Initial Bond Research Articles

Non-Canonical C16 Homoterpene Biosynthesis Widespread in Actinobacteria.

A novel biosynthetic pathway towards the rare and underexplored non-canonical family of homoterpenes was discovered in actinobacteria through targeted genome mining and enzymatic in vitro reconstitution. The pathway comprises initial methylation-induced double bond isomerization of farnesyl diphosphate (FPP) to (2E,7E)-6-methyl-farnesyl diphosphate, catalyzed by a novel family of methyltransferases with unique dual function. The resulting linear C16 double bond isomer of FPP constitutes the specific substrate for a distinct family of type I terpene cyclases, catalyzing diverse cyclization reactions. Functional characterization of nine enzyme pairs led to discovery of five unprecedented homoterpene natural products. The enzymological novelty enables the development of novel biocatalytic and genetically programmable synthetic strategies towards methylated terpenoids with potentially unique properties ("magic methyl effect").

Tensile behaviour of a novel grouted sleeve splice for high-strength rebars

This study introduces a novel type of grouted sleeve fabricated from a standard low-alloy seamless steel pipe using cold-rolling techniques. The main goal is to achieve an effective connection between the high-strength steel (HSS) reinforcements in the joints of precast concrete structures. To investigate the structural performance of the developed splice under uniaxial tensile loading, 24 coupler specimens configured with 28 mm diameter HRB600 reinforcements were prepared. Two primary parameters, namely the embedded length of the spliced bar and number of inner concentric ribs rolled on the sleeve, were considered. By conducting direct pullout tests, the performance of the developed splices was thoroughly assessed based on the failure mode, bond stiffness, bond ductility, and strength. The test results demonstrated that increasing the bar embedded length and number of inner ribs enhances the initial bond stiffness and ductility of the splice. Increasing the quantity of inner ribs only in the inelastic region of the splice is effective for improving its tensile capacity. For grout splices with large-diameter HSS bars, an embedded length of 8db is recommended to guarantee bar fracture failure and satisfy the specification requirements. This length exceeds that of splices with normal-strength reinforcements. Finally, a formula was proposed to estimate the inelastic region length and tensile strength of the proposed splice.

How do you trust in the midst of mistrust? A longitudinal study (2010–2021) on building trust in a professional learning community of science teachers in Chile

ABSTRACT Professional Learning Communities (PLCs) are valuable spaces for collaboration and reflection to promote the transformation of teaching practice and resilience to change. In PLCs that are sustained over time, trust-building is a key element. In Latin America, school systems and educational models are based on mistrust, which in Chile is consistent with a highly unequal, individualistic, and competitive school system, making the generation of PLCs particularly complex. Through a longitudinal study, we describe how trust is built and maintained in a Chilean PLC of science teachers who meet regularly to share and reflect on their practice. We analysed 18 group sessions, six focus groups, and four interviews conducted over 11 years of this PLC. The results show relevant elements to initiate trust, such as building an initial bond of trust between some participants, recognising one’s limitations, and negotiating common meanings and objectives. In the second stage, the free expression of experiences and emotions, reflecting on practice and validating its members’ experiences allows for the construction of a genuine and highly valued space for professional development, which promotes practice transformation.

Asymmetric Palladium Migration for Synthesis of Chiral-at-Cage o-Carboranes.

Metal migration strategy can offer BH functionalization of o-carboranes at different positions from where initial bond activation occurs to achieve bifunctionalized o-carboranes in one reaction. We report in this article an enantioselective 3,4-bifunctionalization of o-carboranes via asymmetric Pd migration with a high efficiency and up to 98 % ee. This asymmetric catalysis has a broad substrates scope, leading to the preparation of a class of chiral-at-cage o-carborane derivatives. The enantiocontrol model is suggested on the basis of density functional theory (DFT) results, where the chiral Trost ligand plays a crucial role in this enantioselective Pd migration from exo-alkenyl sp2 C to the cage B(4) position of o-carborane.

