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RISS 인기검색어
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- 저자 : Shervin (검색결과 54 건)
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Shervin, Shahab,Oh, Seung Kyu,Park, Hyun Jung,Lee, Keon-Hwa,Asadirad, Mojtaba,Kim, Seung-Hwan,Kim, Jeomoh,Pouladi, Sara,Lee, Sung-Nam,Li, Xiaohang,Kwak, Joon Seop,Ryou, Jae-Hyun Institute of Physics Publishing Ltd. 2018 Journal of Physics. D, Applied Physics Vol.51 No.10
<P>We report a new route to improve quantum efficiencies of AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) using mechanical flexibility of recently developed bendable thin-film structures. Numerical studies show that electronic band structures of AlGaN heterostructures and resulting optical and electrical characteristics of the devices can be significantly modified by external bending through active control of piezoelectric polarization. Internal quantum efficiency is enhanced higher than three times, when the DUV LEDs are moderately bent with concave curvatures. Furthermore, an efficiency droop at high injection currents is mitigated and turn-on voltage of diodes decreases with the same bending condition. The concept of bendable DUV LEDs with a controlled external strain can provide a new path for high-output-power and high-efficiency devices.</P>
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The Supplementary Motor Complex in Parkinson’s Disease
Shervin Rahimpour,Shashank Rajkumar,Mark Hallett 대한파킨슨병및이상운동질환학회 2022 Journal Of Movement Disorders Vol.15 No.1
Parkinson’s disease (PD) is a neurodegenerative disorder characterized by both motor and nonmotor symptoms. Although the basal ganglia is traditionally the primary brain region implicated in this disease process, this limited view ignores the roles of the cortex and cerebellum that are networked with the basal ganglia to support motor and cognitive functions. In particular, recent research has highlighted dysfunction in the supplementary motor complex (SMC) in patients with PD. Using the PubMed and Google Scholar search engines, we identified research articles using keywords pertaining to the involvement of the SMC in action sequencing impairments, temporal processing disturbances, and gait impairment in patients with PD. A review of abstracts and full-text articles was used to identify relevant articles. In this review of 63 articles, we focus on the role of the SMC in PD, highlighting anatomical and functional data to create new perspectives in understanding clinical symptoms and, potentially, new therapeutic targets. The SMC has a nuanced role in the pathophysiology of PD, with both hypo- and hyperactivation associated with various symptoms. Further studies using more standardized patient populations and functional tasks are needed to more clearly elucidate the role of this region in the pathophysiology and treatment of PD.
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Damage detection of 3D printed mold using the surface response to excitation method
Shervin Tashakori,Saman Farhangdoust,Amin Baghalian,Dwayne McDaniel,Ibrahim N. Tansel,Armin Mehrabi 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.75 No.3
The life of conventional steel plastic injection molds is long but manufacturing cost and time are prohibitive for using these molds for producing prototypes of products in limited numbers. Commonly used 3D printers and rapid prototyping methods are capable of directly converting the digital models of three-dimensional solid objects into solid physical parts. Depending on the 3D printer, the final product can be made from different material, such as polymer or metal. Rapid prototyping of parts with the polymeric material is typically cheaper, faster and convenient. However, the life of a polymer mold can be less than a hundred parts. Failure of a polymeric mold during the injection molding process can result in serious safety issues considering very large forces and temperatures are involved. In this study, the feasibility of the inspection of 3D printed molds with the surface response to excitation (SuRE) method was investigated. The SuRE method was originally developed for structural health monitoring and load monitoring in thin-walled plate-like structures. In this study, first, the SuRE method was used to evaluate if the variation of the strain could be monitored when loads were applied to the center of the 3D printed molds. After the successful results were obtained, the SuRE method was used to monitor the artifact (artificial damage) created at the 3D printed mold. The results showed that the SuRE method is a cost effective and robust approach for monitoring the condition of the 3D printed molds.
