• Journal of Sensor Science and Technology
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• v.30 no.3
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• pp.165-169
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• 2021

The objective of this study was to fabricate a novel hydrophobic stent for reducing restenosis by employing electron beam equipment. The stent was fabricated from a CoCr alloy tube by using a femtosecond laser and was treated with argon plasma. Subsequently, the stent's surface specification changed from hydrophilic to hydrophobic. Application of the electron beam offers several advantages such as a short processing time, whole surface reforming, and enhancement of material properties. As the surface of the stent was rendered hydrophobic, it can provide equivalent or enhanced mechanical properties and greater functionality with a higher radial force at the extended stent in a blood vessel. The obtained results corresponding to the mechanical properties indicate that the contact angle increased to approximately 130°, and the radial force increased to approximately 3 N. Furthermore, cell culture experiments were conducted for verifying whether cells were cultured on the surface-modified CoCr surface. Based on the obtained results, it is believed that an effective reduction in the restenosis of inserted vascular stents is possible.

• Nuclear Engineering and Technology
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• v.54 no.2
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• pp.449-455
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• 2022

The rapid rise in the application of novel treatment techniques, such as intensity-modulated radiotherapy (IMRT), motivated us to survey the status of Korea's radiation safety management and the shielding designs of facilities employing medical linear accelerators (LINACs). To this end, a questionnaire was used to collect information on LINAC facilities and treatments, workload, shielding design, shielding management, and path of obtaining shielding information. Out of 100 domestic institutions, 52 responded to the survey. Approximately 70% of the institutions utilized IMRT for more than 60% of their cases, and an IMRT factor of 5 was adopted by 75% of these institutions. Over 80% of the institutions accounted for the applied time-averaged dose rate per week and instantaneous dose equivalent rates in their shielding designs. Approximately 45% of the institutions obtained important shielding information via a radiation shielding design company and the NCRP-151 report. Overall, most facilities were shown to follow the standards recommended by the relevant international agencies. However, the requirement to establish standardized shielding design information and clarify ambiguous paths for information acquisition was also highlighted. Therefore, the study's results can be used as a foundation for establishing a safety control system and for creating adequate shielding designs.

• Computers and Concrete
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• v.31 no.3
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• pp.173-184
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• 2023

In this study, the flexural behaviors of one- and two-way reinforced concrete (RC) slabs strengthened with carbon-fiber-reinforced polymer (CFRP) strips under impact loads were investigated. The flexural strengthening of RC slabs under simulated static monotonic loads has been comprehensively studied. However, the flexural behavior of RC slabs strengthened with CFRP strips has not been investigated extensively, particularly those conducted numerically. Nonlinear three-dimensional finite element models were developed, executed, and verified against previous experimental results, producing satisfactory models with approximately 4% error. The models were extended to a parametric study, considering three geometric parameters: the slab rectangularity ratio, CFRP strip width, and CFRP strip configuration. Finally, the main results were used to derive a new formula for predicting the total deflection of RC slabs strengthened with CFRP strips under impact loads with an error of approximately 10%. The proposed equation reflected the slab rectangularity, CFRP strip width, equivalent slab stiffness, and dropped weight. Results indicated that the use of CFRP strips enhanced the overall impact performance, the wider the CFRP width, the better the enhancement. Moreover, the application of diagonally oriented CFRP strips diminished the cracking zone compared to straight strips. Additionally, the diagonal orientation of CFRP strips was more efficient for two-way slabs while the vertical orientation was found to be better in the case of one-way slabs.

• Nuclear Engineering and Technology
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• v.20 no.2
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• pp.132-136
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• 1988

A strategic question in groundwater contaminant transport modeling is whether we need to treat waste packages or drums as individual, discrete sources or as approximately lumped sources. In this paper we present analyses of array sources in porous media. We analyze a planar array of sources in porous media with groundwater flow. We compare the concentration field predicted by a detailed model of individual point sources to concentration fields predicted by an infinite plane source and a single point source, all of the same equivalent strength. From this study we identified three regions: (1) a region close to the sources where the effects of adjacent sources are significant and individual source models should be used, (2) a region extending from a few meters to hundreds to thousands of meters downstream, where an equivalent source of infinite extent gives accurate results, and (3) a far-field region, where in an equivalent source of finite extent gives accurate results.

• Restorative Dentistry and Endodontics
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• v.18 no.1
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• pp.133-143
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• 1993

The aim of this study was to establish reproducible method for measurements of radiopacity and to investigate the level of radiopacity of root canal sealers. The experiments were performed in two parts. In the first part, densitometric readings were performed using an aluminum step wedge as a reference at variable voltages and exposure times. Then standard curves for the aluminum step wedge were compared to comprehend the effect of voltage and exposure time. In the second part, on the basis of these results, appropriate conditions for exposure were adopted for standardized measurements of radiopacity. Under standardized set of conditions, densitometric measurements of ten root canal sealers and one gutta-percha point were performed and the levels of radiopacity referable to an equivalent thickness of aluminum were compared. The following results were obtained : 1. At 50 and 60 kVp, increasing the exposure time caused a decrease in the slope of the standard curve for the aluminum step wedge. However, at 70 kVp increasing the exposure time causing a parallel shift of the standard curve to the right. 2. At constant exposure time, increasing the voltage caused a decrease in the slope of the standard curve. 3. The radiopacity of root canal sealers and a gutta-percha point varied between 2.43 mm Al and 9.20 mm Al equivalent. 4. All the root canal sealers had radiopacities more than dentin, and the radiopacity of the gutta-percha point was approximately 5 times as much as that of dentin in terms of equivalent thickness of aluminum. 5. The AH26 had radiopacity more than the gutta-percha point, and the radiopacities of ZOE, Vitapex, Canals, Kerr PCS, Nogenol were similar to that of the gutta-percha point, and Tubliseal, Apatite II, Apatite III, Silapex were less radiopaque than the gutta-percha point.

