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A balance in nature is maintained by the coexistence of multiple species through interspecific competition. The evolutionary dynamics of cyclic interactions contain interactions that represent different biological behaviors. Biological behavior is influenced by the external environment, which may affect the stability of ecosystems. We investigated the evolutionary dynamics of interspecific competition after a periodic change in the external environment affects species. We consider that when the periodic external environments affect mortality, interspecific cyclical competition may be more pronounced, and thus increase the probability of extinction of species. By performing Monte Carlo simulations, we observed that the evolutionary dynamics of interspecific cyclic competition have different responsivity when subjected to external periodic changes at different frequencies, and stochastic resonance phenomena occurred. We show that the influence of the periodic external environment and its frequency is one of the factors that determine whether ecosystems coexist stably.

Offshore wind farms are integrated into the power grid via AC submarine cables, which may cause severe harmonic problems and reduce the power quality of the grid. To address the problem of excessive harmonics in offshore wind power plants (WPPs), this paper proposes a method applying the static var generator (SVG) with frequency adaptive harmonic mitigation function to the offshore WPPs. Firstly, the SVG model and the mechanism of harmonic mitigation are investigated. Secondly, the proportional and resonant control strategy is proposed according to the internal model theorem and applied to the voltage control loop of SVG. The harmonic suppression performance of SVG is studied through the Bode diagram. Thirdly, to adapt to the uncertainty of harmonic frequencies, the recursive least-squares method is introduced to realize the real-time tracking of harmonic frequencies. And the harmonic compensation bandwidth of the SVG is broadened by adjusting the parameters of the controller. Finally, the offshore WPPs in Jiangsu are built based on the Matlab/Simulink platform to verify the effectiveness of the mitigation strategy. Compared with the LC filter, the improved method can effectively mitigate (inter-) harmonics and has strong robustness and adaptability.

Offshore wind power plants (WPPs) using AC submarine cables connected to the power grid may experience harmonic resonance and harmonic amplification that are not common in onshore wind farms under the action of the distributed capacitance of submarine cables, which seriously threatens the safe and reliable operation of offshore WPPs. To investigate the influencing factors of harmonic amplification in offshore WPPs, a scalable state space-based modeling method for large-scale offshore WPPs were established. Moreover, the root locus method was used to study how the factors including that grid short-circuit capacities, cable parameters and the number of wind turbine generators (WTGs) affect the resonance modes. Finally, an offshore WPP in Jiangsu was built on the MATLAB/Simulink simulation platform, and the analysis results verify the correctness of the theoretical analysis.

We study the bidirectional pedestrian flow in a straight corridor using a floor field cellular automaton model, where a game-theoretical framework is exclusively introduced to deal with conflicts that multiple pedestrians are trying to move to the same target position. The pedestrians can behave as either cooperators or defectors, depending on whether they show gentle or aggressive in face of conflicts, respectively. When competing with cooperators, a defector always obtains a relatively greater payoff, characterizing the advantage of occupying the preferred vacant cell, while a reduced payoff factor δ is introduced for mutual defection due to the possible injuries by aggressiveness. We study how the pedestrian counterflow dynamics depends on δ, the corridor width W and the anticipation floor field parameter k A. It is found that the average separation time of the pedestrians displays a resonance-like behavior as a function of δ, irrespective of the width of the corridor as long as jam does not happen. The way of dealing with conflicts has no qualitative effect on the lane formation, where the jam probability mainly depends on the parameters W and k A as well as the pedestrian density. A large value of k A means a strong tendency to avoid potential future collisions and suppress the overtaking motivation, but, at a cost, increases the average separation time of the two groups of pedestrians when the width of the corridor is not so narrow. Our results provide a meaningful perspective on the understanding of the process of lane formation and jam dissolution in the bidirectional pedestrian flow, and may shed light on designing policies to improve the efficiency of passing through.

Linear mapping is widely used in dynamic modeling and empirical data analysis, but it suffers from the serious shortcoming that it does not work in the common case of time intervals being large. The fundamental cause of the failure is that the linear mapping does not take into account the coupling effects of multiple events within a discrete time interval. Here, we develop a theoretical framework to provide a nonlinear mapping between continuous- and discrete-time dynamics by accounting for the coupling effect. We have verified the effectiveness of our mapping by exploring classical susceptible-infected-susceptible and susceptible-infected-recovered models. In particular, we give a quantitative criterion that the sum of two transition probabilities —from one state to the other and vice versa— must be strictly less than 1 for binary-state dynamics.

