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        검색결과 107

        22.
        2019.08 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The objective of this study is to investigate the influence of powder shape and densification mechanism on the microstructure and mechanical properties of Ti-6Al-4V components. BE powders are uniaxially and isostatically pressed, and PA ones are injection molded because of their high strengths. The isostatically compacted samples exhibit a density of 80%, which is higher than those of other samples, because hydrostatic compression can lead to higher strain hardening. Owing to the higher green density, the density of BE-CS (97%) is found to be as high as that of other samples (BE-DS (95%) and P-S (94%)). Furthermore, we have found that BE powders can be consolidated by sintering densification and chemical homogenization, whereas PA ones can be consolidated only by simple densification. After sintering, BE-CS and P-S are hot isostatically pressed and BE-DS is hot forged to remove residual pores in the sintered samples. Apparent microstructural evolution is not observed in BE-CSH and P-SH. Moreover, BE-DSF exhibits significantly fine grains and high density of low-angle grain boundaries. Thus, these microstructures provide Ti-6Al-4V components with enhanced mechanical properties (tensile strength of 1179 MPa).
        4,000원
        24.
        2018.05 구독 인증기관·개인회원 무료
        Some of the deicer ingredients are the same as fertilizer ingredients from agricultural activities. The goal of this study is to distinguish the components of highway deicer from the components used for agriculture. Among the deicer ingredients, Ca and Cl are substances which can be supplied by fertilizer or livestock manure. However, fertilizer and livestock manure contain plenty of nitrogen, organic matter, phosphoric acid and magnesium, including deicer ingredients. The soil physico-chemical characteristics were analyzed according to the distance from the highway. The physico-chemical analysis items of the soil include electrical conductivity, total nitrogen (TN), available phosphate (Av.P), organic matter (OM), ammonia nitrogen (NH4-N), Cation Exchange Capacity (CEC). In the case of effective phosphoric acid, leaching into the subsoil is very low due to various binding mechanisms in the soil. However, it is considered that the compost (fertilizer) applied to the topsoil is mixed with the soil by the tillage or flattening operation. In addition to the organic matter content of the subsoil appear to 10% or more is that in some cases exhibit a similar level as the topsoil. The average soil organic matter content of about 2.6%. This results shows that an excess of organic compost in the study area flows into subsoil and was mixed with the subsoil. The high EC value at the points outside the snow removal effect range level is not considered to be affected by the deicer. The results of the survey showed that the values were differently detected by agricultural activities, and that they should be approached in a complex way in their interpretation.
        25.
        2018.04 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The objective of this study is to reveal the sintering mechanism of mixed Ti-6Al-4V powders considering the densification and the homogenization between Ti and Al/V particles. It is found that the addition of master alloy particles into Ti enhances densification by the migration of Al into the Ti matrix prior to the self-diffusion of Ti. However, as Ti particles become coarser, sintering of the powders appears to be retarded due to slower inter-diffusion of the particles due to the reduced surface energies of Ti. Such phenomena are confirmed by a series of dilatometry tests and microstructural analyses in respect to the sintering temperature. Furthermore, the results are also consistent with the predicted activation energies for sintering. The energies are found to have decreased from 299.35 to 135.48 kJ·mol-1 by adding the Al/V particles because the activation energy for the diffusion of Al in α-Ti (77 kJ·mol-1) is much lower than that of the self-diffusion of α-Ti. The coarser Ti powders increase the energies from 135.48 to 181.16 kJ·mol-1 because the specific surface areas of Ti decrease.
        4,200원
        28.
