• Journal of Pharmaceutical Investigation
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• v.20 no.2
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• pp.79-88
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• 1990

A numerical model for diffusion and dissolution controlled transport from dispersed matrix is presented. The rate controlling process for transport is considered to be diffusion of drug through a concentration gradient coupled with time-dependent surface change and/or disappearance of the dispersed drug in response to the dissolution. The transport behavior of drug was explained in terms of ${\nu}$ parameter: ${\nu}$ value means a ratio of diffusion time constant and dissolution time constant. This general model has wide range of application from where release is controlled by the diffusion rate to where release is governed by the dissolution rate. Based on this model, theoretical drug concentration, particle size distributions in the polymer matrix system and the resulting release rate were also investigated.

• Structural Engineering and Mechanics
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• v.84 no.1
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• pp.77-83
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• 2022

In the last ten years, many researchers have studied the vibrations of carbon nanotubes using different beam theories. The nano- and micro-scale systems have wavy shape and there is a demand for a powerful tool to mathematically model waviness of those systems. In accordance with the above mentioned lack for the modeling of the waviness of the curved tiny structure, a novel approach is employed by implementing the Timoshenko-beam model. Owing to the small size of the micro beam, these structures are very appropriate for designing small instruments. The vibrations of double walled carbon nanotubes (DWCNTs) are developed using the Timoshenko-beam model in conjunction with the wave propagation approach under support conditions to calculate the fundamental frequencies of DWCNTs. The frequency influence is observed with different parameters. Vibrations of the double walled carbon nanotubes are investigated in order to find their vibrational modes with frequencies. The aspect ratios and half axial wave mode with small length are investigated. It is calculated that these frequencies and ratios are dependent upon the length scale and aspect ratio.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2006.04a
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• pp.55-56
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• 2006

This thesis describes the use of measured aerosol size distributions and size-resolved hygroscopic growth to examine the physical and chemical properties of several particle classes. The primary objective of this work was to investigate the optical and cloud forming properties of a range of ambient aerosol types measured in a number of different locations. The tool used for most of these analyses is a differential mobility analyzer / tandem differential mobility analyzer (DMA / TDMA) system developed in our research group. To collect the data described in two of the chapters of this thesis, an aircraft-based version of the DMA / TDMA was deployed to Japan and California. The data described in two other chapters were conveniently collected during a period when the aerosol of interest came to us. The unique aspect of this analysis is the use of these data to isolate the size distributions of distinct aerosol types in order to quantify their optical and cloud forming properties. I used collected data during the Asian Aerosol Characterization Experiment (ACE-Asia) to examine the composition and homogeneity of a complex aerosol generated in the deserts and urban regions of China and other Asian countries. An aircraft-based tandem differential mobility analyzer was used for the first time during this campaign to examine the size-resolved hygroscopic properties of particles having diameters between 40 and 586 nm. Asian Dust Above Monterey (ADAM-2003) study was designed both to evaluate the degree to which models can predict the long-range transport of Asian dust, and to examine the physical and optical properties of that aged dust upon reaching the California coast. Aerosol size distributions and hygroscopic growth are measured in College Station, TX to investigate the cloud nucleating and optical properties of a biomass burning aerosol generated from fires on the Yucatan Peninsula. Measured aerosol size distributions and size-resolved hygroscopicity and volatility were used to infer critical supersaturation distributions of the distinct particle types that were observed during this period. The predicted CCN concentrations were used in a cloud model to determine the impact of the different aerosol types on the expected cloud droplet concentration. RH-dependent aerosol extinction coefficients are calculated at a wavelength of 550 nm.

• Journal of the Korean Society for information Management
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• v.25 no.3
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• pp.273-296
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• 2008

This study conducted meta-analysis of librarians' job satisfaction using the Hedges & Olkin's Effect Size Model. Sex and Marrage as group variables, and Total Satisfaction and 7 sub-variables(Work Itself, Salary, Promotion, Supervision, Working Conditions, Social Recognition, Self-actualization) as dependent variables were selected from 27 studies. The effect sizes between men and women were significantly different on Supervision, Working conditions, Promotion, and Social Recognition, of which first two were homogeneous. But the difference of Social Recognition was not significant in Random Effect Model. The effect sizes difference between married and unmarried were significant on Self Recognition, Salary, and Work Itself. However the difference of Work Itself was not significant in Random Effect Model. Study Year could not be a moderator.

• Journal of Korean Institute of Industrial Engineers
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• v.24 no.1
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• pp.157-165
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• 1998

This paper considers the single-product production and transportation problem with discrete time, dynamic demand and finite time horizon, an extension of classical dynamic lot-sizing model. In the model, multiple freight container types are allowed as the transportation mode and each order (product) placed in a period is shipped immediately by containers in the period. Moreover, each container has type-dependent carrying capacity restriction and at most one container type is allowed in each shipping period. The unit freight cost for each container type depends on the size of its carrying capacity. The total freight cost is proportional to the number of each container type employed. Such a freight cost is considered as another set-up cost. Also, it is assumed in the model that production and inventory cost functions are dynamically concave and backlogging is not allowed. The objective of this study is to determine the optimal production policy and the optimal transportation policy simultaneously that minimizes the total system cost (including production cost, inventory holding cost, and freight cost) to satisfy dynamic demands over a finite time horizon. In the analysis, the optimal solution properties are characterized, based on which a dynamic programming algorithm is derived. The solution algorithm is then illustrated with a numerical example.

