• Journal of Adhesion and Interface
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• v.11 no.1
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• pp.15-25
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• 2010

In the present study, isothermal stabilization processes for rayon fabrics were performed at two relatively low temperatures $180^{\circ}C$ and $200^{\circ}C$ for a long period of time. The results of weight loss, dimensional shrinkage, X-ray diffraction and scanning electron microscopic observations studied with the rayon fabrics before and after the isothermal stabilization indicated that the chemical and physical changes of rayon precursor fibers proceeded continuously and slowly at the stabilization temperature below $200^{\circ}C$. And the pre-treatment with four different chemical compounds done prior to stabilization process influenced differently the characteristics of rayon fabrics. As a result, it was noticed that under the given stabilization conditions, $H_3PO_4$ and $Na_3PO_4$ played a role in catalyzing the stabilization reaction of rayon fabric whereas $NH_4Cl$ and $ZnCl_2$ played a role in delaying or retarding the reaction. $H_3PO_4$ showed the lowest percent weight loss of the fabric in the second stabilization conducted at $350^{\circ}C$. It was considered that phosphoric acid, which has a function of flame retardant, contributed to retarding somewhat the subsequent reaction even in the second stabilization step.

• Journal of the Korean Ceramic Society
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• v.40 no.10
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• pp.985-990
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• 2003

By heat treating coal tar pitch between 450∼500$^{\circ}C$, mesophase pitch could be obtained. Subsequently, this pitch was oxi-stabilized between 160∼240$^{\circ}C$ in air for the purpose of reducing swelling and distortion. The mechanism of stabilization was analysed using the thermo-gravity and FT-IR. To investigate the effect of oxi-stabilization, the shore hardness and bending stress were measured with carbonized green body which was made from oxi-stabilized coal tar pitch.

• 전기의세계
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• v.31 no.1
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• pp.59-67
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• 1982

This paper suggests easy stabilization methods for linear time-varying systems with delay in the state. While existing methods employ the function space concept, the methods introduced in this paper transform the delay systems into the non-delay systems so that the well known methods for finite dimensional systems can be utilized. Particularly the intervalwise predictor is introduced and shown to satisfy an ordinary system. Control laws stabilizing the non-delay systems satisfied by this predictor will be shown to at least pointwise stabilize the delay systems with the additional strong possibility of true stabilization. In order to combine two steps of the predictor method, first transformation and then stabilization, an intervalwise regulator problem is suggested whose optimal control laws incorporate the intervalwise predictor as an integral part and also at least pointwise stabilize the delay systems. Since the above mentioned methods render the periodic feedback gains for time invariant systems the pointwise predictor and regulator are introduced in order to obtain the constant feedback gains, with additional stability properties. The control laws given in this paper are perhaps simplest and easiest to implement.

• Carbon letters
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• v.15 no.4
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• pp.290-294
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• 2014

New precursors, poly(acrylonitrile-co-crotonic acid) (poly(AN-CA)) and poly(acrylonitrile-co-itaconic acid-co-crotonic acid) (poly(AN-IA-CA)) copolymers, for the preparation of carbon fibers, were explored in this study. The effects of comonomers with acidic groups, such as crotonic acid (CA) and/or itaconic acid (IA), on the stabilization of nanofibrous polyacrylonitrile (PAN) copolymers were studied. The extent of stabilization, evaluated by Fourier transform infrared spectroscopy, revealed that the CA comonomer could retard/control the stabilization rate of PAN, in contrast to the IA comonomer, which accelerated the stabilization process. Moreover, the synthesized PAN copolymers containing CA possessed higher Mv than those of the IA copolymers and also showed outstanding dimension stability of nanofibers during the stabilization, which may be a useful property for improving the dimensional stability of polymer composites during manufacturing.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.3
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• pp.317-322
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• 1989

Effective computational strategies have been proposed in the evaluation of stiffness matrices of rigid-plastic finite element method widely used in simulation of metal forming processes. The stiffness matrices are expressed as the sum of stiffness matrices evaluated by reduced integration and Liu's stabilization matrices which control the occurrence os zero-energy mode due to excessive reduced integration. The proposed method has been applied to the solution of fundamental 3-dimensional problems. The results clarified that the deformed mesh configuration was remarkably stabilized and computation speed attained about 3 times as fast as that of conventional 3-dimensional analyses. Furthermore, computation speed increases by a factor 60 when parallel computation is introduced. This speed has a tendency to increase as the total degree of freedom increases. As a result, this rigid-plastic finite element method enables us to analyze real 3-dimensional forming processes with practically acceptable computation time.