The melting and recrystallization behavior of -iPP crystal induced by β -nucleating agent was studied. A new type of α-modification has been developed by self-seeding process. The growth process of these crystals is just like “photographic development process.” Crystalline phase transformation and the memory effect caused by local order was observed during the melting and annealing process. A high temperature is sufficient to destroy the local order and the β-nucleating agent efficiently induces formation of β-form.

The threshold voltage (V th) of the p-channel metal–oxide–semiconductor field-effect transistors (MOSFETs) is investigated via Silvaco-Atlas simulations. The main factors which influence the threshold voltage of p-channel GaN MOSFETs are barrier height Φ 1,p, polarization charge density σ b, and equivalent unite capacitance C oc. It is found that the thinner thickness of p-GaN layer and oxide layer will acquire the more negative threshold voltage V th, and threshold voltage |V th| increases with the reduction in p-GaN doping concentration and the work-function of gate metal. Meanwhile, the increase in gate dielectric relative permittivity may cause the increase in threshold voltage |V th|. Additionally, the parameter influencing output current most is the p-GaN doping concentration, and the maximum current density is 9.5 mA/mm with p-type doping concentration of 9.5 × 1016 cm−3 at V GS = –12 V and V DS = –10 V.

As one of the important equipment to ensure the normal operation of substation, the performance of grounding grid has been highly concerned. In recent years, researchers propose that the theory of electromagnetic induction can be used to diagnose and identify the corrosion fault of substation grounding grid. In this paper, a fault classification model based on LS-SVM optimized by PSO is proposed to identify the corrosion fault of grounding grid. Firstly, the wavelet packet transform principle is used to filter the original data, and the wavelet packet energy is used to construct the fault eigenvalue as the input of the fault classification model. Based on LS-SVM, a corrosion fault classification model is constructed, and particle swarm optimization method is used to optimize the parameters of the model, which solves the problem of traditional SVM parameter optimization. Through the practical application in substation, the model proposed in this paper can identify the corrosion of grounding grid conductor without excavation and power failure, which provides an effective scheme for engineering application.

In order to explore the changes of mechanical properties of cable-stayed arch composite bridge in different construction stages, this paper takes a 136m tensed-string arch bridge as the engineering background, briefly describes the construction steps of grid lifting, and adopts Madis/Civil finite element analysis software for modeling. The actual construction process of the arch bridge is simulated by classifying different construction stages. The static and dynamic mechanical properties and stability of arch Bridges are studied. Through research and analysis, the main conclusions are drawn that the cables of the tensioned arch bridge bear part of the load of the original arch rib and girder.

In recent years, with the rapid development of network technology and information technology, artificial intelligence has become the development trend of modern technology. Over the past 50 years, scientists from various countries around the world have continuously explored artificial intelligence technology. Up to now, artificial intelligence has achieved great results. Compared with traditional modern technology, artificial intelligence has broken through the shackles of traditional technology, and has been highly sought after in various fields for its advantages such as being more convenient, more effective, saving time, labor and cost. Modern vocational education is an effective part of China’s higher education, mainly providing professional technical talents for the society. At present, vocational education has not been developing in China for a long time, and the application of computer technology in vocational education is even later. In recent years, although the rapid development of computer technology in China has promoted the development of vocational education to a certain extent, the actual application of computer technology in modern vocational education has lagged far behind the development of computer science itself. While many disciplines of artificial intelligence based on “knowledge engineering” have achieved certain results, modern vocational education still evolves traditional computer technology. Obviously, modern vocational education is far from artificial intelligence technology in computer application. How to effectively apply artificial intelligence technology to the summary of modern vocational education, make full use of the potential of computer technology itself, and bring new development opportunities for the development of modern vocational education has become an important issue that modern vocational education workers need to solve urgently. From the perspective of artificial intelligence technology, this paper deeply analyzes the current status and problems of the application of artificial intelligence technology in modern vocational education in China. And on this basis, this paper puts forward the feasibility suggestions for introducing artificial intelligence into modern vocational education technology. The main purpose of the research in this article is to urge our modern vocational education colleges to pay enough attention to artificial intelligence technology and to stimulate the interest of modern vocational education scholars on artificial intelligence. Furthermore, the artificial intelligence technology can be fully and efficiently implemented into modern vocational education, and more high-quality professional and technical personnel can be cultivated for the society.

