in turn interacted with the stalk of the neighboring monomer. We demonstrated that the intra- and intermolecular domain interplay between the BSE and stalk was essential for oligomerization and the antiviral function of MxA. Based on these results, we propose a structural model for the mechano-chemical coupling in ring-like MxA oligomers as the principle mechanism for this unique antiviral effector protein. © 2011 Elsevier Inc.

Doring M.,University of Bonn | Mai M.,University of Bonn | Meissner U.-G.,University of Bonn | Meissner U.-G.,Julich Research Center
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2013

For resonances decaying in a finite volume, the simple identification of state and eigenvalue is lost. The extraction of the scattering amplitude is a major challenge as we demonstrate by extrapolating the physical S11 amplitude of pion-nucleon scattering to the finite volume and unphysical quark masses, using a unitarized chiral framework including all next-to-leading order contact terms. We show that the pole movement of the resonances N(1535)1/2- and N(1650)1/2- with varying quark masses is non-trivial. In addition, there are several strongly coupled S-wave thresholds that induce a similar avoided level crossing as narrow resonances. The level spectrum is predicted for two typical lattice setups, and ways to extract the amplitude from upcoming lattice data are discussed. © 2013 Elsevier B.V.

Tass P.A.,Julich Research Center | Tass P.A.,University of Cologne | Popovych O.V.,University of Cologne
Biological Cybernetics | Year: 2012

Tinnitus is a deafferentation-induced phantom phenomenon characterized by abnormal cerebral synchrony and connectivity. Computationally, we show that desynchronizing acoustic coordinated reset (CR) stimulation can effectively counteract both up-regulated synchrony and connectivity. CR stimulation has initially been developed for the application to electrical deep brain stimulation. We here adapt this approach to non-invasive, acoustic CR stimulation. For this, we use the tonotopic organization of the central auditory system and replace electrical stimulation bursts applied to different brain sites by acoustically delivered tones of different pitch. Based on our simulations, we propose non-invasive acoustic CR stimulation as a possible novel therapy for tinnitus. © 2012 The Author(s).

Schillaci C.D.,University of California at Berkeley | Luu T.C.,Julich Research Center
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2015

We explore the two-body spectra of spin-1/2 fermions in isotropic harmonic traps with external spin-orbit potentials and short-range two-body interactions. Using a truncated basis of total angular momentum eigenstates, nonperturbative results are presented for experimentally realistic forms of the spin-orbit coupling: a pure Rashba coupling, Rashba and Dresselhaus couplings in equal parts, and a Weyl-type coupling. The technique is easily adapted to bosonic systems and other forms of spin-orbit coupling. © 2015 American Physical Society.

Haidenbauer J.,Julich Research Center | Krein G.,Sao Paulo State University
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2010

Predictions for the charm-production reaction over(p, ̄) p → over(Λ, ̄)c - Λc + for energies near the threshold are presented. The calculations are performed in a meson-exchange framework in close analogy to our earlier study on over(p, ̄) p → over(Λ, ̄) Λ by connecting the two processes via SU (4) symmetry. The obtained over(Λ, ̄)c - Λc + production cross sections are in the order of 1 to 7 μb, i.e. a factor of around 10-70 smaller than the corresponding cross sections for over(Λ, ̄) Λ. However, they are 100 to 1000 times larger than predictions of other model calculations in the literature. © 2010 Elsevier B.V. All rights reserved.

Rosato J.,Julich Research Center
American Journal of Physics | Year: 2010

The photon picture of radiation transport is examined. Because the photon has no mass and spin one, a position operator for a photon particle cannot be defined properly. This lack leads to ambiguity if the radiative transfer equation is associated with a quantum transport equation for photons. The issue of photon nonlocalizability is discussed and illustrated through a wavefunction-based approach. It is next shown that the phase space formalism due to Wigner provides a suitable framework for a proper derivation of a photon transport equation from first principles. © 2010 American Association of Physics Teachers.

A generic analytical model for the description of magnetic field lines in poloidal divertor tokamaks in the presence of external resonant magnetic perturbations is proposed. It is based on the Hamiltonian description of magnetic field lines in tokamaks. The safety factor and the spectra of magnetic perturbations are chosen by the requirement to satisfy their generic behaviour near the magnetic separatrix and at the magnetic axis. The field line equations are integrated by the construction of two symplectic and computationally efficient mappings of field lines. The model for internal MHD modes is also proposed. The mapping procedure for field lines which includes the MHD modes is described. It is shown that the numerically calculated diffusion and convection coefficients of field lines are in close agreement with the quasilinear ones. It is found that in the presence of internal MHD modes at the plasma edge the convectional outward transport of field lines may reverse its direction to inward convectional transport. © 2010 IAEA, Vienna.

Ermert J.,Julich Research Center
BioMed Research International | Year: 2014

This brief review gives an overview of newer developments in 18F-chemistry with the focus on small 18F-labelled molecules as intermediates for modular build-up syntheses. The short half-life (<2 h) of the radionuclide requires efficient syntheses of these intermediates considering that multistep syntheses are often time consuming and characterized by a loss of yield in each reaction step. Recent examples of improved synthesis of 18F-labelled intermediates show new possibilities for no-carrier-added ring-fluorinated arenes, novel intermediates for tri[18F]fluoromethylation reactions, and 18F-fluorovinylation methods. © 2014 Johannes Ermert.

Hillnhutter C.,University of Bonn | Sikora R.A.,University of Bonn | Oerke E.-C.,University of Bonn | Van Dusschoten D.,Julich Research Center
Journal of Experimental Botany | Year: 2012

Belowground symptoms of sugar beet caused by the beet cyst nematode (BCN) Heterodera schachtii include the development of compensatory secondary roots and beet deformity, which, thus far, could only be assessed by destructively removing the entire root systems from the soil. Similarly, the symptoms of Rhizoctonia crown and root rot (RCRR) caused by infections of the soil-borne basidiomycete Rhizoctonia solani require the same invasive approach for identification. Here nuclear magnetic resonance imaging (MRI) was used for the non-invasive detection of belowground symptoms caused by BCN and/or RCRR on sugar beet. Excessive lateral root development and beet deformation of plants infected by BCN was obvious 28 days after inoculation (dai) on MRI images when compared with non-infected plants. Three-dimensional images recorded at 56 dai showed BCN cysts attached to the roots in the soil. RCRR was visualized by a lower intensity of the MRI signal at sites where rotting occurred. The disease complex of both organisms together resulted in RCRR development at the site of nematode penetration. Damage analysis of sugar beet plants inoculated with both pathogens indicated a synergistic relationship, which may result from direct and indirect interactions. Nuclear MRI of plants may provide valuable, new insight into the development of pathogens infecting plants below-and aboveground because of its non-destructive nature and the sufficiently high spatial resolution of the method. © 2011 The Author(s).

Suljic S.,Heinrich Heine University Dusseldorf | Pietruszka J.,Heinrich Heine University Dusseldorf | Pietruszka J.,Julich Research Center
Advanced Synthesis and Catalysis | Year: 2014

A convenient arylation of diverse 3,4-dihydrocoumarins with a number of catechols is described leading to a new class of compounds. As key step, a laccase-catalysed oxidation/Michael addition sequence is applied using commercially available laccase from Agaricus bisporus. 3,4-Dihydrocoumarins were obtained in a rapid and facile two-step sequence starting from salicylaldehydes: The corresponding coumarins were synthesised through a Knoevenagel condensation in up to 83% yield followed by a quantitative reduction performed in a flow system. Combining the reductive flow reaction with the laccase-catalysed arylation also led to successful consecutive one-pot approaches. Overall, the enzyme-catalysed arylations were carried out with yields ranging from 63 to 94%. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Paulus D.H.,Friedrich - Alexander - University, Erlangen - Nuremberg | Tellmann L.,Julich Research Center | Quick H.H.,Friedrich - Alexander - University, Erlangen - Nuremberg
Physics in Medicine and Biology | Year: 2013

In positron emission tomography/computed tomography (PET/CT) hybrid imaging attenuation correction (AC) of the patient tissue and patient table is performed by converting the CT-based Hounsfield units (HU) to linear attenuation coefficients (LAC) of PET. When applied to the new field of hardware component AC in PET/magnetic resonance (MR) hybrid imaging, this conversion method may result in local overcorrection of PET activity values. The aim of this study thus was to optimize the conversion parameters for CT-based AC of hardware components in PET/MR. Systematic evaluation and optimization of the HU to LAC conversion parameters has been performed for the hardware component attenuation map (μ-map) of a flexible radiofrequency (RF) coil used in PET/MR imaging. Furthermore, spatial misregistration of this RF coil to its μ-map was simulated by shifting the μ-map in different directions and the effect on PET quantification was evaluated. Measurements of a PET NEMA standard emission phantom were performed on an integrated hybrid PET/MR system. Various CT parameters were used to calculate different μ-maps for the flexible RF coil and to evaluate the impact on the PET activity concentration. A 511 keV transmission scan of the local RF coil was used as standard of reference to adapt the slope of the conversion from HUs to LACs at 511 keV. The average underestimation of the PET activity concentration due to the non-attenuation corrected RF coil in place was calculated to be 5.0% in the overall phantom. When considering attenuation only in the upper volume of the phantom, the average difference to the reference scan without RF coil is 11.0%. When the PET/CT conversion is applied, an average overestimation of 3.1% (without extended CT scale) and 4.2% (with extended CT scale) is observed in the top volume of the NEMA phantom. Using the adapted conversion resulting from this study, the deviation in the top volume of the phantom is reduced to -0.5% and shows the lowest standard deviation inside the phantom in comparison to all other conversions. Simulation of a μ-map misregistration shows acceptable results for shifts below 5 mm for the flexible surface RF coil. The adapted conversion from HUs to LAC at 511 keV within this study can improve hardware component AC in PET/MR hybrid imaging as shown for a flexible RF surface coil. Furthermore, these results have a direct impact on the improvement of the hardware component AC of the examined flexible RF coil in conjunction with position determination. © 2013 Institute of Physics and Engineering in Medicine.

Cryogenic air separation is a mature state-of-the-art technology to produce the high tonnage of oxygen required for oxyfuel power plants. However, this technology represents an important burden to the net plant efficiency (losses between 8% and 12%-points). High temperature ceramic membranes, associated with significantly lower efficiency losses, are foreseen as the best candidate to challenge cryogenics for high tonnage oxygen production. Although this technology is still at an embryonic state of development, the three-end membrane operation mode offers important technical advantages over the four-end mode that can be a good technological option in the near future.This paper analyzes the influence of both, the cryogenic and three-end high temperature membrane air separation units on the net oxyfuel plant efficiency considering the same boundary conditions and different equivalent thermal integrations. Moreover, the oxygen permeation rate, heat recovery, and required membrane area are also evaluated at different membrane operating conditions. Using a state-of-the-art perovskite BSCF as membrane material, net plant efficiency losses up to 5.1%-points can be reached requiring around 400,000m2 of membrane area. Applying this membrane-based technology it is possible to improve the oxyfuel plant efficiency over 4%-points (compared with cryogenic technology); however, it is still necessary to develop new ceramic materials to reduce the amount of membrane area required. © 2010 Elsevier Ltd.

Bachmann M.,Julich Research Center
Physics Procedia | Year: 2010

We discuss general thermodynamic properties of molecular structure formation processes like protein folding by means of simplified, coarse-grained models. The conformational transitions accompanying these processes exhibit similarities to thermodynamic phase transitions, but also significant differences as the systems that we investigate here are very small. The usefulness of a microcanonical statistical analysis of these transitions in comparison with a canonical interpretation is emphasized. The results are obtained by employing sophisticated generalized-ensemble Markov-chain Monte Carlo methodologies. © 2010.

Wilbring E.,University of Bonn | Hammer H.-W.,University of Bonn | Meissner U.-G.,University of Bonn | Meissner U.-G.,Julich Research Center
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2013

The observation of the exotic quarkonium state Zc(3900) by the BESIII and Belle Collaborations supports the concept of hadronic molecules. Charmonium states interpreted as such molecules would be bound states of heavy particles with small binding energies. This motivates their description using an effective theory with contact interactions. In particular, we focus on the electromagnetic structure of the charged state Zc(3900). Using first experimental results concerning spin and parity, we interpret it as an S-wave molecule and calculate the form factors as well as charge and magnetic radii up to next-to-leading order. We also present first numerical estimations of some of these observables at leading order. © 2013 Elsevier B.V.

Zimmermann E.,Julich Research Center
Journal of Neurophysiology | Year: 2013

Saccade adaptation is a mechanism that adjusts saccade landing positions if they systematically fail to reach their intended target. In the laboratory, saccades can be shortened or lengthened if the saccade target is displaced during execution of the saccade. In this study, saccades were performed from different positions to an adapted saccade target to dissociate adaptation to a spatiotopic position in external space from a combined retinotopic and spatiotopic coding. The presentation duration of the saccade target before saccade execution was systematically varied, during adaptation and during test trials, with a delayed saccade paradigm. Spatiotopic shifts in landing positions depended on a certain preview duration of the target before saccade execution. When saccades were performed immediately to a suddenly appearing target, no spatiotopic adaptation was observed. These results suggest that a spatiotopic representation of the visual target signal builds up as a function of the duration the saccade target is visible before saccade execution. Different coordinate frames might also explain the separate adaptability of reactive and voluntary saccades. Spatiotopic effects were found only in outward adaptation but not in inward adaptation, which is consistent with the idea that outward adaptation takes place at the level of the visual target representation, whereas inward adaptation is achieved at a purely motor level. © 2013 the American Physiological Society.

Perez J.,Synchrotron Soleil | Koutsioubas A.,Julich Research Center
Acta Crystallographica Section D: Biological Crystallography | Year: 2015

The application of small-angle X-ray scattering (SAXS) to structural investigations of transmembrane proteins in detergent solution has been hampered by two main inherent hurdles. On the one hand, the formation of a detergent corona around the hydrophobic region of the protein strongly modifies the scattering curve of the protein. On the other hand, free micelles of detergent without a precisely known concentration coexist with the protein-detergent complex in solution, therefore adding an uncontrolled signal. To gain robust structural information on such systems from SAXS data, in previous work, advantage was taken of the online combination of size-exclusion chromatography (SEC) and SAXS, and the detergent corona around aquaporin-0, a membrane protein of known structure, could be modelled. A precise geometrical model of the corona, shaped as an elliptical torus, was determined. Here, in order to better understand the correlations between the corona model parameters and to discuss the uniqueness of the model, this work was revisited by analyzing systematic SAXS simulations over a wide range of parameters of the torus. © 2015.

Bar Sinai Y.,Weizmann Institute of Science | Brener E.A.,Weizmann Institute of Science | Brener E.A.,Julich Research Center | Bouchbinder E.,Weizmann Institute of Science
Geophysical Research Letters | Year: 2012

The failure of frictional interfaces and the spatiotemporal structures that accompany it are central to a wide range of geophysical, physical and engineering systems. Recent geophysical and laboratory observations indicated that interfacial failure can be mediated by slow slip rupture phenomena which are distinct from ordinary, earthquake-like, fast rupture. These discoveries have influenced the way we think about frictional motion, yet the nature and properties of slow rupture are not completely understood. We show that slow rupture is an intrinsic and robust property of simple non-monotonic rate-and-state friction laws. It is associated with a new velocity scale c min, determined by the friction law, below which steady state rupture cannot propagate. We further show that rupture can occur in a continuum of states, spanning a wide range of velocities from cmin to elastic wave-speeds, and predict different properties for slow rupture and ordinary fast rupture. Our results are qualitatively consistent with recent high-resolution laboratory experiments and may provide a theoretical framework for understanding slow rupture phenomena along frictional interfaces. Copyright 2012 by the American Geophysical Union.

Weidner R.,Julich Research Center
Journal of vision | Year: 2013

In order to efficiently deploy our limited visual processing resources, we must decide what information is relevant and to be prioritized and what information should rather be ignored. To detect visual information that we know is relevant but that is not very salient, we need to set our system to prioritize and combine information from different visual dimensions (e.g., size, color, motion). Four experiments examined the allocation of processing resources across different visual dimensions when observers searched for a singleton target defined by a conjunction of size (primary dimension: the target was always large) with either color or motion (secondary dimension: variable across trials) within heterogeneously sized, colored, and moving distractors. The results revealed search reaction times to be substantially increased in a given trial in which the secondary target dimension was changed from the preceding trial--indicative of a suboptimal distribution of dimensional weights carried over from the previous trial and of attentional weight being bound by the (need to filter within the) primary dimension, thereby reducing the weight available for processing the secondary dimensions. Semantic precueing of the secondary dimension and visual marking of the search-irrelevant items in the primary dimension reduced these costs significantly. However, observers were limited in their ability to implement both top-down sets simultaneously. These findings argue in favor of a parallel distribution of dimensional processing resources across multiple visual dimensions and, furthermore, that visual marking releases attentional weight bound to the primary dimension, thus permitting more efficient (parallel) processing in the secondary dimensions.

Pretz J.,Julich Research Center
Physica Scripta | Year: 2015

The electric dipole moment (EDM) is a fundamental property of a particle, like mass, charge and magnetic moment. What makes this property in particular interesting is the fact that a fundamental particle can only acquire an EDM via P and T violating processes. EDM measurements contribute to the understanding of the matter over anti-matter dominance in the universe, a question closely related to the violation of fundamental symmetries. Up to now measurements of EDMs have concentrated on neutral particles. Charged particle EDMs can be measured at storage ring. Plans at Forschungszentrum Jülich and results of first test measurements at the COoler SYnchrotron COSY will be presented. 2015 The Royal Swedish Academy of Sciences.

Guo X.,Julich Research Center
Scripta Materialia | Year: 2011

Works on nanostructured ZrO 2, including nanocrystalline ceramics, polycrystalline and epitaxial thin films, and heterostructures, are evaluated. Lower total conductivity has been achieved for nanocrystalline ceramics and polycrystalline thin films. Higher conductivity was reported for epitaxial films, but this might be an artefact of the substrate. The colossal ionic conductivity that was claimed for heterostructures has now been demonstrated to be electronic in origin. However, distinctively different properties may appear in ZrO 2 for grain sizes <5 nm. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Wang S.,University of Notre Dame | Alekseev E.V.,Julich Research Center | Depmeier W.,University of Kiel | Albrecht-Schmitt T.E.,University of Notre Dame
Chemical Communications | Year: 2011

The use of molten boric acid as a reactive flux for synthesizing actinide borates has been developed in the past two years providing access to a remarkable array of exotic materials with both unusual structures and unprecedented properties. [ThB5O6(OH)6][BO(OH) 2]·2.5H2O possesses a cationic supertetrahedral structure and displays remarkable anion exchange properties with high selectivity for TcO4 -. Uranyl borates form noncentrosymmetric structures with extraordinarily rich topological relationships. Neptunium borates are often mixed-valent and yield rare examples of compounds with one metal in three different oxidation states. Plutonium borates display new coordination chemistry for trivalent actinides. Finally, americium borates show a dramatic departure from plutonium borates, and there are scant examples of families of actinides compounds that extend past plutonium to examine the bonding of later actinides. There are several grand challenges that this work addresses. The foremost of these challenges is the development of structure-property relationships in transuranium materials. A deep understanding of the materials chemistry of actinides will likely lead to the development of advanced waste forms for radionuclides present in nuclear waste that prevent their transport in the environment. This work may have also uncovered the solubility-limiting phases of actinides in some repositories, and allows for measurements on the stability of these materials. © 2011 The Royal Society of Chemistry.

Hoferichter M.,University of Washington | Ruiz de Elvira J.,University of Bonn | Kubis B.,University of Bonn | Meissner U.-G.,University of Bonn | Meissner U.-G.,Julich Research Center
Physics Reports | Year: 2016

We review the structure of Roy-Steiner equations for pion-nucleon scattering, the solution for the partial waves of the t-channel process ππ→NN, as well as the high-accuracy extraction of the pion-nucleon S-wave scattering lengths from data on pionic hydrogen and deuterium. We then proceed to construct solutions for the lowest partial waves of the s-channel process π N→ π N and demonstrate that accurate solutions can be found if the scattering lengths are imposed as constraints. Detailed error estimates of all input quantities in the solution procedure are performed and explicit parameterizations for the resulting low-energy phase shifts as well as results for subthreshold parameters and higher threshold parameters are presented. Furthermore, we discuss the extraction of the pion-nucleon σ-term via the Cheng-Dashen low-energy theorem, including the role of isospin-breaking corrections, to obtain a precision determination consistent with all constraints from analyticity, unitarity, crossing symmetry, and pionic-atom data. We perform the matching to chiral perturbation theory in the subthreshold region and detail the consequences for the chiral convergence of the threshold parameters and the nucleon mass. © 2016 Elsevier B.V.

Qaim S.M.,Julich Research Center
Radiochimica Acta | Year: 2011

In molecular imaging, the importance of novel longer lived positron emitters, also termed as non-standard or innovative PET radionuclides, has been constantly increasing, especially because they allow studies on slow metabolic processes and in some cases furnish the possibility of quantification of radiation dose in internal radiotherapy. Considerable efforts have been invested worldwide and about 25 positron emitters have been developed. Those efforts relate to interdisciplinary studies dealing with basic nuclear data, high current charged particle irradiation, efficient radiochemical separation and quality control of the desired radionuclide, and recovery of the enriched target material for reuse. In this review all those aspects are briefly discussed, with particular reference to three radionuclides, namely 64Cu, 124I and 86Y, which are presently in great demand. For each radionuclide several nuclear routes were investigated but the (p, n) reaction on an enriched target isotope was found to be the best for use at a small-sized cyclotron. Some other positron emitting radionuclides, such as 55Co, 76Br, 89Zr, 82mRb, 94mTc, 120I, etc., were also produced via the low-energy (p,n), (p,α) or (d, n) reaction. On the other hand, the production of radionuclides 52Fe, 73Se, 83Sr, etc. using intermediate energy (p, xn) or (d, xn) reactions needs special consideration, the nuclear data and chemical processing methods being of key importance. In a few special cases, a high intensity 3He-or a-particle beam could be an added advantage. The production of some potentially interesting positron emitters via generator systems, for example 44Ti/ 44Sc, 72Se/ 72As and 140Nd/ 140Pr is considered. The significance of new generation high power accelerators is briefly discussed. © by Oldenbourg Wissenschaftsverlag, München.

