In commodity transport networks such as natural gas, hydrogen and water networks, flows arise from nonlinear potential differences between the nodes, which can be represented by so-called potential-driven network mode...
详细信息
In commodity transport networks such as natural gas, hydrogen and water networks, flows arise from nonlinear potential differences between the nodes, which can be represented by so-called potential-driven network models. When operators of these networks face increasing demand or the need to handle more diverse transport situations, they regularly seek to expand the capacity of their network by building new pipelines parallel to existing ones ("looping"). The paper introduces a new mixed-integer nonlinear programming model and a new nonlinear programming model and compares these with existing models for the looping problem and related problems in the literature, both theoretically and experimentally. On this basis, we give recommendations to practitioners about the circumstances under which a certain model should be used. In particular, it turns out that one of our novel models outperforms the existing models with respect to computational time, the number of solutions found, the number of instances solved and cost savings. Moreover, the paper extends the models for optimizing over multiple demand scenarios and is the first to include the practically relevant option that a particular pipeline may be looped several times.
The development of infectious disease models remains important to provide scientists with tools to better understand disease dynamics and develop more effective control strategies. In this work we focus on the estimat...
详细信息
The development of infectious disease models remains important to provide scientists with tools to better understand disease dynamics and develop more effective control strategies. In this work we focus on the estimation of seasonally varying transmission parameters in infectious disease models from real measles case data. We formulate both discrete-time and continuous-time models and discussed the benefits and shortcomings of both types of models. Additionally, this work demonstrates the flexibility inherent in large-scale nonlinear programming techniques and the ability of these techniques to efficiently estimate transmission parameters even in very large-scale problems. This computational efficiency and flexibility opens the door for investigating many alternative model formulations and encourages use of these techniques for estimation of larger, more complex models like those with age-dependent dynamics, more complex compartment models, and spatially distributed data. However, the size of these problems can become excessively large even for these powerful estimation techniques, and parallel estimation strategies must be explored. Two parallel decomposition approaches are presented that exploited scenario based decomposition and decomposition in time. These approaches show promise for certain types of estimation problems.
Explicit models representing the response variables as functions of the control variables are standard in virtually all scientific fields. For these models, there is a vast literature on the optimal design of experime...
详细信息
Explicit models representing the response variables as functions of the control variables are standard in virtually all scientific fields. For these models, there is a vast literature on the optimal design of experiments (ODoE) to provide good estimates of the parameters with the use of minimal resources. Contrarily, the ODoE for implicit models is more complex and has not been systematically addressed. Nevertheless, there are practical examples where the models relating the response variables, the parameters and the factors are implicit or hardly convertible into an explicit form. We propose a general formulation for developing the theory of the ODoE for implicit algebraic models to specifically find continuous local designs. The treatment relies on converting the ODoE problem into an optimization problem of the nonlinear programming (NLP) class which includes the construction of the parameter sensitivities and the Cholesky decomposition of the Fisher information matrix. The NLP problem generated has multiple local optima, and we use global solvers, combined with an equivalence theorem from the theory of ODoE, to ensure the global optimality of our continuous optimal designs. We consider D- and A-optimality criteria and apply the approach to five examples of practical interest in chemistry and thermodynamics. for this article are available online.
Heart disease diagnosis using few measurements is a challenging an important task considering the increasing population. Artificial Neural Networks (ANNs) are promising mathematical architectures once the training is ...
详细信息
ISBN:
(纸本)9781713867890
Heart disease diagnosis using few measurements is a challenging an important task considering the increasing population. Artificial Neural Networks (ANNs) are promising mathematical architectures once the training is performed in an elegant manner to avoid theoretical challenges related to high nonlinearity, nonconvexity using few input variables to ensure generalization capability. This study shows the impact of the piecewise linear approximation of nonlinear functions in ANN architecture and training problem to benefit from the mixed integer linear problem formulation for the simultaneous input selection and training to obtain mixed integer programming based ANN (MIP-ANN). Proposed formulation is further tailored through linking constraints to remove the connections from the eliminated inputs to favor parameter identifiability. A publicly available dataset is considered as a case study of whose results are also compared to traditional ANN with all inputs (FC-ANN) and a relatively more straightforward but common input selection method (SKB-ANN). The results provide a comparable performance despite significant reduction in the input space in addition to significant computational and theoretical advantages thanks to advanced *** (c) 2022 The Authors This is an open access article under the CC BY-NC-ND license (https://***/licenses/by-nc-nd/4.0/)
A composite score is made up of two or more variables that are conceptually or statistically correlated. There have been many methods to make composite scores, but it is still not easy to construct a desirable composi...
