• Korean Journal of Environmental Biology
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• v.18 no.2
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• pp.279-290
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• 2000

To alleviate the harmful effects from contamination, the Sihwa Lake waters have been regularly fluxed out into the ocean to mix and circulate with the oceanic waters, and then allowed to flow back into the lake. In the present study, eco-environmental impacts by the outflowing contaminated lake waters to the benthic communities of the coastal zones along Kyonggi Bay were examined at three separate areas. A total of 22 groups of meiobenthic animals were commonly found in the subtidal zones of the Bay. All groups of the meiobenthic animals on the 1st and 7th days after the outflow were remarkably reduced in numbers from the selected areas examined, as compared to those observed one day before the outflow. It was also found that the community structure of meiobenthos was changed drastically: At the station near the water gate, for example, where the immediate outflow of the lake water was encountered, the benthic harpacticoids, the group observed to be one of the predominant groups before the outflow, were found to have disappeared completely. For an area that was relatively far away from the water gate, the reduction rate of meiobenthos after the outflow events was slower and more gradual than the nearer sites. An area that is the farthest from the water gate, no reduction in any of the meiobenthos group was observed. The ratio between nematodes/copepods (N/C) was remarkably changed by the outflows at the station near the water gate: One day before the outflow, the ratio was 0.7 while the ratio was 19.0 at the station near the water gate. In contrast, at the stations relatively far from the water gate, the ratio decreased one day after the outflow event, but increasing trends were observed one week later. In the tidal flats, Station 1 exhibited the common observed regional values of the ratio whereas Station 2 showed a very high ratio of 191.3. The results suggested that the contaminated lake water outflows directly effect meiobenthos in a relatively short time period and thus the meiobenthos may be a good indicator animal group for examining the effect of pollution. [Lake Sihwa, contaminat water outflow, meiobenthic animals living]

• Molecular & Cellular Toxicology
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• v.3 no.4
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• pp.314-319
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• 2007

The effects of common variants of CYP1A2 gene (CYP1A2$^*$1C and CYP1A2$^*$1F) on the CYP1A2 activity and inducibility were controversial. The aim of the present study is to investigate the effects of CYP1A2$^*$1C and CYP1A2$^*$1F on the activity of CYP1A2 determined by urinary caffeine metabolite ratio in Koreans. As might be expected, there was large inter-individual variation (16-folds) of CYP1A2 activity ranged from 2.41 to 39.58. The mean CYP1A2 activity of smokers was significantly higher than that of non-smokers. The frequencies of CYP1A2$^*$1C (-3858A) and $^*$1F (-164A) alleles were 0.219 and 0.646, respectively. The effect of CYP1A2$^*$1C on the CYP1A2 activity was not significant. However, the CYP1A2 activity of subjects with AA genotype for CYP1A2$^*$1F allele was significantly lower than that of non-AA genotypes (CC, or CA). Interestingly, the significant effect of CYP1A2$^*$1F allele on CYP1A2 activity was not observed in nonsmokers. Our results suggest that CYP1A2$^*$1F allele rather than CYP1A2$^*$1C allele significantly influences on the inducibility of CYP1A2 in Koreans. Owing to small sample size of our study, further studies should be conducted to reveal the inter-ethnic difference or the gene-environmental interaction.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.4
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• pp.1654-1662
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• 2011

This paper investigates how does cash holdings have effect on investment-cash flow sensitivity in korea firms over the period 1981-2009. According to $\"{O}$.Arslan et al.(2006), I expect that financially constrained firms have more cash holdings. and financially constrained cash-rich firms are likely to have less investment-cash flow sensitivity especially in the financial crisis period. Using financial constraint classification variables(firm size, dividend, cash holdings), we divide whole sample firms into financially constrained firms and financially unconstrained firms, and then I compare investment-cash flow sensitivity in pre-financial crisis(1981-1996), financial crisis(1997-1998) and after-financial crisis(1999-2009) period. This paper's findings are as follows: First, under no financial constraint classification conditions, cash-poor firms exhibit greater investment-cash flow sensitivity than cash-rich firms do during 1981-2009 period except financial crisis period. These findings support the hypothesis that firms have more cash holdings less investment-cash flow sensitivity except in financial crisis period. In financial crisis period, cash holdings have no effect on investment-cash flow sensitivity. Second, this paper findings are somewhat different as $\"{O}$.Arslan et al.(2006)'s. Under the financial constraint classification conditions, financially unconstrained firms have more investment-cash flow sensitivity rather than constrained firms have. The reason is that both dividend and firm size are not a complete classification criteria variables. And there exists other possible determinants of investment-cash flow sensitivity. Finally, this paper find that there are common determinants of corporate cash holdings in all periods. This paper suggests that cash flow and market to book ratio are positive determinants of corporate cash holdings but short-term debt, investment and firm size are negative determinants of corporate cash holdings.

