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Frontiers of Physics

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    2018, Vol.13  No.1

    The special topic edited by F. Mallamace, R. Car & Limei Xu reports eleven contributions jointly written by lecturers and students attending the 2016 “Ettore Majorana” Erice International School on Water and Water Systems. These papers focus on the study of water and its solutions from a molecular perspective, water being a complex system at the intersection of Physics, Chemistry, Biology and Materials Science. On these bases it requires sophisticated expe [Detail] ...

    Table of Contents

, Volume 13 Issue 1

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Traversable braneworld wormholes supported by astrophysical observations
Deng Wang, Xin-He Wang
Front. Phys. . 2018, 13 (1): 139801 .
Abstract   PDF (2451KB)

In this study, we investigate the characteristics and properties of a traversable wormhole constrained by the current astrophysical observations in the framework of modified theories of gravity (MOG). As a concrete case, we study traversable wormhole space–time configurations in the Dvali–Gabadadze–Porrati (DGP) braneworld scenario, which are supported by the effects of the gravity leakage of extra dimensions. We find that the wormhole space–time structure will open in terms of the 2σconfidence level when we utilize the joint constraints supernovae (SNe) Ia+ observational Hubble parameter data (OHD) + Planck+ gravitational wave (GW) and z<0:2874. Furthermore, we obtain several model-independent conclusions, such as (i) the exotic matter threading the wormholes can be divided into four classes during the evolutionary processes of the universe based on various energy conditions; (ii) we can offer a strict restriction to the local wormhole space–time structure by using the current astrophysical observations; and (iii) we can clearly identify a physical gravitational resource for the wormholes supported by astrophysical observations, namely the dark energy components of the universe or equivalent space–time curvature effects from MOG. Moreover, we find that the strong energy condition is always violated at low redshifts.

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Dynamical properties of water in living cells
Irina Piazza, Antonio Cupane, Emmanuel L. Barbier, Claire Rome, Nora Collomb, Jacques Ollivier, Miguel A. Gonzalez, Author_FootNote:Francesca Natali
Front. Phys. . 2018, 13 (1): 138302 .
Abstract   PDF (735KB)
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Dynamical properties of water in living cells Collection
Irina Piazza, Antonio Cupane, Emmanuel L. Barbier, Claire Rome, Nora Collomb, Jacques Ollivier, Miguel A. Gonzalez, Francesca Natali
Front. Phys. . 2018, 13 (1): 138301 .
Abstract   PDF (4828KB)

With the aim of studying the effect of water dynamics on the properties of biological systems, in this paper, we present a quasi-elastic neutron scattering study on three different types of living cells, differing both in their morphological and tumor properties. The measured scattering signal, which essentially originates from hydrogen atoms present in the investigated systems, has been analyzed using a global fitting strategy using an optimized theoretical model that considers various classes of hydrogen atoms and allows disentangling diffusive and rotational motions. The approach has been carefully validated by checking the reliability of the calculation of parameters and their 99% confidence intervals. We demonstrate that quasi-elastic neutron scattering is a suitable experimental technique to characterize the dynamics of intracellular water in the angstrom/picosecond space/time scale and to investigate the effect of water dynamics on cellular biodiversity.

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Dynamics of supercooled confined water measured by deep inelastic neutron scattering Collection
Vincenzo De Michele, Giovanni Romanelli, Antonio Cupane
Front. Phys. . 2018, 13 (1): 138205 .
Abstract   PDF (1407KB)

