| 1. |
- Bellomo, N, et al.
(författare)
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The generalized kinetic modelling of a multicomponent "Real-Life" fluid by means of a single distribution function
- 2003
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Ingår i: Mathematical and computer modelling. - : Elsevier Science B.V., Amsterdam.. - 0895-7177 .- 1872-9479. ; 38:06-May, s. 637-659
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Tidskriftsartikel (refereegranskat)abstract
- work proposes a fully continuum stochastic model of a multicomponent fluid. It is shown that the way to this model leads to a generalized-kinetics (GK) theory. Subsequently, the model is developed as a corresponding extension of this theory. The obtained model presents the overall generalized distribution function. It is described with a nonlinear nonlocal (or "mean-field") system of two scalar equations, no matter how many components are in the fluid, and a special prescription. The system comprises (i) the generalized kinetic equation for the conditional distribution function conditioned with the values of the particle-property stochastic process, and (ii) the McKean-Kolmogorov forward equation for the probability density of this process. The aforementioned prescription determines the number of the fluid components as the number of the modes of this density. The work also includes a theorem that provides an estimation from below for this number in the generic stationary case of the corresponding multidimensional Kolmogorov equation and points out how the modes manifest themselves in the drift and diffusion functions (more specifically, in the Fichera drift function). The discussion on the model and a few directions for future research concludes the work.
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| 2. |
- Jr., A.J. Meade, et al.
(författare)
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Enhancement of a viscous-inviscid-interaction airfoil analysis code using the parallel direct search algorithm
- 1997
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Ingår i: Mathematical and computer modelling. - 0895-7177 .- 1872-9479. ; 25:6, s. 85-96
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Tidskriftsartikel (refereegranskat)abstract
- The coupling mechanism for an existing viscous-inviscid-interaction (VII) code, developed for the analysis of two-dimensional, turbulent, attached flow around airfoils, is enhanced using the parallel direct search (PDS) optimization algorithm. It is demonstrated that this parallel processing implemented optimization scheme leads to faster convergence of the VII code, and therefore, requires less computational time when the number of optimization (or design) variables is low, and a moderate number of processors are available. As the number of design variables increases, more processors are required to maintain this advantage. Results are presented for the NACA-0012 and the RAE-2822 airfoils. The quality of the results obtained is satisfactory and confirms that the enhanced VII code can be an acceptable alternative to reduced Navier-Stokes solvers as an airfoil analysis tool.
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| 3. |
- Mamontov, E, et al.
(författare)
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Stochastic continuum mechanics - A thermodynamic-limit-free alternative to statistical mechanics : Equilibrium of isothermal ideal isotropic uniform fluid
- 2002
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Ingår i: Mathematical and computer modelling. - : Elsevier Science B.V., Amsterdam.. - 0895-7177 .- 1872-9479. ; 36:7-8, s. 889-907
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Tidskriftsartikel (refereegranskat)abstract
- We do not know how to study finite systems in any clean way; that is, the thermodynamic limit is inevitable. The lack of the clean way stressed in this sentence of Resibois and de Leener means the following. To study finite systems, statistical mechanics and kinetic theory offer nothing but the formalism based on the thermodynamic limit (TDL) which in essence disagrees with notion of finite system. The present work proposes the model (almost-equilibrium in a certain sense) enabling one to construct continuous equilibrium descriptions of fluids, discrete multiparticle systems, with no application of TDL. For simplicity, the fluids are assumed to be isothermal, (rheologically) ideal, isotropic and uniform. The core of the model is nonlinear It (o) over tilde s stochastic differential equation (ISDE) for the fluid-particle velocity. The continuous equilibrium description is based on the stationary probability density corresponding to this equation. The construction is described as a simple analytical recipe formulated in terms of quadratures and includes the velocity (or momentum) relaxation times which can be determined theoretically, experimentally, or as the results of numerical simulations and depending on the specific nature of the fluid. The recipe can be applied to an extremely wide range of fluids of the above class. It is illustrated by the derivations of the Maxwell-Boltzmann and Fermi-Dirac descriptions for the classical and fermion fluids in arbitrary space domain, bounded or unbounded. In the particular, TDL case, the derived results are in a complete agreement with those of statistical mechanics.
