Nonlinear Viscoelastic Behavior of Concentrated Xanthan Gum Systems in Large Amplitude Oscillatory Shear (LAOS) Flow Fields : Stress Waveform and Lissajous Pattern Analysis

안혜진,국화윤,이지석,송기원,Ahn, Hye-Jin,Kuk, Hoa-Youn,Lee, Ji-Seok,Song, Ki-Won The Korean Fiber Society 2016 한국섬유공학회지 Vol.53 No.5

The objective of the present study is to phenomenologically characterize the nonlinear rheological behavior of concentrated xanthan gum systems in large amplitude oscillatory shear (LAOS) flow fields by means of stress waveform and Lissajous pattern analysis. Using an Advanced Rheometric Expansion System (ARES), the dynamic viscoelastic behavior of aqueous xanthan gum solutions with different concentrations has been experimentally investigated in LAOS flow conditions with a various combination of several fixed strain amplitudes and constant angular frequencies. The main findings obtained from this study are summarized as follows: (1) When a sinusoidal deformation with large strain amplitude is applied, a distorted and nonsinusoidal but symmetrical stress response waveform is observed with time. (2) A saw-tooth shaped stress signal detected at large strain amplitudes may arise from a unique microstructure of xanthan polymer chains. A small peak of stress wave appearing at the position of maximum and minimum stress represents a nonlinear viscous nature of concentrated xanthan gum systems in LAOS flow fields. (3) As an increase in polymer concentration, the shape of stress wave becomes sharper and more distorted. This trend may be explained by an increase in structural density. (4) As a decrease in angular frequency, the stress wave exhibits a more distorted shape and both of the maximum and minimum peaks of a saw-tooth shaped stress response becomes more dominant. (5) At relatively small strain amplitudes, the Lissajous patterns (stress versus strain rate loops) show an elliptical form and their normalized ones are coincident with each other. When larger strain amplitudes are applied, however, the Lissajous patterns are noticeably nonelliptical, and moreover, as the strain amplitude is further increased, the tips of loops become more pointed with exhibiting a characteristic "S" shape.

The Doi-Edwards Constitutive Equation to Predict the Large Amplitude Oscillatory Shear (LAOS) Flow Behavior of Viscoelastic Polymer Liquids

안혜진,장갑식,송기원,Ahn, Hye-Jin,Chang, Gap-Shik,Song, Ki-Won The Korean Fiber Society 2017 한국섬유공학회지 Vol.54 No.4

The present study has been designed to predict the nonlinear viscoelastic behavior of concentrated polymer systems in large amplitude oscillatory shear (LAOS) flow fields by means of the Doi-Edwards constitutive equation. Using an Advanced Rheometric Expansion System (ARES), the dynamic viscoelastic behavior of aqueous poly (ethylene oxide) (PEO) solutions with various molecular weights and different concentrations has been investigated with a various combination of several fixed strain amplitudes and constant angular frequencies. The linear dynamic data (storage modulus and loss modulus) over a wide range of angular frequencies were also obtained to determine the relaxation spectrum parameters. The experimentally obtained Lissajous patterns (stress-strain rate hysteresis loops) were compared with the Doi-Edwards model predictions over a wide range of strain amplitudes and angular frequencies for all polymer solutions prepared in this work. The nonlinear viscoelastic functions were analyzed by the aid of 3D plots and predicted over a wide range of strain amplitudes to evaluate the overall predictability of the Doi-Edwards model. The main findings obtained from this study are summarized as follows : (1) The Lissajous patterns predicted by the Doi-Edwards model represent a good agreement with the experimentally obtained stress-strain rate hysteresis loops both in linear and nonlinear viscoelastic regions. (2) The predictions of the Doi-Edwards model are closely coincident with the experimental results in the linear viscoelastic region. As the strain amplitude is increased, the predicted nonlinear viscoelastic functions are somewhat larger than that of the experimental data. Nevertheless, all trends of the nonlinear viscoelastic behavior are qualitatively in good agreement with the experimental results. (3) The Doi-Edwards model gives a very good prediction for the first harmonic storage modulus and loss modulus up to the nonlinear viscoelastic region. The third and fifth harmonic storage and loss moduli exhibit an overshoot or an undershoot at large strain amplitudes. This constitutive equation can describe well such excessive behavioral changes in a qualitative sense. (4) The Doi-Edwards model has a slightly better ability than the Wagner model to predict the LAOS flow behavior of concentrated polymer systems.