Shah N.J.,Julich Research Center | Shah N.J.,RWTH Aachen | Shah N.J.,Julich Aachen Research Alliance JARA
Brain Structure and Function | Year: 2015

The aim of this paper is twofold: firstly, to explore the potential of simultaneously acquiring multimodal MR–PET–EEG data in a human 9.4 T scanner to provide a platform for metabolic brain imaging. Secondly, to demonstrate that the three modalities are complementary, with MRI providing excellent structural and functional imaging, PET providing quantitative molecular imaging, and EEG providing superior temporal resolution. A 9.4 T MRI scanner equipped with a PET insert and a commercially available EEG device was used to acquire in vivo proton-based images, spectra, and sodium- and oxygen-based images with MRI, EEG signals from a human subject in a static 9.4 T magnetic field, and demonstrate hybrid MR–PET capability in a rat model. High-resolution images of the in vivo human brain with an isotropic resolution of 0.5 mm and post-mortem brain images of the cerebellum with an isotropic resolution of 320 µm are presented. A 1H spectrum was also acquired from 2 × 2 × 2 mm voxel in the brain allowing 12 metabolites to be identified. Imaging based on sodium and oxygen is demonstrated with isotropic resolutions of 2 and 5 mm, respectively. Auditory evoked potentials measured in a static field of 9.4 T are shown. Finally, hybrid MR–PET capability at 9.4 T in the human scanner is demonstrated in a rat model. Initial progress on the road to 9.4 T multimodal MR–PET–EEG is illustrated. Ultra-high resolution structural imaging, high-resolution images of the sodium distribution and proof-of-principle 17O data are clearly demonstrated. Further, simultaneous MR–PET data are presented without artefacts and EEG data successfully corrected for the cardioballistic artefact at 9.4 T are presented. © 2014, Springer-Verlag Berlin Heidelberg.

Spichtinger P.,Johannes Gutenberg University Mainz | Kramer M.,Julich Research Center
Atmospheric Chemistry and Physics | Year: 2013

The occurrence of high, persistent ice supersaturation inside and outside cold cirrus in the tropical tropopause layer (TTL) remains an enigma that is intensely debated as the ice supersaturation puzzle. However, it was recently confirmed that observed supersaturations are consistent with very low ice crystal concentrations, which is incompatible with the idea that homogeneous freezing is the major method of ice formation in the TTL. Thus, the tropical tropopause ice supersaturation puzzle has become an ice nucleation puzzle. To explain the low ice crystal concentrations, a number of mainly heterogeneous freezing methods have been proposed. Here, we reproduce in situ measurements of frequencies of occurrence of ice crystal concentrations by extensive model simulations, driven by the special dynamic conditions in the TTL, namely the superposition of slow large-scale updraughts with high-frequency short waves. From the simulations, it follows that the full range of observed ice crystal concentrations can be explained when the model results are composed from scenarios with consecutive heterogeneous and homogeneous ice formation and scenarios with pure homogeneous ice formation occurring in very slow (< 1 cm s-1) and faster (> 1 cm s-1) large-scale updraughts, respectively. This statistical analysis shows that about 80% of TTL cirrus can be explained by classical homogeneous ice nucleation, while the remaining 20% stem from heterogeneous and homogeneous freezing occurring within the same environment. The mechanism limiting ice crystal production via homogeneous freezing in an environment full of gravity waves is the shortness of the gravity waves, which stalls freezing events before a higher ice crystal concentration can be formed. © Author(s) 2013. CC Attribution 3.0 License.

Karthauser S.,Julich Research Center
Journal of Physics Condensed Matter | Year: 2011

In this review, possibilities to modify intentionally the electronic transport properties of metal/molecule/metal devices (MMM devices) are discussed. Here especially the influence of the metal work function, the metal-molecule interface, the molecule dipole and different tunneling mechanisms are considered. A route to evaluate the effective surface work function of metal-molecule systems is given and, based on experimental results, an exemplary estimation is performed. The electron transport across different metal-molecule interfaces is characterized by relating transmission coefficients extracted from experimentally derived molecular conductances, decay constants or tunneling barrier heights. Based on the reported results the tunneling decay constant can be assumed to be suitable to characterize intrinsic molecular electron transport properties, while the nature of the metal-molecule contacts is properly described by the transmission coefficient. A clear gradation of transmission efficiencies of metal-anchoring group combinations can be given. © 2011 IOP Publishing Ltd.

Bohn B.,Julich Research Center | Zetzsch C.,University of Bayreuth | Zetzsch C.,Fraunhofer Institute for Toxicology and Experimental Medicine
Physical Chemistry Chemical Physics | Year: 2012

The reversible gas-phase addition of OH radicals to the trimethylbenzenes was investigated in pulsed experiments utilizing VUV flash-photolysis resonance-fluorescence of H2O in the temperature range of 275-340 K. Triexponential OH decays were observed in the presence of the trimethylbenzenes, indicating the participation of more than one adduct species. Analytical solutions for the system of differential equations with two adduct isomers were derived, and the OH decay curves were evaluated based on this reaction model. This led to significant improvements of fit qualities and notable changes in OH rate constants compared to a previous model with a single adduct species. The detailed analysis was confined to 1,3,5-trimethylbenzene where reversible formation of two OH-aromatic ortho- and ipso-adduct isomers is feasible in accordance with the extended reaction model. Only after inclusion of additional isomerization reactions, consistent thermochemical data were obtained from the fitted rate constants. Reaction enthalpies of -83 ± 7 kJ mol-1 and -35 ± 22 kJ mol-1 were derived for the formation of one adduct isomer and the isomerization into the other, respectively. Based on literature data, the more and less stable adducts were assigned to ipso- and ortho-adduct isomers, respectively. The potential isomerization precluded the determination of primary yields of adduct isomers but formation of the ipso-adduct in any case is a minor process. For the rate constants of the OH + 1,3,5-trimethylbenzene reaction an Arrhenius expression kOH = 1.32 × 10-11 cm3 s-1 exp(450 ± 50 K/T) was obtained. Based on the same approach, the rate constants of the OH reactions with 1,2,3-trimethylbenzene and 1,2,4-trimethylbenzene were derived as k OH = 3.61 × 10-12 cm3 s-1 exp(620 ± 80 K/T) and kOH = 2.73 × 10-12 cm3 s-1 exp(730 ± 70 K/T), respectively. This journal is © the Owner Societies.

Cui C.,TU Berlin | Gan L.,TU Berlin | Neumann M.,TU Berlin | Heggen M.,Julich Research Center | And 2 more authors.
Journal of the American Chemical Society | Year: 2014

Colloid-based chemical synthesis methods of bimetallic alloy nanoparticles (NPs) provide good monodispersity, yet generally show a strong variation of the resulting mean particle size with alloy composition. This severely compromises accurate correlation between composition of alloy particles and their size-dependent properties. To address this issue, a general CO adsorption-assisted capping ligand-free solvothermal synthesis method is reported which provides homogeneous bimetallic NPs with almost perfectly constant particle size over an unusually wide compositional range. Using Pt-Ni alloy NPs as an example, we show that variation of the reaction temperature between 160 and 240 °C allows for precise control of the resulting alloy particle bulk composition between 15 and 70 atomic % Ni, coupled with a constant mean particle size of ∼4 nm. The size-confining and Ni content-controlling role of CO during the nucleation and growth processes are investigated and discussed. Data suggest that size-dependent CO surface chemisorption and reversible Ni-carbonyl formation are key factors for the achievement of a constant particle size and temperature-controlled Ni content. To demonstrate the usefulness of the independent control of size and composition, size-deconvoluted relations between composition and electrocatalytic properties are established. Refining earlier reports, we uncover intrinsic monotonic relations between catalytic activity and initial Ni content, as expected from theoretical considerations. © 2014 American Chemical Society.

Cherstvy A.G.,University of Potsdam | Winkler R.G.,Julich Research Center
Journal of Physical Chemistry B | Year: 2012

We analyze theoretically the influence of low-dielectric boundaries on the adsorption of flexible polyelectrolytes onto planar and spherical oppositely charged surfaces in electrolyte solutions. We rationalize to what extent polymer chains are depleted from adsorbing interfaces by repulsive image forces. We employ the WKB (Wentzel-Kramers-Brillouin) quantum mechanical method for the Green function of the Edwards equation to determine the adsorption equilibrium. Scaling relations are determined for the critical adsorption strength required to initiate polymer adsorption onto these low-dielectric supports. Image-force repulsion shifts the equilibrium toward the desorbed state, demanding larger surface charge densities and polyelectrolyte linear charge densities for the adsorption to take place. The effect is particularly pronounced for a planar interface in a low-salt regime, where a dramatic change in the scaling behavior for the adsorption-desorption transition is predicted. For the adsorbed state, polymers with higher charge densities are displaced further from the interface by image-charge repulsions. We discuss relevant experimental evidence and argue about possible biological applications of the results. © 2012 American Chemical Society.

Peksen M.,Julich Research Center
International Journal of Hydrogen Energy | Year: 2011

This paper presents a coupled 3D thermofluid/thermomechanical analysis of a 36-layer planar type SOFC stack. Typical components such as the cell, wire mesh, frame, interconnector plate and glass-ceramic sealant have been considered, including the physical resolution of the air channels and the manifold regions. The coupled computational mechanics study accounts for the nonlinear elastoplastic behaviour of the interconnector plate, as well as the mal flow behaviour that may result in thermomechanical differences within the stack. Locations susceptible to stress within the fuel cell stack could be determined. A feasibility study considering the geometrical effect of the wire mesh structure on the thermomechanical modelling results has been introduced. The study gives an insight how full scale fuel cells can be modelled effectively with the aid to develop and design reliable and robust fuel cell stacks. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Segovia J.,University of Salamanca | Roberts C.D.,Argonne National Laboratory | Schmidt S.M.,Julich Research Center
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

Analyses of the three valence-quark bound-state problem in relativistic quantum field theory predict that the nucleon may be understood primarily as a Borromean bound-state, in which binding arises mainly from two separate effects. One originates in non-Abelian facets of QCD that are expressed in the strong running coupling and generate confined but strongly-correlated colour-antitriplet diquark clusters in both the scalar-isoscalar and pseudovector-isotriplet channels. That attraction is magnified by quark exchange associated with diquark breakup and reformation. Diquark clustering is driven by the same mechanism which dynamically breaks chiral symmetry in the Standard Model. It has numerous observable consequences, the complete elucidation of which requires a framework that also simultaneously expresses the running of the coupling and masses in the strong interaction. Planned experiments are capable of validating this picture. © 2015 Argonne National Laboratory and The Authors.

Pitschmann M.,Vienna University of Technology | Seng C.-Y.,University of Massachusetts Amherst | Roberts C.D.,Argonne National Laboratory | Schmidt S.M.,Julich Research Center
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

A symmetry-preserving Dyson-Schwinger equation treatment of a vector-vector contact interaction is used to compute dressed-quark-core contributions to the nucleon σ-term and tensor charges. The latter enable one to directly determine the effect of dressed-quark electric dipole moments (EDMs) on neutron and proton EDMs. The presence of strong scalar and axial-vector diquark correlations within ground-state baryons is a prediction of this approach. These correlations are active participants in all scattering events and thereby modify the contribution of the singly represented valence quark relative to that of the doubly represented quark. Regarding the proton σ-term and that part of the proton mass which owes to explicit chiral symmetry breaking, with a realistic d- u mass splitting, the singly represented d quark contributes 37% more than the doubly represented u quark; and in connection with the proton's tensor charges, δTu, δTd, the ratio δTd/δTu is 18% larger than anticipated from simple quark models. Of particular note, the size of δTu is a sensitive measure of the strength of dynamical chiral symmetry breaking; and δTd measures the amount of axial-vector diquark correlation within the proton, vanishing if such correlations are absent. © 2015 American Physical Society.

Cherstvy A.G.,Julich Research Center
Journal of Physical Chemistry B | Year: 2011

First, we develop a model of counterion condensation on highly charged polyelectrolyte rings. Using the known analytical results for the electrostatic energy of ring formation, a stronger counterion adsorption is anticipated onto a cyclized polyelectrolyte, as compared to the Manning prediction for a straight rod-like polyelectrolyte. This fact ensures a lower energetic cost of polyelectrolyte bending into a ring. In the main part of the work, we investigate the impact of charges on cyclization of short DNA fragments, both theoretically and by computer simulations. An approximate expression for the electrostatically renormalized DNA cyclization probability is proposed that incorporates the electrostatic energies of polyelectrolyte cyclization and dimerization reactions. Depending on concentration of simple salt and chain length, the probability of formation of ideal polyelectrolyte rings can be either electrostatically inhibited or enhanced. The latter effect is quite counterintuitive. Afterward, simple computer simulations are performed to enumerate the effects of DNA thermal fluctuations onto the electrostatic energies of cyclized and dimerized DNA fragments in solution. Their outcomes support the possibility of electrostatically enhanced polyelectrolyte ring formation reaction in solution. In the end, we discuss some implications of the results obtained for the future DNA cyclization experiments and provide a short analysis of possible DNA-related features neglected in the modeling. © 2011 American Chemical Society.

Beale S.B.,Julich Research Center
International Journal of Hydrogen Energy | Year: 2015

A standard mechanical engineering mass transfer analysis is adapted to obtain performance calculations for the cathode of a typical polymer electrolyte membrane fuel cell. Mathematical details are provided and sample calculations performed, based on a number of simplifying assumptions. The relative advantages of low and high-mass transfer formulations are critically appraised and compared to a highly-simplified method. © 2015 Hydrogen Energy Publications, LLC. All rights reserved.

Mauer G.,Julich Research Center
Plasma Chemistry and Plasma Processing | Year: 2014

Plasma spray-physical vapor deposition (PS-PVD) is a novel coating process based on plasma spraying. In contrast to conventional methods, deposition takes place not only from liquid splats but also from nano-sized clusters and from the vapor phase. This offers new opportunities to obtain advanced microstructures and thus to comply with growing demands on modern functional coatings. In this study, different process conditions were investigated with regard to the application of the PS-PVD process for ceramic thermal barrier coatings. Plasma characteristics were calculated under chemical equilibrium conditions by minimizing the Gibbs energy. The plasma-feedstock interaction was modeled taking into account the particular conditions at very low pressure. Since the plasma is highly rarefied, the small feedstock particles are in the free molecular flow regime. Hence, continuum methods commonly used in fluid mechanics and heat transfer approaches with continuous boundary conditions are not appropriate; alternative methods based on the kinetic theory of gases are required. The experimental results confirm the predictions about the degree of vaporization made by such calculations. In particular, they show that the feedstock treatment mainly takes place within the very first trajectory segment between injector and jet expansion. © 2014 Springer Science+Business Media New York.

Aeberhard U.,Julich Research Center
IEEE Journal on Selected Topics in Quantum Electronics | Year: 2013

Many advanced concepts for high-efficiency photovoltaic devices exploit the peculiar optoelectronic properties of semiconductor nanostructures such as quantum wells, quantum wires, and quantum dots. While the optics of such devices is only modestly affected due to the small size of the structures, the optical transitions and electronic transport can strongly deviate from the simple bulk picture known from conventional solar cell devices. This paper discusses the challenges for an adequate theoretical description of the photovoltaic device operation arising from the introduction of nanostructure absorber and/or conductor components and gives an overview of existing device simulation approaches. © 1995-2012 IEEE.

Tokar M.Z.,Julich Research Center
Journal of Computational Physics | Year: 2010

In diverse media the characteristics of mass and heat transfer may undergo spontaneous and abrupt changes in time and space. This can lead to the formation of regions with strongly reduced transport, so called transport barriers (TB). The presence of interfaces between regions with qualitatively and quantitatively different transport characteristics impose severe requirements to methods and numerical schemes used by solving of transport equations. In particular the assumptions made in standard methods about the solution behavior by representing its derivatives fail in points where the transport changes abruptly. The situation is complicated further by the fact that neither the formation time nor the positions of interfaces are known a priori. A numerical approach, operating reliably under such conditions, is proposed. It is based on the introduction of a new dependent variable related to the variation after one time step of the original one integrated over the volume. In the vicinity of any grid knot the resulting differential equation is approximated by a second order ordinary differential equation with constant coefficients. Exact analytical solutions of these equations are conjugated between knots by demanding the continuity of the total solution and its first derivative. As an example the heat transfer in media with heat conductivity decreasing abruptly when the temperature e-folding length exceeds a critical value is considered. The formation of TB both at a heating power above the critical level and caused with radiation energy losses non-linearly dependent on the temperature is modeled. © 2009 Elsevier Inc. All rights reserved.

Direct and phonon-assisted tunneling currents in InAlGaAs-InGaAs bulk and double-quantum-well interband tunnel heterojunctions are simulated rigorously using the nonequilibrium Green's function formalism for coherent and dissipative quantum transport in combination with a simple two-band tight-binding model for the electronic structure. A realistic band profile and the associated built-in electrostatic field are obtained via self-consistent coupling of the transport formalism to Poisson's equation. The model reproduces experimentally observed features in the current-voltage characteristics of the devices, such as the pronounced current enhancement in the quantum-well junction as compared to the bulk junction and the structure appearing in the negative-differential resistance regime due to quantization of emitter states. Local maps of density of states and the current spectrum reveal the impact of quasibound states, electric fields, and electron-phonon scattering on the interband tunneling current. In this way, resonances appearing in the current through the double-quantum-well structure in the negative-differential resistance regime can be related to the alignment of subbands in the coupled quantum wells. © 2013 American Physical Society.

Oelert W.,Julich Research Center
International Journal of Modern Physics A | Year: 2011

CERN has a long tradition of pursuing fundamental physics on a variety of energy scales. For anti-protons CERN famously produced the high-energy SPS beam but also the world's only and unique sources of low-energy anti-protons - first the Low Energy Anti-proton Ring (LEAR) and thereafter the Anti-proton Decelerator (AD). The scientific demand for low-energy anti-protons at the AD continues to grow. More rapid progress and much higher measurement precision might be possible by upgrading the AD to increase and optimize the number of cold anti-protons that can be trapped and accumulated. To achieve this the construction of an Extra Low ENergy Antiproton (ELENA) ring is proposed which involves both the addition of a small storage ring and electrostatic beam lines to the experiments. The design parameters have been carefully studied and agreed upon over several years. At least during the next decade there is no alternative low-energy anti-proton source for physics to be done now. © 2011 World Scientific Publishing Company.

Friedrich M.,Max Planck Institute for Chemical Physics of Solids | Penner S.,University of Innsbruck | Heggen M.,Julich Research Center | Armbruster M.,Max Planck Institute for Chemical Physics of Solids
Angewandte Chemie - International Edition | Year: 2013

Together we are strong: Immediately after high-temperature reduction, ZnPd/ZnO catalysts are not notably CO2 selective in the methanol steam reforming process. Under methanol steam reforming conditions, high CO 2 selectivity can only be achieved by the rather slow formation of ZnO patches on the surface of intermetallic ZnPd nanoparticles to create a highly synergistic interface. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In this work, single-asperity contact mechanics is investigated for positive and negative work of adhesion Δγ. In the latter case, finite-range repulsion acts in addition to hard-wall constraints. This constitutes a continuum model for a contact immersed in a strongly wetting fluid, which can only be squeezed out in the center of the contact through a sufficiently large normal load FN. As for positive work of adhesion, two stable solutions can coexist in a finite range of normal loads. The competing solutions can be readily interpreted as contacts with either a load-bearing or a squeezed-out fluid. The possibility for coexistence and the subsequent discontinuous wetting and squeeze-out instabilities depend not only on the Tabor coefficient μT but also on the functional form of the finite-range repulsion. For example, coexistence and discontinuous wetting or squeeze-out do not occur when the repulsion decreases exponentially with distance. For positive work of adhesion, the normal displacement mainly depends on FN, Δγ, and μT but - unlike the contact area - barely on the functional form of the finite-range attraction. The results can benefit the interpretation of atomic force microscopy in liquid environments and the modeling of multi-asperity contacts. © 2014 Müser.

Haidenbauer J.,Julich Research Center
Journal of Physics: Conference Series | Year: 2011

The status of our present knowledge on the antinucleon-nucleon interaction at low and medium energies is discussed. Special emphasis is put on aspects related to its spin dependence which are relevant for experiments planned by the PAX collaboration. Predictions for the spin-dependent p̄p cross sections σ1 and σ2 are presented, utilizing N̄N potential models developed by the Jülich group, and compared to results based on the amplitudes of the Nijmegen partial-wave analysis.

