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RISS 인기검색어
- 검색키워드
- 저자 : M. Vaseghi (검색결과 6 건)
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M. Vaseghi,S. Baghshahi,M. Mashhadi,A. Nemati 한양대학교 세라믹연구소 2019 Journal of Ceramic Processing Research Vol.20 No.5
Gel-casting is an appropriate method for manufacturing porous parts with complicated forms, which has also been used in shaping Si3N4 bodies. In the present study, porous bulk Si3N4 samples were fabricated using gel-casting. To this aim Si3N4 slurries were prepared with solid loading of 35 vol%. To the slurry was added 1 and 3 wt% rod-like BN to enhance the mechanical properties. BN was selected to further reduce the dielectric constant and loss of the prepared porous Si3N4 samples. The findings suggested that employing rod-like BN increased the porosity from 38 % to 41 %, reducing the flexural strength from 77 MPa in the part without BN to 56 MPa in the part containing 3 wt% BN. On the other hand, dielectric properties reduced in the parts with BN compared with the part without BN.
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A combination of severe plastic deformation and ageing phenomena in Al-Mg-Si Alloys
Vaseghi, M.,Kim, H.S. Scientific and Technical Press ; Elsevier Science 2012 MATERIALS AND DESIGN Vol.36 No.-
In this paper static and dynamic strain ageing behavior in Al-Mg-Si alloys related to equal channel angular pressing (ECAP) was investigated. In order to examine the combined plastic deformation, solution treatment and ageing effects on strengthening characteristics, experimental results of ageing without ECAP, pre-ECAP ageing, post-ECAP ageing and dynamic ageing inside of ECAP die were compared. In particular, the effects of ageing temperature, ageing time, strain rate in ECAP, and sequence of heat treatment and ECAP on Vickers hardness were discussed. To achieve a higher hardness, an optimum ageing cycle combined with ECAP process is presented based on the results of current study. By employing the proposed schedule the hardness value was increased from 86 HV (as-solution treatment) to 138 HV (peak hardness of the current schedule).
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M. Vaseghi,S. Baghshahi,M. Mashhadi,A. Nemati 한양대학교 세라믹연구소 2019 Journal of Ceramic Processing Research Vol.20 No.2
The gel casting method was used for the production of Si3N4 porous ceramics with 25 vol% solid loading, and the effect ofadding 1 and 3 wt.% of BN whisker-like (synthesized in the laboratory) on the flexural strength of the composites wasinvestigated. The gel-cast samples were prepared using an AM-MBAM monomer system and deionized water solvent. The gelcast bodies were dried at ambient temperature and humidity for 48hrs. The burnout process was carried out at 600 oC for14hrs in the air. The samples were then subjected to heat treatment at 1650 oC for 2 hrs in a bed of 50% Si3N4-50% BN. Resultsshowed that BN whisker-like were agglomerated in deionized water. To solve this problem and to properly disperse thewhisker-like in the slurry, active surface agent groups were employed. Adding BN whisker-like to ceramic bodies, increasedthe porosity from 33% in samples without BN to 46% in samples containing 3 wt% BN whisker-like, resulting in a decreasein the density from 1.8 g/cm3 to about1.61 g/cm3. Since the Si3N4 ceramics require aids for the sintering, SiO2 and Y2O3additives were used with a ratio of 1 to 2, respectively, which led to the formation of Si2N2O phase. Si2N2O is similar to theSi3N4 phase in terms of the thermal expansion coefficient and chemical properties. Because of its rod shaped morphology, ithas a similar function to β-Si3N4 phase in improving the mechanical properties of the ceramic. Although porosity in theceramics containing 3 wt.% BN whisker-like was higher than those containing 1 wt.%, the porosity created vacant spaces forfurther growth of Si2N2O-rod shaped grains and in spite of higher porosity, better flexural strength was achieved for bodieswith 3 wt.% BN whisker-like. Also, in bodies without BN whisker-like, the flexural strength was 88 MPa, due to the lowporosity and the presence of stretched Si2N2O grains.
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Nonlinear optical properties of a hydrogenic impurity in an ellipsoidal finite potential quantum dot
G. Rezaei,M.R.K. Vahdani,B. Vaseghi 한국물리학회 2011 Current Applied Physics Vol.11 No.2
The linear and the third-order nonlinear optical absorption coefficient and refractive index changes of a hydrogenic impurity in an ellipsoidal quantum dot have been investigated, using the compact-density matrix formalism and an iterative method. In this regard, the effect of the size and geometry of the dot,aluminium concentration in GaAs/Al_xGa_1-x_As structures, and optical intensity on the optical absorption coefficient and refractive index changes are investigated. It is found that the light intensity, size and geometry of the dot and aluminium concentration have a great influence on the absorption coefficient and refractive index changes of the dot.
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Induction of superovulation in mature mice and rats using serum of spayed female dogs
Nooranizadeh MH,Mogheiseh A,Kafi M,Sepehrimanesh M,Vaseghi H 한국실험동물학회 2018 Laboratory Animal Research Vol.34 No.4
The following experiments were designed to examine the effect of serum of spayed dogs on superovulation response in mice and rats. In Experiment 1, female mice at diestrus (n=30) were divided into three equal groups and superovulated with either administration of 5 IU pregnant mare serum gonadotropin (PMSG) or recombinant follicle stimulating hormone (rFSH) (reducing dose from 2.5 to 0.5 IU) and 5 IU human chorionic gonadotropin (hCG) administered 48h later. Serum of spayed dogs was administered intraperitoneally at a reduced dose from 0.1 to 0.025 mL in a 48 h period. In Experiment 2, female rats (n=30) at diestrus stage were divided into three equal groups. Superovulation was induced using either 30 IU PMSG, or a dose reduced from 5 to 1 IU rFSH and 25 IU hCG administered 48h later. Serum of spayed dogs was administered in a reduced dose from 0.6 to 0.1 mL in a 48 hour period. Female mice and rats were mated 24 h following hCG administration. On day 14 after mating, animals were euthanized and ovarian sections were fixed for histopathological evaluation and corpus luteum (CL) counting. No significant difference observed in mean (±SEM) number of CLs between the PMSG group and the mice that received serum of spayed dog (10.4±1.3 vs 9.2±1.0). Mean (±SEM) number of CLs tended to be lower in rats that received serum of spayed dog than those of rats which received either PMSG or rFSH (15.1±1.9 vs 23.6±3.1 and 23.1±2.9, P=0.06, respectively). In conclusion, serum of spayed dogs is able to induce a superovulatory response in mice and rats.
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