• Title/Summary/Keyword: K-space

Search Result 26,712, Processing Time 0.066 seconds

Selection and Application of Evaluation Factors for Urban Regeneration Project (도시재생사업의 평가요인 선정 및 적용)

  • Jang, Cheol-Kyu
    • Journal of the Korean Institute of Landscape Architecture
    • /
    • v.47 no.6
    • /
    • pp.53-66
    • /
    • 2019
  • The purpose of this study was to suggest indicator-based selection and improvement plans for evaluating urban regeneration projects. First, we selected the indicators by conducting expert surveys and analysis of the responses received. Additionally, using the selected indicators, we analyzed the residents' opinions in Wongogae Village, where urban regeneration projects were in progress. Based on these, we suggested a plan to improve Wongogae Village. According to the study, we classified the urban regeneration evaluation indicators into 'Physical environment', 'Social environment' and 'Economic environment' according to their characteristics. We selected urban regeneration evaluation factors through the first expert survey and MCB analysis. As a result, we selected six factors for the 'Physical environment' category: 'Traffic and pedestrian environment', 'Residential (housing) environment', 'Safety and security environment', 'Greenspace', 'Landscape improvement' and 'Public space', In the 'Social environment' category, four factors were chosen: 'Resident participation', 'Community activation', 'Role of the local government and support centers' and 'Resident education' while for the 'Economic environment' category three factors were selected: 'Local economic revitalization', 'Creating an economy-based environment', 'Job creation'. Next, we conducted a second expert survey and carried out an AHP analysis using the selected evaluation factors to derive the overall weight for each. Among the evaluation factors for urban regeneration, the 'Residential (housing) environment' has the highest weighted value of 0.108, followed by 'Local economic revitalization' and 'Resident participation'. Lastly, the analysis of the residents' opinions of Wongogae Village using the urban regeneration evaluation factors, Parking environment', 'Maintenance of old houses and living environment', 'Environment for founding town and social enterprises', 'Improve commercial and business environment', 'Maintain and activate existing business' and 'Vitalizing small regional economies such as domestic handicrafts and side-job' had high overall importance, but low satisfaction, which means that it is necessary to improve the focus. Therefore, in order to improve the urban regeneration project in villages, it is necessary to improve the parking environment by expanding public parking lots, eliminate close houses, and idle lands, or open a school playground in the village for the residents. In addition, it is essential to encourage economic activities, such as fostering village enterprises and social enterprises in connection with cooperatives and allow for the selling of the products through resident activities, such as neighboring markets.