Lentzen M.,Julich Research Center
Ultramicroscopy | Year: 2014

In a recent article it is argued that the far-field expansion of electron scattering, a pillar of electron diffraction theory, is wrong (Treacy and Van Dyck, 2012 [1]). It is further argued that in the first Born approximation of electron scattering the intensity of the electron wave is not conserved to first order in the scattering potential. Thus a "mystery of the missing phase" is investigated, and the supposed flaw in scattering theory is seeked to be resolved by postulating a standing spherical electron wave (Treacy and Van Dyck, 2012 [1]). In this work we show, however, that these theses are wrong. A review of the essential parts of scattering theory with careful checks of the underlying assumptions and limitations for high-energy electron scattering yields: (1) the traditional form of the far-field expansion, comprising a propagating spherical wave, is correct; (2) there is no room for a missing phase; (3) in the first Born approximation the intensity of the scattered wave is conserved to first order in the scattering potential. The various features of high-energy electron scattering are illustrated by wave-mechanical calculations for an explicit target model, a Gaussian phase object, and for a Si atom, considering the geometric conditions in high-resolution transmission electron microscopy. © 2013 Elsevier B.V.

Schefold J.,Institute for Energy Research of Germany | Brisse A.,Institute for Energy Research of Germany | Tietz F.,Julich Research Center
Journal of the Electrochemical Society | Year: 2012

An anode-supported solid oxide fuel cell of 45 cm 2+ area was operated during 9000 h as electrolyser cell at about 780°C and -1 Acm -2 current density. The cell consisted of yttria-stabilised zircona (YSZ) as electrolyte, the hydrogen electrode of a nickel-YSZ cermet, and the oxygen electrode of strontium-substituted lanthanum ferritecobaltite (LSCF). The voltage loss under constant current operation over the entire experiment was 3.8 (40 mV)1000 h. This value also accounts for experimental incidents, e.g. contact deterioration due to mechanical shocks or a supply failure of feed gas. Degradation during the initial 5600 h was 2.5 1000 h. It was even lower during the incident-free period of the experiment, i.e. 1.7 1000 h from 2000 to 5600 h, close to the technical target for an electrolyser system. The low cell voltage (initial U cell 1.06 V) together with the known nearly ideal faradaic efficiency mean an (electrical-to-chemical) energy-conversion efficiency η el above the one achieved with electrolysis at low temperature, with η el >100 up to 7600 h (with heat supply). Impedance spectroscopic results indicate that degradation results from an increase in ohmic electrolyte resistance as well as in the reaction overpotential of at least one electrode. © 2011 The Electrochemical Society.

Reigh S.Y.,Julich Research Center
PloS one | Year: 2013

Peritrichous bacteria exploit bundles of helical flagella for propulsion and chemotaxis. Here, changes in the swimming direction (tumbling) are induced by a change of the rotational frequency of some flagella. Employing coarse-grained modeling and simulations, we investigate the dynamical properties of helical flagella bundles driven by mismatched motor torques. Over a broad range of distances between the flagella anchors and applied torque differences, we find a stable bundled state, which is important for a robust directional motion of a bacterium. With increasing torque difference, a phase lag in the flagellar rotations develops, followed by slippage and ultimately unbundling, which sensitively depends on the anchoring distance of neighboring flagella. In the slippage and drift states, the different rotation frequencies of the flagella generate a tilting torque on the bacterial body, which implies a change of the swimming direction as observed experimentally.

Drdla K.,NASA | Mu R.,Julich Research Center
Annales Geophysicae | Year: 2012

Low stratospheric temperatures are known to be responsible for heterogeneous chlorine activation that leads to polar ozone depletion. Here, we discuss the temperature threshold below which substantial chlorine activation occurs. We suggest that the onset of chlorine activation is dominated by reactions on cold binary aerosol particles, without the formation of polar stratospheric clouds (PSCs), i.e. without any significant uptake of HNO3 from the gas phase. Using reaction rates on cold binary aerosol in a model of stratospheric chemistry, a chlorine activation threshold temperature, TACL, is derived. At typical stratospheric conditions, TACL is similar in value to TNAT (within 1-2 K), the highest temperature at which nitric acid trihydrate (NAT) can exist. TNAT is still in use to parameterise the threshold temperature for the onset of chlorine activation. However, perturbations can cause TACL to differ from TNAT: TACL is dependent upon H2O and potential temperature, but unlike TNAT is not dependent upon HNO 3. Furthermore, in contrast to TNAT, TACLis dependent upon the stratospheric sulfate aerosol loading and thus provides a means to estimate the impact on polar ozone of strong volcanic eruptions and some geo-engineering options, which are discussed. A parameterisation of TACL is provided here, allowing it to be calculated for low solar elevation (or high solar zenith angle) over a comprehensive range of stratospheric conditions. Considering TACL as a proxy for chlorine activation cannot replace a detailed model calculation, and polar ozone loss is influenced by other factors apart from the initial chlorine activation. However, TACL provides a more accurate description of the temperature conditions necessary for chlorine activation and ozone loss in the polar stratosphere than TNAT. © 2012 Author(s).

Wang Q.,Julich Research Center
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

The P-wave and S-wave heavy-light mesons and their charge conjugates, i.e., D1(2420)D̄+c.c., D1(2420)D̄*+c.c., and D2(2460) D̄*+c.c., can couple to states with vector quantum number JPC=1 - and exotic quantum number JPC=1-+ in a relative S wave. Near threshold, the heavy-light meson pair may form hadronic molecules due to the strong S-wave coupling, and the mysterious vector state Y(4260) could be such a state of the D1(2420)D̄+c.c. molecule. This implies the possible existence of its conjugate partner made of the same heavy-light mesons but with exotic quantum number JPC=1-+. We evaluate the production rate of such exotic hadronic molecules and propose a direct experimental search for them in e+e- annihilation. Confirmation of such exotic states in experiment will certainly deepen our insights into strong QCD and the arrangement of multiquark degrees of freedom. © 2014 American Physical Society.

Cerfontaine P.,RWTH Aachen | Botzem T.,RWTH Aachen | Divincenzo D.P.,RWTH Aachen | Divincenzo D.P.,Julich Research Center | Bluhm H.,RWTH Aachen
Physical Review Letters | Year: 2014

Single-qubit operations on singlet-triplet qubits in GaAs double quantum dots have not yet reached the fidelities required for fault-tolerant quantum information processing. Considering experimentally important constraints and using measured noise spectra, we numerically minimize the effect of decoherence (including high-frequency 1/f-like noise) and show, theoretically, that quantum gates with fidelities higher than 99.9% are achievable. We also present a self-consistent tuning protocol which should allow the elimination of individual systematic gate errors directly in an experiment. © 2014 American Physical Society.

Boussinot G.,ONERA | Boussinot G.,Julich Research Center | Le Bouar Y.,ONERA | Finel A.,ONERA
Acta Materialia | Year: 2010

We present a 2D and 3D phase-field analysis of microstructure evolution in the presence of a lattice misfit and with inhomogeneous elastic constants. The method is first critically compared with a Monte Carlo modeling at the atomic scale. We then apply the phase-field model to the Ni-Al system under external load along a cubic axis. We find that the microstructure becomes anisotropic and that the situation qualitatively differs depending on the sign of the applied stress. The microstructure evolution operates mainly by shape changes and alignments of precipitates, but also by splitting of precipitates initially elongated along directions perpendicular to the stress-induced, elastically favorable directions. The final microstructure is finally qualitatively analyzed in terms of a mean field theory in which the elastic inhomogeneity is embedded into an effective eigenstrain. This analysis leads to a simple formulation which can be used to easily predict the coherent microstructural anisotropy induced by any external loading condition. © 2010 Acta Materialia Inc. Published by Elsevier Ltd.

Kshirsagar M.,Carnegie Mellon University | Carbonell J.,Carnegie Mellon University | Klein-Seetharaman J.,Carnegie Mellon University | Klein-Seetharaman J.,Julich Research Center | Klein-Seetharaman J.,University of Warwick
Bioinformatics | Year: 2013

Motivation: An important aspect of infectious disease research involves understanding the differences and commonalities in the infection mechanisms underlying various diseases. Systems biology-based approaches study infectious diseases by analyzing the interactions between the host species and the pathogen organisms. This work aims to combine the knowledge from experimental studies of host-pathogen interactions in several diseases to build stronger predictive models. Our approach is based on a formalism from machine learning called 'multitask learning', which considers the problem of building models across tasks that are related to each other. A 'task' in our scenario is the set of host-pathogen protein interactions involved in one disease. To integrate interactions from several tasks (i.e. diseases), our method exploits the similarity in the infection process across the diseases. In particular, we use the biological hypothesis that similar pathogens target the same critical biological processes in the host, in defining a common structure across the tasks.Results: Our current work on host-pathogen protein interaction prediction focuses on human as the host, and four bacterial species as pathogens. The multitask learning technique we develop uses a task-based regularization approach. We find that the resulting optimization problem is a difference of convex (DC) functions. To optimize, we implement a Convex-Concave procedure-based algorithm. We compare our integrative approach to baseline methods that build models on a single host-pathogen protein interaction dataset. Our results show that our approach outperforms the baselines on the training data. We further analyze the protein interaction predictions generated by the models, and find some interesting insights. © The Author 2013.

Haidenbauer J.,Julich Research Center | Krein G.,Sao Paulo State University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

We study the production of charmed mesons (D, Ds) in antiproton-proton (p̄p) annihilation close to the reaction thresholds. The elementary charm production process is described by baryon exchange and in the constituent quark model. Effects of the interactions in the initial and final states are taken into account rigorously. The calculations are performed in close analogy to our earlier study on p̄p→K̄K by connecting the processes via SU(4) flavor symmetry. Our predictions for the DD̄ production cross section are in the order of 10-2-10-1μb. They turned out to be comparable to those obtained in other studies. The cross section for a Ds+Ds- pair is found to be of the same order of magnitude despite the fact that its production in p̄p scattering requires a two-step process. © 2014 American Physical Society.

Zinn T.,University of Oslo | Willner L.,Julich Research Center | Lund R.,University of Oslo
Physical Review Letters | Year: 2014

It is well known that liquids confined to small nanoscopic pores and droplets exhibit thermal behavior very different from bulk samples. Less is known about liquids spontaneously confined through self-assembly into micellar structures. Here we demonstrate, using a very well-defined n-alkyl-poly(ethylene oxide) polymer system with a tunable structure, that n-alkane(s) forming 2-3 nm small micellar cores are affected considerably by confinement in the form of melting point depressions. Moreover, comparing the reduction in melting points, ΔTm, determined through volumetric and calorimetric methods with the micellar core radius, Rc, obtained from small-angle x-ray scattering, we find excellent agreement with the well-known Gibbs-Thomson equation, ΔTm∼Rc-1. This demonstrates that the reduced size, i.e., the Laplace pressure, is the dominant parameter governing the melting point depression in micellar systems. © 2014 American Physical Society.

Jensen A.A.,Copenhagen University | Fahlke C.,Julich Research Center | Bjorn-Yoshimoto W.E.,Copenhagen University | Bunch L.,Copenhagen University
Current Opinion in Pharmacology | Year: 2015

The five excitatory amino acid transporters (EAAT1-5) mediating the synaptic uptake of the major excitatory neurotransmitter glutamate are differently expressed throughout the CNS and at the synaptic level. Although EAATs are crucial for normal excitatory neurotransmission, explorations into the physiological functions mediated by the different transporter subtypes and their respective therapeutic potential have so far been sparse, in no small part due to the limited selection of pharmacological tools available. In the present update, we outline important new insights into the molecular compositions of EAATs and their intricate transport process, the novel approaches to pharmacological modulation of the transporters that have emerged, and interesting new perspectives in EAAT as drug targets proposed in recent years. © 2014 Elsevier Ltd. All rights reserved.

Blossfeld S.,Julich Research Center
Plant and Soil | Year: 2013

Background: The simple term "rhizosphere" is well defined and has inspired numerous studies from a broad field of science since the beginning of the 20th century. However, we still know very little about the spatial and temporal heterogeneity of rhizosphere processes. This is mostly because assessing rhizosphere heterogeneity is not a trivial task. One technology for high-resolution and quantitative imaging of rhizosphere processes is called planar optode technology. This technology can create quantitative maps of key rhizosphere parameters non-invasively and has great potential to reveal new insights into this biogeochemical hotspot. Scope: Rudolph and coworkers in this issue of Plant and Soil have used and improved the application of the planar optode technology for mapping rhizosphere pH dynamics. My commentary discusses the advantages and disadvantages of their approach and those of other published studies that deal with other planar optodes (like O2, CO2 or ammonium concentration) compared to conventional techniques. Conclusions: Planar optodes represent a unique and powerful technology that can be used to investigate a range of rhizosphere processes. For sure there are more steps to take in order to tap the full potential of this technology: we now need concerted interdisciplinary approaches between biology, sensor chemistry and digital image analysis to scope out its full potential. © 2013 Springer Science+Business Media Dordrecht.

Meissner U.-G.,University of Bonn | Meissner U.-G.,Julich Research Center | Wang W.,University of Bonn
Journal of High Energy Physics | Year: 2014

We analyse the Bs 0 → K+l -ν and Bs 0 → K*+ (→ Kπ){ℓ-ν decays that are valuable for extracting the CKM matrix element |V ub|. We calculate the differential and integrated partial widths in units of |V ub|2 based on various calculations of hadronic form factors and in particular the latest Lattice QCD calculation of the B s → K 1 form factors. For the decay Bs 0 →Kπ ℓ ν, we formulate the general angular distributions with the inclusion of the various partial-wave Kπ contributions. Using the results for the Kπ scalar form factor calculated from unitarized chiral perturbation theory, we explore the S-wave effects on angular distribution variables and demonstrate that they may not be negligible, considering the high precision expected in future measurements. We also briefly discuss the impact of the S-wave ππ contributions in the B- → π+π-ℓ v decay and provide estimates for the mode B- → K +K-ℓ v. The studies of these channels in future can not only be used to determine |V ub|, but may also provide valuable information on the Kπ and ππ phase shifts. © 2014 Author(s).

Guo F.-K.,University of Bonn | Meissner U.-G.,University of Bonn | Meissner U.-G.,Julich Research Center
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

The leading order interaction between a Goldstone boson and a matter field is universally dominated by the Weinberg-Tomozawa term. Based on this observation, we predict a rich spectrum of bound states of a kaon and a heavy meson. We argue that, if the lifetime of an excited heavy meson is significantly longer than the range of forces, then the finite width of that state can be neglected in a first approximation. Then, the Ds0*(2317), D s1(2460), DsJ(2860) and DsJ(3040) are generated as DK, D*K, D1(2420)K and D*(2600) K bound states, respectively. In addition to the remarkable agreement with the measured masses, the decay patterns of the DsJ(2860) and D sJ(3040) can also be understood. Two more DsJ states, and kaonic bound states with the bottom mesons as well as the doubly charmed baryon are also predicted. © 2011 American Physical Society.

Bruner E.,National Research Center sobre la Evolucion Humana | Bruner E.,Julich Research Center
Journal of Alzheimer's Disease | Year: 2013

Clinical grade Alzheimer's disease (AD) is only described in humans. Recent imaging studies in early AD patients showed that the parietal areas display the most prominent metabolic impairments. So far, neuroimaging studies have not been able to explain why the medial parietal regions possess this hub characteristic in AD. Paleoneurological and neuroanatomical studies suggest that our species, Homo sapiens, has a unique and derived organization of the parietal areas, which are involved in higher cognitive functions. Combining evidence from neuroimaging, paleontology, and comparative anatomy, we suggest that the vulnerability of the parietal lobe to neurodegenerative processes may be associated with the origin of our species. The species-specific parietal morphology in modern humans largely influenced the brain spatial organization, and it involved changes in vascularization and energy management, which may underlie the sensitivity of these areas to metabolic impairment. Metabolic constraints and anatomical evolutionary changes in the medial parietal regions of modern humans may be important in early AD onset. Taking into account the species-specific adaptations of the modern human parietal areas and their association with AD, we hypothesize that AD can be the evolutionary drawback of the specialized structure of our parietal lobes. The cognitive advantage is associated with increased sensitivity to neurodegenerative processes which, being limited to the post-reproductive period, have a minor effect on the overall genetic fitness. The changes of energy requirements associated with form and size variations at the parietal areas may support the hypothesis of AD as a metabolic syndrome. © 2013 - IOS Press and the authors. All rights reserved.

Oezaslan M.,TU Berlin | Heggen M.,Julich Research Center | Strasser P.,TU Berlin
Journal of the American Chemical Society | Year: 2012

Chemical dealloying of Pt binary alloy precursors has emerged as a novel and important preparation process for highly active fuel cell catalysts. Dealloying is a selective (electro)chemical leaching of a less noble metal M from a M rich Pt alloy precursor material and has been a familiar subject of macroscale corrosion technology for decades. The atomic processes occurring during the dealloying of nanoscale materials, however, are virtually unexplored and hence poorly understood. Here, we have investigated how the morphology and intraparticle composition depend on the particle size of dealloyed Pt-Co and Pt-Cu alloy nanoparticle precursor catalysts. To examine the size-morphology-composition relation, we used a combination of high-resolutionscanning transmission electron microscopy (STEM), transmission electron microscopy (TEM), electron energy loss (EEL) spectroscopy, energy-dispersive X-ray spectroscopy (EDS), and surface-sensitive cycling voltammetry. Our results indicate the existence of three distinctly different size-dependent morphology regimes in dealloyed Pt-Co and Pt-Cu particle ensembles: (i) The arrangement of Pt shell surrounding a single alloy core ("single core-shell nanoparticles") is exclusively formed by dealloying of particles below a characteristic diameter d multiple cores of 10-15 nm. (ii) Above d multiple cores, nonporous bimetallic core-shell particles dominate and show structures with irregular shaped multiple Co/Cu rich cores ("multiple cores-shell nanoparticles"). (iii) Above the second characteristic diameter d pores of about 30 nm, the dealloyed Pt-Co and Pt-Cu particles start to show surface pits and nanoscale pores next to multiple Co/Cu rich cores. This structure prevails up to macroscopic bulklike dealloyed particles with diameter of more than 100 nm. The size-morphology-composition relationships link the nano to the macro scale and provide an insight into the existing material gap of dealloyed nanoparticles and highly porous bulklike bimetallic particles in corrosion science. © 2011 American Chemical Society.

In this paper, the dynamic transition of the liquid-crystal-glass transition is investigated by dynamic light scattering, DLS. From the intensity autocorrelation function, g2(q, t), the short-time dynamic function, D(q), has been determined at different concentrations in both the crystal and glass regions. From D(q), the short-time self-diffusion, ds, was determined. ds speeds up in the crystal state but has very similar characteristics in the liquid and the glass region. The general model in which the colloidal crystallization transition in a spherical colloidal system is driven by an increase in local entropy is also verified by relating d s to the local excess entropy. Experimentally determined structure factors, S(q), are also discussed, and we show the similarity between the glass and the liquid. This investigation shows that the liquid-crystal transition can be identified in addition to the appearance of Bragg peaks with a short-time dynamic transition while no sharp transition in the short-time dynamics or S(q) can be found between the glass and the liquid. © 2014 American Chemical Society.

Roberts C.D.,Argonne National Laboratory | Holt R.J.,Argonne National Laboratory | Schmidt S.M.,Julich Research Center
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2013

Dyson-Schwinger equation treatments of the strong interaction show that the presence and importance of nonpointlike diquark correlations within the nucleon are a natural consequence of dynamical chiral symmetry breaking. Using this foundation, we deduce a collection of simple formulae, expressed in terms of diquark appearance and mixing probabilities, from which one may compute ratios of longitudinal-spin-dependent u- and d-quark parton distribution functions on the domain x≃. 1. A comparison with predictions from other approaches plus a consideration of extant and planned experiments shows that the measurement of nucleon longitudinal spin asymmetries on x≃. 1 can add considerably to our capacity for discriminating between contemporary pictures of nucleon structure. © 2013 Elsevier B.V.

Hanhart C.,Julich Research Center | Kalashnikova Yu.S.,Institute of Theoretical and Experimental Physics | Kudryavtsev A.E.,Institute of Theoretical and Experimental Physics | Nefediev A.V.,Institute of Theoretical and Experimental Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We reanalyze the two- and three-pion mass distributions in the decays X(3872)→ρJ/ψ and X(3872)→ωJ/ψ and argue that the present data favor the 1 ++ assignment for the quantum numbers of the X. © 2012 American Physical Society.

Gliga S.,Argonne National Laboratory | Gliga S.,Max Planck Institute of Microstructure Physics | Kakay A.,Julich Research Center | Hertel R.,CNRS Institute of Genetics and of Molecular and Cellular Biology | And 2 more authors.
Physical Review Letters | Year: 2013

Arrays of suitably patterned and arranged magnetic elements may display artificial spin-ice structures with topological defects in the magnetization, such as Dirac monopoles and Dirac strings. It is known that these defects strongly influence the quasistatic and equilibrium behavior of the spin-ice lattice. Here, we study the eigenmode dynamics of such defects in a square lattice consisting of stadiumlike thin film elements using micromagnetic simulations. We find that the topological defects display distinct signatures in the mode spectrum, providing a means to qualitatively and quantitatively analyze monopoles and strings that can be measured experimentally. © 2013 American Physical Society.

Liebsch A.,Julich Research Center | Wu W.,Universite de Sherbrooke
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

The effect of Coulomb correlations in the half-filled Hubbard model of the honeycomb lattice is studied within the dynamical cluster approximation (DCA) combined with exact diagonalization (ED) and continuous-time quantum Monte Carlo (QMC), for unit cells consisting of six-site rings. The important difference between this approach and the previously employed cluster dynamical mean-field theory (CDMFT) is that DCA preserves the translation symmetry of the system, while CDMFT violates this symmetry. As the Dirac cones of the honeycomb lattice are the consequence of perfect long-range order, DCA yields semimetallic behavior at small on-site Coulomb interactions U, whereas CDMFT gives rise to a spurious excitation gap even for very small U. This basic difference between the two cluster approaches is found regardless of whether ED or QMC is used as the impurity solver. At larger values of U, the lack of translation symmetry becomes less important, so that the CDMFT reveals a Mott gap, in qualitative agreement with large-scale QMC calculations. In contrast, the semimetallic phase obtained in DCA persists even at U values where CDMFT and large-scale QMC consistently show Mott-insulating behavior. © 2013 American Physical Society.

