Smooth Strains Research Articles

Calculation of the Mean Strain of Smooth Non-Uniform Strain Fields Using Conventional FBG Sensors

In the past few decades, fibre Bragg grating (FBG) sensors have gained a lot of attention in the field of distributed point strain measurement. One of the most interesting properties of these sensors is the presumed linear relationship between the strain and the peak wavelength shift of the FBG reflected spectra. However, subjecting sensors to a non-uniform stress field will in general result in a strain estimation error when using this linear relationship. In this paper we propose a new strain estimation algorithm that accurately estimates the mean strain value in the case of smooth non-uniform strain distributions. To do so, we first introduce an approximation of the classical transfer matrix model, which we will refer to as the approximated transfer matrix model (ATMM). This model facilitates the analysis of FBG reflected spectra under arbitrary strain distributions, particularly by providing a closed-form approximation of the side-lobes of the reflected spectra. Based on this new formulation, we derive a maximum likelihood estimator of the mean strain value. The algorithm is validated using both computer simulations and experimental FBG measurements. Compared to state-of-the-art methods, which typically introduce errors of tens of microstrains, the proposed method is able to compensate for this error. In the typical examples that were analysed in this study, mean strain errors of around 60 microstrains were compensated.

Evidence of ovine brucellosis due to Brucella ovis and Brucella melitensis in Karnataka, India

Ovine brucellosis is often neglected contagious bacterial disease causing enormous economic losses to sheep industry. India is recognized as geographical hotspot for brucellosis and there is only one seroprevalence report of Brucella ovis infection in sheep. Ovine brucellosis is caused by both rough and smooth strains of Brucella sp. In the present study, 300 sheep serum samples collected from 9 different districts of Karnataka by 3 stage random sampling approach were screened by antibody and DNA detection tests (RBPT and iELISA) and PCR. Antibodies specific to B. melitensis and B. ovis infection were 8.67% and 5.34%, respectively. In the same set of samples, 5% (15/300) showed Brucella DNA amplification by bcsp31 and IS711 genus specific PCRs. In B. melitensis and B. ovis species specific PCRs, 3.34% and 1.67%, respectively were detected positive indicating presence of both Brucella species in sheep population. Among the 7 districts, Yadgir, Tumkur, Raichur and Bagalkot showed higher prevalence of antibodies against rough and smooth strains of Brucella. This emphasizes the need for sensitization of national system in designing surveillance and control strategies for both B. ovis and B. melitensis infections in sheep.

Neutrophil killing of Mycobacterium abscessus by intra- and extracellular mechanisms.

Mycobacterium abscessus, a rapidly growing nontuberculous mycobacterium, are increasingly present in soft tissue infections and chronic lung diseases, including cystic fibrosis, and infections are characterized by growth in neutrophil-rich environments. M. abscessus is observed as two distinct smooth and rough morphotypes. The environmental smooth morphotype initiates infection and has a relatively limited ability to activate neutrophils. The rough morphotype has increased virulence and immunogenicity. However, the neutrophil response to the rough morphotype has not been explored. Killing of the smooth and rough strains, including cystic fibrosis clinical isolates, was equivalent. Neutrophil uptake of M. abscessus was similar between morphotypes. Mechanistically, both rough and smooth morphotypes enhanced neutrophil reactive oxygen species generation but inhibition of NADPH oxidase activity did not affect M. abscessus viability. However, inhibition of phagocytosis and extracellular traps reduced killing of the smooth morphotype with lesser effects against the rough morphotype. Neutrophils treated with M. abscessus released a heat-labile mycobactericidal activity against the rough morphotype, but the activity was heat-tolerant against the smooth morphotype. Overall, M. abscessus stimulates ineffective neutrophil reactive oxygen species generation, and key mechanisms differ in killing of the smooth (phagocytosis-dependent, extracellular traps, and heat-tolerant secreted factor) and rough (extracellular traps and a heat-labile secreted factor) morphotypes. These studies represent an essential advancement in understanding the host response to M. abscessus, and help explain the recalcitrance of infection.

