Search results for " MODELLI"
showing 10 items of 1472 documents
Mathematical models and their solutions for different heat exchange processes in environment with layered structure
2012
Promocijas darbā tiek apskatīti 3D, 2D un 1D risinājumi stacionārām siltuma vadīšanas problēmām cilindriskā sistēmā ar ribu. Kā arī iztirzāti nestacionāru problēmu risinājumi hiperboliskām siltuma vadīšanas problēmām 1D cilindram un 2D cilindriskai sistēmai ar ribu. Iegūti kvazi-analītiski risinājumi cilindriskai sistēmai ar ribu, izmantojot konservatīvās viduvēšanas metodi. Izmantojot vispārinātu Grīna funkcijas metodi ir konstruēts precīzais analītiskais atrisinājums vairākām cilindriskām sistēmām ar ribu. Daži no stacionāriem modeļiem ir skaitliski konstruēti un sniegti aprēķinu piemēri. Darbā ir analizēti un salīdzināti iegūtie rezultāti. Atslēgas vārdi: konservatīvā viduvēšana, Grīna f…
Sustainable metabolic engineering for sustainability optimisation of industrial biotechnology
2021
Industrial biotechnology represents one of the most innovating and labour-productive industries with an estimated stable economic growth, thus giving space for improvement of the existing and setting up new value chains. In addition, biotechnology has clear environmental advantages over the chemical industry. Still, biotechnology’s environmental contribution is sometimes valued with controversy and societal aspects are frequently ignored. Environmental, economic and societal sustainability of various bioprocesses becomes increasingly important due to the growing understanding about complex and interlinked consequences of different human activities. Neglecting the sustainability issues in th…
Greenhouse gas emissions from integrated urban drainage systems: where do we stand?
2018
As sources of greenhouse gas (GHG) emissions, integrated urban drainage systems (IUDSs) (i.e., sewer systems, wastewater treatment plants and receiving water bodies) contribute to climate change. This paper, produced by the International Working Group on Data and Models, which works under the IWA/IAHR Joint Committee on Urban Drainage, reviews the state-of-the-art and modelling tools developed recently to understand and manage GHG emissions from IUDS. Further, open problems and research gaps are discussed and a framework for handling GHG emissions from IUDSs is presented. The literature review reveals that there is a need to strengthen already available mathematical models for IUDS to take …
The development of the mathematical discourse of biology students working with mathematical modelling
2016
International audience; This poster reports from an ongoing developmental research project in which mathematical modelling tasks are introduced to biology students as a means of motivating them to engage more deeply in mathematical studies. In the present report the focus is on how the mathematical discourse of the students develops as they participate in the project. Data consisting of video recordings of four modelling sessions comprising both group work and whole-class discussion will be analysed using commognitive theory. Data collection is still ongoing, and no analyses have been conducted as yet, but preliminary observations indicate cases of commognitive conflict, as the students str…
Stochastic reconstruction of sandstones
2000
A simulated annealing algorithm is employed to generate a stochastic model for a Berea and a Fontainebleau sandstone with prescribed two-point probability function, lineal path function, and ``pore size'' distribution function, respectively. We find that the temperature decrease of the annealing has to be rather quick to yield isotropic and percolating configurations. A comparison of simple morphological quantities indicates good agreement between the reconstructions and the original sandstones. Also, the mean survival time of a random walker in the pore space is reproduced with good accuracy. However, a more detailed investigation by means of local porosity theory shows that there may be s…
SMAA - Stochastic multiobjective acceptability analysis
1998
Stochastic multiobjective acceptability analysis (SMAA) is a multicriteria decision support technique for multiple decision makers based on exploring the weight space. Inaccurate or uncertain input data can be represented as probability distributions. In SMAA the decision makers need not express their preferences explicitly or implicitly; instead the technique analyses what kind of valuations would make each alternative the preferred one. The method produces for each alternative an acceptability index measuring the variety of different valuations that support that alternative, a central weight vector representing the typical valuations resulting in that decision, and a confidence factor mea…
Hydrological post-processing based on approximate Bayesian computation (ABC)
2019
[EN] This study introduces a method to quantify the conditional predictive uncertainty in hydrological post-processing contexts when it is cumbersome to calculate the likelihood (intractable likelihood). Sometimes, it can be difficult to calculate the likelihood itself in hydrological modelling, specially working with complex models or with ungauged catchments. Therefore, we propose the ABC post-processor that exchanges the requirement of calculating the likelihood function by the use of some sufficient summary statistics and synthetic datasets. The aim is to show that the conditional predictive distribution is qualitatively similar produced by the exact predictive (MCMC post-processor) or …
A Stochastic Soft Constraints Fuzzy Model for a Portfolio Selection Problem
2006
The financial market behavior is affected by several non-probabilistic factors such as vagueness and ambiguity. In this paper we develop a multistage stochastic soft constraints fuzzy program with recourse in order to capture both uncertainty and imprecision as well as to solve a portfolio management problem. The results we obtained confirm the studies carried out in literature addressed to integrate stochastic and possibilistic programming.
Global sensitivity analysis for urban water quality modelling: Terminology, convergence and comparison of different methods
2015
Abstract Sensitivity analysis represents an important step in improving the understanding and use of environmental models. Indeed, by means of global sensitivity analysis (GSA), modellers may identify both important ( factor prioritisation ) and non-influential ( factor fixing ) model factors. No general rule has yet been defined for verifying the convergence of the GSA methods. In order to fill this gap this paper presents a convergence analysis of three widely used GSA methods (SRC, Extended FAST and Morris screening) for an urban drainage stormwater quality–quantity model. After the convergence was achieved the results of each method were compared. In particular, a discussion on peculiar…
MCR-ALS on metabolic networks: Obtaining more meaningful pathways
2015
[EN] With the aim of understanding the flux distributions across a metabolic network, i.e. within living cells, Principal Component Analysis (PCA) has been proposed to obtain a set of orthogonal components (pathways) capturing most of the variance in the flux data. The problems with this method are (i) that no additional information can be included in the model, and (ii) that orthogonality imposes a hard constraint, not always reasonably. To overcome these drawbacks, here we propose to use a more flexible approach such as Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) to obtain this set of biological pathways through the network. By using this method, different constraint…