• Korean Journal of Agricultural Science
• /
• v.17 no.2
• /
• pp.95-101
• /
• 1990

In order to investigate the influence of unconfined compression strength on undisturbed cohesive soil, the unconfined compression test were carried out on the basis of various size of specimen and compression rate. The result of these experiments were summarized as follows. 1. As the section area of specimen increased. the unconfined compression strength was decreased. 2. As the ratio of height and diameter of specimen increased, the unconfined compression strength was decreased. 3. The unconfined compression strength was increased by 3%, but in values over the 3% was decrease. 4. As the compression rate increased. the modulus of deformation was increased.

• Journal of Korea Water Resources Association
• /
• v.33 no.2
• /
• pp.229-235
• /
• 2000

Characteristics of hail occurred during 1989-1998 is studied. Hail is observed mainly at west coast, southwest inland, and Taegwallyong. Average diameter of hailstone is 0.6 cm, and 70% of the occurrence frequency of hail is observed at west coast. During winter and spring, the wet -bulb zero height (WBZ) is low enough to prevent the melting process of hail. But the lack of available low-level moisture (mean mixing ratio in lowest 100 hPa) makes the size of hail small. As a result, smaller size hail is observed frequently over west coast. On the contrary, WBZ is higher during summer, it means that hail is melted before it reaches ground, but the size of hail is bigger. Thus the larger hail is observed mainly Taegwallyong during summer. Hail is observed from 1100 LST to 1500 LST over west coast and around 1800 LST over Taegwallyong. It suggest that thermally driven mesoscale circulations such as land-sea breeze and mountain ridge-valley circulation aid in the formation of hail. Upper and surface air temperature is related to formation of hailstorm. Before formation of hailstorm in November 1998, the upper air temperature decreases. And hails is observed in the spot of strong temperature and dew point temperature gradient coincidently.

• Journal of Forest and Environmental Science
• /
• v.30 no.4
• /
• pp.383-392
• /
• 2014

In this study, we investigated the Fukiage sand dunes of southern Kyushu, Japan. We surveyed the status of recovery of coastal Japanese black pine forests damaged by pine wilt disease and their disaster prevention capability. We placed two transects: Transect 1, in an area that was severely damaged (80-90% damage rate) by pine wilt disease, and Transect 2, in an area that was mostly undamaged (<10% damage rate). Then, we installed survey lines, carried out vegetation surveys, and measured the depth and pH of humus soil. The survey lines were placed perpendicular to the coastline from the top of the fore-dune to the inland area, and divided into five 50 m sections. Before the point 100 m inland from the top of the fore-dune, the number of invasive hardwoods and of Japanese black pines were small because of the poor growth environment in both transects. Past the 100 m point, the species and number of Japanese black pines and broad-leaved trees increased further inland because the growth environment improved. In addition, the recovery metrics of tree height, diameter at breast height, age, and number in Transect 1 were much lower than those in Transect 2, and the basal area of broad-leaved trees and the depth of humus soil in Transect 1 were lower than in Transect 2, and the soil pH of humus soil in Transect 1 was higher than that of Transect 2. The shape ratio of the Japanese black pine forests indicated that they were insufficient for disaster prevention. Therefore, in order to fully promote the disaster prevention capability of coastal Japanese black pine forests, we should not only focus on prevention of pine wilt disease but also undertake continuous control efforts taking into consideration the sound growth environment such as appropriate density and soil management and removal of invasive broad-leaved trees.

• Journal of Bio-Environment Control
• /
• v.21 no.3
• /
• pp.199-206
• /
• 2012

This study was conducted in a glasshouse to examine the possibility of producing tomato plug seedlings in a newly-developed inert phenolic foam medium. Plug seedlings of 'Madison' tomato were grown in four pellet type media, Grodan rockwool, UR rockwool, phenolic foam LC, and phenolic foam LC-lite. Seed germination was checked for 7 days. Seedling growth was measured at 19 days after sowing. The greatest germination was obtained in the phenolic foam LC and phenolic foam LC-lite. Plant height, hypocotyl length, leaf area, dry weight, and fresh weight were significantly greater in the rockwool medium than those in the other media. However, the T/R ratio and stem diameter were the greatest in the phenolic foam LC than those in the other media. The total porosity and container capacity of the phenolic foam LC was higher than in the other media. The air space (%) was lowest in the phenolic foam LC. Overall, the phenolic foam LC and phenolic foam LC-lite produced seedlings with similar growth as the rockwool. These results suggested that both phenolic foam LC and phenolic foam LC-lite have potential to be used in production of plug seedlings of 'Madison' tomato.

