Search results for: Reynolds stress model

Authors: M. A. Askari, M. A. Nazari, P. Perrier, Y. Payan

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Growth and remodeling of biological structures have gained lots of attention over the past decades. Determining the response of the living tissues to the mechanical loads is necessary for a wide range of developing fields such as, designing of prosthetics and optimized surgery operations. It is a well-known fact that biological structures are never stress-free, even when externally unloaded. The exact origin of these residual stresses is not clear, but theoretically growth and remodeling is one of the main sources. Extracting body organs from medical imaging, does not produce any information regarding the existing residual stresses in that organ. The simplest cause of such stresses is the gravity since an organ grows under its influence from its birth. Ignoring such residual stresses might cause erroneous results in numerical simulations. Accounting for residual stresses due to tissue growth can improve the accuracy of mechanical analysis results. In this paper, we have implemented a computational framework based on fixed-point iteration to determine the residual stresses due to growth. Using nonlinear continuum mechanics and the concept of fictitious configuration we find the unknown stress-free reference configuration which is necessary for mechanical analysis. To illustrate the method, we apply it to a finite element model of healthy human face whose geometry has been extracted from medical images. We have computed the distribution of residual stress in facial tissues, which can overcome the effect of gravity and cause that tissues remain firm. Tissue wrinkles caused by aging could be a consequence of decreasing residual stress and not counteracting the gravity. Considering these stresses has important application in maxillofacial surgery. It helps the surgeons to predict the changes after surgical operations and their consequences.

Keywords: growth, soft tissue, residual stress, finite element method

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Authors: Hammadi Larbi

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Water erosion, the main cause of the siltation of a dam, is a natural phenomenon governed by natural physical factors such as aggressiveness, climate change, topography, lithology, and vegetation cover. Currently, a vase from certain dams is released downstream of the dikes during devastation by hydraulic means. The vases are characterized by complex rheological behaviors: rheofluidification, yield stress, plasticity, and thixotropy. In this work, we studied the effect of the aging time of the vase in the dam and the mass concentration of the vase on the flow behavior of a vase from the Fergoug dam located in the Mascara region. In order to test the reproducibility of results, two replicates were performed for most of the experiments. The flow behavior of the vase studied as a function of storage time and mass concentration is analyzed by the Herschel Bulkey model. The increase in the aging time of the vase in the dam causes an increase in the yield stress and the consistency index of the vase. This phenomenon can be explained by the adsorption of the water by the vase and the increase in volume by swelling, which modifies the rheological parameters of the vase. The increase in the mass concentration in the vase leads to an increase in the yield stress and the consistency index as a function of the concentration. This behavior could be explained by interactions between the granules of the vase suspension. On the other hand, the increase in the aging time and the mass concentration of the vase in the dam causes a reduction in the flow index of the vase. The study also showed an exponential decrease in apparent viscosity with the increase in the aging time of the vase in the dam. If a vase is allowed to age long enough for the yield stress to be close to infinity, its apparent viscosity is also close to infinity; then the apparent viscosity also tends towards infinity; this can, for example, subsequently pose problems when dredging dams. For good dam management, it could be then deduced to reduce the dredging time of the dams as much as possible.

Keywords: vase of dam, aging time, rheological behavior, yield stress, apparent viscosity, thixotropy

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Authors: Aviva Lvan, Lipaz Shamoa-Nir

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Recently, has increased the research interest in modern fatherhood especially, the increasing involvement of fathers in the family. However, there is a little research evidence on fathers to children with special needs. Therefore, the purpose of this study was to examine the effects of stress and coping style on involvement in school among fathers to children with special needs in inclusive education. We compared the fathers to children with special needs (N=72) with fathers to non-special needs children (N = 75), and found that higher stress levels, greater educational involvement and greater use of social support coping style, were found among fathers of children with special needs. In addition, mission coping style and emotional coping style predict involvement in the school and emotional coping style predicts high levels of stress. The above findings contribute to the investigation of changes in the perception of the role of fathers and their involvement in their children's lives especially, among fathers to children with special needs. From the applied aspect, the findings may increase the understanding of the role of fathers and their unique contribution to the social, emotional, and academic development of their children.

Keywords: coping style, educational involvement, special needs, stress

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Authors: Nkereke M. Essien

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The intention of this paper is to examine stress in the Educated Nigerian Accent of English (ENAE) with the aim of analyzing stress and rhythmic patterns of Nigerian English. Our aim also is to isolate differences and similarities in the stress patterns studied and also know what forms the accent of these Educated Nigerian English (ENE) which marks them off from other groups or English’s of the world, to ascertain and characterize it and to provide documented evidence for its existence. Nigerian stress and rhythmic patterns are significantly different from the British English stress and rhythmic patterns consequently, the educated Nigerian English (ENE) features more stressed syllables than the native speakers’ varieties. The excessive stressed of syllables causes a contiguous “Ss” in the rhythmic flow of ENE, and this brings about a “jerky rhythm’ which distorts communication. To ascertain this claim, ten (10) Nigerian speakers who are educated in the English Language were selected by a stratified Random Sampling technique from two Federal Universities in Nigeria. This classification belongs to the education to the educated class or standard variety. Their performance was compared to that of a Briton (control). The Metrical system of analysis was used. The respondents were made to read some words and utterance which was recorded and analyzed perceptually, statistically and acoustically using the one-way Analysis of Variance (ANOVA). The Turky-Kramer Post Hoc test, the Wilcoxon Matched Pairs Signed Ranks test, and the Praat analysis software were used in the analysis. It was revealed from our findings that the Educated Nigerian English speakers feature more stressed syllables in their productions by spending more time in pronouncing stressed syllables and sometimes lesser time in pronouncing the unstressed syllables. Their overall tempo was faster. The ENE speakers used tone to mark prominence while the native speaker used stress to mark pronounce, typified by the control. We concluded that the stress pattern of the ENE speakers was significantly different from the native speaker’s variety represented by the control’s performance.

