Efficiency of differential transformation method for nonlinear oscillation: Comparison with HPM and VIM

S. Ghafoori,M. Motevalli,M.G. Nejad,F. Shakeri,D. D. Ganji,M. Jalaal 한국물리학회 2011 Current Applied Physics Vol.11 No.4

In this study, a nonlinear oscillation equation is solved using a series-based analytical method called differential transformation method (DTM). The concept of differential transformation is briefly introduced,and its application for a nonlinear oscillator is studied. The results obtained employing DTMare compared with those achieved by using two other series-based analytical techniques named variation iteration method (VIM) and homotopy perturbation method (HPM) and also an accurate numerical solution to verify the accuracy of the proposed method. As an important result, it is depicted that the DTM results are more accurate in comparison with those obtained by HPM and VIM. After this verification, we analyze the effects of some physical applicable parameters to show the efficiency of DTM for this type of problems. It is shown that inmost cases,DTM is accurate enough; nevertheless some modifications should be applied to enhance the abilities of this technique.

Adhesion of clay to metal surface; Normal and tangential measurement

Basmenj, Amir Khabbazi,Ghafoori, Mohammad,Cheshomi, Akbar,Azandariani, Younes Karami Techno-Press 2016 Geomechanics & engineering Vol.10 No.2

Adhesion in geotechnical engineering is the interaction between cohesive soil and a solid surface which can cause clogging in mechanized tunnelling through clayey formations. Normal piston pull out and modified direct shear tests were performed on clayey soil samples to determine which type of adhesion stress, normal or tangential, could be most effectively measured. Measured values for normal adhesion ranged from 0.9 to 18 kPa. The range of tangential adhesion was 2.4 to 10 kPa. The results indicate normal adhesion results were more accurate than those for the modified direct shear test that measure tangential adhesion. Direct shear test on identical samples did not show any correlation between measured cohesion and normal adhesion values. Normal adhesion values have shown significantly meaningful variation with consistency index and so are compatible with the base of field clogging assessment criteria. But tangential adhesion and cohesion were not compatible with these assessment criteria.

Low-Temperature Preparation of a Carbon Nanotube–ZnO Hybrid on Glass Substrate for Field Emission Applications

M. K. Tabatabaei,H. Ghafoori Fard,J. Koohsorkhi 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2015 NANO Vol.10 No.3

A new method for preparation of a carbon nanotube (CNT)–zinc oxide hybrid on a glass substrate at low temperature is introduced and the stability improvement of field emission of CNTs is reported. The emission current stability and substrate material are the two main commercial parameters for field emission applications of CNTs. The two alternative current (AC) and direct current (DC) plasma enhancement chemical vapor deposition (PECVD) is used to achieve low-temperature growth of vertically aligned CNTs and the hydrothermal processing is used for production of zinc oxide nanowires to improve the emission current stability and properties. The nanoscale junction between a semiconductor and conductive material are critical for electronic applications. The present study examined the field emission properties of CNTs near the crystalline structure of the zinc oxide hybrids and showed the improvement in the field enhancement factor and emission current stability of CNT–ZnO hybrid than the CNT emitters.

Development of Macro-Porous Silicon Based Dye-Sensitized Solar Cells with Improved Light Trapping

Aliaghayee, Mehdi,Fard, Hassan Ghafoori,Zandi, Ashkan The Korean Electrochemical Society 2016 Journal of electrochemical science and technology Vol.7 No.3

The light harvesting efficiency is counted as an important factor in the power conversion efficiency of DSSCs. There are two measures to improve this parameter, including enhancing the dye-loading capacity and increasing the light trapping in the photoanode structure. In this paper, these tasks are addressed by introducing a macro-porous silicon (PSi) substrate as photoanode. The effects of the novel photoanode structure on the DSSC performance have been investigated by using energy dispersive X-ray spectroscopy, photocurrent-voltage, UV-visible spectroscopy, reflectance spectroscopy, and electrochemical impedance spectroscopy measurements. The results indicated that bigger porosity percentage of the PSi structure improved the both anti-reflective/light-trapping and dye-loading capacity properties. PSi based DSSCs own higher power conversion efficiency due to its remarkable higher photocurrent, open circuit voltage, and fill factor. Percent porosity of 64%, PSi(III), resulted in nearly 50 percent increment in power conversion efficiency compared with conventional DSSC. This paper showed that PSi can be a good candidate for the improvement of light harvesting efficiency in DSSCs. Furthermore, this study can be considered a valuable reference for more investigations in the design of multifunctional devices which will profit from integrated on-chip solar power.

Fabrication of High Sensitive UV Photodetector Based on n-ZnO Nanowire/n-Porous-Si Heterojunction

M. M. Haji Shahkarami,J. Koohsorkhi,H. Ghafoori Fard 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2017 NANO Vol.12 No.4

In this paper, we have reported the high sensitive UV detector using ZnO nanowires prepared on porous silicon (PS). The aligned naturally doped n-type zinc oxide (ZnO) nanowires were grown on both PS and n-Si(100) substrates to produce isotype heterojunctions using hydrothermal method. The length of the nanowires ranges 3–4 µm and the diameter 150–200 nm. Grown ZnO nanowires on PS substrate has lower reflectivity value compared with Si substrate. The electrical behavior of such devices has been examined at different intensities of UV radiation. The current– voltage curve of the isotype heterojunction shows rectifying behavior in a dark environment. Under UV light, the current was increased by using PS instead of n-Si under reverse bias. The I–V characteristics of the device show a significant rise in the current for low intensity of UV radiation evidencing the high sensitivity of the reported structure. The sensitivity for such devices is obtained, 2.2 x 10 3, 0.47 x 10 3 and 0.21 x 10 3 at UV radiation of 1.5 mW/cm2 intensity at bias voltage of -0.75 V for three proposed structures. The samples have been analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) to investigate their structures and geometries.