A Time-Strain Separable K-BKZ Constitutive Equation to Describe the Large Amplitude Oscillatory Shear (LAOS) Flow Behavior of Viscoelastic Polymer Liquids

안혜진,장갑식,송기원,Ahn, Hye-Jin,Chang, Gap-Shik,Song, Ki-Won The Korean Fiber Society 2017 한국섬유공학회지 Vol.54 No.4

The present study has been designed to describe the nonlinear viscoelastic behavior of concentrated polymer systems in large amplitude oscillatory shear (LAOS) flow fields using a time-strain separable K-BKZ constitutive equation (i.e., Wagner model). Using an Advanced Rheometric Expansion System (ARES), the dynamic viscoelastic behavior of aqueous poly(ethylene oxide) (PEO) solutions with various molecular weights and different concentrations has been investigated with a various combination of several fixed strain amplitudes and constant angular frequencies. The linear dynamic data (storage modulus and loss modulus) over a wide range of angular frequencies were obtained to determine the relaxation spectrum parameters and the stress relaxation moduli at various deformation magnitudes were measured to determine the damping function. The effects of the number of relaxation spectrum parameters and damping functions on the prediction results of the Wagner model were examined in depth. The nonlinear viscoelastic functions were analyzed by the aid of 3D plots and predicted over a wide range of strain amplitudes to evaluate the overall predictability of the Wagner model. The main findings obtained from this study are summarized as follows : (1) The Lissajous patterns predicted by the Wagner model are in good coincidence with the experimentally obtained stress-strain rate hysteresis loops both in linear and nonlinear viscoelastic regions and are independent of the number of relaxation spectrum parameters used in the calculation of memory function. (2) The effect of damping function on the predictive ability of the Wagner model is more sensitive than that of memory function. When the damping function is smaller than that of the experimental data, the stress amplitude predicted by the Wagner model also becomes smaller. (3) The Wagner model predictions are closely coincident with the experimental results in the linear viscoelastic region. As the strain amplitude is increased, the predicted nonlinear viscoelastic functions are somewhat larger than that of the experimental data. Nevertheless, all trends of the nonlinear viscoelastic behavior are in good agreement with the experimental results in a qualitative sense. (4) The Wagner model predicts the first harmonic loss modulus more exactly than the first harmonic storage modulus. As the strain amplitude is increased, the first harmonic storage modulus is somewhat overpredicted. The third and fifth harmonic storage and loss moduli exhibit an overshoot or an undershoot at large strain amplitudes. This constitutive equation has an ability to qualitatively describe well such dramatic behavioral changes.

Nonlinear Viscoelastic Behavior of Concentrated Xanthan Gum Systems in Large Amplitude Oscillatory Shear (LAOS) Flow Fields : Fourier Transform Rheology

안혜진,국화윤,송기원,Ahn, Hye-Jin,Kuk, Hoa-Youn,Song, Ki-Won The Korean Fiber Society 2017 한국섬유공학회지 Vol.54 No.5