Oxide perovskite crystals type ABCO4:application and growth

  • Pajaczkowska, A.
    • Proceedings of the Korea Association of Crystal Growth Conference
    • /
    • 1996.06a
    • /
    • pp.258-292
    • /
    • 1996
  • In the last year great interest appears to YBCO thin films preparation on different substrate materials. Preparation of epitaxial film is a very difficult problem. There are many requirements to substrate materials that must be fullfilled. Main problems are lattice mismatch (misfit) and similarity of structure. From paper [1] or follows that difference in interatomic distances and angles of substrate and film is mire important problem than similarity of structure. In this work we present interatomic distances and angle relations between substrate materials belonging to ABCO4 group (where A-Sr or Ca, B-rare earth element, C-Al or Ga) of different orientations and YBCO thin films. There are many materials used as substrates for HTsC thin films. ABCO4 group of compounds is characterized by small dielectric constants (it is necessary for microwave applications of HTsC films), absence of twins and small misfit [2]. There most interesting compounds CaNdAlO4, SrLaAlO4 and SrLaGaO4 were investigated. All these compounds are of pseudo-perovskite structure with space group 14/mmm. This structure is very similar to structure of YBCO. SLG substrate has the lowest misfit (0.3%) and dielectric constant. For preparation of then films of substrates of this group of compound plane of <100> orientation are mainly used. Good quality films of <001> orientations are obtained [3]. In this case not only a-a misfit play role, but c-3b misfit is very important too. Sometimes, for preparation of thin films substrates of <001> and <110> orientations were manufactured [3]. Different misfits for different YBCO faces have been analyzed. It has been found that the mismatching factor for (100) face is very similar to that for (001) face so there is possibility of preparation of thin films on both orientations. SrLaAlO4(SLA) and SrLaGaO4(SLG) crystals of general formula ABCO4 have been grown by the Czochralski method. The quality of SLA and SLG crystals strongly depends on axial gradient of temperature and growth and rotation rates. High quality crystals were obtained at axial gradient of temperature near crystal-melt interface lower than 50℃/cm, growth rate 1-3 mm/h and the rotation rate changing from 10-20pm[4]. Strong anisotropy in morphology of SLA and SLG single crystals grown by the Czochralski method is clearly visible. On the basics of our considerations for ABCO4 type of the tetragonal crystals there can appear {001}, {101}, and {110} faces for ionic type model [5]. Morphology of these crystals depend on ionic-covalent character of bonding and crystal growth parameters. Point defects are observed in crystals and they are reflected in color changes (colorless, yellow, green). Point defects are detected in directions perpendicular to oxide planes and are connected with instability of oxygen position in lattice. To investigate facets formations crystals were doped with Cr3+, Er3+, Pr3+, Ba2+. Chromium greater size ion which is substituted for Al3+ clearly induces faceting. There appear easy {110} faces and SLA crystals crack even then the amount of Cr is below 0.3at.% SLG single crystals are not so sensitive to the content of chromium ions. It was also found that if {110} face appears at the beginning of growth process the crystal changes its color on the plane {110} but it happens only on the shoulder part. The projection of {110} face has a great amount of oxygen positions which can be easy defected. Pure and doped SLA and SLG crystals measured by EPR in the<110> direction show more intensive lines than in other directions which allows to suggest that the amount of oxygen defects on the {110} plane is higher. In order to find the origin of colors and their relation with the crystal stability, a set of SLA and SLG crystals were investigated using optical spectroscopy. The colored samples exhibit an absorption band stretching from the UV absorption edge of the crystal, from about 240 nm to about 550 m. In the case of colorless sample, the absorption spectrum consists of a relatively weak band in the UV region. The spectral position and intensities of absorption bands of SLA are typical for imperfection similar to color centers which may be created in most of oxide crystals by UV and X-radiation. It is pointed out that crystal growth process of polycomponent oxide crystals by Czochralski method depends on the preparation of melt and its stoichiometry, orientation of seed, gradient of temperature at crystal-melt interface, parameters of growth (rotation and pulling rate) and control of red-ox atmosphere during seeding and growth (rotation and pulling rate) and control of red-ox atmosphere during seeding and growth. Growth parameters have an influence on the morphology of crystal-melt interface, type and concentration of defects.

  • PDF

Current Status and Future Perspective of PET (PET 이용 현황 및 전망)

  • Lee, Myung-Chul
    • The Korean Journal of Nuclear Medicine
    • /
    • v.36 no.1
    • /
    • pp.1-7
    • /
    • 2002
  • Positron Emission Tomography (PET) is a nuclear medicine imaging modality that consists of systemic administration to a subject of a radiopharmaceutical labeled with a positron-emitting radionuclide. Following administration, its distribution in the organ or structure under study can be assessed as a function of time and space by (1) defecting the annihilation radiation resulting from the interaction of the positrons with matter, and (2) reconstructing the distribution of the radioactivity from a series of that used in computed tomography (CT). The nuclides most generally exhibit chemical properties that render them particularly desirable in physiological studies. The radionuclides most widely used in PET are F-18, C-11, O-15 and N-13. Regarding to the number of the current PET Centers worldwide (based on ICP data), more than 300 PET Centers were in operation in 2000. The use of PET technology grew rapidly compared to that in 1992 and 1996, particularly in the USA, which demonstrates a three-fold rise in PET installations. In 2001, 194 PET Centers were operating in the USA. In 1994, two clinical and research-oriented PET Centers at Seoul National University Hospital and Samsung Medical Center, was established as the first dedicated PET and Cyclotron machines in Korea, followed by two more PET facilities at the Korea Cancer Center Hospital, Ajou Medical Center, Yonsei University Medical Center, National Cancer Center and established their PET Center. Catholic Medical School and Pusan National University Hospital have finalized a plan to install PET machine in 2002, which results in total of nine PET Centers in Korea. Considering annual trends of PET application in four major PET centers in Korea in Asan Medical Center recent six years (from 1995 to 2000), a total of 11,564 patients have been studied every year and the number of PET studies has shown steep growth year upon year. We had 1,020 PET patients in 1995. This number increased to 1,196, 1,756, 2,379, 3,015 and 4,414 in 1996,1997,1998,1999 and 2000, respectively. The application in cardiac disorders is minimal, and among various neuropsychiatric diseases, patients with epilepsy or dementia can benefit from PET studios. Recently, we investigated brain mapping and neuroreceptor works. PET is not a key application for evaluation of the cardiac patients in Korea because of the relatively low incidence of cardiac disease and less costly procedures such as SPECT can now be performed. The changes in the application of PET studios indicate that, initially, brain PET occupied almost 60% in 1995, followed by a gradual decrease in brain application. However, overall PET use in the diagnosis and management of patients with cancer was up to 63% in 2000. The current medicare coverage policy in the USA is very important because reimbursement policy is critical for the promotion of PET. In May 1995, the Health Care Financing Administration (HCFA) began covering the PET perfusion study using Rubidium-82, evaluation of a solitary pulmonary nodule and pathologically proven non-small cell lung cancer. As of July 1999, Medicare's coverage policy expanded to include additional indications: evaluation of recurrent colorectal cancer with a rising CEA level, staging of lymphoma and detection of recurrent or metastatic melanoma. In December of 2001, National Coverage decided to expand Medicare reimbursement for broad use in 6 cancers: lung, colorecctal, lymphoma, melanoma, head and neck, and esophageal cancers; for determining revascularization in heart diseases; and for identifying epilepsy patients. In addition, PET coverage is expected to further expand to diseases affecting women, such as breast, ovarian, uterine and vaginal cancers as well as diseases like prostate cancer and Alzheimer's disease.

