• Journal of the Korean Wood Science and Technology
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• 제23권1호
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• pp.35-41
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• 1995

Persimmon boards of 30mm thick were dried, their temperatures were monitored during drying with 490 and 200watt microwave, and the drying efficacy and problems were investigated. The effects of pretreatments such as presteaming and prefreezing were also examined. The persimmon green lumbers of 80% moisture content were dried to 10% for only 50~60 and 110 minutes with 49watt and 200watt microwave, respectively. Severe internal checks were, however, found in all boards. The presteamed boards collapsed on their surfaces earlier than the controls. It may attribute to the high temperature inside boards during microwave drying and the decrease of their internal tensile strength caused by the presteaming treatment. To increase the internal tensile strength of the pretreated boards and to reduce their internal checks, they were air-dried at room temperature. The air-dried boards could be dried to 10% moisture content clearly and free from defects with 200watt microwave. The heating efficiency were also calculated with the maximum weight loss per minute of 490watt and 200watt.

• Journal of Biosystems Engineering
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• 제10권2호
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• pp.36-46
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• 1985

This study was intended to develop the mathematical model of the head-fed type threshing unit. As the first step, the physical model of the threshing phenomena was considered to consist of four separate processes as 1) detachment process of grains, 2) movement of grains between the cylinder and concave, 3) grain penetration through stems of bundle, and 4) grain passing through concave. The mathematical and computer models were developed based on the physical models. Threshing experiments were performed and determined the distribution of grain accumulation along the cylinder shaft by varying the moisture content of grains, feeding rate, and cylinder speed. It was found that the model developed coincided very well with the experimental results for the varied operational conditions. Greater concentration of grains passing through concave toward the thresher inlet was equally true for the model and experiment work for the threshing of grains with higher moisture content and with higher cylinder-speed. The model could be used for obtaining the optimized design or for optimizing the performance of the head-fed type threshing unit if term as to power requirement for threshing may be additionally included in the developed model.

• Journal of the Korean Wood Science and Technology
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• 제22권2호
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• pp.61-70
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• 1994

This study was executed to find the applicability of press drying of tree disk by investigating the shrinkage and drying defect and to form appropriate model by comparing the actual moisture content(MC) and internal temperature in respect of drying time with calculated values based computer simulation to which was applied finite difference method. In press drying disk, heating period, constant drying rate period maintained plateau temperature at 100$^{\circ}C$ and falling drying rate period were significantly distinguished. Actual MC and internal temperature were analogous to those calculated at comparing points. Heat transfer model formed by Fourier's law using specific heat of moist wood and conduction coefficient considering fractional volume of each element of wood cell wall, bound water, free water and air showed applicability as basic data to developing heat expansion, shrinkage and drying stress during press drying. Also mass transfer model formed by Fick's diffusion law using water vapor diffusion coefficient showed applicability. Longitudinal shrinkage was developed by pressure of hot press and tangential shrinkage was restrained by hygrothermal recovery. The heart check, surface check and ring failure were occurred differently in species, but V-shaped crack didn't develop.

• Asian-Australasian Journal of Animal Sciences
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• 제4권1호
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• pp.99-102
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• 1991

To determine effect of time after feeding on distribution of digesta in the gastro-intestinal tracts of sheep given orchardgrass hay once a day, a total of fifteen ewes (mean live weight $51{\pm}12kg$) were slaughtered at 2, 8, 16 and 24 hours after feeding. Contents in the reticulo-rumen, omasum, abomasums, small intestine, cecum, and colon and rectum were totally collected and weighed. Weights of digesta in the reticulo-rumen were about 6 kg which contributed about 75% of the total in the whole tracts. Digesta on dry-matter basis totaled about 1 kg. The dry-matter concentration of digesta in the whole digestive tract was about 107 h/kg of fresh digesta. Distribution of moisture in the digestive tract changed in parallel with that of fresh digesta. There was no significant correlation observed between time after feeding and weights of digesta in the gastro-intestinal tracts. While, feed intake significantly correlated with digesta in the reticulo-rumen, cecum and whole tracts (p<0.01). Thus, time after feeding was inferred to have no influence upon the content of digesta in the digestive tract, but feed intake influenced on the content of digesta in the digestive tract at a low level of feeding.

