• Structural Engineering and Mechanics
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• 제44권2호
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• pp.127-138
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• 2012

The composite materials may be exposed to environmental (thermal or hygral or both) condition during their service life. The effect of environmental condition is usually adverse from the point of view of design of composite structures. In the present research study the effect of hygrothermal condition on the design of laminated composite structures is investigated. The active fiber composite (AFC) which may be utilized as actuator or sensor is considered in the present analysis. The sensor layer is used to sense the level of response of the composite structures. The sensed voltage is fed back to the actuator through the controller. In this study both displacement and velocity feedback controllers are employed to reduce the response of the composite laminate within acceptable limit. The Newmark direct time integration scheme is employed along with modal superposition method to improve the computational efficiency. It is observed from the numerical study that the laminated composite structures become weak in the presence of hygrothermal load. The response of the structure can be brought to the acceptable level once the AFC layer is activated through the feedback loop.

• Advances in materials Research
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• 제3권2호
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• pp.117-128
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• 2014

Processable conducting polyaniline derivative with free amine functional groups was successfully synthesized from the monomer o-phenylenediamine in aqueous hydrochloric acid medium using ammonium persulfate as an oxidative initiator. The synthesized poly(o-phenylenediamine) (PoPD) in critical condition was found to be completely soluble in common organic solvents like dimethyl sulfoxide, N,N-dimethyl formamide etc. From the intrinsic viscosity measurement, the optimum condition for the polymerization was established. The polymer was characterized by ultraviolet visible spectroscopy, Fourier transform infrared spectroscopy, proton magnetic resonance spectroscopy ($^1HNMR$) and thermogravimetric (TGA) analyses. The weight average molecular weights of the synthesized polymers were determined by the dynamic light scattering (DLS) method. From the spectroscopic analysis the structure was found to resemble that of polyaniline derivative with free amine functional groups attached to ortho/meta position in the phenyl ring. However, very little ladder unit was also present with in the polymer chain. The moderate thermal stability of the synthesized polymer could be found from the TGA analysis. The average DC conductivity of $2.8{\times}10^{-4}S/cm$ was observed for the synthesized polymer pellet after doping with hydrochloric acid.

• Smart Structures and Systems
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• 제3권3호
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• pp.357-372
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• 2007

Parametric density concept is proposed for a long-range pipeline health monitoring. This concept is designed to obtain the attenuation of ultrasonic guided waves propagating in underwater pipelines without complicated calculation of attenuation dispersion curves. For the study, three different pipe materials such as aluminum, cast iron, and steel are considered, ten different transporting fluids are assumed, and four different geometric pipe dimensions are adopted. It is shown that the attenuation values based on the parametric density concept reasonably match with the attenuation values obtained from dispersion curves; hence, its efficiency is proved. With this concept, field engineers or inspectors associated with long-range pipeline health monitoring would take the advantage of easier capturing wave attenuation value, which is a critical variable to decide sensor location or sensors interval.

• 고무기술
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• 제12권1호
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• pp.1-7
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• 2011

Nanotechnology is the fast becoming key technology of the $21^{st}$ century. Due to its fascinating size-dependent properties, it has gained significant important in various sectors. Myths are being formed on the proverbal nanotechnology market, but the reality is the nanotechnology is not a market but a value chain. The chain comprises of - nanomaterials (nanoparticles) and nanointermediates (coatings, compounds, smart fabrics). Elastomer based nanocomposites reinforced with low volume fraction of nanofillers is the first generation nanotechnology products and it has attracted great interest due to their fascinating properties. The incorporation of nanofillers such as nanolayered silicates, carbon nanotubes, nanofibers, metal oxides or silica nanoparticles into elastomers improves significantly their mechanical, thermal, barrier properties, flame retardency etc., Extremely small particle size, high aspect ratio and large interface area yield an excellent improvement of the properties in a wide variety of the materials. Uniform dispersion of the nanofillers is a general prerequisite for achieving desired properties. In this paper, current developments in the area of elastomer based nanocomposites reinforced with layered silicate and carbon nanotube fillers are highlighted.

