High Strain Levels Research Articles

Polygenic liabilities underlying job stress and exhaustion over a 10-year follow-up: A general population study

We investigated whether individuals, who have a high polygenic loading for schizophrenia and major depression (PGL) but have not developed the respective disorders, are still susceptible to experience milder forms of ill-being in terms of job strain or exhaustion. We used the population-based Young Finns Study data (n = 928). PGL was assessed with a cumulative score of the polygenic risk scores for schizophrenia and depression. Participants (24–49-year-olds) evaluated their exhaustion levels and perceived job characteristics over a 10-year follow-up (2001, 2007, 2011). Participants with diagnosed psychotic or affective disorders were excluded. We found that high PGL did not predict less favorable perceptions of job environment (job strain, demands, control, satisfaction, social support at work) but high PGL predicted a higher trajectory of exhaustion in early adulthood and middle age. Additionally, high (vs. low) PGL predicted a stronger increase in exhaustion at increased levels of job strain. These findings remained after controlling for sex, socioeconomic factors, health behaviors, and cognitive performance. In conclusion, individuals with high PGL may have an elevated liability to experience exhaustion especially in early adulthood and middle age (despite they perceive their job environment similarly than others), and especially and at high levels of job strain.

Experimental evaluation of alkali-activated and portland cement-based mortars prepared using waste glass powder in replacement of fly ash

The decreasing trend in coal fly ash production has led to a rapidly growing interest in finding alternative materials to replace fly ash in concrete. In this study, the use of glass powder to replace fly ash in concrete was investigated. The performance of portland cement and alkali-activated slag-based mortars containing fly ash (class F) or glass powder (aluminosilicate-based) was evaluated via a series of experiments, including fresh, physical, mechanical, and restrained cracking tests. Notably, a customized restrained shrinkage test was used to investigate the cracking potential. Results showed that the ultra-fine glass powder performed differently in the two binding systems. In the portland cement system, the use of glass powder yielded higher concrete mechanical performance compared to the concrete containing fly ash, while the opposite conclusion was obtained for the alkali-activated system. Comparing the alkali-activated system with the portland cement system, the alkali-activated materials with either fly ash or glass powder had higher free shrinkage and developed cracks much earlier under the restrained drying shrinkage. However, the alkali-activated materials maintained a high level of strain in the steel ring, which was primarily attributed to the development of multiple cracks and their different bonding at the mortar and steel interface.

Construction of Flexible Piezoceramic Array with Ultrahigh Piezoelectricity via a Hierarchical Design Strategy

AbstractThe µW‐level power density of flexible piezoelectric energy harvesters (FPEHs) restricts their potential in applications related to high‐power multifunctional wearable devices. To overcome this challenge, a hierarchical design strategy is proposed by forming porous piezoceramics with an optimum microstructure into an ordered macroscopic array structure to enable the construction of high performance FPEHs. The porous piezoceramic elements allows optimization of the sensing and harvesting Figure of merit, and the array structure causes a high level of effective strain under a mechanical load. The introduction of a network of polymer channels between the piezoceramic array also provides increased device flexibility, thereby allowing the device to attach and conform to the curved contours of the human body. The unique hierarchical piezoceramic array architecture exhibits superior flexibility, a high open circuit voltage (618 V), high short circuit current (188 µA), and ultrahigh power density (19.1 mW cm−2). This energy density value surpasses previously reported high‐performance FPEHs. The ultrahigh power flexible harvesting can charge a 0.1 F supercapacitor at 2.5 Hz to power high‐power electronic devices. Finally, the FPEH is employed in two novel applications related to fracture healing monitoring and self‐powered wireless position tracking in extreme environments.

