Non-smooth dynamics of Anti Stick–Slip Tool

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Internal mechanics of anti stick–slip tool

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The experimental and numerical analysis of the ballistic performance of elastomer matrix Kevlar composites

In this paper, the behavior of high-velocity impact of Kevlar fabric and elastomer composites was investigated both experimentally and numerically. The experimental tests were performed by a gas gun device and hemispherical projectiles at different velocities, ranging from 122 m/s to 152 m/s for 2- and 4-layer samples. The penetration resistance of these composites during impact was determined using ABAQUS/Explicit. The present study's novelty lies in choosing the finite element model for Kevlar fabric and elastomer matrix in composites with nonlinear behavior to estimate the damage mechanism in the impact zone. For this purpose, the material model of the formable was used to define the damage criteria for Kevlar, and the material model of the VUMAT was used to consider the non-linear behavior and damage evolution of elastomer matrix with one of the damage criteria. Then, the dynamic behavior of the laminate was studied by a Split Hopkinson Pressure Bar. The effect of the number of layers, the shape of the projectile, the energy absorption and failure mechanisms were studied. The verification of this numerical model with experimental observations showed good agreement. The results reveal that elastomeric composites can cause to increase energy absorption and reduce the damaged area

The Efficacy of Intramuscular Calcitonin Injection in the Management of Lumbar Spinal Stenosis

Study DesignA prospective, cross-sectional, non-randomized study.PurposeTo assess the effectiveness of intramuscular calcitonin injection in the treatment of lumbar spinal stenosis (LSS).Overview of LiteratureLSS, manifesting as chronic low back pain and neurogenic claudication, is a chronic condition with an increasing incidence in the elderly population having inadequate effective conservative treatment options.MethodsIn this study, 36 patients with LSS who were diagnosed based on the clinical findings and magnetic resonance imaging were included. Patients received 100 IU of calcitonin per week for one month and were evaluated before and after treatment using the Oswestry disability index (ODI) questionnaire and visual analogue scale (VAS). Before treatment, the patients were divided into two subgroups based on their ODI results: patients with mild to moderate low back pain (disability, 0%-40%) and patients with severe or very severe low back pain (disability, 40%-100%).ResultsIn patients with mild to moderate low back pain, there were no significant changes in the ODI and VAS after calcitonin injection. But in patients with severe or very severe low back pain, pain severity, personal functions, ability to lift and carry objects, time interval between standing and initiation of pain, social life, disability percentage, and VAS were significantly improved after treatment with calcitonin.ConclusionsIt seems that an intramuscular injection of low dose of calcitonin may have some beneficial effects on the pain due to LSS, especially in patients who suffer from severe or very severe low back pain

Impact response of Kevlar/rubber composite

This study aims to investigate the impact performance of composite panels consisting of plain-woven Kevlar fabric and rubber matrix. A finite element (FE) model in conjunction with experimental tests was developed to simulate the response of neat fabric and composite under impact loading. Each warp and weft yarn of fabric was individually modeled and combined with rubber matrix network to form the composite. To understand the effect of natural rubber on impact resistance of Kevlar/rubber composites, two types of rubber with different formulation were considered and their mechanical properties were obtained by split Hopkinson pressure bar tests and assigned to the model. Numerical results showed good agreement with the experimental data for both neat fabric and composite. It was shown that rubber matrix improves the ballistic performance of Kevlar fabric by keeping composite flexibility. High hardness rubber matrix composite has higher energy absorption capacity compared to the low hardness rubber matrix composite, due to presence of stronger intermolecular chains. Additionally, deformation and damage mechanism of fabric and composite were investigated under impact loading. The results were presented, discussed and commented upon

Explaining the psychological experiences of nurses during the first peak COVID-19 pandemic

Introduction: The unexpected spread of COVID-19 with high risk of transmission, fear and anxiety, and a load of negative emotions followed for nurses. It is necessary to assess the psychological experiences of nurses during the first peak COVID-19 pandemic. Materials and Methods: In this qualitative study, with the approach of conventional content analysis approach, the participants were selected through proposed-based sampling and snowball from the COVID-19 centers of Guilan province in March 2020. The number of 20 participants with various demographic characteristics (Gender, age ...) entered the study. The tools used were in-depth and semi-structured interviews. Results: Most of the participants were women, married and nurses. Six categories were obtained: not perception, worries, and pretending, horrible observations, pre-psychological symptoms and psychological symptoms. Conclusion: Psychological experiences of nurses in COVID-19 center in Guilan were expressed in a range of not perceptions and worry until the appearance of numerous pre and psychological symptoms. The psychological needs of this group must be considered at all stages of the crisis. Psychological support by mental health workers should be considered in line with the development of the crisis to reduce the stress on nurses

Ecological interaction between commercial fishes in the Persian Gulf

An ecosystem-based management fishery is a new way of looking at management of living resources. Trophic levels of basic food items, feeding habits, growth and mortality rate of 20 exploited fish species (including commercial and bycatch) are investigated in the Persian Gulf (from the provinces of Khuzestan, Bushehr and Hormozgan) from 2010 to 2012. The model considers trophic interactions among 12 functional group of the ecosystem involving Phytoplankton, Zeoplankton, Cephalopods, Shrimp, Infauna Benthos, Epifaunal Macrobenthos, Demersal Zoobenthos Feeders, Small Pelagic Planktivorous Fish, Benthoplagic Feeder, Piscivorous, Large Benthic Carnivores And Small Benthic Carnivores. In general 7452 of stomach contents samples were analyzed based on the weight and numerical method and were detected about 40 preys. The results demonstrated gaps in our knowledge on the food web structure. The mean trophic levels were varied from L. klunzingeri (2) to S. tumbil (4.64), while the total catch of some species were fluctuating widely. Result of our study showed that Total mortality varied between 0.45 per year (A. suppositus) to 9.5 per year (P. indicus) and food consumption rate also fluctuated by 1.9 (L. johni ) to 89 (L. lineolatus). The results indicated that some fish species including sardine, Anchovies, small carangids, S. stridens with high frequency in ecosystem, have been occupied in the food web as a wasp-waist. The model showed that most hunters groups live in middle levels in the food web such as N. japonicas, A. latus, P. kaakan, L. nebolusus, P. indicus and T. lepturus . Analysis the catch rate during 2001-2011 reveled that there is a clear trend of declining most of fish species catches in this research except for T. lepturus, P. kaakan and sparids which lead to upset the fundamental ecological balance of the Persian Gulf in future