• Tunnel and Underground Space
• /
• v.10 no.3
• /
• pp.447-456
• /
• 2000

Rock bridge in rock masses can be considered as one of several types of opening-mode fractures, and also it has been known to have a great influence on the stability of structures in rock mass. In the beginning of researching a rock bridge it used to be studied only in characteristics of its behavior, as considering resistance of material itself. However the distribution pattern of rock bridges, which can affect the stability of rock structures, is currently researched with a fracture mechanical approach in numerical studies. For investigating the effect of rock bridges on the development pattern of hydraulic fractures, the author analyzed numerically the stress state transition in rock bridges and their phenomena with a different pattern of the rock bridge distributions. From the numerical studies, a two-crack configuration could be defined to be representative of the most critical conditions for rock bridges, only when cracks are systematic and same in their length and angle. Moreover, coalescence stresses and onset of propagation stresses could be known to increase with decreasing s/L ratio or increasing d/L ratio. The effect of pre-existing crack on hydraulic fracturing was studied also in numerical models. Different to the simple hydraulic fracturing modeling in which the fractures propagated exactly parallel to the maximum remote stress, the hydraulic fractures with pre-existing cracks did not propagate parallel to the maximum remote stress direction. These are representative of the tendency to change the hydraulic fractures direction because of the existence of pre-existing crack. Therefore s/L, d/L ratios will be identical as a function effective on hydraulic fractures propagation, that is, the K$_1$ value increase with decreasing s/L ratio or increasing d/L ratio and its magnification from onset to propagation increases with decreasing s/L ratio. The scanline is a commonly used method to estimate the fracture distribution on outcrops. The data obtained from the scanline method can be applied to the evaluation of stress field in rock mass.

• Journal of the Korean Society of Radiology
• /
• v.12 no.1
• /
• pp.47-52
• /
• 2018

Brain perfusion CT scanning is often employed usefully in clinical conditions as it accurately and promptly provides information about the perfusion state of patients having acute ischemic stroke with a lot of time constraints and allows them to receive proper treatment. Despite those strengths of it, it also has a serious weakness that Lens may be exposed to a lot of dose of radiation in it. In this study, as a way to reduce the dose of radiation to Lens in brain perfusion CT scanning, this researcher conducted an experiment with Bismuth shielding and change of patients' position. TLD (TLD-100) was placed on both lens using the phantom (PBU-50), and then, in total 4 positions, parallel to IOML, parallel to IOML (Bismuth shielding), parallel to SOML, and parallel to SOML (Bismuth shielding), brain perfusion scanning was done 5 times for each position, and dose to Lens were measured. Also, to examine how the picture quality changed in different positions, 4 areas of interest were designated in 4 spots, and then, CT number and noise changes were measured and compared. According to the results of conducting one-way ANOVA on the doses measured, as the significance probability was found to be 0.000, so there was difference found in the doses of radiation to crystalline lenses. According to the results of Duncan's post-hoc test, with the scanning of being parallel to IOML as the reference, the reduction of 89.16% and 89.66% was observed in the scanning of being parallel to SOML and that of being parallel to SOML (Bismuth shielding) respectively, so the doses to Lens reduced significantly. Next, in the scanning of being parallel to IOML (Bismuth shielding), the reduction of 37.12% was found. According to the results, reduction in the doses of radiation was found the most significantly both in the scanning of being parallel to SOML and that of being parallel to SOML (Bismuth shielding). With the limit of the equivalent dose to Lens as the reference, this researcher conducted comparison with the dose to occupational exposure and dose to Public exposure in the scanning of being parallel to IOML and found 39.47% and 394.73% respectively; however in the scanning of being parallel to SOML (Bismuth shielding), considerable reduction was found as 4.08% and 40.8% respectively. According to the results of evaluation on picture quality, every image was found to meet the evaluative standards of phantom scanning in terms of the measurement of CT numbers and noise. In conclusion, it would be the most useful way to reduce the dose of radiation to Lens to use shields in brain perfusion CT scanning and adjust patients' position so that their lens will not be in the field of radiation.

