Search Results (56)

Strain localization is a critical phenomenon in geotechnical materials, serving as a precursor to the failure of engineering structures such as slopes, foundations, and tunnels. This paper presents a comprehensive review of the theoretical, experimental, and numerical advances in the study of strain localization. Theoretically, the review spans from classical empirical criteria for shear band inclination to the more rigorous bifurcation theory, which mathematically defines the onset of localization as a loss of uniqueness in the governing equations. Experimentally, various laboratory techniques including direct shear, triaxial, plane strain, and true triaxial tests are discussed, highlighting how they have revealed the influences of microstructure, stress path, and boundary conditions on shear band development. The core of the review focuses on numerical simulations, critically analyzing the limitations of the classical Finite Element Method (FEM) due to mesh dependency. It then elaborates on advanced regularization strategies, encompassing weak discontinuity methods (e.g., Cosserat continuum theory) that introduce an internal length scale to model finite-width shear bands, and strong discontinuity methods (e.g., the Strong Discontinuity Approach, SDA) for simulating discrete cracks. Significant emphasis is placed on innovative coupled approaches, particularly the Cos-SDA model, which integrates the advantages of both weak and strong discontinuity methods to seamlessly simulate the entire progressive failure process from diffuse localization to discrete slip. Furthermore, the application of spectral analysis for evaluating the regularization performance of these numerical methods is examined. Finally, the review concludes by identifying persistent challenges and outlining promising future research directions, including 3D modeling, multi-field coupling, and the integration of data-driven techniques. This synthesis aims to provide a valuable reference for advancing the prediction and management of failure in geotechnical structures. Full article

This study employs coarse-grained molecular dynamics simulations to investigate how the overlap distance between graphene nanosheets influences the mechanical properties of “brick-mortar”-structured graphene–polyethylene nanocomposites. Simulations are conducted in a fixed box size while varying the overlap distance from 2.4 to 24 nm. The stress–strain response exhibits three distinct stages: elastic increase, plastic plateau, and slow decrease. The yield strength increases nearly linearly from 115.3 ± 3.8 to 347.9 ± 33.0 MPa with increasing overlap distance, a trend well captured by an extended shear-lag model incorporating polymer stretch. The critical failure strain, marking the onset of strain localization, first increases and then decreases, peaking at an overlap distance of 4.8 nm. This non-monotonic behavior is attributed to a competition between polymer stretch and polymer shear in interfacial stress transfer. Similarly, the plateau stress and toughness show two-stage evolution: the plateau stress remains constant (~100 MPa) up to 4.8 nm before increasing significantly, while toughness rises from 16.9 ± 0.2 to 51.0 ± 4.0 MJ/m³ across the range. These findings reveal the nanoscale mechanisms behind strength and toughness in bioinspired nanocomposites and provide guidelines for optimizing performance through overlap distance tuning. Full article

Background/Objective: The relationship between Helicobacter pylori (H. pylori) infection and inflammatory bowel disease (IBD) remains controversial. While H. pylori is a well-established pathogen in gastroduodenal diseases, emerging evidence suggests it may exert immunomodulatory effects that influence the pathogenesis and clinical course of IBD. This review aims to explore the association between H. pylori infection and IBD, focusing on infection prevalence among IBD patients, the potential protective or harmful roles of H. pylori, and the impact of eradication therapy on IBD onset and activity. Methods: A comprehensive literature search was conducted using PubMed up to, including clinical studies, meta-analyses, systematic reviews, and observational data. A total of 40 studies met the inclusion criteria and were critically reviewed. Results: The majority of studies indicate a significantly lower prevalence of H. pylori infection among patients with IBD compared to the general population. Several meta-analyses support a potential protective effect, particularly in Crohn’s disease and among CagA-positive H. pylori strains. However, data on the impact of eradication therapy on IBD progression remain inconclusive. Some studies suggest a higher relapse risk post-eradication, while others report no change in disease activity. Variability in outcomes may be influenced by geographic, demographic, and methodological differences, as well as disease activity at the time of eradication. Conclusions: Although numerous studies support an inverse association between H. pylori infection and IBD, the nature and direction of this relationship remain unclear. Given the complex interplay between host immunity, gut microbiota, and antibiotic exposure, the decision to eradicate H. pylori in IBD patients should be individualized. Further prospective studies are needed to clarify the immunological and microbiological mechanisms underlying this association and to inform clinical guidelines. Full article

