• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.5
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• pp.449-456
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• 2010

The HCCI engine is a prospective internal combustion engine with which high diesel-like efficiencies and very low NOx and particulate emissions can be achieved. However, several technical issues must be resolved before HCCI engines can be used for different applications. One of the issues concerning the HCCI engine is that the operating range of this engine is limited by the rapid pressure rise caused by the release of excessive heat. This heat release is because of the self-accelerated combustion reaction occurring in the engine and the resulting engine knock in the high-load region. The purpose of this study is to evaluate the role of thermal stratification and fuel stratification in reducing the pressure rise rate in an HCCI engine. The concentrations of NOx and CO in the exhaust gas are also evaluated to confirm combustion completeness and NOx emission. The computation is carried out with the help of a multizone code, by using the information on the detailed chemical kinetics and the effect of thermal and fuel stratification on the onset of ignition and rate of combustion. The engine is fueled with dimethyl ether (DME), which allows heat release to occur in two stages, as opposed to methane, which allows for heat release in a single stage.

• Progress in Superconductivity
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• v.9 no.2
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• pp.193-198
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• 2008

We fabricated BSCCO-2212(2212) bulk superconductors by using a casting process and evaluated the superconducting properties. The effects of annealing conditions on microstructure and critical properties were studied. It was found that the homogeneous and uniform microstructure improved the critical properties and the microstructures of ingot and annealed rods were different with the size of 2212 rod and tube. The critical current($I_c$) of rods increased with increasing annealing time, probably due to increased grain size of 2212. Annealing time of the highest $I_c$ for the smaller rod(diameter of 10 mm) was shorter(150 hr) than that of the larger rod(diameter of 16 mm, 400 hr). This size effect seems to be related to different grain sizes of the intermediate phases such as 2201 and secondary phases in the ingot. In addition, we fabricated 2212 tubes from the rod by removing the center region which contained inhomogeneous microstructures. The $I_c$ of 2212 tube with the outer diameter of 16 mm and the thickness of 2 mm was measured to 844 A, which corresponds to the critical current density of $1017\;A/cm^2$ at 77 K.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.388-388
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• 2011

Graphene, with its unique physical and structural properties, has recently become a proving ground for various physical phenomena, and is a promising candidate for a variety of electronic device and flexible display applications. The physical properties of graphene depend directly on the thickness. These properties lead to the possibility of its application in high-performance transparent conducting films (TCFs). Compared to indium tin oxide (ITO) electrodes, which have a typical sheet resistance of ~60 ${\Omega}/sq$ and ~85% transmittance in the visible range, the chemical vapor deposition (CVD) synthesized graphene electrodes have a higher transmittance in the visible to IR region and are more robust under bending. Nevertheless, the lowest sheet resistance of the currently available CVD graphene electrodes is higher than that of ITO. Here, we report an ingenious strategy, irradiation of MeV electron beam (e-beam) at room temperature under ambient condition,for obtaining size-homogeneous gold nanoparticle decorated on graphene. The nano-particlization promoted by MeV e-beam irradiation was investigated by transmission electron microscopy, electron energy loss spectroscopy elemental mapping, and energy dispersive X-ray spectroscopy. These results clearly revealed that gold nanoparticle with 10~15 nm in mean size were decorated along the surface of the graphene after 1.0 MeV-e-beam irradiation. The fabrication high-performance TCF with optimized doping condition showed a sheet resistance of ~150 ${\Omega}/sq$ at 94% transmittance. A chemical transformation and charge transfer for the metal gold nanoparticle were systematically explored by X-ray photoelectron spectroscopy and Raman spectroscopy. This approach advances the numerous applications of graphene films as transparent conducting electrodes.

• Journal of Life Science
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• v.9 no.1
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• pp.84-89
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• 1999

To determine phylogenetic relatedness of four silk-producing silkmoths (B. mori, B. mandarina, A. yamamai and A. pernyi), internal coding region of arylphorin which is a storage protein in hemolymph protein of insects were amplified by polymerase chain reaction and then sequenced and compared each other. The nucleotide composition was biased toward adenine and thymine(59% A+T) and a strong bias for use of C in the third position of codons was found for Phe and Tyr. Together TTC(Phe) and TAC(Tyr) account for about 16.8% (10 for TTC and 8 for TAC) of all codon usage. The nucleotide similarity of arylphorin gene from B. mori showed 99%, 98% and 97% homology with those of B. mandarina, A. yamamai and A. pernyi, respectively. Also, the nucleotide sequence of arylphorin gene from B. mandarina showed 98% and 97% homology with those of A. yamamai and A.pernyi, respectively. Between A. yamamai and A. pernyi, the sequence homology was 97%. The deduced amino acid sequences in B. mori, B. mandarina and A. yamamai showed almost 99% homology. Although the aryphorin gene provided insufficient variability among the four insect species, A UPGMA tree is generated that supported the monophyly of silk-producing insects, with M. sexta placed basal to it. It is suggest that silk-producing insects have a close relationship and a homogeneous genetic background from comparison with those of other insects.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.32 no.1
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• pp.52-59
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• 2006