• Smart Structures and Systems
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• 제13권1호
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• pp.111-135
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• 2014

Based on the Reissner mixed variational theorem (RMVT), finite rectangular layer methods (FRLMs) are developed for the three-dimensional (3D) linear buckling analysis of simply-supported, fiber-reinforced composite material (FRCM) and functionally graded material (FGM) sandwich plates subjected to bi-axial compressive loads. In this work, the material properties of the FGM layers are assumed to obey the power-law distributions of the volume fractions of the constituents through the thickness, and the plate is divided into a number of finite rectangular layers, in which the trigonometric functions and Lagrange polynomials are used to interpolate the in- and out-of-plane variations of the field variables of each individual layer, respectively, and an h-refinement process is adopted to yield the convergent solutions. The accuracy and convergence of the RMVT-based FRLMs with various orders used for expansions of each field variables through the thickness are assessed by comparing their solutions with the exact 3D and accurate two-dimensional ones available in the literature.

• Smart Structures and Systems
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• 제14권3호
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• pp.445-468
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• 2014

The objective in this research is to determine the feasibility of using changes on the dynamic properties of a reinforced concrete (RC) structure to identify different levels of seismic induced damage. Damping ratio and natural frequency changes in a RC bridge column are analyzed using different signal processing techniques like Hilbert Transforms, Random Decrement and Wavelet Transforms. The data used in the analysis was recorded during a full-scale RC bridge column shake table test. The structure was subjected to ten earthquake excitations that induced different levels of inelastic demand on the column. In addition, low-intensity white noises were applied to the column in-between earthquakes. The results obtained show that the use of the damping ratio and natural frequency of vibration as damage indicators is arguable.

• International journal of advanced smart convergence
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• 제9권3호
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• pp.239-245
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• 2020

The Ewha Music Database (EMDB) is an online database comprised of primary source materials related to music education from East Asia during the modern era (1880 to 1945) when Korea, Japan, and China were geopolitically and culturally intertwined. We developed the incipit search in EMDB as an embedded tool. This is the first attempt in Korea to implement a unique search function of musical data using alphabets of musical notes. Unlike in traditional search system that uses general literature information search conditions, such as author, title, publisher, year, number of pages, etc., it offers a new way of searching a musical piece/work and sheet music. This study confirms that digital information technology is an important methodology for research of music culture as a field of humanities.

• 한국결정학회지
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• 제11권4호
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• pp.231-237
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• 2000

CMR Materials RE/sub 1-x/Ca/sub x/MnO₃(RE=La, Nd, A=Ca, Sr) were grown using the floating zone image furnace with halogen lamps as heat source. The growth condition was at 2∼10 mm/hr growth rate in air atmosphere, were 445∼50 rpm and 20∼25 rpm of rotation rate of feedrod and growing crystal, respectively. The grown crystals showed shiny black color and annealed at 1500℃ in a box furnace to release the residual stress during cooling. Characterization analyses of the crystal were carried out using XRD and SEM. The crystal structure of Nd/sub 0.7/Ca/sub 0.3/MnO₃ was analyzed with smart CCD XRD was lattice parameter of a=5.425(4)Å, b=5.434(4)Å, and c=7.712(5)Å, an orthorombic system with space group of pbnm.

• 대한치과의사협회지
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• 제54권2호
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• pp.123-133
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• 2016

Currently increasing use of implants, especially in anterior implant esthetics has become a major concern for both the patient and dentist. In the case of thin biotype if the thickness of the gingival soft tissue is less than 2mm, human eye can detect differences of colors depends on underlying materials. The zirconia abutment can be use not only for better esthetics but also for the hygienic because it is less attractive for the plaque deposition when it compare to the metals. Zirconia itself has many advantages as a biomaterial but also has frequent mechanical problems when it use for abutment of internal connection implant. For prevention or reduction of mechanical failures, use of titanium-link with zirconia super-structure which part that connects directly into the implant can be a good alternative. In this literature, I would like to review the clinical considerations of use of titanium link - CAD/CAM zirconia abutment for dental implant in esthetically important areas.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2011년도 춘계학술대회
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• pp.491-494
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• 2011

정보화 시스템 구축에 필요한 유형 무형의 모든 기술과 수단을 아우르는 간접적 가치창출에 무게를 두는 기술을 뜻하는 정보통신 용어로 정보통신 산업의 발전과 함께 정보혁명을 주도하는 기술로 부각되었다. 본 논문에서는 에너지 및 환경문제를 극복하기 위한 Green IT 주요품목에 대한 시장 및 산업동향과 녹색성장 기반구축 현황에 대해 알아본다. 여러 관련자료를 발췌 또는 편집하여 개괄적으로 소개하도록 한다.