        2017.04 구독 인증기관·개인회원 무료
        Ochratoxin A, which is frequently detected in cereals and infant diets worldwidely, is a mycotoxin to damage mainly the kidney and liver. Because ochratoxin A is highly thermostable compound. it is necessary to study ways of reducing level of ochratoxin A by controling processing steps. However, food processes, including extrusion, expansion, roasting, and steam cooking, which are used in order to mitigate the contents of ochratoxin A, are known to produce polycyclic aromatic hydrocarbons, which are generated from radicals decomposed by pyrolysis. Therefore, this study analyzed the levels of 4 polycyclic aromatic hydrocarbons, benz (a) anthracene, chrysene, benzo (b) fluoranthene and benzo (a) pyrene in rice-based products made in high pressure and heating process. Rice samples were finely ground, and homogenized samples were alkaline treatement with 1 M KOH/EtOH and extracted with liquid-liquid extraction method using n-hexane. The extracted solution was pretreated with a silica cartridge. The purified solution was dried with nitrogen gas and dissolved in 1 mL of dichloromethane and injected into GC/MSD. We had overall recoveries for 4 polycyclic aromatic hydrocarbons spiked into rice samples ranging from 92.8 to 110.2%. The limit of quantitations of benz (a) anthracene, chrysene, benzo (b) fluoranthene and benzo (a) pyrene in rice-based product were 0.19 ng/g, 0.38 ng/g, 0.51 ng/g, and 0.31 ng/g, respectively. However, these 4 polycyclic aromatic hydrocarbons in all processed rice samples were not detected.
        32.
        2015.06 구독 인증기관 무료, 개인회원 유료
        Dietary and lifestyle modifications are widely prescribed to prevent recurrence of urolithiasis, although little is known about the clinical and demographic factors associated with patient compliance and urinary metabolic changes. The present study assessed the clinical and demographic factors influencing compliance with a modified diet and lifestyle in first-time ureteric stone formers as well as determined the effects of compliance on urinary stone risk factors. We retrospectively reviewed the medical records of 53 patients presenting with ureteric calcium stones. Using a self-completed questionnaire, patients were classified according to compliance with seven recommendations for modifying diet and lifestyle into good compliance group (complied with ≥ three recommendations) and poor compliance group. Before (on a random diet) and after prescribing the modifications, 24 hour urine samples were collected from those in the good and poor compliance group. The stone size at presentation and initial treatment modality were closely associated with patient compliance (P=0.019, P=0.027, respectively). Citrate excretion significantly increased in the good compliance group after adopting modifications (P=0.012), whereas the poor compliance group did not show a statistically significant difference. Moreover, patients in the poor compliance group showed significantly increased urinary calcium excretion by the end of the study (P=0.040). After adjustments for age, sex, body mass index, and metabolic abnormality status, poor compliance was found to be an independent risk factor for persistence or development of hypocitraturia (OR: 3.885; 95% CI: 1.102~13.694; P=0.035). In conclusion, our results imply that patient education programs regarding diet and lifestyle should be tailored to the individual’s clinical and demographic characteristics.
        4,000원
        34.
        2014.04 구독 인증기관·개인회원 무료
        Dynamics of predator-prey systems are strongly affected by the strategic behavior of both predator and prey. Thus, understanding the relationship between the strategic behavior and the species survival is necessary to comprehend the system resilience and stability. In the present study, we constructed a spatially explicit lattice model to simulate integrative predator (wolf)-prey (two rabbit species)-plant relationships. Wolves have only the hunting strategy, while rabbits have the hunting-escaping strategy. When a rabbit simultaneously encounters its predator (wolves) and prey (plant), either hunting or escaping should take priority. Hunting priority is referred to as hunting preferred strategy (HPS), while escape priority is referred to as escape preferred strategy (EPS). These strategies are associated with some degree of willingness to either hunt (H) or escape (E). One rabbit species takes HPS (HPS-rabbit) and the other rabbit species takes EPS (EPS-rabbit). We investigated the changes in predicted population density for wolves, rabbits, and plant with changes in the value of H and E. Simulation results indicated that EPS-rabbit had a greater chance for survival than HPS-rabbit regardless of the initial density of EPS-rabbit, and the chance was optimized at the appropriate values of E and H. In addition, we briefly discussed the development of our model as a tool for understanding behavioral strategies in specific predatorprey interactions.
