Showing papers by "Frankfurt Institute for Advanced Studies published in 2011"
TL;DR: Transfer entropy (TE) improved the detectability of effective connectivity for non-linear interactions, and for sensor level MEG signals where linear methods are hampered by signal-cross-talk due to volume conduction.
Abstract: Understanding causal relationships, or effective connectivity, between parts of the brain is of utmost importance because a large part of the brain's activity is thought to be internally generated and, hence, quantifying stimulus response relationships alone does not fully describe brain dynamics. Past efforts to determine effective connectivity mostly relied on model based approaches such as Granger causality or dynamic causal modeling. Transfer entropy (TE) is an alternative measure of effective connectivity based on information theory. TE does not require a model of the interaction and is inherently non-linear. We investigated the applicability of TE as a metric in a test for effective connectivity to electrophysiological data based on simulations and magnetoencephalography (MEG) recordings in a simple motor task. In particular, we demonstrate that TE improved the detectability of effective connectivity for non-linear interactions, and for sensor level MEG signals where linear methods are hampered by signal-cross-talk due to volume conduction.
831 citations
TL;DR: In this article, an analysis of the production of light nuclei, hypernuclei, and their antiparticles in central collisions of heavy nuclei is presented, using the statistical model.
331 citations
TL;DR: In this article, the storage and balancing needs of a simplified European power system, which is based on wind and solar power generation only, are derived from an extensive weather-driven modeling of hourly power mismatches between generation and load.
254 citations
TL;DR: This work presents the open-source MATLAB toolbox TRENTOOL, an implementation of transfer entropy and mutual information analysis that aims to support the user in the application of this information theoretic measure.
Abstract: Background
Transfer entropy (TE) is a measure for the detection of directed interactions. Transfer entropy is an information theoretic implementation of Wiener's principle of observational causality. It offers an approach to the detection of neuronal interactions that is free of an explicit model of the interactions. Hence, it offers the power to analyze linear and nonlinear interactions alike. This allows for example the comprehensive analysis of directed interactions in neural networks at various levels of description. Here we present the open-source MATLAB toolbox TRENTOOL that allows the user to handle the considerable complexity of this measure and to validate the obtained results using non-parametrical statistical testing. We demonstrate the use of the toolbox and the performance of the algorithm on simulated data with nonlinear (quadratic) coupling and on local field potentials (LFP) recorded from the retina and the optic tectum of the turtle (Pseudemys scripta elegans) where a neuronal one-way connection is likely present.
231 citations
TL;DR: In this paper, the chiral phase transition line in (2+1)-flavor QCD for small values of the light quark chemical potential has been determined from an analysis of scaling properties of the Chiral condensate and its susceptibilities.
Abstract: We determine the chiral phase transition line in (2+1)-flavor QCD for small values of the light quark chemical potential. We show that for small values of the chemical potential the curvature of the phase transition line can be deduced from an analysis of scaling properties of the chiral condensate and its susceptibilities. To do so we extend earlier studies of the magnetic equation of state in (2+1)-flavor QCD to finer lattice spacings, aT = 1/8. We use these universal scaling properties of the chiral order parameter to extract the curvature of the transition line at two values of the cut-off, aT = 1/4 and 1/8. We find that cut-off effects are small for the curvature parameter and determine the transition line in the chiral limit to leading order in the light quark chemical potential. We obtain Tc(µq)/Tc(0) = 1 0.059(2)(4)(µq/T) 2 + O(µ 4).
228 citations
TL;DR: It is possible to find regions in which HPR is stronger than alpha decay and found isotopes with half-lives in the range of ns to ps for superheavy nuclei with Z = 104-124.