详细信息
Purpose While consumer demand for meat substitutes is growing, their varied composition raises questions regarding their nutritional value. We aimed to identify and characterize the optimal composition of a meat subst...
详细信息
Purpose While consumer demand for meat substitutes is growing, their varied composition raises questions regarding their nutritional value. We aimed to identify and characterize the optimal composition of a meat substitute that would best improve diet quality after complete meat replacement. Methods From an average individual representing the dietary intake of French adults (INCA3, n = 1125), meat was replaced with an equivalent amount of a mostly pulse-based substitute, whose composition was based on a list of 159 possible plant ingredients and optimized non-linearly to maximize diet quality assessed with the PANDiet score (considering adequacy for 32 nutrients), while taking account of technological constraints and applying nutritional constraints to limit the risk of overt deficiency in 12 key nutrients. Results The optimized meat substitute contained 13 minimally processed ingredients. When used to substitute meat, the PANDiet score increased by 5.7 points above its initial value before substitution (versus - 3.1 to + 1.5 points when using other substitutes on the market), mainly because of higher intakes of nutrients that are currently insufficiently consumed (e.g., alpha-linolenic acid, fiber, linoleic acid) and a lower SFA intake. The meat substitute also mostly compensated for the lower provision of some indispensable nutrients to which meat greatly contributed (e.g., vitamin B6, potassium, bioavailable iron), but it could not compensate for bioavailable zinc and vitamin B12. Conclusion Choosing the correct ingredients can result in a nutritionally highly effective meat substitute that could compensate for reductions in many nutrients supplied by meat while providing key nutrients that are currently insufficiently consumed.
In contrast to standard penalty type methods for nonlinear optimiza-tion, penalty-free type methods do not have to determine penalty parameters and have promising numerical results. So they have attracted the attentio...
详细信息
In contrast to standard penalty type methods for nonlinear optimiza-tion, penalty-free type methods do not have to determine penalty parameters and have promising numerical results. So they have attracted the attention of many researchers. Filter method is a classical penalty-free method. In this paper, a different filter tech-nique is introduced for solving nonlinear equality constrained optimization. The opti-mality condition of the nonlinear optimization problem is regarded as a new filter pair which is built in the backtracking line search framework. Then, the trial step size is accepted if one of the two measures in filter is improved after the search direction is de-termined. Under some reasonable assumptions, the global convergence of the algorithm is proved. Some preliminary numerical results are presented to show the usefulness of the proposed algorithm.
In this Note, the analytical state propagation for the two-body linear relative motion in elliptic orbits is derived under an arbitrary continuous-thrust acceleration. In contrast to the commonly used orbital averagin...
详细信息
In this Note, the analytical state propagation for the two-body linear relative motion in elliptic orbits is derived under an arbitrary continuous-thrust acceleration. In contrast to the commonly used orbital averaging technique, which only considers the secular orbital variations, one of the innovations of this Note is to consider the overall orbital variation without separating the secular and periodic terms. For this purpose, the original thrust acceleration is approxi- mated by truncated power and Fourier series in terms of the eccentric anomaly by using the discrete least square approximation, and then the analytical state propagation is derived for both series. In addition, the other innovation of this Note is applying the derived analytical state expression to two classical continuous-thrust boundary value problems, the energy-optimal and the fuel-optimal orbital rendezvous problems. For the energy-optimal orbital rendezvous, the ana- lytical solution is obtained, whereas for the fuel-optimal orbital rendezvous, the problem is transformed into a nonlinear program- ming (NLP) problem to obtain the solution rapidly. The results are compared with the linear quadratic regulator (LQR) and the Gauss pseudospectral method (GPM), respectively.
暂无评论