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Kamran Tavakol,Meysam Bayat,Bahram Nadi,Rassoul Ajalloeian 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.9
Many available stabilisers and reinforcements have been used to enhance the mechanical characteristics of silica sand. So far, many studies have been carried out to understand the influence of various old and new additives such as natural and synthetic fibres or traditional stabilisers on the mechanical characteristics of silica sands. However, there is minimal study on the mechanical characteristics of stabilised or reinforced calcareous sands. The main focus of the current study was to evaluate the influences of relative density (Dr), Portland cement (C) content, rice husk ash (RHA) content and synthetic polypropylene fibre (PPF) content on the mechanical characteristics of a calcareous sand, which were: Dr [30%, 80%], C [0, 3%, 5%, 7.5%], RHA [0, 7%, 7.5%, 10%], and PPF [0%, 1%]. For this purpose, direct shear tests have been conducted on treated calcareous sand subjecting to three curing times (7, 14, and 28 days). The test results indicate that adding cement, rice husk ash and polypropylene fibre increases the shear strength and reduces the volumetric strain under shear loading. Thespecimens containing 7.5% cement and 7.5% RHA generally exhibited the highest shear strength and the lowest volumetric strain. Relative density, cement content, RHA content, fibre content and curing time have more important effects on the cohesion than the friction angle of treated specimens.
Nazari, Tavakol,Khazaeinezhad, Reza,Kassani, Sahar Hosseinzadeh,Jung, Woohyun,Shin, Inchul,Kang, Dooeui,Oh, Kyunghwan Optical Society of America 2014 Optics express Vol.22 No.22
<P>Enhanced optical transmission (EOT) and its polarization extinction ratio (PER) of a sub-wavelength polygonal aperture surrounded by polygonal grooves are investigated numerically by finite difference time domain (FDTD) method. Effects of light polarization on EOT were analyzed and compared for four types of geometrical structures: triangle aperture surrounded by triangle grooves, square aperture surrounded by square grooves, rhombus aperture surrounded by rhombus grooves, and pentagon aperture surrounded by pentagon grooves. The effects of relative angles between the symmetry axes of polygons and the light polarization were thoroughly analyzed. Among these plasmonic polygonal bull's eye structures, the rhombus showed a maximum EOT several times larger than others. In contrast to the prior normal incident condition, we further analyzed the impacts of the incident angle and we found a wideband tunability of EOT wavelengths.</P>
Nazari, Tavakol,Khazaeinezhad, Reza,Jung, Woohyun,Joo, Boram,Kong, Byung-Joo,Oh, Kyunghwan Optical Society of America 2015 Optics express Vol.23 No.14
<P>Dual resonant bands in UV and the visible range were simultaneously observed in the enhanced optical transmission (EOT) through star-shaped plasmonic structures. EOTs through four types of polygonal bull's eyes with a star aperture surrounded by the concentric star grooves were analyzed and compared for 3, 4, 5, and 6 corners, using finite difference time domain (FDTD) method. In contrast to plasmonic resonances in the visible range, the UV-band resonance intensity was found to scale with the number of corners, which is related with higher order multipole interactions. Spectral positions and relative intensities of the dual resonances were analyzed parametrically to find optimal conditions to maximize EOT in UV-visible dual bands.</P>
Mergers and Acquisitions and Greenfield Foreign Direct Investment in Selected ASEAN Countries
Alireza Tavakol Moghadam,Nur Syazwani Mazlan,Lee Chin,Saifuzzaman Ibrahim 세종대학교 경제통합연구소 2019 Journal of Economic Integration Vol.34 No.4
Multinational enterprises undertake Foreign Direct Investments mainly through two different modes: Mergers and Acquisitions and greenfield investments. In the sizable empirical literature that examines the determinants of Foreign Direct Investments, very few studies investigated the determinants of these modes. This article empirically analyzes the extent to which determinants such as market size, exchange rate, and market openness in six selected ASEAN countries (ASEAN-6) influence the choice of one entry mode of Foreign Direct Investments over the other. A robust relationship between market size and exchange rate with greenfield inflows rather than Mergers and Acquisitions sales is found. Additionally, given an increase in market openness, foreign firms prefer Mergers and Acquisitions to greenfield investments. The results also confirm the fire-sale Foreign Direct Investments phenomenon during financial crises.
An investigation on the supersonic ejectors working with mixture of air and steam
Maziar Shafaee,Mohsen Tavakol,Rouzbeh Riazi,Navid Sharifi 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.11
This study evaluated the performance of an ejector using two streams of fluids as suction flow. Three motive flow pressures were consideredwhen investigating ejector performance; the suction flow pressure was assumed to be constant. The suction flow consisted of amixture of air and steam and the mass fraction of air in this mixture varied from 0 to 1. The ejector performance curves were analyzed fordifferent mass fractions of air. The results indicate that variation of the mass fraction of air in the suction flow mixture had a significanteffect on ejector performance. At all motive flow pressures, the ejector entertainment ratio increased as the mass fraction of air in thesuction flow increased. The results also show that the sensitivity of ejector performance to variation in the mass fraction of air in the suctionflow decreases at higher motive flow pressures. An increase in motive flow pressure caused the transition from supersonic to subsonicflow to occur at higher ejector discharge pressures.