3D strain fields in a plant fibre composite during fragmentation test: Micro-CT based DIC and DVC

This paper aims to study the evolution of the 3D strain fields in a single yarn composite during fragmentation test. The internal full-field strains were obtained by coupling micro-CT scans with digital image correlation (DIC) and digital volume correlation (DVC). An ex-situ step-by-step fragmentation test was carried out on a sample made of a hemp yarn and a polymer matrix filled with metal oxide powder, playing the role of a three dimensional speckle. Macroscopic markers were also added to enable a precise geometric alignment during the 3D reconstruction. The analysis of the tomographic images showed a stepwise progression of the damage occurrence: yarn breaks appeared first, followed by internal matrix cracks and then edge cracks occurred for high strain levels. DIC method allowed to easily and quickly determine 2D strain maps in selected planes. The use of DVC was more complex and needed powerful computing systems but it gave the volumetric strains in the whole sample. DVC calculations were compared and validated by DIC results in central planes. Experimental results were also compared with finite element simulations. This study demonstrates the viability and benefits of combining DVC and micro-CT for a deeper understanding of complex 3D strains in single yarn composites.

An experimental study on the influence of fly ash and crumb rubber on the mechanical property and permeability of Engineered Cementitious Composite (ECC)

Interest in using Engineering Cementitious Composites (ECC) for waterproof reinforcement has rapidly risen in recent years. Many studies revealed the excellent mechanical properties and waterproof ability of ECC, and analytical models have been proposed for predicting the permeability of ECC at different strain levels. However, the tailoring theory of ECC leads to the fact that the mechanical properties and waterproof ability can be further improved by incorporating different binders and aggregates and adjusting their proportions. Therefore, the applicability of current permeability models on the ECC with different mix proportions still needs to be researched. This paper focuses on adding fly ash and crumb rubber to enhance the waterproof ability of ECC. Mechanical properties and permeability experiments at different tensile strain were conducted for ECC with various mix proportions, and the effects of fly ash and crumb rubber on the improving the ductility and reducing permeability were revealed. In addition, the accuracy of the model for different mix proportions and different strain levels was studied. It is revealed that both fly ash and crumb rubber lead to a higher ductility, denser crack pattern and lower permeability, and ECC with fly ash has a better performance than ECC with crumb rubber at high strain level. The analytical model for permeability of ECC was proved to be accurate when few crumb rubber is added, while overestimate is observed for high crumb rubber content experiments. The findings of this research will contribute to the mix proportion design of ECC for waterproof reinforcement application.

Effect of temperature on the low cycle fatigue properties of BGA solder joints

Since the restriction of hazardous substances (RoHS) directive, lead-free soldering has been widely broad adopted. In many applications, lead-free alloys have been substituted for conventional SnPb (Tin-Lead) solder. Among lead-free alloys, SAC305(Sn-3.0Ag-0.5Cu) has gained the highest acceptance as a solder alloy. The fatigue performance of solder joints has become an essential reliability assessment criterion due to the transition to more reliable lead-free alloys from highly predictable lead-based alloys. This study examines the shear fatigue characteristics of sandwich test vehicles for SnPb and SAC305 at different temperatures using both Organic Solderability Preservative (OSP) and Electroless Nickel-Immersion Silver (ENIG) surface finishes. The fatigue experiments were performed using an Instron micromechanical tester at a constant strain rate, and microstructural analysis was carried out using Scanning Electron Microscopy (SEM) to identify the Intermetallic Compound (IMC) morphology and failure mode. The stress-strain (hysteresis) loops of SnPb and SAC305 were measured, and the fatigue life of the specimens was estimated using the strain-life equation at various temperatures. SAC305 was observed to have a better fatigue life than SnPb, particularly at higher strain levels or testing temperatures. The OSP surface finish demonstrated superior fatigue properties compared to the ENIG surface finish. Additionally, elevated testing temperatures were found to accelerate fatigue failure in solder joints. The Arrhenius model was utilized to develop a general empirical model that predicts the fatigue life of SAC305 and SnPb solder alloys with OSP and ENIG surface finishes as a function of the strain level and testing temperature.

