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Generally, the 5th Generation (5G) network will be soon available in the near future. It will be one with the feature that some of its network functions are handled by Virtual Machines (VMs), rather than by a dedicated one (like that in the 4th generation (4G) networks). Basically, VMs of a specific network function are managed by their own Software Defined Networking (SDN) Controller, which makes the management and operation of these VMs and OpenvSwitches become easier. On the other hand, the connection between Internet of Things (IoT) devices and a network is often intermittent. Consequently, Authentication Server Function (AUSF) has to frequently authenticate these devices. This is also one of the reasons why a 5G network will prepare an AUSF Pool to distribute its authentication burden, particularly when a huge number of user equipment (UEs) and IoT devices are connected to it. Next, when a VM fails, how do other AUSFs take over for the failed to continue the authentication tasks? This is not completely defined in 5G specifications. In this study, we propose a fault tolerant mechanism for 5G end-device authentication, named Fault Tolerant 5G Authentication Scheme (FT5AS), in which a machine, named Mediator, is added to manage and keep track of authentication steps for end devices. The purpose is that when a VM fails, other AUSFs can successfully take over its authentication tasks on UEs. Also, the FT5AS can detect this failure immediately and react properly, aiming to increase the Quality of Service (QoS) that an UE can receive from 5G networks. Our simulation results indicate that the FT5AS is feasible and its performance is not lower than that of tested schemes.

In this work, different thick TiN thin films were prepared by pulsed laser deposition on GaN substrates at 650°C. The crystal structure and morphology are characterized by X-ray Diffraction and Atomic Force Microscopy. We characterized the sample by cathodoluminescence spectroscopy at room temperature and measured the thickness of the film by a cross-sectional scanning electron microscopy. Combining the attenuation of light intensity and the thickness, the absorption coefficient of the samples can be estimated by the Beer-Lambert law. The absorption coefficients of TiN metal thin film obtained here are closed with each other. The optical properties may not change with increasing thickness.

A modified quantum dots (QDs) structure model is developed in this study. Compared with the traditional model, the gradual composition transition at the interface between the QDs and matrix is taken into account in the modified model. Two dimensional electron gas (2DEG) mobility limited by QDs scattering is studied based on the modified model. The result is compared with the one based on the traditional model. It is found that the contribution of the gradual composition transition region to the electron mobility is too significant to be negligible, especially in the case of high 2DEG density or small QDs radius.

Nowadays encryption is a common technique to protect image data from unauthorized access. In recent years, many scientists have proposed various encryption algorithms based on DNA sequence to provide a new idea for the design of image encryption algorithm. Therefore, a new method of image encryption based on DNA computing technology is proposed in this paper, whose original image is encrypted by DNA coding and 1-D logistic chaotic mapping. First, the algorithm uses two modules as the encryption key. The first module uses the real DNA sequence, and the second module is made by one-dimensional logistic chaos mapping. Secondly, the algorithm uses DNA complementary rules to encode original image, and uses the key and DNA computing technology to compute each pixel value of the original image, so as to realize the encryption of the whole image. Simulation results show that the algorithm has good encryption effect and security.

The role of dislocation scattering in electron mobility in ZnMgO/ZnO heterostructures was studied. It was found that dislocation scattering was dominant in the low-electron concentration region. The total low-temperature mobility was calculated by considering dislocation scattering and interface-roughness scattering (IRS) together. The sheet density of dislocations was chosen as Ndis=1.5 × 108 cm-2 and the IRS parameters were Δ = 5.206 and Λ = 30 Å. We obtained a good fit between our calculated results and experimental data reported in the works referenced.

The PROSAIL canopy radiative transfer model was used to establish leaf area index (LAI) and canopy reflectance lookup-table for Moso bamboo forest. The combination of Landsat Thematic Mapper (TM) image and this model was then used to retrieve LAI. The results demonstrated that the sensitivity of the input parameters in the PROSAIL model decreased in order of LAIchlorophyll content (C(ab))leaf structure parameters (N)mean leaf angle (ALA)equivalent water thickness (C(w))dry matter content (C(m)). The most sensitive factors LAI and C(ab) were then used to construct the LAI-canopy reflectance lookup-table. The LAI estimates from the PROSAIL model had good agreement with the reference data, with the coefficient of determination (R2) reached 0.90. The root mean square error (RMSE) and relative RMSE were 0.58 and 13.0%, respectively. However, the mean LAI estimate was higher than the observed value.

By using x-ray diffraction analysis, we investigate the major structural parameters such as strain state and crystal quality of non-polar a-plane InxGa1−xN thin films grown on r-sapphire substrates by metalorganic chemical vapour deposition. The results of the inplane grazing incidence diffraction technique are analyzed and compared with a complementary out-of-plane high resolution x-ray diffraction technique. When the indium composition is low, the a-plane InxGa1−xN layer is tensile strain in the growth direction (a-axis) and compressive strain in the two in-plane directions (m-axis and c-axis). The strain status becomes contrary when the indium composition is high. The stress in the m-axis direction σyy is larger than that in the c-axis direction σzz. Furthermore, strain in the two in-plane directions decrease and the crystal quality becomes better with the growing of the InxGa1−xN film.

We theoretically study the influence of spacer layer thickness fluctuation (SLTF) on the mobility of a two-dimensional electron gas (2DEG) in the modulation-doped AlxGa1−xAs/GaAs/AlxGa1−xAs quantum well. The dependence of the mobility limited by SLTF scattering on spacer layer thickness and donor density are obtained. The results show that SLTF scattering is an important scattering mechanism for the quantum well structure with a thick well layer.

We calculate the electron mobility limited by the AlxGa1−xN barrier and the GaN well thickness fluctuations scattering of the two-dimensional electron gas (2DEG) at AlxGa1−xN/GaN multi-quantum wells (MQWs) with a triangle potential well. For this potential well, the ground subband energy is governed by the spontaneous and piezoelectric polarization fields and the fields are determined by the barrier and well thicknesses in undoped AlxGa1−xN/GaN MQWs. Thus, the thickness fluctuations of AlxGa1−xN barrier and GaN well will cause a local fluctuation of the ground subband energy, which will reduce the 2DEG mobility.

The morphological evolution of a-GaN deposited by metalorganic chemical vapor deposition (MOCVD) on r-sapphire is studied. The influences of V/III ratio and growth temperature on surface morphology are investigated. V-pits and stripes are observed on the surface of a-GaN grown at 1050°C and 1100°C, respectively. The overall orientation and geometry of V-pits are uniform and independent on the V/III molar ratio in the samples grown at 1050°C, while in the samples grown at 1100°C, the areas of stripes decrease with the adding of V/III ratio. We deduce the origin of V-pits and stripes by annealing the buffer layers at different temperatures. Because of the existence of inclined (101) facets, V-pits are formed at 1050°C. The (101) plane is an N terminated surface, which is metastable at higher temperature, so stripes instead of V-pits are observed at 1100°C. Raman spectra suggest that the growth temperature of the first layer in the two-step process greatly affects the strain of the films. Hence, to improve the growth temperature of the first layer in the two-step method may be an effective way to obtain high quality a-GaN film on r-sapphire.