A hybrid column generation and simulated annealing algorithm for direct aperture optimization.

The purpose of this work was to develop a hybrid column generation (CG) and simulated annealing (SA) algorithm for direct aperture optimization (H-DAO) and to show its effectiveness in generating high quality treatment plans for intensity modulated radiation therapy (IMRT) and mixed photon-electron beam radiotherapy (MBRT). The H-DAO overcomes limitations of the CG-DAO with two features improving aperture selection (branch-feature) and enabling aperture shape changes during optimization (SA-feature). The H-DAO algorithm iteratively adds apertures to the plan. At each iteration, a branch is created for each field provided. First, each branch determines the most promising aperture of its assigned field and adds it to a copy of the current apertures. Afterwards, the apertures of each branch undergo an MU-weight optimization followed by an SA-based simultaneous shape and MU-weight optimization and a second MU-weight optimization. The next H-DAO iteration continues the branch with the lowest objective function value. IMRT and MBRT treatment plans for an academic, a brain and a head and neck case generated using the CG-DAO and H-DAO were compared. For every investigated case and both IMRT and MBRT, the H-DAO leads to a faster convergence of the objective function value with number of apertures compared to the CG-DAO. In particular, the H-DAO needs about half the apertures to reach the same objective function value as the CG-DAO. The average aperture areas are 27% smaller for H-DAO than for CG-DAO leading to a slightly larger discrepancy between optimized and final dose. However, a dosimetric benefit remains. The H-DAO was successfully developed and applied to IMRT and MBRT. The faster convergence with number of apertures of the H-DAO compared to the CG-DAO allows to select a better compromise between plan quality and number of apertures.

High field electron paramagnetic resonance spectroscopy under ultrahigh vacuum conditions--a multipurpose machine to study paramagnetic species on well defined single crystal surfaces.

A new ultrahigh vacuum (UHV) electron paramagnetic resonance (EPR) spectrometer operating at 94 GHz to investigate paramagnetic centers on single crystal surfaces is described. It is particularly designed to study paramagnetic centers on well-defined model catalysts using epitaxial thin oxide films grown on metal single crystals. The EPR setup is based on a commercial Bruker E600 spectrometer, which is adapted to ultrahigh vacuum conditions using a home made Fabry Perot resonator. The key idea of the resonator is to use the planar metal single crystal required to grow the single crystalline oxide films as one of the mirrors of the resonator. EPR spectroscopy is solely sensitive to paramagnetic species, which are typically minority species in such a system. Hence, additional experimental characterization tools are required to allow for a comprehensive investigation of the surface. The apparatus includes a preparation chamber hosting equipment, which is required to prepare supported model catalysts. In addition, surface characterization tools such as low energy electron diffraction (LEED)/Auger spectroscopy, temperature programmed desorption (TPD), and infrared reflection absorption spectroscopy (IRAS) are available to characterize the surfaces. A second chamber used to perform EPR spectroscopy at 94 GHz has a room temperature scanning tunneling microscope attached to it, which allows for real space structural characterization. The heart of the UHV adaptation of the EPR experiment is the sealing of the Fabry-Perot resonator against atmosphere. To this end it is possible to use a thin sapphire window glued to the backside of the coupling orifice of the Fabry Perot resonator. With the help of a variety of stabilization measures reducing vibrations as well as thermal drift it is possible to accumulate data for a time span, which is for low temperature measurements only limited by the amount of liquid helium. Test measurements show that the system can detect paramagnetic species with a density of approximately 5 × 10(11) spins/cm(2), which is comparable to the limit obtained for the presently available UHV-EPR spectrometer operating at 10 GHz (X-band). Investigation of electron trapped centers in MgO(001) films shows that the increased resolution offered by the experiments at W-band allows to identify new paramagnetic species, that cannot be differentiated with the currently available methodology.

A fresh look at an old nano-technology: catalysis.