Passive Q-Switching of an All-Fiber Laser Using WS <sub>2</sub>-Deposited Optical Fiber Taper
Khazaeinezhad, Reza,Nazari, Tavakol,Hwanseong Jeong,Kyung Jun Park,Byoung Yoon Kim,Dong-Il Yeom,Kyunghwan Oh IEEE 2015 IEEE photonics journal Vol.7 No.5
<P>We demonstrate the passive Q-switching operation of an erbium-doped fiber laser using a few-layer WS<SUB>2</SUB>-based saturable absorber with evanescent field interaction. WS<SUB>2</SUB> flakes have been synthesized via a liquid-phase exfoliation method, and an optical fiber taper was selected as a light-material template that causes to achieve a long interaction length of the evanescent wave. Subsequently, the prepared solution was optically deposited around the 3-mm interaction length of the fabricated optical fiber taper with a 5-μm waist diameter. The proposed Q-switched fiber laser based on the WS<SUB>2</SUB>-deposited fiber taper saturable absorber could generate stable output pulses at 1565 nm, with a pulsewidth ranging from 1.3 to 3 μs and a repetition rate of 33-108 kHz.</P>
Hong, Seongjin,Jung, Woohyun,Nazari, Tavakol,Song, Sanggwon,Kim, Taeoh,Quan, Chai,Oh, Kyunghwan Optical Society of America 2017 Optics letters Vol. No.
<P>We report unique thermo-optical characteristics of DNA-Cetyl tri-methyl ammonium (DNA-CTMA) thin solid film with a large negative thermo-optical coefficient of -3.4 x 10(-4)/degrees C in the temperature range from 20 degrees C to 70 degrees C without any observable thermal hysteresis. By combining this thermo-optic DNA film and fiber optic multimode interference (MMI) device, we experimentally demonstrated a highly sensitive compact temperature sensor with a large spectral shift of 0.15 nm/degrees C. The fiber optic MMI device was a concatenated structure with single-mode fiber (SMF)-coreless silica fiber (CSF)-single mode fiber (SMF) and the DNA-CTMA film was deposited on the CSF. The spectral shifts of the device in experiments were compared with the beam propagation method, which showed a good agreement. (C) 2017 Optical Society of America</P>
Enhancement of Surface Wettability by Intra-Helium Plasma for Liquid Core Fiber Lens
Kassani, Sahar Hosseinzadeh,Khazaeinezhad, Reza,Nazari, Tavakol,Wonho Choe,Kyunghwan Oh IEEE 2014 IEEE photonics technology letters Vol.26 No.20
<P>We generated an atmospheric pressure helium plasma inside a silica hollow optical fiber (HOF) and the surface wettability of the inside wall was flexibly controlled by the plasma intensity. By filling the glycerol into the HOF, we experimentally investigated the surface characteristics by contact angle measurements. Liquid-fiber optic lenses with various numerical apertures were proposed and the light intensity patterns through liquid core lens to the air were investigated numerically.</P>
Compact Hexagonal Liquid Core PCF Package Using a Hollow Optical Fiber
Hwang, Jihyun,Park, Jiyoung,Nazari Baresari, Tavakol,Han, Seung-Ryong,Jhon, Young Min,Oh, Kyunghwan IEEE 2018 Photonics Technology Letters Vol.30 No.8
<P>We proposed and demonstrated a novel method to package liquid-core hexagonal photonic crystal fibers (PCFs) by utilizing a hollow optical fiber (HOF) not only as a liquid delivery tube but also as a light launching pedestal. Compact all-fiber packaging with single mode fiber input and output was experimentally achieved. Various configurations of liquid core PCFs were demonstrated by controlling the inner diameter of HOF and offsets. Based on numerical analyses and light launching experiments, we confirmed that this method could substantially enhance the light–liquid interaction efficiency, structurally prevent liquid evaporation within PCF, and providing a new versatile liquid core PCF device platform.</P>
Liquid core photonic crystal fiber with low-refractive-index liquids for optofluidic applications.
Park, Jiyoung,Kang, Doo-Eui,Paulson, Bjorn,Nazari, Tavakol,Oh, Kyunghwan Optical Society of America 2014 Optics express Vol.22 No.14
<P>A defectless hexagonal air-silica photonic crystal fiber (PCF) structure with its central hole selectively filled by a low-refractive-index liquid is numerically analyzed. Despite the fact that the refractive index of the liquid is significantly lower than that of silica, we found an optimal range of waveguide parameters to ensure light guidance through the liquid core in the fundamental mode, maximizing the light-liquid interaction over a desired wavelength range. Using the vectorial finite element method (FEM), we report detailed parametric studies in terms of the effective index, chromatic dispersion, optical loss, and modal intensity distribution of the liquid core PCFs.</P>