The self-consistent quantum-electrostatic problem in strongly non-linear regime

The self-consistent quantum-electrostatic (also known as Poisson-Schr\"odinger) problem is notoriously difficult in situations where the density of states varies rapidly with energy. At low temperatures, these fluctuations make the problem highly non-linear which renders iterative schemes deeply unstable. We present a stable algorithm that provides a solution to this problem with controlled accuracy. The technique is intrinsically convergent including in highly non-linear regimes. We illustrate our approach with (i) a calculation of the compressible and incompressible stripes in the integer quantum Hall regime and (ii) a calculation of the differential conductance of a quantum point contact geometry. Our technique provides a viable route for the predictive modeling of the transport properties of quantum nanoelectronics devices.Comment: 28 pages. 14 figures. Added solution to a potential failure mode of the algorith

Modeling, Analysis, and Optimization Issues for Large Space Structures

Topics concerning the modeling, analysis, and optimization of large space structures are discussed including structure-control interaction, structural and structural dynamics modeling, thermal analysis, testing, and design

CIRCE Version 1.0: Beam Spectra for Linear Collider Physics

I describe parameterizations of realistic $e^\pm$- and $\gamma$-beam spectra at future linear $e^+e^-$-colliders. Emphasis is put on simplicity and reproducibility of the parameterizations, supporting reproducible physics simulations. The parameterizations are implemented in a library of distribution functions and event generators.Comment: 26 pages, LaTeX (using amsmath.sty), PostScript figures included, paper saving version formatted for A4 available from ftp://crunch.ikp.physik.th-darmstadt.de/pub/preprints/IKDA-96-13.ps.g

Experimental Assessment of ‘subgrid’ scale Probability Density Function Models for Large Eddy Simulation

Filtered density functions (FDFs) of mixture fraction are quantified by analyzing experimental data obtained from two-dimensional planar laser-induced fluorescence scalar measurements in the isothermal swirling flow of a combustor operating at a Reynolds number of 28,662 for three different swirl numbers (0.3, 0.58 and 1.07). Two-dimensional filtering using a box filter was performed on the measured scalar to obtain the filtered variables used for presumed FDF for Large Eddy Simulations (LES). A dependant variable from the measured scalar, which was a pre-computed temperature, was integrated over the experimentally obtained FDF as well as over the presumed beta or top-hat FDFs and a relative error in temperature prediction was calculated. The experimentally measured FDFs depended on swirl numbers and axial and radial positions in the flow. The FDFs were unimodal in the regions of low variance and bimodal in the regions of high variance. The influence of the filter spatial dimension on the measured FDF was evaluated and consequences for subgrid modeling for LES discussed

Slope Instability of the Earthen Levee in Boston, UK: Numerical Simulation and Sensor Data Analysis

The paper presents a slope stability analysis for a heterogeneous earthen levee in Boston, UK, which is prone to occasional slope failures under tidal loads. Dynamic behavior of the levee under tidal fluctuations was simulated using a finite element model of variably saturated linear elastic perfectly plastic soil. Hydraulic conductivities of the soil strata have been calibrated according to piezometers readings, in order to obtain correct range of hydraulic loads in tidal mode. Finite element simulation was complemented with series of limit equilibrium analyses. Stability analyses have shown that slope failure occurs with the development of a circular slip surface located in the soft clay layer. Both models (FEM and LEM) confirm that the least stable hydraulic condition is the combination of the minimum river levels at low tide with the maximal saturation of soil layers. FEM results indicate that in winter time the levee is almost at its limit state, at the margin of safety (strength reduction factor values are 1.03 and 1.04 for the low-tide and high-tide phases, respectively); these results agree with real-life observations. The stability analyses have been implemented as real-time components integrated into the UrbanFlood early warning system for flood protection