The development of model catalyst systems for heterogeneous catalysis going beyond the metal single crystal approach, including phenomena involving the limited size of metal nanoparticles supported on oxide surfaces, as well as the electronic interaction through the oxide-metal interface, is exemplified on the basis of two case studies from the laboratory of the authors. In the first case study the reactivity of supported Pd nanoparticles is studied in comparison with Pd single crystals. The influence of carbon contaminants on the hydrogenation reaction of unsaturated hydrocarbons is discussed. Carbon contaminants are identified as a key parameter in those reactions as they control the surface and sub-surface concentration of hydrogen on and in the particles. In the second case study, scanning probe techniques are used to determine electronic and structural properties of supported Au particles as a function of the number of Au atoms in the particle. It is demonstrated how charge transfer between the support and the particle determines the shape of nanoparticles and a concept is developed that uses charge transfer control through dopants in the support to understand and design catalytically active materials.

[Norms for the Mottier-Test from 4- to 6-year old children]. / Normen für den Mottier-Test bei 4- bis 6-jährigen Kindern.

BACKGROUND: The Mottier Test--a diagnostic test of non-word repetition (30 nonsense syllables of varying length)--is designed to measure phonological processing. To assess individual results in 4- to 6-year-olds, only reference values based on raw scores published in 1981 are available. METHOD: Data was collected in 2006 in two German federal states for the purposes of updating reference values. A sample of 308 nursery-school children (154 boys; 154 girls) from Lower Saxony and Northrhine-Westphalia were examined (4-year-olds: n=86; 5-year-olds: n=126; 6-year-olds: n=96). RESULTS: Boy and girls performed more or less the same (mean correctly repeated non-words: boys 13.44; girls 14.08; p=0.15). However, older children performed better than younger ones (4-year-olds: 11.19, SD 3.93; 5-year-olds: 13.95, SD 4.02; 6-year-olds: 15.81, SD 3.97). The difference between the three age groups was highly significant: 4- and 5-year-olds (U=3358.5; p=.000); 5- and 6-year-olds (U=4551.5; p=.002); 4- and 6-year-olds (U=1658; p=.000). The same was true for the difference in the half-yearly performance of the 5-year-olds (60-65 months old: 12.78, SD 3.67; 66-71 months old: 14.96, SD 4.07; U=1317; p=.001). Percentile ranks (and T-scores) specific to age were provided. CONCLUSION: Normative data to evaluate intra- and interindividual performances among German-speaking children aged 4-6 years old contributes to the improvement of diagnostic assurance.

[The Mottier test : psychometric evaluation using scores from children age 4-6 years]. / Der Mottier-Test : Teststatistische Uberprüfung an 4- bis 6-jährigen Kindern.

BACKGROUND: The Mottier test to examine phonological processing is a widespread, frequently used instrument in clinical diagnostics. However, data on its validity and reliability are scarce. The reference scores for non-schoolchildren in 1981 (collected with small samples) have become outdated. METHOD: Three hundred and eight children (154 boys, 154 girls) from the German federal states of Lower Saxony and North Rhine-Westphalia were examined with the Mottier test (4-year-olds: n=86; 5-year-olds: n=126; 6-year-olds: n=96). RESULTS: The average item difficulty P for all children was 45.5 (range 5.8-90.6). On average, the items were easier to perform with increasing age (4-year-olds: P=37.3; 5-year-olds: P=46.5; 6-year-olds: P=52.7). The average item discrimination indices r(it) were 0.49 for 6-year-olds and 0.91 for 4-year-olds. The mean test score for all children was 13.76 (SD 4.35). There was a shift for the worse compared with the mean test scores from 1981 (4-year-olds: 11.19, SD 3.93; 5-year-olds: 13.95, SD 4.02; 6-year-olds: 15.81, SD 3.97). To determine reliability, the internal consistency (Cronbachs alpha=0.77) and split-half reliability were computed (r(tt)=0.86). The criterion-related validity with the convergent criterion "number recall" amounted to r=0.52 (p<0.0001) for all. CONCLUSION: It seems that young children nowadays have more difficulties successfully solving the items in the Mottier test than did children about 25 years ago.

Influence of Pd codeposition on the magnetic properties of Co particles on alumina/NiAl110.

