• Bulletin of the Korean Chemical Society
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• v.28 no.12
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• pp.2279-2282
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• 2007

Highly crystalline, uniform Fe nanoparticles were successfully synthesized and encapsulated in zirconia shell using sol-gel process. Two different approaches have been employed for the coating of Fe nanoparticle with zirconia. The thickness of zirconia shell can be readily controlled by altering molar ratio of Fe nanoparticle core to zirconia precursor in the first case where as reaction time was found to be most effective parameter to controlled the shell thickness in the second method. The structure and magnetic properties of the ZrO2-coated Fe nanoparticles were studied. TEM and HRTEM images show a typical core/shell structure in which spherical α-iron crystal sized of ~25 nm is surrounded by amorphous ZrO2 coating layer. TGA study showed an evidence of weight loss of less than 2% over the temperature range of 50-500 °C. The nanoparticles are basically in ferromagnetic state and their magnetic properties depend strongly on annealing temperature. The thermal treatment carried out in as-prepared sample resulted in reduction of coercivity and an increase in saturation magnetization. X-ray diffraction experiments on the samples after annealing at 400-600 °C indicate that the size of the Fe@ZrO2 particles is increased slightly with increasing annealing temperature, indicating the ZrO2 coating layer is effective to interrupt growing of iron particle according to heat treatment.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.7
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• pp.443-449
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• 2018

We investigated the temperature-dependent photoluminescence spectroscopy of colloidal InZnP/ZnSe/ZnS (core/shell/shell) quantum dots with varying ZnSe and ZnS shell thickness in the 278~363 K temperature range. Temperature-dependent photoluminescence of the InZnP-based quantum dot samples reveal red-shifting of the photoluminescence peaks, thermal quenching of photoluminescence, and broadening of bandwidth with increasing temperature. The degree of band-gap shifting and line broadening as a function of temperature is affected little by shell composition and thickness. However, the thermal quenching of the photoluminescence is strongly dependent on the shell components. The irreversible photoluminescence quenching behavior is dominant for thin-shell-deposited InZnP quantum dots, whereas thick-shelled InZnP quantum dots exhibit superior thermal stability of the photoluminescence intensity.

• Journal of the Korean Ceramic Society
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• v.54 no.3
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• pp.222-227
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• 2017

Flake-type micro hollow silica was synthesized by precipitation method using an $Mg(OH)_2$ inorganic template and sodium silicate and ammonium sulfate as the silica precursors. We investigated the effects of the silica precursor concentration on the shape, shell thickness, and surface of the hollow silica. When the concentration of the silica precursor was 0.5 M, the hollow silica had a smooth and translucent thin shell, but the shell was broken. On the other hand, the shell thickness of the hollow silica changed in the range of 12 nm to 18 nm with the increase of the precursor concentration from 0.7 M to 1.1 M. Simultaneously, unintended spherical silica satellites were created on the shell surface. The number of satellites and the size rose according to the increased concentration of silica precursor. The reason for the formation of spherical silica satellites is that the $NH_4OH$ nucleus generated in the synthesis of hollow silica acted as another silica reaction site.

• Steel and Composite Structures
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• v.34 no.3
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• pp.361-376
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• 2020

This paper presents a free vibration analysis of shell panels made of functionally graded material (FGM) in the form of the ordinary and sandwich FGM and laminated shells using the isogeometric B3-spline finite strip method (IG-SFSM). B3-spline and Lagrangian interpolation are employed along the longitudinal and transverse directions respectively in this type of finite strip. The introduced finite strip formulation is based on the degenerated shell method, which provides variable thickness, arbitrary geometries, and analysis of thin or thick shells. Validity of the obtained natural frequencies by IG-SFSM is checked by comparison with results extracted from references for similar cases in different examples. These examples incorporate several geometries, materials, boundary conditions, and continuous thickness variation. A comparison of these two kinds of results and their proximity showed that the introduced IG-SFSM is a reliable tool which can be used in analysis of shells with the aforementioned properties.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.3
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• pp.383-391
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• 1986

