Classification of stress and non-stress condition using functional near-infrared spectroscopy

Seong-Woo Woo 제어로봇시스템학회 2018 제어로봇시스템학회 국제학술대회 논문집 Vol.2018 No.10

In these days, human health is most affected by the chronic stress, which is a well-known cause of several diseases such as heart disease, obesity, and stroke. The brain imaging modalities can be used as a viable option for the indirect assessment of the stress. In this study, we have used functional near-infrared spectroscopy (fNIRS) to discriminate between the hemodynamic responses of two different conditions (i.e., stress and non-stress). The Montreal Imaging Stress Task (MIST) is used to induce stress in the participants. fNIRS signals related to the stress and non-stress conditions are measured from the prefrontal cortex. The active channels are selected by determining the t-value between the measured fNIRS data and the desired hemodynamic response function. Linear discriminant analysis (LDA) is used to classify the stress and non-stress condition based on the combinations of various features (mean, peak, slope, kurtosis, and skewness values). The results show that the combination of slope and kurtosis yielded the highest classification accuracy of 70% between the stress and non-stress condition. Our preliminary results indicated that fNIRS has an ability to measure and classify stress and non-stress condition of humans.

A Study of Right-Edge Trisyllabic Stress Windows in English

김진두 한국교통대학교 2018 한국교통대학교 논문집 Vol.53 No.-

This paper focuses on the distribution of stress windows in English, which is located at the right-edge of the word. Universally languages have left or right edge stress distribution by statistical survey. Also they tend to have a dominant stress window. However, English has trisyllabic stress windows and trochaic stress from the right edge. According to the parts of speech or grammatical categories, there are some different stress patterns in English. Mainly nouns have penultimate or antepenultimate stress, but verbs have final or penultimate stress. Adjectives have two kinds of stress patterns. Simple adjectives parallel to verb stress pattern, but derived adjectives are the same that of nouns. After examining antepenultimate, penultimate, and final stress windows, we will analyze exceptional stress patterns. These stress windows are analyzed by linear segmental and metrical stress theory respectively. Binary feet and extrametricality are accepted as usual. English parameters are also suggested according to metrical stress theory. In double edge bracket theory cyclic and noncyclic stresses are defined on the foot and the grid based theory. As a more constrained theory a single edge bracket theory could analyze English stress more simply in addition to exceptional stress.

스트레스와 인구학적 특성의 연관성 분석 : 2015년 국민건강영양조사를 중심으로

이성임,김상균,서미경 통계청 2018 통계연구 Vol.23 No.4

Recent surveys indicate that a high percent of Koreans feel a lot of stress. In this paper, we construct the five-dimensional contingency table from the Korean National Health and Nutrition Examination Survey(KNHANES) in 2015. We also analyze the association between sex, age, smoking status, economic activity, and stress by fitting a proper log-linear model. The odds ratio between gender and stress differ across age groups. The odds of feeling more stress appear higher in women than in men especially in the age group ‘over sixty years’. Unlike men, women had little difference in stress between group ‘between forty years and sixty years’ and group ‘over sixty years’. The odds ratios between age groups and economic activity also differ across gender. The odds of participation in economic activity is the highest in group ‘between forty years and sixty years’, and the difference among age groups is higher in men than in women. The results show that there is a relationship between various characteristics and that all the demographic characteristics used in the analysis had a significant relationship with stress. 최근 우리나라는 다양한 조사를 통해 스트레스를 느끼는 사람의 비율이 높은 것으로 나타났다. 본 논문에서는 2015년 국민건강영양조사로부터 수집한 자료를 통해 성별, 나이, 흡연 여부, 경제활동 상태 및 스트레스 간의 연관성에 대해 실증분석 하였고, 5차원 분할표에 로그선형모형을 적합하여 변수 간 연관성을 확인하였다. 성별과 스트레스 인지 정도 간의 오즈비는 나이의 영향을 받는 것으로 나타났는데, 남성과 달리 여성은 중년층과 노년층의 스트레스 차이가 거의 없었다. 또한, 중년층이 경제활동을 참여할 오즈가 가장 크게 나타났는데, 나이와 경제활동 상태 간의 오즈비는 성별의 영향을 받아 남성일 때 연령층별 오즈의 차이가 더 크게 나타났다. 위의 결과를 통해 다양한 특성 사이의 연관성을 확인할 수 있었고, 특히 분석에 사용한 모든 특성은 스트레스와 유의한 연관성이 존재하는 것으로 나타났다.