Comparison of the effect of hand instruments, an ultrasonic scaler, and an erbium-doped yttrium aluminium garnet laser on root surface roughness of teeth with periodontitis: a profilometer study

Amid, Reza,Kadkhodazadeh, Mahdi,Fekrazad, Reza,Hajizadeh, Farzin,Ghafoori, Arash Korean Academy of Periodontology 2013 Journal of Periodontal & Implant Science Vol.43 No.2

Purpose: The present study aimed to measure root surface roughness in teeth with periodontitis by a profilometer following root planning with ultrasonic and hand instruments with and without erbium-doped yttrium aluminium garnet (Er:YAG) laser irradiation. Methods: Sixty single-rooted maxillary and mandibular teeth, extracted because of periodontal disease, were collected. The crowns and apices of the roots were cut off using a diamond bur and water coolant. The specimens were mounted in an acrylic resin block such that a plain root surface was accessible. After primary evaluation and setting a baseline, the samples were divided into 4 groups. In group 1, the samples were root planned using a manual curette. The group 2 samples were prepared with an ultrasonic scaler. In group 3, after scaling with hand instrumentation, the roots were treated with a Smart 1240D plus Er:YAG laser and in group 4, the roots were prepared with ultrasonic scaler and subsequently treated with an Er:YAG laser. Root surface roughness was then measured by a profilometer (MahrSurf M300+RD18C system) under controlled laboratory conditions at a temperature of $25^{\circ}C$ and 41% humidity. The data were analyzed statistically using analysis of variance and a t-test (P<0.05). Results: Significant differences were detected in terms of surface roughness and surface distortion before and after treatment. The average reduction of the surface roughness after treatment in groups 1, 2, 3, and 4 was 1.89, 1.88, 1.40, and 1.52, respectively. These findings revealed no significant differences among the four groups. Conclusions: An Er:YAG laser as an adjunct to traditional scaling and root planning reduces root surface roughness. However, the surface ultrastructure is more irregular than when using conventional methods.

Comparison of the effect of hand instruments, an ultrasonic scaler, and an erbium-doped yttrium aluminium garnet laser on root surface roughness of teeth with periodontitis: a profilometer study

Reza Amid,Mahdi Kadkhodazadeh,Reza Fekrazad,Farzin Hajizadeh,Arash Ghafoori 대한치주과학회 2013 Journal of Periodontal & Implant Science Vol.43 No.2

Purpose: The present study aimed to measure root surface roughness in teeth with periodontitis by a profilometer following root planning with ultrasonic and hand instruments with and without erbium-doped yttrium aluminium garnet (Er:YAG) laser irradiation. Methods: Sixty single-rooted maxillary and mandibular teeth, extracted because of periodontal disease, were collected. The crowns and apices of the roots were cut off using a diamond bur and water coolant. The specimens were mounted in an acrylic resin block such that a plain root surface was accessible. After primary evaluation and setting a baseline, the samples were divided into 4 groups. In group 1, the samples were root planned using a manual curette. The group 2 samples were prepared with an ultrasonic scaler. In group 3, after scaling with hand instrumentation, the roots were treated with a Smart 1240D plus Er:YAG laser and in group 4, the roots were prepared with ultrasonic scaler and subsequently treated with an Er:YAG laser. Root surface roughness was then measured by a profilometer (MahrSurf M300+RD18C system) under controlled laboratory conditions at a temperature of 25°C and 41% humidity. The data were analyzed statistically using analysis of variance and a t-test (P<0.05). Results: Significant differences were detected in terms of surface roughness and surface distortion before and after treatment. The average reduction of the surface roughness after treatment in groups 1, 2, 3, and 4 was 1.89, 1.88, 1.40, and 1.52, respectively. These findings revealed no significant differences among the four groups. Conclusions: An Er:YAG laser as an adjunct to traditional scaling and root planning reduces root surface roughness. However,the surface ultrastructure is more irregular than when using conventional methods.

Pregnancy outcomes following the administration of high doses of dexamethasone in early pregnancy

Ahmadabad, Hasan Namdar,Jafari, Sabah Kayvan,Firizi, Maryam Nezafat,Abbaspour, Ali Reza,Gharib, Fahime Ghafoori,Ghobadi, Yusef,Gholizadeh, Samira The Korean Society for Reproductive Medicine 2016 Clinical and Experimental Reproductive Medicine Vol.43 No.1

Objective: In the present study, we aimed to evaluate the effects of high doses of dexamethasone (DEX) in early pregnancy on pregnancy outcomes. Methods: Pregnant BALB/c mice were treated with high-dose DEX in the experimental group or saline in the control group on gestational days (GDs) 0.5 to 4.5. Pregnant mice were sacrificed on GDs 7.5, 13.5, or 18.5 and their peripheral blood, placentas, fetuses, and uterine tissue were collected. Decidual and placenta cell supernatants were examined to evaluate the effect of DEX on the proliferation of mononuclear cells, the quantity of uterine macrophages and uterine natural killer (uNK) cells, and levels of progesterone and $17{\beta}-estradiol$, as determined by an 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide assay, immunohistochemistry, and enzyme-linked immunosorbent assay, respectively. We also were measured fetal and placental growth parameters on GD 18.5. Results: We found that high doses of DEX were associated with an increased abortion rate, enhancement of the immunosuppressive effect of the decidua, alterations in placental growth parameters, decreased progesterone and $17{\beta}-estradiol$ levels, and a reduced frequency of macrophages and uNK cells. Conclusion: Our data suggest that the high-dose administration of DEX during early pregnancy negatively affected pregnancy outcomes.