In this study, high-temperature uniaxial tensile tests were performed on IN718 superalloy samples fabricated using Wire Arc Additive Manufacturing (WAAM) and compared to wrought IN718 superalloy samples. The mechanical properties and Portevin–Le Chatelier (PLC) behavior of WAAM IN718 were analyzed, with particular attention paid to its anisotropy and differences from its wrought counterpart. WAAM specimens were obtained from three distinct orientations within the printed blocks. The results indicated that WAAM IN718 exhibited a higher yield strength but reduced failure elongation compared to wrought IN718. Among the WAAM samples, the yield strength was highest in the transverse direction, followed by the in-depth direction, and lowest in the growth direction. Post-aging treatment significantly increased the yield strength of WAAM IN718. WAAM IN718 showed a larger critical strain for the onset of serrated flow and smaller stress drop amplitudes compared to wrought IN718 under the PLC effect. Furthermore, as the strain rate decreased, PLC serrations in WAAM specimens from the in-depth direction transitioned from type A to type C. Conversely, specimens from the growth direction maintained type B serrations at a strain rate of ${10}^{-4}{\mathrm{s}}^{-1}$. This study also examined potential factors influencing the differences in PLC behavior and conducted an analysis of the fracture surfaces across various specimens. Full article

This study examines the energy behavior of a strengthening system consisting of a Fiber Reinforced Polymer (FRP) plate bonded to a rigid substrate and subjected to tensile loading, where the adhesive interface is governed by a bilinear bond–slip law with a vertical descending branch. The investigation focuses on the interaction between the elastic energy stored in the FRP and the adhesive interface, as well as the characteristic lengths that control the debonding process. Analytical expressions for the strain energy stored in both the FRP plate and the adhesive interface are derived, enabling the identification and evaluation of two critical characteristic lengths as the bond stress at the loaded end approaches its maximum value $l_c$, at which the elastic energies of the FRP and the adhesive interface converge, signaling energy saturation; and $l_{max}$, where the adhesive interface attains its peak energy absorption. Upon reaching the energy saturation state, the system undergoes failure through the sudden and complete debonding of the FRP from the substrate. The onset of unstable debonding is rigorously analyzed in terms of the first and second derivatives of the total potential energy with respect to the bond length. It is further demonstrated that abrupt debonding may also occur in cases where the length exceeds $l_c$ when the bond stress reaches its maximum, and the bond–slip law is characterized by a vertical branch. The findings provide significant insights into the energy balance and stability criteria governing the debonding failure mode in FRP-strengthened structures, highlighting the pivotal role of characteristic lengths in predicting both structural performance and failure mechanisms. Full article

Diabetes mellitus (DM) is a chronic metabolic disorder characterized by impaired glycemic regulation and persistent hyperglycemia, which drives the onset of microvascular complications such as diabetic neuropathy and nephropathy. Chronic hyperglycemia activates oxidative stress pathways and alters gut microbiota composition, both of which contribute to disease progression. In this context, probiotics have emerged as promising therapeutic agents due to their ability to modulate oxidative stress, improve glycemic control, and influence gut microbial balance. This review summarizes preclinical and clinical evidence supporting the antioxidant potential of probiotics in DM management, with a focus on underlying mechanisms. Strains from the Lactobacillus and Bifidobacterium genera are the most extensively studied and have demonstrated hypoglycemic and antioxidant effects, including the enhancement of key antioxidant enzymes and reductions in lipid peroxidation and nitrosative stress markers. Probiotics have also shown beneficial effects in DM-associated complications, particularly diabetic neuropathy and nephropathy. While clinical data are still limited, recent findings underscore oxidative stress as a critical therapeutic target influenced by probiotic interventions. Overall, current evidence supports probiotics as a complementary strategy for managing DM and its complications, highlighting the need for further well-designed clinical trials exploring diverse strains, formulations, and dosing regimens. Full article

