| 921. |
- Sakovich, Anna
(författare)
-
The Jang Equation and the Positive Mass Theorem in the Asymptotically Hyperbolic Setting
- 2021
-
Ingår i: Communications in Mathematical Physics. - : Springer Nature. - 0010-3616 .- 1432-0916. ; 386:2, s. 903-973
-
Tidskriftsartikel (refereegranskat)abstract
- We solve the Jang equation with respect to asymptotically hyperbolic "hyperboloidal" initial data. The results are applied to give a non-spinor proof of the positive mass theorem in the asymptotically hyperbolic setting. This work focuses on the case when the spatial dimension is equal to three.
|
|
| 922. |
- Sorooshian, Shahryar, 1980, et al.
(författare)
-
From classical interpretive structural modeling to total interpretive structural modeling and beyond: A half-century of business research
- 2023
-
Ingår i: Journal of Business Research. - : Elsevier BV. - 0148-2963. ; 157
-
Tidskriftsartikel (refereegranskat)abstract
- Despite the widespread use of interpretive structural modeling (ISM) in business research, little is known about its overall scientific productivity and impact on business research. This study presents a comprehensive review of the published ISM research and its latest editions in business using text mining. A two-tier review (narrative and systematic) is used to examine the methods and provide a comprehensive bibliometric analysis and an application roadmap. We demonstrate the number of ISM publications has been increasing in the past fifteen years, even though ISM was developed half a century ago. The study provides evidence for the increasing impact of ISM research in business. Content analysis shows an increase in the application of an updated edition of ISM, total interpretive structural modeling (TISM). In addition, the overall scientific productivity of ISM and TISM is assessed, and an ISM/TISM method selection roadmap is proposed. We further develop ISM+, a new integrated framework combining ISM and its latest editions to improve its performance and potential applications in business research.
|
|
| 923. |
- Standar, Christoffer, 1988
(författare)
-
On finite element schemes for Vlasov-Maxwell system and Schrödinger equation
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis treats finite element schemes for two kind of problems, the Valsov-Maxwellsystem and the nonlinear Schrödinger equation. We study streamline diffusion schemes applied for numerical solution of the one and one-half dimensional relativistic Vlasov-Maxwell system. The study is made both in a priori and a posteriori settings. In the a priori setting we derive stability estimates and prove optimal convergence rates, due to the maximal available regularity of the exact solution. In addition to this we also prove existence and uniqueness of the numerical solution. In the a posteriori setting we use dual problems to prove error estimates in L_\infty (H^{-1}) norm. For the Maxwell equation we also prove error estimates in H^{-1} (H^{-1}) norms. Further more we study a hp-version of the streamline diffusion scheme for thethree dimensional Vlasov-Maxwell system in an a priori setting. A Nitsche type scheme is also introduced and analyzed for Maxwell's equations. For the nonlinear Schrödinger equation a two level time discretization is used. Here we derive a priori error estimates both in L_2 and H^1 norms.
|
|
| 924. |
- Starius, Göran Christer, 1944
(författare)
-
On the use of reduced grids in conjunction with the Equator-Pole grid system
- 2020
-
Ingår i: Tellus, Series A: Dynamic Meteorology and Oceanography. - : Stockholm University Press. - 0280-6495 .- 1600-0870. ; 72:1, s. 1-12
-
Tidskriftsartikel (refereegranskat)abstract
- This is a continuation of a previous paper by Starius, where for the solution of the shallow water equations on the sphere, we consider Equator-Pole grid systems consisting of one latitude-longitude grid covering an annular band around the equator, and two orthogonal polar grids based on modified stereographic coordinates. Here, we generalise this by letting an equatorial band be covered with a reduced grid system, which can decrease the total number of grid points by at least 20%, with no substantial change in accuracy. Centred finite differences of high order are used for the spatial discretisation of the underlying differential equations and the explicit fourth order Runge-Kutta method for the integration in time. In the paper mentioned above, we demonstrate accuracy in the total mass, which is much higher than needed for NWP, for smooth solutions. Here we show that this holds also for non-smooth solutions, by considering the Cosine bell no. 1 and the mountain problem no. 5 in Williamson et al., the solutions of which have discontinuous second and first order derivatives, respectively.
|
|
| 925. |
- Stucki, Sandro, 1982, et al.
(författare)
-
A theory of higher-order subtyping with type intervals
- 2021
-
Ingår i: Proceedings of the ACM on Programming Languages. - : Association for Computing Machinery (ACM). - 2475-1421. ; 5:ICFP
-
Tidskriftsartikel (refereegranskat)abstract
- The calculus of Dependent Object Types (DOT) has enabled a more principled and robust implementation of Scala, but its support for type-level computation has proven insufficient. As a remedy, we propose F··ω, a rigorous theoretical foundation for Scala's higher-kinded types. F··ω extends F<:ω with interval kinds, which afford a unified treatment of important type- and kind-level abstraction mechanisms found in Scala, such as bounded quantification, bounded operator abstractions, translucent type definitions and first-class subtyping constraints. The result is a flexible and general theory of higher-order subtyping. We prove type and kind safety of F··ω, as well as weak normalization of types and undecidability of subtyping. All our proofs are mechanized in Agda using a fully syntactic approach based on hereditary substitution.
|
|
| 926. |
- Thaller, Maximilian, 1990, et al.
