• 정보보호학회논문지
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• 제13권5호
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• pp.159-168
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• 2003

유한체 F$_{2}$sup n// 위에서 정의되는 다항식을 이용하여 암호학적으로 좋은 성질을 갖는 부울함수를 생성하는 방법으로 3차 다항식을 이용하여 균형상관면역함수를 생성하는 방법이 [3]에서 제안되었다. 이 논문에서는 n$\leq$14일 때 5차 다항식을 이용하여 비선형치가 높은 균형상관면역함수를 생성하는 방법을 제안하고, 예를 제시한다.

• 대한기계학회논문집
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• 제7권1호
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• pp.28-35
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• 1983

Quantitative analysis have been carried out on the micro-cracks on the surface and into the depth of unnotched smooth mild steel specimen under cyclic stains by rotating bending fatigue tests. Some of the results are; (1) Cracks initiate at the early stage of fatigue life N$_{I}$/ N$_{f}$=10 to 20%, and propagate during the rest of fatigue life. (2) Coalescence of highly crowded small fatigue cracks of random distribution seems to induce the final fracture at higher stress level. (3) The curves of crack initiation and the equal crack length on the graph of stress versus number of cycles are parallel to the S-N curve. (3) The curves of crack initiation and the equal crack length on the graph of stress versus number of cycles are parallel to the S-N curve. (4) The distributions of micro-surface crack length and depth show the composite Weibull distributions which are approximated to two straight lines separated by the value of transient region between stage I and stage II crack.k.k.

• 대한기계학회논문집
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• 제14권1호
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• pp.87-95
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• 1990

본 연구에서는 고온기기의 구조용 부재로 널리 사용되고 있는 304스테인리스 강을 선택하여 상온, $538^{\circ}C$($1000^{\circ}$ F) 및 $593^{\circ}C$($1100^{\circ}C$ F) 고온하의 작은 표면노치 시험편 에서 발생한 표면 피로 균열의 성장거동을 레플리카법에 의하여 상세히 관찰측정하여 파괴역학적으로 해석 연구하고자 한다. 즉 피로균열의 성장특성을 ....$\DELTA\sigma^{n}$a의 매 개변수를 도입하여 정량적으로 평가하고, 수명예측을 실시하여 그 유용성을 비교검토 하였다. 또한 피로균열의 성장에 관한 실험결과 자료들을 PC를 이용하여 전산하고 도식화함으로써 파괴역학적 설계에 유용한 기초적 자료를 제시하고자 하였다.

• 한국수학교육학회지시리즈A:수학교육
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• 제25권3호
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• pp.77-100
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• 1987

Let G : R$^n$${\times}$R\longrightarrowR$^n$ be defined by a Homotopy solving a system F($\chi$)=0 of nonlinear equations. For the vector v$\^$k/ with G'(u$\sub$k/)v$\^$k/=0, ∥v$\^$k/∥=1 where uk is one point in Zero Curve let u$\sub$0/$\^$k/=v$\^$k/＋$\tau$v$\^$k/ be the first prediction for the next point u$\^$k+1/, $\tau$$\in$(0, 1). When u$\sub$0/$\^$k/ approaching too losely to some unwanted point. to follow the Zero Curve may occur the returning or cycling. One lion for it is discussed and tile parametrizied Homotopy algorithm for solving F($\chi$)=0 with it been established. Also some theorems by means of the regular value have been discussed for Zero Curves of G(u)=0 and some theorems for algorithm have been obtained.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.127-132
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• 2002