Grassberger P.,Julich Research Center | Grassberger P.,University of Calgary | Christensen C.,University of Calgary | Bizhani G.,University of Calgary | And 2 more authors.
Physical Review Letters | Year: 2011

We study four Achlioptas-type processes with "explosive" percolation transitions. All transitions are clearly continuous, but their finite size scaling functions are not entirely holomorphic. The distributions of the order parameter, i.e., the relative size smax/N of the largest cluster, are double humped. But-in contrast to first-order phase transitions-the distance between the two peaks decreases with system size N as N -η with η>0. We find different positive values of β (defined via smax/N∼(p-pc)β for infinite systems) for each model, showing that they are all in different universality classes. In contrast, the exponent Θ (defined such that observables are homogeneous functions of (p-pc)NΘ) is close to-or even equal to-1/2 for all models. © 2011 American Physical Society.

Mladek B.M.,University of Cambridge | Mladek B.M.,University of Vienna | Fornleitner J.,Julich Research Center | Martinez-Veracoechea F.J.,University of Cambridge | And 2 more authors.
Physical Review Letters | Year: 2012

We present a coarse-grained model of DNA-functionalized colloids that is computationally tractable. Importantly, the model parameters are solely based on experimental data. Using this highly simplified model, we can predict the phase behavior of DNA-functionalized nanocolloids without assuming pairwise additivity of the intercolloidal interactions. Our simulations show that, for nanocolloids, the assumption of pairwise additivity leads to substantial errors in the estimate of the free energy of the crystal phase. We compare our results with available experimental data and find that the simulations predict the correct structure of the solid phase and yield a very good estimate of the melting temperature. Current experimental estimates for the contour length and persistence length of single-stranded (ss) DNA sequences are subject to relatively large uncertainties. Using the best available estimates, we obtain predictions for the crystal lattice constants that are off by a few percent: this indicates that more accurate experimental data on ssDNA are needed to exploit the full power of our coarse-grained approach. © 2012 American Physical Society.

Galanakis I.,University of Patras | Sasioglu E.,Julich Research Center | Sasioglu E.,Fatih University
Applied Physics Letters | Year: 2011

Extensive ab-initio electronic structure calculations on Heusler alloys suggest that Cr2CoGa is the alloy of choice to achieve the half-metallic fully-compensated ferrimagnetism since (1) it has been already grown experimentally [T. Graf, Z. Anorg. Allg. Chem. 635, 976 (2009)], (2) half-metallic XA structure is favored energetically over all the studied lattice constant range with respect to the L21 which is not half-metallic, (3) the half-metallic gap is wide and the Fermi level falls at the middle of the gap and thus, it presents high degree of spin-polarization for a wide range of lattice constants, and (4) the Curie temperature is extremely high reaching the 1520 K. © 2011 American Institute of Physics.

Cui C.,TU Berlin | Gan L.,TU Berlin | Li H.-H.,Hefei University of Technology | Yu S.-H.,Hefei University of Technology | And 2 more authors.
Nano Letters | Year: 2012

We demonstrate how shape selectivity and optimized surface composition result in exceptional oxygen reduction activity of octahedral PtNi nanoparticles (NPs). The alloy octahedra were obtained by utilizing a facile, completely surfactant-free solvothermal synthesis. We show that the choice of precursor ligands controls the shape, while the reaction time tunes the surface Pt:Ni composition. The 9.5 nm sized PtNi octahedra reached a 10-fold surface area-specific (∼3.14 mA/cmPt2) as well as an unprecedented 10-fold Pt mass based (∼1.45 A/mgPt) activity gain over the state-of-art Pt electrocatalyst, approaching the theoretically predicted limits. © 2012 American Chemical Society.

Chen D.-H.,Baylor College of Medicine | Madan D.,Princeton University | Madan D.,Intellectual Ventures Laboratories | Weaver J.,Texas A&M University | And 7 more authors.
Cell | Year: 2013

The GroEL/ES chaperonin system is required for the assisted folding of many proteins. How these substrate proteins are encapsulated within the GroEL-GroES cavity is poorly understood. Using symmetry-free, single-particle cryo-electron microscopy, we have characterized a chemically modified mutant of GroEL (EL43Py) that is trapped at a normally transient stage of substrate protein encapsulation. We show that the symmetric pattern of the GroEL subunits is broken as the GroEL cis-ring apical domains reorient to accommodate the simultaneous binding of GroES and an incompletely folded substrate protein (RuBisCO). The collapsed RuBisCO folding intermediate binds to the lower segment of two apical domains, as well as to the normally unstructured GroEL C-terminal tails. A comparative structural analysis suggests that the allosteric transitions leading to substrate protein release and folding involve concerted shifts of GroES and the GroEL apical domains and C-terminal tails. © 2013 Elsevier Inc.

Liebsch A.,Julich Research Center | Ishida H.,Nihon University
Journal of Physics Condensed Matter | Year: 2012

Dynamical mean field theory (DMFT), combined with finite-temperature exact diagonalization, is one of the methods used to describe electronic properties of strongly correlated materials. Because of the rapid growth of the Hilbert space, the size of the finite bath used to represent the infinite lattice is severely limited. In view of the increasing interest in the effect of multi-orbital and multi-site Coulomb correlations in transition metal oxides, high-T c cuprates, iron-based pnictides, organic crystals, etc, it is appropriate to explore the range of temperatures and bath sizes in which exact diagonalization provides accurate results for various system properties. On the one hand, the bath must be large enough to achieve a sufficiently dense level spacing, so that useful spectral information can be derived, especially close to the Fermi level. On the other hand, for an adequate projection of the lattice Greens function onto a finite bath, the choice of the temperature is crucial. The role of these two key ingredients in exact diagonalization DMFT is discussed for a wide variety of systems in order to establish the domain of applicability of this approach. Three criteria are used to illustrate the accuracy of the results: (i) the convergence of the self-energy with the bath size, (ii) the quality of the discretization of the bath Greens function, and (iii) comparisons with complementary results obtained via continuous-time quantum Monte Carlo DMFT. The materials comprise a variety of three-orbital and five-orbital systems, as well as single-band Hubbard models for two-dimensional triangular, square and honeycomb lattices, where non-local Coulomb correlations are important. The main conclusion from these examples is that a larger number of correlated orbitals or sites requires a smaller number of bath levels. Down to temperatures of 510meV (for typical bandwidths W2eV) two bath levels per correlated impurity orbital or site are usually adequate. © 2012 IOP Publishing Ltd.

Heinrichs J.-H.,Julich Research Center
Neuroethics | Year: 2012

When new methods of generating information about individuals leave the confined space of research application the possibility of morally dubious application arises. The current propagation of neuroscientific diagnostics leads to new possibilities of misuse and accordingly new needs for the protection of individual privacy emerge. While most current privacy discussion focuses on sensationalist applications which aim/claim to gather information about psychological traits or even the content of thoughts, the more sober but much more realistic endeavour to gather health data from research or medical imaging studies is widely neglected. I will try to answer the question if and in how far data from neuroscientific imaging technologies require special protection. Two developments form the background of the ethical discussion: the increased diagnostic power of neuroimaging techniques and the wider distribution of this technology beyond specialized medical offices and clinics. The first development is likely to broaden the scope of data, which are considered relevant for health care and related decisions. The latter is likely to widen the scope of persons who might have access to diagnostic results without at the time taking the role of a doctor towards the person diagnosed. I will argue that neuroimaging data are currently primarily medical data and that the associated standards of consent and confidentiality are worth protecting. Even nonmedical applications of neuroimaging technology inherit too much of the diagnostic power for which they were originally invented, for it to be advisable to drop the accompanying consent and confidentiality requirements. © Springer Science+Business Media B.V. 2011.

Malzbender J.,Julich Research Center
Journal of the European Ceramic Society | Year: 2010

The technical application of layered functional ceramic components is challenged by curvature effects and residual stresses originating mostly from the thermal mismatch or chemical strains of the joined materials. Based on the general solution for elastic deformation of monolithic and multilayered materials the determination of curvature and residual stress for linear elastic bi-material specimens with chemical strains, chemical reduction in stiffness, shape variations, gradients in elastic modulus or thermal expansion is outlined. The use of the relationships is exemplified for ceramic solid oxide fuel cell (SOFC) and ceramic membrane materials. For SOFCs curvature changes are considered resulting from the reduction of the anode and crystallization of a glass-ceramic sealant with semi-spherical shape. For gas separation membranes which currently under development for fossil power plants the effect of chemical strains is assessed. The limits of using analytical relationships are addressed for the warpage of thin, rectangular SOFCs. © 2010 Elsevier Ltd.

Galanakis I.,University of Patras | Sasoglu E.,Julich Research Center | Sasoglu E.,Fatih University
Applied Physics Letters | Year: 2011

We employ ab initio electronic structure calculations and a model Heisenberg Hamiltonian, and show that the Heusler alloy Ni2 MnAl exhibits a ferrromagnetic-antiferromagnetic phase transition upon Mn-Al disorder. The transition is triggered by the smaller Mn-Mn nearest-neighbors distance in accordance to the Bethe-Slater curve. Our results explain available experimental data and show that the prevention of disorder is essential to achieve maximum performance in Heusler-based devices. © 2011 American Institute of Physics.

Kulikovsky A.A.,Julich Research Center
Electrochimica Acta | Year: 2012

A model for catalyst layer (CL) performance is used to determine optimal shapes of electrolyte content and catalyst loading through the CL thickness. The effect of optimization strongly depends on the dimensionless working current density j̃ 0. At small j̃ 0 characteristic to a hydrogen cell, the effect of cathode optimization is marginal, while at large j̃ 0 typical for a direct methanol fuel cell, optimization of the anode doubles the CL performance. © 2012 Elsevier Ltd. All rights reserved.

Bouchbinder E.,Weizmann Institute of Science | Brener E.A.,Weizmann Institute of Science | Brener E.A.,Julich Research Center | Barel I.,Tel Aviv University | Urbakh M.,Tel Aviv University
Physical Review Letters | Year: 2011

We propose a friction model which incorporates interfacial elasticity and whose steady state sliding relation is characterized by a generic nonmonotonic behavior, including both velocity weakening and strengthening branches. In 1D and upon the application of sideway loading, we demonstrate the existence of transient cracklike fronts whose velocity is independent of sound speed, which we propose to be analogous to the recently discovered slow interfacial rupture fronts. Most importantly, the properties of these transient inhomogeneously loaded fronts are determined by steady state front solutions at the minimum of the sliding friction law, implying the existence of a new velocity scale and a "forbidden gap" of rupture velocities. We highlight the role played by interfacial elasticity and supplement our analysis with 2D scaling arguments. © 2011 American Physical Society.

Luckmann H.C.,Maastricht University | Jacobs H.I.L.,Julich Research Center | Sack A.T.,Maastricht University | Sack A.T.,Maastricht Brain Imaging Center
Progress in Neurobiology | Year: 2014

Neuroimaging studies have repeatedly reported findings of activation in frontoparietal regions that largely overlap across various cognitive functions. Part of this frontoparietal activation has been interpreted as reflecting attentional mechanisms that can adaptively be directed towards external stimulation as well as internal representations (internal attention), thereby generating the experience of distinct cognitive functions. Nevertheless, findings of material- and task-specific activation in frontal and parietal regions challenge this internal attention hypothesis and have been used to support more modular hypotheses of cognitive function. The aim of this review is twofold: First, it discusses evidence in support of the concept of internal attention and the so-called dorsal attention network (DAN) as its neural source with respect to three cognitive functions (working memory, episodic retrieval, and mental imagery). While DAN activation in all three functions has been separately linked to internal attention, a comprehensive and integrative review has so far been lacking. Second, the review examines findings of material- and process-specific activation within frontoparietal regions, arguing that these results are well compatible with the internal attention account of frontoparietal activation. A new model of cognition is presented, proposing that supposedly different cognitive concepts actually rely on similar attentional network dynamics to maintain, reactivate and newly create internal representations of stimuli in various modalities. Attentional as well as representational mechanisms are assigned to frontal and parietal regions, positing that some regions are implicated in the allocation of attentional resources to perceptual or internal representations, but others are involved in the representational processes themselves. © 2014 Elsevier Ltd.

Konstantinidis N.P.,University of Kaiserslautern | Lounis S.,Julich Research Center
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

It is shown that in antiferromagnetic open or closed corrals of magnetic adatoms grown on surfaces, the attachment of a single extra adatom anywhere in the corral impacts on the geometrical topology of the nanosystem and generates complex magnetic structures when a magnetic field is applied or a magnetic coupling to a ferromagnetic substrate exists. The spin configuration of the corral can be tuned to a nonplanar state or a planar noncollinear or ferrimagnetic state by adjusting its number of sites, the location of the extra adatom, or the strength of the coupling to the ferromagnetic substrate. This shows the possibility to generate nontrivial magnetic textures with atom-by-atom engineering anywhere in the corral and not only at the edges. © 2013 American Physical Society.

Van Der Tol C.,University of Twente | Berry J.A.,Carnegie Institution of Washington | Campbell P.K.E.,University of Maryland Baltimore County | Rascher U.,Julich Research Center
Journal of Geophysical Research G: Biogeosciences | Year: 2014

We have extended a conventional photosynthesis model to simulate field and laboratory measurements of chlorophyll fluorescence at the leaf scale. The fluorescence paramaterization is based on a close nonlinear relationship between the relative light saturation of photosynthesis and nonradiative energy dissipation in plants of different species. This relationship diverged only among examined data sets under stressed (strongly light saturated) conditions, possibly caused by differences in xanthophyll pigment concentrations. The relationship was quantified after analyzing data sets of pulse amplitude modulated measurements of chlorophyll fluorescence and gas exchange of leaves of different species exposed to different levels of light, CO2, temperature, nitrogen fertilization treatments, and drought. We used this relationship in a photosynthesis model. The coupled model enabled us to quantify the relationships between steady state chlorophyll fluorescence yield, electron transport rate, and photosynthesis in leaves under different environmental conditions. ©2014. The Authors.

Brown S.,McMaster University | Gao X.,McMaster University | Tisdelle L.,Simon Fraser University | Eickhoff S.B.,RWTH Aachen | And 2 more authors.
NeuroImage | Year: 2011

We present here the most comprehensive analysis to date of neuroaesthetic processing by reporting the results of voxel-based meta-analyses of 93 neuroimaging studies of positive-valence aesthetic appraisal across four sensory modalities. The results demonstrate that the most concordant area of activation across all four modalities is the right anterior insula, an area typically associated with visceral perception, especially of negative valence (disgust, pain, etc.). We argue that aesthetic processing is, at its core, the appraisal of the valence of perceived objects. This appraisal is in no way limited to artworks but is instead applicable to all types of perceived objects. Therefore, one way to naturalize aesthetics is to argue that such a system evolved first for the appraisal of objects of survival advantage, such as food sources, and was later co-opted in humans for the experience of artworks for the satisfaction of social needs. © 2011 Elsevier Inc.

Samm U.,Julich Research Center
Fusion Science and Technology | Year: 2012

The control of wall loads in fusion devices, in particular with respect to the life time limitations of wall components due to material erosion and migration, will be decisive for the realisation of a fusion power plant operating in steady state, while in a pulsed experiment like ITER the primary goal for plasma-wall interaction is the achievement of a high availability. The article describes the grand challenges of plasma-wall interaction research along the needs for ITER and the strategies of ongoing research for further optimization of the design. Addressed are questions related to material limitations, erosion- and transport processes, tritium retention in deposited layers and transient heat loads.

Scaraggi M.,University of Salento | Persson B.N.J.,Julich Research Center
Tribology Letters | Year: 2012

We study the time dependency of the interfacial separation and of the area of real contact between a soft elastic cylinder and a rigid solid with a randomly rough surface, squeezed with normal approach in a fluid. This problem is relevant for biological, as well as for bio-medical, seals and tires applications. An ad-hoc numerical scheme is developed to solve the transient mixed-EHD homogenized lubrication problem.We show that, for the soft contact case, the transition from the EHD to the boundary regime can be much more efficiently studied within a simplified (Grubin-like) problem formulation then with the full numerical scheme. This is not only of great conceptional importance, but also of practical importance as the latter calculation is much simpler and faster than the full scheme calculation. © Springer Science+Business Media, LLC 2012.

Grosbras M.-H.,University of Glasgow | Beaton S.,University of Glasgow | Eickhoff S.B.,Julich Research Center
Human Brain Mapping | Year: 2012

Face, hands, and body movements are powerful signals essential for social interactions. In the last 2 decades, a large number of brain imaging studies have explored the neural correlates of the perception of these signals. Formal synthesis is crucially needed, however, to extract the key circuits involved in human motion perception across the variety of paradigms and stimuli that have been used. Here, we used the activation likelihood estimation (ALE) meta-analysis approach with random effect analysis. We performed meta-analyses on three classes of biological motion: movement of the whole body, hands, and face. Additional analyses of studies of static faces or body stimuli and sub-analyses grouping experiments as a function of their control stimuli or task employed allowed us to identify main effects of movements and forms perception, as well as effects of task demand. In addition to specific features, all conditions showed convergence in occipito-temporal and fronto-parietal regions, but with different peak location and extent. The conjunction of the three ALE maps revealed convergence in all categories in a region of the right posterior superior temporal sulcus as well as in a bilateral region at the junction between middle temporal and lateral occipital gyri. Activation in these regions was not a function of attentional demand and was significant also when controlling for non-specific motion perception. This quantitative synthesis points towards a special role for posterior superior temporal sulcus for integrating human movement percept, and supports a specific representation for body parts in middle temporal, fusiform, precentral, and parietal areas. © 2011 Wiley Periodicals, Inc.

Qaim S.M.,Julich Research Center
Journal of Radioanalytical and Nuclear Chemistry | Year: 2010

A vast knowledge of nuclear data is available and is grouped under three headings, namely, nuclear structure, nuclear decay and nuclear reaction data. Still newer aspects are under continuous investigation. Data measurements are done using a large number of techniques, including the radiochemical method, which has been extensively worked out at Jülich. This method entails preparation of high-quality sample for irradiation, isolation of the desired radioactive product from the strong matrix activity, and preparation of thin source suitable for accurate measurement of the radioactivity. It is especially useful for fundamental studies on light complex particle emission reactions and formation of low-lying isomeric states, both of which are rather difficult to describe by nuclear model calculations. The neutron induced reaction cross section data are of practical application in fusion reactor technology, particularly for calculations on tritium breeding, gas production in structural materials and activation of reactor components. The charged particle induced reaction cross section data, on the other hand, are of significance in medicine, especially for developing new production routes of novel positron emitters and therapeutic radionuclides at a cyclotron. Both neutron and charged particle data also find application in radiation therapy. A brief overview of advances made in all those areas is given, with major emphasis on nuclear reaction cross section data. © 2010 Akadémiai Kiadó.

Polinski M.J.,University of Notre Dame | Wang S.,University of Notre Dame | Alekseev E.V.,Julich Research Center | Depmeier W.,University of Kiel | Albrecht-Schmitt T.E.,University of Notre Dame
Angewandte Chemie - International Edition | Year: 2011

A matter of size: A dramatic change occurs between the reactivity of PuIII and AmIII centers in molten boric acid. The resulting complexes display different inner-sphere ligands and different coordination environments (see Pu[B4O6(OH)2Cl] and Am[B9O13(OH)4]·H2O in the picture). © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Vogt B.A.,Cingulum NeuroSciences Institute | Vogt B.A.,Boston University | Vogt B.A.,Julich Research Center
Neurogastroenterology and Motility | Year: 2013

The article by Agostini et al. (2013) in this issue of Neurogastroenterology and Motility evaluated patients with Crohn's disease (CD) for volumetric changes throughout the brain. They observed decreased gray matter volumes in dorsolateral prefrontal cortex and anterior midcingulate cortex (aMCC) and disease duration was negatively correlated with volumes in subgenual anterior cingulate (sACC), posterior MCC (pMCC), ventral posterior cingulate (vPCC), and parahippocampal cortices. As all patients were in remission and suffered from ongoing abdominal pain, this study provides a critical link between forebrain changes and abdominal pain experience independent of active disease and drug treatment. The aMCC has a role in feedback-mediated decision making and there are specific cognitive tasks that differentiate aMCC and pMCC that can be used to evaluate defects in CD. The sACC is an important area as it has impaired functions in major depression. As depressive symptoms are a feature in a subset of patients with active inflammatory diseases including IBD, treatment targeting this subregion should prove efficacious. Finally, vPCC has a role in ongoing self-monitoring of the personal relevance of sensory stimuli including visceral signals via sACC. This pathway may be interrupted by vPCC atrophy in CD. Cingulate atrophy in CD leads to targeting chronic pain and psychiatric symptoms via cingulate-mediated therapies. These include psychotherapy, guided imagery and relaxation training, analgesic dosages of morphine or antidepressants, and hypnosis. Thus, a new generation of novel treatments may emerge from drug and non-traditional therapies for CD in this formative area of research. © 2013 Blackwell Publishing Ltd.

