• 한국환경과학회지
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• 제27권3호
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• pp.167-177
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• 2018

The removal characteristics of As and Se ions from aqueous solution by hexadecyl trimethyl ammonium bromide (HTMAB) modified anthracite (HTMAB-AT) were investigated under various conditions of contact time, pH and temperature. When the pH is 6, the zeta potential value of anthracite (AT) is -24 mV and on the other hand, the zeta potential value of the HTMAB-AT is +44 mV. It can be seen that the overall increase of about 60 mV. Increasing the (+) potential value indicates that the surface of the adsorbent had a stronger positive charge, so adsorption for the anion metal was increased. The isotherm data was well described by Langmuir and Temkin isotherm model. The maximum adsorption capacity was found to be 7.81 and 6.89 mg/g for As and Se ions from the Langmuir isotherm model at 298 K, respectively. The kinetic data was tested using pseudo first and pseudo second order models. The results indicated that adsorption fitted well with the pseudo second order kinetic model. The mechanism of the adsorption process showed that adsorption was dependent on intra particle diffusion model according to two step diffusion. The thermodynamic parameters(${\Delta}G^{\circ}$, ${\Delta}H^{\circ}$, and ${\Delta}S^{\circ}$) were also determined using the equilibrium constant value obtained at different temperatures. The thermodynamic parameters indicated that the adsorption process was physisorption, and also an endothermic and spontaneous process.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 D
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• pp.2371-2373
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• 2000

This paper presents a new vector control scheme for induction motor. An exact knowledge of the rotor flux position is essential for a high-performance vector control. The position of the rotor flux is measured in the direct scheme and estimated in the indirect schemes. Since the estimation of the flux position requires a priori knowledge of the induction motor parameters, the indirect schemes are machine parameter dependent. The rotor and stator resistance among the parameters change with temperature. Variations in the parameters of induction machine cause deterioration of both the steady state and dynamic operation of the induction motor drive. Several methods have presented to minimize the consequences of parameter sensitivity in indirect scheme. In this paper, new estimation scheme of rotor flux position is presented to eliminate sensitivity due to variation in the resistance. The simulation is executed to verify the proposed vector control performance and to compare its performance with that of indirect vector control.

• 한국응용곤충학회지
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• 제39권2호
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• pp.73-82
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• 2000

지금까지 우리 나라에서 배를 가해하는 나무이과(Psyllidae) 해충은 배나무이(Cacoosylla pyrisuga)와 꼬마배나무이(C. pyricola) 두 종으로 알려져 있었으나, 정확한 생태가 아직 밝혀지지 않았다. 본 연구는 꼬마배나무이의 생태를 구명하여 방제기초 자료를 마련하고자 월동생태 및 발생소장, 온도발육 실험 등을 수행하였다. 꼬마배나무이는 겨울형 성충태로 배나무 거친 껍질 밑에서 월동하였으며, 월동성충은 2월 중순경부터 활동을 시작하였다. 성충과 약충이 배나무 잎이나 과실을 흡즙하면서 그을음병을 유발시켜 피해가 발생하였다. 꼬마배나무이의 포장발생 정도는 이상저온이었던 1993년에는 연중 다발생되었고, 한발고온이었던 1994년에는 7월 이후 발생이 급격히 감소하였으며, 기온이 평년수준이었던 1995년에는 7~8월에 발생이 감소하는 경향이었으나 9, 10월 발생이 다시 증가하는 특성을 보였다. 꼬마배나무이 알의 온도별 발육기간은 15, 20, 25, 30, $35^{\circ}C$에거 각각 13.33, 9.32, 7.82, 6.60, 7.75일 이었으며, 1영에서 5영까지 온도별 발육기간은 15, 20, 25, $30^{\circ}C$에서 각각 33.75, 23.77, 15.21, 17.40일 이었다. 고온영역에서 꼬마배나무이의 발육기간은 증가하였고 사망률도 증가하였다. 또한 온도와 꼬마배나무이 발육율과의 관계를 비서형 발육모형과 선형발육모형을 통하여 검토하였다.

