A disk-shaped domain integral method for the computation of stress intensity factors using tetrahedral meshes

A novel domain integral approach is introduced for the accurate computation of pointwise J-integral and stress intensity factors (SIFs) of 3D planar cracks using tetrahedral elements. This method is efficient and easy to implement, and does not require a structured mesh around the crack front. The method relies on the construction of virtual disk-shaped integral domains at points along the crack front, and the computation of domain integrals using a series of virtual triangular and line elements. The accuracy of the numerical results computed for through-the-thickness, penny-shaped, and elliptical crack configurations has been validated by using the available analytical formulations. The average error of computed SIFs remains below 1% for fine meshes, and 2–3% for coarse ones. The results of an extensive parametric study suggest that there exists an optimum mesh-dependent domain radius at which the computed SIFs are the most accurate. Furthermore, the results provide evidence that tetrahedral elements are efficient, reliable and robust instruments for accurate linear elastic fracture mechanics calculations

A finite element framework for modeling internal frictional contact in three-dimensional fractured media using unstructured tetrahedral meshes

AbstractThis paper introduces a three-dimensional finite element (FE) formulation to accurately model the linear elastic deformation of fractured media under compressive loading. The presented method applies the classic Augmented Lagrangian(AL)-Uzawa method, to evaluate the growth of multiple interacting and intersecting discrete fractures. The volume and surfaces are discretized by unstructured quadratic triangle-tetrahedral meshes; quarter-point triangles and tetrahedra are placed around fracture tips. Frictional contact between crack faces for high contact precisions is modeled using isoparametric integration point-to-integration point contact discretization, and a gap-based augmentation procedure. Contact forces are updated by interpolating tractions over elements that are adjacent to fracture tips, and have boundaries that are excluded from the contact region. Stress intensity factors are computed numerically using the methods of displacement correlation and disk-shaped domain integral. A novel square-root singular variation of the penalty parameter near the crack front is proposed to accurately model the contact tractions near the crack front. Tractions and compressive stress intensity factors are validated against analytical solutions. Numerical examples of cubes containing one, two, twenty four and seventy interacting and intersecting fractures are presented

On the use of quarter-point tetrahedral finite elements in linear elastic fracture mechanics

This paper discusses the reproduction of the square root singularity in quarter-point tetrahedral (QPT) finite elements. Numerical results confirm that the stress singularity is modeled accurately in a fully unstructured mesh by using QPTs. A displacement correlation (DC) scheme is proposed in combination with QPTs to compute stress intensity factors (SIF) from arbitrary meshes, yielding an average error of 2–3%. This straightforward method is computationally cheap and easy to implement. The results of an extensive parametric study also suggest the existence of an optimum mesh-dependent distance from the crack front at which the DC method computes the most accurate SIFs

The study of correlation between forward head posture and neck pain in Iranian office workers

Objectives: Factors such as prolonged sitting at work or improper posture of head during work may have a great role in neck pain occurrence among office employees, particularly among those who work with computers. Although some studies claim a significant difference in head posture between patients and pain-free participants, in literature the forward head posture (FHP) has not always been associated with neck pain. Since head, cervical and thoracic postures and their relation with neck pain has not been studied in Iranian office employees, the purpose of this study was to investigate the relationship between some work-related and individual factors, such as poor posture, with neck pain in the office employees. Material and Methods: It was a cross-sectional correlation study carried out to explore the relationship between neck pain and sagittal postures of cervical and thoracic spine among office employees in forward looking position and also in a working position. Forty-six subjects without neck pain and 55 with neck pain were examined using a photographic method. Thoracic and cervical postures were measured using the high thoracic (HT) and craniovertebral (CV) angles, respectively. Results: High thoracic and CV angles were positively correlated with the presence of neck pain only in working position (p 0.05). Conclusions: Our findings have revealed that office employees had a defective posture while working and that the improper posture was more severe in the office employees who suffered from the neck pain

Jackiw-Teitelboim Gravity Generates Horndeski via Disformal Transformations

We show that the most general two-dimensional dilaton gravity theory with second-order field equations, which includes Horndeski and Kinetic Gravity Braiding families, may be obtained from the Jackiw-Teitelboim (JT) gravity through a general disformal transformation, up to boundary terms. We also show that this most general family of theories is closed under generic disformal transformations.Comment: 13 pages, 1 figure

A hybrid approach to achieve organizational agility: An empirical study of a food company