Double-stranded and single-stranded well-entangled DNA solutions under LAOS: A comprehensive study

The nonlinear rheological behaviors of concentrated double-stranded (ds) and single-stranded (ss) DNA solutions were studied under standard oscillatory and large amplitude oscillatory shear (LAOS) deformations. To decompose the total stress into the elastic and viscous components, the raw nonlinear waveforms were analyzed using the MITlaos software package. We found that smooth and rigorous intracycle strain stiffening and shear thinning dominate the elastic and viscous decomposition, respectively, of the ds DNA sample. In contrast, the ss DNA sample exhibits initial intracycle strain stiffening, followed by a transition region and a terminal flow behavior. Insights into the nonlinear response of the DNA solutions were achieved by performing particle image velocimetry (PIV) at a wide range of imposed strain amplitudes and two angular frequencies. The rheo-PIV results of the ds DNA sample show a substantially modified flow field with distinct strain-driven shear bands at both angular frequencies examined. The bands formed by the ss DNA sample were weak even at the maximum strain amplitude. The results from this work are insightful from a traditional bulk rheological perspective, as well as for further single-molecular studies.

Smoothed Particle Finite-Element Method for Large-Deformation Problems in Geomechanics

This study presents a novel smoothed particle FEM (SPFEM) for large-deformation problems in geomechanics. Within the framework of the particle FEM (PFEM), a strain smoothing technique for nodal integration is incorporated. The problem domain is divided into strain smoothing cells associated with particles, and the equilibrium of the continuum medium is achieved at these strain smoothing cells. The corresponding computational formulations and numerical procedure are given. Compared with the original PFEM, the SPFEM possesses the following advantages: (1) all the field variables are calculated and stored at the particles, and the frequent information transfer between Gauss points and particles, which inevitably introduces error and adds considerable complexity to solution procedures, is avoided; (2) the SPFEM possesses the upper bound property, providing a conservative estimation for problems in geomechanics; and (3) linear elements can be used directly without suffering from the volumetric locking, so special treatment to bypass the volumetric locking is not required. By solving two benchmark examples, the SPFEM has been verified to be a promising numerical method for analyzing large-deformation problems in geomechanics.

Selective inhibition of smooth muscle plasma membrane transport Са2+,Mg2+-АТРase by calixarene C-90 and its activation by IPT-35 compound.

We investigated the influence of calixarene C-90 and IPT-35 on plasma membrane Ca2+- pumping АТРase (PMCA), intracellular calcium homeostasis and myometrium smooth muscle strain contractions. It has been shown that both effectors (100 μM) affect PMCA enzymatic activity: calixarene C-90 inhibits it by 75% and IPT-35 activates it by 40%. These compounds don't affect the Mg2+-АТРase, Mg2+-independent Са2+-АТРase and Na+,K+-АТРase enzymatic activities. C-90 inhibition coefficient I0.5 magnitude was approximately 20 μM and the Hill coefficient nH was 0.55. For IPT-35 activation, constant А0.5 was 6.4 and nH was 0.7. Mathematical modeling demonstrated the implication of calixarene C-90 on unexcited myocytes, which allows for a precise change in cytoplasm Ca2+ concentration and an influence on basal muscle tonus. By the same method, we determined that IPT-35 has a little influence on Ca2+ concentration in unexcited myocytes. It was also shown that calixarene C-90 in vitro can increase velocity of oxytocin-initiated contractions, whereas IPT-35 can suppress this aforementioned parameter. These results are promising for the design of new pharmacological compounds as better regulators of uterine contractions. Calixarene C-90 can be used in obstetric cases for the simultaneous use of oxytocin for enhancing uterine contractions, and IPT-35 for its antispasmodic effect on uterine tone.

