فهرست مطالب s. rouhi

In this study, we investigated the influence of process parameters on the mechanical properties of AZ91C magnesium alloy joints produced by friction stir welding (FSW). A Taguchi L9 orthogonal array was employed to design the experimental matrix, and the input variables were analyzed. Tensile strength and hardness values were measured for different input parameters, and their interactions were assessed through interaction plots for ultimate tensile strength (UTS) and Vickers hardness (HV). The signal-to-noise (S/N) ratios were calculated, and S/N ratio plots were generated to further understand the effects of the input parameters on the mechanical properties. Microstructural evaluations were carried out on the base metal and stir zone (SZ) of the specimens produced under various process conditions. Additionally, the appearances of the FSW samples with the minimum and maximum tensile strengths were compared. The results revealed complex relationships between the process parameters and mechanical properties, with both main effects and interactions playing significant roles in determining the performance of the FSW joints. Notably, an optimal combination of process parameters (tool rotation speed of 1250 rpm, welding speed of 40 mm/min, and plunge depth of 0.3 mm) resulted in the highest ultimate tensile strength (UTS) and hardness (HV) values. Microstructural analysis showed that FSW significantly refined the grain size, contributing to the improvement of mechanical properties.

People who are infected with Human Immunodeficiency Viruses (HIV) are more prone to opportunistic fungal infections than other patients. The immune system of these patients becomes weaker when they are also infected with Coronavirus disease (COVID-19). Involvement of the central nervous system caused by fungal infections in these patients is of concern and fatal if diagnosed late. The aim of this research is to investigate a woman with COVID-19 and HIV who was diagnosed with cryptococcal meningitis.

Case Report:

 The patient is a 53-year-old woman who complained of severe headache and nausea after infection with COVID-19. White blood cells, erythrocyte sedimentation rate, lymphocyte, creatinine, aspartate aminotransferase, alanine aminotransferase and blood urea nitrogen were increased compared to the standard level. Cerebrospinal fluid testing showed that glucose was lower and protein was higher than normal. Microscopic examination, staining and culture of cerebrospinal fluid deposits showed the presence of double wall yeasts similar to Cryptococcus. The patient was positive for COVID-19 and HIV. The level of CD4 (cluster of differentiation 4) was lower than the standard. The patient was treated with amphotericin B at a dose of 100 mg for two weeks and was discharged from the hospital after the conditions were stabilized.

Cryptococcal meningitis can often occur in immunosuppressive conditions such as HIV. Therefore, quick follow-up, diagnosis and treatment should be considered in these patients.

In this paper, the effect of strain on the efficiency of GaAs solar cell isinvestigated. It has been shown that the applied strain during the synthesizing of carbonnanotubes (CNTs) leads to changing some of its physical properties. This means that strainscan cause numerous changes in the structures. By using a strained layer of the carbonnanotubes on the GaAs solar cell, the effect of this layer on the performance of the GaAssolar cell is evaluated. This CNT layer can be used for several purposes. The first is tocreate a transparent electrical conductor at the cell surface to increase the output current.This purpose is one of the most important applications of this layer. But the second andmore important goal is to capture more photons and reduce the emission or reflection oflight emitted onto the cell surface. It is found that the mentioned goals cannot be satisfiedsimultaneously. Accordingly, to solve this problem, two different layers were used toachieve the ideal conditions. It has been shown that the use of a 10% uniaxial strained CNTlayer leads to increase the photon absorption rate onto a non-strained CNT layer forelectrical purposes. The efficiency of the single-junction GaAs solar cell with the aboveconditions reaches about 31% which is about 2% higher than the model without strain.

The multi-scale finite element method is used to study the vibrational characteristics of polymer matrix reinforced by single-walled silicon carbide nanotubes. For this purpose, the nanoscale finite element method is employed to simulate the nanotubes at the nanoscale. While, the polymer is considered as a continuum at the larger scale. The polymer nanotube interphase is simulated by spring elements. The natural frequencies of nanocomposites with different nanotube volume percentages are computed. Besides, the influences of nanotube geometrical parameters on the vibrational characteristics of the nanocomposites are evaluated. It is shown that reinforcing polymer matrix by single-walled silicon carbide nanotubes leads to increasing the natural frequency compared to neat resin. Increasing the length of the nanotubes at the same diameter results in increasing the difference between the frequencies of nanocomposite and pure polymer. Besides, it is observed that clamped-free nanocomposites experience a larger increase in the presence of the nanotubes than clamped-clamped nanotube reinforced polymers.