• 한국미생물·생명공학회지
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• 제21권3호
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• pp.200-206
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• 1993

The effect of pH (7, 5 and 4) and nisin (100 and 200IU/ml) on heat resistance of Listeria monocytogenes Scott A were determined using citrate-phosphate buffer system. Heat resistance of vegetative and starved cell was decreased as pH value was lower at 65 and 72C. Starved L. monocytogenes was more resistant than vegetative cell at both temperature. Heat resistance of vegetative and starved cell was decreased significantly with treatment of nisin. The effect of nisin was increased significantly at low pH(5, 4). Adherent microcolony was more resistant to heat and nisin than planktonic cell. Contamination of L. monocytogenes may be prevent by using nisin in food and food processing environments.

• 대한기계학회논문집A
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• 제21권9호
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• pp.1422-1431
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• 1997

When the structures are exposed to their own an application for a long period, a number of variables such as strength properties and corrosion resistance, so on are expected to change. In the present investigation the corrosion behavior and resistance for the original and degraded materials of Ni-Cr-Mo-V steel were evaluated under the conditions of pH 3, 6, 9 and 12 in a distilled water environment. The electrochemical polarization technique was employed in this investigation. Based upon the experimental results obtained, the following conclusions were drawn. A severe and uniform corrosion was observed for both original and degraded materials under the condition of pH 3. At pH 6 and pH 9, these materials showed the degradation by a pitting corrosion. The materials under pH 12 environment were degraded by a uniform corrosion. The corrosion rate per year were the highest in the pH 3 environment, followed by pH 12, pH 6 and pH 9 environment in order. The corrosion resistance was decreased from the original material, slow cooled material (10.deg. C/hr) and step cooled material in order.

• 미생물학회지
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• 제23권4호
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• pp.282-290
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• 1985

Small size antibiotic resistance plasmids having molecular weights less than 10 Mdal were isolated and characterized from ten clinically isolated multiple resistant Staphylococcus aureus. Agarose gel electrophoresis profiles and antibiotic resistance patterns divided these strains into four groups. Strain 2-23-6, the representative strain of a group of five strains conferred two plasmids of molecular weights $1.6{\times}10^6\;dal\;and\;2.0{\times}10^6$ dal. The small plasmid (pSBK 112) specified macrolides, lincosamides and streptogramin type B (MLS) resistance gene which are expressed constitutively. Lage plasmid (pSBK 125) specified chloramphenicol resistance gene which is inducible. Strain 10-5 conferred a $3.0{\times}10^6$ dal plasmid (pSBK 141) which carry an inducible ampicillin resistance gene and strain P-H-2 conferred and $1.6{\times}10^6$ dal plasmid (pSBK 190) which carry a constitutive MLS resistance gene. Strain D-H-1 conferred four plasmids of molecular weights $0.8{\times}10^6$ dal (pSBK 201), $1.6{\times}10^6$ dal (pSBK 202), $2.5{\times}10^6$ dal (pSBK 203), and $1.2{\times}10^7$ dal (pDBK 204), respectively. Among those four plasmids, only pSBK 203 specified chloramphenicol resistance gene. Curing of constitutive MLS resistance using acriding orange or ethidium bromide in 2-23-6 and P-H-2 strains produced 'inducible' MLS resistance strains which are less resistant to MLS than the wild type strains, suggesting that there are two resistance genes in both strains; one is constitutive and the other is inducible.

