• Elastomers and Composites
• /
• 제34권4호
• /
• pp.321-331
• /
• 1999

타이어 가황공정(curing process)은 타이어 제조를 위한 최종공정으로 여러 개의 고무배합물 층으로부터 성형된 그린타이어(green tire)를 가황기(mold)내에서 고압/고온 조건하에 유지시킴으로써 원하는 형상을 얻게 하고, 아울러 각 고무배합물이 고탄성을 갖도록 물성을 변화시키는 공정이다. 본 연구에서는 타이어 품질의 향상을 위해 가황공정을 수치적으로 최적화하는 기법을 개발하였다. 먼저, 가황공정 중 가황매체(cure media)의 최적공급 조건을 경정하기 위해 제약조건을 갖는 동적최적화문제(dynamic constrained optimization problem)로 정형화하였다. 즉, 가황기 내의 전열 및 가황 반응 현상을 묘사하는 공정모델로 표현되는 등위제약조건(equality constraint)과 가황매체가 갖는 온도의 한계를 표현하는 부등위제약조건(Inequality constraint) 아래 목적함수를 최적화 시켰다. 다음, 공급되는 가황매체의 최적조건을 결정하기 위해 구성된 최적화문제를 유한요소법(FEM)과 complex 알고리즘을 적용하여 풀었다.

• Membrane and Water Treatment
• /
• 제11권3호
• /
• pp.231-235
• /
• 2020

Industrialization and modern developments have led to an influx of toxic heavy metals into the aquatic environment, and the accumulation of heavy metals has serious adverse effects on humans. Among the various heavy metal treatment methods, adsorption is very useful and frequently used. Plastic materials, such as polypropylene and polyethylene, have been widely used as filter media due to their mechanical and chemical stability. However, the surface of plastic material is inert and therefore the adsorption capability of heavy metals is very limited. In this study, granular media and fiber media composed of polypropylene and polyethylene are used, and the surface modification was conducted in order to increase adsorption capability toward heavy metals. Oxygen plasma generated hydroxyl groups on the surface of the media to activate the surface, and then acrylic acid was synthesized on the surface. The grafted carboxyl group was confirmed by FT-IR and SEM. Heavy metal adsorption capability of pristine and surface modified adsorbents was also evaluated. Overall, heavy metal adsorption capability was increased by surface modification due to electrostatic interaction between the carboxyl groups and heavy metal ions. Fibrous PP/PE showed lower improvement compared to granular PP media because pore blockage occurred by the surface modification step, thereby inhibiting mass transfer.

• 한국병원경영학회지
• /
• 제4권2호
• /
• pp.60-84
• /
• 1999

Hospitals under competitive environment are getting more interested in PR(public relations) as a means of marketing. A typical form of public relations for the hospital is publicity, and its principal instrument is the press release that provides the mass media with the raw material and background for a news story. The purpose of this paper is to examine and analyze the public relations articles associated with hospitals in the section of health care in major daily newspapers. Three major daily newspapers, Chosun, Joongang and Hankyoreh have been analyzed for a year from January 1, 1998 to December 31, 1998. All articles in the health care section are classified by content, size, press comments, and style. This study has found some perverse aspects of the public relations such as the preponderance of health articles on tertiary medical institutions, inappropriate publicity focused on certain medical treatments, doctors, and hospitals, and the positive press comments on the hospitals that are affiliated with the same corporate group as the newspaper.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
• /
• pp.354-354
• /
• 2008

Recently, due to the tremendous growth of media technology, demands of the aspheric glass lens which is a high-performance and miniaturized is gradually increasing. Generally, the aspheric glass lens is manufactured by GMP(Grass Molding Press) method using WC(tungsten carbide) mold core. In this study, the thermal deformation which occurs in the cooling step of GMP was considered, and it was compensated the form of mold core. The lens which was molded by compensated mold core was satisfied that can be applied to the actual specifications.

• 한국방사선학회논문지
• /
• 제9권1호
• /
• pp.47-53
• /
• 2015

본 연구에서 3.0 T에서 조영제 몰 농도에 따른 뇌 대사물질의 MR spectrum을 Phantom에서 PRESS 펄스 파형으로 분석하고자 하였다. 뇌 대사물질인 N-Acetyl Asparatate(NAA), Choline(Cho), Creatine(Cr)의 spectrum은 획득할 수 있었지만, Lactate(Lac)는 획득할 수 없었다. 조영제가 없는 대조군의 TR 2000 ms가 NAA, Cho에서 TR 1700 ms와 TR 1500 ms보다 높게 측정되었고, Cr에서는 TR 1500 ms에서 높게 측정되었다. 조영제가 희석된 TR 1700 ms에서 $0.1mmol/{\ell}$의 NAA 73%, Cho 249%, Cr 37%로 다른 TR 값보다 가장 높게 측정되었고, $0.3mmol/{\ell}$에서도 신호크기가 증가하였다. $0.5mmol/{\ell}$에서는 뇌 대사물질들의 신호크기가 감소하였으며, 특히 TR 1500 ms과 TR 2000 ms에서는 대조군보다도 감소하였다. NAA/Cr, Cho/Cr에서도 조영제 농도가 $0.1mmol/{\ell}$, $0.3mmol/{\ell}$, $0.5mmol/{\ell}$로 증가할수록 신호크기가 감소하였다. 조영제에 의한 MRS PRESS 펄스파형의 적정화를 위하여 3.0T에서 TR 2000 ms 보다 조영제 농도가 낮은 $0.1mmol/{\ell}$와 $0.3mmol/{\ell}$에서 신호크기가 가장 높고, 조영제 농도가 높은 $0.5mmol/{\ell}$에서는 신호크기가 가장 적게 감소한 TR 1700 ms로 반복시간을 단축시켜 사용하는 것이 유용할 것으로 사료된다.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2006년도 하계학술발표대회 논문집
• /
• pp.95-98
• /
• 2006