Abstract: The concept of heavy-particle radioactivity (HPR) is changed to allow emitted particles with Z(e) > 28 from parents with Z > 110 and daughter around (208)Pb. Calculations for superheavy (SH) nuclei with Z = 104-124 are showing a trend toward shorter half-lives and larger branching ratio relative to α decay for heavier SHs. It is possible to find regions in which HPR is stronger than alpha decay. The new mass table AME11 and the theoretical KTUY05 and FRDM95 masses are used to determine the released energy. For 124 we found isotopes with half-lives in the range of ns to ps.
192 citations
TL;DR: In this article, the authors derived the gravity field equations by varying the action for an ultraviolet complete quantum gravity and determined an exact black hole solution for the case of a static source term and found a regular spacetime geometry: in place of the conventional curvature singularity extreme energy fluctuations of the gravitational field at small length scales provide an effective cosmological constant in a region locally described in terms of a de Sitter space.
190 citations
TL;DR: It is suggested that high γ-band activity is impaired in neuropsychiatric disorders, such as schizophrenia and epilepsy, through establishing correlations between the modulation of oscillations in the 60-200 Hz frequency and specific cognitive functions.
Abstract: γ-band oscillations are thought to play a crucial role in information processing in cortical networks. In addition to oscillatory activity between 30 and 60 Hz, current evidence from electro- and magnetoencephalography (EEG/MEG) and local-field potentials (LFPs) has consistently shown oscillations >60 Hz (high γ-band) whose function and generating mechanisms are unclear. In the present paper, we summarize data that highlights the importance of high γ-band activity for cortical computations through establishing correlations between the modulation of oscillations in the 60-200 Hz frequency and specific cognitive functions. Moreover, we will suggest that high γ-band activity is impaired in neuropsychiatric disorders, such as schizophrenia and epilepsy. In the final part of the paper, we will review physiological mechanisms underlying the generation of high γ-band oscillations and discuss the functional implications of low vs. high γ-band activity patterns in cortical networks.
183 citations
TL;DR: It is found that the elliptic flow in √S(NN)=200 GeV Au+Au collisions at RHIC is dominated by the viscosity in the hadronic phase and in the phase transition region, but largely insensitive to the Viscosity of the quark-gluon plasma (QGP).
Abstract: We investigate the influence of a temperature-dependent shear viscosity over entropy density ratio {eta}/s on the transverse momentum spectra and elliptic flow of hadrons in ultrarelativistic heavy-ion collisions We find that the elliptic flow in {radical}(s{sub NN})=200 GeV Au+Au collisions at RHIC is dominated by the viscosity in the hadronic phase and in the phase transition region, but largely insensitive to the viscosity of the quark-gluon plasma (QGP) At the highest LHC energy, the elliptic flow becomes sensitive to the QGP viscosity and insensitive to the hadronic viscosity
176 citations
TL;DR: The structure of PR was solved in the short-chain lipid diC7PC combining long-range NOEs with restraints derived from paramagneticrelaxation enhancement (PRE) and residual dipolar cou-plings (RDCs) and the loop betweenhelices D and E is longer than predicted by the secondary structure prediction program TMHMM.
Abstract: and we show herein the de novo structure ofthegreenvariantofproteorhodopsinsolvedbysolutionNMRspectroscopy.The structure of PR (Figure 1) was solved in the short-chain lipid diC7PC (diheptanoyl-phosphocholine) combininglong-range NOEs with restraints derived from paramagneticrelaxation enhancement (PRE) and residual dipolar cou-plings (RDCs). The seven transmembrane helices are con-nected by short loops. Instead of the anti-parallel b-sheet thatis observed between helices B and C in other microbialrhodopsins, torsion angles derived from the protein backbonedihedral angle prediction program TALOS+ suggest that PRresidues G87–P90 form a short b-turn. The loop betweenhelices D and E is longer than predicted by the secondarystructure prediction program TMHMM.
171 citations
TL;DR: In this paper, the authors investigate the production of hadrons in nuclear collisions within the framework of the thermal (or statistical hadronization) model and provide predictions for the LHC energy.