Marques M.A.L.,University of Lyon | Marques M.A.L.,University Claude Bernard Lyon 1 | Oliveira M.J.T.,University of Coimbra | Burnus T.,Julich Research Center
Computer Physics Communications | Year: 2012

The central quantity of density functional theory is the so-called exchange-correlation functional. This quantity encompasses all non-trivial many-body effects of the ground-state and has to be approximated in any practical application of the theory. For the past 50 years, hundreds of such approximations have appeared, with many successfully persisting in the electronic structure community and literature. Here, we present a library that contains routines to evaluate many of these functionals (around 180) and their derivatives. © 2012 Elsevier B.V. All rights reserved.

Marchenko D.,Helmholtz Center Berlin | Varykhalov A.,Helmholtz Center Berlin | Scholz M.R.,Helmholtz Center Berlin | Bihlmayer G.,Julich Research Center | And 4 more authors.
Nature Communications | Year: 2012

Graphene in spintronics is predominantly considered for spin current leads of high performance due to weak intrinsic spin-orbit coupling of the graphene π electrons. Externally induced large spin-orbit coupling opens the possibility of using graphene in active elements of spintronic devices such as the Das-Datta spin field-effect transistor. Here we show that Au intercalation at the graphene-Ni interface creates a giant spin-orbit splitting (∼100 meV) of the graphene Dirac cone up to the Fermi energy. Photoelectron spectroscopy reveals the hybridization with Au 5d states as the source for this giant splitting. An ab initio model of the system shows a Rashba-split spectrum around the Dirac point of graphene. A sharp graphene-Au interface at the equilibrium distance accounts for only ∼10 meV spin-orbit splitting and enhancement is due to the Au atoms in the hollow position that get closer to graphene and do not break the sublattice symmetry. © 2012 Macmillan Publishers Limited. All rights reserved.

Liang Y.,Julich Research Center
Fusion Science and Technology | Year: 2011

The next generation of fusion machines like ITER and DEMO will need a reliable method for controlling the periodic transient expulsion of a considerable amount of energy onto the plasma-facing components caused by instabilities at the plasma edge. The good plasma confinement in these tokamak devices will result in a steepened pressure profile at the plasma edge. When the pressure gradient exceeds a critical value, so-called edgelocalized modes (ELMs) are destabilized. These modes feature a periodic fast collapse of the edge pressure, a sudden loss of the confinement, and a subsequent release of heat and particles onto plasma-facing components. The associated transient heat loads might cause excess erosion and lead to a strong reduction of the plasmafacing component lifetime. In this lecture, an overview of recent development of several ELM control methods for next-generation tokamaks, e.g., ITER is given. Some key physics issues related to the mechanism of ELM control are discussed.

Meissner U.-G.,University of Bonn | Meissner U.-G.,Julich Research Center | Oller J.A.,University of Murcia
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

Making use of a recently proposed formalism, we analyze the composite nature of the Pc(4450) resonance observed by LHCb. We show that the present data suggest that this state is almost entirely made of a χc1 and a proton, due to the close proximity to this threshold. This also suppresses the decay modes into other, lighter channels, in our study represented by J/Ψp. We further argue that this is very similar to the case of the scalar meson f0(980) which is located closely to the KK- threshold and has a suppressed decay into the lighter ππ channel. © 2015 The Authors.

In a recent contribution to this journal, Magazù, Migliardo, and Benedetto suggest to determine relaxation times from inflection points in the elastic neutron scattering intensity as function of (1) resolution time or (2) temperature. Method (1) can be generalized into a scaling law. Method (2) is only approximately valid; its application to protein data does not back a wavenumber-independent dynamic transition. © 2012 American Institute of Physics.

Tokar M.Z.,Julich Research Center
Journal of Computational Physics | Year: 2011

In plasmas bounded by material surfaces the Bohm criterion has to be satisfied at the entrance of the Debye sheath near the surface. With a single ion species this constraint prescribes a boundary condition for the momentum balance equation governing the ion mass velocity. If, however, several ion species are present a generalization of the Bohm criterion does not provide enough number of boundary conditions. Additional " intermediate" conditions follow from the requirement that spatial derivatives of the ion velocities are finite everywhere within the plasma volume. The amount of such independent conditions is sufficient to determine, in an iterative way, also the position in the plasma where they have to be imposed. A numerical approach to find unique regular solutions of fluid motion equations, satisfying the generalized Bohm criterion at the plasma boundary, is elaborated and realized for the case of two ion species. © 2011 Elsevier Inc.

Lu A.,Harvard University | Magupalli V.G.,Harvard University | Ruan J.,Harvard University | Yin Q.,Harvard University | And 7 more authors.
Cell | Year: 2014

Inflammasomes elicit host defense inside cells by activating caspase-1 for cytokine maturation and cell death. AIM2 and NLRP3 are representative sensor proteins in two major families of inflammasomes. The adaptor protein ASC bridges the sensor proteins and caspase-1 to form ternary inflammasome complexes, achieved through pyrin domain (PYD) interactions between sensors and ASC and through caspase activation and recruitment domain (CARD) interactions between ASC and caspase-1. We found that PYD and CARD both form filaments. Activated AIM2 and NLRP3 nucleate PYD filaments of ASC, which, in turn, cluster the CARD of ASC. ASC thus nucleates CARD filaments of caspase-1, leading to proximity-induced activation. Endogenous NLRP3 inflammasome is also filamentous. The cryoelectron microscopy structure of ASCPYD filament at near-atomic resolution provides a template for homo- and hetero-PYD/PYD associations, as confirmed by structure-guided mutagenesis. We propose that ASC-dependent inflammasomes in both families share a unified assembly mechanism that involves two successive steps of nucleation-induced polymerization. PaperFlick © 2014 Elsevier Inc.

Spatschek R.,The Interdisciplinary Center | Brener E.,Julich Research Center | Karma A.,Northeastern University
Philosophical Magazine | Year: 2011

Fracture is a fundamental mechanism of materials failure. Propagating cracks can exhibit a rich dynamical behavior controlled by a subtle interplay between microscopic failure processes in the crack tip region and macroscopic elasticity. We review recent approaches to understand crack dynamics using the phase field method. This method, developed originally for phase transformations, has the well-known advantage of avoiding explicit front tracking by making material interfaces spatially diffuse. In a fracture context, this method is able to capture both the short-scale physics of failure and macroscopic linear elasticity within a self-consistent set of equations that can be simulated on experimentally relevant length and time scales. We discuss the relevance of different models, which stem from continuum field descriptions of brittle materials and crystals, to address questions concerning crack path selection and branching instabilities, as well as models that are based on mesoscale concepts for crack tip scale selection. Open questions which may be addressed using phase field models of fracture are summarized. © 2011 Taylor & Francis.

Cherstvy A.G.,Julich Research Center
Physical Chemistry Chemical Physics | Year: 2011

In this perspective article, we focus on recent developments in the theory of charge effects in biological DNA-related systems. The electrostatic effects on different levels of DNA organization are considered, including the DNA-DNA interactions, DNA complexation with cationic lipid membranes, DNA condensates and DNA-dense cholesteric phases, protein-DNA recognition, DNA wrapping in nucleosomes, and inter-nucleosomal interactions. For these systems, we develop a theoretical framework to describe the physical-chemical mechanisms of structure formation and anticipate some biological consequences. General biophysical principles of DNA compaction in chromatin fibers and DNA spooling inside viral capsids are discussed in the end, with emphasis on electrostatic aspects. © 2011 the Owner Societies.

Pieters B.E.,Julich Research Center
2014 IEEE 40th Photovoltaic Specialist Conference, PVSC 2014 | Year: 2014

Inhomogeneities and series resistance have a pronounced impact on solar module performance. In the last few years many tools have been developed which model the impact of lateral inhomogeneities and the series resistance arising from the lateral current transport. Particularly popular are SPICE-based models, which use a SPICE circuit simulator to model the solar module (i.e. the involved differential equations are solved through an electronic network equivalent). In this paper we present our new free and open source solar module simulator. Our simulator features a variable, adaptive mesh, which allows fast and accurate simulation of large devices with small geometrical details. Furthermore, the program provides a flexible set of tools to define and simulate complex geometries. Finally, our tool does not depend on SPICE to do the simulations but has its own built-in solver. This reduces overhead as no netlist needs to be generated for SPICE, and, in addition, it allows to use numerical methods optimized for the given problem where the methods used in SPICE are intended for generic electronic circuits. © 2014 IEEE.

Schnabel S.,University of Georgia | Janke W.,University of Leipzig | Bachmann M.,Julich Research Center
Journal of Computational Physics | Year: 2011

The investigation of freezing transitions of single polymers is computationally demanding, since surface effects dominate the nucleation process. In recent studies we have systematically shown that the freezing properties of flexible, elastic polymers depend on the precise chain length. Performing multicanonical Monte Carlo simulations, we faced several computational challenges in connection with liquid-solid and solid-solid transitions. For this reason, we developed novel methods and update strategies to overcome the arising problems. We introduce novel Monte Carlo moves and two extensions to the multicanonical method. © 2011 Elsevier Inc.

Hertel K.,Friedrich - Alexander - University, Erlangen - Nuremberg | Hupkes J.,Julich Research Center | Pflaum C.,Friedrich - Alexander - University, Erlangen - Nuremberg
Optics Express | Year: 2013

We present an algorithm for generating a surface approximation of microcrystalline silicon (mc-Si) layers after plasma enhanced chemical vapor deposition (PECVD) onto surface textured substrates, where data of the textured substrate surface are available as input.We utilize mathematical image processing tools and combine them with an ellipsoid generator approach. The presented algorithm has been tuned for use in thin-film silicon solar cell applications, where textured surfaces are used to improve light trapping. We demonstrate the feasibility of this method by means of optical simulations of generated surface textures, comparing them to simulations of measured atomic force microscopy (AFM) scan data of both Aluminum-doped zinc oxide (AZO, a transparent and conductive material) and mc-Si layers. © 2013 Optical Society of America.

Poorter H.,Julich Research Center | Sack L.,University of California at Los Angeles
Frontiers in Plant Science | Year: 2012

Plants can differentially allocate biomass to leaves, stems, roots, and reproduction, and follow ontogenetic trajectories that interact with the prevailing climate. Various methodological tools exist to analyze the resulting allocation patterns, based either on the calculation of biomass ratios or fractions of different organs at a given point in time, or on a so-called allometric analysis of biomass data sampled across species or over an experimental growth period. We discuss the weak and strong points of each of these methods. Although both approaches have useful features, we suggest that often a plot of biomass fractions against total plant size, either across species or in the comparison of treatment effects, combines the best of both worlds. © 2012 Poorter and Sack.

Blenau W.,Goethe University Frankfurt | Rademacher E.,Free University of Berlin | Baumann A.,Julich Research Center
Apidologie | Year: 2012

The parasitic mite Varroa destructor is the main cause of the severe reduction in beekeeping during the last few decades. Therefore, efforts have been made to develop chemical treatments against the parasite. In the past, synthetic products were preferentially used to combat Varroa mites. Nowadays, mainly plant essential oils and organic acids are applied because they are safer and impose less unfavorable effects on the environment. Essential oils contain mixtures of mostly volatile and odorous terpenoid constituents. The molecular targets of these substances are tyramine and/or octopamine receptors that control and modulate vital functions ranging from metabolism to behavior. Disturbing the native function of these receptors in the mite results in deleterious effects in this parasite. This overview considers not only tyramine and octopamine receptors but also other potential targets of essential oils including ionotropic GABAA receptors, TRP type ion channels, and acetylcholinesterase. © INRA, DIB and Springer-Verlag, France, 2012.

Reiser D.,Julich Research Center
Physics of Plasmas | Year: 2012

The problem of energy conserving global drift fluid simulations is revisited. It is found that for the case of cylindrical plasmas in a homogenous magnetic field, a straightforward reformulation is possible avoiding simplifications leading to energetic inconsistencies. The particular new feature is the rigorous treatment of the polarisation drift by a generalization of the vorticity equation. The resulting set of model equations contains previous formulations as limiting cases and is suitable for efficient numerical techniques. Examples of applications on studies of plasma blobs and its impact on plasma target interaction are presented. The numerical studies focus on the appearance of plasma blobs and intermittent transport and its consequences on the release of sputtered target materials in the plasma. Intermittent expulsion of particles in radial direction can be observed and it is found that although the neutrals released from the target show strong fluctuations in their propagation into the plasma column, the overall effect on time averaged profiles is negligible for the conditions considered. In addition, the numerical simulations are utilised to perform an a-posteriori assessment of the magnitude of energetic inconsistencies in previously used simplified models. It is found that certain popular approximations, in particular by the use of simplified vorticity equations, do not significantly affect energetics. However, popular model simplifications with respect to parallel advection are found to provide significant deterioration of the model consistency. © 2012 EURATOM.

Doring M.,University of Bonn | Meissner U.-G.,University of Bonn | Meissner U.-G.,Julich Research Center
Journal of High Energy Physics | Year: 2012

Simulating the κ(800) on the lattice is a challenging task that starts to become feasible due to the rapid progress in recent-years lattice QCD calculations. As the resonance is broad, special attention to finite-volume effects has to be paid, because no sharp resonance signal as from avoided level crossing can be expected. In the present article, we investigate the finite volume effects in the framework of unitarized chiral perturbation theory using next-to-leading order terms. After a fit to meson-meson partial wave data, lattice levels for πK scattering are predicted. In addition, levels are shown for the quantum numbers in which the σ(600), f0(980), α0(980), θ(1020), K*(892), and p(770) appear, as well as the repulsive channels. Methods to extract the κ(800) signal from the lattice spectrum are presented. Using pseudo-data, we estimate the precision that lattice data should have to allow for a clear-cut extraction of this resonance. To put the results into context, in particular the required high precision on the lattice data, the σ(600), the P-wave resonances K*(892) and κ(770), and the repulsive πK, ππ phases are analyzed as well. © SISSA 2012.

Two approaches of how hot gas cleaning above the ash melting point, which has been successfully demonstrated for the Pressurized Pulverized Coal Combustion Combined Cycle (PPCC), could be integrated in an IGCC with CO 2 removal are described. The main advantage is the avoidance of slagging and fouling problems without the need for a gas quench. This is a prerequisite for the trouble-free operation of a highly efficient heat exchanger, a turbine, and a catalytic membrane, which offer the possibility of a significant increase in efficiency. © 2011 Elsevier Ltd. All rights reserved.

Vad T.,TU Dresden | Sager W.F.C.,Julich Research Center
Journal of Applied Crystallography | Year: 2011

Two simple iterative desmearing procedures - the Lake algorithm and the Van Cittert method - have been investigated by introducing different convergence criteria using both synthetic and experimental small-angle neutron scattering data. Implementing appropriate convergence criteria resulted in stable and reliable solutions in correcting resolution errors originating from instrumental smearing, i.e. finite collimation and polychromaticity of the incident beam. Deviations at small momentum transfer for concentrated ensembles of spheres encountered in earlier studies are not observed. Amplification of statistical errors can be reduced by applying a noise filter after desmearing. In most cases investigated, the modified Lake algorithm yields better results with a significantly smaller number of iterations and is, therefore, suitable for automated desmearing of large numbers of data sets. © 2011 International Union of Crystallography Printed in Singapore-all rights reserved.

Cherstvy A.G.,Julich Research Center
Journal of Biological Physics | Year: 2011

We study the deformations of charged elastic rods under applied end forces and torques. For neutral filaments, we analyze the energetics of initial helical deformations and loop formation. We supplement this elastic approach with electrostatic energies of bent filaments and find critical conditions for buckling depending on the ionic strength of the solution. We also study force-induced loop opening, for parameters relevant for DNA. Finally, some applications of this nano-mechanical DNA model to salt-dependent onset of DNA supercoiling are discussed. © Springer Science+Business Media B.V. 2011.

Aeberhard U.,Julich Research Center
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

Quantum well solar cells have been introduced as high efficiency photovoltaic energy conversion devices nearly twenty years ago. Since then, their capability to outperform bulk devices under concentrated illumination was established and efficiencies close to the single gap Shockley-Queisser limit for the corresponding bulk materials were reached. In order to further increase the efficiency, the mechanisms behind the extraordinary performance need to be analyzed and understood. To this end, novel theoretical approaches to the simulation of quantum optoelectronic devices are required, since the device behavior depends on complex processes between localized and extended states, such as carrier capture and escape into and from quantum wells, which cannot be consistently described by the combination of macroscopic semiconductor transport equations with detailed balance rate models conventionally used in photovoltaics. This paper presents a suitable theoretical framework based on the nonequilibrium Green's function formalism that allows the unification of quantum optics and dissipative quantum transport on the quantum kinetic level and is thus able to provide insight into the microscopic mechanisms of quantum photovoltaic device operation. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Valdau Y.,Julich Research Center | Wilkin C.,University College London
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011

It is shown that a recent extraction of the total cross section for pp→K+nΣ+ from inclusive K+ production data by the HIRES Collaboration [Phys. Lett. B 692 (2010) 10] is in conflict with experimental data on the exclusive pp→K+pλ reaction. The HIRES result may be interpreted as an upper bound, which is not inconsistent with the much lower values that already exist in the literature. © 2010 Elsevier B.V.

Persson B.N.J.,University of Toyama | Persson B.N.J.,Julich Research Center | Ueba H.,University of Toyama
Journal of Physics Condensed Matter | Year: 2010

We study the heat transfer between graphene and amorphous SiO2. We include both the heat transfer from the area of real contact, and between the surfaces in the non-contact region. We consider the radiative heat transfer associated with the evanescent electromagnetic waves which exist outside of all bodies, and the heat transfer by the gas in the non-contact region. We find that the dominant contribution to the heat transfer results from the area of real contact, and the calculated value of the heat transfer coefficient is in good agreement with the value deduced from experimental data. © 2010 IOP Publishing Ltd.

Lounis S.,University of California at Irvine | Dederichs P.H.,Julich Research Center
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

Mapping the magnetic exchange interactions from model Hamiltonian to density-functional theory is a crucial step in multiscale modeling calculations. Considering the usual magnetic force theorem but with arbitrary rotational angles of the spin moments, a spurious anisotropy in the standard mapping procedure is shown to occur provided by bilinear like contributions of high-order spin interactions. The evaluation of this anisotropy gives a hint on the strength of nonbilinear terms characterizing the system under investigation. © 2010 The American Physical Society.

Lacour A.,University of Bonn | Oller J.A.,University of Murcia | Meissner U.-G.,University of Bonn | Meissner U.-G.,Julich Research Center
Annals of Physics | Year: 2011

Recently we have developed a novel chiral power counting scheme for an effective field theory of nuclear matter with nucleons and pions as degrees of freedom [1]. It allows for a systematic expansion taking into account both local as well as pion-mediated multi-nucleon interactions. We apply this power counting in the present study to the evaluation of the pion self-energy and the energy density in nuclear and neutron matter at next-to-leading order. To implement this power counting in actual calculations we develop here a non-perturbative method based on Unitary Chiral Perturbation Theory for performing the required resummations. We show explicitly that the contributions to the pion self-energy with in-medium nucleon-nucleon interactions to this order cancel. The main trends for the energy density of symmetric nuclear and neutron matter are already reproduced at next-to-leading order. In addition, an accurate description of the neutron matter equation of state, as compared with sophisticated many-body calculations, is obtained by varying only slightly a subtraction constant around its expected value. The case of symmetric nuclear matter requires the introduction of an additional fine-tuned subtraction constant, parameterizing the effects from higher order contributions. With that, the empirical saturation point and the nuclear matter compressibility are well reproduced while the energy per nucleon as a function of density closely agrees with sophisticated calculations in the literature. © 2010 Elsevier Inc.

Cherstvy A.G.,Julich Research Center
Journal of Molecular Recognition | Year: 2011

First, we summarize recent experimental facts on homologous DNA pairing in vitro and discuss possible mechanisms of DNA-DNA sequence recognition. Then, we overview the mechanism of DNA-DNA recognition based on complementarity of DNA charge patterns. The theory predicts the recognition energy up to 10 k BT for close parallel homologous DNA fragments of gene-relevant lengths. We argue why this estimate cannot be directly applied to pairing of homologous DNA loci in experiments on yeast chromosomes. Namely, DNA-DNA distances assessed from experiments are much larger than those typically used in theory. Finally, we suggest some experiments that could help to judge whether short-range electrostatic forces indeed govern DNA pairing. This viewpoint paper introduces recently developed theoretical concepts to molecular biologists, with a hope to generate a junction between theory and future experiments on DNA recognition. © 2010 John Wiley & Sons, Ltd.

Haustein S.,Julich Research Center | Haustein S.,Heinrich Heine University Dusseldorf | Siebenlist T.,Heinrich Heine University Dusseldorf
Journal of Informetrics | Year: 2011

Web 2.0 technologies are finding their way into academics: specialized social bookmarking services allow researchers to store and share scientific literature online. By bookmarking and tagging articles, academic prosumers generate new information about resources, i.e. usage statistics and content description of scientific journals. Given the lack of global download statistics, the authors propose the application of social bookmarking data to journal evaluation. For a set of 45 physics journals all 13,608 bookmarks from CiteULike, Connotea and BibSonomy to documents published between 2004 and 2008 were analyzed. This article explores bookmarking data in STM and examines in how far it can be used to describe the perception of periodicals by the readership. Four basic indicators are defined, which analyze different aspects of usage: Usage Ratio, Usage Diffusion, Article Usage Intensity and Journal Usage Intensity. Tags are analyzed to describe a reader-specific view on journal content. © 2011 Elsevier Ltd.