On singular ES-FEM for fracture analysis of solids with singular stress fields of arbitrary order

The singular edge-based smoothed finite element method (sES-FEM) using triangular (T3) mesh with a special layer of five-noded singular elements (sT5) connected to the singular point, was proposed to model fracture problems in solids. This paper aims to extend the previous studies on singular fields of any order from −0.5 to 0, by developing an analytical means for integration to obtain the smoothed strains. We provide a more efficient practical formulae to estimate the stress intensity factor(SIF) for singular fields of mentioned order. The sT5 element has an additional node at each of the two edges connected to the crack tip, and the displacements are enriched with necessary terms to simulate the singularity. A weakened weak (W2) formulation is used to avoid the differentiation to the assumed displacement functions. The stiffness matrix is computed by using the smoothed strains calculated analytically from the enriched shape functions. Furthermore, our analytical integration techniques reduces the dependency on the order of numerical integration during the computation of the smoothed strain matrix. Several examples have been presented to demonstrate the reliability of the proposed method, excellent agreement between numerical results and reference observations shows that sES-FEM is an efficient numerical tool for predicting the SIF for singular fields.

A computationally efficient multiscale finite element formulation for dynamic and postbuckling analyses of carbon nanotubes

The efficient multiscale membrane locking free shell elements are developed to study the dynamic and postbuckling characteristics of carbon nanotubes incorporating material and geometric nonlinearities. The constitutive relation at continuum level is derived through the Cauchy–Born rule incorporating the effect of curvature tensor on bond lengths and using the Tersoff–Brenner atomic interaction potential per unit area of a unit cell. The membrane locking is eliminated by using the smoothed shape functions derived through the least square strain smoothing technique for the interpolation of the transverse displacement in the circumferential strain. The performance of the four/eight noded inconsistent/consistent Kirchhoff rectangular and improved discrete Kirchhoff quadrilateral (IDKQ) shell elements is investigated. It is found that the four noded elements with smoothed interpolation of transverse displacement in the circumferential strain yield accurate results and are computationally efficient. The multiscale modelling results are found to be in close agreement with the molecular mechanics simulations. The significant effect of material nonlinearity on the nonlinear dynamic and postbuckling responses is predicted.

Linear smoothed extended finite element method

SummaryThe extended finite element method was introduced in 1999 to treat problems involving discontinuities with no or minimal remeshing through appropriate enrichment functions. This enables elements to be split by a discontinuity, strong or weak, and hence requires the integration of discontinuous functions or functions with discontinuous derivatives over elementary volumes. A variety of approaches have been proposed to facilitate these special types of numerical integration, which have been shown to have a large impact on the accuracy and the convergence of the numerical solution. The smoothed extended finite element method (XFEM), for example, makes numerical integration elegant and simple by transforming volume integrals into surface integrals. However, it was reported in the literature that the strain smoothing is inaccurate when non‐polynomial functions are in the basis. In this paper, we investigate the benefits of a recently developed Linear smoothing procedure which provides better approximation to higher‐order polynomial fields in the basis. Some benchmark problems in the context of linear elastic fracture mechanics are solved and the results are compared with existing approaches. We observe that the stress intensity factors computed through the proposed linear smoothed XFEM is more accurate than that obtained through smoothed XFEM.

GalK-based suicide vector mediated allelic exchange in Mycobacterium abscessus.

Mycobacterium abscessus is a fast-growing environmental organism and an important emerging pathogen. It is highly resistant to many antibiotics and undergoes a smooth to rough colony morphology change that appears to be important for pathogenesis. Smooth environmental strains have a glycopeptidolipid (GPL) on the surface, while certain types of clinical strains are often rough and lack this GPL, due to mutations in biosynthetic genes or the mmpL4b transporter gene. We report here the development and evaluation of an allelic exchange system for unmarked alleles in M. abscessus ATCC19977, using a suicide vector bearing the E. coli galK gene and 2-deoxygalactose counterselection. We describe here two variant galK suicide vectors, and demonstrate their utility in constructing a variety of mutants with deletion alleles of the mmpL4b GPL transporter gene, the mbtH GPL biosynthesis gene, the known β-lactamase gene MAB_2875 and a putative β-lactamase gene, MAB_2833. We also show that a novel allele of the E. coli aacC4 gene, conferring apramycin resistance (aacC41), can be used as a selectable marker in M. abscessus ATCC19977 at single copy.

