• 한국가시화정보학회:학술대회논문집
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• 2004.04a
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• pp.1-7
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• 2004

When a vortex diffracts upon encountering a vortex, many strong and weak waves are produced in the course of interaction. They are the cause of shock wave attenuation and noise production. This phenomenon is fundamental to understanding the more complex supersonic turbulent Jet noise. In this paper we have reviewed the research on shock-vortex interaction we have carried on last seven years. We have computationally investigated the parameter effect. When a shock is strong, shock diffraction pattern becomes complex since the slip lines from the triple points on Mach stem curl into the vortex, causing an entropy layer. When the vortex is unstable, vortexlets are brought about each of which make shock diffraction of a reduced intensity. Strong vortex produces quadrupole noise as it impinges into a vortex. Elementary interaction models such as shock splitting, shock reflection, and shock penetration are presented based on shock tube experiment. These models are also verified by computational approach. They easily explain production and propagation of the aforementioned quadrupole noise, Diverging acoustics are explained in terms of shock-vortexlet interactions for which a computational model Is constructed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.418-422
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• 2005

In this study, the die design and die series on the surface residual stress of cold drawn eutectoid steel wire has been investigated. Test pieces were fabricated using die series with different mean and final reduction ratio. Surface residual stresses in the axial direction were measured by X-ray diffraction, Broker's 2-dimensional GADDS system. Results were compared with stress profiles which were calculated by 3D and 2D finite element simulation, Hibbitt's ABAQUS 6.4 program in Finite Element Analysis. By means of FEA method, optimal die shape considering delta-parameter were induced and applied in order to determine die sequence designs. Balance of the drawing stresses was also introduced to optimize die sequence.

• Transactions of Materials Processing
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• v.15 no.2 s.83
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• pp.153-157
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• 2006

In this study, the die design and die series on the surface residual stress of cold drawn eutectoid steel wire have been investigated. Test pieces were fabricated using die series with different mean and final reduction ratios. Surface residual stresses in the axial direction were measured by X-ray diffraction, Bruker's 2-dimensional GADDS system. The results were compared with stress profiles that were calculated by 3D and 2D finite element simulations, ABAQUS 6.4 program in finite element analysis(FEA). By means of the FEA method, optimal die shape considering delta-parameter were induced and applied in order to determine die sequence designs. Balance of the drawing stresses was also introduced to optimize die sequence.

• Korean Journal of Optics and Photonics
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• v.8 no.1
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• pp.73-79
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• 1997

We analyzed the variation of the focus error signal with the effect of land and groove, wavefront error, and optical system parameter variation for the knife-edge and astigmatism methods on the Land/Groove recordable optical disc, using a numerical simulation method. We verified causes of the zero-cross-shift that took place by the effect of land and groove by analyzing the diffraction beam including defocus wavefront errors. We also found that the sensitivty of the focus error signal was reduced by the effect of land and groove in the astigmatism method, as in the analysis of the focus error signal with the each order of the diffraction beam.

• Proceedings of the Korea Crystallographic Association Conference
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• 2002.11a
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• pp.17-17
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• 2002

Time-of-flight impact collision ion scattering spectroscopy (TOF-ICISS) was applied to study the geometrical structure of the epitaxially grown BaTiO₃ layers on the MgO(100) surface. Hetero-epitaxial BaTiO₃ layers can be deposited by the following steps: first thermal evaporation of titanium onto the MgO(100) surface in the atmosphere of oxygen at 400℃, secondly thermal evaporation of barium in the same manner, and finally annealing at 800℃. Well ordered perovskite BaTiO₃ was confirmed from the ICISS spectra and reflection high electron energy diffraction (RHEED) patterns. It was also revealed that BaTiO₃ had cubic structure with the same lattice parameter of bulk phase.