• Journal of the Korean Society of Radiology
• /
• v.14 no.6
• /
• pp.841-848
• /
• 2020

In the field of radiation therapy using photon beams and electron beams, since each patient has a different sensitivity to radiation, skin side effects may occur even at the same dose. Therefore, if there is a risk of excessive dose to the skin, a dosimeter is attached to verify whether the correct dose is being investigated. However, since the skin dosimeter checks the attachment site visually by measuring a point dose, it is difficult to confirm an accurate dose distribution. As a result, the measurement and simulation errors of the material HgI₂ in the 6 MV photon beam were 3.73% and 5.24%, respectively, at the minimum thickness of 25 ㎛, and the material PbI₂ was 4.73% and 5.65%, respectively. On the other hand, as a result of the 6 MeV electron beam, the measurement and simulation errors of the material HgI₂ were 1.35% and 1.12%, respectively, at a minimum thickness of 25 ㎛, and the material PbI₂ showed relatively low attenuation error, 1.67% and 1.20%, respectively. Therefore, it was evaluated that the thickness of the photon beam within 25 ㎛ and the electron beam within 100 ㎛ is suitable to have a reduction rate error within 5%. This study presents a new research direction for a flexible dosimeter attached to the human body that is required in clinical practice and the construction conditions of a future skin dosimeter.

• Journal of Soil and Groundwater Environment
• /
• v.12 no.5
• /
• pp.105-114
• /
• 2007

The most advanced oxidation processes (AOPs) are based on reactivity of strong and non-selective oxidants such as hydroxyl radical (${\cdot}OH$). Decomposition of typical DNAPL chlorinated compounds (TCE, PCE) using various advanced oxidation processes ($UV/Fe^{3+}$-chelating agent/$H_2O_2$ process, $UV/H_2O_2$ process) was approached to develop appropriate methods treating chlorinated compound (TCE, PCE) for further field application. $UV/H_2O_2$ oxidation system was most efficient for degrading TCE and PCE at neutral pH and the system could remove 99.92% of TCE after 150 min reaction time at pH 6($[H_2O_2]$ = 147 mM, UVdose = 17.4 kwh/L) and degrade 99.99% of PCE within 120 min ($[H_2O_2]$ = 29.4 mM, UVdose = 52.2 kwh/L). Whereas, $UV/Fe^{3+}$-chelating agent/$H_2O_2$ system removed TCE and PCE ca. > 90% (UVdose = 34.8 kwh/L, $[Fe^{3+}]$ = 0.1 mM, [Oxalate] = 0.6 mM, $[H_2O_2]$ = 147 mM) and 98% after 6hrs (UVdose = 17.4 kwh/L, $[Fe^{3+}]$ = 0.1 mM, [Oxalate] = 0.6 mM, $[H_2O_2]$ = 29.4 mM), respectively. We improved the reproduction system with addition of UV light to modified Fenton reaction by increasing reduction rate of $Fe^{3+}$ to $Fe^{2+}$. We expect that the system save the treatment time and improve the removal efficiencies. Moreover, we expect the activity of low molecular organic compounds such as acetate or oxalate be effective for maintaining pH condition as neutral. This oxidation system could be an economical, environmental friendly, and practical treatment process since the organic compounds and iron minerals exist in nature soil conditions.

• Korean Journal of Soil Science and Fertilizer
• /
• v.12 no.1
• /
• pp.15-23
• /
• 1979

