• Title, Summary, Keyword: Degradation

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Thermal Degradation and Cyclodepolymerization of Poly(ethylene terephthalate-co-isophthalate)s

  • Yoo, Dong Il;Shin, Younsook;Youk, Ji Ho
    • Fibers and Polymers
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    • v.2 no.2
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    • pp.75-80
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    • 2001
  • The thermal degradation of poly(ethylene terephthalate-co-isophthalate)s (PETIs) is investigated by using isothermal thermogravimetric analysis at the temperature range of 280-31$0^{\circ}C$. The degradation rate of PETIs is increased as the mole ratio of ethylene isophthaloyl (EI) units in PETIs increases. The activation energies for the thermal degradation of poly(ethylene terephthalate), PETI(5/5), and poly(ethylene isophthalate) are 33.4, 16.6, and 8.9 kcal/mole, respectively. The degradation rate of PETIs is influenced by their volatile cyclic oligomer components formed during the polymerization and the thermal degradation. It is simulated by the rotational isomeric state model that the content of cyclic dimer in PETIs, which is the most volatile cyclic oligomer component, increases with the EI units in PETIs.

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Evaluation of Material Degradation Using Electrical Resistivity Method (전기비저항법을 이용한 재료열화 평가)

  • Kim, Jeong-Pyo;Bae, Bong-Kook;Kim, Dong-Joong;Seok, Chang-Sung
    • Proceedings of the KSME Conference
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    • pp.129-136
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    • 2001
  • The remaining life estimation for the aged components in power plants as well as chemical plants are very important beacuse mechanical properties of the components are degraded with time of service exposure in high temperature. Since it is difficult to take specimens from the operating components to evaluate mechanical properties of components, nondestructive techniques are needed to estimate the degradation. In this study, test materials with 4 different degradation levels were prepared by isothermal aging heat treatment at $630^{\circ}C$. And the DC potential drop method and destructive methods such as tensile, $K_{IC}$ and hardness tests were used in order to evaluate the degradation of 1Cr-1Mo-0.25V steels. The objective of this study is to investigate the possibility of the application of DCPD method to estimate the material degradation, and to analyse the relationship between the electrical resistivity and the degree of material degradation.

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DEGRADATION OF NUCLEIC ACIDS BY CELL-FREE EXTRACT OF MIXED RUMEN PROTOZOA OF BUFFALO RUMEN

  • Sinha, P.R.;Dutta, S.M..
    • Asian-Australasian Journal of Animal Sciences
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    • v.1 no.4
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    • pp.219-222
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    • 1988
  • Degradation of deoxyribonucleic acid(DNA) and ribonucleic acid(RNA) by cell-free extract of mixed rumen protozoa of buffalo rumen was investigated. DNA was observed to be degraded rapidly during an initial incubation period of 2 hr with simultaneous appearance of degradation products. RNA on the other hand recorded a rapid degradation during an initial incubation period of 1 hr. RNA degradation products appeared upto an incubation period of 2 hr. DNA was observed to degrade into oligo- and mononucleotides. pyrimidine nucleosides, purine nucleoside adenosine and bases xanthine, hypoxanthine and thymine. Degradation products of RNA comprised of pyrimidine nucleosides, purine nucleoside, adenosine and bases xanthine, hypoxanthine and uracil besides oligo- and mononucleotides.

Degradation of Clavulanic Acid During the Cultivation of Streptomyces clavuligerus; Instability of Clavulanic Acid by Metabolites and Proteins from the Strain

  • Ishida Kenji;Hung Trinh Viet;Lee Hei-Chan;Liou Kwang-Kyoung;Shin Chang-Hun;Yoon Yeo-Joon;Sohng Jae-Kyung
    • Journal of Microbiology and Biotechnology
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    • v.16 no.4
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    • pp.590-596
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    • 2006
  • Clavulanic acid (CA) produced by Streptomyces clavuligerus is degraded during the bacterial cultivation. The degradation was examined in three different aspects, including physical, chemical, and enzymatic effects, in order to understand the degradation during the cultivation. The result showed that CA was unstable in the production medium containing ammonium salts and amino acids, owing to ammonium ions and amine groups. In addition, the degradation was not only due to instability of CA by metabolites and proteins, but also enzymes from S. clavuligerus such as $\beta-lactamase$ and penicillin-binding proteins. However, the degradation caused by these enzymes was not highly significant compared with the degradation during the cultivation, owing to irreversible reactions between CA and enzymes.

Service life prediction of CFRP bar for concrete reinforcement based on accelerated degradation tests (가속열화시험에 의한 콘크리트용 탄소섬유 강화플라스틱 바의 사용수명 예측)

  • Kwon, Young-Il;Kim, Seung-Jin;Lee, Hyoung-Wook
    • Journal of Applied Reliability
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    • v.9 no.2
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    • pp.71-80
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    • 2009
  • This paper discusses the service life prediction methods for CFRP bar for concrete reinforcement using accelerated degradation tests. The relationship between performance degradation and the rate of a failure-causing chemical reaction is assumed for the temperature accelerated degradation tests. Methods of obtaining acceleration factors and predicting service life of the CFRP bar using the degradation model are presented.