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The effect of material and flushing water type on urine scale formation
Hashemi, Shervin,Han, Mooyoung,Kim, Tschungil IWA Publishing 2015 Water Science & Technology Vol.72 No.11
<P>One of the important challenges with current sanitation practices is pipe blockage in urinals caused by urine scale formation. Urinal material and flushing water type are the two most important factors affecting scale formation. This paper examines the scale formation process on different materials which are commonly used in urinal manufacturing and exposed to different urine-based aqua cultures. This study shows that urine scale formation is the greatest for carbon steel material, and the least for PVC. Additionally, material exposure to the urine-rainwater mixture resulted in the smallest amount of scale formation. Based on these results, two new methods for improving sanitation practices are proposed: (1) using PVC as production material for urinals and pipelines; and (2) using rainwater for flushing systems.</P>
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Identification of urine scale problems in urinals and the solution using rainwater
Hashemi, Shervin,Han, Mooyoung,Kim, Tschungil IWA Publishing 2015 Journal of water, sanitation, and hygiene for deve Vol.5 No.2
<P>Water-saving urinals, such as waterless and low-flush urinals, have a great potential for water conservation by using 0 ∼ 0.8 l/flush compared with ordinary urinals, which use 2 ∼ 4 l/flush. However in some cases, water-saving urinals are not desirable because of technical problems, such as urine scale formation which makes the urinal dirty and blocks pipes. Also, some cultures do not allow the use of waterless urinals because of their notion of cleanliness. In this paper, factors causing urine scale formation have been identified from laboratory tests on pure urine and several types of flushing water. Some meaningful solutions for managing and solving urine scale problems have been suggested. In particular, the results show that mixing urine with seawater or high salinity groundwater will increase the potential of urine scale formation by increasing total dissolved solids (TDS) and pH. However, using rainwater for urinal flushing can significantly reduce the TDS and pH. These findings could support the use of water-saving toilets in Islamic societies by ensuring that the cleanliness of urinals can still be achieved.</P>
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Control of urine odor in different sanitation practices and its implication on water saving
Hashemi, Shervin,Han, Mooyoung IWA Publishing 2017 Journal of water, sanitation, and hygiene for deve Vol.7 No.1
<P>To avoid odor in sanitation systems, urine is usually diluted with water (flushed), which leads to high water consumption. The smell may remain in sanitation systems if the systems are not well managed, or if the urine is flushed with insufficient amounts of water. In this study, using the standard threshold odor number (TON) measurement as an indicator of urine odor, the effects of the pH and temperature of the diluting water regarding the amount of water:urine dilution ratio were studied. The effects of temperature and pH of the diluting water on TON when the dilution ratio was constant were investigated. Results show that lowering the pH and temperature of the diluting water can reduce the minimum dilution ratio needed to achieve TON = 0. At constant dilution ratio, reducing pH seemed to be more efficient, sustainable, and economical in comparison to adjusting the temperature of the diluting water. It was found that, based on the specific pH and temperature of the diluting water, there is a minimum dilution ratio required to avoid urine odor. Therefore, in sanitation systems, the amount of flushing should be adjusted based on the characteristics of the flushing water as well as on the amount of urination.</P>
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Effect of geometrical configuration on seismic behavior of GFRP-RC beam-column joints
Ghomia, Shervin K.,El-Salakawy, Ehab Techno-Press 2020 Advances in concrete construction Vol.9 No.3
Glass fiber-reinforced polymer (GFRP) bars have been introduced as an effective alternative for the conventional steel reinforcement in concrete structures to mitigate the costly consequences of steel corrosion. However, despite the superior performance of these composite materials in terms of corrosion, the effect of replacing steel reinforcement with GFRP on the seismic performance of concrete structures is not fully covered yet. To address some of the key parameters in the seismic behavior of GFRP-reinforced concrete (RC) structures, two full-scale beam-column joints reinforced with GFRP bars and stirrups were constructed and tested under two phases of loading, each simulating a severe ground motion. The objective was to investigate the effect of damage due to earthquakes on the service and ultimate behavior of GFRP-RC moment-resisting frames. The main parameters under investigation were geometrical configuration (interior or exterior beam-column joint) and joint shear stress. The performance of the specimens was measured in terms of lateral load-drift response, energy dissipation, mode of failure and stress distribution. Moreover, the effect of concrete damage due to earthquake loading on the performance of beam-column joints under service loading was investigated and a modified damage index was proposed to quantify the magnitude of damage in GFRP-RC beam-column joints under dynamic loading. Test results indicated that the geometrical configuration significantly affects the level of concrete damage and energy dissipation. Moreover, the level of residual damage in GFRP-RC beam-column joints after undergoing lateral displacements was related to reinforcement ratio of the main beams.
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