Ungermann J.,Julich Research Center | Ungermann J.,U.S. National Center for Atmospheric Research
Atmospheric Measurement Techniques | Year: 2013

Modern airborne infrared limb sounders are capable of measuring profiles so fast that neighbouring profiles are very similar to one another. This can be exploited by retrieving whole 2-D cross-sections instead of simple 1-D profiles. This paper presents algorithms that are able to perform such a large-scale retrieval and that efficiently produce typical diagnostic quantities. The characteristics and capabilities of the proposed method are analysed and demonstrated in a detailed case study using a series of profiles that were measured by CRISTA-NF (Cryogenic Infrared Spectrometers and Telescope for the Atmosphere-New Frontiers). It is shown that cross-section retrievals can either reduce noise-induced artefacts or produce finer vertical structures while maintaining the same image noise level. Further, it is discussed how the presented methodology can also be applied to improve the retrievals for other instrument types including current satellite-borne nadir-sounders and near-future satellite-borne limb sounders. © Author(s) 2013. CC Attribution 3.0 License.

Yue J.,Hampton University | Hoffmann L.,Julich Research Center | Joan Alexander M.,NorthWest Research Associates, Inc.
Journal of Geophysical Research: Atmospheres | Year: 2013

We report the first joint observations of convectively generated gravity waves (GWs) using an OH airglow imager in Colorado and the Atmospheric Infrared Sounder (AIRS) onboard the Aqua satellite. Convective GWs, appearing as concentric rings, are observed over the western Great Plain regions of North America in the evening of 3 June 2008 in the airglow images. Inspecting both weather radars and AIRS radiances at 8.1 μm, strong convective clouds are found near the center of the concentric rings. The AIRS data at 4.3 μm show semicircular GWs with horizontal wavelengths of 60-80 km at 0900 UT, whereas the airglow imager observed circular GWs with horizontal wavelengths of ~44 km and airglow emission perturbation of ~6% at the same geographic location at 0910 UT. Large-scale GWs (horizontal wavelengths greater than 100 km) emanating northwestward can be seen in both AIRS data and airglow images at different times. The imager observed small-scale ripples associated with unstable concentric GWs in the mesopause in the early evening. Given that the brightness temperature perturbation of the GWs in the AIRS data is about 0.16 K and assuming that the GWs propagate without dissipation from the stratosphere to the upper mesosphere, the expected airglow emission perturbation caused by the GWs would be 4%-17%. Ray tracing simulations are performed to demonstrate that the GWs seen in AIRS and in the imager were likely excited by the same convective system. ©2013. American Geophysical Union. All Rights Reserved.

Schiller U.D.,Julich Research Center
Computer Physics Communications | Year: 2014

A unified framework to derive discrete time-marching schemes for the coupling of immersed solid and elastic objects to the lattice Boltzmann method is presented. Based on operator splitting for the discrete Boltzmann equation, second-order time-accurate schemes for the immersed boundary method, viscous force coupling and external boundary force are derived. Furthermore, a modified formulation of the external boundary force is introduced that leads to a more accurate no-slip boundary condition. The derivation also reveals that the coupling methods can be cast into a unified form, and that the immersed boundary method can be interpreted as the limit of force coupling for vanishing particle mass. In practice, the ratio between fluid and particle mass determines the strength of the force transfer in the coupling. The integration schemes formally improve the accuracy of first-order algorithms that are commonly employed when coupling immersed objects to a lattice Boltzmann fluid. It is anticipated that they will also lead to superior long-time stability in simulations of complex fluids with multiple scales. © 2014 Elsevier B.V. All rights reserved.

Bauer G.S.,Julich Research Center
Journal of Nuclear Materials | Year: 2010

From a modest beginning of a few kW of beam power spallation sources have now evolved into systems that must be able to handle several MW, mostly delivered in short pulses of less than microsecond duration. The high radiation field and high instantaneous heat deposition which spallation targets, in particular for the new high power sources, are subject to have led to several different design concepts which aim at circumventing or reducing the deleterious effects on the materials in the targets. Efficient cooling and high neutron source density are competing requirements which can be best reconciled by moving the target material out of the reaction zone and removing the heat elsewhere before returning the material back into the proton beam. One option is the use of a flowing liquid metal, which has been the method of choice in most of the recent spallation source designs, but requires solutions to a variety of new problems, such as liquid metal corrosion, cavitation erosion and e.g. in the case of PbBi, or Pb, high temperature gradients. Using a rotating solid target is an option in certain cases but still has to cope with the instantaneous load levels. While it may help to keep the average heat load and radiation damage in the target material low and thus extend the target life time by more than an order of magnitude, it still has its own design and materials issues. Opportunities to carry out research in this field are rather limited because the effects can hardly be simulated off line and, apart from spallation targets in operation, almost no facilities are available. © 2009.

Schniger A.,University of Stuttgart | Schniger A.,BoSS Consult GmbH | Nowak W.,University of Stuttgart | Hendricks Franssen H.-J.,Julich Research Center
Water Resources Research | Year: 2012

Ensemble Kalman filters (EnKFs) are a successful tool for estimating state variables in atmospheric and oceanic sciences. Recent research has prepared the EnKF for parameter estimation in groundwater applications. EnKFs are optimal in the sense of Bayesian updating only if all involved variables are multivariate Gaussian. Subsurface flow and transport state variables, however, generally do not show Gaussian dependence on hydraulic log conductivity and among each other, even if log conductivity is multi-Gaussian. To improve EnKFs in this context, we apply nonlinear, monotonic transformations to the observed states, rendering them Gaussian (Gaussian anamorphosis, GA). Similar ideas have recently been presented by Béal et al. (2010) in the context of state estimation. Our work transfers and adapts this methodology to parameter estimation. Additionally, we address the treatment of measurement errors in the transformation and provide several multivariate analysis tools to evaluate the expected usefulness of GA beforehand. For illustration, we present a first-time application of an EnKF to parameter estimation from 3-D hydraulic tomography in multi-Gaussian log conductivity fields. Results show that (1) GA achieves an implicit pseudolinearization of drawdown data as a function of log conductivity and (2) this makes both parameter identification and prediction of flow and transport more accurate. Combining EnKFs with GA yields a computationally efficient tool for nonlinear inversion of data with improved accuracy. This is an attractive benefit, given that linearization-free methods such as particle filters are computationally extremely demanding. Copyright 2012 by the American Geophysical Union.

Kirschner A.,Julich Research Center
Fusion Science and Technology | Year: 2010

An overview of erosion and deposition processes in fusion machines is presented. The underlying physical and chemical mechanisms are explained. The impact of erosion and deposition on wall lifetime and tritium retention, which define the availability of future fusion machines such as ITER, is discussed. Also, examples of erosion and deposition observed in present fusion experiments are presented.

Cui C.,TU Berlin | Gan L.,TU Berlin | Heggen M.,Julich Research Center | Rudi S.,TU Berlin | Strasser P.,TU Berlin
Nature Materials | Year: 2013

Shape-selective monometallic nanocatalysts offer activity benefits based on structural sensitivity and high surface area. In bimetallic nanoalloys with well-defined shape, site-dependent metal surface segregation additionally affects the catalytic activity and stability. However, segregation on shaped alloy nanocatalysts and their atomic-scale evolution is largely unexplored. Exemplified by three octahedral Pt x Ni 1-x alloy nanoparticle electrocatalysts with unique activity for the oxygen reduction reaction at fuel cell cathodes, we reveal an unexpected compositional segregation structure across the {111} facets using aberration-corrected scanning transmission electron microscopy and electron energy-loss spectroscopy. In contrast to theoretical predictions, the pristine Pt x Ni 1-x nano-octahedra feature a Pt-rich frame along their edges and corners, whereas their Ni atoms are preferentially segregated in their {111} facet region. We follow their morphological and compositional evolution in electrochemical environments and correlate this with their exceptional catalytic activity. The octahedra preferentially leach in their facet centres and evolve into 'concave octahedra'. More generally, the segregation and leaching mechanisms revealed here highlight the complexity with which shape-selective nanoalloys form and evolve under reactive conditions. © 2013 Macmillan Publishers Limited. All rights reserved.

Peksen M.,Julich Research Center
International Journal of Hydrogen Energy | Year: 2015

Full commercialisation of the solid oxide fuel cell (SOFC) technology is limited by technological challenges, in particular due to the thermomechanical reliability of the components. The long-term thermomechanical behaviour is especially affected by the operation environment. Most of the research and development studies, as well as laboratory studies are performed within furnaces rather than operating in a real system environment. However, the thermomechanical response of fuel cells operating in the furnace, especially operating with different fuel gas compositions is not fully understood, yet. The present study investigates the thermomechanical comparison of H2, 77% CH4 and 38% CH4 operation. A three dimensional coupled CFD/FEM sub-model, derived from a whole stack model and experimentally determined data is used. The analyses account both for the thermo fluid flow and the nonlinear elastoplastic, creep strain material behaviour. The thermomechanical behavior of the most favourable operation condition has been analysed for 1200h operation time. The results are validated qualitatively and quantitatively using post-mortem images and creep strain data, respectively. © 2015 Hydrogen Energy Publications, LLC.

Epelbaum E.,Ruhr University Bochum | Krebs H.,Ruhr University Bochum | Lee D.,North Carolina State University | Meissner U.-G.,University of Bonn | Meissner U.-G.,Julich Research Center
Physical Review Letters | Year: 2011

The Hoyle state plays a crucial role in the helium burning of stars heavier than our Sun and in the production of carbon and other elements necessary for life. This excited state of the carbon-12 nucleus was postulated by Hoyle as a necessary ingredient for the fusion of three alpha particles to produce carbon at stellar temperatures. Although the Hoyle state was seen experimentally more than a half century ago nuclear theorists have not yet uncovered the nature of this state from first principles. In this Letter we report the first abAAinitio calculation of the low-lying states of carbon-12 using supercomputer lattice simulations and a theoretical framework known as effective field theory. In addition to the ground state and excited spin-2 state, we find a resonance at -85(3)MeV with all of the properties of the Hoyle state and in agreement with the experimentally observed energy. © 2011 American Physical Society.

Hanhart C.,Julich Research Center
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2012

A new approach to the parameterization of pion form factors is presented and for illustration applied to the pion vector form factor. It has the correct analytic structure, is at low energies consistent with recent high accuracy analyses of ππ scattering phase shifts and, at high energies, maps smoothly onto the well-known, successful isobar model. © 2012 Elsevier B.V.

The diagnosis of probable Alzheimer's disease (AD) can be established premortem based on clinical criteria like neuropsychological tests. Post mortem, specific neuropathological changes like amyloid plaques define AD. However, the standard criteria based on medical history and mental status examinations do not take into account the long preclinical features of the disease, and a biomarker for improved diagnosis of AD is urgently needed. In a large number of studies, amyloid-β (Aβ) monomer concentrations in CSF of AD patients are consistently and significantly reduced when compared to healthy controls. Therefore, monomeric Aβ in CSF was suggested to be a helpful biomarker for the diagnosis of preclinical AD. However, not the monomeric form, but Aβ oligomers have been shown to be the toxic species in AD pathology, and their quantification and characterization could facilitate AD diagnosis and therapy monitoring. Here, we review the current status of assay development to reliably and routinely detect Aβ oligomers and high-molecular-weight particles in CSF. Copyright © 2011 Susanne Aileen Funke.

Zorn R.,Julich Research Center
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2012

For high resolution time-of-flight neutron scattering spectrometers, a significant contribution to the instrumental resolution broadening will be due to the flight path uncertainty induced by the sample size. In linear approximation, this contribution is an additional convolution of the resolution function with the scaled distribution of flight path lengths. This distribution, its moments, and its Fourier transform will be calculated for flat film and hollow-cylindrical sample geometry. The minima in the Fourier transform are shown to correspond to experimentally inaccessible ranges of the intermediate scattering function. © 2012 Elsevier B.V. All rights reserved.

Belitsky V.,University of Sao Paulo | Schutz G.M.,Julich Research Center
Journal of Statistical Physics | Year: 2015

We consider a two-component asymmetric simple exclusion process (ASEP) on a finite lattice with reflecting boundary conditions. For this process, which is equivalent to the ASEP with second-class particles, we construct the representation matrices of the quantum algebra Uq[gl(3)] that commute with the generator. As a byproduct we prove reversibility and obtain in explicit form the reversible measure. A review of the algebraic techniques used in the proofs is given. © 2015, Springer Science+Business Media New York.

Ishida H.,Nihon University | Liebsch A.,Julich Research Center
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

The role of Coulomb correlations in the iron pnictide LaFeAsO is studied by generalizing exact diagonalization dynamical mean-field theory to five orbitals. For rotationally invariant Hund's rule coupling a transition from a paramagnetic Fermi-liquid phase to a non-Fermi-liquid metallic phase exhibiting frozen moments is found at moderate Coulomb energies. For Ising-like exchange, this transition occurs at a considerably lower critical Coulomb energy. The correlation-induced scattering rate as a function of doping relative to half filling, i.e., δ=n/5-1, where n=6 for the undoped material, is shown to be qualitatively similar to the one in the two-dimensional single-band Hubbard model which is commonly used to study strong correlations in high- Tc cuprates. In this scenario, the parent Mott insulator of LaFeAsO is the half-filled n=5 limit, while the undoped n=6 material corresponds to the critical doping region δc ≈0.2 in the cuprates, on the verge between the Fermi-liquid phase of the overdoped region and the non-Fermi-liquid pseudogap phase in the underdoped region. © 2010 The American Physical Society.

Ishida H.,Nihon University | Liebsch A.,Julich Research Center
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

We present a dynamical mean-field theory (DMFT) study of strongly correlated heterostructures. In contrast to previous DMFT work on multilayered systems, which was mainly based on the single-site approximation, we investigate the role of interplanar Coulomb correlations by using cellular DMFT. Accordingly, the self-energy matrix exhibits off-diagonal components in the layer index. As a model system we consider the single-band Hubbard model in a thin film geometry. The films can be either free standing or sandwiched between semi-infinite metallic leads. For isolated thin films, it is shown that the metal-insulator phase transition occurs either via a conventional mechanism, with a diverging imaginary part of the local self-energy, or via another one involving a discontinuous change of the real part of the off-diagonal self-energy. When the film is connected to metallic leads, the former phase transition disappears due to the normal-metal proximity effects, whereas the latter survives and significantly influences the electronic properties of the thin film. The leakage of metallic states into the Mott gap of the correlated film is greatly reduced compared to single-site DMFT calculations. © 2010 The American Physical Society.

Liebsch A.,Julich Research Center
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

The spectral weight of states induced in the Mott gap via hole doping in the two-dimensional Hubbard model is studied within cluster dynamical mean-field theory combined with finite-temperature exact diagonalization. If the cutoff energy is chosen to lie just below the upper Hubbard band, the integrated weight per spin is shown to satisfy W+ (δ) ≥δ (δ denotes the total number of holes), in agreement with model predictions by Eskes [Phys. Rev. Lett. 67, 1035 (1991)]10.1103/PhysRevLett.67.1035. However, if the cutoff energy is chosen to lie in the range of the pseudogap, W+ (δ) remains much smaller than δ and approximately saturates near δ≈0.2,...,0.3. The analysis of recent x-ray absorption spectroscopy data therefore depends crucially on the appropriate definition of the integration window. © 2010 The American Physical Society.

Atodiresei N.,Julich Research Center | Raman K.V.,Indian Institute of Science
MRS Bulletin | Year: 2014

Organic molecules adsorbed on magnetic surfaces offer the possibility to merge the concepts of molecular electronics with spintronics to build future nanoscale data storage, sensing, and computing multifunctional devices. In order to engineer the functionalities of such hybrid spintronic devices, an understanding of the electronic and magnetic properties of the interface between carbon-based aromatic materials and magnetic surfaces is essential. In this article, we discuss recent progress in the study of spin-dependent chemistry and physics associated with the above molecule-ferromagnet interface by combining state-of-the-art experiments and theoretical calculations. The magnetic properties such as molecular magnetic moment, electronic interface spin-polarization, magnetic anisotropy, and magnetic exchange coupling can be specifically tuned by an appropriate choice of the organic material and the magnetic substrate. These reports suggest a gradual shift in research toward an emerging subfield of interface-assisted molecular spintronics. © Materials Research Society 2014.

Aeberhard U.,Julich Research Center
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

The generation of photocurrents due to coupling of electrons to both classical and quantized electromagnetic fields in thin semiconductor films is described within the framework of the nonequilibrium Green's function formalism. For the coherent coupling to classical fields corresponding to single field operator averages, an effective two-time intraband self-energy is derived from a band decoupling procedure. The evaluation of coherent photogeneration is performed self-consistently with the propagation of the fields by using for the latter a transfer matrix formalism with an extinction coefficient derived from the electronic Green's functions. For the "incoherent" coupling to fluctuations of the quantized fields, which need to be considered for the inclusion of spontaneous emission, the first self-consistent Born self-energy is used, with full spatial resolution in the photon Green's functions. These are obtained from the numerical solution of Dyson and Keldysh equations including a nonlocal photon self-energy based on the same interband polarization function as used for the coherent case. A comparison of the spectral and integral photocurrent generation pattern reveals a close agreement between coherent and incoherent coupling for the case of an ultrathin, selectively contacted absorber layer at short circuit conditions. © 2014 American Physical Society.

Zorn R.,Julich Research Center
Macromolecular Theory and Simulations | Year: 2014

In this paper the scattering from an ideal polymer chain in strong confinement (d≪Rg) is calculated. It is possible to derive analytical closed-form expressions analogous to the Debye form factor. The results can be written in terms of one hypergeometric function 2F2 for all geometries (channel, film, unconfined). It is shown that the result is consistent with a recent calculation of the form factor for a polymer chain in a radial harmonic potential. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Aydin H.,Justus Liebig University | Korte C.,Julich Research Center | Rohnke M.,Justus Liebig University | Janek J.,Justus Liebig University
Physical Chemistry Chemical Physics | Year: 2013

Heterophase boundaries can offer fast transport paths in solid electrolyte materials. In recent studies an enhancement of the ionic conductivity was indeed observed in micro-/nanoscaled Y2O3-stabilised ZrO 2 (YSZ) composites and hetero multilayers of thin films. As space charge regions can be neglected due to high charger carrier concentrations, we assume that strain and microstructural changes at the heterophase boundaries are responsible for the observed conductivity effects. In order to obtain independent information on the role of heterophase boundaries for fast transport in strained solid electrolytes, systematic measurements of the 18O-tracer diffusion coefficient in nanoscaled YSZ/Y 2O3 multilayers were performed. Multilayer samples were prepared by Pulsed Laser Deposition (PLD) on (0001) Al2O3 substrates and characterised by X-Ray Diffraction (XRD), Scanning Electron Microscopy (HRSEM) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). To separate interface and bulk transport from the total oxygen diffusivity of the multilayer system, the (average) thickness of the YSZ-layers in the multilayers was varied from 45 nm to 12 nm. Upon decreasing the thickness of the YSZ layers, respectively increasing the density of parallel interfaces, the total diffusion coefficient of the multilayer system is increased by a factor of 2 compared to bulk YSZ. The experimental results agree well with formerly published data for ionic conductivity measurements. They also support a negligible contribution of partial electronic conductivity in the multilayer. © 2013 The Owner Societies.

Pavon Valderrama M.,Julich Research Center | Pavon Valderrama M.,Institute Fisica Corpuscular IFIC
Physical Review C - Nuclear Physics | Year: 2011

We study the perturbative renormalizability of chiral two-pion exchange for singlet and triplet channels within effective field theory, provided that the one-pion exchange piece of the interaction has been fully iterated. We determine the number of counterterms/subtractions needed to obtain finite results when the cutoff is removed, resulting in three counterterms for the singlet channel and six for the triplet. The results show that perturbative chiral two-pion exchange reproduce the data up to a center-of-mass momentum of k∼200-300 MeV in the singlet channel and k∼300-400 MeV in the triplet. © 2011 American Physical Society.

Zorn R.,Julich Research Center
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

The vibrational density of states (VDOS) of disordered systems shows a low-frequency excess, the so-called boson peak. Experiments show a change in the shape of the boson peak when the systems are spatially confined. Depending on the type of confinement (hard or soft) the low-frequency wing of the boson peak is either suppressed or enhanced. Here, a simple model, a crystalline system with disordered nearest-neighbor force constants, is studied with boundary conditions mimicking the confinement. The VDOS calculated by numerical diagonalization shows qualitatively the same confinement effect as the experiment. In this model, the effect is a consequence of modes of the bulk system being shifted up or down for hard and soft confinement, respectively. A simple rescaling procedure is suggested to convert the VDOS of the bulk into that of the confined system. © 2010 The American Physical Society.

Dwyer C.,Julich Research Center
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

Electrons with kinetic energies ∼100 keV are potentially capable of exciting atomic vibrational states from a distance of microns. Despite such a large interaction distance, our detailed calculations show that the scattering physics permits a high-energy electron beam in a scanning transmission electron microscope to locate vibrational excitations with atomic-scale spatial resolution. Attempts to realize this capability experimentally could potentially benefit numerous fields across the physical sciences. © 2014 American Physical Society.

Catelani G.,Julich Research Center
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

The transmon superconducting qubit is being intensely investigated as a promising approach for the physical implementation of quantum information processing, and high-quality factors of order 106 have been achieved both in two- and three-dimensional architectures. These high-quality factors enable detailed investigations of decoherence mechanisms. An intrinsic decoherence process originates from the coupling between the qubit degree of freedom and the quasiparticles that tunnel across Josephson junctions. In a transmon, tunneling of a single quasiparticle is associated with a change in parity. Here we present the theory of the parity-switching rates in single-junction transmons and compare it with recent measurements. We also show that parity switching can have an important role in limiting the coherence time. © 2014 American Physical Society.