• Ocean Systems Engineering
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• v.1 no.2
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• pp.171-194
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• 2011

A method to design a boundary controller for global stabilization of three-dimensional nonlinear dynamics of flexible marine risers is presented in this paper. Equations of motion of the risers are first developed in a vector form. The boundary controller at the top end of the risers is then designed based on Lyapunov's direct method. Proof of existence and uniqueness of the solutions of the closed loop control system is carried out by using the Galerkin approximation method. It is shown that when there are no environmental disturbances, the proposed boundary controller is able to force the riser to be globally exponentially stable at its equilibrium position. When there are environmental disturbances, the riser is stabilized in the neighborhood of its equilibrium position by the proposed boundary controller.

• Journal of the Korean Wood Science and Technology
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• v.23 no.4
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• pp.1-9
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• 1995

This study was carried out to experiment the dimensional stabilization of woods of red pine (Pinus densiflora S. et Z.) and sugi(Cryptomeria japonica D. Don) by vacuum impregnation of polyehtylene glycols(PEG) with mo. wt. 200, 400, 600, 1000; polypropylene glycols (PPG) with mo. wt. 425,725 ; PEG-acryloylates, and PPG-acryloylates synthesized, and then by water soaking. The results obtained are as follows: 1. The density of sapwood and heartwood was different from each other in both species. 2. The PEG and PEG-macromers with lower molecular weight by impregnation has increased the density of wood specimens more higher, thereby caused their higher volume expansion, and those with higher molecular weight than 600 has tended to down their density increment. 3. Before and after water soaking, the density decrease of specimen impregnated was high in woods impregnated with simple PEG and PPG, while lower in specimens impregnated with PEG-macromers and PPG-macromers. 4. So PEG-macromer was expected to hold the original dimension of decayed wood for antiques, but it was necessary to develop another penetration method as well as aqueous solvent.

• 한국전산유체공학회:학술대회논문집
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• 2004.03a
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• pp.91-98
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• 2004

In two dimensional incompressible flows, a preconditioning technique called Hierarchical Iterative Procedure(HIP) has been implemented on a stabilized finite element formulation. The stabilization has been peformed by a modified residual method proposed by Illinca et. al.[3]. The stabilization which is necessary to escape from the LBB constraint renders an equal order formulation. In this paper, we increased the order of interpolation whithin an element up to cubic. The conjugate gradient squared(CGS) method is used for the outer iteration, and the HIP for the preconditioning for the incompressible Navier-Stokes equation. The hierarchical elements has been used to achieve a higher order accuracy in fluid flow analyses, but a proper efficient iterative procedure for higher order finite element formulation has not been available so far. The numerical results by the present HIP for the lid driven cavity flow showed the present procedure to be stable, very efficient and useful in flow analyses in conjunction with hierarchical elements.

• Biomolecules & Therapeutics
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• v.21 no.6
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• pp.423-434
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• 2013

The adoption of oligonucleotide aptamer is well on the rise, serving an ever increasing demand for versatility in biomedical field. Through the SELEX (Systematic Evolution of Ligands by EXponential enrichment), aptamer that can bind to specific target with high affinity and specificity can be obtained. Aptamers are single-stranded nucleic acid molecules that can fold into complex three-dimensional structures, forming binding pockets and clefts for the specific recognition and tight binding of any given molecular target. Recently, aptamers have attracted much attention because they not only have all of the advantages of antibodies, but also have unique merits such as thermal stability, ease of synthesis, reversibility, and little immunogenicity. The advent of novel technologies is revolutionizing aptamer applications. Aptamers can be easily modified by various chemical reactions to introduce functional groups and/or nucleotide extensions. They can also be conjugated to therapeutic molecules such as drugs, drug containing carriers, toxins, or photosensitizers. Here, we discuss new SELEX strategies and stabilization methods as well as applications in drug delivery and molecular imaging.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.188-191
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• 2005

A common feature in various methods of optical interferometry for absolute distance measurements is the use of multiple monochromatic light components either in sequence or in parallel at the same time. Two or multiple wavelength synthesis has been studied though its performance is vulnerable to the frequency instability of the light source. Recently continuous frequency modulation is considered a promising method with availability of wide band tunable diode lasers, which also have frequency instability errors. We can lock frequencies of these third-party light sources to the modes of the femtosecond laser which is stabilized to the precision of the standard radio frequency. To this end, we have stabilized all the modes of the femtosecond laser to the atomic frequency standard by using powerful tools of frequency-domain laser stabilization.