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STUDIES ON THE PROPAGATION OF ABALONE (전복의 증식에 관한 연구)

  • PYEN Choong-Kyu
    • Korean Journal of Fisheries and Aquatic Sciences
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    • v.3 no.3
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    • pp.177-186
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    • 1970
  • The spawning of the abalone, Haliotis discus hannai, was induced In October 1969 by air ex-position for about 30 minutes. At temperatures of from 14.0 to $18.8^{\circ}C$, the youngest trochophore stage was reached within 22 hours after the egg was laid. The trochophore was transformed into the veliger stage within 34 hours after fertilization. For $7\~9$ days after oviposition the veliger floated in sea water and then settled to the bottom. The peristomal shell was secreted along the outer lip of the aperture of the larval shell, and the first respiratory pore appears at about 110 days after fertilization. The shell attained a length of 0.40 mm in 15 days, 1.39 mm in 49 days, 2.14 mm in 110 days, 5.20 mm in 170 days and 10.00 mm in 228 days respectively. Monthly growth rate of the shell length is expressed by the following equation :$L=0.9981\;e^{0.18659M}$ where L is shell length and M is time in month. The density of floating larvae in the culture tank was about 10 larvae per 100 co. The number of larvae attached to a polyethylene collector ($30\times20\;cm$) ranged from 10 to 600. Mortality of the settled larvae on the polyethylene collector was about $87.0\%$ during 170 days following settlement. The culture of Nauicula sp. was made with rough polyethylene collectors hung at three different depths, namely 5 cm, 45 cm and 85 cm. At each depth the highest cell concentration appeared after $15\~17$ days, and the numbers of cells are shown as follows: $$5\;cm\;34.3\times10^4\;Cells/cm^2$$ $$45\;cm\;27.2\times10^4\;Cells/cm^2$$ $$85\;cm\;26.3\times10^4\;Cells/cm^2$$ At temperatures of from 13.0 to $14.3^{\circ}C$, the distance travelled by the larvae (3.0 mm In shell length) averaged 11.36 mm for a Period of 30 days. Their locomation was relatively active between 6 p.m. and 9 p.m., and $52.2\%$ of them moved during this period. When the larvae (2.0 mm in shell length) were kept in water at $0\;to\;\~1.8^{\circ}C$, they moved 1.15cm between 4 p.m. and 8 p.m. and 0.10 cm between midnight and 8 a.m. The relationships between shell length and body weight of the abalone sampled from three different localities are shown as follows: Dolsan-do $W=0.2479\;L^{2.5721}$ Huksan-do $W=0.1001\;L^{3.1021}$ Pohang $W=0.9632\;L^{2.0611}$

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THE EFFECTS OF THE PLATELET-DERIVED GROWTH FACTOR-BB ON THE PERIODONTAL TISSUE REGENERATION OF THE FURCATION INVOLVEMENT OF DOGS (혈소판유래성장인자-BB가 성견 치근이개부병변의 조직재생에 미치는 효과)

