محمدرضا ناطقی

The hydro-acoustic behavior and noise of marine propellers, especially in underwater vessels and submarines is of great importance. The main purpose of this article, is numerical modeling of the hydrodynamic noise of a high skew propeller sample from MAU marine standard series using computational fluid dynamics method with the help of Ansys-Fluent software under open water conditions. In the numerical simulation, the DES turbulence model was used, which is a good model for small vortices modeling near the wall. In order to validate the hydrodynamic and hydr-oacoustic results, the available data from the DTMB4119 benchmark propeller has been used. Comparison of the sound pressure level obtained for the DTMB4119 propeller in the present work and the available data from the reference shows a good compliance at frequencies higher than 20 Hz, but at frequencies lower than 20 Hz, about 20% error is observed. Based on the obtained results, with the increase in the number of propeller blades, the amount of vortex density around the blades decreases. The increase in the number of propeller blades has caused an increase in the average level of radiation noise in receivers at the axial direction. Increasing the number of propeller blades from 2 to a maximum of 7 blades has been able to reduce the radiated noise level in the axial direction by 15 decibels. In the radial direction, except the two-bladed propeller, the dipole radiated noises caused by the 3-7-bladed propellers have similar fluctuations.

Due to limited space and energy, increasing the performance of the underwater marine vehicle motor is one of the most important parameters in the design process. Increasing the performance of the underwater marine vehicle motor is directly related to increasing the efficiency of its cooling heat exchanger. In this paper, the aim is to use the geometric changes of the fins and increase the contact surface between the heat exchanger and the passing fluid in order to increase the turbulence of the flow to increase the efficiency of the heat exchanger. The existing experimental heat transfer relations have been used to validate the numerical solution method. Ansys fluent software has been used for numerical simulation. In this simulation, the pressure-based solver is used to solve the Navier Stokes equations along with the RNG k-ε turbulent model, and the solution is intended steady with air as working fluid. The effect of fluid flow velocity on circular fines at three different velocities has been investigated and then the effect of geometric changes of teeth has been evaluated in the speed of 3.0428 m / s. In the case of circular fins, the increase of fluid velocity increases heat transfer, and in the case of toothed fin, increasing the height of the teeth causes a slight increase in heat transfer and pressure drop, but as the number of teeth increases, the Nusselt number and pressure drop decrease significantly.

A magnetic metal-organic framework MOF composite, MIL-101Fe @PDopa@Fe3O4, was synthesized as the stable adsorbent for removal of Congo red CR from water. A very thin film of 3,4-dihydroxy-L-phenylalanine L-Dopa was used as an efficient and environmentally friendly binder between Fe3O4 nanoparticles and MIL-101Fe. The synthesized nanocomposite was investigated by SEM, TEM, FT-IR, XRD and TGA analyzes. Magnetic properties of the composite were studied by vibrating sample magnetometer VSM. Zeta potential analysis was also performed to determine the surface charge of the nanocomposite. Influencing factors such as pH, contact time, adsorbent dosage, temperature, and initial dye concentration on the adsorption ability of the MIL-101Fe @PDopa@Fe3O4 were investigated. The very excellent adsorption capacity about 909 mg/g for CR was achieved. Adsorption kinetics and isotherms studies indicated that CR adsorption followed Langmuir isotherm model and pseudo second-order kinetic model. Studies have also shown that The MIL-101Fe @ PDopa@Fe3O4 was found to be recyclable for removal of CR.

Lime juice is used to add flavor to foods and to prepare soft drinks. Basically, fresh lime juice is stored at ambient, cold or freezing temperatures immediately after being packed. In this research, the effects of different storage temperatures on physicochemical properties (pH, acidity, total soluble solid, polyphenolic compounds, antioxidant activity, ascorbic acid, and color), microbial features (mold and yeast, total count) and sensory properties of lime juice during the storage period (45 days) were evaluated. The results showed significant changes in pH, acidity and brix of lime juice so that the pH of product decreased, but acidity and brix increased, as the storage temperature of lime juice increased. The range of these changes in the freezer was less than that in other types of storage temperatures. Antioxidant capacity and total phenolic content decreased slightly over time at different temperatures that were higher at ambient storage. The maximum reduction, from 52.66 mg/g in 1st day to 11.16 mg/g in 45th day, was recorded for ascorbic acid at ambient temperature. The storage temperature also had a significant effect on counts of mold, yeast and total bacteria in lime juice during 45 days of storage. The microbial count of lime juice increased as storage duration and temperature increased but it was higher in ambient and cold storage. The results of sensory evaluation indicated a significant decrease in taste, odor, color and overall acceptance of lime juice as duration of storage and temperature increased. These results suggested that freezing of lime juice could have positive effects on preservation method to prolong shelf life with minimum qualitative changes in lime juice.

