• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.7
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• pp.578-583
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• 2011

We report on the design of a holographic homogenizer composed of a periodic hologram and a condensing lens. If the hologram is periodic, the homogenizer is free from the alignment error of the incident laser beam. Holographic homogenizer also has an advantage of the flexibility in the size of the target beam. We calculated theoretically the Fraunhofer diffracted wave function when a rectangular laser beam is incident on a periodic hologram. The diffracted wave is the sum of sinc functions at regular distance. The width of each sinc function depends on the size of the incident laser beam and the distance between the sinc functions depends on the period of the hologram. We calculated numerically the diffracted light intensity for various ratios of the size of the incident laser beam to the period of the hologram. The results show that it is possible to make the diffracted beam uniform at a certain value of the ratio. The uniformity is high at the central part of the target area and low near the edge. The more sinc functions are included in the target area, the larger portion of the area becomes uniform and the higher is the uniformity at the central part. Therefore, we can make efficient homogenizer if we design a hologram so that the maximum number of the diffracted beams may be included in the target area.

• Steel and Composite Structures
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• v.15 no.6
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• pp.585-603
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• 2013

Generally the required strength and stiffness of an I-shaped beam to the box-shaped column connection is achieved if continuity plates are welded to the column flanges from all sides. However, welding the forth edge of a continuity plate to the column flange may not be easily done and is normally accompanied by remarkable difficulties. This study was aimed to propose an alternative for box columns with continuity plates to diminish such problems. For this purpose a double-web I-shaped column was proposed. In this case the strength and rotational stiffness of the connection was provided by nearing the column webs to each other. Finite element studies on about 120 beam-column connections showed that the optimum proportion of the distance between two column webs and the width of the column flange (parameter ${\beta}$) was a function of the ratio of the beam flange width to the column flange width (parameter ${\alpha}$). Hence, based on the finite element results, an equation was proposed to estimate the optimum value of parameter ${\beta}$ in terms of parameter ${\alpha}$ to achieve the highest connection performance. Results also showed that the strength and ductility of post-Northridge connections of such columns are in average 12.5 % and 54% respectively higher than those of box-shaped columns with ordinary continuity plates. Therefore, a double-web I-shaped column of optimum arrangement might be a proper replacement for a box column with continuity plates when beams are rigidly attached to it.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1311-1320
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• 2000

In this study, shape memory alloy(SMA) wires and piezoceramic actuators(PZT's) are employed in order to generate higher modes on the beam deformations. Compressive force is generated and applied to the beam by the pre-strained SMA wires attached at both ends of the beam. PZT's apply concentrated moments to several locations on the beam. Combinations of the compressive force and concentrated moments are investigated in order to understand the higher-mode deformation of beams. The first desired mode shape is obtained by controlling the temperature of the SMA wires. The first and third mode shapes are performed experimentally by heating SMA wires up to phase transformation temperature. The adaptive wing is defined as a wing whose shape parameters such as the camber, wing twist and thickness can be varied in order to change the wing shape for various flight conditions. In this research, control of the camber has been studied. The wing model consists of three plates and many ribs. Two of the plates are placed parallel to each other and they are clamped at one edge. Third plate connects the other edges of the parallel plates together. Each rib is made of SMA wire and connected to the parallel plates. It generates concentrated force and applies to the plates in oblique directions. The PZT's are bonded onto the plates and exert concentrated moments upon the plate at several locations. The object of this research is to generate various shape of wing by combining the concentrated forces and moments.

• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.3
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• pp.54-65
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• 1997

To quantify the LII signals from soot particle of flames in diesel engine cylinder, a new method has been proposed for correcting LII signal attenuated by soot particles between the measuring point and the detector. It has been verified by an experiment on a laminar jet ethylene-air diffusion flame. Being proportional to the attenuation, the ratio of LII signal at two different detection wavelengths can be used to correct the measured LIIsignal and obtain the unattenuated LII signal, from which the soot volume fraction in the flame can be estimated. Both the 1064-nm and frequency-doubled 532-nm beams from the Nd : YAG laser are used. Single-shot, one-dimensional(1-D) line images are recorded on the intensified CCD camera, with the rectangular-profile laser beam using 1-mm-diameter pinhole. Two broadband optical interference filters having the center wavelengths of 647 nm and 400 nm respectively and a bandwidth of 10 nm are used. This two-wavelength correction has been applied to the ethylene-air coannular laminar diffusion flame, previously studied on soot formation by the laser extinction method in this laboratory. The results by the LII measurement technique and the conventional laser extinction method at the height of 40 nm above the jet exit agreed well with each other except around outside of the peaks of soot concentration, where the soot concentration was relatively high and resulting attenuation of the LII signal was large. The radial profile shape of soot concentration was not changed a lot, but the absolute value of the soot volume fraction around outside edge changed from 4ppm to 6.5 ppm at r=2.8mm after correction. This means that the attenuation of LII signal was approximately 40% at this point, which is higher than the average attenuation rate of this flame, 10~15%.

• Steel and Composite Structures
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• v.22 no.6
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• pp.1417-1443
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• 2016

Cellular and castellated steel beams are used to obtain higher stiffness and bending capacity using the same weight of steel. In addition, the beam openings may be used as a pass for different mechanical fixtures such as ducts and pipes. The aim of this study is to investigate the effect of different parameters on both elastic and inelastic critical buckling stresses of steel web plates with openings. These parameters are plate aspect ratio; opening shape (circular or rectangular); end distance to the first opening; opening spacing; opening size; plate slenderness ratio; steel grade; and initial web imperfection. The web/flange interaction has been simplified by web edge restraints representing simply supported boundary conditions. A numerical parametric study has been performed through linear and nonlinear finite element (FE) models, where the FE results have been verified against both experimental and numerical results in the literature. The web plates are subject to in-plane linearly varying compression with different loading patterns, ranging from uniform compression to pure bending. A buckling stress modification factor (${\beta}$-factor) has been introduced as a ratio of buckling stress of web plate with openings to buckling stress of the corresponding solid web plate. The variation of ${\beta}$-factor against the aforementioned parameters has been reported. Furthermore, the critical plate slenderness ratio separating elastic buckling and yielding has been identified and discussed for two steel grades of DIN-17100, namely: ST-37/2 and ST-52/3. The FE results revealed that the minimum ${\beta}$-factor is 0.9 for web plates under uniform compression and 0.7 for those under both compression and tension.

• Journal of Radiation Protection and Research
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• v.27 no.1
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• pp.1-10
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• 2002

