• Journal of the Microelectronics and Packaging Society
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• v.28 no.4
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• pp.11-18
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• 2021

A novel microwave dielectric composite material for ultra-low temperature co-fired ceramics (ULTCC) with (1-x)BaWO₄-xBaV₂O₆ (x=0.54~0.85) composition was prepared by firing a mixture of BaWO₄ and BaV₂O₆. Shrinkage tests showed that the ceramic composite begins to densify at a temperature as low as 550℃ and can be sintered at 650℃ with 98% of relative density under the influence of BaV₂O₆. X-ray diffraction analysis showed that BaWO₄ and BaV₂O₆ coexisted and no secondary phase was detected in the sintered bodies, implying good chemical compatibility between the two phases. Near-zero temperature coefficients of the resonant frequency (𝛕_f) could be achieved by controlling the relative content of the two phases, due to their positive and negative 𝛕_f values, respectively. With increasing BaV₂O₆ (x from 0.53 to 0.85), the 𝛕_f value of the composites increased from -7.54 to 14.49 ppm/℃, ε_r increased from 10.08 to 11.17 and the quality factor (Q×f value) decreased from 47,661 to 37,131 GHz. The best microwave dielectric properties were obtained for x=0.6 samples with ε_r=10.4, Q×f=44,090 GHz, and 𝛕_f=-2.38 ppm/℃. Chemical compatibility experiments showed the developed composites are compatible with aluminum electrode during co-firing process.

• Journal of Korean Society of Forest Science
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• v.16 no.1
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• pp.33-62
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• 1972

Pitch pine (Pinus rigida Miller) in Korea has become one of the major silvicultural species for many years since it was introduced from the United States of America in 1907. To attain the more rational wood utilization basical researches on wood properties are primarily needed, since large scale of timber production from Pitch Pine trees has now been accomplishing in the forested areast hroughout the country. Under the circumustances, this experiment was carried out to study the wood anatomical, physical and mechanical properties of Pitch Pine grown in the country. Materials used in this study had been prepared by cutting the selected pitch pine trees from the Seoul National University Forests located in Suwon. To obtain and compare the anatomical and physical properties of the different parts of tree such as stem, branch, top and rootwood, this study had been divided into two categories (anatomical and physical). For the anatomical study macroscopical and microscopical features such as annual ring, intercellular cannal, ray, tracheid, ray trachid, ray parenchyma cell and pit etc. were observed and measured by the different parts (stem, branch, root and topwood) of tree. For the physical and mechanical properties the moisture content of geen wood, wood specific gravity, shrinkage, compression parallel to the grain, tension parallel and perpendicular to the grain, radial and tangential shear, bending, cleavage and hardness wree tested. According to the results this study may be concluded as follows: 1. The most important comparable features in general properties of wood among the different parts of tree were distinctness and width of annual ring, transition from spring to summerwood, wood color, odor and grain etc. In microscopical features the sizes of structural elements of wood were comparable features among the parts of tree. Among their features, length, width and thickness of tracheids, resin ducts and ray structures were most important. 2. In microscopical features among the different parts of tree stem and topwood were shown simillar reults in tissues. However in rootwood compared with other parts on the tangential surface distinctly larger ray structures were observed and measured. The maximum size of unseriate ray was attained to 27 cell ($550{\mu}$) height in length and 35 microns in width. Fusiform rays were formed occasionally the connected ray which contain one or several horizontal cannals. Branchwood was shown the same features like stemwood but the measured values were very low in comparing with other parts of tree. 3. Trachid length measured among the different parts of tree were shown largest in stem and shortest in branchwood. In comparing the tracheid length among the parts the differences were not shown only between stem and rootwood, but shown between all other parts of tree. Trachid diameters were shown widest in rootwood and narrowest in branchwood, and the differences among the different parts were not realized. Wall thickness were shown largest value in rootwood and smallest in branchwood, and the differences were shown between root and top or branchwood, and between stem and branch or top wood, but not shown between other parts of tree. 4. Moisture contents of green wood were shown highest in topwood and lowest in heartwood of stem. The differences among the different parts were recognized between top or heartwood and other parts of tree, but not between root and branchwood or root and sapwood. 5. Wood specific gravities were shown highest in stem and next order root and branchwood, but lowest in topwood. The differences were shown clearly between stemwood and other parts of tree, but not root and branchwood. However the significant difference is realized as most lowest value in topwood. 6. In compression strength parallel to the grain compared among the different parts of tree at the 14 percent of moisture content, highest strength was appeared in stem, next order branch and rootwood, but lowest in topwood. 7. In bending strength compared among the different parts of tree at the 14 percent of moisture content clearly highest strength was shown in branchwood, next order stem and root, but lowest in topwood. Though the branchwood has lower specific gravity than stemwood it was shown clearly high bending strength.