• 에너지공학
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• 제24권2호
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• pp.167-173
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• 2015

본 연구에서는 2005년부터 2013년 동안의 분기별 평균기온자료와 소득, 전력가격, 전력사용량 자료를 사용하여 전력수요함수를 추정하였다. 시계열 데이터의 효과적 활용을 위하여 내생시차변수 모형을 활용하였고, 수요함수의 모수에 대한 강건한 추정치를 얻기 위해 최소자승법 추정법을 사용하였다. 전력수요의 단기 가격탄력성 및 소득탄력성은 각각 -0.569, 0.631로 추정되었으며 유의수준 1%에서 통계적으로 유의하였다. 또한 전력수요의 장기 소득 탄력성과 가격탄력성은 각각 1.589, -1.433으로 소득탄력성과 가격탄력성 모두 탄력적인 것으로 추정되었으며 이 또한 유의수준 1%에서 통계적으로 유의한 것으로 나타났다. 기온과 전력수요와의 관계는 여러 선행 연구들에 의해 U자 모양을 갖는 것으로 추정된 바 있으며, 본 연구에서 추정한 임계기온은 $15.2^{\circ}C$인 것으로 나타났다. 내생시차변수모형을 이용한 경우 이중로그모형을 이용하여 추정했을 때 보다 통계적 설명력이 높고 적합도 또한 높아지는 것으로 나타났다.

• 약학회지
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• 제41권1호
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• pp.38-47
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• 1997

Using a concentric cylinder type, rheometer. the steady shear flow properties of vaseline were measured over the temperature range of 20~70${\circ}$C. In this paper, the shea rate and temperature dependencies of its flow behavior were investigated and the validity of some flow models was examined. In addition, the flow characteristics over a wide temperature range were quantitatively evaluated by calculating the various material parameters. Main findings obtained from this study can be summarized as follows: (1) At relatively lower temperature range, vaseline is a plastic fluid with a yield stress and its flow behavior shows shear-thinning characteristics. (2) As the temperature increases, the value of a yield stress and the degree of shear-thinning become smaller, consequently, the Newtonian flow behavior occurs at a lower shear rate range. (3) At temperature range lower than 45${\circ}$C, the flow behavior shows much stronger temperature dependence, and a larger activation energy is needed for flow. (4) The Herschel-Bulkley model is the most effective one g$^3$ to predict the flow behavior of vaseline having a yield stress. The validity of the Bingham and Casson models becomes more available with increasing temperature. The flow behavior of vaseline at temperature range higher than 45${\circ}$C can be perfectly described by the Newton model.

• 동력기계공학회지
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• 제4권3호
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• pp.19-24
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• 2000

This study concerns the performance of the heat transfer of the thermosyphon having 80 internal groove in which boiling and condensation occur. Distilled water has been used as a working fluid. The liquid filling as the ratio of working fluid volume to total volume of thermosyphon has been used as the experimental parameters. The heat flux and heat transfer coefficient at the condenser are estimated from the experimental results. The experimental results have been assessed and compared with the existing theories. As a result of the experimental investigation, the maximum heat flow rate in the thermosyphon is proved to be dependent upon the liquid fill quantity. relatively high rates of heat transfer have been achieved operating in the thermosyphon with the internal groove. Also, a thermosyphon with the internal groove can be used to achieve some inexpensive and compact heat exchangers in low temperature. In addition, overall heat transfer coefficients and the characteristics as an operating temperature are obtained for the practical applications.

