• Korean Journal of Materials Research
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• v.33 no.2
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• pp.54-62
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• 2023

The most comprehensive and particularly reliable method for non-destructively measuring the residual stress of the surface layer of metals is the sin²ψ method. When X-rays were used the relationship of ε_φψ-sin²ψ measured on the surface layer of the processing metal did not show linearity when the sin²ψ method was used. In this case, since the effective penetration depth changes according to the changing direction of the incident X-ray, σ_φ becomes a sin²ψ function. Since σ_φ cannot be used as a constant, the relationship in ε_φψ-sin²ψ cannot be linear. Therefore, in this paper, the orthogonal function method according to Warren's diffraction theory and the basic profile of normal distribution were synthesized, and the X-ray diffraction profile was calculated and reviewed when there was a linear strain (stress) gradient on the surface. When there is a strain gradient, the X-ray diffraction profile becomes asymmetric, and as a result, the peak position, the position of half-maximum, and the centroid position show different values. The difference between the peak position and the centroid position appeared more clearly as the strain (stress) gradient became larger, and the basic profile width was smaller. The weighted average strain enables stress analysis when there is a strain (stress) gradient, based on the strain value corresponding to the centroid position of the diffracted X-rays. At the 1/5 I_max max height of X-ray diffraction, the position where the diffracted X-ray is divided into two by drawing a straight line parallel to the background, corresponds approximately to the centroid position.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.177-177
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• 1999

The surface structure of epitaxial $\alpha$-Fe2O3(0001) grown on $\alpha$-Al2O3(0001) has been investigated using intermediate-energy x-ray photoelectron diffraction. Comparison of experiment with quantum mechanical scattering theory reveals that the surface is Fe-terminated, and that the first four layer spacings are -41%, +18%, -8%, and +47% of the associated bulk values, respectively. these results agree reasonably well with the predictions of molecular mechanics and spin-density functional theory previously reported in the literature for the Fe-terminated surface. however, we find no evidence for and O-terminated surface predicted to be stable by spin-density functional theory.

• Journal of the Optical Society of Korea
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• v.14 no.4
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• pp.333-336
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• 2010

The generation of coherent x-ray beams by using a multi-slit diffraction phenomenon is presented. The mode-confinement conditions in the x-ray waveguide (XWG) needed to obtain single-mode beams are determined. The XWGs are stacked to form an XWG array. The core of the XWG array is used as a slit in an opaque screen, similar to those used for visible light. Diffraction patterns that interfered constructively in the XWG array are investigated based on multi-slit diffraction theory. The irradiance distributions are studied at on observation screen. The FWHM of diffracted x-ray spectra were between $1.67{\times}10^{-4}$ to $3.30{\times}10^{-5}$ radians which lead to a spot-size of a few tens of micrometers on the screen at distance of 1 m. The intensities decrease with increase in the period of the XWG array, i.e. a thicker cladding, due to growth of the higher-order diffraction peaks.

• Korean Journal of Optics and Photonics
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• v.10 no.4
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• pp.348-353
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• 1999

Ray-optics approach based on the rigorous coupled wave theory, called by the rigorous ray-optics method (RROM), is developed for the calculation of couling coefficients of waveguide grating devices. The coupling coefficients of several grating structures, such as rectangular, sinusoidal, triangle, and trapezoidal shapes, are determined by the RROM, and they are compared with those obtained by conventional methods of the ray-optics method (ROM) and the coupled mode method (CMM). In the case of rectangular gratings, the coupling coefficients is evaluated in detail by various depths and duty-cycles of the grating. We have found that the RROM gives more exact solutions for the coupling coefficients of even arbitrary shapes of diffractive waveguide grating devices than the other conventional methods.

