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  • Publication . Other literature type . Article . Preprint . 2022
    Open Access English
    Authors: 
    Jennifer Schober; Igor Rogachevskii; Axel Brandenburg;
    Country: Switzerland
    Project: SNSF | Magnetohydrodynamical dyn... (185863)

    In relativistic magnetized plasmas, asymmetry in the number densities of left- and right-handed fermions, i.e., a non-zero chiral chemical potential mu_5, leads to an electric current along the magnetic field. This causes a chiral dynamo instability for a uniform mu_5, but our simulations reveal a dynamo even for fluctuating mu_5 with zero mean. It produces magnetically-dominated turbulence and generates mean magnetic fields via the magnetic alpha effect. Eventually, a universal scale-invariant k^(-1) spectrum of mu_5 and a k^(-3) magnetic spectrum are formed independently of the initial condition. 6 pages, 4 figures, published in Phys. Rev. Lett

  • Publication . Other literature type . Article . Preprint . 2022
    Open Access English
    Authors: 
    Jennifer Schober; Igor Rogachevskii; Axel Brandenburg;
    Country: Switzerland
    Project: SNSF | Magnetohydrodynamical dyn... (185863)

    We study the dynamics of magnetic fields in chiral magnetohydrodynamics, which takes into account the effects of an additional electric current related to the chiral magnetic effect in high energy plasmas. We perform direct numerical simulations, considering weak seed magnetic fields and inhomogeneities of the chiral chemical potential mu_5 with a zero mean. We demonstrate that a small-scale chiral dynamo can occur in such plasmas if fluctuations of mu_5 are correlated on length scales that are much larger than the scale on which the dynamo growth rate reaches its maximum. Magnetic fluctuations grow by many orders of magnitude due to the small-scale chiral dynamo instability. Once the nonlinear backreaction of the generated magnetic field on fluctuations of mu_5 sets in, the ratio of these scales decreases and the dynamo saturates. When magnetic fluctuations grow sufficiently to drive turbulence via the Lorentz force before reaching maximum field strength, an additional mean-field dynamo phase is identified. The mean magnetic field grows on a scale that is larger than the integral scale of turbulence after the amplification of the fluctuating component saturates. The growth rate of the mean magnetic field is caused by a magnetic alpha effect that is proportional to the current helicity. With the onset of turbulence, the power spectrum of mu_5 develops a universal k^(-1) scaling independently of its initial shape, while the magnetic energy spectrum approaches a k^(-3) scaling. 22 pages, 22 figures

  • Publication . Article . Preprint . 2022
    Open Access English
    Authors: 
    Yonghui Lin; Hans-Werner Hammer; Ulf-G. Meißner;
    Publisher: APS
    Project: EC | STRONG-2020 (824093)

    We present a combined analysis of the electromagnetic form factors of the nucleon in the space- and timelike regions using dispersion theory. Our framework provides a consistent description of the experimental data over the full range of momentum transfer, in line with the strictures from analyticity and unitarity. The statistical uncertainties of the extracted form factors are estimated using the bootstrap method, while systematic errors are determined from variations of the spectral functions. We also perform a high-precision extraction of the nucleon radii and find good agreement with previous analyses of spacelike data alone. For the proton charge radius, we find $r_E^p = 0.840^{+0.003}_{-0.002}{}^{+0.002}_{-0.002}$~fm, where the first error is statistical and the second one is systematic. The Zemach radius and third moment are in agreement with Lamb shift measurements and hyperfine splittings. The combined data set of space- and timelike data disfavors a zero crossing of $\mu_p G_E^p/G_M^p$ in the spacelike region. Finally, we discuss the status and perspectives of modulus and phase of the form factors in the timelike region in the context of future experiments as well as the onset of perturbative QCD. Comment: 7 pages, 4 figures

  • Open Access
    Authors: 
    Duglas Ugulava; David Zarnadze;
    Publisher: Elsevier BV

    Abstract The equation A u = f with a linear symmetric positive definite operator A : D ( A ) ⊂ H → H having a discrete spectrum and dense image in a complex Hilbert space H is considered. This equation is transferred into the Hilbert space of finite orbits D ( A n ) as well as into the Frechet space of all orbits D ( A ∞ ) , that is, the projective limit of the sequence of spaces { D ( A n ) } . For an approximate solution of the inverse of A, linear spline central algorithms in these spaces are constructed. The convergence of the sequence of approximate solutions to the exact solution is proved. The obtained results are applied to the quantum harmonic oscillator operator A u ( t ) = − u ″ ( t ) + t 2 u ( t ) , t ∈ R , in the Hilbert space of finite orbits D ( A n ) , and in the Frechet space of all orbits D ( A ∞ ) that in this case coincides with the Schwartz space of rapidly decreasing functions. Some quantum mechanical interpretations of obtained results are also given.