Recent deepwater offshore structures in Gulf of Mexico utilize butt welded tubular joints. Application of welded tubular joint includes tendons, production risers, and steel catenary risers. Fatigue life assessment of these joints becomes more critical because the structures to which they are attached are allowed to undergo cyclic and sometimes large displacements around an anchored position. Estimating the fatigue behavior of these tubular members in the design stage is generally conducted by using S-N curves specified in the codes and standards. Applying the stress concentration factor of the welded structure to S-N approach often results in very conservative assessment because the stress field acting on the tubular has a non-uniform distribution through the thickness. Fracture mechanics and fitness for service (FFS) technology have been applied in the design of the catenary risers. This technology enables the engineer to establish proper requirements on weld quality and inspection acceptance criteria to assure satisfactory structural integrity during its design life. It also provides guidance on proper design curves to be used and a methodology for accounting for the effects of non-uniform stress distribution through the wall thickness. An attempt was made to develop set of S-N curves based on fracture mechanics approach by considering non-uniform stress distribution and a threshold stress intensity factor. Series of S-N curves generated from this approach were compared to the existing S-N curves. For flat plate butt joint, the S-N curve generated from fracture mechanics matches with the IIW class 100 curve when initial crack depth was 0.5 mm (0.02"). Similar comparison with API X′ was made for tubular joint.. These initial crack depths are larger than the limits of inspection by current Non-destructive examination (NDE) means, such as Automatic Ultrasonic Inspection (AUT). Thus a safe approach can be taken by specifying acceptance criteria that are close to limits of sizing capability of the selected NDE method. The comparison illustrates conservatism built into the S-N design curve.

• Elastomers and Composites
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• 제53권4호
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• pp.213-219
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• 2018

The degradation mechanism and physical properties of an FKM O-ring were observed with thermal aging in this experiment. From X-ray photoelectron spectroscopy (XPS) analysis, we could observe carbon (285 eV), fluoro (688 eV), and oxygen (531 eV) peaks. Before thermal aging, the concentration of fluoro atoms was 51.23%, which decreased to 8.29% after thermal aging. The concentration of oxygen atoms increased from 3.16% to 20.39%. Under thermal aging, the FKM O-ring exhibited debonding of the fluoro-bond by oxidation. Analysis of the C1s, O1s, and F1s peaks revealed that the degradation reaction usually occurred at the C-F, C-F2, and C-F3 bonds, and generated a carboxyl group (-COOH) by oxidation. Due to the debonding reaction and decreasing mobility, the glass transition temperature of the FKM O-ring increased from $-15.91^{\circ}C$ to $-13.79^{\circ}C$. From the intermittent CSR test, the initial sealing force was 2,149.6 N, which decreased to 1,156.2 N after thermal aging. Thus, under thermal aging, the sealing force decreased to 46.2%, compared with its initial state. This phenomenon was caused by the debonding reaction and decreasing mobility of the FKM O-ring. The S-S curve exhibited a 50% increase in modulus, with break at a low strain and stress state. This was also attributed to the decreasing mobility due to thermal aging degradation.

• Structural Engineering and Mechanics
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• 제6권4호
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• pp.467-471
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• 1998

A mathematical model is developed to predict the fatigue notch factor of butt welds subject to number of parameters such as weld geometry, residual stresses under dynamic combined loading conditions (tensile and bending). Linear elastic fracture mechanics, finite element analysis, dimensional analysis and superposition approaches are used for the modelling. The predicted results are in good agreement with the available experimental data. As a result, scatters of the fatigue data can be significantly reduced by plotting S-N curve as ($S{\cdot}K_f$) vs. N.

• 한국터널지하공간학회 논문집
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• 제22권3호
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• pp.293-310
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• 2020

본 연구에서는 지하철 승강장에서 화재가 발생하는 경우, 제연모드에 따른 위험도를 정량적 위험도 평가기법에 따라서 비교하여 안전확보에 가장 효과적인 제연모드를 제시함을 목적으로 한다. 이를 위해 전형적인 지하철 승장장을 모델로 하여 제연모드별로 대피개시간 및 화재발생열차의 위치에 따른 화재발생 시나리오를 작성하고, 시나리오별로 화재발생률(F)을 산정하고 화재해석과 대피해석을 수행하여 사망자수(N)를 정량적으로 추정하였다. 시나리오별 사고발생률(Frequency)과 사망자수(N:Fatalities)를 추정하여 F/N 선도로 작성하고 이를 사회적 위험도 평가기준과 비교하여 화재 안전성을 평가하였으며, 다음과 같은 결론을 얻었다. 정거장 열차화재 시 인명안전을 위해서는 최대 600 s 이전에 대피가 개시되어야 하며, 정거장 양단배기 시스템이 없는 승강장에서는 승강장 공조시스템을 급기로 운영하여 승강장을 가압하는 것이 대피안전성 확보에 유리한 것으로 나타났다. 승강장 열차화재시나리오에 따른 F/N선도를 작성하여 사회적 위험도 평가기준과 비교한 결과, 제연을 하지 않는 경우에는 한계기준을 상당히 초과하며, 양단배기를 수행하고 승강장을 가압운전모드에서 운영하는 제연모드가 대피안전에 가장 효과적인 것으로 나타났다.