• Asia pacific journal of information systems
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• v.13 no.2
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• pp.119-143
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• 2003

Trust has been identified as a key component in many e-Commerce studies. The purpose of this study is to find out which factors play a major role in building trust and how the built-up trust affect consumer's purchase intention in Internet used-car transactions. Based on the information asymmetry, TAM(Technology Acceptance Model), and the trust theory, our research model includes factors such as a buyer's propensity-to-trust, institutional characteristics(inspection and warranty policy), word-of-mouth referral, perceived size, and perceived benefits as independent variables. The model also includes trust as a mediate variable, intention to purchase as a dependent variable and perceived quality risk as a moderate variable. The research model is tested by analyzing 787 sample data gathered from Internet used-car transaction sites. The result shows that the trust has significant effects on the online purchase intention, and institutional characteristics has been identified as the most significant factor for the trust of Internet used-car sites. The independent factors influencing trust vary depending on the level of perceived quality risk. For users who perceive the quality risk low, the perceived benefits explain a little portion of the purchase intention. However, those who perceive quality risk high would purchase used-cars only when they have trust on the Internet sites, indicating that trust play an important role as a mediate variable. This study suggests that enhancing the trust in Internet used-car sites is important to increase online transactions.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.11
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• pp.32-41
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• 2000

A new anatomical head model was implemented based on the MR and CT images of the head of a volunteer whose head shape is close to the domestic standard. In order to compare SARs (specific absorption rates) of heads with different shapes, we calculated SARs in the two anatomical head models. The one is the new model and the other is that of the black race and was made at National Library Medicine in USA. The head model and a phone model were arranged in the computational space to be the touch or cheek position of CENELEC (European Committee for Electrotechnical Standardisation) and FCC guidelines. From the obtained results, we can see that the smaller head produces the higher whole head-averaged SAR. However, it seems that the localized SAR averaged over 1 g or 10 g is more dependent on the shape of the auricle rather than that of the head size.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.51 no.12
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• pp.670-675
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• 2002

AC loss is an important issue in the design of high-T$_{c}$ superconducting Power cables. The cables consists of a number of Bi-2223 tapes wound on a former. In such cables tapes have different critical current characteristics intrinsically. And they are electrically connected to each other and current leads by soldering. These make loss measurements considerably complex, especially for short samples of laboratory size. Special cautions are required in the positioning of voltage leads for measuring the true loss voltage. In this work the at losses in a single layer model cable have been experimentally investigated for different contacts and arrangements of voltage leads. The results show that the losses are not dependent on both arrangements and contact positions of the voltage leads. This implies that loss flux is only in a cylindrical conductor section. The measured losses also agree well with those based on a monoblock model and are independent of frequencies. This means that the measured AC loss of the model cable is purely hysteretic in nature.e.

• Structural Engineering and Mechanics
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• v.78 no.1
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• pp.31-39
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• 2021

To investigate numerically the effect of all parameters on the outcome of an aircraft impact into robust engineering structures like nuclear power plant containments is a tedious task. In order to reduce the problem to a manageable size, we propose a single dimensionless parameter, the damage potential, to characterize the main features of the impact. The damage potential, which is the ratio of the initial kinetic energy of the aircraft to the work required to crush it, enables us to find the crucial parameter settings that need to be modelled numerically in detail. We show in this paper that the damage potential is indeed the most important parameter of the impact that determines the time-dependent reaction force when either finite element (FE) modelling or the Riera model is applied. We find that parameters that do not alter the damage potential, like elasticity of the target, are of secondary importance and if parameters are altered in a way that the damage potential remains the same then the course of the impact remains similar. We show, however, that the maximum value of the reaction force can be higher in case of elastic targets than in case of rigid targets due to the vibration of the target. The difference between the Riera and FE model results is also found to depend on the damage potential.

• The Journal of Korea Robotics Society
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• v.17 no.3
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• pp.381-386
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• 2022

We develop a business model for facade cleaning service robot system that provides service by meeting the market needs and environments. The size of the facade cleaning market is growing rapidly in recent years due to the increasing importance of indoor space and the modern trend of building construction methods. Also, maintenance of exterior appearance of buildings has become an important factor in residential and commercial facilities. Though demand for facade cleaning services is rising, the current facade cleaning services are performed dangerously in a human labor-dependent way. It is desirable that the existing human resource service should be replaced with robot-based services. In addition, quantitative analysis of rental pricing model was conducted to propose effective launch of products to the market. The robot system is economically attractive from the consumer's point of view. When the actual facade cleaning robot service is released, it is expected that verification of the business models and more accurate analysis with specific figures can be performed.