• Fibers and Polymers
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• v.3 no.1
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• pp.8-13
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• 2002

The effect of block sequence on the self-assembly of ABC-type triblock copolymers in the ordered state is investigated using an isothermal-isobaric molecular dynamics simulation. The block sequence has an important effect ,on the ]norphology of ABC triblock copolymers. Different morphologies are observed depending on the block sequence as well as the block composition. The triblock copolymers with the volume fraction of 1 : 1 : 1 ($f_A$=$f_B$=$f_C$= 0.33) show the three phase and four layered lamellar structures irrespective of the block sequence. The $A_{32}$$B_{16}$$C_{32}$triblock copolymer with $f_B$=0.2 shows a morphology In which cylinders of midblock B are formed at the interface between A and C lamellae, whereas the morphology of triblock copolymer $B_{16}$$C_{32}$ $A_{32}$ and $C_{32}$ $A_{32}$ $B_{16}$ show a cylindrical core-shell structure and a lamellar type morphology, respectively. The $A_{20}$$B_{40}$$C_{20}$the triblock copolymer with the block B as a major component shows a tricontinuous structure, whereas both $B_{40}$$C_{20}$$A_{20}$ and $C_{20}$$A_{20}$$B_{40}$ triblock coolymers exhibit the lamellar structures. When the block B has larger volrome fraction with $f_B$=0.75, the matrix is composed of block B, and other two blocks A and C form spherical domains.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.27 no.2
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• pp.234-242
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• 2017

This study investigates vibro-acoustic characteristics of a short, thick cylinder containing a slot given a pined-free boundaries. Using the finite element analysis results, structural modes of the asymmetric cylinder (with a slot) are expressed as the linear combinations of modes of the symmetric cylinder made of same material with identical geometry except the slot. Based on synthesized modal vibrations, acoustic modes of the asymmetric cylinder are obtained with two approaches, i.e., Rayleigh integral calculation and modal expansion of the acoustic modes of the symmetric cylinder. Also, acoustic powers, max. sound pressure and directivity pattern are obtained from acoustic modes and verified with the boundary element analyses. Based on these results, the accuracy of proposed approaches in calculating the vibro-acoustic properties of a short, thick, asymmetric cylinder has been confirmed. The procedure can be applied to the similar cylinders with other boundaries or asymmetric properties. Also, attenuation of vibration and/or sound radiation of the cylinder type practical components can be studied using these approaches.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.12
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• pp.1-8
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• 2005

A parametric study has been accomplished to figure out the effects of the elliptic cylinder thickness, angle of attack, and Reynolds number on the lift and drag forces exerted on the elliptic cylinder. A two-dimensional incompressible Navier-Stokes flow solver is developed using SIMPLER method to analyze the unsteady viscous flow over elliptic cylinder. Thickness-to-chord ratios of 0.2, 0.4, and 0.6 elliptic cylinders are simulated at different Reynolds numbers of 400 and 600, and angles of attack of $10^{\circ}$, $20^{\circ}$, and $30^{\circ}$. Through this study, it is observed that the elliptic cylinder thickness, angle of attack, and Reynolds number affect significantly not only the time-mean values and the amplitudes of the drag and lift forces but also the frequencies of the force oscillations.

• Bulletin of the Society of Naval Architects of Korea
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• v.22 no.3
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• pp.9-18
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• 1985

The numerical calculation for solving boundary-value problem related to potential flows with a free surface is carried out by application of the localized finite element method. Only forced motion of 2-D body in infinitely deep fluid is considered, although this schemes is equally applicable to any first order time-harmonic problems of similar nature. The infinite domain of the fluid is separated into the inner flow field and the outer flow field with common inter-surface boundary. The finite element method is applied to obtain the solution in the inner flow field and the Green functions are utilized to represent the solution in the outer flow field. At the inter-surface boundary, the continuity of the value of potential and the normal derivative of the potential(i.e. matching condition) is conserved. The present method has better computational efficiency than the previous LFEM and the integral equation method of Frank. This enhanced computational efficiency is presumably due to the fact that the present method gives a symmetric coefficient matrix and requires less computational time in calculating the influence coefficient matrix of Green function than the integral equation method. And the irregular frequency desen't exist because the uniqueness of the solution is assured by the such that the exact free surface condition is satisfied on the boundary of the localized finite element region(i.e. inner region). As an example of the above method, the hydrodynamic forces for the circular cylinder and the rectangular cylinders are calculated. In the computed results, the small number of singularity distribution segments($3{\sim}6$) give good result relative to Ursell's and Vugts'.