Abstract: We investigate the production of hadrons in nuclear collisions within the framework of the thermal (or statistical hadronization) model. We discuss the light-quark hadrons as well as charmonium and provide predictions for the LHC energy. Even as its exact magnitude is dependent on the charm production cross section, not yet measured in Pb–Pb collisions, we can confidently predict that at the LHC the nuclear modification factor of charmonium as a function of centrality is larger than that observed at RHIC and compare the experimental results to these predictions.
TL;DR: One line of universal (UNIV) curve for cluster radioactivities is obtained by plotting the sum of the decimal logarithm of the half-life and cluster preformation probability versus the decidability of the penetrability of external barrier as discussed by the authors.
Abstract: One single line of universal (UNIV) curve for $\ensuremath{\alpha}$ decay and cluster radioactivities is obtained by plotting the sum of the decimal logarithm of the half-life and cluster preformation probability versus the decimal logarithm of the penetrability of external barrier. This fission-like theory is compared to the universal decay law (UDL) derived using $\ensuremath{\alpha}$-like $R$-matrix theory. The experimental data on heavy cluster decay in three groups of even-even, even-odd, and odd-even parent nuclei are reproduced with comparable accuracy by both types of universal curves, UNIV and UDL.
TL;DR: In this paper, the authors developed a framework for event-by-event ideal hydrodynamics to study the differential elliptic flow, which is measured at different centralities in Au + Au collisions at the Relativistic Heavy Ion Collider (RHIC).
Abstract: We develop a framework for event-by-event ideal hydrodynamics to study the differential elliptic flow, which is measured at different centralities in Au + Au collisions at the Relativistic Heavy Ion Collider (RHIC). Fluctuating initial energy density profiles, which here are the event-by-event analogs of the wounded nucleon profiles, are created using a Monte Carlo Glauber model. Using the same event plane method for obtaining v{sub 2} as in the data analysis, we can reproduce both the measured centrality dependence and the p{sub T} shape of charged-particle elliptic flow up to p{sub T}{approx}2 GeV. We also consider the relation of elliptic flow to the initial-state eccentricity using different reference planes and discuss the correlation between the physical event plane and the initial participant plane. Our results demonstrate that event-by-event hydrodynamics with initial-state fluctuations must be accounted for before a meaningful lower limit for viscosity can be obtained from elliptic flow data.
TL;DR: In this paper, the thermal suppression of the Pb-Pb collisions was studied and the suppression of each of these states was estimated as a function of centrality, rapidity, and transverse momentum.
Abstract: I compute the thermal suppression of the $\ensuremath{\Upsilon}(1s)$ and ${\ensuremath{\chi}}_{b1}$ states in $\sqrt{{s}_{NN}}=2.76\text{ }\text{ }\mathrm{TeV}$ Pb-Pb collisions. Using the suppression of each of these states I estimate the total ${R}_{AA}$ for the $\ensuremath{\Upsilon}(1s)$ state as a function of centrality, rapidity, and transverse momentum. I find less suppression of the ${\ensuremath{\chi}}_{b1}$ state than would be traditionally assumed; however, my final results for the total $\ensuremath{\Upsilon}(1s)$ suppression are in good agreement with recent preliminary CMS data.
TL;DR: In this article, the authors presented a thermal emission rate analysis of the direct photon production in nuclear collisions at the Relativis-tic Heavy-Ion Collider (RHIC).