        35.
        2013.08 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Nickel-based superalloy IN 713C powders have been consolidated by hot isostatic pressing (HIPing). The microstructure and mechanical properties of the superalloys were investigated at the HIPing temperature ranging from 1030o C to 1230o C. When the IN 713C powder was heated above γ' solvus temperature (about 1180o C), the microstruc- ture was composed of the austenitic FCC matrix phase γ plus a variety of secondary phases, such as γ' precipitates in γ matrix and MC carbides at grain boundaries. The yield and tensile strengths of HIPed specimens at room temperature were decreased while the elongation and reduction of area were increased as the processing temperature increased. At 700o C, the strength was similar regardless of HIPing temperature; however, the ductility was drastically increased with increasing the temperature. It is considered that these properties compared to those of cast products are originated from the homogeneity of microstructure obtained from a PM process.
        4,000원
        36.
        2012.10 구독 인증기관 무료, 개인회원 유료
        Cleanroom could be largely classified into industrial cleanroom that can be contaminated by particlesand bio-cleanroom that can be contaminated by biological particles. Electrical manufacturing companies such as precision machines and electrical parts essentially have industrial cleanroom facilities and clean technologies to produce defects free products due to particles.Industrial cleanroom should be controlled in respect of 4M1E to prevent from foreign materials of submicro unit and to keep out contamination sources from outside. In this paper, a concept for a quantitative methodology to measure the particles from running components was suggested by combining both newly making clean booth such as wear tester and laser particle counter.
        4,000원
        37.
        2012.06 구독 인증기관·개인회원 무료
        Hyperacture rejection (HAR) of pig organs, upon xenotransplantation into primates, could partly be overcome by knocking out the alpha-Gal gene. However, xenotransplanted organs may still undergo immunological acture rejection (AR) or acute vascular rejection (AVR). Among several genes involved in AR and AVR, the hCD47 evades the monocyte/ macrophage mediated phagocytosis by identifying the self/non-self signal (CD47-SIRPa) whereas hTFPI participates in the regulation of coagulation pathway by acting upstream of the thrombin. In this study, we investigated hCD47 and hTFPI as two possible candidates for avoiding AR and AVR, respectively upon pig-to-human xenotransplantation. A co-expression vector for hCD47 and hTFPI was constructed using 2A peptides system (F2A) and transfected into the porcine kidney cell line (PK-15). The transfected cells stably expressed both hCD47 and hTFPI mRNA and proteins. Co-culture of non-transfected, hCD47-transfected, hTFPI-transfected or hCD47+hTPFI-transfected PK15 cells with natural killer (NK) cells, monocytes and macrophages confirmed the cytotoxic effect of hCD47 and revealed a synergistic effect of hCD47 and hTFPI co-transfection. There was an attractive survivability of 25~30% on each type of innate immune cell, NK cell and macrophage. These results suggest that transgenic pigs, genetically modified for hCD47 and hTFPI may be useful for overcoming xenograft rejection. Furthermore, cotransfection with hTFPI may enhance the cytotoxic effect of hCD47, possibly by assisting the hCD47-SIRPa binding by an unknown mechanism.
        38.