High energy photon beams from medical linear accelerators produce large scattered radiation by various components of the treatment head, collimator and walls or objects in the treatment room including the patient. These scattered radiation do not provide therapeutic dose and are considered a hazard from the radiation safety perspective. Scattered dose of therapeutic high energy radiation beams are contributed significant unwanted dose to the patient. ICRP take the position that a dose of 500mGy may cause abortion at any stage of pregnancy and that radiation detriment to the fetus includes risk of mental retardation with a possible threshold in the dose response relationship around 100 mGy for the gestational period. The ICRP principle of as low as reasonably achievable (ALARA) was recommended for protection of occupation upon the linear no-threshold dose response hypothesis for cancer induction. We suggest this ALARA principle be applied to the fetus and testicle in therapeutic treatment. Radiation dose outside a photon treatment filed is mostly due to scattered photons. This scattered dose is a function of the distance from the beam edge, treatment geometry, primary photon energy, and depth in the patient. The need for effective shielding of the fetus and testicle is reinforced when young patients ate treated with external beam radiation therapy and then shielding designed to reduce the scattered photon dose to normal organs have to considered. Irradiation was performed in phantom using high energy photon beams produced by a Varian 2100C/D medical linear accelerator (Varian Oncology Systems, Palo Alto, CA) located at the Yonsei Cancer Center. The composite phantom used was comprised of a commercially available anthropomorphic Rando phantom (Phantom Laboratory Inc., Salem, YN) and a rectangular solid polystyrene phantom of dimensions $30cm{\times}30cm{\times}20cm$. the anthropomorphic Rando phantom represents an average man made from tissue equivalent materials that is transected into transverse 36 slices of 2.5cm thickness. Photon dose was measured using a Capintec PR-06C ionization chamber with Capintec 192 electrometer (Capintec Inc., Ramsey, NJ), TLD( VICTOREEN 5000. LiF) and film dosimetry V-Omat, Kodak). In case of fetus, the dosimeter was placed at a depth of loom in this phantom at 100cm source to axis distance and located centrally 15cm from the inferior edge of the $30cm{\times}30cm^2$ x-ray beam irradiating the Rando phantom chest wall. A acryl bridge of size $40cm{\times}40cm^2$ and a clear space of about 20 cm was fabricated and placed on top of the rectangular polystyrene phantom representing the abdomen of the patient. The leaf pot for testicle shielding was made as various shape, sizes, thickness and supporting stand. The scattered photon with and without shielding were measured at the representative position of the fetus and testicle. Measurement of radiation scattered dose outside fields and critical organs, like fetus position and testicle region, from chest or pelvic irradiation by large fie]d of high energy radiation beam was performed using an ionization chamber and film dosimetry. The scattered doses outside field were measured 5 - 10% of maximum doses in fields and exponentially decrease from field margins. The scattered photon dose received the fetus and testicle from thorax field irradiation was measured about 1 mGy/Gy of photon treatment dose. Shielding construction to reduce this scattered dose was investigated using lead sheet and blocks. Lead pot shield for testicle reduced the scatter dose under 10 mGy when photon beam of 60 Gy was irradiated in abdomen region. The scattered photon dose is reduced when the lead shield was used while the no significant reduction of scattered photon dose was observed and 2-3 mm lead sheets refuted the skin dose under 80% and almost electron contamination. The results indicate that it was possible to improve shielding to reduce scattered photon for fetus and testicle when a young patients were treated with a high energy photon beam.

• Journal of radiological science and technology
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• v.21 no.2
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• pp.36-42
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• 1998

Treatment of a large diseased area with electron often requires the use of two or more adjoining fields. In such cases, not only electron beam divergence and lateral scattering but also fields overlapping and separation may lead to significant dose inhomogeneities(${\pm}20%$) at the region of junction of fields. In this study, we made Acrylic Electron Wedges to improve dose inhomogeneities(${\pm}5%$) in these junction areas and to apply it to clinical practices. All measurements were made using 6, 9, 12, 16, 20 MeV Electron beams from a linear accelerator for a $10{\times}10\;cm$ field at 100cm of SSD. Adding a 1 mm sheet of acryl gradually from 1 mm to 15 mm acquires central axis depth dose beam profile and isodose curves in water phantom. As a result, for all energies, the practical range was reduced by approximately the same distance according to the acryl insert, e.g. a 1 mm thick acryl insert reduces the practical range by approximately 1 mm. For every mm thickness of acryl inserted, the beam energy was reduced to approximately 0.2 MeV. These effects were almost Independent of beam energy and field size. The use of Acrylic Electron Wedges produced a small increase(less than 3%) in the surface dose and a small increase(less than 1%) in X-ray contamination. For acryl inserts, thickness of 3 mm or greater, the penumbra width increased nearly linear for all energies and isodose curves near the beam edge were nearly parallel with the incident beam direction at the point of penumbra width($35\;mm{\sim}40\;mm$). We decide heel thickness and angle of the wedge at this point. These data provide the information necessary to design Acrylic Electron Wedge which can be used to improve dose uniformity at electron field junctions and it will be effectively applied to clinical practices.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.3
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• pp.248-256
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• 2009

EB(Eigen-Beamforming) has widely been applied to MIMO(Multiple-Input Multiple-Output) systems to form beams which maximize the effective signal-to-interference plus noise ratio(SINR) of the receiver using the singular value decomposition(SVD) of the MIMO channel. However, the signal detection performance for the mobile station near the cell boundary is severely degraded and the transmission efficiency decreases due to the influence of the interference signal from the adjacent cells. In this paper, we propose an adaptive interference mitigation method for the EB transmission, and evaluate the reception performance. In particular, a reception strategy which adaptively utilizes optimal combining(OC) and minimum mean-squared error for Intercell spatial demultiplexing(MMSE-lSD) is proposed, and the reception performance is investigated in terms of the effective SINR and system capacity. For the average system capacity, the proposed adaptive reception demonstrates the performance enhancement compared to the conventional EB reception using the receiver beamforming vector, and up to 2 bps/Hz performance gain is achieved for mobile station located at the cell edge.

