• Journal of Practical Agriculture & Fisheries Research
• /
• v.19 no.1
• /
• pp.5-14
• /
• 2017

This study was conducted to investigate the effects of nutrient solution strength on growth and nutrient element concentrations in leaf lettuce (Lactuca sativa L. cv. 'Dduksum') by hydroponic culture under fluorescent lamp and LED. Leaf lettuce were grown in closed hydroponic cultivation systems supplied with 1/2, 1 and 2 strength of nutrient solution recommended by horticultural experiment station in Japan. The growth of 'Dduksum' was highest in the 2 strength of standard nutrient solution. The amount of nutrient element in the recycled nutrient solution was higher at 2, 1 and 1/2 strength of nutrient solution. The concentration of NO₃-N, Ca²⁺, Mg²⁺ in the recycled nutrient solutions increased in 1 and 2 strength of nutrient solution but that of NH₄-N decreased gradually in 1/2 and 1 strength of nutrient solution. The concentration of K, Ca, Mg in leaf lettuce was maintained in the normal range, whereas the concentration of phosphorous was 1.3 to 1.6%, which was higher than proper range. As the concentration of NH₄-N decreases gradually in all the treatments, it is necessary to raise the rate of NH₄-N or add it.

• Advances in concrete construction
• /
• v.9 no.3
• /
• pp.267-278
• /
• 2020

This paper reports on the result of an experimental investigation carried out to study the compressive strength and sorptivity properties of blended cement concrete exposed to 5% and 10% MgSO₄ solution using fly ash (FA) and silpozz. Usually in sulphate environment the minimum grade of concrete is M30 and the mix design is done for target mean strength of 39 MPa. Silpozz is manufactured by burning of agro-waste rice husk in designed furnace in between 600° to 700℃ which is one of the main agricultural residues obtained from the outer covering of rice grains during the milling process. There are four mix series taken with control mix. The control mix made 0% replacement of FA and silpozz with Ordinary Portland Cement (OPC). The first mix series made 0% FA and 10-30% replacement of silpozz with OPC. The second mix series made with 10% FA and 10-40% replacement of silpozz with OPC. The third mix series made 20% FA and 10-30% replacement of silpozz with OPC and the fourth mix series made 30% FA and 10-20% silpozz replaced with OPC. The samples (cubes) are prepared and cured in normal water and 5% and 10% MgSO₄ solution for 7, 28 and 90 days. The studied parameters are compressive strength and strength deterioration factor (SDF) for 7, 28 and 90 days. The water absorption and sorptivity tests have been done after 28 days of normal water and magnesium sulphate solution curing. The investigation reflects that the blended cement concrete incorporating FA and silpozz showing better resistance against MgSO₄ solution when compared to normal water curing (NWC) samples.

• Journal of Veterinary Clinics
• /
• v.20 no.4
• /
• pp.482-488
• /
• 2003

Transplanted cortical bone grafts of freeze-dried bones also function as sustaining for defected bones, however, it has less strength and is fragile without rehydration. In this study, strength and stiffness of freeze-dried bone from bovine cortical bones were evaluated by three point bending test according to different time frames such as rehydration times of 0.5, 3, 6, 12 and 24 hrs in electrolyte solution and was compared with those of frozen bones. The strength and stiffness of frozen bone were $264.4\pm36.7$ MPa, $17.0\pm1.5$ GPa, respectively. The strength and stiffness of freeze-dried bone which fat was removed by treatments of chloroform-methanol solutions for 6 days, then was freeze-dried at $-80^{\circ}C$ and sterilized with ethylene oxide gas, were $224.9\pm27.6$ MPa, $19.2\pm2.8$ GPa, respectively. The strength and stiffness of feeze-dried bone were decreased 15.0% and increased 13.2% than these of frozen bone, respectively. The strength and stiffness of freeze-dried bone rehydrated for 6 hrs were restored to 96.0% strength and 99.2% stiffness of frozen bone. The rehydration time of freeze-dried bone which had the highest strength and stiffness was six hours and three hours, respectively. The results of the mathematica program for the variation of the strength and stiffness showed 3 hours and 30 minutes of rehydration time in electrolyte solution for the best condition in the strength and stiffness which was adequate to treat freeze-dried cortical bone.

• Journal of Advanced Marine Engineering and Technology
• /
• v.27 no.6
• /
• pp.783-789
• /
• 2003

An experimental method to investigate the fracture strength and fracture toughness for the silicon nitrides sintered at various sintering temperature is established. The erosion rate for these materials in the various concentration of NaOH solution is also investigated. In result, the fracture strength of Si3N4 is decreased with the increase of sintering temperature. On the other hand, the fracture toughness KIC is increased with the increase of sintering temperature. The erosion rate of silicon nitride in the NaOH solution depend largely on the grain size and the concentration of NaOH solution. The erosion rate of silicon nitride sintered at $1800^{\circ}C$ was much higher than that at $1950^{\circ}C$. These results are due to the unique columnar structure of silicon nitride.

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.241-246
• /
• 2003

In order to develop a method of corrosion fatigue design and estimate reliability of TMCP steel using as the material of heavy industries and plants, its corrosion susceptibilities, corrosion fatigue strength, and determination of fatigue design criterion considering corrosion degradation were investigated. From the results, the corrosion characteristic of TMCP steel is very susceptible in 3.5wt.% NaCl solution. Its susceptibility was linearly increased with the solution temperature increase. The corrosion fatigue strength in $25${\circ}$, 3.5wt.% NaCl solution is very lower than that of in air. And also, it was decreased with the frequency decrease in the same environment. It is expected that the developed corrosion fatigue design method for TMCP steel is useful. However, it is necessary to verify its reliability for actual application.