With the increase of the grid-connected capacity of wind power, the influence of power system forced oscillation caused by wind power is becoming bigger and bigger, so it is necessary to understand its production mechanism and general characteristics. In this paper, the nonlinear and non-stationary signal generated by the unstable wind speed is analyzed to speculate the characteristics of wind-induced oscillation. Secondly, the bispectrum analysis and the bicoherence analysis are introduced. The obtained bispectrum and bicoherence coefficients are used to analyze the oscillation caused by wind power and the quadratic phase coupling relationship between oscillation modes. Finally, the simulation is operated considering small wind farm connected to a 4-generator-2-area (4G2A) system. The simulation results verify the correctness of the proposed speculation and the effectiveness of the proposed method.

Subsynchronous Oscillation (SSO) may exist in doubly-fed induction generator (DFIG)-based wind farms connected with a series compensated transmission network, also called subsynchronous control interaction (SSCI). Different from thermal power units, the SSO frequency of wind farm varies with the change of system operating conditions, and has the characteristic of time-varying. When the operating conditions change, the existing mitigation strategies may lose the effect. To address this issue, a SSO mitigation strategy based on adaptive band-stop filter (ABSF) is proposed in this paper: When SSO occurs in the system, the ABSF parameter is adjusted according to the oscillation frequency measured by PASTd algorithm to filter out the subsynchronous component in the RSC loop effectively, so as to break the generation path of SSO and suppress SSO. Compared with the existing mitigation strategies, the proposed strategy doesn’t need the mathematical model of the system, and can ensure strong robustness under various operating conditions. Finally, the effectiveness and robustness of the proposed strategy are verified on the Matlab/Simulink.

It is well known that the quantum Hall conductivity in the presence of constant magnetic field is expressed through the topological TKNN invariant. The same invariant is responsible for the intrinsic anomalous quantum Hall effect (AQHE), which, in addition, may be represented as one in momentum space composed of the two point Green's functions. We propose the generalization of this expression to the QHE in the presence of non-uniform magnetic field. The proposed expression is the topological invariant in phase space composed of the Weyl symbols of the two-point Green's function. It is applicable to a wide range of non-uniform tight-binding models, including the interacting ones., Comment: Latex, 11 pages, proceedings of ICNFP2019, misprints corrected. arXiv admin note: text overlap with arXiv:1905.11097

There has been much interest in studying quasi-periodic events on earthquake models. Here we investigate quasi-periodic events in the avalanche time series on structured earthquake models by the analysis of the autocorrelation function and the fast Fourier transform. For random spatial earthquake models, quasi-periodic events are robust and we obtain a simple rule for a period that is proportional to the choice of unit time and the dissipation of the system. Moreover, computer simulations validate this rule for two-dimensional lattice models and cycle graphs, but our simulation results also show that small-world models, scale-free models, and random rule graphs do not have periodic phenomena. Although the periodicity of avalanche does not depend on the criticality of the system or the average degree of the system or the size of the system, there is evidence that it depends on the time series of the average force of the system.

GaN crystal growth on Ga-face and N-face of HVPE-GaN seeds was investigated using Na flux liquid phase epitaxial (LPE) method, respectively. The phase structure and morphology of as-grown GaN crystals were characterized using X-ray diffraction (XRD) and the scanning electron microscope (SEM), respectively. Under the growth temperature of 850 °C and keeping nitrogen pressure 3.0 MPa for 150 h, the typical pyramidal GaN poly-crystals with wurtize structure grew by spontaneous nucleation growth on the Ga-face of GaN -HVPE seeds. In contrast, GaN single crystals could be obtained by epitaxial growth on the N-face of GaN-HVPE seeds. From the observation of the side view of as-grown GaN crystals grown on the N-face, there were two apparent stages along the growth direction (-c direction) during the crystal epitaxial growth process. The typical hexagonal layered structure of as-grown GaN crystals occurred in the initial stage, and then the typical hexagonal pyramidal structure of it occurred in the second growth stage. In addition, from the observation of optical microscope, the as-grown GaN crystal with the initial growth stage only presented different morphology from that with the two-growth stage. The continuous lateral equilibrium epitaxial growth on N-face of GaN crystal seed may be of great significance for the growth of large size GaN single crystal.