• Journal of the Korean Geotechnical Society
• /
• v.34 no.2
• /
• pp.33-42
• /
• 2018

In this study, the EMI (electro-mechanical impedance) of a small piezoelectric sensor was applied for measuring a unit weight and cementation (strength) of sand. Three different sizes of uncemented Nakdong River sand were filled loosely or densely into a compaction mold. A piezoelectric sensor with 20 mm in diameter was installed within sand for impedance measurement. A small Nakdong River sand was mixed with cement ratios of 4, 8 12, 16% and then compacted into a specimen with 50 mm in diameter and 100 mm in height. The specimen consisted of 6 layers with a sensor at the third layer. The impedance signals for 3 days and unconfined compressive strength at the 3rd day were measured. As the unit weight of uncemented sand increased, the resonant frequency increased slightly from 102 to 105 kHz but a conductance at resonant frequency decreased. For cemented sands, as the curing time and cement ratio increased, the resonant frequency increased significantly from 129 to 266 kHz but the conductance at resonant frequency decreased. The unconfined compressive strength (UCS) of cemented sands was between 289 and 1,390 kPa for different cement ratios. The relationship of UCS and resonant frequency linearly increased but one with a conductance at resonant frequency was in inverse proportion.

• Restorative Dentistry and Endodontics
• /
• v.34 no.2
• /
• pp.130-136
• /
• 2009

The aim of this study was to develop a method for measuring the slumping resistance of flowable resin composites and to evaluate the efficacy using rheological methodology. Five commercial flowable composites (Aelitefil flow:AF, Filtek flow:FF, DenFil flow:DF, Tetric flow:TF and Revolution:RV) were used. Same volume of composites in a syringe was extruded on a glass slide using a custom-made loading device. The resin composites were allowed to slump for 10 seconds at $25^{\circ}C$ and light cured. The aspect ratio (height/diameter) of cone or dome shaped specimen was measured for estimating the slumping tendency of composites. The complex viscosity of each composite was measured by a dynamic oscillatory shear test as a function of angular frequency using a rheometer. To compare the slumping tendency of composites, one way-ANOVA and Turkey's post hoc test was performed for the aspect ratio at 95% confidence level. Regression analysis was performed to investigate the relationship between the complex viscosity and the aspect ratio. The results were as follows. 1. Slumping tendency based on the aspect ratio varied among the five materials (AF

• Korean Journal of Soil Science and Fertilizer
• /
• v.43 no.6
• /
• pp.858-863
• /
• 2010

The blueberry farming requires the soil condition of well-drainage, pH of 4.5 to 5.2, and high in organic matters for stable growth and development. Most of soil type of cultivated land in Korea, however, belongs to alkaline soils with low organic matter content and poor drainage. Therefore, the blueberry farmers use peat moss heavily to improve the soil condition, but the guideline on the effective and economic ratio of peat moss is not established yet. This study was performed to determine the cost effective peat moss ratio for amending soils, and to investigate the feasibility of using sawdust and coco peat as soil amendments. Peat moss, coco peat and sawdust are mixed with soil at the ratio of 0, 12.5, 50 and 100% (v/v). Among 3 organic materials with various mixture ratios, the pH of soil was the lowest in 100% peat moss and sawdust mixtures (pH 3.67 and pH 3.73, respectively), followed by pH 5.30 at 50% peat moss. The soil organic matter content are directly proportional to the mixture ratios in all three organic materials and the same trend was observed in the variation of content of exchangeable potassium in the coco peat treatments. On the contrary, the content of available phosphate, exchangeable calcium and magnesium decreased with increasing the ratio of organic materials. The nitrogen content in the leaves decreased as increasing the ratio of peat moss and coco peat in soil, but not of sawdust. The content of phosphate decreased but potassium increased as the ratio of sawdust and coco peat increased. There was no clear difference in the contents of magnesium and calcium among 3 organic materials. The plant height, stem diameter and dry weight of blueberry plants were the highest in 50 % peat moss, followed by 12.5% peat moss and 12.5% coco peat. The plants in 100% peat moss showed very poor growth. It can be concluded that peatmoss, when applied and managed appropriately, will be a good material for improving soil condition as well as securing desirable growth for blueberry. Upon coupling economic aspect, the optimum mixing ratio of peatmoss for blueberry farming is approximately 25-50%.