A Numerical Study of Hydraulic Fractures Propagation with Rock Bridges (Rock bridges를 고려한 수치 해석적 수압파쇄 균열거동 연구)

  • 최성웅
    • 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.

  • PDF

A Study on the Determinants of Investment in Startup Accelerators (스타트업 액셀러레이터의 투자결정요인에 대한 연구)

  • Heo, Joo-yeun
    • Asia-Pacific Journal of Business Venturing and Entrepreneurship
    • /
    • v.15 no.5
    • /
    • pp.13-35
    • /
    • 2020
  • Startup accelerators are a new type of investors providing a certain amount of shares for imparting education, mentoring, networking, and providing space and seed money that can directly resolve the difficulties faced by nascent entrepreneurs (Clarysse, 2016). Startup accelerators have expanded worldwide as their influence over the startup ecosystem has increasingly been established (Pauwels et al., 2016; Cohen & Hochberg, 2014). This study was conducted to derive investment determinants of startup accelerators that are emerging as major investment players around the world. To this end, the accelerator-type determinants of investment were derived. As previous research on this topic is nonexistent, this process involved qualitative meta-synthesis, literature reviews, observation, and in-depth interviews. First, more than 30 research papers were examined for the determinants of investment for firms at an early stage of their foundation, and the categories and determinants of investment in the relevant studies were comparatively analyzed using qualitative meta-synthesis. Further, related data were investigated to identify the characteristics of accelerators, and the startup evaluation process of US accelerators was studied. The more than 100 questions raised during this process were coded to examine the determinants of investment that accelerators considered important. In-depth interviews were conducted with four US accelerators to identify the characteristics of accelerators and key determinants of investment. Ultimately, 5 categories of accelerator-type determinants of investment and 26 subordinate determinants of investment were derived. The results were verified and supplemented by consulting with seven accelerators in Korea. The results were confirmed after pilot tests and verification by seven domestic accelerators. After confirming the accelerator-type determinants, the reliability of them was verified by examining the importance and priority of each category through the quantitative survey of Korean accelerators. The research that elicited the accelerator-type investment determinants is the first research and is expected to be a major reference to the progress of subsequent studies. This research that systematically derived the investment determinants of the accelerator is expected to make major contributions to the progress of follow-up studies, the process of selecting startups, and the investment decision-making process of the accelerators.