• Steel and Composite Structures
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• v.13 no.6
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• pp.501-519
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• 2012

As an alternative to current conventional force-based assessment methods, the energy-based seismic performance of a code-designed 20-storey high-rise steel building is evaluated in this paper. Using 3D nonlinear dynamic time-history method with consideration of additional material damping effect, the influences of different restoring force models and P-${\Delta}/{\delta}$ effects on energy components are investigated. By combining equivalent viscous damping and hysteretic damping ratios of the structure subjected to strong ground motions, a new damping model, which is amplitude-dependent, is discussed in detail. According to the analytical results, all energy components are affected to various extents by P-${\Delta}/{\delta}$ effects and a difference of less than 10% is observed; the energy values of the structure without consideration of P-${\Delta}/{\delta}$ effects are larger, while the restoring force models have a minor effect on seismic input energy with a difference of less than 5%, but they have a certain effect on both viscous damping energy and hysteretic energy with a difference of about 5~15%. The paper shows that the use of the hysteretic energy at its ultimate state as a seismic design parameter has more advantages than seismic input energy since it presents a more stable value. The total damping ratio of a structure consists of viscous damping ratio and hysteretic damping ratio and it is found that the equivalent viscous damping ratio is a constant for the structure, while the equivalent hysteretic damping ratio approximately increases linearly with structural response in elasto-plastic stage.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1876-1878
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• 2004

A systematic approach of measurement, modeling and analysis of grounding system impedance is presented. The measurement and analysis system of ground impedance is based on a computer aided technique. The ground impedances of the ground rod are considerably dependent on the frequency. The ground impedance is mainly resistive in the frequency range of 3-20 kHz. At higher frequencies, the reactive components of the ground impedances are no longer negligible and the inductance of the ground rod was found to be the core factor deciding the ground impedance. As a consequence, the equivalent circuit model based on the measured data was proposed, and the calculated results were in approximately agreement with the measured data.

• Journal of Korean Society of Transportation
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• v.6 no.1
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• pp.5-16
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• 1988

Development is given to an optimal network design method using continuous design variables. Modified Hooke-and-Jeeves algorithm is implemented in order to solve nonlinear programming problem which is approximately equivalent to the real network design problem with system efficiency crieteria and improvement cost as objective function. the method was tested for various forms of initial solution, and dimensions of initial step size of link improvements. At each searching point of evaluating the objective function, a link flow problem was solved with user equilibrium principles using the Frank-Wolfe algorithm. The results obtained are quite promising interms fo numbers of evaluation, and the speed of convergence. Suggestions are given to selections of efficient initial solution, initial step size and convergence criteria. An approximate method is also suggested for reducing computation time.

• Proceedings of the KIPE Conference
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• 1997.07a
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• pp.97-100
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• 1997

A new control method for the robust position control of a brushless DC(BLDC) motor using the asymptotically stable adaptive load torque observer is presented. A precision position control is obtained for the BLDC motor system approximately linearized using the field-orientation method. And the application of the load torque observer is published in [1] using fixed gain. However, the flux linkage is not exactly known for a load torque observer. Therefore, a model reference adaptive observer is considered to overcome the problem of the unknown parameter in this paper. And stability analysis is carried out using Liapunov stability theorem. As a result, asymptotically stable observer gain can be obtained without affecting the overall system response. The load disturbance detected by the asymptotically stable adaptive observer is compensated by feedforwarding the equivalent current having the fast response.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.1023-1030
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• 2002

From the early 1980s, the New Austrian Tunnelling Method (NATM) has been developed as a one of the standard tunneling method in Korea. Approximately 10 years ago, wet-mix shotcrete with sodium silicate accelerator (waterglass) was introduced and widely used to tunnel lining and underground support. However, this accelerator had some disadvantages due to the decrease of long-term strength compared to plain concrete (without accelerator) and low quality of the hardened shotcrete. In order to compensate for these disadvantages, recently developed alkali-free accelerator has been successfully demonstrated in numerous projects and applications as a new material to make tunnels more durable and safer. An experimental investigation was carried out in order to verify the strength behavior of wet-mix Steel Fiber Reinforced Shotcrete (SFRS) with alkali-free accelerator. Compressive strength, flexural strength and equivalent flexural strength were measured by testing specimens extracted from the shotcrete panels. From the results, wet-mix SFRS with alkali-free accelerator exhibited excellent strength improvement compared to the conventional shotcrete accelerator.