Fast solvers and efficient numerical cfd techniques for dynamic porous media problems

We present a fully implicit, monolithic finite element solution scheme to efficiently solve the governing set of differential algebraic equations of incompressible poroelastodynamics. Thereby, we proceed from a two-dimensional, biphasic, saturated porous medium model with intrinsically coupled and incompressible solid and fluid constituents. Our approach, motivated by well-accepted CFD techniques and originally developed for the efficient simulation of incompressible flow problems, is characterized by the following aspects: (1) a special treatment of the algebraically coupled volume balance equation leading to a reduced form of the boundary conditions; (2) usage of a higher-order accurate mixed LBB-stable finite element pair with piecewise discontinuous pressure for the spatial discretization; (3) application of the fully implicit 2nd-order Crank-Nicolson scheme for the time discretization; (4) use of a special fast multigrid solver for the resulting discrete linear equation system. For the purpose of validation and to expose the merits and benefits of our new solution strategy in comparison to other established approaches, canonical one- and two-dimensional wave propagation problems are solved. Finally, a large-scale, dynamic soil-structure interaction problem serves to reveal the efficiency of the special multigrid solver in combination with the chosen finite element discretization

First-principles calculations of magnetization relaxation in pure Fe, Co, and Ni with frozen thermal lattice disorder

The effect of the electron-phonon interaction on magnetization relaxation is studied within the framework of first-principles scattering theory for Fe, Co, and Ni by displacing atoms in the scattering region randomly with a thermal distribution. This "frozen thermal lattice disorder" approach reproduces the non-monotonic damping behaviour observed in ferromagnetic resonance measurements and yields reasonable quantitative agreement between calculated and experimental values. It can be readily applied to alloys and easily extended by determining the atomic displacements from ab initio phonon spectra

Spin-dependent Transparency of Ferromagnet/Superconductor Interfaces

Because the physical interpretation of the spin-polarization of a ferromagnet determined by point-contact Andreev reflection (PCAR) is non-trivial, we have carried out parameter-free calculations of PCAR spectra based upon a scattering-theory formulation of Andreev reflection generalized to spin-polarized systems and a tight-binding linear muffin tin orbital method for calculating the corresponding scattering matrices. PCAR is found to measure the spin-dependent interface transparency rather than the bulk polarization of the ferromagnet which is strongly overestimated by free electron model fitting.Comment: 4 pages, 1figure. submitte

Semiclassical form factor for spectral and matrix element fluctuations of multi-dimensional chaotic systems

We present a semiclassical calculation of the generalized form factor which characterizes the fluctuations of matrix elements of the quantum operators in the eigenbasis of the Hamiltonian of a chaotic system. Our approach is based on some recently developed techniques for the spectral form factor of systems with hyperbolic and ergodic underlying classical dynamics and f=2 degrees of freedom, that allow us to go beyond the diagonal approximation. First we extend these techniques to systems with f>2. Then we use these results to calculate the generalized form factor. We show that the dependence on the rescaled time in units of the Heisenberg time is universal for both the spectral and the generalized form factor. Furthermore, we derive a relation between the generalized form factor and the classical time-correlation function of the Weyl symbols of the quantum operators.Comment: some typos corrected and few minor changes made; final version in PR

Tuneable 2D self-assembly of plasmonic nanoparticles at liquid|liquid interfaces

Understanding the structure and assembly of nanoparticles at liquid|liquid interfaces is paramount to their integration into devices for sensing, catalysis, electronics and optics. However, many difficulties arise when attempting to resolve the structure of such interfacial assemblies. In this article we use a combination of X-ray diffraction and optical reflectance to determine the structural arrangement and plasmon coupling between 12.8 nm diameter gold nanoparticles assembled at a water|1,2-dichloroethane interface. The liquid|liquid interface provides a molecularly flat and defect-correcting platform for nanoparticles to self-assemble. The amount of nanoparticles assembling at the interface can be controlled via the concentration of electrolyte within either the aqueous or organic phase. At higher electrolyte concentration more nanoparticles can settle at the liquid|liquid interface resulting in a decrease in nanoparticle spacing as observed from X-ray diffraction experiments. The plasmonic coupling between the nanoparticles as they come closer together is observed by a red-shift in the optical reflectance spectra. The optical reflectance and the X-ray diffraction data are combined to introduce a new 'plasmon ruler'. This allows extraction of structural information from simple optical spectroscopy techniques, with important implications for understanding the structure of self-assembled nanoparticle films at liquid interfaces.</p

