Interaction of metals with an organic semiconductor: Ag and In on PTCDA

The interaction of Ag and In with a thin film of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) was studied by near-edge X-ray absorption fine structure (NEXAFS). Upon Ag deposition on a PTCDA film of 20 nm thickness the relative intensities and lineshapes, as well as the angular dependence of the spectra remains unchanged, illustrating the formation of a chemically unreactive Ag/PTCDA interface. On the other hand, the adsorption of 0.3 nm In strongly decreases the intensity of the π^* resonances in C and O K-edge NEXAFS spectra. This is attributed to a strong charge transfer between In and PTCDA, leading to a redistribution of the charge in the molecule. However, the absence of a strong shift or new features and negligible dependence of peak intensities corresponding to π^* resonances on the In thickness indicate that the interaction between In and PTCDA is not accompanied by a covalent bond formation.     

Hadron masses and matrix elements from the QCD Schrödinger functional

We explain how masses and matrix elements can be computed in lattice QCD using Schrödinger functional boundary conditions. Numerical results in the quenched approximation demonstrate that good precision can be achieved. For a statistical sample of the same size, our hadron masses have a precision similar to what is achieved with standard methods, but for the computation of matrix elements such as the pseudoscalar decay constant the Schrödinger functional technique turns out to be much more efficient than the known alternatives.     

An empirical study of common traffic congestion features based on traffic data measured in the USA,the UK,and Germany

Based on real traffic data measured on American, UK and German freeways, we study common features of traffic congestion. We have found that traffic features [J] and [S] defining traffic phases “wide moving jam” (J) and “synchronized flow” (S) in Kerner’s three-phase theory are indeed common spatiotemporal traffic features observed in the UK, the USA and Germany. For the testing of Kerner’s “line J”, representing the propagation of the wide moving jam’s downstream front, four different methods for a study of moving jam propagation in empirical data are studied and compared for each congested traffic situation occurring in the three countries. A statistical study of velocities of wide moving jam fronts is presented, which has been performed through the analysis of database containing more than 280.000 min of observed wide moving jams measured on about 1200 km long freeway network in Hessen (Germany) during more than two years.     

Relaxation and thermal vibrations at the NaF(100) surface

The relaxation and the thermal vibrations of the NaF(100) surface are investigated in the temperature range between 25 K and 230 K by means of low-energy electron diffraction (LEED) and a subsequent I(V) structure analysis based on the tensor LEED approach (TLEED). According to the experiments, the NaF(100) surface is not significantly relaxed and has the ideal truncated bulk structure. The thermal vibrational amplitudes of the ions in the topmost layer are significantly enhanced compared to the bulk by a factor of 1.35 ± 0.15 and are equal within the error-bars for Na⁺ and F^? ions. Moreover, the relaxation and the dynamics of the NaF(100) surface are investigated using periodic density functional theory (DFT) calculations using pseudopotentials. In agreement with the experimental findings, the calculated relaxation of the NaF(100) surface is weak with static shifts of the ions of 0.01 Å to 0.02 Å. In the topmost layer, the Na⁺ ions are predicted to be slightly inward shifted, whereas the F^? ions are outward shifted, in accordance to predictions of previous shell-model calculations. A Born Oppenheimer molecular dynamics (BO-MD) simulation of the dynamics at the NaF(100) surface leads to a smaller enhancement of thermal motions of the ions at the surface compared to the experiment.     

Fast volumetric spatial-spectral MR imaging of hyperpolarized C-labeled compounds using multiple echo 3D bSSFP

Purpose

The goal of this work was to develop a fast 3D chemical shift imaging technique for the noninvasive measurement of hyperpolarized ¹³C-labeled substrates and metabolic products at low concentration.

Materials and Methods

Multiple echo 3D balanced steady state magnetic resonance imaging (ME-3DbSSFP) was performed in vitro on a syringe containing hyperpolarized [1,3,3-2H3; 1-¹³C]2-hydroxyethylpropionate (HEP) adjacent to a ¹³C-enriched acetate phantom, and in vivo on a rat before and after intravenous injection of hyperpolarized HEP at 1.5 T. Chemical shift images of the hyperpolarized HEP were derived from the multiple echo data by Fourier transformation along the echoes on a voxel by voxel basis for each slice of the 3D data set.

Results

ME-3DbSSFP imaging was able to provide chemical shift images of hyperpolarized HEP in vitro, and in a rat with isotropic 7-mm spatial resolution, 93 Hz spectral resolution and 16-s temporal resolution for a period greater than 45 s.

Conclusion

Multiple echo 3D bSSFP imaging can provide chemical shift images of hyperpolarized ¹³C-labeled compounds in vivo with relatively high spatial resolution and moderate spectral resolution. The increased signal-to-noise ratio of this 3D technique will enable the detection of hyperpolarized ¹³C-labeled metabolites at lower concentrations as compared to a 2D technique.     

Resonant Raman scattering by strained and relaxed germanium quantum dots

This paper reports on the results of resonant Raman scattering investigations of the fundamental vibrations in Ge/Si structures with strained and relaxed germanium quantum dots. Self-assembled strained Ge/Si quantum dots are grown by molecular-beam epitaxy on Si(001) substrates. An ultrathin SiO₂ layer is grown prior to the deposition of a germanium layer with the aim of forming relaxed germanium quantum dots. The use of resonant Raman scattering (selective with respect to quantum dot size) made it possible to assign unambiguously the line observed in the vicinity of 300 cm^?1 to optical phonons confined in relaxed germanium quantum dots. The influence of confinement effects and mechanical stresses on the vibrational spectra of the structures with germanium quantum dots is analyzed.     

Template assisted formation of micro- and nanotubular carbon nitride materials

Micro- and nanotubes of an amorphous carbon nitride material were synthesized by metathesis reactions between cyanuric chloride (C₃N₃Cl₃) and different nitrogen sources, such as Li₂(CN₂) or Li₃(BN₂). The intermediate formation of needle-shaped crystals of N(C₃N₃Cl₂)₃ was always observed in our reactions, and investigated with respect to their role as a template in the formation of tubes. Chemical analyses of the micro- and nanotubes reveal carbon to nitrogen ratios near 3:4, consistent with the suspected material C₃N₄. Synthesized carbon nitride materials were thermally stable up to 600 ^°C in inert atmosphere. They were inspected by a number of physical measurements, mainly using TEM, EDX and IR investigations.     

Epistemic Horizons and the Foundations of Quantum Mechanics

In-principle restrictions on the amount of information that can be gathered about a system have been proposed as a foundational principle in several recent reconstructions of the formalism of quantum mechanics. However, it seems unclear precisely why one should be thus restricted. We investigate the notion of paradoxical self-reference as a possible origin of such epistemic horizons by means of a fixed-point theorem in Cartesian closed categories due to Lawvere that illuminates and unifies the different perspectives on self-reference.