• Korean Journal of Optics and Photonics
• /
• v.7 no.4
• /
• pp.434-439
• /
• 1996

To investigate influence of the incident beams which have the truncated Gaussian amplitude and of the shapes of bump on read-out signal is an optical disc, and the point spread function on bump, the scalar diffraction theory is used in this paper. We consider the truncated Gaussian amplitudes which are $\sigma$=0, 0.5, 1.5, and 2.5, the height of bump which is given by $n{\Delta}_0={\lambda}/4$, and the phase height of bump which is then given by ${\Phi}_0={\pi}$. We also consider the shapes of the bump which are a rectangular shape, a frustoconical shape, and a conical shape. It is shown that as the truncation of incident beam reduces the radius of central spot on bump decreases, the maximum value of read-out signal increases, and that the size of bump decreases. From these results, we get better read-out signal and the reduced cross-talk in optical disc when the truncation of incident beam reduces. Therefore a laser beam having less truncated Gaussian amplitude may useful for an actual optical disc.

• Journal of the Korea Concrete Institute
• /
• v.16 no.1 s.79
• /
• pp.18-26
• /
• 2004

The cost of underground work is a dominant factor to determine the total construction fee. It is generally 2 ${\~}$ 2.5 times higher than that of above ground for building with the same height. 'A new precast prestressed framing plan for underground parking building' was suggested with the beam of the least depth - U-type beams. The depth of regular rectangular reinforced concrete beam which is currently used in the underground parking of apartments could be reduced up to 12 ${\~}$ 34cm/story due to the development of a U-beams from the optimum process. Two full scale prototype U-beams were tested in this study. It was found that the Wide U-beams in the test showed higher strength than calculated nominal and design, however need to provide temporary supports to meet the flexural moment of construction load at the simply supported state before the lopping concrete hardens.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.25 no.2
• /
• pp.175-182
• /
• 2012

In this paper we are concerned with the performance of structural stability of torsion in square cross section of a beam with holes. The critical load is defined as the smallest load at which the equilibrium of the structure fails to be stable as the load is slowly increased from zero. The beams subjected to torsion are frequently encountered in general structures and these forces influence to the stability of structure. The boundary element method is found to be very efficient and accurate for the analysis of torsion problems including complex boundary conditions with respect to its simplicity and generality. In this paper, it is required to derive the boundary element formulation for torsion problem and integrate directly on the discrete boundary. To investigate the validity of the developed computer program, three distinctly solid cross-sections which are elliptical, rectangular and triangular one are analyzed, and comparisons are made with analytical approaches where these can also be used.

• Journal of the Korea Concrete Institute
• /
• v.14 no.4
• /
• pp.492-502
• /
• 2002

The dapped ends of the Gerber's beam were designed by PCI(Prestressed Concrete Institute) and CPCI(Canadian Prestressed Concrete Institute) methods. The depths of nibs with precast and topping concrete, which were halves of the total beam depth, were 77 cm md 18.2 cm, respectably. Shear tests were performed on four full scale beam ends. All specimens designed by PCI and CPCI methods showed crackings at the re-entrant coner of dap before the 32 ％ of full service design loading, and failed at the load level higher than their design strength but less than their calculated nominal strength. The specimens with increased hanger reinforcement show more effective in development of initial crackings, more ductile in failure with distributed crackings, and failed in higher strength than those of PCI requirement. The tested specimens designed by CPCI method were more ductile in failure than those of the PCI methods.

• Current Optics and Photonics
• /
• v.1 no.1
• /
• pp.23-28
• /
• 2017

The laser has been regarded as the potential illumination source for the next generation of projectors. However, currently the major issues in applying the laser as an illumination source for projectors are beam shaping and laser speckle. We present a compact solution for both issues by using a vibrating diffractive optical element (DOE). The DOE is designed and fabricated, and it successfully transforms the circular Gaussian laser beam to a low speckle contrast uniform rectangular pattern. Under a vibration frequency of 150 Hz and amplitude of $200{\mu}m$, the speckle contrast value is reduced from 67.67% to 13.78%, and the ANSI uniformity is improved from 24.36% to 85.54%. The experimental results demonstrate the feasibility and potential of the proposed scheme, and the proposed method is a feasible approach to the miniaturization of laser projection display illumination systems.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.2A
• /
• pp.289-295
• /
• 2008