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| 4. |
- Wiktorsson, Magnus, et al.
(författare)
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An optimal production flow control problem with impulsive demand
- 1997
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Ingår i: Mathematical and computer modelling. - 0895-7177 .- 1872-9479. ; 26:2, s. 53-67
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Tidskriftsartikel (refereegranskat)abstract
- We consider a system consisting of a single machine cell and producing one part type. The machine cell has a finite capacity and is reliable. We consider a finite planning horizon containing N impulsive demands. The demand occurs instantaneously. Each such demand is known by its size and when it occurs in the planning horizon. In order to keep the production as close to the demand as possible there is a trade off between building up inventory and letting customers wait. An optimal control problem is formulated to determine the optimal production strategy. Solution technique is developed via Pontryagin's Minimum Principle.
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| 5. |
- Jesudason, Christopher Gunaseelan
(författare)
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Focus on the Clausius Inequalities as a consequence of modeling thermodynamic systems as a series of open Carnot cycles
- 2009
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Ingår i: Mathematical and computer modelling. - : Elsevier BV. - 0895-7177 .- 1872-9479. ; 49:04-mar, s. 835-842
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Tidskriftsartikel (refereegranskat)abstract
- Various results in thermodynamics developed recently are brought into focus by further refinement to set in less ambiguous form topics connected to irreversibility and the so called ""Clausius Inequality''. This singular ""Clausius Inequality'' for both closed and open systems was traditionally deduced from the Riemann ""integration'' of closed Carnot cycle loops for irreversible transitions. Evidently topological problems might be expected to arise concerning boundary conditions when ""open'' and ""closed'' systems exists simultaneously in such a scheme. It has hitherto been assumed that in this scheme, only one central Clausius Inequality can exist coupling all processes. Based on a new recent development of open system Carnot cycles, it is shown that other analogous inequalities can be derived, due to the presence of another fundamental entropy state function derived in the recent development, implying non-singularity. Their properties are such as to indicate that no new non-equilibrium entropy can arise from the inequalities as has been proposed over the decades. It is shown that a sequence of points along a non-equilibrium state space must have excess variables augmenting those for the equilibrium situation, which demonstrates that the often used Principle of Local Equilibrium (PLE) is only an approximation, implying that far-from-equilibrium theories should be developed ab initio from irreversible dynamical laws rather than from PLE. Examples presented from actual computations for both systems in equilibrium and non-equilibrium appears to support this deduction. Large scale and extensive thermodynamical theories have been created based on the assumption of a single Clausius-like inequality, such as those stemming from the very influential and extensive Truesdale school, and so such pervasive developments are also open to question.
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| 6. |
- Johansson, Björn, et al.
(författare)
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The application of an oblique-projected Landweber method to a model of supervised learning
- 2006
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Ingår i: Mathematical and computer modelling. - : Elsevier BV. - 0895-7177 .- 1872-9479. ; 43:7-8, s. 892-909
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Tidskriftsartikel (refereegranskat)abstract
- This paper brings together a novel information representation model for use in signal processing and computer vision problems, with a particular algorithmic development of the Landweber iterative algorithm. The information representation model allows a representation of multiple values for a variable as well as an expression for confidence. Both properties are important for effective computation using multi-level models, where a choice between models will be implementable as part of the optimization process. It is shown that in this way the algorithm can deal with a class of high-dimensional, sparse, and constrained least-squares problems, which arise in various computer vision learning tasks, such as object recognition and object pose estimation. While the algorithm has been applied to the solution of such problems, it has so far been used heuristically. In this paper we describe the properties and some of the peculiarities of the channel representation and optimization, and put them on firm mathematical ground. We consider the optimization a convexly constrained weighted least-squares problem and propose for its solution a projected Landweber method which employs oblique projections onto the closed convex constraint set. We formulate the problem, present the algorithm and work out its convergence properties, including a rate-of-convergence result. The results are put in perspective with currently available projected Landweber methods. An application to supervised learning is described, and the method is evaluated in an experiment involving function approximation, as well as application to transient signals. © 2006 Elsevier Ltd. All rights reserved.
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| 7. |
- Lidestam, Helene, et al.
