Search

Machining of metal matrix composites (MMC) is a challenging process as they are difficult to cut and cutting tools get worn out in a short time. In this paper, the performance of two industrial carbide grades and a cubic boron nitride (CBN) tool are assessed when machining of AZ91/SiC composites. Mg-based composites with different volume fractions and particle sizes are machined at various cutting conditions to evaluate the tools wear resistance and finished surface. The surface of the worn-out tools and machined samples are analyzed by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), and roughness tester. Results revealed that the tool wear increased for composites reinforced by smaller particles regardless of the tool type. Additionally, tool grade TH1000 resulted in longer tool life when machining of Mg-based composites compared to the CP500 grade so that at a cutting speed of 70 m/min and feed rate of 0.1 mm/rev, tool life improved nearly 250%. CBN tools showed the best performance when machining of Mg-based composites as tools became worn out after 255 s which is considerable compared to carbide tools. Also, the finished surface caused by cemented carbide CP500 indicated the worst quality. [ABSTRACT FROM AUTHOR]

Teacher in the educational system and the teaching-learning process, as a main leading should need to knowledge and professional skills. Therefore, evaluation of professional development is important. This study aims to design and modify Construction and Validation of professional development questionnaire of teachers. This research based on methodology and data collection procedure was descriptive-surveyed. The population consists of 400 teachers from high in Birjand in the academic year 2013-2014. A sample of 246 was estimated by Krejcie and Morgan. The instrument used in this study is a researcher's questionnaire of teachers' professional development. In order to assess the reliability and validity was used the content and construct validity by using of exploratory and confirmatory factor analysis and Cronbach's alpha. Results show that the questionnaire has good reliability and validity. According to the results of a factor analysis of the eight factors (components) were identified for professional development of teachers that explains a total of 54/69% of total variance. It can be concluded that the questionnaire would be a suitable tool for the professional development of teachers.

The home learning environment (HLE) index is composed of seven questions regarding educational parent-child interactions. To compare the psychometric characteristics of the six items of HLE index between the two different contexts of Germany and Iran, a sample including 468 preschool children from the National Educational Panel Study (NEPS), Germany, and 465 preschool children from the Longitudinal Study of Iranian Children (LSIC; Growing Up in Iran) were examined. Rasch analysis supports the fitness of the five items of HLE into the model in both countries. However, differential item functioning (DIF) results revealed significant differences between items functioning across the two samples. According to the item difficulty maps, reading to children was the most reported item in the German families, while Iranian parents tended to paint and draw with their children more. While findings support the construct validity and reliability of five of the six items in both samples, different Rasch results may reveal the effects of the cultural dimensions of each country on HLE items.

Background: This study assessed the prevalence of gastroesophageal reflux disease (GERD) in a general adult population in Iran. The association between GERD and various factors was also evaluated. Methods: We performed a cross-sectional study on 163,018 individuals aged over 35 who were enrolled in the PERSIAN cohort. GERD was defined as the occurrence of heartburn and/or regurgitation symptoms at least several days a month. Survey design analysis for pooled data was performed and multiple regression analysis was conducted to determine the independent risk factors for GERD. Results: The prevalence of GERD in our study was estimated at 21.86% (95% confidence interval:17.4%-36.4%). The mean age of the participants was 49.84 years±9.25 (35–70) and 44.75% of the participants were male. Symptoms of heartburn and regurgitation were reported in 18.65% (n: 29,170) and 6.06% (n: 9,717) of participants, respectively. In the multivariate analysis, several factors were found to be associated with a higher prevalence of GERD: female sex, age >50, current smoking, opium use, weekly consumption of fried foods, frequent consumption of hot tea, less than 6 hours of sleep per night, psychiatric disorders, usage of NSAIDs, and poor oral hygiene, were associated with a higher prevalence of GERD. Conversely, higher education levels and average physical activity were found to be less commonly associated with GERD. Conclusion: We found a relatively high prevalence of GERD (21.86%) in this population-based study in Iran. By identifying modifiable risk factors, this research offers opportunities for targeted interventions and lifestyle modifications to reduce the burden of GERD. [ABSTRACT FROM AUTHOR]

Metal matrix composites (MMC) introduced special features such as resistance to wear and high strength to weight ratio and these characteristics categorized them as difficult-to-cut materials in the field of machining. In the current paper, a novel study on the cutting fluid emulsion 5% role in the machinability of a magnesium-based metal matrix composite reinforced by silicon carbide (SiC) particles is presented. AZ91 magnesium alloy, with nominal composition Mg-9Al-1Zn, composites were made using stir casting method. Then, the composite samples were machined and the cutting parameters such as cutting speed, feed rate and side cutting edge angle were varied to assess their effects on the wear and surface roughness. To measure and analyze the wear, optical and scanning electron microscope (SEM) were used. Also, elemental analysis through energy-dispersive X-ray spectroscopy (EDS) was accomplished. Surface roughness of machined samples were measured by a profilometer and 3D surface topography. Results of SEM and EDS images indicated that SiC particles included in the composites act as grinders and remove the surface of tool even in a short time because of the severe abrasion. Additionally, surface of machined MMCs contains some defects such as cracks, broken SiC, and unwanted deformations. Using cutting fluid emulsion 5% enhanced the tool life as well as the surface quality remarkably for different cutting speeds, feed rates and cutting edge angles although finished surface of the samples were oxidized. Also, the cutting fluid considerably reduced the amount of adhered materials on the flank face. [ABSTRACT FROM AUTHOR]

Background: Opium use is a significant social and public health issue. There are numerous effects of opium documented as affecting the pancreatobiliary system. The aim of the study was to assess the pancreatobiliary changes in patients with opium addiction by endoscopic ultrasonography (EUS). Methods: During the study period, consecutive patients who were referred for EUS of submucosal upper gastrointestinal lesions were included. The history of opium addiction and clinical symptoms were recorded prospectively. Diameters of the common bile duct (CBD), pancreatic duct (PD), size of the ampulla of Vater, and gallbladder abnormalities were evaluated using EUS. Results: A total of 254 patients (53.1% male, mean age of 55.4 ± 14.2 years) were studied. A history of opium addiction was present in 56 patients (22.0%). Choledocholithiasis was found in two patients (3.6%) and one control (0.5%) patient (P = 0.06). Gallbladder stones were found in 13 opium-addict (23.2%) and 16 control (8.1%) patients (P = 0.002). The mean diameter of the CBD, size of the ampulla of Vater (P < 0.001), and PD (P = 0.04) were all significantly greater in patients with opium addiction. Conclusion: Dilation of the biliary and PDs is seen more commonly in patients addicted to opium. However, the clinical implications of these findings need to be further evaluated in future studies. [ABSTRACT FROM AUTHOR]