        2012.06 구독 인증기관·개인회원 무료
        Poly(ADP-ribosyl)ation is post-translational modification of cellular proteins related to cell survival, cell death, cellular proliferation and epigenetic events. It has recently been shown to be important for pre-implantation development of mouse embryos. However, its function during early embryonic development of pig is not clear. This study investigated the importance of poly(ADP-ribosyl)ation during in vitro development of pig embryos produced by in vitro fertilization(IVF) or parthenogenetic activation (PA). Results showed that, chemical inhibition of PARP by 3-aminobenzamide (3-AB) did not influence the in vitro development of pig embryos up to morula stage (20±3.1 vs. 28.1±1.2%; p>0.05) but significanlty reduced the rate of blastocyst formation (5.2±2.1 vs. 20±3.1%; p<0.05) when compared to non-treated controls. Furthermore, culture of morula stage embryos in the pressence of 3-AB for 24h significantly reduced the rate of blastocyst formation (19.6± 4.6 vs. 41.4±5.3%; p<0.05) and expansion (4.7±3.0 vs. 28.1±6.1; p<0.05). The proportion of large-sized blastocyst (>200 μm) having higher blastocoel volume (15.3×106 μm3) was significantly reduced (p<0.05) in treatment group (32.2±7.8%) compared to non-treated control group (65.7±9.0%). TUNEL assay revealed that poly(ADP-ribosyl)ation-inhibited blastocyst had significantly increased indices of apoptosis than those of non-treated controls (10.88±0.02 vs. 2.71±0.01; p<0.05). These data suggest that Poly(ADP-ribosyl)ation may be important for blastocyst formation in pig embryo.
        39.
        2011.10 구독 인증기관·개인회원 무료
        Urokinas type plasminogen activator (uPA) has been used as a therapeutic agent for treating human diseases such as thrombosis. Attempts to transgenically overexpress the uPA in animal bioreactors have been hampered due to side effects associated with this functional protein hormone on homeostasis. Recently, chicken has been emerged as a potential candidate for use as bioreactor to produce proteins of pharmaceutical importance. Since this species has low homology uPA sequence with mammals, we hypothesized that chicken could be used as a potential bioreactor for production of human uPA. In this study, using replication‐defective Murine Leukemia Virus (MLV)‐based retrovirus vectors encapsidated with Vesicular Stomatitis Virus G Glycoprotein (VSV‐G), we attempted to make transgenic chicken expressing human uPA (huPA). The recombinant retrovirus was injected beneath the blastoderm of non‐incubated chicken embryos (stage X, at laying). After 21 days of incubation (at hatching), all of the 38 living chicks that assayed, were found to express the vector‐encoded huPA gene in various organs and tissues, which was under the control of the Rous Sarcoma Virus (RSV) or Cytomegalovirus (CMV) promoter. Using specific primer set for huPA, PCR and RTPCR analyses of gDNA isolated from these samples demonstrated these chickens were transgenic for huPA. Furthermore, successful germ line transmission of huPA transgene was confirmed and next generation whole body huPA transgenic chickens were also produced. We also assayed huPA protein titer in blood (17.1 IU/ml) and eggs (4.4 IU/ml) of whole body huPA transgenic chicken. Thus, our results demonstrated that chicken could be used as bioreactors to produce huPA.
        40.
        2011.03 구독 인증기관 무료, 개인회원 유료
        The faulty regulation of imprinting gene lead to the abnormal development of reconstructed embryo after nuclear transfer. However, the correlation between the imprinting status of donor cell and preimplantation stage of embryo development is not yet clear. In this study, to determine this correlation, we used the porcine spermatogonial stem cell (pSSC) and fetal fibroblast (pFF) as donor cells. As the results, the isolated cells with laminin matrix selection strongly expressed the GFRα-1 and PLZF genes of SSCs specific markers. The pSSCs were maintained to 12 passages and positive for the pluripotent marker including OCT4, SSEA1 and NANOG. The methylation analysis of H19 DMR of pSSCs revealed that the zinc finger protein binding sites CTCF3 of H19 DMRs displayed an androgenic imprinting pattern (92.7%). Also, to investigate the reprogramming potential of pSSCs as donor cell, we compared the development rate and methylation status of H19 gene between the reconstructed embryos from pFF and pSSC. This result showed no significant differences of the development rate between the pFFs (11.2±0.8%) and SSCs (13.3±1.1%). However, interestingly, while the CTCF3 methylation status of pFF-NT blastocyst was decreased (36.3%), and the CTCF3 methylation status of pSSC-NT blastocyst was maintained. Therefore, this result suggested that the genomic imprinting status of pSSCs is more effective than that of normal somatic cells for the normal development because the maintenance of imprinting pattern is very important in early embryo stage.
        4,000원
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