• 대한기계학회논문집A
• /
• 제33권3호
• /
• pp.196-200
• /
• 2009

Lithium niobate ($LN:LiNbO_3$) is a compound of niobium, lithium and oxygen. The characteristics of LN are piezoelectricity, ferroelectricity and photoelectricity, and which is widely used in surface acoustic wave (SAW). To manufacture LN devices, the LN surface should be a smooth surface and defect-free because of optical property, but the LN material is processed difficult b traditional processes such as grinding and mechanical polishing (MP) because of its brittleness. To decrease defects, chemical mechanical polishing (CMP) was applied to the LN wafer. In this study, the suitable parameters such as down force and relative velocity, were investigated for the LN CMP process To improve roughness, the LN CMP was performed using the parameters that were the highest removal rate among process parameters. And, evaluation of optical property was performed by the optical reflectance.

• 한국식품영양과학회지
• /
• 제26권5호
• /
• pp.788-793
• /
• 1997

Addition of sugar, enzymatic hydrolysis and salt concentration were evaluated for their effects on the changes in some characteristics of Kimchi juice during fermentation. The Kimchi juice was prepared by brining and grinding of outer layer leaves of chinese cabbage, one of the wastes products of Kimchi processing, followed by fermentation proceeded significantly faster. Addition of sucrose or glucose at the ange of 0.5~2.0 % also improved the fermentation but the concentration effect was little. Enzymatic hydrolysis on the brined cabbage prior to fermentation with a commercial polysaccharides hydrolases also increased the fermentation. However the solid concentration in Kimchi juice was rather decreased by higher concentration of NaCl and enzymatic hydrolysis. The reducing sugar content showed a rapid decrease from 24 hours of fermentation and the effect of enzymatic hydrolysis was little.

• Tribology and Lubricants
• /
• 제17권6호
• /
• pp.476-481
• /
• 2001

This paper has been presented the hydrodynamic effect by the journal speed, eccentricity and source positions in order to overcome the defects of air bearing such as low stiffness and damping coefficient. Choosing the two row source position of air bearing is different from existed investigations in the side of pressure distribution of air film because of the high speed of journal and the wedge effects by the eccentricity. These optimal chooses of the two row source positions enable us to improve the performance of the film reaction force and loading force as making the high speed spindle. In this paper, The pressure behavior in theory of air film according to the eccentricity of journal and the source positions analyzed. The theoretical analysis have been identified by experiments. The results of investigated characteristics may be applied to precision devices like ultra-precision grinding machine and ultra high speed milling.

• International Journal of Precision Engineering and Manufacturing
• /
• 제6권2호
• /
• pp.5-11
• /
• 2005

Among the micro machining techniques, micro EDM is generally used for machining micro holes, pockets, and micro structures on difficult-cut-materials. Micro EDM parameters such as applied voltage, capacitance, peak current, pulse width, duration time are very important to fabricate the tool electrode and produce the micro structures. Developed micro EDM machine is composed of a 3-axis driving system and RC circuit equipped with pulse generator. In this paper, using micro EDM machine, the characteristics of micro EDM process are investigated and it is applied to micro holes, slots, and pockets machining. Through experiments, relations between machined surface and voltages and between MRR and feedrate are investigated. Also the trends of tool wear are investigated in case of hole and slot machining.

• 한국공작기계학회논문집
• /
• 제14권5호
• /
• pp.13-20
• /
• 2005

Micro EDM process is generally used for machining microholes, cavities, and three dimensional shapes. For machining micro structures, first of all, micro tool electrode is indispensable and WEDG system is proposed for tool fabrication method. When using WEDG, its machining characteristics are highly affected by many EDM parameters such as applied voltage, current, rotation speed, capacitance, and pulse duration. Therefore, the design of experiment is introduced to fully understand the effect of the EDM parameters on machining tool electrode. And an attempt has been made to develop the mathematical model for predicting the size of the tool electrode by calculating spark distance. The suggested model was verified with experiment and predicted working gap distance is in good accord with the measured value.