The Origin and Formation of Korean Public Art Theories in the 1980s (1980년대 민중미술론의 기원과 형성)

  • Choi, Youl
    • The Journal of Art Theory & Practice
    • /
    • no.7
    • /
    • pp.37-64
    • /
    • 2009
  • The theories of Korean Public Art originated by the artists who were against dictatorship and they associated with democratic politicians. They criticized the Fine art that were supported by the dictatorship and gave their efforts for restoration of 'resistance paintings(against dictatorship)', 'proletarian painting', 'realism painting'. In addition, they participated new social ideology(democracy) movement and demonstrated for their rights in arts. These became the main kernel the public art theory was initiated. The public artists splitted into several different parts and participated in the democratic social movement as well as the art movement for freedom. They opened various art exhibitions within different genre, diverse space for various art section such as an exhibition hall, a factories, a university, or a congregation square. Furthermore, the public art theorists published their divergent views through newspaper/broadcasting or unauthorized printed materials. Most of the public artist and the theorists kept their relationship strongly until 1985, the time when 'National Arts Association' started. In 1983 and 1984, they were clearly separated into two parts; artists(move only in art museums) and activists(move in public spaces like school, convention square etc). Their ideological separation also took out national problems. The division; professional artists and armatures, became the social issue as a social stratification matter. And in creating method, there are also other conflicts; critical realism, and public realism as well as western painting and traditional one. These kinds of separation and conflicts made different Public artists associations, under divergent names; 'Reality and Speak'(R&S), 'KwangJu Art Association', 'Durung', 'Dang(Land)', and 'Local Youth Students Association'. In addition, their ideology and pursuit toward art movements were very difference. However, the differences and conflicts weakened When the oppression of democratic education from new dictatorship(Pres. Jun, Doo Hwan) came out. In August. 1985 the government opened to the public so called, 'The draft of School stabilization law'(Hankwon Anjung Bup) to control the teachers' rights and that initiated bigger street demonstration and conflicts between police and educators. In November.1985, assembly meeting of National Arts Association in democracy opened as 'ONE' combined organization. In this presentation, I'd like to summarize the stream of art movement until 1984, and clarify the main art theories that lead the Public Art Movements in 1980s. The main theories in 1980s are crucial because they become the origin of public art theories. This presentation started with O,youn's "Hyunsil Dong In the first declaration" and explained the absent of practice in 1970s. In addition, Won, Dong Suk 's theory was mentioned as all over struggles in theories before 1980s. GA and R&S 's founding declarations in 1970s were the start of public art theorists' activities and this article reported the activities after the declarations. First, realism base on the consciousness of reality. Second, practice art democratization based on the ideology. Third, the subject of public art movement based on understanding people's social stratification structure. Fourth, the matters of national forms and creative ways in arts based on showing reality. Fifth, the strong points in arts that the practitioners accepted. About the public art theories around 1984, I discussed the dividing point of public art theories that were shown in 'generation theory', 'organization theory', and 'popularization theory' by the practitioners. The public realism theory that subjects the contradiction of reality and point out the limits of critical realism not only showing the new creative ways but also giving the feeling of solidarity to the public art activist groups. After that, public art movements expressed 'Dismentlement of Capitalism' and 'Public revolution'. In addition, the direction of public art movements were established strongly. There were various opinions and views during the start and formation of the public art theories. The foundation of theorists activities derived from the practitioners who had the concept based on stratification and nationalism. The strong trend of group division spreaded out by practitioners who opened art work together in factories, universities, squares and rural areas. Now many lively active practitioners are gone to the other field not related with arts, and others join into professional art field not public art one with unknown reason. The theorists have the same situation with the practitioners. It means to me that theory always have to be based on the practice.

  • PDF

Difference in the Sense of Community in Open-Structure Central Squares in Apartment Complexes (공동주택 중앙광장의 개방 구조에 따른 지역 공동체의식의 차이)