Keywords: accent, Nigerian English, rhythm, stress

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Authors: Rodlyn Remina Hines

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Africans who migrate to the United States (U.S.) go through an acculturation period. When they join the U.S. workforce during the period they are still acquainting to the new geographic area and culture, they may experience work and family conflict in addition to the stressors of acculturation. This study investigated the impact of acculturation stress and work-family conflict on the health and wellbeing of African immigrants in the U.S. using a growing immigrant population. Ghanaian immigrants (n = 100, males= 43%; females= 56%) residing in New York and Massachusetts, United States (U.S.), were recruited via purposive sampling to investigate the role acculturation stress and work-family conflict play on the health and wellbeing of African immigrants in the U.S. Using the Sociocultural theory, three hypotheses were proposed: (1) High acculturation stress will lead to high work-family conflict, (2) High work-family conflict will result in poor health and wellbeing, and (3) Work-family conflict will mediate the relationship between acculturation stress and health and wellbeing. The results fully supported the first hypothesis and partially supported the second and third. High acculturation stress led to high work-family conflict. Although high work-family conflict resulted in poorer health and wellbeing, high family support mediated work-family conflict and health and wellbeing. Participants who reported poor health also reported a lack of family or other support and those who reported strong family or other support also reported excellent health and wellbeing even with high work-family conflict. The latter group did not expect their health and wellbeing to get worse. I draw on these findings to conclude that African immigrants in the U.S. experience significant acculturation stress and work-family conflict resulting in poor health and wellbeing during their acculturation period if there is a lack of family or other support. These findings have implications for practitioners and policymakers.

Keywords: acculturation stress, work-family conflict, Ghanaian immigrants, health and wellbeing

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Authors: Zine Kechrid

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This study was carried out to investigate the antioxidant effect of vitamin C on oxidative stress induced by dietary Zn-deficiency in albino diabetic rats. Thirty two males alloxan-diabetic rats divided into two groups of 16 individuals each; the first group was fed a zinc adequate diet (54 mg zinc/kg). The second group had given low zinc diet (1 mg zinc/kg). Then, half of each group was treated with vitamin C (1 g/l) in drinking water. After four weeks, animals were sacrificed and different parameters were determined. The findings showed that dietary deficiency zinc intake significantly increased serum glucose. Zn-deficiency was also led to an increase in oxidative stress, which was indicated by an increase of MDA level and glutathione-S-transferase activity. Meanwhile it was result in a decrease of reduced glutathione (GSH) content, glutathione peroxidase GSH-Px and catalase activities in liver. However, the administration of vitamin C restored all the previous parameters approximately to their normal values. In conclusion, vitamin C probably played a key role strong as antioxidant factor against oxidative stress provoked by dietary zinc inadequate. Therefore, it might be contributed in reduction diabetes complications.

Keywords: vitamin C, oxidative stress, zinc, experimental diabetes, rats

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Authors: William Mahony, L. Jacqueline Hirth, Richard Rupp, Sandra Gonzalez, Roger Zoorob

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Background: The impact of the COVID-19 pandemic on physicians has been considered by many researchers, but less is known about non-physician healthcare workers. The aim of this study is to examine the association of COVID-19 safety training and communication with stress. Methods: A 91-item online survey was distributed, starting January 2, 2021, to non-physician healthcare workers, including physician assistants, nurse practitioners, and medical assistants (MAs) in the United States through email and social media. A $1 donation was made to the Red Cross for each completed survey. The survey consisted of demographics, occupational questions, and perceived stress (perceived stress scale, PSS). Items on the PSS were combined for an overall score and categorized according to the severity of perceived stress. Chi-square tests were performed for bivariate analyses of categorical variables. Results: Of the 284 participants consenting to complete the survey, 197 participants completed the full survey. MAs made up most of the sample at 79%. Among all respondents, 47% had moderate PSS scores (scored between 14 and 26), and 51% had severe PSS scores (scored between 27 and 40). Unvaccinated participants reported statistically significantly lower levels of perceived stress (p = 0.002). Performing tasks outside of typical job responsibilities was not associated with PSS scores (p = .667). Discussion: Non-physician healthcare workers demonstrated a high level of perceived stress overall. The association between vaccination status and perceived stress should be examined in order to evaluate whether vaccination levels could be improved with further education about the virus and associated risks.

Keywords: COVID-19, SARS-Cov-2, nursing, public health

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Authors: Sudha Summarwar, Sudesh Agarwal, Deepali Lall, Nalini Kataria, Jyotsana Pandey

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Assessment of antioxidant status is an effective tool to appraise the presence of oxidative stress. A combination of assays can be used to evaluate the antioxidant status like serum catalase (CAT), superoxide dismutase (SOD) and monoamine oxidase (MAO). In human medicine pregnancy is known to be associated with oxidative stress. Oxidative stress produces harmful effects to the developing foetus. Several metabolic changes occur in the maternal body to meet the demand of energy of developing foetus. Due to these changes susceptibility of maternal body increases to oxidative stress. There is paucity of research work on this aspect in nondescript goats. Therefore, the present study was intended to appraise the oxidative stress in pregnant and non-pregnant non-descript goat. Blood samples were collected for serum separation in otherwise healthy pregnant and non-pregnant nondescript goats. Mean values of serum CAT, SOD and MAO were found on a higher side (p≤0.05) with serum SOD values showing a rise of 2.5 times higher than the control healthy value. Correlations among all the three parameters were found to be highly significant (p≤0.01) especially greatest in youngest group of pregnant animals. Illustration of result enlightened the veracity of bumped up production of free radicals in pregnant animals. Technical savoir-faire of oxidative stress supervision is essential for upholding of health status of foetus. The upshot of present study undoubtedly implied the development of oxidative stress in pregnant goats on the basis of altered antioxidant status. These findings conclude that initially the oxidative stress due to pregnancy is critically combated by the intricate defensive mechanism of natural antioxidant system of the body. It appears that this imbalance between oxidant and antioxidant must be checked in time to prevent cellular damage by regularly appraising the antioxidant status through laboratory methods.

