• Title/Summary/Keyword: a diffusion model

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Advance of geophysical exploration techniques for investigation of seawater intrusion (해수침투 평가를 위한 물리탐사기술의 진전)

  • 이상규;황학수;황세호;박인화;성낙훈
    • The Journal of Engineering Geology
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    • v.10 no.2
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    • pp.172-188
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    • 2000
  • This paper presents the state of art and the role of geophysical exploration techniques with evaluating the trend of domestic and worldwide seawater intrusion research, and illustrates advanced techniques obtained through the project of 'Development of the techniques for estimation, prediction, and prevention of seawater intrusion' funded by the Ministry of Science and Technology of Korea. The advanced geophysical interpretation was achieved by adding the digital geophysical logging data. DC resistivity and TEM monitorings were applied to determine whether or not the seawater intrusion was in progress. Induced Polarization technique using electric current monitoring channel was introduced to discriminate seawater contaminated zone from highly conductive layer caused by clay minerals. A conceptual model was suggested with spatial visualization of the study area to predict the diffusion of seawater contamination. Finally, the future work of the development of geophysical techniques was suggested with the base of the present level of them.

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Measurement of mass Transfer Coefficients for Adsorptive Bulk Gas Separation with Velocity Variations (기체속도가 변하는 벌크기체의 흡착공정에서 물질전달계수의 측정)

  • Min, Jun-Ho;Choi, Min-Ho;Suh, Sung-Sup
    • Applied Chemistry for Engineering
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    • v.10 no.2
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    • pp.310-318
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    • 1999
  • The concentration breakthrough curves were examined to predict mass transfer coefficients of nitrogen and oxygen in adsorption column for design data of PSA process. Experimental breakthrough curves for bulk gas flow were compared with theoretical simulation results. For quantitative analysis of the adsorption, coupled Langmuir isotherm was considered and LDF model was used to describe the mass transfer effect. In the experimental and theoretical results, it was found that mass transfer coefficient was not affected by flow rate but strongly affected by pressure. As a result of this tendency, mass transfer resistance in this system was proved to belong to the macropore diffusion controlling region and the mass transfer coefficients could be expressed by exponential functions of pressure change. The mass transfer coefficients for one component, nitrogen or oxygen, were successfully applied to breakthrough curves for bulk mixed gases. The experimental curves were reasonably in consistent with the theoretical curves and the error time was less than 5 percent.

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A Study on Factors Affecting the Continued Usage Intention of Ubiquitous Services (유비쿼터스 서비스의 지속적 이용의도에 영향을 미치는 요인에 관한 연구: 유비쿼터스 시스템적 특성과 서비스 품질 요인을 중심으로)

  • Jang, Ki-Sup;Kim, Ki-Su
    • The Journal of Information Systems
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    • v.17 no.3
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    • pp.175-204
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    • 2008
  • Ubiquitous computing is enhancing computer use by making many computers available throughout the physical environment without being noticed to the users. To facilitate successful adoption and diffusion of ubiquitous systems, it is important to find out the factors affecting their uses. Although researches related to ubiquitous computing have been vigorously conducted from the aspect of system and service provider, there have been very few studies that focus on the user's perspective. This study attempts to find out major factors which are dedicated to the development of ubiquitous systems and services and the relationships between these factors and user satisfaction factors. This study derived the specific factors that characterize ubiquitous services, such as ubiquity, contextual offer, user affinity, privacy, reliability, responsiveness, assurance, and empathy. We also considered service quality factors of ubiquitous services. Then these factors were combined with the Expectation Confirmation Theory (ECT) model and the path analysis was applied to find out the factors affecting user satisfaction and the intention to use the systems. The research findings indicate that ubiquity, contextual offer, privacy, reliability, and responsiveness affect the perceived usefulness. The perceived ease of use and confirmation were found to affect the perceived usefulness. The perceived usefulness, perceived ease of use, and confirmation fumed out to influence the satisfaction. It turned out that the result of this study on the relationship between the perceived usefulness and user satisfaction was identical with the findings in previous related ECT researches. We think this study makes two significant contributions to the development of ubiquitous services. First, this study provides basic implications for better ubiquitous services by considering important characteristics of ubiquitous systems as services. Second, this study also suggests important factors that need to be considered when ubiquitous service providers develop new ubiquitous services to improve user satisfaction and the intention to use the services.

