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Showing 206 results for Strength
Volume 0, Issue 0 (2-2024)
Abstract
The purpose of this research is to determine the average perceptual strength of the five senses in the Persian language based on average perceptual strength hierarchy by Lynott and Connell (2009). To achieve this goal, (100) commonly used Persian sensory adjectives and (25) native Persian-speaking subjects were used to express their level of sensory perception of each adjective based on the 5-point Likert Scale. Also, (20) other subjects were asked to choose names for the given adjectives. These tests were carried out to answer these questions: what percentage of adjectives are exclusively attributed to one of the five senses, how much was the total score of each sense on the 5-point Likert Scale, and as overall which sense has the highest average perceptual strength؟ Also is the rate of collocations of names and adjectives of the same domain more than the collocations of nouns and adjectives of different domains, as Lynott and Connell believe? The results showed the average perceptual strength of the senses in Persian data is different from the findings of Lynott and Connell (2009) only in the position of the sense of hearing, also according to their findings, the sense of vision has the highest and the sense of smell has the lowest average perceptual strength among the five senses. In terms of collocation of names and adjectives, it was found that with a little consideration, Lynott and Connell’s idea about the larger number of the same-domain sensory name- adjective collocations can be accepted.
Volume 0, Issue 0 (1-2024)
Abstract
Land use severely affects the carbon and nitrogen stock and the soil's physical, mechanical, hydraulic and chemical characteristics of the soil. This study aims to investigate the effect of land use type on some soil characteristics, including carbon stock (CS), nitrogen stock (NS), S-index, structural stability index (SSI), soil pore size distribution, soil shear strength (τ), internal friction angle (φ˚), shear cohesion (C), soil water characteristic curve (SWCC), relative field capacity (RFC), available water (AW), aeration porosity (AP) and effective porosity (Pe) in Shandiz city, Khorasan Razavi province (northeast Iran) was studied. For this purpose, 60 soil samples were taken from the surface layer (0-20 cm) in pasture and agricultural land uses. The results showed that S-Index, SSI, RFC, AW, Pe, Cs, and Ns in pasture land use were significantly higher than agricultural land use. The values of τ, C, and φ˚ in the pasture land use were significantly (p<0.01) less than the pasture land use. The relationship between soil organic carbon stock index and bulk density (r=-0.69), coarse fragments (r=-0.73), cohesion (r=-0.70), and internal friction angle (r=-0.52) were significant and negative. The amounts of carbon and nitrogen stock indices in pasture land use were 61.6 and 33.1 % greater than agricultural land use, respectively. Therefore, it can be concluded that as a result of land use change, the carbon and nitrogen stock, S-index, relative field capacity, structural stability index, available water, aeration porosity, effective porosity, and consequently, the soil quality decrease, and soil degradation increase in agricultural land use.
Volume 0, Issue 0 (8-2024)
Abstract
Shotcrete, a pneumatically sprayed concrete mixture, has gained significant popularity in the construction industry due to its versatility and adaptability. However, the demand for high-strength shotcrete has intensified, driven by advancements in equipment and admixtures. Fiber-reinforced high-strength shotcrete (FRHSS) offers enhanced quality, adhesion, and construction speed, making it ideal for stabilizing excavations and slopes, strengthening masonry and concrete structures, and reinforcing underground structures. Additionally, the increased strength allows for reduced section dimensions, leading to more economical designs.
This research investigates the effects of aggregate gradation and admixtures, including micro silica, superplasticizer, accelerator, and micro recycled steel fibers (MRSFs), on the strength and performance of FRHSS. The study employs wet-mix and dry-mix shotcrete methods, examining the properties through laboratory and field experiments.
The results demonstrate that achieving high-strength shotcrete is more feasible with the wet-mix method. Fiber-reinforced wet-mix shotcrete attained a 28-day compressive strength of 987 kg/cm², representing an 80% and 77% increase in compressive strength and energy absorption, respectively, compared to conventional fiber-reinforced wet-mix shotcrete. Furthermore, fracture toughness tests revealed that MRSFs effectively prevent microcrack propagation and control deformations. FRHSS incorporating MRSFs exhibited a 28% and 97% increase in compressive strength and energy absorption, respectively, compared to the corresponding mix without fibers.