Asymmetric Palladium Migration for Synthesis of Chiral‐at‐Cage o‐Carboranes

AbstractMetal migration strategy can offer BH functionalization of o‐carboranes at different positions from where initial bond activation occurs to achieve bifunctionalized o‐carboranes in one reaction. We report in this article an enantioselective 3,4‐bifunctionalization of o‐carboranes via asymmetric Pd migration with a high efficiency and up to 98 % ee. This asymmetric catalysis has a broad substrates scope, leading to the preparation of a class of chiral‐at‐cage o‐carborane derivatives. The enantiocontrol model is suggested on the basis of density functional theory (DFT) results, where the chiral Trost ligand plays a crucial role in this enantioselective Pd migration from exo‐alkenyl sp2 C to the cage B(4) position of o‐carborane.

Rebar corrosion and bond in concrete with recycled glass granules

Waste glass granules are considered a cost-effective alternative material to replace aggregates in concrete. However, the bond degradation of corroded concrete containing recycled glass granules has not been explored. This study investigated the effect of glass granules on rebar corrosion and the bond loss between rebars and concrete subjected to accelerating corrosion. The compressive strength and pore structure of the concrete were first evaluated, and the corrosion rate and pull-out testing of rebar in concrete were conducted after corrosion. The results show that, despite reducing the initial bond strength before corrosion, a high replacement of recycled glass granules improved the concrete's resistance to corrosion due to the optimized microstructure of concrete. In addition, the compressive strength of the concrete dominated the initial bond strength, which reduced with increasing the corrosion period. However, this negative effect of corrosion was mitigated by increasing the recycled glass granules, followed by reduced bond strength loss and a lower rebar corrosion rate.

Evaluation of bond strength in bamboo reinforced-high grade concrete at elevated temperature

Abstract Concrete traditionally relies on steel reinforcement to address its weak tensile strength. However, due to concerns such as high production costs, non-renewability, and sustainability issues associated with steel, developing countries like India and African nations are turning to locally available bamboo as a reinforcement material in low-cost buildings. This study explores the feasibility of bamboo reinforcement in fly ash concrete (FAC) by examining the post-fire behavior of the bond strength between bamboo and FAC through pull-out tests. Initial tensile strength assessments of locally available bamboo strips are carried out. Various mechanical and chemical treatments, including grooving, wire wrapping, clamping, and epoxy-based sand coating, are applied to investigate their impact on post-fire bond strength. Despite certain treatments exhibiting higher initial bond strengths, their susceptibility to the fire test emphasizes the need for ongoing research and refinement. Notably, the treatment involving plain bamboo with epoxy-based sand coating and wire wrapping emerges as a promising option, demonstrating resilience with only a 21% drop in bond strength after exposure to fire.

Trimetallic Alloys as an Electrocatalyst for Fuel Cells: The Case of Methyl Formate on Pt3Pd3Sn2.

The shift toward renewable energy sources plays a central role in the quest for a circular economy. In this context, methyl formate (MF) has garnered attention as a compelling hydrogen carrier and alternative fuel, because of its remarkable characteristics (energy density, ease of storage and transport, and low boiling point). In this study, DFT calculations supported by online electrochemical mass spectroscopy (OE-MS) were performed to investigate the MF electro-oxidation (MFEO) on Pt3Pd3Sn2 (111). The DFT calculations provide insight into the role of Pt, Pd, and Sn atoms in MFEO. Pt and Pd together provide a preferred active site for initiating MFEO through the O-H bond scission, and Sn plays an essential role in the mitigation of CO through oxygenation or water activation. By comparing the reaction energies and activation barriers for all possible reactions in MFEO, the suggested path necessitates a minimum energy of 0.14 eV to initiate the MFEO. This value was supported by the experimental results, showing that the oxidation wave of MF starts at 0.15 V (70 °C). Density functional theory (DFT) results, supported by OE-MS, indicate that the hydrolysis of MF prior to MFEO is not preferred on Pt3Pd3Sn2 (111) surfaces, although the formation of methanol is plausible via a CH3O intermediate. Among the three small organic molecules (SOMs) studied─MF, methanol, and formic acid─MF has the lowest activation energy for the initial bond breaking that starts the whole oxidation process (0.13 eV), compared to formic acid (0.45 eV) and methanol (0.61 eV); thus, MF is the preferred fuel on Pt3Pd3Sn2 (111).

