International Journal of Modern Physics B

Recent years have witnessed the increasing of available network data; however, much of those data is incomplete. Link prediction, which can find the missing links of a network, plays an important role in the research and analysis of complex networks. Based on the assumption that two unconnected nodes which are highly similar are very likely to have an interaction, most of the existing algorithms solve the link prediction problem by computing nodes' similarities. The fundamental requirement of those algorithms is accurate and effective similarity indices. In this paper, we propose a new similarity index, namely similarity based on activity and connectivity (SAC), which performs link prediction more accurately. To compute the similarity between two nodes, this index employs the average activity of these two nodes in their common neighborhood and the connectivities between them and their common neighbors. The higher the average activity is and the stronger the connectivities are, the more similar the two nodes are. The proposed index not only commendably distinguishes the contributions of paths but also incorporates the influence of endpoints. Therefore, it can achieve a better predicting result. To verify the performance of SAC, we conduct experiments on 10 real-world networks. Experimental results demonstrate that SAC outperforms the compared baselines.

We analyze two theoretical approaches to ensemble averaging for integrable systems in quantum chaos, spectral averaging (SA) and parametric averaging (PA). For SA, we introduce a new procedure, namely, rescaled spectral averaging (RSA). Unlike traditional SA, it can describe the correlation function of spectral staircase (CFSS) and produce persistent oscillations of the interval level number variance (IV). PA while not as accurate as RSA for the CFSS and IV, can also produce persistent oscillations of the global level number variance (GV) and better describes saturation level rigidity as a function of the running energy. Overall, it is the most reliable method for a wide range of statistics.

Conduction band-edge nonparabolicity effect on linear and nonlinear optical properties related to 1s–1p intra-conduction band transition in unstrained wurtzite (In, Ga)N–GaN symmetric quantum well (QW) is investigated incorporating an additional external probe as well as the nonresonant intense laser field (ILF) effect. Using the compact density matrix approach and the iterative procedure, the analytical expressions of optical absorption coefficients (ACs) are calculated. The numerical results are obtained within the single-band effective mass and the one-parabolic-band approximations under finite potential barrier. It is found that the internal and external perturbations show an important impact on the optical spectrum. A critical value of the laser-dressed parameter (LDP) is obtained by limiting two behaviors. Moreover, the ILF can be used as a way to control the optical properties of the QW structures and to reduce the lift of the conduction band-edge.

We discuss the rules for designing nanostructured plasmonic backcontact of thin-film crystalline silicon solar cells using two-dimensional finite-difference time-domain (2D-FDTD) method. A novel efficient quasi-periodic plasmonic nanograting is designed. Numerical calculations demonstrate that broadband and polarization-insensitive absorption enhancement is achieved by the proposed structure which is based on a supercell geometry containing N subcells in each of which there is one Ag nanowire deposited on the backcontact of the solar cell. The proposed structure offers the possibility of controlling the number and location of photonic and plasmonic modes and outperforms the periodic plasmonic nanogratings which only utilize plasmonic resonances. We start by tuning the plasmonic mode of one subcell and then construct the supercell based on the final design of the subcell. Our findings show that with a proper choice of key parameters of the nanograting, several photonic and plasmonic modes can be excited across the entire spectral region where crystalline silicon (c-Si) is absorbing. The absorption enhancement is significant, particularly in the long wavelength region where c-Si is weakly absorbing.

Transient phonon transport across cross-planes of aluminum–silicon–aluminum combined films is investigated and the Boltzmann transport equation is incorporated to formulate the energy transport in the combined films. Since electrons and phonons thermally separate in the thin aluminum film during heating, the Boltzmann equation is used separately in the electron and lattice subsystems to account for the energy transport in the aluminum film. Electron–phonon coupling is incorporated for the energy exchange between electron and lattice subsystems in the film. Thermal boundary resistance (TBR) is introduced at the interfaces of the silicon–aluminum films. In order to examine the ballistic contribution of phonons on the phonon intensity distribution in the silicon film, frequency-dependent solution of the Boltzmann equation is used in the silicon film and the film thickness is varied to investigate the size effect on the thermal conductivity in the film. It is found that equivalent equilibrium temperature of phonons remains high at silicon–aluminum interface because of the ballistic contribution of the phonons. Equivalent equilibrium temperature for the electron subsystem becomes higher than that corresponding to phonon temperature at the aluminum–silicon interface.

