• 대한수학회지
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• 제38권5호
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• pp.1047-1059
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• 2001

The classical Geometric Brownian motion (GBM) model for the price of a risky asset, from which the huge financial derivatives industry has developed, stipulates that the log returns are iid Gaussian. however, typical log returns data show a distribution with much higher peaks and heavier tails than the Gaussian as well as evidence of strong and persistent dependence. In this paper we describe a simple replacement for GBM, a fractal activity time Geometric Brownian motion (FATGBM) model based on fractal activity time which readily explains these observed features in the data. Consequences of the model are explained, and examples are given to illustrate how the self-similar scaling properties of the activity time check out in practice.

• 대한전기학회논문지
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• 제44권7호
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• pp.901-907
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• 1995

The switching characteristics of As$_{10}$ Ge$_{15}$ Te$_{75}$ thin film were investigated under d.c. bias. And the frequency dependence of the conductivity was analysed with regard to the temperature dependence, in order to find the physical properties of the As$_{10}$ Ge$_{15}$ Te$_{75}$ thin film ; a characteristic relaxation time (.tau.$_{0}$ ), the spatial density of defect states (N), and the localized wavefunction (.alpha.$^{-1}$ ). It was formed that the threshold voltage depends on thickness, electrode distance, annealing time and temperature, respectively. The threshold voltage is increased as the thickness and the electrode distance is increased, while the threshold voltage is decreased in proportion to the increased annealing time and temperature.

• 한국세라믹학회지
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• 제26권1호
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• pp.1-6
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• 1989

The phenomena that the electrical conductivity of rutile single crystal changes with time were investigated along the a and c crystallographic axes, at 85$0^{\circ}C$ and Po2 in the range of 1~10-18.5atm. The D.C. conductivity decreased with and saturated some value after ca. 100 hours. But the A.C. conductivity showed no time dependence in the whole Po2 range. These experimental results suggest that the time dependence of D.C. conductivity of rutile single crystal is due to space charge polarization effect; the electrode was Pt which is complete electronic conductor, while the sample was TiO2 which is mixed conductor.

• 한국멀티미디어학회논문지
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• 제2권3호
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• pp.289-296
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• 1999

본 논문에서는 데이타 의존성과 벡터왜곡척도를 이용하여 개선된 칼라영상을 복호화하였다. 프랙탈칼라영상의 복원방법은 Zhang과 Po의 벡터왜곡척도를 이용한 RGB 칼라 성분간의 상관관계를 고려하여 부호화한 압축파일을 사용하여 수렴 될 복원영상을 부호화시 만들어진 변환표의 정보를 바탕으로 참조된 정 의 역 부분이 기존의 독립적인 반복변환에 의해 수렴되었고 참조되지 않은 부분의 정의역은 데이타의존성을 갖는 영역으로 이미 수렴된 부분에 존재하므로 마지막 반복변환시 한번만에 복호화가 가능하다. 데이타의존성 부분이 차지 하는 만큼 복호화 과정에서 불필요한 계산량이 제거되었고, R영역에서 검색한 데이타 의존영역을 G,B영역에 그대로 사용하여 고속복호화가 가능하였다.

• 응용통계연구
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• 제30권2호
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• pp.215-231
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• 2017

미국 대통령 예선은 선거인단이 시차를 두고 여러 회에 걸쳐 진행되는 특징이 있음에도 많은 연구가 진행되지 않았다. 본 연구에서는 다양한 자기로지스틱 모형을 통해 미국 대통령 예비선거 결과와 사회경제적 변수간의 시공간 의존성의 관계를 파악하고자 한다. 2016년 데이터에 적용한 분석결과 각 카운티의 노년층, 흑인, 여성 그리고 히스패닉 인구 비율이 높은 지역일수록 힐러리 클린턴을 지지할 확률이 높은 것으로 나타났다. 또한, 주변 카운티에서 많은 지지를 받은 후보가 이웃 지역에서도 많이 지지를 받을 확률이 높고 이전 선거에서 많은 지지를 받는 것과 다음 선거 지역의 결과 간의 상관관계도 확인되었다. 시공간 의존성을 알아보기 위한 모형 중에서 슈퍼화요일의 선거 결과가 이후 선거와 관련이 있다고 가정한 모형의 설명력이 가장 높은 것으로 판명되었다.

• Tuberculosis and Respiratory Diseases
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• 제85권4호
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• pp.349-357
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• 2022

Background: The most consistently identified mortality determinants for the new coronavirus 2019 (COVID-19) infection are aging, male sex, cardiovascular/respiratory diseases, and cancer. They were determined from heterogeneous cohorts that included patients with different disease severity and previous conditions. The main goal of this study was to determine if activities of daily living (ADL) dependence measured by Barthel's index could be a predictor for COVID-19 mortality. Methods: A prospective cohort study was performed with a consecutive sample of 340 COVID-19 patients representing patients from all over the northern region of Portugal from October 2020 to March 2021. Mortality risk factors were determined after controlling for demographics, ADL dependence, admission time, comorbidities, clinical manifestations, and delay-time for diagnosis. Central tendency measures were used to analyze continuous variables and absolute numbers (proportions) for categorical variables. For univariable analysis, we used t test, chi-square test, or Fisher exact test as appropriate (α=0.05). Multivariable analysis was performed using logistic regression. IBM SPSS version 27 statistical software was used for data analysis. Results: The cohort included 340 patients (55.3% females) with a mean age of 80.6±11.0 years. The mortality rate was 19.7%. Univariate analysis revealed that aging, ADL dependence, pneumonia, and dementia were associated with mortality and that dyslipidemia and obesity were associated with survival. In multivariable analysis, dyslipidemia (odds ratio [OR], 0.35; 95% confidence interval [CI], 0.17-0.71) was independently associated with survival. Age ≥86 years (pooled OR, 2.239; 95% CI, 1.100-4.559), pneumonia (pooled OR, 3.00; 95% CI, 1.362-6.606), and ADL dependence (pooled OR, 6.296; 95% CI, 1.795-22.088) were significantly related to mortality (receiver operating characteristic area under the curve, 82.1%; p<0.001). Conclusion: ADL dependence, aging, and pneumonia are three main predictors for COVID-19 mortality in an elderly population.

