• Elastomers and Composites
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• v.46 no.4
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• pp.295-303
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• 2011

A series of new aromatic polyhydroxyamides (PHAs) containing imide ring were prepared by direct polycondensation reaction of imide-diacids and two types of bis(o-aminophenol)s including 3,3'-dihydroxybenzidine and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane. The polymers were characterized by FT-IR, FT-NMR, DSC and TGA. The inherent viscosities of the PHAs measured at $35^{\circ}C$ in DMAC solution were in the range of 0.49-1.13 dL/g. PHA 2 and 3, except PHA 1, were soluble in polar solvents such as DMAc, DMF and NMP. PHA 4, 5, and 6 containing 6F group showed a higher solubility in less polar solvents. But the polybenzoxazoles (PBOs,) were insoluble in a variety of solvents except partially soluble in sulfuric acid. The PBO 1, 2 and 3 showed maximum weight loss temperature in the range of $650-656^{\circ}C$ and relatively high char yields in the range of 57.4-61.9 % under a nitrogen atmosphere. These results suggested that the introduction of imide or diimide ring in the main chain was effective in improving the thermal stability of PHAs and PBOs.

• Elastomers and Composites
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• v.42 no.4
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• pp.238-248
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• 2007

A series of polyhydroxyamides(PHAs) having ether linkages in the polymer backbone were prepared via solution polycondensation at low temperature. These polymers were studied by FT-IR, $^1H-NMR$, DSC, TGA and PCFC. The PHAs exhibited inherent viscosities in the range of $0.5{\sim}1.1dL/g\;at\;35^{\circ}C$ in DMAc solution. Most of PHAs except PHA 3 were soluble in polar organic solvents such as N,N-dimethylacetamide(DMAc), N-methyl-2-pyrrolidone(NMP), and N,N-dimethylform-amide(DMF). Subsequent thermal treatment of PHAs afforded polybenzoxazols(PBOs). However, the PBOs were insoluble in a variety of solvents. Most of the PBOs except PBO 3 showed glass-transition temperature($T_g$) in the range of $200{\sim}246^{\circ}C$ by DSC and maximum weight loss temperature in the range of $597{\sim}697^{\circ}C$ in nitrogen by TGA. PBOs showed high char yields in the range of $51{\sim}64%$. PCFC results of the PBOs showed the heat release(HR) capacity, $8{\sim}65J/gK$ and total heat release(total HR), $2.4{\sim}4.7kJ/g$.

• Journal of Korea Multimedia Society
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• v.12 no.7
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• pp.962-970
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• 2009

This paper presents a data gathering and scheduling scheme for wireless sensor networks. We use a data gathering tree for sending the data from the sensor node to the base station. For an energy efficient operation of the sensor networks in a distributed manner, a time tree is built in order to reduce the collision probability and to minimize the total energy required to send data to the base station. A time tree is a data gathering tree where the base station is the root and each sensor node is either a relaying or a leaf node of the tree. Each tree operates in a different time schedule with possible different activation rate. Through the simulation, we found that the proposed scheme that uses time trees shows better characteristics in energy and data arrival rate when compared with other schemes such as SMAC and DMAC.

• Membrane and Water Treatment
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• v.7 no.5
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• pp.377-401
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• 2016

To study the effect of titanium dioxide ($TiO_2$) nanoparticles on membrane performance and structure and to explore possible improvement of using mixed solvents in the casting solution, composite polyvinylidene fluoride (PVDF) ultrafiltration membranes were prepared via immersion precipitation method using a mixture of two solvents triethyl phosphate (TEP) and dimethylacetamide (DMAc) and addition of $TiO_2$ nanoparticles. Properties of the neat and composite membranes were characterized using scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), Atomic force microscopy (AFM) and contact angle and membrane porosity measurements. The neat and composite membranes were further investigated in terms of BSA rejection and flux decline in cross flow filtration experiments. Following hydrophilicity improvement of the PVDF membrane by addition of 0.25 wt.% $TiO_2$, (from $70.53^{\circ}$ to $60.5^{\circ}$) degree of flux decline due to irreversible fouling resistance of the composite membrane reduced significantly and the flux recovery ratio (FRR) of 96.85% was obtained. The results showed that using mixed solvents (DMAc/TEP) with lower content of $TiO_2$ nanoparticles (0.25 wt.%) affected the sedimentation rate of nanoparticles and consequently the distribution of nanoparticles in the casting solution and membrane formation which influenced the properties of the ultimate composite membranes.

