The future energy policy,long-term energy supply plan,and necessity of power system interconnection are discussed considering the climate change agreement and national carbon neutrality policy.Although several studies...The future energy policy,long-term energy supply plan,and necessity of power system interconnection are discussed considering the climate change agreement and national carbon neutrality policy.Although several studies have been conducted on power system interconnection related projects,a few reviews have been performed related to the Greenhouse Gas Convention in North-East Asian(NEA)regions.Therefore,the future directions and possible scenarios on power system interconnection are studied by combining the issues by comprehensively considering carbon neutrality policy according to the perspective of Korea.展开更多
A novel 50 kW fast charger was proposed for electric vehicles. The proposed fast charger is divided into two main sections an AC-DC converter performing a PFC function and a DC-DC converter performing a charging funct...A novel 50 kW fast charger was proposed for electric vehicles. The proposed fast charger is divided into two main sections an AC-DC converter performing a PFC function and a DC-DC converter performing a charging function. A transformer including leakage inductances was used in the AC-DC converter in order to obtain isolation and inductance. A series-connection topology was used in the DC-DC converter between the DC-bus and outlet. This topology enables high power conversion efficiency up to 95% for the DC-DC converter. In order to reduce the impact of the 50 kW charging on the AC grid, the proposed fast charger system includes a buffering battery unit between the two main power conversion units. This leads to reductions in the power installation costs of power companies and to improvements in the power quality were verified through simulations and experimental results. on the AC grid. The performances of the proposed fast charger system展开更多
A novel technique is proposed to improve the performance of voice activity detection(VAD) by using deep belief networks(DBN) with a likelihood ratio(LR). The likelihood ratio is derived from the speech and noise spect...A novel technique is proposed to improve the performance of voice activity detection(VAD) by using deep belief networks(DBN) with a likelihood ratio(LR). The likelihood ratio is derived from the speech and noise spectral components that are assumed to follow the Gaussian probability density function(PDF). The proposed algorithm employs DBN learning in order to classify voice activity by using the input signal to calculate the likelihood ratio. Experiments show that the proposed algorithm yields improved results in various noise environments, compared to the conventional VAD algorithms. Furthermore, the DBN based algorithm decreases the detection probability of error with [0.7, 2.6] compared to the support vector machine based algorithm.展开更多
This study presents the development of an ultrasonic transducer with a radius horn for an ultrasonic milling spindle(UMS)system.The ultrasonic transducer was intended to have a working frequency of approximately 30 kH...This study presents the development of an ultrasonic transducer with a radius horn for an ultrasonic milling spindle(UMS)system.The ultrasonic transducer was intended to have a working frequency of approximately 30 kHz.Two different materials were considered in the study:stainless steel(SS 316L)and titanium alloy(Ti-6Al-4V).Titanium alloy gave a higher resonance frequency(33 kHz)than stainless steel(30 kHz)under the same preload compression stress.An electromechanical impedance simulation was carried out to predict the impedance resonance frequency for both materials,and the effect of the overhanging toolbar was investigated.According to the electromechanical impedance simulation,the overhanging toolbar length affected the resonance frequency,and the error was less than 3%.Harmonic analysis confirmed that the damping ratio helps determine the resonance amplitude.Therefore,damping ratios of 0.015-0.020 and 0.005-0.020 were selected for stainless steel and titanium alloy,respectively,with an error of less than 1.5%.Experimental machining was also performed to assess the feasibility of ultrasonic-assisted milling;the result was a lesser cutting force and better surface topography of Al 6061.展开更多
This paper aims to identify and clarify the cyber security risks and their interaction with the power system in Smart Grid. The SCADA system and other communication networks interact with the power system on a real ti...This paper aims to identify and clarify the cyber security risks and their interaction with the power system in Smart Grid. The SCADA system and other communication networks interact with the power system on a real time basis, so it is important to understand the interaction between two layers to protect the power system from potential cyber threats. This paper has shown the risks of the open architecture SCADA in a quantitative method and proposed effective security measures through case studies.展开更多
