Comparison of Teaching Geometry Between China and USA : From an Oriental Perspective

Wang, Linquan,Wu, Yuezhong 한국수학교육학회 2002 수학교육연구 Vol.6 No.2

Geometry is one of the important parts of Chinese school mathematics. There is a large difference in teaching and contents (standards, curriculum) between the US and China. Many mathematics educators in both countries are trying to reform the instruction of geometry and have made some progress. Close attention has been given to the Principles and Standards for School Mathematics (NCTM 2000), in which we have found many good ideas. In this paper, we introduce new developments of school geometry in China and have made some comparisons between the US and China. The new technology is becoming popular step by step in Chinese high schools. We believe we should learn from each other and exchange the ideas. In doing this mathematics teaching will be improved.

Construction of a Streptomyces lydicus A01 Transformant with a chit42 Gene from Trichoderma harzianum P1 and Evaluation of Its Biocontrol Activity against Botrytis cinerea

Qiong Wu,Linquan Bai,Weicheng Liu,Yingying Li,Caige Lu,Yaqian Li,Kehe Fu,Chuanjin Yu,Jie Chen 한국미생물학회 2013 The journal of microbiology Vol.51 No.2

Streptomyces lydicus A01 and Trichoderma harzianum P1are potential biocontrol agents of fungal diseases in plants. S. lydicus A01 produces natamycin to bind the ergosterol of the fungal cell membrane and inhibits the growth of Botrytis cinerea. T. harzianum P1, on the other hand, features high chitinase activity and decomposes the chitin in the cell wall of B. cinerea. To obtain the synergistic biocontrol effects of chitinase and natamycin on Botrytis cinerea, this study transformed the chit42 gene from T. harzianum P1 to S. lydicus A01. The conjugal transformant (CT) of S. lydicus A01 with the chit42 gene was detected using polymerase chain reaction (PCR). Associated chitinase activity and natamycin production were examined using the 3, 5-dinitrosalicylic acid (DNS)method and ultraviolet spectrophotometry, respectively. The S. lydicus A01-chit42 CT showed substantially higher chitinase activity and natamycin production than its wild type strain (WT). Consequently, the biocontrol effects of S. lydicus A01-chit42 CT on B. cinerea, including inhibition to spore germination and mycelial growth, were highly improved compared with those of the WT. Our research indicates that the biocontrol effect of Streptomyces can be highly improved by transforming the exogenous resistance gene, i.e. chit42from Trichoderma, which not only enhances the production of antibiotics, but also provides a supplementary function by degrading the cell walls of the pathogens.

Effect of Ammonium in Medium on Ansamitocin P-3 Production by Actinosynnema pretiosum

Jinxia Lin,Linquan Bai,Zixin Deng,Jian-Jiang Zhong 한국생물공학회 2010 Biotechnology and Bioprocess Engineering Vol.15 No.1

Ansamitocin P-3 (AP-3) is an antitumor agent produced by Actinosynnema pretiosum with a market demand for large and cheap supply, but its productivity is yet low. This work investigated the effects of ammonium in medium on the productivity, enzyme activities, and gene transcription for AP-3 biosynthesis. As observed, AP-3 production was depressed by medium ammonium, although the dry cell weight and the consumption of total sugar and isobutanol were not influenced obviously. From the onset of AP-3 accumulation, isobutyrate accumulation showed a different behavior in medium with or without ammonium. Isobutanol dehydrogenase activity was enhanced during production phase in medium with ammonium, but valine dehydrogenase activity was not substantially changed. qRT-PCR analysis revealed that transcriptional levels of structure genes asm14, asm24, asm43, and asm19 were down-regulated by medium ammonium. The transcription of regulatory gene asm2, asm29, and asm31 were slightly up-regulated while that of asm39 was down-regulated by ammonium. The results indicated that inhibition of AP-3 production by ammonium might be related to the AP-3 ester side chain supply and the repression of gene transcription responsible for 3-amino-5-hydroxybenzoic acid and methoxymalonyl-ACP biosynthesis. The information is useful for future AP-3 productivity enhancement.

