فهرست مطالب abbas zolfaghari

The combined effect of the number of joints, opening, type and thickness of filling on the amount of vibration caused by the propagation of waves in four identical dry limestone blocks with dimensions of 10*10*50 cm was studied. The maximum vibration of particles in intact and jointed rock blocks in three perpendicular directions was recorded by a three-component geophone. In block number 1 with a joint in the middle of the block, the amount of joint opening was changed from 3-6-9-12-15-18-21 mm and the measurements were made for each amount of opening in two series. In the first series, the joint filled with clay was tested, and in the second series, the joint filled with sandy soil was tested. This series of tests were also performed on blocks No. 2 with two joints, Block No. 3 with three joints, and Block No. 4 with four joints. The results of the tests showed that the presence of joints in rock blocks reduced the maximum vibration of particles in all three directions with different proportions. The relationship between the increase in the joint index and the decrease in the maximum vibration of the particles is nonlinear.

The use of Additive Manufacturing (AM) techniques in medical science has resulted in a great change in this field, especially in bone tissue engineering. One of these techniques is the Fused Deposition Modeling (FDM) which is used to make bone scaffolds. From view point of bone tissue engineering, bone scaffolds must have acceptable mechanical properties in addition to the required biological properties. In this study, at first the printing parameters including layer height, printing speed and number of filaments in each row were determined and bone scaffolds were made with two different materials polylactic acid (PLA) and polycaprolactone (PCL) and were subjected to the compression tests. The results of Young’s modulus and yield stress analyzed in Design Expert software showed that increasing the layer height reduces the mechanical properties. Also, increasing the number of filaments in each row increases the elastic modulus of the scaffold. For example, for scaffolds made of PLA, the maximum modulus of elasticity belongs to 12 filament scaffolds with a layer height of 0.1, which is equal to 319 MPa, and the minimum elastic modulus belongs to 8 filament scaffolds with a layer height of 0.3, which is equal to 143 MPa. Printing speed for scaffolds made of PLA does not have a significant effect on the Young’s modulus and yield stress. But for scaffolds made of PCL, increasing the printing speed reduces the modulus of elasticity but it doesn’t have a significant effect on yield stress.

The Koushk Zn-Pb shale-hosted massive sulfide deposit is located in the north east of Bafq area within the sequence of lithostratigraphical Rizu unit in the Central Iran (Posht-Badam block). During this study, for the first time in Iran, unknown pink vein minerals are contemporaneous with quartz, located in most of the north and south Pahno stratigraphic units has been introduced as Kutnohorite mineral in the Koushk deposit. Kutnohorite is a type of manganese carbonate with the chemical formula "CaMn2+(CO3)2", belong to the dolomite group. Sampling and geochemical analyses of volcanic-sedimentary host rocks (rhyolite, tuff, shale and dolomite) indicate that high amounts of chlorite, sericite, clinochlore, and euhedral pyrite minerals are found with kutnohorite-quartz veins and associated with galena and sphalerite ores at north Pahno section of the Koushk deposit. According to determining the types of alteration associated with kutnohorite-bearing zone using Ishikawa and chlorite-carbonate-pyrite (CCPI) indices showed that this mineral is an indicator and exploratory key in the Zn-Pb shale-hosted massive sulfide deposits such as the Koushk ore deposit.

Cement grouting is a common method for sealing and consolidating dam foundations. Since grouting is a cost and time- consuming process, understanding the amount of cement consumption is essential to estimate the cost of any dam construction. The geological setting is one of the main factors affecting the amount of cement take. In this paper, an attempt has been made to investigate the relation between the amount of cement take and the values of Rock Quality Designation (RQD), permeability, joint spacing, and joint aperture, measured in pilot holes drilled at the Khersan II Dam site (west Iran). The amount of cement take shows a direct relation with the values of permeability and joint aperture but presents a reverse relation with the values of RQD and joint spacing. Among the mentioned parameters, the Lugeon value has the highest correlation with cement consumption, however, poor correlation indicates the influence of other factors. To reduce the influence of other factors, the values of cement take were normalized to the injection pressure and then its correlation with the mentioned parameters was investigated again. Results show a significant improvement, especially between the normalized cement take and Lugeon values, resulted in at least the coefficient of determination of 0.7. After validation, the presented equation could be used to estimate the value of cement consumption at similar dam sites.

In recent years, 3D printing methods (additive manufacturing) have been attracted in research centers and industry. Among several 3D printing processes, fused deposition modeling (FDM) was more popular. In this method, plastic filaments were used for rapid prototyping or manufacture of a structural part. In this research, composite filaments compounded by a polymeric matrix and different volume fraction of aluminum oxide (alumina), were produced. Mechanical and physical properties of printed parts by these filaments were evaluated. Tensile test results showed that with increase of the volume fraction of alumina, tensile strengths were decreased because of inter layer voids. For 20% volumetric of alumina, tensile strength was decreased up to 70%. But in compression test, compressive strength was decreased 74% with increase of alumina till 10% and then compressive strength increased. Also, heat deflection temperature test was conducted and 11% decrease in heat deflection temperature was obtained, because of lower strengths of composites. Thermogravimetric analysis (TGA) showed that with increase of alumina, thermal stability of printed parts was increased. Linear shrinkage was measured for printed part in three directions and anisotropic shrinkage was explained. Also with increase of alumina till 15% volumetric, hardness was decreased to 27% and after that the hardness was increased a little. With increase of alumina till 20% volumetric, warpage of parts was decreased to 91%.