  • Cho, Moo-Hyun;Park, Kwang-Beom;Park, Joon-Bong
    • Journal of Periodontal and Implant Science
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    • v.23 no.3
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    • pp.535-563
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    • 1993
  • New techniques for regenerating the destructed periodontal tissue have been studied for many years. Current acceptable methods of promoting periodontal regeneration alre basis of removal of diseased soft tissue, root treatment, guided tissue regeneration, graft materials, biological mediators. Platelet-derived growth factor (PDGF) is one of polypeptide growth factor. PDGF have been reported as a biological mediator which regulate activities of wound healing progress including cell proliferation, migration, and metabolism. The purposes of this study is to evaluate the possibility of using the PDGF as a regeneration promoting agent for furcation involvement defect. Eight adult mongrel dogs were used in this experiment. The dogs were anesthetized with Pentobarbital Sodium (25-30 mg/kg of body weight, Tokyo chemical Co., Japan) and conventional periodontal prophylaxis were performed with ultrasonic scaler. With intrasulcular and crestal incision, mucoperiosteal flap was elevated. Following decortication with 1/2 high speed round bur, degree III furcation defect was made on mandibular second(P2) and fourth(P4) premolar. For the basic treatment of root surface, fully saturated citric acid was applied on the exposed root surface for 3 minutes. On the right P4 20ug of human recombinant PDGF-BB dissolved in acetic acid was applied with polypropylene autopipette. On the left P2 and right P2 PDGF-BB was applied after insertion of ${\beta}-Tricalcium$ phosphate(TCP) and collagen (Collatape) respectively. Left mandibular P4 was used as control. Systemic antibiotics (Penicillin-G benzathine and penicillin-G procaine, 1 ml per 10-25 1bs body weight) were administrated intramuscular for 2 weeks after surgery. Irrigation with 0.1% Chlorhexidine Gluconate around operated sites was performed during the whole experimental period except one day immediate after surgery. Soft diets were fed through the whole experiment period. After 2, 4, 8, 12 weeks, the animals were sacrificed by perfusion technique. Tissue block was excised including the tooth and prepared for light microscope with H-E staining. At 2 weeks after surgery, therer were rapid osteogenesis phenomenon on the defected area of the PDGF only treated group and early trabeculation pattern was made with new osteoid tissue produced by activated osteoblast. Bone formation was almost completed to the fornix of furcation by 8 weeks after surgery. New cementum fromation was observed from 2 weeks after surgery, and the thickness was increased until 8 weeks with typical Sharpey’s fibers reembedded into new bone and cementum. In both PDGF-BB with TCP group and PDGF-BB with Collagen group, regeneration process including new bone and new cementum formation and the group especially in the early weeks. It might be thought that the migration of actively proliferating cells was prohibited by the graft materials. In conclusion, platelet-derived growth factor can promote rapid osteogenesis during early stage of periodontal tissue regeneration.

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Protoplast Fusion of Nicotiana glauca and Solanum tuberosum Using Selectable Marker Genes (표식유전자를 이용한 담배와 감자의 원형질체 융합)

  • Park, Tae-Eun;Chung, Hae-Joun
    • The Journal of Natural Sciences
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    • v.4
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    • pp.103-142
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    • 1991
  • These studies were carried out to select somatic hybrid using selectable marker genes of Nicotiana glauca transformed by NPTII gene and Solanum tuberosum transformed by T- DNA, and to study characteristics of transformant. The results are summarized as follows. 1. Crown gall tumors and hairy roots were formed on potato tuber disc infected by A. tumefaciens Ach5 and A. rhizogenes ATCC15834. These tumors and roots could be grown on the phytohormone free media. 2. Callus formation from hairy root was prompted on the medium containing 2, 4 D 2mg/I with casein hydrolysate lg/l. 3. The survival ratio of crown gall tumor callus derived from potato increased on the medium containing the activated charcoal 0. 5-2. 0mg/I because of the preventions on the other hand, hairy roots were necrosis on the same medium. 4. Callus derived from hairy root were excellently grown for a short time by suspension culture on liquid medium containing 2, 4-D 2mg/I and casein hydrolysate lg/l. 5. The binary vector pGA643 was mobilized from E. coli MC1000 into wild type Agrobacteriurn tumefaciens Ach5, A. tumefaciens $A_4T$ and disarmed A. tuniefaciens LBA4404 using a triparental mating method with E. ccli HB1O1/pRK2013. Transconjugants were obtained on the minimal media containing tetracycline and kanamycin. pGA643 vectors were confirmed by electrophoresis on 0.7% agarose gel. 6. Kanamycin resistant calli were selected on the media supplemented with 2, 4-D 0.5mg/1 and kanamycin $100\mug$/ml after co- cultivating with tobacco stem explants and A. tumefaciens LBA4404/pGA643, and selected calli propagated on the same medium. 7. The multiple shoots were regenerated from kanamycin resistant calli on the MS medium containing BA 2mg/l. 8. Leaf segments of transformed shoot were able to grow vigorusly on the medium supplemented with high concentration of kanamycin $1000\mug$/ml. 9. Kanamycin resistant shoots were rooting and elongated on medium containing kanamycin $100\mug$/ml, but normal shoot were not. 10. For the production of protoplast from potato calli transformed by T-DNA and mesophyll tissue transformed by NPTII gene, the former was isolated in the enzyme mixture of 2.0% celluase Onozuka R-10, 1.0% dricelase, 1.0% macerozyme. and 0.5M mannitol, the latter was isolated in the enzyme mixture 1.0% Celluase Onozuka R-10, 0.3% macerozyme, and 0.7M mannitol. 11. The optimal concentrationn of mannitol in the enzyme mixture for high protoplast yield was 0.8M at both transformed tobacco mesophyll and potato callus. The viabilities of protoplast were shown above 90%, respectively. 12. Both tobacco mesophyll and potato callus protoplasts were fused by using PEG solution. Cell walls were regenerated on hormone free media supplemented with kanamycin after 5 days, and colonies were observed after 4 weeks culture.

