Highlights of the Science and Life of Peter Varga (1946—2018)

Peter Varga has passed on October 27, 2018. His pioneering discoveries of chemical resolution at the atomic scale on surface alloys, atomic resolution of ultrathin alkali halides, nucleation of bcc iron in ultrathin films, and the microscopic structure of ultrathin alumina films stimulated worldwide research. In recognition of his outstanding scientific contributions, in December 2017 the Japanese Society for the Promotion of Science (JSPS) awarded him a prize for his distinguished contribution on the clarification of surface phenomena by atomic level investigations and the development of novel functional materials. This contribution highlights the life of Peter Varga as a scientist and as a person. With his elegance, his energy, his wit, and his generosity he was a close friend and role model to many of us, and showed us how to combine scientific curiosity and creativity with the lightness of being

Does ursodeoxycholic acid change the proliferation of the colorectal mucosa? A randomized, placebo-controlled study

Background: In animal models ursodeoxycholic acid (UDCA) showed a chemoprotective effect against colon cancer. To explain this, a reduced proliferation of the colorectal mucosal proliferation was suggested. We, therefore, examined the influence of UDCA on the proliferation of normal colorectal mucosa in humans. Methods: Following endoscopic polypectomy, 20 patients with colorectal adenomas were randomized to receive either UDCA (750 mg/day, n = 10, group A) or placebo (n = 10, group B) for 6 months in a double-blinded way. Colorectal biopsies were sampled before and at the end of the medication by total colonoscopy. Colorectal mucosal proliferation was measured by FACScan analysis of propidium iodine labeling. Serum was sampled, and serum bile acids were analyzed by gas chromatography. Results: The proliferation rates at the end of the study were similar in both groups (median 15.4%; range 12.0-20.9 in group A; median 16.0%, 14.0-20.2 in group B, p = 0.41). Serum lithocholic acid levels at the end of the study were significantly higher in group A (1.3 mumol/l, 0.9-1.8) than in group B (0.7 mumol/l, 0-1.7, p < 0.02), whereas serum deoxycholic acid levels were similar in both groups. Conclusions: In this study, UDCA treatment for 6 months does not seem to induce changes in the proliferative behavior of the colorectal mucosa in patients with adenomas. It seems likely that a putative chemopreventive effect of UDCA in humans is not exerted by a reduction of the colorectal proliferation. Copyright (C) 2003 S. Karger AG, Basel

Structure and apparent topography of TiO2 (110) surfaces

We present self-consistent ab-initio total-energy and electronic-structure calculations on stoichiometric and non-stoichiometric TiO2 (110) surfaces. Scanning tunneling microscopy (STM) topographs are simulated by calculating the local electronic density of states over an energy window appropriate for the experimental positive-bias conditions. We find that under these conditions the STM tends to image the undercoordinated Ti atoms, in spite of the physical protrusion of the O atoms, giving an apparent reversal of topographic contrast on the stoichiometric 1x1 or missing-row 2x1 surface. We also show that both the interpretation of STM images and the direct comparison of surface energies favor an added-row structure over the missing-row structure for the oxygen-deficient 2x1 surface.Comment: 6 pages, two-column style with 5 postscript figures embedded. Uses REVTEX and epsf macros. Also available at http://www.physics.rutgers.edu/~dhv/preprints/index.html#ng_tio

Multiple shifts and fractional integration in the us and uk unemployment rates

This paper analyses the long-run behaviour of the US and UK unemployment rates by testing for possibly fractional orders of integration and multiple shifts using a sample of over 100 annual observations. The results show that the orders of integration are higher than 0 in both series, which implies long memory. If we assume that the underlying disturbances are white noise, the values are higher than 0.5, i.e., nonstationary. However, if the disturbances are autocorrelated, the orders of integration are in the interval (0, 0.5), implying stationarity and mean-reverting behaviour. Moreover, when multiple shifts are taken into account, unemployment is more persistent in the US than in the UK, implying the need for stronger policy action in the former to bring unemployment back to its original level

FlashCam: a fully-digital camera for the medium-sized telescopes of the Cherenkov Telescope Array

