• Computational Structural Engineering
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• v.8 no.1
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• pp.137-146
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• 1995

Structural stress under shock or impact load is varied with the lapse of time and the structural stress is called stress wave. Propagating longitudinal stress wave is studied in a 2-dimensional plate. A finite element program for elastic stress wave propagation is developed in order to investigate the shape of stress field at time increment. The longitudinal stress wave is generated by unit step function. According to the finite element analysis results, the longitudinal stress wave propagates to the similar direction of impact load and the front of stress wave propagates with the same speed as analytic solution and the shape of stress field is similar to that of analytic solution. The shear wave is occurred after the longitudinal stress wave and declined at an angle of 45 degrees compared with longitudinal stress wave and the speed of shear wave is about a half of the longitudinal stress wave. The intensity of shear wave is larger than that of longitudinal stress wave.

• Korean Journal of Crystallography
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• v.12 no.2
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• pp.102-112
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• 2001

The mechanical properties of silicon crystals are important from the viewpoint of wafer and device fabrication processes. It is now widely recognized that silicon undergoes a series of phase transformations when subjected to high pressures, using conventional high pressure devices, such as diamond anvils or indenters. Diamond tip scratching on a silicon surface in the various conditions introduces various kinds of mechanical damage and stressed states. Micro Raman spectroscopy was used to observe the phase transition of single crystal silicon. As results, different morphologies were observed as functions of scratching speed and loading condition and various phases were observed as functions of scratching speed and loading condition.

• The Journal of Engineering Geology
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• v.5 no.1
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• pp.21-29
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• 1995

Among the index properties of granite and andesite, the relation between porosity and water content is highly correlated, but specific gravity, porosity and water content have loW relation with P wave velocity and their relationship showed dispersed zone type. With raising the temperature, Brazilian tensile strength was not changed remarkably, but decreased near $100^{\circ}C$. After the strength increased at $150^{\circ}C$, it decreased near $200^{\circ}C$ in granite. In andesite, however, the strength was increased up to $200^{\circ}C$, and then decreased. The variations of P wave velocity at each temperature zone are similar to those of tensile strength.

• The Korean Journal of Nuclear Medicine
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• v.27 no.1
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• pp.18-21
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• 1993

이상에서 $^{99m}Tc$-MAA 도관스캔을 고찰하여 보면 다음과 같이 요약할 수 있다. 1) $^{99m}Tc$-MAA 도관스캔은 반복 시행할 수 있고, 그 방법이 간단하나 도관의 위치를 알아내는데 매우 정확하다. 2) 방사선학적 방법인 혈관조영술은 조영제 주입시 실제 항암제를 주입하는 속도보다 매우 빠르게 주입하므로써 야기될 수 있는 동맥의 연축(spasm), 층류 등의 원인에 의하여 항암제를 주입할 때와 다른 양상을 보여 암종의 헐류분포나 주변의 다른동맥으로 항암제가 주입 되는지의 여부를 정확히 알 수 없는 반면, $^{99m}Tc$-MAA 도관스캔은 항암제 주입속도와 동일하게 주입하므로써 보다 정확하게 암종의 혈류분포나 부작용을 예측할 수 있다. 3) 골반내 종양의 경우와 같이 도관을 양측의 동맥에 삽입하여야 하는 경우에는 암종에 대한 각 동맥으로부터의 혈류분포를 비교하여 항암제의 투여량을 변화시키므로써 치료효과의 상승과부작용의 감소를 꾀할 수 있다. 나아가서 둔부동맥으로의 혈류가 많은 경우에는 둔부동맥을 색전화하여 부작용을 극소화할 수도 있다. 4) 여러 종류의 종양, 특히 간종양의 경우에는 폐의 방사능섭취를 측정하여 종양내 동정맥단락을 정량화 할 수 있어 치료후 그 변화를 관찰하여 치료효과를 추측할 수도 있다.

• Korean Journal of Microbiology
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• v.36 no.1
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• pp.8-13
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• 2000

We have examined the mode of transglycosylation, catalyzed by an extracellular $\beta$-glucosidase purified from Trichoderma koningii ATCC 26113, using cellobiose, sophorose, laminaribiose and gentiobiose as substrates. The dimers separated from the reaction mixture by HPLC were analyzed by $^(1)H$-NMR spectroscopy. When cellobiose was subjected to the action of the $\beta$-glucosidase, the products included laminaribiose, sophorose and gentiobiose. When laminaribiose, sophorose or gentiobiose was used as a substrate, the $\beta$-glucosidase accumulated transglycosylation products possessing different types of $\beta$-glycosidic linkages from the original one. The amount of dimers accumulated as reaction proceeded seemed to be dependent on the velocity of hydrolysis but not on that of formation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.5
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• pp.534-544
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• 1997

The permittivity distribution of a two-dimensional high-contrast object with large size, which leads to the global minimum of cost function, is reconstructed by iteratively using the hybrid algorithm of Levenberg-magquardt algorithm(LMA) plus Genetic Algorithm(GA). The scattered fields calculated in a cost function are expanded in angular spectral modes, of which only effective propagating modes are used. The definition of cost function based on the effective propagating modes enables us to formulate the minimum number of incident waves for the reconstruction of object. It is numerically shown that LMA has an advantage of fast convergence but can't reconstruct a high-contrast object with large size and GA can reconstruct a high-contrast object with large size but has an disadvantage of slow convergence, whereas an inverse scattering technique using the hybrid algorithm adopts only advantages of LMA and GA.

