• Journal of Mechanical Science and Technology
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• v.20 no.1
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• pp.76-84
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• 2006

Arrayed ultrasonic sensors based on the piezoelectric thin film (lead-zirconate-titanate: Pb($Zr_{0.52}Ti_{0.48})O_{3}$) having composite membrane structure are fabricated. Different thermal and elastic characteristics of each layer generate the residual stress during the high temperature deposition processes, accomplished diaphragm is consequently bowing. We present the membrane deflection effects originated from the residual stress on the resonant frequencies of the sensor chips. The resonant frequencies ($f_r$) measured of each sensor structures are located in the range of $87.6{\sim}111\;kHz$, these are larger $30{\sim}40\;kHz$ than the resultant frequencies of FEM. The primary factors of $f_r$ deviations from the ideal FEM results are the membrane deflections, and the influence of stiffness variations are not so large on that. Membrane deflections have the effect of total thickness increase which sensitively change the $f_r$ to the positive direction. Stress generations of the membrane are also numerically predicted for considering the effect of stiffness variations on the $f_r$.

• Transactions of the Korean Society of Mechanical Engineers
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• v.6 no.2
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• pp.107-112
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• 1982

In order to analyze and investigate in the fatigue behavior of the notched specimens under the two level stressing, the U-notched specimens of structural carbon steel which is generally used is prepared. The obtained results are summarized as follows; (1) The fatigue limit of the U-notched specimens is lower than that of the unnotched. The fatifue notch factor (.betha.) of the U-notched specimens is 1.44 for mild steel and 1.52 for harden steel. The notch sensitivity (q) is 0.68 for mild steel and o.8 for harden steel. That is, these facts show that harden steel is more sensitive to the notch than mild steel. (2) The fatigue life time of the U-notched specimens under the overstressing is shorter than under the constant stressing, and the degree of fatigue life time decrease is different to each stress level; the degree for the high stress level is more than for the low stress level. (3) The fatigue life time of the U-notched specimes under the understressing is longer than under the constant stressing, and the degree of fatigue life time increase for the low stress level is more than for the high stress level.

• Geomechanics and Engineering
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• v.15 no.4
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• pp.987-995
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• 2018

In this study, a relationship between small-strain shear modulus ($G_{max}$) and overconsolidation ratio (OCR) based on shear wave velocity ($V_S$) measurement was established to identify the stress history of centrifuge model ground. A centrifuge test was conducted in various centrifugal acceleration levels including loading and unloading sequences to cause various stress histories on centrifuge model ground. The $V_S$ and vertical effective stress were measured at each level of acceleration. Then, a sensitivity analysis was conducted using testing data to ensure the suitability of OCR function for the tested cohesionless soils and found that OCR can be estimated based on $V_S$ measurements irrespective of normally-consolidated or overconsolidated loading conditions. Finally, the developed $G_{max}$-OCR relationship was applied to centrifuge models constructed and tested under various induced stress-history conditions. Through a series of tests, it was concluded that the induced stress history on centrifuge model by compaction, g-level variation, and past overburden load can be analysed quantitatively, and it is convinced that the OCR evaluation technique will contribute to better interpret the centrifuge test results.

• Journal of Korean Clinical Nursing Research
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• v.22 no.1
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• pp.68-77
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• 2016

Purpose: The present study was done to identify the relationship of cultural competence, self efficacy and job stress of nurses working on wards for foreign patients. Methods: The participants were 133 clinical nurses who agreed to participate in the study and were working on wards for foreign patients in three general hospitals in Seoul. A structured questionnaire that covered the three tested constructs was conducted between Dec. 15, 2014 and Jan. 15, 2015. Data were analyzed using descriptive statistics, t-test, one-way ANOVA, and Pearson correlation coefficients with SPSS/WIN 21.0 program. Results: Cultural competence was found to have a significant positive correlation with self efficacy (r=.464, p<.001) and self efficacy had a significant negative correlation with job stress (r=-.397, p<.001). Conclusion: The findings of the study suggest that programs designed to nourish cultural sensitivity and cultural skills need to be developed in order to promote cultural competence. The results also suggest that in these programs to improve self efficacy and reduce job stress should be considered.