Persson B.N.J.,Julich Research Center
Journal of Physics Condensed Matter | Year: 2014

In a recent work Gotsmann and Lantz have observed that the thermal interface conductivity for a nano-sized nominal contact area is proportional to the normal contact pressure in a wide pressure range, with a prefactor which is typically ∼103 higher than observed for the same materials at the macroscale. Here I discuss the cross-over from the nanoscale to the macroscale. I show that for macroscopic solids the spreading resistance will dominate the interfacial resistance in most cases. © 2014 IOP Publishing Ltd.

Barz B.,Drexel University | Barz B.,Julich Research Center | Urbanc B.,Drexel University
Journal of Physical Chemistry B | Year: 2014

Molecular self-assembly is ubiquitous in nature, yet prediction of assembly pathways from fundamental interparticle interactions has yet to be achieved. Here, we introduce a minimal self-assembly model with two attractive and two repulsive beads bound into a tetrahedron. The model is associated with a single parameter η defined as the repulsive to attractive interaction ratio. We explore self-assembly pathways and resulting assembly morphologies for different η values by discrete molecular dynamics. Our results demonstrate that η governs the assembly dynamics and resulting assembly morphologies, revealing an unexpected diversity and complexity for 0.5 ≥ η < 1. One of the key processes that governs the assembly dynamics is assembly breakage, which emerges spontaneously at η > 0 with the breakage rate increasing with η. The observed assembly pathways display a broad variety of assembly structures characteristic of aggregation of amyloidogenic proteins, including quasi-spherical oligomers that coassemble into elongated protofibrils, followed by a conversion into ordered polymorphic fibril-like aggregates. We further demonstrate that η can be meaningfully mapped onto amyloidogenic protein sequences, with the majority of amyloidogenic proteins characterized by 0.5 ≥ η < 1. Prion proteins, which are known to form highly breakage-prone fibrils, are characterized by η > 1, consistent with the model predictions. Our model thus provides a theoretical basis for understanding the universal aspects of aggregation pathways of amyloidogenic proteins relevant to human disease. As the model is not specific to proteins, these findings represent an important step toward understanding and predicting assembly dynamics of not only proteins but also viruses, colloids, and nanoparticles. © 2014 American Chemical Society.

Blugel S.,Julich Research Center
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

The fundamental aspects of spin-dependent transport processes and their interplay with temperature gradients, as given by the spin Seebeck coefficient, are still largely unexplored and a multitude of contributing factors must be considered. We used density functional theory together with a Monte-Carlo-based statistical method to simulate simple nanostructures, such as Co nanowires and films embedded in a Cu host or in vacuum, and investigated the influence of spin disorder scattering on electron transport at elevated temperatures. While we show that the spin-dependent scattering of electrons due to temperature-induced disorder of the local magnetic moments contributes significantly to the resistance, thermoelectric, and spin-caloric transport coefficients, we also conclude that the actual magnitude of these effects cannot be predicted, quantitatively or qualitatively, without such detailed calculations. © 2014 American Physical Society.

Muller M.,Albert Ludwigs University of Freiburg | Sprenger G.A.,University of Stuttgart | Pohl M.,Julich Research Center
Current Opinion in Chemical Biology | Year: 2013

The present review summarizes recent achievements in enzymatic thiamine catalysis during the past three years. With well-established enzymes such as BAL, PDC and TK new reactions have been identified and respective variants were prepared, which enable access to stereoisomeric products. Further we highlight recent progress with 'new' ThDP-dependent enzymes like MenD and PigD, which catalyze the Stetter-like 1,4 addition of aldehydes and YerE, which is the first known ThDP-dependent enzyme accepting ketones as acceptors. © 2013 Elsevier Ltd.

Leitner D.,University of Vienna | Felderer B.,ETH Zurich | Vontobel P.,Paul Scherrer Institute | Schnepf A.,Julich Research Center | Schnepf A.,University of Natural Resources and Life Sciences, Vienna
Plant Physiology | Year: 2014

Root system traits are important in view of current challenges such as sustainable crop production with reduced fertilizer input or in resource-limited environments. We present a novel approach for recovering root architectural parameters based on imageanalysis techniques. It is based on a graph representation of the segmented and skeletonized image of the root system, where individual roots are tracked in a fully automated way. Using a dynamic root architecture model for deciding whether a specific path in the graph is likely to represent a root helps to distinguish root overlaps from branches and favors the analysis of root development over a sequence of images. After the root tracking step, global traits such as topological characteristics as well as root architectural parameters are computed. Analysis of neutron radiographic root system images of lupine (Lupinus albus) grown in mesocosms filled with sandy soil results in a set of root architectural parameters. They are used to simulate the dynamic development of the root system and to compute the corresponding root length densities in the mesocosm. The graph representation of the root system provides global information about connectivity inside the graph. The underlying root growth model helps to determine which path inside the graph is most likely for a given root. This facilitates the systematic investigation of root architectural traits, in particular with respect to the parameterization of dynamic root architecture models. © 2014 American Society of Plant Biologists. All Rights Reserved.

Maxwell R.M.,Integrated Groundwater Modeling Center | Condon L.E.,Integrated Groundwater Modeling Center | Kollet S.J.,Julich Research Center
Geoscientific Model Development | Year: 2015

Interactions between surface and groundwater systems are well-established theoretically and observationally. While numerical models that solve both surface and subsurface flow equations in a single framework (matrix) are increasingly being applied, computational limitations have restricted their use to local and regional studies. Regional or watershed-scale simulations have been effective tools for understanding hydrologic processes; however, there are still many questions, such as the adaptation of water resources to anthropogenic stressors and climate variability, that can only be answered across large spatial extents at high resolution. In response to this grand challenge in hydrology, we present the results of a parallel, integrated hydrologic model simulating surface and subsurface flow at high spatial resolution (1 km) over much of continental North America (∼6.3 M km2). These simulations provide integrated predictions of hydrologic states and fluxes, namely, water table depth and streamflow, at very large scale and high resolution. The physics-based modeling approach used here requires limited parameterizations and relies only on more fundamental inputs such as topography, hydrogeologic properties and climate forcing. Results are compared to observations and provide mechanistic insight into hydrologic process interaction. This study demonstrates both the feasibility of continental-scale integrated models and their utility for improving our understanding of large-scale hydrologic systems; the combination of high resolution and large spatial extent facilitates analysis of scaling relationships using model outputs. © Author(s) 2015.

Kang K.,Julich Research Center
Soft Matter | Year: 2014

It has recently been shown that suspensions of long and thin charged fibrous viruses (fd) form a glass at low ionic strengths. The corresponding thick electric double layers give rise to long-ranged repulsive electrostatic interactions, which lead to caging and structural arrest at concentrations far above the isotropic-nematic coexistence region. Structural arrest and freezing of the orientational texture are found to occur at the same concentration. In addition, various types of orientational textures are equilibrated below the glass transition concentration, ranging from a chiral-nematic texture with a large pitch (of about 100 μm), an X-pattern, and a tightly packed domain texture, consisting of helical domains with a relatively small pitch (of about 10 μm) and twisted boundaries. The dynamics of both particles as well as the texture are discussed, below and above the glass transition. Dynamic light scattering correlation functions exhibit two dynamical modes, where the slow mode is attributed to the elasticity of helical domains. On approach of the glass-transition concentration, the slow mode increases in amplitude, while as the amplitudes of the fast and slow mode become equal at the glass transition. Finally, interesting features of the "transient" behaviors of charged fd-rod glass are shown as the initial caging due to structural arrest, the propagation of flow originating from stress release, and the transition to the final metastable glass state. In addition to the intensity correlation function, power spectra are presented as a function of the waiting time, at the zero-frequency limit that may access to the thermal anomalities in a charged system. © 2014 the Partner Organisations.

Cai W.,TU Dresden | Chen L.,Robert Koch Institute | Chen L.,Max Planck Institute for the Physics of Complex Systems | Ghanbarnejad F.,Robert Koch Institute | And 3 more authors.
Nature Physics | Year: 2015

The spreading of contagions can exhibit a percolation transition, which separates transitory prevalence from outbreaks that reach a finite fraction of the population. Such transitions are commonly believed to be continuous, but empirical studies have shown more violent spreading modes when the participating agents are not limited to one type. Striking examples include the co-epidemic of the Spanish flu and pneumonia that occurred in 1918 (refs,), and, more recently, the concurrent prevalence of HIV/AIDS and a host of diseases. It remains unclear to what extent an outbreak in the presence of interacting pathogens differs from that due to an ordinary single-agent process. Here we study a mechanistic model for understanding contagion processes involving inter-agent cooperation. Our stochastic simulations reveal the possible emergence of a massive avalanche-like outbreak right at the threshold, which is manifested as a discontinuous phase transition. Such an abrupt change arises only if the underlying network topology supports a bottleneck for cascaded mutual infections. Surprisingly, all these discontinuous transitions are accompanied by non-trivial critical behaviours, presenting a rare case of hybrid transition. The findings may imply the origin of catastrophic occurrences in many realistic systems, from co-epidemics to financial contagions. © 2015 Macmillan Publishers Limited. All rights reserved.

Xiang D.,Seoul National University | Jeong H.,Seoul National University | Lee T.,Seoul National University | Mayer D.,Julich Research Center
Advanced Materials | Year: 2013

A mechanically controllable break junction (MCBJ) represents a fundamental technique for the investigation of molecular electronic junctions, especially for the study of the electronic properties of single molecules. With unique advantages, the MCBJ technique has provided substantial insight into charge transport processes in molecules. In this review, the techniques for sample fabrication, operation and the various applications of MCBJs are introduced and the history, challenges and future of MCBJs are discussed. A mechanically controllable break junction (MCBJ) represents a fundamental technique for the investigation of molecular electronic junctions, especially for the study of electron transport through single molecules. This review summarizes the progress of the MCBJ technique including sample fabrication, potential applications, and challenges. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Abdullaev S.S.,Julich Research Center
Physics of Plasmas | Year: 2015

The drifts of electron orbits induced by the toroidal electric field in tokamaks are analyzed. Based on the relativistic Hamiltonian equations for guiding centre motion, the formula for the drift velocity vdr is derived. It describes the outward drift of passing particles as well as the inward drift (the Ware pinch) of trapped particles. Unlike the approximate formula for vdr given in Guan et al. [Phys. Plasmas 17, 092502 (2010)] for circular electron orbits, it describes qualitatively new features of the outward drift of electron orbits. Particularly, the new formula describes the evolution of the orbit's shape, the formation of X-point and the associated separatrix. It is shown that the outward drift velocity is proportional to the inverse aspect ratio of tokamaks. © 2015 EURATOM.

Kobler U.,Julich Research Center
Acta Physica Polonica A | Year: 2015

In earlier experimental studies we have shown that in accordance with the principles of renormalization group theory the spin dynamics of ordered magnets is controlled by a boson guiding field instead by exchange interactions between nearest magnetic neighbors. In particular, thermal decrease of the magnetic order parameter is given by the heat capacity of the boson field. The typical signature of boson dynamics is that the critical power functions either at T = Tc or at T = 0 hold up to a considerable distance from critical temperature. The critical power functions of the atomistic models hold asymptotically at T = Tc or at T = 0 only. In contrast to the atomistic magnons field bosons cannot directly be observed using inelastic neutron scattering. However, for some classes of magnets the field bosons seem to have magnetic moment and thus are able to interact directly with magnons. This interaction, although weak in principle, leads to surprisingly strong functional modifications in the magnon dispersions at small q-values. In particular, the magnon excitation gap seems to be due to the magnon-boson interaction. In this communication we want to show that for small q-values the continuous part of the magnon dispersions can be fitted over a finite q-range by a power function of wave vector. The power function can be identified with the dispersion of the field bosons. It appears that for low q-values magnon dispersions get attracted by the boson dispersion and assume the dispersion of the bosons. This allows for an experimental evaluation of the boson dispersions from the known magnon dispersions. Exponent values of 1, 1.25, 1.5, and 2 have been identified. The boson dispersion relations and the associated power functions of temperature for the heat capacity of the boson fields are now empirically known for all dimensions of the field and for magnets with integer and half-integer spin quantum number. These are two 2×3 exponent schemes.

Qaim S.M.,Julich Research Center
Radiochimica Acta | Year: 2013

Nuclear reaction cross section data are of great significance in optimisation of production routes of radionuclides. This article deals with some newer aspects of data research related to production of both standard and novel radionuclides. The recent work to standardise the known data is discussed and new measurements with regard to further optimisation of production routes of some commonly used radionuclides are mentioned. Attempts to increase the specific activity of some reactor-produced radionuclides through the use of charged-particle induced reactions are outlined. The jeopardy in the supply of 99mTc via a fission-produced 99Mo/99mTc generator is considered and its possible direct production at a cyclotron is briefly discussed. Regarding the novel radionuclides, development work is presently focussed on non-standard positron emitters for diagnosis and on low-range highly ionising radiation emitters for internal radiotherapy. Recent nuclear reaction cross section measurements related to the production of the two types of radionuclides are briefly reviewed and some anticipated trends in nuclear data research are considered. © 2013 Oldenbourg Wissenschaftsverlag München.

Jones R.O.,Julich Research Center
Reviews of Modern Physics | Year: 2015

In little more than 20 years, the number of applications of the density functional (DF) formalism in chemistry and materials science has grown in an astonishing fashion. The number of publications alone shows that DF calculations make up a huge success story, and many younger colleagues are surprised to learn that the widespread application of density functional methods, particularly in chemistry, began only after 1990. This is indeed unexpected, because the origins are usually traced to the papers of Hohenberg, Kohn, and Sham more than a quarter of a century earlier. The DF formalism, its applications, and prospects were reviewed for this journal in 1989. About the same time, the combination of DF calculations with molecular dynamics promised to provide an efficient way to study structures and reactions in molecules and extended systems. This paper reviews the development of density-related methods back to the early years of quantum mechanics and follows the breakthrough in their application after 1990. The two examples from biochemistry and materials science are among the many current applications that were simply far beyond expectations in 1990. The reasons why - 50 years after its modern formulation and after two decades of rapid expansion - some of the most cited practitioners in the field are concerned about its future are discussed. © 2015 American Physical Society.

Stencel-Baerenwald J.E.,Vanderbilt University | Reiss K.,University of Tubingen | Reiss K.,Julich Research Center | Reiter D.M.,University of Tubingen | And 4 more authors.
Nature Reviews Microbiology | Year: 2014

Viral infections are initiated by attachment of the virus to host cell surface receptors, including sialic acid-containing glycans. It is now possible to rapidly identify specific glycan receptors using glycan array screening, to define atomic-level structures of virus-glycan complexes and to alter the glycan-binding site to determine the function of glycan engagement in viral disease. This Review highlights general principles of virus-glycan interactions and provides specific examples of sialic acid binding by viruses with stalk-like attachment proteins, including influenza virus, reovirus, adenovirus and rotavirus. Understanding virus-glycan interactions is essential to combating viral infections and designing improved viral vectors for therapeutic applications.

Kronenberg T.,Julich Research Center
Ecological Economics | Year: 2010

Post-Keynesian economics and ecological economics have in common that they are considered to be 'heterodox' schools of thought. Aside from that, there has not been a strong connection between them. Previous books on post-Keynesian economics contain no chapter on environmental or ecological issues. This neglect has led leading ecological economists to criticize post-Keynesians for succumbing to the same growth paradigm as the neoclassical school. This paper argues that the two approaches are complementary in the sense that they each have different strong points. Ecological economics has correctly pointed out that the growth of the global economy may not be welfare-improving anymore, whereas post-Keynesians have gained valuable insights into the functioning of the capitalist growth process. To determine the feasibility of a synthesis between the two schools, the paper compares their approaches to the problems of production, consumption, and economic dynamics as well as the associated policy recommendations. It shows that on a theoretical level the two schools have much in common, but their policy conclusions differ with regard to the desirability of further growth. The paper concludes that a synthesis of both approaches may lead to a better understanding of how a capitalist economy operates in a natural environment with limits to growth and to better-informed policy advice. © 2010 Elsevier B.V. All rights reserved.

Guo F.-K.,University of Bonn | Meissner U.-G.,University of Bonn | Meissner U.-G.,Julich Research Center
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

The distribution of the QCD topological charge can be described by cumulants, with the lowest one being the topological susceptibility. The vacuum energy density in a θ-vacuum is the generating function for these cumulants. In this paper, we derive the vacuum energy density in SU(2) chiral perturbation theory up to next-to-leading order keeping different up and down quark masses, which can be used to calculate any cumulant of the topological charge distribution. We also give the expression for the case of SU(. N) with degenerate quark masses. In this case, all cumulants depend on the same linear combination of low-energy constants and chiral logarithm, and thus there are sum rules between the N-flavor quark condensate and the cumulants free of next-to-leading order corrections. © 2015 The Authors.

Konopka P.,Julich Research Center | Pan L.L.,NCAR
Journal of Geophysical Research: Atmospheres | Year: 2012

We present a case study on the formation and structure of the Extratropical Transition Layer (ExTL) using in situ observations and a Lagrangian chemical transport model. The results show that the model with mixing parameterized from the large-scale flow deformations well reconstructs the observed asymmetric structure of the ExTL with a deeper transition layer on the cyclonic side of the jet stream. Information from the model and observations are integrated using tracer-tracer correlations between ozone (O3) and carbon monoxide (CO). Transport of chemical tracers from the stratospheric or tropospheric background to the ExTL through mixing is identified by the change of the CO-O3 correlation in the CO-O3 space. The ExTL formation process simulated by the model, therefore, provides a scenario to connect the mixed air parcels to the history of mixing. An estimate of timescales of ExTL formation is made using model experiments. The results show that the fastest formation of the ExTL occurs on the isentropic levels below the subtropical jet core, e.g. around 3 weeks for 310 K, whereas at 360 K level (jet core) the formation of the ExTL needs around 3 months. Overall, this result demonstrates the important role of mixing in transport of trace gases across the tropopause.© 2012. American Geophysical Union.

Philipps V.,Julich Research Center
Journal of Nuclear Materials | Year: 2011

The use of tungsten (W) as material for plasma-facing components (PFM) in fusion devices is reviewed with respect to its plasma and material compatibility under burning plasmas conditions. Fusion-relevant plasma operation with W walls is characterised by the need to operate at high edge densities, no or moderate density peaking, and external tools to control the W transport in the plasma core. Several surface and material issues related with the high particle fluencies in fusion devices needs further R&D but are not considered from present view to seriously limit the use of W as PFM. Reliable control of Edge Localised Modes (ELMs) and disruptions is indispensable for the application of W, both to control the W transport in the edge and to avoid target melting in uncontrolled events which can seriously detoriate the operational performance of the device. For DEMO and reactors, the behaviour of W under large neutron fluencies has to be further clarified and measures must be developed to mitigate degradation of material properties by neutron damage. © 2010 Elsevier B.V. All rights reserved.

Brezinsek S.,Culham Center for Fusion Energy | Brezinsek S.,Julich Research Center
Journal of Nuclear Materials | Year: 2015

Abstract The JET ITER-Like Wall experiment (JET-ILW) provides an ideal test bed to investigate plasma-surface interaction (PSI) and plasma operation with the ITER plasma-facing material selection employing beryllium in the main chamber and tungsten in the divertor. The main PSI processes: material erosion and migration, (b) fuel recycling and retention, (c) impurity concentration and radiation have be1en studied and compared between JET-C and JET-ILW. The current physics understanding of these key processes in the JET-ILW revealed that both interpretation of previously obtained carbon results (JET-C) and predictions to ITER need to be revisited. The impact of the first-wall material on the plasma was underestimated. Main observations are: (a) low primary erosion source in H-mode plasmas and reduction of the material migration from the main chamber to the divertor (factor7) as well as within the divertor from plasma-facing to remote areas (factor30-50). The energetic threshold for beryllium sputtering minimises the primary erosion source and inhibits multi-step re-erosion in the divertor. The physical sputtering yield of tungsten is low as 10-5 and determined by beryllium ions. (b) Reduction of the long-term fuel retention (factor10-20) in JET-ILW with respect to JET-C. The remaining retention is caused by implantation and co-deposition with beryllium and residual impurities. Outgassing has gained importance and impacts on the recycling properties of beryllium and tungsten. (c) The low effective plasma charge (Zeff=1.2) and low radiation capability of beryllium reveal the bare deuterium plasma physics. Moderate nitrogen seeding, reaching Zeff=1.6, restores in particular the confinement and the L-H threshold behaviour. ITER-compatible divertor conditions with stable semi-detachment were obtained owing to a higher density limit with ILW. Overall JET demonstrated successful plasma operation in the Be/W material combination and confirms its advantageous PSI behaviour and gives strong support to the ITER material selection. © 2014 The Authors.

