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.

Pseudorapidity distribution and decorrelation of anisotropic flow within the open-computing-language implementation CLVisc hydrodynamics

Abstract: Studies of fluctuations and correlations of soft hadrons and hard and electromagnetic probes of the dense and strongly interacting medium require event-by-event hydrodynamic simulations of high-energy heavy-ion collisions that are computing intensive. We develop a $(3+1)$-dimensional viscous hydrodynamic model---CLVisc that is parallelized on a graphics processing unit (GPU) by using the open computing language (OpenCL) with 60 times performance increase for spacetime evolution and more than 120 times for the Cooper--Frye particlization relative to that without GPU parallelization. The model is validated with comparisons with different analytic solutions, other existing numerical solutions of hydrodynamics, and experimental data on hadron spectra in high-energy heavy-ion collisions. The pseudorapidity dependence of anisotropic flow ${v}_{n}(\ensuremath{\eta})$ are then computed in CLVisc with initial conditions given by the a multiphase transport (ampt) model, with energy density fluctuations both in the transverse plane and along the longitudinal direction. Although the magnitude of ${v}_{n}(\ensuremath{\eta})$ and the ratios between ${v}_{2}(\ensuremath{\eta})$ and ${v}_{3}(\ensuremath{\eta})$ are sensitive to the effective shear viscosity over entropy density ratio ${\ensuremath{\eta}}_{v}/s$, the shape of the ${v}_{n}(\ensuremath{\eta})$ distributions in $\ensuremath{\eta}$ do not depend on the value of ${\ensuremath{\eta}}_{v}/s$. The decorrelation of ${v}_{n}$ along the pseudorapidity direction due to the twist and fluctuation of the event planes in the initial parton density distributions is also studied. The decorrelation observable ${r}_{n}({\ensuremath{\eta}}^{a},{\ensuremath{\eta}}^{b})$ between ${v}_{n}{\ensuremath{-}{\ensuremath{\eta}}^{a}}$ and ${v}_{n}{{\ensuremath{\eta}}^{a}}$ with the auxiliary reference window ${\ensuremath{\eta}}^{b}$ is found not to be sensitive to ${\ensuremath{\eta}}_{v}/s$ when there is no initial fluid velocity. For small ${\ensuremath{\eta}}_{v}/s$, the initial fluid velocity from mini-jet partons introduces sizable splitting of ${r}_{n}({\ensuremath{\eta}}^{a},{\ensuremath{\eta}}^{b})$ between the two reference rapidity windows ${\ensuremath{\eta}}^{b}\ensuremath{\in}[3,4]$ and ${\ensuremath{\eta}}^{b}\ensuremath{\in}[4.4,5.0]$, as has been observed in experiment. The implementation of CLVisc and guidelines on how to efficiently parallelize scientific programs on GPUs are also provided.

Network Self-organization Explains the Statistics and Dynamics of Synaptic Connection Strengths in Cortex

Abstract: The information processing abilities of neural circuits arise from their synaptic connection patterns. Understanding the laws governing these connectivity patterns is essential for understanding brain function. The overall distribution of synaptic strengths of local excitatory connections in cortex and hippocampus is long-tailed, exhibiting a small number of synaptic connections of very large efficacy. At the same time, new synaptic connections are constantly being created and individual synaptic connection strengths show substantial fluctuations across time. It remains unclear through what mechanisms these properties of neural circuits arise and how they contribute to learning and memory. In this study we show that fundamental characteristics of excitatory synaptic connections in cortex and hippocampus can be explained as a consequence of self-organization in a recurrent network combining spike-timing-dependent plasticity (STDP), structural plasticity and different forms of homeostatic plasticity. In the network, associative synaptic plasticity in the form of STDP induces a rich-get-richer dynamics among synapses, while homeostatic mechanisms induce competition. Under distinctly different initial conditions, the ensuing self-organization produces long-tailed synaptic strength distributions matching experimental findings. We show that this self-organization can take place with a purely additive STDP mechanism and that multiplicative weight dynamics emerge as a consequence of network interactions. The observed patterns of fluctuation of synaptic strengths, including elimination and generation of synaptic connections and long-term persistence of strong connections, are consistent with the dynamics of dendritic spines found in rat hippocampus. Beyond this, the model predicts an approximately power-law scaling of the lifetimes of newly established synaptic connection strengths during development. Our results suggest that the combined action of multiple forms of neuronal plasticity plays an essential role in the formation and maintenance of cortical circuits.

Decay properties and stability of heaviest elements

Abstract: Decay properties and stability of heaviest nuclei with Z≤132 are studied within the macro-microscopical approach for nuclear ground state masses and phenomenological relations for the half-lives with respect to α-decay, β-decay and spontaneous fission. We found that at existing experimental facilities the synthesis and detection of nuclei with Z>120 produced in fusion reactions may be difficult due to their short half-lives (shorter than 1 μs). The nearest (more neutron-rich) isotopes of superheavy elements with 111≤Z≤115 to those synthesized recently in Dubna in 48Ca-induced fusion reactions are found to be β+-decaying. This fact may significantly complicate their experimental identification. However it gives a chance to synthesize in fusion reactions the most stable superheavy nuclei located at the center of the island of stability. Our calculations yield that the β-stable isotopes 291Cn and 293Cn with a half-life of about 100 years are the longest-living superheavy nuclei located at the island of stability.