• Journal of Magnetics
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• 제19권2호
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• pp.126-129
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• 2014

We report the crystallographic and magnetic properties of $Ni_{0.3}Fe_{0.7}Ga_2S_4$ by means of X-ray diffractometer (XRD), a superconducting quantum interference device (SQUID) magnetometer, and a M$\ddot{o}$ssbauer spectroscopy. In particular, $Ni_{0.3}Fe_{0.7}Ga_2S_4$ was studied by M$\ddot{o}$ssbauer analysis for evidence of spin reorientation. The chalcogenide material $Ni_{0.3}Fe_{0.7}Ga_2S_4$ was fabricated by a direct reaction method. XRD analysis confirmed that $Ni_{0.3}Fe_{0.7}Ga_2S_4$ has a 2-dimension (2-D) triangular lattice structure, with space group P-3m1. The M$\ddot{o}$ssbauer spectra of $Ni_{0.3}Fe_{0.7}Ga_2S_4$ at spectra at various temperatures from 4.2 to 300 K showed that the spectrum at 4.2 K has a severely distorted 8-line shape, as spin liquid. Electric quadrupole splitting, $E_Q$ has anomalous two-points of temperature dependence of $E_Q$ curve as freezing temperature, $T_f=11K$, and N$\acute{e}$el temperature, $T_N=26K$. This suggests that there appears to be a slowly-fluctuating "spin gel" state between $T_f$ and $T_N$, caused by non-paramagnetic spin state below $T_N$. This comes from charge re-distribution due to spin-orientation above $T_f$, and $T_N$, due to the changing $E_Q$ at various temperatures. Isomer shift value ($0.7mm/s{\leq}{\delta}{\leq}0.9mm/s$) shows that the charge states are ferrous ($Fe^{2+}$), for all temperature range. The Debye temperature for the octahedral site was found to be ${\Theta}_D=260K$.

• Korean Journal of Radiology
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• 제25권2호
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• pp.189-198
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• 2024

Objective: To investigate the prognostic utility of radiomics features extracted from ¹⁸F-fluorodeoxyglucose (FDG) PET/CT combined with clinical factors and metabolic parameters in predicting progression-free survival (PFS) and overall survival (OS) in individuals diagnosed with extranodal nasal-type NK/T cell lymphoma (ENKTCL). Materials and Methods: A total of 126 adults with ENKTCL who underwent ¹⁸F-FDG PET/CT examination before treatment were retrospectively included and randomly divided into training (n = 88) and validation cohorts (n = 38) at a ratio of 7:3. Least absolute shrinkage and selection operation Cox regression analysis was used to select the best radiomics features and calculate each patient's radiomics scores (RadPFS and RadOS). Kaplan-Meier curve and Log-rank test were used to compare survival between patient groups risk-stratified by the radiomics scores. Various models to predict PFS and OS were constructed, including clinical, metabolic, clinical + metabolic, and clinical + metabolic + radiomics models. The discriminative ability of each model was evaluated using Harrell's C index. The performance of each model in predicting PFS and OS for 1-, 3-, and 5-years was evaluated using the time-dependent receiver operating characteristic (ROC) curve. Results: Kaplan-Meier curve analysis demonstrated that the radiomics scores effectively identified high- and low-risk patients (all P < 0.05). Multivariable Cox analysis showed that the Ann Arbor stage, maximum standardized uptake value (SUVmax), and RadPFS were independent risk factors associated with PFS. Further, β2-microglobulin, Eastern Cooperative Oncology Group performance status score, SUVmax, and RadOS were independent risk factors for OS. The clinical + metabolic + radiomics model exhibited the greatest discriminative ability for both PFS (Harrell's C-index: 0.805 in the validation cohort) and OS (Harrell's C-index: 0.833 in the validation cohort). The time-dependent ROC analysis indicated that the clinical + metabolic + radiomics model had the best predictive performance. Conclusion: The PET/CT-based clinical + metabolic + radiomics model can enhance prognostication among patients with ENKTCL and may be a non-invasive and efficient risk stratification tool for clinical practice.