Rectification effects in coherent transport through single molecules

A minimal model for coherent transport through a donor/acceptor molecular junction is presented. The two donor and acceptor sites are described by single levels energetically separated by an intramolecular tunnel barrier. In the limit of strong coupling to the electrodes a current rectification for different bias voltage polarities occurs. Contacts with recent experiments of molecular rectification are also given.Comment: 10 pages, 4 figure

Scylla and Charybdis. The European Economy and Poland's Adherence to Gold, 1928-1936

This paper examines the timing of exit from the gold-exchange standard for European countries based on a panel of monthly observations 1928-1936 for two purposes: first it aims to understand the enormous variation in monetary policy choices across Europe. I show that the pattern of exit from gold can be understood in terms of variation in factors commonly suggested in the theoretical literature, which makes it possible to predict with reasonable accuracy the very month when a country will exit gold in the 1930s. Second, I analyse the case of Poland more closely because it appears to be an intriguing outlier. Poland did not leave gold until April 1936 and suffered through one of the worst examples of a depression, with massive deflation and a complete collapse of industrial production. The estimated model fares worst for Poland, and predicts an exit even later than April 1936. By closer inspection, the factors that drive this prediction are the non-democratic character of the regime and a surprisingly high degree of trade integration with France. I argue that Poland's monetary policy was determined by attempts of the Piłsudski regime to defend Poland against foreign (esp. German) aggression. I provide evidence that strongly supports this view until about mid-1933. Ironically, just when Poland had joined the gold-bloc there were signs of a broad strategic reorientation, which paved the way for an exit in 1936.Gold-Exchange Standard, Interwar Period, Europe, Poland

Survey of DMSP Charging During the Period Preceding Cycle 24 Solar Maximum

It has been well established that polar orbiting satellites can see mild to severe charging levels during solar minimum conditions (Frooninckx and Sojka, 1992, Anderson and Koons, 1996, Anderson, 2012). However, spacecraft operations during solar maximum cannot be considered safe from auroral charging. Recently, we have seen examples of high level charging during the recent approach to solar maximum. We present here a survey of charging events seen by the Defense Meteorological Satellite Program (DMSP) satellites (F16, F17) during the solstices of 2011 and 2012. In this survey, we summarize the condition necessary for charging to occur in this environment, we describe how the lower than normal maximum conditions are conducive to the environment conditions necessary for charging in the polar orbit, and we show examples of the more extreme charging events, sometimes exceeding 1 kV, during this time period. We also show examples of other interesting phenomenological events seen in the DMSP data, but which are not considered surface charging events, and discuss the differences

Electrical characteristics of layered palladium alkanethiolates by conducting atomic force microscopy

Current-voltage measurements on individual Pd(II) alkanethiolate nanostructures of varying bilayer thicknesses (hexyl to hexadecyl) employing conducting atomic force microscopy have shown the presence of a low current region near zero bias, the width of which increases with the bilayer thickness. The resistance in this region varies exponentially with the bilayer thickness with a low decay parameter value of 0.2±0.04 Å-1 indicating a long-range nonresonant tunneling through the alkyl chains. The changeover from low current to high current with increasing bias is accompanied by a negative differential resistance feature, which arises due to Pd-S charge transfer

Interplay between the edge-state magnetism and long-range Coulomb interaction in zigzag graphene nanoribbons: quantum Monte Carlo study

We perform projective quantum Monte Carlo simulations of zigzag graphene nanoribbons within a realistic model with long-range Coulomb interactions. Increasing the relative strength of nonlocal interactions with respect to the on-site repulsion does not generate a phase transition but has a number of nontrivial effects. At the single-particle level we observe a marked enhancement of the Fermi velocity at the Dirac points. At the two-particle level, spin- and charge-density-wave fluctuations compete. As a consequence, the edge magnetic moment is reduced but the edge dispersion relation increases in the sense that the single-particle gap at momentum $q=\pi/|{\pmb a}_1|$ grows. We attribute this to nonlocal charge fluctuations which assist the spin fluctuations to generate the aforementioned gap. In contrast, the net result of the interaction-induced renormalization of different energy scales is a constant spin-wave velocity of the edge modes. However, since the particle-hole continuum is shifted to higher energies---due to the renormalization of the Fermi velocity---Landau damping is reduced. As a result, a roughly linear spin-wave-like mode at the edge spreads out through a larger part of the Brillouin zone.Comment: 11 pages, 11 figures, comment about doped nanoribbon

