• Nuclear Engineering and Technology
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• v.22 no.4
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• pp.337-350
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• 1990

A post-irradiation annealing study was conducted with use of reactor pressure vessel(RPV) steel A533B Cl.1 base metal irradiated to a dose of 4.84$\times$10$^{18}$ n/$\textrm{cm}^2$ at about 38$0^{\circ}C$. Microhardness and positron annihilation (PA) methods were used to obtain better understanding of the recovery of radiation hardening. Isochronal anneal experiments indicated that two recovery processes occur during annealing of irradiated specimens. The first recovery process occurs in the temperature range of 280-3O5$^{\circ}C$, Michrohardness and positron annihilation (PA) methods were used to obtain better understanding of the recovery of radiation hardening. Isochronal anneal experiments indicated that two recovery processes occur during annealing of irradiated specimens. The first recovery process occurrs in the temperature range of 280-305$^{\circ}C$. The variations of Ip, Iw and R parameters indicated that the formation of vacancy clusters by vacancy agglomeration and the annihilation of monovacancies are the first recovery process. The second recovery process occurs in the range of 405-49$0^{\circ}C$ and positron annihilation parameters measured indicated that the dissolution of carbon atoms decorated around vacancy-type defects and possible precipitates, and the annihilation of monovacancies give rise to the second recovery process. It was further indicated that radiation anneal hardening (RAH) in the range of 305-405$^{\circ}C$ between the temperature ranges for the two processes occurs due to the formation of carbon-decorated vacancy clusters and precipitates. The activation energies, orders of reaction and other characteristics of recovery processes were determined by the Meechan-Brinkman method. The activation energy for the first recovery process was determined as 1.76 eV and that for the second recovery process as 2.00eV. These values are lower than those obtained by other workers. This difference may be attributed to the lower copper content of the RPV steel used in the present study. The order of reaction for the first recovery process was determined as 1.78, while that for the second recovery process as 1.67 Non-integer orders of reaction for recovery processes seem to be attributed to the fact that several mechanisms for the first order and the second order of reaction are compounded in one process. This result also supports for the above conclusions from measurements of PA parameters.

• Clean Technology
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• v.24 no.2
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• pp.127-134
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• 2018

To reduce the environmental pollution by $NO_x$ from ship engine, International maritime organization (IMO) announced Tier III regulation, which is the emmision regulation of ship's exhaust gas in Emission control area (ECA). Selective catalytic reduction (SCR) process is the most commercial $De-NO_x$ system in order to meet the requirement of Tier III regulation. In generally, commercial ceramic honeycomb SCR catalyst has been installed in SCR reactor inside marine vessel engine. However, the ceramic honeycomb SCR catalyst has some serious issues such as low strength and easy destroution at high velocity of exhaust gas from the marine engine. For these reasons, we design to metallic structured catalyst in order to compensate the defects of the ceramic honeycomb catalyst for applying marine SCR system. Especially, metallic structured catalyst has many advantages such as robustness, compactness, lightness, and high thermal conductivity etc. In this study, in order to support catalyst on metal substrate, coating slurry is prepared by changing binder. we successfully fabricate the metallic structured catalyst with strong adhesion by coating, drying, and calcination process. And we carry out the SCR performance and durability such as sonication and dropping test for the prepared samples. The MFC01 shows above 95% of $NO_x$ conversion and much more robust and more stable compared to the commercial honeycomb catalyst. Based on the evaluation of characterization and performance test, we confirm that the proposed metallic structured catalyst in this study has high efficient and durability. Therefore, we suggest that the metallic structured catalyst may be a good alternative as a new type of SCR catalyst for marine SCR system.

