• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.8
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• pp.744-749
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• 2011

In this study, determination method of initial optimal nozzle expansion in pintle rocket was investigated. The initial optimal initial nozzle expansion was decided by maximizing the mass-averaged thrust coefficient that is calculated from thrust coefficient of minimum and maximum chamber pressure. The determination of initial optimal initial nozzle expansion was equivalent to that of the minimum propellant mass which was required for obtaining the desired mission performance. The highest pressure, thrust turndown ratio and total impulse ratio effected on the initial optimal nozzle expansion. Among them, total impulse ratio had great influence on the initial optimal nozzle expansion.

• Explosives and Blasting
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• v.18 no.3
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• pp.15-28
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• 2000

국내에서는 Heavy ANFO로 더 잘 알려져 있는 Emulsion Blends는 왁스 대신 오일을 사용 하여 상온에서 펌핑이 가능하도록 한 에멀젼과 ANFO(또는 초안)의 혼합물을 일컫는다. ANFO는 저렴하고 안전하며 장약이 쉽고 밀장전되는 장점이 있지만, 내수성이 거의 없고 폭발 속도가 느리며 장약 비중이 0.75∼0.90g/cc 정도로 낮아 폭약으로서 그 위력이 작은 단점을 갖고 있다. Blends는 수용성 ANFO 입자 사이의 빈 공간을 내수성 에멀젼이 태우고 있는 형태로서 에멀젼 함량 25%부터 내수성이 나타나기 시작하여 에멀젼 함량 40% 이상에서는 완전한 내수성을 갖게 되며, 에멀젼의 함량이 증가할수록 폭발속도는 카트리지 에멀젼 폭약에 근접하게 된다. 장약 비중은 에멀젼의 함량이 증가하여 45% 근처에서 1.25∼ 1.30g/cc의 최대 값을 갖지만, 그 이상의 에멀젼 함량에서는 기폭 감도 저하로 예감제를 사용하여 비중을 감소시키는 것이 바람직하다. Blends는 자체에 물을 함유하고 있으므로 열역학적으로 계산된 단위 중량당 반응열은 ANFO에 비해 매우 적지만, 폭발속도, detonation pressure(폭굉압), borehole pressure(폭발압력) 등이 ANFO에 비해 크므로 폭발압력에서부터 암석의 파괴가 가능한 압력가지의 단위 중량당 유효한 에너지의 양은 암석의 강도가 커질수록 ANFO에 비해 매우 적지만, 폭발속도, ANFO와 비슷해진다. 따라서 장약 비중이 ANFO의 130∼145%로 높은 Blends는 동일한 천공에 더 많이 장약할 수 있어 단위 천공당 암석 파괴에 이용되는 유효 에너지의 총 양이 커지게 되므로, 공간격과 저항선을 늘릴 수 있어 총 천공수를 감소시킬 수 있다. 결론적으로, Blends의 장점은 내수성과 함께 비장약량은 비슷하거나 약간 증가하는데 비해, 천공수는 크게 감소하여 전체적으로는 발파 현장의 경제성이 향상된다는데 있다.

• Journal of Oral Medicine and Pain
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• v.24 no.3
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• pp.269-280
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• 1999

구강안면동통환자의 발통점에 대한 보존적 치료방법중 저출력레이저의 효과를 평가하기 위해 교근, 측두근과 승모근에 발통점을 가진 치과대학생 69명을 무작위로 분류하여 37명에게는 GaAlAs 반도체 레이저를 조사하였고 나머지 32명은 레이저를 실제로 조사하지 않고 대조군으로 삼았다. 50mW, 820nm의 GaAlAs 반도체 레이저를 이용하여, 4주 동안 첫 주는 2회, 이후 3주 동안 1회씩 총 5회 조사하였고 전자통각계를 이용하여 압력통각역치를 측정한 후 이를 대조군과 비교한 바 다음과 같은 결과를 얻었다. 1. 남녀 및 조사군과 비조사군의 치료 전 압력통각역치는 차이가 없었다. 2. 조사군의 각 근육에서 측정한 압력통각역치는 레이저 치료 2주 후부터 유의하게 높아졌으나 비조사군에서는 차이가 없었다, 3. 비조사군의 치료 전, 후 압력통각역치에는 성 차가 없었다. 반면 종사군의 압력통각역치는 치료 전에는 성 차가 없었으나 치료 후에는 남성이 여성보다 유의하게 높았다.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.4
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• pp.12-18
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• 2021

