직업병연구에 있어서 시간의존형 폭로변인의 의의

문재동 大韓産業醫學會 1997 대한직업환경의학회지 Vol.9 No.2

Although the final cumulative exposure has been used as a exposure variable on the cohort study for the relation between exposure and disease, the bias from the use of fixed exposure can be developed because the exposure amount changes across the time. We developed the program to handle the Cox model with irregularly changing time-dependent exposure variable and covariates, and the validity about the application of time-dependent exposure variable and lagged interval was practically evaluated by analyzing the data collected for typical retrospective cohort study with that program. The results were as follows : The exposure-response relations between the deaths from lung cancer and exposures(fixed or time-dependent) were not clear when 0 year lagged interval was applied. When 15 years lagged interval was applied, the exposure-response relations between the deaths from lung cancer and the time-dependent exposures to crystalline silica were observed and relative risks increased like 1.00, 1.17, 1.30 and 2.45 across the exposure levels. The relative risk estimates for lung cancer with time-dependent exposure variable were higher than those with fixed exposure variable without regard to the application of lagged interval. The exposure-response relations between the deaths from non-malignant respiratory disease(NMRD) and exposures (fixed or time-dependent) were observed across exposure levels when 0 year lagged interval was applied. When 15 years lagged interval was applied, the exposure-response relations between the deaths from NMRD and the time-dependent exposures to crystalling silica were observed, but were not with fixed exposure variable. The relative risk estimates for NMRD mortality with time-dependent exposure variable were higher than those with fixed exposure variable, and the application of lagged interval on the evaluation of NMRD mortality was meaningless. The results suggest that the application of time-dependent exposure variable on the study of exposure-effect relation should be considered and the application of lagged interval should be decided according to the time needed from disease detection to death.

Construction of Exact Ermakov-Pinney Solutions and Time-Dependent Quantum Oscillators

Sang Pyo Kim,Won Kim 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.10

The harmonic oscillator with a time-dependent frequency has a family of linear quantum invariants for the time-dependent Schr¨odinger equation, which are determined by any two independent solutions to the classical equation of motion. Ermakov and Pinney have shown that a general solution to the time-dependent oscillator with an inverse cubic term can be expressed in terms of two independent solutions to the time-dependent oscillator. We explore the connection between linear quantum invariants and the Ermakov-Pinney solution for the time-dependent harmonic oscillator. We advance a novel method to construct Ermakov-Pinney solutions to a class of time-dependent oscillators and the wave functions for the time-dependent Schr¨odinger equation. We further show that the first and the second P¨oschl-Teller potentials belong to a special class of exact time-dependent oscillators. A perturbation method is proposed for any slowly-varying time-dependent frequency.

On the Exact Solutions of the Damped Harmonic Oscillator with a Time-dependent Damping Constant and a Time-dependent Angular Frequency

Jihun Cha,장은지,정민,김도연,김다홍,이영규,박순철,김균석,정완상 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.2

In this paper, we consider the damped harmonic oscillator with a time-dependent damping constant and a time-dependent angular frequency, which is actually the generalized Caldirola-Kanai Hamiltonian. For some choices of the time-dependent damping constant and the time-dependent angular frequency, we investigate the exact solutions. We also obtain the corresponding conserved quantities and finally discuss the quantum damped harmonic oscillator with a time-dependent damping constant and a time-dependent angular frequency.