In the first paper of the series the five soil fertility factors were evaluated by means of principal component analysis and varimax method. They are interpreted as representing, 1) skeletal available phosporus status, 2) organnic matter status, 3) salt status 4) base status, and 5) free oxide status. In order to resynthesize such fragmented information for the overall soil fertility evaluation, the method of multiple regression analysis was adopted, using the five factor scores and yield data for Korean paddy soils as independent and dependent variables respectively. As test of linear models with different combinations of independent variables the results of t-test of regression coefficient were revealed that the organic matter status (FII) has no relevance to the yield of paddy and that the free oxides and salt supply has by it self only an insignificant contribution to the yield. The multiple correlation coefficient (R) revealed its multiple regression analysis was as low as 0.43. Introduction of quadratic terms to the linear model bettered the result. Thus multiple correlation coefficient (R) was increased as 0.59. Therefore, a coefficient of determination 0.35 was obtained by a quadratic model with interaction terms among the five fertility constituents. Generally we think that the fertility factor has more contribution to raise the rice yield in paddy and that the failure of yield prediction by fertility factor scores was caused by one of follows; 1) the roughness of the yield inspection, and 2) missextraction of fertility constituents. The second step in this study, assuming that the residuals by multiple regression analysis were due to factors other than soil fertility, we can now proceed to predicting the yield from the field characters with the classified fertility groups by means of Hayashi's theory of quantification No. 1. Such variables as fertility groups (FTYG), water availability (WATER), soil drainage (DRNG), climatic zone (CLIZ), surface soil's stickiness (STCKT), surface soil's dry consistence (DCNST), and surface soil's texture (FTEXT) are taken up as the explanatory variables. The quantification appears reasonable; the well to extremely well in soil drainage, very sticky of surface soil, inefficiency in water availability, coarse texture, and very hard to extremely hard dry consistence in soil are detrimental to the rice yield. The R was as high as 0.90 for the set of variables. But the given explanatory variables in this study were not quite effective in explaining rice yield. The method developed seems to be promising only if properly collected data are available. Conditions that should be satisfied in the yield inspection obtained from common cultivator for the purpose of deriving a prediction equation were put forward.

• Korean Journal of Soil Science and Fertilizer
• /
• v.25 no.3
• /
• pp.249-254
• /
• 1992

This research was conducted to investigate the effects of fly ash applications on growth and yield parameters of corn (Zea mays L.), and soil chemical properties. Corn height at silking stage, and height and dry matter ratio at harvesting stage were enhanced by applications of fly ashes derived from bituminous coal and anthracite, respectively. Effects of fly ash treatment on growth parameters of corn were varied with kinds and levels of fly ash application and growth periods, but relatively small without revealing a major negative effect as compared to the control. Yield of corn was increased by applying fly ash of anthracite origin, but other yield components were not influenced negatively by fly ash treatment. Soil total carbon contents, cation exchange capacity, and phosphorus contents of soils sampled after harvest of corn were significantly increased by fly ash treatment, although there were slightly different effects according to kinds and levels of fly ash application. Exchangeable cations of soils were varied within an experimental error range. Phosphorus taken up by corn was enhanced by treating fly ash of the bituminous coal to the soil and there were a positive correlation between phosphorus uptake and soil Phosphorus level. Cation uptake by corn was changed a little, but no significant reduction was observed in cation uptake due to fly ash treatment. It seems to be difficult to figure out the mechanism of fly ash effects on growth and nutrient uptake by corn with one year field experiment, however treatment of fly ash enhanced some parameters of growth and yield, and nutrient uptake by corn without revealing any major negative effects. To determine the value of fly ash as a fertilizer source, continuous researches under various soil and crop conditions were considered to be necessary.

• The Korean Journal of Air & Space Law and Policy
• /
• v.4
• /
• pp.7-35
• /
• 1992