• Food Science and Preservation
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• v.6 no.3
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• pp.319-323
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• 1999

This study was conducted to minimize the deterioration of dried kiwifruit quality. Osmotic dehydration was carried out as pretreatment before drying. After the kiwifruits were pretreated under optimized osmotic dehydration conditions, they were dried by three drying methods(hot air drying, vacuum drying, freeze drying). Hot air drying and vacuum drying were superior to freeze drying in the drying speed. But vacuum and freeze drying preserved more vitamin C than hot air drying. Also, osmotic dehydrated kiwifruit kept better quality than nontreated kiwifruit. Diffusion coefficient which describes moisture transfer, was high in drying process pretreated with osmosis. The changes of vitamin-C followed the second-order reaction rate equation with high RE, respectively.

• KSBB Journal
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• v.7 no.1
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• pp.27-31
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• 1992

Xylose represents a major component of cellulosic materials. This paper describes patterns of ethanol fermentation by Saccharomyces cerevisiae from xylulose, which is an isomer of xylose. Special emphasis was placed on the effects of xylulose concentration and growth temperature on cell growth and ethanol yield. The maximum specific growth of $0.087 1/hr^{-1}$ was obtained at an initial xylulose concentration of 5 g/1. The ethanol yield was propotional to initial xylulose concentrations. A xylulose concentration of 16 g/l resulted in the maximum ethanol yield of 0.49 g EtOH/g xylulose, which corresponds to 90% of a theoretical value. It is interesting to nota that xylulose metabolism was accelerated by the presence of glucose as a carbon source.

• The Journal of Engineering Geology
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• v.4 no.3
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• pp.269-281
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• 1994

Microscopic study and X-ray diffraction analysis were carried out to find out rock type, tock forming minerals; and weathering characteristics of rocks at the constructing site of the churyong Tunnel, Kyongju-Gun, Kyongbuk. Seismic velocity and compressional strength were measured to evaluate mechanical properties of rock. The rock of the study area is Jurassic tuff consisting of clay minerals, crystals of quartz and feldspar, fragments of volcanic rocks and shale. Fresh tuff has compressional strength of about $443kg/\textrm{cm}^2$ and seismic velocity of about 3680m/sec in average. It is classified as soft rock. Rock fragment within tuff is andesite and it has compressional strength of about $2500kg/\textrm{cm}^2$ and seismic velocity of about 4340m/sec in average. It is classified as hard rock. A good linear relationship is found between compressional streangth and seismic velocity in both laboratory sample and in-situ rocks. Laboratory samples has seismic velocities faster about 1.5km/sec than those in-situ rocks. It is interpreted that joints, fractures, and water content in the in-situ rocks result in decreas of seismic velocity. As Tuff has more than 50% of clay minerals in matrix and shale fragments, it absorbs water easily in atmospheric condition. Therefore, though the rock in the study area is medium hard rock before weathering, it is weathered very easily in the case of exposure to natural environment, comparing with other rock.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.139-150
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• 2010

Recently, full-scale research about a passenger tube train system is being progressed as a next-generation transportation system in Korea in light of global green technology. The Korea Railroad Research Institute (KRRI) has commenced official research on the construction of a tube train system. In this paper, we studied various parameters of the tube train system such as the internal tube pressure, blockage ratio, and operating speed through computational analysis with a symmetric and elongated vehicle. This study was about the aerodynamic characteristics of a tube train that operated under standard atmospheric pressure (open field system, viz., ground) and in various internal tube environments (varying internal tube pressure, blockage ratio, and operating speed) with the same shape and operating speed. Under these conditions, the internal tube pressure was calculated when the energy efficiency had the same value as that of the open field train depending on various combinations of the operating speed and blockage ratio (the P-D relation). In addition, the dependence of the relation between the internal tube pressure and the blockage ratio (the P-${\beta}$ relation) was shown. Besides, the dependence of the relation between the total drag and the operating speed depending on various combinations of the blockage ratio and internal tube pressure (the D-V relation) was shown. Also, we compared the total (aerodynamic) drag of a train in the open field with the total drag of a train inside a tube. Then, we calculated the limit speed of the tube train, i.e., the maximum speed, for various internal tube pressures (the V-P relation) and the critical speed that leads to shock waves under various blockage ratios, which is related to the efficiency of the tube train (the critical V-${\beta}$ relation). Those results provide guidelines for the initial design and construction of a tube train system.