Volume 0, Issue 0 (8-2024)
Abstract
Fire can not only lead to many human and financial losses, but also can cause structures to collapse and destroy them. For this reason, it is necessary and inevitable to protect buildings against fire and conduct more research in the field of better understanding the effects of combining different materials with each other and obtaining materials with greater resistance to fire. Concrete and concrete structures are always used by construction engineers due to their resistance, availability and resilience against fire. Ordinary concrete loses its strength at high temperatures, and the use of unreinforced concrete is not very useful due to its brittleness and weakness in tensile strength. In concrete, the tensile strength is lower than its compressive strength, and for this reason, researchers are trying to increase the resistance to fire and heating by improving the tensile strength of concrete. Reinforcing concrete with rebar is always a solution to increase the tensile strength in concrete parts, one of the most important weaknesses of using rebar in concrete is that the reinforcements form a small part of the concrete cross-section and actually cause the concrete to be inhomogeneous. In this research, double-bent steel fibers have been used to overcome the mentioned weakness and reinforce the concrete. It should be noted that concrete containing steel fibers has favorable compressive and tensile strength due to the high tensile strength of steel fibers. In order to achieve this goal and achieve fiber concrete that has good fire resistance, we defined seven different mixing plans with different percentages of steel fibers and lubricants. Concrete samples were produced using double-bent steel fibers in amounts of 0.5, 1, and 1.2 percent by volume of concrete and superlubricant in 0.5, 1, and 1.3 percent by weight of cement, and then in Cubic molds with dimensions of 10x10x10 cm and cylindrical ones were sampled as standard, and after setting the cement, the 28-day-old concrete samples, after heating and placing inside the electric heater with different temperatures, were divided into two The method of gradual cooling with ambient air and fog spraying (water spraying) is similar to what firefighters do when extinguishing a fire, after measuring the amount of weight loss of the heated samples, the weight loss values were presented in the form of a diagram, then the samples were subjected to tests Compressive strength, tensile strength (Brazilian test) and ultrasonic wave speed (ultrasonic test) were placed, and the results and data of each of them for each mixing design were presented in the form of a diagram after examination and classification, so that the effect of high heat on Concrete containing steel fibers and super-lubricant should be determined. The results clearly showed the improvement of the tensile strength in three volume percentages of fibers by 14.6, 16.8 and 64.5%, respectively, compared to concrete without fibers, and also the compressive strength of concrete after bearing the heat of 250 degrees Celsius and cooling to the fogging method had 44.5, 31.6, and 9.3 percent, respectively, and in the gradual air cooling method, the compressive strength was 43.3, 44.9, and 50 percent, respectively.
Volume 0, Issue 0 (8-2024)
Abstract
So far, the performance of masonry walls against in-plane lateral loads such as earthquake loads has been extensively studied, but less attention has been paid to out-of-plane loads such as explosions. Due to their large surface area, walls endure significant forces during explosions, leading to extensive damage and potentially causing severe financial losses and casualties. Given the increase in terrorist and sabotage attacks, reinforcing these structures seems necessary. In recent years, fiber-reinforced polymers (FRP) have been widely and effectively used in the reinforcement and performance improvement of these structures. Their light weight, high stiffness and high strength, and corrosion resistance are among the properties that have attracted researchers to use these materials. Finite element modeling not only provides a basis for better understanding the behavior of masonry walls but also is very useful in predicting the behavior of these members after reinforcement, especially in the absence of experimental results. In this study, using numerical modeling in ABAQUS software, the behavior of masonry walls reinforced with FRP strips against a blast with an explosive charge equivalent to 150 kg of TNT (the weight of explosive likely to be carried in a sabotage attempt via a vehicle) at a distance of 5 meters was investigated. Lagrangian equations were used to model the mechanical behavior of the structure, and the solver used in this research is an explicit solver to account for the time factor in the software’s integration process. The total time considered for the entire explosion process is 1 second, and the explosive load was applied to the studied structure using the Conwep method. The type of fibers, width, thickness, area, and angle of the FRP strips were important and influential parameters that were examined for the efficiency of this reinforcement method. The modeling results indicate that this reinforcement technique is highly effective in strengthening masonry walls against explosions, as it has reduced the deflection of the wall by at least 70% and its energy by up to 90%. It can also be inferred that an arrangement for reinforcing masonry walls with FRP strips is suitable if it covers the areas prone to damage, which in masonry walls are the mortar joints between the bricks. Therefore, the horizontal arrangement shows better performance compared to the vertical and diagonal arrangements. Similarly, reinforcing 100% of the wall area performs much better than reinforcing 50% and 25% of the wall area, but it is not economically acceptable. In general, similar to structural elements, non-structural elements can also exhibit plastic behavior in critical situations, preventing the collapse of these elements due to the absorbed energy. Therefore, walls with higher plastic energy show better behavior against explosive loads. Additionally, based on the hysterical displacement and kinetic energy diagrams of the wall, it can be seen that the behavior of reinforced walls is oscillatory, while the behavior of unreinforced walls is noticeably pulsating. Finally, the optimal arrangement of FRP strips proposed for reinforcing masonry walls against explosions in this study is the use of CFRP strips horizontally, with a thickness of 1 mm, a width of 24 cm, and covering 50% of the surface area; This configuration successfully decreased the deflection of the wall from 63.1 cm to 7.7 cm and damped approximately 13% of the blast wave energy.
