• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.70.4-70.4
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• 2019

Complex organic molecules (COMs) are increasingly observed in the environs of young stellar objects (YSOs), including hot cores/corinos around high-mass/low-mass protostars and protoplanetary disks. It is widely believed that COMs are first formed in the ice mantle of dust grains and subsequently released to the gas by thermal sublimation at high temperatures (T>100 K) in strong stellar radiation fields. In this paper, we report a new mechanism that can desorb COMs from icy grain mantles at low temperatures (T<100K), which is termed rotational desorption. The rotational desorption process of COMs comprises two stages: (1) ice mantles on suprathermally rotating grains spun-up by radiative torques (RATs) are first disrupted into small fragments by centrifugal stress, and (2) COMs and water ice then evaporate rapidly from the tiny fragments (i.e., radius a <1nm) due to thermal spikes or enhanced thermal sublimation due to increased grain temperature for larger fragments (a>1 nm). We discuss the implications of rotational desorption for releasing COMs and water ice in the inner region of protostellar envelopes (hot cores and corinos), photodissociation regions, and protoplanetary disks (PPDs). In shocked regions of stellar outflows, we find that nanoparticles can be spun-up to suprathermal rotation due to supersonic drift of neutral gas, such that centrifugal force can be sufficient to directly eject some molecules from the grain surface, provided that nanoparticles are made of strong material. Finally, we find that large aggregates (a~ 1-100 micron) exposed to strong stellar radiations can be disrupted into individual icy grains via RAdiative Torque Disruption (RATD) mechanism, which is followed by rotational desorption of ice mantles and evaporation of COMs. In the RATD picture, we expect some correlation between the enhancement of COMs and the depletion of large dust grains in not very dense regions of YSOs.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.10
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• pp.834-839
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• 2000

The structural properties that SEM photograph of ZnO varistors surface studied by fractal mathematics program were investigated to verify the relations of electrical characteristics. The SEM photograph of ZnO varistors surface were changed by binary code and the grain shape of that were analyzed by fractal dimension. The void of ZnO varistors surface was found by fractal program. The relation between grain density and electrical properties depend on fractal dimension. The grain size in ZnO varistors surface was decreased by increasing of Sb$_2$O$_3$ addition. The spinel structure was formed by Sb$_2$O$_3$addition and it was depressed the ZnO grain formation. The grain size of ZnO by Sb$_2$O$_3$addition were from 5 to 10[${\mu}{\textrm}{m}$]. Among of ZnO varistors, fractal dimension of ZnO4 was very high as a 1.764. The density of grain boundary in ZnO2 and ZnO3 varistors surface was 15[%] by formed spinal structure. The breakdown electric field of ZnO2 that fractal dimension has 1.752 was very high to be 8.5[kV/cm]. When the fractal dimensin was high, the grain shape of ZnO varistors was complex and the serial layers of ZnO grain was increased.

• Proceedings of the Korean Society of Food Science and Nutrition Conference
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• 2004.11a
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• pp.37-42
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• 2004

The relatively new concept of functional foods is supportive of sales of food products that deliver isolated 'nutrient' or 'food compound' substances, much as is done by dietary supplements. Whether such isolated substances have benefit must be investigated in each instance; such investigations can be complex. At the same time, simply prepared natural plant foods contain a myriad of substances that, in accord with the concept of food synergy, are beneficial for health. Whole grain foods are an example of such healthy fare, based on strong epidemiologic and experimental evidence. If the concept of functional foods is to be of use for the public health, it should support the consumption of healthy traditional foods as well as promoting 'novel' foods; in this sense, whole grain foods, which have great functionality, should be regarded as functional foods.

• Journal of the Korean Ceramic Society
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• v.39 no.1
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• pp.16-20
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• 2002

Semiconducting (Ba.Sr)TiO$_3$ceramic device, which shows the PTCR effect, has been usually used as a current limiter. In this case, the device should endure the condition under the high electric field. In this study, the dynamic electrical properties of the PTCR device under high voltage has been evaluated. Two different formulated powders were used and the sintered bodies exhibited the different grain size and porosity. The wide range of characterization such as complex impedance spectroscopy, microstructure, I-V characteristics and voltage dependence of resistivity of the samples were performed. The PTCR effect of the specimen containing coarse grains was very sensitively dependent on the AC electric field, showing that it was inversely pro-portional to the grain boundary potential barrier. The withstanding voltage was proportional to the potential barrier of grain boundary.

• Transactions of Materials Processing
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• v.5 no.4
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• pp.305-319
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• 1996

In this paper a finite element based system is presented for the prediction of the distributions of the recrystallized grain sizes in the workpiece in hot forging. The system adopts a fully coupled finite element thermo-mechanical model for predicting plastic deformation and heat transfer occurring in the workpiece and employs existing metallurgical models relating the recrystalliza-tion behavior with the thermo-mechanical variables such as temperatures strain and strain rate. The system is applied to upsetting of cylindrical preform. The predicted grain sizes are compared with the measurements. It is further applied to forging of a complex-shaped product.