The expansion of air transport on a global scale with ever increasing traffic densities has brought about problems that must be solved through new multilateral mechanisms. Looking to the immediate future, air transport will require new forms of international cooperation in technical and economic areas. Air transport by its very nature should have been a counterforce to nationalism. Yet, the regulatory system in civil aviation is still as firmly rooted in the principle of national sovereignty as when it was first proclaimed at t-11e Paris Convention of 1919 and reaffirmed in the Chicago Convention. Sovereignty over the airspace has remained the cornerstone of relations between states in all respects of air transport. The importance of sovereignty over air space embodied in article 1 of the Chicago Conrenton also is responsible for restricting the authority of ICAO as an intergovernmental regulatory agency. The Orgenization, for all its extensive efforts, has only limited authority. ICAO sets standards but cannot enforce them; it devises solutions but cannot impose them. To implement its rules ICAO most rely not so much on legal requirements as on the goodwill of states. It has been forty-eight years since international community set the foundations of the international system in civil aviation action. Profound political, economic and technological changes have taken place in air transport. The Chicago Convention is living proof that staes can work together to make air transport a safe mode of travel. The law governing international civil auiation is principally based on international treaties and on other regulation agreed to by governments, for the most part through the mechanism of ICAO. The role of ICAO international standards and recommended practices and procedures dealing with a broad range of technical matters could hardly be overestimated. The organization's ability to develop these standards and procedures, to adapt them continuously to the rapid sate of change and development of air transport, should be particularly stressed. The role of ICAO in the area of the development of multilateral conventions on international air law has been successful but to a certain degree. From the modest starting-point of the Tokyo Convention, we have seen more adequate international instruments prepared within the scope of ICAO activities, adopted: the Hague Convention of 1970 for the suppression of Unlawful Seizure of Aircraft and the Montreal Convention of 1971 for the Suppression of Unlawful Acts against the Safety of Civil Aviation. The work of ICAO in the new domain of international law conventions concerning what has been loosely termed above as the criminal problems connected with international air transport, in particular the problem of armed aggression against aircraft, should be positively appreciated. But ICAO records in the domain of developing a uniform legal system of international carriage by air are rather disappointing. The problem of maintaining and developing the uniformity of this regulation exceeds the scope of interest and competence of governmental transport agencies. The expectations of mankind linked to it are too great to give up trying to restore the uniform legal system of international air carriage that would create proper conditions for its further growth. It appears that ICAO has, at present, a good opportunity for doing this. The hasty preparation of ICAO draft conventions should be definitely excluded. Every Preliminary draft convention ought to be sent to Governments of all member-States for consideration, So that they could in form ICAO in due time of their observation. The problom of harmonizing a uniform law of international air carriage with that of other branches of international transport should demand more and more of its attention. ICAO cooperation with other international arganization, especially these working in the field of international transport, should be strengthened. ICAO is supposed to act as a link and a mediator among, at times the conflicting interests of member States, serving the happiness and peace of all of the world. The transformation of the contemporary world of developing international relations, stimulated by steadily growing international cooperation in its various dimensions, political, economic, scientific, technological, social and cultural, continuously confronts ICAO with new task.

• The Korean Journal of Air & Space Law and Policy
• /
• no.spc
• /
• pp.137-163
• /
• 2007

The air market in Asia has already entered upon the age of limitless competition. It means a very important moment in Asia air market. Each Asian country thus has put a lot of effort into a development plan and support to their hub airport. In order to achieve such a plan, first of all we should build closer cooperation system between the two countries Japan and Korea. The Korea and Japan are very fast growing in the northeast countries within the global air transport market. Air passenger and cargo traffic volumes between Korea and Japan have increased dramatically, since the 1990s. In response to such a trend, both countries have opened new airports and expanded existing facilities in the hopes of laying claims to the main international hub airport in Asia. Apart from the trend, air transportation between Korea and Japan's metropolitan areas is the only transportation in substance, even if they are located very closely in geographical position. The air transportation between the two countries shows that it is necessary to get fast and more convenient because of the economic and cultural interchange and exchange concentrated on the metropolitan areas, and that will promote the economic growth of Korea and Japan. However, within the air transportation industry field, there have no sufficient seats/slots to supply the air demand from the capital cities of each country, as well as no counterplan for some problems regarding capacityand sustain ability of metropolitan airports. Thus, it is necessary for us to consider in all aspects and solve them to improve air transportation between Korea and Japan. This paper is to try to demonstrate this matter and from all angles, that is, in legal and political aspects, facilities and given environmental conditions and cooperation between Korea and Japan. I think that it is indeed a great necessary and convenient for many Korean and Japanese tourists to conclude a new 'Open Sky Agreement' between Japan and Korea in order to the prepare the increase of the shuttle flight between Haneda-Gimpo and opening of air route newly for shuttle flight between Haneda and Cheongju as well as opening of air route for shuttle flight between Haneda-Shanghai Hongqiao International Airport and Beijing International Airport for the 2008 Beijing Olympic Games. Furthermore it is a great desirable thing for us to conclude a new 'Open Sky Agreement' in cooperation reciprocally among the Japan, China and Korea for opening the new air route by the shuttle flight.