• The Journal of Korean Society for Radiation Therapy
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• v.10 no.1
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• pp.60-68
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• 1998

Treatment of a large diseased area with electron often requires the use of two or more adjoining fields. In such cases, not only electron beam divergence and lateral scattering but also fields overlapping and separation may lead to significant dose inhomogeneities(${\pm}20\%$) at the field junction area. In this study, we made Acrylic Electron Wedges to improve dose homogeneities(${\pm}5\%$) in these junction areas and considered application it to clinical practices. All measurements were made using 6, 9, 12, 16, 20MeV Electron beams from a linear accelerator for a $10{\times}10cm$ field at 100cm SSD. Adding a 1 mm sheet of acryl gradually from 1 mm to 15 mm, We acquired central axis depth dose beam profile and isodose curves in water phantom. As a result, for all energies, the practical range was reduced by approximately the same distance as the thickness of the acryl insert, e.g. a 1 mm thick acryl insert reduce the practical range by approximately 1 mm. For every mm thickness of acryl inserted, the beam energy was reduced by approximately 0.2MeV. These effects were almost independent of beam energy and field size. The use of Acrylic Electron Wedges produced a small increase $(less\;than\;3\%)\;in\;the\;surface\;dose\;and\;a\;small\;Increase(less\;than\;1\%)$ in X-ray contamination. For acryl inserts, thickness of 3 mm or greater, the penumbra width increased nearly linear for all energies and isodose curves near the beam edge were nearly parallel with the incident beam direction, and penumbra width was $35\;mm{\sim}40\;mm$. We decide heel thickness and angle of the wedge at this point. These data provide the information necessary to design Acrylic Electron Wedge which can be use to improve dose uniformity at electron field junctions and it will be effectively applicated in clinical practices.

• Progress in Medical Physics
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• v.21 no.2
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• pp.232-237
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• 2010

The shielding materials designed for replacement of lead equivalent materials for lighter apron than that of lead in diagnostic photon beams. The absorption characteristics of elements were applied to investigate the lead free material for design the shielding materials through the 50 kVp to 110 kVp x-ray energy in interval of 20 kVp respectively. The idea focused to the effect of K-edge absorption of variable elements excluding the lead material for weight reduction. The designed shielding materials composited of Tin 34.1%, Antimon 33.8% and Iodine 26.8% and Polyisoprene 5.3% gram weight account for 84 percent of weight of lead equivalent of 0.5 mm thickness. The size of lead-free shielder was $200{\times}200{\times}1.5\;mm^3$ and $3.2\;g/cm^3$ of density which is equivalent to 0.42 mm of Pb. The lead equivalent of 0.5 mm thickness generally used for shielding apron of diagnostic X rays which is transmitted 0.1% for 50 kVp, 0.9% for 70 kVp and 3.2% for 90 kVp and 4.8% for 110 kVp in experimental measurements. The experiment of transmittance for lead-free shielder has showed 0.3% for 50 kVp, 0.6% for 70 kVp, 2.0% for 90 kVp and 4.2% for 110 kVp within ${\pm}0.1%$. respectively. Using the attenuation coefficient of experiments for 0.5 mm Pb equivalent of lead-free materials showed 0.1%. 0.3%, 1.0% and 2.4%, respectively. Furthermore, the transmittance of lead-free shielder for scatter rays has showed the 2.4% in operation energy of 50 kVp and 5.9% in energy of 110 kVp against 2.4% and 5.1% for standard lead thickness within ${\pm}0.2%$ discrepancy, respectively. In this experiment shows the designed lead-free shielder is very effective for reduction the apron weight in diagnostic radiation fields.