• Journal of computational fluids engineering
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• v.11 no.1 s.32
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• pp.8-15
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• 2006

The existing approximations of diffusion flux in unstructured cell-centered finite volume methods are examined in detail with each other and clarified to have indefinite expressions in several respects. A new numerical approximation of diffusion flux at cell face center is then proposed, which is second-order accurate even on irregular grids and may be easily implemented in CFD code using cell-centered finite volume method with unstructured grids composed of arbitrary convex polyhedral shape.

• Journal of Korean Institute of Industrial Engineers
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• v.41 no.5
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• pp.488-498
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• 2015

Research on stem cells can be divided into three categories : pluripotent stem cell, adult stem cell, and induced pluripotent stem cell. Technology life cycle (TLC) on research stage is analyzed for the three stem cell categories based on diffusion model. Three diffusion models-logistic, Bass, and Bass model with integration constant (BMIC)-are applied to the number of articles related to each stem cell category in SCOPUS lists. Two different parameter estimation methods is used for each of logistic and Bass model. Results show that (1) the current year, 2015, lies in growth period at pluripotent stem cell and adult stem cell, and lies in growth period or maturity period at induced pluripotent stem cell. (2) Model fitness is the highest at BMIC model. (3) Imitation effect works best at the research area of induced pluripotent stem cell.

• Journal of the Korean Society of Visualization
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• v.5 no.1
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• pp.12-15
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• 2007

Macromolecule diffusion in cells and tissues is important for cell signaling, metabolism and locomotion. Biophysical methods, including non-invasive or minimally invasive in-vivo photobleaching techniques and single quantum-dot tracking, have been used to measure the rates of macromolecule diffusion in living cells and tissues, including central nervous system and tumors. Mathematical modeling and statistical analysis of experimental data revealed various modes of diffusion, which are strongly coupled with spatiotemporal changes in nanoscale structures and material properties.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.489-492
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• 2006

A chloride is an important deteriorating factor which governs the durability of the reinforced-concrete structures under marine environments. Also, the main penetration mechanism of chloride ion into concrete is a diffusion phenomenon and numerous methods have been proposed to determine the diffusion coefficient of chloride ion quickly. In this study, electrically accelerated experiments were carried out in order to evaluate diffusion coefficient of the chloride ion into concrete. The methods were diffusion cell test method in which the voltage of 15V(DC) was applied. The type of cement is blended cement in which the admixtures of blast-furnace slag and fly ash were used. In conclusion, the diffusion coefficient of chloride ion is much affected according to mineral admixtures and the diffusion coefficient of ternary blended cement showed very low values. it is presumably said that this result is due to highly densified pore structures by the aid of slag substitution and pozzolanic activity of fly ash.

• Investigative Magnetic Resonance Imaging
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• v.25 no.1
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• pp.23-34
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• 2021

Purpose: Differentiating between glioblastoma and solitary metastasis is very important for the planning of further workup and treatment. We assessed the ability of various morphological parameters using conventional MRI and diffusion-based techniques to distinguish between glioblastomas and solitary metastases in tumoral and peritumoral regions. Materials and Methods: We included 38 patients with solitary brain tumors (21 glioblastomas, 17 solitary metastases). To find out if there were differences in the morphologic parameters of enhancing tumors, we analyzed their shape, margins, and enhancement patterns on postcontrast T1-weighted images. During analyses of peritumoral regions, we assessed the extent of peritumoral non-enhancing lesion on T2- and postcontrast T1-weighted images. We also aimed to detect peritumoral neoplastic cell infiltration by visual assessment of T2-weighted and diffusion-based images, including DWI, ADC maps, and exponential DWI, and evaluated which sequence depicted peritumoral neoplastic cell infiltration most clearly. Results: The shapes, margins, and enhancement patterns of tumors all significantly differentiated glioblastomas from metastases. Glioblastomas had an irregular shape, ill-defined margins, and a heterogeneous enhancement pattern; on the other hand, metastases had an ovoid or round shape, well-defined margins, and homogeneous enhancement. Metastases had significantly more extensive peritumoral T2 high signal intensity than glioblastomas had. In visual assessment of peritumoral neoplastic cell infiltration using T2-weighted and diffusion-based images, all sequences differed significantly between the two groups. Exponential DWI had the highest sensitivity for the diagnosis of both glioblastoma (100%) and metastasis (70.6%). A combination of exponential DWI and ADC maps was optimal for the depiction of peritumoral neoplastic cell infiltration in glioblastoma. Conclusion: In the differentiation of glioblastoma from solitary metastatic lesions, visual morphologic assessment of tumoral and peritumoral regions using conventional MRI and diffusion-based techniques can also offer diagnostic information.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.76.1-76.1
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• 2010

Recently, many efforts to solve the durability problem of PEM fuel cell are carried on constantly. However, despite this attention, durability researches of gas diffusion layer (GDL) are not much reported yet. Generally, GDL of PEM fuel cell experiences three external attacks, which are dissolution of water, erosion of gas flow, corrosion of electric potential. In this study, among these degradation factors, carbon corrosion of electric potential was focused and investigated with accelerated carbon corrosion test. Through the test, it is confirmed that carbon corrosion occurred at GDL, and corroded GDL decreased a performance of operating fuel cell. The property changes of GDL were measured with various methods such as air permeability meter, pore distribution analyzer, thermo gravimetric analyzer, and tensile stress test to discover the effects of carbon corrosion. Carbon corrosion caused not only loss of weight and thickness, but also degradation of mechanical strength of GDL. In addition, to analysis the reason of GDL property changes, a surface and a cross section of GDL were observed with scanning electron microscope. After 100 hours test, the GDL showed serious damage in center of layer.

