• Geomechanics and Engineering
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• v.25 no.4
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• pp.317-330
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• 2021

This paper reports the results of advanced data analysis involving artificial neural networks for the prediction of the unconfined compressive strength of granite using only two non-destructive test indexes. A data-independent site-independent unbiased database comprising 182 datasets from non-destructive tests reported in the literature was compiled and used to train and develop artificial neural networks for the prediction of the unconfined compressive strength of granite. The results show that the optimum artificial network developed in this research predicts the unconfined compressive strength of weak to very strong granites (20.3-198.15 MPa) with less than ±20% deviation from the experimental data for 70% of the specimen and significantly outperforms a number of available models available in the literature. The results also raise interesting questions with regards to the suitability of the Pearson correlation coefficient in assessing the prediction accuracy of models.

• Journal of Biomedical Engineering Research
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• v.43 no.6
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• pp.369-374
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• 2022

Purpose: Focused ultrasound is an emerging technology for treating the brain locally in a noninvasive manner. In this study, we have investigated the influence of skull properties on simulating transcranial pressure field. Methods: A 3D computational model of transcranial focused ultrasound was constructed using female and male CT data to solve for intracranial pressure. For heterogeneous model, the acoustic properties were calculated from CT Hounsfield units based on a porosity. The homogeneous model assigned constant acoustic properties for the single-layered skull. Results: A computational model was validated against empirical data. The homogeneous models were then compared with the heterogeneous model, resulted in 10.87% and 7.19% differences in peak pressure for female and male models respectively. For the focal volume, homogeneous model demonstrated more than 94% overlap compared with the heterogeneous model. Conclusion: Homogeneous model can be constructed using MR images that are commonly used for the segmentation of the skull. We propose the possibility of the homogeneous model for the simulating transcranial pressure field owing to comparable focal volume between homogeneous model and heterogeneous model.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.263-268
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• 2010

Thermal characterization of geomaterials has significant implication on the geothermal energy, disposal of nuclear wastes, geological sequestration of carbon dioxides and recovery of hydrocarbon resources. Heat transfer in multiphase materials is dominated by the thermal conductivity of consisting components, porosity, degree of saturation and overburden pressure, which have been investigated by the empirical correlation at macro-scale. The thermal measurement by Transient Plane Source (TPS) and associated algorithm for interpretation of thermal behavior in geomaterials corroborate the robustness of sensing techniques. The method simultaneously provides thermal conductivity, diffusivity and volumetric heat capacity. The newly introduced thermal network model enables estimating thermal conductivity of geomaterials subjected to the effective stress, which has not been evaluated using previous thermal models. The proposed methods shows the applicability of reliability of TPS technique and thermal network model.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.242.2-242.2
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• 2011

Molecularly imprinted polymer thin films were applied to develop a gas sensor based on the surface plasmon resonance phenomenon for small gaseous molecules such as toluene and xylene. The imprinted polymer films were synthesized via photo-polymerization method using various combination of templates, functional monomers and cross-linkers. The temperature of pre-polymerization solutions and the power of UV light were controlled for optimized performance of gas sensing. The morphology and porosity of the polymer films were controlled by varying the mixing ratios of the pre-polymerization solutions and confirmed by atomic force microscopy. By fitting the adsorption/desorption sensorgrams to conventional kinetic models, the effects of different templates and cross-linkers were interpreted in term of the structural differences of the polymer networks formed on the gold film. The sensitivity and selectivity of sensors were estimated for toluene and xylene, and also for humidity and other gaseous molecules such as formaldehyde and ammonia.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.551-554
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• 2008

In this study, numerical methods for the code development of the interior ballistics have been conducted. Mathematical models and numerical methods for the analysis technique of the granular solid propellants have been investigated. As the results of applying the methods of errors have been generated by calculation for the specific surface area of the granular solid propellants. To remove these error, the developed Eulerian-Larangian method for multiphase flows has been suggested.

• Journal of Powder Materials
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• v.24 no.1
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• pp.17-23
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• 2017

In this study, a finite element analysis approach is proposed to predict the fluid-structure interaction behavior of active materials for lithium-ion batteries (LIBs), which are mainly composed of graphite powder. The porous matrix of graphite powder saturated with fluid electrolyte is considered a representative volume element (RVE) model. Three different RVE models are proposed to consider the uncertainty of the powder shape and the porosity. P-wave modulus from RVE solutions are analyzed based on the microstructure and the interaction between the fluid and the graphite powder matrix. From the results, it is found that the large surface area of the active material results in low mechanical properties of LIB, which leads to poor structural durability when subjected to dynamic loads. The results obtained in this study provide useful information for predicting the mechanical safety of a battery pack.

