Civil Aviation University of China

About: Civil Aviation University of China is a education organization based out in Tianjin, China. It is known for research contribution in the topics: Air traffic control & Civil aviation. The organization has 5647 authors who have published 4559 publications receiving 29825 citations. The organization is also known as: Zhōngguó Mínháng Dàxué.

Optimal replacement policy with minimal repair and preventive maintenance of an aircraft structure subjected to corrosion

Abstract: This study focuses on a replacement policy using preventive maintenance and periodic inspections with minimal repairs for a deteriorating aircraft structure suffering from corrosion damage. The type of structure component operates normally when its cumulative corroded depth that does not exceed the maintenance allowance threshold and satisfies the reliability requirement. We assume that the number of minimal repairs and preventive maintenance time are both stochastic variables with a independent geometric distribution, and the lifetime has a Weibull distribution. An optimal replacement model is formulated to minimize the expected cost rate with two constraints: corrosion threshold and reliability level. The optimal time interval $$T^{*}$$ between the two successive periodic inspections with minimal repairs and the number of preventive maintenance $$N^{*}$$ can be obtained by an improved iteration algorithm using the golden section method and quadratic interpolation method based on stochastic simulation. Finally, a numerical example using parameters sensitivity analysis is illustrated to verify the proposed model and algorithm.

A Three-Layer Defense Mechanism Based on WEB Servers Against Distributed Denial of Service Attacks

Abstract: It is widely recognized that distributed denial of service (DDoS) attacks can disrupt web service and cause large revenue losses. However, effective defenses continue to be mostly unavailable. We design a novel DDoS security mechanism, which is a three-layer defense mechanism based on Web servers. Combining the characteristic of the traffic of web servers and aiming at TCP/IP reference model, it utilizes the means of statistical filtering and traffic limit in the network layer, transport layer and application layer to filter the illegitimate traffic to secure the pass of the normal traffic. A majority of illegitimate traffic is filtered by the algorithm of SHCF (Simplified Hop Count Filtering) on network layer. The rest of illegitimate traffic is filtered by the algorithm of SYN Proxy Firewall on transmission layer. And traffic limit is used on the application layer for DDoS attacks using legitimate IP. By the collaborative defense of the three-layer mechanism, sustaining availability of Web services can be ensured under DDoS attacks. The defense mechanism is implemented and tested inside the Linux kernel. The result indicates that the three-layer defense mechanism can defend DDoS attacks effectively.

Life-cycle performance prediction for rigid runway pavement using artificial neural network

Abstract: Pavement performance of airport runway plays a key role in the process of aircraft landing and takeoff. To predict runway pavement performance in life cycle, a novel artificial neural network (ANN)...

Theoretical Investigations of Si-Ge Alloys in P4₂/ncm Phase: First-Principles Calculations.

Abstract: The structural, mechanical, anisotropic, electronic and thermal properties of Si, Si0.667Ge0.333, Si0.333Ge0.667 and Ge in P42/ncm phase are investigated in this work. The calculations have been performed with an ultra-soft pseudopotential by using the generalized gradient approximation and local density approximation in the framework of density functional theory. The achieved results for the lattice constants and band gaps of P42/ncm-Si and P42/ncm-Ge in this research have good accordance with other results. The calculated elastic constants and elastic moduli of the Si, Si0.667Ge0.333, Si0.333Ge0.667 and Ge in P42/ncm phase are better than that of the Si, Si0.667Ge0.333, Si0.333Ge0.667 and Ge in P42/mnm phase. The Si, Si0.667Ge0.333, Si0.333Ge0.667 and Ge in P42/ncm phase exhibit varying degrees of mechanical anisotropic properties in Poisson’s ratio, shear modulus, Young’s modulus, and universal anisotropic index. The band structures of the Si, Si0.667Ge0.333, Si0.333Ge0.667 and Ge in P42/ncm phase show that they are all indirect band gap semiconductors with band gap of 1.46 eV, 1.25 eV, 1.36 eV and 1.00 eV, respectively. In addition, we also found that the minimum thermal conductivity κmin of the Si, Si0.667Ge0.333, Si0.333Ge0.667 and Ge in P42/ncm phase exhibit different degrees of anisotropic properties in (001), (010), (100) and (01¯0) planes.