Growth Characteristics of a Pyruvate Decarboxylase Mutant Strain of Zymomonas mobilis

Xun Zhao(순 자오),Peter L. Rogers(피터 로저스),Eilhann E. Kwon(권일한),Sang Chul Jeong(정상철),Young Jae Jeon(전용재) 한국생명과학회 2015 생명과학회지 Vol.25 No.11

에탄올 생산 세균 Zymomonas mobilis에서 에탄올 생산 경로의 핵심으로 작용하는 효소인, pyruvate decarboxylase (pdc) 유전자의 불활성 실험을 통해, PDC 활성이 50% 감소된 PDC 활성 변형균주가 분리되었다. 이러한 균주들의 에탄올 탄소대사 흐름이 고부가가치 화합물인 피루브산, 숙신산 및 젖산 등으로 전환되는지를 발효실험을 통해 평가하였다. 하지만 pdc의 발현을 중지시키기 위해 cat-삽입형-pdc와 pdc-결손형 아형 유전자를 전기 천공법을 이용해 야생형 균주 ZM4의 염색체에 이식하기 위한 다수의 시도에도 불구하고, 이러한 방법을 통해 분리된 균주들은 대부분 부분적 유전자 불활성 특성을 보였으며, PDC 활성이 완전히 손실된 삭제 돌연변이 균주를 획득할 수는 없었다. PDC활성이 변형된 돌연변이 균주의 발효 실험에서, 야생형 균주와 비교 시 감소된 PDC효소 활성의 변화로 인해 기질 흡수율과 에탄올 생산율이 감소되어 피루브산 생산이 약 2.5 g l-1 정도로 증가함을 확인하였으나, 젖산과 숙신산의 생산에 현저한 농도 변화를 보이지 못했다. 이러한 결과는 Z. mobilis의 산화환원 에너지가 PDC 효소 활성에 의한 에탄올 생산 경로에 전적으로 의존하여 발생한다는 것을 암시하였다. 상기 결과를 토대로 pdc 유전자의 완전한 불활성 유도와 산화환원 에너지의 균형은, 젖산 생산을 위한 lactate dehydrogenase, 숙신산 생산을 위한 pyruvate dehydrogenase와 malic enzyme과 같은 효소의 활성 증가를 통해, 세포내 NAD와 NADH 농도의 산화환원 균형이 이루어져야 발생할 수 있음을 시사하였다. Studies of the inactivation of a gene encoding pyruvate decarboxylase, pdc, in an ethanol-producing bacterium, Zymomonas mobilis, identified a mutant strain with 50% reduced PDC activity. To evaluate the possibility of a carbon-flux shift from an ethanol pathway toward higher value fermentation products, including pyruvate, succinate, and lactate, fermentation studies were carried out. Despite attempts to silence pdc expression in the wild-type strain ZM4 using cat-inserted pdc and pdc-deleted homologs by electroporation, the strain isolated showed partial gene activation. Fermentation experiments with the PDC mutant strain showed that the reduced expression level of PDC activity resulted in decreased rates of substrate uptake and ethanol production, together with increased pyruvate accumulation of 2.5 g l-1, although lactate and succinate concentrations were not significantly enhanced in these modified strains. Despite numerous attempts, no strains were isolated in which complete pdc inactivation occurred. This result indicates that the ethanol fermentation pathway of this bacterium is totally dependent on the activity of the PDC enzyme. To ensure a redox balance of intracellular NAD and NADH levels, other enzymes, such as lactate dehydrogenase for lactate, and enzymes involved in the production of succinic acid, such as pyruvate dehydrogenase (PDH) and malic enzymes, may be needed for their increased end-product production.

Numerical Simulation on Characteristics of Debris Clouds Produced by Conical Projectiles Hypervelocity Impact on Thin Plates

Xun Liu,Fangfang Gai,Su Cheng 보안공학연구지원센터 2015 International Journal of Hybrid Information Techno Vol.8 No.6

With the unceasing development of space activity, the total number of space debris is ever increasing, which greatly threatens orbiting space vehicles. To research the characteristics of debris clouds which are produced by conical projectiles hypervelocity impact on thin plates, SPH (smoothed particle hydrodynamics) methods in AUTODYN is used. Characteristics of debris cloud produced by conical projectiles with different ratio between length and diameter hypervelocity impact on thin plates are investigated with the same mass and velocity by numerical simulation. Effects of the ratio between length and diameter of the projectiles affecting on the form of debris cloud, axial location of debris clouds, radial extension of debris cloud and tip particle velocity of debris cloud are obtained. It is shown that the degree of fragmentation of the projectiles and debris cloud diffusion is changed with the velocity of the projectiles, the ratio between length and diameter and the impacting direction. The increasing ratio between length and diameter of projectiles can reduce the damage of thin plates but rise the damage of the wall of spacecraft by the debris clouds impact on with the same mass and velocity.