• 대한방사선기술학회지:방사선기술과학
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• 제11권1호
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• pp.33-41
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• 1988

This study was measured the radiation-induced current - X-ray dose, dose rate, X-ray quality, time, temperature, electric field characteristics and the dependence of gap length in insulating oil under of D.C. Voltage before, during and after X-ray irradiation. The obtained results can be summarized as following. 1. The radiation - induced current is more the dependence of X-ray quality (tube voltage) than quantity (tube current), the dependence of quantity is appeared at the high than low X-.ay tube voltage. 2. The dependence of dose rate is appeared at the more dose rate, and ${\triangle}\;=\;0.64{\sim}0.74$. 3. The higher temperature of insulating oil and X-ray tube voltage (X-ray quality) is increased, at the low electric field, the more radiation-induced current. 4. $G_{eq}-G_{o}(={\triangle}G)$ is increased at the low than high temperature, high than low X-ray quality. 5. The dependence of temperature is appeared before than during X-ray irradiation. 6. The RIC saturation region is appeared at the high than low insulating oil temperature during (1000 V/cm above) than before (4000 V/cm above) X-ray irradiation.

• 재활복지공학회논문지
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• 제11권2호
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• pp.107-114
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• 2017

본 연구는 초등학생의 스마트폰 의존도 프로파일을 탐색하고, 프로파일에 나타난 집단별 특성을 살펴보는데 목적이 있다. 한국청소년정책연구의 한국아동 청소년패널조사(Korea Chilren and Youth Panel Survey, KCYPS)의 초등학생 5차년도 자료를 이용하여 1,585명의 초등학생을 대상으로 스마트폰 의존도에 대한 잠재프로파일분석으로 실시하였다. 분석 결과, 적합도 지수와 잠재계층 분류율에 따라 3개 계층 유형이 선택되었다. 유형 1은 모든 지표에서 낮게 나타나 저의존집단(50.1%)으로, 유형 2는 모두 지표에서 높게 나타나 고의존집단(10.7%)으로, 유형3은 모든 지표에서 중간 수준으로 나타나 중의존집단(39.2%)으로 명명하였다. 스마트폰 의존도 특성을 예측하기 위해 다항로지스틱회귀분석을 실시한 결과, 고의존집단을 기준으로 중의존집단과 비교했을 때, 자아존중감이 높을수록, 또래애착이 낮을수록 중의존집단에 속할 가능성이 높게 나타났다. 저의존집단과 비교한 결과에서는 자아존중감이 높을수록, 친구교제시간이 적을수록, 방임의 정도가 낮을수록, 또래애착이 낮을수록 저의존집단에 속할 가능성이 높게 나타났다. 본 연구의 시사점, 제한점, 후속연구의 방향을 제시하였다.

• 한국사회복지학
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• 제63권4호
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• pp.83-107
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• 2011

본 연구는 한국복지패널 1~4차년도 조사 자료를 활용하여 국민기초생활보장제도 수급탈출의 기간의존성을 분석하였다. 수급기간이 길어질수록 수급탈출률이 낮아지는 기간의존성의 존재는 복지의존을 시사하는 중요한 증거가 될 수 있다. 실증적 분석 결과, 성, 연령, 교육수준, 결혼지위, 건강상태, 취업 형태 등의 관찰된 특성을 통제한 후에도 수급기간이 길어질수록 수급탈출률이 낮아지는 현상이 관찰되지만, 관찰되지 않은 이질성을 통제하면 수급기간의 영향이 통계적으로 유의하지 않은 것으로 나타났다. 이러한 결과에 따르면, 수급기간이 길어질수록 수급탈출률이 낮아지는 현상의 상당부분은 수급자 집단의 이질성으로 인한 허위관계이고 수급탈출의 기간의존성은 크지 않은 것으로 판단된다.

• 한국주거학회논문집
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• 제6권1호
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• pp.19-29
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• 1995

This study is to analyze the effect of neighborhood commercial facilities on the homeproduction activities and the family expenditure(or household work time). For this purpose. data are collected by using questionnaires distributed to 522 housewives in Seoul. The results shows that in the highly goods-intensive environment. the way of homeproduction is goods-intensive. Market dependence of the family is affected by homeproduction predisposition. income. and husband's job. Household work dependence of the .family is affected by neighborhood facility environment. family type. income. and house value. Low home production supportability is apparent in the high family income. full-time housewives and low job status of housewife. On the other hand. high homeproduction supportability is apparent in the moderate income and high job status of housewife. As a result. housewives have much time and money resourses are not well supported by the neighborhood facility environment.