Background and Aims: When composite resin polymerizes, shrinkage stresses tend to produce gaps at the tooth/ restoration interfaces. Surface sealants may reduce or avoid problems related to the marginal interface. The aim of this study was to evaluate the effect of two different surface sealants (Fortify and Optiguard) on the microleakage of class V resin composite restorations.Materials and Methods: Twenty three sound noncarious molars were collected. Totally, 45 Class V cavities with the occlusal margins in enamel and cervical margins in cementum were prepared in both buccal and lingual surfaces. The specimens were randomly assigned in three groups (15 cavities in each group) and then restored with a resin composite. After the finishing and polishing procedures, the restorations in each group were covered with a specific surface sealant, except for the control samples, which were not sealed. After placing restorations, the specimens were thermocycled and then immersed in a 50% silver nitrate solution (tracer agent) for four hours, sectioned longitudinally and analyzed for leakage using a stereomicroscope in a blind manner. The marginal microleakage was evaluated at the occlusal and cervical interfaces and compared among the three groups using the Kruskall-Wallis and the Mann-Whitney U tests.Results: Microleakage was found in all groups at both occlusal and cervical margins. Significantly greater leakage was observed at the cervical margins compared to the enamel margins of the material groups (P=0.005).There was no statistically significant difference among the groups at occlusal margins (P=0.66). In the cervical region, Fortify showed improved results and statistically presented the lowest degree of microleakage (P=0.003).Conclusion: The used sealant materials presented different rates of effectiveness and Fortify decreased marginal microleakage significantly.

Introduction: Kojic acid with the chemical structure of 5-hydroxy-2-hydroxymethyl-ˠ-Piron is an organic acid that is biologically produced through aerobic fermentation process by using various substrates and via the function of variety of fungi. This study was aimed to study the optimization of Kojic acid production by Locally Isolated Fungi Aspergillus sp., using ‘Response Surface Methodology’.Materials and Methods: Kojic acid was produced by fermentation of isolated strain of genus Aspergillus in submerged culture medium. Initial investigation in Kojic acid production process was performed via Plackett-Burman method and by using different nitrogen sources such as yeast extract, peptone, ammonium sulfate, ammonium chloride, urea as well as different carbon sources, including fructose, sucrose, glucose, lactose and maltose.Results: Based on our study, peptone and glucose were the most effective factors with carbon and nitrogen sources in production of kojic acid (P<0.05). The next step was production of 34.4g/L kojic acid by optimizing the effect of environmental factors such as temperature, pH, glucose and peptones, such as carbon and nitrogen sources, used in production of kojic acid and by employing ‘Response Surface Methodology’.Conclusion: Based on the results of this study, the maximum production of kojic acid can be achieved by using; glucose (%8.71), peptone (37.4%), temperature (29.9oC) and adjusting pH to 6.75 in the production process.

Introduction: Students use a set of mental activities while studying to apply different study approaches according to their performance, the nature of the curriculum and their mastery during the study. This study aimed to compare study approaches and academic performance of male and female medical students in the first, second, third and fourth years (basic sciences and physiopathology). Methods: The method of this study is descriptive-cross-sectional.The sample of this study is 287 medical students in basic sciences and physiopathology in Tehran University of Medical Sciences in the academic year 2018-2019 who were selected through Stratified sampling. The tools of approaches to study and learning Were used. Analysis was performed by Anova test. Results: The results showed that the score of surface approaches to study of first year students is significantly lower than third year and fourth year students. Third-year students' use of the strategic & deep approach was significantly lower than second, third and fourth year students. Conclusions: The present study has shown new results on the transition of the use of approaches  to study during the four years of general medicine. Students' use of surface, deep and strategic approaches has grown transitionly and in higher years, the use of surface approach has decreased and more deep and strategic approaches are used.  after the second year due to the different structure of the curriculum, academic failure is observed.

Performance of a WIG vessel (Wing in Ground effect) moving close to the water free surface is an important issue in aerodynamic design of such vessels. Reliable prediction and analysis for wings as well as considering different factors can have significant effects on WIG design. Hence, aerodynamic modeling of wing sections close to the water surface is studied and some practical results are derived in this paper. Furthermore, this paper introduces important procedures and numerical implementations for aerodynamic analyses. The accuracy and efficiency of the methods are discussed and the results are presented. In addition the effects of flexible water free surface versus the ground are studied and compared with each other. Some other factors such as viscosity and turbulence are taken into account and their effects are evaluated. Finally some conclusions are summarized based on numerical results.