Tailoring nanostructures is a general approach used to obtain enhanced thermoelectric properties for halfHeusler compounds because the wide areas of grain and phase boundaries could be scattering centers that lower la...Tailoring nanostructures is a general approach used to obtain enhanced thermoelectric properties for halfHeusler compounds because the wide areas of grain and phase boundaries could be scattering centers that lower lattice thermal conductivity.However,a common fabrication method based on the sintering of crystalline precursors crushed from as-cast alloy ingots has limitations in obtaining a homogeneous microstructure without microsized impurity phases,owing to residual elemental segregation from casting.In this study,we used amorphous NbCoSn alloys as a precursor for the sintered specimen to obtain a homogeneous NbCoSn bulk specimen without microsized impurity phases and segregation,which led to the enhanced Seebeck coefficient due to the high purity of the half-Heusler phase after crystallization.Moreover,superplasticity originating from amorphous features enabled the powders to be largely deformed during the sintering process,even at a low sintering temperature(953 K).This resulted in less oxidation at both,the grain boundary and the interior,as the O diffusion pathway was blocked during the sintering process.As a result,the NbCoSn0.95Sb0.05 specimen using an amorphous precursor exhibited an enhanced zT of 0.7,due to the increase in the power factor and a decrease in lattice thermal conductivity compared to the specimen using a crystalline precursor.展开更多
Interfacial engineering of two-dimensional(2D)monometallic phosphides enables remarkable structural and electrochemical properties in energy storage devices.Herein,2D nanosheets(NSs)of FeP_(2)/Co_(2) P were grown on N...Interfacial engineering of two-dimensional(2D)monometallic phosphides enables remarkable structural and electrochemical properties in energy storage devices.Herein,2D nanosheets(NSs)of FeP_(2)/Co_(2) P were grown on Ni-foam(FCP)using a solution-based and phosphorization approach to be used as freestanding for high-performance energy storage devices.An effective phosphorization strategy is successfully de-veloped to improve the overall crystalline phase,tailor the morphology,and boost the electrochemical performances of electrodes.The FCP NSs electrode exhibits a battery-type redox behavior with a maxi-mum high areal capacity of 1.96 C cm^(-2) at 4 mA cm^(-2) in 6 M KOH aqueous electrolyte compared to the other counterparts.The superior electrochemical performance was achieved by increasing the electroac-tive sites and high conductivity via surface tailoring and fast redox reactions.Moreover,a supercapattery was assembled utilizing FCP and activated carbon(AC)electrodes and it revealed maximum specific en-ergy(E_(s))and specific power(P_(s))of 41.2 Wh kg^(-1) and 7578 W kg^(-1) with good cycling stability of 91%after 10,000 cycles at 5 A g^(-1).Eventually,the supercapattery has been explored in practical applications by lighting up light-emitting diodes(LEDs),representing the real-time performance of superior energy storage devices.展开更多
The development of portable X-ray detectors is necessary for diagnosing fractures in unconscious patients in emergency situations.However,this is quite challenging because of the heavy weight of the scintillator and s...The development of portable X-ray detectors is necessary for diagnosing fractures in unconscious patients in emergency situations.However,this is quite challenging because of the heavy weight of the scintillator and silicon photodetectors.The weight and thickness of X-ray detectors can be reduced by replacing the silicon layer with an organic photodetectors.This study presents a novel bithienopyrroledione-based polymer donor that exhibits excellent photodetection properties even in a thick photoactive layer(~700 nm),owing to the symmetric backbone and highly soluble molecular structure of bithienopyrroledione.The ability of bithienopyrroledione-based polymer donor to strongly suppress the dark current density(Jd~10−10 A cm^(−2))at a negative bias(−2.0 V)while maintaining high responsivity(R=0.29 A W−1)even at a thickness of 700 nm results in a maximum shot-noise-limited specific detectivity of D_(sh)^(*)=2.18×10^(13)Jones in the organic photodetectors.Printed organic photodetectors are developed by slot-die coating for use in X-ray detectors,which exhibit D_(sh)^(*)=2.73×10^(12)Jones with clear rising(0.26 s)and falling(0.29 s)response times upon X-ray irradiation.Detection reliability is also proven by linear response of the X-ray detector,and the X-ray detection limit is 3 mA.展开更多
The power expansion planning is large and capital intensive capacity planning. In the past, the expansion planning was established with the proper supply reliability in order to minimize social cost. However, such pla...The power expansion planning is large and capital intensive capacity planning. In the past, the expansion planning was established with the proper supply reliability in order to minimize social cost. However, such planning cannot be used in the power markets with many market participants. This paper proposed the power expansion planning process in the power markets. This system is composed of Regulator and Generation Company （GENCO）＇s model. Multi-criteria decision making rule is used for regulator model and several scenarios for GENCO model are applied.展开更多
