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Research subject: Superabsorbents are hydrophilic hydrogels that can accommodate large amounts of water in their three-dimensional structures and have wide applications in various sciences such as pharmaceuticals, medicine, and agriculture. These materials are hydrophilic polymers that are physically or chemically cross-linked. Conversion and swelling ratio of synthesized hydrogels are two counter effects. Therefore, determining the appropriate conditions for polymerization to achieve optimal properties and swelling rate of hydrogels is a challenge for researchers.
Research approach: In this study, optimizing the synthesis conditions of semi-interpenetrating poly (acrylic acid)/xanthan hydrogels, the response surface methodology (RSM) was used by Box-Behnken design (BBD). The variables of this method were the molar ratio of the cross-linking agent (X₁), the weight percentage of xanthan gum (X₂) as the reaction medium, and the amount of initiator (X₃), each of which was considered at three levels. The evaluated responses in RSM were the rate of polymerization conversion (Y₁) and the rate of swelling (Y₂) of the hydrogels in the water.
 
Main results: Based on the 17 experiments proposed by RSM (BBD), the cross-linker, xanthan gum, and initiator were combined and radical polymerization was performed into silicone molds at 65 ° C. The results of ANOVA analysis showed that the data error of this study was small and the coefficient of determination (R2) of both proposed models for the responses Y₁ and Y₂ was higher than 0.9. The 46 experiments proposed for the optimal point by RSM (BBD) with the desirability of more than 50% indicate the synthesis of hydrogels that have both a good conversion rate and an optimal amount of swelling. For example, by 13% of cross-linking agent, 0.043 g of initiator and 1% wt. the solution of xanthan, hydrogels with a 95% conversion rate, and 102% water uptake were prepared. These hydrogels can be used in a variety of fields, including the treatment of colored wastes in factories, agriculture, pharmaceutical systems, medical attractions, and more.

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Production of recombinant proteins in Escherichia coli has been very common in recent decades. Many studies and experiments have been done in order to optimize the production and expression of recombinant proteins in E.coli. One strategy is using high cell density to increase recombinant protein production such as β-NGF in the cell. Therefore, in this study for the first time bacterial cell culture in high cell density was done using glycerol and yeast extract as carbon and nitrogen sources and MgCl2 as a growth effective factor. Also the effects of overnight culture conditions on bacterial growth were evaluated. Meanwhile culture conditions were optimized using response surface methodology (RSM) and the optimum conditions were as follows: 18/23 g/lit glycerol, 14.44 g/lit yeast extract and 10mM MgCl2. Also the obtained results indicated that the 14 hours incubation at 37 °C and 180 rpm were optimum conditions for the overnight culture. Our results showed that the rate of cell growth and recombinant β-NGF production in optimized condition is significantly higher than in basic medium.

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Hyaluronic acid (HA) is a natural and linear polymer that finds a wide-range of applications in medicine, cosmetics, and nutraceuticals because of excellent viscoelasticity, high moisture retention capacity, high biocompatibility and non-toxicity. HA has been recently produced in industrial scale by Streptococcal species. Streptococci are nutritionally fastidious lactic acid bacteria and cannot synthesize some amino acids. Therefore, it is necessary to study and select some commercial culture media for their growth. In this study, HA production and hyaluronidase activity of S. zooepidemicus ATCC 43079 in three culture media were investigated. Regarding the detrimental effect of this enzyme on HA amount, 6-O-Palmitoyl-L-ascorbic acid as hyaluronidase inhibitor was added to culture medium during fermentation. The effect of three variables consisted of glucose concentration, yeast extract concentration and medium pH each at 3 levels were considered and (response surface methodology (RSM) was used for statistical design of experiments to study the HA production by this strain. The results showed that maximum HA production was obtained when glucose concentration, yeast extract concentration and pH were 21.2 g L^-1, 43.6 g L^-1 and 6.6, respectively. Under optimum conditions, HA was produced as 370±15 mg L^-1 which was ~150% more than of HA concentration in basal medium (150±10 mg L^-1) and productivity reached 56.74 g L^-1 h^-1 that was increased 2 fold compared to central point.

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In this paper, dry electro-discharge machining (Dry EDM), one of the newest machining processes which differs mainly from conventional EDM in using gaseous dielectric along with tool electrode rotation, has been studied. Gap voltage, discharge current, pulse-on-time, pulse-off time, dielectric gas pressure, and electrode rotational speed have been considered as effective input parameters. Response surface methodology (RSM) has been used to optimize the machining performance with respect to material removal rate (MRR). Base on the results and analysis of running experiments, it can be concluded that MRR increases by increasing gap voltage, discharge current, the ratio of pulse-on time over pulse-off time, input gas pressure, and electrode rotational speed. There also exists an optimum amount of pulse-on time determined according to the machining circumstances. Also the material removal rate in dry EDM has been improved compared with that in conventional EDM in identical conditions. Keywords: Dry electro-discharge machining (Dry EDM), Gaseous dielectric, Response surface methodology (RSM) Keywords: Dry electro-discharge machining (Dry EDM), Gaseous dielectric, Response surface methodology (RSM) Keywords: Dry electro-discharge machining (Dry EDM), Gaseous dielectric, Response surface methodology (RSM)