In this study, the structure of the inverted planer solar cell was used because of its prominent features, such as low temperature construction and low cost construction, the effect of two layers of PDOT:PSS and PTAA as the underlying perovskite on the morphology perovskite layer and parameters affecting solar cell performance Jsc, Voc, FF, PCE were investigated.
SEM and AFM images showed that Proper morphology and high coverage of perovskite film with PTAA compared to perovskite film with PEDOT: PSS resulted in increased light absorption and efficiency in perovskite solar cell with PTAA. Their yields reached 11.37, while the maximum PDOT: PSS-based solar cell efficiency was 9.23.

In the present research, after preparation of initial materials, nano-clay-polypropylene polymeric rice composite and rice bran were prepared by melt blending method with different percentages of nanoparticles. Its properties and structural was investigated by XRD, electronic microscopy imagines and tensile strength was investigated.  Mechanical properties including nanocomposite structure, tensile strength, impact resistance, water vapor absorption, oxidation resistance, melting point were investigated. The tensile strength increases with increasing nanoparticle content but decreases with increasing consumption by more than 5%. By increasing the concentration of nanoparticles in the matrix in the percent Higher weights, impact properties and water absorption and oxidation resistance decrease, but the melting point of the samples increases with increasing nanoparticles, indicating a uniform phase between the nanoparticles and the polymer surface and the shrinkage of the container will be reduced. According to the microscopic images of the specimens, it was found that there is a special bond between the two phases, in fact, there is actually a single phase in the composites

Organic-inorganic perovskite (CH3NH3PbI3), due to an appropriate energy gap to absorb sunlight, is used as an absorbent layer in third generation solar cells. Crystallinity of light absorbing layer plays an important role in the performance of perovskite solar cells and substrate plays an important role on crystallinity of light absorbing layer. In superstructure solar cells, alumina (aluminum oxide) is used as the substrate of light absorbing layer. In this paper, alpha and gamma aluminum oxide are used as the substrate of perovskite layer. The effect of this work on the crystallinity of perovskite layer and parameters that affect the performance of solar cells have been investigated. It was found that by taking into account all the parameters that affect the performance of solar cells, alpha phase aluminum oxide to the gamma phase is more suitable for use in perovskite solar cells that fabricated by two step deposition.

Oral habits have hazardous effects on children's speech which are sometimes irreversible and permanent. This study was planned to assess these oral habits among children in day-care centers of Tehran, Iran. In this descriptive, cross-sectional study, 400 children were selected through multistage sampling from 16 day-care centers in Tehran, Iran, They were 24 to 72-month old. Bottle feeding, pacifier usage and digit sucking were determined. After interviewing parents, oral examination [using Paediatric oral skills package (POSO)] and doing standard Phonetic test, a questionnaire was completed for each child. Sixty eight had one oral habit. The most prevalent habit was digit sucking (52.9%). The prevalence of bottle feeding, both digit sucking with bottle feeding, and pacifier habit were 38.2%, 7.3% and 1.4%, respectively. There were significant relationship between digit sucking and malocclusion (p<0.001, r=0.4) and hard palate malformationand (p<0.001, r=0.39). Besides, a significant relationship between bottle feeding and malocclusion (p<0.001, r=0.25) was conduted. Digit sucking had significant relationship with lisping, too (p<0.001, r=0.37). There was no gender priority in oral habits. Oral habits cause permanent structural conversion in speech producing and oral status.

Introduction & Stress urinary incontinence is a common problem among middle-aged women and can affect their quality of life. This study evaluated the effects of pelvic floor muscle exercise on quality of life outcomes in women with stress urinary incontinence. This clinical trial study was conducted at Shahid Akbarabadi Hospital of Tehran in 2009. After baseline evaluation, fifty women were assigned to this clinical trial. Participants were trained to do pelvic floor muscle exercises for 3 months and their quality of life were measured before and 3 months after intervention. The collected data were analyzed by the SPSS software using descriptive statistical tests and paired T experimental test. forty-six women completed the trial. After 12 weeks, the descriptive statistical tests and paired T experimental test showed significant difference in the quality of life scores of women with stress urinary incontinence before and after intervention(P<0.0001). 12 weeks exercise of pelvic floor muscle significantly improved the quality of life outcomes of women with stress urinary incontinence.