Access to safe drinking water is an important means of safeguarding public health. This cross-sectional study was designed to investigate the performance of electrocoagulation in the treatment of surface waters. For this purpose, water samples were taken from the intake to the Soleymanshah-Songhor Dam. Treatment was carried out in a reactor operating in the batch mode. Experiment runs were designed using the Design Expert Software (Stat-Ease Inc., Version 6.0.6) to investigate the effects of voltage (5-25), reaction time (20-60), temperature (10-30L), and rapid mixing (200-400) on the Mn (II), Fe (II), hardness, alkalinity, and turbidity removal efficiencies as a result of treatment with aluminum electrodes. After the treatment process, the study parameters and the dissolved metal content due to the dissolution of the anode electrode were measured. Maximum removal efficiencies for Fe (II), Mn (II), hardness, and alkalinity were 96.2%, 94.6%, 26.6%, and 12.2%, respectively, while turbidity reduced from 0.6 to 0.15 NTU. Moreover, the dissolved Al content in the treated sample was found to be higher than the standard limit allowed for drinking water. Thus, the electrocoagulation process seems to be effective in the removal of the investigated contaminants from surface waters. However, the factor limiting the use of this method under maximum efficiency conditions is the dissolved metal content due to the dissolution of the anode electrode, which is a significant concern for the public health. In contrast, the electrocoagulation process seems to be an efficient and safe pretreatment method using aluminum electrodes if operated for achieving optimum efficiencies.

Simulation of the flow around propeller is a complex fluid flow problem, especially when the propeller is close to free surface. In this study, the effect of immersion depth, advance velocity and the ventilation phenomenon on the performance of a B-Wageningen series propeller close to surface of water have been numerically investigated. For this purpose the ANSYS-FLUENT commercial software has been used to solve the viscous, incompressible and two phase flow field. The rotation of the propeller has been implemented using the rotating reference frame model for steady flow and the sliding mesh for unsteady flow. For turbulent flow modeling and free surface simulation, the k- SST model and the volume of fluid method have been used, respectively. For validation of numerical results due to lack of access to experimental results of propeller close to surface, numerical solution in open water condition has been performed and performance coefficients have been calculated. Comparing the numerical results with the experiment ones shows good agreement and confirms the results of numerical simulation. Results of the numerical solution show that the submergence ratio and ventilation phenomenon affect the performance of propeller so that by reducing submergence ratio from 2.2 to 1.4 in advance ratio J=0.4, ratio of thrust and torsional moment coefficients to open water performance coefficients reduced to 7.7% and 6%, respectively.

Appreciating the crucial importance of roads in keeping different areas connected to one another, road maintenance and repair represent a vital role of any road transportation management. Microsurfacing is an important preventive method for paved road maintenance. The present research is aimed at investigating the effect of adding polypropylene fibers into microsurfacing mix on its performance. For this purpose, performance evaluation of the microsurfacing mix was conducted by preparing five different mixes containing polypropylene fibers at different dosages, namely 0, 0.05, 0.10, 0.15, and 0.20% by weight to the weight of total aggregate. Analyses were performed by doing wet cohesion test, loaded wheel test, and wet track abrasion test according to ASTM D6372. Results showed that the polypropylene fiber-reinforced mixes exhibited improved microsurfacing performance. Among other mixes, the one containing the fibers at 0.10% showed 20.6 and 21.1% higher bitumen cohesion in the 30- and 60-min cohesion tests, respectively. Also using this mix, vertical and lateral displacements could be reduced by 38.2 and 28.9%, respectively, resistance to abrasion improved by 35.6%, and bleeding decreased by 25.4%. Compared to the control specimen, the mix containing polypropylene fibers at 0.10% exhibited 1.6% higher bitumen emulsion, providing for achieving the desired cohesion within a predefined period of time. The other results showed that excessive incorporation of the polypropylene fibers into the microsurfacing mix would inhibit optimal dispersion of the fibers across the mix, leading to accumulation of the fibers in the form of nodules and hence deteriorating the mix performance.