38,319 research outputs found
An algebraic multigrid method for mixed discretizations of the Navier-Stokes equations
Algebraic multigrid (AMG) preconditioners are considered for discretized
systems of partial differential equations (PDEs) where unknowns associated with
different physical quantities are not necessarily co-located at mesh points.
Specifically, we investigate a mixed finite element discretization of
the incompressible Navier-Stokes equations where the number of velocity nodes
is much greater than the number of pressure nodes. Consequently, some velocity
degrees-of-freedom (dofs) are defined at spatial locations where there are no
corresponding pressure dofs. Thus, AMG approaches leveraging this co-located
structure are not applicable. This paper instead proposes an automatic AMG
coarsening that mimics certain pressure/velocity dof relationships of the
discretization. The main idea is to first automatically define coarse
pressures in a somewhat standard AMG fashion and then to carefully (but
automatically) choose coarse velocity unknowns so that the spatial location
relationship between pressure and velocity dofs resembles that on the finest
grid. To define coefficients within the inter-grid transfers, an energy
minimization AMG (EMIN-AMG) is utilized. EMIN-AMG is not tied to specific
coarsening schemes and grid transfer sparsity patterns, and so it is applicable
to the proposed coarsening. Numerical results highlighting solver performance
are given on Stokes and incompressible Navier-Stokes problems.Comment: Submitted to a journa
Low energy spin fluctuations in the heavy fermion compound CeLaRuSi
We report inelastic neutron scattering measurements performed on a single
crystal of the heavy fermion compound CeLaRuSi,
which is at the borderline between an antiferromagnetically ordered and a
paramagnetic ground state. Intensity maps as a function of wavevector and
energy ( meV) were obtained at temperatures and 2 K, using
the time-of-flight spectrometer IRIS. An unexpected saturation of the
relaxation rate and static susceptibility of the spin fluctuations is found at
low temperatures.Comment: 2 pages, 2 figures, SCES'04 Proceeding
Amending the Wagner Act: The Problem From the Manufacturerâs Viewpoint
Till följd av den globala finanskrisen Är 2008 stÀlldes det europeiska samarbetet pÄ prov. I och med detta presenterade EU ett förslag till ett direktiv angÄende en finansiell transaktionsskatt för samtliga lÀnder inom EU. Elva av EU:s 28 medlemslÀnder har valt att stÀlla sig bakom förslaget om en finansiell transaktionsskatt, vilket innebÀr att dessa lÀnder avser införa en finansiell transaktionsskatt. Tidigare empiriska erfarenheter har dock visat att en finansiell transaktionsskatt Àr mindre effektiv Àn vad föresprÄkarna gör gÀllande, varken pÄverkan pÄ skatteintÀkter eller marknadens volatilitet har i dessa fall levt upp till de önskvÀrda effekterna. Denna uppsats syfte Àr att analysera vad som ligger till grund för lÀndernas stÀllningstagande och uppsatsens hypotes ger vid handen att det föreligger ett positivt samband mellan finanskrisens pÄverkan pÄ respektive EU land, inhemsk opinion och ett positivt stÀllningstagande till en finansiell transaktionsskatt inom EU. För att testa hypotesen anvÀnds en induktiv metod vilken Àr uppbyggd pÄ vetenskapliga artiklar och ekonomisk litteratur. Vidare genomförs flera regressionsanalyser i syfte att pÄvisa de positiva samband som hypotesen antar föreligger. I de uppvisade resultaten framgÄr att det gÄr att stödja uppsatsens hypotes. Uppsatsen kommer dÀrför fram till att det föreligger ett positivt samband mellan finanskrisens pÄverkan pÄ respektive EU-land, inhemsk opinion och ett positivt stÀllningstagande till en finansiell transaktionsskatt.In the aftermath of the 2008 financial crisis the European Union was put to the test. As a result, the EU submitted a proposal for a directive regarding a financial transactions tax levied throughout every nation in the European Union. Eleven of the 28 EU member states decided to support the proposal for a financial transactions tax. The eleven member states adopted the stance to support the proposal in spite of the historical empirical evidence indicating a financial transactions tax to not be as effective as the advocators claim. This paper aims to analyse the basis of the EU member states adopted stance towards a financial transactions tax. The thesis statement suggest that there is a positive correlation between the impact of the financial crisis on each respective EU country, domestic public opinion and a positive stance towards a financial transactions tax in the EU. To test the thesis statement an inductive method, based on academic articles and economic literature, is applied. Furthermore a regression analysis is used to prove the appearance of the expected positive relationships in the thesis statement. The results of the paper indicate the thesis statement to be probable. Therefore, this paper concludes that there is a positive relationship between the impact of the financial crisis in the EU states, domestic opinion and a positive stance to a financial transactions tax
Exact results in a slave boson saddle point approach for a strongly correlated electron model
We revisit the Kotliar-Ruckenstein (KR) slave boson saddle point evaluation
for a two-site correlated electron model. As the model can be solved
analytically, it is possible to compare the KR saddle point results to the
exact many particle levels. The considered two site cluster mimics an
infinite- single-impurity Anderson model with a nearest neighbor Coulomb
interaction: one site is strongly correlated with an infinite local Coulomb
repulsion which hybridizes with the second site, on which the local Coulomb
repulsion vanishes. Making use of the flexibility of the representation we
introduce appropriate weight factors in the KR saddle point scheme. Ground
state and all excitation levels agree with the exact diagonalization results.
Thermodynamics and correlation functions may be recovered in a suitably
renormalized saddle point evaluation.Comment: 4 page
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