Mode shapes and natural frequencies of the bell type shell are analyzed numerically by the finite element method. The impulse hammer method and the Fast Fourier Transform analyzer are used for the experimental test. All types of mode shapes are expressed by the computer graphics. Numerical solutions are good agreement with the experimental results. The sustaining sound of the typical bell-type shell depend upon the first flexural mode (0-2 mode) and the second flexural mode (0-3 mode), and their mode shapes are independent upon thickness Dangjwas, holes, and added mass effects. Asymmetric effects by Dangjwas, holes and added mass give rise to beat frequencies, and the added mass is found to be most effective.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.1-4
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• 2005

A higher order zig-zag shell theory is developed to refine accurately predict deformation and stress of smart shell structures under the mechanical, thermal, and electric loading. The displacement fields through the thickness are constructed by superimposing linear zig-zag field to the smooth globally cubic varying field. Smooth parabolic distribution through the thickness is assumed in the transverse deflection in order to consider transverse normal deformation. The mechanical, thermal, and electric loading is applied in the sinusoidal distribution function in the in-surface direction. Thermal and electric loading is given in the linear variation through the thickness. Especially, in electric loading case, voltage is only applied in piezo-layer. The layer-dependent degrees of freedom of displacement fields are expressed in terms of reference primary degrees of freedom by applying interface continuity conditions as well as bounding surface conditions of transverse shear stresses. In order to obtain accurate transverse shear and normal stresses, integration of equilibrium equation approach is used. The numerical examples of present theory demonstrate the accuracy and efficiency of the proposed theory. The present theory is suitable for the predictions of behaviors of thick smart composite shell under mechanical, thermal, and electric loadings combined.

• Structural Engineering and Mechanics
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• v.37 no.2
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• pp.253-256
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• 2011

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.1
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• pp.33-39
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• 2015

This paper investigates the underwater acoustic radiation from a periodically stiffened cylindrical shell excited resiliently mounted machinery. Underwater acoustic radiation is important to a submarine. Generally, submarine structure can be modeled as stiffened cylindrical shell immersed in water. Analytical model is derived for the far-field acoustic radiation from machinery installed inside cylindrical shell. The analytical model includes the effect of fluid loading and interactions between periodic ring stiffeners. Transmitted force from machine to a shell through isolator can be different by the impedance of shell. In this paper the effect of a shell impedance for acoustic radiation is investigated. Impedance of a shell should be considered if thickness of a shell is thin.

• The Journal of the Acoustical Society of Korea
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• v.29 no.3E
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• pp.140-145
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• 2010

In the present study, tubular polyvinyl chloride (PVC) cortical bone mimics that simulate the cortical shell of long bones were used to validate the axial transmission technique for assessing the cortical thickness by measuring the ultrasonic velocities along the cortical shell of long bones. The ultrasonic velocities in the 9 PVC cortical bone mimics with wall thicknesses from 4.0 to 16.1 mm and inner diameters from 40 to 300 mm were measured as a function of the thickness by using a pair of custom-made transducers with a diameter of 12.7 mm and a center frequency of 200 kHz. In order to clarify the measured behavior, they were also compared with the predictions from a theory of guided waves in thin plates. This phantom study using the PVC cortical bone mimics provides useful insight into the dependencies of ultrasonic velocities on the cortical thickness in human long bones.

• Structural Engineering and Mechanics
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• v.58 no.6
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• pp.1001-1020
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• 2016

The study is to investigate the free vibration of antisymmetric angle-ply conical shells having non-uniform sinusoidal thickness variation. The arbitrarily varying thickness is considered in the axial direction of the shell. The vibrational behavior of shear deformable conical shells is analyzed for three different support conditions. The coupled differential equations in terms displacement and rotational functions are obtained. These displacement and rotational functions are invariantly approximated using cubic spline. A generalized eigenvalue problem is obtained and solved numerically for an eigenfrequency parameter and an associated eigenvector of spline coefficients. The vibration characteristic of the shells is examined for cone angle, aspect ratio, sinusoidal thickness variation, layer number, stacking sequence, and boundary conditions.