• The Korean Journal of Ecology
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• 제21권4호
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• pp.321-328
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• 1998

To describe the major environmental factors operating in coastal wetland and to characterize the distribution of the plant species over the wetland in relation to the major environmental gradients, 12 soil physical and chemical properties were determined. The gradient of water and osmotic potential of soil, electrical conductivity, sodium and chloride content and soil texture alsong the three habitat types of salt marshes, salt swamp and sand dune were occurred. The 24 coastal plant communities from principal component analysis (PCA) on the 12 variables were at designated as a gradient for soil texture and water potential related with salinity by Axis I and as a gradient for soil moisture and total nitrogen gradient by Axis II On Axis I were divided into 3 groups (1) 9 salt marsh communities including Salicornia herbacea communities (2) 5 salt swamp communities including Scirpus fluviatilis communities and (3) 10 sand dune communities including Jmperata cylindrica communities on Axis II were divided into 2 groups (1) salt marsh and sand dune communities, and (2) 3 salt swamp communities. The results could account for the zonation of plant communities on coastal wetland observed alsong envionmental gradients.

• The Korean Journal of Ecology
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• 제11권3호
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• pp.131-136
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• 1988

The continuum analyses and polar ordinations were applied for the ordination of forest vegetation in Mt. Naejang, national park in Korea. In the continuum analyses the sequence of Pinus densiflora, Quercus mongolica, Quercus variabilis, Carpinus laxiflora, Carpinus tschonoskii, Lindera erythrocapa and Zelkova serrata community was arranged along the continuum gradient as in moisture gradient analyses. The positive correlation of r=0.83 between continuum index and soil moisture content was observed. In the polar ordinations ten communities of Pinus densiflora, Quercus monogolica, Quercus variabilis, Carpinus laxiflora, Daphniphyllum macropodum, carpinus tschonoskii, Quercus aliena-Carpinus tschonoskii, Torreya nucifera, Cornus controversa-Lindera erythrocarpa and Zelkova serrata were identified. However, continuous distribution pattern of ten communities mentioned above could be regarded as a vegetational continuum. The results of these ordinations also were corresponded to those of phytosociological classification.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회
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• pp.1151-1155
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• 2010

Frost depth is one of important factors to design roadway structure, and it can be estimated with numerical simulation on thermal distribution through subgrade soils. Thermal conductivity is a key parameter for accurate prediction on thermal distribution, but there are few studies on thermal conductivity of subgrade soils in Korea. Thermal conductivity can be affected by several factors such as dry density, moisture content, and saturation degree based on previous researches. Two empirical equations to estimate thermal conductivity are applied to access the accuracy of these equations with experimental data. Results indicate that the equation can be used to estimate thermal conductivity with proper quartz fraction.

• 미생물학회지
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• 제12권1호
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• pp.15-24
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• 1974

This experiment has been carried out with a view to elucidating the distribution of Azotobacter and their population size in rhizosphere and sea and designed ro compare the results with some environmental factors. Results of the experiment are summarized as follows: 1) It was observed that the population sizes of Azotobacter were decided upon the moisture content of soil and that the soil pH was one of the most impertant factors influencing the distribution of Azotobacter. 2)Population sizes of Azotobacter in rhizosphere were changed in accordance with the kinds of vegetation on soil: The rhizosphere where bamboo, corn, legume, and oak inhabit showed the largest population size of Azotobacter. On the other hand, rhizosphere of ginseng revealed no Azotobacter. However, the largest population of general fungi were measured at the rhizosphere. 3)Comparing the population sizes of general microbes in rhizosphere with those of non-rhizosphere, the population sizes of microbes in rhizosphere are larger than those of non-rhizosphere. 4)In coastal environments, population sizes of Azotobacter in surface water of sea are similar to those of the soil(mud) of tidal land. But the sizes are generally smaller than those of terrestrial soils.

• Journal of the Korean Wood Science and Technology
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• 제37권2호
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• pp.141-147
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• 2009

The fluctuation of physical properties in wood or wood composites is an important subject when the materials in building and construction. Sorption and desorption occur in wood when exposed to the open air, and the temperature distribution in wood can fluctuate as a result of changes in environmental temperature, solar radiation, humidity, and wind velocity. In this study, the temperature difference and fluctuation caused by outdoor environment among different wood species were analyzed using a numerical method. The effect on the process of heat transfer in wood caused by environmental factors was investigated using 1-dimensional partial differential equation with real boundary and initial conditions. The experimental data have been used to check the accuracy of programming code. Through analysis, it was found out that density and moisture content have a negative effect on thermal diffusivity of wood.

• 조명전기설비학회논문지
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• 제29권12호
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• pp.33-39
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• 2015

This paper examines the insulation performance of synthetic air and dry air. This examination was conducted based on dielectric strength in uniform and non-uniform field, electric field distribution by interior structure and defects in gas insulation switchgear (GIS) and insulation performance in different temperatures. From this review, it was found that eco-insulation gas required to possess low moisture content for power equipment in the distribution class. The results of this paper are valuable to ensure the insulation design and insulation reliability of GIS using air.