Extending Monte Carlo Simulations to Represent and Propagate Uncertainties in Presence of Incomplete Knowledge: Application to the Transfer of a Radionuclide in the Environment

This work is devoted to some recent developments in uncertainty analysis of environmental models in the presence of incomplete knowledge. The classical uncertainty methodology based on probabilistic modeling provides direct estimations of relevant statistical measures to quantify the uncertainty on the model responses thanks to a nice mixing between Monte Carlo simulations and the use of efficient statistical treatments. However, this approach may lead to unrealistic results when not enough information is available to specify the probability distribution functions (pdfs) of input parameters. For example, if a fixed (i.e., the pdf is a Dirac distribution) variable is unknown between a and b, the proper way to model this knowledge is to consider a set of δc distributions (a δc distribution means that the probability that the parameter is equal to c is 1 and 0 elsewhere), c belonging to [a,b]. This is quite different from assume an equidistribution. Thus, to respect the real state of knowledge in industrial applications, a new modeling based on the theory of evidence is introduced. It allows an extension of classical Monte Carlo simulations by relaxing assumptions related to the choice of probability distribution functions and possible dependencies between uncertain parameters. To illustrate the principle of our modeling, a comparison with the probabilistic modeling is given in the case of the transfer of a radionuclide in the environment.     

Bayesian Model Calibration Using Geotechnical Centrifuge Tests

The predicted performance using a geotechnical prediction model is expected to deviate from reality. A practical approach to assess the model error is through calibration with observed performances in physical model tests. In this paper, a Bayesian framework of model calibration using centrifuge modeling tests is proposed and the procedure of model calibration is illustrated. Two centrifuge tests conducted to investigate the performance of soil slopes under rainfall conditions are used to calibrate a coupled hydromechanical analysis model. It is found that for centrifuge tests with different levels of soil variability, the test with a smaller variability of soil properties is more efficient for model calibration. According to the concept of random field, a centrifuge model with a larger model size and accelerated to a lower acceleration is better for model calibration. When the discrepancy between the performance interpreted from the centrifuge model and the field performance is small, the improvement of the reliability estimation for a new slope is significant. However, when there is little information about the discrepancy, the reliability estimation cannot be significantly improved by the information from centrifuge modeling. The proposed procedure is shown to be able to quantify the calibration effects of centrifuge tests and may be used to achieve a more reliable calibration.     

Optimal control of an aluminum casting furnace: Part I. The control model

This is a series of two articles on the control of an aluminum casting furnace to bring a mass of liquid aluminum from a known initial temperature to a desired final temperature in a given time with minimal fuel cost. An analytic model of the furnace already exists but is too complex for control purposes. Here in Part I, a simplified nonlinear control model is derived from the analytic model. In Part II, an optimization of the fuel flow is performed on the control model using Pontryagin’s maximum principle. The first article shows that despite the complexity of the analytic model, a tenth-order nonlinear control model with good representativity can be obtained. The second article shows that the maximum principle applied to this problem leads to a solution with optimal fuel cost. If modeling industrial processes is a complex problem in itself, obtaining a control model therefrom is just as delicate. This series of articles proposes an approach that works for the casting furnace and is indeed applicable to other industrial processes as well. In the existing analytic model, the casting furnace is treated as two one-dimensional conducting media (metal and refractories), while its chamber is seen as a well-stirred reactor. In this article, a control model is derived therefrom by a statistical method. The analytic model is run several times to obtain a set of predicted data on which a least-squares approximation is performed to determine the best parameter values to be used for the control model equations. The conduction equations in the two media are linear. The expressions for heat generation in the chamber and for radiative-convective heat transfer from the chamber to the two media are nonlinear and are kept to ensure maximum representativity. The result is a highly representative tenth-order control model, the degree of representativity being assessed by comparing the temperature outputs and the energy balances obtained from the analytic model with those obtained from the control model.     

BCD: A Soil Modulus Device for Compaction Control

There is a trend toward using the modulus as an alternative to dry density in compaction control because of the undesirable nuclear source in the current field density gage and because a modulus is often used in the design of roadway bases and compacted fills. The Briaud compaction device (BCD) is a new instrument used to obtain a soil modulus in only a few seconds; it consists of leaning on a rod equipped with a thin circular metal plate at the bottom end and recording the bending of that plate under a standard load. This article describes the theory and the experiments that have been performed to validate the new instrument. This validation is based on a comparison to a simple plate test and on a numerical simulation of the BCD test. A recommended procedure is outlined in the conclusions. The BCD is used in the lab on top of the soil in the Proctor mold to obtain the lab modulus versus water content curve and select a target value. Then the BCD is used in the field to verify that the target modulus has been achieved.     

