• Tribology and Lubricants
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• 제21권1호
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• pp.8-15
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• 2005

In this study a general Galerkin FE lubrication analysis method is utilized to analyze the complex lubrication performance of a spiral groove seal, which is being designed and developed for a high-speed flying object application operating at a high-speed of over 50,000 rpm. As at the equilibrium seal clearance the axial stiffness of the seal is predicted to have almost such a constant high value of $1.04\times10^8\;N/m$ regardless of a rotating speed, the seal is expected to maintain a stable thickness of lubrication film under a certain external excitation acting. Also, as even at an ultra high-speed of 80,000 rpm the axial damping of the seal is shown to have a rotatively high value of 5,775 N-s/m, the dynamic stability of the seal system at the axial degree of freedom is assured well enough.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 추계학술대회 논문집 학회본부
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• pp.282-284
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• 1997

Ultrasonic motors using piezoelectric ceramics and brass metal endcaps were fabricated, which is operated by single - phase high frequency. The structure of the ultrasonic motors has the wind-mill type. The stator part consists of a piezoelectric disk and two metal endcaps slotted wind-mill type. According to the piezoceramic disk vibrates as a radial mode, two metal endcaps provide both longitudinal and torsional displacements simultaneously. Because the metal endcaps have a nonsymmetric structure. the principle of the ultrasonic motor is not well understood. The dimension of the ultrasonic motor is diameter in 12.7 mm and thickness in 2.0 mm, and especially the PMN-PT-PZ piezoelectric disk was used. The maximum revolution speed 700 rpm and the maximum torque 0.22 mN.m were obtained. The ultrasonic motor for rotation was Supplied only single phase AC.

• 한국재료학회지
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• 제27권7호
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• pp.364-368
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• 2017

We performed temperature dependent current-voltage (I-V) measurements to characterize the electrical properties of $Au/Al_2O_3/n-Ge$ metal-insulator-semiconductor (MIS) diodes prepared with and without $H_2O$ prepulse treatment by atomic layer deposition (ALD). By considering the thickness of the $Al_2O_3$ interlayer, the barrier height for the treated sample was found to be 0.61 eV, similar to those of Au/n-Ge Schottky diodes. The thermionic emission (TE) model with barrier inhomogeneity explained the final state of the treated sample well. Compared to the untreated sample, the treated sample was found to have improved diode characteristics for both forward and reverse bias conditions. These results were associated with the reduction of charge trapping and interface states near the $Ge/Al_2O_3$ interface.

• 아시안잔디학회지
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• 제13권4호
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• pp.201-212
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• 1999

In use of pesticides in golf courses has been increased steadily. Environmental concern as well as decrease in efficiency led the turfgrass management into an alternate approach of using beneficial microorganism to deal with turfgrass pests. This study was focused on the use of such microorganisms for improving cultural environment and minimizing the use of pesticides. Microorganisms antagonistic to turfgrass diseases were applied to zoysiagrass fairways and creeping bentgrass greens in Yusung country club. Tharch accumulation, disease occurrence, and other cultural environments were compared among the combinations of microorganisms and suppliemental N applications. The application of microorganisms antagonistic to turfgrass diseases improved turf resiliency. Thatch thickness was 3.03cm in the control plot but it was 2.11cm in plots treated by microorganisms, indicating significant effects of microorganism application on reduction of thatch accumulation. Number of microorganism that can decompose of cellulose was higher at the plots treated with useful microbial products and it was considered that existence of higher population of microorganisms resulted in reduction of thatch accumulation. In the evaluation of relationship between thatch accumulation and disease occurrence, greater thatch accumulation was observed at the golf courses which have been frequently infested by large patch. However, the rate of thatch accumulation varied among surveyed golf courses regardless of the year of turf establishment. Therefore, management practice which can be effective for reduction of thatch could result in large patch suppression. The application of microorganisms on the established turfgrasses reduced the occurrence rate of pythium blight and yellow path diseases, whereas occurrence of brown patch and dollar spot increased.

• 한국진공학회지
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• 제4권S2호
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• pp.131-138
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• 1995