Volume 0, Issue 0 (8-2024)
Abstract
Reactive Powder Concrete (RPC) is recognized as one of the most innovative types of concrete, notable for its exceptional strength and durability. This type of concrete is composed of essential components such as cement, silica fume, quartz powder, silica sand, superplasticizer, and water. Due to its superior mechanical properties, RPC is widely utilized in specialized projects and structures that require outstanding strength and durability. However, the high cost of its components, particularly quartz powder, significantly increases the overall production cost, limiting its widespread application in larger, cost-sensitive projects. Quartz powder is scarce in the Azerbaijan region of Iran and is often sourced from mines in Hamedan and Isfahan. By replacing it with more locally available, affordable materials, final production costs can be reduced. To address this issue and optimize the use of available resources, the possibility of substituting quartz powder with local, cheaper, and more accessible materials has been explored. Micronized quartz powder is crystalline, though some of its finer particles have a minor pozzolanic effect. In contrast, diatomite powder, which contains both amorphous and crystalline particles with a high percentage of amorphous silica, exhibits significantly greater pozzolanic activity. These enhanced reactions contribute to the formation of a denser and stronger concrete matrix, improving its mechanical properties. The purpose of this study was to investigate the feasibility of replacing quartz powder with diatomite powder in different proportions—specifically 25%, 50%, 75%, and 100%. The goal was to evaluate how this substitution affects the concrete's strength while also reducing overall production costs. In this research, concrete samples were tested at various curing ages, including 7, 14, and 28 days. Mechanical tests such as compressive strength and tensile strength were conducted to assess the effects of the substitution on the concrete's performance. Additionally, parameters such as standard water absorption, water absorption during curing, density, and consistency were measured. To simulate real-world construction conditions and avoid the use of specialized equipment, the samples were cured in a water tank at 25°C. This curing method not only eliminated the need for expensive equipment like autoclaves but also made the concrete more applicable to typical site conditions, further lowering production costs. The test results were promising. The strength of the modified concrete mixtures improved significantly when diatomite powder replaced quartz powder. In samples where 100% of the quartz powder was substituted with diatomite, the compressive strength increased from 543 MPa to 806 MPa (approximately 49%), and the tensile strength increased from 543 MPa to 806 MPa (approximately 18%) at 28 days. In addition to the improvements in mechanical properties, the use of diatomite powder offers significant economic advantages. Diatomite is abundantly available in various regions, and its accessibility reduces both production and transportation costs. As a result, the overall production cost of the concrete is significantly lowered, which is especially beneficial for large-scale construction projects where cost efficiency is critical. In conclusion, replacing quartz powder with diatomite powder is a practical solution that brings both technical and economic benefits. The enhanced strength of the concrete, coupled with reduced production costs and the efficient utilization of local resources, makes this approach a practical and effective method for producing high-performance concrete.
Volume 0, Issue 0 (8-2024)
Abstract
Deep reinforced concrete beams are very important structural elements that are used in concrete structures such as high-rise buildings, marine structures, silos, and etc. Because of the importance of these elements, they sometimes need to be strengthened. One common method of strengthening reinforced concrete structures is the use of carbon polymer sheets (CFRP). In recent decades, little research has been done to investigate the effect of various variables affecting the behavior of concrete deep beam, strengthened using polymers reinforced with single or multi-directional fibers. The valuable features of composite materials such as simple and fast installation and corrosion resistance have led to the increasing use of these materials. It is possible to strengthen the reinforced concrete deep beams by gluing FRP plates or strips in a full-cross-section, gluing in a U shape or mounting on the sides of the beam at different angles to the longitudinal axis. Laboratory and analytical results prove that the external installation method, EBR, can be used as an acceptable solution in strengthening the shear of reinforced concrete members. Other methods such as installation Near the Surface Method (NSM) or methods that prevent them from separating from the concrete surface by inhibiting Composite tape can be used as an EBR alternative method that delays separation. Despite extensive research on strengthening and strengthening conventional reinforced concrete beams with FRP sheets, little research has been done on deep concrete beams. As we know, many parameters affect the NSM and EBR method. The lack of research in this field has caused these methods and details to be narrowly stated in the statutes.
One of the problems with using polymer sheets is their separation when loading a prototype. Therefore, this article attempts to use near-surface mounting methods (NSM) to strengthen such beams. This method plays a significant role in reducing the separation of reinforcement sheets. By reducing the effect of early detachment of polymer sheets, increasing the load capacity, increasing the formability and maximizing the use of the material capacity can be expected. Six deep reinforced concrete beams with a span-to-height ratio of 2, 3 and 4 are laboratory-loaded and reinforced by the NSM-EBR method using CFRP and their shear behavior is investigated. Given that the desired failure in deep beams is of the shear type, the NSM reinforcement grooves are installed perpendicular to the direction of the main diagonal cracks and reinforced with carbon polymer fibers. By strengthening the beam in shear using the EBR-NSM method, the type of beam failure did not change, but the number of cracks and tensile bands increased, which caused increase the load-bearing capacity of the beams. In the failure modes, it was observed that no delamination and slippage in the EBR-NSM strengthening system. Due to the presence of the adhesive at a greater depth of the beam, there is no slippage and delamination in the CFRP fibers within the tested specimen. This system has high reliability in terms of stability against slippage. The results showed the shear capacity of the deep beams increase by implementing this approach. Based on the results, it can be concluded that the amount of beam shear load capacity in samples with a span ratio of 2, 3 and 4 increased by 30%, 19% and 12.5% respectively
Volume 0, Issue 0 (12-2024)
Abstract
Aim and Introduction:
Vulnerable employment, a segment of the informal economy, includes home-based businesses that emerge due to a lack of opportunities for formal employment. These businesses often operate without essential benefits such as medical insurance, social security, bonuses, and pensions, which exposes workers to economic instability. Consequently, many individuals engaged in vulnerable employment seek loans and financial assistance to expand their business activities and transition to the formal sector. Banks, as the primary providers of such loans, request collateral from borrowers – typically in the form of property documents – to ensure repayment and mitigate financial risk. Strengthening legal rights related to loan collateral enhances banks’ confidence in issuing loans, thereby increasing access to credit for vulnerable workers.