• 한국축산식품학회지
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• 제31권4호
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• pp.551-556
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• 2011

본 연구는 표준균주 C. sakazakii(CAFM2)와 4개의 야생균주(EB 1, EB 5, EB 7, EB 41)를 사용하여 pH를 조정한 산성 환경에서의 저항성을 살펴보았다. C. sakazakii는 pH 4.5 TSB에서 5시간, 10시간 동안 적응한 경우, pH 4.5 TSB에서 적응하지 않은 경우와 비교하여 EB 7을 제외한 모든 균주가 pH 2.5 TSB에서의 D값이 유의적으로 높게 나타났다(p<0.05). 따라서 약산성 환경에서 적응한 균주는 강산성 환경에서의 저항성이 증가하였다. C. sakazakii는 pH 4.5 TSB에서 배양한 경우, pH 7.2 TSB에서 배양한 경우와 비교하여 모든 균주가 pH 2.5 TSB에서의 D값이 유의적으로 높게 나타났다(p<0.05). 따라서 약산성 환경에서 배양한 균주는 강산성 환경에서의 저항성이 증가하였다. 본 연구를 통해 C. sakazakii는 약산성 환경에 적응한 경우 강산성 환경에서의 저항성이 증가하는 것으로 나타났다. 이러한 acid adaptation response는 C. sakazakii와 관련된 식품 가공 산업에서의 hurdle technology를 적용하는데 있어서 안전성 확보와 관련된 시사점을 제공할 수 있을 것으로 판단된다.

• 한국표면공학회지
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• 제52권3호
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• pp.156-162
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• 2019

Electroless Ni-P coatings are widely used in the chemical, mechanical, and electronic industries because of their excellent wear and abrasion resistance. In this study, The influence of pH values on properties of Ni-P-PTFE composite coatings was investigated. To improve mold lubrication, Ni-P-PTFE composite coatings at different pH value were studied. The morphology and phase structure of Ni-P-PTFE composite coatings were analyzed by scanning electron microscopy(SEM) and X-ray diffractometry(XRD). The result showed that Ni-P-PTFE composite coating is composed of Ni, P and PTFE. It exhibits an amorphous structure and good Corrosion Resistance to the substrate. Ni-P-PTFE composite coatings have higher open circuit potential than that of the substrate, which obtained at pH value of 5.0 optimal integrated properties.

• 청정기술
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• 제12권4호
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• pp.232-237
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• 2006

본 연구에서는 분무건조법으로 유동층용 아연계 탈황제를 제조하는 과정에서, 슬러리의 pH와 점도가 성형된 탈황제의 내마모성에 미치는 영향이 조사되었다. 아연계 탈황제의 내마모성을 개선하기 위하여 무기성 결합제로 알루미나 졸이 사용되었으며 슬러리에 들어있는 무기 결합제의 효과적인 분산을 위하여 슬러리의 pH가 조절되었다. 슬러리의 pH가 높아 알칼리성인 경우 알루미나 졸이 겔 상태로 변하여 슬러리의 점도가 높아지며 성형된 탈황제의 내마모성이 저하 되었다. 본 연구의 실험결과, 슬러리의 pH가 6으로 조절되어 성형된 탈황제가 가장 좋은 내마모성을 나타내었다. 또한 슬러리의 점도에 따라 성형된 탈황제의 밀도와 표면적 그리고 기공도가 달라졌으며, 이로부터 탈황제의 마모 특성이 결정됨을 알 수 있었다. 성형된 탈황제의 내마모성은 밀도가 높고, 표면적과 기공도가 낮을수록 높아지는 것으로 나타났으며, 최적 점도범위는 약 400-550 cP 정도였다.

• Corrosion Science and Technology
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• 제8권3호
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• pp.110-115
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• 2009

