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Levitation Time Measurement of Water Drops on the Surface of Liquid Nitrogen
김희태,이영희,조훈영 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.6
The levitation of water drops on the surface of liquid nitrogen is studied. The water drop evaporates the liquid nitrogen, which makes a nitrogen vapor film between the water drop and the surface of the liquid nitrogen. The temperature of the drop falls from the initial temperature of the drop to the melting temperature and then eventually reaches the Leidenfrost temperature at which an ice sphere falls into the liquid nitrogen. The floating time of the water drop on the surface of liquid nitrogen corresponds to how long the temperature of the water drop takes to go from the initial temperature to the Leidenfrost temperature. We measured the floating time of the water drop on the surface of the liquid nitrogen as a function of the size of the drop and the initial temperature of the drop. The floating time increases linearly with increasing drop size and increases linearly with increasing initial temperature of drop, which can be explained reasonably well by assuming uniform cooling of the drop by heat conduction.
임상적 관점에서 본 Primary Dystonia와 Dystonia-plus Syndrome
김희태 대한신경과학회 2004 대한신경과학회지 Vol.22 No.6
Dystonia is a disorder of movement caused by involuntary, sustained muscle contractions affecting one or more sites of body, frequently causing twisting and repetitive movements, or postures. Dystonic movements and postures can produce a wide range of clinical presentations. Some distinguishing clinical features of dystonia can help the appropriate diagnosis of primary dystonia. The direction of contraction is almost consistent. Action dystonia and occupational dystonia are related to a movement or task-specific movement, respectively. Sensory tricks or gestes antagonistes are usually seen in patients with dystonia. Two types of tremors can be seen in patients with dystonia: a postural and/or action tremor that resembles essential tremor and a rhythmic expression of dystonic tremor. Sometimes dystonic tremor appears to be less regular and can be associated with myoclonus. Onset age of dystonia, body distribution and etiologies are important to correct diagnosis of primary dystonia. It is well known that the age of onset has important prognostic implications. This article highlights general concepts of phenomenology, classification that are relevant for the purpose a clinical diagnosis.
김희태,오재석,박의준,이영순,김병철 한국전자파학회 2000 한국전자파학회논문지 Vol.11 No.8
본 논문에서는 다이오드의 비선형 특성을 선형화하고 온도에 따른 특성 변화를 보상하는 방법에 대해 연구하였다. 입력전력에 대한 다이오드의 비선형성을 선형화학 위해 Square root 회로를 사용하였으며, 온도에 따른 다이오드의 특성변화를 보상하기 위해서는 2개의 동일한 다이오드와 기준전위를 가변시킬 수 있는 OP-Amp를 사용하였다. 그 결과로써, (Square root 회로와 온도보상회로를 이용하여) 설계된 다이오드 전력 검출기는 입력전력이 -6㏈m보다 큰 경우에 0.23$\pm$0.025 V/㏈m의 비율로 선형적으로 출력전력을 검출하였으며, 상온에서 8$0^{\circ}C$까지의 온도변화에 대해 출력전압의 변화없이 안정적으로 동작하였다. In this paper, the method to linearize the non-linearity of diode and to compensate the characteristics change of diode with the temperature is studied. Square root circuit is used to linearize the non-linearity of diode about the input power, and two identical diodes and OP-Amps, which have variable reference, are used to compensate the characteristic change of diode with the temperature. As the result, designed diode power detector (with the square root circuit and temperature compensation circuit) can detect the output power linearly with the 0.23 $\pm$0.025V/dBm rate in the case the input power is greater than -6 dBm, and the designed circuit operates stably with no variation in the output data about the temperature change from the room temperature to 8$0^{\circ}C$.