The effect of bond ownership structure on ESG performance

We examine whether firms' ESG performance is influenced by bondholder preferences. We argue that insurance companies have unique incentives to monitor bond issuers' ESG performance because insurers face enhanced exposures to ESG shocks in their balance sheets and trading operations. Consistent with this argument, we find that firms with higher bond ownership by insurance companies are associated with higher future ESG ratings. To address potential identification concerns, we test changes in bond issuers' ESG ratings following the initial bond investment by insurance companies. We find that firms' ESG performance improves after insurance companies' initial bond investment. We also find that this improvement in ESG performance is concentrated in firms with greater reliance on bond financing and investment capital from insurance companies. Our study underscores the importance of bond ownership structure in influencing corporate ESG performance.

Impact of functional monomers, bioactive particles, and HEMA, on the adhesive performance of self-etch adhesive systems applied to simulated altered dentin

ObjectivesThis study aimed to evaluate how self-etching/universal dental adhesive systems (DASs) with differing compositions interact with sound (S), post-radiotherapy (irradiated; I), and artificially eroded (E) dentin in terms of bonding properties. Methods: The DASs tested were Adper Scotchbond Multipurpose (MP; control), Clearfil SE Bond (SE), FL Bond II (FL), Adper Single Bond Universal (SU) and BeautiBond Xtreme (BX). They were analyzed for initial and 6-month microtensile bond strength (µTBS, n = 12), mode of failure (40 x), scanning electron microscopy (SEM), surface wettability (W, n = 10), and degree of conversion (DC, n = 3) via Fourier-transform infrared spectroscopy (FTIR). Normal and homogeneous distribution of the data allowed their analyses through ANOVA and Tukey tests (p < 0.05). Results: All DASs except BX exhibited higher µTBS for S decreasing for I and E. BX demonstrated the greatest stability among the altered substrates. FL showed the most hydrophobic properties, likely due to its bioactive components. Universal DASs achieved higher DC, regardless of composition. Conclusions: HEMA-free formulation combined with carboxylic and phosphoric acids in BX, achieved the most stable performance for altered substrates. Clinical SignificanceSince radiotherapy and erosion affect dentin, their characteristics compromise adhesive performance and impair the achievement of durable and satisfactory restorations. The use of universal adhesives less dependent on calcium seems less susceptible to hydrolytic degradation and may be a promising option for maintaining adhesive stability over time.

Experimental study on bond behavior of corroded reinforced concrete under coupling effect of fatigue load and elevated temperature

The bond properties of corroded reinforcing bars in concrete are mainly determined by the failure time and ultimate capacity of reinforced concrete (RC) structures. In this study, 98 cube specimens were used to study the corrosion effect on the bond failure mechanism of RC structures under transient high temperature. Firstly, an electrification accelerated corrosion test was carried out to fabricate the corroded specimen with various corrosion degrees (0 %, 5 %, 10 %, and 15 %). Secondly, the undamaged specimen was conducted by pull-out test at ambient temperature to obtain the initial bond strength, and then a transient temperature test under sustained load was also performed to analyze the effects of different load ratios, concrete strength, and corrosion degrees on the bond behavior. SEM (Scanning Electron Microscope) was conducted to verify the damage level by comparing the interfacial transition zone. Test results indicate that the coupling effect of corrosion, fatigue load, and high temperature increases the carbonization level of the specimens and reduces the concrete compressive strength after bonding damage. The ultrasonic pulse velocity decreases with increasing corrosion degree and sustained load level and decreases with increasing concrete strength grade. Under the coupling effect of corrosion, high temperature, and sustained load, the bonding failure time is significantly affected by the sustained load ratio, and the failure slip is determined by corrosion and temperature. Finally, an empirical slip-location constitutive model was proposed, incorporating the sustained load ratio, corrosion degree, and temperature. The accuracy of the predicted model agrees with the error requirement, and the constitutive model provides a theoretical basis for the collapse warning of corroded structures under fire.