Trazendo o ‘passatempo nacional’ para a arena Olímpica: Leslie Mann e as forças condutoras para a internacionalização do beisebol nos anos 1930

The main objective of this study is to trace historical efforts to include baseball in the 1936 Olympics, paralleled with the internationalization of that sport. This study is presented in the format of a historical narrative. The research material was mainly drawn from primary sources located in the United States of America and Canada. Results show that Leslie Mann, a former American player, was one who significantly contributed to make the 1936 baseball Olympic exhibition distinctly better organized than previous experiences. The 1936 Olympic baseball demonstration was one of the most important accomplishments to the internationalization of baseball and an important benchmark to Baseball in the Olympic scenario.El objetivo principal es estudiar los esfuerzos históricos para incluir el béisbol en los Juegos Olímpicos de 1936, en paralelo con la internacionalización del deporte. El estudio se presenta en un formato narrativo histórico. Los datos son principalmente fuentes primarias ubicadas en los Estados Unidos de América y Canadá. Los resultados demuestran que Leslie Mann, un ex jugador profesional estadounidense, fue un personaje que contribuyó significativamente a hacer que la exhibición de béisbol en los Juegos de 1936 fuera claramente mejor organizada que en experiencias anteriores. Se argumenta que esa demostración fue uno de los esfuerzos más importantes para la internacionalización del béisbol y su presencia en el escenario olímpico.O principal objetivo deste estudo é traçar esforços históricos para incluir o beisebol nos Jogos Olímpicos de 1936, em paralelo com a internacionalização do esporte. O estudo é apresentado em formato de narrativa histórica. Os dados são, pincipalmente, fontes primárias localizadas nos Estados Unidos da América e Canadá. Os resultados demonstram que Leslie Mann, um ex-jogador professional americano, foi um personagem que contribuiu significativamente para tornar a exibição do beisebol nos Jogos de 1936 distintamente mais bem organizada do que em experiências anteriores. Argumenta-se que aquela demonstração foi um dos esforços mais importantes para a internacionalização do beisebol e sua inserção no cenário Olímpico

Systematic search for low-enthalpy sp3 carbon using evolutionary metadynamics

We present a systematic search for low-energy metastable superhard carbon allotropes by using the recently developed evolutionary metadynamics technique. It is known that cold compression of graphite produces an allotrope at 15-20 GPa. Here we look for all low-enthalpy structures accessible from graphite. Starting from 2H- or 3R-graphite and applying the pressure of 20 GPa, a large variety of intermediate $sp^3$ carbon allotropes were observed in evolutionary metadynamics simulation. Our calculation not only found all the previous proposed candidates for `superhard graphite', but also predicted two allotropes (\emph{X}-carbon and \emph{Y}-carbon) showing novel 5+7 and 4+8 topologies. These superhard carbon allotropes can be classified into five families based on 6 (diamond/lonsdaleite), 5+7 (\emph{M/W}-carbon), 5+7 (\emph{X}-carbon), 4+8 (bct C$_4$), and 4+8 (\emph{Y}-carbon) topologies. This study shows evolutionary metadynamics is a powerful approach both to find the global minima and systematically search for low-energy metastable phases reachable from given starting materials.Comment: 6 pages, 7 figure

Damage accumulation in thin ruthenium films induced by repetitive exposure to femtosecond XUV pulses below the single shot ablation threshold

The process of damage accumulation in thin ruthenium films exposed to multiple femtosecond XUV free electron laser FEL pulses below the critical angle of reflectance at the Free electron LASer facility in Hamburg FLASH was experimentally analyzed. The multi shot damage threshold is found to be lower than single shot damage threshold. Detailed analysis of the damage morphology and its dependence on irradiation conditions justifies the assumption that cavitation induced by the FEL pulse is the prime mechanism responsible for multi shot damage in optical coating