Type 1 Diabetes (T1D) is a progressive autoimmune disease often identified in childhood or adolescence, with early stages detectable through pre-diabetic markers such as autoantibodies and subclinical beta-cell dysfunction. The identification of the pre-T1D stage is critical for preventing complications, such as diabetic ketoacidosis, and for enabling timely interventions that may alter disease progression. This review examines the multifaceted approach to managing T1D risk in adolescents and teens, emphasizing early detection, nutritional interventions, beta-cell preservation strategies, and psychosocial support. Screening for T1D-associated autoantibodies offers predictive insight into disease risk, particularly when combined with education and family resources that promote lifestyle adjustments. Although nutritional interventions alone are not capable of preventing T1D, certain lifestyle interventions, such as weight management and specific nutritional choices, have shown the potential to preserve insulin sensitivity, reduce inflammation, and mitigate metabolic strain. Pharmacological strategies, including immune-modulating drugs like teplizumab, alongside emerging regenerative and cell-based therapies, offer the potential to delay disease onset by protecting beta-cell function. The social and psychological impacts of a T1D risk diagnosis are also significant, affecting adolescents’ quality of life, family dynamics, and mental health. Supportive interventions, including counseling, cognitive-behavioral therapy (CBT), and group support, are recommended for managing the emotional burden of pre-diabetes. Future directions call for integrating universal or targeted screening programs within schools or primary care, advancing research into nutrition and psychosocial support, and promoting policies that enhance access to preventive resources. Advocacy for the insurance coverage of screening, nutritional counseling, and mental health services is also crucial to support families in managing T1D risk. By addressing these areas, healthcare systems can promote early intervention, improve beta-cell preservation, and support the overall well-being of adolescents at risk of T1D. Full article

We develop a new analytical and numerical approach, based on existing models, to describe the onset of lateral–torsional buckling (LTB) for simply supported thin-walled steel members. The profiles have uniform I cross-sections with variable lengths of the flanges, to describe also H cross-sections, they are prestressed by external tendons, and they are subjected to fire and various loadings. Our approach manages to update the value of the prestressing force, accounting for thermal and loads; the critical multipliers result from an eigenvalue problem obtained applying Galërkin’s approach to a system of nonlinear equilibrium equations. Our results are compared to buckling, steady state, and transient state analyses of a Finite Element Method (FEM) simulation, in which an original expression for an equivalent thermal expansion coefficient for the beam–tendon system that accounts for both mechanical and thermal strains is introduced. Our aim is to find estimates for the critical conditions with no geometric imperfections and accounting for the decay of material properties due to fire, thus providing limit values useful for conservative design. This approach can surpass others in the literature and in the existing technical norms. Full article

This study presents the results of adapting an existing mathematical model of concrete, originally based on the isotropic properties of traditional cast concrete, to the conditions of 3D printing technology using layer-by-layer horizontal extrusion. The adaptation of the mathematical model is grounded in experimental investigations of the deformation and failure processes of 3DCP concrete samples under various loading schemes. These experiments take into account the structure of the concrete and compare the results with the loading behavior of samples produced using traditional concreting methods. The research findings reveal that the mechanical properties of 3DCP concrete exhibit pronounced anisotropy, determined by the layered structure of the material within the construction. Concrete in structures produced via horizontal layer-by-layer extrusion is a piecewise-homogeneous, layered orthotropic material with differing mechanical properties along mutually orthogonal axes. The experiments demonstrate that under compression and tension perpendicular to the extrusion layers, the behavior of the concrete can be described using mathematical expressions similar to those for traditional concrete, albeit with adjusted key constants reflecting the actual properties. Conversely, under tensile loading parallel to the extrusion layers, the stress–strain relationship can be approximated as a straight line from the onset of loading to failure, with the limit corresponding to the adhesion strength (R_adh). In this regime, failure occurs in a brittle manner. The specific deformation and failure mechanisms of 3DCP concrete under tensile loading parallel to the extrusion layers represent a critical distinction from traditional cast concrete. This characteristic prevents the direct application of existing calculation methods to justify the strength and reliability of 3DCP concrete structures. Full article