Pectin Micro- and Nano-capsules of Retinyl Palmitate as Cosmeceutical Carriers for Stabilized Skin Transport

  • Ro, Jieun;Kim, Yeongseok;Kim, Hyeongmin;Park, Kyunghee;Lee, Kwon-Eun;Khadka, Prakash;Yun, Gyiae;Park, Juhyun;Chang, Suk Tai;Lee, Jonghwi;Jeong, Ji Hoon;Lee, Jaehwi
    • The Korean Journal of Physiology and Pharmacology
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    • v.19 no.1
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    • pp.59-64
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    • 2015
  • Retinyl palmitate (RP)-loaded pectinate micro- and nano-particles (PMP and PNP) were designed for stabilization of RP that is widely used as an anti-wrinkle agent in anti-aging cosmeceuticals. PMP/PNP were prepared with an ionotropic gelation method, and anti-oxidative activity of the particles was measured with a DPPH assay. The stability of RP in the particles along with pectin gel and ethanolic solution was then evaluated. In vitro release and skin permeation studies were performed using Franz diffusion cells. Distribution of RP in each skin tissue (stratum corneum, epidermis, and dermis) was also determined. PMP and PNP could be prepared with mean particle size diameters of $593{\sim}843{\mu}m$ (PMP) and 530 nm (i.e., $0.53{\mu}m$, PNP). Anti-oxidative activity of PNP was greater than PMP due largely to larger surface area available for PNP. The stability of RP in PMP and PNP was similar but much greater than RP in pectin bulk gels and ethanolic solution. PMP and PNP showed the abilities to constantly release RP and it could be permeated across the model artificial membrane and rat whole skin. RP was serially deposited throughout the skin layers. This study implies RP loaded PMP and PNP are expected to be advantageous for improved anti-wrinkle effects.

Equilibrium Kinetics and Thermodynamic Parameters Studies for Eosin Yellow Adsorption by Activated Carbon (활성탄에 의한 Eosin Yellow의 흡착에 대한 평형, 동력학 및 열역학 파라미터에 관한 연구)

  • Lee, Jong Jib
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.15 no.5
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    • pp.3319-3326
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    • 2014
  • Eosin yellow is used a dye and colorant but it is harmful toxic substance. In this paper, batch adsorption studies were carried out for equilibrium, kinetics and thermodynamic parameters for eosin yellow adsorption by activated carbon with varying the operating variables like pH, initial concentration, contact time. Equilibrium adsorption data were fitted into Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms. By estimated Langmuir constant value, $R_L$=0.067-0.083, and Freundlich constant value, $\frac{1}{n}=0.237-0.267$, this process could be employed as effective treatment for removal of eosin yellow. From calculated Temkin constant, value, B=1.868-2.855 J/mol, and Dubinin-Radushkevich constant, value, E=5.345-5.735 kJ/mol, this adsorption process is physical adsorption. From kinetic experiments, the adsorption process were found to confirm to the pseudo second order model with good correlation coefficient($r^2$=0.995-0.998). The mechanism of the adsorption process was determined two step like as boundary and intraparticle diffusion.

Phytochemical Screening and Biological Studies of Boerhavia Diffusa Linn

  • Gautam, Prakriti;Panthi, Sandesh;Bhandari, Prashubha;Shin, Jihoon;Yoo, Jin Cheol
    • Journal of Integrative Natural Science
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    • v.9 no.1
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    • pp.72-79
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    • 2016
  • Hexane, ethyl acetate and methanol extracts of whole plant of Boerhavia diffusa were screened for phytochemical and biological activities. Qualitative phytochemical screening via colorimetric method and the quantitative estimation of phenolic and flavonoid content were performed. Antioxidant assay using DPPH scavenging method was studied. Antimicrobial screening of plant extracts was done by cup diffusion technique. Cytotoxic activity of B. diffusa was studied by brine shrimp bioassay and anthelminthic activity was evaluated in vitro in Pheretima posthuma. This study revealed B. diffusa as a source of various phyto-constituents such as alkaloids, glycosides, saponins, tannins, carbohydrates, cardiac glycosides, flavonoids and terpenoids. Quantitative estimation of total phenol was found to be maximum in BEE i.e. $29.73{\pm}0.88$, BME $19.8{\pm}2.02$ and in BHE $9.15{\pm}0.304mgGAE/g$. Similarly, the total flavonoid content was found to be $17.44{\pm}0.75$ in BEE, $14.43{\pm}0.23$ in BHE and 3.678 mg QE/g in BME. Ethyl acetate extract showed its antibacterial activity against all tested pathogens except Escherichia coli whereas Staphylococcus aureus and Salmonella Typhi were resistant to methanol and hexane extract. The zone of inhibition (ZOI) of ethyl acetate extract against S. Typhi and B. cereus was found to be 18 mm and 14 mm respectively. The MIC value of BEE in S. Typhi was $3.125{\mu}g/ml$ and in B. cereus was $12.5{\mu}g/ml$. The preliminary screening of anticancer property of B. diffusa i.e. BSLT in methanol was found to be $165.19{\mu}g/ml$. B. diffusa was also found to contain anthelmintic property. The study helped in further exploration of medicinal properties of B. diffusa by phytochemical screening and biological activities paving the path for study and investigation in this plant.

