A polyacrylamide hydrogel for application at high temperature and salinity tolerance in temporary well plugging

In addition to conventional approach to ensure the successful application of polymer hydrogels in maintaining temporary well plugging, exact analysis of gel formation and gel strength properties in wellbore are necessary. In this work, bottles and rheology tests are used to investigate the polymer hydrogel gelation time and cross-linking kinetics of sol–gel systems which consist of polyacrylamide and chromium acetate hydroxide as a cross-linker. The effects of temperature of 90 °C and pressure of 3000 psi (typical Iranian oil well condition) were studied in relation to gelation time, strength and the mechanical properties of the hydrogel. The average molecular weight of the polymer chains between cross-link ties was evaluated using an oil-well laboratory system and compressive strength test. Differential scanning calorimeter (DSC) analysis of dried gel and the effect of temperature on the kinetics of the gel swelling in different solutions such as distilled water, tap water, formation water and oil were studied. The results showed that the number of tie points between each entanglement has not much reduced under pressure. Therefore, the prepared hydrogel can maintain its chemical structure under the Iranian oil well pressure and can be proposed to field studies. The degree of sol–gel reaction of prepared hydrogel and the activation energy based on the Arrhenius equation were calculated to be 1.5 and 274 kJ/mol, respectively.     

Nonlinear interactive analysis of cooling tower–foundation–soil interaction under unsymmetrical wind load

This paper deals with physical and material modelling of a cooling tower–foundation–soil system. The physical modelling has been carried out using solid 20-noded isoparametric element to model the cooling tower, annular raft foundation and soil media. The cooling tower–foundation–soil system was analysed under vertical and lateral load generated due to self-weight and wind loads. The soil nonlinearity has been taken into consideration using hyperbolic nonlinear elastic constitutive law. The response of the structure has been investigated with respect to displacement and stresses. Moreover, an attempt has been made to study the effect of the linear and nonlinear interactive analyses compared with conventional analysis. It was seen that the interactive analysis of the cooling tower–foundation–soil media plays a major role in releasing the stresses in the cooling tower, particularly at the bottom ring beam.     

Subjective perception of safety in healthy individuals working with 7 T MRI scanners: a retrospective multicenter survey

Objective

To retrospectively assess perception of safety of healthy individuals working with human 7 Tesla (T) magnetic resonance imaging (MRI) scanners.

Materials and methods

A total of 66 healthy individuals with a mean age of 31 ± 7 years participated in this retrospective multicentre survey study. Nonparametric correlation analysis was conducted to evaluate the relation between self-reported perception of safety and prevalence of sensory effects while working with 7 T MRI scanners for an average 47 months.

Results

The results indicated that 98.5 % of the study participants had a neutral or positive feeling about safety aspects at 7 T MRI scanners. 45.5 % reported that they feel very safe and none of the participants stated that they feel moderately or very unsafe while working with 7 T MRI scanners. Perception of safety was not affected by the number of hours per week spent in the vicinity of the 7 T MRI scanner or the duration of experience with 7 T MRI. More than 50 % of individuals experienced vertigo and metallic taste while working with 7 T MRI scanners. However, participants’ perceptions of safety were not affected by the prevalence of MR-related symptoms.

Conclusions

The overall data indicated an average perception of a moderately safe work environment. To our knowledge, this study delineates the first attempt to assess the subjective safety perception among 7 T MRI workers and suggests further investigations are indicated.

     

Design of an integrated process for simultaneous chemical looping hydrogen production and electricity generation with CO2 capture

This study was aimed at proposing a novel integrated process for co-production of hydrogen and electricity through integrating biomass gasification, chemical looping combustion, and electrical power generation cycle with CO₂ capture. Syngas obtained from biomass gasification was used as fuel for chemical looping combustion process. Calcium oxide metal oxide was used as oxygen carrier in the chemical looping system. The effluent stream of the chemical looping system was then transferred through a bottoming power generation cycle with carbon capture capability. The products achieved through the proposed process were highly-pure hydrogen and electricity generated by chemical looping and power generation cycle, respectively. Moreover, LNG cold energy was used as heat sink to improve the electrical power generation efficiency of the process. Sensitivity analysis was also carried out to scrutinize the effects of influential parameters, i.e., carbonator temperature, steam/biomass ratio, gasification temperature, gas turbine inlet stream temperature, and liquefied natural gas (LNG) flow rate on the plant performance. Overall, the optimum heat integration was achieved among the sub-systems of the plant while a high energy efficiency and zero CO₂ emission were also accomplished. The findings of the present study could assist future investigations in analyzing the performance of integrated processes and in investigating optimal operating conditions of such systems.     