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Design of Accelerated Degradation Test with Tightened Critical Values under Random Coefficient Degradation Rate Model (확률계수 열화율 모형하에서 판정가속을 도입한 가속열화시험의 설계)

  • Cho, You-hee;Seo, Sun-keun
    • Journal of Korean Institute of Industrial Engineers
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    • v.34 no.1
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    • pp.23-31
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    • 2008
  • This paper presents accelerated degradation test plans considering adoption of tightened critical values. Under arandom coefficient degradation rate and log-linear acceleration models, the asymptotic variance of an estimatorfor a lifetime quantile at the use condition as the optimization criterion is derived where the degradation ratefollows a lognormal and Reciprocal Weibull distributions, respectively and then the low stress level andproportions ofunits allocated to each stress level are determined. We also show that the developed test plans canbe applied to the multiplicative model with measurement error.

Nondestructive Characterization and In-situ Monitoring of Corrosion Degradation by Backward Radiated Ultrasound

  • Song, Sung-Jin;Kim, Young H.;Bae, Dong-Ho;Kwon, Sung D.
    • Corrosion Science and Technology
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    • v.4 no.3
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    • pp.114-119
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    • 2005
  • Since the degradation caused by corrosion is restricted to the surface of materials, conventional ultrasonic nondestructive evaluation methods based on ultrasonic bulk waves are not applicable to characterization of the corrosion degradation. To take care of this difficulty, a new nondestructive evaluation method that uses ultrasonic backward radiation has been proposed recently. This paper explores the potential of this newly developed method for nondestructive characterization and in-situ monitoring of corrosion degradation. Specifically, backward radiated ultrasounds from aged thermo-mechanically controlled process (TMCP) steel specimens by corrosion fatigue were measured and their characteristics were correlated to those of the aged specimens. The excellent correlation observed in the present study demonstrates the high potential of the backward radiated ultrasound as an effective tool for nondestructive characterization of corrosion degradation. In addition, the potential of the backward radiated ultrasound to in-situ monitoring of corrosion degradation is under current investigation.

Thermal Degradation Behavior of Poly(alkylene terephthalate)s (테레프탈레이트계 폴리에스터의 열분해 거동에 관한 연구)

  • Kim Ki Jeong;Yeo Jeong Sup;Yoon Ji Young;Kim Joon Ho
    • Textile Science and Engineering
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    • v.42 no.4
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    • pp.228-234
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    • 2005
  • Thermal degradation behavior of the three homologous polyesters, poly(ethylene terephthalate)(PET), poly(trimethylene terephthalate)(PTT) and poly(butylene terephthalate)(PBT) were investigated by using thermogravimetric analysis(TGA) and pyrolysis-gas chromatography-mass spectrometry(PGC-MS). From the results of isothermal thermogravimetry, it was revealed that PTT has higher activation energy of thermal degradation than the other two polyesters. In PGC-MS analysis, the highly volatile products of the polyesters such as acetaldehyde and acetic acid evolved in the early stage of pyrolysis as common degradation products. Benzoic acid, methyl ester of benzoic acid, terephthalic acid and higher oligomers were produced as the main degradation products of poly(alkylene terephthalate)s at longer pyrolysis times. In isothermal pyrolysis, PTT showed the fastest thermal degradation rate among the three polyesters.

Optimal Design of Accelerated Degradation Tests with Two Stress Variables in the Case that the Degradation Characteristic Follows Weibull Distribution (열화특성치가 와이블분포를 따르는 경우 두 가지 스트레스 변수를 고려한 가속열화시험의 최적 설계)

  • Lim, Heonsang;Kim, Yong Soo
    • Journal of Applied Reliability
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    • v.13 no.2
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    • pp.87-98
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    • 2013
  • Accelerated degradation tests (ADTs) measuring failure-related degradation characteristic at the accelerated condition are widely used to assess the reliability of highly reliable products. Often, however, little degradation could be observed even in single-stress ADTs due to the high reliability of test unit, and as a result poor estimate of the reliability may be obtained. ADTs with multiple stress variables can be employed to overcome such difficulties. In this paper, optimal ADT plans with two stress variables are developed assuming that the degradation characteristic follows Weibull distribution by determining the stress levels, the proportion of test units allocated to each stress level such that the asymptotic variance of the maximum likelihood estimator of the q-th quantile of the lifetime distribution at the use condition is minimized.

Microbial Degradation and Toxicity of Hexahydro-1,3,5-Trinitro-1,3,5-Triazine

  • Khan, Muhammad Imran;Lee, Jaejin;Park, Joonhong
    • Journal of Microbiology and Biotechnology
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    • v.22 no.10
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    • pp.1311-1323
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    • 2012
  • In the present work, current knowledge on the potential fate, microbial degradation, and toxicity of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) was thoroughly reviewed, focusing on the toxicological assessment of a variety of potential RDX degradation pathways in bacteria and fungi. The present review on microbial degradation pathways and toxicities of degradation intermediates suggests that, among aerobic RDX degradation pathways, the one via denitration may be preferred in a toxicological perspective, and that among anaerobic pathways, those forming 4-nitro-2,4-diazabutanal (NDAB) via ring cleavage of 1-nitroso-3,5-dinitro-1,3,5-triazinane (MNX) may be toxicologically advantageous owing to its potential mineralization under partial or complete anoxic conditions. These findings provide important information on RDX-degrading microbial pathways, toxicologically most suitable to be stimulated in contaminated fields.