• Proceedings of the Computational Structural Engineering Institute Conference
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• 2005.04a
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• pp.335-342
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• 2005

Using higher order Mindlin plates and piezoelectric materials, eigenvalue problems are considered. Since piezoelectric crystal resonators produce a proper amount of electric signal for a thickness-shear frequency, the objective is to decouple the thickness-shear mode from the others. Design variables are the bulk material densities corresponding to the mass of masking plates for electrodes. The design sensitivity expressions for the thickness-shear frequency and mode shape vector are derived using direct differentiation method(DDM). Using the developed design sensitivity analysis (DSA) method, we formulate a topology optimization problem whose objective function is to maximize the thickness-shear component of strain energy density at the thickness-shear mode. Constraints are the allowable volume and area of masking plate. Numerical examples show that the optimal design yields an improved mode shape and thickness-shear energy.

• Journal of Power System Engineering
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• v.17 no.1
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• pp.36-41
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• 2013

A study of the possible axisymmetric modes that propagate at low frequencies in buried, water-filled pipes is presented. It is well known that for a vacuum-pipe-vacuum system the sole non-torsional axisymmetric mode that exists at low frequencies is the fundamental L(0,1) mode. When a pipe is filled with water and still surrounded by a vacuum it is also known that another mode then appears which at low frequencies is characterized by predominantly axial water-borne displacements. In addition to these modes. this paper explores two other, less well known axisymmetric modes whose exitence depends on the acoustic properties of the outer medium that surrounds a pipe. The predicted characteristics of these modes are presented and the likelihood of them propagating over any significant distance in a buried water pipe is discussed.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.8
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• pp.13-22
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• 2010

Independent-Gate-Mode Double-Gate(IGM-DG) MOSFET overcomes the limitation of bulk-MOSFET's channel controllability and enables to control the front and back-gate voltages independently. Therefore, circuit designs utilizing the IGM-DG MOSFETs provide the advantage of setting 4-terminal freely, hence achieving not only the performance improvement but also the larger scale integration. This paper presents a 15Gb/s optical receiver with a 1.0V power supply voltage, which consists of a transimpedance amplifier (TIA), a feedforward limiting amplifier (LA), and an output buffer. HSPICE simulations were conducted to confirm the circuit performance, and also to verify the circuit stability issues which may occur from the variations of process and supply voltage.

• Restorative Dentistry and Endodontics
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• v.48 no.4
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• pp.35.1-35.14
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• 2023

Objectives: The purpose of this study was to evaluate the impact of dentin roughening and the type of composite resin used (either bulk-fill flowable or nanohybrid) on the restoration of non-carious cervical lesions (NCCLs) with an 18-month follow-up period. Materials and Methods: This prospective split-mouth study included 36 patients, each with a minimum of 4 NCCLs. For each patient, 4 types of restorations were performed: unroughened dentin with nanohybrid composite, unroughened dentin with bulk-fill flowable composite, roughened dentin with nanohybrid composite, and roughened dentin with bulk-fill flowable composite. A universal bonding agent (Tetric N Bond Universal) was applied in self-etch mode for all groups. The restorations were subsequently evaluated at 6, 12, and 18 months in accordance with the criteria set by the FDI World Dental Federation. Inferential statistics were computed using the Friedman test, with the level of statistical significance established at 0.05. Results: The 4 groups exhibited no significant differences in relation to fracture and retention, marginal staining, marginal adaptation, postoperative hypersensitivity, or the recurrence of caries at any follow-up point. Conclusions: Within the limitations of the present study, over an 18-month follow-up period, no significant difference was present in the clinical performance of bulk-fill flowable and nanohybrid composite restorations of non-carious cervical lesions. This held true regardless of whether dentin roughening was performed.

• JSTS:Journal of Semiconductor Technology and Science
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• v.13 no.4
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• pp.361-366
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• 2013

A full-range analytic drain current model for depletion-mode long-channel surrounding-gate nanowire field-effect transistor (SGNWFET) is proposed. The model is derived from the solution of the 1-D cylindrical Poisson equation which includes dopant and mobile charges, by using the Pao-Sah gradual channel approximation and the full-depletion approximation. The proposed model captures the phenomenon of the bulk conduction mechanism in all regions of device operation (subthreshold, linear, and saturation regions). It has been shown that the continuous model is in complete agreement with the numerical simulations.