  • Kang, Yon-Ju;Park, Jong-Wan;Im, Seung-Bin
    • Journal of the Korean Institute of Landscape Architecture
    • /
    • v.37 no.3
    • /
    • pp.21-32
    • /
    • 2009
  • As an alternative for restoring a sense of community which has been broken up due to urban residence redevelopment, this study focuses on structural characteristics according to physical location of central squares in apartment complexes. Central squares do not simply function as inner-aiming and self-completed spaces for the residents, but their role can be expanded to a core location which encourages neighbors to communicate and interact with each other. The suppositions for this study are as follows. Structural characteristics according to the physical locations of the central squares in apartment complexes affect apartment residents' openness toward their neighbors and non-residents' accessibility to the square. At the same time, it influences the sense of community. In addition, psychological distance which is represented as psychological openness and accessibility forms a reciprocal relationship with the sense of community. For the study, we first categorized central squares as either open-structure or closed-structure based on how accessible it is from outside the apartment complex. According to these types of central squares, Sillim Prugio, Banghak Deasang Town Hyundai, Gwanak Prugio and Banghak Samsung Raemian 1 which have similar conditions and different structures were selected as sites of the study. Then each apartment complex was classified by apartment residents and non-residents so that eight groups were prepared for the survey. The results of the questionnaire survey especially regarding measuring the sense of community, psychological openness and accessibility indicated that the suppositions were right. Hence, the sense of community, psychological openness and accessibility are high in a central square with an open-structure while high standards of psychological openness and accessibility guarantee a positive sense of community. This study is meaningful in that it verifies that the physical location of central squares is reciprocally related to psychological openness, accessibility and a sense of community. At the same time, this study may serve as theoretical grounds for the planning and construction of practical central squares.

A Study on the Adaptation and Change of Amusement Culture on the Case of Wolmido Pleasure Ground during the Japanese Colonial Era (일제강점기 월미도유원지를 통한 행락 문화의 수용과 변화에 관한 연구)

  • Kim, Jeoung-Eun
    • Journal of the Korean Institute of Landscape Architecture
    • /
    • v.42 no.5
    • /
    • pp.134-147
    • /
    • 2014
  • Pleasure grounds, which were introduced during the Japanese colonial era, were places for organizing new amusement activities, and developed into a large-scale private spaces and a new type of public space at the same time. This study explores the scenery and accommodations of pleasure grounds and the changes of the amusement culture through the Wolmido Pleasure Grounds, which was a typical pleasure grounds of the time. At that time, Wolmido became a comprehensive amusement/entertainment place with many elements of both Western and Japanese pleasure grounds such as exotic buildings harmonized with trees, a beach, a seaside school, public playing field, and zoo constructed on the Island. Wolmido Pleasure Ground, which was connected with Kyungsung by Kyungin railroad during the Japanese colonial era, is a good example showing the process of the popularization and commercialization of the amusement culture. The process of popularization of amusement shows the spreading of the enjoyment of leisure time with amusement activities through appreciating the beautiful scenery of the pleasure grounds among various social classes. The caste system was broken and anyone could use the pleasure grounds by paying the fee, of which there were many kinds, so the distinction between genders and the different classes, such as the Chosun people and Japanese, regarding amusement in pleasure grounds disappeared gradually. Also, pleasure grounds were a place for Western hobby-sports activities and were the means to generalize collective and dynamic activities through summer school and various sport games. At the same time, there were places for deviation from the existing social norms when it was combined with entertainment facilities. The commercialization of amusement took place in the form of an artificial entertainment culture within an artificial environment. First, the scenery was artificially constructed and this scenery created the image of paradise such as 'captivating summer vacation spot' and 'water kingdom'. This was the result of the combined intentions of the colonial authority, the railroad company and the amusement corporation to produce economic profits and encourage development in the area. Second, an artificial spectacle was constructed using nature as the backdrop. Buildings of various styles created a modernized and exotic image when they were combined with each other. Artifacts such as breakwaters and arcades created new attractions for people that enabled them to view both nature and the crowds from a whole different perspective. Third, pleasure grounds contributed to the advent of passive users who would just follow the given use and instructions. In this way, one can find the prototype of popular entertainment places of today such as sightseeing complexes, amusement parks, and theme parks through the construction of amusement grounds as a place for providing dynamic activities.

The Joseon Confucian Ruling Class's Records and Visual Media of Suryukjae (Water and Land Ceremony) during the Fifteenth and Seventeenth Centuries (조선 15~17세기 수륙재(水陸齋)에 대한 유신(儒臣)의 기록과 시각 매체)