In this paper, we present the results of deep inelastic neutron scattering (DINS) measurements on supercooled water confined within the pores (average pore diameter ~20 Å) of a disordered hydrophilic silica matrix obtained through hydrolysis and polycondensation of the alkoxide precursor Tetra-Methyl- Ortho-Silicate via the sol-gel method. Experiments were performed at two temperatures (250 K and 210 K, i.e., before and after the putative liquid–liquid transition of supercooled confined water) on a “wet” sample with hydrationh~40% w/w, which is high enough to have water-filled pores but low enough to avoid water crystallization. A virtually “dry” sample ath ~7% was also investigated to measure the contribution of the silica matrix to the neutron scattering signal. As is well known, DINS measurements allow the determination of the mean kinetic energy and the momentum distribution of the hydrogen atoms in the system and therefore, allow researchers to probe the local structure of supercooled confined water. The main result obtained is that at 210 K the hydrogen mean kinetic energy is equal or even slightly higher than at 250 K. This is at odds with the predictions of a semiempirical harmonic model recently proposed to describe the temperature dependence of the kinetic energy of hydrogen in water. This is a new and very interesting result, which suggests that at 210 K, the water hydrogens experience a stiffer intermolecular potential than at 250 K. This is in agreement with the liquid–liquid transition hypothesis.

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Signature of the hydrogen-bonded environment of liquid water in X-ray emission spectra from first-principles calculations Collection
Huaze Shen, Mohan Chen, Zhaoru Sun, Limei Xu, Enge Wang, Xifan Wu
Front. Phys. . 2018, 13 (1): 138204 .
Abstract   PDF (3016KB)

Based on ab initio molecular dynamics simulations and density functional theory, we performed a systematic theoretical study to elucidate the correlation between the H-bonded environment and Xray emission spectra of liquid water. The spectra generated from excited water molecules embedded in an intact H-bonded environment yield broader spectral peaks and a larger spectral range than the spectra generated from water molecules in a broken H-bonded environment. Such differences are caused by the local electronic structures on the excited water molecules within the core-hole lifetime that evolve differently through the rearrangement of neighboring water molecules in different H-bonded environments.

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High-temperature dynamic behavior in bulk liquid water: A molecular dynamics simulation study using the OPC and TIP4P-Ew potentials Collection
Andrea Gabrieli, Marco Sant, Saeed Izadi, Parviz Seifpanahi Shabane, Alexey V. Onufriev, Giuseppe B. Suffritti
Front. Phys. . 2018, 13 (1): 138203 .
Abstract   PDF (802KB)

Classical molecular dynamics simulations were performed to study the high-temperature (above 300 K) dynamic behavior of bulk water, specifically the behavior of the diffusion coefficient, hydrogen bond, and nearest-neighbor lifetimes. Two water potentials were compared: the recently proposed “globally optimal” point charge (OPC) model and the well-known TIP4P-Ew model. By considering the Arrhenius plots of the computed inverse diffusion coefficient and rotational relaxation constants, a crossover from Vogel–Fulcher–Tammann behavior to a linear trend with increasing temperature was detected atT*≈309 and T*≈285 K for the OPC and TIP4P-Ew models, respectively. Experimentally, the crossover point was previously observed atT*≈315±5 K. We also verified that for the coefficient of thermal expansion αP (T, P), the isobaric αP(T) curves cross at about the same T* as in the experiment. The lifetimes of water hydrogen bonds and of the nearest neighbors were evaluated and were found to cross nearT*, where the lifetimes are about 1 ps. For T<T*, hydrogen bonds persist longer than nearest neighbors, suggesting that the hydrogen bonding network dominates the water structure at T<T*, whereas for T>T*, water behaves more like a simple liquid. The fact that T* falls within the biologically relevant temperature range is a strong motivation for further analysis of the phenomenon and its possible consequences for biomolecular systems.

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NMR investigation of degradation processes of ancient and modern paper at different hydration levels Collection
Domenico Mallamace, Sebastiano Vasi, Mauro Missori, Francesco Mallamace, Carmelo Corsaro
Front. Phys. . 2018, 13 (1): 138202 .
Abstract   PDF (2450KB)

The degradation process of cellulose-made materials was investigated by means of nuclear magnetic resonance (NMR) spectroscopy, with particular emphasis on the role of water and on the hydration mechanism of cellulose fibrils. To accomplish this, the structure and dynamics of water within ancient and modern samples with different aging histories were investigated. The results mainly indicated that hydrolytic and oxidative reactions provoked the formation of acidic by-products. Furthermore, degradation processes were enhanced by higher amounts of water giving a progressive consumption of the amorphous regions of the cellulose. We propose NMR experiments as a benchmark for characterization of the degradation state of paper, as well as for investigating the effectiveness of restoration treatments.

