| 931. |
- Vromans, Arthur, 1989-
(författare)
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A pseudoparabolic reaction-diffusion-mechanics system : Modeling, analysis and simulation
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, parabolic-pseudoparabolic equations are derived coupling chemical reactions, diffusion, flow and mechanics in a heterogeneous medium using the framework of mixture theory. The weak solvability in 1-D of the obtained models is studied. Furthermore, it is numerically illustrated that approximate solutions according to the Rothe method exhibit expected realistic behaviour. For a simpler model formulation, the periodic homogenization in higher space dimensions is performed.
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| 932. |
- Wiklund, Stig Johan, et al.
(författare)
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Replenishing the pipeline: A quantitative approach to optimising the sourcing of new projects
- 2023
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Ingår i: Pharmaceutical Statistics. - 1539-1604 .- 1539-1612. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- Large pharmaceutical companies maintain a portfolio of assets, some of which are projects under development while others are on the market and generating revenue. The budget allocated to R&D may not always be sufficient to fund all the available projects for development. Much attention has been paid to the selection of optimal subsets of available projects to fit within the available budget. In this paper, we argue the need for a forward-looking approach to portfolio decision-making. We develop a quantitative model that allows the portfolio management to evaluate the need for future inflow of new projects to achieve revenue at desired levels, often aspiring to a certain annual revenue growth. Optimisation methods are developed for the presented model, allowing an optimal choice of number, timing and type of projects to be added to the portfolio. The proposed methodology allows for a proactive approach to portfolio management, prioritisation, and optimisation. It provides a quantitatively based support for strategic decisions regarding the efforts needed to secure the future development pipeline and revenue stream of the company.
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| 933. |
- Wilczek, Frank, 1951-
(författare)
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Ambiguity, invisibility, and negativity
- 2024
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Ingår i: Journal of Physics A. - 1751-8113 .- 1751-8121. ; 57:18
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Tidskriftsartikel (refereegranskat)abstract
- Many widely different problems have a common mathematical structure wherein limited knowledge leads to ambiguity that can be captured conveniently using a concept of invisibility that requires the introduction of negative values for quantities that are inherently positive. Here I analyze three examples taken from perception theory, rigid body mechanics, and quantum measurement.
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| 934. |
- Willander, Magnus, 1948, et al.
(författare)
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Modelling living fluids with the subdivision into the components in terms of probability distributions
- 2004
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Ingår i: Math. Models Methods Appl. Sci.. - : World Scientific. - 0218-2025. ; 14:10, s. 1495-1520
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Tidskriftsartikel (refereegranskat)abstract
- As it follows from the results of C. H. Waddigton, F. E. Yates, A. S. Iberall, and other well-known bio-physicists, living fluids cannot be modelled within the frames of the fundamental assumptions of the statistical-mechanics formalism. One has to go beyond them. The present work does it by means of the generalized kinetics (GK), the theory enabling one to allow for the complex stochasticity of internal properties and parameters of the fluid particles. This is one of the key features which distinguish living fluids from the nonliving ones. It creates the disparity of the particles and hence breaks the each-fluid-component-uniformity requirement underlying statistical mechanics. The work deals with the corresponding modification of common kinetic equations which is in line with the GK theory and is the complement to the latter. This complement allows a subdivision of a fluid into the fluid components in terms of nondiscrete probability distributions. The treatment leads to one more equationthat describes the above internal parameters. The resulting model is the system of these two equations. It appears to be always nonlinear in case of living fluids. In case of nonliving fluids, the model can be linear. Moreover, the living-fluid model, as a whole, cannot have the thermodynamic equilibrium, only partial equilibriums (such as the motional one) are possible. In contrast to this, in case of nonliving fluids, the thermodynamic equilibrium is, of course, possible. The number of the fluid components is treated as the number of the modes of the particle-characteristic probability density. In so doing, a fairly general extension of the notion of the mode from the one-dimensional case to the multidimensional case is proposed. The work also discusses the variety of the time-scales in a living fluid, the simplest quantum-mechanical equation relevant to living fluids, and the non-equilibrium nonlinear stochastic hydrodynamics option. The latter is simpler than, but conceptually comparable to, stochastickinetic equations. A few directions for future research are suggested. The work notes a cohesion of mathematical physics and fluid mechanics with the living-fluid-related fields as a complex interdisciplinary problem.
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| 935. |
- Yau, Estelle, et al.
(författare)
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Global Sensitivity Analysis of the Rodgers and Rowland Model for Prediction of Tissue: Plasma Partitioning Coefficients: Assessment of the Key Physiological and Physicochemical Factors That Determine Small-Molecule Tissue Distribution
- 2020
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Ingår i: AAPS Journal. - : Springer Nature. - 1550-7416. ; 22:2, s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- In physiologically based pharmacokinetic (PBPK) modelling, the large number of input parameters, limited amount of available data and the structural model complexity generally hinder simultaneous estimation of uncertain and/or unknown parameters. These parameters are generally subject to estimation. However, the approaches taken for parameter estimation vary widely. Global sensitivity analyses are proposed as a method to systematically determine the most influential parameters that can be subject to estimation. Herein, a global sensitivity analysis was conducted to identify the key drug and physiological parameters influencing drug disposition in PBPK models and to potentially reduce the PBPK model dimensionality. The impact of these parameters was evaluated on the tissue-to-unbound plasma partition coefficients (Kpus) predicted by the Rodgers and Rowland model using Latin hypercube sampling combined to partial rank correlation coefficients (PRCC). For most drug classes, PRCC showed that LogP and fraction unbound in plasma (fup) were generally the most influential parameters for Kpu predictions. For strong bases, blood:plasma partitioning was one of the most influential parameter. Uncertainty in tissue composition parameters had a large impact on Kpu and Vss predictions for all classes. Among tissue composition parameters, changes in Kpu outputs were especially attributed to changes in tissue acidic phospholipid concentrations and extracellular protein tissue:plasma ratio values. In conclusion, this work demonstrates that for parameter estimation involving PBPK models and dimensionality reduction purposes, less influential parameters might be assigned fixed values depending on the parameter space, while influential parameters could be subject to parameters estimation.