Vapor Flow to Trench in Leaky Aquifer

Soil-vapor extraction has become the most common innovative technology for treating subsurface soils contaminated with volatile and semivolatile organic compounds. This popularity is due partly to the low cost of vapor extraction and partly to the fact that mitigation is completed in situ. Previous applications of this technology have generally considered flow to either vertical or horizontal wells. However, vapor flow to a trench offers the advantages of a more uniform velocity field and lower construction costs at sites with shallow water tables. Therefore, an analytical solution is obtained for steady flow to a trench. The trench is assumed to partially penetrate an anisotropic aquifer and to have a finite horizontal length. The bottom aquifer boundary is assumed to be an impermeable water table, and the top boundary is a semipermeable aquitard. A comparison is made with field measurements to illustrate the application of the solution and to give confidence in its use.     

Development in smelting reduction processes

Corex process is a smelting reduction process to produce hot metal of blast-furnace quality. Coal is used instead of coke, and this replacement makes production costs of hot metal decrease. Iron ore reduction and melting is separated into two steps: in a melter gasifier reducing gas is generated and melting energy is produced by coal gasification; iron ore is reduced in a shaft furnace. Due to this separation, a great variety of untreated coals can be used. The Corex process is designed to operate under elevated pressure, up to 5 bar. Reducing gas is generated in a fluidized bed by partial oxidation of coal. After leaving the melter gasifier, the gas is mixed with cooling gas to obtain a temperature suitable for direct reduction, i.e. approximately 850–900°C. The fines captured in a hot cyclone are re-injected into the gasifier. Reducing gas is fed into the reduction furnace and ascends through the iron burden according to the counterflow principle. The hot DRI having a temperature of 800–900°C is continuously charged into the melter gasifier, where further reduction is effected and melting occurs. Hot metal and slag drop to the bottom of the melter-gasifier. Analogous to blast-furnace practice hot metal and slag are discharged by conventional tapping.     

用粉末冶金方法制造压缩机法兰

为防止压缩机在运行中变形,用粉末冶金方法制造了带减压槽的压缩机法兰。将制造法兰的粉末材料装于模腔中,然后,将熔点比粉末材料低的熔渗件置于减压槽位置进行成形;将粉末材料与熔渗件压制成形为法兰;在粉末材料与熔渗件熔点之间的温度下进行烧结,使熔渗件熔化和渗入粉末材料之中。用新方法制造的法兰比用常规方法生产的强度高、密封性好。根据分析,在烧结时,由于熔渗件熔化与渗透到法兰结构中,改进了气密性,增高了强度。     

Riprap Failure at Circular Bridge Piers

Riprap of bridge piers is placed to prevent scour and to secure the pier from failure. Riprap is therefore an addition to a pier to increase its performance against scour. The present research intends to present three basic scour mechanisms associated with circular-shaped bridge piers in rivers first, to introduce then a number of selected experiments for a range of hydraulic, geometric, and sedimentologic conditions, and finally to describe a novel procedure for assessing the safety of these river elements against failure. This procedure is based on the Shields diagram relating to sediment entrainment in a uniform and flat sediment bed subjected by a water flow. The Shields approach is extended for the presence of a circular-shaped pier that is protected by a circular-arranged riprap layer of equal size elements. The design procedure presented in the following thus reduces to the entrainment condition of a pier for equal riprap and the sediment sizes and to the Shields entrainment condition when the pier diameter degenerates to 0.     

Sequential monitoring of survival data with the Wilcoxon statistic

When a spending function is used in sequential data monitoring of a clinical trial, it is important to know the information fraction at the times of interim analysis. In a maximum duration designed study, the information fraction is unknown when data are monitored, and it has to be estimated. The modified Wilcoxon statistic developed by Peto and Peto and modified by Prentice is often used to compare two survival curves in a clinical trial. We give guidelines for estimating the information fraction in a maximum duration trial when this statistic is employed. When there is a relatively low event rate or the survival time is approximately exponential, the information fraction for the Peto-Peto-Prentice Wilcoxon statistic is very close to that of the popular logrank statistic. In other cases, it would be helpful to estimate the information fraction as a function of elapsed calendar time. We discuss both group sequential and continuous monitoring.     

Measurement of head-turn in ocular torticollis

There is a need for a simple and accurate method to measure head-turn in patients who suffer from torticollis secondary to ocular disease. In the technique described here, a fixation object is moved from a point in front of the patient to a point at which the patient's face is straight. The distance that the object is moved is proportional to the amount of head-turn the patient has. With a simple mathematical calculation, the angle of head-turn can be determined, even during a routine clinical evaluation.     