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Contrasting microscopic interactions determine the properties of water/methanol solutions Collection
Carmelo Corsaro, Francesco Mallamace, Sebastiano Vasi, Sow-Hsin Chen, H. Eugene Stanley, Domenico Mallamace
Front. Phys. . 2018, 13 (1): 138201 .
Abstract   PDF (979KB)

Herein we study the different microscopic interactions occurring in water/methanol solutions at different methanol molar fractions, using NMR spctroscopy. Temperature was found to determine which interaction dominates. It was found that the mixing between water and methanol is non-ideal because of the presence of interactions like hydrophobicity and hydrophilicity. These results indicate that the competition between hydrophilic and hydrophobic interactions is different in different thermal regions, and that the physical properties of the solution are determined by the character of the solution itself, which in turn depends on the mole fraction of methanol and on the temperature.

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Transport evidence of 3D topological nodal-line semimetal phase in ZrSiS
Junran Zhang, Ming Gao, Jinglei Zhang, Xuefeng Wang, Xiaoqian Zhang, Minhao Zhang, Wei Niu, Rong Zhang, Yongbing Xu
Front. Phys. . 2018, 13 (1): 137201 .
Abstract   PDF (9047KB)

Topological nodal-line semimetal is a new emerging material, which is viewed as a three-dimensional (3D) analog of graphene with the conduction and valence bands crossing at Dirac nodes, resulting in a range of exotic transport properties. Herein, we report on the direct quantum transport evidence of the 3D topological nodal-line semimetal phase of ZrSiS with angular-dependent magnetoresistance (MR) and the combined de Hass-van Alphen (dHvA) and Shubnikov-de Hass (SdH) oscillations. Through fitting by a two-band model, the MR results demonstrate high topological nodal-line fermion densities of approximately 6×1021 cm−3 and a perfect electron/hole compensation ratio of 0.94, which is consistent with the semi-classical expression fitting of Hall conductance Gxy and the theoretical calculation. Both the SdH and dHvA oscillations provide clear evidence of 3D topological nodal-line semimetal characteristic.

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Structural properties of water confined by phospholipid membranes Collection
Fausto Martelli, Hsin-Yu Ko, Carles Calero Borallo, Giancarlo Franzese
Front. Phys. . 2018, 13 (1): 136801 .
Abstract   PDF (1416KB)

Biological membranes are essential for cell life and hydration. Water provides the driving force for the assembly and stability of many cell components. Here, we study the structural properties of water in a phospholipid membrane. We characterize the local structures, inspecting the intermediate range order (IRO) and adopting a sensitive local order metric recently proposed by Martelli et al. that measures and grades the degree of overlap of the local environment with the structures of perfect ice. Close to the membrane, water acquires a high IRO and changes its dynamical properties; i.e., its translational and rotational degrees of freedom slow in a region that extends over ≃ 1 nm from the membrane interface. Surprisingly, we show that at distances as far as ≃ 2:5 nm from the interface, although the bulk-like dynamics are recovered, the IRO of water is still slightly higher than that in the bulk under the same thermodynamic conditions. Therefore, the water-membrane interface has a structural effect at ambient conditions that propagates further than the often-invoked 1-nm length scale. Consequently, this should be considered when analyzing experimental data of water confined by membranes and could help us to understand the role of water in biological systems.

