| 1. |
- Kim, Kyung Ho, 1984, et al.
(author)
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Probing variable range hopping lengths by magneto conductance in carbonized polymer nanofibers
- 2018
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 8:1
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Journal article (peer-reviewed)abstract
- Using magneto transport, we probe hopping length scales in the variable range hopping conduction of carbonized polyacetylene and polyaniline nanofibers. In contrast to pristine polyacetylene nanofibers that show vanishing magneto conductance at large electric fields, carbonized polymer nanofibers display a negative magneto conductance that decreases in magnitude but remains finite with respect to the electric field. We show that this behavior of magneto conductance is an indicator of the electric field and temperature dependence of hopping length in the gradual transition from the thermally activated to the activation-less electric field driven variable range hopping transport. This reveals magneto transport as a useful tool to probe hopping lengths in the non-linear hopping regime.
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| 2. |
- Park, D. -M, et al.
(author)
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Comparative study on added resistance of a container ship in waves
- 2019
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In: Proceedings of the International Offshore and Polar Engineering Conference. - : International Society of Offshore and Polar Engineers. - 9781880653852 ; , s. 4418-4425
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Conference paper (peer-reviewed)abstract
- This paper presents a comparative study on the motion responses and added resistance of a container ship. Eight institutions participated in the comparative study, and ten numerical results were compared with two experimental results. Two experimental results were obtained from Seoul National University towing tank and Sweden SSPA seakeeping basin. The results of two experimental institutions in head sea condition were compared and showed good agreement with each other. The difference in motion responses and added resistance according to the numerical analysis method were compared. Even though the same program was used, it was observed that different results were obtained depending on the users. The comparison of the motion response and the added resistance according to the change of wave slope showed that the added resistance greatly changed according to the wave slope. This tendency was the same in experimental results and CFD analysis results. From the comparative study, the influence of the experiment method on the added resistance, and the characteristics of numerical each code were identified.
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| 3. |
- Kim, Kyung Ho, 1984, et al.
(author)
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Apparent Power Law Scaling of Variable Range Hopping Conduction in Carbonized Polymer Nanofibers
- 2016
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 6
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Journal article (peer-reviewed)abstract
- We induce dramatic changes in the structure of conducting polymer nanofibers by carbonization at 800 degrees C and compare charge transport properties between carbonized and pristine nanofibers. Despite the profound structural differences, both types of systems display power law dependence of current with voltage and temperature, and all measurements can be scaled into a single universal curve. We analyze our experimental data in the framework of variable range hopping and argue that this mechanism can explain transport properties of pristine polymer nanofibers as well.
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| 4. |
- Park, D. -M, et al.
(author)
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Experimental and numerical studies on added resistance of ship in oblique sea conditions
- 2019
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In: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 186
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Journal article (peer-reviewed)abstract
- In this paper, the added resistance of a large tanker is estimated experimentally and numerically in oblique sea. Experiments on ship motion response and added resistance in oblique sea are performed in the SSPA seakeeping basin. The experiments are conducted using the self-propulsion test for seven wave directions between 180° and 0°. In the self-propulsion test, the added resistance is estimated from the difference between the thrust of the propeller in calm water and waves. In the case of the head sea, the results are compared with those obtained from the captive test at the towing test of Seoul National University. As numerical method, two methods are selected: the strip method and the 3D Rankine panel method. The maximum value of the added resistance is observed between the incident wave directions of 180° and 150°. From 120°, the added resistance tends to decrease and the peak of the added resistance shifted to the short waves. Through the two numerical analysis methods, the tendency of added resistance and the cause of the change of the added resistance in the oblique sea are investigated.
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| 5. |
- Park, M. S., et al.
(author)
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InAs/GaAs p-i-p quantum dots-in-a-well infrared photodetectors operating beyond 200 K
- 2014
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In: Electronics Letters. - Stevenage, United Kingdom : Institution of Engineering and Technology (IET). - 1350-911X .- 0013-5194. ; 50:23, s. 1731-1732
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Journal article (peer-reviewed)abstract
- High-temperature operating performance of p-i-p quantum dots-in-awell infrared photodetectors (QDIPs) is successfully demonstrated. The optically active region consists of 10 layers of p-doped selfassembled InAs quantum dots (QDs) asymmetrically positioned in In0.15Ga0.85As quantum wells (QWs). The dark current is suppressed by an incorporated superlattice (SL) structure composed of 10 pairs of AlGaAs/GaAs heterostructure. The very low recorded dark current makes the fabricated p-i-p QDIPs suitable for high-temperature operation. The measured photoresponse reveals broad mid-wave infrared (MWIR) detection up to 200 K.
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| 6. |
- Rostaghi-Chalaki, Mojtaba, et al.
(author)
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Classification and comparison of AC and DC partial discharges by pulse waveform analysis
- 2021
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In: International Journal of Electrical Power & Energy Systems. - : Elsevier Ltd. - 0142-0615 .- 1879-3517. ; 125
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Journal article (peer-reviewed)abstract
- This study aims to classify and compare AC and DC partial discharge (PD) based on PD pulse waveform analysis. To achieve this goal, we designed a testbed that enables precise measurements of individual PD pulses. The testbed is used for collecting data from four different types of PDs including cavity, surface, corona, and floating potential discharges generated by individual PD source samples. All samples were examined under AC, positive DC, and negative DC electrical stresses, through which we captured thousands of PD pulses. We classify the waveforms of each PD type into representative groups associated to their discharge mechanisms. The statistical data of the measured pulses are utilized to identify the differences between AC and DC PDs while the clustered patterns of PD amplitude versus their temporal characteristics serve as a means to classify the types of PDs under AC and DC electrical stresses.
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