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Backgrounds: Staphylococcus aureus is one of the major causes of nosocomial infections. Biofilm formation is an important virulence factor of S. aureus, leading to its high resistance to antibiotics and evasion from host defenses. This study aimed to assess the prevalence and antimicrobial resistance profile of biofilm-producing S. aureus strains and characterize genes involved in biofilm formation.
Materials & Methods: A total of 79 S. aureus strains were isolated from 1000 clinical samples and characterized using phenotypic, biochemical, and molecular tests. The biofilm production ability of isolates was examined using the microtiter assay. Moreover, the expression of genes involved in biofilm production (psm A and psm B) was screened using real-time PCR. Finally, antibiotic susceptibility testing was done using the Kirby-Bauer method and interpreted according to the CLSI M100 standard.
Findings: Out of 79 S. aureus isolates, 43 (54.4%) isolates were strong biofilm producers, 21 (26.6%) isolates were weak biofilm producers, and 15 (19%) isolates were non-adhesive. The results of real-time PCR showed that 55 (86%), 60 (93.7%), and 46 (58.2%) isolates were positive for psm A, psm B, and both genes, respectively. The results of antibiotic susceptibility testing showed that all the isolates were resistant to two or more antibiotics.
Conclusion: The high prevalence of biofilm-forming S. aureus strains in hospital environments could be a major health challenge with serious outcomes for hospitalized patients. Thus, it is necessary to disinfect hospital environments to reduce the risk of infection and spread of these microorganisms.
 

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In this research the possibility of mass reduction in a two-module cubic microsatellite with skin – frame structure is studied. Natural frequencies and effective mass distribution change by replacing isogrid structure with sandwich panel (honeycomb). Modal effective mass is a dynamic characteristic of structure and depends on natural frequencies, mode shapes, general masses and eigenvectors. Modal effective mass is a quantity that shows the importance of a mode when satellite is under acceleration loads through the baseplate. High modal effective mass shows high reaction loads on baseplate in corresponding frequency. Also acting dynamic loads are affected by distribution of modes in frequency range. The sum of effects of different modes creates significant reaction loads. Hence, study of frequency and effective mass changes by converting the structure design from isogrid to sandwich structure is necessary. In this paper, first two isogrid and sandwich structures with equal masses are compared. Then mass of sandwich structure is decreased such a way that natural frequencies of light sandwich structure approach natural frequencies of isogrid structure. In equal masses case, natural frequencies of sandwich structure are twice the natural frequencies of isogrid structure but effective mass distribution of isogrid structure is better along the launch direction. By changing the isogrid structure design to sandwich panel structure and optimization of the new structure characteristics a noticeable reduction in mass and improvement in modal behavior could be obtained.

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Curing process of composites results in the formation of residual stress and distortion. According to costs of composites fabrication, simulation of the fabrication process in order to avoid wasting investment is important. A common and simple method of composite fabrication is hand lay-up. In this research plane stress due to temperature change of composite laminates has been investigated and its resultant curvature has been analyzed. So, two symmetric and un-symmetric laminates with eight plies are subjected to 100-degree centigrade temperature change and normal and shear stresses have been calculated. First, by classical lamination theory which is the most important theory in stress analysis of composites, mechanical properties of glass/epoxy composite with 70 percent volume fraction, temperature change and stacking sequence are input variables of the written program. Three in-plane stress component is read and the amount of curvature has achieved that shows it is negligible for the symmetric sample. To validate the residual stress field, finite element simulation for both samples has been done that resulted in finding the same results with negligible errors. Assumptions are considered in finite element modeling and classical lamination theory which result in deviation of outputs from reality. In spite of these assumptions, the thermal simulation of composite laminations in ABAQUS software can have the desired prediction of reality. The innovation of the research is the use of this software and the verification of code.
 

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Composites usage according to their properties such as high strength to weight ratio, high resistance to corrosion and their ability to build complex shapes in different industries are increased, but due to their Vulnerability against unwanted impact loads, their usage has been limited. Relatively higher costs of carrying out low velocity impact (LVI) test and data sampling limit due to short experiment time in one side and adaptation of quasi-static impact (QSI) test results with LVI on the other, convinced researchers to use QSI instead of LVI. This research investigated the effect of different percentage of nanoclay (1%, 3%, 5% and 7%) on impact properties of glass-epoxy composite. For this purpose, QSI test was used to forecast this nano-composite’s behavior. To disperse and distribute nanoclay homogeneously inside the resin, mechanical and ultrasonic mixers have been used; EDAX photograph token from nano-resin section confirmed the success of this process. QSI test results showed that adding 3% nanoclay to glass-epoxy composite, increases absorbed energy up to 16% and stiffness up to 12%. It was also determined by perusing SEM photographs that specimens containing 7% nanoclay had a decreased in mechanical properties due to adhesion of nanoparticles.

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In thermal barrier coatings (TBC), surface cracks, debonding, and thickness degradation may occur during the manufacturing process or life cycle, leading to poor performance and ultimately a dangerous system failure. The main goal of non-destructive testing of thermal barrier coatings is to detect these defects and determine the health of the coating. Various non-destructive inspection methods have been proposed to evaluate thermal barrier coatings, and due to the numerous advantages of thermography, including high speed, low cost, safety, no need for direct contact, automation capability, and inspection of a large area of ​​the part, this method has received special attention from researchers. This study will present a method for manufacturing samples with different diameters of artificial separation defects. The following is the equipment's arrangement and the sample's thermography process. It was concluded that blackening the surface of the sample by increasing the amount of thermal energy absorption increased the ability to identify separation defects and increased the signal-to-noise ratio by 257%. Finally, by implementing different filters on the recorded raw thermal images, it has been shown that in both cases the best filter in terms of SNR is the median filter and then the Gaussian filter. The background removal filter also had no noticeable effect on increasing the signal-to-noise ratio and acted as a complement to the median and Gaussian filters by reducing the fixed error