• Nuclear Engineering and Technology
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• v.55 no.8
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• pp.2773-2784
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• 2023

It is essential to evaluate the blasting-enhanced permeability (BEP) feasibility of a low-permeability sandstone-type uranium deposit. In this work, the mineral composition, reservoir physical properties and rock mechanical properties of samples from sandstone-type uranium deposits were first measured. Then, the reformability evaluation method was established by the analytic hierarchy process-entropy weight method (AHP-EWM) and the fuzzy mathematics method. Finally, evaluation results were verified by the split Hopkinson Pressure Bar (SHPB) experiment and permeability test. Results show that medium sandstone, argillaceous sandstone and siltstone exhibit excellent reformability, followed by coarse sandstone and fine sandstone, while the reformability of sandy mudstone is poor and is not able to accept BEP reservoir stimulation. The permeability improvement and the distribution of damage fractures before and after the SHPB experiment confirm the correctness of evaluation results. This research provides a reformability evaluation method for the BEP of the low-permeability sandstone-type uranium deposit, which contributes to the selection of the appropriate regional and stratigraphic horizon of the BEP and the enhanced ISL of the low-permeability sandstone-type uranium deposit.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1A
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• pp.183-190
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• 2006

Minimizing the self weight of long-span deck slabs is one of the key factors for the practical and economic design of a composite two-girder bridge. In this paper, the minimum design thickness and rebar details of prestressed concrete deck slabs for composite two-girder bridges with girder span length from 4 m to 12 m are studied based on the safety and serviceability. The bridge deck slab with minimum thickness is designed as a one-way slab considering orthotropic behavior. Then fatigue safety of the deck slab is examined. Serviceability requirements for the deck slab such as deflection and crack width limits are also examined. The result shows that rebars with diameter less than 16 mm is recommended for the improved fatigue behavior, and, for the deck slab with span length longer than 8 m, the deflection limit governs the minimum design thickness. The result also shows that, for the deck slab with span length longer than 4 m, the distribution rebar requirement in the current Korea Highway Bridge Design Code is not sufficient to maintain the structural continuity in bridge axis as expected from the deck slab with span length shorter than 3 m.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4A
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• pp.761-766
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• 2006

Polymer composite are increasingly considered as structural components for use in civil engineering, on account of their enhanced strength-to-weight ratios. Unsaturated polyester (UP) resin have been widely used for the matrix of composites such as FRP and polymer composite, due to its excellent adhesive. Polymer nanocomposites are new class of composites derived from the nano scale inorganic particles with dimensions typically in the range of 1 to 1000 nm that are dispersed in the polymer matrix homogeneously. Owing to the high aspect ratio of the fillers, mechanical, thermal, flame, retardant and barrier properties are enhanced without significant loss of clarity, toughness or impact strength. To prepare the MMT (Montmorillonite)-UP exfoliated nanocomposites, UP was mixed with MMT at $60^{\circ}C$ for 3 hours by using pan mixer. XRD (X-ray diffraction) pattern of the composites and TEM (Transmission Electron Micrographs) showed that the interlayer spacing of the modified MMT were exfoliated in polymer matrix. The mechanical properties also supported these findings, since in general, tensile strength, modulus with modified MMT were higher than those of the composites with unmodified MMT. The thermal stability of MMT-UP nanocomposite is better than that of pure UP, and its glass transition temperature is higher than that of pure UP. The polymer concrete made with MMT-UP nanocomposite has better mechanical properties than of pure UP. Therefore, it is suggested that strength and elastic modulus of polymer concrete was found to be positively tensile strength and tensile modulus of the MMT-UP nanocomposites.

