Pressureless sintering of SiC matrix composites reinforced with nano-β-SiC and graphene

Razmjoo Ali,Baharvandi Hamid Reza,Ehsani Nasser 한국세라믹학회 2022 한국세라믹학회지 Vol.59 No.5

Silicon carbide (SiC) is an effective material for high-temperature engineering applications owing to its desirable properties such as high elastic modulus, high hardness, and melting temperature, high thermal conductivity, good corrosion and oxi- dation resistance, low density, and coefficient of thermal expansion compared with other advanced ceramics. Nevertheless, poor sinterability and low toughness limit its use, which can be overcome using appropriate additives. In this study, the eff ect of different amounts of nano-β-SiC (0, 5, 10, and 15 wt.%) and graphene (0, 1, 2, and 3 wt.%) particles on the sinterability behavior and microstructure of SiC composite has been investigated. After weighing, dispersing nano-β-SiC and graphene, and mixing the starting materials, milling was carried out at 180 rpm for 3 h. The materials obtained were then compressed uniaxially under a pressure of 75 MPa and then were compressed again through CIP under 150 MPa. To remove volatile products, the pyrolysis process was performed at 800 °C under Ar atmosphere. Finally, the samples were sintered at 2200 °C for 2 h by the pressureless sintering process. XRD analysis was used to investigate the phases and FESEM images were used to study the microstructure. According to the XRD patterns, β-SiC particles were converted to α-SiC, which was accompa- nied by the elongation of SiC grains. Also, no reaction was observed between graphene and the SiC matrix. According to the FESEM images, the samples containing 5 wt.% nano-β-SiC and 1 wt.% graphene showed a uniform distribution of rein- forcement particles but with increasing the amount of the reinforcement particles, agglomeration was observed. According to the results, upon increasing the nano-β-SiC up to 5 wt% and graphene up to 1 wt.%, all the measured properties including relative density, and linear shrinkage improved and reached 99.04%, and 18.01%, respectively. However, with increasing the additives, these properties deteriorated due to increasing porosity and agglomeration in the composite structure.

A Content Analysis of the TEFL M.A. Entrance Examinations (Case Study: Majors Courses)

( Seyyed Ayatollah Razmjoo ),( Hossein Heydari Tabrizi ) 범태평양응용언어학회 2010 범태평양응용언어학회지 Vol.14 No.1

The MA Entrance Examinations (MAEE) held in Iran since 1990 are frequently criticized as being invalid, unstandardized exams with lots of problem in terms of principles of testing in general and test construction in particular (for instance, Jafarpur, 1996). To make sound judgments about such objections, the present study dealt with a content analysis of the TEFL MAEE held in 2007. Actually, the purpose of this study was two-fold. First, it aimed at analyzing the content of the MAEE``s in order to see if any pattern be at work in the process of devising such exams. Naturally, through such an analysis, some problems of these exams were also determined. Thus, the second aim of the present study was to pinpoint and describe the problems with these exams as well as to offer some suggestions to remedy the problems. In so doing, a coding system encompassing a checklist of the possible content categories was developed by the researchers themselves and its validity and reliability were established as well. The finding of such an analysis, especially the unequal distribution of the content categories, supported the idea that the validity of the exam is not strongly established due to the exclusion of or de-emphasis over the content categories given significant credit in the B.A. Program. The problems found during the analysis showed that the exam is not a standard one; still some of the basic principles of language testing are not observed in the process of constructing the exam.