• Journal of Korean Society on Water Environment
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• v.28 no.2
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• pp.232-237
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• 2012

Total suspended solids (TSS), settleable suspended solids (SSS) and nonsettleable suspended solids (NSSS) were compared in streams and lakes during rain events. Samples were collected in Lake Soyang and nine agricultural streams during storm events over two years. To measure NSSS, samples were settled in 1 L cylinders for one hour and then 50% of the total sample volume was taken from the center of the cylinder. The SSS/TSS ratio in streams (0.50) was higher than in Lake Soyang (0.20). The ratio of TSS to turbidity decreased from 1.21 in the inflowing river to 0.69 in the reservoir outlet. Turbidity and NSSS showed higher correlation ($r^2$=0.82) compared with the correlation between turbidity and TSS ($r^2$=0.66). Median particle size decreased from $11.4\;{\mu}m$ in the inflowing river to $4.2\;{\mu}m$ in the lake outlet. The results indicate that only fine particles of less than $5{\sim}10\;{\mu}m$ can be transported downstream of the lake. Because fast-flowing water in streams includes not only fine particles but also coarse particles, an overestimation of suspended sediment concentration results if only TSS is measured. Consequently, TSS and NSSS should be measured separately to evaluate the effect of suspend sediment loadings of turbid streams on aquatic habitat during the monsoon season.

• The Journal of Advanced Prosthodontics
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• v.10 no.3
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• pp.205-210
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• 2018

PURPOSE. The purpose of this study was to evaluate the efficiency of a gas-phase fluorination method under different fluorination periods through using two resin cements. MATERIALS AND METHODS. 84 zirconia specimens in dimensions of $5mm{\times}5mm{\times}2mm$ were prepared and surface treated with $50{\mu}m$ aluminum oxide particles or gas phase fluorination for 2 min, 5 min, or 10 min. One specimen in each group was surface analyzed under scanning electron microscope. The remaining specimens were bonded to composite cylinders in dimensions of 2 mm diameter and 3 mm high with Panavia SA Plus or Variolink N. Then, the specimens were stored in $37^{\circ}C$ distilled water for 24 hours and shear bond strength test was applied at a speed of 1 mm/min. RESULTS. The highest shear bond strength values were observed in the samples fluorinated for 5 minutes and cemented with Panavia SA Plus. Variolink N did not elicit any statistical differences between surface treatments. Panavia SA Plus resin cement and Variolink N resin cements featured statistically significant difference in shear bond strength values only in the case of 5 minutes of fluorination treatment. CONCLUSION. According to the results of this study, application of 5 minutes of fluorination with 10-methacryloyloxydecyl dihydrogen phosphate monomer (MDP) containing Panavia SA Plus resin cement increased the resin bond strength of zirconia. Fluorination of the zirconia surface using conventional resin cement, Variolink N, did not lead to an increase in bond strength.

• The Journal of Advanced Prosthodontics
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• v.12 no.5
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• pp.291-298
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• 2020