Lithium metal is considered one of the most promising anode materials for application in next-generation batteries.However,despite decades of research,practical application of lithium metal batteries has not yet been ...Lithium metal is considered one of the most promising anode materials for application in next-generation batteries.However,despite decades of research,practical application of lithium metal batteries has not yet been achieved because the fundamental interfacial mechanism of lithium dendrite growth is not yet fully understood.In this study,a series of reactive molecular dynamics (MD) simulations was performed to investigate the electrochemical dynamic reactions at the electrode/electrolyte interface.It allows quantitative characterization of morphological phenomena and real-time interfacial visualization of the dynamic growth of dead lithium and dendrites during repeated charging.This computational protocol was utilized to investigate the dendrite mitigation mechanism when an electrolyte additive (hydrogen fluoride) is dissolved in an organic ethylene carbonate (EC) electrolyte solvent.It was confirmed that beneficial decomposition reactions between electrolyte components form a protective film on the anode surface,suppressing large interphase volume changes and unnecessary degradation reactions.展开更多
We demonstrate a femtosecond Cr：YAG laser mode-locked by a carbon nanotube saturable absorber mirror（CNT-SAM） at a repetition rate of 550 MHz. By employing the CNT-SAM, which exhibits a modulation depth of 0.51% an...We demonstrate a femtosecond Cr：YAG laser mode-locked by a carbon nanotube saturable absorber mirror（CNT-SAM） at a repetition rate of 550 MHz. By employing the CNT-SAM, which exhibits a modulation depth of 0.51% and a saturation fluence of 28 μJ∕cm^2 at 1.5 μm, we achieved a compact bulk Cr：YAG laser with selfstarting mode-locked operation near 1.5 μm, delivering an average output power of up to 147 m W and a pulse duration of 110 fs. To our knowledge, this system provides the highest repetition rate among reported CNT-SAM mode-locked Cr：YAG lasers and the shortest pulse duration among saturable absorber mode-locked Cr：YAG lasers with repetition rates above 500 MHz.展开更多
文摘The future energy policy,long-term energy supply plan,and necessity of power system interconnection are discussed considering the climate change agreement and national carbon neutrality policy.Although several studies have been conducted on power system interconnection related projects,a few reviews have been performed related to the Greenhouse Gas Convention in North-East Asian(NEA)regions.Therefore,the future directions and possible scenarios on power system interconnection are studied by combining the issues by comprehensively considering carbon neutrality policy according to the perspective of Korea.
基金Project supported by Changwon National University in 2011-2012
文摘A novel 50 kW fast charger was proposed for electric vehicles. The proposed fast charger is divided into two main sections an AC-DC converter performing a PFC function and a DC-DC converter performing a charging function. A transformer including leakage inductances was used in the AC-DC converter in order to obtain isolation and inductance. A series-connection topology was used in the DC-DC converter between the DC-bus and outlet. This topology enables high power conversion efficiency up to 95% for the DC-DC converter. In order to reduce the impact of the 50 kW charging on the AC grid, the proposed fast charger system includes a buffering battery unit between the two main power conversion units. This leads to reductions in the power installation costs of power companies and to improvements in the power quality were verified through simulations and experimental results. on the AC grid. The performances of the proposed fast charger system
基金supported by the KERI Primary Research Program through the Korea Research Council for Industrial Science & Technology funded by the Ministry of Science,ICT and Future Planning (No.15-12-N0101-46)
文摘A novel technique is proposed to improve the performance of voice activity detection(VAD) by using deep belief networks(DBN) with a likelihood ratio(LR). The likelihood ratio is derived from the speech and noise spectral components that are assumed to follow the Gaussian probability density function(PDF). The proposed algorithm employs DBN learning in order to classify voice activity by using the input signal to calculate the likelihood ratio. Experiments show that the proposed algorithm yields improved results in various noise environments, compared to the conventional VAD algorithms. Furthermore, the DBN based algorithm decreases the detection probability of error with [0.7, 2.6] compared to the support vector machine based algorithm.