• Elastomers and Composites
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• v.53 no.3
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• pp.141-149
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• 2018

A series of aromatic poly(o-hydroxyamide)s (PHAs) were synthesized by the direct polycondensation reaction of 4,4′-(2,3-quinoxalinedioxy) dibenzoic acid and/or 4,4′-(2,3-pyridinedioxy) dibenzoic acid with bis(o-aminophenol) including 2,2-bis-(amino-4-hydroxyphenyl)hexafluoropropane. The PHAs exhibited inherent viscosities in the range of 0.17-0.35 dL/g at $35^{\circ}C$ in a DMAc solution. These polymers showed low inherent viscosities and yielded brittle films. All the PHAs showed excellent solubility in aprotic solvents such as DMAc, DMSO, NMP, and DMF at room temperature and in less polar solvents such as pyridine and THF. However, all the PBOs were only partially soluble in $H_2SO_4$. The PBOs exhibited 10% weight loss at temperatures in the range of $537-551^{\circ}C$. The maximum weight loss temperature increased with an increase in the content of the quinoxaline-containing monomer. The residue of the PBOs showed a weight loss of 45.8-56.7% at $900^{\circ}C$ in a nitrogen atmosphere.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.7B
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• pp.827-833
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• 2011

Directional MAC protocols have drawn great attentions recently in super high speed wireless local/personal area networks due to their higher antenna gain, better spatial reuse, longer transmission range, and lower interference. Despite of these merits, directional MAC protocols suffer from deafness problem. The deafness problem occurs if a node does not answer an RTS frame addressed to it. To overcome this problem, directional MAC protocols have aimed at avoiding the deafness problem using multiple control frames or advance notice techniques or distinguishing deafness from collision. In this paper, we analyze the performance of these schemes in deafness environments with some scenarios. Through performance analysis, we compare the performance of these schemes through evaluating actual network throughput.

• KSBB Journal
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• v.8 no.3
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• pp.237-242
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• 1993

Chitin-based fibers have low mechanical strength and hence cannot be used as surgery fiber due to fast degradation In tissues. A new fiber Chitulose was made by mixing chitin with cellulose, both of which have similar structure. A mixture of dimethylacetamide (DMAc) and 6% lithium chloride (LiCl) was found to be an effective solvent system for dissolvoing chitin and cellulose. The Chitulose fiber made by wet spinning of a mixture of chitin and cellulose resulted in the highest degree of strength and flexibility when the ratio of chitin to cellulose was 1.5; 0.2. The fiber maintained mechanical structure even after autoclaving, indicating thermal stability. A biodegradability test of the Chitulose fiber by imbeding in a rat showed that degradation was initiated in 14 days and completely done in 40 days.

• Proceedings of the Korean Society of Dyers and Finishers Conference
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• 2008.04a
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• pp.153-155
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• 2008

M-aramid(in DMAc)를 전기 방사하여, chlorine을 부착시켜 항균성을 가지게 하였고, 부착된 chlorine의 농도는 titration을 통해 확인하였다. 15cm를 유지하여 방사했을 경우 10cm일 때에 비해 비드의 양이 적고, 비교적 균일한 형태로 방사되었다. 방사거리를 15cm로 유지시켜 방사한 m-aramid의 oxidized chlorine의 농도를 측정한 결과, 매우 우수한 수치를 보였고, 전압이 증가할수록 조금씩 감소하였다.

• Proceedings of the IEEK Conference
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• 2005.11a
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• pp.971-974
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• 2005

In this paper, we describe photonic sensor interface in SOPC(System on a programmable chip) platform. This platform uses device that has ARM922T processor and APEX FPGA area on a chip. We use two development kits. The one is embedded kit that using Intel's Xscale device, the another is SOPC kit that using Altera's Excalibur device. We implement some device logic that DMAC, ADCC, etc. and application.

• Proceedings of the Korean Society of Dyers and Finishers Conference
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• 2008.10a
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• pp.63-64
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• 2008

본 연구에서는 최근 염색성 향상에 관해 많은 연구가 이루어지고 있는 m-aramid를 사용하여 film으로 제조한 뒤, 표면적 증가에 따른 염색성 및 기타 다른 특성의 차이를 측정하여 비교하였다. DMAc를 용매로 하여 제조한 m-aramid 용액을 film으로 제조한 결과, 응고욕의 종류별로 염색성 및 기타 특성에 대해 상이한 결과를 보였다.