• Journal of the Korean Geotechnical Society
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• v.22 no.10
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• pp.77-91
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• 2006

Domestic practices in shotcrete use have developed in many respects even now, but it still has issues about material, construction, quality standard and so on. In overseas, the construction using high strength shotcrete with $39.2{\sim}58.8 MPa$ of compressive strength is becoming common based on the shotcrete technology of high strength and durability. However, domestic shotcrete design strength is low at around 20.6 MPa of compressive strength and a long term durability is also insufficient. In this paper, field tests using high-quality additives and accelerators were performed to obtain the improvement of shotcrete strength and EFNARC standard was used to evaluate the field test results. In addition, deterioration test combined with the freezing-thawing and carbonation was also performed in order to investigate a long-term durability of high-strength shotcrete. As a result of the field test, the promotion ratio of early strength was $90{\sim}97%$ in case of using alkali-free accelerators. And the compressive strength of the shotcrete using Micro-silica fume was $45.2{\sim}55.8MPa$ and flexible strength was $5.01{\sim}6.66MPa$, so the promotion ratio of strength was $37{\sim}79%$ and $17{\sim}61%$ respectively. The promotion effect of strength by silica fine additives ratio of $7.5{\sim}10%$ for cement mass was much superior to the other cases. It was especially examined that using Micro-silica fume reduced deterioration due to mixed steel fiber and improved a long-term durability of shotcrete.

• The Journal of Korean Academy of Prosthodontics
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• v.42 no.6
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• pp.664-670
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• 2004

Statement of problem. One of the common problems of dental implant prosthesis is the loosening of the screw that connects each component, and this problem is more common in single implant-supported prostheses with external connection. Purpose. The purpose of this study was to examine the changes of detorque values of abutment screws with external connection in different abutment heights. Materials and methods. After cyclic loading on three different abutment heights, detorque values were measured. Abutments were retained with titanium abutment screws tightened to 30 Ncm (30.5 kgmm) with digital torque gauge as recommended by the manufacturer. Replacing abutments, implants and titanium abutment screws with new ones at every measurement, initial detorque values were measured six times. In measuring de torque values after cyclic loading, Avana Cemented Abutments of 4.0 mm collar, 7.0 mm height (Osstem Co., Ltd., Seoul, Korea) were used with three different lengths of 5.0, 8.0, 11.0 mm. Shorter abutments were made by milling of 11.0 mm abutment to have the same force-exercised area of 4.5 mm diameter. Sine curve force (20N-320N, 14Hz) was applied, and detorque values were measured after cyclic loading of 2 million times by loading machine. Detorque values of initial and after-loading were measured by digital torque gauge. One-way ANOVA was employed to see if there was any influence from different abutment heights. Results. The results were as follows: 1. The initial detorque value was 27.8$\pm$0.93 kgmm, and the ratio of the initial detorque value to the tightening torque was 0.91(27.8/30.5). 2. Measured detorque values after cyclic loading were declined as the height of the abutment increased, that was, 5.0 mm; 22.3$\pm$0.82 kgmm, 8.0 mm; 21.8$\pm$0.93 kgmm, and 11.0 mm; 21.3$\pm$0.94 kgmm. 3. One-way ANOVA showed no statistically significant differences among these (p>0.05). 4. Noticeable mobility at the implant-abutment interface was not observed in any case after cyclic loading at all.