단열 조건을 만족시키는 시간의존 자기장 내에서 전자의 운동

연규황,임은지 한국물리학회 2014 새물리 Vol.64 No.6

Faraday's law says that a time-dependent induced electric field is generated when a time-dependent magnetic field is applied. The equation of motion of an electron within the electric and magnetic fields is described with a coupled differential equation, which can be converted into separate differential equations when its variables are transformed with a matix form. However, the differential equation can be completely solved if the time-dependent magnetic field is known. In those fields, the electron moves in a circular-type motion, and its center oscillates with time while its radius changes with time. When the time variable is fixed, the motion of the electron is circular. We find an invariant quantity of the system in the time-dependent fields. Both the electron's motion and the invariant quantity are obtained in time-dependent magnetic fields under the adiabatic condition. Although the invariant quantity of this system is highly difficult to calculate, we know the general equation motion can be described in the same form regardless of the used canonical-variable sets, which is related to the canonical transform. Faraday 법칙으로부터 시간의존 자기장이 가해진 경우 유도 전기장이 생성됨을 알 수 있다. 그 전기장과 자기장내에서 전자의 운동 방정식은 서로 연결된 미분 방정식으로 나타난다. 행렬방정식으로 바꾸어 변수변환을 하면 분리된 미분 방정식으로 표현된다. 그러나 자기장의 시간 의존성이 알려져야 이 미분 방정식은 풀린다. 미분 방정식의 해의 모양이 중심이 진동하고 반경이 시간에 따라 변하는 원형임을 보이고, 시간을 일정하게 놓으면 언제나 원이 됨을 보인다. 시간 의존 전자기장내에서 불변량을 계산한다. 이 계의 불변 연산자의 직접 계산은 매우 복잡하지만 정준 변환 관계인 어떤 정준 변수조로 일반 운동 방정식을 나타내면 모두 같은 모양으로 주어진다는 고전역학 결과로부터 불변량을 계산 할 수 있다. 가한 시간의존 자기장이 단열 조건을 이룰 때 전자의 운동과 불변량을 구한다.

Time-dependent analysis of cable trusses -Part I. Closed-form computational model

Kmet, S.,Tomko, M. Techno-Press 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.38 No.2

In this paper the time-dependent closed-form static solution of the suspended pre-stressed biconcave and biconvex cable trusses with unmovable, movable and elastic or viscoelastic yielding supports subjected to various types of vertical load is presented. Irvine's forms of the deflections and the cable equations are modified because the effects of the rheological behaviour needed to be incorporated in them. The concrete cable equations in the form of the explicit relations are derived and presented. From a solution of a vertical equilibrium equation for a loaded cable truss with rheological properties, the additional vertical deflection as a time-function is determined. The time-dependent closed-form model serves to determine the time-dependent response, i.e., horizontal components of cable forces and deflection of the cable truss due to applied loading at the investigated time considering effects of elastic deformations, creep strains, temperature changes and elastic supports. Results obtained by the present closed-form solution are compared with those obtained by FEM. The derived time-dependent closed-form computational model is used for a time-dependent simulation-based reliability assessment of cable trusses as is described in the second part of this paper.

Non-linear time-dependent post-elastic analysis of suspended cable considering creep effect

Kmet, S.,Tomko, M.,Brda, J. Techno-Press 2006 Structural Engineering and Mechanics, An Int'l Jou Vol.22 No.2

In this paper, the non-linear time-dependent closed-form, discrete and combined solutions for the post-elastic response of a geometrically and physically non-linear suspended cable to a uniformly distributed load considering the creep effects, are presented. The time-dependent closed-form method for the particularly straightforward determination of a vertical uniformly distributed load applied over the entire span of a cable and the accompanying deflection at time t corresponding to the elastic limit and/or to the elastic region, post-elastic and failure range of a suspended cable is described. The actual stress-strain properties of steel cables as well as creep of cables and their rheological characteristics are considered. In this solution, applying the Irvine's theory, the direct use of experimental data, such as the actual stress-strain and strain-time properties of high-strength steel cables, is implemented. The results obtained by the closed-form solution, i.e., a load corresponding to the elastic limit, post-elastic and failure range at time t, enable the direct use in the discrete non-linear time-dependent post-elastic analysis of a suspended cable. This initial value of load is necessary for the non-linear time-dependent elastic and post-elastic discrete analysis, concerning incremental and iterative solution strategies with tangent modulus concept. At each time step, the suspended cable is analyzed under the applied load and imposed deformations originated due to creep. This combined time-dependent approach, based on the closed-form solution and on the FEM, allows a prediction of the required load that occurs in the post-elastic region. The application of the described methods and derived equations is illustrated by numerical examples.

Second quantized scalar QED in homogeneous time-dependent electromagnetic fields

Academic Press 2014 Annals of physics Vol.351 No.-

We formulate the second quantization of a charged scalar field in homogeneous, time-dependent electromagnetic fields, in which the Hamiltonian is an infinite system of decoupled, time-dependent oscillators for electric fields, but it is another infinite system of coupled, time-dependent oscillators for magnetic fields. We then employ the quantum invariant method to find various quantum states for the charged field. For time-dependent electric fields, a pair of quantum invariant operators for each oscillator with the given momentum plays the role of the time-dependent annihilation and the creation operators, constructs the exact quantum states, and gives the vacuum persistence amplitude as well as the pair-production rate. We also find the quantum invariants for the coupled oscillators for the charged field in time-dependent magnetic fields and advance a perturbation method when the magnetic fields change adiabatically. Finally, the quantum state and the pair production are discussed when a time-dependent electric field is present in parallel to the magnetic field.

