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Control over the emission properties of impregnated dispenser cathodes via surface pore density
Yongjun Hong,Seong Lee,Jin-Woo Shin,Sung Ho Lee,Joon-Ho So 한국물리학회 2016 Current Applied Physics Vol.16 No.10
Metal injection molding (MIM) was used to fabricate impregnated dispenser cathodes. The emission properties of tungsten cathodes were adjusted by controlling the number of exposed surface pores via mechanical polishing after completion of the impregnation process with 4BaO:CaO:Al2O3 (4:1:1) at 1600 ~ 1900C. The average distance between neighboring pores decreased as the number of pores increased. Three cathode samples having various surface pore densities were compared. Emission improved as the surface pore density increased. An average distance between exposed pores of 3.32 mm resulted in an emission current of 2.14 A (7.57 A/cm2) at 1030Cbr, corresponding to a work function of 1.92 eV, which is comparable to that of an M-type cathode. Thus, control of the surface pore density of impregnated cathodes provides a simple, cost-effective means to produce high current density thermionic electron guns.
A Study on Bird Deterrent System to Improve the Performance of Repelling Harmful Birds
Yongjun Cho(조용준),Haeyong Yun(윤해룡),Hyunggil Hong(홍형길),Jangseok Oh(오장석),Senongyong Woo(우성용),Suhwan Song(송수환),Dongwoo Kim(김동우),Minsu Gang(강민수),Kabho Seo(서갑호),Youngtae Lee(이영태),Jaedoo Jo(조재두) 한국기계가공학회 2020 한국기계가공학회지 Vol.19 No.8
We improved the sound pressure of the speaker and allowed the speaker to rotate 360 degrees to improve the effectiveness of the acoustic type bird repellent system. The prototype of the bird repellent system was developed by evaluating sound pressure characteristics by distance and direction and installing orchards. As a result of the evaluation, the extermination sound pressure increased from a distance of about 30 m to a maximum of 60 m, and through the rotary speaker, the extermination distance could be widened in all directions without specific direction.
Enabling Energy Efficient Image Encryption using Approximate Memoization
Hong, Seongmin,Im, Jaehyung,Islam, SM Mazharul,You, Jaehee,Park, Yongjun The Institute of Electronics and Information Engin 2017 Journal of semiconductor technology and science Vol.17 No.3
Security has become one of the most important requirements for various devices for multi-sensor based embedded systems. The AES (Advanced Encryption Standard) algorithm is widely used for security, however, it requires high computing power. In order to reduce the CPU power for the data encryption of images, we propose a new image encryption module using hardware memoization, which can reuse previously generated data. However, as image pixel data are slightly different each other, the reuse rate of the simple memoization system is low. Therefore, we further apply an approximate concept to the memoization system to have a higher reuse rate by sacrificing quality. With the novel technique, the throughput can be highly improved by 23.98% with 14.88% energy savings with image quality loss minimization.
Vacuum-depositable thiophene- and benzothiadiazole-based donor materials for organic solar cells
Jeon, Yongjun,Kim, Tae-Min,Kim, Jang-Joo,Hong, Jong-In The Royal Society of Chemistry 2015 NEW JOURNAL OF CHEMISTRY Vol.39 No.12
<P>Three (D–A–D)-type electron donor materials, containing 2,1,3-benzothiadiazole as the electron-withdrawing core, and benzothiophene, naphthalene, and thiophene as electron-donating terminal groups, were synthesized for vacuum-depositable small-molecule organic solar cells. The donor material containing thiophene as the terminal group, <B>DT</B>, shows a maximum power conversion efficiency of 4.13%, a short-circuit current density of 9.89 mA cm<SUP>−2</SUP>, an open-circuit voltage of 0.86 V, and a fill factor of 0.48, in a bulk heterojunction solar cell with a blend ratio of <B>DT</B> : C<SUB>70</SUB> = 1 : 4 under simulated AM 1.5 solar irradiation at 100 mW cm<SUP>−2</SUP>.</P> <P>Graphic Abstract</P><P>A bulk heterojunction device based on <B>DT</B> : C<SUB>70</SUB> = 1 : 4 exhibited an efficient power conversion efficiency of 4.13%. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5nj01860a'> </P>