• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.48 no.8
• /
• pp.591-597
• /
• 1999

The propagation characteristics of high power microwave pulse in an air-breakdown environment are examined. The maximum electron density produced by microwave air-breakdown is limited to $10^6cm^{-3}$ by the tail-erosion effect. Inorder to increase the electron density, the scheme using two pulses intersecting at a desired height is considered. Increasing the carrier frequency, it is shown that microwave pulse can be transferred without the serious erosion in the numerical simulation. This result is useful for the above scheme. Also, an experiment is conducted to show the tail-erosion effect and confirm that a rapidly generated lossy plasma can cause spectral breaking and frequency shift of a high-power microwave pulse. The experimental results are presented by comparing the frequency spectrum of an incident pulse with that of the pulse transmitted through a self-induced air-breakdown environment. The experimental results show that the amount of frequency upshift is co-related with the ionization rate, whereas that of frequency downshift is correlated with the energy losses from the pulse in the self-generated plasma.

• Wind and Structures
• /
• v.27 no.4
• /
• pp.213-221
• /
• 2018

In the desert and Gobi regions with strong wind and large sediment discharge, sand transporting engineering is more effective than sand blocking and sand fixing measures in sand prevention. This study uses the discrete phase model of 3D numerical simulation to study the motion trail, motion state and distribution rule of sand particles with different grain diameters when the included angle between the main shaft of the feather-row lateral transportation sand barrier and the wind direction changes, and conducts a comparison in combination with the wind tunnel test and the flow field rule of common sand barrier. According to the comparison, when wind-sand incoming flow passes through a feather-row sand barrier, sand particles slow down and deposit within the deceleration area under the resistance of the feather-row sand barrier, move along the transportation area formed by the transportation force, and accumulate as a ridge at the tail of the engineering. With increasing wind speed, the eolian erosion of the sand particles to the ground and the feather-row sand barrier is enhanced, and the sand transporting quantity and throw-over quantity of the feather-row sand barrier are both increased. When sand particles with different grain diameters bypass the feather-row sand barrier, the particle size of the infiltrating sands will increase with the included angle between the main shaft of the feather-row sand barrier and the wind direction. The obtained result demonstrates that, at a constant wind speed, the flow field formed is most suitable for the lateral transportation of the wind-drift flow when the included angle between the main shaft of the feather-row sand barrier lateral transportation engineering and the wind speed is less than or equal to $30^{\circ}$.

• The Journal of Korean Physical Therapy
• /
• v.21 no.2
• /
• pp.117-124
• /
• 2009

Purpose: This study examined the effects of swimming exercise and Achyranthes Radix extracts on the inflammatory and behavioral responses in type II collagen-induced arthritic rats for 28 days. Methods: Sprague-Dawley rats were allocated randomly to one of the following four groups: only type II collageninduced (group Ⅰ), application of swimming exercise after type II collagen-induced (group II), application of Achyranthes Radix ointment after type II collagen-induced (group III), application of swimming exercise and Achyranthes Radix ointment after type II collagen-induced (group IV). Arthritis was established in SD rats by an intradermal injection of Chick type II collagen plus incomplete Freund's adjuvant at the base of the tail of the animals. The swimming exercise program consisted of a 25 min swimming session/day with a load corresponding to 5.5% of the weight bearing, three days/week for four weeks. The Achyranthes Radix ointment (0.1g) was applied twice a day for five days. The changes in behavior, H & E stain, and cyclooxygenase-2 (COX-2) level in the knee joint were assessed. Results: The gross and histological examination, after RA induction showed reddening, edema and erythema. The H & E stain revealed the destruction of articular cartilage, bony erosion and the infiltration of inflammatory cells after RA induction. The mechanical allodynia test results were significantly higher in group I than in groups II, III and IV (p<0.01). The immunohistochemistrical response of COX-2 in the knee joint showed that groups II, III, IV had a lower response effect than group I. Conclusion: Swimming exercise training and Achyranthes Radix ointment decreased the inflammatory responses and enhanced the behavioral responses in the arthritic rats.