  • Open Access
    Authors: 
    Ketevan Janashia; Levan Tvildiani; Tamar Tsibadze; Nikoloz Invia;
    Publisher: Elsevier BV

    Abstract Evolutionarily, a human organism is adapted to the natural geomagnetic environment and its slight alterations. However, during geomagnetic storms (GMSs), the strength of the geomagnetic field (GMF) sharply increased hundreds of times and can pose a serious threat to people. We examine the effects of controlled compensation in the time-varying components of the GMF, using a specially created experimental setup with electrically shielding solutions, providing an electromagnetically quiet environment. The measurement of heart rate variability (HRV) on 25 healthy young male volunteers was carried out in the laboratory using the experimental setup at different levels of outdoor geomagnetic activity (GMA). The geomagnetic K-index was used to characterize the magnitude of GMSs; volunteers were tested during quiet magnetic days (K = 1–3), days with K = 4, and days with GMSs (K ≥ 5) in the period of solar cycle maximum. During quiet magnetic days, the comparison between HRV baseline values with values measured under GMF time-varying components compensation mode (CM) did not reveal any changes. On days with K = 4 some HRV indices shifted from their initial values, but it was statistically not significant. However, on days with GMSs statistically significant changes in SDNN* (p = 0.033) and LF* (p = 0.011) indices of HRV were observed in the GMS CM compared to their baseline values. The experiments showed that GMSs cause a sensitive reaction of the heart rate regulatory mechanism, the effect of which can be canceled in the GMS CM. The efficiency of the used technology is supported by the results of this study. * SDNN (Standard Deviation Normal to Normal R-R of cardiointervals), LF (Low frequency spectral band of cardiointervals).

  • Publication . Conference object . Preprint . Article . 2022
    Open Access
    Authors: 
    A. P. Misra; D. Chatterjee; A. Roy; T. D. Kaladze;
    Publisher: Institute of Electrical and Electronics Engineers (IEEE)

    The theory of low-frequency internal gravity waves (IGWs) is readdressed in the stable stratified weakly ionized Earth's ionosphere. The formation of dipolar vortex structures and their dynamical evolution, as well as, the emergence of chaos in the wave-wave interactions are studied both in presence and absence of the Pedersen conductivity. The latter is shown to inhibit the formation of solitary vortices and the onset of chaos. 6 pages, 4 figures; Submitted for consideration to IEEE Transactions on Plasma Science (Special Issue on Plenary, Invited, and Selected Minicourse Papers from ICOPS2021)

  • Open Access English
    Authors: 
    Leslie Hogben; Carolyn Reinhart;

    Distance matrices of graphs were introduced by Graham and Pollack in 1971 to study a problem in communications. Since then, there has been extensive research on the distance matrices of graphs -- a 2014 survey by Aouchiche and Hansen on spectra of distance matrices of graphs lists more than 150 references. In the last ten years, variants such as the distance Laplacian, the distance signless Laplacian, and the normalized distance Laplacian matrix of a graph have been studied. After a brief description of the early history of the distance matrix and its motivating problem, this survey focuses on comparing and contrasting techniques and results for the four types of distance matrices. Digraphs are treated separately after the discussion of graphs, including discussion of similarities and differences between graphs and digraphs. New results are presented that complement existing results, including results for some the matrices on unimodality of characteristic polynomials for graphs, preservation of parameters by cospectrality for graphs, and bounds on spectral radii for digraphs.