Due to the oil-dependent nature of OPEC economies and their reliance on oil revenues, many of these countries often lack robust production infrastructures capable of generating sufficient formal employment opportunities. This study aims to analyze the effect of strengthening loan-related legal rights on vulnerable employment in OPEC member countries, including Iran, Iraq, Algeria, Angola, Congo, Gabon, Kuwait, Saudi Arabia, the United Arab Emirates, Venezuela, Guinea, Libya, and Nigeria, during the period from 2013 to 2021.
Methodology:
Following the approach of Herkenhoff et al. (2021), this study employs a model in which the independent variables include the strength of legal rights related to loans, oil revenues, secondary school enrollment rates, and the urbanization ratio. Given the study’s objective of analyzing the threshold effects of legal loan rights on vulnerable employment, the Panel Smooth Transition Regression (PSTRmouseout="msoCommentHide('_com_1')" onmouseover="msoCommentShow('_anchor_1','_com_1')">[A1] ) method is used to estimate the model.
Results and Discussion:
The analysis identifies a 6.22% threshold in the legal rights index, distinguishing two distinct regimes. In the first regime, the strength of legal loan rights does not significantly impact vulnerable employment. However, in the second regime, a higher index value reduces vulnerable employment, suggesting that more substantial legal loan rights facilitate the transition of workers from the vulnerable to the formal sector. Additionally, oil revenues and secondary school enrollment rates exhibit a negative effect on vulnerable employment, while the urbanization ratio has a positive effect.
Conclusion:
The findings of this study indicate that strengthening legal loan rights has contributed to a reduction in vulnerable employment, which is a subset of informal employment. This shift has contributed to growth in formal sector employment. Banking regulations and enhanced requirements for obtaining collateral have increased banks’ confidence in lending, as they are better able to mitigate the risk of non-repayment. However, this system primarily benefits individuals who can pledge valid collateral, such as real estate and housing documents. Given the high value of such collateralized assets, borrowers are more likely to invest their loans in business development, transitioning their employment from the informal to the formal sector. In addition to securing stable employment, they also gain access to social benefits such as insurance and social security. This financial stability enables them to make timely loan repayments, preventing defaults and preserving their financial credibility.
Based on these findings, it is recommended that governments and banking authorities in the investigated countries implement strict laws and regulations to guarantee loan security and identify factors contributing to bank insolvency. Such measures would help prevent financial resource mismanagement in the banking sector and reduce the probability of bank failures. Strengthening financial regulations and risk management strategies would facilitate lending, ultimately promoting employment growth in the formal sector and reducing the prevalence of vulnerable employment.
Furthermore, the study reveals that oil revenues negatively impact vulnerable employment, which may be attributed to increased government spending on productive investments and formal job creation. This suggests that redirecting oil revenues toward investment, production, and employment generation—rather than short-term expenditures—can facilitate the transition of workers from the informal to the formal sector. Thus, policymakers are encouraged to prioritize long-term economic strategies that allocate oil revenues to sectors that foster sustainable employment opportunities.
The findings also highlight the positive effect of education on labor force transition. Higher levels of education and training result in a more skilled workforce, increasing their acceptance and employability in formal job markets. Therefore, governments should allocate additional resources to public education, provide free schooling, and expand access to higher education for economically disadvantaged groups. Promoting scientific education and fostering a culture that values learning can further enhance workforce skills and economic mobility.
Finally, the study finds that urbanization has had a positive effect on vulnerable employment, indicating that increasing urbanization has not been accompanied by industrial advancements or skill development, thereby failing to support the expansion of the formal sector. Instead, urbanization in the studied countries has often been driven by unfavorable business environments, weak regulatory frameworks, and a lack of political transparency, contributing to the growth of the informal economy. To address these challenges, policymakers should focus on improving governance, strengthening legal and economic structures, and fostering a business-friendly environment that supports formal employment
Vulnerable employment, a segment of the informal economy, includes home-based businesses that emerge due to a lack of opportunities for formal employment. These businesses often operate without essential benefits such as medical insurance, social security, bonuses, and pensions, which exposes workers to economic instability. Consequently, many individuals engaged in vulnerable employment seek loans and financial assistance to expand their business activities and transition to the formal sector. Banks, as the primary providers of such loans, request collateral from borrowers – typically in the form of property documents – to ensure repayment and mitigate financial risk. Strengthening legal rights related to loan collateral enhances banks’ confidence in issuing loans, thereby increasing access to credit for vulnerable workers.
