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.

RAPTOR I: Time-dependent radiative transfer in arbitrary spacetimes

Abstract: Context. Observational efforts to image the immediate environment of a black hole at the scale of the event horizon benefit from the development of efficient imaging codes that are capable of producing synthetic data, which may be compared with observational data.Aims. We aim to present RAPTOR, a new public code that produces accurate images, animations, and spectra of relativistic plasmas in strong gravity by numerically integrating the equations of motion of light rays and performing time-dependent radiative transfer calculations along the rays. The code is compatible with any analytical or numerical spacetime. It is hardware-agnostic and may be compiled and run both on GPUs and CPUs.Methods. We describe the algorithms used in RAPTOR and test the code’s performance. We have performed a detailed comparison of RAPTOR output with that of other radiative-transfer codes and demonstrate convergence of the results. We then applied RAPTOR to study accretion models of supermassive black holes, performing time-dependent radiative transfer through general relativistic magneto-hydrodynamical (GRMHD) simulations and investigating the expected observational differences between the so-called fast-light and slow-light paradigms.Results. Using RAPTOR to produce synthetic images and light curves of a GRMHD model of an accreting black hole, we find that the relative difference between fast-light and slow-light light curves is less than 5%. Using two distinct radiative-transfer codes to process the same data, we find integrated flux densities with a relative difference less than 0.01%.Conclusions. For two-dimensional GRMHD models, such as those examined in this paper, the fast-light approximation suffices as long as errors of a few percent are acceptable. The convergence of the results of two different codes demonstrates that they are, at a minimum, consistent.

Conformal anomaly and the vector coupling in dense matter

Abstract: We construct an effective chiral Lagrangian for hadrons implemented by the conformal invariance and discuss the properties of nuclear matter at high density. The model is formulated based on two alternative assignment, ``naive'' and mirror, of chirality to the nucleons. It is shown that taking the dilaton limit, in which the mended symmetry of Weinberg is manifest, the vector-meson Yukawa coupling becomes suppressed and the symmetry energy becomes softer as one approaches the chiral phase transition. This leads to softer equations of state (EoS) and could accommodate the EoS without any exotica consistent with the recent measurement of a $1.97\ifmmode\pm\else\textpm\fi{}0.04{M}_{\ensuremath{\bigodot}}$ neutron star.

Threshold Complex-Valued Neural Associative Memory

Abstract: In this brief, threshold complex-valued neural associative memory is proposed for information retrieval. The introduction of threshold improves network performance by excluding rotated patterns from spurious memories. A design method for constructing different types of network is developed based on complex matrix decomposition, which is capable of designing nonthreshold, threshold, non-Hermitian, and Hermitian networks. Further, we illustrate the performance of the proposed method by reconstructing noisy 256 grayscale and true color images. The results show that constructed networks can work efficiently, threshold networks have better performance than nonthreshold ones and networks with small asymmetry in weight matrix function as well as Hermitian ones.