판재의 성형한계 결정을 위한 시간의존적 방법의 제안

김성곤,김형종 한국소성∙가공학회 2018 소성가공 : 한국소성가공학회지 Vol.27 No.2

Most domestic and international standards on the forming limit diagram (FLD) including ISO 12004-2, use a ‘position-dependent method,’ which determines the forming limit from a strain distribution measured on the specimen after necking or fracture. However, the position-dependent method has inherent problemssuch as the incidence of asymmetry of a strain distribution, the estimation of missing data near fracture, the termination time of test, and the deformation due to the new stress equilibrium after a fracture, which is blamed for causing sometimes a significant lab-to-lab variation. The ‘time-dependent method,’ which is anticipated to be a new international standard for evaluating the forming limit, is expected to greatly improve these intrinsic disadvantages of the position-dependent method. It is because the time-dependent method makes it possible to identify and accurately determine the forming limit, just before the necking point from the strain data as continuously measured in a short time interval. In this study, we propose a new time-dependent method based on a Gaussian fitting of strain acceleration with the introduction of ‘normalized correlation coefficient.’ It has been shown in this study that this method can determine the forming limit very stably and gives a higher value, which is in comparison with the results of the previously studied position-dependent and time-dependent methods.

Upgraded quadratic inference functions for longitudinal data with type II time-dependent covariates

Cho, Gyo-Young,Dashnyam, Oyunchimeg The Korean Data and Information Science Society 2014 한국데이터정보과학회지 Vol.25 No.1

Qu et. al. (2000) proposed the quadratic inference functions (QIF) method to marginal model analysis of longitudinal data to improve the generalized estimating equations (GEE). It yields a substantial improvement in efficiency for the estimators of regression parameters when the working correlation is misspecified. But for the longitudinal data with time-dependent covariates, when the implicit full covariates conditional mean (FCCM) assumption is violated, the QIF can not provide more consistent and efficient estimator than GEE (Cho and Dashnyam, 2013). Lai and Small (2007) divided time-dependent covariates into three types and proposed generalized method of moment (GMM) for longitudinal data with time-dependent covariates. They showed that their GMM type II and GMM moment selection methods can be more ecient than GEE with independence working correlation (GEE-ind) in the case of type II time-dependent covariates. We develop upgraded QIF method for type II time-dependent covariates. We show that this upgraded QIF method can provide substantial gains in efficiency over QIF and GEE-ind in the case of type II time-dependent covariates.

Heuristics for Job Shop Scheduling Problems with Progressive Weighted Tardiness Penalties and Inter-machine Overlapping Sequence-dependent Setup Times

Mongkalig, Chatpon,Tabucanon, Mario T.,Hop, Nguyen Van Korean Institute of Industrial Engineers 2005 Industrial Engineeering & Management Systems Vol.4 No.1

This paper presents new scheduling heuristics, namely Mean Progressive Weighted Tardiness Estimator (MPWT) Heuristic Method and modified priority rules with sequence-dependent setup times consideration. These are designed to solve job shop scheduling problems with new performance measures - progressive weighted tardiness penalties. More realistic constraints, which are inter-machine overlapping sequence-dependent setup times, are considered. In real production environments, inter-machine overlapping sequence-dependent setups are significant. Therefore, modified scheduling generation algorithms of active and nondelay schedules for job shop problems with inter-machine overlapping sequence-dependent setup times are proposed in this paper. In addition, new customer-based measures of performance, which are total earliness and progressive weighted tardiness, and total progressive weighted tardiness, are proposed. The objective of the first experiment is to compare the proposed priority rules with the consideration of sequence-dependent setup times and the standard priority rules without setup times consideration. The results indicate that the proposed priority rules with setup times consideration are superior to the standard priority rules without the consideration of setup times. From the second experiment and the third experiment to compare the proposed MPWT heuristic approach with the efficient priority rules with setup times consideration, the MPWT heuristic method is significantly superior to the Batched Apparent Tardiness Cost with Sequence-dependent Setups (BATCS) rule, and other priority rules based on total earliness and progressive weighted tardiness, and total earliness and tardiness.