Due to the oil-dependent nature of OPEC economies and their reliance on oil revenues, many of these countries often lack robust production infrastructures capable of generating sufficient formal employment opportunities. This study aims to analyze the effect of strengthening loan-related legal rights on vulnerable employment in OPEC member countries, including Iran, Iraq, Algeria, Angola, Congo, Gabon, Kuwait, Saudi Arabia, the United Arab Emirates, Venezuela, Guinea, Libya, and Nigeria, during the period from 2013 to 2021.
Methodology:
Following the approach of Herkenhoff et al. (2021), this study employs a model in which the independent variables include the strength of legal rights related to loans, oil revenues, secondary school enrollment rates, and the urbanization ratio. Given the study’s objective of analyzing the threshold effects of legal loan rights on vulnerable employment, the Panel Smooth Transition Regression (PSTRmouseout="msoCommentHide('_com_1')" on
Results and Discussion:
The analysis identifies a 6.22% threshold in the legal rights index, distinguishing two distinct regimes. In the first regime, the strength of legal loan rights does not significantly impact vulnerable employment. However, in the second regime, a higher index value reduces vulnerable employment, suggesting that more substantial legal loan rights facilitate the transition of workers from the vulnerable to the formal sector. Additionally, oil revenues and secondary school enrollment rates exhibit a negative effect on vulnerable employment, while the urbanization ratio has a positive effect.
Conclusion:
The findings of this study indicate that strengthening legal loan rights has contributed to a reduction in vulnerable employment, which is a subset of informal employment. This shift has contributed to growth in formal sector employment. Banking regulations and enhanced requirements for obtaining collateral have increased banks’ confidence in lending, as they are better able to mitigate the risk of non-repayment. However, this system primarily benefits individuals who can pledge valid collateral, such as real estate and housing documents. Given the high value of such collateralized assets, borrowers are more likely to invest their loans in business development, transitioning their employment from the informal to the formal sector. In addition to securing stable employment, they also gain access to social benefits such as insurance and social security. This financial stability enables them to make timely loan repayments, preventing defaults and preserving their financial credibility.
Based on these findings, it is recommended that governments and banking authorities in the investigated countries implement strict laws and regulations to guarantee loan security and identify factors contributing to bank insolvency. Such measures would help prevent financial resource mismanagement in the banking sector and reduce the probability of bank failures. Strengthening financial regulations and risk management strategies would facilitate lending, ultimately promoting employment growth in the formal sector and reducing the prevalence of vulnerable employment.
Furthermore, the study reveals that oil revenues negatively impact vulnerable employment, which may be attributed to increased government spending on productive investments and formal job creation. This suggests that redirecting oil revenues toward investment, production, and employment generation—rather than short-term expenditures—can facilitate the transition of workers from the informal to the formal sector. Thus, policymakers are encouraged to prioritize long-term economic strategies that allocate oil revenues to sectors that foster sustainable employment opportunities.
The findings also highlight the positive effect of education on labor force transition. Higher levels of education and training result in a more skilled workforce, increasing their acceptance and employability in formal job markets. Therefore, governments should allocate additional resources to public education, provide free schooling, and expand access to higher education for economically disadvantaged groups. Promoting scientific education and fostering a culture that values learning can further enhance workforce skills and economic mobility.
Finally, the study finds that urbanization has had a positive effect on vulnerable employment, indicating that increasing urbanization has not been accompanied by industrial advancements or skill development, thereby failing to support the expansion of the formal sector. Instead, urbanization in the studied countries has often been driven by unfavorable business environments, weak regulatory frameworks, and a lack of political transparency, contributing to the growth of the informal economy. To address these challenges, policymakers should focus on improving governance, strengthening legal and economic structures, and fostering a business-friendly environment that supports formal employment
mouseout="msoCommentHide('_com_1')" onmouseover="msoCommentShow('_anchor_1','_com_1')" style="text-align: justify;">
mouseout="msoCommentHide('_com_1')" onmouseover="msoCommentShow('_anchor_1','_com_1')" style="text-align: justify;">
mouseout="msoCommentHide('_com_1')" onmouseover="msoCommentShow('_anchor_1','_com_1')" style="text-align: justify;"> [A1]The written abbreviation is for “the Panel Smooth Transition Regression”
Volume 1, Issue 1 (11-2009)
Abstract
adopted here is Social Distance Theory. According to this view, the more social distance among people the less they influence each other. From this viewpoint an increase in social distance among kinsfolk leads to a decrease in mutual influence and this, in turn, affect the emigration tendency. This study is aimed at the investigation of the relationship between kinship solidarity and emigration tendency among educated people. The theoretical framework Based on this theoretical foundation, we have suggested that 4 main variables, the size of kinship network, the strength of kinship relationship, the frequency of kinship relationship, and the profundity of kinship relationship, have negative influences on educated people’s tendency to emigrate. A sample of social sciences and electrical engineering students of the University of Tehran has been surveyed and the empirical data have been analysed both in description and explanation levels. The results indicate that all of the above mentioned variables affect emigration tendency negatively and significantly. Also, our findings suggest that, generally speaking, a negative correlation between the above independent variables and dependent variable of emigration tendency is predictable. In particular, two variables (the strength of kinship relationship, and the profundity of kinship relationship) explain 35% of variances of dependent variable of the tendency to emigrate.