基金supported by Korea Electrotechnology Research Institute(KERI)Primary Research Program through the National Research Council of Science&Technology(NST)funded by the Ministry of Science and ICT(MSIT)in 2023(No.23A01021)the National Research Foundation of Korea(NRF)grant funded by the Korean Government(MSIT)(No.RS-2023-00278890).
文摘This study presents the development of an ultrasonic transducer with a radius horn for an ultrasonic milling spindle(UMS)system.The ultrasonic transducer was intended to have a working frequency of approximately 30 kHz.Two different materials were considered in the study:stainless steel(SS 316L)and titanium alloy(Ti-6Al-4V).Titanium alloy gave a higher resonance frequency(33 kHz)than stainless steel(30 kHz)under the same preload compression stress.An electromechanical impedance simulation was carried out to predict the impedance resonance frequency for both materials,and the effect of the overhanging toolbar was investigated.According to the electromechanical impedance simulation,the overhanging toolbar length affected the resonance frequency,and the error was less than 3%.Harmonic analysis confirmed that the damping ratio helps determine the resonance amplitude.Therefore,damping ratios of 0.015-0.020 and 0.005-0.020 were selected for stainless steel and titanium alloy,respectively,with an error of less than 1.5%.Experimental machining was also performed to assess the feasibility of ultrasonic-assisted milling;the result was a lesser cutting force and better surface topography of Al 6061.
文摘This paper aims to identify and clarify the cyber security risks and their interaction with the power system in Smart Grid. The SCADA system and other communication networks interact with the power system on a real time basis, so it is important to understand the interaction between two layers to protect the power system from potential cyber threats. This paper has shown the risks of the open architecture SCADA in a quantitative method and proposed effective security measures through case studies.
基金the Basic Science Research Program of the National Research Foundation of Korea(NRF)(Nos.2021R1A4A2001658 and 2021R1A6A3A03045488).
文摘Tailoring nanostructures is a general approach used to obtain enhanced thermoelectric properties for halfHeusler compounds because the wide areas of grain and phase boundaries could be scattering centers that lower lattice thermal conductivity.However,a common fabrication method based on the sintering of crystalline precursors crushed from as-cast alloy ingots has limitations in obtaining a homogeneous microstructure without microsized impurity phases,owing to residual elemental segregation from casting.In this study,we used amorphous NbCoSn alloys as a precursor for the sintered specimen to obtain a homogeneous NbCoSn bulk specimen without microsized impurity phases and segregation,which led to the enhanced Seebeck coefficient due to the high purity of the half-Heusler phase after crystallization.Moreover,superplasticity originating from amorphous features enabled the powders to be largely deformed during the sintering process,even at a low sintering temperature(953 K).This resulted in less oxidation at both,the grain boundary and the interior,as the O diffusion pathway was blocked during the sintering process.As a result,the NbCoSn0.95Sb0.05 specimen using an amorphous precursor exhibited an enhanced zT of 0.7,due to the increase in the power factor and a decrease in lattice thermal conductivity compared to the specimen using a crystalline precursor.
基金supported by Basic Science Research Pro-gram through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(No.NRF-2014R1A6A1030419)supported by the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)(No.2020112382).
文摘Interfacial engineering of two-dimensional(2D)monometallic phosphides enables remarkable structural and electrochemical properties in energy storage devices.Herein,2D nanosheets(NSs)of FeP_(2)/Co_(2) P were grown on Ni-foam(FCP)using a solution-based and phosphorization approach to be used as freestanding for high-performance energy storage devices.An effective phosphorization strategy is successfully de-veloped to improve the overall crystalline phase,tailor the morphology,and boost the electrochemical performances of electrodes.The FCP NSs electrode exhibits a battery-type redox behavior with a maxi-mum high areal capacity of 1.96 C cm^(-2) at 4 mA cm^(-2) in 6 M KOH aqueous electrolyte compared to the other counterparts.The superior electrochemical performance was achieved by increasing the electroac-tive sites and high conductivity via surface tailoring and fast redox reactions.Moreover,a supercapattery was assembled utilizing FCP and activated carbon(AC)electrodes and it revealed maximum specific en-ergy(E_(s))and specific power(P_(s))of 41.2 Wh kg^(-1) and 7578 W kg^(-1) with good cycling stability of 91%after 10,000 cycles at 5 A g^(-1).Eventually,the supercapattery has been explored in practical applications by lighting up light-emitting diodes(LEDs),representing the real-time performance of superior energy storage devices.