(författare)
-
Uniqueness of static, isotropic low-pressure solutions of the Einstein-Vlasov system
- 2020
-
Ingår i: Letters in Mathematical Physics. - : Springer Science and Business Media LLC. - 0377-9017 .- 1573-0530. ; 110:7, s. 1877-1901
-
Tidskriftsartikel (refereegranskat)abstract
- In Beig and Simon (Commun Math Phys 144:373-390, 1992) the authors prove a uniqueness theorem for static solutions of the Einstein-Euler system which applies to fluid models whose equation of state fulfills certain conditions. In this article it is shown that the result of Beig and Simon (1992) can be applied to isotropic Vlasov matter if the gravitational potential well is shallow. To this end we first show how isotropic Vlasov matter can be described as a perfect fluid giving rise to a barotropic equation of state. This Vlasov equation of state is investigated, and it is shown analytically that the requirements of the uniqueness theorem are met for shallow potential wells. Finally the regime of shallow gravitational potential is investigated by numerical means. An example for a unique static solution is constructed, and it is compared to astrophysical objects like globular clusters. Finally we find numerical indications that solutions with deep potential wells are not unique.
|
|
| 927. |
- Torabi, Sina, 1990, et al.
(författare)
-
A method for performance analysis of a genetic algorithm applied to the problem of fuel consumption minimization for heavy-duty vehicles
- 2019
-
Ingår i: Applied Soft Computing Journal. - : Elsevier BV. - 1568-4946. ; 80, s. 735-741
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a general method for assessment of the performance of a genetic algorithm (GA)in cases where the global optimum of the objective function is unknown. The method involves discretization of the search space, making it possible to apply a brute force calculation to find the global optimum for the discretized case. Then, this method is used to study the performance of a GA applied to the problem of speed profile optimization for heavy-duty vehicles, in which the optimization must be carried out within a rather short time. In this performance analysis, the discretization involves generating speed profiles as piecewise linear functions. It is demonstrated that the GA is able to find near-optimal solutions for the cases considered here: The speed profiles generated by the GA have objective function values that are typically within 2% of the global optimum.
|
|
| 928. |
- Tu, Vinh, 1995, et al.
(författare)
-
Variationally consistent homogenization of electrochemical ion transport in a porous structural battery electrolyte
- 2023
-
Ingår i: European Journal of Mechanics, A/Solids. - : Elsevier BV. - 0997-7538. ; 98
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we develop a multi-scale modeling framework for a multiphysics problem characterized by electro-chemically coupled ion transport in a Structural Battery Electrolyte (SBE). The governing equations of the problem are established by coupling Gauss law with mass conservation for each mobile species. By utilizing variationally consistent homogenization, we are able to establish a two-scale model where both the macro-scale and sub-scale equations are deduced from a single-scale problem. Investigations of the sub-scale RVE problem show that the transient effects are negligible for the length scales relevant to the studied application, which motivates the assumption of micro-stationarity. In the special case of linear constitutive response, we get a numerically efficient solution scheme for the macro-scale problem that is based on a priori upscaling. As a final step, we demonstrate the numerically efficient solution scheme by solving a 2D macro-scale problem using upscaled constitutive quantities based on a 3D RVE.
|
|
| 929. |
- Tzeng, Ruo-Chun, 1993-, et al.
(författare)
-
Improved analysis of randomized SVD for top-eigenvector approximation
- 2022
-
Ingår i: International Conference On Artificial Intelligence And Statistics, Vol 151. - : ML Research Press.
-
Konferensbidrag (refereegranskat)abstract
- Computing the top eigenvectors of a matrix is a problem of fundamental interest to various fields. While the majority of the literature has focused on analyzing the reconstruction error of low-rank matrices associated with the retrieved eigenvectors, in many applications one is interested in finding one vector with high Rayleigh quotient. In this paper we study the problem of approximating the top-eigenvector. Given a symmetric matrix A with largest eigenvalue lambda(1), our goal is to find a vector (u) over cap that approximates the leading eigenvector u(1) with high accuracy, as measured by the ratio R((u) over cap) = lambda(-1)(1) (u) over cap (T)A (u) over cap/(u) over cap (T)(u) over cap. We present a novel analysis of the randomized SVD algorithm of Halko et al. (2011b) and derive tight bounds in many cases of interest. Notably, this is the first work that provides non-trivial bounds for approximating the ratio R((u) over cap) using randomized SVD with any number of iterations. Our theoretical analysis is complemented with a thorough experimental study that confirms the efficiency and accuracy of the method.
|
|
| 930. |
- Umavathi, Jawali C, et al.
(författare)
-
Effect of Time-Periodic Boundary TemperatureModulations on the Onset of Convection in a Maxwell Fluid-Nanofluid Saturated Porous Layer
- 2016
-
Ingår i: Engineering Mathematics I. - Cham : Springer. - 9783319420813 - 9783319420820 ; , s. 221-245
-
Bokkapitel (refereegranskat)abstract
- The linear stability of Maxwell fluid-nanofluid flow in a saturated porous layer is examined theoretically when the walls of the porous layers are subjected to time-periodic temperature modulations. A modified Darcy-Maxwell model is used to describe the fluid motion, and the nanofluid model used includes the effects of the Brownian motion. The thermal conductivity and viscosity are considered to be dependent on the nanoparticle volume fraction. A perturbation method based on a small amplitude of an applied temperature field is used to compute the critical value of the Rayleigh number and the wave number. The stability of the system characterized by a critical Rayleigh number is calculated as a function of the relaxation parameter, the concentration Rayleigh number, the porosity parameter, the Lewis number, the heat capacity ratio, the Vad´asz number, the viscosity parameter, the conductivity variation parameter, and the frequency of modulation. Three types of temperature modulations are considered, and the effects of all three types of modulations are found to destabilize the system as compared to the unmodulated system.
|
|