Keywords: antioxidant, oxidative stress, pregnancy, serum catalase

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Authors: Seung Ju Yeon, Seul Ki Min, Jun Sang Park, Yeo Seon Kwon, Hoo Cheol Lee, Hyun Jung Shim, Il-Doo Kim, Ja Kyeong Lee, Hwa Sung Shin

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In brain injury, depleting oxidative stress is the most effective way to reduce the brain infarct size. C-phycocyanin (C-Pc) is a well-known antioxidant protein that has neuroprotective effects obtained from green microalgae. Astrocyte is glial cell that supports the nerve cell such as neuron, which account for a large portion of the brain. In brain injury, such as ischemia and reperfusion, astrocyte has an important rule that overcomes the oxidative stress and protect from brain reactive oxygen species (ROS) injury. However little is known about how C-Pc regulates the anti-oxidants effects of astrocyte. In this study, when the C-Pc was treated in oxidized astrocyte, we confirmed that inflammatory factors Interleukin-6 and Interleukin-3 were increased and antioxidants enzyme, Superoxide dismutase (SOD) and catalase was upregulated, and neurotrophic factors, brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) was alleviated. Also, it was confirmed to reduce infarct size of the brain in ischemia and reperfusion because C-Pc has anti-oxidant effects in middle cerebral artery occlusion (MCAO) animal model. These results show that C-Pc can help astrocytes lead neuroprotective activities in the oxidative stressed environment of the brain. In summary, the C-PC protects astrocytes from oxidative stress and has anti-oxidative, anti-inflammatory, neurotrophic effects under ischemic situations.

Keywords: c-phycocyanin, astrocyte, reactive oxygen species, ischemia and reperfusion, neuroprotective effect

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Authors: Manana Chumburidze, David Lekveishvili

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We have considered the harmonic oscillations and general dynamic (pseudo oscillations) systems of theory generalized Green-Lindsay of couple-stress thermo-elasticity for isotropic, homogeneous elastic media. Approximate solution of some mixed boundary value problems for finite domain, bounded by the some closed surface are constructed.

Keywords: the couple-stress thermoelasticity, boundary value problems, dynamic problems, approximate solution

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Authors: Shamsulhaq Amin

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Unbound granular materials (UGMs) are pivotal in ensuring long-term quality, especially in the layers under the surface of flexible pavements and other constructions. This study seeks to better understand the behavior of the UGMs by looking at popular models for predicting lasting deformation under various levels of stresses and load cycles. These models focus on variables such as the number of load cycles, stress levels, and features specific to materials and were evaluated on the basis of their ability to accurately predict outcomes. The study showed that these factors play a crucial role in how well the models work. Therefore, the research highlights the need to look at a wide range of stress situations to more accurately predict how much the UGMs bend or shift. The research looked at important factors, like how permanent deformation relates to the number of times a load is applied, how quickly this phenomenon happens, and the shakedown effect, in two different types of UGMs: granite and limestone. A detailed study was done over 100,000 load cycles, which provided deep insights into how these materials behave. In this study, a number of factors, such as the level of stress applied, the number of load cycles, the density of the material, and the moisture present were seen as the main factors affecting permanent deformation. It is vital to fully understand these elements for better designing pavements that last long and handle wear and tear. A series of laboratory tests were performed to evaluate the mechanical properties of materials and acquire model parameters. The testing included gradation tests, CBR tests, and Repeated load triaxial tests. The repeated load triaxial tests were crucial for studying the significant components that affect deformation. This test involved applying various stress levels to estimate model parameters. In addition, certain model parameters were established by regression analysis, and optimization was conducted to improve outcomes. Afterward, the material parameters that were acquired were used to construct graphs for each model. The graphs were subsequently compared to the outcomes obtained from the repeated load triaxial testing. Additionally, the models were evaluated to determine if they demonstrated the two inherent deformation behaviors of materials when subjected to repetitive load: the initial phase, post-compaction, and the second phase volumetric changes. In this study, using log-log graphs was key to making the complex data easier to understand. This method made the analysis clearer and helped make the findings easier to interpret, adding both precision and depth to the research. This research provides important insight into picking the right models for predicting how these materials will act under expected stress and load conditions. Moreover, it offers crucial information regarding the effect of load cycle and permanent deformation as well as the shakedown effect on granite and limestone UGMs.

Keywords: permanent deformation, unbound granular materials, load cycles, stress level

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Authors: Emad Hafez, Mahmoud Seleiman

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Two field experiments were carried out in order to investigate the effect of chemical inducers [benzothiadiazole 0.9 mM L-1, oxalic acid 1.0 mM L-1, salicylic acid 0.2 mM L-1] on physiological and technological traits as well as on yields and antioxidant enzyme activities of barley grown under abiotic stress (i.e. water surplus and deficit conditions). Results showed that relative water content, leaf area, chlorophyll and yield as well as technological properties of barley were improved with chemical inducers application under water surplus and water-stress conditions. Antioxidant enzymes activity (i.e. catalase and peroxidase) were significantly increased in barley grown under water-stress and treated with chemical inducers. Yield and related parameters of barley presented also significant decrease under water-stress treatment, while chemical inducers application enhanced the yield-related traits. Starch and protein contents were higher in plants treated with salicylic acid than in untreated plants when water-stress was applied. In conclusion, results show that chemical inducers application have a positive interaction and synergetic influence and should be suggested to improve plant growth, yield and technological properties of water stressed barley. Salicylic acid application was better than oxalic acid and benzothiadiazole in terms of plant growth and yield improvement.