• Journal of the Korean Society of Safety
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• v.14 no.1
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• pp.208-215
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• 1999

The creep behavior of a rapidly solidified and consolidated Al-9.45wt%Fe-4.45wt%Cr alloy were investigated in the stress range 40 to 115 MPa and temperature range 300(0.53Tm) to 441$^{\circ}C$(0.66Tm). It is of use to available aerospace and automobile industries for the improved performance of materials used at high temperature. Because Al alloys with improved creep resistance offer the potential for lower weight and reduced costs in aerospace and automobile components (e.g., structural members and engine parts) through the replacement of heavier and more costly materials, the safety in use at high temperature is good. The alloy is characterized by high stress exponents and activation energies for creep, which are greatly dependent on the stress and temperature. Because the creep stress is seen to cause a strongly significant enhancement of coarsening, the coarsening rate of the dispersed particles in all crept specimens is faster than that in isothermally annealed specimens. Dislocations connecting dispersoids are observed more cofrequently in crept specimens with higher stress and lower temperature. The creep strain rates in the power law creep regime were found to be predicted much better by the Shorty and Rosler/Arzt equation with the inclusion of a threshold stress and dislocation detachment mechanism. The dispersoids in this alloy were acting a source of void nucleation that finally leaded to ductile fracture within the grain so called intergranular. Each void was initiated, grown and failed at the dispersoids in the aluminium matrix. Grain boundary accommodation of the slip produced, which result in initiation of the void and then final transgranular fracture. Therefore, it was confirmed that these dispersoids played an important role in the fracture mechanism by the formation of $Al_{13}Fe_4$, $Al_{13}Cr_2$ and $Al_2O_3$.

• Earthquakes and Structures
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• v.23 no.4
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• pp.373-384
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• 2022

To improve the seismic performance of suspended ceiling structures, various vibration-damping devices have been developed. However, the devices made of metals have a limit in that they cause large deformation and seriously damages the exterior of the suspended ceiling structure from the wall. As a results, their strengthening effect of the suspended ceiling structure was minimal. Thus, this study employed a spring and vibration-proof rubber effectively controlled vibrations without increasing horizontal seismic loads on the ceiling to enhance the seismic resistance of suspended ceiling structures. The objective of the study is to examine the dynamic properties of a seismic damping-isolation unit (SDI) with various details developed. The developed SDI was composed of a spring, embossed rubbers, and prestressed bolts, which were the main factors enhancing the damping effect. The shaking table tests were performed on eight SDI specimens produced with the number of layers of embossed rubber (n_s), presence or absence of a spring, prestressed force magnitude introduced in bolts (f_ps), and mass weight (W_m) as the main parameters. To identify the enhancement effect of the SDI, the dynamic properties of the control specimen with a conventional hanger bolt were compared to those of the SDI specimens. The SDI specimens were effective in reducing the maximum acceleration (A_{c max}), acceleration amplification factor (α_p), relative displacement (δ_R), and increasing the damping ratio (ξ) when compared to the control specimen. The A_{c max}, α_p, and δ_R of the SDI specimens with two rubbers, spring, and f_ps of 0.1f_by, where f_by is the yielding strength of the screw bolt were 57.8%, 58.0%, and 61.9% lower than those of the conventional hanger bolt specimens, respectively, resulting in the highest ξ (=0.127). In addition, the α_p of the SDI specimens was 50.8% lower than those specified in ASCE 7 and FEMA 356. Consequently, to accurately estimate the α_p of the SDI specimens, a simple model was proposed based on the functions of f_ps, stiffness constant of the spring (K), W_m, and n_s.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.4
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• pp.9-14
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• 2022

Silica aerogel is a porous material with a very low density and high specific surface area. Still, its application is limited due to its weak mechanical properties due to structural features. To solve this problem, a method of complexing it with various polymers has been proposed. We synthesized polyimide cross-linked silica aerogel by the sol-gel process to obtain high mechanical properties. Tetraethyl orthosilicate (TEOS) was used as a precursor to make silica aerogel, and 3- aminopropyltriethoxysilane (APTES) was used as a coupling agent for cross-linking polyimide. Polyimide was synthesized using pyromellitic dianhydride and 3,5-diaminobenzoic acid, and mechanical properties were improved by crosslinking polyimide with 10 repeating units in the polyimide chain using the reaction formula ${\frac{n_1}{n_2}}={\frac{n}{n+1}}$ To realize silica aerogel, polyimide having various weight ratios was added before gelation, resulting in a 19-fold or greater increase in maximum compressive strength compared to pure silica aerogel. From this study, an enhancement of silica aerogel could be enhanced through polymer cross-linking bonds.