Modeling of the Nitrate Adsorption Kinetics onto $ZnCl_2$ Treated Granular Activated Carbon (염화아연으로 표면개질된 입상활성탄의 질산성질소 흡착속도의 모델링 연구)

  • Ji, Min-Kyu;Jung, Woo-Sik;Bhatnagar, Amit;Jeon, Byong-Hun
    • Journal of Soil and Groundwater Environment
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    • v.13 no.3
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    • pp.21-26
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    • 2008
  • Nitrate adsorption from aqueous solutions onto zinc chloride ($ZnCl_2$) treated coconut Granular Activated Carbon (GAC) was studied in a batch mode at two different initial nitrate concentrations (25 and 50 mg/L). The rate of nitrate uptake on prepared media was fast in the beginning, and 50% of adsorption was occurred within 10 min. The adsorption equilibrium was achieved within one hour. The mechanism of adsorption of nitrate on $ZnCl_2$ treated coconut GAC was investigated using four simplified kinetic models : the rate parameters were calculated for each model. The kinetic analysis indicated that pseudo-second-order kinetic with pore-diffusion-controlled was the best correlation of the experimental kinetic data in the present adsorption study.

Applicability of hiding-exposure effect to suspension simulation of fine sand bed (가는 모래의 부유 모의시 차폐효과 고려의 영향)

  • Byun, Jisun;Son, Minwoo
    • Journal of Korea Water Resources Association
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    • v.54 no.8
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    • pp.607-616
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    • 2021
  • The purpose of this study is to simulate the transport of nonuniform sediment considering the hiding-exposure effect numerically. In order to calculate the transport of multi-disperse suspended sediment mixtures, the set of advection-diffusion equations for each particle class is solved. The applicability of the numerical model is examined by comparing the simulation results with experimental data. In this study, we calculate the vertical distribution of total concentration of sediment particles using two approaches: (1) by considering the mixture as represented by a single size; and (2) by combining the concentration of the sediment corresponding to several particle size classes; From the simulation results, it is shown that both approaches calculate reasonable results due to the narrow range of size distribution. Under the condition of nonuniform sediment, the critical shear stress of the sediment particle is influenced by the size-selective entrainment, i.e., hiding-exposure effect. It is shown in this study that the effect of hiding-exposure effect on the erosion rates of fine sand is negligibly small.

Updated Primer on Generative Artificial Intelligence and Large Language Models in Medical Imaging for Medical Professionals

  • Kiduk Kim;Kyungjin Cho;Ryoungwoo Jang;Sunggu Kyung;Soyoung Lee;Sungwon Ham;Edward Choi;Gil-Sun Hong;Namkug Kim
    • Korean Journal of Radiology
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    • v.25 no.3
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    • pp.224-242
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    • 2024
  • The emergence of Chat Generative Pre-trained Transformer (ChatGPT), a chatbot developed by OpenAI, has garnered interest in the application of generative artificial intelligence (AI) models in the medical field. This review summarizes different generative AI models and their potential applications in the field of medicine and explores the evolving landscape of Generative Adversarial Networks and diffusion models since the introduction of generative AI models. These models have made valuable contributions to the field of radiology. Furthermore, this review also explores the significance of synthetic data in addressing privacy concerns and augmenting data diversity and quality within the medical domain, in addition to emphasizing the role of inversion in the investigation of generative models and outlining an approach to replicate this process. We provide an overview of Large Language Models, such as GPTs and bidirectional encoder representations (BERTs), that focus on prominent representatives and discuss recent initiatives involving language-vision models in radiology, including innovative large language and vision assistant for biomedicine (LLaVa-Med), to illustrate their practical application. This comprehensive review offers insights into the wide-ranging applications of generative AI models in clinical research and emphasizes their transformative potential.