The present study has been performed to quantitatively characterize the nonlinear rheological behavior of concentrated xanthan gum systems in large amplitude oscillatory shear (LAOS) flow fields by means of the methodology of Fourier transform (FT) rheology. Using an Advanced Rheometric Expansion System (ARES), the dynamic viscoelastic behavior of aqueous xanthan gum solutions with different concentrations has been experimentally investigated in LAOS flow conditions with a various combination of several fixed strain amplitudes and constant angular frequencies. The nonlinear viscoelastic functions were derived from the Fourier spectra of stress responses, and then the fundamental and higher harmonic contributions were calculated from discrete Fourier transform (DFT). The nonlinear viscoelastic behavior was interpreted by displaying 3D plots, and then the effects of strain amplitude and angular frequency on the nonlinear behavior were discussed in depth. A comparison of the experimentally obtained stress response with the stress waves calculated from higher harmonic nonlinear viscoelastic functions was made to clarify the role of higher harmonic contributions. The main findings obtained from this study are summarized as follows : (1) When the strain amplitude becomes larger than a critical value of 50%, the higher nonlinear viscoelastic functions must be considered to explain the nonlinear viscoelastic behavior. However, the fundamental stress amplitude is dominantly larger than those of higher harmonics. (2) As the strain amplitude is increased, the fundamental stress amplitude is steeply increased within the linear viscoelastic region beyond which followed by an approximately constant magnitude at large deformations. This strain dependence may be explained as a distinction between linear and nonlinear viscoelastic behavior. (3) When the strain amplitude exceeds a critical value of 50%, the higher stress amplitudes are sharply increased with an increase in strain amplitude at large deformations, indicating that the higher stress harmonics exert an influence on the nonlinear viscoelastic behavior. (4) In order to interpret the complicated nonlinear viscoelastic behavior occurring at large deformations, the fundamental terms as well as the higher harmonics of phase angles defined at the odd terms should be deliberated for a quantitatively advanced analysis. (5) An overall shape of the experimentally obtained stress response is strongly affected by the higher harmonic contributions. As the angular frequency is decreased, a more distorted and a sharper stress waveform is observed at LAOS deformations. (6) A distorted stress waveform is qualitatively inclined to the left side with respect to a sinusoidal curve. In order to explain the nonlinear viscoelastic behavior of concentrated xanthan gum systems in LAOS flow fields, the nonlinear viscoelastic functions from the first to at least seventh harmonics should be considered for an accurate analysis.

쌀보리 종실 내 미생물 분포와 생균제 접종이 발효특성에 미치는 영향

안혜진,김기현,조은석,김조은,김광식,김영화,송태화,박종호,강환구,장선식,오영균,천동원,설국환,Ahn, Hye-Jin,Kim, Ki Hyun,Jo, Eun Seok,Kim, Jo Eun,Kim, Kwang-Sik,Kim, Young Hwa,Song, Tae Hwa,Park, Jong Ho,Kang, Hwan Ku,Jang, Sun Sik,Oh, Young K 한국초지조사료학회 2015 한국초지조사료학회지 Vol.35 No.4

본 시험은 동계작물인 쌀보리의 알곡에 대한 사료로서의 활용도를 제고하고자 미생물 분포를 분석하고, 발효과정중 이화학적 및 미생물학적 특성의 변화 분석을 통하여 효과적인 발효사료 제조방법을 제시하고자 수행하였다. 즉, 수확된 쌀보리 종실에 시판 생균제를 기준에 맞게 접종한 후 공기와 접촉하지 않도록 밀봉하여 $37^{\circ}C$에서 7일간 발효를 통해 쌀보리 종실의 저장성과 안전성을 증진시킬 수 있다. 쌀보리 종실 자체에 Staphylococcus속과 Bacillus속의 미생물들이 다수 존재하여 자연발효의 가능성이 있음을 보여 주었다. 또한 생균제를 접종하지 않은 쌀보리 종실도 기간이 경과됨에 따라 산도가 저하되고 유산균 수가 증가하여 발효가 이루어지고 있는 것으로 나타났다. 그러나 쌀보리 종실에 생균제를 접종하였을 경우, 발효 7일차에 pH가 $4.33{\pm}0.02$로 발효가 더 빨리 진행되었으며, 유산균의 수도 전체 발효기간 동안 미 접종 대조구에 비해 높게 유지되었으나, 효모의 수에 있어서는 차이가 나타나지 않았다. 발효에 의해 쌀보리 종실의 산도가 저하됨에 따라 초기 $10^7cfu/g$ 이상 검출되었던 대장균이 발효 7일차 이후부터는 전혀 검출되지 않아 발효가 쌀보리 종실의 안전성을 유지시키는 데 있어 효과적인 저장방법으로 나타났다. This study was performed to analyze the resident microbial flora and the effects of probiotic inoculation on the fermentation characteristics of whole grain naked barley (Hordeum Vulgare L.) with the goal of evaluating the possibility of utilization as fermented feedstuff. Naked barley grains were harvested 35 days after heading, and the microbial flora was analyzed using MALDI-TOF mass spectrometer. After inoculation of commercial microbes to the naked barley grain (BT), the pH and number of bacteria, such as aerobic bacteria, lactic acid bacteria, yeast and E. coli, were measured and compared with the non-inoculated control (BC). A total of 122 colonies was isolated from the naked barley grain and the most popular bacteria species was Staphylococcus xylosus (n = 30, 24.59%). The pH value decreased more rapidly in BT than in BC, and was significantly lower after 7 days of fermentation at $4.33{\pm}0.02$ and $4.83{\pm}0.01$, respectively. The number of aerobic bacteria, lactic acid bacteria and yeast showed an increasing trend within the first 7 days of fermentation, however, their numbers decreased at 28 and 42 days of fermentation. The population of lactic acid bacteria in BT was higher than in BC, but there was no significant different at 7 days of fermentation, with respective levels of $9.24{\pm}0.20$ and $9.01{\pm}0.10logCFU/g$ (p>0.05). The initial number of E. coli was very high in the naked barley grain but subsequently decreased significantly. After 7 days of fermentation, E. coli was not detected in either BT or BC samples. From these results, it appears that the fermentation of naked barley grain proceeded adequately after 7 days, and that fermentation contributes to the safety of naked barley grain during storage.