차분 선부호화 구조를 적용한 LTE-A 상향링크 시스템의 성능 분석

Xun Li,박노윤(Noe Yoon Park),김영주(Young Ju Kim) 大韓電子工學會 2012 電子工學會論文誌-TC (Telecommunications) Vol.49 No.5

LTE 시스템에서는 폐회로 기반의 다중 안테나 기술이 적용되었으며, 차분 코드북을 비롯한 다양한 다중 안테나 기반의 선부호화 기술들이 향상된 LTE (LTE-Advanced) 시스템의 요구조건을 만족시키기 위해 제안되었다. 차분 코드북 설계와 관련하여 이전에 연구된 내용은 준 대각(quasi-diagonal) 단위 행렬 및 구면 캡(spherical cap)에 중점을 두었지만, 이는 동 이득 성질을 만족하지 못한다. 동 이득 성질은 특히 상향 링크에서 첨두 전력 대 평균 전력비 (PAPR)에 상당한 영향을 미치므로 매우 중요하다. 본 논문에서는 각 송신 안테나에 동 이득을 유지하는 성질을 이용한 새로운 차분 코드북을 상향 링크 기반 차분 선부호화 시스템에 적용하고, 이를 통해 비트 오류율(BER)과 첨두 전력 대 평균 전력비를 분석하였다. 특히, 송신기의 비선형 증폭기를 고려하여 다양한 차분 선부호화 기법들의 성능을 분석하였다. 모의 실험을 통해 선형 증폭기를 고려할 경우 기존에 제안된 차분 코드북이 우수한 성능을 보이지만, 비선형 증폭기를 고려할 경우에는 제안하는 차분 코드북의 우수함을 증명하였다. The closed-loop multiple-input multiple-output (MIMO) system has been adopted by long term evolution (LTE) system. Many techniques are proposed to enhance the transmission of LTE's advanced version to meet the increasing requirement, in which differential codebook gains a lot of interest. Previous researches on designing differential codebooks focused on quasi-diagonal unitary matrix which cannot guarantee the equal gain property. The equal gain property is very important to uplink because the performance of uplink is very sensitive to the peak-to-average power ratio (PAPR). In this paper, we derive the analytical expression of average bit error rate and PAPR for differential precoding MIMO system. Using the analytical results, we investigate the performances of several differential precoding schemes considering non-linear amplifier at the transmitter. Some selected simulation results indicate that the conventional differential precoding schemes have good performances without the consideration of non-linear amplifier. While considering non-linear amplifier, the proposed differential codebook outperforms other differential precoding schemes because it maintains the equal gain per transmit antenna.

Numerical investigation of the effect of surface roughness on the flow coefficient of an eccentric butterfly valve

Xun Sun,김현수,양승덕,김철규,윤준용 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.6

Butterfly valves are used widely as flow controllers in many industrial applications. In order to design and select an appropriate valvefor a particular application, it is important to predict correctly its flow coefficient. The flow coefficient of a valve can be affected by anumber of factors. This study presents a numerical investigation of the effect of friction on the flow coefficient of a triple eccentric butterflyvalve with various valve opening degrees. Since the Reynolds number and cavitation can affect the flow coefficient under certainconditions, these effects are discussed and analyzed based on previously reported experimental data before studying the effects of friction. Under the test conditions recommended in IEC 60534-2-3, it is found that the effects of the Reynolds number and cavitation are quitesmall and can be ignored. The flow coefficients obtained from numerical simulations that take into account friction are found to be ingood agreement with the experimentally determined ones. The differences in the flow coefficients obtained from numerical simulationsthat consider friction and those that ignore it are discussed. There is a maximum difference of 17 % for a fully open valve. The resultsshow that increases in the roughness height significantly increase the frictional pressure drop. The effect of the roughness height on thefrictional pressure drop and total pressure drop can be fitted well using fitting functions for fixed opening degree. It is found that the effectof the roughness can cause the determined flow coefficient to be different from the actual value. Thus, the measured flow coefficientsand pressure drops for such valves can be determined with accuracy through experimental techniques and numerical simulationsthat account for the effect of roughness.