Dynamical correlations in multiorbital Hubbard models: Fluctuation-exchange approximations

We study the two band degenerate Hubbard model using the Fluctuation Exchange approximation (FLEX) method and compare the results with Quantum Monte-Carlo calculations. Both the self-consistent and the non-self-consistent versions of the FLEX scheme are investigated. We find that, contrary to the one band case, in the multiband case, good agreement with the Quantum Monte-Carlo results is obtained within the electron-electron T-matrix approximation using the full renormalization of the one-particle propagators. The crossover to strong coupling and the formation of satellites is more clearly visible in the non-self-consistent scheme. Finally we discuss the behavior of the FLEX for higher orbital degeneracy.Comment: 18 pages with 12 PS figure

A Large Cross-Sectional Study of Health Attitudes, Knowledge, Behaviour and Risks in the Post-War Croatian Population (The First Croatian Health Project*)

As the liberation of occupied Croatian territories ended the war in the country in 1995, the Ministry of Health and Croatian Health Insurance Institute have agreed to create the new framework for developing a long-term strategy of public health planning, prevention and intervention. They provided financial resources to develop the First Cro-atian Health Project, the rest of the support coming from the World Bank loan and the National Institute of Public Health. A large cross-sectional study was designed aiming to assess health attitudes, knowledge, behaviour and risks in the post-war Croatian population. The large field study was carried out by the Institute for Anthropological Research with technical support from the National Institute of Public Health. The field study was completed between 1995–1997. It included about 10,000 adult volunteers from all 21 Croatian counties. The geographic distribution of the sample covered both coastal and continental areas of Croatia and included rural and urban environments. The specific measurements included antropometry (body mass index and blood pressure). From each examinee a blood sample was collected from which the levels of total plasma cholesterol (TC), triglycerides (TG), HDL-cholesterol (High Density Lipoprotein), LDL-cholesterol (Low Density Lipoprotein), lipoprotein Lp(a), and haemostatic risk factor fibrinogen (F) were determined. The detailed data were collected on the general knowledge and attitudes on health issues, followed by specific investigation of smoking history, alcohol consumption, nutrition habits, physical activity, family history of chronic non-communicable diseases and occupational exposures. From the initial database a targeted sample of 5,840 persons of both sexes, aged 18–65, was created corresponding by age, sex and geographic distribution to the general Croatian population. This paper summarises and discusses the main findings of the project within this representative sample of Croatian population

Bosonization and Scale Invariance on Quantum Wires

We develop a systematic approach to bosonization and vertex algebras on quantum wires of the form of star graphs. The related bosonic fields propagate freely in the bulk of the graph, but interact at its vertex. Our framework covers all possible interactions preserving unitarity. Special attention is devoted to the scale invariant interactions, which determine the critical properties of the system. Using the associated scattering matrices, we give a complete classification of the critical points on a star graph with any number of edges. Critical points where the system is not invariant under wire permutations are discovered. By means of an appropriate vertex algebra we perform the bosonization of fermions and solve the massless Thirring model. In this context we derive an explicit expression for the conductance and investigate its behavior at the critical points. A simple relation between the conductance and the Casimir energy density is pointed out.Comment: LaTex 31+1 pages, 2 figures. Section 3.6 and two references added. To appear in J. Phys. A: Mathematical and Theoretica

Field Theory Approach to Quantum Interference in Chaotic Systems

We consider the spectral correlations of clean globally hyperbolic (chaotic) quantum systems. Field theoretical methods are applied to compute quantum corrections to the leading (`diagonal') contribution to the spectral form factor. Far-reaching structural parallels, as well as a number of differences, to recent semiclassical approaches to the problem are discussed.Comment: 18 pages, 4 figures, revised version, accepted for publication in J. Phys A (Math. Gen.