• Nuclear Engineering and Technology
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• v.39 no.5
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• pp.603-616
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• 2007

Roy Huddle, having invented the coated particle in Harwell 1957, stated in the early 1970s that we know now everything about particles and coatings and should be going over to deal with other problems. This was on the occasion of the Dragon fuel performance information meeting London 1973: How wrong a genius be! It took until 1978 that really good particles were made in Germany, then during the Japanese HTTR production in the 1990s and finally the Chinese 2000-2001 campaign for HTR-10. Here, we present a review of history and present status. Today, good fuel is measured by different standards from the seventies: where $9*10^{-4}$ initial free heavy metal fraction was typical for early AVR carbide fuel and $3*10^{-4}$ initial free heavy metal fraction was acceptable for oxide fuel in THTR, we insist on values more than an order of magnitude below this value today. Half a percent of particle failure at the end-of-irradiation, another ancient standard, is not even acceptable today, even for the most severe accidents. While legislation and licensing has not changed, one of the reasons we insist on these improvements is the preference for passive systems rather than active controls of earlier times. After renewed HTGR interest, we are reporting about the start of new or reactivated coated particle work in several parts of the world, considering the aspects of designs/ traditional and new materials, manufacturing technologies/ quality control quality assurance, irradiation and accident performance, modeling and performance predictions, and fuel cycle aspects and spent fuel treatment. In very general terms, the coated particle should be strong, reliable, retentive, and affordable. These properties have to be quantified and will be eventually optimized for a specific application system. Results obtained so far indicate that the same particle can be used for steam cycle applications with $700-750^{\circ}C$ helium coolant gas exit, for gas turbine applications at $850-900^{\circ}C$ and for process heat/hydrogen generation applications with $950^{\circ}C$ outlet temperatures. There is a clear set of standards for modem high quality fuel in terms of low levels of heavy metal contamination, manufacture-induced particle defects during fuel body and fuel element making, irradiation/accident induced particle failures and limits on fission product release from intact particles. While gas-cooled reactor design is still open-ended with blocks for the prismatic and spherical fuel elements for the pebble-bed design, there is near worldwide agreement on high quality fuel: a $500{\mu}m$ diameter $UO_2$ kernel of 10% enrichment is surrounded by a $100{\mu}m$ thick sacrificial buffer layer to be followed by a dense inner pyrocarbon layer, a high quality silicon carbide layer of $35{\mu}m$ thickness and theoretical density and another outer pyrocarbon layer. Good performance has been demonstrated both under operational and under accident conditions, i.e. to 10% FIMA and maximum $1600^{\circ}C$ afterwards. And it is the wide-ranging demonstration experience that makes this particle superior. Recommendations are made for further work: 1. Generation of data for presently manufactured materials, e.g. SiC strength and strength distribution, PyC creep and shrinkage and many more material data sets. 2. Renewed start of irradiation and accident testing of modem coated particle fuel. 3. Analysis of existing and newly created data with a view to demonstrate satisfactory performance at burnups beyond 10% FIMA and complete fission product retention even in accidents that go beyond $1600^{\circ}C$ for a short period of time. This work should proceed at both national and international level.

• Korean Journal of Optics and Photonics
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• v.27 no.1
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• pp.1-17
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• 2016

Over the past two decades, fiber-based lasers have made remarkable progress, now having reached power levels exceeding kilowatts and drawing a huge amount of attention from academy and industry as a replacement technology for bulk lasers. In this paper we review the significant factors that have led to the progress of fiber lasers, such as gain-fiber regimes based on ytterbium-doped silica, optical pumping schemes through the combination of laser diodes and double-clad fiber geometries, and tandem schemes for minimizing quantum defects. Furthermore, we discuss various power-limitation issues that are expected to incur with respect to the ultimate power scaling of fiber lasers, such as efficiency degradation, thermal hazard, and system-instability growth in fiber lasers, and various relevant methods to alleviate the aforementioned issues. This discussion includes fiber nonlinear effects, fiber damage, and modal-instability issues, which become more significant as the power level is scaled up. In addition, we also review beam-combining techniques, which are currently receiving a lot of attention as an alternative solution to the power-scaling limitation of high-power fiber lasers. In particular, we focus more on the discussion of the schematics of a spectral beam-combining system and their individual requirements. Finally, we discuss prospects for the future development of fiber laser technologies, for them to leap forward from where they are now, and to continue to advance in terms of their power scalability.