Abstract: Cyclotron Institute and Department of Physics&Astronomy,Texas A&M University, College Station, Texas 77843-3366, USA(Dated: August 11, 2011)We update our calculations of thermal-photon production in nuclear collisions at the Relativis-tic Heavy-Ion Collider (RHIC). Specifically, we address the recent experimental observation of anelliptic flow of direct photons comparable in magnitude to that of pions, which is at variance withexpectations based on quark-gluon plasma (QGP) dominated photon radiation. Our thermal emis-sion rate is based on previous work, i.e., resummed leading-order QGP emission and in-mediumhadronic rates in the confined phase. These rates are nearly degenerate at temperatures close to theexpected QCD-phase change. The rates are convoluted over an improved elliptic-fireball expansionwith transverse- and elliptic-flow fields quantitatively constrained by empirical light- and strange-hadron spectra. The resulting direct-photon spectra in central Au-Au collisions are characterized byhadron-dominated emission up to transverse momenta of ∼ 2-3 GeV. The associated large ellipticflow in the hadronic phase mitigates the discrepancy with the measured photon-v
TL;DR: In this article, the authors present a consistent theoretical approach for the study of nonequilibrium effects in chiral fluid dynamics within the framework of the linear $\ensuremath{\sigma}$ model with constituent quarks.
Abstract: We present a consistent theoretical approach for the study of nonequilibrium effects in chiral fluid dynamics within the framework of the linear $\ensuremath{\sigma}$ model with constituent quarks. Treating the quarks as an equilibrated heat bath, we use the influence functional formalism to obtain a Langevin equation for the $\ensuremath{\sigma}$ field. This allows us to calculate the explicit form of the damping coefficient and the noise correlators. For a self-consistent derivation of both the dynamics of the $\ensuremath{\sigma}$ field and the quark fluid, we have to employ the 2PI (two-particle irreducible) effective action formalism. The energy dissipation from the field to the fluid is treated in the exact formalism of the 2PI effective action where a conserved energy-momentum tensor can be constructed. We derive its form and comment on approximations generating additional terms in the energy-momentum balance of the entire system.
TL;DR: In this article, the spin-orbital coupling via parton interaction in a viscous quark-gluon plasma with an initial laminar flow has been studied and the final polarization is found to be sensitive to the viscosity and the initial shear of local longitudinal flow.
Abstract: Quarks produced in the early stage of noncentral heavy-ion collisions could develop a global spin polarization along the opposite direction of the reaction plane due to the spin-orbital coupling via parton interaction in a medium that has finite longitudinal flow shear along the direction of the impact parameter. We study how such polarization evolves via multiple scattering in a viscous quark-gluon plasma with an initial laminar flow. The final polarization is found to be sensitive to the viscosity and the initial shear of local longitudinal flow.
TL;DR: It is found that cortical networks lack scale-free behavior, but show a small, but significant small-world structure, and assuming a simple distance-dependent probabilistic wiring between neurons, this connectivity structure can account for all of the networks’ observed small- world ness.
Abstract: The simultaneous recording of the activity of many neurons poses challenges for multivariate data analysis. Here, we propose a general scheme of reconstruction of the functional network from spike train recordings. Effective, causal interactions are estimated by fitting Generalized Linear Models (GLMs) on the neural responses, incorporating effects of the neurons' self-history, of input from other neurons in the recorded network and of modulation by an external stimulus. The coupling terms arising from synaptic input can be transformed by thresholding into a binary connectivity matrix which is directed. Each link between two neurons represents a causal influence from one neuron to the other, given the observation of all other neurons from the population. The resulting graph is analyzed with respect to small-world and scale-free properties using quantitative measures for directed networks. Such graph-theoretic analyses have been performed on many complex dynamic networks, including the connectivity structure between different brain areas. Only few studies have attempted to look at the structure of cortical neural networks on the level of individual neurons. Here, using multi-electrode recordings from the visual system of the awake monkey, we find that cortical networks lack scale-free behavior, but show a small, but significant small-world structure. Assuming a simple distance-dependent probabilistic wiring between neurons, we find that this connectivity structure can account for all of the networks' observed small-world-ness. Moreover, for multi-electrode recordings the sampling of neurons is not uniform across the population. We show that the small-world-ness obtained by such a localized sub-sampling overestimates the strength of the true small-world-structure of the network. This bias is likely to be present in all previous experiments based on multi-electrode recordings.