지진하중 조건의 비선형 유한요소해석에서 반복경화 거동고려를 위한 Bi-linear 응력-변형률 곡선

정현준,김진원,김종성,구경회 한국압력기기공학회 2018 한국압력기기공학회 논문집 Vol.14 No.2

This study compares true stress-true strain curves obtained by tensile tests of various piping materials with bi-linear stress-strain approximation suggested in the JSME Code Case(CC) Draft, a guideline for piping seismic inelastic response analysis. Based on the comparisons, the reliability of the bi-linear approximation is evaluated. It is found that bi-linear stress-strain curve of TP316 stainless steel is in good agreement with its true stress-true strain curve. However, Bi-linear stress-strain curves of TP304 stainless steel and carbon steels determined by the approximation cannot appropriately estimate their stress-strain behavior. Accordingly new bi-linear approximations for carbon steels and low-alloy steels are proposed. The proposed bi-linear approximations for carbon and low-alloy steels, which include the temperature effect on strength and hardening of material, estimate their stress-strain behavior reasonably well.

용접 잔류응력장 중에서의 Aluminum-Alloy 용접재의 피로균열 성장거동 연구(Ⅱ) : 잔류응력 재 분포 Redistribution of the Residual Stress

최용식,정영석 成均館大學校 科學技術硏究所 1988 論文集 Vol.39 No.1

It is well known that welding residual stress has a great influence on fatigue crack growth rate in welded structure. In the general area of fatigue crack growth in the presence of residual stress, it is noted that the correction of stress intensity factor(K) to account for residual stress is important for the determination of both stress intensity factor range(ΔK) and stress ratio (R) during a loading cycle. The superposition technique can be applied generally for determination of K. The crack growth rate of the welds correlated with the effective stress intensity factor range, ΔK_eff, which was estimated by superposition of the respective stress intensity factors for the residual stress fields and for the applied stresses. However, redistribution of residual stress occurs during crack growth and its effect is not negligible. In this study, fatigue crack growth characteristics of the weld joint were examined by using superposition of redistributed residual stress and examined in comparison with that of the initial residual stress superposition.

Effects of the Non-linear Stress-Strain Behavior of RAP Concrete on Structural Responses for Rigid Pavement Application

김국주,천상현,박봉석,티아 맹 한국도로학회 2017 한국도로학회논문집 Vol.19 No.1

PURPOSES: This study is primarily focused on evaluating the effects of the non-linear stress-strain behavior of RAP concrete on structural response characteristics as is applicable to concrete pavement. METHODS : A 3D FE model was developed by incorporating the actual stress-strain behavior of RAP concrete obtained via flexural strength testing as a material property model to evaluate the effects of the non-linear stress-strain behavior to failure on the maximum stresses in the concrete slab and potential performance prediction results. In addition, a typical linear elastic model was employed to analyze the structural responses for comparison purposes. The analytical results from the FE model incorporating the actual stress-strain behavior of RAP concrete were compared to the corresponding results from the linear elastic FE model. RESULTS : The results indicate that the linear elastic model tends to yield higher predicted maximum stresses in the concrete as compared to those obtained via the actual stress-strain model. Consequently, these higher predicted stresses lead to a difference in potential performance of the concrete pavement containing RAP. CONCLUSIONS : Analysis of the concrete pavement containing RAP demonstrated that an appropriate analytical model using the actual stress-strain characteristics should be employed to calculate the structural responses of RAP concrete pavement instead of simply assuming the concrete to be a linear elastic material.

Non-linear analysis of skew thin plate by finite difference method

김치경,황명환 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.4

This paper deals with a discrete analysis capability for predicting the geometrically nonlinear behavior of skew thin plate subjected to uniform pressure. The differential equations are discretized by means of the finite difference method which are used to determine the deflections and the in-plane stress functions of plates and reduced to several sets of linear algebraic simultaneous equations. For the geometrically non-linear, large deflection behavior of the plate, the non-linear plate theory is used for the analysis. An iterative scheme is employed to solve these quasi-linear algebraic equations. Several problems are solved which illustrate the potential of the method for predicting the finite deflection and stress. For increasing lateral pressures, the maximum principal tensile stress occurs at the center of the plate and migrates toward the corners as the load increases. It was deemed important to describe the locations of the maximum principal tensile stress as it occurs. The load-deflection relations and the maximum bending and membrane stresses for each case are presented and discussed.

