Ionic films on vicinal metal surfaces: enhanced binding due to charge modulation

NaCl films on Cu(311) exhibit a remarkably strong and localized binding between adlayer and substrate. The binding sites of the ions in the NaCl film with respect to the Cu surface are determined from atomically resolved scanning tunneling microscopy images. A new model is proposed in which the binding mechanism is controlled by the charge modulation of a regularly stepped surface due to the Smoluchowski effect. This model can be extended to explain the growth of ionic adlayers on regularly stepped and kinked metal surfaces in general.     

Optimal control of single-server fluid networks

We consider a stochastic single-server fluid network with both a discounted reward and a cost structure. It can be shown that the optimal policy is a priority index policy. The indices coincide with the optimal indices in a semi-Markovian Klimov problem. Several special cases like single-server reentrant fluid lines are considered. The approach we use is based on sample path arguments and Pontryagins maximum principle. This revised version was published online in June 2006 with corrections to the Cover Date.     

On the linearization of operators related to the full waveform inversion in seismology

In this work, we analyze the parameter‐to‐solution map of the acoustic wave equation with respect to its parameters wave speed and mass density. This map is a mathematical model for the seismic inverse problem where one wants to recover the parameters from measurements of the acoustic potential. We show its complete continuity and Fréchet differentiability. To this end, we provide necessary existence, stability, and regularity results. Moreover, we discuss various implications of our findings on the inverse problem and comment on the Born series. Copyright © 2013 John Wiley & Sons, Ltd.     

Optimality of the fully discrete filtered backprojection algorithm for tomographic inversion

Although the filtered backprojection algorithm (FBA) has been the standard reconstruction algorithm in 2D computerized tomography for more than 30 years, its convergence behavior is not completely settled so far. Relying on convergence results by Rieder and Faridani for the semi-discrete FBA [SIAM J. Numer. Anal., 41(3), 869–892, 2003], we show optimality of the fully discrete version for reconstructing sufficiently smooth density distributions. Further, we introduce MFBA, a modified version of FBA, and prove its optimality under weaker smoothness requirements. Remarkably MFBA may have a larger convergence order in the angular than in the lateral variable, thus allowing optimal convergence in case of angular under- sampling. Moreover, MFBA can be seen as a limit of the phantom view method introduced to increase angular resolution.     

Polarity change in capillary GC by serial-column temperature optimization (SECAT mode in capillary GC)

GC, including capillary GC, is rather inflexible, if a certain column length and stationary phase has been fixed for a given analytical problem. If the sample composition changes, one often has to change the column length and/or stationary phase, at least when something like optimum analytical conditions are needed. Temperature changes (or heating rates) can change the selectivity of a given column only within very limited ranges, due to the exponential effect of temperature on retention time. By serial coupling two chemically different capillaries, each run at another temperature, even the slightest changes of these two temperature values have a dramatic effect on the selectivity of the system for polar substances. We call this technique the SECAT mode of GC. Results are reported as retention index shifts, dependent on SECAT temperature data. This technique can in future easily be automated, thus enabling the analyst, for polar sample analysis, to adjust a given chroma-tographic system to his specific sample composition without touching the instrument.     

Surface phonons of GaP(1 1 0) and InAs(1 1 0)

The dispersions of low energy surface phonon modes of GaP(1 1 0) and InAs(1 1 0) measured with inelastic He-atom scattering along the and 0 0 1 directions are presented. Aside from the Rayleigh mode, additional distinct acoustic modes are observed as well as indications of optical modes. Contrary to results for GaAs(1 1 0), a rocking mode was not observed. The experimentally determined phonon dispersions are in excellent agreement with recent ab initio calculations by C. Eckl, et al. [1].