The broad beam ion sources of hot filament plasma type have widely used for modifications of materials and thin films, and the new type intensive current broad beam metal ion source including reactive gaseous ion beams is needed for preparing the hard coating films such as DLC, $\beta-C_3N_4$ Carbides, Nitrides, Borides etc. Now a electorn beam evaporation(EBE) broad beam metal ion source has been developed for this purpose in our lab. CN film has been formed by the EBE ion source. Study of the CN film shows that it has high hardness(HK=5800kgf/$\textrm {mm}^2$)and good adhesion. This method can widely changes the ratio of C/N atom's concentrations from 0.14 to 0.6 and has high coating rate. The low energy pocket ion source which was specially designed for surface texturing of medical silicon rubber was also developed. It has high efficiency and large uniform working zone. Both nature texturing and mesh masked texturing of silicon rubbers were performed. The biocompatibility was tested by culture of monocytes, and the results showed improved biocompatibility for the treated silicon rubbers. In addition, the TiB2 film synthesized by IBED is being studied recently in our lab. In this paper, the results which include the hardness, thickness of the films and the AES, XRD analysis as well as the tests of the oxidation of high temperature and erosion will be presented.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1997년도 Proceedings of the 12th KACG Technical Meeting and the 4th Korea-Japan EMGS (Electronic Materials Growth Symposium)
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• pp.19-22
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• 1997

The surface modificaion of alumina by $Al_2$O$_3$/SiC nanocomposite coating was studied in terms of processing and microstructure. A powder slurry of 5 vol% SiC composition was dipcoated onto presintered alumina bodies and pressurelessly sintered at 1$700^{\circ}C$ for 2 h in $N_2$. The used of organic binder and plasticizer in the slurry preparation, and the control of the density of presintered alumina body were found to be necessary to avoid cracking and warping during processing. The nanocomposite coating well bonded to the alumina body with thickness about 110 ${\mu}{\textrm}{m}$. The average grain size of coating (2 ${\mu}{\textrm}{m}$) was much finer than that of alumina body (13 ${\mu}{\textrm}{m}$). Fracture surface observations revealed mostly transgranular fracture for the coating, whereas intergranular fracture for the alumina body. Some pores (about 6%) were observed in the coating layer, although the alumina body showed fully dense microstructure.

• 열처리공학회지
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• 제23권2호
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• pp.75-82
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• 2010

A new advanced combined PVD/CVD technique of DLC film deposition has been developed. Deposition of a DLC film was carried out using a pulsed carbon arc discharge in vapor hydrocarbon atmosphere. The arc plasma enhancing CVD process promotes dramatic increase in the deposition rate and decrease of compressive stress as well as improvement of film thickness uniformity compared to that obtained with a single PVD pulsed arc process. The optical spectroscopy investigation reveals great increase in radiating components of $C_2$ Swan system molecular bands due to acetylene molecules decomposition. AFM, Raman spectroscopy, XPS and nano-indentation were used to characterize DLC films. The method ensures obtaining a new superhard DLC nano-material for deposition of protective coatings onto various industrial products including those used in medicine.

• Steel and Composite Structures
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• 제7권6호
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• pp.469-486
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• 2007

The paper is concerned with the behavior of tapered steel plate girders, primarily subjected to shear loading; experimental as well as finite element results obtained from the studies are presented in this paper. In the experimental study, 11 large-scale girders, one of uniform section and 10 tapered, were tested to failure and all girders were analysed by finite element method. The results are compared and the accuracy of the finite element modeling established. A parametric study was carried out with thickness of web, loading direction and taper angle as parameters. An analytical model, based on Cardiff model for girders of uniform cross-section, is also proposed in the paper.

• 소성∙가공
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• 제26권3호
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• pp.150-155
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• 2017

To obtain the Goss texture, {110}<001>, IF steel sheets were asymmetrically rolled by 50-89% reduction in the thickness at room temperature and subsequently annealed at 200, 900, and $1200^{\circ}C$ in a box furnace under air atmosphere. The asymmetrically rolled specimens and annealed specimens show well-developed Goss texture, {110}<001>. After the IF steel sheets were asymmetrically rolled at room temperature and subsequently annealed at $900^{\circ}C$ for 1 h in a box furnace under air atmosphere, the intensity of the Goss texture, {110}<001> was high in the IF steel sheets.

• E2M - 전기 전자와 첨단 소재
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• 제10권10호
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• pp.1034-1040
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• 1997

A solar cell conversion effiency was degraded by grain boundary effect in polycrystalline silicon. Grain boundaries acted as potential barriers as well as recombination centers for the photo-generated carriers. To reduce these effects of the grain boundaries we investigated various influencing factors such as emitter thickness thermal treatment preferential chemical etching of grain boundaries grid design contact metal and top metallization along boundaries. Pretreatment in $N_2$atmosphere and gettering by POCl$_3$and Al were performed to obtain multicrystalline silicon of the reduced defect density. Structural electrical and optical properties of slar cells were characterized before and after each fabrication process. Improved conversion efficiencies of solar cell were obtained by a combination of pretreatment above 90$0^{\circ}C$ emitter layer of 0.43${\mu}{\textrm}{m}$ Al diffusion in to grain boundaries on rear side fine grid finger top Yb metal and buried contact metallization along grain boundaries.