Peksen M.,Julich Research Center
International Journal of Hydrogen Energy | Year: 2013

Hermetic sealing and long-term structural reliability of fuel cell stacks depend strongly on the thermomechanically induced stress-strain behaviour. These are especially affected by the environment; the fuel cell is operating in. Most of the research and development studies, as well as laboratory studies are conducted within electrically heated furnaces rather than operating in an insulated system environment. The thermomechanical comparison of them is not fully understood, yet. The present study utilises a previously developed full scale three dimensional planar type 6-cell SOFC short stack model to shed light on the thermomechanical response of high temperature fuel cells operating in system and furnace environments. The physically resolved coupled computational fluid dynamics and computational structural mechanics model has been improved, accounting for the rate dependent creep strain, as well as including the furnace domain and thermal radiation to fully describe the thermal and deformation behaviour of the stack. The non-linear elastoplastic behaviour of the metal components as a function of temperature is considered. The results are validated using creep strain data from the literature and in-house post-mortem images. The study gives an insight about the critical regions prone to failure due to creep strain operating in different environments and the long-term fuel cell behaviour. Moreover, the critical locations appear to be prone to high creep strain after 1000 h operation time. © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

The ability of mammalian cells to adhere and to migrate is an essential prerequisite to form higher organisms. Early migratory events include substrate sensing, adhesion formation, actin bundle assembly and force generation. Latest research revealed that filopodia are important not only for sensing the substrate but for all of the aforementioned highly regulated processes. However, the exact regulatory mechanisms are still barely understood. Here, we demonstrate that filopodia of human keratinocytes exhibit distinct cycles of repetitive elongation and persistence. A single filopodium thereby is able to initiate the formation of several stable adhesions. Every single filopodial cycle is characterized by an elongation phase, followed by a stabilization time and in many cases a persistence phase. The whole process is strongly connected to the velocity of the lamellipodial leading edge, characterized by a similar phase behavior with a slight time shift compared to filopodia and a different velocity. Most importantly, re-growth of existing filopodia is induced at a sharply defined distance between the filopodial tip and the lamellipodial leading edge. On the molecular level this re-growth is preceded by a strong filopodial reduction of the actin bundling protein fascin. This reduction is achieved by a switch to actin polymerization without fascin incorporation at the filopodial tip and therefore subsequent out-transport of the cross-linker by actin retrograde flow.

Shrestha P.,University of Bonn | Sulis M.,University of Bonn | Masbou M.,German Weather Service | Kollet S.,Julich Research Center | Simmer C.,University of Bonn
Monthly Weather Review | Year: 2014

A highly modular and scale-consistent Terrestrial Systems Modeling Platform (TerrSysMP) is presented. The modeling platform consists of an atmospheric model (Consortium for Small-Scale Modeling; COSMO), a land surface model (theNCARCommunity Land Model, version 3.5; CLM3.5), and a 3Dvariably saturated groundwater flow model (ParFlow). An external coupler (Ocean Atmosphere Sea Ice Soil, version 3.0; OASIS3) with multiple executable approaches is employed to couple the three independently developed component models, which intrinsically allows for a separation of temporal-spatial modeling scales and the coupling frequencies between the component models. Idealized TerrSysMP simulations are presented, which focus on the interaction of key hydrologic processes, like runoff production (excess rainfall and saturation) at different hydrological modeling scales and the drawdown of the water table through groundwater pumping, with processes in the atmospheric boundary layer. The results show a strong linkage between integrated surface-groundwater dynamics, biogeophysical processes, and boundary layer evolution. The use of the mosaic approach for the hydrological component model (to resolve subgrid-scale topography) impacts simulated runoff production, soil moisture redistribution, and boundary layer evolution, which demonstrates the importance of hydrological modeling scales and thus the advantages of the coupling approach used in this study. Real data simulations were carried out with TerrSysMP over the Rur catchment in Germany. The inclusion of the integrated surface-groundwater flow model results in systematic patterns in the root zone soil moisture, which influence exchange flux distributions and the ensuing atmospheric boundary layer development. In a first comparison to observations, the 3D model compared to the 1D model shows slightly improved predictions of surface fluxes and a strong sensitivity to the initial soil moisture content. © 2014.

Buchenau U.,Julich Research Center
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2016

The crossover from back-and-forth jumps between structural minima to the no-return jumps of the viscous flow is modeled in terms of an ensemble of double-well potentials with a finite decay probability. The ensemble is characterized by the Kohlrausch-exponent β of the time dependence tβ of the response at short times. The model is applied to shear and dielectric data from the literature. © 2016 American Physical Society.

Koch H.,Potsdam Institute for Climate Impact Research | Vogele S.,Julich Research Center
Energy | Year: 2013

In recent years there have been several heat waves affecting the use of thermoelectric power plants, e.g. in Europe and the U.S. In this paper the linkage between hydro-climatic conditions and possible electricity generation restrictions is described. The coupling of hydrological models and a power plant model is presented. In this approach each power plant is considered separately with its technical specifications. Also environmental regulations, e.g. permissible rise in the cooling water temperature, are considered for the respective power plant. The hydrological models developed to simulate river runoff and water temperature are also site specific.The approach presented is applied to Krümmel nuclear power plant in Germany. Analysed are the uncertainties with regard to electricity generation restrictions on account of climatic developments and corresponding higher water temperatures and low flows. Overall, increased water temperatures and declining river runoff lead to more frequent and more severe generation restrictions. It is concluded that the site-specific approach is necessary to reliably simulate power plants water demand, river runoff and water temperature. Using a simulation time step of one day, electricity generation restrictions are significantly higher than for simulations at monthly time step. © 2013 Elsevier Ltd.

Vogele S.,Julich Research Center | Rubbelke D.,Basque Center For Climate Change 3 | Rubbelke D.,Ikerbasque
Energy | Year: 2013

Decisions of electricity suppliers on investments in low-carbon energy technologies like PV (photovoltaics) and CCS (carbon capture and storage) depend on the expected profits or surpluses that can be earned. For an assessment of the profitability of investments in PV (and other renewable energy technologies), additional costs caused by the fluctuation in PV power plants' productivity and by the need for backup capacities have to be taken into account. Changes in the rest of the power plant stock will via their influence on the merit-order curve also affect the return on investment. Bearing these aspects in mind, it might become more attractive to invest in alternative technologies like CCS than to channel the investments towards PV in combination with backup power plants. In our study we compare investments in CCS and PV regarding possible merit-order effects and profitability, using investments in Germany as an example. © 2013 Elsevier Ltd.

Peksen M.,Julich Research Center
Progress in Energy and Combustion Science | Year: 2015

Over the last decade, many computational models have been presented to describe the complex thermomechanical behaviour of solid oxide fuel cells. The present study elucidates a detailed literature review of the proposed numerical models, ranging from a single channel or unit layer, up to coupled 3D high-end system models. Thermomechanical modelling foundations, including material properties and thermomechanical stress sources in SOFCs are emphasized. Employed material models for SOFC components are highlighted. Thermomechanical modelling issues such as geometrical idealisation, initial and boundary conditions for the highly coupled fluid and solid mechanics problem, as well as numerical solutions have been discussed. Thermomechanical stress-strain formulation of the common fuel cell components is highlighted. Finally, an overview of the numerically solved thermomechanical modelling studies in solid oxide fuel cells is given. Case studies are used throughout this review to exemplify and shed light on several modelling aspects. © 2014 Elsevier Ltd. All rights reserved.

Grushko B.,Julich Research Center
Journal of Alloys and Compounds | Year: 2013

The Al-Pd phase diagram was experimentally reinvestigated in the region around the equiatomic composition. The high-temperature β-phase (CsCl-type structure) forming around AlPd transforms by cooling to a rhombohedral β′-phase, which only being metastable, strongly resists transformation to the stable low-temperature μ-phase (FeSi-type structure). The composition of the β-phase ranges between Al57.5Pd 42.5 (at 949 °C) and Al45Pd55 (at 1315 °C). The highest existence temperature of the μ-phase is 745 °C at ∼Al52Pd48. The reaction β ↔ μ + δ occurs at 735 °C and Al53Pd47 composition; the reaction β ↔ μ + ν occurs (provisionally) at somewhat below 630 °C and ∼Al48Pd52 composition. No eutectoid decomposition of the ν-phase was observed down to 400 °C. A compositional continuity of the high-temperature complex ε6 and ε28 phases is argued. © 2013 Elsevier B.V. All rights reserved.

Denig A.,Johannes Gutenberg University Mainz | Guo F.-K.,University of Bonn | Hanhart C.,Julich Research Center | Nefediev A.V.,National Research Nuclear University MEPhI
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014

Direct production of the charmonium-like state X(3872) in e +e - collisions is considered in the framework of the vector meson dominance model. An order-of-magnitude estimate for the width Γ(X→e +e -) is found to be ≳0.03 eV. The same approach applied to the χc1 charmonium decay predicts the corresponding width of the order 0.1 eV in agreement with earlier estimates. Experimental perspectives for the direct production of the 1 + + charmonia in e +e - collisions are briefly discussed. © 2014.

Lathiotakis N.N.,National Hellenic Research Foundation | Helbig N.,Julich Research Center | Rubio A.,University of the Basque Country | Gidopoulos N.I.,Durham University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

We propose a scheme to bring reduced-density-matrix-functional theory into the realm of density functional theory (DFT) that preserves the accurate density functional description at equilibrium, while incorporating accurately static and left-right correlation effects in molecules and keeping the good computational performance of DFT-based schemes. The key ingredient is to relax the requirement that the local potential is the functional derivative of the energy with respect to the density. Instead, we propose to restrict the search for the approximate natural orbitals within a domain where these orbitals are eigenfunctions of a single-particle Hamiltonian with a local effective potential. In this way, fractional natural occupation numbers are accommodated into Kohn-Sham equations allowing for the description of molecular dissociation without breaking spin symmetry. Additionally, our scheme provides a natural way to connect an energy eigenvalue spectrum to the approximate natural orbitals and this spectrum is found to represent accurately the ionization potentials of atoms and small molecules. © 2014 American Physical Society.

Lu W.,University of Michigan | Jeong D.S.,Korea Institute of Science and Technology | Kozicki M.,Arizona State University | Waser R.,Julich Research Center
MRS Bulletin | Year: 2012

A range of material systems exist in which nanoscale ionic transport and redox reactions provide the essential mechanisms for memristive switching. One class relies on mobile cations, which are easily created by electrochemical oxidation of the corresponding electrode metal, transported in the insulating layer, and reduced at the inert counterelectrode. These devices are termed electrochemical metallization (ECM) memories, also called conductive bridge random access memories. The memristive characteristics of the ECM cells provide opportunities for circuit design and computational concepts that go beyond those in traditional complementary metal oxide semiconductor (CMOS) technology. Passive memory arrays open up paths toward ultradense and 3D stackable memory and logic gate arrays. Furthermore, the multivalued conductance characteristics allow for potential exploitation of the cells as synapses in neuromorphic circuits in future energy efficient high-performance computer architectures. Despite exciting results obtained in recent years, many challenges have to be met before these physical effects can be turned into competitive industrial technology. Here, we briefly review the basic working principle, the different possible and potential material combinations, and the fundamental electrochemical processes in ECM cells and their implications for device operations. The prospects of ECM-based resistive random access memory as an emerging memory technology are also reviewed in terms of switching speed and scalability. © 2012 Materials Research Society.

Szalay P.G.,Eotvos Lorand University | Muller T.,Julich Research Center | Gidofalvi G.,Gonzaga University | Lischka H.,Texas Tech University | And 2 more authors.
Chemical Reviews | Year: 2012

Recent developments on gradient theory, calculation of molecular properties, nonadiabatic coupling between electronic states, and relativistic and spin-orbit effects, are discussed. Shepard et al. proposed the subspace projected approximate matrix (SPAM) method that employs a sequence of one or more approximations to the H matrix. Duch and Diercksen compared the formulas and concluded that the DuchDiercksen and Pople corrections clearly outperform the original Davidson correction and its renormalized variants. Tanaka and co-workers developed multireference coupled pair approximation (MRCPA) method that is size-consistent for noninteracting electron pairs and can be applied to excited states, but analytic gradient calculations are not available. Chan and Head-Gordon used a reverse CuthillMcKee reordering of the orbitals to make the one-electron integral matrix close to band-diagonal.

The C library libkww provides functions to compute the Kohlrausch-Williams- Watts function, i.e., the Laplace-Fourier transform of the stretched (or compressed) exponential function exp(-tβ) for exponents β between 0.1 and 1.9 with double precision. Analytic error bounds are derived for the low and high frequency series expansions. For intermediate frequencies, the numeric integration is enormously accelerated by using the Ooura-Mori double exponential transformation. The primitive of the cosine transform needed for the convolution integrals is also implemented. The software is hosted at http://apps.jcns.fz-juelich.de/kww; version 3.0 is deposited as supplementary material to this article. © 2012 by the authors.

Valov I.,RWTH Aachen | Valov I.,Julich Research Center | Waser R.,RWTH Aachen
Advanced Materials | Year: 2013

Filament formation and dissolution in the system Ag(Cu)/ZrO2/Pt were observed by Liu et al. [Adv. Mater. 2012, 24, 1844]. Their explanation of the phenomena is shown here to be inappropriate. Various situations, including the "bipolar electrode" shown in the figure, are considered and the difference between the behavior in electrochemical metallization memories (ECMs) and valence change memories (VCMs) outlined. Of crucial importance for distinguishing ECM from VCM behavior, that is, the effects of cation and anion migration, is the choice of the solid materials used to transport metal cations. A possible explanation of the phenomena is proposed. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Huhn C.,Julich Research Center | Pyell U.,University of Marburg
Journal of Chromatography A | Year: 2010

Theory of field-amplified sample stacking (FASS) also called field-enhanced sample stacking is reevaluated considering the early work of Chien, Burgi and Helmer. The classical theory presented by Chien, Helmer and Burgi predicts the existence of maxima, which are ascribed to the counteracting principles of zone focusing and hydrodynamic dispersion. In contrast to their work, we here focus on cationic analytes separated in an acidic background electrolyte providing a very low electroosmotic flow velocity. Therefore, peak broadening due to differences in the local electroosmotic flow velocities in different compartments of the capillary can be regarded to be negligible. Consequently, peak broadening resulting from hydrodynamic dispersion will not be the dominant limitation of the accessible enrichment efficiency. In our experimental studies we, however, obtain an optimum value for the field enhancement factor (maximum of the enrichment efficiency, when varying the electric conductivity of the sample and the size of the sample injection plug) corresponding to a 10-fold dilution of the BGE in the sample solution. Comparing these experimental data with data modeled according to the revised theory, we show that this limitation of the loadability is caused by the unavoidable decrease of the analyte migration velocity in the BGE compartment of the capillary when injecting of a sample plug of lower electric conductivity (decrease in the local electric field strength). The additional diffusional band broadening limits the obtainable enrichment efficiency. © 2010 Elsevier B.V.

Herzog H.,Julich Research Center | Van Den Hoff J.,Helmholtz Center Dresden
Quarterly Journal of Nuclear Medicine and Molecular Imaging | Year: 2012

The integration of positron emission tomography (PET) and magnetic resonance imaging (MRI) in a combined PET/MR scanner is attracting much interest. With this new bimodal approach novel functional-anatomical and multiparametric applications become feasible, which can be expected to deliver information beyond that accessible by separately applied modalities. Although the two technologies where initially regarded as inherently incompatible, different solutions have been developed and implemented to realise PET/MR instruments for both small animal and human bimodal imaging. The present review first summarizes the basic options for possible PET/MR designs. A chronological outline describes the evolution from the first ideas, how PET and MR imaging might be combined, over different experimental solutions to the systems recently realized by industry. The BrainPET/MR and the mMR developed by Siemens and the Philips Ingenuity TF PET/MR are characterised and application examples are provided illustrating the features of these instruments. Based on own experiences and those reported in different publications a number of open issues are discussed. Finally a short comparative analysis on the status and perspectives of human PET/MR imaging is given.

Ziegler M.,University of Kiel | Soni R.,University of Kiel | Patelczyk T.,University of Kiel | Ignatov M.,University of Kiel | And 3 more authors.
Advanced Functional Materials | Year: 2012

Neuromorphic plasticity is the basic platform for learning in biological systems and is considered as the unique concept in the brains of vertebrates, which outperform today's most powerful digital computers when it comes to cognitive and recognition tasks. An emerging task in the field of neuromorphic engineering is to mimic neural pathways via elegant technological approaches to close the gap between biological and digital computing. In this respect, functional, memristive devices are considered promising candidates with yet unknown benefit for neuromorphic circuits. It is demonstrated that a single Pt/Ge 0.3Se 0.7/SiO 2/Cu memristive device implemented in an analogue circuitry mimics non-associative and associative types of learning. For Pavlovian conditioning, different threshold voltages for the memristive device and the comparator are essential. Similarities to neurobiological correlates of learning are discussed in the framework of hebbian learning rule, plasticity, and long-term potentiation. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Volokitin A.I.,Julich Research Center | Volokitin A.I.,Samara State Aerospace University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2015

The friction force acting on a small neutral particle during relativistic motion relative to the blackbody radiation is calculated in the framework of fluctuation electrodynamics. It is shown that the particle acceleration is determined by the friction force in the particle rest reference frame (K′ frame), which, in general, is not equal to the friction force in the frame of the blackbody radiation (K frame). The difference between the friction forces in the different frames is connected to the change of the rest mass of a particle due to the absorption and emission of radiation. The friction force in the K′ frame is determined only by the interaction of a particle with the blackbody radiation. In the K frame the interaction of a particle with its own thermal radiation also contributes to the friction force. For the steady-state temperature of a particle the friction forces in the K′ and K frames are equal. For an atom the blackbody friction is determined by the electronic linewidth broadening, which is calculated considering the interaction of an atom with its own radiation. In the ultrarelativistic case (1-β→0) for an atom the friction force diverges as (1-β)-3, and the (average) temperature of an atom T2≈(1-β)-3/8T1, where T1 is the temperature of the blackbody radiation and β=V/c. Controversies in the theory of the blackbody friction are discussed. © 2015 American Physical Society.

Herholz K.,University of Manchester | Langen K.-J.,Julich Research Center | Schiepers C.,University of California at Los Angeles | Mountz J.M.,University of Pittsburgh
Seminars in Nuclear Medicine | Year: 2012

This review addresses the specific contributions of nuclear medicine techniques, and especially positron emission tomography (PET), for diagnosis and management of brain tumors. 18F-Fluorodeoxyglucose PET has particular strengths in predicting prognosis and differentiating cerebral lymphoma from nonmalignant lesions. Amino acid tracers including 11C-methionine, 18F-fluoroethyltyrosine, and 18F-L-3,4-dihydroxyphenylalanine provide high sensitivity, which is most useful for detecting recurrent or residual gliomas, including most low-grade gliomas. They also play an increasing role for planning and monitoring of therapy. 18F-fluorothymidine can only be used in tumors with absent or broken blood-brain barrier and has potential for tumor grading and monitoring of therapy. Ligands for somatostatin receptors are of particular interest in pituitary adenomas and meningiomas. Tracers to image neovascularization, hypoxia, and phospholipid synthesis are under investigation for potential clinical use. All methods provide the maximum of information when used with image registration and fusion display with contrast-enhanced magnetic resonance imaging scans. Integration of PET and magnetic resonance imaging with stereotactic neuronavigation systems allows the targeting of stereotactic biopsies to obtain a more accurate histologic diagnosis and better planning of conformal and stereotactic radiotherapy. © 2012 Elsevier Inc.

Granite M.,Technion - Israel Institute of Technology | Radulescu A.,Julich Research Center | Cohen Y.,Technion - Israel Institute of Technology
Langmuir | Year: 2012

Amphiphilic block copolymers are excellent dispersants for single-walled carbon nanotubes (SWCNT) in aqueous environments, where their noncovalent attachments do not affect the π chemical bonding. In this small-angle neutron scattering (SANS) study, we investigate whether the coverage of Pluronic F127 polymers around the CNTs depends on the solution concentration in the range of 1-6% (w/w). The observations indicate that at these concentrations the SWCNT surface is fully saturated at about 14 chains per unit length of 100 Å. Furthermore, we seek to verify whether the unusual effect observed in a previous study by contrast variation, interpreted as being due to a dense hydration layer around the polymer chains, also appears using a homopolymer (polyvinylpyrrolidone - PVP) that does not contain poly(ethylene oxide) (PEO) units. The SANS patterns showed again a minimal intensity value at much higher solvent composition (75% D 2O) than the expected value of 29% D 2O. The minimum scattering curve exhibited a nearly q -1 power law at small angles, an indication of rodlike entities. A model of a CNT thin bundle with loosely adsorbed polymer chains around it (core-chains) was reasonably well fitted to the data. The polymer chains are assumed to be surrounded by a water layer with a slightly higher density than bulk water, having partial selectivity for D 2O. © 2012 American Chemical Society.

Grushko B.,Julich Research Center | Kapush D.,Frantsevich Institute for Problems of Materials Science
Journal of Alloys and Compounds | Year: 2014

Phase equilibria in the Al-Ni-Pt alloy system were specified. The total compositional region of the ternary phase diagram can coarsely be divided into three peculiar subregions. Above ∼70 at.% Al this alloy system is characterized by the formation of complex binary and ternary phases. Between ∼40 and 70 at.% Al the structures based on the CsCl-type configuration dominate, while below ∼40 at.% Al the structures are based on the FCC (Ni, Pt) solid solution. The high-Al subregion was completed with the recently revealed binary high-temperature "Al3Pt" ξ-phase (Bmmb (No. 63), a = 1.9718, b = 1.6228, c = 1.4266 nm), which was found to extend up to 1.6 at.% Ni. In the medium-Al subregion the ternary extension of the Al 2Pt phase (β*) separates the compositional regions extending from Al3Ni2 and Al3Pt 2. At 900-1100 C no complete separation was revealed between the compositional fields of the β-phase and β*. With decreasing temperature the total β + β* field shrinks around the compositional lines Al2Pt-Al2NiPt and AlNi-Al2NiPt. In the low-Al subregion the low-Ni limit of the γâ™-phase region, probably extending at low temperatures from Al3Ni5, was found to be below 4 at.%. © 2014 Elsevier B.V. All rights reserved.