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Topological superradiant state in Fermi gases with cavity induced spin–orbit coupling
Dongyang Yu, Jian-Song Pan, Xiong-Jun Liu, Wei Zhang, Wei Yi
Front. Phys. . 2018, 13 (1): 136701 .
Abstract   PDF (543KB)

Coherently driven atomic gases inside optical cavities hold great promise for generating rich dynamics and exotic states of matter. It was shown recently that an exotic topological superradiant state exists in a two-component degenerate Fermi gas coupled to a cavity, where local order parameters coexist with global topological invariants. In this work, we characterize in detail various properties of this exotic state, focusing on the feedback interactions between the atoms and the cavity field. In particular, we demonstrate that cavity-induced interband coupling plays a crucial role in inducing the topological phase transition between the conventional and topological superradiant states. We analyze the interesting signatures in the cavity field left by the closing and reopening of the atomic bulk gap across the topological phase boundary and discuss the robustness of the topological superradiant state by investigating the steady-state phase diagram under various conditions. Furthermore, we consider the interaction effect and discuss the interplay between the pairing order in atomic ensembles and the superradiance of the cavity mode. Our work provides many valuable insights into the unique cavity– atom hybrid system under study and is helpful for future experimental exploration of the topological superradiant state.

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PEG-PLGA electrospun nanofibrous membranes loaded with Au@Fe2O3 nanoparticles for drug delivery applications Collection
Salvatore Spadaro, Marco Santoro, Francesco Barreca, Angela Scala, Simona Grimato, Fortunato Neri, Enza Fazio
Front. Phys. . 2018, 13 (1): 136201 .
Abstract   PDF (21042KB)

A PEGylated-PLGA random nanofibrous membrane loaded with gold and iron oxide nanoparticles and with silibinin was prepared by electrospinning deposition. The nanofibrous membrane can be remotely controlled and activated by a laser light or magnetic field to release biological agents on demand. The nanosystems were characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and thermogravimetric analyses. The drug loading efficiency and drug content percentages were determined by UV-vis optical absorption spectroscopy. The nanofibrous membrane irradiated by a relatively low-intensity laser or stimulated by a magnetic field showed sustained silibinin release for at least 60 h, without the burst effect. The proposed low-cost electrospinning procedure is capable of assembling, via a one-step procedure, a stimuli-responsive drug-loaded nanosystem with metallic nanoparticles to be externally activated for controlled drug delivery.

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Fragile to strong crossover and Widom line in supercooled water: A comparative study Collection
Margherita De Marzio, Gaia Camisasca, Mauro Rovere, Paola Gallo
Front. Phys. . 2018, 13 (1): 136103 .
Abstract   PDF (444KB)

The aim of this paper is to discuss the relationship between the dynamics and thermodynamics of water in the supercooled region. Reviewed case studies comprehend bulk water simulated with the SPC/E, TIP4P and TIP4P/2005 potentials, water at protein interfaces, and water in solution with electrolytes. Upon supercooling, the fragile to strong crossover in the-relaxation of water is found to occur when the Widom line emanating from the liquid-liquid critical point is crossed. This appears to be a general characteristic of supercooled water, not depending on the applied interaction potential and/or different local environments.

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Core-softened potentials, multiple liquid–liquid critical points, and density anomaly regions: An exact solution Collection
Eduardo O. Rizzatti, Marco Aurélio A. Barbosa, Marcia C. Barbosa
Front. Phys. . 2018, 13 (1): 136102 .
Abstract   PDF (586KB)

The pressure versus temperature phase diagram of a system of particles interacting through a multiscale shoulder-like potential is exactly computed in one dimension. The N-shoulder potential exhibits N density anomaly regions in the phase diagram if the length scales can be connected by a convex curve. The result is analyzed in terms of the convexity of the Gibbs free energy.

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Hydrogen mean force and anharmonicity in polycrystalline and amorphous ice Collection
A. Parmentier, C. Andreani, G. Romanelli, J. J. Shephard, C. G. Salzmann, R. Senesi
Front. Phys. . 2018, 13 (1): 136101 .
Abstract   PDF (2654KB)

The hydrogen mean force from experimental neutron Compton profiles is derived using deep inelastic neutron scattering on amorphous and polycrystalline ice. The formalism of mean force is extended to probe its sensitivity to anharmonicity in the hydrogen-nucleus effective potential. The shape of the mean force for amorphous and polycrystalline ice is primarily determined by the anisotropy of the underlying quasi-harmonic effective potential. The data from amorphous ice show an additional curvature reflecting the more pronounced anharmonicity of the effective potential with respect to that of ice Ih.