• Journal of Veterinary Clinics
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• v.18 no.3
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• pp.257-264
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• 2001

This study was performed to investigate the effects of chitosan-trimer (CT) on the prevention of postoperative adhesion formation in the rate model. All animals divided into PBS (control), 1% CT, 3% CT, and chitin treated group. The mean adhesion score in 1% CT group (1.03$\pm$0.63), 3% CT group (0.64$\pm$0.53) and chitin group (1.67$\pm$0.71) was found to be lower than that in control group (2.07$\pm$0.81). More favorable adhesion prevention was achieved in 3% CT group (0.64$\pm$0.53) in comparison with the control group, 1% CT group, and chitin group without any hemorrhagic complications. A statistically significant difference was observed in adhesion formation between control group and 3% CT group (p<0.001). In control group, 44 of 45 sites (97.7%) formed adhesions between the intestine defects. In contrast, 3% CT was effective in reducing the incidence of adhesion formation to 17 to 45 sites (62.2%) (p<0.05). The locations of adhesions were observed in serosa-serosa (60%), serosa-mesentery (13.3%), serosa-connective tissue of testis (10%), omentum-liver (10%), serosa-omentum (3.3%), serosa-cecum (3.3%), and serosa-incision (0%). On the results of histological analysis, grade of inflammation and fibrosis at the sites of postoperative peritoneal adhesion formation were not significantly different in all groups. But, 3% CT showed the lowest score of inflammation and fibrosis. In 3% CT group, the rate of increase of plasma fibrinogen was significantly lower compared with that in control group from pre-operation to 10 days later (p<0.05). There were no appreciable difference in the CBC, leukocyte differential counts and total protein concentrations among four groups. In conclusion, our data suggested that CT should be effective on reducing adhesion formation in experimental rat models. The results also showed that 3% CT does not adversely affect normal wound healing and healthy recovery after operation.

• Journal of Genetic Medicine
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• v.8 no.1
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• pp.71-75
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• 2011

A male infant was diagnosed with obstetric brachial plexus injury, congenital muscular torticollis and cleft palate 17 days after birth. His mother presented with gestational diabetes and premature rupture of membranes. Although it is possible that these three disorders arose independently, it is very likely that all three have the same etiologic cause, and we propose that a possible mechanism for this concurrence is related to maternal gestational diabetes. Maternal hyperglycemia mostly affects fetal structures deriving from the neural crest, including the palatine bone, and may have caused the cleft palate observed in this case. Gestational diabetes is also associated with increased frequency of large for gestational age infants and, by extension, with increased risk of birth injuries such as obstetric brachial plexus injury or congenital muscular torticollis associated with large for gestational age infants. Since the children of mothers with gestational diabetes are at increased risk for congenital defects such as cleft palate as well as being large for gestational age, precautions indicated for each respective disorder must be taken during prenatal testing and during birth. However, further studies of more cases are required to evaluate whether the concurrence of obstetric brachial plexus injury, congenital muscular torticollis and cleft palate in this case are complications specifically associated with gestational diabetes or just a simple coincidence.

• Korean Journal of Plant Resources
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• v.29 no.1
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• pp.136-142
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• 2016

Lespedeza species are mainly used for wildlife food and cover and for erosion control. The germination of these species can be enhanced after a fire occurrence in forest, which is known as fire-activated seeds to germinate. While the heat treatment could break seed dormancy of Lespedeza, its germination rate was quite low. We investigated that chemical scarification could promote germination of L. tomentosa. Seeds were soaked in 100% sulfuric acid (H₂SO₄) for 0, 1, 3, 6, 12, 24, 48, 96, 192, and 384 min, and then washed in distilled water for 24 h. Very few seeds were germinated in control (H₂SO₄ for 0 min). More than 90% of seeds were germinated in H₂SO₄ for 24, 48, and 92 min. However, some damage was observed in roots and cotyledons of seedling dipped in H₂SO₄ for a long time. To search the optimal soaking time in H₂SO₄ without defects, seeds scarified in H₂SO₄ for 30, 60, 90, 120, 150, 180, and 300 min were sown the commercial soil medium. Seeds treated with H₂SO₄ for 90 min and 150 min emerged by about 92% and 84%, respectively. Therefore, H₂SO₄ treatment could break the seed dormancy of Lespedeza species, and especially in case of L. tomentosa the optimal treatment time in sulfuric acid was one to two hours. Germination of L. tomentosa began promptly following the scarification and was completed within about one month, indicating that seeds has no physiological dormancy, just has physical dormancy.