리그닌과 셀룰로오스의 섭식 능력을 이용한 흰개미의 식용과 사료로서 활용방안에 따른 온실가스 발생량 및 질소의 순환 효율성 평가

안혜진 ( Hye-jin Ahn ),임성린 ( Seong-rin Lim ) 한국폐기물자원순환학회(구 한국폐기물학회) 2017 한국폐기물자원순환학회 추계학술발표논문집 Vol.2017 No.-

국제연합식량농업기구(FAO, United Nations Food and Agriculture Organization)의 보고서에 따르면 21세기전 세계의 인구는 2050년 약 90억에 달할 것으로 예측되며, 이러한 인구팽창으로 인한 식량부족 및 사료공급의 문제는 생산 시 야기되는 자원고갈 및 환경영향에 대한 우려와 함께 전 세계의 큰 관심사로 화두되었다. 이렇듯 현대사회가 직면한 복합적인 문제점을 해결하기 위해 전 세계적으로 새로운 미래자원에 대한 탐색이 이루어졌으며, 곤충이 하나의 유망자원으로서 새롭게 각광받기 시작하였다. 특히 목질을 섭식하는 흰개미의 경우 난분해성 물질인 리그닌과 셀룰로오스의 분해능력으로 인해 해외에서는 이미 오래전부터 흰개미의 장내 미생물을 이용하여 목질계 바이오매스로부터 바이오에탄올을 생산하는 방법에 대해 연구가 진행되어왔다. 하지만 국내에서는 흰개미를 목조 문화재를 가해하는 해충으로 분류하여 흰개미의 방제에 초점을 맞추어 연구가 많이 진행되어왔을 뿐 유용자원으로서의 흰개미의 잠재성에 대한 관심과 연구가 미흡한 실정이다. 또한, 흰개미는 우수한 단백질 공급원으로서 일부 국가에서는 식용 및 사료로서 활용하고 있지만 이에 따른 환경영향 및 효율에 관한 연구 역시 미흡하다. 따라서 본 연구는 국내에 분포하는 일본흰개미(Reticulitermes speratus kyushuensis Morimoto)를 대상으로 흰개미가 주로 섭식하는 폐목재를 먹이로 주어 사육하였을 때, 생산되는 식용과 사료의 온실가스 발생량(LCA, Life cycle assessment)과 질소의 순환효율(ROI, Return on Investment)을 정량화하여 환경적·경제적 이점을 도출하고자 하였다.정량화된 온실가스 발생량과 질소의 순환효율은 식용으로 활용할 경우 기존의 단백질원인 한우, 양돈, 육계, 대두와 비교하고, 사료의 경우 대두박과 비교하였다. 그 결과 흰개미를 식용과 사료로 이용할 경우 온실가스 발생량 측면에서 비교적 높은 값을 나타내었으며, 질소의 순환효율에서는 상대적으로 우수한 결과를 나타내었다. 미래 유망자원으로서 보다 다양한 곤충에 대한 탐색이 이루어질 필요성이 있으며, 곤충활용에 따른 환경적·경제적 이점의 정량화는 향후 곤충산업의 발전방향을 제시하고 활성화하는데 이바지할 수 있을 것으로 예상한다.