Keywords: antioxidant enzymes, drought stress, Hordeum vulgare L., quality, yield

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Authors: Al-Tammar M. Shahah

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Background and Objective: A novel pneumonia caused by coronavirus disease 2019 (COVID-19), which is spreading domestically and internationally, has been identified by the Chinese city of Wuhan since the end of December 2019. Limited studies examined the psychological experience such as anxiety, depression, and stress during Corona pandemic. Moreover, to the best of author's knowledge, there is no study to date has examined the psychological resilience and mental health during Corona pandemic in Kuwait. Therefore, the present research investigates the role of psychological resilience in predicting psychological distress among Kuwaiti adults during Corona pandemic. Method: Kuwaiti citizens (N = 735) completed an online survey, which includes four scales the Hospital Anxiety and Depression Scale HADS (anxiety and depression), the Connor-Davidson Resilience Scale (CD-RISC-25), and the Perceived Stress Scale (PSS). A cross-sectional correlational design was used. Results: A high level of stress was observed, with 59% reported moderate to severe stress. In contrast, low levels of anxiety and depression were observed; with 70% reporting no anxiety symptoms and 74% report no depression symptoms. Psychological resilience was negatively correlated with anxiety, depression, and stress, consistent with previous studies. As expected, resilience was found to account for significant variance in anxiety and stress after controlling for quarantine variables and demographic variables. Conclusion: The findings suggest that increasing psychological resilience might help reduce psychological distress after confronting with stressful live events in Kuwaiti citizen.

Keywords: anxiety, corona, depression, psychological resilience, stress

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Authors: Mehrab Karimian

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This study investigates the intricate relationships among Iranian EFL teachers’ motivation, creativity, and job stress in Shiraz and Fasa institutes. The primary aim is to explore these links using quantitative methods, providing a comprehensive understanding of how these factors interact within the educational context. The research employed convenient sampling, gathering data from 101 EFL teachers through three specific questionnaires: the Motivation to Teach Questionnaire, Teacher Creativity Questionnaire, and Job Stress Questionnaire. The methodology involved rigorous statistical analyses, including Pearson correlation and multiple regression, to interpret the collected data. The findings revealed positive relationships between motivation and creativity, as well as between motivation and job stress. However, no significant link was observed between creativity and job stress. Notably, creativity emerged as a strong predictor of motivation, highlighting its crucial role in the motivational dynamics of EFL teachers. The theoretical importance of this study lies in its contribution to understanding how motivation can influence both creativity and job stress among EFL teachers. By emphasizing the complex interplay of these factors, the study provides valuable insights that can inform future research and educational practices. The data collection process was thorough, utilizing well-established questionnaires to ensure the reliability and validity of the findings. Statistical analyses such as Pearson correlation and multiple regression were employed to interpret the relationships between motivation, creativity, and job stress. These analyses provided a detailed understanding of how these variables interact, offering a nuanced view of the motivational and stress dynamics in the teaching profession. The study addressed key questions regarding the influence of motivation on creativity and job stress, underscoring the predictive power of creativity on motivation. The conclusion drawn from the study suggests that motivated EFL teachers may experience higher levels of job stress. This finding highlights the need for targeted interventions to support teacher well-being and maintain their motivation. Such interventions could include professional development programs, stress management workshops, and creative teaching strategies to help teachers manage stress while fostering their motivation and creativity. Reviewers have commended the study for its contribution to the field, particularly in revealing the intricate dynamics between motivation, creativity, and job stress in EFL teachers. They recommend enhancing the methodology by considering potential confounding variables and incorporating qualitative approaches to complement the quantitative findings. These suggestions aim to provide a more comprehensive understanding of the factors influencing EFL teachers’ motivation, creativity, and job stress.

Keywords: creativity, Job stress, gender, years of teaching experience

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Authors: S. M. Rifat, André L. Marchildon, Mark F. Tachie

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The effect of upstream surface roughness over a smooth forward facing step in an open channel was investigated using a particle image velocimetry technique. Three different upstream surface topographies consisting of hydraulically smooth wall, sandpaper 36 grit and sand grains were examined. Besides the wall roughness conditions, all other upstream flow characteristics were kept constant. It was also observed that upstream roughness decreased the approach velocity by 2% and 10% but increased the turbulence intensity by 14% and 35% at the wall-normal distance corresponding to the top plane of the step compared to smooth upstream. The results showed that roughness decreased the reattachment lengths by 14% and 30% compared to smooth upstream. Although the magnitudes of maximum positive and negative Reynolds shear stress in separated and reattached region were 0.02Ue for all the cases, the physical size of both the maximum and minimum contour levels were decreased by increasing upstream roughness.