TL;DR: In this article, the authors present a proof of independence of volume fluctuations for quantities from both families within the framework of the grand canonical ensemble, and the influence of conservation laws and resonance decays is also discussed.
Abstract: Analysis of fluctuations of hadron production properties in collisions of relativistic particles profits from use of measurable intensive quantities which are independent of system size variations. The first family of such quantities was proposed in 1992; another is introduced in this paper. Furthermore we present a proof of independence of volume fluctuations for quantities from both families within the framework of the grand canonical ensemble. These quantities are referred to as strongly intensive ones. Influence of conservation laws and resonance decays is also discussed.
Abstract: We show how the linearized equations of motion of any dissipative current are determined by the analytical structure of the associated retarded Green's function. If the singularity of Green's function, which is nearest to the origin in the complex-frequency plane, is a simple pole on the imaginary frequency axis, the linearized equations of motion can be reduced to relaxation type equations for the dissipative currents. The value of the relaxation time is given by the inverse of this pole. We prove that, if the relaxation time is sent to zero, or equivalently, the pole to infinity, the dissipative currents approach the values given by the standard gradient expansion.
TL;DR: In this article, the authors study the non-boost-invariant evolution of a quark-gluon plasma subject to large early-time momentum-space anisotropies.
TL;DR: In this paper, a chiral model based on the parity doublet formulation of chiral symmetry including hyperonic degrees of freedom is introduced, and the phase structure of the model is determined.
Abstract: A chiral model is introduced that is based on the parity doublet formulation of chiral symmetry including hyperonic degrees of freedom. The phase structure of the model is determined. Depending on the masses of the chiral partners, the transition to the chirally restored phase shows a first-order line with critical end points as a function of chemical potential and temperature in additional to the standard liquid-gas phase transition of self-bound nuclear matter. We extend the parity doublet model to describe the deconfinement phase transition which is in quantitative agreement with lattice data at ${\ensuremath{\mu}}_{B}=0$. The phase diagram of the model is presented which shows a decoupling of chiral symmetry restoration and deconfinement. Loosening the constraint of strangeness conservation, we also investigate the phase diagram at net strangeness density. We calculate the strangeness per baryon fraction and the baryon-strangeness correlation factor, two quantities that are sensitive on deconfinement and that can be used to interpret lattice calculations.
09 Sep 2011
TL;DR: The main contribution is to formalise the problem of inverse reinforcement learning as statistical preference elicitation, via a number of structured priors, whose form captures the authors' biases about the relatedness of different tasks or expert policies.
Abstract: We generalise the problem of inverse reinforcement learning to multiple tasks, from multiple demonstrations. Each one may represent one expert trying to solve a different task, or as different experts trying to solve the same task. Our main contribution is to formalise the problem as statistical preference elicitation, via a number of structured priors, whose form captures our biases about the relatedness of different tasks or expert policies. In doing so, we introduce a prior on policy optimality, which is more natural to specify. We show that our framework allows us not only to learn to efficiently from multiple experts but to also effectively differentiate between the goals of each. Possible applications include analysing the intrinsic motivations of subjects in behavioural experiments and learning from multiple teachers.
TL;DR: In this paper, an effective model for the QCD equation of state, taking into account chiral symmetry restoration as well as the deconfinement phase transition, was constructed, and the model shows a rapid crossover for both order parameters, as expected from lattice calculations.
Abstract: We construct an effective model for the QCD equation of state, taking into account chiral symmetry restoration as well as the deconfinement phase transition. The correct asymptotic degrees of freedom at the high and low temperature limits are included (quarks ↔ hadrons). The model shows a rapid crossover for both order parameters, as expected from lattice calculations. We then compare the thermodynamic properties of the model at μB = 0 which turn out to be in qualitative agreement with lattice data, while apparent quantitative differences can be attributed to hadronic contributions and excluded-volume corrections. Furthermore we discuss the effects of a repulsive vector-type quark interaction at finite baryon number densities on the resulting phase diagram of the model. Our current model is able to reproduce a first-order liquid–gas phase transition as expected, but does not show any signs of a first-order deconfinement or chiral phase transition. Both transitions rather appear as a very wide crossover in which heavily medium modified hadron coexists with free quarks.
