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J. Petrovic

Publications and source records attributed to J. Petrovic.

7 recordsLinked to original sources
arXiv2025

Multifractal features of multimodal cardiac signals: Nonlinear dynamics of exercise recovery

We investigate the recovery dynamics of healthy cardiac activity after physical exertion using multimodal biosignals recorded with a polycardiograph. Multifractal features derived from the singularity spectrum capture the scale-invariant properties of cardiovascular regulation. Five supervised classification algorithms - Logistic Regression (LogReg), Suport Vector Machine with RBF kernel (SVM-RBF), k-Nearest Neighbors (kNN), Decision Tree (DT), and Random Forest (RF) - were evaluated to distinguish recovery states in a small, imbalanced dataset. Our results show that multifractal analysis, combined with multimodal sensing, yields reliable features for characterizing recovery and points toward nonlinear diagnostic methods for heart conditions.

nlin.PS↗
arXiv2018

A New Method for Multi-Bit and Qudit Transfer Based on Commensurate Waveguide Arrays

The faithful state transfer is an important requirement in the construction of classical and quantum computers. While the high-speed transfer is realized by optical-fibre interconnects, its implementation in integrated optical circuits is affected by cross-talk. The cross-talk between densely packed optical waveguides limits the transfer fidelity and distorts the signal in each channel, thus severely impeding the parallel transfer of states such as classical registers, multiple qubits and qudits. Here, we leverage on the suitably engineered cross-talk between waveguides to achieve the parallel transfer on optical chip. Waveguide coupling coefficients are designed to yield commensurate eigenvalues of the array and hence, periodic revivals of the input state. While, in general, polynomially complex, the inverse eigenvalue problem permits analytic solutions for small number of waveguides. We present exact solutions for arrays of up to nine waveguides and use them to design realistic buses for multi-(qu)bit and qudit transfer. Advantages and limitations of the proposed solution are discussed in the context of available fabrication techniques.

math-ph↗
arXiv2006

Radio emission of highly inclined cosmic ray air showers measured with LOPES

LOPES (LOFAR Prototype Station) is an array of dipole antennas used for detection of radio emission from air showers. It is co-located and triggered by the KASCADE (Karlsruhe Shower Core and Array Detector) experiment, which also provides informations about air shower properties. Even though neither LOPES nor KASCADE are completely optimized for the detection of highly inclined events, a significant number of showers with zenith angle larger than 50$^o$ have been detected in the radio domain, and many with very high field strengths. Investigation of inclined showers can give deeper insight into the nature of primary particles that initiate showers and also into the possibility that some of detected showers are triggered by neutrinos. In this paper, we show the example of such an event and present some of the characteristics of highly inclined showers detected by LOPES.

astro-ph↗
arXiv2005

Nanofabricated media with negative permeability at visible frequencies

We report a nanofabricated medium made of electromagnetically coupled pairs of gold dots with geometry carefully designed at a 10-nm level. The medium exhibits strong magnetic response at visible-light frequencies, including bands with negative μ. The magnetism arises due to the excitation of quadrupole plasmon resonances. Our approach shows for the first time the feasibility of magnetism at optical frequencies and paves a way towards magnetic and left-handed components for visible optics.

physics.optics↗
arXiv2003

Binary evolution models with rotation

We discuss the first available binary evolution models which include up-to-date rotational physics for both components, as well as angular momentum accretion and spin-orbit coupling. These models allow a self-consistent computation of the mass transfer efficiency during Roche-lobe overflow phases, and a determination of the transition from quasi-conservative to non-conservative evolution. Applications to massive binary systems lead to predictions for the spin rates of compact objects in binaries, and for the occurrence of gamma-ray bursts from collapsars in binaries. Rotational effects in accreting white dwarfs are found to stabilise the shell burning and decrease the carbon abundance in progenitor models for Chandrasekhar-mass Type Ia supernovae, and to potentially avoid a detonation of the white dwarf within the sub-Chandrasekhar mass scenario.

astro-ph↗
arXiv1997

A Note on the Total Absorption Cross-section of Galaxies

In this work we shall sketch a further piece of evidence for the plausibility of hypothesis of galactic origin of Ly-$α$ forest absorption systems. Two basic premises of our discussion are (1) HDF redshift surface densities in the redshift interval 0<z<6; and (2) validity of low-redshift results on redshift coincidences, showing average absorption cross-section corresponding to radius of 160$h^{-1}$ kpc for $L^*$ galaxies. Low-redshift analysis also showed covering factor nearing unity, which will be used and discussed in further considerations. Semantic problems concerned with the interpretation of galaxy absorption cross-section are discussed in some details, and importance of distinction between size of the absorbers and absorption coherence length is emphasized. It is shown that HDF data predict huge number of absorption systems, in fact much larger than observed, which shows frequently quoted argument that number of galaxies is insufficient to account for all absorption lines to be wrong. Road to achieving higher compatibility with the empirical statistics is shown to lie in applying the luminosity scaling, possibly with cut-off. This is significant for recent attempts to explain the association of the Ly-$α$ forest systems with normal galaxies.

astro-ph↗