Finite element modeling and shake-table testing of unidirectional infill masonry walls under out-of-plane dynamic loads

The dynamic out-of-plane response of unreinforced masonry walls is investigated. The study combines analytical, numerical, and experimental methodologies. The paper focuses on structural schemes that involve supporting at the base and the top and yield a unidirectional (one-way) flexural action. First, the modeling concepts for the nonlinear dynamic analysis are discussed and used as a basis for a finite element formulation. The element is based on a first-order shear deformation theory with large displacements, moderate rotations, small strains, material nonlinearity, and a Rayleigh type of viscoelastic damping. The nonlinearities due to cracking and the inelastic response under cyclic compression are introduced through the constitutive model for the mortar. The experimental part includes shake-table testing under different levels of out-of-plane excitation and compressive loading. The experimental results and the numerical model quantify a range of physical phenomena, including the dynamic arching and rocking effects, the coupling of the axial (in the height direction) and the out-of-plane responses, the role of axial loading, and the vulnerability of the masonry construction to dynamic loads. The comparison between the numerical results and the experimental results examines the capabilities of the model and gains insight into the nonlinear dynamics of the masonry wall.     

On reducing computational effort in topology optimization: how far can we go?

An approximate approach to solving the nested analysis equations in topology optimization is proposed. The procedure consists of only one matrix factorization for the whole design process and a small number of iterative corrections for each design cycle. The approach is tested on 3D topology optimization problems. It is shown that the computational cost can be reduced by one order of magnitude without affecting the outcome of the optimization process.     

High Temperature Plasticity of Bimetallic Magnesium and Aluminum Friction Stir Welded Joints

The high temperature deformation of a bimetallic AZ31/AA6061 Friction Stir Welded joint was investigated in the present study by constant load creep experiments carried out at 473 K (200 °C). The microstructural analysis revealed the strongly inhomogeneous nature of the weld, which was characterized by an extremely fine grain size in the magnesium-rich zones and by the extensive presence of intermetallic phases. In the high stress regime, the creep strain was concentrated in the refined and particle-rich microstructure of the weld zone, while the AA6061 base metal remained undeformed. In the low stress regime, deformation became more homogeneously distributed between the AZ31 base metal and the weld zone. The creep behavior of the weld was found to obey the constitutive equation describing the minimum creep rate dependence on applied stress for the base AZ31, slightly modified to take into account the finer microstructure and the role of secondary phase particles, i.e., the retardation of grain growth and the obstruction of grain boundary sliding.     

FDI Experience Location and Subsidiary Mortality

Purpose: This study examines the relationship between an MNE’s experience with foreign direct investments (FDI) and subsidiary mortality when considering learning limitations that an MNE are susceptible to under the influence of national cultural differences. Methods: We apply event history analysis on a sample of subsidiaries of Korean MNEs during 1990–2006. Results: We find that subsidiary mortality has a negative relationship with FDI experience from countries culturally similar to both the MNE’s home country and the focal host country; an inverse U-shaped relationship with both experience from countries culturally similar to the home country but different from the focal host country, and experience from countries culturally different from the home country but similar to the focal host country. Experience from countries culturally dissimilar to both the focal host country and the home country has a negative effect when a subsidiary is located in countries dissimilar to the home country, and an insignificant effect when a subsidiary is located in countries similar to the home country. Conclusions: Our findings show that prior experience has different effects depending on where it is accumulated and that MNEs are susceptible to limitations both when drawing inferences from their FDI experiences and when applying these experiences toward subsequent FDIs.     

Dynamic analysis of walls strengthened with composite materials

The bidirectional dynamic behavior of walls strengthened with composite materials is studied. For that purpose, a multi-layered high order finite element is developed. The finite element accounts for the bidirectional (plate-type) dynamic behavior and for the interfacial interaction between the adhesively bonded components. The formulation uses a viscoelastic first order shear deformation orthotropic plate theory for the independent modeling of the existing wall and the composite layers and a high order theory for the displacement fields of the adhesive layers. The Finite element framework simplifies the coupling with adjacent structural elements and the use of standard computational procedures. The convergence of the formulation and two numerical examples are studied. The first case studies the response of a strengthened wall to a step base acceleration. The second case studies a wall built in a surrounding frame and strengthened on the outer face. The numerical study examines the capabilities of the model and reveals some of the unique aspect of the dynamic response, including the effects of the orthotropy and orientation of the strengthening system. It also highlights the potential of the high order finite element to become a platform for the modeling and dynamic analysis of the strengthened wall.     

TRIM25 and DEAD-Box RNA Helicase DDX3X Cooperate to Regulate RIG-I-Mediated Antiviral Immunity

The cytoplasmic retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs) initiate interferon (IFN) production and antiviral gene expression in response to RNA virus infection. Consequently, RLR signalling is tightly regulated by both host and viral factors. Tripartite motif protein 25 (TRIM25) is an E3 ligase that ubiquitinates multiple substrates within the RLR signalling cascade, playing both ubiquitination-dependent and -independent roles in RIG-I-mediated IFN induction. However, additional regulatory roles are emerging. Here, we show a novel interaction between TRIM25 and another protein in the RLR pathway that is essential for type I IFN induction, DEAD-box helicase 3X (DDX3X). In vitro assays and knockdown studies reveal that TRIM25 ubiquitinates DDX3X at lysine 55 (K55) and that TRIM25 and DDX3X cooperatively enhance IFNB1 induction following RIG-I activation, but the latter is independent of TRIM25’s catalytic activity. Furthermore, we found that the influenza A virus non-structural protein 1 (NS1) disrupts the TRIM25:DDX3X interaction, abrogating both TRIM25-mediated ubiquitination of DDX3X and cooperative activation of the IFNB1 promoter. Thus, our results reveal a new interplay between two RLR-host proteins that cooperatively enhance IFN-β production. We also uncover a new and further mechanism by which influenza A virus NS1 suppresses host antiviral defence.     

The route expropriation problem

This paper considers the problem of selecting obnoxious routes (e.g., routes used to transport hazardous material) on a transportation network assuming that population centers on or outside the network within a certain distance from the selected routes can be expropriated at a given price. The objective is to select the routes so as to minimize the total weighted transportation and expropriation costs. For the single-flow problem, a polynomial algorithm is developed. For the multiple-flow problem, a branch-and-price algorithm using column generation is developed and its efficiency is tested with computational experiments.