A proposed approach for accurate fatigue quantification of the base asphalt binders coupling nonlinear viscoelastic effects in S-VECD theoretical framework

The nonlinear viscoelasticity (NLVE) effects at high loading amplitudes are neglected in the stiffness evolution and fatigue quantification for asphalt binders. This study is to determine the applicability of the simplified viscoelastic continuum damage (S-VECD) model considering NLVE effects to the fatigue test protocols of asphalt binders at high strain levels, and to identify the real damage degradation and fatigue life quantification. An equivalent non-linear complex modulus (|G*|NLVE) of the NLVE-based S-VECD model was proposed and quantified by incremental stress sweep testing. A refined fatigue failure criterion GRNL was proposed in the NLVE model. The effectiveness of NLVE on the released pseudo-strain energy (PSE) and failure criteria was also verified. |G*|NLVE values in NLVE region are lower than |G*|LVE values in LVE region. The linear viscoelasticity (LVE)-based S-VECD model overestimates the damage effectiveness on the stiffness degradation. A significant difference exists between the NLVE and LVE models in the damage characteristic curves of the asphalt binders. The actual damage quantified by the NLVE model is lower than that of the LVE model. For both types of binder, the GRNL parameter remains well linear with the fatigue life (Nf). The linear relationship between the released PSE shrinkage values (ΔΣWrR) and the reduced damage (ΔS) is clear when comparing the LVE and NLVE models. The NLVE model predicted a higher fatigue life for asphalt binders than that predicted by the LVE model. The fatigue life determined by the NLVE model exhibits a linear functionality to that quantified by the LVE model, which further validates the applicability and validity of the NLVE model for the diagnosis of fatigue measurement. In contrast, the NLVE-based S-VECD model predicts the fatigue life of asphalt binders under practical service conditions more closely to the mechanical response under actual traffic loads.

Topotactically induced oxygen vacancy order in nickelate single crystals

The strong structure-property coupling in rare-earth nickelates has spurred the realization of new quantum phases in rapid succession. Recently, topotactic transformations have provided a new platform for the controlled creation of oxygen vacancies and, therewith, for the exploitation of such coupling in nickelates. Here, we report the emergence of oxygen vacancy ordering in Pr$_{0.92}$Ca$_{0.08}$NiO$_{2.75}$ single crystals obtained via a topotactic reduction of the perovskite phase Pr$_{0.92}$Ca$_{0.08}$NiO$_{3}$, using CaH$_2$ as the reducing agent. We unveil a brownmillerite-like ordering pattern of the vacancies by high-resolution scanning transmission electron microscopy, with Ni ions in alternating square-pyramidal and octahedral coordination along the pseudocubic [100] direction. Furthermore, we find that the crystal structure acquires a high level of internal strain, where wavelike modulations of polyhedral tilts and rotations accommodate the large distortions around the vacancy sites. Our results suggest that atomic-resolution electron microscopy is a powerful method to locally resolve unconventional crystal structures that result from the topotactic transformation of complex oxide materials.

DRX mechanisms of a Ni-Co-W type superalloy with typical columnar grains during hot compression

Columnar evolution and DRX mechanisms of a Ni-Co-W type superalloy with typical columnar grains during hot deformation were investigated processed at the γ′ sub/super-solvus temperatures. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) was employed to characterize the nucleation at columnar boundary. The results show that columnar grains gradually replaced by new dynamic recrystallization (DRX) grains and nucleation was prioritized at original columnar boundary or/and folding position. Meanwhile, DRX mechanisms of the columnar structure associated with γ′ phase were identified deeply. Discontinuous dynamic recrystallization (DDRX) was the main mechanism when deformation processed at γ′ sub/super-solvus temperatures. Bulging columnar grain boundaries are first as the nucleation sites of the new DDRX grains under various conditions. High angle grain boundaries (HAGBs: θ > 15°) bends to the side with γ′ phase, and then the DRX grains formed at the bulging grain boundary. In addition, high dislocation density zone occurred around the large size γ′ phases (more than 1 µm), leading to the misorientation generated rapidly and then the HAGBs formed. The formation of DRX grains by this way is also called particle stimulated nucleation (PSN) mechanism. Continuous dynamic recrystallization (CDRX) occurs when hot deformation processed at γ′ sub-solvus temperature with high strain level, which is accompanied by dislocation accumulation and an obviously increase in the fraction of grain boundaries with 10–15° misorientation angle. The findings help to understand different DRX mechanisms of Ni-based superalloy with columnar structure during microstructure evolution under hot forming, and are also beneficial for optimizing the microstructure to control the required properties of the Ni-based superalloys for manufacturing turbine disc.

