Frankfurt Institute for Advanced Studies

About: Frankfurt Institute for Advanced Studies is a facility organization based out in Frankfurt am Main, Germany. It is known for research contribution in the topics: Baryon & Quark–gluon plasma. The organization has 798 authors who have published 2733 publications receiving 82799 citations. The organization is also known as: FIAS.

Application of time-independent cumulant expansion to calculation of Franck-Condon profiles for large molecular systems

Abstract: In this contribution, advantages and disadvantages of the time-independent and time-dependent approaches for Franck–Condon profile calculations are discussed within the displaced–distorted–rotated harmonic oscillator approximation. Particular strengths and prospects of a previously developed time-independent cumulant expansion in the calculation of a Franck–Condon profile for UV/Vis absorption spectra are demonstrated for the specific case of the S0(1Ag) → S1(1B3u) transition of terrylene at various temperatures.

Kilohertz QPOs in low-mass X-ray binaries as oscillation modes of tori around neutron stars - I

Abstract: There have been many efforts to explain the dynamical mechanisms behind the phenomenology of quasi-periodic oscillations (QPOs) seen in the X-ray light curves of low-mass X-ray binaries. Up to now, none of the models can successfully explain all the frequencies observed in the power spectral density of the light curves. After performing several general-relativistic hydrodynamic simulations of non-selfgravitating axisymmetric thick tori with constant specific angular momentum oscillating around a neutrons star such as the one associated with the low-mass X-ray binary 4U 1636-53, we find that the oscillation modes give rise to QPOs similar to those seen in the observational data. In particular, when matching pairs of kilohertz QPOs from the numerical simulations with those observed, certain combinations reproduce well the observations, provided we take a mass for the neutron star that is smaller than what generally assumed. At the same time, we find that tori with constant specific angular momentum cannot match the entire range of frequencies observed for 4U 1636-53 due to physical constraints set on their size. Finally, we show that our results are consistent with the observed shifts in QPO frequency that could accompany state transitions of the accretion disc.

Active efficient coding explains the development of binocular vision and its failure in amblyopia.

Abstract: The development of vision during the first months of life is an active process that comprises the learning of appropriate neural representations and the learning of accurate eye movements. While it has long been suspected that the two learning processes are coupled, there is still no widely accepted theoretical framework describing this joint development. Here, we propose a computational model of the development of active binocular vision to fill this gap. The model is based on a formulation of the active efficient coding theory, which proposes that eye movements as well as stimulus encoding are jointly adapted to maximize the overall coding efficiency. Under healthy conditions, the model self-calibrates to perform accurate vergence and accommodation eye movements. It exploits disparity cues to deduce the direction of defocus, which leads to coordinated vergence and accommodation responses. In a simulated anisometropic case, where the refraction power of the two eyes differs, an amblyopia-like state develops in which the foveal region of one eye is suppressed due to inputs from the other eye. After correcting for refractive errors, the model can only reach healthy performance levels if receptive fields are still plastic, in line with findings on a critical period for binocular vision development. Overall, our model offers a unifying conceptual framework for understanding the development of binocular vision.

Influence of the neutron-skin effect on nuclear isobar collisions at energies available at the BNL Relativistic Heavy Ion Collider

Abstract: The unambiguous observation of a chiral magnetic effect (CME)--driven charge separation is the core aim of the isobar program at the Relativistic Heavy Ion Collider (RHIC), consisting of $_{40}^{96}\mathrm{Zr}+_{40}^{96}\mathrm{Zr}$ and $_{44}^{96}\mathrm{Ru}+_{44}^{96}\mathrm{Ru}$ collisions at $\sqrt{{s}_{\mathrm{NN}}}=200$ GeV. We quantify the role of the spatial distributions of the nucleons in the isobars on both eccentricity and magnetic field strength within a relativistic hadronic transport approach (simulating many accelerated strongly interacting hadrons, SMASH). In particular, we introduce isospin-dependent nucleon-nucleon spatial correlations in the geometric description of both nuclei, deformation for $_{44}^{96}\mathrm{Ru}$ and the so-called neutron skin effect for the neutron-rich isobar, i.e., $_{40}^{96}\mathrm{Zr}$. The main result of this study is a reduction of the magnetic field strength difference between $_{44}^{96}\mathrm{Ru}+_{44}^{96}\mathrm{Ru}$ and $_{40}^{96}\mathrm{Zr}+_{40}^{96}\mathrm{Zr}$ by a factor of 2, from $10%$ to $5%$ in peripheral collisions when the neutron-skin effect is included. Further, we find an increase of the eccentricity ratio between the isobars by up to 10% in ultracentral collisions as due to the deformation of $_{44}^{96}\mathrm{Ru}$ while neither the neutron skin effect nor the nucleon-nucleon correlations result into a significant modification of this observable with respect to the traditional Woods-Saxon modeling. Our results suggest a significantly smaller CME signal to background ratio for the experimental charge separation measurement in peripheral collisions with the isobar systems than previously expected.

Decomposition of fluctuating initial conditions and flow harmonics

Abstract: Collective flow observed in heavy-ion collisions is largely attributed to initial geometrical fluctuations, and it is the hydrodynamic evolution of the system that transforms those initial spatial irregularities into final state momentum anisotropies. Cumulant analysis provides a mathematical tool to decompose those initial fluctuations in terms of radial and azimuthal components. It is usually thought that a specified order of azimuthal cumulant, for the most part, linearly produces flow harmonics of the same order. In this work, by considering the most central collisions (0%–5%), we carry out a systematic study on the connection between cumulants and flow harmonics using a hydrodynamic code called NeXSPheRIO. We conduct three types of calculation, by explicitly decomposing the initial conditions into components corresponding to a given eccentricity and studying the out-coming flow through hydrodynamic evolution. It is found that for initial conditions deviating significantly from Gaussian, such as those from NeXuS, the linearity between eccentricities and flow harmonics partially breaks down. Combined with the effect of coupling between cumulants of different orders, it causes the production of extra flow harmonics of higher orders. We argue that these results can be seen as a natural consequence of the non-linear nature of hydrodynamics, and they can be understood intuitively in terms of the peripheral-tube model.