Influence of machining parameters on part geometrical error in abrasive waterjet offset-mode turning

Geometrical error in abrasive waterjet turned parts is an important challenge toward the commercialization of abrasive waterjet turning process. A systematic study has not been done yet to investigate the effects of process parameters on geometrical error in abrasive waterjet offset-mode turning. In this article, a comprehensive study has been performed to investigate the influence of several machining parameters on the geometrical error (part diameter percent error) in turning AA2011-T4 aluminum alloy round bars. Water pressure, cutting head traverse speed, workpiece rotational speed, abrasive mass flow rate and depth of cut were considered as the main machining parameters in a five-level statistical experimental design. Based on central composite rotatable design, a total of 52 experiments were carried out. The main effects of the parameters and interactions among them were analyzed based on the analysis of variance technique, and the response contours for the part geometrical error were obtained using a quadratic regression model (i.e. response surface methodology). The model predictions were found to be in good agreement with experimental data. Furthermore, among the significant parameters, water pressure, depth of cut and traverse speed are the most influential parameters, with percent contribution of almost 25% each. Abrasive mass flow rate is the least influential parameter with a percent contribution of 4%

Assessing the role of Ca2+ in skeletal muscle fatigue using a multi-scale continuum model

The Calcium ion Ca2+ plays a critical role as an initiator and preserving agent of the cross-bridge cycle in the force generation of skeletal muscle. A new multi-scale chemo-mechanical model is presented in order to analyze the role of Ca2+ in muscle fatigue and to predict fatigue behavior. To this end, a cross-bridge kinematic model was incorporated in a continuum based mechanical model, considering a thermodynamic compatible framework. The contractile velocity and the generated active force were directly related to the force-bearing states that were considered for the cross-bridge cycle. In order to determine the values of the model parameters, the output results of an isometric simulation were initially fitted with experimental data obtained for rabbit Extensor Digitorum Longus muscle. Furthermore, a simulated force-velocity curve under concentric contractions was compared with reported experimental results. Finally, by varying the Ca2+ concentration level and its kinetics in the tissue, the model was able to predict the evolution of the active force of an experimental fatigue protocol. The good agreement observed between the simulated results and the experimental outcomes proves the ability of the model to reproduce the fatigue behavior and its applicability for more detailed multidisciplinary investigations related to chemical conditions in muscle performance

Vibration Analysis of a New Type of Compliant Mechanism with Flexible-Link, Using Perturbation Theory

Vibration analysis of a new type of compliant parallel mechanism with flexible intermediate links is investigated. The application of the Timoshenko beam theory to the mathematical modeling of the intermediate flexible link is described, and the equations of motion of the flexible links are obtained by using Lagrange’s equation of motion. The equations of motion are obtained in the form of a set of ordinary differential equations by using assumed mode method theory. The governing differential equations of motion are solved using perturbation method. The assumed mode shapes and frequencies are to be obtained based on clamped-clamped boundary conditions. Comparing perturbation method with Runge-Kutta-Fehlberg 4, 5th leads to highly accurate solutions, and the results are performed and discussed

Evaluación de la prescripción y uso de medicamentos supresores de ácido en hospitales centrales en la región de Abha, Arabia Saudita

Objective: The aim of this study was to study and assess the indications of acid suppressive drugs and to find out percentage of irrational prescriptions with acid suppressive drugs. Material/Methods: It is a prospective observational study conducted in the Armed Forces Hospitals Southern Region and Abha Maternity Hospital, both in Abha in Assir region (Saudi Arabia). The sample size of study was 185 patients. The case sheets of the patients’ prescription order were reviewed for acid suppressive drugs prescription and relevant data was taken. Patients’ age above 18 were identified. The duration of study was 8 weeks, between May and June 2017. Results: Our results showed that the majority of the prescriptions of proton pump inhibitors (68.1%) were unjustifiable and that proton pump inhibitor was the most commonly prescribed acid suppressive drugs for the patients (97.8%). The frequency of prescribing for the autism spectrum disorders in our study was found to be higher in patients with an existing risk factor and was mostly recommended by physicians as concomitant medications (67.6%). The most common concomitant medications used with the proton pump inhibitors were non-steroidal anti-inflammatory drugs (29.2%) in which aspirin composed 13.5% of the non-steroidal anti-inflammatory drugs prescribed followed by antimicrobials (9.2%). Conclusion: Acid suppressive drugs are the most commonly prescribed drugs with no proper indications hence irrational. Based on the results of this study, creating awareness about reasonable use of acid suppressive drugs is a necessity.Objetivo: El objetivo de este estudio fue estudiar y evaluar las indicaciones de los medicamentos supresores de ácidos y averiguar el porcentaje de recetas irracionales con medicamentos supresores de ácidos. Material / Métodos: es un estudio observacional prospectivo realizado en los Hospitales de las Fuerzas Armadas del Sur y en el Hospital de Maternidad Abha, ambos en Abha en la región de Assir (Arabia Saudita). El tamaño muestral del estudio fue de 185 pacientes. Se revisaron las hojas de casos de orden de prescripción de los pacientes para la prescripción de medicamentos supresores de ácido y se tomaron los datos pertinentes. Se identificó la edad de los pacientes mayores de 18 años. La duración del estudio fue de 8 semanas, entre mayo y junio de 2017. Resultados: nuestros resultados mostraron que la mayoría de las prescripciones de inhibidores de la bomba de protones (68,1%) eran injustificables y que este era el fármaco supresor de ácido más comúnmente prescrito para los pacientes (97,8%). La frecuencia de prescripción para los trastornos del espectro autistas en nuestro estudio, fue mayor en pacientes con un factor de riesgo existente y fue recomendada principalmente por los médicos como medicamentos concomitantes (67,6%). Los medicamentos concomitantes más comunes que se usaron con los inhibidores de la bomba de protones fueron los antiinflamatorios no esteroideos (29.2%) en los cuales la aspirina supuso el 13,5% de los antiinflamatorios no esteroideos prescritos, seguidos por los antimicrobianos (9.2%) Conclusión: los medicamentos supresores de ácido son los medicamentos más comúnmente recetados sin indicaciones adecuadas, por lo que son irracionales. Basado en los resultados de este estudio, crear conciencia sobre el uso razonable de los medicamentos supresores del ácido es una necesidad