Brucella Rough Mutant Induce Macrophage Death via Activating IRE1α Pathway of Endoplasmic Reticulum Stress by Enhanced T4SS Secretion.

Brucella is a Gram-negative facultative intracellular pathogen that causes the worldwide zoonosis, known as brucellosis. Brucella virulence relies mostly on its ability to invade and replicate within phagocytic cells. The type IV secretion system (T4SS) and lipopolysaccharide are two major Brucella virulence factors. Brucella rough mutants reportedly induce the death of infected macrophages, which is T4SS dependent. However, the underlying molecular mechanism remains unclear. In this study, the T4SS secretion capacities of Brucella rough mutant and its smooth wild-type strain were comparatively investigated, by constructing the firefly luciferase fused T4SS effector, BPE123 and VceC. In addition, quantitative real-time PCR and western blotting were used to analyze the T4SS expression. The results showed that T4SS expression and secretion were enhanced significantly in the Brucella rough mutant. We also found that the activity of the T4SS virB operon promoter was notably increased in the Brucella rough mutant, which depends on quorum sensing-related regulators of VjbR upregulation. Cell infection and cell death assays revealed that deletion of vjbR in the Brucella rough mutant absolutely abolished cytotoxicity within macrophages by downregulating T4SS expression. This suggests that up-regulation of T4SS promoted by VjbR in rough mutant ΔrfbE contribute to macrophage death. In addition, we found that the Brucella rough mutant induce macrophage death via activating IRE1α pathway of endoplasmic reticulum stress. Taken together, our study provide evidence that in comparison to the Brucella smooth wild-type strain, VjbR upregulation in the Brucella rough mutant increases transcription of the virB operon, resulting in overexpression of the T4SS gene, accompanied by the over-secretion of effecter proteins, thereby causing the death of infected macrophages via activating IRE1α pathway of endoplasmic reticulum stress, suggesting novel insights into the molecular mechanisms associated with Brucella rough mutant-induced macrophage cytotoxicity.

Numerical and experimental validation of a particle Galerkin method for metal grinding simulation

In this paper, a numerical approach with an experimental validation is introduced for modelling high-speed metal grinding processes in 6061-T6 aluminum alloys. The derivation of the present numerical method starts with an establishment of a stabilized particle Galerkin approximation. A non-residual penalty term from strain smoothing is introduced as a means of stabilizing the particle Galerkin method. Additionally, second-order strain gradients are introduced to the penalized functional for the regularization of damage-induced strain localization problem. To handle the severe deformation in metal grinding simulation, an adaptive anisotropic Lagrangian kernel is employed. Finally, the formulation incorporates a bond-based failure criterion to bypass the prospective spurious damage growth issues in material failure and cutting debris simulation. A three-dimensional metal grinding problem is analyzed and compared with the experimental results to demonstrate the effectiveness and accuracy of the proposed numerical approach.

Effect of amikacin on cell wall glycopeptidolipid synthesis in Mycobacterium abscessus.

Cultivation of the smooth colony Mycobacterium abscessus at the sub-minimum inhibitory concentration (MIC) of amikacin changed its growth pattern including its colony morphology (smooth to rough) and cell arrangement (dispersed to cord formation). In addition, reduced sliding motility and biofilm formation were observed. The amount of glycogpetidolipid (GPL) and mRNA expression of key genes involved in GPL synthesis were decreased in the amikacin-treated M. abscessus strain. An in vitro infection assay revealed that the amikacin-treated smooth M. abscessus strain induced more pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) than that of the smooth strain in murine macrophage cells. These results suggest that long-term exposure to a low concentration of amikacin causes a physical change in the cell wall which may increase its virulence.