• Journal of Korean Society of Forest Science
• /
• v.104 no.3
• /
• pp.411-420
• /
• 2015

This study examined methods for stand density control by using shape ratio (tree height/DBH) and its application for effective management of Pinus thunbergii coastal disaster prevention forests. We analyzed the present conditions (height, DBH, and density) of P. thunbergii coastal disaster prevention forests at 123 study sites on Jeju Island and west, south, and east coasts of South Korea and compared them with results from previous studies. The average shape ratio for P. thunbergii showed positive correlations with stand density and was significantly higher on the west coast (66.32) than on the south (49.57) and east (48.19) coasts and Jeju Island (48.29). Stands with shape ratio higher than 70 accounted for 50% of the total study sites on the west coast, indicating a decrease in their disaster prevention function compared to that of other previous studies. The stand density in most coastal areas, except the east coast, was significantly higher than the standards recommended by the Korea Forest Service and the Forestry and Forest Products Research Institute of Japan, indicating the need for stand density control. According to the growth estimation equation for P. thunbergii in the coastal area of South Korea, density control is required for young stands less than 14 years old, which show drastic increase in the shape ratio, to conserve their disaster prevention function. Particularly, the first thinning of P. thunbergii forests should be implemented before the stand age of 8 years that a shape ratio exceeds 70. For disaster-prone young stands (${\leq}20cm$ DBH) of P. thunbergii, the stand density was higher in the standard of Japan considering shape ratio than in that of Korea aiming timber production. Hence, the standard guidelines employed in Japan, which assign higher importance to disaster prevention function based on field surveys, can be applied effectively for controlling the stand density of P. thunbergii coastal forests in South Korea, to improve their disaster prevention function.

• Journal of Korean Society of Forest Science
• /
• v.83 no.4
• /
• pp.545-555
• /
• 1994

The objective of the study was to provide the useful scientific data on the early rehabilitation of the legging road after timber harvesting in the forest area. This study was carried out at logging roads which were constructed during 1989 and 1994 in Mt. Baekwoon. The field survey was conducted in July, 1991. Judging from the analysis of soil bulk density, time required for recovery as the undisturbed forest soil condition was more than 10 years in the road which was left, and the regression equation is as follows, $$Y_1=1.4195-0.0744{\cdot}X(R^2=0.91)$$ $$Y_2=1.4673-0.0688{\cdot}X(R^2=0.73)$$ (X : elapsed year after road construction. $Y_1$, $Y_2$ : soil bulk density($g/cm^3$) at 0~7.5cm, and 7.5~15.0cm, respectively) Especially soil bulk density with buffer strip-woods was $0.890-0.903g/cm^3$, so it was 20% lower than that of logging road surface without buffer strip-woods. Among the 7 factors, location, sand content, and soil hardness had statistically significant effect on the soil bulk density in logging road surface. The pioneer species on logging road surface were Rhus cratargifolius, Prunus chinensis, and Lespedeza cyrtobotrya, etc. in woody species, and Pteridium aquilinum, Arundinella hirta, and Lysimachia clethroides, etc. in herb species. So, in process of year, average plant coverage were 70% on cutting and banking slope and 20% on logging road surface which elapsed 6 years after logging road construction. Through this research, buffer strip-woods must be remained for environmental conservation of forest conditions, and from the time to be closed the road, planting, seeding, and grazing works could be effective to the soil condition and vegetation recovery.