An Enhanced Perturbational Study on Spectral Properties of the Anderson Model

The infinite-$U$ single impurity Anderson model for rare earth alloys is examined with a new set of self-consistent coupled integral equations, which can be embedded in the large $N$ expansion scheme ($N$ is the local spin degeneracy). The finite temperature impurity density of states (DOS) and the spin-fluctuation spectra are calculated exactly up to the order $O(1/N^2)$. The presented conserving approximation goes well beyond the $1/N$-approximation ({\em NCA}) and maintains local Fermi-liquid properties down to very low temperatures. The position of the low lying Abrikosov-Suhl resonance (ASR) in the impurity DOS is in accordance with Friedel's sum rule. For $N=2$ its shift toward the chemical potential, compared to the {\em NCA}, can be traced back to the influence of the vertex corrections. The width and height of the ASR is governed by the universal low temperature energy scale $T_K$. Temperature and degeneracy $N$-dependence of the static magnetic susceptibility is found in excellent agreement with the Bethe-Ansatz results. Threshold exponents of the local propagators are discussed. Resonant level regime ($N=1$) and intermediate valence regime ($|\epsilon_f| <\Delta$) of the model are thoroughly investigated as a critical test of the quality of the approximation. Some applications to the Anderson lattice model are pointed out.Comment: 19 pages, ReVTeX, no figures. 17 Postscript figures available on the WWW at http://spy.fkp.physik.th-darmstadt.de/~frithjof

Automated code generation for discontinuous Galerkin methods

A compiler approach for generating low-level computer code from high-level input for discontinuous Galerkin finite element forms is presented. The input language mirrors conventional mathematical notation, and the compiler generates efficient code in a standard programming language. This facilitates the rapid generation of efficient code for general equations in varying spatial dimensions. Key concepts underlying the compiler approach and the automated generation of computer code are elaborated. The approach is demonstrated for a range of common problems, including the Poisson, biharmonic, advection--diffusion and Stokes equations

Combined riblet and lebu drag reduction system

The invention is a system of flow control devices which result in reduced skin friction on aerodynamic and hydrodynamic surfaces. The devices cause a breakup of large-scale disturbances in the boundary layer of the flow field. The riblet device acts to reduce disturbances near the boundary layer wall by the use of longitudinal striations forming V-shaped grooves. These grooves are dimensional on the order of the wall vortices and turbulent burst dimensions. The large eddy breakup device is a small strip or airfoil which is suspended in the upper region of the boundary layer. Various physical mechanisms cause a disruption of the large-scale vortices. The combination of the devices of this invention result in a substantial reduction in skin friction drag

Renormalization Group Approach to Spectral Properties of the Two-Channel Anderson Impurity Model

The impurity Green function and dynamical susceptibilties for the two-channel Anderson impurity model are calculated. An exact expression for the self-energy of the impurity Green function is derived. The imaginary part of the self-energy scales as \sqrt{|\w/T_K|} for $T\to 0$ serving as a hallmark for non-Fermi behavior. The many-body resonance is pinned to a universal value $1/(2\pi\Delta)$ at \w=0. Its shape becomes increasingly more symmetric for the Kondo-regimes of the model. The dynamical susceptibilities are governed by two energy scales $T_K$ and $T_h$ and approach a constant value for \w\to 0, whereas relation \chi''(\w)\propto \w holds for the single channel model.Comment: 4 pages, 4 figure, revte

Dynamics of large anisotropic spin in a sub-ohmic dissipative environment close to a quantum-phase transition

We investigate the dynamics of a large anisotropic spin whose easy-axis component is coupled to a bosonic bath with a spectral function J(\w)\propto \omega^s. Such a spin complex might be realized in a single-molecular magnet. Using the non-perturbative renormalization group, we calculate the line of quantum-phase transitions in the sub-ohmic regime ($s<1$). These quantum-phase transitions only occur for integer spin $J$. For half-integer $J$, the low temperature fixed-point is identical to the fixed-point of the spin-boson model without quantum-tunneling between the two levels. Short-time coherent oscillations in the spin decay prevail even into the localized phase in the sub-ohmic regime. The influence of the reorganization energy and the recurrence time on the decoherence in the absence of quantum-tunneling is discussed.Comment: 14 pages,7 figure