• 열처리공학회지
• /
• 제19권5호
• /
• pp.262-269
• /
• 2006

The development of eco-friendly low pressure carburizing system with high pressure gas quenching(LPC-GQ, 500kg/charge) led to new stage in the fundamental case-hardening treatments. This is due to its ability to provide tighter tolerances on the carburizing process with notable reductions in distortion of the carburized and hardened workpiece. This system is characteristics by high uniformity and reproducibility of heat treatment results, absence of an intergranular oxidation layer, carburizing of complex shapes, reduced cycle time, low operating costs, simplified production, eliminate post washing, and reduced grinding costs.

• 수면정신생리
• /
• 제12권1호
• /
• pp.23-26
• /
• 2005

Bruxism is defined as 'diurnal or nocturnal parafunctional activity including clenching, bracing, gnashing, and grinding of the teeth'. Bruxism and clenching are two of the most common contributing factors in patients with temporomandibular disorders and craniofacial pain disorders. Even though many studies report the high prevalence of bruxism, its cause is still not clear. Occlusal interference has been regarded as a major etiologic factor. Nowadays, psychological stress and sleeping disorders are generally regarded as major possible etiologic factors. More than likely, the cause is multifactoral and overlapping, which makes it difficult for the practitioner to apply comprehensive and effective management strategies. Although dentists and psychologists generally believe that effective treatment is best achieved with a better understanding of the etiology of a given disorder, for now treatment for this type of disorder must proceed without a clear understanding of etiology. To overcome this obstacle, evidence-based comprehensive management protocols based on accumulated scientific findings should be provided. In this presentation, epidemiology, etiology, and the characteristics of bruxism are reviewed. Diagnostic procedures and management strategies focused on occlusal appliances and behavioral approaches are also discussed.

• 한국공작기계학회:학술대회논문집
• /
• 한국공작기계학회 2005년도 춘계학술대회 논문집
• /
• pp.377-382
• /
• 2005

This paper describes the design of micro machine tools system for mechanical machining of micro/meso scale mechanical parts. The micro machining systems such as $\mu-Late$, $\mu-milling/drilling$ machine and $\mu-grinding$ machine are the basic elements constructing $\mu-factory$ which gains more attention recently because of increasing needs of mico and nano-parts in various industrial and medical area. A miniaturized 3-axis milling machine with VCM stage and air spindle and palm-top size micro-late are designed, and air bearing stage and stepwise linear motion system with PZT are studied for motion system. The micro cutting characteristics are investigated experimentally, and reconfigurable machine structures are also considered.

• 한국공작기계학회논문집
• /
• 제10권6호
• /
• pp.109-115
• /
• 2001

This paper investigates the mechanical characteristics of angle-ply laminates with non-woven carbon tissue. The lami- nates were made by inserting non-woven carbon tissue at the interface. Specimens were rounded near the tabs by grinding and polishing to reduce the stress concentration. Cyclic loads were applied to the specimens and the stress and fatigue life curves were obtained. The matrix crack density was also evaluated to check the effects of non-woven carbon tissue on the fracture resistance of composite laminates. C-Sean technique was used to evaluate the delamination, and SEM was used to understand the fracture mechanisms of the laminates. Experimental results show that the fatigue strength and life of composite laminates were increased by inserting non- woven carbon tissues. The results also show that the matrix crack density and delamination area were reduced by inserting non-woven carbon tissues.

• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2001년도 학술논문발표회
• /
• pp.82-87
• /
• 2001

The purpose of this study is for the active use of the fly ash, which is a by-product of the combustion pulverizes coal thermal power plants, to compensate for the lack of landfill and for conservation of energy, by using fly ash as the supplementary cementitious material, and to prove its possibility as the related products of the cement. First of all, the ordinary fly ash is grinded in a special method and its fineness is controlled from 6000$\textrm{cm}^2$/g to 8000$\textrm{cm}^2$/g, then replaced it with the 10% to 80% of the cement mortar in order to test physics characteristics. The first experiment conducts on the strength development in fly ash replacing content and fineness. and the changes of the flow values, incorporating fly ash into cement. The second one is about the slow development of the strength of the fly ash mortar in early ages, and improves its strength with the activator $Na_{2}SO_{4}$, using high volume fly ash.