Simulation of current spreading for GaN-based light-emitting diodes

Uniform current spreading is crucial for the performance of light-emitting diodes (LEDs). It has been reported that the reliability and light distribution are affected by non-uniform current spreading. In this paper, the impact of different electrode patterns on the performance of LED chips is investigated. A hybrid modeling method is employed to analyze the electrical and thermal characteristics of LEDs with two different electrode mesa structures. Corresponding experiments are also carried out to validate the calculation results. It is found that increasing amount of p-electrodes in interdigitated electrode patterns is effective in improving the performance of LEDs.     

Mechanics and energy analysis on molten pool spreading during laser solid forming

This paper studies the issue that the molten pool width gradually increases under some conditions during laser solid forming (LSF), which can decrease the shape and dimension accuracy of LSFed component to a large extent. By using the statics analysis method and calculating the interfacial tensions at the solid-liquid-gas triple point of molten pool, the proposed two-dimensional (2D) cross-sectional model of single deposition layer illustrates qualitatively that the deposition width would increase with the increasing pool temperature at a certain powder feeding rate, which we called the pool spread behavior here. Meanwhile, by calculating the maximum equilibrium contact angle for keeping solid-liquid-gas triple point balance, it is found that the molten pool is solidified during non-equilibrium state. Furthermore, in order to control the pool temperature and decrease pool spread amount, the optimal match of pool energy and mass inputs is determined for obtaining an optimum balance between the energy input and deposition efficiencies.     

Spatial‐temporal basic reproduction number and dynamics for a dengue disease diffusion model

A reaction‐diffusion system with free boundary is proposed to describe the transmission of the dengue disease from mosquitoes to humans. In addition to the classical basic reproduction number R₀, the spatial‐temporal basic reproduction number is introduced to determine the persistence and eradication of the disease. Some sufficient conditions for the disease vanishing or spreading are obtained. The disease will go extinct under one of the conditions: the classical basic reproduction number R₀ < 1 and the spatial‐temporal basic reproduction number with small expanding capability. The spread of the disease in the whole area is possible if for some t≥0. Numerical simulations are also given to illustrate the theoretical results.     

一类病毒自身发生变异的传染病模型的近似解

针对一类病毒变异前后传染病患者具有不同传染率的情形,利用同伦映射方法,得到其相应分阶段传播的动力学生态模型的渐近解.     

Time-varying human mobility patterns with metapopulation epidemic dynamics

In this paper, explicitly considering the influences of an epidemic outbreak on human travel, a time-varying human mobility pattern is introduced to model the time variation of global human travel. The impacts of the pattern on epidemic dynamics in heterogeneous metapopulation networks, wherein each node represents a subpopulation with any number of individuals, are investigated by using a mean-field approach. The results show that the pattern does not alter the epidemic threshold, but can slightly lower the final average density of infected individuals as a whole. More importantly, we also find that the pattern produces different impacts on nodes with different degree, and that there exists a critical degree _kc$k_c$. For nodes with degree smaller than _kc$k_c$, the pattern produces a positive impact on epidemic mitigation; conversely, for nodes with degree larger than _kc$k_c$, the pattern produces a negative impact on epidemic mitigation.     

Rumor spreading on random regular graphs and expanders

Broadcasting algorithms are important building blocks of distributed systems. In this work we investigate the typical performance of the classical and well‐studied push model. Assume that initially one node in a given network holds some piece of information. In each round, every one of the informed nodes chooses independently a neighbor uniformly at random and transmits the message to it. In this paper we consider random networks where each vertex has degree d ≥ 3, i.e., the underlying graph is drawn uniformly at random from the set of all d ‐regular graphs with n vertices. We show that with probability 1 ‐ o(1) the push model broadcasts the message to all nodes within (1 + o(1))C_d lnn rounds, where Particularly, we can characterize precisely the effect of the node degree to the typical broadcast time of the push model. Moreover, we consider pseudo‐random regular networks, where we assume that the degree of each node is very large. There we show that the broadcast time is (1 + o(1))Clnn with probability 1 ‐ o(1), where \begin{align*}C = \lim_{d\to\infty}C_d = \frac{1}{\ln2} + 1\end{align*}. © 2012 Wiley Periodicals, Inc. Random Struct. Alg., 2013     

Study of carrier concentration profiles in Al‐implanted Ge by micro‐Raman spectroscopy under different excitation wavelengths

The distribution profile of Al implanted in crystalline Ge has been investigated by micro‐Raman spectroscopy. Using different excitation laser lines, corresponding to different optical penetration depths, the Al concentration at different depths beneath the sample surface has been studied. We have found a strong correlation between the intensity of the Al–Ge Raman peak at ~370 cm⁻¹, which is due to the local vibrational mode of substitutional Al atoms, and the carrier concentration profile, obtained by the spreading resistance profiling analysis. A similar connection has been also observed for both shape and position of the Ge–Ge Raman peak at ~300 cm⁻¹. According to these experimental findings, we propose here a fast and nondestructive method, based on micro‐Raman spectroscopy under different excitation wavelengths, to estimate the carrier concentration profiles in Al‐implanted Ge. Copyright © 2013 John Wiley & Sons, Ltd.     

Reducing mosquito-borne disease outbreak size: The relative importance of contact and transmissibility in a network model

The complex biological and environmental factors involved in the transmission of mosquito-borne diseases in humans have made their control elusive in many instances. Conceptual models contribute to gain insight and help to reduce the risk of taking poor managerial decisions. The focus of this paper is to compare, using a contact network model, the impact that perturbation of the number infectious contacts and of transmissibility have on the size of an outbreak. We illustrate the analysis on a contact network parametrized with data that associates humans and the mosquito Culex quinquefasciatus, a vector for lymphatic filariasis. The model suggests that, if the values corresponding to transmissibility and number of infectious contacts is relatively large, variations in the size of an outbreak are significantly in favor of control measures to reduce infectious contacts.     

Spreading of spatially partially coherent polychromatic beams in atmospheric turbulence

Taking the polychromatic Gaussian Schell-model (GSM) beam as a typical example of spatially partially coherent polychromatic beams, the spreading of polychromatic GSM beams in atmospheric turbulence is studied. The mean-squared width of polychromatic GSM beams in turbulence is derived by using the effective source and the strong fluctuation models. It is shown that the same result is obtained using both the models. The diffraction, atmospheric turbulence and beam polychroism result in a spreading of polychromatic GSM beams. If the scaling law fails, the spreading of polychromatic GSM beams increases with increasing bandwidth Γ, but the influence of Γ on the spreading of polychromatic GSM beams becomes small as the structure constant C_n² of the refractive index and spatial correlation parameter α increase. The spreading of polychromatic GSM beams increases as C_n² increases and α decreases. Spatially partially coherent polychromatic beams are less sensitive to the effects of atmospheric turbulence than spatially fully coherent polychromatic beams.     

Criticality of Parasitic Disease Transmission in a Diffusive Population

Through using the methods of finite-size effect and short time dynamic scaling, we study the critical behavior of parasitic disease spreading process in a diffusive population mediated by a static vector environment. Through comprehensive analysis of parasitic disease spreading we find that this model presents a dynamical phase transition from disease-free state to endemic state with a finite population density. We determine the critical population density, above which the system reaches an epidemic spreading stationary state. We also perform a scaling analysis to determine the order parameter and critical relaxation exponents. The results show that the model does not belong to the usual directed percolation universality class and is compatible with the class of directed percolation with diffusive and conserved fields.