At the onset of corrosion of steel in concrete, hydrogen ions usually evolve in the process of electrochemical reaction, thereby decreasing the pH of the pore solution, which can be buffered by cement hydration products, as being representatively illustrated by calcium hydroxide. Hence, a fall in the pH is dependent on properties of cement hydration (i.e. hydration products and degree of hydration). The present study tested acid neutralization capacity (ANC) of cementitious binders of OPC(Ordinary Portland Cement), 30% PFA(Pulverized Fuel Ash), 60% GGBS(Ground Granulated Blast Furnace Slag), 10% SF(Silica Fume) to quantify the resistance of cement matrix to a pH fall. Cement pastes were cast at 0.4 of a free W/C ratio with 1.5% chlorides by weight of binder in cast. Powder samples obtained crushed and ground specimen after 200 days of curing were diluted in still water combined with different levels of 1M nitric acid solution, ranging from 0.5 to 20 mol/kg. Then, the pH of diluted solution was monitored until any further change in the pH did not take place. It was seen that the pH of the diluted solution gradually decreased as the molar amount of nitric acid increased. At some particular values of the pH, however, a decrease in the pH was marginal, which can be expressed in the peak resistances to a pH fall in the ANC curve. The peaks occurred at the variations in the pH, depending on binder type, but commonly at about 12.5 in the pH, indicate a resistance of precipitated calcium hydroxide. The measurement of water soluble chloride at the end of test showed that the amount of free chloride was significantly increased at the pH corresponding to the peaks in the ANC curve, which may reflect the adsorption of hydration products to chlorides.

• Corrosion Science and Technology
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• 제12권5호
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• pp.220-226
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• 2013

The uncertainty in statistical noise resistance measurement was evaluated for a type 316 stainless steel in NaCl solutions at room temperature. Sensitivity coefficients were determined for measurands or variables such as NaCl concentration, pH, solution temperature, surface roughness, inert gas flow rate and bias potential amplitude. The coefficients were larger for the variables such as NaCl concentration, pH, inert gas flow rate and solution temperature, and they were the major factors increasing the combined standard uncertainty of noise resistance. However, the contribution to the uncertainty in noise resistance measurement from the above variables was remarkably low compared to that from repeated measurements of noise resistance, and thus, it is difficult to lower the uncertainty in noise resistance measurement significantly by lowering the uncertainties related with NaCl concentration, pH, inert gas flow rate and solution temperature. In addition, the uncertainty in noise resistance measurement was high amounting to 17.3 % of the mean, indicating that the reliability in measurement of noise resistance is low.

• 분석과학
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• 제8권3호
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• pp.293-298
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• 1995

수용액에서 pH와 일정공급전위 변화에 따른 강철심에 도금된 놋쇠의 안정성을 교류 임피던스로 측정하여 연구하였다. 일정 pH에서 일정공급전위가 양전위로 감에 따라 코팅기공저항은 감소된다. 그 사실은 일정공급전위가 양전위로 감에 따라 도금된 놋쇠층이 용액에 더 용해됨을 나타낸다. 강철심에 도금된 놋쇠의 안정성은 pH=7.1 > pH=4.0 > pH=10.0 순으로 감소한다. 위와 같은 실험결과는 전자현미경 (SEM)/에너지분산분광계(EDS)의 자료에 의해 증명된다.

• Journal of Microbiology and Biotechnology
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• 제13권1호
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• pp.90-98
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• 2003

In vivo $^31p$ Nuclear Magnetic Resonance ($^31p$NMR) and metabolic studies were carried out on an acetic acid tolerant mutant, Zymomonas mobilis $ZM4/Ac^R$, and compared to those of the parent strain, Z. mobilis ZM4, to evaluate possible mechanisms of acetic acid resistance. This investigation was initiated to determine whether or not the mutant strain might be used as a suitable recombinant host far ethanol production from lignocellulose hydrolysates containing various inhibitory compounds. $ZM4/Ac^R$ showed multiple resistance to other lignocellulosic toxic compounds such as syringaldehyde, furfural, hydroxymethyl furfural, vanillin, and vanillic acid. The mutant strain was resistant to higher concentrations of ethanol or lower pH in the presence of sodium acetate, compared to ZM4 which showed more additive inhibition. in vivo $^31p$ NMR studies revealed that intracellular acidification and de-energization were two mechanisms by which acetic acid exerted its inhibitory effect. For $ZM4/Ac^R$, the internal pH and the energy status were less affected by sodium acetate compared to the parent strain. This resistance to pH change and de-energization caused by acetic acid is a possible explanation for the development of resistance by this strain.