주택 매매 및 전세시장의 변화와 은행의 건전성

남재현(Jaihyun Nahm),이림천(Linquan Li) 한국경제발전학회 2015 經濟發展硏究 Vol.21 No.2

본 논문은 국내 부동산 시장이 은행 건전성에 미치는 영향을 실증적으로 분석하였다. 기존 연구의 누락 변수 문제를 해결하기 위하여 본 연구에서는 매매 시장만이 아니라 전세 시장까지 포함한 주택 시장의 변화를 살펴보았다. 구체적으로 2000년 1/4분기부터 2013년 4/4분기까지의 패널 자료를 이용하여 거시 경제 변수와 은행별 미시 재무 변수를 통제 변수로 한 고정효과 모형을 추정한 결과 일반은행의 고정이하여신비율에 주택매매가격지수는 부(-), 전세 가격지수는 정(+)의 영향을 주는 것으로 나타났다. 또한 주택 시장의 호경기를 주택 매매가격지수 증가율이 양수인 경우로 정의하거나, 그 증가율이 전 분기 증가율보다 큰 경우로 정의하거나, 또는 그 증가율이 전세가격지수 증가율보다 큰 경우로 정의할 경우 모두에 걸쳐 주택시장의 경기가 좋을 때 매매가격지수 증가율이나 전세가격지수 증가율의 변화가 은행 건전성에 미치는 효과의 크기보다 경기가 좋지 않는 경우에 매매가격지수 증가율이나 전세가 격지수 증가율의 변화가 은행 건전성에 미치는 효과의 크기가 더 큰 비대칭성이 발견되었다(JEL: G2, L85). This study analyzes the effect of the changes in the housing sector on the soundness of the credit assets in the banking sector. We consider changes in the housing chonsei prices as well as the housing sales prices to avoid omitted variables problem of the previous studies. Specifically, we estimate the fixed effect panel models by using the quarterly data of year 2000~2013, with the sample of seven nationwide commercial banks and six regional banks. We find the significant positive (+) correlation between the non-performing loan ratio and the growth rate of the housing chonsei prices, in addition to the usual significant negative (-) correlation between the npl ratio and the growth rate of the housing sales prices. The additional analysis shows that the effect of both the sales prices and the chonsei prices on the bank soundness is amplified during the housing price downturns. That is, the change of the non-performing loans of the commercial banks is more striking when the sales prices or the growth rate of the sales prices fall. It is also more striking when the growth rate of the chonsei prices exceed that of sales prices.

Investigation of Carbon–Carbon Nozzle Throat Erosion in a Solid Rocket Motor Under Acceleration Conditions

Liwu Wang,Weiping Tian,Linquan Chen,Yunqiang Guo 한국항공우주학회 2021 International Journal of Aeronautical and Space Sc Vol.22 No.1

Based on the serious issue of the significant ablation (erosion) difference of nozzle throat in a solid rocket motor (SRM) during its operation on the ground and in the atmosphere, a numerical and experimental investigation of carbon–carbon (C/C) nozzle throat erosion in solid rocket motor under specific acceleration (overload) conditions was conducted. This paper work’s results show that the erosion rate of nozzle throat in the acceleration direction is significantly higher than it is in the non-overload direction, which is defined as throat deviant ablation. In the case studied in this paper, the nozzle throat’s deviant ablation rate in the overload direction is 5 times greater than it is in the non-overload direction when the lateral overload reaches 30 g. Moreover, a sharp, and nearly linear, rise in the nozzle throat’s deviant ablation is observed as the lateral overload increases. Since the lateral acceleration will change the particles’ trajectory, the particles will move towards the lateral direction. This will in turn aggravate the chemical ablation and mechanical erosion processes, leading to throat deviant ablation. This means that the increase in the throat erosion rate in the overload region is so abominable that it must be taken into account in the design of a nozzle and the prediction of SRM performance under acceleration conditions.

A Decentralized Optimal Load Current Sharing Method for Power Line Loss Minimization in MT-HVDC Systems

Yiqi Liu,Wenlong Song,Ningning Li,Linquan Bai,Yanchao Ji 전력전자학회 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.6

This paper discusses the elimination of DC voltage deviation and the enhancement of load current sharing accuracy in multi-terminal high voltage direct current (MT-HVDC) systems. In order to minimize the power line losses in different parallel network topologies and to insure the stable operation of systems, a decentralized control method based on a modified droop control is presented in this paper. Averaging the DC output voltage and averaging the output current of two neighboring converters are employed to reduce the congestion of the communication network in a control system, and the decentralized control method is implemented. By minimizing the power loss of the cable, the optimal load current sharing proportion is derived in order to achieve rational current sharing among different converters. The validity of the proposed method using a low bandwidth communication (LBC) network for different topologies is verified. The influence of the parameters of the power cable on the control system stability is analyzed in detail. Finally, transient response simulations and experiments are performed to demonstrate the feasibility of the proposed control strategy for a MT-HVDC system.