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Superalloys are extensively used in various industries like aerospace, chemical and petrochemical industries due to their properties such as high strength at elevated temperature and good corrosion resistance. On the other hand, owing to these properties, superalloys are classified as difficult to cut materials. In the present work, the effect of cutting parameters on tool life in turning of N-155 iron-nickel-base superalloy is investigated. Cutting speed and feed rate each at five level were selected as cutting variables. Relationship between cutting parameters and output variable i.e. tool life was modeled by using response surface methodology (RSM). The results showed that there was a good agreement between the experimental results and the predicted values using the developed mathematical model. Additionally, analysis of variance was implemented to evaluate the adequacy of the regression model and respective variables. ANOVA results indicated that the cutting speed had more effect on tool life than feed rate. Moreover, wear mechanisms and failure modes of the cutting edges were analyzed by using the images of scanning electron microscope (SEM) at different cutting speeds and feed rates. It was observed that abrasion and adhesion were the most dominant wear mechanisms in this study. Finally, desirability function was used so as to predict optimum cutting parameters for achieving maximum tool life.

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Nowadays high velocity forming methods have become popular among industrial companies due to their capability at improving formability in various materials in comparison to conventional methods. Electrohydraulic forming (EHF) is a high velocity sheet metal forming process in which two electrodes are positioned in a water filled chamber and a high-voltage discharge between the electrodes generates a high-pressure to form the sheet metal. In this work, extensive experimental tests have been designed based on design of experiments (DOE) technique to investigate the effective parameters in EHF (with bridge wire between electrodes). Discharge energy, material, length and diameter of bridge wire have been considered as effective input parameters. Response surface methodology (RSM) has been used to model and optimize the EHF performance with respect to drawing depth for Brass 260. Base on the results, it can be stated that maximum drawing depth is obtained when discharge energy is maximum. It was found that the aluminum wire was more efficient than copper and tungsten. There also exists an optimum amount of length and diameter of bridge wire determined according to the process conditions.

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Coconut is a good source of bioactive compounds due to the presence of tocopherols and phytosterols, which are increasingly used to enrich various food products. The use of coconut powder in the formulation of flavored milk with regard to its phytosterol compounds can increase the nutritional value of milk and its organoleptic acceptability among consumers. However, one of the major challenges in the flavored milk industry is their physical instability, which can be effective in using hydrocolloids at the appropriate concentration. Therefore, the aim of this study was to determine the optimal formulation of coconut milk containing tragacanthin gum (solution of tragacanth) to achieve a product with Desirable quality characteristics. For this purpose, the response surface method with the central composite investigated the effect of tragacanthin gum on 5 levels (0, 0.075, 0.15, 0.225 and 0.3%) and coconut powder on 5 levels (2, 3.5, 5, 6/5 and 8%) on the physical, chemical and sensory properties of coconut milk was used. Statistical results showed that increasing coconut powder and tragacanthin gum in coconut milk formulation significantly decreased pH and increased acidity (p<0.05). According to the results of the viscosity test, the viscosity increased as the formulation of tragacanthin and coconut powder increased (p<0.05). Results show an increase of sedimentation amount once the coconut powder increased. While by increasing the gum tragacanthin concentration, there was a twofold effect in sedimentation amount and in average level of gum, the minimum amount of sediment was observed. Also, the sensory evaluation of coconut milk samples indicated that the highest sensory acceptability was for samples containing intermediate amounts of coconut powder. But tragacanthin gum only influenced the flavor and consistency of parameters. Finally, the sample consisted of 4.28% coconut powder and 0.15% tragacanthin gum as optimum sample with desirable physical, chemical and sensory properties.
 

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In this study, effects of zeta potential distribution and geometrical specifications are investigated on mixing efficiency in electroosmotic flows. Flow geometry in this research is a series of converging-diverging microchannels with different diverging ratios. Governing equations including the Navier Stokes equation for fluid flow and the Poisson-Boltzmann equation for internal electrical field are solved numerically in a two-dimensional domain by using the lattice Boltzmann method. Numerical simulations are validated against available analytic solutions for electroosmotic flow in homogeneous straight channels. The response surface methodology (RSM) is then employed to investigate relationship between flow variables and consequently to optimize mixing efficiency and flow rate of the channel. Results indicate that increasing the zeta potential ratio and diverging ratio, leads to increased value of flow rate, while meanwhile it decreases the mixing efficiency. Zeta potential pattern does not affect flow rate considerably, but its effects on mixing efficiency is noticeable. Furthermore, it is found that mixing efficiency and flow rate are more sensitive to zeta potential ratio than diverging ratio. At last, optimum parameters are determined by RSM which are 0.5 for zeta potential ratio, 0.6 for diverging height, and pp-nn pattern for zeta potential distribution, all associated to simultaneously maximized flow rate and mixing efficiency.

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