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Air Pollution and Its Effects on E.N.T. Field (대기오염과 이비인후과)

  • 박인용
    • Proceedings of the KOR-BRONCHOESO Conference
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    • 1972.03a
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    • pp.6-7
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    • 1972
  • The air pollutants can be classified into the irritant gas and the asphixation gas, and the irritant gas is closely related to the otorhinolaryngological diseases. The common irritant gases are nitrogen oxides, sulfur oxides, hydrogen carbon compounds, and the potent and irritating PAN (peroxy acyl nitrate) which is secondarily liberated from photosynthesis. Those gases adhers to the mucous membrane to result in ulceration and secondary infection due to their potent oxidizing power. 1. Sulfur dioxide gas Sulfur dioxide gas has the typical characteristics of the air pollutants. Because of its high solubility it gets easily absorbed in the respiratory tract, when the symptoms and signs by irritation become manifested initially and later the resistance in the respiratory tract brings central about pulmonary edema and respiratory paralysis of origin. Chronic exposure to the gas leads to rhinitis, pharyngitis, laryngitis, and olfactory or gustatory disturbances. 2. Carbon monoxide Toxicity of carbon monoxide is due to its deprivation of the oxygen carrying capacity of the hemoglobin. The degree of the carbon monoxide intoxication varies according to its concentration and the duration of inhalation. It starts with headache, vertigo, nausea, vomiting and tinnitus, which can progress to respiratory difficulty, muscular laxity, syncope, and coma leading to death. 3. Nitrogen dioxide Nitrogen dioxide causes respiratory disturbances by formation of methemoglobin. In acute poisoning, it can cause pulmonary congestion, pulmonary edema, bronchitis, and pneumonia due to its strong irritation on the eyes and the nose. In chronic poisoning, it causes chronic pulmonary fibrosis and pulmonary edema. 4. Ozone It has offending irritating odor, and causes dryness of na sopharyngolaryngeal mucosa, headache and depressed pulmonary function which may eventually lead to pulmonary congestion or edema. 5. Smog The most outstanding incident of the smog occurred in London from December 5 through 8, 1952, because of which the mortality of the respiratory diseases increased fourfold. The smog was thought to be due to the smoke produced by incomplete combustion and its byproduct the sulfur oxides, and the dust was thought to play the secondary role. In new sense, hazardous is the photochemical smog which is produced by combination of light energy and the hydrocarbons and oxidant in the air. The Yonsei University Institute for Environmental :pollution Research launched a project to determine the relationship between the pollution and the medical, ophthalmological and rhinopharyngological disorders. The students (469) of the "S" Technical School in the most heavily polluted area in Pusan (Uham Dong district) were compared with those (345) of "K" High School in the less polluted area. The investigated group had those with subjective symptoms twice as much as the control group, 22.6% (106) in investigated group and 11.3% (39) in the control group. Among those symptomatic students of the investigated group. There were 29 with respiratory symptoms (29%), 22 with eye symptoms (21%), 50 with stuffy nose and rhinorrhea (47%), and 5 with sore thorat (5%), which revealed that more than half the students (52%) had subjective symptoms of the rhinopharyngological aspects. Physical examination revealed that the investigated group had more number of students with signs than those of the control group by 10%, 180 (38.4%) versus 99 (28.8%). Among the preceding 180 students of the investigated group, there were 8 with eye diseases (44%), 1 with respiratory disease (0.6%), 97 with rhinitis (54%), and 74 with pharyngotonsillitis (41%) which means that 95% of them had rharygoical diseases. The preceding data revealed that the otolaryngological diseases are conspicuously outnumbered in the heavily polluted area, and that there must be very close relationship between the air pollution and the otolaryngological diseases, and the anti-pollution measure is urgently needed.