Purpose: The purpose of this study was to evaluate the influence of apical-coronal implant position on the stress distribution after occlusal and oblique loading. Materials and Methods: The cortical and cancellous bone was assumed to be isotropic, homogeneous, and linearly elastic. The implant was apposed to cortical bone in the crestal region and to cancellous bone for the remainder of the implant-bone interface. The cancellous core was surrounded by 2-mm-thick cortical bone. An axial load of 200 N was assumed and a 200-N oblique load was applied at a buccal inclination of 30 degrees to the center of the pontic and buccal cusps. The 3-D geometry modeled in Iron CAD was interfaced with ANSYS. Results: When only the stress in the bone was compared, the minimal principal stress at load Points A and B, with a axial load applied at 90 degrees or an oblique load applied at 30 degrees, for model 5. The von Mises stress in the screw of model 5 was minimal at Points A and B, for 90- and 30-degree loads. When the von Mises stress of the abutment screw was compared at Points A and B, and a 30-degree oblique load, the maximum principal stress was seen with model 2, while the minimum principal stress was with model 5. In the case of implant, the model that received maximum von Mises stress was model 1 with the load Point A and Point B, axial load applied in 90-degree, and oblique load applied in 30-degree. Discussion and Conclusions: These results suggests that implantation should be done at the supracrestal level only when necessary, since it results in higher stress than when implantation is done at or below the alveolar bone level. Within the limited this study, we recommend the use of supracrestal apical-coronal positioning in the case of clinical indications.

• Nuclear Engineering and Technology
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• v.43 no.3
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• pp.257-270
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• 2011

A set of reflood tests has been performed using ATLAS, which is a thermal-hydraulic integral effect test facility for the pressurized water reactors of APR1400 and OPR1000. Several important phenomena were observed during the ATLAS LBLOCA reflood tests, including core quenching, down-comer boiling, ECC bypass, and steam binding. The present paper discusses those four topics based on the LB-CL-11 test, which is a best-estimate simulation of the LBLOCA reflood phase for APR1400 using ATLAS. Both homogeneous bottom quenching and inhomogeneous top quenching were observed for a uniform radial power profile during the LB-CL-11 test. From the observation of the down-comer boiling phenomena during the LB-CL-11 test, it was found that the measured void fraction in the lower down-comer region was relatively smaller than that estimated from the RELAP5 code, which predicted an unrealistically higher void generation and magnified the downcomer boiling effect for APR1400. The direct ECC bypass was the dominant ECC bypass mechanism throughout the test even though sweep-out occurred during the earlier period. The ECC bypass fractions were between 0.2 and 0.6 during the later test period. The steam binding phenomena was observed, and its effect on the collapsed water levels of the core and down-comer was discussed.

• Korean Journal of Ichthyology
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• v.31 no.4
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• pp.208-213
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• 2019

Spermatozoa of Aphyocypris chinensis was studied by transmission electron microscopy. The investiation revaled that, spermatozoa display a round head, a small midpiece and a long tail region. In the spermatozoa, the nucleus contains highly condensed homogeneous chromation with small electron lucent areas. The base of the nucleus is slightly invaginated laterally by the nuclear fossa which contains the proximal centriole. The two centrioles orientated at an obtus angle (130°) to each other. The midpiece encircles the flagellum and is completely separated from it by the cytoplasmic channel. The midpiece contains more than 12 mitochondria. The mitochondria are arranged in 4~5 layer and are asymmetrically distributed in the postnuclear cytoplasm. The mitochondria surround the proximal part of the flagellum. The flagellum has classical 9+2 axoneme and no lateral fins. The spermatozoa of A. chinensis are similar to those of other cyprinids having a spherical head with a shallow nuclear fossa, a short midpiece including the asymmetrical arrangement of mitochondria and the lateral insertion of flagellum. However, there are some differences in the orientation of centrioles and the number of the mitochondria.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.1
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• pp.81-92
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• 1999

In this paper, we propose a new image segmentation algorithm which can be use din object-based image coding applications such as MPGA-4. Since the conventional objet segmentation methods based on mathematical morphology tend to yield oversegmented results, they normally need a postprocess which merges small regions to obtain a larger one. To solve this oversegmentation problem, in this paper, we prosed a block-based segmentation algorithm that can identify large texture regions in the image. Also, by applying the watershed algorithm to the image blocks between the homogeneous regions, we can obtain the exact pixel-based contour. Experimental results show that the proposed algorithm yields larger segments, particularly in the textural area, and reduces the computational complexities.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.42 no.5 s.305
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• pp.73-78
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• 2005

Images coded by DCT based compression contain several quality degradations by quantization process. Among them contrast distortion is the important one because human eyes are sensitive to contrast. In case of low bit-rate coded image, we can not get an image having good quality due to quantization error. In this paper, we suggest a new scheme to enhance image's contrast in DCT domain. Proposed method enhances only edge regions. Homogeneous regions are not considered in this method. $8{\times}8$ DCT coefficient blocks are decomposed to $4{\times}4$ sub-blocks for detail edge region discrimination. we could apply this scheme to real-time application because proposed scheme is DCT based method.

• Advances in pediatric surgery
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• v.2 no.1
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• pp.64-67
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• 1996

Aberrant migration of thymic tissue occurs as an ectopic thymus in the mediastinum, base of skull, tracheal bifurcation, and cervical region. A recent review of the literature by Nowak et al. showed over 70 reported cases of aberrant thymus or thymic cyst in patients who presented with primary neck masses. Authors experienced a case of ectopic cervical thymus and reviewed the literature. A one-year-old boy with left neck swelling which had been noticed since one month of age visited out patient clinic. Ultrasonography showed a well-defined cystic mass containing homogeneous, low-echogenic content locating in the lateral aspect of the left carotid sheath. Operation was performed under the impression of branchial cleft cyst. At surgery, a multiseptated, well-encapsulated, brownish and doughy mass which was extending into the vicinity of the carotid bifurcation with sland stalk-like portion ending between the hypoglossal nerve and external carotid artery was excised completely. The cut-surface showed homogenous solid mass, and on frozen section the tissue revealed a normal thymic histology. Postoperative ultrasonography showed bilateral thymus in the superior mediastinum. The patient has no immunologic problem and is doing well now.