A Decentralized Optimal Load Current Sharing Method for Power Line Loss Minimization in MT-HVDC Systems

Liu, Yiqi,Song, Wenlong,Li, Ningning,Bai, Linquan,Ji, Yanchao The Korean Institute of Power Electronics 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.6

This paper discusses the elimination of DC voltage deviation and the enhancement of load current sharing accuracy in multi-terminal high voltage direct current (MT-HVDC) systems. In order to minimize the power line losses in different parallel network topologies and to insure the stable operation of systems, a decentralized control method based on a modified droop control is presented in this paper. Averaging the DC output voltage and averaging the output current of two neighboring converters are employed to reduce the congestion of the communication network in a control system, and the decentralized control method is implemented. By minimizing the power loss of the cable, the optimal load current sharing proportion is derived in order to achieve rational current sharing among different converters. The validity of the proposed method using a low bandwidth communication (LBC) network for different topologies is verified. The influence of the parameters of the power cable on the control system stability is analyzed in detail. Finally, transient response simulations and experiments are performed to demonstrate the feasibility of the proposed control strategy for a MT-HVDC system.

Structural analysis and biosynthetic engineering of a solubility-improved and less-hemolytic nystatin-like polyene in Pseudonocardia autotrophica.

Lee, Mi-Jin,Kong, Dekun,Han, Kyuboem,Sherman, David H,Bai, Linquan,Deng, Zixin,Lin, Shuangjun,Kim, Eung-Soo Springer International 2012 Applied microbiology and biotechnology Vol.95 No.1

<P>Polyene antibiotics such as nystatin are a large family of very valuable antifungal polyketide compounds typically produced by soil actinomycetes. Previously, using a polyene cytochrome P450 hydroxylase-specific genome screening strategy, Pseudonocardia autotrophica KCTC9441 was determined to contain an approximately 125.7-kb region of contiguous DNA with a total of 23 open reading frames, which are involved in the biosynthesis and regulation of a structurally unique polyene natural product named NPP. Here, we report the complete structure of NPP, which contains an aglycone identical to nystatin and harbors a unique di-sugar moiety, mycosaminyl-(α1-4)-N-acetyl-glucosamine. A mutant generated by inactivation of a sole glycosyltransferase gene (nppDI) within the npp gene cluster can be complemented in trans either by nppDI-encoded protein or by its nystatin counterpart, NysDI, suggesting that the two sugars might be attached by two different glycosyltransferases. Compared with nystatin (which bears a single sugar moiety), the di-sugar containing NPP exhibits approximately 300-fold higher water solubility and 10-fold reduced hemolytic activity, while retaining about 50% antifungal activity against Candida albicans. These characteristics reveal NPP as a promising candidate for further development into a pharmacokinetically improved, less-cytotoxic polyene antifungal antibiotic.</P>

A pilot-scale test on the treatment of biological pretreated leachate by the synergy of ozonation-biological treatment-catalytic ozonation

Yuanmei Chen,Yutang Xiao,Guanping Wang,Wei Shi,Linquan Sun,Yanfang Chen,Aichun Miao 대한환경공학회 2021 Environmental Engineering Research Vol.26 No.4

In this pilot-scale test, the ozonation-biological treatment-catalytic ozonation system was performed to treat complex organics and highly-concentrated total nitrogen (TN) in biological pretreated incineration leachate. The test results showed that the ratio of five-day biochemical oxygen demand (BOD5) / chemical oxygen demand (COD) increased from 0.059 to 0.237, which indicated that the concentration of biodegradable COD (CODbio) increased by ozonation pre-treatment process. In addition, the TN removal mainly occurred in anaerobic zone due to direct denitrification by the activated bacteria, which were domesticated through different influent ratio. Moreover, it was necessary to add catalytic ozonation process to reach higher direct effluent discharge criteria. After 60 days repeated debugging, the removal rate of COD and TN reached 88.5% and 98.2%, respectively. Finally, the total cost of this system was ￥ 6.65 /㎥ ($ 0.95 /㎥), which was acceptable for the treatment of biological pretreated leachate. This pilot-scale test could provide some guiding information for the treatment of leachate containing highly-concentrated TN with low CODbio/N by the composite system.