금속폼 DPF의 Clean Filter 성능에 관한 연구

Khai Nguyen(Khai Nguyen),권오채(Oh Chae Kwon),성낙원(Nakwon Sung),조규백(Gyubaek Cho),오권오(Kwonoh Oh),이의성(Euisung Lee) 한국자동차공학회 2005 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2005 No.11_1

Pressure drops in metallic foam diesel particulate filters (DPFs) were experimentally and computationally studied in order to understand effects of various design parameters on the fundamental clean filter performance. Axial type filters of Nickel-based super alloy (Inconel) foam, which is a new valuable medium for DPFs due to lower cost, higher temperature corrosion, light-weight. ductility and design flexibility compared to conventional honeycomb wall-flow monoliths, were considered for volume flow rates of 500 to 3000 1/min, filter thickness of 25 to 50 ㎜, pore size of 450 to 600 ㎛, and inlet cone angles of 0 to 50. Predicted and measured pressure drops for the various conditions agreed well each other, indicating that the present modeling using a 3-dimensional CFD code combined with a porous media model can provide reliable predictions.

Low-Complexity Block Diagonalization Precoder Hardware Implementation for MU-MIMO 4×4

Khai, Lam Duc The Korea Institute of Information and Commucation 2019 Journal of information and communication convergen Vol.17 No.1

In this paper, we present the block diagonalization (BD) algorithm for the multiple-user multiple input multiple output (MU-MIMO) $4{\times}4$ system using specific purpose processor (SPP) hardware. Our objective is to improve the single-user MIMO (SU-MIMO) system using the MU-MIMO technology, which is remarkably fast and allows more users to connect simultaneously. To that end, our MU-MIMO precoder uses the BD algorithm to ensure signal integrity when connecting multiple users; but remains accurate and stable. However, a precoder that uses the BD algorithm is computationally complex; therefore, we use an SPP with special functions designed to compute the BD algorithm. The implementation test results show that our SPP computes the BD algorithm faster than the software solution.

Dyeing of Silk with Natural Lac Dye from Laccifer lacca Kerr. and Evaluation of Antibacterial and UV-Protective Properties

Khai Ly Do,Miao Su,Asim Mushtaq,Feng Zhao 한국섬유공학회 2023 Fibers and polymers Vol.24 No.8

Insect-based colorants have been utilized for textile dyeing since antiquity due to their color variation and easy availability. In the past few years, the ancient sources of colorants have gained both academic and industrial importance due to the increasing global interest in environmentally friendly and safe products. The lac dye, extracted from lac insect (Laccifer lacca Kerr.), is the main object of this study, focusing on its efficacy in coloration and antibacterial and ultraviolet (UV)-protective functionalization of silk. The anthraquinone components of the dye extract were clarified using Fourier transform infrared spectroscopy (FTIR) and UV–visible spectroscopy (UV–Vis). Besides, the highest color yield of the dye extract was obtained with a material to liquor ratio of 1:10, extraction time of 120 min, extraction temperature of 80 ℃, and pH 7. For the further enhancement of the dyeability of silk, chitosan biopolymer was used as a natural mordant, while alum and copper were used as metallic mordants in the dyeing process. Experimental results indicated that the dyed silk samples had good fastness against washing, rubbing, and lighting. Furthermore, the mordanted–dyed silk presented remarkable bacterial inhibition up to 91.90 and 71.94% against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), respectively, as well as excellent UV-protective properties with UV blockage percentages up to 99.2 and 99.6% for UV-A and UV-B rays, individually. The findings of this study specified the potential of an insect-based colorant as a functional textile dye to replace synthetic dyes and chemical agents.

EFFECTS OF SPLIT INJECTION AND OXYGEN-ENRICHED AIR ON SOOT EMISSIONS IN A DIESEL ENGINE

Khai Nguyen,Nakwon Sung,Sangsu Lee 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11

Effects of split injection and oxygen-enriched air on soot emissions in a DI diesel engine were studied by the KIVA-3V code. When split injection is applied, the second injection of fuel into a cylinder results in two separate stoichiometric zones which increases soot oxidation. As a result, soot emissions are decreased with split injection. When oxygenenriched air is applied together with split injection, higher concentration of oxygen helps secondary combustion which results in a higher temperature in the cylinder. The increased temperature promotes growth reaction of acetylene with soot but doesn’t improve the acetylene formation during the second injection of fuel. As more acetylene is consumed in the growth reaction of acetylene, the net acetylene mass in the cylinder is decreased, which leads to a decrease of soot formation. With an increase of soot oxidation caused by split injection, the soot emissions are decreased significantly. However, to avoid excessive NOx emissions with increased oxygen concentration, the level of oxygen concentration should be lower than 22% in volume.