An in situ investigation of neighborhood effects in a ferrite-containing quenching and partitioning steel: Mechanical stability, strain partitioning, and damage

Understanding the micromechanical consequences of transformation-induced plasticity (TRIP)-assisted steels is challenging, due to the presence of multiple phase constituents and difficulties in spatially and temporally resolving the transformation of sub-micron scale retained austenite. Local stress or strain partitioning among constituents is considered important in determining the stability of retained austenite, which often competes with other effects such as composition or crystal orientation. In this work, we study the neighborhood effects on micromechanical behaviors of multi-phase TRIP steel using a ferrite-containing quenching and partitioning steel as a model system by employing in situ SEM/EBSD and in situ synchrotron X-ray diffraction tensile tests, phase-specific nanoindentation, and atom probe tomography. Our results reveal that retained austenite, bainite, and tempered martensite clusters behave similarly due to underlying strengthening mechanisms, resulting in the early transformation of retained austenite surrounded by bainite and tempered martensite matrices. Conversely, in large ferrite grains, the intragranular strain distribution develops heterogeneously, which retards the transformation of some embedded retained austenite grains. The in situ microstructure-based strain mapping also demonstrates that the local strain increment of the retained austenite inside ferrite grains decreases as the deformation level increases, leading to a non-linear strain partitioning behavior at high strain levels. Another neighborhood-induced effect is observed in ferrite grains. When ferrite grains are neighbored by hard fresh martensite, their lateral contraction is inhibited, causing a plane strain tension path locally in ferrite, even when the globally applied strain path is uniaxial tension.

Time-dependent behaviour of RC beams under eccentric combined loads as a unit of beam-column joint assemblies made from normal strength concrete without/with CFRP wraps

The influence of sustained eccentric loads including torsion on the time-dependent behaviour of monolithically framed RC beams into columns is investigated in this paper. The adopted experimental program entails a number of beam-column assemblies tested under sustained concentric and eccentric combined loads (bending, shear, and torsion). The presence of Fibre Reinforced Polymers (FRP) wraps applied to the beam is considered and the time-dependent performance was thoroughly assessed. The outcomes of the experimental program complemented with finite element (F.E.) results illustrated a significant increase in the time-dependent beam’s twisting and deflection levels. The rise in the beam’s time-dependent deflections was quantified in comparison with those predicted according to Eurocode 2. This rise can be explained by the extent of torsional cracks observed, accompanied by high strain levels, resulting from the interaction between combined loads and the time-dependent deformations of concrete. While the FRP wraps considerably improved the time-dependent torsional stiffness compared to the un-strengthened specimens. The numerical models under different loads ratios (torsion to bending-shear ratio) confirmed the role of the level of combined loads and the developed time-dependent cracks of reducing the members’ stiffness and affecting the twisting levels and hence increased the deflection values. A refined approach of the Eurocode 2 modal has been proposed which considers the interaction of combined forces and hence, the developed stresses on the degrees of the loss of tension stiffening.

Quasi-random distribution of distorted nanostructures enhances thermoelectric performance of high-entropy chalcopyrite

Here, we suggest that the quasi-random distribution of distorted nanostructures (QDDN), which is unique in high-entropy materials, is the reason for superior thermoelectric properties. The general high entropy material consists of several atoms with disordered lattice in atomic scale. Our QDDN showed nanoscale disorder because the consisting atoms were not distributed fully randomly. The order of compositional distribution was found as 40–60 nm, which causes high level of lattice-strain-induced distortion. The underlying mechanism of phonon scattering by QDDN was clarified by theoretical analysis. The high level of lattice strain induced by QDDN causes strong phonon scattering in entire phonon spectrum. A low κlat of ∼0.38 W/m-K at 850 K was achieved in a CuGaTe2-based high-entropy chalcopyrite material. However, the power factor was not significantly affected due to ther high crystallinity, despite the QDDN. Therefore, a zT of ∼1.56 at 850 K was attained in a Cu0.8Ag0.2[Ga0.8In0.2]0.99Zn0.01Te2 compound, which represented a 132% enhancement from pure CuGaTe2. These results elucidate recent zT increases in high-entropy materials and can be a step towards further enhancements of zT in thermoelectric materials.