West Nile Virus, an arthropod-borne RNA virus, may result in severe neurological disease. West Nile neuroinvasive disease is characterized by meningitis, encephalitis, and possible acute flaccid paralysis. Here, we report a case of neuroinvasive WNV in a 65-year-old woman hospitalized for hyperpyrexia, chills, intense asthenia, and continuous vomiting. Within days, her clinical condition worsened with the onset of severe neurological symptoms, leading to her death within 10 days despite supportive therapies being administered. The diagnosis of West Nile disease was made through nucleic acid amplification testing (NAAT) on blood and cerebrospinal fluid. However, in the final stages of the illness, cerebrospinal fluid collection was not possible due to the patient’s critical condition, and a nasopharyngeal swab was used instead. The nasopharyngeal swab facilitated the collection of a sample, which was subsequently analyzed for the presence of the virus and allowed for sequencing, showing that it was a strain that had been circulating in Sardinia for some time and had demonstrated its pathogenicity by causing the death of a hawk in 2021. This case report highlights the rapid progression and severity of WNV infection, particularly in vulnerable individuals, and suggests the potential utility of nasopharyngeal swabs as a less invasive option for sample collection. It also underscores the potential for the zoonotic transmission of the virus from birds to humans through vectors, emphasizing the importance of monitoring and controlling WNV outbreaks, especially in regions where such circulation is observed. Full article

Objective: Numerous studies have highlighted the prevalence of mental health disorders among healthcare professionals during the COVID-19 pandemic, with varying indications of emotional strain. This study compares the psychological functioning of healthcare workers at the onset of the pandemic and two years later, offering a comprehensive assessment of their emotional and mental health status in the evolving context of COVID-19. Methods: This longitudinal analysis examined the relationship between stress, emotional processing, and their positive/negative impacts on medical personnel working in Polish hospitals and outpatient clinics in 2020 (n = 285) and 2022 (n = 252). The study employed the Toronto Alexithymia Scale-20 (TAS-20), Cohen’s Perceived Stress Scale (PSS-10), Mini-COPE, Acceptance of Illness Scale (AIS), Emotional Processing Scale (EPS), STAI, and PANAS to assess psychological responses and coping mechanisms. Results: Findings revealed a significant increase in denial, substance use, self-blame, negative mood, and impaired psychological and somatic functioning, alongside heightened symptoms of depression and anxiety. Conversely, a marked decrease in planning, positive reinterpretation, acceptance, religious coping, and seeking social support (both emotional and instrumental) was observed over the two-year period. Conclusion: The prolonged nature of the COVID-19 pandemic has profoundly affected the psychological resilience of healthcare professionals, eroding critical emotional resources necessary for maintaining interpersonal relationships and mental well-being. These results underscore the need for targeted interventions to support the mental health of medical staff in the ongoing crisis. Full article

Atherosclerosis, as the main root cause, makes cardiovascular diseases (CVDs) a substantial worldwide health concern. Inflammation and disrupted cholesterol metabolism are the primary clinical risk elements contributing to the onset of atherosclerosis. Few works exist on the improvement effect of gut microbiota on atherosclerosis. One specific probiotic strain, Enterococcus faecium NCIMB11508, has shown promise in mitigating inflammation. Consequently, it is critical to investigate its potential in reducing the progression of atherosclerosis. In our study, we administered E. faecium NCIMB11508 orally to ApoE^−/− mice, resulting in a decrease in the formation of atherosclerotic lesions. Additionally, it demonstrated the ability to lower the inflammatory factor levels both in the aorta and blood serum while maintaining the integrity of the small intestine against lipopolysaccharides. Moreover, E. faecium NCIMB11508 had a beneficial impact on the gut microbiota composition by increasing the levels of short-chain fatty acids (SCFAs), which in turn helped to reduce inflammation and protect the intestine. The probiotic E. faecium NCIMB11508, according to our research, has a definitive capacity to prevent atherosclerosis progression by beneficially altering the SCFA composition in the gut microbiota of ApoE^−/− mice. Full article

