In this study, the mechanical properties and corrosion resistance of LA143 alloy specimens produced by severe plastic deformation (SPD) were investigated. It was found that SPD was an effective way ...to simultaneously improve the Vickers hardness and corrosion resistance of LA143 alloy specimens in 3.5 mass% NaCl aqueous solution.
Principal component analysis (PCA) is an essential method for analyzing single-cell RNA-seq (scRNA-seq) datasets, but for large-scale scRNA-seq datasets, computation time is long and consumes large ...amounts of memory.
In this work, we review the existing fast and memory-efficient PCA algorithms and implementations and evaluate their practical application to large-scale scRNA-seq datasets. Our benchmark shows that some PCA algorithms based on Krylov subspace and randomized singular value decomposition are fast, memory-efficient, and more accurate than the other algorithms.
We develop a guideline to select an appropriate PCA implementation based on the differences in the computational environment of users and developers.
This paper studies stability- and symmetry-preserving H 2 optimal model reduction problems of linear systems, which include linear gradient systems as a special case. The problem is formulated as a ...nonlinear optimization problem on the product manifold of the manifold of symmetric positive-definite matrices and two Euclidean spaces. To solve the problem by using the trust-region method, the gradient and Hessian of the objective function are derived. Furthermore, it is shown that if we restrict our systems to gradient systems, the gradient and Hessian can be obtained more efficiently. More concretely, by symmetry, we can reduce linear matrix equations to be solved. In addition, by a simple example, we show that the solutions to our problem and a similar problem in some literature works are not unique, and the solution sets of both problems do not contain each other in general. Also, it is revealed that the attained optimal values do not coincide. Numerical experiments show that the proposed method gives a reduced system with the same structure with the original system although the balanced truncation method does not.
MOEA/D is one of the promising evolutionary algorithms for multi- and many-objective optimization. To improve the search performance of MOEA/D, this work focuses on the solution update method in the ...conventional MOEA/D and proposes its alternative, the chain-reaction solution update. The proposed method is designed to maintain and improve the variable (genetic) diversity in the population by avoiding duplication of solutions in the population. In addition, the proposed method determines the order of existing solutions to be updated depending on the location of each offspring in the objective space. Furthermore, when an existing solution in the population is replaced by a new offspring, the proposed method tries to reutilize the existing solution for other search directions by recursively performing the proposed chain-reaction update procedure. This work uses discrete knapsack and continuous WFG4 problems with 2–8 objectives. Experimental results using knapsack problems show the proposed chain-reaction update contributes to improving the search performance of MOEA/D by enhancing the diversity of solutions in the objective space. In addition, experimental results using WFG4 problems show that the search performance of MOEA/D can be further improved using the proposed method.
•This paper presents the Hager-Zhang (HZ)-type Riemannian conjugate gradient method that uses the exponential retraction.•We present global convergence analyses of our proposed method under two kinds ...of assumptions.•We numerically compare our proposed methods with the existing methods by solving two kinds of Riemannian optimization problems.•Our proposed method has much higher performance than existing methods in computing the stability number of graphs problem.
This paper presents the Hager–Zhang (HZ)-type Riemannian conjugate gradient method that uses the exponential retraction. We also present global convergence analyses of our proposed method under two kinds of assumptions. Moreover, we numerically compare our proposed methods with the existing methods by solving two kinds of Riemannian optimization problems on the unit sphere. The numerical results show that our proposed method has much better performance than the existing methods, i.e., the FR, DY, PRP, and HS methods. In particular, they show that it has much higher performance than existing methods including the hybrid ones in computing the stability number of graphs problem.
In this study, the high temperature uniaxial tensile creep deformation behavior of (α + β)-Mg-9 mass%Li-4 mass%Al-1 mass%Zn (LAZ941) alloy was investigated. The creep strength of the LAZ941 alloy was ...significantly improved by heat treatment. The creep deformation behavior of the heat-treated LAZ941 alloy was unique. As the results of creep tests, it is found that the stress exponent of LAZ941 was about 3. The activation energies of creep at the early and middle stages of deformation were 114.7 and 84.6 kJ･mol−1, respectively, indicating that the diffusing elements controlling the viscous glide of the dislocation changed during creep deformation.
•The creep strength of the LAZ941 alloy is improved by heat treatment.•The time to reach 0.1 creep strain is about 9 times longer due to heat treatment.•The creep deformation behavior of heat-treated LAZ941 alloy is unique.•The activation energy of creep for LAZ941 alloy changes during deformation.
Access control is a fundamental security aspect and has been adopted in diverse systems. Particularly, fine-grained access control models present good flexibility and scalability to adapt to ...complicated systems. However, building a trustworthy fine-grained access control mechanism in untrustworthy distributed environments such as Internet of Things (IoT) environments is challenging. Conventional access control mechanisms encounter security and privacy issues caused by centralized entities, such as single point of failure and data tampering. To address these issues, we have proposed Bloccess, a fine-grained access control framework based on the consortium blockchain, in our previous work. By leveraging blockchain technology, we formulate a set of protocols to enforce a tamper-proof access control mechanism in untrustworthy distributed environments. In this paper, we refine our previous work and present the extended version of Bloccess. We optimize our protocols and extend them to support a hybrid blockchain structure. We also formulate complete identification protocols for the administration mechanism in Bloccess. Besides, we show Bloccess in practice with a Bloccess-enabled IoT system. Furthermore, we conduct a semi-formal analysis to prove the security properties of Bloccess and evaluate its security through a security model and a threat model.
Recently, the approximate Karush–Kuhn–Tucker (AKKT) conditions, also called the sequential optimality conditions, have been proposed for nonlinear optimization in Euclidean spaces, and several ...methods to find points satisfying such conditions have been developed by researchers. These conditions are known as genuine necessary optimality conditions because all local optima satisfy them with no constraint qualification (CQ). In this paper, we extend the AKKT conditions to nonlinear optimization on Riemannian manifolds and propose an augmented Lagrangian (AL) method that globally converges to points satisfying such conditions. In addition, we prove that the AKKT and KKT conditions are indeed equivalent under a certain CQ. Finally, we examine the effectiveness of the proposed AL method via several numerical experiments.
In this paper, we study Cayley-transform-based gradient and conjugate gradient algorithms for optimization on Grassmann manifolds. We revisit the Cayley transform on Grassmann manifolds as a ...retraction in the framework of quotient manifolds constructed by Lie group actions and obtain an efficient formula for this retraction in low-rank cases. We also prove that this retraction is the restriction of the Cayley transform on Stiefel manifolds to horizontal spaces. To develop vector transports on Grassmann manifolds, we introduce a concept called induced vector transports on quotient manifolds. Based on this concept, three vector transports associated with the Cayley transform are obtained. The first vector transport is the traditional orthogonal projection onto horizontal spaces, whereas the other two vector transports are newly proposed herein. We show that one of the new vector transports satisfies the Ring–Wirth non-expansion condition and that the other is isometric. We also simplify the formulae of the new vector transports in low-rank cases. Riemannian gradient and conjugate gradient algorithms are established via the Cayley transform and the three abovementioned vector transports. Numerical experiments on two mean-of-subspaces problems demonstrate the effectiveness of the proposed algorithms.
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