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Studies on the Kiln Drying Characteristics of Several Commercial Woods of Korea (국산 유용 수종재의 인공건조 특성에 관한 연구)

  • Chung, Byung-Jae
    • Journal of the Korean Wood Science and Technology
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    • v.2 no.2
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    • pp.8-12
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    • 1974
  • 1. If one unity is given to the prongs whose ends touch each other for estimating the internal stresses occuring in it, the internal stresses which are developed in the open prongs can be evaluated by the ratio to the unity. In accordance with the above statement, an equation was derived as follows. For employing this equation, the prongs should be made as shown in Fig. I, and be measured A and B' as indicated in Fig. l. A more precise value will result as the angle (J becomes smaller. $CH=\frac{(A-B') (4W+A) (4W-A)}{2A[(2W+(A-B')][2W-(A-B')]}{\times}100%$ where A is thickness of the prong, B' is the distance between the two prongs shown in Fig. 1 and CH is the value of internal stress expressed by percentage. It precision is not required, the equation can be simplified as follows. $CH=\frac{A-B'}{A}{\times}200%$ 2. Under scheduled drying condition III the kiln, when the weight of a sample board is constant, the moisture content of the shell of a sample board in the case of a normal casehardening is lower than that of the equilibrium moisture content which is indicated by the Forest Products Laboratory, U. S. Department of Agriculture. This result is usually true, especially in a thin sample board. A thick unseasoned or reverse casehardened sample does not follow in the above statement. 3. The results in the comparison of drying rate with five different kinds of wood given in Table 1 show that the these drying rates, i.e., the quantity of water evaporated from the surface area of I centimeter square per hour, are graded by the order of their magnitude as follows. (1) Ginkgo biloba Linne (2) Diospyros Kaki Thumberg. (3) Pinus densiflora Sieb. et Zucc. (4) Larix kaempheri Sargent (5) Castanea crenata Sieb. et Zucc. It is shown, for example, that at the moisture content of 20 percent the highest value revealed by the Ginkgo biloba is in the order of 3.8 times as great as that for Castanea crenata Sieb. & Zucc. which has the lowest value. Especially below the moisture content of 26 percent, the drying rate, i.e., the function of moisture content in percentage, is represented by the linear equation. All of these linear equations are highly significant in testing the confficient of X i. e., moisture content in percentage. In the Table 2, the symbols are expressed as follows; Y is the quantity of water evaporated from the surface area of 1 centimeter square per hour, and X is the moisture content of the percentage. The drying rate is plotted against the moisture content of the percentage as in Fig. 2. 4. One hundred times the ratio(P%) of the number of samples occuring in the CH 4 class (from 76 to 100% of CH ratio) within the total number of saplmes tested to those of the total which underlie the given SR ratio is measured in Table 3. (The 9% indicated above is assumed as the danger probability in percentage). In summarizing above results, the conclusion is in Table 4. NOTE: In Table 4, the column numbers such as 1. 2 and 3 imply as follows, respectively. 1) The minimum SR ratio which does not reveal the CH 4, class is indicated as in the column 1. 2) The extent of SR ratio which is confined in the safety allowance of 30 percent is shown in the column 2. 3) The lowest limitation of SR ratio which gives the most danger probability of 100 percent is shown in column 3. In analyzing above results, it is clear that chestnut and larch easly form internal stress in comparison with persimmon and pine. However, in considering the fact that the revers, casehardening occured in fir and ginkgo, under the same drying condition with the others, it is deduced that fir and ginkgo form normal casehardening with difficulty in comparison with the other species tested. 5. All kinds of drying defects except casehardening are developed when the internal stresses are in excess of the ultimate strength of material in the case of long-lime loading. Under the drying condition at temperature of $170^{\circ}F$ and the lower humidity. the drying defects are not so severe. However, under the same conditions at $200^{\circ}F$, the lower humidity and not end coated, all sample boards develop severe drying defects. Especially the chestnut was very prone to form the drying defects such as casehardening and splitting.