Not a barrier but a key: How bacteriophages exploit host's O-antigen as an essential receptor to initiate infection.

Tailed bacteriophages specific for Gram-negative bacteria encounter lipopolysaccharide (LPS) during the first infection steps. Yet, it is not well understood how biochemistry of these initial interactions relates to subsequent events that orchestrate phage adsorption and tail rearrangements to initiate cell entry. For many phages, long O-antigen chains found on the LPS of smooth bacterial strains serve as essential receptor recognized by their tailspike proteins (TSP). Many TSP are depolymerases and O-antigen cleavage was described as necessary step for subsequent orientation towards a secondary receptor. However, O-antigen specific host attachment must not always come along with O-antigen degradation. In this issue of Molecular Microbiology Prokhorov et al. report that coliphage G7C carries a TSP that deacetylates O-antigen but does not degrade it, whereas rough strains or strains lacking O-antigen acetylation remain unaffected. Bacteriophage G7C specifically functionalizes its tail by attaching the deacetylase TSP directly to a second TSP that is nonfunctional on the host's O-antigen. This challenges the view that bacteriophages use their TSP only to clear their way to a secondary receptor. Rather, O-antigen specific phages may employ enzymatically active TSP as a tool for irreversible LPS membrane binding to initiate subsequent infection steps.

Phylogenetic analysis of Mycobacterium massiliense strains having recombinant rpoB gene laterally transferred from Mycobacterium abscessus.

Recent multi locus sequence typing (MLST) and genome based studies indicate that lateral gene transfer (LGT) events in the rpoB gene are prevalent between Mycobacterium abscessus complex strains. To check the prevalence of the M. massiliense strains subject to rpoB LGT (Rec-mas), we applied rpoB typing (711 bp) to 106 Korean strains of M. massiliense infection that had already been identified by hsp65 sequence analysis (603 bp). The analysis indicated 6 smooth strains in M. massiliense Type I (10.0%, 6/60) genotypes but no strains in M. massiliense Type II genotypes (0%, 0/46), showing a discrepancy between the 2 typing methods. Further MLST analysis based on the partial sequencing of seven housekeeping genes, argH, cya, glpK, gnd, murC, pta and purH, as well as erm(41) PCR proved that these 6 Rec-mas strains consisted of two distinct genotypes belonging to M. massiliense and not M. abscessus. The complete rpoB sequencing analysis showed that these 6 Rec-mas strains have an identical hybrid rpoB gene, of which a 478 bp partial rpoB fragment may be laterally transferred from M. abscessus. Notably, five of the 6 Rec-mas strains showed complete identical sequences in a total of nine genes, including the seven MLST genes, hsp65, and rpoB, suggesting their clonal propagation in South Korea. In conclusion, we identified 6 M. massiliense smooth strains of 2 phylogenetically distinct genotypes with a specific hybrid rpoB gene laterally transferred from M. abscessus from Korean patients. Their clinical relevance and bacteriological traits remain to be elucidated.

Co-rotational shell element for numerical analysis of laminated piezoelectric composite structures

Abstract Laminated composite structures consisting of load-carrying and multifunctional materials represent a rather powerful material system. The passive, load-carrying layers can be made of isotropic material or fiber-reinforced composites, while piezoelectric materials represent the most common choice of multifunctional materials for active layers. The multifunctionality of piezoelectric layers is provided by their inherent property to couple mechanical and electric fields. The property can thus be used to sense deformations or produce actuating forces. A highly efficient 3-node shell element is developed for modeling piezoelectric laminated composite shells. The equivalent single-layer approach and Mindlin-Reissner kinematics are used in the element formulation together with the discrete shear gap (DSG) technique to resolve the shear locking and strain smoothing technique to improve the performance. Piezoelectric layers are assumed to be polarized in the thickness direction thus coupling the in-plane strains with the electric field oriented in the thickness direction. The co-rotational FE formulation is used to account for geometrically nonlinear effects. Numerical examples cover linear and geometrically nonlinear static and dynamic cases with piezoelectric layers used as actuators and sensors.

