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Distinctive differences in the granulation of saline and non-saline enriched anaerobic ammonia oxidizing(AMX)bacteria

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Journal of Environmental Sciences 2022年第12期34卷 162-173页

作者： Victory Fiifi Dsane Sumin An Younggyun choi Department of Environmental Engineering Chungnam National UniversityDaejeon 305-764Korea Department of Food Process Engineering University of GhanaLegonGhana Department of Environmental&IT Convergence Engineering Chungnam National UniversityDaejeon 305-764Korea

The growing interest in the anaerobic ammonium oxidizing(AMX)process in treating high nitrogen containing wastewaters and a comprehensive study into the granulation mechanism of these bacteria under diverse environmental conditions over the years have been *** this effect,the distinctive differences in saline adapted AMX(S_AMX)and nonsaline adapted AMX(NS_AMX)granules are presented in this *** was observed that substrate utilisation profiles,granule formation mechanism,and pace towards granulation differed marginally for the two adaptation *** different microbial dominant aggregation types aided in splitting the 471 days operated lab-scale SBRs into three distinct *** both reactors,phase III(granules dominant phase)showed the highest average nitrogen removal efficiency of 87.9%±4.8%and 85.6%±3.6%for the S_AMX and NS_AMX processes,*** extracellular polymeric substances(EPS)quantity and major composition determined its role either as a binding agent in granulation or a survival mechanism in saline *** was also observed that granules of the S_AMX reactor were mostly loosely and less condensed aggregates of smaller sub-units and flocs while those of the NS_AMX reactor were compact *** ionic gradient in saline enrichment led to an increased activity of the Na^(+)/K^(+)–ATPase,hence enriched granules produced higher cellular adenosine triphosphate molecules which finally improved the granules active biomass ratio by 32.96%.Microbial community showed that about three to four major known AMX species made up the granules consortia in both *** and expression of functional genes differed for these different species.

关键词： AMX Granulation EPS Enrichment Na^(+)/K^(+)-ATPase

Advanced metal–organic frameworks for aqueous sodium-ion rechargeable batteries

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Journal of Energy Chemistry 2021年第2期30卷 396-406,I0014页

作者： Dongkyu choi Seonguk Lim Dongwook Han School of Nano Convergence Technology Hallym UniversityChuncheon 24252Gangwon-doRepublic of Korea Nano Convergence Technology Center Hallym UniversityChuncheon 24252Gangwon-doRepublic of Korea

Inexpensive and abundant sodium resources make energy storage systems using sodium chemistry promising replacements for typical lithium-ion rechargeable batteries(LIBs).Fortuitously,aqueous sodium-ion rechargeable batteries(ASIBs),which operate in aqueous electrolytes,are cheaper,safer,and more ionically conductive than batteries that operate in conventional organic electrolytes;furthermore,they are suitable for grid-scale energy storage *** electrode materials for storing Na~+ ions in ASIBs,a variety of multifunctional metal-organic frameworks(MOFs) have demonstrated great potential in terms of having porous 3 D crystal structures,compatibility with aqueous solutions,long cycle lives(≥1000 cycles),and ease of *** present review describes MOF-derived technologies for the successful application of MOFs to ASIBs and suggests future challenges in this area of research based on the current understanding.

关键词： Metal–Organic Framework(MOF) Prussian blue Metal hexacyanoferrate Aqueous electrolyte Sodium-ion Rechargeable battery

Effect of change of sand properties on travel distance of ricocheted debris

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Defence Technology（防务技术） 2021年第4期17卷 1486-1495页

作者： Yoon Keon Kim Woo Chun choi Department of Mechanical Engineering Korea University145 Anam-roSeongbuk-guSeoul02841Republic of Korea

The debris from exploded buildings can ricochet after colliding with the ground,thus increasing the debris travel distance and danger from any associated impacts or *** reduce this danger,the travel distance of ricocheted debris must be accurately *** study analyzed the change in the travel distance of ricocheted concrete debris relative to changes in the properties of a sand *** shear tests were conducted to measure the change in internal friction angle as a function of temperature and water content of the *** element analysis(FEA)was then applied to these variables to predict the speed and angle of the debris after *** FEA results were compared with results of low-speed ricochet experiments,which employed variable temperature and water *** travel distance of the debris was calculated using MATLAB,via trajectory equations considering the drag *** the internal friction angle decreased,the shear stress decreased,leading to deeper penetration of the debris into the *** the loss of kinetic energy increased,the velocity and travel distance of the ricocheted debris *** in the ricochet velocity and travel distance of the debris,according to changes in the internal friction angle,indicated that the debris was affected by the environment.