• Proceedings of the Microbiological Society of Korea Conference
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• 2002.10a
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• pp.76-78
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• 2002

Heat shock proteins (HSPs) are induced in most living cells by mild heat treatment, ethanol, heavy metal ions and hypoxia. In yeast Saccharomyces cerevisiae, mild heat pretreatment strongly induces Hsp104 and thus provide acquired thermotolerance. The ability of hsp104 deleted mutant $({\triangle}hsp104)$ to acquire tolerance to extreme temperature is severely impaired. In providing thermotolerance, two ATP binding domains are indispensible, as demonstrated in ClpA and ClpB proteases of E. coli. The mechanisms by which Hsp104 protects cells from severe heat stress are not yet completely elucidated. We have investigated regulation of mitochondrial metabolic pathways controlled by the functional Hsp104 protein using $^{13}C_NMR$ spectroscopy and observed that the turnover rate of TCA cycle was enhanced in the absence of Hsp104. Production of ROS, which are toxic to kill cells radiply via oxidative stress, was also examined by fluorescence assay. Mitochondrial dysfunction was manifested in increased ROS levels and higher sensitivity for oxidative stress in the absence of Hsp104 protein expressed. Finally, we have identified mitochondrial complex I and Ferritin as binding protein(s) of Hsp104 by yeast two hybrid experiment. Based on these observations, we suggest that Hsp104 protein functions as a protector of oxidative stress via either keeping mitochondrial integrity, direct binding to mitochonrial components or regulating metal-catalyzed redox chemistry.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.2
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• pp.121-129
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• 2016

As the lifespan of concrete structures increases, their load carrying capacity decreases owing to cyclic loads and long-term effects such as creep and shrinkage. For these reasons, there is a necessity for stress state monitoring of concrete members. Particularly, it is necessary to evaluate the concrete structures for behavioral changes by using a technique that can overcome the measuring limitations of usual ultrasonic nondestructive evaluation methods. This paper proposes the use of a nonlinear ultrasonic method, namely, nonlinear resonant ultrasonic spectroscopy (NRUS) for the measurement of nonlinearity parameters for stress monitoring. An experiment compared the use of NRUS method and a linear ultrasonic method, namely, ultrasonic pulse velocity (UPV) to study the effects of continuously increasing loads and cyclic loads on the nonlinearity parameter. Both NRUS and UPV methods found a similar direct relationship between load level and that parameter. The NRUS method showed a higher sensitivity to micro-structural changes of concrete than UPV method. Thus, the experiment confirms the possibility of using the nonlinear ultrasonic method for stress state monitoring of concrete members.

• Proceedings of the Korean Society for Emotion and Sensibility Conference
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• 1999.03a
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• pp.127-132
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• 1999

Cardiovascular, respiratory and electrodermal responses to acute stress episodes modeled by combined presentation of intense white noise and performance of word recognition task with noise background were studied in 15 college students. Experimental procedure consisted in sessions with white noise, word recognition task presentation with noise background and test with noise background. Recorded physiological variables were analyzed in terms of their sensitivity to detect activation of sympathetic and parasympathetic branches of autonomic nervous system and thus reflect autonomic arousal level during shout-term stress-inducing experimental manipulations. It was shown that performance of effortful mental task with noise background elicited significant physiological responses typical for active coping behavior, namely electrodermal arousal and increased cardiovascular activity. this response profile was more profound as compared to white noise only or attending task in noise background. However, all physiological responses were mostly phasic, without long-term tonic changes, since almost all variables recovered to their initial baseline levels, suggesting that dominant autonomic mechanisms in transient acute stress episodes were of parasympathetic nature (withdrawal in stress with subsequent activation in restoration period), while sympathetic contribution was not long-lasting. Nevertheless, increased number of stressors and their longer exposure may result in higher profile of tonic sympathetic arousal and reduced functional role of vagal mechanisms in autonomic balance regulation.