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Evolution of finite energy Airy beams in cubic-quintic atomic vapor system
Zhen-Kun Wu, Hao Guo, Wei Wang, Yu-Zong Gu
Front. Phys. . 2018, 13 (1): 134201 .
Abstract   PDF (22526KB)

In a numerical investigation, we demonstrate the evolution of a one-dimensional and two-dimensional finite energy Airy beam in a ?-type three-level atomic vapor with linear, cubic, and quintic susceptibilities considered simultaneously with the dressing effect. Quasi-solitons and soliton pairs are observed due to this competition mechanism. We find that the frequency detuning of the pump field and its power greatly affect the formation and evolution of generated solitons. In general, around the twophoton resonance point and for low intensities of the pump field, it is less difficult to form solitons. This investigation enriches the study of the propagation properties of Airy beams and soliton generation in atomic vapor.

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Two-dimensional matter-wave solitons and vortices in competing cubic-quintic nonlinear lattices
Xuzhen Gao, Jianhua Zeng
Front. Phys. . 2018, 13 (1): 130501 .
Abstract   PDF (839KB)

The nonlinear lattice — a new and nonlinear class of periodic potentials — was recently introduced to generate various nonlinear localized modes. Several attempts failed to stabilize two-dimensional (2D) solitons against their intrinsic critical collapse in Kerr media. Here, we provide a possibility for supporting 2D matter-wave solitons and vortices in an extended setting — the cubic and quintic model — by introducing another nonlinear lattice whose period is controllable and can be different from its cubic counterpart, to its quintic nonlinearity, therefore making a fully “nonlinear quasi-crystal”.

A variational approximation based on Gaussian ansatz is developed for the fundamental solitons and in particular, their stability exactly follows the inverted Vakhitov–Kolokolov stability criterion, whereas the vortex solitons are only studied by means of numerical methods. Stability regions for two types of localized mode — the fundamental and vortex solitons — are provided. A noteworthy feature of the localized solutions is that the vortex solitons are stable only when the period of the quintic nonlinear lattice is the same as the cubic one or when the quintic nonlinearity is constant, while the stable fundamental solitons can be created under looser conditions. Our physical setting (cubic-quintic model) is in the framework of the Gross–Pitaevskii equation or nonlinear Schrödinger equation, the predicted localized modes thus may be implemented in Bose–Einstein condensates and nonlinear optical media with tunable cubic and quintic nonlinearities.

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Multipartite quantum correlations among atoms in QED cavities
J. Batle, A. Farouk, O. Tarawneh, S. Abdalla
Front. Phys. . 2018, 13 (1): 130305 .
Abstract   PDF (2351KB)

We study the nonlocality dynamics for two models of atoms in cavity quantum electrodynamics (QED); the first model contains atoms in a single cavity undergoing nearest-neighbor interactions with no initial correlation, and the second contains atoms confined in ndifferent and noninteracting cavities, all of which were initially prepared in a maximally correlated state of nqubits corresponding to the atomic degrees of freedom. The nonlocality evolution of the states in the second model shows that the corresponding maximal violation of a multipartite Bell inequality exhibits revivals at precise times, defining, nonlocality sudden deathsand nonlocality sudden rebirths, in analogy with entanglement. These quantum correlations are provided analytically for the second model to make the study more thorough. Differences in the first model regarding whether the array of atoms inside the cavity is arranged in a periodic or open fashion are crucial to the generation or redistribution of quantum correlations. This contribution paves the way to using the nonlocality multipartite correlation measure for describing the collective complex behavior displayed by slightly interacting cavity QED arrays.