• 한국축산식품학회지
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• 제32권3호
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• pp.293-300
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• 2012

This study investigated the effects of a low-voltage ohmic heating process (2.5 and 3.8 V/cm) on the thawing characteristics and NaCl diffusion of pork. The thawing rate of pork was dependent on the applied voltages and brine salinities, and few differences were obtained in pork quality parameters (color, water-holding capacity, and shear force) regarding the different treatments. The NaCl concentration of pork after ohmic thawing was higher than that following brine-immersion thawing, however, the NaCl diffusion did not differ from when fresh meat was immersed in brine. For application of the ohmic process in fresh pork, various ohmic pulses were generated in order to prevent the meat from overheating, and the results indicated that the ohmic process was a better way to enhance NaCl diffusion compared with immersing pork at high temperature. Although the mechanisms involved in NaCl diffusion at low-voltage electric field strength were unclear, the present study demonstrated that the ohmic process has a potential benefit in the application of meat processing.

• Bulletin of the Korean Chemical Society
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• 제34권11호
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• pp.3312-3316
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• 2013

Single crystals of hexagonal graphenes were successfully grown on Cu foils using the atmospheric pressure chemical vapor deposition (CVD) method. We investigated the effects of reaction parameters, such as the growth temperature and annealing time, on the size, coverage, and density of graphene domains grown over Cu foil. The mean size of the graphene domains increased significantly with increases in both the growth temperature and annealing time, and similar phenomena were observed in graphene domains grown by low pressure CVD over Cu foil. From the comparison of micro Raman spectroscopy in the graphene films grown with different annealing times, we found that the nucleation and growth of the domains were strongly dependent on the annealing time and growth temperature. Therefore, we confirmed that when reaction time was same, the number of layers and the degree of defects in the synthesized graphene films both decreased as the annealing time increased.

• 한국수소및신에너지학회논문집
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• 제27권1호
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• pp.42-48
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• 2016

This study presents an experiment investigation on natural convection heat transfer of air-cooling Proton exchange membrane fuel cells (PEMFCs) in a enclosure system for unmanned aerial vehicles (UAVs). Considered are replacing fuel cell stack with Aluminum block for heat generating inside a enclosure chamber. The volume ratio of fuel cell stack and chamber for simulation to the actual size of aerial vehicle is 1 to 15. The parameters considered for experimental study are the environmental temperature range from $25^{\circ}C$ to $-60^{\circ}C$ and the block heat input of 10 W, 20 W and 30 W. Effect of the thermal conductivity of the block and power level on heat transfer in the chamber are investigated. Experimental results illustrate the temperature rise at various locations inside the chamber as dependent upon heat input of fuel cell stack and environmental temperature. From the results, dimensionless correlation in natural convection was proposed with Nusselt number and Rayleigh number for designing air-cooling PEMFC powered high altitude long endurance (HALE) UAV.

• 한국자원식물학회지
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• 제11권2호
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• pp.119-123
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• 1998

Effects of elevated CO2 and temperature on nitrogen (N) uptake , leaf N concentration, N partitioning , N use efficiency (NUE) and grain yield of pot and field grown rice (Oryza sativa. L.cv. Chukwangbyeo) under canopy-like conditions were studied over three years. Rice plants were grown in pots and in the field in temperature gradient chambers containing either ambient(350ppm) or elevated CO2 concentrations (690 or 650ppm) in conbination with either four or seven temperature regimes ranging form ambient temperature(AT) to AT plus 3$^{\circ}C$. There were three N supplies 94g or 6g m-2 to 20g or 48g m-2.Elevated CO2 increased N uptake in field-grown rice ; the magnitude of this effect was thelargest (+15%) at the highest N level. However, in pot-grown rice, N uptake was suppressed with the effect was the largest at high N levels. Leaf N concentration declined at elevated CO2 mainly due to a decrease in N partitiioning to the leaf blades. Air temperature had little effect on the N parameters mentioned previously, wherease NUE for spikelet production declined rapidly with increased temperature irrespective of CO2 concentration. The response of the biomass to elevated CO2 varied with N level, with the greatest response at 20g N m-2 (+30%) . At AT, where high temperature-induced sterility was generally not observed, elevated CO2 increased yield. However, the magnitude of this effect varied greatly (2-39%) with N level, and was mainly dependent on the magnitude of the increase in spikelet number.