• Korean Journal of Optics and Photonics
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• v.13 no.3
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• pp.189-196
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• 2002

The components and alignment parameters of a flat-field soft x-ray spectrometer used in the wavelength range below 50 $\AA$ are determined, and the characteristics of the spectrometer are analyzed. It consists of a toroidal mirror, a slit, a varied line-spacing concave grating, and a soft x-ray detector. The space-resolved spectral image of a source is formed on a single plane using the tordidal mirror and the 2400-grooves/mm varied line-spacing concave grating. The former is used to compensate for the astigmatism caused by the grazing incidence of soft x-ray light on the concave grating. The spectral and spatial resolutions of the spectrometer are calculated by applying the wave front aberration theory, and the diffraction efficiency is calculated by applying the scalar diffraction theory.

• Current Optics and Photonics
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• v.4 no.1
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• pp.9-15
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• 2020

Fresnel zone plates have been widely used in many applications, such as x-ray telescopes, microfluorescence, and microimaging. To obtain an x-ray Fresnel zone plate, many fabrication methods, such as electron-beam etching, ion-beam etching and chemical etching, have been developed. Fresnel zone plates fabricated by these methods will inevitably lead to some nonideal factors, which have an impact on the focusing characteristics of the zone plate. In this paper, the influences of these nonideal factors on the focusing characteristics of the zone plate are studied systematically, by numerical simulations based on scalar diffraction theory. The influence of the thickness of a Fresnel zone plate on the absolute focusing efficiency is calculated for a given incident x-ray's wavelength. The diffraction efficiency and size of the focal spot are calculated for different incline angles of the groove. The simulations of zone plates without struts, with regular struts, and with random struts are carried out, to study the effects of struts on the focusing characteristics of a zone plate. When a Fresnel zone plate is used to focus an ultrashort x-ray pulse, the effect of zone-plate structure on the final pulse duration is also discussed.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.3
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• pp.73-86
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• 2002

Prognostic characteristics of hypothetical tsunamis in the East Sea are discussed based on numerical model simulations of linear long wave theory and wave ray for 28 source zones of tsunamigenic earthquake selected by the seismic gap theory. As a result, the propagation patterns of tsunamis due to hypothetical earthquake are presented and analyses also lead to selection of the geographical zones with low risk of tsunamis.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1444-1449
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• 2000

This environmental influence of the noise produced by a number of air-conditioner out-door units in a multi-unit housing is predicted and evaluated. The method based on Ray tracing theory and mirror image source theory is utilized. Each ventilation window in a machine room is considered as a sound source which contributes to the overall noise level of the surrounding environment. The adopted method has been found a very efficient tool to assess the environmental noise impact.

• Ocean Systems Engineering
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• v.3 no.1
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• pp.71-77
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• 2013

The effective tracking area of ultra short baseline (USBL) systems strongly relates to the safety of autonomous underwater vehicles (AUVs). This problem has not been studied previously. A method for determining the effective tracking area using acoustic theory is proposed. Ray acoustic equations are used to draw rays which ascertain the effective space. The sonar equation is established in order to discover the available range of the USBL system and the background noise level using sonar characteristics. The available range defines a hemisphere like enclosure. The overlap of the effective space with the hemisphere is the effective area for USBL systems tracking AUVs. Lake and sea trials show the proposed method's validity.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.42.2-42.2
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• 2011

Noise generated from wind turbines has been predicted by numerical methods. Sound pressure level(SPL) on the turbines is predicted after aerodynamic analysis is carried out by Wind Turbine Flow, Aeroacoustics and Structure analysis (WINFAS) code. The level of each panel of acoustic sphere is determined by the sum of tonal, turbulence ingestion and airfoil self noise. With the noise source database, the acoustic sphere, SPL on the ground is calculated using the model based on acoustic ray theory. The model has been designed to consider the effects on the condition of terrain and atmosphere. The variations of SPL on the ground occur not only because of the different source level but also because of the nonuniform distributions of the sound speed along the height. Hence, the profile of an effective sound speed which is the sum of the contribution of sound speed to a temperature gradient and a wind speed variation is used by the theory based on atmospheric stability. With the integrated numerical method, the prediction of sound propagation on the wind farm is carried out with the states of the atmospheric stability.