The medical and biochemical knowledge of health care professionals regarding the management of MERS-CoV: lessons from 2019 pilgrimage season in Al-Madinah, Saudi Arabia: A cross-sectional study

Background: Middle East respiratory syndrome coronavirus (MERS-CoV) epidemic was a serious healthcare concern not responding to conventional anti-viral therapies between 2012 and 2017 with high fatality rates. Saudi Arabia is still among the best world examples in combating both MERS-CoV and COVID-19 pandemics. Objectives: Investigating the medical and biochemical knowledge of healthcare professionals in Al-Madinah, Saudi Arabia on preventive, diagnostic and therapeutic measures against MERS-CoV epidemic. Subjects and methods: In 2019, this cross-sectional study included 416 healthcare personnel of which 402 participants answered the questions with a response rate of 96.7%. Specialties of participants were medical students (1.4%), physicians (64.4%), nurses (23.6%) and others (10.7%). Results: The vast majority of the investigated healthcare personnel gave the right answers. 96.7% of the participants answered that washing hands using water helps prevent MERS-CoV. 90.8% of the participants answered that wearing a clean non-sterile long-sleeved gown and gloves does helps prevent MERS-CoV infection. 94.7% of participants answered that using alcohol-based hand rub helps prevent MERS-CoV infection. 92.03% of the participants thought that wearing protective equipment does help preventing MERS-CoV infection. 86.1% answered that there is no vaccine available against MERS-CoV infection and 86.1% answered that taking vaccines is suitable for preventing MERS-CoV infection. 90.04% of the participants answered that MERS-CoV patients should be diagnosed using PCR and 84.3% thought that the highest levels of anti-CoV antibodies are in abattoir workers while 87.8% thought that isolation of suspected cases helps preventing MERS-CoV infection. Conclusion: The investigated healthcare workers had a satisfactory knowledge on the preventive and therapeutic measures and biochemical knowledge against MERS-CoV epidemic at mass gatherings as pilgrimage season

Experimental study to evaluate the pretreatment of Melissa Officinalis extract against lethal seizures induced by Pentylentetrazole in Wistar rats

Abstract: Melissa officinalis is a well known medicinal plant. Different studies performed in mice have shown the sedative, hypnotic, analgesic, antiviral and antimicrobial effects of this plant. The present investigation was undertaken to evaluate the effect of percolated extract of this plant against lethal seizure induced by intraperitonal injection of pentylenetetrazole (PTZ) in wistar rats. The study was performed on three groups of animals pretreated with different doses of extract via intraperitonal injection. After 30 minutes each animal received high dose of PTZ (90 mg/kg) for induction of lethal seizure. The control group received normal saline. In addition a positive control group pretreated with diazepam, a well known drug in the treatment of seizure, was used for comparison. The efficacy of the extract to protect the animals against lethal seizure was based on the latency of the appearance of the first sign of seizure or the latency of the different epileptic manifestations and decrease of mortality rate in each group. The results showed that various epileptic manifestations are delayed in diazepam pretreated animals and extract compared with control group. The dose of 50 mg/kg of the extract appeared to be significantly effective on the tremors and the myoclonic jerks of epileptic manifestations (P<0.05). In addition the mortality rate was significantly reduced in pretreated animals with this dose compared with control group (P<0.05). Mortality rate was 88% in saline group, 13% in 50mg group and zero percent in diazepam group. The results indicated that the extract of Melissa officinalis possesses anticonvulsant property. Keywords: Melissa officinalis, Seizure, Pentylentetrazole, Anticonvulsant activity, Ra