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Effects of Defects on Effective Material Properties of Triaxial Braided Textile Composite
Mekonnen Abebaw Abie,우경식 한국항공우주학회 2020 International Journal of Aeronautical and Space Sc Vol.21 No.3
In this study, the effects of defects in a triaxial braided textile composite was studied at unit cell level using three-dimensional finite element analysis. The manufacturing defects such as void defect and tow misalignments were considered in the model and the effect of their presence at different scale on the effective material properties were studied. The configuration of the finite element model was based on the geometric data extracted from an experimental test specimen. The representative unit cells (RUC) that repeat itself to build the whole braid were sliced out from the full interlaced geometry of axial and bias tows. Periodic boundary condition (PBC) was used to simulate the repeating nature of the unit cells. Then, numerical tests were performed to compute three-dimensional effective material properties for triaxial braided RUCs with predetermined void volume fractions and axial tow misalignment under uniaxial tension and shear loadings in different directions. It was observed that the void defects severely affected the out-of-plane properties of the material, while the tow misalignments influenced the axial modulus mostly.
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Giweta Mekonnen 한국생태학회 2020 Journal of Ecology and Environment Vol.44 No.2
In the forest ecosystems, litterfall is an important component of the nutrient cycle that regulates the accumulation of soil organic matter (SOM), the input and output of the nutrients, nutrient replenishment, biodiversity conservation, and other ecosystem functions. Therefore, a profound understanding of the major processes (litterfall production and its decomposition rate) in the cycle is vital for sustainable forest management (SFM). Despite these facts, there is still a limited knowledge in tropical forest ecosystems, and further researches are highly needed. This shortfall of research-based knowledge, especially in tropical forest ecosystems, may be a contributing factor to the lack of understanding of the role of plant litter in the forest ecosystem function for sustainable forest management, particularly in the tropical forest landscapes. Therefore, in this paper, I review the role of plant litter in tropical forest ecosystems with the aims of assessing the importance of plant litter in forest ecosystems for the biogeochemical cycle. Then, the major factors that affect the plant litter production and decomposition were identified, which could direct and contribute to future research. The small set of studies reviewed in this paper demonstrated the potential of plant litter to improve the biogeochemical cycle and nutrients in the forest ecosystems. However, further researches are needed particularly on the effect of species, forest structures, seasons, and climate factors on the plant litter production and decomposition in various types of forest ecosystems.
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( Mahlet Mekonnen ),( Gabrielle Hovis ),( Natalie Mahgerefteh ),( Anubhav Chandla ),( Yelena Malkhasyan ),( Ashley B. Zhang ),( Isaac Yang ) 대한뇌종양학회·대한신경종양학회·대한소아뇌종양학회 2023 Brain Tumor Research and Treatment Vol.11 No.4
Background DuraMatrix-Onlay<sup>®</sup> Plus is a collagen dura membrane derived from purified bovine Achilles tendon. The matrix provides a scaffold for collagen synthesis and is intended to be used as an onlay without the need for dural sutures. The study aims to describe our experience with 33 consecutive patients who underwent a duraplasty procedure using the novel DuraMatrix-Onlay<sup>®</sup> Plus collagen dura membrane. Methods This is a retrospective case series of 33 patients who underwent a duraplasty procedure at a single academic hospital in Los Angeles, CA, USA between May 2016 and March 2017. The primary outcome was the incidence rate of cerebrospinal fluid (CSF) leak. Secondary outcomes included rates of patient infection, dural substitute complication, and removal. Results Thirty-three patients underwent a duraplasty procedure using the DuraMatrix-Onlay<sup>®</sup> Plus material. The average age of the patients was 41.12±7.34 years (range 2-75 years). There were 18 (54.5%) females and 15 (45.5%) males. The majority of procedures were elective operations for the resection of a lesion (n=19, 58%), and the average graft size was 17.69±4.73 cm². At an average follow- up of 3 months, there were no postoperative CSF leaks. The rates of patient infection, dural substitute complication, and removal were 6%, 6%, and 3%, respectively. Conclusion DuraMatrix-Onlay<sup>®</sup> Plus is associated with a low rate of postoperative CSF leakage and an acceptable complication profile. This result supports the use of collagen matrices for dural closure in general neurosurgical procedures.
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Hussen Mekonnen,Fikre Enquselassie 한국역학회 2017 Epidemiology and Health Vol.39 No.-
OBJECTIVES: With access to antiretroviral therapy (ART), people living with human immunodeficiency virus (HIV) are able to consider childbearing to a greater extent than previously. In many cases, ART has transformed their intentions to have children. The present study aimed to assess changes in fertility intentions 12 months after ART initiation among HIV-positive women in Addis Ababa, Ethiopia. METHODS: An institution-based follow-up study was conducted among 360 HIV-positive women in Addis Ababa. A logistic regression model was used to assess the influence of socio-demographic, reproductive health, and clinical characteristics on changes in the fertility intentions of women. RESULTS: Overall, 40.8% (147 of 360) of the women reported that they desired to have a child in the future at the baseline visit, while 48.3% (174 of 360) did so at the 12-month follow-up. The proportion of women who reported that they desired to have a child 12 months after ART initiation was higher among ART-initiated women (55.8%, 106 of 190) than ART-naïve women (40.0%, 68 of 170). The adjusted analysis indicated that a change in fertility intentions between baseline and the follow-up visit was significantly associated with ART use (adjusted odds ratio [aOR], 2.47; 95% confidence interval [CI], 1.20 to 5.20) and marital status, with single (aOR, 5.33; 95% CI, 1.10 to 25.92) and married (aOR, 6.35; 95% CI, 1.44 to 27.99) women being more likely to report fertility intentions than divorced/widowed women. CONCLUSIONS: ART use was a significant predictor of change in fertility intentions between the baseline and follow-up visit, which suggests that additional efforts are necessary to integrate family planning and HIV services to address the safe fertility goals of women in the study area.