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Effect of Non-Agricultural Facilities on Water Quality and Contamination in Rural Area (농촌용수 수질관리를 위한 비농업시설의 영향 연구)

  • Lee, Byung-Sun;Um, Jae-Yeon;Kim, Yang-Bin;Woo, Nam-Chil;Nam, Kyoung-Phile;Lee, Jong-Min
    • Journal of Soil and Groundwater Environment
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    • v.14 no.2
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    • pp.1-9
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    • 2009
  • This study was objected to identify the effect on water quality and contamination by non-agricultural facilities in 'A' reservoir watershed located in OO city, Kyounggi-do, Korea. Ground- and stream water samples showed (Na+K)-Cl, Ca(Cl, SO$_4$) and Ca-Cl type in an illegally discharging area of sewage and a densely industrial area indicating water contamination. Stream water of an illegally discharging area of sewage had high COD, T-N and T-P. In this area, direct incoming of sewage into stream water was induced ground water system by well pumping, and it made a progress of ground water contaminations with those components. Groundwater of a densely industrial area showed high concentrations of T-N, NO$_3$N. From a nitrogen isotope analysis, stream water of an illegally discharging area of sewage has ${\delta}^{15}N-NO_3$values of 0.7%0 was strongly affected by nitrogen originated from agrochemicals, and a densely industrial area of 19.7%0 from septic system. Ground- and stream water of a livestock fanning area were contaminated with NH$_3$-N and Mn, which was affected by intensive livestock facilities. SAR-conductivity plot indicates the water does not pose either alkalinity or salinity hazard for irrigation. COD, T-N, T-P, NO$3$-N, NH$_3$N and Mn concentrations from contaminated areas were diminished by mixing with 'A' reservoir water. There were no water contaminations in silver towns, vacationlands around reservoir and golf links. Consequently, it should be made a plan of systematic managements for past and- present possible contaminants and sewage systems in preventing water contamination by non-agricultural facilities.

Effects of Dissolved Compounds in Groundwater on TCE Degradations Reaction by Nanoscale Zero-Valent Iron (나노영가철의 TCE 분해반응 시 지하수 용존물질의 영향)

  • Kim, Tae-Ho;Kim, Hong-Seok;Lee, Jin-Yong;Cheon, Jeong-Yong;Lee, Kang-Kun;Hwang, In-Seong
    • Journal of Korean Society of Environmental Engineers
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    • v.33 no.6
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    • pp.413-419
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    • 2011
  • Nanoscale zero-valent iron (NZVI) particles were tested as remediation media for groundwater contaminated by organic pollutants (e.g., TCE, trichloroethylene). The contaminated groundwater contained anions ($NO_3^-$, $Cl^-$, $SO_4^{2-}$, and $HCO_3^-$) and natural organic matter (NOM). Treatability of commercial NZVI particles (NANOFER 25, Nanoiron, Czech) was tested by using a synthetic groundwater and the field groundwater samples. More than 95% of 1.8 mM TCE was removed within 20 hours with a NZVI dosage of 25 g/L ($k=0.15hr^{-1}$). Repetitive degradation experiments revealed that the removal capacity of NANOFER 25 was 0.19 mmole TCE/g NZVI. TCE degradation reactions were not substantially affected by the presence of each anion with concentrations as high as 100 times the average field concentrations. However, when the four anions ($NO_3^-$, $Cl^-$, $SO_4^{2-}$, $HCO_3^-$) were present simultaneously. the degradation reactivity and removal capacity were decreased by 60% ($k=0.069hr^{-1}$) and 10%, respectively. The k value of TCE degradation in the presence of NZVI (25 g/L) with dissovled organic carbon of 2.5 mg/L was also decreased by 84% ($k=0.025hr^{-1}$). In the experiments with the field groundwater, more than 90% of $1.8{\mu}M$ TCE, which is the concentration of TCE at the source zone, was removed within 10 hours with a NANOFER 25 dosage of 25 g/L. The results imply that the contaminated groundwater can effectively be treated by NANOFER 25 with more information on the hydrogeology of the site.