Keywords: forward facing step, open channel, separated and reattached turbulent flows, wall roughness

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Authors: Vered Shenaar-Golan, Nava Wald, Uri Yatzkar

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Background: Parenting children with mental health problems poses multiple challenges, including coping with difficult behavior and negative child emotions. The impact on parents includes financial strain, negative social stigma, and negative feelings of guilt or blame, resulting in significant stress and lower levels of well-being. Given findings that self-compassion plays a significant role in reducing stress and improving well-being, the current study examined the role of self-compassion in the experience of parents raising a child with mental health problems. The study tested (1) whether child behavioral/emotional problem severity is associated with higher parental stress and lower parental well-being; (2) whether self-compassion is associated with lower parental stress and higher parental well-being; and (3) whether self-compassion is a stronger predictor of parental stress and well-being than child behavioral/emotional problem severity. Methods: Three hundred and six mothers and two hundred and fifty-six fathers of children attending a hospital child and adolescent psychiatric center were assessed at admission. Consenting parents completed four questionnaires: Child Strength and Difficulty – parent version, Self-compassion, Parent Feeling Inventory, and Well-Being. Results: Child behavioral/emotional problem severity was associated with higher parental stress and lower parental well-being, and self-compassion was a stronger predictor of parental stress and well-being levels than child behavioral/emotional problem severity. For children with internalizing but not externalizing behavioral/emotional problems, parental self-compassion was the only predictor of parental well-being beyond the severity of child behavioral/emotional problems. Conclusions: Cultivating self-compassion is important in reducing parental stress and increasing parental well-being, particularly with internalizing presentations, and should be considered when designing therapeutic interventions for parents.

Keywords: parenting children with mental health problems, self-compassion, parental stress, feelings, well-being

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Authors: Kriti Singh, Saurabh Tripathi, Pankaj Chaudhary, Abid Ali Ansari, Seema Nigam

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Introduction: The introduction of android and iOS has changed our lives dramatically over the past few years. The new generation is more dependent on their mobile phones for carrying out their daily pursuits. Smartphones have revolutionized our lives. The cutdown in rates of mobile network services has been affecting us drastically. A new type of dependence is seen among the people for Smartphones. A cross-sectional study was conducted to determine the state of addiction among the group of medical students, along with its association with sleep hygiene and anxiety. Material and Method: Study included 50 individuals in the age group of 18-35 years. Smartphone Addiction Scale Short Version, Sleep Hygiene Index, and Perceived Stress Scales were used conducting the study. Results: Mean age of 22 years (12%). The majority of subjects were 20-year olds (15 out of 50), the majority were males with few females. Mean Smartphone addiction score 39 (very severe), Mean Sleep Hygiene Index score 26.76 (moderate maladaptive hygiene and Mean Perceived Stress score of 19.92 (moderate stress). Conclusion: In majority students were found to have a very severe Smartphone Addiction with moderate sleep hygiene and a moderate level of perceived stress. The Smartphone was being used was for surfing social media applications.

Keywords: addiction perceived stress, sleep hygiene index, smartphone

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Authors: Ahmet Calik

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In present study, the effect of adherend geometry on the tensile strength of adhesively single lap aluminum structures joint, bonded was numerically studied using by three dimensional finite element model. Six joint model were investigated. Analyses were performed in ANSYS commercial software. The results shows that the adherends shape has the highest effect on peel and shear stresses.

Keywords: adhesive, adherend, single lap joints, finite element

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Authors: A. H. Alenezi

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Cooling by impingement jet is known to have a significant high local and average heat transfer coefficient which make it widely used in industrial cooling systems. The heat transfer characteristics of an impinging jet on rib-roughened flat plate has been investigated numerically. This paper was set out to investigate the effect of rib height on the heat transfer rate. Since the flow needs to have enough spacing after passing the rib to allow reattachment especially for high Reynolds numbers, this study focuses on finding the optimum rib height which would be the best to maximize the heat transfer rate downstream the plate. This investigation employs a round nozzle with hydraulic diameter (Dh) of 13.5 mm, Jet-to-target distance of (H/D) of 4, rib location=1.5D and and finally jet angels of 45˚ and 90˚ under the influence of Re =10,000.

Keywords: jet impingement, CFD, turbulence model, heat transfer

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Authors: Mahdi Fakoor, Seyed Mohammad Navid Ghoreishi

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Initiation and propagation of cracks may cause catastrophic failures in rotating disks, and hence determination of fracture parameter in rotating disks under the different working condition is very important issue. In this paper, a comprehensive study of stress intensity factors in rotating disks containing 3D semi-elliptical cracks under the different working condition is investigated. In this regard, after verification of modeling and analytical procedure, the effects of mechanical properties, rotational velocity, and orientation of cracks on Stress Intensity Factors (SIF) in rotating disks under centrifugal loading are investigated. Also, the effects of using composite patch in reduction of SIF in rotating disks are studied. By that way, the effects of patching design variables like mechanical properties, thickness, and ply angle are investigated individually.

Keywords: stress intensity factor, semi-elliptical crack, rotating disk, finite element analysis (FEA)

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Authors: M. H. Ahmadi, A. Mortazavi, H. Zarei

