Numerical modeling of fluid flow, heat, and mass transfer for similar and dissimilar laser welding of Ti-6Al-4V and Inconel 718

AbstractMost of the researches published on the numerical modeling of laser welding are looking at similar welding, mainly due to the difficulty of simulating the mixing phenomenon that occurs in dissimilar welding. Furthermore, numerical modeling of dissimilar laser welding of titanium and nickel alloys has been rarely reported in the literature. In this study, a 3D finite volume numerical model is proposed to simulate fluid flow, heat, and mass transfer for similar and dissimilar laser welding of Ti-6Al-4V and Inconel 718. The laser source was simulated by volumetric heat distribution, which considers the effects of keyhole and heat transfer on the workpiece. The heat source parameters were calibrated through preliminary experiments, by comparing the simulated and experimental weld pool shapes and dimensions. The model was used to simulate both homogenous and dissimilar laser weldings of Ti-6Al-4V and Inconel 718, and a systematic comparison was carried out through a number of selected experiments. The effects of three distinct levels of laser power (1.25 kW, 1.5 kW, 2.5 kW) on temperature distribution and velocity field in the welds pool were analyzed. Results highlighted the effects of Marangoni forces in the weld pool formation. Furthermore, in order to analyze the mass transfer phenomenon in dissimilar welding, species transfer equations were considered, demonstrating the important role played by the mass mixture in the weld pool formation. Finally, a high level of agreement between simulations and experiments—in terms of weld pool shape and dimensions—was observed in all cases analyzed. This proves the ability of the proposed numerical model to properly simulate both the similar and dissimilar welding of Ti-6Al-4V and Inconel 718 alloys

Geometric Motion Planning for Inertial Systems

In order to enable better visualization and understanding of the effect of the robot's geometry and inertia on the robot's trajectories, this dissertation proposes to use geometric mechanics to bridge the gap between the physical motion of a robot and its mathematical structure. The main focus of this research is to investigate the system geometry and inertia and their relationship with the curves and acceleration that produce the most efficient trajectories or gaits. This dissertation ‘s approach has an advantage over the state-of-the-art method, which uses numerical forward dynamic simulations. Such numerical simulations are computationally expensive and dependent on starting parameters. The proposed geometric motion planning framework allows the user to design a trajectory with respect to the requirements without any need for forward simulation. Furthermore, the proposed framework enables the user to understand the system's movement from its mathematical model rather than computing the results and exploring the outputs. Unlike previous works that were focusing on the system geometry to gain insight about the system's movement, this dissertation uses the geometry and inertia to describe the system's movement. This is achieved using two tools to gain insight into the underlying locomotion: constructing geodesics and constructing metric fields. The geodesic illustrates the robots geometric structure of the natural dynamic path which is defined as the straightest path. The metric field in mechanical systems is obtained from the system's inertia which illustrates where it is easier to move in parameterized space. In this research we consider four classes of systems: (1) fixed base systems such as robotic arms, (2) crawling systems in an inertial based environment such as floating snakes, (3) flying object with an abrupt change in momentum such as casting manipulator, and (4) system with fast energy release such as jumping robots

Survey of crude oil toxicity component removal by adsorbtion with powdered activated carbon

زمینه و هدف: نفت خام ترکیبی بسیار پیچیده بوده که حاوی هزاران هیدروکربن با اثرات مضری مثل سرطان زایی و اثرات خونی می باشد. به دلیل حجم نسبتاً زیاد ورود آن به محیط های آبی، انجام تصفیه موثر روی پساب های حاوی نفت خام بسیار مهم می باشد. این مطالعه با هدف بررسی حذف ترکیبات عامل سمیت نفت خام در آب به وسیله جذب سطحی با کربن فعال پودری انجام شد. روش بررسی: در این مطالعه تجربی نمونه استاندارد قسمت محلول نفت خام با اختلاط یک قسمت نفت خام با 9 قسمت آب تهیه گردید. جهت آزمون سمیت از غلظت های مختلف قسمت محلول نفت خام و لارو ماهی قزل آلا استفاده شد. قبل و بعد از اضافه کردن 10، 20، 40 و 60 میلی گرم بر میلی لیتر کربن فعال پودری، آزمون سمیت و کربن آلی کل روی نمونه ها انجام گردید. غلضت کشنده 50 (LC50) نمونه ها توسط برنامه آماری پروبیت محاسبه شده و نتایج مورد تجزیه و تحلیل قرار گرفت. یافته ها: غلظت کشنده 50 محلول نفت خام قبل از استفاده از کربن فعال در زمان های 24، 48 و 96 ساعت به ترتیب 5/129، 5/69 و 6 به دست آمد. این غلظت با افزودن کربن فعال افزایش داشت که این افزایش وابسته به غلظت بود. به طوری که غلظت کشنده 50 96 ساعته بعد از اضافه کردن کربن فعال با غلظت های 10، 20، 40، 50، 60 میلی گرم بر لیتر به ترتیب 8/94، 6/106، 8/117، 3/138 و 5/181 میلی گرم بر لیتر اندازه گیری شد. مقادیر کربن آلی کل در غلظت های 0، 10، 20، 40، 50 و 60 میلی گرم بر لیتر کربن فعال به ترتیب 89/54، 81/44، 88/43، 16/38، 62/36 و 14/35 میلی گرم بر لیتر بود. نتیجه‌گیری: کربن فعال باعث کاهش سمیت و کربن آلی کل نمونه ها گردید. با افزایش میزان کربن فعال مورد استفاده، سمیت کاهش بیشتری را نشان داده اما کربن آلی کل با شدت سمیت کاهش نیافت. در صورت بروز حوادث و ورود نفت خام به منابع آب آشامیدنی استفاده از روش کربن فعال پودری می تواند مورد نظر قرار گیرد