• Korean Journal of Microbiology
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• v.41 no.1
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• pp.67-73
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• 2005

Photoautotrophic bacteria are promising candidates for the production of poly(3-hydroxybutyrate) (PHB) since they can address the critical problem of substrate costs. In this study, we isolated 25 Tn5-inserted mutants of the Synechocystis sp. PCC 6803 which showed enhanced PHB accumulation compared to the wild-type strain. After 5-days cultivation under nitrogen-limited mixotrophic conditions, the intracellular levels of PHB content in these mutants reached up to $10-30\%$ of dry cell weight (DCW) comparable to $4\%$ of DCW in the wild-type strain. Using the method of inverse PCR, the affected genes of the mutants were mapped on the completely known genome sequence of Synechocystis sp. PCC 6803. As a result, the increased PHB accumulation in 5 mutants were found to be resulted from defects of genes coding for NADH-ubiquinone oxidoreductase, O-succinylbenzoic-CoA ligase, photosystem II PsbT protein or histidine kinase, which are involved in photosystem in thylakoid inner membrane of the cell. The values of $NAD(P)H/NAD(P)^+$ ratio in the cells of these mutants were much higher than that of the wild-type strain as measured by using pulse-amplitude modulated fluorometer, suggesting that PHB synthesis could be enhanced by increasing the level of cellular NAD(P)H which is a limiting substrate for NADPH-dependent acetoacetyl-CoA reductase. From these results, it is likely that NAD(P)H would be a limiting factor for PHB synthesis in Synechocystis sp. PCC 6803.

• Clinical and Experimental Pediatrics
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• v.53 no.3
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• pp.380-391
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• 2010

Purpose : Respiratory syncytial virus (RSV) is one of the main pathogens causing lower respiratory infections (LRI) in young children, usually of limited severity. However, in congenital heart disease (CHD) patients, one of the high-risk groups for RSV infection, RSV can cause serious illnesses and fatal results. To elucidate the effects of RSV infection in CHD patients, we observed RSV infection cases among CHD patients and non-CHD patients. Methods : On admission of 343 LRI patients over 3 years, 77 cases of RSV infection were detected by the RSV antigen rapid test of nasopharyngeal secretion. We compared RSV infection cases among groups of CHD and non-CHD patients. Results : During the winter season, RSV caused 20-0% of LRI admissions in children. In patients with completely repaired simple left to right (L-R) shunt diseases such as ventricular septal defect, atrial septal defect, and patent ductus arteriosus, RSV infections required short admission days similar to non-CHD patients. In patients with repaired CHD other than simple L-R shunt CHD, for whom some significant hemodynamic problems remained, RSV infection required long admission days with severe clinical course. In children with unrepaired CHD, RSV infection mostly occurred in early infant age, with long admission days. RSV infections within a month after cardiac surgery also required long admission days and severe clinical course. Conclusion : To avoid the tragedic outcome of severe RSV infection in the CHD patients, efforts to find the subgroups of CHD patients at high risk to RSV infection are needed, and effective preventive treatment should be applied.

• Journal of Korean Society of Forest Science
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• v.36 no.1
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• pp.26-32
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• 1977

Press drying was used on sapwood and heartwood of oak (Qercus acutissima Carruthers) to find profitable means of drying low grade logs. This study was designed to investigate the process of press drying considering core temperature, current moisture content, drying rate, drying time, final moisture content, dimensional change and drying defects. The drying tests were conducted using 1.5 centimeter thick material at platen temperature of $175^{\circ}C$ and pressure of 35psi. The results were summarized as fallows. 1. Core temperature was divided into three stages of drying characterized by initial heating period, plateau temperature, and period of rising core temperature. Plateau temperature of heartwood material was higher and longer than that of sapwood material. 2. The predicting equation for change in drying rate of sapwood material was log y=-2.7925-0.0811x as function of time. That of heartwood material was log y=-3.3382-0.0468x. 3. Sapwood material reduced the moisture content from 59 to 2.5 percent in 45minutes. Heartwood material reduced the moisture content from 64 to 3.3 percent in 55 minutes. 4. Shrinkage during press drying were 20.4 percent in thickness direction and 2.5 percent in width direction. Recovery on equilibrium conditioning at 65 percent relative humidity and temperature of $20^{\circ}C$. were 11.4 percent in thickness direction and 49.4 percent in width direction. 5. Heartwood material developed severe honeycombing and moderate checking. The sapwood material dried without honeycombing, checking and collapse. All material kept wood flat.