Research on Efficiency and Security for Emerging Distributed Applications

Distributed computing has never stopped its advancement since the early years of computer systems. In recent years, edge computing has emerged as an extension of cloud computing. The main idea of edge computing is to provide hardware resources in proximity to the end devices, thereby offering low network latency and high network bandwidth. However, as an emerging distributed computing paradigm, edge computing currently lacks effective system support. To this end, this dissertation studies the ways of building system support for edge computing. We first study how to support the existing, non-edge-computing applications in edge computing environments. This research leads to the design of a platform called SMOC that supports executing mobile applications on edge servers. We consider mobile applications in this project because there are a great number of mobile applications in the market and we believe that mobile-edge computing will become an important edge computing paradigm in the future. SMOC supports executing ARM-based mobile applications on x86 edge servers by establishing a running environment identical to that of the mobile device at the edge. It also exploits hardware virtualization on the mobile device to protect user input. Next, we investigate how to facilitate the development of edge applications with system support. This study leads to the design of an edge computing framework called EdgeEngine, which consists of a middleware running on top of the edge computing infrastructure and a powerful, concise programming interface. Developers can implement edge applications with minimal programming effort through the programming interface, and the middleware automatically fulfills the routine tasks, such as data dispatching, task scheduling, lock management, etc., in a highly efficient way. Finally, we envision that consensus will be an important building block for many edge applications, because we consider the consensus problem to be the most important fundamental problem in distributed computing while edge computing is an emerging distributed computing paradigm. Therefore, we investigate how to support the edge applications that rely on consensus, helping them achieve good performance. This study leads to the design of a novel, Paxos-based consensus protocol called Nomad, which rapidly orders the messages received by the edge. Nomad can quickly adapt to the workload changes across the edge computing system, and it incorporates a backend cloud to resolve the conflicts in a timely manner. By doing so, Nomad reduces the user-perceived latency as much as possible, outperforming the existing consensus protocols

An Experimental Study on the Determination of Shale <i>K</i>_IC by Semi-Disk Three-Point Bending

In order to accurately test the KIC of the vertical stratification direction of shale, a semi-circular bending specimen with a linear chevron notch ligament (LCNSCB) was designed. The minimum dimensionless stress intensity factor (Y*min) of the LCNSCB specimen was calculated by the finite element method and the slice synthesis method, respectively. Two sets of prefabricated samples of the LCNSCB specimen under arrester and divider mode were used to conduct three-point bending loading experiments. The dispersion of the measured KIC value of the specimens was analyzed by standard deviation and coefficient of variation, and the reason that the KIC dispersion of specimens in divider mode was larger than in arrester mode was discussed. Compared with the experimental data of the existing literature, the data of this experiment shows that the LCNSCB specimen can avoid the disadvantage of lower measured KIC values due to a larger fracture processing zone featured in the CSTSCB and CCNBD specimens, combined with the merits of a shorter fracture processing zone of the SR or CR specimens, and the render measured the KIC value to be closer to the material’s true fracture toughness value. The narrow ligament of the LCNSCB specimen has a favorable crack propagation guiding effect, can generate consistent KIC values, and could be used to accurately test the fracture toughness of rock material in vertical bedding direction

Numerical Simulation of the Effect of Freeze-Thaw Cycles on the Axial Compression Strength of Rubber Concrete

The incorporation of rubber can enhance concrete’s durability and effectively reduce the damage caused by freeze-thaw cycling (FTC). Still, there has been only limited research on the damage mechanism of RC at the fine view level. To gain insight into the expansion process of uniaxial compression damage cracks in rubber concrete (RC) and summarize the internal temperature field distribution law during FTC, a fine RC thermodynamic model containing mortar, aggregate, rubber, water, and interfacial transition zone (ITZ) is established in this paper, and the cohesive element is selected for the ITZ part. The model can be used to study the mechanical properties of concrete before and after FTC. The validity of the calculation method was verified by comparing the calculated results of the compressive strength of concrete before and after FTC with the experimental results. On this basis, this study analyzed the compressive crack extension and internal temperature distribution of RC at 0, 5, 10, and 15% replacement rates before and after 0, 50, 100, and 150 cycles of FTC. The results showed that the fine-scale numerical simulation method can effectively reflect the mechanical properties of RC before and after FTC, and the computational results verify the applicability of the method to rubber concrete. The model can effectively reflect the uniaxial compression cracking pattern of RC before and after FTC. Incorporating rubber can impede temperature transfer and reduce the compressive strength loss caused by FTC in concrete. The FTC damage to RC can be reduced to a greater extent when the rubber incorporation is 10%

Numerical Simulation of Fatigue Life of Rubber Concrete on the Mesoscale

Rubber concrete (RC) exhibits high durability due to the rubber admixture. It is widely used in a large number of fatigue-resistant structures. Mesoscale studies are used to study the composition of polymers, but there is no method for fatigue simulation of RC. Therefore, this paper presents a finite element modeling approach to study the fatigue problem of RC on the mesoscale, which includes the random generation of the main components of the RC mesoscale structure. We also model the interfacial transition zone (ITZ) of aggregate mortar and the ITZ of rubber mortar. This paper combines the theory of concrete damage to plastic with the method of zero-thickness cohesive elements in the ITZ, and it is a new numerical approach. The results show that the model can simulate reasonably well the random damage pattern after RC beam load damage. The damage occurred in the middle of the beam span and tended to follow the ITZ. The model can predict the fatigue life of RC under various loads