Experimental study of bond-slip relationships in high-performance self-consolidating concrete with plain steel bars

Self-consolidating concrete is being used more frequently in structures with high density of reinforcement bars or prestressing strands therefore, it is important to carefully consider whether bond stress-slip relations defined for normal strength concrete can be safely applied to high-strength and self-consolidating concrete. This paper aims to investigate the bond behaviour between plain steel bars and high-performance self-consolidating concrete, with a focus on studying the effect of embedment length and concrete compressive strength on bonding performance. The main parameters that were tested are the active bonded length and the compressive strength of the concrete. The value of adhesive bond stress is discussed, as a factor in determining whether the bar slips against the adhering concrete. Based on the results, it can be observed that the maximum bond stress tends to increase with higher concrete compressive strength, while it decreases with longer embedment length of plain steel bar. Conversely, the adhesive bond tends to increase with longer embedment length and higher concrete compressive strength. The experimental investigations indicate that the bond strength increases proportionally to the square root of the compressive strength of concrete, regardless of the concrete compressive strength. Furthermore, a new bond stress-slip model has been analyzed, which takes into account the initial bond strength (adhesive bond) and the lower convex property to predict the post-peak branch. The model has been compared to the test results, and good agreement has been achieved.

Multi-scale experimental investigation on the structural behaviour of novel nanocomposite/natural textile-reinforced mortars

Natural fibre composites present a very appealing area of research for the structural strengthening of masonry structures. Natural fibres possess several drawbacks, such as low initial stiffness and poor interfacial bond behaviour with inorganic matrices that hinder their functions. Such challenges were overcome by applying an innovative nanocomposite-based impregnation system that was pre-engineered and presented by the authors previously. In this paper, a full experimental study involving pullout, tensile tests and large-scale testing via diagonal compression test was carried out to evaluate the structural efficiency of the developed system. Remarkable improvement at yarn-to-matrix level upon nanocomposite coating was observed. At a medium bond length, yarn rupture was observed, highlighting the great anchorage provided by the nanocomposite coating within the matrix. Coupons cast with the developed system demonstrated outstanding composite behaviour and multicracking under tensile loading. Finally, wallets strengthened with the developed system displayed multiple cracks and maintained high shear capacity (40–60 % of τmax) at remarkably large displacements developed at later stages of the test. Such ductility is crucial for retrofitting masonry structures, especially in seismic areas.

Surface Treatments' Influence on the Interfacial Bonding between Glass Fibre Reinforced Elium® Composite and Polybutylene Terephthalate.

This study examines the process of using injection moulding to join two different materials to manufacture bi-component moulded products with improved performance characteristics. The two-component process, which combines the advantages of two different technologies-the high efficiency of the injection moulding process and the excellent mechanical properties of long glass fibre composites produced by resin transfer moulding (RTM) technology-offers a particular advantage and improved applicability of the prepared lightweight products in both the automotive and aerospace sectors. The composite studied here consists of Elium® thermoplastic resin (30%) reinforced with unwoven glass fibre fabric (70%) using the RTM process. The Elium® composite sample is consequently used as an insert overmoulded with polybutylene terephthalate (PBT) homopolymer reinforced with 20% w/w of short glass fibre through injection moulding. The influence of different mould temperatures and surface treatments on the adhesion between the materials used is investigated by evaluating the mechanical performance using tensile shear strength tests. It was found that while an increase in mould temperature from 40 °C to 120 °C resulted in a doubling of the initial average bond strength between untreated Elium® RTM inserts and overmoulded PBT parts (0.9 MPa), sandblasting the inserts ensured a further tripling of the bond strength of the composites to a value of 5.4 MPa.