TL;DR: In this paper, the hard-thermal-loop perturbation theory (HTLpt) framework is used to calculate the thermodynamic functions of a quark-gluon plasma to three-loop order.
Abstract: The hard-thermal-loop perturbation theory (HTLpt) framework is used to calculate the thermodynamic functions of a quark-gluon plasma to three-loop order. This is the highest order accessible by finite temperature perturbation theory applied to a non-Abelian gauge theory before the high-temperature infrared catastrophe. All ultraviolet divergences are eliminated by renormalization of the vacuum, the HTL mass parameters, and the strong coupling constant. After choosing a prescription for the mass parameters, the three-loop results for the pressure and trace anomaly are found to be in very good agreement with recent lattice data down to T similar to 2 - 3 T(c), which are temperatures accessible by current and forthcoming heavy-ion collision experiments.
TL;DR: In this article, a complete set of transport coefficients, consistent with the Curie and Onsager principles, is derived for thermal conduction, as well as shear and bulk viscosities.
TL;DR: In this article, the hard-thermal-loop perturbation theory (HTLpt) framework is used to calculate the thermodynamic functions of a quark-gluon plasma to three-loop order.
Abstract: The hard-thermal-loop perturbation theory (HTLpt) framework is used to calculate the thermodynamic functions of a quark-gluon plasma to three-loop order. This is the highest order accessible by finite temperature perturbation theory applied to a non-Abelian gauge theory before the high-temperature infrared catastrophe. All ultraviolet divergences are eliminated by renormalization of the vacuum, the HTL mass parameters, and the strong coupling constant. After choosing a prescription for the mass parameters, the three-loop results for the pressure and trace anomaly are found to be in very good agreement with recent lattice data down to $T \sim 2-3\,T_c$, which are temperatures accessible by current and forthcoming heavy-ion collision experiments.
TL;DR: In this article, a two-flavor linear sigma model with global chiral symmetry and (axial-) vector mesons as well as an additional glueball degree of freedom is presented.
Abstract: We present a two-flavor linear sigma model with global chiral symmetry and (axial-)vector mesons as well as an additional glueball degree of freedom. We study the structure of the well-established scalar resonances ${f}_{0}(1370)$ and ${f}_{0}(1500)$: by a fit to experimentally known decay widths we find that ${f}_{0}(1370)$ is predominantly a $\overline{q}q$ state and ${f}_{0}(1500)$ is predominantly a glueball state. The overall phenomenology of these two resonances can be well described. Other assignments for our mixed quarkonium-glueball states are also tested, but turn out to be in worse agreement with the phenomenology. As a by-product of our analysis, the gluon condensate is determined.
TL;DR: The structure of the GABARAPL-1/NBR1-LIR complex is determined and the results indicate that the presence of a tryptophan residue in the LIR motif increases the binding affinity, indicating that different LIRs can interact with autophagy modifiers with unique binding properties.
TL;DR: In this paper, the authors numerically study the evolution of a boost-invariant SYM medium using AdS/CFT, and provide a toy model for the early time evolution of the bulk system in heavy-ion collisions at RHIC and the LHC.
Abstract: We numerically study the evolution of a boost-invariant SYM medium using AdS/CFT. We consider a toy model for the collision of gravitational shock waves, finding that the energy density first increases, reaches a maximum and then starts to decrease, matching hydrodynamics for late times. For the initial conditions we consider, the hydrodynamic scale governing the late time behavior is to very good approximation determined by the area of the black hole horizon at initial times. Our results provide a toy model for the early time evolution of the bulk system in heavy-ion collisions at RHIC and the LHC.