Wavefunction extended Lagrangian Born-Oppenheimer molecular dynamics

Extended Lagrangian Born-Oppenheimer molecular dynamics [Niklasson, Phys. Rev. Lett. 100 123004 (2008)] has been generalized to the propagation of the electronic wavefunctions. The technique allows highly efficient first principles molecular dynamics simulations using plane wave pseudopotential electronic structure methods that are stable and energy conserving also under incomplete and approximate self-consistency convergence. An implementation of the method within the planewave basis set is presented and the accuracy and efficiency is demonstrated both for semi-conductor and metallic materials.Comment: 6 pages, 3 figure

From ferromagnetism to spin-density wave: Magnetism in the two channel periodic Anderson model

The magnetic properties of the two-channel periodic Anderson model for uranium ions, comprised of a quadrupolar and a magnetic doublet are investigated through the crossover from the mixed-valent to the stable moment regime using dynamical mean field theory. In the mixed-valent regime ferromagnetism is found for low carrier concentration on a hyper-cubic lattice. The Kondo regime is governed by band magnetism with small effective moments and an ordering vector \q close to the perfect nesting vector. In the stable moment regime nearest neighbour anti-ferromagnetism dominates for less than half band filling and a spin density wave transition for larger than half filling. $T_m$ is governed by the renormalized RKKY energy scale \mu_{eff}^2 ^2 J^2\rho_0(\mu).Comment: 4 pages, RevTeX, 3 eps figure

The diving beetles of the Kuril Archipelago in the Far East of Russia (Coleoptera: Dytiscidae).

Nach Literaturangaben sowie Untersuchungen von Museumsmaterial und Ausbeuten der in den letzten Jahren durchgeführten Expeditionen sind die Schwimmkäfer (Dytiscidae) auf den Kurilen im Nordwest-Pazifik mit 24 Arten vertreten. Über die 357 adulten und 50 larvalen Dytisciden, die während der gemeinsamen amerikanisch-japanisch-russischen Expedition 1994 und 1995 auf den südlichen und mittleren Kurilen gesammelt wurden, wird detailliert berichtet. Die folgenden fünf Arten werden erstmals für die Kurilen nachgewiesen: Hydroporus uenoi Nakane, Platambus pictipennis (Sharp), Agabus japonicus Sharp, Ilybius nakanei Nilsson, und Graphoderus zonatus (Hoppe). Die Zahl der auf den einzelnen Inseln festgestellten Arten lag zwischen 1 und 11; den höchsten Artenreichtum zeigen die größten Inseln auf beiden Seiten des Großen Kurilen-Kamms. Auf den südlichen Kurilen dominieren die ussurisch-japanischen Arten, die auch von Sakhalin und Hokkaido bekannt sind, während sich die Fauna der nördlichen Kurilen durch einen hohen Anteil holarktischer und paläarktischer Arten auszeichnet, die auch in Kamtschatka vorkommen.The species of predaceous diving beetles (Coleoptera, Dytiscidae) ocurring in the Kuril Archipelago in the northwest Pacific are reviewed. Based on literature records, the study of museum collections, and material from recent expeditions 24 species are known from the archipelago. A detailed report is given on the 357 adult and 50 larval specimens collected in the South and Mid Kuril Islands by the joint American-Japanese-Russian expeditions in 1994 and 1995. The following five species are here recorded from the Kurils for the first time: Hydroporus uenoi Nakane, Platambus pictipennis (Sharp), Agabus japonicus Sharp, Ilybius nakanei Nilsson, and Graphoderus zonatus (Hoppe). The number of species recorded on individual islands ranged from 1 to 11, with the largest islands at either end of the Greater Kuril Ridge being the most diverse. The South Kurils are dominated by Ussurian-Japanese species known also from Sakhalin and Hokkaido, whereas the North Kuril fauna includes a high proportion of Holarctic or Palearctic species known also from Kamchatka