Changes of the magnetic properties of ferromagnetic Co particles deposited at room temperature on a thin alumina film grown on a NiAl(110) substrate were investigated as a function of Pd coverage by subsequent deposition of Pd onto deposited Co particles. From previous x-ray photoelectron spectroscopy, IR, and temperature programmed desorption experiments it was concluded that Pd forms a shell on top of Co particles. However, the current experiments indicate that Pd does induce structural rearrangements within the Co particles which may also involve the intermixing of small amounts of Pd into the Co particles. The latter is inferred from a change in the g-value for small particles. The impact of a larger intermixture of Co and Pd on the magnetic properties will be emphasized by a reversed deposition order where Pd particles were deposited first and subsequently covered by Co. The reversal of the deposition order increases the magnetic anisotropy of the particles considerably.

Au dimers on thin MgO(001) films: flat and charged or upright and neutral?

A combination of low temperature scanning tunneling microscopy (STM) and theoretical calculations is used to investigate Au dimers, supported on thin MgO(001) films, whose thickness was chosen such that charge transfer from the Ag substrate to the deposited Au is possible. Au dimers exist not only in an upright geometry--as theoretically predicted to be the most stable configuration--but also as flat lying dimers which populate a manifold of different azimuthal orientations. Apart from the difference in adsorption configurations, these two isomers exhibit rather different electronic structures: while upright dimers are neutral, flat ones are charged.

Reorganization of small Co particles on Al2O3 surfaces monitored by ferromagnetic resonance.

Changes of the magnetic properties of ferromagnetic Co particles deposited on the radical31 x radical31R +/- 9 degrees reconstructed alpha-Al2O3(0001) as well as on a thin alumina film grown on a NiAl(110) substrate were investigated as a function of thermal annealing. On the thin film changes of the magnetic response were found above 500 K which correlates with changes in the particle size distribution. Annealing to 870 K leads to a permeation of the metal though the oxide film which causes significant changes in the ferromagnetic resonance response. On the alpha-Al2O3 single crystal sintering of particles requires temperatures above 600 K being about 100 K higher as compared to the thin alumina film. For large clusters intraparticle redistribution takes place already below 600 K a phenomenon not observed for the small clusters. In addition, a significant dependence of the measured g values from the substrate as well as the thermal treatment is found which can be understood in terms of the structural properties of the systems.

Structure and dynamics of annexin 12 bound to a planar lipid bilayer.

Site directed spin labeling is used to investigate the protein annexin 12 absorbed on a single planar phospholipid bilayer of approximately 2-3 cm(2). Electron paramagnetic resonance spectra of nitroxide side chain at several topological sites reveal a conserved tertiary fold of the protein in the absorbed state, in agreement with earlier diffraction results. The angular dependent spectra of the two-dimensional microcrystals are shown to provide information on the degree of ordering of spin labels in a alpha-helix and in turn on the orientation of the alpha-helix with respect to the surface.

Cluster, facets, and edges: site-dependent selective chemistry on model catalysts.

More than activity, selectivity of catalytic reactions is the focus of research in the 21(st) century. We review studies on model systems that address the issue of directing a catalytic reaction on disperse metal catalysts by controlling the specific surface site. Three examples are explored: methanol dehydrogenation over Pd/alumina, NO dissociation on Pd/alumina, and reaction studies for molecules relevant in a Fischer-Tropsch scenario on a bimetallic Pd/Co/alumina model catalyst. We show how surface science can be used by combining a variety of experimental techniques to study the chemistry of model catalysts at the atomic level.

A new formula for prenatal ultrasonographic weight estimation in extremely preterm fetuses.

A new formula for the prenatal estimation of the weight of extremely preterm fetuses was derived using ultrasound measurements and birth weights of 73 premature infants delivered before 30 completed weeks of pregnancy and weighing between 400 and 1,680 g at birth. The actual birth weight lay within +/- 15% of the estimated weight calculated with this formula in 92% of the cases. Preliminary testing of the reliability of the formula was performed on a further test group of 19 nonselected cases. The formula developed in this study offers a reliable and simple method of prenatal estimation of fetal weight between 23 and 30 weeks of gestation.