• Progress in Superconductivity
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• v.2 no.1
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• pp.6-10
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• 2000

New cuprates with the nominal composition $(Pb_{0.75}Sn_{0.25})Sr_2(Ca_{1-x}Lu_x)Cu_2O_z(x=0.4{\sim}1.0)$ have been synthesized. These materials exhibit superconducting properties for 0.4 $\leq$ x $\leq$ 0.7. It is also observed that the superconductivity of the as-prepared sample is enhanced by post-annealing at high temperature followed by quenching. X-ray diffraction analysis reveals that the c lattice parameter decreases as x increases whereas the a lattice parameter is nearly independent of the value of x for both the as-prepared and the post-treated samples. The thermoelectric power measurements indicate that the post-heat-treatments result in an increase in the hole carrier density which account for the observed increase of $T_c$. Bulk superconductivity with a $T_c$ value of 60 K is observed in this system.

• Journal of the Korean Ceramic Society
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• v.20 no.3
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• pp.217-226
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• 1983

Adquate amount of calcia was added to the regent-grade Zirconia body. Here the amount and the form of calcia were 7-21 mol% and regent-grade calcium cabonate respectively. The specimens were fired at 175$0^{\circ}C$ for 0, 3, 5 and 7 hours respectively. The phase Strength X-ray diffraction analysis and Scaning electron microscopy. The results were as follows (1) As the additive amount of calcia was increased the firing linear shrinkage apparent density compressive strength and modulus of rupture decreased but the apparent porosity increased. (2) The specimens soaked and containing calcia displayed the grain growth. (3) Monoclinic and cubic zirconia were seen in the sepcimens containing 7 mol% calcia. When without soaking the specimens containing 7-10 mol% calcia had the volume change by monoclinic$\rightleftharpoons$tetragonal transformation. (4) The lattice parameter increased according as the calcia additive was increased. The specimens containing above 19mol% calcia had the costant lattice parameter. The value of that was from 5.1264 to 5.1396 $\AA$ in the case of 7 hours soaking.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.04a
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• pp.69-76
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• 2002

In this paper, several improved Element-Free Galerkin (EFG) methods containing singular expression in their approximation functions are compared one another through a patch test with near-tip field. Intrinsic enrichments that expand the basis function partially and fully with known near-tip displacement field and a local enrichment using auxiliary supports based on the partition of unity concept are examined by evaluating a relative stress norm error and the stress intensity factor. Some numerical examinations graphically show that how the size of compact support, dilation parameter and the diffraction parameter can affect the accuracy of the improved EFG methods in the error and the stress intensity factor.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.69-72
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• 2002

The high temperature deformation behavior of SiCp/2124Al composite and 2124Al alloy was investigated by hot compression test in a temperature ranged $400~475^{\circ}C$ over a strain rate ranged $10^{-3}~1s^{-1}$. The billets of 2124Al alloy and SiCp/2124Al composite were fabricated by vacuum hot pressing process. The stress-strain curve during high temperature deformation exhibited a peak stress, and then the flow stress decreased gradually into a steady state stress with increasing the strain. It was found that the flow-softening behavior was attributed to the dynamic recovery, local dynamic recrystallization and dynamic precipitation during the deformation. The precipitation phases were identified as S' and S by TEM diffraction pattern. Base on the TEM inspection, the relationship between the Z-H parameter and subgrain size was found based on the experiment data. The dependence of flow stress on temperature and strain rate could be formulated well by a hyperbolic-sinusoidal relationship using the Zener-Hollomon parameter.

• Journal of the Korean Vacuum Society
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• v.15 no.3
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• pp.273-279
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• 2006

This study explored the possibility of porous Si (PS) formed by indirect electrode anodization used for effective isolation material for radio frequency integrated circuits (RFIC). We investigated the effect of current density and reaction time on the porosity size and depth, and X-ray diffraction of bulk Si and porous Si to evaluate the change in lattice parameter. Porosity size and depth usually increases with an increase in the current density and reaction time. PS increases the lattice parameter of Si compared to the bulk Si which causes the compressive stress of around 8 MPa. PS formed by the method is believed to be suitable for isolation material for RFIC because it is simple process as well as good compatibility to Si VLSI process.