• KOREAN JOURNAL OF CROP SCIENCE
• /
• v.53 no.3
• /
• pp.292-296
• /
• 2008

Clay-coated rice seeds (clay-coated seeds A and B) were directly sown on dry paddy and their growth and yield were compared with the normal drill-sown seeds on dry flat paddy. In clay-coated seeds, germination was 1 day earlier and the emergence rate was higher up to 5% than that of normal drill-sown seeds. But the apparent number of seedling stand per $m^2$ was lower than that of normal drill-sown seeds, which is due to the smaller amount of seeding in clay-coated seeds. At the early growth stage, the plant height of clay-coated seeds A was taller than that of drill-sown seeds, while the plant height of clay-coated seeds B was 0.7 cm shorter than that of drill-sown seeds. At the late growth stage, however, the difference was insignificant in both cases. The maximum tillering stage was 10 days earlier in drill-sown seeds. Lodging index was the lowest in clay-coated seeds B and there was no difference between clay-coated seeds A and drill-sown seeds. The ratio of stem base weight, culm diameter and culm wall thickness were higher in clay-coated seeds, while the lower internodes (4th, 5th and 6th) length was shorter in claycoated seeds than in drill-sown seeds. In clay-coated seeds, the number of panicle per $m^2$ was smaller, while the number of spikelet per panicle was a little larger than in drill-sown seeds. The rate of ripened grain and brown rice 1,000 grain weight were lower in the clay-coated seeds, thus the yield was $98{\sim}99%$ level of drill-sown seeds. Considering that the amount of seeding in clay-coated seeds was two-thirds of that in drill-sown seeds, it is expected that clay coating method could become an additional technique for direct seeding cultivation.

• Korean Journal of Medicinal Crop Science
• /
• v.4 no.4
• /
• pp.271-276
• /
• 1996

This studies were conducted to basic information on growth characteristics and root yield in progeny the derived from different bolting years and to establish optimum seed production time in Angelica gigas. Plant height of early and mid-growing stages had decreased with each year increase in bolting year, but showed no significance in late growing stage at different bolting years. Root charac­teristics including root length, root diameter and dry root weight was slightly good and it had high root/ shoot ratio in third year seed production. respectively. Bolting rate showed that first year seed 38.1%, second year seed 10.4% and third year seed 1.2%, respectively. Therefore, optimum seed production time revealed third year seed for reduce bolting rate. Root yield at different bolting years showed average 1,690kg per hectare as fresh root weight on first year seed, 2,860kg on second year and 2,940kg on third year seed, respectively. A significant positive correlation was appeared between bolting rate and plant height in mid-growing stage. On the other hard, there was highly significant negative correlation between bolting rate and root yield.

• Journal of Korean Society of Forest Science
• /
• v.99 no.3
• /
• pp.323-330
• /
• 2010

This study was undertaken to compare early growth characteristics, such as height, diameter at root collar (DRC), and the dry weights of stem, branches, needles and roots between naturally regenerated and planted stands of Pinus densiflora for. erecta in Dae-gi and Bo-gwang site, Gangwon province, Republic of Korea. Average DRC growth was similar between the naturally regenerated and the planted stands in Dae-gi area, however, difference was statistically significant (P<0.01) between the naturally regenerated and the planted stands in Bo-gwang area, 4.66 cm and 2.61 cm, respectively. Average height of the naturally regenerated stands was significantly greater (P<0.01) than that of planted stands in both Dae-gi and Bo-gwang areas. The composition ratio of the dry weights for each part of measured trees was the highest in the stem in the naturally regenerated stands, but in the planted stands, the needle was the highest in both sites. The root/shoot ratio in the Dae-gi and Bo-gwang areas in the planted stands were much greater than those in the naturally regenerated stands, 0.25-0.30 and 0.17-0.18, respectively. The ratio of needle to stem biomass (N/S), branch to stem biomass (B/S), and needle to branch biomass (N/B) was significantly greater in the planted stands than those in the naturally regenerated stands in both sites. The results of this study represent that the regeneration methods, natural and artificial regenerations, can have an influence on the early growth of P densiflora for. erecta. This results not only provide the need for a correct planting method, but also will be useful in studies on the environmental adaptability of trees.