• Korean Journal of Head & Neck Oncology
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• v.13 no.2
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• pp.221-227
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• 1997

The authors reviewed 106 cases of parotid gland tumor at Presbyterian Medical Center seen during the past 10 years between January, 1986 and December, 1995. The results were obtained as follows; 1) 86 cases(81.1%) were benign tumors and 20 cases(18.9%) were malignant tumors. 2) Overall male and female sex ratio was 1 : 1.4. 3) For benign tumors, the mean age was 47.9 and for malignant tumors, the mean age was 43.4. 4) Clinical manifestations in benign tumors were palpable mass in 86 cases(100%), pain in 6 cases(6.9%), facial nerve palsy in 2 cases(2.3%), lymphadenopathy in 1 case(1.2%); and in malignant tumors, palpable mass in 20 cases(100%), pain in 7 cases(35%), facial nerve palsy in 2 cases(10%) and lymphadenopathy in 3 cases(15%). Thus, the presence of pain, facial nerve palsy and lymphadenopathy suggest malignant tumors. 5) Operative procedures in benign tumors included superficial parotidectomy in 53 cases(61.6%), total parotidectomy in 10 cases(11.6%), local excision in 23 cases(26.7%); and in malignant tumors, superficial parotidectomy in 3 cases, total parotidectomy in 1 case, local excision in 1 case, superficial parotidectomy with supraomohyoid neck dissection in 6 cases, total parotidectomy with supraomohyoid neck dissection in 8 cases, total parotidectomy with radical neck dissection in 1 case. 6) Postoperative complications in benign tumors were transient facial nerve palsy in 14 cases, Frey's syndrome in 2 cases. In malignant tumors complications included transient facial nerve palsy in 3 cases and permanent facial nerve palsy in 1 case. 7) Pleomorphic adenoma was the most common benign parotid tumor and mucoepidermoid carcinoma was the most common malignant tumor. 8) In our review of 20 patients with malignant parotid tumors, all patients who received supraomohyoid neck dissection and postoperative radiation therapy remain alive from 1986 to 1995 years. Two deaths in this series were adenoid cystic carcinoma patients who failed to receive postoperative radiation therapy. These series of cases have been studied in order to determine whether supraomohyoid neck dissection and postoperative radiation therapy may have further therapeutic effect.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.26 no.2
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• pp.133-145
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• 1996

Aspirating or swallowing foreign bodies is a common occurrence. If they are wholly or partly radiopaque, their localization in and progress through the gastrointestinal tract can be more effective. Of the dental origin foreign materials swallowed, the most common things are fragments of anterior maxillary partial denture. But the radiopacity of denture base resins is not sufficient to determine the location of the objects. The purpose of this study was to develop a radiopaque dental acrylic resin, which has clinically detectible radiopacity with minimal change of mechanical properties and color. The radiopacity, color change(CIE 6..E) and microhardness of acrylic resins were determined after mixing barium sulfate or iodide compound. Thermocycling course was conducted to determine the change of characteristic of resins after using for a long time in the mouth. Five or ten percent of barium sulfate to total weight of cured material was mixed with heat curing dental acrylic resin or chemically curing orthodontic resin. In the case of iodide compound, the mixing ratio was two or three percent. After mixing the high radiopaque materials, resin was cured to 20×20×2 mm plate, polished with #600 sand paper and finally polished with Microcloth(Buehler). The specimens were thermocycled in 5 and 55 t distilled water for 2,000 times, and the measurement of radiopacity, color and Vickers hardness was repeated every 500 times thcrmocycling. The radiopacity of specimens on the X -ray films was measured with densitometer(X-rite). The color change was detennined with differential colorimeter(Model TC-6FX, Tokyo Denshoku), and the Vickers hardness number was measured with microhardness tester(Mitsuzawa). The following results were obtained : 1. All the three variables, the kinds of acrylic resins, the mixing or the kinds of high radiopaque materials and thermocycling, had combined effect on the radiopacity of the dental acrylic resins(p<0.0l). 2. The two variables, the mixing or the kinds of high radiopaque materials and thermocycling, influenced on the radiopacity of the dental acrylic resins(p<0.01). But the kinds of acrylic resins did not influence on the color change of mixed dental acrylic resins(p>0.05). 3. Each of the three variables, the kinds of acrylic resins, the mixing or the kinds of high radiopaque materials and thermocycling, influenced on the radiopacity of dental acrylic resins(p<0.0l). 4. The high radiopaque materials used in this study did not yield clinically usable radiopacity, and the color change was great after mixing those materials.