Volume 1, Issue 2 (3-2018)
Abstract
In general, temporary well plugging is essential for repairing of oil and gas wells due to their long life time. One of the newest methods used for this purpose is gel polymer plugging. The strength of the gel in the well conditions is one of the most important challenges in the application of gel polymer in the temporary well plugging in work over operation. In this study, silica nanoparticles were used to improve the strength of polymer hydrogels. The bottle and rheological tests were used to determine the gel strength in desired well conditions (high temperature and high salinity). Also, the gel strength properties and swelling behavior were studied in various conditions such as distilled water, formation water, tap water and oil. It was observed that the strength of the gel increased from 520Pa to about 36kPa (5000% increase) by adding nanoparticles. Also, the gel swelling in the aqueous solution has been significantly reduced. Based on the results obtained in this study, a polymer gel containing 9 wt.% of silica nanoparticles with structural strength and thermal stability at 90 °C was introduced for field studies.
Volume 1, Issue 3 (9-2023)
Abstract
Changes in pore fluid can significantly impact the geotechnical behavior of soil, especially clayey soil. One source of soil contamination is leachate, which can infiltrate nearby soil during the collection, transportation, and deposition stages of the residential waste disposal process, exerting geotechnical influences on the soil in the surrounding area. To assess these effects, four leachate samples were collected from different sites. The specimen comprises fine soil, created from a mixture of sand, bentonite, and kaolinite. Experimental results reveal a decreasing trend in the liquid limit, compaction parameters, and cohesion values of the soil with an increase in contamination level. However, the internal friction angle exhibits an increasing trend with higher leachate concentration, resembling the behavior of sandy soil, as opposed to the typical behavior of clay.
Volume 1, Issue 4 (2-2021)
Abstract
Examining the dimensions of mental strength in the performance of athletes
Volume 2, Issue 1 (1-2017)
Abstract
Work-related Musculoskeletal Disorders (WMD) are a common health related problem throughout the world. The aim of this study was to evaluate the effect of hydrotherapy training on health, function, motion, and occupational performance of the police personnel in Iran.
In this before/after prospective study, 30 participants were selected purposefully and divided into two experimental (n = 15) and control groups randomly (n = 15). The 8-week hydrotherapy training program was just assigned for intervention. The occupational performance and physical fitness tests, Health related Quality of Life (HRQoL) questionnaire and Visual analog Scale (VAS) were measured for both groups before and after intervention. data were analyzed through SPSS 16
Volume 3, Issue 1 (5-2019)
Abstract
Research subject: In recent years, many attempts have been devoted to industrial usage of bio-based adhesives, as a result of fossil resources shortage and unusual increase in oil-based products prices. Adhesion strength of this category of adhesives, however, needs improvement.
Research approach: In the current study, lap-shear strength of joints made of a natural polymer, Persian gum (PG), exuded from wild almond tree, and three various substrates, glass, poly(ethylene terephthalate), and cellulose fabric, was investigated. Furthermore, in order to prepare powder acrylic adhesive and evaluate its adhesion to aforementioned substrates, the gum dispersion was blended with synthesized poly(methyl methacrylate-co-butyl acrylate) random copolymer containing 30 wt.% methyl methacrylate (MBC30). Molecular interactions in PG, MBC30, and 50 wt. % PG-containing blend were characterized by Fourier transform infrared spectroscopy. Moreover, morphology of blends containing various amounts of PG was evaluated using scanning electron microscopy of their fractured cross sections.
Main results: The textile joint made with PG dispersion in water showed high shear strength of about 340 kPa. However, PG could not form a suitable joint with glass and polyester substrates, as a consequence of its inability to form a homogeneous film, excessive brittleness, and its inability to diffuse and mechanically interlock with the substrates. Results showed that using an adhesive system containing 50/50 PG/MBC30, besides enabling preparation of powder adhesive, shear strength increased to 20, 11, and 14-fold with respect to pristine MBC30 on glass, poly(ethylene terephthalate), and textile substrates, respectively. In other words, shear strength of an adhesive could be improved by promoting the adhesive constituents interactions and subsequent increase in the blend cohesiveness, on the one hand, and increment of its adhesion to substrate, on the other hand. In the current research, Persian gum was introduced as a water-redispersing agent for acrylic pressure-sensitive adhesives and new adhesive systems were invented with usability in cellulose industry.
Research approach: In the current study, lap-shear strength of joints made of a natural polymer, Persian gum (PG), exuded from wild almond tree, and three various substrates, glass, poly(ethylene terephthalate), and cellulose fabric, was investigated. Furthermore, in order to prepare powder acrylic adhesive and evaluate its adhesion to aforementioned substrates, the gum dispersion was blended with synthesized poly(methyl methacrylate-co-butyl acrylate) random copolymer containing 30 wt.% methyl methacrylate (MBC30). Molecular interactions in PG, MBC30, and 50 wt. % PG-containing blend were characterized by Fourier transform infrared spectroscopy. Moreover, morphology of blends containing various amounts of PG was evaluated using scanning electron microscopy of their fractured cross sections.