• International Journal of Highway Engineering
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• v.13 no.3
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• pp.21-30
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• 2011

As well known, dowel bars are used to transfer traffic load acting on one edge to another edge of concrete slab in concrete pavement system. The dowel bars widely used in South Korea are round shape steel bar and they shows satisfactory performance under bending stress which is developed by repetitive traffic loading and environment loading. However, they are not invulnerable to erosion that may be caused by moisture from masonry joint or bottom of the pavement system. Especially, the erosion could rapidly progress with saline to prevent frost of snow in winter time. The problem under this circumstance is that the erosion not only drops strength of the steel dower bar but also comes with volume expansion of the steel dowel bar which can reduce load transferring efficiency of the steel dowel bar. To avoid this erosion problem in reasonable expenses, dowers bars with various materials are being developed. Fiber reinforced plastic(FRP) dower that is presented in this paper is suggested as an alternative of the steel dowel bar and it shows competitive resistance against erosion and tensile stress. The FRP dowel bar is developed in tube shape and is filled with high strength no shrinkage. Several slab thickness designs with the FRP dowel bars are performed by evaluating bearing stress between the dowel bar and concrete slab. To calculated the bearing stresses, theoretical formulation and finite element method(FEM) are utilized with material properties measured from laboratory tests. The results show that both FRP tube dowel bars with diameters of 32mm and 40mm satisfy bearing stress requirement for dowel bars. Also, with consideration that lean concrete is typical material to support concrete slab in South Korea, which means low load transfer efficiency and, therefore, low bearing stress, the FRP tube dowel bar can be used as a replacement of round shape steel bar.

• Journal of the Korean Wood Science and Technology
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• v.17 no.1
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• pp.3-11
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• 1989

This study was carried out to investigate the physical and mechanical properties. durability of adhesive bond and paint film for the basic data which were required to determine the suitability as a raw material for furniture the laminated veneer lumber (LVL) with pitch pine (Pinus rigida Mill). The results obtained were as follows; 1) The proper pressing time for making the LVL was over 45 second per milimeter of LVL thickness. 2) The bending strength of the LVL was lower than that of the solid wood but the compressive strength of the LVL was similar to that of the solid wood. The strength increased with the decrease of veneer thickness. 3) The impact bending absorbed energy of the LVL was 0 to 0.3 kg.m/$cm^2$ in the direction of parallel to the grain. The energy of the LVL was lower than that of the solid wood (0.68 kg.m/$cm^2$). 4) In warm water soaking and cold-dry tests, delamination of adhered layers surface crack, swelling, and color change were not found when the hot pressing time was over 45 second per milimeter of LVL thickness. As a result of soak under vacuum test shrinkage in the direction of parallel to the grain was about -1.0 percent and. was about 3.0 percent in the direction of the perpendicular to the grain. 6) The film cacks on the LVL's surface after the wet and cold-dry test were not found at all. 7) In the use of the LVL for interior decoration it was considered that the surface of the LVL be overlaid crossly with fancy veneers of birch and paulownia, etc. This cross overlayirg methods have resulted in few cracks on the fancy veneer.

• International Journal of Highway Engineering
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• v.8 no.2 s.28
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• pp.55-62
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• 2006