The Representation of Multiple Intelligences Types in the Top-notch Series: A Textbook Evaluation

( Seyyed Ayatollah Razmjoo ),( Zahra Jozaghi ) 범태평양응용언어학회 2010 범태평양응용언어학회지 Vol.14 No.2

This study aims at evaluating Top-Notch series through a checklist devised by the researchers based on the elements of the Multiple Intelligences (MI) theory proposed by Gardner (1998). With the shift from teacher-centered classrooms to learner-centered one, more and more research is/is needed to be done in the realm of students` need analysis. One of the undeniable needs of the students to be fulfilled is for them to learn through the intelligence they are most capable at while the educational system mainly addresses students` verbal intelligence. This study has evaluated Top Notch series in terms of taking the nine intelligences into consideration through answering these two questions: 1. To what extent does Top-Notch series represent the MI features? 2. How frequently each of the eight intelligences is used in each book of the series? The results confirm that Top Notch is rich in addressing verbal intelligence followed by the visual, logical, musical, interpersonal, bodily, and intrapersonal one while to some extent poor in representing natural and existential intelligences. It also shows that there exists a pattern of some of the intelligences-addressing through different levels, for example unlike visual intelligence, verbal-intelligence-addressing enhances as the books grow in level. The comparison of the results with that of Interchange series evaluation illustrated that Top Notch is more representative of the intelligences and that it is a suitable alternative to the Interchange in terms of addressing the elements of MI principles or as Lezear (1991) puts it "Ways of Knowing".

Language Proficiency Tests in the Iranian Context: Do They Represent Communicative Language Testing Model?

( Seyyed Ayatollah Razmjoo ) 범태평양응용언어학회 2011 범태평양응용언어학회지 Vol.15 No.2

The Communicative Ability in language testing originates from a theory of language as communication proposed by Hymes (1972) and known as "communicative competence". The literature on language testing suggests that the practicality of communicative language testing (CLT) varies depending on how the instructors and teachers conceptualize CLT. As far as the researcher knows, no study has been done on the type of proficiency model behind language tests in the Iranian context. Therefore, the objective of this study is, firstly, to explore the language proficiency model based on which the tests are designed and constructed in Iranian high school and institutes. Secondly, the study aims at developing language proficiency model for the context of Iran as a basis so that teachers construct and design tests. To fulfill the objectives, two final tests of Iranian high school and institutes were analyzed. The analysis of the data indicated that high school and institute tests represent a short version of Lado``s model (1961) which is not in line with new trends in language testing and aims at discovering whether the correct habits have been formed.

Irrigation effect on yield and desirable metabolites of pot marigold (Calendula officinalis L.) genotypes

Iman Ghadyeh Zarrinabadi,Jamshid Razmjoo,Alireza Abdali Mashhadi,Hassan Karimmojeni,Te-Ming Tseng 한국원예학회 2019 Horticulture, Environment, and Biotechnology Vol.60 No.4

Managed irrigation water may induce industrially desirable metabolites in pot marigold. Thus, the effects of three irrigation regimes (35% [I1], 60% [I2], and 85% [I3] depletion of the available soil water) on the yield, irrigation water use efficiency, and secondary metabolite content of nine pot marigold genotypes were examined during 2015 to 2016 and 2016 to 2017 growing seasons in Ahwaz, Iran. Carotenoid, alkaloid, and flavonoid contents as well as antioxidant activity increased under I2 and I3 treatments, while phenol content increased under I2 and reduced under I3 treatments. The Isfahan2 genotype produced the highest flavonoid content under I1 and I2 and the highest phenol content under I1, I2, and I3. The Zen-gold genotype produced the highest flavonoid content under I3. The highest carotenoid content was obtained under I1 and I2, while the highest alkaloid content was detected under I3 in Tehran. The Gitana genotype contained the highest carotenoid content under I3, while Isfahan1 produced the highest alkaloid content under the I1 irrigation regime. Gitana under I2 and Zen-gold under I3 had the highest antioxidant activity. Gitana under I1 and I3 and Candy-man under I2 had the highest extract content. The Candy-man genotype produced the highest petal yield and extract yield under I1, I2, and I3 irrigation regimes. The results from our findings suggest that the production of secondary metabolites in pot marigold was dependent on metabolite, genotype, and irrigation regime. The results also demonstrate that drought had positive effects on measured metabolites, especially under the I2 irrigation regime, but a negative effect on dry petal yield and extract yield. Thus, the number and amount of irrigation could be reduce while metabolite contents increase under selected irrigation regimes and genotypes.