• Journal of Welding and Joining
• /
• v.1 no.2
• /
• pp.61-68
• /
• 1983

Austenitic stainless steel has been investigated widely for creep strength of heat resistant material and effects of grain sizes due to various solution treatment time under constant temperature. It was studied that effects of grain sizes subject to solution treatment temperature 1100.deg. C, 1125.deg. C, 1175.deg. C, 1250.deg C, and 1300.deg. C respectively on the creep strength, fracture behaviour and fractography of SUS 316 stainless steel. The experimental results obtained were as follows. 1. The optimum grain size for the maximum creep strength did not vary with creep testing temperatures and stress levels. 2. Among various grain sizes due to different solution treatment temperature, the optimum grain size for the creep strength was found 0.044mm. Also the size showed the minimum initial strain regardless creep temperature. 3. Garofalo's equation of creep rupture life was applied well to SUS 316 stainless steel. 4. The fractography of optimum size was ductile intergranular fracture of dimple type and showed along with the increase of grain size intergranular fracture of w type.

• The Korean Journal of Ceramics
• /
• v.3 no.4
• /
• pp.235-238
• /
• 1997

Basic properties of new cement pastes based on the system $CaO-Al_2O_3-P_O_5-H_2O$were studied Phosphoric acid solutions and calcium dialuminate clinkers synthesized by the hydration-burning method were used for liquid and powder components of the paste, respectively Variation in the compositions of the paste was achieved by changing the liquid/powder ratio and the concentration of phosphoric acid solution. The hardening rate of the paste was so largely affected by the amount of phosphoric acid that hardening was inhibited with the low-concentrated solution but was explosively accelerated with the high-concentrated solution. The phosphoric acid solutions of concentration of 45~50% and the liquid/powder ratio of 0.5~1.5 were favoured for the high early-strength cement paste with the reasonable hardening rate and high strength. The binding phase of hardened paste was the dense amorphous gel of the system $CaO-Al_2O_3-P_O_5-H_2O$. in which the unreacted calcium dialuminate grains were embeded.

• Structural Monitoring and Maintenance
• /
• v.1 no.3
• /
• pp.323-338
• /
• 2014

In this study a new innovative method of earthquake-resistant strengthening of reinforced concrete structures is presented for the first time. Strengthening according to this new method consists of the construction of steel fiber ultra-high-strength concrete jackets without conventional reinforcement which is usually applied in the construction of conventional reinforced concrete jackets. An innovative solution is proposed also for the first time that ensures a satisfactory seismic performance of existing reinforced concrete structures, strengthened by using composite materials. The weak point of the use of such materials in repairing and strengthening of old R/C structures is the area of beam-column joints. According to the proposed solution, the joints can be strengthened with a steel fiber ultra-high-strength concrete jacket, while strengthening of columns can be achieved by using CFRPs. The experimental results showed that the performance of the subassemblage strengthened with the proposed mixed solution was much better than that of the subassemblage retrofitted completely with CFRPs.

• Restorative Dentistry and Endodontics
• /
• v.45 no.1
• /
• pp.6.1-6.8
• /
• 2020

Objectives: This study investigated the effects of a hydrofluoric acid (HA; solution of hydrogen fluoride [HF] in water)-based smart etching (SE) solution at an elevated temperature on yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics in terms of bond strength and morphological changes. Materials and Methods: Eighty sintered Y-TZP specimens were prepared for shear bond strength (SBS) testing. The bonding surface of the Y-TZP specimens was treated with 37% phosphoric acid etching at 20℃-25℃, 4% HA etching at 20℃-25℃, or HA-based SE at 70℃-80℃. In all groups, zirconia primers were applied to the bonding surface of Y-TZP. For each group, 2 types of resin cement (with or without methacryloyloxydecyl dihydrogen phosphate [MDP]) were used. SBS testing was performed. Topographic changes of the etched Y-TZP surface were analyzed using scanning electron microscopy and atomic force microscopy. The results were analyzed and compared using 2-way analysis of variance. Results: Regardless of the type of resin cement, the highest bond strength was measured in the SE group, with significant differences compared to the other groups (p < 0.05). In all groups, MDP-containing resin cement yielded significantly higher bond strength values than MDP-free resin cement (p < 0.05). It was also shown that the Y-TZP surface was etched by the SE solution, causing a large change in the surface topography. Conclusions: Bond strength significantly improved when a heated HA-based SE solution was applied to the Y-TZP surface, and the etched Y-TZP surface was more irregular and had higher surface roughness.

• Textile Coloration and Finishing
• /
• v.34 no.4
• /
• pp.241-249
• /
• 2022

As for military backpacks in Korea, utility backpack products equipped with various functions along with comfort and convenience are being developed. As a result, the volume and weight of the backpack increase, and many lightweight studies of the materials forming the backpack are being conducted. This study is a basic study on frame lightweight using fiber-reinforced composites to deal with aluminum, a back frame that maintains the shape of a backpack and provides stability when worn by combatants. As is known, only fiber-reinforced composites have sufficient light weight and mechanical properties, but the mechanical properties were reviewed by drilling holes to maximize the light weight. Tensile strength and flexural strength were measured by drilling 6mm, 12mm, 18mm, and 24mm holes, and the tensile strength and flexural strength were measured when 1, 3, 5, and 7 holes of 12mm were increased. As a result, even when the number of holes was increased, tensile strength did not change significantly, and the flexural strength showed to be higher in the case of 3 holes and 5 holes than in the case of 1 hole.