Transverse cracks in continuously reinforced concrete pavement (CRCP) occur at early ages due to temperature and moisture variations. The width and spacing of transverse cracks have a significant effect on pavement performance such as load transfer efficiency and punchout development. Also, crack widths in CRCP depend on 'zero-stress temperature,' which is defined as a temperature where initial concrete stresses become zero, as well as drying shrinkage of concrete. For good long-term performance of CRCP, transverse cracks need to be kept tight. To keep the crack widths tight throughout the pavement life, zero-stress temperature must be as low as practically possible. Thus, temperature control at early ages is a key component In ensuring good CRCP performance. In this study, concrete temperatures were predicted using PavePro, a concrete temperature prediction program, for a CRCP construction project, and those values were compared with actual measured temperatures obtained from field testing. The cracks were also surveyed for 12 days after concrete placement. Findings from this study can be summarized as follows. First, the actual maximum temperatures are greater than the predicted maximum temperature in the ranges of 0.2 to 4.5$^{\circ}C$. For accurate temperature predictions, hydration properties of cementitious materials such as activation energy and adiabatic constants, should be evaluated and accurate values be obtained for use as input values. Second, within 24 hours of concrete placement, temperatures of concrete placed in the morning are higher than those placed in the afternoon, and the maximum concrete temperature occurred in the concrete placed at noon. Finally, from the 12 days of condition survey, it was noted that the rate of crack occurrence in the morning placed section was 25 percent greater than that in the afternoon placed section. Based on these findings, it is concluded that maximum concrete temperature has a significant effect on crack development, and boner concrete temperature control is needed to ensure adequate CRCP performance.

• 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.

• Anatomy & Biological Anthropology
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• v.31 no.4
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• pp.121-131
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• 2018

Stature is one of the unique biological properties of a person, which can be used for identification of the individual. In this regard, statures are estimated for the unknown victims from crimes and disasters. However, the accuracy of estimates may be compromised by inappropriate methodologies and/or practices of stature estimation. Discussed in this study are the methodological issues related to the current practices of forensic anthropological stature estimation in Korea, followed by suggestions to enhance the accuracy of the stature estimates. Summaries of forensic anthropological examinations for 560 skeletal remains, which were conducted at the National Forensic Service (NFS), were reviewed. Mr. Yoo Byung-eun's case is utilized as an example of the NFS's practices. To estimate Mr. Yoo's stature, Trotter's (1970) femur equation was applied even though the fibula equation of a lower standard error was available. In his case report, the standard error associated with the equation (${\pm}3.8cm$) was interpreted as an 'error range', which gave a hasty impression that the prediction interval is that narrow. Also, stature shrinkage by aging was not considered, so the estimated stature in Mr. Yoo's case report should be regarded as his maximum living stature, rather than his stature-at-death. Lastly, applying Trotter's (1970) White female equations to Korean female remains is likely to underestimate their statures. The anatomical method will enhance the accuracy of stature estimates. However, in cases that the anatomical method is not feasible, the mathematical method based on Korean samples should be considered. Since 1980's, effort has been made to generate stature estimation equations using Korean samples. Applying the equations based on Korean samples to Korean skeletal remains will enhance the accuracy of the stature estimates, which will eventually increase the likelihood of successful identification of the unknowns.

• Journal of Korean Society of Forest Science
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• v.71 no.1
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• pp.14-21
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• 1985

This study was carried out in order to prevent the devaluation of wood itself and wood products causing by anisotropy, hygroscopicity, shrinkage and swelling - properties that wood itself only have, in order to improve utility of wood, by emphasizing the natural beautiful figures of wood, to develop the dimensional stabilization techniques of wood with PEG that it is a cheap, non-toxic and the impregnation treatment is not difficult, on the effects of PEG molecular weights (200, 400, 600, 1000, 1500, 2000, 4000, 6000) and species (Pinus densiflora S. et Z., Larix leptolepis Gordon., Cryptomeria japonica D. Don., Cornus controversa Hemsl., Quercus variabilis Blume., Prunus sargentii Rehder.). The results were as follows; 1) PEG loading showed the maximum value (137.22%, Pinus densiflora, in PEG 400), the others showed that relatively slow decrease. The lower specific gravity, the more polymer loading. 2) Bulking coefficient didn't particularly show the correlation with specific gravity, for the most part, indicated the maximum values in PEG 600, except that the bulking coefficient of Quercus variabilis distributed between the range of 12-18% in PEG 400-2000. In general, the bulking coefficient of hardwood was higher than that of softwood. 3) Although there was more or less an exception according to species, volumetric swelling reduction was the greatest in PEG 400. That is, its value of Cryptomeria japonica was the greatest value with 95.0%, the others indicated more than 80% except for Prunus sargentii, while volumetric swelling reduction was decreased less than 70% as the molecular weight increase more than 1000. 4) The relative effectiveness of hardwood with high specific gravity was outstandingly higher than softwood. In general, the relative effectiveness of low molecular weight PEG was superior to those of high molecular weight PEG except that Quercus variabilis showed more than 1.6 to the total molecular weight range, while it was no significant difference as the molecular weight increase more than 4000. 5) According to the analysis of the results mentioned above, the dimensional stabilization of hardwood was more effective than softwood. Although volumetric swelling reduction was the greatest at a molecular weight of 400. In the view of polymer loading, bulking coefficiency reduction of swelling and relative effectiveness, it is desirable to use the mixture of PEG of molecular weight in the range of 200-1500. To practical use, it is recommended to study about the effects on the mixed ratio on the bulking coefficient, reduction of swelling and relative effectiveness.