This study aimed at preparing the solid propellants featuring high pressure exponent available for throttleable rocket system development. The combustion properties of solid propellant based on PCP as a prepolymer were investigated with the different nitramine oxidizer, HMX and HNIW. As a main oxidizer, HNIW could deliver higher burning rate, specific impulse and flame temperature than HMX. In addition, the introduction of AP as a co-oxidizer in PCP/Nitramine propellants could enhance burning rate, specific impulse and flame temperature, showing the lower pressure exponent with increasing the content of fine-sized AP, total solids and plasticizer. Moreover, we examined the temperature sensitivity on burning rate of propellants between 150 psia and 2,500 psia.

• Korean Journal of Optics and Photonics
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• v.6 no.3
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• pp.214-221
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• 1995

When the broad pressure region (0.5-3.5 atm) of laser media is pumped by 70 ns [FWHM] electronbeam accelerator (800 kV, 21 kA), the correlation between free-runnuing XeF$(C\rightarrowA$ excimer laser output and Xe concentration are studied. The resonator consisted of dichroic output coupler, and the laser output is optimized with laser media $(Xe/F_2/Ar)$ as functions of total pressure and gas mixing ratio. Under the condition of F2 0.46% fixed, the laser intrinsic efficiencies of 0.38%, 1.03%, and 0.29% are obtained at 1. 2, and 3 atm, respectively. So then the peaks of laser intrinsic efficiency occured to the higher Xe concentration with decreasing total gas pressure. By analyzing the kinetics for the $XeF^*(C)$ formation efficiency and XeF$(C\rightarrowA$ laser extraction efficiency the dependence of Xe concentration on their correlation is explained. As the results we propose efficient operation of an atmosphericpressure XeF$(C\rightarrowA$ laser. laser.

• Journal of the korean Society of Automotive Engineers
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• v.5 no.2
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• pp.1-14
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• 1983

총차량 중량이 15ton이 넘는 대형 트럭의 경우 1970년도에 18%에 불과하던 터보 챠저엔진의 비율은 점차 증가하여 1977년에 42%에 달하였고 1990년도에는 75%까지 증가할 것으로 예상 된다. 또한 현재 터보 챠저엔진의 BMEP는 11.2kg/$cm^{2}$, after cooled엔진은 13.6kg/$cm^{2}$에 이르나 앞으로는 after cooled엔지의 BMEP는 13-17kg/$cm^{2}$로 증대할 것이다. 그러나 터보 챠저엔진의 최대의 단점은 저속에서의 낮은 boost압력과 고속에서의 over boost압력을 갖는다는 것이나, 현재까지는 뚜렷한 해결책을 찾지 못하고 있는 실정이다. 따라서 1980년대에는 현재 사용되고 있는 터보 챠저나 이를 개선한 고성능 터보챠저를 부 착한 엔진이나 after cooled엔진이 주로 사용될 것으로 보인다. 앞으로 터보 챠저가 대형트럭용 엔진에 더욱 확대 사용되고 또 소형 디이젤 엔진이나 가솔린 엔진에서도 이용되기 위해서는 (1) 저속에서의 boost압력 증대 (2) 압력비의 증대 (3) 압축기 사용 flow range의 확대 (4) 소형 터보 챠저의 개발 등이 수반되어야 하며 이외에도 배기가스의 효율적인 에너지전달, 콤푸레샤 효율의 증대, 굉음의 감소, 저렴한 터보 챠저 및 after cooler의 개발, 터보 챠저의 소형화 등이 이루어져야 할 것이다.

