Mode III fracture analysis by Trefftz boundary element method

This paper presents a hybrid Trefftz (HT) boundary element method (BEM) by using two indirect techniques for mode III fracture problems. Two Trefftz complete functions of Laplace equation for normal elements and a special purpose Trefftz function for crack elements are proposed in deriving the Galerkin and the collocation techniques of HT BEM. Then two auxiliary functions are introduced to improve the accuracy of the displacement field near the crack tips, and stress intensity factor (SIF) is evaluated by local crack elements as well. Furthermore, numerical examples are given, including comparisons of the present results with the analytical solution and the other numerical methods, to demonstrate the efficiency for different boundary conditions and to illustrate the convergence influenced by several parameters. It shows that HT BEM by using the Galerkin and the collocation techniques is effective for mode III fracture problems

Fracture analysis of mode iii problems by the Trefftz boundary element approach

"Trefftz approach can be referred to the boundary-type solution procedure employing the regular T-complete function satisfying the governing equation. Since Trefftz [1] in 1926 applied his approach that was forced to satisfy the boundary condition to achieve the outcomes, numerous papers, concerning fundamentals, applications and analysis, have emerged in the literature. For the Trefftz boundary element method, Cheung et al [2] developed a direct formulation for solving two-dimensional potential problem. Kita et al [3] studied the same problem by the direct formulation and domain decomposition approach. Portela and Charafi [4] applied Trefftz Boundary element formulation to potential problems with thin internal or edge cavities. Sladek et al [5] presented a global and local Trefftz bpundary integral approach to solve Helmholtz equation. Domingues et al [6] extended the Trefftz boundary element approach to the analysis of linear elastic fracture mechanics. Most of the developments in the field can also be found in [7]."--p. 321

In-situ X-ray radiography of twinned crystal growth of primary Al13Fe4

The faceted growth of primary Al13Fe4 intermetallic compounds was studied using in-situ X-ray radiography in a solidifying Al-3Fe alloy. Microscopic twins were frequently observed in the growing intermetallics and were confirmed by post-solidification electron backscatter diffraction. A twin plane re-entrant growth mechanism was suggested, where repeated formation of re-entrant corners facilitated crystal growth along a preferential direction, forming elongated plates. In contrast, for intermetallics where this preferential growth was constrained by surrounding crystals, formation of layered twins perpendicular to the preferential direction was promoted and led to lower aspect ratios, known to be less deleterious to tensile properties.</p

An energy efficient and runtime-aware framework for distributed stream computing systems

Task scheduling in distributed stream computing systems is an NP-complete problem. Current scheduling schemes usually have a pause or slow start process due to the fluctuation of input data stream, which affects the performance stability, especially the high throughput and low latency goals. In addition, idle compute nodes at runtime may result in large idle load energy consumption. To address these problems, we propose an energy efficient and runtime-aware framework (Er-Stream). This paper thoroughly discusses the framework from the following aspects: (1) The communication between real-time data streaming tasks is investigated; stream application, resource and energy consumption are modeled to formalize the scheduling problem. (2) After an initial topology is submitted to the cluster, task pairs with high communication cost are processed on the same compute node through a lightweight task partitioning strategy, minimizing the communication cost between nodes and avoiding frequent triggering of runtime scheduling. (3) At runtime, reliable task migration is performed based on node communication and resource usage, which in turn helps the dynamic adjustment of the node energy consumption. (4) Metrics including latency, throughput, resource load and energy consumption are evaluated in a real distributed stream computing environment. With a comprehensive evaluation of variable-rate input scenarios, the proposed Er-Stream system provides promising improvements on throughput, latency and energy consumption compared to the existing Storm's scheduling strategies

Chiral covalent organic frameworks: design, synthesis and property

Covalent organic frameworks (COFs) are constructed using reticular chemistry with the building blocks being connected via covalent bonds and have emerged as a new series of porous materials for multitudinous applications. Most COFs reported to date are achiral, and only a small fraction of COFs with chiral nature are reported. This review covers the recent advances in the field of chiral COFs (CCOFs), including their design principles and synthetic strategies, structural studies, and potential applications in asymmetric catalysis, enantioselective separation, and chiral recognition. Finally, we illustrate the remaining challenges and future opportunities in this field

An Anonymous Authentication and Key Agreement Protocol in Smart Living

Wireless Sensor Networks (WSNs) play an indispensable role in the application of smart homes, smart healthcare, and precision agriculture. However, WSNs confront privacy risks that hinder its practical applications. The leakage of privacy is one of the key factors to restrict the development of WSNs. Hence, in this paper, we propose an Anonymous Authentication and Key Agreement protocol (AAKA) to accomplish identity authentication and privacy protection. Based on the dynamic sequence number, the shared secret value, and the dynamic random number, the AAKA protocol implements a two-way authentication and keys negotiation among users, gateway, and sensors, which achieves the secure access control of legitimate users to WSNs and ensures the confidential transmission of data over the public channel. We perform the security proof with BAN logic for security evaluation. The performance analysis demonstrates that compared with other WSNs authentication schemes, the AAKA protocol obtained better security features, smaller storage, and more efficient communication. Therefore, it is more suitable for applications in smart living