Effect of corrosion on bond slipping between steel and concrete in SRC structures

Corrosion critically impacts bond performance in steel-reinforced concrete (SRC) structures. In this study, we investigate the impact of corrosion on bond-slipping between steel components and concrete within SRC structures. Initially, SRC specimens were subjected to electrochemical corrosion tests to induce varying corrosion rates. Then, pull-out tests were conducted to study the specimens' failure modes, bond stress–slip curves, and displacement distribution. The experimental results indicate that lower corrosion rates can increase bond strength due to enhanced steel surface roughness. As the corrosion rate increased from 0% to 5%, the initial bond stress, peak bond stress, and residual bond stress increased by 133%, 101%, and 102%, respectively. However, when the corrosion rate increased from 5% to 15%, these stresses decreased by 57.1%, 49.6%, and 49.6%, respectively. Furthermore, with an increase in corrosion rate from 15% to 20%, the initial, peak, and residual bond stresses decreased by 100%, 67.6%, and 69.0%, respectively. Corrosion considerably affected the initial and peak slipping observed between the steel components and the concrete, yet its impact on residual slip was relatively minor. In addition, a nonlinear finite element model for characterising the corrosion and pull-out tests was developed and validated according to the experimental results. The numerical results showed that the four shear transfer mechanisms, including chemical bonding, micromechanical interlocking, macromechanical interlocking, and rust interface bonding, exhibited distinct behaviours at different loading stages. Finally, a parametric study was conducted using a finite element model. With variations in corrosion rates, four modes of cracking patterns on the concrete surface were observed.

Seismic Performance of Steel-Reinforced High Strength Concrete Joints Considering Bond Slip Effect

This study presents a solution for push-out failure for the staged bond-slip constitutive relationship between the structural steel and high strength concrete, taking into account the concrete strength grade, anchoring length, and stirrup ratio. The critical point coordinates for different stages are determined by the tests of 14 steel-reinforced high strength concrete (SRHSC) specimens. It is observed that with the increase in the concrete strength grade and anchorage length, the ultimate load of the specimens increased significantly, but the influence on the residual bond strength was not significant. The effect of the stirring ratio was mainly manifested in a slight increase in the initial bond strength. The formula for calculating SRHSC characteristic bond strength and characteristic slip value is established, and the bond-slip constitutive relation of SRHSC is proposed based on the tests. The material constitutive model considering the effect of bond-slip is implanted into the software in the case of the ABAQUS finite element platform. The material is applied to the numerical simulation analysis of the SRHSC exterior joints. The rationality and accuracy of the new material are verified by comparing the simulation results with the test results.

Features of bond-slip relations: 3D finite element analysis based on tests of short RC ties

The interaction between concrete and reinforcement is highly complex and is of fundamental importance for predicting the behaviour of reinforced concrete (RC) structures. While the interaction of the two materials is often characterised by a bond – slip law, there are currently no such laws capable of accurately predicting serviceability characteristics, such as deflection, crack spacing, and width. This paper examines the effect of various parameters on the shape of bond – slip relation at loads before yielding of reinforcement. The study is based on a mesoscopic numerical analysis, utilizing the finite element method along with a friction cohesive zone model to explore the bond-slip phenomena in short RC ties. The numerical model is combined with an experimental campaign involving six short concrete ties reinforced with 20 mm bars. Steel strain profiles were monitored within the reinforcement using electrical strain gauges. These experimental steel strain profiles served as a robust tool for controlling and calibrating numerical models. The numerical models employed solid finite elements to simulate both reinforcement and concrete, with special zero-thickness plain elements applied to simulate the friction cohesive contact at the steel-concrete interface. Bond-slip relations were obtained from the numerically modelled reinforcement strain profiles. It was shown that concrete strains can be ignored when assessing slip. The effect of the embedded length of reinforcement under the fully confined conditions was demonstrated to have little effect on bond-slip relations. It was also shown that the maximum bond stress is strongly related to the thickness of the concrete cover. The effect of load intensity on the bond – slip behaviour was investigated. It was shown that under full confinement, the initial bond stiffness was not affected by load intensity. However, degradation of bond stiffness with increasing load due to internal cracking took place in the RC ties with a small cover/diameter ratio.