Bayesian Updating of Structural Models and Reliability using Markov Chain Monte Carlo Simulation

In a full Bayesian probabilistic framework for “robust” system identification, structural response predictions and performance reliability are updated using structural test data D by considering the predictions of a whole set of possible structural models that are weighted by their updated probability. This involves integrating h(θ)p(θ∣D) over the whole parameter space, where θ is a parameter vector defining each model within the set of possible models of the structure, h(θ) is a model prediction of a response quantity of interest, and p(θ∣D) is the updated probability density for θ, which provides a measure of how plausible each model is given the data D. The evaluation of this integral is difficult because the dimension of the parameter space is usually too large for direct numerical integration and p(θ∣D) is concentrated in a small region in the parameter space and only known up to a scaling constant. An adaptive Markov chain Monte Carlo simulation approach is proposed to evaluate the desired integral that is based on the Metropolis-Hastings algorithm and a concept similar to simulated annealing. By carrying out a series of Markov chain simulations with limiting stationary distributions equal to a sequence of intermediate probability densities that converge on p(θ∣D), the region of concentration of p(θ∣D) is gradually portrayed. The Markov chain samples are used to estimate the desired integral by statistical averaging. The method is illustrated using simulated dynamic test data to update the robust response variance and reliability of a moment-resisting frame for two cases: one where the model is only locally identifiable based on the data and the other where it is unidentifiable.     

Future Environmental Regulation Issues to Promote Energy Efficiency

It is accepted that fossil fuel is the major source of energy in use today. The technology to use this fuel is well-developed and relatively safe. However, there are two fundamental problems facing the industry that is so dependent on this type of fuel. One, it is a limited resource with only decades of life left. Second is the pollution resulting from its use, primarily the CO2 greenhouse gas generated, and acid rain from NOx and SO2. Until suitable substitutes are found, developed, and implemented, the next best option is to reduce the consumption of the fuel through higher efficiency. Recent research projects with regard to environmental issues send a clear signal to both governments and the energy manufacturing industry that they need to act quickly in order to sustain the environmental conditions. Cogeneration is a technology which can achieve this, but it is important that financial and taxation systems are designed and implemented in a way that recognizes a broader scope for accountability of the needs of industry. Due to increase in the world economy there is a need for further technological progress and environmental legislation. This paper describes a potential fiscal model which could be used to encourage the responsible use of modern clean cogeneration plants to reduce the environmental impact and to allow some political influence over fuel use.     

Theory of Seepage into an Auger Hole in a Confined Aquifer Overlying a Gravel Substratum

An analytical solution is presented to the problem of steady groundwater flow seeping into a pumped cylindrical hole partially penetrating a homogeneous and anisotropic confined aquifer overlying a gravel substratum. Solutions are obtained for two general cases of the problem: (1) when the level of the pumped hole is below the confining layer; (2) when it is above it. The validity of the proposed theory is tested by comparing analytical predictions obtained for a few flow situations with corresponding results obtained by numerical means. The theory presented here can be utilized to convert the rate of rise of water in a pumped auger hole into directional conductivities of soil, in areas where water is found to be in a confined state overlying a gravel substratum. The study shows that the conductivity values calculated by neglecting the confining pressure of an artesian aquifer with a gravel base [i.e., by applying the existing (Boast and Kirkham in 1971), auger hole seepage theory for a phreatic aquifer with a gravel base to confined situations] may result in serious error; hence, the artesian head of an aquifer must be accounted for while computing the conductivity values. Further, it is observed that the area contributing flow to a pumped auger hole/well with a gravel base is mostly restricted to a short radial distance from the center of the hole, particularly for situations where the gravel substratum is located close to the bottom of the hole. This is in contrast to auger hole flow situations overlying an impervious substratum, where the domain contributing flow is mostly spread out to a considerable distance from the center of the hole.     

Intention to kill--the deciding criterion between allowed and prohibited assisted euthanasia

The difference between the allowed and forbidden euthanasia is--on account of the dominant opinion--the criterion of acting and forbearance. It is not punishable to let a terminally ill patient die, but it is punishable to kill a patient on purpose. This distinctive mark is not forcible, because the acting is similar to the forbearance, when the actor has a guaranter's obligation--this is always the case between a doctor and his patient--and it is questionable, if the stopping of apparatuses for support of life is a kind of acting or forbearance. To overcome this dilemma, the author proposes to establish the distinctive mark of "intention to kill" in the law. Then the euthanasia is a punishable act if the actor or the person, who forbears, practices euthanasia with the intention to kill the patient. The euthanasia is not punishable, however, if the euthanasia overwhelms the blockade of dying or softens the pains.     

高平行度双稳态夹持机构设计与分析

采用刚体代替综合法设计了一个以高平行度的双四边形机构为提升平台的平面折展柔顺机构,克服了单平行四边形提升机构的缺点,提高了提升平台与地面的平行度.设计了一个双稳态夹持机构,通过限制夹持机构滑块的位移控制加持力的大小,以稳态二为工作状态保证加持力的稳定.最后通过辅助机构将两机构组合在一起,使一个驱动能够同时完成提升和夹持两个动作.建立了该机构的伪刚体模型,分析了该机构输入力矩与转角和位移之间的关系,并通过实例的理论计算和有限元仿真分析,验证了伪刚体模型的正确性和机构设计的实用性.      