关键词： Ricochet Exploded debirs Environmental change Sand Temperature Water content Internal friction angle Travel distance

Applicability of cement-based grout for ground heat exchanger considering heating-cooling cycles

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Science China(Technological Sciences) 2011年第7期54卷 1661-1667页

作者： Moonseo PARK SunhongMIN Jeehee LIM Jong Min choi Hangseok choi School of civil Environmental and Architectural Engineering Korea University Seoul Republic of Korea Department of Mechanical Engineering Hanbat National University Daejeon Republic of Korea

The applicability of cement grout （or cement-based grout） has been considered as an alternative to bentonite grout commonly used to backfill closed-loop vertical ground heat exchangers. In a geothermal heat pump system, repeated heating-cooling cycles may cause adverse effects on the integrity of cement grout in the ground heat exchanger. To account for the temperature cycling effect, the strength degradation of cement grout due to temperature cycling has been examined by measuring the unconfined compression strength of cured specimens in a humidity-temperature controlling chamber with applying temperature cycles between -5℃ and 50℃. There is a tendency that the unconfined compression strength decreases with an increase in the number of temperature cycles. On the other hand, an equivalent hydraulic conductivity of a pipe-embedded cement grout specimen was evaluated by carrying out a modified flexible wall permeameter test equipped with a water circulating system to control temperature inside the pipe section. The applied operating temperature range was from 5 to 35℃. After three cycles of heating-cooling circulation, the equivalent hydraulic conductivity becomes asymptotic to a constant value, which implies there is no severe detachment of the pipe from the cement grout.

关键词： cement grout bentonite grout thermal conductivity workability equivalent permeability coefficient

Efficient splitting schemes for magneto-hydrodynamic equations

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Science China Mathematics 2016年第8期59卷 1495-1510页

作者： choi Heejun SHEN Jie Department of Mathematics Purdue University

We present in this paper several efficient numerical schemes for the magneto-hydrodynamic(MHD)equations. These semi-discretized(in time) schemes are based on the standard and rotational pressure-correction schemes for the Navier-Stokes equations and do not involve a projection step for the magnetic field. We show that these schemes are unconditionally energy stable, present an effective algorithm for their fully discrete versions and carry out demonstrative numerical experiments.

关键词： magneto-hydrodynamic (MHD) incompressible stability error analysis spectral method

Self-Driving Algorithm and Location Estimation Method forSmall Environmental Monitoring Robot in Underground Mines

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Computer Modeling in Engineering & Sciences 2021年第6期127卷 943-964页

作者： Heonmoo Kim Yosoon choi Department of Energy Resources Engineering Pukyong National UniversityBusan48513Korea

In underground mine environments where various hazards exist,such as tunnel collapse,toxic gases,the application of autonomous robots can improve the stability of exploration and efficiently perform repetitive exploratory *** this study,we developed a small autonomous driving robot for unmanned environmental monitoring in underground *** developed autonomous driving robot controls the steering according to the distance to the tunnel wall measured using the light detection and ranging sensor mounted on the robot to estimate its location by simultaneously considering the measured values of the inertial measurement unit and encoder *** addition,the robot autonomously drives through the underground mine and performs environmental monitoring using the temperature/humidity,gas,and particle sensors mounted on the *** a result of testing the performance of the developed robot at an amethyst mine in Korea,the robot was found to be able to autonomously drive through tunnel sections with∼28 m length,∼2.5 m height,and∼3 m width *** average error of location estimation was approximately 0.16 *** environmental monitoring sensors,temperature of 15–17◦C,humidity of 42%–43%,oxygen concentration of 15.6%–15.7%,and particle concentration of 0.008–0.38 mg/m3 were measured in the experimental area,and no harmful gases were *** addition,an environmental monitoring map could be created using the measured values of the robot’s location coordinates and environmental factors recorded during autonomous driving.

