國民學校 敎師 自然 및 算數科 再敎育의 分析的 硏究 : Based on the Choong Buk Province

黃秉德,梁仁煥,崔炳文,趙璇衡,朴根生 淸州大學校 科學敎育硏究所 1977 淸州大學校 科學敎育硏究所 Vol.1 No.-

Our college has retrained many primary school teachers during 5 years is science, and during 4 years in case of mathematics. Many problems are found out in the process of retraining them in our school. This study is aimed to research the actual condition of the retraining and to find out the way to improvement from the problems. However, Our study will have some limitation as follows: (1) For our study, only 300 teachers are chosen from the total 1,869 attended at our college(Cheong Ju Teachers College) in 1976. (2) The administrational and financial affairs are analyzed only according to the Ministry of Education with UNICEF funds from 1972 to 1976, and (3) We didn't take any consideration of Ministry of Education Project in Suggesting the way of improvement. Following are some problems found in our study: 1) Throughout the nation, only 23% of primary school teachers were taught in science and mathematice reservice work during the 5 years, and it can be said that it takes about 20 years to retrained all the teachers without consideration of natural increase of teachers. 2) The proportion of selecting primary school teachers in all the country for this reservice training is extreme, for example, Jeju Province is 57.9%, Seoul 17.7%. 3) The proportion of woman teachers selected in Choong Buk primary school is only 3.5% of total woman teachers, who takes 32% of total Choong Buk primary teachers during 5 years. Therefore, it is said that the number is very little. 4) Some teachers have been reselected in the reservice training. In case of the Choong Buk Board of Education. the 6% of teachers selected once were reselected for 5 years. 5) When the test are enforced on attendants to get data before the reservice training. We could find that they didn't understand the basic concept of science except a grade under their charge. 6) In the process of inquiry study, they didn't know even the scientific terms of expectation and reasoning. 7) After 60 hours of reservice training course. We tested them about understanding of the contents of text, and their marks are from 10 to 100. the marks show large individual difference among them. 8) Some teachers may have neither teaching ability nor knowledge of the basic concept, that is 11.3% of total attendants are less than 30 marks in mathematics test. 9) It is too very large work to study reservice text during the 60 hours. 10) There are many difficult signs in the mathematics reservice text having no connection with the actual primary school mathematics text book. 11) In the reservice text of science, there are omitted the method of teaching materials production, the model of inquiry learning, and the evaluation method. 12) From the analysis of questionary response for finding the actual condition of administration of teaching materials, We could find out 15% of primary schools in Choong Buk Province do almost not prepare teaching materials, and 15% of its never put them to practical use. Therefore, We could say that total 30% of them have been teaching without teaching materials. 13) The 42% of attendants in mathematics class answer that they do not understand the new mathematical signs, and 42% of them answer the shortage of hours (60 hours) to understand their reservice text book. 14) The 25% of them answer that they teach children with cramming education, and almost of them want good teachers guide books. As mentioned above, there are found many problems to be solved for reservice training of science education in our country. Some of them will be solved in our study. So We find out its and We suggest the ways solving the problems as follows: A. On the administration of reservice training. 1) The reservice training work for primary school teachers is very significant and will have to be continued. 2) It will be done in not only summer vacation but also winter one for finishing immediatly all over the country. 3) The 60 hours of science reservice training course work are very short, and the classmember of attendants will be regulated. 4) The funds for reservice operation and travelling expenses for attendants will be realized. B. On selecting the attendants 1) When the attendants are selected, there will be consideration of age, rank, term of their service, sex and academic background. 2) as far as possible, it will be selected as homogeous groups, and it will be effective to teach them with division between class teacher and nonclass teacher. 3) When select attendants are it will be taken consideration of balance between city and province for the diffusion effect and parallel development in reservice training work. 4) It must give a chance to woman as same as to man teacher according to a rule of equal select chance. 5) The principal, instructor and school inspector will be reeducated for fixing of science curriculum. C. On reservice training text book 1) The text book must reedit moderatly for 60 hours, or the time of retraining for the text book finished will be extented. In our opinion, it is to be desired that the time have to be added. 2) The difficult signs must be omitted, taking into account for the mathematics knowledge and time of education period. 3) In the science reservice training text book, it must supplement the tack for framming of inquiry teaching plan, the method for making teaching materials, and the skill for replacing of teaching materials. D. For the curriculum management of science. 1) The Governmental Company must settle the shortage of science teaching materials in primary school. 2) For the charge of the old state of teaching method, the teachers must devote themselves to teach children without miscellaneous duties. 3) The authorities concerned (for example, Ministry of Education, Teachers College, etc.) must make guide books for science teachers, and supply them to primary school teachers. 4) It must be given the chance of long period reeducation to the incompetent primary school teachers, and problem will have to be studied under the situation of educational administration.