One Modified FE‐model to Simulate the Process Chain of Forming and Welding

This paper presents a possibility of creating a virtual process chain consisting of forming and welding. Independent of any manufacturing process, a variable Finite Element model is introduced. This model can be an input for more than one simulation by means of the Finite Element Method (FEM). The process chain forming and welding is chosen to demonstrate the need and the importance to simulate a process chain in comparison to a single process simulation. Each simulation has its own specifications and intentions. Therefore, an FE‐model for a forming simulation is different from a model for a welding simulation. In this paper a way is shown how to keep the model and the results of a forming simulation for the succeeding simulation of welding. The results of the forming simulation remain as an initial state in the welding simulation. Thereby, a spring‐back behaviour can be modelled. A few adjustments have to be done to satisfy the specifications of the welding simulation. The used material for the integrated simulation is a DC 04 steel. Therefore, metallurgical phases must be considered to achieve sufficient results. For reasons of further industrial applications commercial FE‐solvers are used for calculations. The method of integration is applied to different examples. The verified results are presented and discussed. The simulated transient distortional behaviour of a formed and welded part is presented and compared to a mere welding simulation. A significant improvement of the distortion as a result of the welding simulation is reached by consideration of a previous forming simulation.     

Gabapentin: pharmacokinetics, efficacy, and safety

Gabapentin is a new antiepileptic drug (AED) with an attractive pharmacokinetic profile. It is absorbed by an active and saturable transport system, and has a high volume of distribution. Gabapentin is not bound to plasma proteins, does not induce hepatic enzymes and is not metabolized. At steady state, it has a half-life of 6-8 h, and is eliminated unchanged by renal route with a plasma clearance proportional to the creatinine clearance. It is devoid of significant drug-drug interactions when administered with the established AEDs or with oral contraceptives. Gabapentin used as an add-on AED significantly reduced the frequency of partial seizures and secondarily generalized tonic-clonic seizures in three large double-blind, placebo-controlled, parallel-group clinical trails. It is well tolerated, with transient somnolence and dizziness being the most frequent adverse effects. Although the mechanism of action of gabapentin is not fully established, there is strong evidence to suggest a novel mechanism of action. Gabapentin is a unique and promising drug that could improve the quality of life of patients with epilepsy and is a welcome addition to the armamentarium of currently available AEDs for the treatment of patients with seizures of partial onset.     

Simple Model of Frequency-Dependent Impedance Functions in Soil-Structure Interaction Using Frequency-Independent Elements

This study presents a methodology to make a simple equivalent model of frequency-dependent impedance functions of soil-structure interactions using a frequency-independent spring and dashpot, together with a proposed element called “gyromass.” The gyromass is frequency independent and is defined as a unit system that generates a reaction force due to the relative acceleration of the nodes between which the gyromass is placed. It is found that a model consisting of a spring, dashpot, and gyromass may generate various types of frequency-dependent impedance characteristics. This study proposes two types of simple models that express typical frequency-independent impedance functions of soil-structure interactions by using the gyromass. The advantage of these models is that the frequency-dependent characteristics can easily be expressed by a small number of elements and degrees of freedom. Moreover, they can be applied directly to conventional time-history analyses, even beyond the elastic region of the structural members. An example in which a simple model is applied to the time-history analysis of a soil-pile-superstructure system with an inelastic structural member when subjected to an earthquake wave is illustrated.     

Effects of Size and Slenderness on Ductility of Fracturing Structures

The ductility of an elastic structure with a growing crack may be defined as the ratio of the additional load-point displacement that is caused by the crack at the moment of loss of stability under displacement control to the elastic displacement at no crack at the moment of peak load. The stability loss at displacement control is known to occur when the load-deflection curve of the whole structural system with the loading device (characterized by a spring) reaches a snapback point. Based on the known stress intensity factor as a function of crack length, the well-known method of linear elastic fracture mechanics is used to calculate the load-deflection curve and determine the states of snapback and maximum loads. An example of a notched three-point bend beam with a growing crack is analyzed numerically. The ductility is determined and its dependence of the structure size, slenderness, and stiffness of the loading device is clarified. The family of the curves of ductility versus structure size at various loading device stiffnesses is found to exhibit at a certain critical stiffness a transition from bounded single-valued functions of D to unbounded two-valued functions of D. The method of solution is general and is applicable to cracked structures of any shape. The flexibility (force) method can be adapted to extend the ductility analysis to structural assemblages provided that the stress intensity factor of the cracked structural part considered alone is known. This study leads to an improved understanding of ductility, which should be useful mainly for design against dynamic loads.