基金granted by the Korea Research Institute of Chemical Technology(KRICT)of the Republic of Korea(No.2422-10)the National Research Foundation(NRF)(NRF-2021R1C1C2007445 and RS-2023-00280495)of Republic of Korea.
文摘The development of portable X-ray detectors is necessary for diagnosing fractures in unconscious patients in emergency situations.However,this is quite challenging because of the heavy weight of the scintillator and silicon photodetectors.The weight and thickness of X-ray detectors can be reduced by replacing the silicon layer with an organic photodetectors.This study presents a novel bithienopyrroledione-based polymer donor that exhibits excellent photodetection properties even in a thick photoactive layer(~700 nm),owing to the symmetric backbone and highly soluble molecular structure of bithienopyrroledione.The ability of bithienopyrroledione-based polymer donor to strongly suppress the dark current density(Jd~10−10 A cm^(−2))at a negative bias(−2.0 V)while maintaining high responsivity(R=0.29 A W−1)even at a thickness of 700 nm results in a maximum shot-noise-limited specific detectivity of D_(sh)^(*)=2.18×10^(13)Jones in the organic photodetectors.Printed organic photodetectors are developed by slot-die coating for use in X-ray detectors,which exhibit D_(sh)^(*)=2.73×10^(12)Jones with clear rising(0.26 s)and falling(0.29 s)response times upon X-ray irradiation.Detection reliability is also proven by linear response of the X-ray detector,and the X-ray detection limit is 3 mA.
文摘The power expansion planning is large and capital intensive capacity planning. In the past, the expansion planning was established with the proper supply reliability in order to minimize social cost. However, such planning cannot be used in the power markets with many market participants. This paper proposed the power expansion planning process in the power markets. This system is composed of Regulator and Generation Company （GENCO）＇s model. Multi-criteria decision making rule is used for regulator model and several scenarios for GENCO model are applied.
基金This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (NRF-2017M3A9E9073371).
文摘Lithium metal is considered one of the most promising anode materials for application in next-generation batteries.However,despite decades of research,practical application of lithium metal batteries has not yet been achieved because the fundamental interfacial mechanism of lithium dendrite growth is not yet fully understood.In this study,a series of reactive molecular dynamics (MD) simulations was performed to investigate the electrochemical dynamic reactions at the electrode/electrolyte interface.It allows quantitative characterization of morphological phenomena and real-time interfacial visualization of the dynamic growth of dead lithium and dendrites during repeated charging.This computational protocol was utilized to investigate the dendrite mitigation mechanism when an electrolyte additive (hydrogen fluoride) is dissolved in an organic ethylene carbonate (EC) electrolyte solvent.It was confirmed that beneficial decomposition reactions between electrolyte components form a protective film on the anode surface,suppressing large interphase volume changes and unnecessary degradation reactions.
基金supported by the Korea Electrotechnology Research Institute Primary research program through the National Research Council of Science & Technology(NST)funded by the Ministry of Science,ICT and Future Planning(MSIP)(No.18-12-N0101-41)the Creative Allied Project of the NST(No.CAP-15-06-ETRI)the National Research Foundation(NRF)of Korea funded by MSIP(Nos.2016R1A2A1A05005381 and2017R1A4A1015426)
文摘We demonstrate a femtosecond Cr：YAG laser mode-locked by a carbon nanotube saturable absorber mirror（CNT-SAM） at a repetition rate of 550 MHz. By employing the CNT-SAM, which exhibits a modulation depth of 0.51% and a saturation fluence of 28 μJ∕cm^2 at 1.5 μm, we achieved a compact bulk Cr：YAG laser with selfstarting mode-locked operation near 1.5 μm, delivering an average output power of up to 147 m W and a pulse duration of 110 fs. To our knowledge, this system provides the highest repetition rate among reported CNT-SAM mode-locked Cr：YAG lasers and the shortest pulse duration among saturable absorber mode-locked Cr：YAG lasers with repetition rates above 500 MHz.