Main results: The textile joint made with PG dispersion in water showed high shear strength of about 340 kPa. However, PG could not form a suitable joint with glass and polyester substrates, as a consequence of its inability to form a homogeneous film, excessive brittleness, and its inability to diffuse and mechanically interlock with the substrates. Results showed that using an adhesive system containing 50/50 PG/MBC30, besides enabling preparation of powder adhesive, shear strength increased to 20, 11, and 14-fold with respect to pristine MBC30 on glass, poly(ethylene terephthalate), and textile substrates, respectively. In other words, shear strength of an adhesive could be improved by promoting the adhesive constituents interactions and subsequent increase in the blend cohesiveness, on the one hand, and increment of its adhesion to substrate, on the other hand. In the current research, Persian gum was introduced as a water-redispersing agent for acrylic pressure-sensitive adhesives and new adhesive systems were invented with usability in cellulose industry.
Volume 3, Issue 3 (12-2019)
Abstract
Research Subject: Poor mechanical strengths and lack of thermal stabilities of hydrogels confine their extensive practical applications in many areas. The growing scientific need for solving this problem and achievement to the hydrogels with improved properties has led to the design and production of the nanocomposite hydrogels.
Research Approach: The polymeric networks of nanocomposite hydrogels compared to the ordinary hydrogels have improved elasticity and rheological properties. Other points that increase the importance of structural studies of nanocomposite hydrogels are the high strength of these materials versus the application of external forces, as well as maintaining its structure against increasing of temperatures. In this regard, the type and amounts of nanomaterial, the preparation method and formation of hydrogel network have a significant role in improving the physical, chemical and biological properties of hydrogels, and, it must be noted that these parameters will depend on the application of nanocomposite hydrogels. This also highlights the need for the production of nanocomposite tailored hydrogels. Therefore, orientation of the range of nanomaterials, the preparation method and product identification, along with sufficient information on the application of these materials, might have an important role in ensuring the success of these materials, requiring comprehensive library research and studies on polymerization processes, morphology and rheology.
Main Results: In this review article, the scientific advances in the field of nanocomposite hydrogels, focusing on its types based on the type of nanoparticles, its properties, preparation methods, identification methods with a new perspective on rheology, thermal analysis and morphology is investigated. Finally, the applicability of these materials is collected in a comprehensive table in various fields such as tissue engineering, enhanced oil recovery, agriculture, and etc…
Volume 4, Issue 1 (6-2020)
Abstract
Research subject: The rubber Springs with spong structure must have acceptable tear resistance in addition to desirable compression set. Usually enhancing each of these properties leads to the weakening of the other property.
Research approach: Simultaneously providing the optimum value of these two properties in the rubber spring compound requires consideration of the effective factors by performing several tests. Therefore, in this study, a test plan based on the Taguchi statistical analysis technique was presented to design the optimal formulation in exchange for reducing the number of tests required. Thus, the impact of four factors: weight percent of Natural rubber (NR), concentration of zinc oxide (ZnO), dicumyl peroxide (DCP) and ethylene glycol dimethacrylate (EDMA) on the ratio of tear resistance to compression set (design criterion, Q) was determined.
Main results: Data given of ANOVA showed that the amount of DCP with 66.93% has the highest influence on the design of the rubber spring compound. In addition, it was revealed that the curing system is a solution for the simultaneous optimization to maximum tear energy and minimum compression set of the compound. Statistical analysis predicted that the optimal formulation contained 60 weight percent of NR and 1, 4 and 2 phr of DCP, ZnO and EDMA, respectively. Experimental test results confirmed the predicted Q value for optimal conditions.
Research approach: Simultaneously providing the optimum value of these two properties in the rubber spring compound requires consideration of the effective factors by performing several tests. Therefore, in this study, a test plan based on the Taguchi statistical analysis technique was presented to design the optimal formulation in exchange for reducing the number of tests required. Thus, the impact of four factors: weight percent of Natural rubber (NR), concentration of zinc oxide (ZnO), dicumyl peroxide (DCP) and ethylene glycol dimethacrylate (EDMA) on the ratio of tear resistance to compression set (design criterion, Q) was determined.
Main results: Data given of ANOVA showed that the amount of DCP with 66.93% has the highest influence on the design of the rubber spring compound. In addition, it was revealed that the curing system is a solution for the simultaneous optimization to maximum tear energy and minimum compression set of the compound. Statistical analysis predicted that the optimal formulation contained 60 weight percent of NR and 1, 4 and 2 phr of DCP, ZnO and EDMA, respectively. Experimental test results confirmed the predicted Q value for optimal conditions.
Volume 5, Issue 2 (9-2021)
Abstract
Research subject: Expandable Poly Styrene (EPS) has many applications. This polymer prepared by the radical polymerization. This material has many uses in packaging and insulation industries Some of the properties of this polymer like low mechanical strength caused its applications to be limited. By adding some materials, these properties can be improved. Styrene Butadiene Styrene (SBS) is from the materials that which by adding it to the EPS it can improve its quality.