‘로자리오 비얀코’(Vitis vitisvinifera)와 ‘캠벨’( Vitis labrusca) 포도과실의 유황패드 처리에 따른 저장성 향상

임병선(Byung-Seon Lim),이신희(Shin Hee Lee),조미애(Mi-Ae Jo),황정환(Jung Hwan Hwang),황용수(Yong Su Hwang2) 한국원예학회 2010 한국원예학회 학술발표요지 Vol.2010 No.10

The effect of combined Rehmannia glutinosa Libosch and Eleutherococcus senticosus Max(OPB) extracts on bone mineral density in ovariectomized rats.

Kim,Jung-Keun 대한구강생물학회 2007 International Journal of Oral Biology Vol.32 No.4

This study was conducted to investigate the preventingeffects of OPB (Rehmannia glutinosa Libosch and Eleuth-erococcus senticosus Max extracts) and combined OPB/Calcium therapy on bone loss in ovariectomized rats. SixtySprague Dawley rats of 12-week-old were divided into eightgroups: OVX (ovariectomized), OPBL (OPB 50mg/kg),OPBM (OPB100mg/kg), OPBH (OPB 200mg/kg), OPBL/CAL(OPBL+CAL), OPBM/CAL (OPBM+CAL), OPBH/CAL (OPBH+CAL) and CAL (Calcium citrate 88.33mg/kg+1α, 25-dihydroxy-vitamin D3 33.33IU/kg). Bone mineraldensity (BMD), bone mineral content (BMC), bone strengthindices and cortical thickness were analyzed by peripheralquantitative computerized tomography (pQCT). pQCTscanning showed that OVX induced a significant decreasein trabecular bone mineral density and bone mineralcontent in the proximal tibia (-36.4±2.4%, -21.8±12.7%).These decreases were significantly prevented by theadministration of OPBM and OPBM/CAL. Cortical BMDand BMC of tibia were slightly enhanced by OPB and OPB/CAL. However there was no significant difference betweenOVX and OPB, OPB/CAL treated group. Bone strengthindices and cortical thickness were not significantly different.Our results suggest that OPB and combined OPB/Calciumtherapy are effective in preventing the development of boneloss induced by ovariectomy in rats.

Dead Time Compensation Method for Voltage-Fed PWM Inverter

Seon-Hwan Hwang,Jang-Mok Kim IEEE 2010 IEEE transactions on energy conversion Vol.25 No.1

<P>A new dead time compensation method for a pulsewidth modulation (PWM) inverter is proposed. In the PWM inverter, voltage distortion due to the dead time effects produces fifth and seventh harmonics in the phase currents of the stationary reference frame, and a sixth harmonic in the <I>d</I>- and <I>q</I>-axis currents of the synchronous reference frame, respectively. In this paper, the sixth harmonic of the integrator output of the synchronous <I>d</I>-axis proportional-integral (PI) current regulator is used to compensate the output voltage distortion due to the dead time effects, since the integrator output has ripple corresponding to six times the stator fundamental frequency. The proposed method can be easily implemented by feedforwardly adding compensation voltages to the output reference voltage of the synchronous PI current regulator. The proposed method, therefore, has some significant advantages such as simple implementation without additional hardware, easy mathematical computation, no offline experimental measurements, and application in both the steady state and the transient state. The validity of the proposed compensation algorithm is shown through several experiments.</P>

Control Algorithms of Large Synchronous Machines for Starting Gas Turbosets

Seon-Hwan Hwang,Jang-Mok Kim,Ho-Seon Ryu,Gi-Gab Yoon 전력전자학회 2009 JOURNAL OF POWER ELECTRONICS Vol.9 No.2

The static frequency converter (SFC) systems are used as a method of driving large synchronous machines in many power and industrial plants. In this paper, new control algorithms of SFC systems for starting gas turbosets are proposed for a four quadrant operation: start-up at standstill; an acceleration up to the speed of the rated voltage; field weakening to reach the rated speed; synchronization to the main alternating current (AC) source; and dynamic braking to stop safely within the rating of the synchronous machine. Experimental results show that the proposed algorithms are proper and effective.