This study investigates the micro-mechanical behavior of mortar under uniaxial compression using a three-phase model in PFC^3D. By simulating mortar as a composite of cement, sand, and the interfacial transition zone (ITZ), the research examines the impact of particle size on stress–strain behavior, crack propagation, porosity distribution, contact forces, and energy transformation. The simulations reveal that reducing sand particle size from 1–2 mm to 0.25–0.5 mm leads to a significant increase in uniaxial compressive strength, with peak strength values rising from 65.3 MPa to 89.6 MPa. The elastic modulus similarly improves by approximately 20% as particle size decreases. The study also finds that tensile cracks dominate failure, accounting for over 95% of total cracks, with their onset occurring at lower strains as the particle size is reduced. Porosity analysis shows that smaller particles result in a more uniform distribution, with the final porosity at peak strength ranging between 0.26 and 0.29, compared to 0.22 to 0.31 for larger particles. Additionally, energy dissipation patterns reveal that as particle size decreases, the boundary energy transformation into strain energy becomes more efficient, with a 15% increase in strain energy storage observed. These findings provide critical insights into optimizing mortar microstructure for enhanced mechanical performance in construction applications. Full article

Tissue engineering endeavors to create in vitro constructs that replicate the properties of native tissue, such as skeletal muscle. This study investigated the use of mechanical stimulation to promote myogenic differentiation and enhance the functionality of bioengineered tissues. Specifically, it aimed to facilitate the differentiation of myoblasts within a three-dimensional scaffold using a defined pattern of mechanical stimulation. C2C12 cells were cultured on a collagen-coated PCL microfilament scaffold and subjected to 24 h of uniaxial static strain using a biomechanical stimulation system. Two onset times of stimulation, 72 h and 120 h post-seeding, were evaluated. Cell proliferation, myogenic marker expression, and alterations in cell morphology and orientation were assessed. Results indicate that static strain on the scaffold promoted myoblast differentiation, evidenced by morphological and molecular changes. Notably, strain initiated at 72 h induced an early differentiation stage marked by MyoD expression, whereas stimulation beginning at 120 h led to a mid-stage differentiation characterized by the co-expression of MyoD and Myogenin, culminating in myotube formation. These results highlight the critical influence of myoblast maturity at the time of strain application on the differentiation outcome. This study provides insights that could guide the optimization of mechanical stimulation protocols in tissue engineering applications. Full article

This comprehensive review examines the phenomena of stress corrosion cracking (SCC) and chloride-induced stress corrosion cracking (Cl-SCC) in materials commonly used in the oil and gas industry, with a focus on austenitic stainless steels. The study reveals that SCC initiation can occur at temperatures as low as 20 °C, while Cl-SCC propagation rates significantly increase above 60 °C, reaching up to 0.1 mm/day in environments with high chloride concentrations. Experimental methods such as Slow Strain Rate Tests (SSRTs), Small Punch Tests (SPTs), and Constant-Load Tests (CLTs) were employed to quantify the impacts of temperature, chloride concentration, and pH on SCC susceptibility. The results highlight the critical role of these factors in determining the susceptibility of materials to SCC. The review emphasizes the importance of implementing various mitigation strategies to prevent SCC, including the use of corrosion-resistant alloys, protective coatings, cathodic protection, and corrosion inhibitors. Additionally, regular monitoring using advanced sensor technologies capable of detecting early signs of SCC is crucial for preventing the onset of SCC. The study concludes with practical recommendations for enhancing infrastructure resilience through meticulous material selection, comprehensive environmental monitoring, and proactive maintenance strategies, aimed at safeguarding operational integrity and ensuring environmental compliance. The review underscores the significance of considering the interplay between mechanical stresses and corrosive environments in the selection and application of materials in the oil and gas industry. Low pH levels and high temperatures facilitate the rapid progression of SCC, with experimental results indicating that stainless steel forms passive films with more defects under these conditions, reducing corrosion resistance. This interplay highlights the need for a comprehensive understanding of the complex interactions between materials, environments, and mechanical stresses to ensure the long-term integrity of critical infrastructure. Full article