• JSTS:Journal of Semiconductor Technology and Science
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• v.10 no.2
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• pp.152-159
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• 2010

We propose a semi-analytical current conduction model for depletion-mode n-type nanowire field-effect transistors (NWFETs) with top-gate structure. The NWFET model is based on an equivalent circuit consisting of two back-to-back Schottky diodes for the metal-semiconductor (MS) contacts and the intrinsic top-gate NWFET. The intrinsic top-gate NWFET model is derived from the current conduction mechanisms due to bulk charges through the center neutral region as well as of accumulation charges through the surface accumulation region, based on the electrostatic method, and thus it includes all current conduction mechanisms of the NWFET operating at various top-gate bias conditions. Our previously developed Schottky diode model is used for the MS contacts. The newly developed model is integrated into ADS, in which the intrinsic part of the NWFET is developed by utilizing the Symbolically Defined Device (SDD) for an equation-based nonlinear model. The results simulated from the newly developed NWFET model reproduce considerably well the reported experimental results.

• Nuclear Engineering and Technology
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• v.51 no.4
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• pp.1117-1131
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• 2019

Tanks are used extensively in many engineering areas for spent fuel pool structures at nuclear power plants or for water storage tanks in bulk carriers. To ensure the structural integrity of such tanks when under dynamic loads, modal characteristics such as natural frequencies, participation factors and mode shapes should be known. Investigated in this study are the modal characteristics of a square tank by the finite element method. This approach can be used with subsequent dynamic analyses such as a response spectrum analysis or a harmonic analysis. Finite element models are prepared to determine the natural frequencies and mode shapes, which are easy to find the modal characteristics of a fluid-filled square tank. The effects of the fluid contained in the tank and the boundary conditions at top and bottom ends on the modal characteristics are assessed by several finite element analyses.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.15 no.3
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• pp.1-11
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• 2016

The present study aims to evaluate transfer resistance factors in railway stations and draw new implications. The data used for the model estimation are RP (revealed preference) data and SP (stated preference) data. Two types of models were used for the analysis: integration model which combined line-haul stage, transfer stage and shuttle stage and separation model which assessed the three stages separately. The results revealed that while bulk freight shippers mainly focused on line-haul stage, they put emphasis on transfer stage as well. It's especially notable that transfer stage was considered more important than shuttle stage. Therefore, in future transportation policies concerning rail freight, it would be crucial not only to enhance the competitiveness of line-haul stage but also make improvements in transfer stage regarding railway stations.

• Journal of the Korean Society for Railway
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• v.18 no.6
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• pp.596-608
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• 2015

Freight transport by railway is gaining more attention at present as a countermeasure against global warming. In keeping with this purpose, the present study examined various methods for promoting railway use through minimization of the transfer resistance of bulk freight at railway stations. First, the transfer-related factors that shippers consider as important when choosing railway as a transport mode were identified. Also, the relative importance and the level of influence of each factor during the transfer stage were evaluated. Policy directions for reducing transfer resistance in railway stations were then proposed based on the analysis of the transfer resistance factors. The policy directions include both hardware and software approaches. The necessary reduction ranges with regard to the transfer cost and time through policy implementation efforts were suggested as well.

• Journal of the Korea Society of Computer and Information
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• v.26 no.7
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• pp.127-132
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• 2021

This paper applies a machine learning model to forecasting freight rates in dry bulk and tanker markets with wavelet decomposition and empirical mode decomposition because they can refect both information scattered in the time and frequency domain. The decomposition with wavelet is outperformed for the dry bulk market, and EMD is the more proper model in the tanker market. This result provides market players with a practical short-term forecasting method. This study contributes to expanding a variety of predictive methodologies for one of the highly volatile markets. Furthermore, the proposed model is expected to improve the quality of decision-making in spot freight trading, which is the most frequent transaction in the shipping industry.