• Journal of Astronomy and Space Sciences
• /
• v.26 no.2
• /
• pp.237-266
• /
• 2009

In 1631 A.D. Jeong Duwon, an ambassador of the Joseon dynasty was sent to the Ming dynasty. There he met $Jo\tilde{a}o$ Rodrigues, a Jesuit missionary, in Dengzhou of Shandong peninsula. The missionary gave the ambassador a number of results of latest European innovations. A detailed description on this event was written in 'Jeong's official report regarding a message from an European country'(西洋國奇別狀啓), which is an important literature work to understand the event. Since the document was written in classical Chinese, we make a comprehensive translation to Korean with detailed notes. According to the report, the items that Rodrigues presented include four books written in Chinese that describe European discoveries about the world, a report on the tribute of new cannons manufactured by Portuguese in Macao, a telescope, a flintlock, a Foliot-type mechanical clock, a world atlas drawn by Matteo Ricci, an astronomical planisphere, and a sun-dial. We discuss the meaning of each item in the Korean history of science and technology. In particular, Jeong's introduction is an important event in the history of Korean astronomy, because the telescope he brought was the first one to be introduced in Korean history. Even though king Injo and his associates of the Joseon dynasty were well aware of the value as military armaments of new technologies such as telescopes, cannons, and flintlocks, they were not able to quickly adopt such technologies to defend against the military threat of Jurchen. We revisit the reason in view of the general history of science and technology of east-Asian countries in the 17th century.

• Proceedings of the KIEE Conference
• /
• 1997.07d
• /
• pp.1478-1480
• /
• 1997

We investigated the breakdown characteristic of mineral oil according to applied voltage and tip radius. In this experiment, electrode system was point-plane geometry. The tip radius of needle was 5, 10, 20 and $25{\mu}m$, respectively. Applied voltage was AC and DC. We measured breakdown voltage for each tip radius with increasing electrode gap, 2mm to 10mm. Under nonuniform electric field, breakdown strength was higher when needle was negative than when needle was positive. Because it is polarity effects due to space charge. And the more sharp tip radius, whether we applied AC or DC, the higher breakdown strength. As tip radius increase, breakdown strength decreases exponentially.

• Journal of the Korean Society of Visualization
• /
• v.17 no.2
• /
• pp.32-38
• /
• 2019

A comparison study between computational-fluid-dynamics simulation and wind tunnel test for a megawatt-class wind turbine is conducted. For the study, flow-field in wake, basic aerodynamic performance, and effect of the yaw error for a 1/86 scaled-down model of the NREL offshore 5 MW wind turbine are numerically calculated using commercial software "FloEFD" with $k-{\varepsilon}$ turbulence model. The computed results are compared to the wind tunnel test performed by the constant-velocity mode for the model. It is shown that discrepancy are found between the two results at lower tip-speed ratio and higher yaw angle, however, the velocity-defection distribution in the wake, the torque coefficient at moderated and high tip-speed ratios are in good agreement with the wind tunnel test.

• Journal of Oral Medicine and Pain
• /
• v.41 no.4
• /
• pp.200-204
• /
• 2016

Numb chin syndrome, or mental neuropathy is a rare sensory neuropathy characterized by abnormal sensation such as hypoesthesia, paresthesia, or dysesthesia in the chin and lower lip innervated by the mental nerve. Sensory neuropathy of mental nerve is somewhat familiar to dentists because it can occur following nerve damage by trauma or dental treatment such as implant surgery or third molar extraction. It can also result from dental causes including abscess or osteomyelitis. However, it can be the first sign of the systemic disease or malignancy if it is not related to dental causes. In this study, we present the case of a patient who present with hypoesthesia and pain in chin area without other symptoms and is later diagnosed with diffuse large B-cell lymphoma.

• Journal of Oral Medicine and Pain
• /
• v.41 no.2
• /
• pp.72-75
• /
• 2016

Lichen planus is a chronic disease characterized by bilateral and multiple lesions on the skin or oral mucosa. Lichen planus is caused by immune mediated degeneration along the border between epithelium and connective tissue. The incidence of oral squamous cell carcinoma in patients diagnosed with oral lichen planus (OLP) is reported to be between 0.4%-5.6% in different studies and the World Health Organization has categorized lichen planus as "a potentially malignant disorder". However, the correlation between OLP and oral cancer still remains controversial as some reported that the reason for increased incidence of squamous cell carcinoma in OLP patient is misdiagnosis of dysplastic lesion as OLP. This report aims to discuss the correlation between OLP and oral cancer through a case of middle aged woman diagnosed with OLP who was successfully treated but developed squamous cell carcinoma 8 years later.