QUALITY OF SERVICES IN REHABILITATION CENTERS FROM THE PATIENTS' PERSPECTIVE, USING THE IMPORTANCE-PERFORMANCE ANALYSIS IN AHVAZ, 2015

Quality of service is a key factor in the success of health care organizations, including the rehabilitation centers. Nowadays, rehabilitation centers are faced with many challenges in the quality of service and there are many differences between patients' expectations and perceptions of the service quality received at these centers. So, this study aimed to determine the quality of services in rehabilitation centers from the patients' perspective in Ahvaz using the importance - performance analysis (IPA). In this analytical-descriptive study, the study population was all patients who referred to the five selected rehabilitation centers in Ahvaz in 2015. In this study, 110 patients were selected as samples by a random sampling method. Using a standard 22- item SERVQUAL questionnaire, the quality of service provided in the centers in 5 dimensions of two parts "importance" and "performance was investigated. Data were analyzed using the SPSS and Excel software. All dimensions of service quality in the centers studied, were in the first area of the importance- performance matrix, namely at optimal levels. A significant difference was seen between scores of the importance and performance of the dimensions of the quality of service at the centers studied (p=0. 001). The highest (-0.75) and the lowest (-0.49) gap was estimated for the dimensions of "tangibility" and "empathy", respectively. Services offered in any of the dimensions were not beyond the expectations of clients and still there is much possibility for improving the process. Keywords: Quality of service; Importance-Performance Analysis (IPA); Rehabilitation center

Removal of methylene blue from aqueous solutions using raw and modified rice husk

ABSTRACT, one of the most important environmental pollutants is dye containing wastewaters. Methylene blue (MB) is a cationic dye that has carcinogenic and mutagenic effects on human. This study was investigated to remove methylene blue dye from aqueous solutions by raw and modified rice husk (Raw-RH and Modified-RH). The influence of various parameters including pH, contact time, adsorbent dose and initial dye concentration was studied on the dye removal efficiencyin a batch system. The results showed that the equilibrium was obtained at the contact time of 90 min and the maximum dye removal was also occurred at pH 10 for both the Raw-RH and Modified-RH adsorbents. The experimental data were analyzed by the Langmuir and Freundlich isotherm models. The findings showed that the data were best fitted with the Freundlich isotherm. The obtained data for MB adsorption onto the Raw-RH and Modified-RH were also fitted via the pseudo-first order and pseudo-second order kinetic models. The correlation coefficients values (R2 ) showed that the adsorption kinetic described well by the pseudo-second order model. The results of this study indicated that rice husk can be used as an effective and low-cost adsorbent for the removal of methylene blue from aqueous solutions

A constructability assessment model based on BIM in urban renewal projects in limited lands

One of the most significant concerns in urban development today is the organization of areas of cities that have become run-down over time. In order to complete previous constructability studies in other fields of construction, the current study evaluates constructability based on BIM, specifically in the context of the Tehran limited land renewal project. The motivation for this study is the current difficulties facing renewal designs for limited lands, and the lack of a quantitative constructability model for urban renewal projects in Iran. This paper aims (1) to discuss the design elements that should be considered in the design phase of urban renewal projects; (2) to identify the factors that may affect constructability; and (3) to propose a framework for assessing urban renewal designs by considering constructability factors using building information modeling (BIM). To meet these needs, this paper investigates constructability factors and their relative importance, considering the design elements that should be acknowledged in limited land renewal, using a multicriteria techniques. Some 28 constructability factors are identified through a literature review, and based on 52 responses received from a questionnaire survey, the factors are ranked using pairwise comparisons of the analytic hierarchy process (AHP). The final constructability factors that are identified through the technique for order preference using the similarity to ideal solution (TOPSIS) method are standard dimensions, safety, simplification of structure, resource intelligence and alignment, and skilled labor availability. The contribution of this research to the body of knowledge is, firstly, the development of constructability factors for measuring the constructability of urban renewal designs, and secondly, the introduction of BIM as a most beneficial tool for assessing the constructability of the proposed designs. In using the constructability assessment framework and identifying the trade-offs between the constructability of renewal projects in the limited areas of urban spaces, design alternatives become more feasible