Multi-modality examinations have been extensively applied in current clinical cancer management. Leveraging multi-modality medical images can be highly beneficial for automated tumor segmentation as they provide complementary information that could make the segmentation of tumors more accurate. This paper investigates CNN-based methods for automated nasopharyngeal carcinoma (NPC) segmentation using computed tomography (CT) and magnetic resonance (MR) images. Specially, a multi-modality convolutional neural network (M-CNN) is designed to jointly learn a multi-modal similarity metric and segmentation of paired CT-MR images. By jointly optimizing the similarity learning error and the segmentation error, the feature learning processes of both modalities are mutually guided. In doing so, the segmentation sub-networks are able to take advantage of the other modality's information. Considering that each modality possesses certain distinctive characteristics, we combine the higher-layer features extracted by a single-modality CNN (S-CNN) and M-CNN to form a combined CNN (C-CNN) for each modality, which is able to further utilize the complementary information of different modalities and improve the segmentation performance. The proposed M-CNN and C-CNN were evaluated on 90 CT-MR images of NPC patients. Experimental results demonstrate that our methods achieve improved segmentation performance compared to their counterparts without multi-modal information fusion and the existing CNN-based multi-modality segmentation methods.

Based on the Prisoner's Dilemma game, this paper investigates the evolution of extortion behavior with cooperation and defection strategies on the Barabasi-Albert (BA) scale-free network under the normalized payoff framework. Using Monte Carlo simulations, we show that the cooperation-extortion alliance emerges, and extortioners can act as catalysts to help cooperators survive on the scale-free network. Moreover, we find the non-trivial influence of the extortion factor on the evolution of cooperation, which implies that there exists an optimal value of the extortion factor with which the cooperation-extortion alliance is mostly favored and may defeat defectors on the networks with the normalized payoff framework.

The effects of annealing on the chemical states of N dopant, electrical, and optical properties of N-doped ZnO film grown by molecular beam epitaxy (MBE) are investigated. Both the as-grown ZnO:N film and the film annealed in N2 are of n-type conductivity, whereas the conductivity converts into p-type conductivity for the film annealed in O2. We suggest that the transformation of conductivity is ascribed to the change in ratio of the N molecular number on O site (N2)O to the N atom number on O site (NO) in ZnO:N films under the various annealed atmosphere. For the ZnO:N film annealed in N2, the percentage content of (N2)O is larger than that of NO, i.e. the ratio > 1, resulting in the n-type conductivity. However, in the case of the ZnO:N film annealed in O2, the percentage content of (N2)O is fewer than that of NO, i.e., the ratio < 1, giving rise to the p-type conductivity. There is an obvious difference between low-temperature (80 K) PL spectra of ZnO:N film annealed in N2 and that of ZnO:N film annealed in O2. An emission band located at 3.358 eV is observed in the spectra of the ZnO:N film after annealed in N2, this emission band is due to donor-bound exciton (D0X). After annealed in O2, the PL of the donor-bound exciton disappeared, an emission band located at 3.348 eV is observed, this emission band is assigned to acceptor-bound exciton (A0X).