Association between physiological and perceptual heat strain while wearing stab-resistant body armor

In this study, we explored the association between physiological and perceptual heat strain while wearing stab-resistant body armor (SRBA). Human trials were performed on ten participants in warm and hot environments. Physiological responses (core temperature, skin temperature, and heart rate), and perceptual responses (thermal sensation vote, thermal comfort vote, restriction of perceived exertion (RPE), wetness of skin, and wetness of clothing) were recorded throughout the trials, and subsequently, the physiological strain index (PSI), and perceptual strain index (PeSI) were calculated. The results indicated that the PeSI showed a significant moderate association with the PSI, and was capable of predicting PSI for low (PSI = 3) and high (PSI = 7) levels of physiological strain with the areas under the curves of 0.80 and 0.64, respectively. Moreover, Bland-Altman analysis indicated that the majority of the PSI ranged within the 95% confidence interval, and the mean difference between PSI and PeSI was 0.14 ± 2.02 with the lower 95% limit and upper 95% limit being −3.82 to 4.10, respectively. Therefore, the subjective responses could be used as an indicator for predicting physiological strain while wearing SRBA. This study could provide fundamental knowledge for the usage of SRBA, and the development of physiological heat strain assessment.

Microstructure evolution and constitutive modeling of as-cast A356 aluminum alloy in semi-solid deformation regime

The present work deals with the semi-solid deformation behavior of A356 aluminum alloys with an emphasis on microstructure evolution and constitutive modeling. The main idea of this research is based on investigating the semi-solid deformation behavior starting with primary dendritic cast structure, instead the conventional approach in which a feedstock is prepared through the various spheroidization process. Toward this end, hot compression tests in the semi-solid temperature range (580, 590, and 600 °C) under different strain rates (0.001, 0.01, 0.1 s−1) and different initial holding times (1, 7, and 14 min) have been conducted. Compared with the thixotropic deformation in which the solid globules slide within the liquid matrix through lubricated flow mechanisms, in the present case, the strain compensation through the deformation of solid grains was increased. The higher portion of the solid-grains from the applied strain provided a proper condition for substructure development and dynamic recrystallization in the semisolid temperature range. The penetration of the liquid phase along the newly developed boundaries was introduced as another factor influencing on the softening behavior of the material. Under these conditions, the specimens were deformed up to the high strain level (>0.5) without creating cracks or tearing under very low stresses less than 2 MPa. A phenomenological-physical constitutive equation was also developed considering deformation parameters (temperature, strain rate, and strain) and material's parameters (grain size, strain rate sensitivity, viscosity) which was capable of predicting the semisolid flow stress behavior of the material.

The influence of AGEs and enzymatic cross-links on the mechanical properties of collagen fibrils