PURPOSE. The aim of this study is to evaluate the influence of repeated surface treatments on wettability and surface roughness for zirconia surface and bond strength of zirconia-based ceramics to resin cement. MATERIALS AND METHODS. Seventy blocks (10 × 10 × 3 mm) of zirconia-based ceramics were fabricated and divided into two groups according to the surface treatments: (A) 110 ㎛ Al₂O₃ airborne-particle abrasion and (R) 110 ㎛ silica modified Al₂O₃ airborne-particle abrasion. At stage 2, each group was subdivided into 5 groups according to the surface retreatments: (a) 110 ㎛ Al₂O₃ airborne-particle abrasion, (r) 110 ㎛ silica modified Al₂O₃ airborne-particle abrasion, (D) diamond bur, (Da) diamond bur + 110 ㎛ Al₂O₃ airborne-particle abrasion, and (Dr) diamond bur + 110 ㎛ silica modified Al₂O₃ airborne-particle abrasion. Cylinders of self-adhesive resin cement were cemented onto each treated ceramic surface and subjected to micro-shear bond strength test. Additional specimens were prepared for roughness and wettability analyses. The data were subjected to t-test and One-way ANOVA followed by Tukey's post hoc test (α=.05). RESULTS. At stage 1, group R presented higher bond strength values than group A (P=.000). There was a statistically significant increase of bond strength at stage 2 for group A (P=.003). The diamond bur influenced the surface roughness, increasing the values (P=.023). Group R provided better wettability. Regardless of the applied surface treatment, most of failures were adhesive. CONCLUSION. The combination of application and reapplication of Rocatec Plus showed the best results of bond strength. Surface retreatment and recementation might be an indicated clinical strategy.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.5D
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• pp.705-717
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• 2011

The number of horizontal tower cranes, major hoisting machineries for lifting approximately 50% of entire materials in construction projects, is rapidly increasing, but a number of accidents related to the tower cranes are being continuously occurred in construction sites as well. In particular, telescoping works in the horizontal tower cranes have showed the greatest safety concerns such as falls and collapses. It is due to the fact that tasks inserting a new mast in the space made after raising telescoping cage by fluid pressure and ascending it to the required height in the telescoping works include a series of dangerous factors in safety aspects, and might cause very serious and unexpected accidents in construction sites. The primary objective of this research is to propose two conceptual models for automating the telescoping work in horizontal tower crane and conduct their technical feasibility analyses. In this study, a design concept, a position control system using hydraulic cylinders is suggested as a better alternative for automating the telescoping work. Its potential safety improvement rate compared to the conventional method is also analyzed and presented in this study.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.9
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• pp.341-347
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• 2018

The purpose of this study is to develop a new type of hybrid artificial reef that can solve the problems of construction, installation and operation of existing concrete type and steel type artificial reef, and to evaluate basic structural performance through static loading test. For this purpose, we evaluated the strengths and weaknesses of concrete type and steel type artificial reef in literature, and developed a new type of hybrid artificial reef which can effectively overcome the problems of each artificial reefs while maintaining the advantages of two artificial reefs as an alternative respectively. In order to evaluate the merits of the proposed hybrid artificial reef, it was confirmed that the possibility of securing the convenience of the proposed hybrid artificial reef in the field and the possibility of securing the desired advantages were confirmed. Also, the static loading test was performed to evaluate the basic structural performance of the artificial reef. Through the above study, it was confirmed that the developed hybrid artificial reef exhibited proper structural performance while securing easiness of making and assemble.mm) can be predicted to have a low value up to 60% of the strength of cylinders without reinforcement.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2003.11a
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• pp.124-129
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• 2003

In case that the mixing weight ratio of waste form between boric acid and paraffin was 3.3/l, which had been adopted in the concentrate waste drying system (CWDS) of domestic nuclear power plants. Using several specimens with different diameters and heights, 50/100mm specimens. compressive strength were measured. The experiment result showed that the small diameter specimens of compressive strength are increased more than large diameter specimens. (d=50＞75＞100mm) The average compressive strength of specimens showed that the range from 22.43 $\kg/textrm{cm}^2$ to 38.57$\kg/textrm{cm}^2$ (NRC standard$\geq$4.1 $\kg/textrm{cm}^2$). NRC standard is recommended that the compressive strength test specimens be right circular cylinders, 2 to 3 inches in diameter, with a height-to-diameter(H/D) ratio of approximately two. and compressive strength were increased more than large loading rate. As test result, this conditions are a good agreement, and estimated.