We present a new algorithm for solving large-scale unconstrained optimization problems that uses cubic models, matrix-free subspace minimization, and secant-type parameters for defining the cubic terms. We also propose and analyze a specialized trust-region strategy to minimize the cubic model on a properly chosen low-dimensional subspace, which is built at each iteration using the Lanczos process. For the convergence analysis we present, as a general framework, a model trust-region subspace algorithm with variable metric and we establish asymptotic as well as complexity convergence results. Preliminary numerical results, on some test functions and also on the well-known disk packing problem, are presented to illustrate the performance of the proposed scheme when solving large-scale problems.

Polynomial interpolation or regression models are an important tool in Derivativefree Optimization, acting as surrogates of the real function. In this work, we propose the use of these models in the multiobjective framework of directional direct search, namely the one of Direct Multisearch. Previously evaluated points are used to build quadratic polynomial models, which are minimized in an attempt of generating nondominated points of the true function, defining a search step for the algorithm. Numerical results state the competitiveness of the proposed approach.

The interfacial behaviour between ribbed steel rebars and concrete has been extensively studied because the contribution of the adherence between these two materials is of the utmost importance for the behaviour of Reinforced Concrete (RC) structures. The majority of the available studies on this topic indicate that the local adherence between these two materials can be defined through a bond-slip relationship, which is obtained with short embedded lengths. Although this seems to be widely accepted, some incoherencies, mainly regarding the local and the global detachment process in that “conventional theory”, are identified in the present work. To facilitate the understanding of the detachment process between a ribbed steel rebar and concrete, an analytical solution is developed. An experimental program with 33 pull-out tests covering three different ribbed steel rebars with different diameters and embedded lengths was carried out. Based on the experimental load–displacement at the pulled end responses, a new local bond-slip relationship with friction is proposed. In the end, the new bond-slip relationship, as well as other known relationships, is implemented into a Finite Element (FE) commercial code and the results are compared to the experimental data. Based on these preliminary results and up to the yielding point of the steel rebars, the new proposed local bond-slip model is the only one able to clearly distinguish and simulate either the local and the global performances of the tested specimens. © 2020 Institution of Structural Engineers

The bonding technique has received extensive attention in the recent decades. Unlike the use of metallic screws, screws or rivets, some of the advantages of this bonding technique include the elimination of stress concentration, lighter weight and the extension of the life cycle of the adhesively bonded structures. The stiffness and strength of a material are increased after bonding with another reinforced material, but it can only be effective if the interface is able to transfer bond stresses. However, how the bond stress transfer is carried out when the joint, reinforcement and substrate are subjected to a thermal loading is not yet well understood. One way to facilitate and improve such knowledge is to develop analytical solutions that, despite their simplicity, allow parameters to be identified that may directly influence the bond between materials. Therefore, the present study aims to develop a series of closed-form solutions able to describe the debonding process of bonded joints with different characteristics using two different exponential softening laws. The results mainly describe the interfacial slips, bond stresses and strains in both materials during the temperature increase process. In total, 108 examples with different bonding conditions are studied and, at the same time, numerically modelled through the Finite Element Method (FEM). The numerical results were compared to the proposed closed-form solutions and a satisfactory agreement was obtained between the numerical and analytical results, validating the latter. When considered in the simulations, the glass transition temperature (Tg) of the adhesive greatly affected the bond stress transfer between materials and compromising the initial integrity of the adhesively bonded structure. © 2020

The Externally Bonded Reinforcement (EBR) of timber structures with Carbon Fiber Reinforced Polymers (CFRP) is a solution that has been increasing. Like CFRP strengthened concrete structures, it is known that the premature debonding of the CFRP also occurs on timber structures. To study other alternative solutions to the EBR technique, the Near Surface Mounted (NSM) and six other situations with an additional anchorage were considered. A total of 33 single-lap shear tests were carried out. The experimentally obtained load-slip responses, the strains developed in the CFRP strips or the local bond-slip relationships are all reported and discussed. Compared to the EBR technique, the efficiency of each anchorage system and/or bonding technique is also analysed. The current preliminary results suggest that using two superposed metallic L-shape profiles or embedding the CFRP strip into the timber substrate are the best anchorage systems for the reinforcement of a timber structure with CFRP strips. The NSM technique has also led to high load capacities of the CFRP-to-timber interface. © 2020 Elsevier Ltd

The aim of this study is to evaluate the elemental composition of six food supplements of plant origin, commonly sold in the Portuguese market, by energy dispersive X-ray fluorescence. The presence of arsenic in all the Maca, Ashwagandha, Camu-Camu and Hemp protein samples (except the generic form) is a reason of concern due to the long-term effects of As mainly in its inorganic form. Thus, great caution must be taken on some food supplements, particularly the cases of Moringa from Egypt and Yellow/Xpresso Maca, whose inorganic As concentrations are in line with the upper bound concentration for the 95th dietary exposure according to the European Food Safety Authority which is 0.64 μg/kg bw/day. In what regards Hemp protein, if the supplier’s daily intake recommendation (30 g) is followed, values as high as 1.75 μg/kg bw/day of inorganic As will be consumed, which are dangerously above the upper bound. In this case this specific supplement lot should be removed from the market. Also the consumption of Hemp protein leads to a daily intake of Mn above the Daily Reference Intake (DRI) and Adequate Intakes (AIs) for adults. The contamination of Goji berries by Pb is a reason for concern—organic berries contained 11.3 μg/g while berries derived from conventional agriculture 11.6 μg/g, leading to daily intake doses of 315.3 μg and 324.8 μg, respectively, if the recommended daily intake of 28 g is followed. Our findings point out to an inadequacy of the recommended intakes by the supplier vis a vis the concentrations observed, greatly increasing the risk for public health.

Understanding the specific molecular interactions between proteins and β1,3-1,4-mixed-linked d-glucans is fundamental to harvest the full biological and biotechnological potential of these carbohydrates and of proteins that specifically recognize them. The family 11 carbohydrate-binding module from Clostridium thermocellum (CtCBM11) is known for its binding preference for β1,3-1,4-mixed-linked over β1,4-linked glucans. Despite the growing industrial interest of this protein for the biotransformation of lignocellulosic biomass, the molecular determinants of its ligand specificity are not well defined. In this report, a combined approach of methodologies was used to unravel, at a molecular level, the ligand recognition of CtCBM11. The analysis of the interaction by carbohydrate microarrays and NMR and the crystal structures of CtCBM11 bound to β1,3-1,4-linked glucose oligosaccharides showed that both the chain length and the position of the β1,3-linkage are important for recognition, and identified the tetrasaccharide Glcβ1,4Glcβ1,4Glcβ1,3Glc sequence as a minimum epitope required for binding. The structural data, along with site-directed mutagenesis and ITC studies, demonstrated the specificity of CtCBM11 for the twisted conformation of β1,3-1,4-mixed-linked glucans. This is mediated by a conformation–selection mechanism of the ligand in the binding cleft through CH-π stacking and a hydrogen bonding network, which is dependent not only on ligand chain length, but also on the presence of a β1,3-linkage at the reducing end and at specific positions along the β1,4-linked glucan chain. The understanding of the detailed mechanism by which CtCBM11 can distinguish between linear and mixed-linked β-glucans strengthens its exploitation for the design of new biomolecules with improved capabilities and applications in health and agriculture. Database Structural data are available in the Protein Data Bank under the accession codes 6R3M and 6R31.