We investigate the dynamics of random walks on weighted networks. Assuming that the edge's weight and the node's strength are used as local information by a random walker, we study two kinds of walks, weight-dependent walk and strength-dependent walk. Exact expressions for stationary distribution and average return time are derived and confirmed by computer simulations. We calculate the distribution of average return time and the mean-square displacement for two walks on the BBV networks, and find that a weight-dependent walker can arrive at a new territory more easily than a strength-dependent one., Comment: 4 pages, 5 figures. minor modifications. Comments and suggestions are favored by the authors

TiO2−xNx thin films are deposited onto Si(100) and quartz substrates by a rf magnetron sputtering method using a titanium metal disc as a target in Ar, N2, and O2 atmospheres. The substrate temperature is kept at 300°C. The O2 and Ar gas flow rates are kept to be constants and the N gas flow rate is varied. TiO2−xNx films with different N contents are characterized by x-ray diffraction and x-ray photoelectron spectroscopy. The results indicate that the TiO2−xNx thin films can be obtained at 13% N and 15% N contents in the film, and the films with mixed TiO2 and TiN crystal can be obtained at 13% N and 15% N contents in the film. In terms of the results of x-ray photoelectron spectroscopy, N 1s of β-N (396 eV) is the main component in the TiO2−xNx thin films. Because the energy level of β-N is positioned above the valence-band maximum of TiO2, an effective optical-energy gap decreases from 2.8 eV (for pure TiO2 film deposited by the same rf sputtering system) to 2.3 eV, which is verified by the optical-absorption spectra.

We investigate the origin of ultraviolet (UV) emission from Mg0.12Zn0.88O alloy thin films with a wurtzite structure fabricated on c-plane Al2O3 substrates by plasma assisted molecular beam epitaxy. At room temperature, the absorption edge and UV emission band of the Mg0.12Zn0.88O film shift to high-energy side compared with ZnO films. Temperature dependence of the photoluminescence spectra shows that the UV emission is composed of free exciton and neutral donor bound exciton emissions. Two-step dissociation processes of the UV emission are observed with the increasing temperature. The thermal quenching mechanism is attributed to the dissociation of the free exciton from the neutral donor bound exciton in the low temperature region and the dissociation of free electron and hole from the free exciton in the high temperature region.

A coupling structure of CdSe quantum dots (QDs) and a ZnCdSe quantum well (QW) is fabricated by using the molecular-beam epitaxy technique. The effect of temperature on the photoluminescence (PL) of the structure is studied. The results reveal that the activation energy of exciton dissociation in the coupling QDs/QW structure is much higher than that of simple CdSe QDs, which is attributed to the exciton tunnelling from the QW to QDs through a thin ZnSe barrier layer. The results also reveal that the position and width of the emission band of the QDs vary discontinuously at certain temperatures. This phenomenon is explained by the QD ionization and exciton tunnelling from the QW to the QDs. It is demonstrated that the coupling structure significantly improves the PL intensity of CdSe QDs.

Room-temperature P-band emission induced by an exciton–exciton collision process was observed in ZnO micro-rods. Both temperature- and excitation-intensity-dependent photoluminescence (PL) measurements were conducted. The excitation-intensity-dependent measurement illustrated that the P-band emission could occur at far lower excitation intensity than that reported in the literature. Higher-order transitions were also observed at the excitation intensity of 7.1 kW/cm2 or above. The temperature-dependent PL showed that the P-band emission process was thermally activated. It is suggested that both the density and activity of free excitons played important roles in the exciton–exciton collision process.

ZnTe films have been prepared on Si substrates by metal-organic chemical vapour deposition (MOCVD), and the temperature-dependent photoluminescence (PL) properties were investigated. The near-band-edge (NBE) emission of the ZnTe sample at 83 K shows an asymmetry line shape, which can be decomposed into two Gaussian lines labelled by FE and BE. Temperature-dependent PL intensity of the NBE peak shows two variation regions, and an expression with two dissociation channels fits well to the experimental data. The results of the temperature-dependent full width at half maximum (FWHM) and peak energy were well understood under the framework of the two-dissociation-channel model. That is, at low temperature, the emission from bound excitons governs the NBE peak, while above 157 K, the free exciton emission becomes dominant gradually. A simple model with three energy levels was employed to describe the variation in emission intensity of BE and FE with temperature.

A linear accelerator as a new injector for the Separated Sector Cyclotron at the Heavy Ion Research Facility of LAN Zhou is being designed. The Drift-Tube-Linac (DTL) has been designed to accelerate 238U34+ from 0.140 MeV/u to 0.97 MeV/u [1]. The 3D finite element analysis of thermal behavior is presented in this paper. During operation, the cavity will produce Joule heat. The cavity will not work normally due to the high temperature and thermal deformation will lead to frequency drift. So it is necessary to perform thermal analysis to ensure the correct working temperature is used. The result of the analysis shows that after the water cooling system is put into the cavity the temperature rise is about 20 degrees and the frequency drift is about 0.15%.