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Uncertainty relations for quantum coherence with respect to mutually unbiased bases
Alexey E. Rastegin
Front. Phys. . 2018, 13 (1): 130304 .
Abstract   PDF (149KB)

The concept of quantum coherence, including various ways to quantify the degree of coherence with respect to the prescribed basis, is currently the subject of active research. The complementarity of quantum coherence in different bases was studied by deriving upper bounds on the sum of the corresponding measures. To obtain a two-sided estimate, lower bounds on the coherence quantifiers are also of interest. Such bounds are naturally referred to as uncertainty relations for quantum coherence. We obtain new uncertainty relations for coherence quantifiers averaged with respect to a set of mutually unbiased bases (MUBs). To quantify the degree of coherence, the relative entropy of coherence and the geometric coherence are used. Further, we also derive novel state-independent uncertainty relations for a set of MUBs in terms of the min-entropy.

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Cavity control as a new quantum algorithms implementation treatment
M. AbuGhanem, A. H. Homid, M. Abdel-Aty
Front. Phys. . 2018, 13 (1): 130303 .
Abstract   PDF (8110KB)

Based on recent experiments [Nature 449, 438 (2007) and Nature Physics 6, 777 (2010)], a new approach for realizing quantum gates for the design of quantum algorithms was developed. Accordingly, the operation times of such gates while functioning in algorithm applications depend on the number of photons present in their resonant cavities. Multi-qubit algorithms can be realized in systems in which the photon number is increased slightly over the qubit number. In addition, the time required for operation is considerably less than the dephasing and relaxation times of the systems. The contextual use of the photon number as a main control in the realization of any algorithm was demonstrated. The results indicate the possibility of a full integration into the realization of multi-qubit multiphoton states and its application in algorithm designs. Furthermore, this approach will lead to a successful implementation of these designs in future experiments.

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Clock frequency estimation under spontaneous emission
Xi-Zhou Qin (秦锡洲), Jia-Hao Huang (黄嘉豪), Hong-Hua Zhong (钟宏华), Chaohong Lee (李朝红)
Front. Phys. . 2018, 13 (1): 130302 .
Abstract   PDF (1449KB)

We investigate the quantum dynamics of a driven two-level system under spontaneous emission and its application in clock frequency estimation. By using the Lindblad equation to describe the system, we analytically obtain its exact solutions, which show three different regimes: Rabi oscillation, damped oscillation, and overdamped decay. From the analytical solutions, we explore how the spontaneous emission affects the clock frequency estimation. We find that under a moderate spontaneous emission rate, the transition frequency can still be inferred from the Rabi oscillation. Our results enable potential practical applications in frequency measurement and quantum control under decoherence.

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Hidden antiunitary symmetry behind “accidental” degeneracy and its protection of degeneracy
Jing-Min Hou, Wei Chen
Front. Phys. . 2018, 13 (1): 130301 .
Abstract   PDF (106KB)

In quantum mechanics, accidental degeneracy refers to energy degeneracy that occurs coincidentally, without any protection by symmetry. Here, we prove a theorem stating that any two-fold degeneracy (accidental or not) in a quantum system is protected by a novel hidden symmetry, which can be expressed by an antiunitary operator with its square being −1. In this sense, the so-called accidental degeneracy is not really accidental, and this actually implies a hidden antiunitary symmetry.

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Mean-field approximations of fixation time distributions of evolutionary game dynamics on graphs
Li-Min Ying, Jie Zhou, Ming Tang, Shu-Guang Guan, Yong Zou
Front. Phys. . 2018, 13 (1): 130201 .
Abstract   PDF (1280KB)

The mean fixation time is often not accurate for describing the timescales of fixation probabilities of evolutionary games taking place on complex networks. We simulate the game dynamics on top of complex network topologies and approximate the fixation time distributions using a mean-field approach. We assume that there are two absorbing states. Numerically, we show that the mean fixation time is sufficient in characterizing the evolutionary timescales when network structures are close to the well-mixing condition. In contrast, the mean fixation time shows large inaccuracies when networks become sparse. The approximation accuracy is determined by the network structure, and hence by the suitability of the mean-field approach. The numerical results show good agreement with the theoretical predictions.

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