Collagen, one of the main building blocks for various tissues, derives its mechanical properties directly from its structure of cross-linked tropocollagen molecules. The cross-links are considered to be a key component of collagen fibrils as they can change the fibrillar behavior in various ways. For instance, enzymatic cross-links (ECLs), one particular type of cross-links, are known for stabilizing the structure of the fibril and improving material properties, while cross-linking AGEs (Advanced-Glycation Endproducts) have been shown to accumulate and impair the mechanical properties of collageneous tissues. However, the reasons for whether and how a given type of cross-link improves or impairs the material properties remain unknown, and the exact relationship between the cross-link properties and density, and the fibrillar behavior is still not well understood. Here, we use coarse-grained steered molecular models to evaluate the effect of AGEs and ECLs cross-links content on the deformation and failure properties of collagen fibrils. Our simulations show that the collagen fibrils stiffen at high strain levels when the AGEs content exceeds a critical value. In addition, the strength of the fibril increases with AGEs accumulation. By analyzing the forces within the different types of cross-links (AGEs and ECLs) as well as their failure, we demonstrate that a change of deformation mechanism is at the origin of these observations. A high AGEs content reinforces force transfer through AGEs cross-links rather than through friction between sliding tropocollagen molecules, which leads to failure by breaking of bonds within the tropocollagen molecules. We show that this failure mechanism, which is associated with lower energy dissipation, results in more abrupt failure of the collagen fibril. Our results provide a direct and causal link between increased AGEs content, inhibited intra-fibrillar sliding, increased stiffness, and abrupt fibril fracture. Therefore, they explain the mechanical origin of bone brittleness as commonly observed in elderly and diabetic populations. Our findings contribute to a better understanding of the mechanisms underlying impaired tissue behavior due to elevated AGEs content and could enable targeted measures regarding the reduction of specific collagen cross-linking levels.

Ruggedness Evaluation of Dynamic Modulus Test Using Small-Scale Test Specimens for Asphalt Mixture Performance Tester

The small specimen dynamic modulus test (AASHTO TP 132-19) is of paramount importance for the asphalt community since it can be used to characterize and compare asphalt mixtures and the test outcomes can be used as input for pavement performance predictions. Even though the small specimen dynamic modulus test is broadly used, acceptable limits for controlling critical experimental factors still need to be developed. This paper presents the method and outcomes of a ruggedness evaluation of the Asphalt Mixture Performance Tester (AMPT) dynamic modulus test using small-scale test specimens. Three mixtures were evaluated and seven experimental factors were selected: strain peak-to-peak magnitude, specimen perpendicularity, platen-to-specimen diameter difference, specimen height, temperature, compensation springs, and end friction reducers. The analysis identified the statistically significant factors and it was found that the strain peak-to-peak magnitude and temperature were the most statistically significant factors. The specimen height and the type of end friction reducer were not found to be statistically significant factors. Also, higher strain levels and the use of compensation springs resulted in the overestimation of modulus at higher temperatures. Finally, tolerance limits were determined for each ruggedness factor and modifications to the small specimen dynamic modulus test and related standards were proposed.

Microstructure and mechanical properties of a novel twinning induced plasticity steel with two different grain morphologies

A novel heterogeneous-structure (HS) twinning-induced plasticity (TWIP) steel containing alternating columnar grain (CG) and equiaxed grain (EG) domains was successfully fabricated via prestraining, partial recrystallization, and directional solidification. Compared with the traditional EG sample, the HS sample exhibited a better tensile strength–elongation combination (yield strength ≈ 263 MPa, ultimate tensile strength ≈ 573 MPa, total elongation ≈ 101.5%). The mutually constrained structure could effectively control the unique deformation modes of the EG and CG domains at different deformation stages. The HS sample exhibited stable and continuous plastic deformation owing to the timely release of localized high strain or stress, postponed plastic instability, and restrained crack propagation owing to the constrained structure. The stress relaxation was due to twinning and the effects of geometrically necessary dislocations, which accommodated deformation incompatibility. The improved mechanical properties of the HS sample were due to the persistent occurrence of the TWIP effect under very low to high strain levels during the entire deformation process, the effective grain boundary hardening in the EG domain, and the additional work hardening provided by the GNDs.