Analyzing the statistical features of fluctuation is remarkably significant for financial risk identification and measurement. In this study, the asymmetric detrended fluctuation analysis (A-DFA) method was applied to evaluate asymmetric multifractal scaling behaviors in the Shanghai and New York gold markets. Our findings showed that the multifractal features of the Chinese and international gold spot markets were asymmetric. The gold return series persisted longer in an increasing trend than in a decreasing trend. Moreover, the asymmetric degree of multifractals in the Chinese and international gold markets decreased with the increase in fluctuation range. In addition, the empirical analysis using sliding window technology indicated that multifractal asymmetry in the Chinese and international gold markets was characterized by its time-varying feature. However, the Shanghai and international gold markets basically shared a similar asymmetric degree evolution pattern. The American subprime mortgage crisis (2008) and the European debt crisis (2010) enhanced the asymmetric degree of the multifractal features of the Chinese and international gold markets. Furthermore, we also make statistical tests for the results of multifractatity and asymmetry, and discuss the origin of them. Finally, results of the empirical analysis using the threshold autoregressive conditional heteroskedasticity (TARCH) and exponential generalized autoregressive conditional heteroskedasticity (EGARCH) models exhibited that good news had a more significant effect on the cyclical fluctuation of the gold market than bad news. Moreover, good news exerted a more significant effect on the Chinese gold market than on the international gold market.

In this paper, we demonstrate that an electromagnetically induced transparency (EIT)-like behavior is induced by the coupling of two magnetic resonances in a planar terahertz (THz) metamaterial structure, which consists of a U-shaped split ring (USR) as one bright resonator and a cut wire pair (CWP) as one dark resonator. It is found that the EIT-like spectral response is insensitive to the lateral distance between the two magnetic resonators, whereas an on-to-off modulation of the amplitude of the transparency window can be achieved by moving the USR vertically along the CWP. The underlying physical mechanism is mainly attributed to magneto-inductive excitation of the CWP. This investigation may provide an insight of the role of magnetic coupling in achieving EIT-like effect, inspiring interest in the developments of magnetically tunable transparency metamaterial for a wide range of optical devices with switching and modulation capabilities.

Superatomic molecular orbitals (SAMOs) in C₆₀ are ideal building blocks for functional nanostructures. However, imaging them spatially in the gas phase has been unsuccessful. It is found experimentally that if C₆₀ is excited by an 800-nm laser, the photoelectron casts an anisotropic velocity image, but the image becomes isotropic if excited at a 400-nm wavelength. This diffuse image difference has been attributed to electron thermal ionization, but more recent experiments (800 nm) reveal a clear nondiffuse image superimposed on the diffuse image, whose origin remains a mystery. Here we show that the nondiffuse anisotropic image is the precursor of the f SAMOs. We predict that four 800-nm photons can directly access the 1f SAMO, and with one more photon, can image the orbital, with the photoelectron angular distribution having two maxima at 0° and 180° and two humps separated by 56.5°. Since two 400-nm photons only resonantly excite the spherical 1s SAMO and four 800-nm photons excite the anisotropic 1f SAMO, our finding gives a natural explanation of the nondiffuse image difference, complementing the thermal scenario.

Extensive studies of the geometric structures, stabilities and electronic properties of gallium nitride (GaN)_n tubelike clusters and single-walled GaN nanotubes (GaNNTs) were carried out using density-functional theory (DFT) calculations. A family of stable tubelike structures with Ga–N alternating arrangement was observed when n≥8 and their structural units (four-membered rings (4MRs) and six-membered rings (6MRs)) obey the general developing formula. The size-dependent properties of the frontier molecular orbital surfaces explain why the long and stable tubelike clusters can be obtained successfully. They also illustrate the reason why GaNNTs can be synthesized experimentally. Our results also reveal that the single-walled GaNNTs, which as semiconductors with a large bandgap, can be prepared by using the proper assembly of tubelike clusters.

In this paper, we discuss the mathematical structure of the s-wave superconducting gap and other quantitative characteristics of superconducting systems. In particular, we evaluate and discuss integrals inherent in fundamental equations describing superconducting systems. The results presented here extend the approach formulated by Abrikosov and Maki, which was restricted to the first-order expansion. A few infinite families of integrals are derived and allow us to express the fundamental equations by means of analytic formulas. They can be then exploited in order to find some quantitative characteristics of superconducting systems by the method of successive approximations. We show that the results can be applied to some modern formalisms in order to study high-T_c superconductors and other superconducting materials of the new generation.