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Several authors have described the main mechanism of formation of cracks in the segment lining during the construction of tunnels with tunnel boring machines. A comprehensive analysis of segmental lining joints may help to guarantee a safe construction during Tunneling and serviceable stages. The most frequent types of segment damage are caused by a condition of uneven segment matching due to contact deficiencies. This paper investigated the interaction mechanism of precast concrete lining joints in tunnels. The Discrete Element Method (DEM) was used to analyze a typical segmental lining model consisting of six segment rings. In the analyses, typical segmental lining design parameters of the Ghomrood water conveyance tunnel, Iran were employed in the study. In the conducted analysis, the worst-case scenario of loading faced during the boring of Ghomrood tunnel was considered. This was associated with the existence of a crushed zone dipping at 75 degree at the location of the key segment. In the analysis, moreover, the effect of changes in horizontal stress ratio on the loads on the segment was assessed. The boundary condition associated with K (ratio of the horizontal to the vertical stress) values of 0.5, 1, 1.5 and 2 were applied to the model and separate analysis was conducted for each case. Important parameters such as stress, moments, and displacements were measured at joint locations and the surrounding rock. Accordingly, the segment joint interactions were assessed and analyzed. Moreover, rock mass properties of the Ghomrood in Ghom were adopted. In this study, the load acting on segments joints are included a crushed zone stratum force that intersect tunnel with 75 slopes in the location of the key segment, gravity force of segments and earth pressures. A numerical investigation was used for different coefficients of stress concentration of 0.5, 1, 1.5, 2 and different geological conditions of saturated crushed zone under the critical scenario. The numerical results also demonstrate that maximum bending moments in longitudinal joints occurred for crushed zone with the weaken strengths (Sandstone). Besides that, increasing the load in segment-stratum interfaces affected radial stress in longitudinal joints and finally the opening of joints occurred.

Keywords: joint, interface, segment, contact

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Authors: Sohrab Jafarpour, Hamed Farokhi, Mohammad Rahmati, Alireza Gholipour

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In the current study, a nonlinear fluid-structure interaction (FSI) biomechanical model of atherosclerosis in the left anterior descending (LAD) coronary artery is developed to perform a detailed sensitivity analysis of the geometrical features of an atheroma plaque. In the development of the numerical model, first, a 3D geometry of the diseased artery is developed based on patient-specific dimensions obtained from the experimental studies. The geometry includes four influential geometric characteristics: stenosis ratio, plaque shoulder-length, fibrous cap thickness, and eccentricity intensity. Then, a suitable strain energy density function (SEDF) is proposed based on the detailed material stability analysis to accurately model the hyperelasticity of the arterial walls. The time-varying inlet velocity and outlet pressure profiles are adopted from experimental measurements to incorporate the pulsatile nature of the blood flow. In addition, a computationally efficient type of structural boundary condition is imposed on the arterial walls. Finally, a non-Newtonian viscosity model is implemented to model the shear-thinning behaviour of the blood flow. According to the results, the structural responses in terms of the maximum principal stress (MPS) are affected more compared to the fluid responses in terms of wall shear stress (WSS) as the geometrical characteristics are varying. The extent of these changes is critical in the vulnerability assessment of an atheroma plaque.

Keywords: atherosclerosis, fluid-Structure interaction modeling, material stability analysis, and nonlinear biomechanics

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Authors: Mihai Palade, Gina Cecilia Pistol, Mariana Stancu, Veronica Chedea, Ionelia Taranu

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Nutrition is an important determinant of general health status, with especially focus on prevention and/or attenuation of the inflammatory-associated pathologies. People with chronic kidney disease can experience chronic inflammation that can lead to cardiovascular disease and even an increased rate of death. There are important links between chronic kidney diseases, inflammation and nutritional strategies that may prevent or protect against undesirable inflammation and oxidative stress. The grape by-products either seeds or pomace are rich in polyphenols which may be beneficial in prevention of inflammatory, antioxidant and antimicrobial processes. As a model for studying the impact of grape seeds on renal inflammation and oxidative stress, we used in this study weaned piglets. After a feeding trial of 30 days with a control diet and an experimental diet containing 5% grape seed (GS), kidney samples were collected. In renal tissues were determined the expression and activity of important markers of immune respose and oxidative stress: pro-inflammatory cytokines (TNF-alpha, IL-1 beta, IL-6, IL-8, IFN-gamma), anti-inflammatory cytokines (IL-4, IL-10), anti-oxidant enzymes (catalase CAT, superoxide dismutase SOD, glutathione peroxidise GPx) and important mediators belonging to nuclear receptors (NF-kB1, Nrf-2 and PPAR-gamma). Gene expression was evaluated by qPCR, whereas protein concentration was determined using proteomic techniques (ELISA). The activity of anti-oxidant enzymes was determined using specific kits. Our results showed that GS enriched in polyphenols does not have effect on TNF-alpha, IL-6 and IL-1 beta gene expression and protein concentration in kidney. By contrast, the gene expression and protein level of IL-8 and IFN-gamma were decreased in GS kidney. Anti-inflammatory cytokines IL-4 and IL-10 gene levels were increased in kidneys collected from GS piglets in comparison with controls, with no modification of protein levels between the two groups. The activities of anti-oxidant enzymes CAT and GPx were increased in kidney by GS, whereas SOD activity was unmodified in comparison with control samples. Also, the GS diet was associated with no modulation of mRNAs for nuclear receptors NF-kB1, Nrf-2 and PPAR-gamma gene expressions in kidneys. In conclusion, our results demonstrated that GS enriched in bioactive compounds such polyphenols could modulate inflammation and oxidative stress markers in kidney tissues. Further studies are necessary to elucidate the mechanism of action of GS compounds in case kidney inflammation associated with oxidative stress, and signalling molecules involved in these mechanisms.