  • Jeong, Myounghee
    • Korean Journal of Heritage: History & Science
    • /
    • v.53 no.1
    • /
    • pp.184-203
    • /
    • 2020
  • The Confucian ruling class of the Joseon Dynasty regarded Buddhist rituals as "dangerous festivals." However, these Buddhist ceremonies facilitated transitions between phases of life from birth till death and strengthened communal unity through their joint practice of the rites. Ritual spaces were decorated with various utensils and objects that transformed them into wondrous arenas. Of these ornaments, Buddhist paintings served as the most effective visual medium for educating the common people. As an example, a painting of the Ten Kings of the Underworld (siwangdo) could be hung as a means to illustrate the Buddhist view of the afterlife, embedded in images not only inside a Buddhist temple hall, but in any space where a Buddhist ritual was being held. Demand for Buddhist paintings rose considerably with their use in ritual spaces. Nectar ritual paintings (gamnodo), including scenes of appeasement rites for the souls of the deceased, emphasized depictions of royal family members and their royal relatives. In Chinese paintings of the water and land ceremony (suryukjae), these figures referred to one of several sacred groups who invited deities to a ritual. However, in Korean paintings of a nectar ritual, the iconography symbolized the patronage of the royal court and underlined the historicity and tradition of nationally conducted water and land ceremonies. This royal patronage implied the social and governmental sanction of Buddhist rituals. By including depictions of royal family members and their royal relatives, Joseon Buddhist paintings highlighted this approval. The Joseon ruling class outwardly feared that Buddhist rituals might undermine observance of Confucian proprieties and lead to a corruption of public morals, since monks and laymen, men and women, and people of all ranks mingled within the ritual spaces. The concern of the ruling class was also closely related to the nature of festivals, which involved deviation from the routines of daily life and violation of taboos. Since visual media such as paintings were considered to hold a special power, some members of the ruling class attempted to exploit this power, while others were apprehensive of the risks they entailed. According to Joseon wangjo sillok (The Annals of the Joseon Dynasty), the Joseon royal court burned Buddhist paintings and ordered the arrest of those who created them, while emphasizing their dangers. It further announced that so many citizens were gathering in Buddhist ritual spaces that the capital city was being left vacant. However, this record also paradoxically suggests that Buddhist rituals were widely considered festivals that people should participate in. Buddhist rituals could not be easily suppressed since they performed important religious functions reflecting the phases of the human life cycle, and had no available Confucian replacements. Their festive nature, unifying communities, expanded significantly at the time. The nectar ritual paintings of the late Joseon period realistically delineated nectar rituals and depicted the troops of traveling actors and performers that began to emerge during the seventeenth century. Such Buddhist rituals for consoling souls who encountered an unfortunate death were held annually and evolved into festivals during which the Joseon people relieved their everyday fatigue and refreshed themselves. The process of adopting Buddhist rituals-regarded as "dangerous festivals" due to political suppression of Buddhism in the Confucian nation-as seasonal customs and communal feasts is well reflected in the changes made in Buddhist paintings.

Sorption Studies of $Cd^{2+}$ on Calcite: Kinetics and Reversibility (방해석의 $Cd^{2+}$ 흡착현상에 대한 연구)

  • Yoon, Hyeon;Reeder, Richard J.
    • Journal of the Mineralogical Society of Korea
    • /
    • v.15 no.2
    • /
    • pp.104-113
    • /
    • 2002
  • The sorption of Cd$^{2+}$ on calcite was studied in aqueous solutions of several electrolytes. The Cd$^{2+}$ concentration, 10$^{-8}$ M, was kept well below saturation with respect to CdCO$_3$(s). Sorption behavior of Cd$^{2+}$ in different ionic strengths of NaClO$_4$solutions shows that sorption is independent of ionic strength. This result suggests that Cd$^{2+}$ sorption on calcite surface is of a specific nature, and adsorption is controlled by an inner-sphere type of surface complex. Two stages in the sorption behavior could be identified: an initial rapid uptake, followed by slower uptake reaching a maximum steady state by 145 hrs. No evidence was observed for surface precipitation, although it can not be entirely ruled out. Desorption of Cd$^{2+}$ from the calcite surface after resuspension into Cd-free solution is initially very rapid, but depends partly on the previous sorption history. Desorption behavior of Cd$^{2+}$ show that an initial rapid desorption followed either by slow uptake reaching a maximum, as in the adsorption experiments, or slowing desorption to reach a steady state minimum. This irreversible behavior of Cd$^{2+}$ sorption and desorption may act as one of the controls for regulating the mobility of dissolved Cd$^{2+}$ natural aqueous systems. Calculated adsorption partition coefficients suggest that overall sorption and desorption process in the concentration range are controlled by d single mechanism.ingle mechanism.