• Journal of Environmental Science International
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• v.21 no.3
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• pp.267-276
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• 2012

Spaceflights results in the reduction of immune status of human beings and increase in the virulence of microorganisms, especially gram negative bacteria. The growth of Klebsiella pneumoniae is enhanced by catecholamines and during spaceflight, elevation in the levels of cortisols occurs. So it is necessary to know the changes in physiology, virulence, antibiotic resistance and gene expression of K. pneumoniae under microgravity conditions. The present study was undertaken to study effect of simulated microgravity on growth, morphology, antibiotic resistance and cross stress resistance of K. pneumoniae to various stresses. The susceptibility of simulated microgravity grown K. pneumoniae to ampicillin, penicillin, streptomycin, kanamycin, hygromycin and rifampicin were evaluated. The growth of bacteria was found to be fast compared with normal gravity grown bacteria and no significant changes in the antibiotic resistance were found. The bacteria cultured under microgravity conferred cross stress resistance to acid, temperature and osmotic stress higher than the normal gravity cultured bacteria but the vice versa was found in case of oxidative stress.

• Korea-Australia Rheology Journal
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• v.15 no.2
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• pp.97-105
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• 2003

In the previous paper (Hyun et al.,2002), we have investigated the shape of storage modulus (G') and loss modulus (G") of complex fluids under large amplitude oscillatory shear (LAOS) flow. As the strain amplitude increases, owever, the stress curve becomes distorted and some important information may be smothered during data processing. Thus we need to investigate the stress data more precisely and systematically. In this work, we have obtained the stress data using high performance ADC (analog digital converting) card, and investigated the nonlinear response of complex fluids, 4wt% xanthan gum (XG), 2 wt% PVA/ 1 wt% Borax, and 1 wt% hyaluronic acid (HA) solutions, using Fourier transformation (FT) rheology. Comparing the strain signals in time domain with FT parameters in frequency domain, we could illustrate the sensitivity and importance of FT rheology. Diverse and unique stress patterns were observed depending on the material system as well as flow environment. It was found that they are not the outcome of experimental deficiency like wall slip but characteristics of the material system. When nonlinear response of complex fluids is analyzed, the intensity and phase angle of higher harmonic contributions should be considered together, and the shape of the stress signal was found to be strongly dependent upon phase angle.ngle.

• Journal of Korean Orthopaedic Sports Medicine
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• v.10 no.1
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• pp.35-40
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• 2011

Purpose: This study was performed to evaluate the diagnostic usefulness of ankle stress radiograph for evaluation of chronic lateral ankle instability. Materials and Methods: Among patients undergoing the modified-Brostrom procedure, 42 cases with complete rupture of the anterior talofibular ligament were enrolled in this study. Sixty Korean adults (120 cases) were recruited as the control group. Radiologic measurement of talar tilt and anterior talar translation was performed through stress radiographs using Telos device. We obtained the normal range of Korean adults, and used as a standard value for judgment of mechanical instability. We analyzed the sensitivity, specificity, positive and negative prediction value of ankle stress radiograph. Results: On ankle stress radiograph, normal range of talar tilt angle and anterior talar translation was below $8.3^{\circ}$, below 7.6mm. Talar tilt angle on varus stress radiograph showed 57% of sensitivity, 97% of specificity, 89% of positive and 86% of negative prediction value. Anterior talar translation on anterior drawer stress radiograph showed 69% of sensitivity, 97% of specificity, 91% of positive and 90% of negative prediction value. Conclusion: Ankle stress radiograph had a good specificity, positive and negative prediction value for the evaluation of mechanical instability. However it underestimated the mechanical instability of ankle joint. It must be remembered that normal stress radiograph does not exclude ankle instability.