• Journal of the Korean Ceramic Society
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• v.28 no.3
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• pp.179-188
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• 1991

The semiconducting BaTiO3 ceramics used in this study were sintered in the reducing atomosphere(hydrogen gas) and neutral atmosphere(nitrogen gas), then were heat-treated in air to vary defect concentrations. In this experiment, the correlations between the composition analysis and electrical characteristics of these samples were investigated. When the BaTiO3 ceramics were sintered in N2 atmosphere, it was observed that the Ba contents near the interface were lower than that of the grain center, and these samples showed superior PTCR effects. From analysis of the resistivities of grains and grain boundaries by CIRM(Complex Impedance Resonance Method), it was confirmed that the PTCR effects were caused by the resistivity of grain boundaries. And from measurement of the capacitance at each temperature, the samples sintered in N2 atmosphere show the increase of room temperature resistance and the decrease of capacitance as a result of the increase of the charge depletion layers. This phenomenon agrees well with the cation deficiencies in the analytical results.

• Journal of the Korea Convergence Society
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• v.11 no.5
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• pp.165-173
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• 2020

The emergence of unmanned agricultural machinery has brought new research content to the development of precision agriculture. In order to speed up the research on key technologies of unmanned agricultural machinery, classification of intelligence level of unmanned agricultural machinery has become a primary task. In this study, the researchers take the complex interactive system consisting of unmanned grain harvester, task and driving environment as the research object, and carry out a research on the grading and classification of intelligent level of unmanned grain harvester. The researchers of this study also establish an evaluation model of unmanned grain harvester vehicle, which consists of human intervention degree, environmental complexity, and task complexity. Besides, the grading and classification of intelligence level of the unmanned grain harvester is carried out according to the human intervention degree, environmental complexity and the task complexity of the unmanned grain harvester. It provides a direction for the future development of unmanned agricultural machinery.

• Korean Journal of Materials Research
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• v.31 no.3
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• pp.139-149
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• 2021

In this study, three kinds of bainitic steels are fabricated by controlling the contents of vanadium and boron. High vanadium steel has a lot of carbides and nitrides, and so, during the cooling process, acicular ferrite is well formed. Carbides and nitrides develop fine grains by inhibiting grain growth. As a result, the low temperature Charpy absorbed energy of high vanadium steel is higher than that of low vanadium steel. In boron added steel, boron segregates at the prior austenite grain boundary, so that acicular ferrite formation occurs well during the cooling process. However, the granular bainite packet size of the boron added steel is larger than that of high vanadium steel because boron cannot effectively suppress grain growth. Therefore, the low temperature Charpy absorbed energy of the boron added steel is lower than that of the low vanadium steel. HAZ (heat affected zone) microstructure formation affects not only vanadium and boron but also the prior austenite grain size. In the HAZ specimen having large prior austenite grain size, acicular ferrite is formed inside the austenite, and granular bainite, bainitic ferrite, and martensite are also formed in a complex, resulting in a mixed acicular ferrite region with a high volume fraction. On the other hand, in the HAZ specimen having small prior austenite grain size, the volume fraction of the mixed acicular ferrite region is low because granular bainite and bainitic ferrite are coarse due to the large number of prior austenite grain boundaries.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.632-638
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• 2002

Electron beam (EB) and Gas tungsten arc (TIG) welds were performed on 12.7 mm thick Ti-6Al-4V plate (ASTM Titanium Grade 5). Charpy-V toughness and hardness, as well as, microstructure of the welds and penetration from the macrostructure were studied. It appears that by EB welding rather smaller $\beta$-grains than with TIG welding can be obtained. Next to the fusion line the $\beta$-grain size in the HAZ was 50 ${\mu}{\textrm}{m}$l while in the weld metal it was 150 ${\mu}{\textrm}{m}$. Charpy-V toughness of the EB weld metal was equal or even better to that of base metal, which shows that the $\alpha$-martensite per se is not particularly brittle if only the grain size is fine enough. This is similar to behavior of low carbon martensite in steel. The grain size was studied with light optical and scanning electron (SEM) microscopes. Thus for products, for products which can be manufactured automatically with very narrow fit, the EB welding of Ti-6Al-4V appears to yield satisfactory toughness without any complex post weld heat treatment. ill this study as in earlier studies the TIG welds gave lower toughness than that of the base material due to the higher heat input and slower cooling as compared to EB welding.

• Progress in Superconductivity
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• v.8 no.1
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• pp.8-15
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• 2006

The size of the superconducting domains and the critical current density inside these domains have to be enhanced for most of cryomagnetic applications of melt-textured YBCO bulks. To enlarge the size of the domains we studied the multi-seeding technique based on a well-established procedure for preparing high quality YBCO monoliths using self-made SmBCO seeds. The distance between the seeds was optimised as a result of the investigation of the effects of various seed distances on the characteristics of the grain boundary Junctions. The influences of a-b plane intersections and c-axis misalignments were researched. Thereby, a small range of tolerance of the misorientations between the seed crystals was found. Field mapping was applied to control the materials quality and the superconductor's grain structure was investigated using polarisation microscopy. YBCO function elements with iou. seeds in a line and an arrangement of making type (100)/(100) and (110)/(110) boundary junctions, respectively, were processed. The trapped field profile in both sample types shows single domain behaviour. To demonstrate the potential of the multi-seeding method a ring-shaped sample was processed by placing sixteen seeds in a way to make both (100)/(100) and (110)/(110) grain junctions at the same time. The results up to now are very promising to prepare large single domain melt-textured YBCO semi-finished products in complex shapes.