• Korean Journal of Soil Science and Fertilizer
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• v.33 no.1
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• pp.8-14
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• 2000

Long term cultivation crops like tomato, capsicum, melon etc. demand much amount of continuous supplying of nutrition during the whole growing periods. It is not easy to cover satisfactorily the nutritional demands for them by splitted top dressings, slow release fertilizer applications and fertigation systems. To overcome these problems, the "CULTAN" (Controlled Uptake Long Term Ammonium Nutrition) Beaker Deposit techniques have been developed and it was put into PVC beaker with the combined nitrogen fertilizer type mixed with the ratio of one-third of ammonium sulfate-N and two-thirds of urea-N, in which nitrogen was loaded on the demanding amount of a tomato plant during the growing period. Gypsum was mixed as a binder, and loamy soil and compost were used as a diffusion regulator. It was placed upside down into root zone of tomato at the transplanting. Tomato roots were spreaded into the Deposit beaker by ammonium ions which attract root growth. The tomato fruit yield and nitrogen uptake by plant were increased by application of $NH_4$-Beaker deposit fertilizer rather than those of common fertilizer treatment. In conclusion, it was able to improve economic and ecological benefits through CULTAN system compared with common fertilization systems. CULTAN system was estimated as a prospective alternative to enhance productivity and minimize nutrient lose. In addition, it shows further developing possibility of CULTAN system by the supplement of micro-nutrients and pesticides in the macro-nutrient beaker deposits.

• Journal of Korean Dental Science
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• v.5 no.2
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• pp.68-76
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• 2012

Purpose: The headache is a symptom that various somatic or non-somatic disorders gives an effect to head and neck system. The neck and the shoulder pain is a common muscle pain that can not control and bothers the patient after chronic state. The headache and the neck and the shoulder muscle pain are treated with various conventional treatment methods. But, there are cases that symptoms did not resolve or increased in some clinical cases. And generally, the result of temporomandibular disorders (TMD) treatment is good. But, despite of a normal treatment was performed for TMD, there are cases that TMD symptoms did not resolved in clinical cases. In template clinic of Soonchunhyang University Bucheon Hospital, co-operative neurophysiologic treatment of Department of Neurosurgery and Dentistry are done for patients, who had head and neck pain or atypical symptoms that did not treated with various conventional treatment method such as surgery or medication etc. Materials and Methods: Four hundred fifty one patients who have treated in the template clinic, Soonchunhyang University Bucheon Hospital, from January of 2006 to December of 2008 were subjected in this study. Result: Overall average age was 31.9 years old. Ratio of numbers is 74.3% in female and 25.7% in male. The success rate of treatment in TMD symptom was 89.9%, in headache was 88.8%, in muscle pain was 81.6%. Statistically significance of differences visual analogue scale evaluation between before and after had been treated patients who have over average grade headache was calculated by paired t-test. P<0.05 was considered significant. Conclusion: We suggest the template appliance can be attempted for cases whose headache, the neck and the shoulder muscle pain and TMD are not resolved with various conventional treatment methods.

• International Journal of Fluid Machinery and Systems
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• v.4 no.4
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• pp.367-374
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• 2011

Water hammer pumps can effectively use the water hammer phenomenon in long-distance pipeline networks that include pumps and allow fluid transport without drive sources, such as electric motors. The results of experiments that examined the effect of the geometric form of water hammer pumps by considering their major dimensions have been reported. In addition, a paper has also been published analyzing the water hammer phenomenon numerically by using the characteristic curve method for comparison with experimental results. However, these conventional studies have not fully evaluated the pump performance in terms of pump head and flow rate, common measures indicating the performance of pumps. Therefore, as a first stage for the understanding of water hammer pump performance in comparison with the characteristics of typical turbo pumps, the previous paper experimentally examined how the hydrodynamic characteristics were affected by the inner diameter ratio of the drive and lifting pipes, the form of the air chamber, and the angle of the drive pipe. To understand the behavior of the components attached to the valve chamber and the air chamber that affects the performance of water hammer pumps, the previous study also determined the relationship between the water hammer pump performance and temporal changes in valve chamber and air chamber pressures according to the air chamber capacity. For the geometry of components attached to the drain valve, which is another major component of water hammer pumps, this study experimentally examines how the water hammer pump performance is affected by the length of the spring and the angle of the drain pipe.