The FlashCam group is currently preparing photomultiplier-tube based cameras proposed for the medium-sized telescopes (MST) of the Cherenkov Telescope Array (CTA). The cameras are designed around the FlashCam readout concept which is the first fully-digital readout system for Cherenkov cameras, based on commercial FADCs and FPGAs as key components for the front-end electronics modules and a high performance camera server as back-end. This contribution describes the progress of the full-scale FlashCam camera prototype currently under construction, as well as performance results also obtained with earlier demonstrator setups. Plans towards the production and implementation of FlashCams on site are also briefly presented.Comment: 8 pages, 6 figures. In Proceedings of the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherlands. All CTA contributions at arXiv:1508.0589

Performance Verification of the FlashCam Prototype Camera for the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is a future gamma-ray observatory that is planned to significantly improve upon the sensitivity and precision of the current generation of Cherenkov telescopes. The observatory will consist of several dozens of telescopes with different sizes and equipped with different types of cameras. Of these, the FlashCam camera system is the first to implement a fully digital signal processing chain which allows for a traceable, configurable trigger scheme and flexible signal reconstruction. As of autumn 2016, a prototype FlashCam camera for the medium-sized telescopes of CTA nears completion. First results of the ongoing system tests demonstrate that the signal chain and the readout system surpass CTA requirements. The stability of the system is shown using long-term temperature cycling.Comment: 5 pages, 13 figures, Proceedings of the 9th International Workshop on Ring Imaging Cherenkov Detectors (RICH 2016), Lake Bled, Sloveni

Au/TiO2(110) interfacial reconstruction stability from ab initio

We determine the stability and properties of interfaces of low-index Au surfaces adhered to TiO2(110), using density functional theory energy density calculations. We consider Au(100) and Au(111) epitaxies on rutile TiO2(110) surface, as observed in experiments. For each epitaxy, we consider several different interfaces: Au(111)//TiO2(110) and Au(100)//TiO2(110), with and without bridging oxygen, Au(111) on 1x2 added-row TiO2(110) reconstruction, and Au(111) on a proposed 1x2 TiO reconstruction. The density functional theory energy density method computes the energy changes on each of the atoms while forming the interface, and evaluates the work of adhesion to determine the equilibrium interfacial structure.Comment: 20 pages, 11 figure

Non-stoichiometric oxide and metal interfaces and reactions

We have employed a combination of experimental surface science techniques and density functional calculations to study the reduction of TiO2(110) surfaces through the doping with submonolayer transition metals. We concentrate on the role of Ti adatoms in self doping of rutile and contrast the behaviour to that of Cr. DFT+U calculations enable identification of probable adsorption structures and their spectroscopic characteristics. Adsorption of both metals leads to a broken symmetry and an asymmetric charge transfer localised around the defect site of a mixed localised/delocalised character. Charge transfer creates defect states with Ti 3d character in the band gap at similar to 1-eV binding energy. Cr adsorption, however, leads to a very large shift in the valence-band edge to higher binding energy and the creation of Cr 3d states at 2.8-eV binding energy. Low-temperature oxidation lifts the Ti-derived band-gap states and modifies the intensity of the Cr features, indicative of a change of oxidation state from Cr3+ to Cr4+. Higher temperature processing leads to a loss of Cr from the surface region, indicative of its substitution into the bulk

Small Polarons in Transition Metal Oxides

The formation of polarons is a pervasive phenomenon in transition metal oxide compounds, with a strong impact on the physical properties and functionalities of the hosting materials. In its original formulation the polaron problem considers a single charge carrier in a polar crystal interacting with its surrounding lattice. Depending on the spatial extension of the polaron quasiparticle, originating from the coupling between the excess charge and the phonon field, one speaks of small or large polarons. This chapter discusses the modeling of small polarons in real materials, with a particular focus on the archetypal polaron material TiO2. After an introductory part, surveying the fundamental theoretical and experimental aspects of the physics of polarons, the chapter examines how to model small polarons using first principles schemes in order to predict, understand and interpret a variety of polaron properties in bulk phases and surfaces. Following the spirit of this handbook, different types of computational procedures and prescriptions are presented with specific instructions on the setup required to model polaron effects.Comment: 36 pages, 12 figure