Effects of coolant temperature on particulate deposition and cooling efficiency of EGR coolers

Xun Zhang,Wei Tian,Jinhui Li,Zhiqiang Han,Xueshun Wu 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.7

Porous fouling layers formed by particulate deposition in the EGR cooler tubes degrade the cooling efficiency of the EGR coolers. This research has investigated the changes of the particulate concentration under varied coolant temperature conditions and the effects of the coolant temperature on the cooling efficiency of the cooler tubes by measuring the particulate concentration and size distribution at the cooler inlet and outlet. The experiment results indicate that for the particulates of different sizes, the thermophoretic force acting on them and the regeneration vary under the same experiment conditions, presenting distinctive effects on the particulate concentration distribution in the exhaust gas and causing concentrations of nuclear particulates and aggregated particulates to change, respectively. The mass of fouling layers inside the cooler tubes increases as the coolant temperature decreases. Decreasing the coolant temperature not only increases the quantity of fouling particulates but also forms more particulates of big sizes, causing cooling efficiency of the cooler tube per unit length to decrease with the decrease of coolant temperature and the increase of the tube length.

Learning New Knowledge without influencing the Old in Expert Systems Based on Neural Network

Xun Liang,Ji Hong Du,Shawei Xia,Li Li 대한전자공학회 1994 ICONIP : International Conference On Neural Inform Vol.3 No.2

Construct a Binary Three-Layer Perceptron with Less Memory Size

Xun Liang,Shao Wei Xia,Zhong Ren Liu,Hui Su 대한전자공학회 1994 ICONIP : International Conference On Neural Inform Vol.1 No.3

Robust Digital Watermarking for High-definition Video using Steerable Pyramid Transform, Two Dimensional Fast Fourier Transform and Ensemble Position-based Error Correcting

( Xun Jin ),( Jongweon Kim ) 한국인터넷정보학회 2018 KSII Transactions on Internet and Information Syst Vol.12 No.7

In this paper, we propose a robust blind watermarking scheme for high-definition video. In the embedding process, luminance component of each frame is transformed by 2-dimensional fast Fourier transform (2D FFT). A secret key is used to generate a matrix of random numbers for the security of watermark information. The matrix is transformed by inverse steerable pyramid transform (SPT). We embed the watermark into the low and mid-frequency of 2D FFT coefficients with the transformed matrix. In the extraction process, the 2D FFT coefficients of each frame and the transformed matrix are transformed by SPT respectively, to produce two oriented sub-bands. We extract the watermark from each frame by cross-correlating two oriented sub-bands. If a video is degraded by some attacks, the watermarks of frames contain some errors. Thus, we use an ensemble position-based error correcting algorithm to estimate the errors and correct them. The experimental results show that the proposed watermarking algorithm is imperceptible and moreover is robust against various attacks. After embedding 64 bits of watermark into each frame, the average peak signal-to-noise ratio between original frames and embedded frames is 45.7 dB.

Optimizing the Novel Formulation of Liposome-Polycation-DNA Complexes (LPD) by Central Composite Design

Xun Sun,Zhirong Zhang 대한약학회 2004 Archives of Pharmacal Research Vol.27 No.7

LPD vectors are non-viral vehicles for gene delivery comprised of polycation-condensed plasmid DNA and liposomes. Here, we described a novel anionic LPD formulation containing protamine- DNA complexes and pH sensitive liposomes composed of DOPE and cholesteryl hemisuccinate (Chems). Central composite design (CCD) was employed to optimize stable LPD formulation with small particle size. A three factor, five-level CCD design was used for the optimization procedure, with the weight ratio of protamine/DNA (X1), the weight ratio of Chems/ DNA (X2) and the molar ratio of Chems/DOPE in the anionic liposomes (X3) as the independent variables. LPD size (Y1) and LPD protection efficiency against nuclease (Y2) were response variables. Zeta potential determination was utilized to define the experimental design region. Based on experimental design, responses for the 15 formulations were obtained. Mathematical equations and response surface plots were used to relate the dependent and independent variables. The mathematical model predicted optimized X1-X3 levels that achieve the desired particle size and the protection efficiency against nuclease. According to these levels, an optimized LPD formulation was prepared, resulting in a particle size of 185.3 nm and protection efficiency of 80.22%.

Optimized Identification Method for Digital Music Pieces in BitTorrent

Xun Jin,Jongweon Kim 보안공학연구지원센터 2015 International Journal of Multimedia and Ubiquitous Vol.10 No.1

In this paper, we propose a methodology for identification of MP3 audio pieces downloaded by BitTorrent client program using cross-correlation of 12 chroma features extracted from audio signal. To prevent illegal distribution of copyrighted audio files from spreading over the internet, the file pieces split by torrent file must be detected as accurately as possible. In order to improve the probability of successfully identifying the audio pieces, we use Peak In Piece Position (PIPP) method which means the maximum peak appeared in a range corresponding to piece position and length is selected to reduce the probability of misidentification. The experimental results show probabilities of successfully identification of the pieces with different piece properties, comparisons between the proposed algorithms and conventional algorithm in terms of precisions and robustness of the proposed algorithms.