발생액과 현금흐름이 현금배당 공시시점의 주가반응에 미치는 영향

안혜진 ( Hye Jin Ahn ),곽수근 ( Su Keun Kwak ),최삼열 ( Sam Yeol Choi ) 한국회계학회 2014 회계학연구 Vol.39 No.6

이익은 현금흐름과 발생액의 두 요소로 구분할 수 있다. 특정 정보가 공시될 때의 주가반응 수준은 해당 정보의 신뢰성에 따라 달라지게 된다. 본 연구에서는 현금배당 공시시점에 나타나는 주가반응이 이익수준에 연관성이 있는지를 살펴보고, 또한 주가반응이 현금흐름및 발생액과 각각 관련되어 있는지도 살펴보았다. 2001년부터 2011년까지의 2,550개 기업-연도 표본을 이용하여 분석한 결과, 주가반응은 이익뿐만 아니라 현금흐름 및 발생액과 모두 관련되어 있다는 점을 발견하였다. 또한 배당을 배당증가와 감소의 경우로 구분하여 분석한 결과, 배당감소 표본의 경우에서만 유의적인 발견이 도출되었다. 즉 시장은 배당감소 소식을 더 신뢰성이 높은 소식으로 판단하여 강하게 반응한다는 증거다. 그러나 배당증가 소식의 경우, 배당이 상당한 수준으로 증가한 경우에서만 유의적인 관련성이 발견되었다. 현금흐름에 대한 반응과 발생액에 대한 반응의 크기가 다르다는 증거는 발견되지 않았다. 이런 발견은 배당 공시시점에서 시장의 반응에 대한 결정요인을 밝혔다는 측면에서 많은 공헌점을 가지고 있다. Earnings can be decomposed into two components: cash flows and accruals. The cash flows are regarded as a reliable information on firm performance and as persistent for longer period of time. In contrast, accruals are regarded not as reliable as cash flows and not persistent. As a result, when investors observe information on earnings, they respond differently depending on the perceived reliability of the information. This study investigates how investors respond to the cash flows components and accruals components of earnings separately when dividends are announced in the stock market. Dividends policy is a very important decision among corporate financial decisions. In return for the financial investments by shareholders, firms pay dividends to the shareholders. Dividends payments provide important information to the shareholders on the future prospects of the firm as well as the current financial status and operating performance. These perspectives on dividends are collectively called as signaling hypothesis of dividends (Miller and Rock 1985). As a result, when dividends are announced, stock market strongly responds to the announcements (Aharony and Swary 1980; Asquith and Mullins 1983; Woolridge 1983; Grullon et al. 2002). Especially, when firms announce dividend increase or initiation (decrease or suspension), stock price significantly increases (decreases). The magnitude of the reaction is greater when firms announce dividend decrease or suspension than that when firms announce dividend increase or initiation. The findings suggest that investors regard the dividend decrease or suspension as more reliable information than dividend increase or initiation. In accounting area, studies link dividends to earnings. They find that the magnitude of the market reaction at the time of dividends announcements is positively associated with the level and quality of earnings (Healy and Palepu 1987; Manakyan and Carroll 1991; Nissim and Ziv 2001; Mikahil et al. 2003; Koch and Sun 2004). When the pattern of earnings stream supports the change of dividends, the market regards the dividends information as more credible and responds more strongly. Investors may treat the components of earnings differently. Healy and Palepu(1993), Sloan (1996) and Subramanyam (1996) argue that accruals may reflect the information component (which conveys inside information to external financial statement users) and earnings management component (which distort true financial performance of the firm). Depending on the market``s perception on the reliability of accruals, the market treats accruals as important information or evidence of earnings management. If investors regard the information as the former (later), market is (not) likely to respond to the component of accruals at the time of the dividend announcements. We empirically test this prediction whether the market responds differently to the two components of earnings at the time of dividends announcements. Our samples are 2,550 firm-year observations that announce cash dividends during the period from year 2001 to year 2010 in Korean Stock Market. Among them, 1,077 observations increased their dividends while 522 observations decreased their dividends. There were no change of the dividends from pervious years for the remaining 951 observations. In terms of sample size, this study is one of the rare works that use extensive samples collected over long period in Korean stock market. Most prior Korean studies, that mostly use small sample of dividends, even had a trouble to find the significant market reaction at the time of dividends announcements. Empirical results using these samples are summarized as follows. First, as documented in prior studies, we find that earnings of the year is positively associated with the magnitude of the market``s reaction (measured by the cumulative abnormal returns during the event period) at the time of cash dividends announcements. Second, when we divide the earnings into accruals and cash flows, we find that both components are significantly associated with the magnitude of the market``s reaction. In addition, the magnitudes are not significantly differ between cash flow component and accruals component. It implies that the market regard the accruals as a credible signal of private information rather than the output of discretionary earnings management by insiders. Third, when divide the samples to the subsamples, the firms with dividend increase and the other firms with dividend decrease, we find that all the significant results are due to the subsamples with dividend decrease. For the samples with dividend increase, we fail to find any significant relations, suggesting that investors trust dividend decrease as more credible signal than dividend increase. Otherwise, it could be the evidence of asymmetrically stronger investor response to bad news disclosure compared with good news disclosure (Kahneman and Tversky 1979). Fourth, above explained results are not sensitive in various analyses, suggesting the robustness of our findings. These findings provide valuable insights into the market``s behavior at the time of dividends announcements.