• Food Science and Preservation
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• v.30 no.5
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• pp.896-904
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• 2023

The texturization characteristics of textured vegetable protein (TVP) were investigated based on the extent of soybean decoating during the pretreatment of defatted soybean flour used for TVP. The raw materials for TVP consisted of 50% defatted soybean flour, 30% gluten, and 20% corn starch. The weight ratios of soybean seed coat to soybean flour were 9%, 6%, 3%, and zero. Extrusion was performed using an extruder equipped with a cooling die, maintaining a barrel temperature of 190℃ and screw speed of 250 rpm, Water was injected at a rate of 9 rpm using a metering pump. Regarding the textures of the extruded TVPs produced from defatted soybean flour, an increase in the soybean seed coat content led to a decrease in the apparent fibrous structural layer and an increase in hardness. However, there were no significant changes in elasticity and cohesion. Moreover, as the soybean seed coat content increased, the pH of TVPs decreased. A higher soybean seed coat content also tended to lower the moisture content, increasing water absorption, solids elution, and turbidity. These results suggest that an increased seed coat content reduces the proportion of protein, and the fibers present in the seed coats prevent texturization.

• Journal of the Korea Fashion and Costume Design Association
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• v.4 no.1
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• pp.111-130
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• 2002

This study performed a structural questionnaire survey and non-structural interview of the ladies apparel manufacturers in Daegu on the qualification for the employees, skills required for job performance, job training, automatic manufacturing systems, and the use of computer. The results are as follows. 1. Almost all of the apparel manufacturing systems were Pair System, except one Line System in one company. In terms of outsourcing, most of the manufacturers answered “yes,” and in 1998 the outsourcing process was sewing, but in the year 2002, outsourcing has been increased :12 manufacturers(57.1%) outsourcing most of the processes except patterning, 3(14.3%) outsourcing the finish of sewing. 2. The workforce of 1998 and that of 2002 shows a significant difference(P＜. 01) between office work and management. The number of office workers has decreased from 15 down to 5.3 people. On the other hand, that of the management has slightly increased from 5.3 to 9.2 people. The number of the manual workers has decreased from 32.2 to 28.7 people. And the number of tailoring and patterning workers has slightly decreased, but the number has increased in sewing from 3.7 to 7.0 people. 3. The wage of an employee shows a significant difference between a sewing assistant(P＜. 01) and a production manager(P＜. 05), and the wage of a sewing assistant, in particular, has slightly raised from ￦905,000 to ￦1,054,000. 4. The qualifications required of employees are “cooperative human relations”(30.8％), “diligence,” and “ability for job analysis”(26.9％), and “positive thinking” (15.4％) in 1998, and “ability for job analysis”(38.5％), “cooperative human relations”(34.6％), and “positive thinking” (15.4％) in 2002. The areas for job openings are significantly different(P＜. 01) depending on the year. Job openings in the design section has increased from 1(3.8％) to 16 manufacturers (61.5％), and decreased in tailoring section from 22(84.6％) to 2 manufacturers(7.7％). Job openings in the sewing section have increased form 2(7.7％) to 6 manufacturers (23.1％). In terms of sex of the employees, there is a significant difference(P＜. 001). 19 companies(73.1％) wanted “male” in 1998, but 8 companies(30.8％) answered that they want “female” and 17 companies(65.4％) answered that “it does not matter.” About the educational background, there was a significant difference between the years. The number of the companies that want junior college graduates with an associate degree has increased(15 companies(57.7％). There was a significant difference(P＜. 05) in major of the employee. The number of the companies that want fashion majors has increased from 5(19.2％) to 20(76.9％). 5. In terms of job skills required, there was no significant difference. In 1998, “production skills” (46.2％) and “ability for job analysis” (26.9％) were required, and in 2002, “ability for job analysis” (42.3％) and “emotional skills” (26.9％). 6. In regard to training for job skills, “fashion professional training” has slightly decreased from 65.4％ in 1998 to 46.2％ in 2002, however, “training for job analysis” has slightly increased from 30.8％ in 1998 to 46.2％ in 2002, which indicates the fact that “fashion professional training” and “ability for job analysis” have been emphasized. 7. The number of the manufacturers purchased apparel CAD has increased from 1(3.8％) to 3(11.5％), and the number of the manufacturers that have no plan for purchase has increased from 16(61.5％) in 1998 to 15(57.7％), still taking up a big proportion. 8. About the use of computers in manufacturing, there is a significant difference(P＜. 05). The number of the manufacturers using computer has increased from 5(19.2％) to 15(57.7％) and that of the manufacturers which do not use computers has decreased from 17(57.7％) to 8(30.8％). 9. In the interviews with the owners of the manufacturers, they pointed that schools should give more weight on practical training courses, the invitation of experts in the specific field, complex production systems, training courses for sewing, field trip courses, and furthering specialty education, personality and vocational education.

