The Atomic Slide Puzzle: Self-Diffusion of an Impure Atom

In a series of recent papers van Gastel et al have presented first experimental evidence that impure, Indium atoms, embedded into the first layer of a Cu(001) surface, are not localized within the close-packed surface layers but make concerted, long excursions visualized in a series of STM images. Such excursions occur due to continuous reshuffling of the surface following the position exchanges of both impure and host atoms with the naturally occuring surface vacancies. Van Gastel et al have also formulated an original lattice-gas type model with asymmetric exchange probabilities, whose numerical solution is in a good agreement with the experimental data. In this paper we propose an exact lattice solution of several versions of this model.Comment: Latex, 4 pages, 2 figures, to appear in Phys. Rev. E (RC

Partial regularity for almost minimizers of quasi-convex integrals

We consider almost minimizers of variational integrals whose integrands are quasiconvex. Under suitable growth conditions on the integrand and on the function determining the almost minimality, we establish almost everywhere regularity for almost minimizers and obtain results on the regularity of the gradient away from the singular set. We give examples of problems from the calculus of variations whose solutions can be viewed as such almost minimizers

Imaging ultra thin layers with helium ion microscopy: Utilizing the channeling contrast mechanism

Background: Helium ion microscopy is a new high-performance alternative to classical scanning electron microscopy. It provides superior resolution and high surface sensitivity by using secondary electrons.\ud \ud Results: We report on a new contrast mechanism that extends the high surface sensitivity that is usually achieved in secondary electron images, to backscattered helium images. We demonstrate how thin organic and inorganic layers as well as self-assembled monolayers can be visualized on heavier element substrates by changes in the backscatter yield. Thin layers of light elements on heavy substrates should have a negligible direct influence on backscatter yields. However, using simple geometric calculations of the opaque crystal fraction, the contrast that is observed in the images can be interpreted in terms of changes in the channeling probability.\ud \ud Conclusion: The suppression of ion channeling into crystalline matter by adsorbed thin films provides a new contrast mechanism for HIM. This dechanneling contrast is particularly well suited for the visualization of ultrathin layers of light elements on heavier substrates. Our results also highlight the importance of proper vacuum conditions for channeling-based experimental methods\u

Spinodal decomposition driven formation of Pt-nanowires on Ge(001)

Using low energy electron microscopy, we have found that the deposition of Pt on Ge(001) leads to the formation of a surface confined eutectic liquid when the system is heated above 980 K. From the bulk phase diagram we derive the composition of the eutectic phase: Ge$_{0.78}$Pt$_{0.22}$. Upon solidification and further cooling down, two distinct types of terrace emerge, the so-called α and β terraces, which have been assigned previously as relatively Pt-poor and Pt-rich, respectively. Immediately after solidification β terraces fully cover the surface, while further cooling leads to their partial transformation into α terraces. Subsequently, Pt nanowire domains nucleate and grow exclusively on β terraces at about 600 K. The results are discussed using spinodal decomposition concepts and reveal a new pathway for nanowire formation

Dissociative symptoms and sleep parameters: an all-night polysomnography study in patients with insomnia

AbstractBackgroundDissociative disorders encompass a range of symptoms varying from severe absent-mindedness and memory problems to confusion about one's own identity. Recent studies suggest that these symptoms may be the by-products of a labile sleep–wake cycle.MethodsIn the current study, we explored this issue in patients suffering from insomnia (N=46). We investigated whether these patients have raised levels of dissociative symptoms and whether these are related to objective sleep parameters. Patients stayed for at least one night in a specialized sleep clinic, while sleep EEG data were obtained. In addition, they completed self-report measures on dissociative symptoms, psychological problems, and sleep characteristics.ResultsDissociative symptom levels were elevated in patients suffering from insomnia, and were correlated with unusual sleep experiences and poor sleep quality. Longer REM sleep periods and less time spent awake during the night were predictive of dissociation.ConclusionsThis is the first study to show that insomnia patients have raised dissociative symptom levels and that their dissociative symptoms are related to objective EEG parameters. These findings are important because they may inspire sleep-related treatment methods for dissociative disorders

Spectroscopic and Theoretical Study on Siloxy-Based Molybdenum and Tungsten Alkylidyne Catalysts for Alkyne Metathesis

A combined spectroscopic and theoretical study on triphenyl- and dimethyl-phenyl siloxy molybdenum and tungsten alkylidyne catalysts for alkyne metathesis is reported. Using NMR, X-ray, UV-VIS, Resonance Raman spectroscopy and DFT calculations, the influence of different ligand systems and metal centers on the geometric and electronic structure and thermochemistry of different intermediates is investigated, that is the starting alkylidyne and the derived metallacyclobutadiene and metallatetrahedrane. This includes a mechanistic and kinetic study on the formation and isomerization of metallacyclobutadienes and metallatetrahedranes. Upon changing from monodentate to tripodal siloxy ligands, higher steric strain is imposed, which modulates the relative energies of the different intermediates. Additionally, intramolecular dispersion interactions between bound substrate and ligand can be operative. Tungsten as the central metal leads to stronger M-C σ-bonds, which overstabilize the reaction intermediates and preclude effective turnover. Furthermore, kinetic modeling strongly suggests that metallatetrahedranes are off-cycle intermediates based on the high barriers for direct formation but low barriers for isomerization from metallacyclobutadienes. We infer from our findings that effective catalysis can only be achieved when factors that (over)stabilize intermediates, such as strong M-C bonds or large dispersion interactions, are prevented by appropriate catalyst design

Economic impact of port activity : a disaggregate analysis. The case of Antwerp

The economic impact of the port sector is usually measured at an aggregate level by indicators such as value added, employment and investment. This paper tries to define the economic relevance for the regional as well as for the national economy at a disaggregate level. It attempts to identify, quantify and locate the mutual relationships between the various port players themselves and between them and other Belgian industries. Due to a lack of information foreign trade is only tackled very briefly but the method outlined in this paper can be used to measure the national effects of changes in port activity at a detailed level. A sector analysis is made by compiling a regional (regional as geographically opposed to national, not to be mistaken for the Belgian Regions Brussels, Flanders and Wallonia) input-output table, resorting to microeconomic data: a bottom-up approach. The main customers and suppliers of the port's key players or stakeholders are identified. A geographical analysis can also be carried out by using data at a disaggregate level. Each customer or supplier can be located by means of their postcode. In so doing, the economic impact of the port is quantified, both functionally and geographically. In the case of the port of Antwerp, the results show important links between freight forwarders and agents. The geographical analysis suggests the existence of major agglomerating effects in and around the port of Antwerp, referred to as a major transhipment location point. Key words: port economics, regional input-output table, sector analysis, geographical analysis.port economics, regional input-output table, sector analysis, geographical analysis