An Anonymous Authentication and Key Agreement Protocol in Smart Living

Wireless Sensor Networks (WSNs) play an indispensable role in the application of smart homes, smart healthcare, and precision agriculture. However, WSNs confront privacy risks that hinder its practical applications. The leakage of privacy is one of the key factors to restrict the development of WSNs. Hence, in this paper, we propose an Anonymous Authentication and Key Agreement protocol (AAKA) to accomplish identity authentication and privacy protection. Based on the dynamic sequence number, the shared secret value, and the dynamic random number, the AAKA protocol implements a two-way authentication and keys negotiation among users, gateway, and sensors, which achieves the secure access control of legitimate users to WSNs and ensures the confidential transmission of data over the public channel. We perform the security proof with BAN logic for security evaluation. The performance analysis demonstrates that compared with other WSNs authentication schemes, the AAKA protocol obtained better security features, smaller storage, and more efficient communication. Therefore, it is more suitable for applications in smart living

A state lossless scheduling strategy in distributed stream computing systems

Stateful scheduling is of critical importance for the performance of a distributed stream computing system. In such a system, inappropriate task deployment lowers the resource utilization of cluster and introduces more communication between compute nodes. Also an online adjustment to task deployment scheme suffers slow state recovery during task restart. To address these issues, we propose a state lossless scheduling strategy (Sl-Stream) to optimize the task deployment and state recovery process. This paper discusses this strategy from the following aspects: (1) A stream application model and a resource model are constructed, together with the formalization of problems including subgraph partitioning, task deployment and stateful scheduling. (2) A multi-factor topology partitioning method is proposed using a quantum particle swarm algorithm. The assignment between tasks and nodes is optimized using a bipartite graph minimum matching algorithm. (3) A hierarchical local topology migration is performed when an online scheduling is triggered, which ensures the processing sustainability of data streams. (4) A fragment loss-tolerant jerasure tool is used to divide the state data into fragments and periodically save them in upstream vertex instances, which ensures the available fragments be able to reconstruct the whole state in parallel. (5) Metrics including latency, throughput and state recovery time are evaluated in a real distributed stream computing environment. With a comprehensive evaluation of variable-rate input scenarios, the proposed Sl-Stream system provides promising improvements on throughput, latency and state recovery time compared to the existing Storm's scheduling strategies

Lattice-based Batch Authentication Scheme with Dynamic Identity Revocation in VANET

Aggregate signatures allow someone to aggregate multiple signatures into one signature, which is suitable for resource-constrained and computationally inefficient environments. Identify-based aggregate signature can solve the storage problem of public key certificates while achieving efficient signature verification. However, in most of the identity-based aggregate signature schemes, the user identity revocation process is time-consuming and cannot resist quantum attacks. To solve above problems, this paper proposes a lattice-based aggregate signature scheme with dynamic identity revocation by combining lattice-based cryptography and an aggregate signature scheme. The security of the proposed lattice-based aggregate signature scheme with dynamic identity revocation has been proved in the random oracle model. In addition, the verification efficiency of the aggregate signature has been improved compared with multiple different signatures. Much of the data transfer in Vehicular Ad Hoc Network (VANET) is carried out wirelessly, which makes VANET vulnerable to identity spoofing attacks. Identity authentication technology can prevent attackers from impersonating legitimate users, thus ensuring the security of VANET. Based on the proposed lattice-based aggregate signature scheme with dynamic identity revocation, this paper proposes a lattice-based batch authentication scheme with dynamic identity revocation in VANET. Through the proposed batch authentication scheme, we can effectively resist the impersonation attack of VANET in the quantum computer environment, and the efficiency of authentication is improved.</p

Lattice-based Batch Authentication Scheme with Dynamic Identity Revocation in VANET

Aggregate signatures allow someone to aggregate multiple signatures into one signature, which is suitable for resource-constrained and computationally inefficient environments. Identify-based aggregate signature can solve the storage problem of public key certificates while achieving efficient signature verification. However, in most of the identity-based aggregate signature schemes, the user identity revocation process is time-consuming and cannot resist quantum attacks. To solve above problems, this paper proposes a lattice-based aggregate signature scheme with dynamic identity revocation by combining lattice-based cryptography and an aggregate signature scheme. The security of the proposed lattice-based aggregate signature scheme with dynamic identity revocation has been proved in the random oracle model. In addition, the verification efficiency of the aggregate signature has been improved compared with multiple different signatures. Much of the data transfer in Vehicular Ad Hoc Network (VANET) is carried out wirelessly, which makes VANET vulnerable to identity spoofing attacks. Identity authentication technology can prevent attackers from impersonating legitimate users, thus ensuring the security of VANET. Based on the proposed lattice-based aggregate signature scheme with dynamic identity revocation, this paper proposes a lattice-based batch authentication scheme with dynamic identity revocation in VANET. Through the proposed batch authentication scheme, we can effectively resist the impersonation attack of VANET in the quantum computer environment, and the efficiency of authentication is improved.</p