Effect of Dietary Live or Killed Kimchi Lactic Acid Bacteria on Growth Performance, Nutrient Utilization, Gut Microbiota and Meat Characteristics in Broiler Chicken (사료 내 생균 또는 사균 형태 김치 유산균의 첨가가 육계의 생산성, 영양소 이용률, 장내 미생물 및 계육 특성에 미치는 영향)

  • Lee, Jeong Heon;Kim, Sang Yun;Lee, Jun Yeop;Ahammed, Musabbir;Ohh, Sang Jip
    • Korean Journal of Poultry Science
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    • v.40 no.1
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    • pp.57-65
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    • 2013
  • This study was conducted to evaluate the effect of dietary Weissella koreensis (Wk), a prominent kimchi lactic acid bacteria supplementation on growth performance, nutrients utilization, gut microbiota and meat characteristics in broiler chicken. Both live and killed Wk was compared to know which could be more efficacious as a feed probiotics. Three Wk supplemented groups and no Wk supplemented group were designated according to supplementation levels and cell status. Those were; Control (no Wk), 0.1 % live Wk (LWk 0.1), 0.5% live Wk (LWk 0.5) and 0.5% killed Wk (KWk 0.5). Body weight gain and feed conversion efficiency were improved (P<0.05) by dietary LWk supplementation. KWk did not exert any benefit on growth performance. Crude protein utilizability of KWk supplemented diet was lower (P<0.05) than that of other diets. However, there were no differences among treatments in other nutrients utilization. Serum IgG concentration and relative weight of bursa of Fabricius was highest (P<0.05) in broiler chicken fed KWk 0.5 diet. Cecal anaerobic lactic acid bacteria count of LWk groups were higher (P<0.05) than those of control and KWk 0.5 groups. Dietary Wk supplementation failed to lower the count of cecal and fecal E. coli. There was no effect of dietary Wk on TBARS values and fatty acids profile of broiler leg meat. However, the dietary supplementation of Wk exerted characteristic difference on electronic nose flavor of broiler meat. This study showed that dietary supplementation of LWk was able to improve body weight gain, feed conversion efficiency and cecal lactic acid bacterial count in broiler chicken. Further, the result of this study implemented that a live kimchi lactic acid bacteria, LWk, but not killed Wk, could be used as a probiotic feed supplement for broiler.

Multi-level Analysis of the Antecedents of Knowledge Transfer: Integration of Social Capital Theory and Social Network Theory (지식이전 선행요인에 관한 다차원 분석: 사회적 자본 이론과 사회연결망 이론의 결합)