Evaluation of the Effects of Hydrothermal Treatment on Rice Flour and Its Related Starch

The main aim of this research was to compare the effects of hydrothermal treatment on rice flour and its related rice starch. The treatment was performed at 120°C for 3 and 5 h. Scanning electron microscopy results showed that the proteins of hydrothermaled rice flour were denatured and formed clusters and the granules of hydrothermaled rice starch became aggregated and had an irregular surface. The treatment reduced water solubility and water absorption and decreased peak viscosity while increased pasting temperature. It increased the final visosity of modified rice flour while reduced the final viscosity of modified rice starch. Following hydrothermal treatment, the hardness and elasticity of the gels increased. The cohesiveness of rice flour gels decreased while that of the rice starch gels remained unchanged. This study showed how the hydrothermal treatment can have different effects on rice flour and its related rice starch. The effects of hydrothermal treatment on rice flour were stronger than rice starch. Increasing the treatment time from 3 to 5 h was more effective on rice starch.     

Extraction conditions for removal of oxidized sulfur compounds in gas oil

An experimental study was conducted to investigate the extraction of oxidized sulfur compounds from gas oil. Solvents used for this purpose included acetone, acetonitrile, methanol and propanol. The effect of solvent concentration, solvent to gas oil ratio, temperature, time and number of stages was studied. To select the best solvent and conditions for extraction, two criteria were considered: high desulfurization and more hydrocarbon recovery. Results showed that extraction time and temperature have no significant effect. Methanol for low ability of extraction of oxidized sulfur compounds and propanol for low hydrocarbon recovery were excluded from further experiments. After the tests, the optimum conditions for extraction were determined to be 85% acetone, solvent/feed ratio of 1, two stages extraction in ambient temperature and enough time for mixing. In this condition 85% of sulfur compounds of gas oil containing 1,670 ppmw S were separated and 95% of gas oil was recovered.     

A novel high voltage lateral double diffused metal oxide semiconductor (LDMOS) device with a U-shaped buried oxide feature

A novel U-shape buried oxide lateral double diffused metal oxide semiconductor (LDMOS) is reported in this paper. The proposed structure features ionized charges in both sides of dielectric between source and gate region to enhance the breakdown voltage. The dielectric between drain and drift region affects on the breakdown voltage by adding a new peak in the electric field profile. Two dimensional simulation with a commercial software tool predicts significantly improved performance of the proposed device as compared to conventional LDMOS structures.     

Postbuckling analysis of piezoelectric multiscale sandwich composite doubly curved porous shallow shells via Homotopy Perturbation Method

In this study postbuckling behaviors of multiscale composite sandwich doubly curved piezoelectric shell with a flexible core and MR layers by employing Homotopy Perturbation Method in hygrothermal environment has been investigated. By using Reddy third shear deformable theory the face sheets and third-order polynomial theory of the flexible core the strains and stresses are obtained. A mathematical model for the multiscale composite layered shell with a flexible core and magnetorheological layer (MR) that incorporates the nonlinearity of the in-plane and the vertical displacements of the core is assumed. Three-phase composite shells with polymer/Carbon nanotube/fiber and polymer/Graphene platelet/fiber either uniformly or non-uniformly based on different patterns according to Halpin–Tsai model have been considered. The governing equations of multiscale shell have been derived by implementing Hamilton’s principle. Meanwhile, simply supported boundary conditions are employed to the shell. For investigating correctness and accuracy, this paper is validated by other previous researches. Finally, different parameters such as temperature rise, various distribution patterns, magnetic fields and curvature ratio are considered in this article. It is found these parameters have significant effect on the frequency–amplitude curves.

     

Software Agent with Reinforcement Learning Approach for Medical Image Segmentation

Many image segmentation solutions are problem-based. Medical images have very similar grey level and texture among the interested objects. Therefore, medical image segmentation requires improvements although there have been researches done since the last few decades. We design a self-learning framework to extract several objects of interest simultaneously from Computed Tomography (CT) images. Our segmentation method has a learning phase that is based on reinforcement learning (RL) system. Each RL agent works on a particular sub-image of an input image to find a suitable value for each object in it. The RL system is define by state, action and reward. We defined some actions for each state in the sub-image. A reward function computes reward for each action of the RL agent. Finally, the valuable information, from discovering all states of the interest objects, will be stored in a Q-matrix and the final result can be applied in segmentation of similar images. The experimental results for cranial CT images demonstrated segmentation accuracy above 95%.