• Journal of the Korean Wood Science and Technology
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• v.10 no.1
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• pp.5-37
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• 1982

Plywood used for construction as a decorative inner material is inflammable to bring large fire accidents and burn out human life and their properties. To diminish the fire disaster, fire retardant plywood has been required indeed. In the methods of manufacturing the fire retardant plywood the soaking method is occasionally used. However after soaking plywood into fire retardant chemical solutions, redrying of soaked plywood is the most important. In this study, 3.5mm thin and 5.0mm thick plywoods were selected for fire retardant treatment. Treating solutions were prepared for 20% dilute solutions of ammonium sulfate, monoammonium phosphate, diammonium phosphate, borax-boric acid and minalith, and water solution. 1-, 3-, 6-, and 9 hour-soaking treatments were applied and after treatments hot plate drying was applied to those treated plywoods at $90^{\circ}C$, $120^{\circ}C$ and $150^{\circ}C$, of press temperature. Drying rates, drying curves, water absorption rates of fire retardant chemicals, weight per volume and fire retardant degree of plywood were investigated. The results may be summarized as follows: 1. The plywoods treated with ammonium sulfate, monoammonium phosphate and diammonium phosphate and diammonium phosphate showed increase of chemical absorption rate with proportion to increase of treating time, but not in case of the plywood treated with borax-boric acid and minalith. 2. In the treatment of definite time, the absorption rate per unit of volume of plywood showed higher in thin plywood (thickness of 3.5mm) than in thick plywood (thickness of 5.0mm). In both thin and thick plywoods, the highest absorption rate was observed in 9 hour-treatment of ammonium sulfate. The value was 1.353kg/$(30cm)^3$ in thin plywood and 1.356kg/$(30cm)^3$ in thick plywood. 3. The volume per weight of plywood after chemical treatment increased remarkably and. after hot plate drying, the values were to a little extent higher than before chemical treatment. 4. The swelling rates of thickness in chemical-treated plywoods increased similarly with that of water-treated plywood in 1- and 3 hour-treatment of both thin and thick plywoods. But in 6- and 9 hour-treatment, the greater increased value showed in water-treated ply wood than any other chemical, especially in thick plywood. 5. The shrinkage rates after hot plate drying showed the same tendency as the swelling rate, and the rate showed the increasing tendency with proportion to increase of treating time in thick plywood of both chemical and water treatments. 6. Among drying curves, the curves of water-treated plywood placed more highly than chemical-treated plywood without-relation to thickness in 6- and 9 hour-treatment except in 1- and 3 hour-treatment. 7. The drying rate related to thickness of treated plywood, was twice above in thin plywood compared with thick plywood. 8. The drying rate remarkably increased with proportion to increase of the plate temperature and, the values were respectively 1.226%/min., 6.540%/min., 25.752%/min. in hot plate temperature of $90^{\circ}C$, $120^{\circ}C$, $150^{\circ}C$ in thin plywood and 0.550%/min., 2.490%/min, 8.187%/min, in hot plate temperature of $90^{\circ}C$, $120^{\circ}C$, $150^{\circ}C$ in thick plywood. 9. In the treatment at $120^{\circ}C$ of hot plate temperature, the drying rates of chemical-treated plywood showed the highest value in monoammonium phosphate of thin plywood and in diammonium phosphate of thick plywood. But the drying rate of water-treated plywood was highest in 6- and 9 hour-treatment. 10. The fire retardant degree of chemical-treated plywood was higher than that of the untreated plywood as shown in loss of weight, burning time, flame-exhausted time and carbonized area. 11. The fire-retardant effect among fire retardant chemicals were the greatest in diammonium phosphate, the next were in monoammonium phosphate and ammonium sulfate, and the weakest were in borax-boric and minalith.