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Fikru Mekonnen,Firew Mekbib,Shiv Kumar,Seid Ahmed,TR Sharma 한국작물학회 2016 Journal of crop science and biotechnology Vol.19 No.1
Knowledge of genetic diversity in germplasm is essential for formulating effective germplasm collection, conservation, utilization strategies in and crop improvement programs. It also provides an opportunity to take corrective steps infusing new genes to avoid risks associated with a narrow genetic bases. Genetic diversity analysis of 119 lentil genotypes of including 83 germplasm and 36 exotic genotypes from International Center for Agricultural Research in the Dry Areas was studied using 27 primers of simple sequence repeat (SSR) marker. Molecular analysis of variance showed variations of 82% within and 18% of the among population variance was explained. Degree of polymorphism observed among the populations was 100%. A total 122 alleles were detected, with 2 to 7 alleles per locus, with a mean of 4.52 alleles per locus. The estimated gene diversity value for 27 loci was 0.64. The average Shannon’s information index value of 1.19 was obtained showed the existence of high genetic variation within the genotypes. The genetic similarity indices ranged from 0.21 to 1.00. The SSR markers showed an average polymorphic information content (PIC) value of 0.58. Cluster analysis grouped the genotypes into five major clusters as distinct genetic populations. Diversity analyses revealed the existence of a high level of genetic variation among genotypes. This molecular diversity information provides a basis for future germplasm collection, utilization, and conservation strategies in gene banks and introducing exotic germplasm to widen the genetic base of the current lentil breeding population.
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Sick at work: prevalence and determinants among healthcare workers, western Ethiopia
Tesfaye Hambisa Mekonnen,Mekuriaw Alemayewu Tefera,Yayehirad Alemu Melsew 대한직업환경의학회 2018 대한직업환경의학회지 Vol.30 No.-
Background: Going to work despite feeling sick also known as sickness presenteeism is one of the emerging global occupational health challenges. Sickness presenteeism negatively affects both health of work forces and productivity of organizations in general. However, there is insufficient research exploring this situation in majority of the Sub-Saharan African countries, including Ethiopia. Thus this study intended to investigate the prevalence and determinant factors of sickness presenteeism among health care workers, Western Ethiopia. Methods: This study used an institution based cross-sectional quantitative study design. The study period was from February to March, 2017. We employed simple random sampling method to select 360 study samples. Data collection was performed by pre-tested structured and self- administered questionnaire. We used SPSS version 20 to carry out binary logistic regression analysis. Odds ratio with 95% confidence intervals was calculated and significance of associations was determined at p-value < 0.05. Results: A total of 344 respondents fully completed the survey questionnaire. Mean age with standard deviation was 30. 28 ± 6.181. Prevalence of sickness Presenteeism was 52.6% [95%CI: (47.4, 57.8)] in the past 12 months. Educational status [AOR:2.1, 95%CI: (1.17,3.90)], financial problem [AOR:1.9,95%CI:(1.07,3.46)], sickness absenteeism [AOR:2.7,95% CI:(1.50,5.02)], lack of staff replacement [AOR:2.7,95%CI:(1.50,5.02)], absence of occupational health services [AOR:3.0,95%CI:(1.34,6.70)], and pressure from supervisor [AOR:1.8,95% CI:(1.01,3.31)] were significant predictors of the dependent variable. Conclusion: Relatively higher proportions of workers indicated sickness presenteeism as compared to other studies. Risk factors like educational status, personal financial problem, sickness absenteeism, lack of staff replacement, absence of occupational health services, and pressure from supervisors considerably increased the likely occurrence of employees’ sick attendance. It is advisable for health care managers to hire adequate health care staffs, to implement basic occupational health services and to design strategies which reduce pressure from supervisors.
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Abebaw Abie Mekonnen,우경식,강민송,김인걸 한국항공우주학회 2020 International Journal of Aeronautical and Space Sc Vol.21 No.1
In this paper, buckling, post-buckling, and delamination behavior of composite laminates subjected to axial compression was studied. First, compression tests were performed for composite laminate specimens with through-width delamination and the history of buckling and delamination propagation was measured. Next, the tests were simulated using two-dimensional finite-element models. A geometrically non-linear post-buckling analysis was performed for the finite-element mesh seeded with small amount of geometric imperfection based on eigenmodes. The growth of delamination due to sub-laminates buckling was simulated using the cohesive zone modeling. The analysis results were compared with the test results for the verification of the numerical model. Then, the analysis results were examined to study the relation between geometric parameters of initial delamination and buckling loads and post-buckling delamination propagation behavior of the composite laminates. The effects of different sizes and locations of initial delamination on the delamination behavior were systematically investigated. It was found that the buckling loads, mode shapes, and the delamination growth behavior are affected by the geometry variation of pre-included delamination. The long and shallow initial delaminations prompt local buckling the deep delaminations induce global buckling mode.
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