• Asian-Australasian Journal of Animal Sciences
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• 제21권6호
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• pp.769-775
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• 2008

This study was on the relative net income (RNI) for 18,286 Iranian Holstein cows from 799 herds, with first freshening between 1991 and 2000. Two kinds of production system, which differed mainly in milk pricing system and feed cost, were considered. Four different models adopted from the literature were examined to find the optimum model. They differed by the cost of rearing and growth after first calving and they needed different amounts of economic data at the farm level. Results showed that four measures of RNI were highly correlated (>0.96) and could be used equally to measure lifetime profitability of cows. Therefore, in herds without a regular system for recording economic and management data, use of the simplest model is recommended. Multiple regression analysis revealed that RNI was affected by age at first freshening, milk yield and days of productive life (DPL), regardless of production system, and a similar breeding goal could be defined for the two systems. Multiple regression analysis of RNI showed that in order to obtain an unbiased estimate of economic value for DPL, the per day milk yield, not total lifetime milk yield, should be included in the regression model along with DPL. Regression analysis suggested that it is possible to predict RNI using information on age at first freshening along with the length of first lactation and per day milk yield with a coefficient of determination ranging from 0.44 to 0.47.

• Steel and Composite Structures
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• 제18권4호
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• pp.909-924
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• 2015

This paper investigates the vibration phenomenon of a nanobeam subjected to a time-dependent heat flux. Material properties of the nanobeam are assumed to be graded in the thickness direction according to a novel exponential distribution law in terms of the volume fractions of the metal and ceramic constituents. The upper surface of the functionally graded (FG) nanobeam is pure ceramic whereas the lower surface is pure metal. A nonlocal generalized thermoelasticity theory with dual-phase-lag (DPL) model is used to solve this problem. The theories of coupled thermoelasticity, generalized thermoelasticity with one relaxation time, and without energy dissipation can extracted as limited and special cases of the present model. An analytical technique based on Laplace transform is used to calculate the variation of deflection and temperature. The inverse of Laplace transforms are computed numerically using Fourier expansion techniques. The effects of the phase-lags (PLs), nonlocal parameter and the angular frequency of oscillation of the heat flux on the lateral vibration, the temperature, and the axial displacement of the nanobeam are studied.

• Coupled systems mechanics
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• 제10권1호
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• pp.21-38
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• 2021

This work is an attempt to design a dynamic model for a non local bio-thermoelastic medium with diffusion. The system of governing equations are formulated in terms of displacement vector field, chemical potential and the tissue temperature in the context of non local dual phase lag (NL DPL) theories of heat conduction and mass diffusion. Based on this considered model, we study the fundamental solution and propagation of plane harmonic waves in tissues. In order to analyze the behavior of the NL DPL model, we construct basic theorem in the terms of elementary function which determine the existence of three longitudinal and one transverse wave. The effects of various parameters on the characteristics of waves i.e., phase velocity and attenuation coefficients are elaborated by plotting various figures of physical quantities in the later part of the paper.

• Structural Engineering and Mechanics
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• 제75권2호
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• pp.133-144
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• 2020

This investigation is to study the effect of gravitational field and diffusion on a microstretch thermoelastic medium heating by a non-Gaussian laser beam. The problem was studied in the context of the dual-phase-lag model. The normal mode analysis is used to solve the problem to obtain the exact expressions for the non-dimensional displacement components, the micro-rotation, the stresses, and the temperature distribution. The effect of time parameter, heat flux parameter and gravity response of three theories of thermoelasticity i.e. dual-phase-lag model (DPL), Lord and Shulman theory (L-S) and coupled theory (CT) on these quantities have been depicted graphically for a particular model.

• Geomechanics and Engineering
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• 제28권4호
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• pp.347-358
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• 2022

The main concern of this article is to discuss the problem of a two-temperature fiber-reinforced micropolar thermoelastic medium with voids under the effect rotation, mechanical force in the context four different theories with memory-dependent derivative (MDD) and variable thermal conductivity. The three-phase-lag model (3PHL), dual-phase-lag model (DPL), Green-Naghdi theory (G-N II, G-N III), coupled theory, and the Lord-Shulman theory (L-S) are employed to solve the present problem. Analytical expressions of the physical quantities are obtained by using Laplace-Fourier transforms technique. Numerical results are shown graphically and the results obtained are analyzed. The most significant points are highlighted.

• Smart Structures and Systems
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• 제18권4호
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• pp.707-731
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• 2016

A unified mathematical model of the equations of generalized magneto-thermoelasticty based on fractional derivative heat transfer for isotropic perfect conducting media is given. Some essential theorems on the linear coupled and generalized theories of thermoelasticity e.g., the Lord- Shulman (LS) theory, Green-Lindsay (GL) theory and the coupled theory (CTE) as well as dual-phase-lag (DPL) heat conduction law are established. Laplace transform techniques are used. The method of the matrix exponential which constitutes the basis of the state-space approach of modern theory is applied to the non-dimensional equations. The resulting formulation is applied to a variety of one-dimensional problems. The solutions to a thermal shock problem and to a problem of a layer media are obtained in the present of a transverse uniform magnetic field. According to the numerical results and its graphs, conclusion about the new model has been constructed. The effects of the fractional derivative parameter on thermoelastic fields for different theories are discussed.

• Structural Engineering and Mechanics
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• 제82권4호
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• pp.459-467
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• 2022

We investigated the influence of variable thermal conductivity on waves propagating through the elastic medium. Infinitesimal deformation results in generation of thermal signal, and is analyzed by using dual phase lag heat (DPL) conduction model. The medium considered is homogenous, isotropic and bounded by thermal shock. The elastic waves propagating through the medium are considered to be harmonic in nature, and expressions for the physical variables are obtained accordingly. Analytically, we obtained the expressions for displacement components, temperature, micro-temperature component and stresses. The theoretical results obtained are computed graphically for the particular medium by using MATLAB.

• 한국건설관리학회논문집
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• 제5권3호
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• pp.97-105
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• 2004

사업기획 및 타당성분석단계는 사업을 추진하는데 가장 큰 영향을 미치는 단계로써, 정확한 프로젝트 타당성 검토 수행은 프로젝트를 추진하는데 결정적인 기회를 제공해주므로 직관적인 접근방식보다는 객관적이고 정확한 방법의 제시가 요구되는 바이다. 사업타당성을 정확하게 분석하기 위하여 본 논문에서는 프로젝트 진행에 영향을 주는 리스크 인자를 식별하고 이 인자들을 성격별로 그룹화한다. 소규모 임대주택의 사례를 바탕으로 기존 방식인 금융부분의 프로젝트 타당성 분석을 실시한다. 위에서 식별된 리스크 인자들 중 금융부분을 포함하여 인자들간의 상관관계를 Influence Diagram으로 파악하여 리스크를 분석하고, 각 인자별의 중요도를 판별하기 위한 민감도 분석을 실시한다. 이와 같은 과정을 통하여, 기존의 프로젝트 타당성분석에서 사용하는 금융부분의 타당성분석 뿐만 아니라, 프로젝트 진행시에 나타나는 비정형적이고 주관적인 요소들을 리스크 인자로써 포함하여 분석할 수 있는 장점이 있다. 또한, 도출된 모든 리스크 인자를 정량화하여 객관적인 분석 및 의사결정을 할 수 있기 때문에 기존 방법보다 발전된 프로젝트 타당성 분석 방안을 본 논문에서 제시하였다.