Filtration by fibrous filter is one of the Principle methods used for removing pollutant particles in the liquid. Because of the increasing need to protect both human health and valuable devices from exposure to fine particles, filtration has become more important. Filters have been developed with modified surface charge characteristics to capture and adsorb particles by electrokinetic interaction between the filter surface and particles contained in water. The main purposes of this study are to develop and evaluate the performance evaluation of the apparatus for making a positively charged porous filter media and to analyze the surface characteristics of the filter media for capturing negavitely charged contaminants mainly bacteria and virus from water. The experimental apparatus consists of a mixing tank, a vacuum pumping system, a injection nozzle, a roller press and a controller. The filter media is composed of glass fiber(50-750 nm), cellulose($10-20{\mu}m$) and colloidal charge modifier. The characteristics of filter media is analyzed by SEM(Scanning Electron Microscopy), AFM(Atomic Force Microscopy) and quantified by measuring the zeta potential values.

• Interaction and multiscale mechanics
• /
• 제1권1호
• /
• pp.83-101
• /
• 2008

A derivation is given of two-scale models that are able to describe deformation and flow in a fluid-saturated and progressively fracturing porous medium. From the micromechanics of the flow in the cavity, identities are derived that couple the local momentum and the mass balances to the governing equations for a fluid-saturated porous medium, which are assumed to hold on the macroscopic scale. By exploiting the partition-of-unity property of the finite element shape functions, the position and direction of the fractures are independent from the underlying discretization. The finite element equations are derived for this two-scale approach and integrated over time. The resulting discrete equations are nonlinear due to the cohesive crack model and the nonlinearity of the coupling terms. A consistent linearization is given for use within a Newton-Raphson iterative procedure. Finally, examples are given to show the versatility and the efficiency of the approach.

• Steel and Composite Structures
• /
• 제32권6호
• /
• pp.821-832
• /
• 2019

An analysis on thermal buckling and postbuckling of composite laminated plates reinforced with a low amount of graphene platelets is performed in the current investigation. It is assumed that graphaene platelets are randomly oriented and uniformly dispersed in each layer of the composite media. Elastic properties of the nanocomposite media are obtained by means of the modified Halpin-Tsai approach which takes into account the size effects of the graphene reinforcements. By means of the von $K{\acute{a}}rm{\acute{a}}n$ type of geometrical nonlinearity, third order shear deformation theory and nonuniform rational B-spline (NURBS) based isogeometric finite element method, the governing equations for the thermal postbuckling of nanocomposite plates in rectangular shape are established. These equations are solved by means of a direct displacement control strategy. Numerical examples are given to study the effects of boundary conditions, weight fraction of graphene platelets and distribution pattern of graphene platelets. It is shown that, with introduction of a small amount of graphene platelets into the matrix of the composite media, the critical buckling temperature of the plate may be enhanced and thermal postbuckling deflection may be alleviated.

• Wind and Structures
• /
• 제9권2호
• /
• pp.147-158
• /
• 2006

The purpose of this paper is to find a more accurate method to evaluate pedestrian wind by computational fluid dynamics approach. Previous computational fluid dynamics studies of wind environmental problems were mostly performed by simplified models, which only use simple geometric shapes, such as cubes and cylinders, to represent buildings and structures. However, to have more accurate and complete evaluation results, various shapes of blocking objects, such as trees, should also be taken into consideration. The aerodynamic effects of these various shapes of objects can decrease wind velocity and increase turbulence intensity. Previous studies simply omitted the errors generated from these various shapes of blocking objects. Adding real geometrical trees to the numerical models makes the calculating domain of CFD very complicated due to geometry generation and grid meshing problems. In this case the function of Porous Media Condition can solve the problem by adding trees into numerical models without increasing the mesh grids. The comparison results between numerical and wind tunnel model are close if the parameters of porous media condition are well adjusted.

• Structural Engineering and Mechanics
• /
• 제61권2호
• /
• pp.221-230
• /
• 2017

In this paper, we investigated the propagation of thermoelastic surface waves in fibre-reinforced anisotropic general viscoelastic media of higher order of nth order including time rate of strain under the influence of rotation. The general surface wave speed is derived to study the effectsof rotation andthermal onsurface waves. Particular cases for Stoneley, Love and Rayleighwaves are discussed.The results obtained in this investigation are more general in the sense that some earlier published results are obtained from our result as special cases. Our results for viscoelastic of order zero are well agreed to fibre-reinforced materials. Comparison was made with the results obtained in the presence and absence of rotation and parameters for fibre-reinforced of the material medium. It is also observed that, surface waves cannot propagate in a fast rotating medium.Numerical results for particular materials are given and illustrated graphically. The results indicate that the effect of rotation on fibre-reinforced anisotropic general viscoelastic media are very pronounced.