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Stefan Thurner

Publications and source records attributed to Stefan Thurner.

173 records · Page 10Linked to original sources

A Dynamical Thermostat Approach To Financial Asset Price Dynamics

A dynamical price formation model for financial assets is presented. It aims to capture the essence of speculative trading where mispricings of assets are used to make profits. It is shown that together with the incorporation of the concept of risk aversion of agents the model is able to reproduce several key characteristics of financial price series. The approach is contrasted to the conventional view of price formation in financial economics.

cond-mat↗

Chirality tubes along monopole trajectories

We classify the lattice by elementary 3-cubes which are associated to dual links occupied by, or free of monopoles. We then compute the quark condensate, the quark charge and the chiral density on those cubes. By looking at distributions we demonstrate that monopole trajectories carry considerably more chirality with respect to the free vacuum.

hep-lat↗

Receiver-Operating-Characteristic Analysis Reveals Superiority of Scale-Dependent Wavelet and Spectral Measures for Assessing Cardiac Dysfunction

Receiver-operating-characteristic (ROC) analysis was used to assess the suitability of various heart rate variability (HRV) measures for correctly classifying electrocardiogram records of varying lengths as normal or revealing the presence of heart failure. Scale-dependent HRV measures were found to be substantially superior to scale-independent measures (scaling exponents) for discriminating the two classes of data over a broad range of record lengths. The wavelet-coefficient standard deviation at a scale near 32 heartbeat intervals, and its spectral counterpart near 1/32 cycles per interval, provide reliable results using record lengths just minutes long. A jittered integrate-and-fire model built around a fractal Gaussian-noise kernel provides a realistic, though not perfect, simulation of heartbeat sequences.

physics.med-ph↗

Chiral condensate, quark charge and chiral density

We study the topological and fermionic vacuum structure of four-dimensional QCD on the lattice by means of correlators of fermionic observables and topological densities. We show the existence of strong local correlations between the topological charge density and the quark condensate, charge and chiral density. By analysis of individual gauge configurations, we visualize that instantons (antiinstantons) carry positive (negative) chirality, whereas the quark charge density fluctuates in sign within instantons.

hep-lat↗

ROC Analysis and a Realistic Model of Heart Rate Variability

We have carried out a pilot study on a standard collection of electrocardiograms from patients who suffer from congestive heart failure, and subjects without cardiac pathology, using receiver-operating-characteristic (ROC) analysis. The scale-dependent wavelet-coefficient standard deviation σ_{wav}(m), a multiresolution-based analysis measure, is found to be superior to two commonly used measures of cardiac dysfunction when the two classes of patients cannot be completely separated. A jittered integrate-and-fire model with a fractal Gaussian-noise kernel provides a realistic simulation of heartbeat sequences for both heart-failure patients and normal subjects.

chao-dyn↗

Multiresolution wavelet analysis of heartbeat intervals discriminates healthy patients from those with cardiac pathology

We applied multiresolution wavelet analysis to the sequence of times between human heartbeats (R-R intervals) and have found a scale window, between 16 and 32 heartbeats, over which the widths of the R-R wavelet coefficients fall into disjoint sets for normal and heart-failure patients. This has enabled us to correctly classify every patient in a standard data set as either belonging to the heart-failure or normal group with 100% accuracy, thereby providing a clinically significant measure of the presence of heart-failure from the R-R intervals alone. Comparison is made with previous approaches, which have provided only statistically significant measures.

adap-org↗

Conservation laws in coupled multiplicative random arrays lead to $1/f$ noise

We consider the dynamic evolution of a coupled array of N multiplicative random variables. The magnitude of each is constrained by a lower bound w_0 and their sum is conserved. Analytical calculation shows that the simplest case, N=2 and w_0=0, exhibits a Lorentzian spectrum which gradually becomes fractal as w_0 increases. Simulation results for larger $N$ reveal fractal spectra for moderate to high values of w_0 and power-law amplitude fluctuations at all values. The results are applied to estimating the fractal exponents for cochlear-nerve-fiber action-potential sequences with remarkable success, using only two parameters.

adap-org↗

Analysis, Synthesis, and Estimation of Fractal-Rate Stochastic Point Processes

Fractal and fractal-rate stochastic point processes (FSPPs and FRSPPs) provide useful models for describing a broad range of diverse phenomena, including electron transport in amorphous semiconductors, computer-network traffic, and sequences of neuronal action potentials. A particularly useful statistic of these processes is the fractal exponent $α$, which may be estimated for any FSPP or FRSPP by using a variety of statistical methods. Simulated FSPPs and FRSPPs consistently exhibit bias in this fractal exponent, however, rendering the study and analysis of these processes non-trivial. In this paper, we examine the synthesis and estimation of FRSPPs by carrying out a systematic series of simulations for several different types of FRSPP over a range of design values for $α$. The discrepancy between the desired and achieved values of $α$ is shown to arise from finite data size and from the character of the point-process generation mechanism. In the context of point-process simulation, reduction of this discrepancy requires generating data sets with either a large number of points, or with low jitter in the generation of the points. In the context of fractal data analysis, the results presented here suggest caution when interpreting fractal exponents estimated from experimental data sets.

adap-org↗

Visualization of topological objects in the deconfinement phase of pure QCD

In the last years it turned out that instantons and monopoles have a certain local correlation in four-dimensional QCD. It was demonstrated by several groups independently and by different methods that at the locations of instantons also monopoles in the maximal abelian projection can be found with enhanced probability. Further we observed such nontrivial correlation functions in the deconfinement phase. We continue our visualization project to analyze several specific gauge-field configurations.

hep-lat↗

Visualization of topological structure and chiral condensate

We perform a mutual analysis of the topological and chiral vacuum structure of four-dimensional QCD on the lattice at finite temperature. We demonstrate that at the places where instantons are present, amplified production of quark condensate takes place. It turns out for full QCD that the clusters of nontrivial chiral condensate have a size of about 0.4 fm corresponding to the instanton sizes in the same configurations.

hep-lat↗

Visualization of chiral condensate at finite temperature on the lattice

We perform an analysis of the topological and chiral vacuum structure of four-dimensional QCD on the lattice at finite temperature. From correlation functions we show the existence of local correlations between the topological charge density and the quark condensate on gauge average. We comment on sizes of clusters of nontrivial chiral condensate and of instantons in full QCD. By analysis of individual gauge configurations, we demonstrate that at the places in Euclidian space-time, where instantons are present, amplified production of quark condensate occurs.

hep-lat↗