Electronic Word-of-Mouth in B2C Virtual Communities: An Empirical Study from CTrip.com (B2C허의사구중적전자구비(B2C虚拟社区中的电子口碑): 관우휴정려유망적실증연구(关于携程旅游网的实证研究))

  • Li, Guoxin;Elliot, Statia;Choi, Chris
    • Journal of Global Scholars of Marketing Science
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    • v.20 no.3
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    • pp.262-268
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    • 2010
  • Virtual communities (VCs) have developed rapidly, with more and more people participating in them to exchange information and opinions. A virtual community is a group of people who may or may not meet one another face to face, and who exchange words and ideas through the mediation of computer bulletin boards and networks. A business-to-consumer virtual community (B2CVC) is a commercial group that creates a trustworthy environment intended to motivate consumers to be more willing to buy from an online store. B2CVCs create a social atmosphere through information contribution such as recommendations, reviews, and ratings of buyers and sellers. Although the importance of B2CVCs has been recognized, few studies have been conducted to examine members' word-of-mouth behavior within these communities. This study proposes a model of involvement, statistics, trust, "stickiness," and word-of-mouth in a B2CVC and explores the relationships among these elements based on empirical data. The objectives are threefold: (i) to empirically test a B2CVC model that integrates measures of beliefs, attitudes, and behaviors; (ii) to better understand the nature of these relationships, specifically through word-of-mouth as a measure of revenue generation; and (iii) to better understand the role of stickiness of B2CVC in CRM marketing. The model incorporates three key elements concerning community members: (i) their beliefs, measured in terms of their involvement assessment; (ii) their attitudes, measured in terms of their satisfaction and trust; and, (iii) their behavior, measured in terms of site stickiness and their word-of-mouth. Involvement is considered the motivation for consumers to participate in a virtual community. For B2CVC members, information searching and posting have been proposed as the main purpose for their involvement. Satisfaction has been reviewed as an important indicator of a member's overall community evaluation, and conceptualized by different levels of member interactions with their VC. The formation and expansion of a VC depends on the willingness of members to share information and services. Researchers have found that trust is a core component facilitating the anonymous interaction in VCs and e-commerce, and therefore trust-building in VCs has been a common research topic. It is clear that the success of a B2CVC depends on the stickiness of its members to enhance purchasing potential. Opinions communicated and information exchanged between members may represent a type of written word-of-mouth. Therefore, word-of-mouth is one of the primary factors driving the diffusion of B2CVCs across the Internet. Figure 1 presents the research model and hypotheses. The model was tested through the implementation of an online survey of CTrip Travel VC members. A total of 243 collected questionnaires was reduced to 204 usable questionnaires through an empirical process of data cleaning. The study's hypotheses examined the extent to which involvement, satisfaction, and trust influence B2CVC stickiness and members' word-of-mouth. Structural Equation Modeling tested the hypotheses in the analysis, and the structural model fit indices were within accepted thresholds: ${\chi}^2^$/df was 2.76, NFI was .904, IFI was .931, CFI was .930, and RMSEA was .017. Results indicated that involvement has a significant influence on satisfaction (p<0.001, ${\beta}$=0.809). The proportion of variance in satisfaction explained by members' involvement was over half (adjusted $R^2$=0.654), reflecting a strong association. The effect of involvement on trust was also statistically significant (p<0.001, ${\beta}$=0.751), with 57 percent of the variance in trust explained by involvement (adjusted $R^2$=0.563). When the construct "stickiness" was treated as a dependent variable, the proportion of variance explained by the variables of trust and satisfaction was relatively low (adjusted $R^2$=0.331). Satisfaction did have a significant influence on stickiness, with ${\beta}$=0.514. However, unexpectedly, the influence of trust was not even significant (p=0.231, t=1.197), rejecting that proposed hypothesis. The importance of stickiness in the model was more significant because of its effect on e-WOM with ${\beta}$=0.920 (p<0.001). Here, the measures of Stickiness explain over eighty of the variance in e-WOM (Adjusted $R^2$=0.846). Overall, the results of the study supported the hypothesized relationships between members' involvement in a B2CVC and their satisfaction with and trust of it. However, trust, as a traditional measure in behavioral models, has no significant influence on stickiness in the B2CVC environment. This study contributes to the growing body of literature on B2CVCs, specifically addressing gaps in the academic research by integrating measures of beliefs, attitudes, and behaviors in one model. The results provide additional insights to behavioral factors in a B2CVC environment, helping to sort out relationships between traditional measures and relatively new measures. For practitioners, the identification of factors, such as member involvement, that strongly influence B2CVC member satisfaction can help focus technological resources in key areas. Global e-marketers can develop marketing strategies directly targeting B2CVC members. In the global tourism business, they can target Chinese members of a B2CVC by providing special discounts for active community members or developing early adopter programs to encourage stickiness in the community. Future studies are called for, and more sophisticated modeling, to expand the measurement of B2CVC member behavior and to conduct experiments across industries, communities, and cultures.