关键词： Underground mine environmental monitoring autonomous driving geographic information system

An optimized framework for degree distribution in LT codes based on power law

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Journal of Central South University 2013年第10期20卷 2693-2699页

作者： Asim Muhammad choi GoangSeog Department of Information and Communication Engineering Chosun University

LT codes are practical realization of digital fountain codes, which provides the concept of rateless coding. In this scheme, encoded symbols are generated infinitely from k information symbols. Decoder uses only(1+α)k number of encoded symbols to recover the original information. The degree distribution function in the LT codes helps to generate a random graph also referred as tanner graph. The artifact of tanner graph is responsible for computational complexity and overhead in the LT codes. Intuitively, a well designed degree distribution can be used for an efficient implementation of LT codes. The degree distribution function is studied as a function of power law, and LT codes are classified into two different categories: SFLT and RLT codes. Also, two different degree distributions are proposed and analyzed for SFLT codes which guarantee optimal performance in terms of computational complexity and overhead.

关键词： fountain codes degree distribution overhead computational complexity power law

Iwasawa Theory of Quadratic Twists of X0（49）

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Acta Mathematica Sinica,English Series 2018年第1期34卷 19-28页

作者： Junhwa choi John COATES Department of Mathematics POSTECH Emmanuel College Cambridge University

The field K ---- Q（x/-AT） is the only imaginary quadratic field with class number 1, in which the prime 2 splits, and we fix one of the primes p of K lying above 2. The modular elliptic curve X0 （49） has complex multiplication by the maximal order O of K, and we let E be the twist of Xo （49） by the quadratic extension K（v/M）/K, where M is any square free element of O with M -- i mod 4 and （M, 7） = 1. In the present note, we use surprisingly simple algebraic arguments to prove a sharp estimate for the rank of the MordeII-Weil group modulo torsion of E over the field F∞=k（Ep∞ ）, where Epic denotes the group of p∞-division points on E. Moreover, writing B for the twist of X0（49） by K（C/ET）/K, our Iwasawa-theoretic arguments also show that the weak form of the conjecture of Birch and Swinnerton-Dyer implies the non-vanishing at s =1 of the complex L-series of B over every finite layer of the unique Z2-extension of K unramified outside p. We hope to give a proof of this last non-vanishing assertion in a subsequent paper.

关键词： Birch-Swinnerton-Dyer conjecture elliptic curves Iwasawa theory

Grade-4 commercially pure titanium with ultrahigh strength achieved by twinning-induced grain refinement through cryogenic deformation

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Journal of Materials Science & Technology 2021年第7期66卷 193-201页

作者： Seong-Woo choi Jae Sukjeong Jong Woo Won Jae Keun Hong Yoon Suk choi Titanium Department.Korea Institute of Materials Science Changwon51508Republic of Korea School of Materials Science and Engineering Pusan National UniversityPusan.46241Republic of Korea Materials and Manufacturing Development Team Doosan Heavy Industries and ConstructionChangwon51711Republic of Korea

The yield strength of commercially pure(CP) Ti of ASTM grade 4, the strongest among all the CP-Ti grades, is too low for structural applications that require high-strength materials. Here, we demonstrate the strengthening of grade-4 CP Ti by cryogenic-temperature rolling(CTR), which enables deformation twinning in grade-4 CP Ti to achieve twinning-induced grain refinement. CTR activated {11.22} twinning and {10.12} twinning, which are the most common twinning systems in pure Ti, whereas room-temperature rolling(RTR) did not activate any twinning system. CTR with imposing an area reduction of just 30% significantly increased the yield strength of the CP Ti to 946 MPa, which is not achievable through typical processes performed at or above room temperature and is comparable to that of commercial Ti-6 Al-4 V. The significant increase in strength was due to microstructural strengthening caused by twinning-induced grain refinement, combined with dislocation accumulation. In contrast to RTR, CTR greatly increased the stress concentration at grain boundaries(GBs), which caused the unusual activation of twinning in the grade-4 CP Ti by facilitating twin nucleation at GBs. The stress concentration increased because CTR activated the slip to a lesser extent compared to RTR, thereby reducing the strain compatibility between neighboring grains. These results will contribute to development of ultrahigh-strength CP Ti and may thereby extend its use to structural applications that require high-strength materials.

关键词： Titanium Twinning Cryogenic deformation Grain refinement Tensile properties