We present a simple and useful method for preparing high-quality nanocrystalline ZnO thin films, i.e. the thermal oxidation of high-quality ZnS films prepared by the low-pressure metal-organic chemical vapour deposition technique. The x-ray diffraction measurements reveal that the nanocrystalline ZnO has a hexagonal wurtzite structure. Raman spectra show that the longitudinal optical phonon with the E1-mode appears at 578 cm-1. The multiple phonon scattering process is also observed, indicating the formation of a high-quality nanocrystalline ZnO thin film. The photoluminescence spectrum has a single emission peak at 3.264 eV from the free-exciton mission, under the condition of low excitation power at room temperature. However, when excitation intensities exceed the threshold of 150 kW/cm2, a new and narrow peak emerges at lower energies, which are attributed to exciton-exciton collisions, and is called the P line. The intensity of this peak increases superlinearly with the pumping power over a threshold value. This supplies strong evidence of stimulated emission. The multiple longitudinal cavity modes observed in the stimulated emission spectrum indicate the successful realization of optically pumped lasing from nanocrystalline ZnO films at room temperature.

A series of Cd0.44Zn0.56Se/ZnSe sandwich structures with different Cd0.44Zn0.56Se embedded layer thicknesses were fabricated by metal organic chemical vapor deposition. When the embedded layer thickness exceeded 3.0 nm, the photoluminescence spectra of the sample changed into the two-band structure from the one-band structure, and atomic force microscopy images indicate that Cd0.44Zn0.56Se quantum dots were formed. In the two-band photoluminescence spectrum, the band at the low energy side was attributed to be from quantum dots, and the high-energy one arose from the wetting layer. Thinning of the wetting layer with quantum dots forming was confirmed indirectly by the significant blue shift of the wetting-layer photoluminescence band compared to the photoluminescence band of the samples for which the Cd0.44Zn0.56Se layer thickness was less than 3.0 nm. This thinning arose from mass migration during the Stranski–Krastanow growth of Cd0.44Zn0.56Se quantum dots.

The influence of nitrogen on the microstructure of a-C:H film is investigated by infrared, photoluminescence (PL), and transmittance-reflectance spectra. It is indicated that nitrogen incorporation into a-C:H network will weaken some C-H bonds, which is confirmed by differential scanning calorimeter experimental results. It is also demonstrated that nitrogen entering into a-C:H film can raise luminescence intensity. On the other hand, nitrogenation will reduce PL thermal stability.

The room-temperature blue cathodoluminescence (CL) from highly Er-doped ZnO thin films has been studied by using different electron beam currents (EBCs). The ZnO:Er thin films used in our experiment were prepared by simultaneous evaporation from two sources. The x-ray diffraction spectra show that the thin films have a strong preferential c-axis (0002) orientation with a hexagonal crystalline structure. The blue emission at 455 nm originating from the intra-4f shell transition (4F5/24I15/2) in Er3+ ions was observed at room temperature. The nonlinear dependence of the CL intensity on the EBC shows a more intense blue emission above the threshold EBC of 0.6 µA, which is attributed to the phonon bottleneck effect.

We study the optical properties of ZnCdSe/ZnMgSe multiple quantum wells using photoluminescence (PL) and Raman scattering spectra. In the PL spectra, an intense emission band coming from the free exciton luminescence of the quantum wells can be observed from 80 K to 300 K. The exciton binding energy is evaluated by the dependence of PL intensity on the temperature, showing the behaviour of the better two-dimensional excitons. The result indicates that the enhancement of the confinement effect is due to containing Mg in the barrier layers. At room temperature, Raman scattering spectra are classified into confined optical modes and folded optical modes. This confirms the formation of a multilayer system with a higher crystalline quality.

A temperature-dependent photoluminescence measurement is performed in CdSe/ZnSe quantum dots with a ZnCdSe quantum well. We deduce the temperature dependence of the exciton linewidth and peak energy of the zero-dimensional exciton in the quantum dots and two-dimensional exciton in the CdSe wetting layer. The experimental data reveal a reduction of homogeneous broadening of the exciton line in the quantum dots in comparison with that in the two-dimensional wetting layer, which indicates the decrease of exciton and optical phonon coupling in the CdSe quantum dots.