• The Journal of the Acoustical Society of Korea
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• v.29 no.2E
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• pp.64-72
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• 2010

Osteoporosis is a skeletal disease characterized by two factors: reduced bone mass and microstructure disruption of bone tissue. These symptoms increase bone fragility and can contribute to eventual fracture. In recent years, quantitative ultrasound (QUS) technologies have played a growing role in the diagnosis of osteoporosis. Most of the commercial bone sonometers measure speed of sound and/or broadband ultrasound attenuation at peripheral skeletal sites. However, QUS parameters are purely empirical measures that have not yet been firmly linked to physical parameters, such as bone strength or porosity, and the underlying physics for their variations in cancellous bone is not well understood yet. This paper reviews the QUS technologies for the diagnosis of osteoporosis and also addresses several theoretical models, such as the Biot model, the scattering model, the stratified model, and the modified Biot-Attenborough model, for ultrasonic wave propagation in bone.

• Journal of Mechanical Science and Technology
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• v.20 no.10
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• pp.1680-1690
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• 2006

As a promising and novel manufacturing technology, laser aided direct metal deposition (DMD) process produces near-net-shape functional metal parts directly from 3-D CAD models by repeating laser cladding layer by layer. The key of the build-up mechanism is the effective control of powder delivery and laser power to be irradiated into the melt-pool. A feedback control system using two sets of optical height sensors is designed for monitoring the melt-pool and real-time control of deposition dimension. With the feedback height control system, the dimensions of part can be controlled within designed tolerance maintaining real time control of each layer thickness. Clad nugget shapes reveal that the feedback control can affect the nugget size and morphology of microstructure. The pore/void level can be controlled by utilizing pulsed-mode laser and proper design of deposition tool-path. With the present configuration of the control system, it is believed that more innovation of the DMD process is possible to the deposition of layers in 3-D slice.

• Advances in concrete construction
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• v.4 no.4
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• pp.305-317
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• 2016

Porous materials such as concrete could be subjected to aggressive ions transport. Durability of cement paste is extremely depended on water and ions penetration into its interior sections. These ions transport could lead different damages depending on reactivity of ions, their concentrations and diffusion coefficients. In this paper, chloride diffusion process in cement hydrates is simulated at atomistic scale using molecular dynamics. Most important phase of cement hydrates is calcium silicate hydrate (C-S-H). Tobermorite, one of the most famous crystal analogues of C-S-H, is used as substrate in the simulation model. To conduct simulation, a nanopore is considered in the middle of simulation cell to place water molecules and aggressive ions. Different chloride salts are considered in models to find out which one is better for calculation of the transport properties. Diffusion coefficients of water molecules and chloride ions are calculated and validated with existing analytical and experimental works. There are relatively good agreements among simulation outputs and experimental results.

• CELLMED
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• v.4 no.2
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• pp.14.1-14.6
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• 2014

KH-BaRoKer-SeongJangTang (KBS) is a recently developed formulation by using traditional drugs considering traditional medical theory of Oriental books such as ShinNongBonChoGyeong and JuRye, which has been used to improve the growth of child in Korea. Although KBS is usually prescribed to many children who are in retard for their age, its pharmacological effects have not been fully understood in experimental models. The aim of this study was to evaluate the effects of KBS on bone growth. Growth plate thickness and bone parameters such as bone volume/tissue volume (BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N), connection density (Conn.D), and total porosity were analyzed by means of microcomputed tomography. Serum insulin-like growth factor-I (IGF-I) levels were measured by enzyme-linked immunosorbent assay. Hepatic IGF-I mRNA expression was analyzed by real-time polymerase chain reaction. Phosphorylation of signal transducer and activator of transcription5 (STAT5) was investigated using Western blot analysis and immunohistochemistry. The thickness of growth plate was increased by KBS. BV/TV, Tb.Th, TbN, Conn.D, and total porosity were improved by KBS. Hepatic IGF-I mRNA and serum IGF-I levels were elevated by KBS. Phosphorylation of STAT5 was increased with administration of KBS. These results suggest that KBS would be helpful to children who are in retard for their age through the elevation of IGF-I.