(författare)
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Use of Lagrangian decomposition in supply chain planning
- 2011
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Ingår i: Mathematical and computer modelling. - : Elsevier. - 0895-7177 .- 1872-9479. ; 54:9-10, s. 2428-2442
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Tidskriftsartikel (refereegranskat)abstract
- The integrated planning of transportation of raw material, production and distribution of products of the supply chain for a large pulp company is studied. The planning period is one year and a number of time periods are considered. The tactical decisions included in the model regard transportation of raw materials from harvest areas to pulp mills, production mix and contents at pulp mills, distribution of pulp products from mills to customers either via terminals or directly, and the selection of potential orders and their levels at customers. A mixed integer linear programming model for the supply chain problem is developed. The main solution method in this paper is a Lagrangian heuristic method based on Lagrangian decomposition. The heuristic divides the problem into two subproblems representing different physical stages in the supply chain, each including several time periods. The advantage of the proposed solution approach is that it generates feasible solutions of high quality in short time. A number of cases based on real data is analysed.
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| 8. |
- Mamontov, Eugen, 1955, et al.
(författare)
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Stochastic mechanics in the context of the properties of living systems
- 2006
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Ingår i: Mathl Comput. Modelling. - : Elsevier BV. - 0895-7177 .- 1872-9479. ; 44:7-8, s. 595-607
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Tidskriftsartikel (refereegranskat)abstract
- Many features of living systems prevent the application of fundamental statistical mechanics (FSM) to study such systems. The present work focuses on some of these features. After discussing all the basic approaches of FSM, the work formulates an extension of the kinetic theory paradigm (based on the reduced one-particle distribution function) that exhibits all of the living-system properties considered. This extension appears to be a model within the generalized kinetic theory developed by N. Bellomo and his co-authors. In connection with this model, the work also stresses some other features necessary for making the model relevant to living systems. A mathematical formulation of homeorhesis is also derived. An example discussed in the work is a generalized kinetic equation coupled with a probability-density equation representing the varying component content of a living system. The work also suggests a few directions for future research. [All rights reserved Elsevier]
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| 9. |
- Martínez-Ortega, José-Fernán, et al.
(författare)
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Composition and deployment of e-Health services over Wireless Sensor Networks
- 2011
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Ingår i: Mathematical and computer modelling. - : Elsevier BV. - 0895-7177 .- 1872-9479. ; 53:3-4, s. 485-503
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Tidskriftsartikel (refereegranskat)abstract
- Providing necessary background for provisioning of a new generation of enriched services over Wireless Sensor Networks is the main effort that the scientific community is currently carrying out. These services have improved a great number of aspects related to pervasive systems such as saving resources, efficiency, reliability, scalability and low power consumption. In this paper, μSMS middleware, using an event-based service model, is presented. This novel approach makes up the design requirements previously mentioned by implementing a dynamic memory kernel and a variable payload multiplexing mechanism for the information events in order to provide advanced services. The results obtained over real-world deployments, especially those related with provision of e-Health services, reflect a significant improvement over other similar proposals, such as the RUNES approach: 50% lower memory overhead, 53% lower software components load time and 12% lower event's propagation time.
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| 10. |
- Piotrowska, Monika, 1979, et al.
(författare)
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A model and simulation for homeorhesis in the motion of a single individual
- 2008
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Ingår i: Mathematical and Computer Modelling. - : Elsevier BV. - 0895-7177 .- 1872-9479. ; 48:7-8, s. 1122-1143
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Tidskriftsartikel (refereegranskat)abstract
- In contrast to nonliving systems, all living systems perform homeorhesis. The system state tends to the so-called necessary path, or creode, when the exogenous signals are in a certain system-relevant range. The present work develops the homeorhesis-aware dynamical model for the motion of a single individual (e.g., human). The model allows for the purposeful behaviour of the individual, the creode, the exogenous forces, and the individual-specific sensitivity to their influences. The model also describes the homeorhetic-dysfunction movements. The transparency of the model is such that it allows a physical analogue in the form of electronic circuits. The model is a first step towards the construction of sociologically relevant models for the prediction of human behaviour. It is indispensable for analyses of dangerous scenarios where experiments are impossible, for example when predicting the behaviour of panic-stricken crowds in life-threatening situations. The work illustrates the corresponding numerical-simulation results with a series of figures and suggests topics for future research.
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