Purpose: In today’s intense global competition, agility is advocated as a fundamental characteristic for business survival and competitiveness. The purpose of this paper is to propose a practical methodology to achieve and enhance organizational agility based on strategic objectives. Design/methodology/approach: In the first step, a set of key performance indicators (KPIs) of the organization being studied are recognized and classified under the perspectives of balanced scorecard (BSC). Critical success factors are then identified by ranking the KPIs according to their importance in achieving organizational strategic objectives using the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). In the second step, three houses of quality (HOQs) are constructed sequentially to identify and rank the main agile attributes, agile enablers, and improvement paths. In addition, in order to translate linguistics judgments of practitioners into numerical values in building HOQs, fuzzy logic is employed. Findings: The capability of the proposed methodology is demonstrated by applying it to a case of a multi-national food company in Iran. Through the application, the company could find the most suitable improvement paths to improve its organizational agility. Research limitations/implications: A limited number of KPIs were chosen due to computational and visual constraints related to HOQs. Another limitation, similar to other agility studies, which facilitate decision making among agility metrics, was that the metrics were more industry-specific and less inclusive. Practical implications: A strong practical advantage for the application of the methodology over directly choosing agility metrics without linking them is that through the methodology, the right metrics were selected that match organization’s core values and marketing objectives. While metrics may ostensibly seem unrelated or inappropriate, they actually contributed to the right areas where there were gaps between the current and desired level of agility. It would otherwise be impossible to choose the right metrics without a structured methodology. Originality/value: This paper proposes a novel methodology for achieving organizational agility. By utilizing and linking several tools such as BSC, fuzzy TOPSIS, and quality function deployment (QFD), the proposed approach enables organizations to identify the most appropriate agile attributes, agile enablers, and subsequently agile improvement paths

Mesenchymal stem cells improve ischemic stroke injury by anti-inflammatory properties in rat model of middle cerebral artery occlusion

Background: Ischemic stroke is a major cause of permanent disability and inflammation has a prominent role in stroke pathology. Stem cell therapy is a new approach for stroke treatment. Mesenchymal stem cells (MSCs) are appropriate for this approach due to neuroprotective and immunomodulatory effects. Objectives: In this experimental study, the neuroprotective effects of mesenchymal stem cells (MSCs) on brain injury after transient middle cerebral artery occlusion (tMCAO) in rats was investigated with emphasis on inflammatory factors. Methods: Mesenchymal Stem Cells were isolated from bone marrow of rats and expanded by cell culture. Thirty-six male Wistar rats were randomly selected and divided to 6 groups. The MCAO model was performed in 4 groups with 24 and 72 hours of reperfusion. A single infusion of 2 × 106 MSCs was transplanted in one of the 24-hour and 72-hour groups and others received saline. In the sham groups, surgery was done without MCAO. Behavioral tests were evaluated and infarct volume was measured by staining of brain sections. Serum levels of Interleukin (IL) 1β and Tumor necrosis factor (TNF) α were measured by the enzyme linked immunosorbent assay (ELISA). Relative expression of Interleukin (IL)1β, tumor necrotizing factor (TNF)α, and IL6 genes were assessed in penumbra of the ischemic region using real time polymerase chain reaction (PCR). Results: The study results indicated that total behavioral scores were increased 72 hours after MSC transplantation (14.5 ± 2.0, P < 0.01). Moreover, MSCs decreased the infarct volume both 24 hours (18.82 ± 1.58, P < 0.01) and 72 hours (14.4 ± 1.53, P < 0.05) after MCAO. Serum levels of IL-1β and TNFα were increased after MCAO, yet MSCs transplantation decreased IL-1β (368.3 ± 109.5, P < 0.001) and TNFα (126.9 ± 38.6, P < 0.01) compared to saline. Also, relative gene expression of IL1β, TNFα, and IL6 was decreased by MSCs transplantation (P < 0.05). Conclusions: The MSCs had a neuroprotective effect in ischemic stroke via modulation of inflammatory response, and serum levels of IL1β and TNFα could be used as markers for evaluating anti-inflammatory effects of MSCs

Sexual orientation, theory of mind and empathy: A comparison of male homosexual and male and female heterosexuals

Background: Researchers have been investigating similarities of and differences between homosexuals and heterosexuals for past few decades. Several studies have shown that in the particular domain (e.g., spatial ability), male homosexuals would resemble female heterosexuals better than male heterosexuals. Executive function, however, has received more attention than social cognition in this line of research. Methods: This study focuses on theory of mind and empathy as two important components of social cognition in male homosexuals (N=14), male heterosexuals (N=15) and female heterosexuals (N=14). Results: Applying Reading the Mind in the Eyes test and the Empathy Quotient, no significant difference between groups was identified. Conclusion: This study suggests that similarities of male homosexuals and female heterosexuals may be confined to executive function and not extended to some social cognition abilities like theory of mind or empathy