• Journal of The Korean Society of Grassland and Forage Science
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• v.22 no.2
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• pp.115-122
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• 2002

In this study, the effects of alfalfa hay included in different ratios of 60%(A), 50%(B), 40%(C) and 30%(D) for the diets of young weaned Korean native goats were investigated on feed intake, digestibilities of nutrients, nitrogen retention, average daily gain and feed efficiency. Crude protein contents of experimental diets were 18% in all treatments. The contents of ADF, NDF and crude ash were higher in A as 26.1, 37.0 and 9.0% compared to the lowest values in D of 20.3, 30.4 and 6.6%. However the contents of non-structural carbohydrates was in the opposite tendency. Daily feed intake (DM) was highest in A (414.4g) and B (417.7g) and significantly (p<0.05) lower in D(362.6g). Dry matter intake per metabolic basal weight (DM g/kg of $BW^{0.75}$ ) were highest in A(73.9g) and lowest in D(64.0g). Average daily gain and feed efficiencies were in the range of 33.3~48.7g and 8.1~13.4% respectively with no statistical differences, however with the increasing trends according to higher percent of roughage in the diets. Digestibilities of dry matter (DM), organic matter (OM), crude protein (CP), ADF, NBF, crude ash (CA) and non-structural carbohydrates (NSC) were in the tendency of becoming higher according to higher ratios of concentrate but becoming lower according to higher ratio of alfalfa hay in the diets fed to Korean native goats. Nitrogen retention was lowest in A (1.8g, 15.5%) and highest in D (2.7g, 25.7%). In overall, inclusion of 30~40% alfalfa hay as a roughage in the diets of weaned Korean native goats was superior to the higher rates of inclusion of alfalfa hay in aspects of average daily gain and feed efficiency. The fixed 18% of crude protein content in the diets was efficient for the growth of weaned goats.

• Journal of The Korean Society of Grassland and Forage Science
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• v.22 no.2
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• pp.145-152
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• 2002

To compare the Carbon metabolic response to high temperature stress in Zoysiagrass [Zoysia matrella (L.) Merr.] and Creeping bentgrass (Agrostis palustris Huds) with respect to heat tolerance, C metabolites were determined from April to September. Sampling was carried out on an established golf course (Muan Country Club, Chonnam, Korea). Shoot mass(g Dry weight per hole cup) of creeping bentgrass started to decrease from June and recovered from August whereas that of zoysiagrass was less varied. Chlorophyll content in creeping bentgrass was significantly higher than zoysiagrass until July, and then decreased by 43% from July to August. Zoysiagrass contained higher soluble sugar than creeping bentgrass throughout experimental period. Soluble sugar in zoysiagrass increased about 58% from April to May, and less varied until August. Soluble sugar in creeping bentgrass slightly increased until July and sharply decreased at August. Starch concentration in zoysiagrass continuously decreased to September after a significant increase from April to May. A remarkable fluctuation in both starch and fluctuation concentration was observed between June and August showing high accumulation for June to July and high degradation for July to August. These results suggest that through creeping bentgrass suffers much severely from high temperature stress than zoysiagrass especially June to August. An active accumulation and degradation in nonstructural carbohydrate in creeping bentgrass during this period might be associated with heat stress.