The Quadratic Constitutive Model Based on Partial Derivative and Taylor Series of Ti6242s Alloy and Predictability Analysis

To solve the problem of insufficient predictability in the classical models for the Ti6242s alloy, a new constitutive model was proposed, based on the partial derivatives from experimental data and the Taylor series. Firstly, hot compression experiments on the Ti6242s alloy at different temperatures and different strain rates were carried out, and the Arrhenius model and Hensel-Spittel model were constructed. Secondly, the partial derivatives of logarithmic stress with respect to temperature and logarithmic strain rate at low, medium and high strain levels were analyzed. Thirdly, two new constitutive models with first- and second-order approximation were proposed to meet the requirements of high precision. In this new model, by analyzing the high-order differential data of experimental data and combining the Taylor series theory, the minimum number of terms that can accurately approximate the experimental rheological data was found, thereby achieving an accurate prediction of flow stress with minimal material parameters. In the new model, by analyzing the high-order differential of the experimental data and combining the theory of the Taylor series, the minimum number of terms that can accurately approximate the experimental rheological data was found, thereby achieving an accurate prediction of flow stress with minimal material parameters. Finally, the prediction accuracies for the classical model and the new model were compared, and the predictabilities for the classical models and the new model were proved by mathematical means. The results show that the prediction accuracies of the Arrhenius model and the Hensel-Spittel model are low in the single-phase region and high in the two-phase region. In addition, second-order approximation is required between the logarithmic stress and logarithmic strain rate, and first-order approximation is required between logarithmic stress and temperature to establish a high-precision model. The order of prediction accuracy of the four models from high to low is the quadratic model, Arrhenius model, linear model and HS model. The prediction accuracy of the quadratic model in all temperatures and strain rates had no significant difference, and was higher than the other models. The quadratic model can greatly improve prediction accuracy without significantly increasing the material parameters.

Complex Strain Scapes in Reconstructed Transition-Metal Dichalcogenide Moiré Superlattices.

We investigate the intrinsic strain associated with the coupling of twisted MoS2/MoSe2 heterobilayers by combining experiments and molecular dynamics simulations. Our study reveals that small twist angles (between 0 and 2°) give rise to considerable atomic reconstructions, large moiré periodicities, and high levels of local strain (with an average value of ∼1%). Moreover, the formation of moiré superlattices is assisted by specific reconstructions of stacking domains. This process leads to a complex strain distribution characterized by a combined deformation state of uniaxial, biaxial, and shear components. Lattice reconstruction is hindered with larger twist angles (>10°) that produce moiré patterns of small periodicity and negligible strains. Polarization-dependent Raman experiments also evidence the presence of an intricate strain distribution in heterobilayers with near-0° twist angles through the splitting of the E2g1 mode of the top (MoS2) layer due to atomic reconstruction. Detailed analyses of moiré patterns measured by AFM unveil varying degrees of anisotropy in the moiré superlattices due to the heterostrain induced during the stacking of monolayers.

Detection and prevalence of extended spectrum β-lactamases production among Enterobacteriaceae isolated from urinary tract infections

Urinary tract infections (UTIs) by extended-spectrum β-lactamase producing Enterobacteriaceae (ESBL-E) have become an important public health problem with a substantial economic burden, as they lead to more complicated infections, longer duration of treatment, and increases in patient mortality. A total of 1267 urine samples were collected from patients during the period of 2018 to 2020. The isolates were identified based on colony morphology and biochemical tests. Antimicrobial susceptibility testing was done by modified Kirby Bauer disc diffusion method. Resistant isolates to third generation cephalosporins were tested for ESBL production by double-disk synergy test (DDST), DDST methods on MH agar plates supplemented with cloxacillin and by confirmatory double disk test (DDT). 400 strains causing UTIs were identified and classified as members of Enterobacteriaceae. The results of antimicrobial susceptibility tests showed that 68.5% (274/400) of the Enterobacteriaceae isolates were multi-drug resistant (MDR) strains. The overall prevalence of ESBL-E was 59.5% (238/400). The highest frequencies of ESBL-E were observed in internal medicine devices (68/400) and the highest ESBL production was observed in E. coli (85/238). The ESBL producing isolates were significantly resistant to penicillins and cephalosporins compared to non-ESBL producers. However, those ESBL-E strains were sensitive to imipenem (80.2%) and nitrofurantoin (87.8%). High levels of MDR strains and ESBL-E in our study highlights the need for applying specific infection control measures, and accordingly we urge physicians to opt for specific strategies for regular surveillance of uropathogenic bacteria.