The European Physical Journal B最新文献

Samples of the CuCr_1-xAl_xO₂ system with x = 0, 0.25, 0.5, 0.75, 1 were synthesized using conventional ceramic technology. X-ray diffraction phase analysis data indicate the formation of an unlimited solid solution in the system with the delafossite crystal structure (a = 2.97–2.95 Å, c = 17.1–16.9 Å, sp. gr. R-3 m). Scanning electron microscopy data show that in samples with x = 0.25, 0.5, 0.75, particles of large and small sizes are embedded into each other. The calculated average grain sizes of the samples vary from 1.2 to 7.5 µm. The temperature dependencies of the electrical resistance of the samples under direct current were studied in the temperature range from 77 to 300 K with electric field strengths of 0.001, 0.94, 1.27, and 1.5 kV/cm. The current–voltage characteristics of the samples were studied in the range of electric field strengths up to 4.5 kV/cm at temperatures of 120, 175, and 220 K. It was established that the application of a constant electric field of 0.94, 1.27, and 1.5 kV/cm leads to switching from a high resistance state to a low resistance state. This switching is manifested in the form of giant resistance jumps (up to six orders of magnitude) in the temperature range of 90–200 K, as well as in the form of S-shaped volt-ampere characteristics containing a region of negative differential resistance. An interpretation of the observed switching effect is provided based on the polaron mechanism of conductivity.

A novel virus begin to spread worldwide in 2020. Many studies have been conducted to better understand the outbreak that continues to affect the global population. The contribution of the present study is to provide an overview of the papers published in the first months since recognition of the first case of COVID-19. For this, a survey of scientific publications during the first 5 months of the outbreak was conducted. Semantic, coauthorship and citation networks were used to identify the most relevant themes and authors during the cited period. Coauthorship indicated that scientists from several countries had joined forces in the fight against the pandemic to produce many joint scientific publications on the newly discovered virus and the disease it caused. Coauthorship was spread across 1170 author groups. Regarding the semantic network of titles, we found that it was a hybrid network because it presented the small-world phenomenon and a power law in its degree distribution and was therefore scale invariant. Considering the citation network, we found that the distribution of indegrees followed a power law, and with it, we observed the most cited works due to their importance to the area and their cumulative advantage. The coauthorship, semantic, and citation networks clearly show some characteristics of complex systems.

Neurons within the pre-Bötzinger complex have been found experimentally to exhibit different firing activities. Mixed bursting is a special firing activities which has been found in neuron model and biological experiments. The traditional fast and slow dynamics analysis method encounters some difficulties in analyzing mixed bursting. Therefore, how to analyze the dynamic mechanism of mixed bursting generation and transition is a very important issue. In this paper, based on fast-slow decomposition, multiple timescale dynamics and one- and two-parameter bifurcation analysis, we investigate the mixed bursting and their transition mechanisms in pre-Bötzinger complex neurons. The results show that the generation mechanism of the mixed bursting is related to the multiple timescale of the neuron model. The results obtained in this paper is instructive for further understanding the dynamical behaviours and generation mechanisms of complex firing activities in biological nervous systems.

The uniform prior probability density for the means of normal data leads to inconsistent Bayesian inference of their mean power and jeopardizes the possibility of selecting among different models that explain the data. We reinvestigated the problem avoiding delivering unrecognised information and looking at it in a novel way. Namely, to consider a finite power, we used a normal prior minimally diverging from the uniform one, hyperparameterised by the mean and variance, and left the data to choose the most supported parameters. We also obtained an extended James–Stein estimator averaging the hyper-parameters and avoiding empirical Bayes techniques.

We present a perspective of simple models of nonequilibrium directed transport described in terms of a Langevin equation formalism. We consider a Brownian particle under various circumstances and driven by thermal (equilibrium) and non-thermal (active) fluctuations. Three examples of startling behavior are unveiled: giant transport, multiple current reversal and negative mobility.