  • Open Access English
    Authors: 
    Krys, Kuba; Yeung, June Chun; Capaldi, Colin A.; Lun, Vivian Miu-Chi; Torres, Claudio; van Tilburg, Wijnand A. P.; Bond, Michael Harris; Zelenski, John M.; Haas, Brian W.; Park, Joonha; +54 more
    Publisher: Taylor and Francis
    Countries: Italy, Croatia, Portugal, Switzerland, Lithuania, Serbia, Netherlands, Croatia, Netherlands, Lithuania ...

    In this paper, we introduce the concept of ‘societal emotional environment’: the emotional climate of a society (operationalized as the degree to which positive and negative emotions are expressed in a society). Using data collected from 12, 888 participants across 49 countries, we show how societal emotional environments vary across countries and cultural clusters, and we consider the potential importance of these differences for well-being. Multilevel analyses supported a ‘double-edged sword’ model of negative emotion expression, where expression of negative emotions predicted higher life satisfaction for the expresser but lower life satisfaction for society. In contrast, partial support was found for higher societal life satisfaction in positive societal emotional environments. Our study highlights the potential utility and importance of distinguishing between positive and negative emotion expression, and adopting both individual and societal perspectives in well- being research. Individual pathways to happiness may not necessarily promote the happiness of others.

  • Publication . Article . 2022 . Embargo End Date: 31 Jan 2023
    Open Access English
    Authors: 
    Saverio Bartolini-Lucenti; Joan Madurell-Malapeira; Bienvenido Martínez-Navarro; Omar Cirilli; Luca Pandolfi; Lorenzo Rook; Maia Bushkhianidze; David Lordkipanidze;
    Country: Spain

    Altres ajuts: CERCA Programme/Generalitat de Catalunya The carnivore guild of the Early Pleistocene site of Dmanisi is among the most diverse of the Early Pleistocene of the entire Old World. It includes 14 carnivoran taxa: Homotherium latidens, Megantereon whitei, Panthera onca georgica, Acinonyx pardinensis, Lynx issiodorensis; Pachycrocuta brevirostris; Canis (Xenocyon) lycaonoides, Canis borjgali, Vulpes alopecoides; Ursus etruscus; Lutra sp., Martes sp., Meles sp., and Pannonictis sp. The analysis of this rich carnivore guild was carried out under different methodological approaches to compare the assemblage with other chronological coeval European, Asian, and African sites from a paleobiological perspective. To achieve the goal, we used a permutational hierarchical method called boostrapping cluster analysis based on taxonomic absence/presence matrices (at both generic and specific level) and on ecological matrices (considering dietary preferences/hunting strategies of each carnivoran) and carried out Mantels tests assessing magnitude of time, space, ecology, and taxonomy as source of difference between guilds. Our results suggest a close similarity among the Dmanisi carnivore assemblage and other guilds recorded from European late Villafranchian sites such as Pirro Nord, Venta Micena, and Apollonia 1 and, in a lesser extent, to European Epivillafranchian sites as Vallonnet, Untermassfeld, or the Vallparadís Section. Early to Middle Pleistocene Asian carnivore assemblages display several similarities with the Dmanisi guild mainly in the record and diversity of felid and the canid ecomorphotypes. Eastern African sites such as Olduvai and Omo, as well as South African sites, display a lower similarity with the studied sample, basically for the most diverse hyenid taphocoenoses. To sum up, the present study suggests a close similarity between the Dmanisi carnivore guild and other European Late Early Pleistocene assemblages without close parallels with African or Asian assemblages.

  • Open Access
    Authors: 
    Andria Rogava; Stefaan Poedts; Ekaterine Dadiani;
    Publisher: Elsevier BV

    Abstract The problem of the existence of self-similar solutions for astrophysical magnetohydrodynamic (MHD) transient flows is considered. Our approach is based on the pioneering works by B.C. Low for coronal transients and their further generalizations. The axiomatic basis of the approach is adjusted and verified. It is shown that the introduction of a new type of “triple-compound” variable may lead to the appearance of new classes of analytic self-similar solutions, possibly relevant for a number of interesting astrophysical situations. The possibility of the development of a self-similar model for a strongly magnetized plasma with pressure anisotropy is indicated. It is argued that proper changes of the model’s geometric and kinematic features may lead to the discovery of other, more complex and less idealized classes of self-similar solutions.

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