NO₂ gas sensing based on graphene synthesized via chemical reduction process of exfoliated graphene oxide

Khai, Tran Van,Prachuporn, Maneeratanasarn,Shim, Kwang-Bo The Korea Association of Crystal Growth 2012 韓國結晶成長學會誌 Vol.22 No.2

Single and few-layer graphene nanosheets (GNs) have successfully synthesized by a modified Hummer's method followed by chemical reduction of exfoliated graphene oxide (GO) in the presence of hydrazine monohydrate. GO and GNs were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), X-ray diffractions (XRD), Raman spectroscopy, Transmission electron microscopy (TEM), Atomic force microscopy (AFM), Optical microscopy (OM) and by electrical conductivity measurements. The result showed that electrical conductivity of GNs was significantly improved, from $4.2{\times}10^{-4}$ S/m for GO to 12 S/m for GNs, possibly due to the removal of oxygen-containing functional group during chemical reduction. In addition, the $NO_2$ gas sensing characteristics of GNs are also discussed.

Enhanced Production of 1-Deoxynojirimycin in Bacillus subtilis subsp. inaquosorum by Random Mutagenesis and Culture Optimization

Khai Ngoc Nguyen,김윤아,Sawarot Maibunkaew,박지수,Mien Thi Nguyen,오두병,권오석 한국생물공학회 2021 Biotechnology and Bioprocess Engineering Vol.26 No.2

1-Deoxynojirimycin (DNJ) is a potent inhibitor of α-glucosidase having antidiabetic and antiviral activities. In the present study, DNJ production by Bacillus subtilis subsp. inaquosorum KCTC 13429 (B. subtilis IWT) was confirmed and a mutant B. subtilis I.247 strain showing 52% increased DNJ production than wild-type strain after cultivation in 5% defatted soybean meal (DFS) for five days was isolated by UV random mutagenesis. The optimum culture conditions to maximize DNJ production by B. subtilis I.247 was predicted using response surface methodology to cultivate in medium containing 3.4% sorbitol and 2.4% yeast extract as carbon and nitrogen sources, respectively, at a temperature of 32ºC. Under these conditions B. subtilis I.247 was able to produce 359 mg/L after five days of cultivation. Furthermore, when the B. subtilis I.247 transformant harboring a vector expressing a gabT1-yktc1- gutB1 DNJ biosynthetic gene cluster was cultured under the optimized condition, DNJ production was increased to 773 mg/L, representing a level 6.2-fold higher than that of the wild-type strain cultured in 5% DFS for five days.

Leaking Thoracic Aorta Aneurysm Causing Pleural Effusion: A Potential Disaster

( Khai Lip Ng ),( Hema Yamini Devi A ),( P Yamarmuty ),( Kunji Kannan A/l Sivaraman Kannan ) 대한결핵 및 호흡기학회 2021 대한결핵 및 호흡기학회 추계학술대회 초록집 Vol.129 No.-

Introduction Thoracentesis is the first step in diagnosing a unilateral pleural effusion. Although malignancy remains the most common cause of a hemoserous effusion, we must be aware of other causes such as uremia, pulmonary infarction, post cardiac injury syndrome etc. We report a rare case of leaking thoracic aortic aneurysm masquerading as a unilateral hemoserous pleural effusion. Case Report A 79-year-old female with underlying hypertension, dyslipidemia and chronic kidney disease presented with a 2-weeks history of cough and dyspnea. She also reported a weight loss of 5 kilograms in 1 month. A Chest X-Ray (CXR) on presentation revealed a large left pleural effusion. She has exudative effusion based on Light's criteria. pleural fluid culture and cytology was negative. As her main differential diagnosis was malignancy, she was subjected to pleuroscopy to obtain a tissue diagnosis. During pleuroscopy, 1 liter of hemoserous fluid was drained. Apart from thickened parietal pleura, a large cystic mass was seen adhered to the parietal pleura posteriorly. Biopsies were taken from the parietal pleura and decision was made not to biopsy or aspirate the cystic mass during pleuroscopy. Computed tomography of the thorax done few weeks later showed a large thoracic aorta aneurysm with multiple penetrating atherosclerotic ulcers and mural thrombus. There was no pleural or lung mass detected. Patient was counseled for surgical repair but opted for conservative management. Discussion and conclusion Leaking thoracic aneurysm is an uncommon but potentially dangerous cause of hemoserous pleural effusion. A blind thoracentesis or biopsy of the cystic mass during pleuroscopy would have led to rupture of the aneurysm. Depending on the clinical context, it is safer to obtain a CT thorax prior to pleuroscopy when dealing with undiagnosed pleural effusion.