• Nuclear Engineering and Technology
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• v.27 no.5
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• pp.775-783
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• 1995

This study is to assess the effects of increasing wall thickness on the safety margin of pressure tube in operating and of lowering initial hydrogen concentration on the DHC growth in respect to the improvement of the reliability of pressure tube in CANDU reactors. The pressure tube with thicker wall of 5.2 mm shows much higher safety margin for flaw tolerance by 25％ than the current 4.2mmm tube. The thicker pressure tubes have a great benefit in LBB assessment including the initial crack depth at which DHC occurs, the crack length at onset of leaking and the available time for action. The resistance for the pressure tube ballooning at LOCA accident is also increased with the thicker tube. The calculations for Heq concentration after 20 years of operation as a function of wall thickness and initial hydrogen concentration show that the 5.2 mm nil thickness tube with 5 ppm initial hydrogen concentration is the most resistant to DHC. with the lower initial hydrogen concentration, TSS temperature for the precipitation or hydride decreases and the crack growth during cooldown reduces.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.5
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• pp.385-390
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• 2015

The flow characteristics in micro shock tube are investigated experimentally. Studies were carried out using a stainless steel micro shock tube. Shock and expansion wave was measured using 8 pressure sensors. The initial pressure ratio was varied from 4.3 to 30.5, and the diameter of tube was also changed from 3mm to 6mm. Diaphragm conditions were varied using two types of diaphragms. The results obtained show that the shock strength in the tube becomes stronger for an increase in the initial pressure ratio and diameter of tube. For the thinner diaphragm, the highest shock strength was found among varied diaphragm condition. Shock attenuation was highly influenced by the diameter of tube.

• Tuberculosis and Respiratory Diseases
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• v.44 no.3
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• pp.592-600
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• 1997

Background : The level of imposed work of breathing (WOB) is important for patient-ventilator synchrony and during weaning from mechanical ventilation. Triggering methods and the sensitivity of demand system are important determining factors of the imposed WOB. Flow triggering method is available on several modern ventilator and is believed to impose less work to a patient-triggered breath than pressure triggering method. We intended to compare the level of imposed WOB on two different methods of triggering and also at different levels of sensitivities on each triggering method (0.7 L/min vs 2.0 L/min on flow triggering ; $-1\;cmH_2O$ vs $-2cm\;H_2O$ on pressure triggering). Methods : The subjects were 12 patients ($64.8{\pm}4.2\;yrs$) on mechanical ventilation and were stable in respiratory pattern on CPAP $3\;cmH_2O$. Four different triggering sensitivities were applied at random order. For determination of imposed WOB, tracheal end pressure was measured through the monitoring lumen of Hi-Lo Jet tracheal tube (Mallincrodt, New York, USA) using pneumotachograph/pressure transducer (CP-100 pulmonary monitor, Bicore, Irvine, CA, USA). Other data of respiratory mechanics were also obtained by CP-100 pulmonary monitor. Results : The imposed WOB was decreased by 37.5% during 0.7 L/min on flow triggering compared to $-2\;cmH_2O$ on pressure triggering and also decreased by 14% during $-1\;cmH_2O$ compared to $-2\;cmH_2O$ on pressure triggering (p < 0.05 in each). The PTP(Pressure Time Product) was also decreased significantly during 0.7 L/min on flow triggering and $-1\;cmH_2O$ on pressure triggering compared to $-2\;cmH_2O$ on pressure triggering (p < 0.05 in each). The proportions of imposed WOB in total WOB were ranged from 37% to 85% and no significant changes among different methods and sensitivities. The physiologic WOB showed no significant changes among different triggering methods and sensitivities. Conclusion : To reduce the imposed WOB, flow triggering with sensitivity of 0.7 L/min would be better method than pressure triggering with sensitivity of $-2\;cm\;H_2O$.

• Korean Journal of Organic Agriculture
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• v.24 no.4
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• pp.893-905
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• 2016

Puff processing is one of the preparation and processing methods of herbal medicines. This study analyzed the quality characteristics in schisandra chinensis extracts by puff processing ($1kgf/cm^2$, $3kgf/cm^2$, $5kgf/cm^2$) through changes of the lignan contents and antioxidant activity. The lignan contents and antioxidant activity of puff processing schisandra chinensis extracts (PPSCE) increased higher than compared to a control. Also, as lignan contents and antioxidant activity of PPSCE was increased with the increasing pressure but it was reduced from $5kgf/cm^2$. The results suggest that puff processing was attributed to the quality increase schisandra chinensis.