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| 936. |
- Zamani Salimi, Salar, et al.
(författare)
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A Volume-of-Fluid method for multicomponent droplet evaporation with Robin boundary conditions
- 2024
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Ingår i: Journal of Computational Physics. - : Elsevier BV. - 0021-9991 .- 1090-2716. ; 514
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Tidskriftsartikel (refereegranskat)abstract
- We propose a numerical method tailored to perform interface-resolved simulations of evaporating multicomponent two-phase flows. The novelty of the method lies in the use of Robin boundary conditions to couple the transport equations for the vaporized species in the gas phase and the transport equations of the same species in the liquid phase. The Robin boundary condition is implemented with the cost-effective procedure proposed by Chai et al. [1] and consists of two steps: (1) calculating the normal derivative of the mass fraction fields in cells adjacent to the interface through the reconstruction of a linear polynomial system, and (2) extrapolating the normal derivative and the ghost value in the normal direction using a linear partial differential equation. This methodology yields a second-order accurate solution for the Poisson equation with a Robin boundary condition and a first-order accurate solution for the Stefan problem. The overall methodology is implemented in an efficient two-fluid solver, which includes a Volume-of-Fluid (VoF) approach for the interface representation, a divergence-free extension of the liquid velocity field onto the entire domain to transport the VoF, and the temperature equation to include thermal effects. We demonstrate the convergence of the numerical method to the analytical solution for multicomponent isothermal evaporation and observe good overall computational performance for simulating non-isothermal evaporating two-fluid flows in two and three dimensions.
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| 937. |
- Zhao, Ming, et al.
(författare)
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A hierarchical reconstruction for DG/FV method with low dispersion: Basic formulation and applications
- 2021
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Ingår i: Computers and Fluids. - : Elsevier BV. - 0045-7930. ; 231
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the numerical dispersion of a hierarchical reconstruction strategy for DG/FV method has been optimized. For the hierarchical strategy, the cell averages and the first derivatives are reconstructed based on the Hermite WENO method; the second derivatives are reconstructed via Green-Gauss integration and WENO reconstruction. Then, the numerical dispersion has been optimized by minimizing error with bandwidth optimization technique. Furthermore, to adjust the loss of compactness due to the reconstructed second derivatives, two modifications were also proposed with optimal weights. Eventually, from the implementations in scalar and compressible Euler equations, the superiority of numerical dispersion and accuracy of present methods could be validated. The shock capturing capacity has also been validated in 1D and 2D cases.
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| 938. |
- Zhdanov, Vladimir, 1952
(författare)
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Diffusion-limited association of nanoparticles in fluid: Beyond the no-slip boundary conditions
- 2022
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Ingår i: Colloids and Interface Science Communications. - : Elsevier BV. - 2215-0382. ; 46
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Tidskriftsartikel (refereegranskat)abstract
- In the treatments of diffusion-limited association of suspended nanoparticles (NPs), their diffusion coefficients are usually considered to be constant or depend on the interparticle distance as determined by fluid dynamics with the no-slip boundary condition. In the latter case, due to the corresponding slowdown of diffusion at short distances, the association rate constant is smaller than that calculated by ignoring this slowdown and using the diffusion coefficients corresponding to single NPs. The no-slip boundary condition can, however, be violated, and now there is evidence that it may happen more often than one could expect. In such situations, the partial-slip boundary condition is more suitable. Employing the latter boundary condition, I derive herein general integral expressions for the rate constant of association of spherically shaped NPs without and with the NP-NP interaction. Simple analytical results have been obtained in various situations.
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| 939. |
- Zhdanov, Vladimir, 1952
(författare)
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How the partial-slip boundary condition can influence the interpretation of the DLS and NTA data
- 2020
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Ingår i: Journal of Biological Physics. - : Springer Science and Business Media LLC. - 0092-0606 .- 1573-0689. ; 46:2, s. 169-176
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Tidskriftsartikel (refereegranskat)abstract
- Dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA) are widely used to determine the size of biological nanoparticles in liquid. In both cases, one first measures the nanoparticle diffusion coefficient and then converts it to the nanoparticle radius via the Stokes-Einstein relation. This relation is based on the no-slip boundary condition. Now, there is evidence that this condition can be violated in biologically relevant cases (e.g., for vesicles) and that in such situations the partial-slip boundary condition is more suitable. I show (i) how the latter condition can be employed in the context of DLS and NTA and (ii) that the use of the former condition may result in underestimation of the nanoparticle radius by about 10 nm compared with the nominal one.
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| 940. |
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