Compact Hardware Multiple Input Multiple Output Channel Emulator for Wireless Local Area Network 802.11ac

Khai, Lam Duc,Tien, Tran Van The Korea Institute of Information and Commucation 2020 Journal of information and communication convergen Vol.18 No.1

This paper proposes a fast-processing and low-cost hardware multiple input multiple output (MIMO) channel emulator. The channel emulator is an important component of hardware-based simulation systems. The novelty of this work is the use of sharing and pipelining functions to reduce hardware resource utilization while maintaining a high sample rate. In our proposed emulator, the samples are created sequentially and interpolated to ensure the sample rate is equal to the base band rate. The proposed 4 × 4 MIMO requires low-cost hardware resource so that it can be implemented on a single field-programmable gate array (FPGA) chip. An implementation on Xilinx Virtex-7 VX980T was found to occupy 10.47% of the available configurable slice registers and 12.58% of the FPGA's slice lookup tables. The maximum frequency of the proposed emulator is 758.064 MHz, so up to 560 different paths can be processed simultaneously to generate 560 × 758 million × 2 × 32 bit complex-valued fading samples per second.

High-quality ZnO nanowire arrays directly synthesized from Zn vapor deposition without catalyst

Khai, Tran Van,Prachuporn, Maneeratanasarn,Choi, Bong-Geun,Kim, Hyoun-Woo,So, Dae-Sup,Lee, Joon-Woo,Park, No-Hyung,Huh, Hoon,Tung, Ngo Trinh,Ham, Heon,Shim, Kwang-Bo The Korea Association of Crystal Growth 2011 韓國結晶成長學會誌 Vol.21 No.4

Vertically well-aligned ZnO nanowire (NW) arrays were synthesized directly on GaN/sapphire and Si substrate from Zn vapor deposition without catalysts. Experimental results showed that the number density, diameter, crystallinity and degree of the alignment of ZnO NWs depended strongly on both the substrate position and kind of the substrates used for the growth. The photoluminescence (PL) characteristics of the grown ZnO NW arrays exhibit a strong and sharp ultraviolet (UV) emission at 379 nm and a broad weak emission in the visible range, indicating that the obtained ZnO NWs have a high crystal quality with excellent optical properties. The as-grown ZnO NWs were characterized by using scanning electron microscopy (SEM), high resolution transmission electronic microscopy (HR-TEM), and X-ray diffraction (XRD).

Successful Treatment of Excessive Dynamic Airway Collapse with Noninvasive Positive Pressure Ventilation - A Case Report

( Khai Lip Ng ),( Nai Chien Huan ),( Mona Zaria Nasaruddin ),( Noorul Afidza Muhammad ),( Ummi Nadira Daut ),( Jamalul Azizi Abdul Rahaman ) 대한결핵 및 호흡기학회 2021 대한결핵 및 호흡기학회 추계학술대회 초록집 Vol.129 No.-

Introduction Excessive central airway collapse (ECAC) can present as unexplained dyspnea, wheezing or stridor. ECAC can easily be misdiagnosed as bronchial asthma, COPD and heart failure. ECAC can occur as a result of tracheobronchomalacia or excessive dynamic airway collapse (EDAC).There are various Methods of diagnosis and treatment of ECAC but it has to be tailored according patient’s circumstances. Case Report We present a 75-year-old lady with multiple comorbidities including vascular dementia who was brought in by her daughter after she noticed that her mother had wheezing, shortness of breath and reduced effort tolerance for the past 2 months. Her symptoms were worse on exertion and during sleep. She was given bronchodilator without any improvements. She was overweight and her STOPBANG score of 6. CT thorax showed posterior indentation of mid distal trachea with significant luminal narrowing. Unfortunately, she couldn’t comply to dynamic chest CT test due to vascular dementia. Flexible bronchoscopy done under conscious sedation confirmed almost total occlusion of both left and right main bronchus together with narrowing of tracheal diameter of more than 80% that were present only during expiration. Partial sleep study done showed evidence of OSA with an AHI of 58/hour, and a lowest oxygen saturation at 51%. Both her EDAC and OSA was treated successfully with a CPAP machine. On subsequent follow up, her daughter reported that her symptoms has resolved together with improvements in her effort tolerance. Discussion and Conclusion There are various Methods to diagnose and manage a patient with EDAC, some of which are invasive and thus are risky for elderly patients with multiple co-morbidities. Choices of investigations and treatment for this condition need to be tailored according to patient’s need and circumstances. CPAP in this case was given without real time titration under flexible bronchoscopy with success in her case.