Keywords: animal model, kidney inflammation, oxidative stress, grape seed

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Authors: Madara Nikolajenko, Jevgenija Kondratjeva

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Stress is a response of the body to physical or psychological environmental stressors. Cortisol level in blood serum is determined as the main indicator of stress, but the blood collection, the animal preparation and other activities can cause unpleasant conditions and induce increase of these hormones. Therefore, less invasive methods are searched to determine stress hormone levels, for example, by measuring the cortisol level saliva. The aim of the study is to find out the changes of stress hormones in blood and saliva in home and experimental dogs in simulated short-term stress conditions. The study included clinically healthy experimental beagle dogs (n=6) and clinically healthy home American Staffordshire terriers (n=6). The animals were let into a fenced area to adapt. Loud drum sounds (in cooperation with 'Andžeja Grauda drum school') were used as a stressor. Blood serum samples were taken for sodium, potassium, glucose and cortisol level determination and saliva samples for cortisol determination only. Control parameters were taken immediately before the start of the stressor, and next samples were taken immediately after the stress. The last measurements were taken two hours after the stress. Electrolyte levels in blood serum were determined using direction selective electrode method (ILab Aries analyzer) and cortisol in blood serum and saliva using electrochemical luminescence method (Roche Diagnostics). Blood glucose level was measured with glucometer (ACCU-CHECK Active test strips). Cortisol level in the blood increased immediately after the stress in all home dogs (P < 0,05), but only in 33% (P < 0,05) of the experimental dogs. After two hours the measurement decreased in 83% (P < 0,05) of home dogs (in 50% returning to the control point) and in 83% (P < 0,05) of the experimental dogs. Cortisol in saliva immediately after the stress increased in 50% (P > 0,05) of home dogs and in 33% (P > 0,05) of the experimental dogs. After two hours in 83% (P > 0,05) of the home animals, the measurements decreased, only in 17% of the experimental dogs it decreased as well, while in 49% measurement was undetectable due to the lack of material. Blood sodium, potassium, and glucose measurements did not show any significant changes. The combination of short-term stress indicators, when, after the stressor, all indicators should immediately increase and decrease after two hours, confirmed in none of the animals. Therefore the authors can conclude that each animal responds to a stressful situation with different physiological mechanisms and hormonal activity. Cortisol level in saliva and blood is released with the different speed and is not an objective indicator of acute stress.

Keywords: animal behaivor, cortisol, short-term stress, stress indicators

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Authors: Hassan Gholibeigian, Kazem Gholibeigian

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In this paper, our goal is determination of loading versus time in crust. For this goal, we present a computational procedure to propose a cumulative strain energy time profile which can be used to predict the approximate location and time of the next major earthquake (M > 4.5) along a specific fault, which we believe, is more accurate than many of the methods presently in use. In the coming pages, after a short review of the research works presently going on in the area of earthquake analysis and prediction, earthquake mechanisms in both the jerk and sequence earthquake direction is discussed, then our computational procedure is presented using differential equations of equilibrium which govern the nonlinear dynamic response of a system of finite elements, modified with an extra term to account for the jerk produced during the quake. We then employ Von Mises developed model for the stress strain relationship in our calculations, modified with the addition of an extra term to account for thermal effects. For calculation of the strain energy the idea of Pulsating Mantle Hypothesis (PMH) is used. This hypothesis, in brief, states that the mantle is under diurnal cyclic pulsating loads due to unbalanced gravitational attraction of the sun and the moon. A brief discussion is done on the Denali fault as a case study. The cumulative strain energy is then graphically represented versus time. At the end, based on some hypothetic earthquake data, the final results are verified.

Keywords: pulsating mantle hypothesis, inner core’s dislocation, outer core’s bulge, constitutive model, transient hydro-magneto-thermo-mechanical load, diurnal stress, jerk, fault behaviour

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Authors: Markus Rütten, Olaf Wünsch

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Non-Newtonian fluid properties can change the flow behaviour significantly, its prediction is more difficult when thermal effects come into play. Hence, the focal point of this work is the wake flow behind a heated circular cylinder in the laminar vortex shedding regime for thermo-viscous shear thinning fluids. In the case of isothermal flows of Newtonian fluids the vortex shedding regime is characterised by a distinct Reynolds number and an associated Strouhal number. In the case of thermo-viscous shear thinning fluids the flow regime can significantly change in dependence of the temperature of the viscous wall of the cylinder. The Reynolds number alters locally and, consequentially, the Strouhal number globally. In the present CFD study the temperature dependence of the Reynolds and Strouhal number is investigated for the flow of a Carreau fluid around a heated cylinder. The temperature dependence of the fluid viscosity has been modelled by applying the standard Williams-Landel-Ferry (WLF) equation. In the present simulation campaign thermal boundary conditions have been varied over a wide range in order to derive a relation between dimensionless heat transfer, Reynolds and Strouhal number. Together with the shear thinning due to the high shear rates close to the cylinder wall this leads to a significant decrease of viscosity of three orders of magnitude in the nearfield of the cylinder and a reduction of two orders of magnitude in the wake field. Yet the shear thinning effect is able to change the flow topology: a complex K´arm´an vortex street occurs, also revealing distinct characteristic frequencies associated with the dominant and sub-dominant vortices. Heating up the cylinder wall leads to a delayed flow separation and narrower wake flow, giving lesser space for the sequence of counter-rotating vortices. This spatial limitation does not only reduce the amplitude of the oscillating wake flow it also shifts the dominant frequency to higher frequencies, furthermore it damps higher harmonics. Eventually the locally heated wake flow smears out. Eventually, the CFD simulation results of the systematically varied thermal flow parameter study have been used to describe a relation for the main characteristic order parameters.

Keywords: heat transfer, thermo-viscous fluids, shear thinning, vortex shedding

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Authors: Belkheir Noura, Rabah Kerfah, Boumehani Abdellah

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The influence of solidity variations on the aerodynamic performance of H type vertical axis wind turbine is studied in this paper. The wind turbine model used in this paper is the three-blade wind turbine with the symmetrical airfoil, NACA0021. The length of the chord is 0.265m. Numerical investigations were implemented for the different solidity by changing the radius and blade number. A two-dimensional model of the wind turbine is employed. The approach a Reynolds-Averaged Navier–Stokes equations, completed by the K- ώ SST turbulence model, is used. Motion mesh model capability of a computational fluid dynamics (CFD) solver is used. For each value of the solidity, the aerodynamics performances and the characteristics of the flow field are studied at several values of the tip speed ratio, λ = 0.5 to λ = 3, with an incoming wind speed of 8 m/s. The results show that increasing the number of blades will reduce the maximum value of the power coefficient of the wind turbine. Also, for the VAWT with a lower solidity can obtain the maximum Cp at a high tip speed ratio. The effects of changing the radius and blade number on aerodynamic performance are almost the same. Finally, for the validation, experimental data from the literature and computational results were compared. In conclusion, to study the influence of the solidity in the performances of the wind turbine is to provide the reference for the design of H type vertical axis wind turbines.