식사형태와 식사능력에 따른 요양병원 여자 노인 환자의 영양섭취조사

안혜진(Hye Jin Ahn),강주희(Ju Hee Kang),이홍미(Hong Mie Lee) 대한지역사회영양학회 2014 대한지역사회영양학회지 Vol.19 No.2

This study was carried out to determine nutritional status of elderly patients in a long-term care hospital according to meal type and eating ability. Methods: Subjects were 47 female patients aged over 65 (79.3 ± 7.1 years) who resided in a long-term care hospital in Seoul. Thirty seven patients who ate diet orally were grouped according to meal type (27 general diet and 10 soft diet) and eating ability (26 eating by oneself and 11 eaten with help) and 10 were on tube feeding. Nutritional status was determined by food consumption and mid-arm circumference. Results: The mean adequacy ratios (MARs) of 12 nutrients (protein, calcium, phosphorus, zinc, vitamin A, vitamin B1, vitamin B2, vitamin B6, niacin, folic acid, vitamin C) were 0.687 for general diet, 0.565 for soft diet, 0.680 for eating by oneself and 0.677 for eaten with help, which were significantly lower than 0.982 for tube feeding (p < 0.05 or p < 0.01). The patients on tube feeding had significantly lower % arm circumference compared to those who ate general diet (84.0% vs. 95.4%, respectively, p < 0.05). Nutrients intakes, nutrient adequacy ratio (NAR) and index of nutritional quality (INQ) were not different between meal types as well as eating ability. The most insufficiently consumed nutrients by the patients on diet were folic acid, vitamin B2, and calcium (NAR 0.334~0.453, 0.515~ 0.539, and 0.516~0.533, respectively). Conclusions: The results suggested that regardless of meal type or eating ability, the subjects who were on diets in this study might have inadequate intake of folic acid as well as vitamin B2, and calcium, which need to be reflected on menu planning. The measurement of mid-arm circumference presented more risk of malnutrition of patients on tube feeding than those on diets, despite apparently better nutrient consumption.

일반논문 : 18세기 가사를 통해 본 경향사족간 의식의 거리 -향촌문제를 중심으로

안혜진 ( Hye Jin Ahn ) 한국고전연구학회 2007 한국고전연구 Vol.0 No.15

베체트병과 동반된 심부정맥 혈전증 1예

안혜진 ( Hye-jin Ahn ),신은재 ( Eun-jae Shin ),곽민재 ( Min-jae Gwak ),정기헌 ( Ki-heon Jeong ),이무형 ( Mu-hyoung Lee ) 대한피부과학회 2018 대한피부과학회지 Vol.56 No.5

Behcet’s disease is a multisystem inflammatory disorder with a chronic relapsing course. It is considered a nonspecific systemic vasculitis involving both, venous and arterial circulation. Although lower extremity vein thrombosis (LEVT) is one of the most common manifestations of vascular involvement, a few cases are reported in the literature and to our knowledge, and only 2 cases were reported in Korea. We report a case of a 40-year-old Korean man with localized erythematous macules and patches on both lower extremities with a marked painful swelling on the right leg. The patient reported a history of similar lesions 10 years prior to presentation and also a history of recurrent aphthous oral ulcerations. Based on phlebographic findings of old LEVT in the right femoral vein, the patient was diagnosed with Behcet’s disease associated with LEVT. (Korean J Dermatol 2018;56(5):325∼ 328)