The Impact of Motivation Types (Instrumental Versus Integrative) upon Speaking Ability among Iranian Female Students

( Ismaeil Fazel ),( Seyyed Ayatollah Razmjoo ) 범태평양응용언어학회 2007 범태평양응용언어학회지 Vol.11 No.1

Analytical Consideration of Surface Dose and Kerma for Megavoltage Photon Beams in Clinical Radiation Therapy

Birgani, Mohammad Javad Tahmasebi,Behrooz, Mohammad Ali,Razmjoo, Sasan,Zabihzadeh, Mansour,Fatahiasl, Jafar,Maskni, Reza,Abdalvand, Neda,Asgarian, Zeynab,Shamsi, Azin Asian Pacific Journal of Cancer Prevention 2016 Asian Pacific journal of cancer prevention Vol.17 No.1

Background: In radiation therapy, estimation of surface doses is clinically important. This study aimed to obtain an analytical relationship to determine the skin surface dose, kerma and the depth of maximum dose, with energies of 6 and 18 megavoltage (MV). Materials and Methods: To obtain the dose on the surface of skin, using the relationship between dose and kerma and solving differential equations governing the two quantities, a general relationship of dose changes relative to the depth was obtained. By dosimetry all the standard square fields of $5cm{\times}5cm$ to $40cm{\times}40cm$, an equation similar to response to differential equations of the dose and kerma were fitted on the measurements for any field size and energy. Applying two conditions: a) equality of the area under dose distribution and kerma changes in versus depth in 6 and 18 MV, b) equality of the kerma and dose at $x=d_{max}$ and using these results, coefficients of the obtained analytical relationship were determined. By putting the depth of zero in the relation, amount of PDD and kerma on the surface of the skin, could be obtained. Results: Using the MATLAB software, an exponential binomial function with R-Square >0.9953 was determined for any field size and depth in two energy modes 6 and 18MV, the surface PDD and kerma was obtained and both of them increase due to the increase of the field, but they reduce due to increased energy and from the obtained relation, depth of maximum dose can be determined. Conclusions: Using this analytical formula, one can find the skin surface dose, kerma and thickness of the buildup region.

Evaluation of Visual Quality of Bermudagrass (Cynodon dactylon L.) Population

Nematollah Etemadi,Zabiollah Zamani,Khorshid Razmjoo 한국원예학회 2006 한국원예학회 기타간행물 Vol.- No.-

Bloom, Maturity, and Fruit Set of Pistachio in Response to Early Season Application of Ethephon

Ehsan Askari,Sayareh Irani,Khorshid Razmjoo 한국원예학회 2011 Horticulture, Environment, and Biotechnology Vol.52 No.1

Spring frost damage has been a problem in pistachio producing areas. This experiment was conducted to evaluate the effect of ethephon application rate and date on bloom and maturity delay, fruit set, and yield of ’Kalleh-guchi’ pistachio in Rafsanjan, Iran. Fourteen-year-old whole trees were sprayed with 0, 250, 500, and 750 mg・L-1 ethephon on February 10 or March 1 for single application and both dates for two applications. With increasing the application rate, timings of the initial and full bloom and the maturity were delayed by 11.2, 12.6, and 7.6 days in 2007 and 11.3, 10.7, and 5.4 days in 2008, respectively. The double spray was the most effective in delaying bloom and maturity, and in increasing yield. The double spray with 750 mg・L-1 ethephon delayed initial and full bloom, and maturity by 14, 15, and 10 days in 2007 and 15, 15, and 8 days in 2008, respectively. This treatment increased the yield by about 64% in both years. It was concluded that ethephon may be applied to pistachio in late winter to delay bloom in spring without any apparent side effects, and thus to prevent spring frost damage and increase the yield.