The purpose of this study was to examine the flexural behavior of reinforced concrete beams strengthened with CFRP strips. A total of 12 rectangular beams were tested. Test variables in this study were the shapes, bonded length and the number of longitudinal layers of CFRP strips. From the experimental study, flexural capacity of the beams strengthened with CFRP strips significantly increased compared to the reinforced concrete beam without a CFRP strip. Maximum increase of ultimate strength was found about 120% more than the control beam. In this test, most of the strengthened beams failed suddenly due to the debonding of CFRP strips. It is also observed that the debonding of the strip was initiated in the flexural zone of the beam and propagated rapidly to the end of the beam. The ultimate tensile strains of CFRP strips in this test were occurred at the level of 36% of rupture tensile strength of the CFRP strip, and an analytical approach to compute the flexural strength of reinforced beams strengthened with CFRP strips based on the effective stresses was conducted.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.16 no.2
• /
• pp.10-18
• /
• 2012

Most of studies on existing strengthening methods were mainly on increase of stiffness and strength of shear strengthening to rectangular beam. As concrete of beam and slab is poured simultaneously on the characteristics of construction in reinforced concrete beam-slab structure, adjacent slab uniformed after hardening has T-shaped beam cross section which makes the flange of beam, enhances the stiffness of the beam and widens the area supporting compressive strength, but available data of flexural behavior of T-shaped beam are lacking. In this research the T-shaped beams would be made, then the reinforced effects and structural properties can be estimated according to the kinds of reinforced materials and reinforced position. The conclusions are shown as below. To sum up the experimental results, The specimen which was reinforce by CB embedded inside of concrete indicated excellent resistive behavior, internal force and stiffness when it was destroyed. The steel plate reinforced specimen of stiffness and internal force were increase but it expressed lower reinforce effects because of lowering anchored force between concrete. Fiber sheet strengthening showed superior effects but the interfacial delamination was found due to the lack of anchored force in destruction. So the measure is needed now.

• Solar Energy
• /
• v.14 no.2
• /
• pp.75-90
• /
• 1994

Thermal energy transport in a two-dimensional horizontal and vertical channel with an isothermal rectangular beam attached to one adiabatic wall is investigated from the numerical solution of Navier-Stokes and energy equations. The solutions have been obtained for dimensionless aspect equations. The solutions have been obtained for dimensionless aspect ratios of beam, H/B=$0.25{sim}4$, Reynolds numbers, Re=$50{\sim}500$ and Grashof numbers, Gr=$0{\sim}5{\times}10^4$. The mean Nusselt number, $\overline{Nu}$ for horizontal and vertical channels shows same value at Gr=0 and increases as Gr increases and decreases as H/B increases at Re=100. $\overline{Nu}$ of vertical channel shows higher in $0.25{\leq}H/B<1.1$ and lower in $1.1{\leq}H/B{\leq}4.0$ than that of horizontal channel at $Gr=10^4$, Re=100. $\overline{Nu}$ of vertical channel shows higher in $0.25{\leq}H/B<1.1$ and lower in $1.1{\leq}H/B=1.0$ than that of horizontal channel at Re=100, $0<Gr{\leq}5{\times}10^4$. A comparison between the experimental and numerical results shows good agreement.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.13 no.11
• /
• pp.5447-5451
• /
• 2012

This paper presents a pattern-switchable microstrip patch antenna with loop structure. The loop structure for switchable radiation beam pattern is connected with feeding line of the microstrip patch antenna. As changing switch on/off state, the radiation beam pattern can be changed. The target frequency is 2.4 GHz and maximum radiation gain is 3.2dBi. The proposed antenna is useful for diversity antenna and smart antenna in modern wireless communication including MIMO (Multi-Input Multi-Output) and WLAN system. The sizes of the rectangular patch and the ground plane are $28mm{\times}28mm$ and $40mm{\times}50mm$, respectively. The simulation and experimental results show that the antenna radiation pattern can be changed with switch on/off configuration.

• Structural Engineering and Mechanics
• /
• v.73 no.2
• /
• pp.167-179
• /
• 2020

This study provides a simplified method for the evaluation of shear lag stress in rectangular box T-joints. The occurrence of shear lag phenomenon in the box T-joint generates stress concentration localized at both web-flange junctions of the beam, which leads to cracking or failure in the weld region of the joint. To prevent such critical circumstance, peak stress at the weld region is required to be checked during a preliminary design stage. In this paper, the shear lag stresses in the T-joints were evaluated using least-work solution in which the longitudinal displacements of the beam flange and web were presumed. The evaluation process considered particularly the effect of column flange flexibility, which was represented by an axial spring model, on the shear lag stress distribution. A simplified method for stress evaluation was provided to avoid solving complex mathematical problems using a stress modification factor β_s from a parametric study. The results showed that the proposed method was valid for predicting the shear lag stress in the box T-joints manually, as well compared with finite element results. The results are further summarized, discussed, and clarified that more flexible column flange caused higher stress concentration.