Three-dimensional concrete impact and penetration simulations using the smoothed particle Galerkin method

In this paper, we model the three-dimensional concrete impact and penetration problems using a stabilized meshfree method. The present method is established using a non-residual penalty term from strain smoothing as a means of stabilizing the meshfree nodal integration method under the Galerkin framework. As a result, the meshfree discretization leads to a dual stress point algorithm with the stabilization parameterized by a measure of a local length scale. An adaptive anisotropic Lagrangian kernel is considered in junction with the stabilized meshfree formulation for the severe deformation analysis. In order to avoid the spurious damage growth and material self-healing in concrete failure analysis, a bond-based failure criterion is introduced. A frictionless self-contact algorithm is also developed to model the interaction between concrete debris in damage. Several impact examples are investigated including the study of scabbing and perforation of concrete under high velocity impact. The numerical results are compared with the experimental data to demonstrate the effectiveness of the present method.

Improvement on MITC3 plate finite element using edge-based strain smoothing enhancement for plate analysis

An improved three-node triangular plate finite element is presented for plate analysis. The key idea is to enhance the performance of the original MITC3 element with an edge-based strain smoothing technique. To address this derivation, the MITC3 is explicitly formulated to obtain constant gradient matrices. All strain fields are then averaged over edge-based integration domains defined by two nodes of an element’s edge and the centroid(s) of element(s) sharing the element’s edge. A stabilized coefficient factor is also used for the shearing stiffness. We name this element as ES-MITC3, and it is then employed to analyze various plate problems under static loading and free vibration. Numerical results show that the ES-MITC3 element is free of “shear locking” and performs well for static and vibration behaviors. The present element exhibits a good competitor with other several existing three-node triangular plate elements, even the four-node MITC4 element.

An Extended Cell-Based Smoothed Three-Node Mindlin Plate Element (XCS-MIN3) for Free Vibration Analysis of Cracked FGM Plates

A cell-based smoothed three-node Mindlin plate element (CS-MIN3) was recently proposed and proven to be robust for static and free vibration analyses of Mindlin plates. The method improves significantly the accuracy of the solution due to softening effect of the cell-based strain smoothing technique. In addition, it is very flexible to apply for arbitrary complicated geometric domains due to using only three-node triangular elements which can be easily generated automatically. However so far, the CS-MIN3 has been only developed for isotropic material and for analyzing intact structures without possessing internal cracks. The paper hence tries to extend the CS-MIN3 by integrating itself with functionally graded material (FGM) and enriched functions of the extended finite element method (XFEM) to give a so-called extended cell-based smoothed three-node Mindlin plate (XCS-MIN3) for free vibration analysis of cracked FGM plates. Three numerical examples with different conditions are solved and compared with previous published results to illustrate the accuracy and reliability of the XCS-MIN3 for free vibration analysis of cracked FGM plates.

Strain smoothing for compressible and nearly-incompressible finite elasticity

We present a robust and efficient form of the smoothed finite element method (S-FEM) to simulate hyperelastic bodies with compressible and nearly-incompressible neo-Hookean behaviour. The resulting method is stable, free from volumetric locking and robust on highly distorted meshes. To ensure inf-sup stability of our method we add a cubic bubble function to each element. The weak form for the smoothed hyperelastic problem is derived analogously to that of smoothed linear elastic problem. Smoothed strains and smoothed deformation gradients are evaluated on sub-domains selected by either edge information (edge-based S-FEM, ES-FEM) or nodal information (node-based S-FEM, NS-FEM). Numerical examples are shown that demonstrate the efficiency and reliability of the proposed approach in the nearly-incompressible limit and on highly distorted meshes. We conclude that, strain smoothing is at least as accurate and stable, as the MINI element, for an equivalent problem size.