The European Physical Journal B最新文献

The life cycle of Avianca Brasil Airlines is investigated by employing complex network analysis. Various network parameters are discussed including average path length, clustering coefficient, connectance, and network similarity. These factors are compared with financial data to characterize the company’s network evolution over the years. Our results show that the airline network evolved toward a small-world configuration, maintaining short path lengths and increasing clustering, while two major hub relocations marked the most pronounced structural transitions. We further note that a later period of rising operational costs coincided with network expansion to more cities and a decrease in connectance, reflecting a sparser configuration. The present study highlights the importance of network-oriented strategies in the highly competitive airline industry.

We investigate the rise and fall of Avianca Brasil through the lens of complex network theory. By reconstructing the airline’s domestic flight network from 2010 to 2019, we reveal how strategic decisions, including hub relocations and route expansions, impacted the structure and efficiency of its operations. Key metrics such as path length, clustering coefficient, and network similarity show that the company evolved toward a small-world topology while expanding its market presence. This map depicts the domestic flight network of Avianca Brasil as of September 2013, showcasing its small-world characteristics and hub-centric structure.

The stochastic resonance (SR) phenomenon for a memristive three-dimensional Hindmarsh–Rose (HR) neuronal model with multiplicative and additive white noise driven by weak periodic force and stochastic telegraph signal is investigated. The three-dimensional HR model is transformed into a one-dimensional Langevin equation applying equilibrium point method. Based on adiabatic approximation condition and two-state theory, the system output signal-to-noise ratio (SNR) is deduced. The result shows that memristor coupling strength of the HR model can induce two peaks as the SNR changes with the coupling strength. Double SR appears when the SNR varies with the intensities of the multiplicative and additive noise. One resonance peak takes place as the SNR varies with the amplitude of the stochastic telegraph signal. The non-monotonous dependence of the SNR on system parameter is discussed.

Achieving coherent spin injection at room temperature has become a major challenge in organic spin valve (OSV) devices due to strong spin pinning at ferromagnet/organic semiconductor interface. In this article, we report a study on the impact of Co/Rubrene interface on coherent spin injection across ITO/V(TCNE)(_{2})/Rubrene/Co/Au OSV device. The application of high magnetic field has been found to create strong pinning effects at the interfacial defect states. Magnetoresistance versus voltage response of the device shows anomalous field dependence which has been attributed to the spin pinning induced transport through filled and vacant states of V(3d) and (pi ^{*})+U_C energy levels of TCNE (tetracyanoethylene), respectively.

In this review, we briefly discuss the complexities in having a theory of Ising spin glasses. We further discuss the applications of Ising spin glass physics in the inference problems, annealing in transverse Ising spin glass models and problems relating to social sciences.

Since the pioneering work Lohani et. al.. Phys. Rev. X 9, 041063 (2019), it became clear that quantum skyrmions have highly unusual properties as compared to the classical skyrmions and, due to their quantumness, cannot be described by continuous magnetic textures akin to the classical skyrmions. Competing nearest-neighbor and next-nearest-neighbor ferromagnetic and antiferromagnetic interactions in triangular spin-frustrated magnets lead to the formation of quantum skyrmion states. In frustrated magnets, skyrmions are characterized by the helical degree of freedom, which can store quantum information. In the limit of a weak electric field, the system can be described as a two-level system, i.e., a skyrmion qubit. Here, we propose a more general formulation of the problem and obtain general analytic solution of the model previously introduced in Psaroudaki et. al. Phys. Rev. Lett. 127, 067201 (2021). Our solution is valid not only for small barrier but also for the arbitrary electric field. In the case of a significant barrier, we prove that the system’s state is not a Skyrmion qubit as it was thought before, but a Skyrmion qudit. We constructed the density matrix of the Skyrmion qudit and studied its evolution in time. The obtained results suggest that the proposed model can be exploited further to meet the needs of quantum information theory and quantum skyrmionics. We showed that the (l_1) norm of coherence of the skyrmion qudit is a thousand times larger than the coherence of the skyrmion qubit. The obtained result opens new perspectives for quantum skyrmion-based resource theory.

The parquet equations present a cornerstone of some of the most important diagrammatic many-body approximations and methods currently on the market for strongly correlated materials: from non-local extensions of the dynamical mean-field theory to the functional renormalization group. The recently introduced single-boson exchange decomposition of the vertex presents an alternative set of equivalent equations in terms of screened interactions, Hedin vertices, and rest functions. This formulation has garnered much attention for several reasons: opening the door to new approximations, for avoiding vertex divergences associated with local moment formation plaguing the traditional parquet decomposition, and for its interpretative advantage in its built-in diagrammatic identification of bosons without resorting to Hubbard–Stratonovich transformations. In this work, we show how the fermionic diagrams of the particle–particle and particle–hole polarizations in the SBE formalism can be mapped to diagrammatics of a bosonic self-energy of two respective bosonic theories with pure bosonic constituents, solidifying the identification of the screened interaction with a bosonic propagator. Resorting to a spin-diagonalized basis for the bosonic fields and neglecting the coupling between singlet and triplet components are shown to recover the trace log theory known from Hubbard–Stratonovich transformations. Armed with this concrete mapping, we revisit a conjecture claiming that universal aspects of the parquet approximation coincide with those of the self-consistent screening approximation for a bosonic O(N) model. We comment on the role of the self-energy and crossing symmetry in enforcing the Hohenberg–Mermin–Wagner theorem in parquet-related approaches.