Subjective and simulation-based analysis of discomfort glare metrics in office buildings with light shelf systems

Glare is a kind of physiological phenomenon that influences occupants’ visual comfort. Discomfort glare scenes in comparison to other levels of glare have been difficult to estimate and need accurate and reliable metrics. In contemporary architecture, the glass façade is so popular since it can remarkably minimize energy consumption in buildings and maximize daylight utilization as a natural energy. However, it is necessary to consider occupants’ visual discomfort due to the daylighting glare risks during the initial stage of design. Since the measured glare metrics should have an acceptable correlation with the human subject data study, the agreement on the glare indices is complicated. This paper presents a comparison between subjective and simulation-based analysis of discomfort glare metrics in offices with a light shelf system. The discomfort glare metrics considered in this study include Daylight Glare Index (DGI), CIE Glare Index (CGI), Visual Comfort Probability (VCP), Unified Glare Rating (UGR), and Daylight Glare Probability (DGP). The parallel comparison was conducted by using simulation and questionnaire surveys to determine which criteria are more useful under different conditions. According to the findings, DGP yields the most reliable results in different levels of glare based on the subjective analysis and VCP has the lowest accuracy in each stage. UGR also has the highest accuracy rate for evaluating perceptible glare, DGI is applicable for assessing imperceptible glare, and CGI can be an acceptable index for approximating intolerable glare. The study results significantly reduce the complexity of the problem and can provide useful guidance for designers to select the most reliable glare metric based on climatic conditions

Impact of dietary and lifestyle on vitamin D in healthy student girls aged 11-15 years

Objective : To study daily intake of calcium, phosphorus and vitamin D,to determine the biochemical findings of rickets and the effect of sunlight exposure and vitamin D supplemention in school girls with hypovitaminosis D. Methods: A cross-sectional study was conducted on school girls aged 11-15 years selected randomly from various areas of Tehran, Iran. Dietary information and amount of sunlight exposure were estimated by a 7 day recalling method using self-reported questionnaire. Hypovitaminosis D defined as low serum 25-hydroxyvitamin D concentration with two or more others abnormal biochemical findings. Girls with hypovitaminoses D were randomly divided into two groups. The faces and hands of girls in group 1were exposed to sunlight for one hour per day for twenty days, while those in group 2 were administered vitamin D capsules, 50,000 IU per day for the same period. Results : four-hundred fourteen girls evaluated, mean daily calcium intake, sunlight exposure and vitamin D acquirement were 360 mg, 10minutes and 119 IU, respectively. Mean serum 25-hydroxyvitamin D concentration was 30 ng/ml among all girls whereas in 15 (3.63%) of 414 girls was 7.8 ng/ml. Abnormal biochemical findings in these girls included hypocalcemia (n=4), hypophosphatemia (n=5), raised serum alkaline phosphatase (n=13), and parathyroid hormone (n=15). After intervention, mean serum 25-hydroxyvitamin D concentration in sunlight exposure (n=8) and vitamin D (n=7) supplementation increased to 14.4±4 ng/ml and 23±4 ng/ml respectively. There was a significant difference between the two groups (plt0.05). Conclusion: Vitamin D deficiency developed in rapid growth period of girls without clear clinical rickets in sunny temperate climate city in Iran which vitamin D supplemention improved biochemical findings better than sunlight exposure

The impact of Supplementation With Fish Oil on Lipid Profile of Pregnant Mothers: A Randomized Controlled Trial

Objective: The impact of supplementation with omega-3 fatty acid during gestational period on lipid profile levels remains unknown. The objective of this trial was to investigate the impact of supplementation with fish oil on maternal lipid profile. Materials and Methods: This research was a randomized triple blinded controlled trial. The study population was comprised healthy pregnant subjects who had family records at health care centers in Tabriz, Iran. A total of 150 women who were eligible for study were randomized into two groups, one group took fish oil supplement capsules (1000 mg/day), and another group took placebo. A total of 92 women fulfilled the study which 45 participants were in the supplemented group and 47 participants were in the placebo group. Consumption of fish oil capsules and placebo was daily one capsule from the beginning of the 21th week of gestation until delivery which was about 20 weeks. At the start of trial (16th-20th weeks) and in the fifth care of gestation (during 35th-37th weeks) 3 cc blood samples collected and sent to the laboratory for evaluation of lipid profile levels. Results: Despite substantial increases in total cholesterol, triglycerides and Low-density lipoprotein (LDL) levels with advancing pregnancy, there was no statistically significant discrepancy between the intervention and placebo groups. (P = 0.345, 0.299, 0.109, respectively). Despite a significant decrease in the levels of high-density lipoprotein (HDL) cholesterol with advancing pregnancy, there was no statistically meaningful difference between two groups (P = 0.786) Conclusion: We found no effect of supplementation with fish oil during gestation on plasma lipid profile of pregnant mothers