Research approach: In this research, EPS having different percentages of SBS (0, 0.01, 0.02, 0.03) in different conversion percentages (0.6, 0.63, 0.66, 0.69) has been prepared. Different tests like Impact Test, Modular Melt Flow test, Vicat Softening Temperature test, Tensile at Break test, K-value test, Rochwell Hardness test and Elongation at Break test are done on the prepared polymer. Laboratory gained data has been simulated by Multi-Layer Perceptron (MLP) method of artificial neural networks (ANN) and the simulated data covers the laboratory data perfectly.
Main Results: Investigating the tests show that in constant percentages of SBS in EPS with increase in conversion percentage of EPS, the numerical amount of the tests increases except MFI test (low MFI number means better quality). Increase in SBS percentage in the EPS, increases the properties of polymer. In addition, the results of simulation show that the laboratory data covers the the simulated data perfectly. The data obtained from the results of this reasearch can be used for predicting the data for the points which has not been tested. Adding SBS in different weight percentages of poly styrene in different conversion percentages in order to increase the properties of poly styrene has been used for the first time in this research and the laboratory data results in points which has not been tested has been acquired by applications of ANN.
Volume 5, Issue 3 (7-2003)
Abstract
A consideration of the design and development of any harvesting machine is required to determine the physical and biomechanical properties of the tree and its fruit. Biome-chanical properties such as pull, bending and torsion strengths must be determined. In the field experiments, trees were selected from an orchard in Rafsanjan, Kerman Prov-ince, Iran. Parameters related to fruit properties were measured using load cells. In Raf-sanjan’s Pistachio Research Institute laboratory, subsequent measurements were made using similar instrumentation. In a randomized design layout, 18 tree cultivars with five replications were selected. The maximum pull, bending, and torsion strengths were found respectively for Badami Ravar, Momtaze Tajabadi and Italiaee cultivar clusters. Mini-mum pull, bending, and torsional strengths were obtained for Ghazvini, Louk and Kalleh Ghoochi clusters. The cultivars Kalleh Ghoochi, Rezaee Zoodras and Khanjari Damghan were found to have fruit with the highest pull, bending, and torsional strengths, with the lowest strengths belonging to the Italiaee cultivar.
Volume 5, Issue 4 (5-2016)
Abstract
Experts Experts believe that human resource system due to causal ambiguity and complexity can create competitive advantage as a valuable, rare, inimitable and non-substitutable source, but few supporting studies have been conducted. This study investigates the relationship between high performance work system and organizational entrepreneurship while investigates the moderating role of HR system strength. data was gathered from 242 knowledge employees of five premier dairy production companies in Mazandaran province. Reliability of the measures was evaluated by Cronbach's alpha and construct validity was evaluated by confirmatory factor analysis. The hypotheses were tested using hierarchical regression based on Baron and Kenny's method. According to the results of this study, HPWS has positively significant effect on organizational entrepreneurship. Also, HR system's strength moderates the relationship between the independent and dependent variables. results show that only considering content of HR system is not enough, but HR system must be strong enough to differentiate an organization from others and create competitive advantage.
Volume 5, Issue 4 (4-2021)
Abstract
Research subject: In recent years, several studies have been performed for improving the adhesion properties of polyurethane and acrylic pressure-sensitive adhesives (PSAs). Generally, polyurethane PSAs are of higher shear strength, while acrylic PSAs have higher tack. This research is a feasibility study of exploiting the properties of both of these adhesives through a simple blending method, and the adhesion properties were evaluated.
Research approach: First, acrylic copolymer (Ac) consisting of 82 vol. % butyl acrylate and 18 vol. % methyl methacrylate was solution polymerized. On the other hand, a thermoplastic polyurethane (TPU) containing 17.5 wt. % hard segment was prepared by bulk polymerization. Blending of these two polymers was performed by solution mixing. Solutions of the pure polymers and their blends at different contents were cast on polyethylene terephthalate backing and dried at room temperature. Fourier transform infrared spectroscopy, gel permeation chromatography, and differential scanning calorimetry were used to identify TPU and Ac. Loop tack, static shear strength, dynamic mechanical behavior, contact angle of sessile drop, morphology, and haze of the PSAs were evaluated.
Main results: Tack of the acrylic PSA was higher than TPU PSA. Tack of the blend PSAs containing 20, 40, and 60 wt. % TPU was higher than the pure components and that of the blend containing 40 wt. % TPU was maximum. This blend demonstrated the lowest water contact angle compared to the other blends and the shortest relaxation time compared to the pure polymers, which resulted in better wetting and higher tack. The shear strength of the PSAs increased with increase in the content of TPU to higher than 40 wt. % in the blends compared to the acrylic PSA; so that the pure TPU showed the highest modulus at various frequencies and hence exhibited high-shear PSA characteristics in the Chang’s viscoelastic window and the highest adhesion strength. The immiscibility of the blends was confirmed by measuring the haze and calculating the Hansen solubility parameter.