열처리 방법에 따른 SOI 기판의 스트레스변화

서태윤,이상현,송오성,Seo, Tae-Yune,Lee, Sang-Hyun,Song, Oh-Sung 한국재료학회 2002 한국재료학회지 Vol.12 No.10

It is of importance to know that the bonding strength and interfacial stress of SOI wafer pairs to meet with mechanical and thermal stresses during process. We fabricated Si/2000$\AA$-SiO$_2$ ∥ 2000$\AA$-SiO$_2$/Si SOI wafer pairs with electric furnace annealing, rapid thermal annealing (RTA), and fast linear annealing (FLA), respectively, by varying the annealing temperatures at a given annealing process. Bonding strength and interfacial stress were measured by a razor blade crack opening method and a laser curvature characterization method, respectively. All the annealing process induced the tensile thermal stresses. Electrical furnace annealing achieved the maximum bonding strength at $1000^{\circ}C$-2 hr anneal, while it produced constant thermal tensile stress by $1000^{\circ}C$. RTA showed very small bonding strength due to premating failure during annealing. FLA showed enough bonding strength at $500^{\circ}C$, however large thermal tensile stress were induced. We confirmed that premated wafer pairs should have appropriate compressive interfacial stress to compensate the thermal tensile stress during a given annealing process.

Delamination of non-linear viscoelastic beams under bending in the plane of layers

Victor I. Rizov Techno-Press 2023 Coupled systems mechanics Vol.12 No.4

This paper deals with delamination analysis of non-linear viscoelastic multilayered beam subjected to bending in the plane of the layers. For this purpose, first, a non-linear viscoelastic model is presented. In order to take into account the non-linear viscoelastic behaviour, a non-linear spring and a non-linear dashpot are assembled in series with a linear spring connected in parallel to a linear dashpot. The behaviours of the non-linear spring and dashpot are described by applying non-linear stress-strain and stress-rate of strain relationships, respectively. The constitutive law of the model is derived. Due to the non-linear spring and dashpot, the constitutive law is non-linear. This law is used for describing the time-dependent mechanical behaviour of the beam under consideration. The material properties involved in the constitutive law vary along the beam length due to the continuous material inhomogeneity of the layers. Solution of the strain energy release rate for the delamination is obtained by analyzing the balance of the energy with considering of the non-linear viscoelastic behaviour. The strain energy release rate is found also by using the complementary strain energy for verification. A parametric study is carried-out by using the solution obtained. The solutions derived and the results obtained help to understand the time-dependent delamination of non-linear viscoelastic beams under loading in the plane of layers.

방학분산제 실시가 청소년의 학업스트레스에 미치는 영향 분석

김나영(Kim Nayoung),손윤희(Son Yoonhee) 부산대학교 교육발전연구소 2019 교육혁신연구 Vol.29 No.1

연구목적: 이 연구의 목적은 방학분산제 정책 실시 여부 및 유형이 청소년의 학업스트레스에 미치는 영향을 실증적으로 분석함으로써 방학분산제 정책의 효과성을 살펴보는 데 있다. 연구방법: 이 연구에서는 경기교육종단연구(GEPS) 초등학교 패널 5차년도(2016) 자료를 활용하였으며, 위계적 선형 모형(HLM) 분석을 실시하였다. 연구결과: 첫째, 학생 및 학교수준 공변인을 통제하였을 때, 방학분산제 시행은 청소년의 학업스트레스에 유의한 부적 영향을 미치는 것으로 나타났다. 즉, 정책의 주요 기대효과 중 하나인 학생의 학업스트레스 완화에 있어서 방학분산제의 정책적 효과를 확인할 수 있었다. 둘째, 학생 및 학교수준 공변인을 통제하였을 때, 방학분산제 네 가지 유형(‘일반형’, ‘봄·가을 균등형’, ‘봄·가을 강화형’, ‘겨울방학 전 학사운영 종료형’) 중 ‘봄·가을 강화형’만이 학생의 학업스트레스에 유의한 부적 영향을 주는 것으로 나타났다. 논의 및 결론: 이러한 연구결과를 바탕으로 학교 현장에서 방학분산제의 효과적인 운영 및 청소년의 학업스트레스를 완화시키기 위한 교육적 지원 방안에 대해 논의하였다. Purpose: The purpose of this study is to investigate the effect of vacation policy(the Four Seasons Vacation Policy) on adolescents academic stress based on whether or not the vacation policy is implemented. In addition, the study also examines the differential effect of the types of vacation on students academic stress. Method: The analysis was based on hierarchical linear model(HLM) using the fifth middle school panel data from the Gyeonggi Educational Panel Study(GEPS). Results: After controlling for student and school level covariates, the four seasons vacation policy had a significantly positive effect on decreasing students’ academic stress. Next, after controlling for student and school level covariates, among the four types of vacation such as general type , balancing type of spring and autumn vacation , extending type of spring and autumn vacation and finishing curriculum type before winter vacation , only extending type of spring and autumn vacation had a significantly positive effect on decreasing students academic stress. Conclusion: Based on these findings, the educational implications for the improvement of policy implementation and reduction of adolescents academic stress are discussed.