Offset error compensation algorithm for grid voltage measurement of grid-connected single-phase inverters based on SRF-PLL

Hwang, Seon-Hwan,Seo, Sung-Woo The Korean Institute of Power Electronics 2020 JOURNAL OF POWER ELECTRONICS Vol.20 No.3

This paper proposes a method for compensating the offset error in the grid voltage measurement process of grid-connected single-phase inverters. In general, the offset error in the grid voltage sampling process results in a fundamental frequency component in the synchronous reference frame phase locked loop (SRF-PLL). As a result, the dq-axis currents and phase current based on the synchronous reference frame PI current regulator include the unwanted DC component, as well as first- and second-order harmonic ripples when compared with the grid frequency due to the distorted grid angle. Therefore, in this paper, the influences of the offset error are mathematically analyzed based on the SRF-PLL. In particular, the d-axis integrator output of the SRF-PLL with a PI controller is selected to detect the offset error. Then it is compensated using a simple proportional-integral controller. Moreover, the root mean square function is easily applied to obtain the offset error. The usefulness of the proposed algorithm is verified through simulation and experimental results.

DC Offset Error Compensation for Synchronous Reference Frame PLL in Single-Phase Grid-Connected Converters

Seon-Hwan Hwang,Liming Liu,Hui Li,Jang-Mok Kim IEEE 2012 IEEE TRANSACTIONS ON POWER ELECTRONICS - Vol.27 No.8

<P>This letter proposes a dc offset error compensation algorithm for synchronous reference frame phase-locked loop (PLL) in single-phase grid-connected converters. The errors generated from the grid voltage measurement circuits can be divided into dc offset and scaling errors. These errors may cause the undesirable periodic ripples with grid frequency in the synchronous reference frame PLL. As a result, the performance of the power conversion systems is degraded. In this letter, the effects of the dc offset and scaling errors are comprehensively analyzed based on the synchronous dq frame PLL. In particular, the dc offset error can be estimated and compensated by controlling the synchronous d-axis voltage in a PLL system to be zero. The proposed algorithm does not require any additional hardware and can be implemented by a simple proportional-integral controller and an integral operation. Experimental results are presented to demonstrate the effective- ness of the proposed dc offset error compensation algorithm.</P>

Parameter Identification of a Synchronous Reluctance Motor by using a Synchronous PI Current Regulator at a Standstill

Seon-Hwan Hwang,Jang-Mok Kim,Huynh Van Khang,Jin-Woo Ahn 전력전자학회 2010 JOURNAL OF POWER ELECTRONICS Vol.10 No.5

This paper proposes an estimation algorithm for the electrical parameters of synchronous reluctance motors (SynRMs) by using a synchronous PI current regulator at standstill. In reality, the electrical parameters are only measured or estimated in limited conditions without fully considering the effects of the switching devices, connecting wires, and magnetic saturation. As a result, the acquired electrical parameters are different from the real parameters of the motor drive system. In this paper, the effects of switching devices, connecting wires, and the magnetic saturation are considered by simultaneously using the short pulse and closed loop equations of resistance and synchronous inductances. Therefore, the proposed algorithm can be easily and safely implemented with a reduced measuring time. In addition, it does not need any external or additional measurement equipment, information on the motor’s dimensions, and material characteristics as in the case of FEM. Several experimental results verify the effectiveness of the proposed algorithm.

Coordinated Control of an Independent Multi-phase Permanent Magnet-type Transverse Flux Linear Machine Based on Magnetic Levitation

Seon-Hwan Hwang,Soon-Kurl Kwon,Young-Gi Hwang,Deok-Je Bang 한국조명·전기설비학회 2014 조명·전기설비학회논문지 Vol.28 No.12

This paper proposes a coordinated control for an independent multi-phase transverse flux linear synchronous motor (IM-TFLSM) based on magnetic levitation. The stator structures of the IM-TFLSM are composed of a two set, which has independent three-phase windings and a double-sided air-gap as opposed to the conventional Y-connected three-phase linear motors. A suitable control algorithm is necessary to operate the applied linear machine. This study proposes a coordinated control algorithm for adjusting the mover air-gap and thrust force of the IM-TFLSM in order to maintain air-gap and phase shifted current control of the independent 3-phase modules. In addition, the principle of operation and its special structures are described in detail and the validity and effectiveness of the control algorithm is verified through multiple experimental results.

Control Algorithms of Large Synchronous Machines for Starting Gas Turbosets

Hwang, Seon-Hwan,Kim, Jang-Mok,Ryu, Ho-Seon,Yoon, Gi-Gab The Korean Institute of Power Electronics 2009 JOURNAL OF POWER ELECTRONICS Vol.9 No.2

The static frequency converter (SFC) systems are used as a method of driving large synchronous machines in many power and industrial plants. In this paper, new control algorithms of SFC systems for starting gas turbo sets are proposed for a four quadrant operation: start-up at standstill; an acceleration up to the speed of the rated voltage; field weakening to reach the rated speed; synchronization to the main alternating current (AC) source; and dynamic braking to stop safely within the rating of the synchronous machine. Experimental results show that the proposed algorithms are proper and effective.