Keywords: wind energy, darrieus h type vertical axis wind turbine, computational fluid dynamic, solidity

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Authors: Mahmoud M. AbuAlSamen, Tamam El-Elimat

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Amid the economic crisis in Jordan, the Jordanian government has opted for a knowledge economy where education is promoted as a mean for economic development. University education usually comes at the expense of study-related stress that may adversely impact the health of students. Since stress is a latent variable that is difficult to measure, a valid tool should be used in doing so. The effort-reward imbalance (ERI) is a model used as a measurement tool for occupational stress. The model was built on the notion of reciprocity, which relates ‘effort’ to ‘reward’ through the mediating ‘over-commitment’. Reciprocity assumes equilibrium between both effort and reward, where ‘high’ effort is adequately compensated with ‘high’ reward. When this equilibrium is violated (i.e., high effort with low reward), this may elicit negative emotions and stress, which have been correlated to adverse health conditions. The theory of ERI was established in many different parts of the world, and associations with chronic diseases and the health of workers were explored at length. While much of the effort-reward imbalance was investigated in work conditions, there has been a growing interest in understanding the validity of the ERI model when applied to other social settings such as schools and universities. The ERI questionnaire was developed in Arabic recently to measure ERI among high school teachers. However, little information is available on the validity of the ERI questionnaire in university students. A cross-sectional study was conducted on 833 students in Jordan to measure the validity and reliability of the ERI questionnaire in Arabic among university students. Reliability, as measured by Cronbach’s alpha of the effort, reward, and overcommitment scales, was 0.73, 0.76, and 0.69, respectively, suggesting satisfactory reliability. The factorial structure was explored using principal axis factoring. The results fitted a five-solution model where both the effort and overcommitment were uni-dimensional while the reward scale was three-dimensional with its factors, namely being ‘support’, ‘esteem’, and ‘security’. The solution explained 56% of the variance in the data. The established ERI theory was replicated with excellent validity in this study. The effort-reward ratio in university students was 1.19, which suggests a slight degree of failed reciprocity. The study also investigated the association of effort, reward, overcommitment, and ERI with participants’ demographic factors and self-reported health. ERI was found to be significantly associated with absenteeism (p < 0.0001), past history of failed courses (p=0.03), and poor academic performance (p < 0.001). Moreover, ERI was found to be associated with poor self-reported health among university students (p=0.01). In conclusion, the Arabic ERI questionnaire is reliable and valid for use in measuring effort-reward imbalance in university students in Jordan. The results of this research are important in informing higher education policy in Jordan.

Keywords: effort-reward imbalance, factor analysis, validity, self-reported health

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Authors: Chun-Ying Lee, Kuan-Hui Cheng, Mei-Wen Wu

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The nickel-manganese (Ni-Mn) alloy coating prepared from DC electrodeposition process in sulphamate bath was studied. The effects of process parameters, such as current density and electrolyte composition, on the cathodic current efficiency, microstructure, internal stress and mechanical properties were investigated. Because of its crucial effect on the application to the electroforming of microelectronic components, the development of low internal stress coating with high leveling power was emphasized. It was found that both the coating’s manganese content and the cathodic current efficiency increased with the raise in current density. In addition, the internal stress of the deposited coating showed compressive nature at low current densities while changed to tensile one at higher current densities. Moreover, the metallographic observation, X-ray diffraction measurement, transmission electron microscope (TEM) examination, and polarization curve measurement were conducted. It was found that the Ni-Mn coating consisted of nano-sized columnar grains and the maximum hardness of the coating was associated with (111) preferred orientation in the microstructure. The grain size was refined along with the increase in the manganese content of the coating, which accordingly, raised its hardness and mechanical tensile strength. In summary, the Ni-Mn coating prepared at lower current density of 1-2 A/dm2 had low internal stress, high leveling power, and better corrosion resistance.

Keywords: Ni-Mn coating, DC plating, internal stress, leveling power

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Authors: Hafsa Raheel

Abstract:

Objectives: Secondary school girls, ages 15–19 years old were surveyed to find out the coping strategies they used when stressed. Adolescents, who are affected with stress and depression early in life, suffer from depression throughout their lives, especially if they are utilizing improper ways to cope with it. Methods: A cross-sectional school-based survey among 1028 adolescent girls was conducted among the secondary schools in Riyadh city, Kingdom of Saudi Arabia. Results: About 25% stated that they cry, 19% listen to music, 15% start eating a lot, 12% sit alone/isolate themselves, 11% pray/read the Quran, 10% get into a verbal argument or a fight. Only a few, 3% exercise, and 2% stated that they find someone to discuss and talk to. Conclusion: The majority of the adolescent girls in our survey rely on emotion-related coping mechanisms rather than problem-solving mechanisms. This can cause long-term implications in these adolescents as there is an increased probability to develop depression later on in life. Policy makers need to implement strategies for early identification of stress and depression. Talking to friends and family can serve as an effective way to cope with stress.

Keywords: adolescents, stress, Saudi Arabia, mental health

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