• Korean Journal of Radiology
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• v.20 no.5
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• pp.791-800
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• 2019

Objective: To compare various models of diffusion-weighted imaging including monoexponential apparent diffusion coefficient (ADC), biexponential (fast diffusion coefficient [D_f], slow diffusion coefficient [D_s], and fraction of fast diffusion), stretched-exponential (distributed diffusion coefficient and anomalous exponent term [α]), and kurtosis (mean diffusivity and mean kurtosis [MK]) models in the differentiation of renal solid masses. Materials and Methods: A total of 81 patients (56 men and 25 women; mean age, 57 years; age range, 30-69 years) with 18 benign and 63 malignant lesions were imaged using 3T diffusion-weighted MRI. Diffusion model selection was investigated in each lesion using the Akaike information criteria. Mann-Whitney U test and receiver operating characteristic (ROC) analysis were used for statistical evaluations. Results: Goodness-of-fit analysis showed that the stretched-exponential model had the highest voxel percentages in benign and malignant lesions (90.7% and 51.4%, respectively). ADC, D_s, and MK showed significant differences between benign and malignant lesions (p < 0.05) and between low- and high-grade clear cell renal cell carcinoma (ccRCC) (p < 0.05). α was significantly lower in the benign group than in the malignant group (p < 0.05). All diffusion measures showed significant differences between ccRCC and non-ccRCC (p < 0.05) except D_f and α (p = 0.143 and 0.112, respectively). α showed the highest diagnostic accuracy in differentiating benign and malignant lesions with an area under the ROC curve of 0.923, but none of the parameters from these advanced models revealed significantly better performance over ADC in discriminating subtypes or grades of renal cell carcinoma (RCC) (p > 0.05). Conclusion: Compared with conventional diffusion parameters, α may provide additional information for differentiating benign and malignant renal masses, while ADC remains the most valuable parameter for differentiation of RCC subtypes and for ccRCC grading.

• Journal of Surface Science and Engineering
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• v.22 no.2
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• pp.55-61
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• 1989

A fuel cell which causes electrochemical ratio of conventional with oxygen consists of mainly there parts, such as electrolyte, fuel and oxidant electrode. IN this paper, most efforts were delivered to manufacturing PETE-bonded gas-diffusion electrode, and preparation methods of the porous electrodes has been discussd. A medio temperature, phosphoric acid fuel cell (PAFC) provided with fuel (hydrogen) and oxygen showed oxygen showed excellent performance characteristics with made electrodes. Performance data obtained from hydrgen-oxygen cell were presented to illustrate their properties. It was found that the optimum amounts of platinum in clectrode for hydrgen-oxygen PAFC were about 3mg/cm3 and the PTFE content of gas diffusion layer and catalyst layer were 25% and 15%, respectively.

• YAKHAK HOEJI
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• v.34 no.3
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• pp.161-165
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• 1990

An automated, simple, and reliable method was developed for determining in vitro drug release rate from transdermal delivery dosage forms. The patch is held in position in the heating block by sandwiching it between the middle plate and the bottom plate of diffusion cell. The dissolution profile of the commercially available transdermal scopolamine patch was determined over a 72-h period, and the results were compared with those obtained with other methods; paddle-over-disk method, reciprocating method, and diffusion cell method. It was demonstrated that the flow-through method is equivalent in terms of release rate profile and accumulated released drug amount over the lifetime of the dosage form tested. Also this method is simple, reliable and reproducible. Therefore, this technique can be used in a quality control for assuring product uniformity.

• Journal of the Korean Electrochemical Society
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• v.10 no.4
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• pp.306-310
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• 2007

Characteristics of GDL (Gas Diffusion Layer) mainly determine the gas diffusion and water removal in a cell, thereby changing the performance and affecting durability of PEFC. To optimize the water management and understand the two phase flow in a GDL, it is important to study the behaviors of GDL micro structure under the real operating condition. In the clamped condition of cell, the GDL beneath the rib is more compressed than beneath the channel. Many researches on physical, electrochemical, mechanical behaviors of gas diffusion layer has been conducted. However, changes in surface properties under clamped condition have rarely studied. In present study, the morphology of broken connections of carbon fibers and detachment of PTFE coatings on the fibers were shown from the microscopic observations. In addition, changes in wetting properties of GDL by compression were investigated by using XPS and liquid uptake methods. The hydrophobic characteristics of GDL surface beneath the rib of the flow field plate are changed due to the deformation of micro structure.