  • Kang, Minhyung;Hau, Yong Sauk
    • Asia pacific journal of information systems
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    • v.22 no.3
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    • pp.75-97
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    • 2012
  • Knowledge residing in the heads of employees has always been regarded as one of the most critical resources within a firm. However, many tries to facilitate knowledge transfer among employees has been unsuccessful because of the motivational and cognitive problems between the knowledge source and the recipient. Social capital, which is defined as "the sum of the actual and potential resources embedded within, available through, derived from the network of relationships possessed by an individual or social unit [Nahapiet and Ghoshal, 1998]," is suggested to resolve these motivational and cognitive problems of knowledge transfer. In Social capital theory, there are two research streams. One insists that social capital strengthens group solidarity and brings up cooperative behaviors among group members, such as voluntary help to colleagues. Therefore, social capital can motivate an expert to transfer his/her knowledge to a colleague in need without any direct reward. The other stream insists that social capital provides an access to various resources that the owner of social capital doesn't possess directly. In knowledge transfer context, an employee with social capital can access and learn much knowledge from his/her colleagues. Therefore, social capital provides benefits to both the knowledge source and the recipient in different ways. However, prior research on knowledge transfer and social capital is mostly limited to either of the research stream of social capital and covered only the knowledge source's or the knowledge recipient's perspective. Social network theory which focuses on the structural dimension of social capital provides clear explanation about the in-depth mechanisms of social capital's two different benefits. 'Strong tie' builds up identification, trust, and emotional attachment between the knowledge source and the recipient; therefore, it motivates the knowledge source to transfer his/her knowledge to the recipient. On the other hand, 'weak tie' easily expands to 'diverse' knowledge sources because it does not take much effort to manage. Therefore, the real value of 'weak tie' comes from the 'diverse network structure,' not the 'weak tie' itself. It implies that the two different perspectives on strength of ties can co-exist. For example, an extroverted employee can manage many 'strong' ties with 'various' colleagues. In this regards, the individual-level structure of one's relationships as well as the dyadic-level relationship should be considered together to provide a holistic view of social capital. In addition, interaction effect between individual-level characteristics and dyadic-level characteristics can be examined, too. Based on these arguments, this study has following research questions. (1) How does the social capital of the knowledge source and the recipient influence knowledge transfer respectively? (2) How does the strength of ties between the knowledge source and the recipient influence knowledge transfer? (3) How does the social capital of the knowledge source and the recipient influence the effect of the strength of ties between the knowledge source and the recipient on knowledge transfer? Based on Social capital theory and Social network theory, a multi-level research model is developed to consider both the individual-level social capital of the knowledge source and the recipient and the dyadic-level strength of relationship between the knowledge source and the recipient. 'Cross-classified random effect model,' one of the multi-level analysis methods, is adopted to analyze the survey responses from 337 R&D employees. The results of analysis provide several findings. First, among three dimensions of the knowledge source's social capital, network centrality (i.e., structural dimension) shows the significant direct effect on knowledge transfer. On the other hand, the knowledge recipient's network centrality is not influential. Instead, it strengthens the influence of the strength of ties between the knowledge source and the recipient on knowledge transfer. It means that the knowledge source's network centrality does not directly increase knowledge transfer. Instead, by providing access to various knowledge sources, the network centrality provides only the context where the strong tie between the knowledge source and the recipient leads to effective knowledge transfer. In short, network centrality has indirect effect on knowledge transfer from the knowledge recipient's perspective, while it has direct effect from the knowledge source's perspective. This is the most important contribution of this research. In addition, contrary to the research hypothesis, company tenure of the knowledge recipient negatively influences knowledge transfer. It means that experienced employees do not look for new knowledge and stick to their own knowledge. This is also an interesting result. One of the possible reasons is the hierarchical culture of Korea, such as a fear of losing face in front of subordinates. In a research methodology perspective, multi-level analysis adopted in this study seems to be very promising in management research area which has a multi-level data structure, such as employee-team-department-company. In addition, social network analysis is also a promising research approach with an exploding availability of online social network data.

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Properties of Plywood Bonded with Adhesive Resins Formulated with Enzymatically-Hydrolyzed Rapeseed Flour (유채박의 효소 가수분해물로 조제한 접착제를 사용한 합판의 접착특성)

  • Yang, In;Han, Gyu-Seong;Choi, In-Gyu;Kim, Yong-Hyun;Ahn, Sye-Hee;Oh, Sei-Chang
    • Journal of the Korean Wood Science and Technology
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    • v.40 no.3
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    • pp.164-176
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    • 2012
  • In the present study, rapeseed flour (RSF), which is a by-product from the production of edible oil and biodiesel extracted from rapeseed, was used to develop alternative adhesives for the production of plywood panels. To examine the effects of the enzyme on the adhesive properties and formaldehyde emission of the RSF-based adhesive resins, three enzymes, such as cellulase (CEL), pectinase (PEC) and protease (ALC), were used either separately or together. As a crosslinking agent, PF prepolymers, which were prepared with 1.5, 1.8 and 2.1 mole formaldehyde and 1 mol phenol (1.8-, 2.1- and 2.4-PF), were added into the RSF hydrolyzates. The adhesive resins formulated with CEL- or CEL-PEC-RSF hydrolyzates and 1.8-F/P PF prepolymers exhibited excellent adhesive strengths and formaldehyde emission. The tensile shear strength and formaldehyde emission of the plywood panels bonded with the formulate resins were satisfied with the minimum requirement of the KS standard for ordinary plywood panels (0.6 N/$mm^2$). In addition, formaldehyde emissions of the plywood panels approached to that of E0 specified in the KS standard (0.5 mg/${\ell}$), and even had much better than those of commercial UF glue mixes. Overall, the use of RSF-based adhesive resins for the production of plywood panels might provide durable adhesive properties and an environmentally friendly substitute for petroleum-based adhesive resins. However, further researches - the increase of solid content of RSF-based adhesives for reducing press time and the microscopic observation of plywood specimen for identifying the relationship between tensile shear strength and the penetration of adhesives into wood structure - are required to commercialize the RSF-based adhesives.