We study the photoluminescence (PL) of ultra thin layer ZnSe quantum wells in ZnS barriers. Samples with different well widths are grown by vapour phase epitaxy and the PL spectra of these samples are measured by the excitation of a 500 W Hg lamp. The peak positions of the bands coming from the excitonic luminescence show a larger blueshift with respect to the energy of free excitons in the ZnSe bulk material. The observed variation of the full width at half maximum and peak position of the bands in the spectra with the well width are interpreted to the formation of the ZnSxSe1-x alloy layer due to the interdiffusion in the interfaces between ZnSe and ZnS. According to the behaviour of the excitons in the smaller conduction band offset, the exciton binding energy is estimated from the dependence of the PL intensity on the temperature. From this result, excitons seem to show nearly three-dimensional characteristics.

The effects of thermal annealing on photoluminescence (PL) and structural properties of a-Si1-xCx:H films deposited by plasma enhanced chemical vapour deposition from CH4+SiH4 mixtures are studied by using infrared, PL and transmittance-reflectance spectra. In a-SiC:H network, high-temperature annealing gives rise to the effusion of hydrogen from strongly bonded hydrogen in SiH, SiH2, (SiH2)n, SiCHn and CHn configurations and the break of weak C-C, Si-Si and C-Si bonds. A structural rearrangement will occur, which causes a significant correlation of the position and intensity of the PL signal with the annealing temperature. The redshift of the PL peak is related to the destruction of the confining power of barriers. However, the PL intensity does not have a significant correlation with the annealing temperature for a C-rich a-SiC:H network, which refers to the formation of π-bond cluster as increasing carbon content. It is indicated that the thermal stability of C-rich a-Si1-xCx:H films is better than that of Si-like a-Si1-xCx:H films. PACS: 78. 55. Hx, 78. 66. Jg, 61. 43. Dq

High quality AlN thin films doped with TbF3 were prepared by rf magnetron reaction sputtering. High purity Al metal and TbF3 were used as target materials with N2 and Ar as sputtering gases. The influence of preparation conditions on the photoluminescence brightness was studied, and the electroluminescence was found to have a similar dependence on the concentration of TbF3 and substrate temperature. The characteristic emission of Tb3+ ions was obtained in an AlN:TbF3 alternating current thin film electroluminescence device prepared with 600° C substrate temperature and 4.0 mol% concentration of TbF3.

Individual heterogeneity in the reproductive rate is found to play an important role in the emergence and persistence of cooperation. Most of the existing literature focused mainly on the enhancement of cooperation by the introduction of inhomogeneous teaching capability of the individuals. It is far from clear how the heterogeneous learning ability of the individuals affects the evolution of cooperation. To fill this research gap, we make comparative studies of the evolutionary spatial prisoner's dilemma game with reduced learning or teaching ability of the players, under both synchronous and asynchronous strategy updating schemes. By carrying out extensive computer simulations, we show that cooperation can always be facilitated if the inhomogeneous teaching ability of the players is considered, irrespectively of the strategy updating manner. By contrast, cooperation is promoted (inhibited) in the case of synchronous (asynchronous) strategy updating, if heterogeneous learning ability is considered, which is attributed to the reduced ability of cooperators to expand their domains.

Recently, a class of interesting strategies, named extortion strategies, has attracted considerable attention since such extortion strategies can dominate any opponent in a repeated prisoner's dilemma game. In this paper, we investigate the influence of the strategy-selection timescale on the evolution of extortion and cooperation in networked systems. Through connecting the lifetime of individuals' strategies with their fitness, we find that extortioners can form long-term stable relationships with cooperative neighbors, whereas the lifetime of a defection strategy is short according to the myopic best response rule. With the separation of interaction and strategy-updating timescales, the extortioners in a square lattice are able to form stable, cross-like structures with cooperators due to the snowdrift-like relation. In scale-free networks the hubs are most likely occupied by extortioners, who furthermore induce their low-degree neighbors to behave as cooperators. Since extortioners in scale-free networks can meet more cooperators than their counterparts in the square lattice, the latter results in higher average fitness of the whole population than the former. The extortioners play the role of a catalyst for the evolution of cooperation, and the diversity of strategy-selection timescale furthermore promotes the maintenance of extortioners with cooperators in networked systems.