Effectively joining metals and composites in an efficient manner is challenging due to their dissimilar physical compositions and mechanical properties. Failure of bonded joints is generally strongly influenced by the non-uniform distribution of stresses and strains that usually with the maximum value, commonly located near the ends of the overlaps. In this study, carbon is used as a reinforcing element in the adhesive layer and to improve the distribution of stress, properties are graded by fibers along the overlap. Also, using a new method, the effect of the reverse step on joint strength has been investigated. In addition, finite element modeling is used to express the distribution of shear and peel stresses in the adhesive layer and also to analyze the reasons for increasing joint strength in stepped specimens. Use of carbon at the joint surface, grading of the joint area and mechanical interference through reverse steps, have positive effects on strength. By grading the overlap by carbon and glass, the distribution of shear and peel stress have become more uniform and load and displacement of failure compared to the base specimen, which has a shear strength of 1.92 kN, increased by 34%. Creating the reverse step changes the failure mode. The presence of one step 40%, and the placement of carbon at the joint interface of that, has increased 112% of strength. But the greatest increase in strength and displacement failure is achieved using two reverse steps and carbon in the joint surface, by a significant amount of 172%.

The main concern in designing of multi-cavity molds is flow balance between cavities. Any departure in flow balancing of the cavities can resulte difficulties in processing and quality of injected parts. In this paper, flow balance in a two-cavity plastic injection mold with different sizes (or called family-cavity mold) was investigated. Moldflow software was implemented to predict the filling phase through the cavities. Diameters of runners related to each cavity were adjusted to attain a balanced flow. Evaluating the flow balance was conducted by injection molding as short-shot and measuring the weight of each cavity. A high density polyethylene (HDPE) was applied as plastic material in this research. Good agreement was observed between experimental and simulation results. Moreover, in this paper one of the runners could be resized while injection molding via an insert located in the mold. The effect of flow balance on the tensile properties of the injection molded specimens was investigated. The results indicated that the parts obtained from the balanced mold exhibit a higher tensile strength and elongation at break up to 14% and 18%, respectively. The dimensions of injected parts were measured. It was found that there are not any differences between the shrinkage of specimens obtained by balanced and unbalanced mold.

In recent years a high attention has been conducted to the structural application of wood plastic composites (WPCs). Regarding that the WPCs have lower mechanical strengths, fiber reinforcements have been applied for strengthening the WPCs. Hybrid wood plastic composites (HWPCs) include two types of reinforcements of glass fibers and wood flours that are added to a polymeric matrix. WPC pallets as an example can exploit the mechanical strength of HWPCs. In previous work, wood plastic composite was reinforced by continuous glass fibers by a unique extrusion process. Embedding the continuous glass fibers in WPC matrix resulted in significant improvements in mechanical properties such as tensile and impact strengths. In this paper, a model has been proposed to predict the tensile strength and modulus of the WPCs reinforced with unidirectional glass fibers. The methodology applied in this research considers the WPC as matrix and the glass fibers as reinforcements. Since WPC matrix is brittle, the rule of mixtures corresponding to the brittle matrix composites was used to predict the tensile strength. Results indicated that the predicted tensile properties were in good agreement with experimental data. The obtained mean errors between the experimental and theoretical results for tensile strength and modulus were 9.5% and 8.6% respectively.

Nocturnal enuresis is the most common pediatric urologic problem in outpatient clinics.. To assess the effect of various monotherapies, and comparing the effects of desmopressin, imipramine, and oxybutynin in children with enuresis, as well as the influence of socioeconomic and cultural factors of their families on the response and relapse rates..Patients and The study was a randomized clinical trial conducted on 92 children aged 5 - 14 years, referred to the pediatric clinic of Semnan University Hospital in Semnan, Iran. Children with primary nocturnal enuresis were randomly allocated to three different treatment groups: desmopressin (n = 30), imipramine (n = 31), and oxybutynin (n = 31) all for 6 weeks. The socioeconomic and demographic characteristics of all participants were recorded. The number of wet nights per week was noted at the end of the 6-week-trial, and children were followed up to three months for relapse.. Children in the oxybutynin group showed a slightly higher response rate (71.0% success) and a lower relapse rate (31.8%), while in the desmopressin group the response and relapse rates were 63.3% and 57.9%, respectively, and in the imipramine group 61.3% and 63.2%, respectively. However, the difference between the 3 groups in terms of response (P = 0.701) and relapse rates (P = 0.095) was not statistically significant.. There is no significant difference between monotherapy with desmopressin, imipramine or oxybutynin in children with enuresis. However, oxybutynin showed a higher response rate and a lower relapse rate compared to other medications. More clinical trials with a larger sample size are needed to clarify these uncertainties..

The main objective of an extrusion die is flow balancing as an unbalanced flow causes a distorted product together with residual stress. In this paper a strategy is presented for flow balancing a U-shaped profile with different wall thicknesses. For this purpose, a choker bar is provided at thicker wall to locally restrict excessive flow passing through the thicker section. For optimal design some of die dimensions are considered parametric which will be variable in three levels. The analysis of flow was performed using FLUENT software in order to get the best combination of the parameters which produces the best balance. After the optimum design was obtained, an experimental die is manufactured. It is considered in the manufacture of the die that height of choker to be variable during extrusion for finely adjusting the balance. Results demonstrate that experiments are in good agreement with simulations.