Unlocking carbene reactivity by metallaphotoredox α-elimination.

The ability to tame high-energy intermediates is important for synthetic chemistry, enabling the construction of complex molecules and propelling advances in the field of synthesis. Along these lines, carbenes and carbenoid intermediates are particularly attractive, but often unknown, high-energy intermediates1,2. Classical methods to access metal carbene intermediates exploit two-electron chemistry to form the carbon-metal bond. However, these methods are usually prohibitive because of reagent safety concerns, limiting their broad implementation in synthesis3-6. Mechanistically, an alternative approach to carbene intermediates that could circumvent these pitfalls would involve two single-electron steps: radical addition to metal to forge the initial carbon-metal bond followed by redox-promoted α-elimination to yield the desired metal carbene intermediate. Here we realize this strategy through a metallaphotoredox platform that exploits iron carbene reactivity using readily available chemical feedstocks as radical sources and α-elimination from six classes of previously underexploited leaving groups. These discoveries permit cyclopropanation and σ-bond insertion into N-H, S-H and P-H bonds from abundant and bench-stable carboxylic acids, amino acids and alcohols, thereby providing a general solution to the challenge of carbene-mediated chemical diversification.

Experimental Study on the Bonding Performance between Shaped Steel and High-Strength Concrete

The integration of steel fibers into high-strength concrete (HSC) offers a solution to address the brittleness and limited ductility typically associated with conventional HSC structures. To investigate the bonding properties between shaped steel and high-strength concrete with steel fiber (SFRC), thirteen tests of the shaped steel/SFRC specimens are conducted to explore the effects of various factors such as steel fiber volume ratio, concrete strength grade, reinforcement ratio, steel embedment depth, and cover thickness on bond–slip behavior. Three distinct failure modes, such as pushout failure, bond splitting, and yielding failure of steel, are identified during the pushout tests. Three different types of bond strength, such as the initial bond strength, the ultimate bond strength, and the residual bond strength, are observed from the load–slip curves between the shaped steel and concrete. By incorporating nonlinear spring elements, a numerical model for accurately simulating the bond performance between the shaped steel and SFRC specimens is developed. The bond strength between the shaped steel and concrete increase as the concrete strength, cover thickness, steel fiber volume ratio, and stirrup ratio increase, while it decreases as the steel embedment depth increases. A model for the bond strength between shaped steel and SFRC is developed, and it agrees well with the test data.

The influence of rolling on the corrosion and wear resistance of the MAO coating on ZM5 alloy

PurposeThe impact of rolling on the performance of micro arc oxidation (MAO) coatings on ZM5 alloy has been underreported. The purpose of this study is to explore the correlation between rolling and the failure mechanism of MAO coatings in greater depth.Design/methodology/approachThe influence of rolling on the corrosion and wear properties of MAO coating was investigated by phase structure, bond strength test (initial bond strength and wet adhesion), electrochemical impedance spectroscopy and wear test. The change of the surface electrochemical properties was studied by first principles analysis.FindingsThe results showed that the MAO coating on rolled alloy had better corrosion and wear resistance compared to cast alloy, although the structure and component content of two kinds of MAO coating are nearly identical. The difference in interface bonding between MAO coating and Mg substrate is the primary factor contributing to the disparity in performance between the two types of samples. Finally, the impact of the rolling process on MAO coating properties is explained through first-principle calculation.Originality/valueA comprehensive explanation of the impact of the rolling process on MAO coating properties will provide substantial support for enhancing the application of Mg alloy anticorrosion.Graphical abstract