The Raman scattering in Zn0.74Cd0.26Se/ZnSe superlattices under hydrostatic pressures up to 4.53 GPa at room temperature has been studied. The pressure-dependences of the ZnSe-like LO-phonon (LOb) and the Zn0.74Gd0.26Se-like LO-phonon (LOw) have been obtained. At 2.7 GPa, the pressure-coefficients of both LOb and LOw phonon energies increase abruptly. The 2LOw-phonon resonance has been observed at 1.82 GPa with 488.0 nm excitation for the Zn0.75Cd0.25Se/ZnSe superlattices.

Despite extensive work on the interplay between traffic dynamics and epidemic spreading, the control of epidemic spreading by routing strategies has not received adequate attention. In this paper, we study the impact of an efficient routing protocol on epidemic spreading. In the case of infinite node-delivery capacity, where the traffic is free of congestion, we find that that there exist optimal values of routing parameter, leading to the maximal epidemic threshold. This means that epidemic spreading can be effectively controlled by fine tuning the routing scheme. Moreover, we find that an increase in the average network connectivity and the emergence of traffic congestion can suppress the epidemic outbreak.

Whether or not to change behavior depends not only on the personal success of each individual, but also on the success and/or behavior of others. Using this as motivation, we incorporate the impact of peer pressure into a susceptible-vaccinated-infected-recovered (SVIR) epidemiological model, where the propensity to adopt a particular vaccination strategy depends both on individual success as well as on the strategies of neighbors. We show that plugging into the peer pressure is a double-edged sword, which, on the one hand, strongly promotes vaccination when its cost is below a critical value, but, on the other hand, it can also strongly impede it if the critical value is exceeded. We explain this by revealing a facilitated cluster formation process that is induced by the peer pressure. Due to this, the vaccinated individuals are inclined to cluster together and therefore become unable to efficiently inhibit the spread of the infectious disease if the vaccination is costly. If vaccination is cheap, however, they reinforce each other in using it. Our results are robust to variations of the SVIR dynamics on different population structures.

In this paper, we investigate a networked prisoner's dilemma game where individuals' strategy-selection time scale evolves based on their historical learning information. We show that the more times the current strategy of an individual is learnt by his neighbors, the longer time he will stick on the successful behavior by adaptively adjusting the lifetime of the adopted strategy. Through characterizing the extent of success of the individuals with normalized payoffs, we show that properly using the learned information can form a positive feedback mechanism between cooperative behavior and its lifetime, which can boost cooperation on square lattices and scale-free networks.

We study evolutionary games on scale-free networks with tunable degree distribution. The heterogeneity of networks is controlled by the exponent of power-law degree distribution. It is found that there exists an optimal value of the exponent, for which the level of cooperation becomes highest. This phenomenon indicates that, although degree heterogeneity plays an important role in maintaining cooperation, too strong heterogeneity may counterintuitively encourage defection. We observe that, for strong heterogeneity, large-degree nodes are no longer certainly occupied by cooperators. Our results yield insights into the effect of degree heterogeneity on cooperation.

One of the prototypical mechanisms in understanding the ubiquitous cooperation in social dilemma situations is the win?stay, lose?shift rule. In this work, a generalized win?stay, lose?shift learning model?a reinforcement learning model with dynamic aspiration level?is proposed to describe how humans adapt their social behaviors based on their social experiences. In the model, the players incorporate the information of the outcomes in previous rounds with time-dependent aspiration payoffs to regulate the probability of choosing cooperation. By investigating such a reinforcement learning rule in the spatial prisoner's dilemma game and public goods game, a most noteworthy viewpoint is that moderate greediness (i.e.?moderate aspiration level) favors best the development and organization of collective cooperation. The generality of this observation is tested against different regulation strengths and different types of network of interaction as well. We also make comparisons with two recently proposed models to highlight the importance of the mechanism of adaptive aspiration level in supporting cooperation in structured populations.