Modeling Heat Dissipation at the Nanoscale: An Embedding Approach for Chemical Reaction Dynamics on Metal Surfaces

We present an embedding technique for metallic systems that makes it possible to model energy dissipation into substrate phonons during surface chemical reactions from first principles. The separation of chemical and elastic contributions to the interaction potential provides a quantitative description of both electronic and phononic band structure. Application to the dissociation of O$_2$ at Pd(100) predicts translationally "hot" oxygen adsorbates as a consequence of the released adsorption energy (ca. 2.6 eV). This finding questions the instant thermalization of reaction enthalpies generally assumed in models of heterogeneous catalysis.Comment: 6 pages, 2 figure

EU cohesion policy and the equity-efficiency trade-off - Adding dynamics to Martin's model

As a result of the combination of endogenous growth theory with the approach of the new economic geography (NEG), several models have been developed to explain spatial income inequality and to formulate possible policy strategies taking into account the equity-efficiency trade-off. The dynamics of this problem should be considered as fundamentally important for the enlargement of the EU, because with respect to the new Member States from Central and Eastern Europe (CEECs), EU cohesion policy is confronted with a double challenge: how can it contribute to attain higher national growth (and therefore convergence towards the EU average income per capita) and at the same time contribute to the decrease of regional disparities within the new Member States? This analysis is particularly appealing against the background of the alleged equity-efficiency trade-off that regional policies often suffer from. After the introduction, in the second part of this paper, some light is shed on this equity-efficiency trade-off in the framework of an overview surveying the theoretical literature on the issue. In the third part of the paper, a model presented by Philippe Martin (1999) is presented. Martin’s model combines the approaches of NEG and endogenous growth theory. In the fourth part, we develop a very simple dynamic version of the Martin model, followed by its formal analysis. We examine the effect of a monetary transfer to the poorer region, financed by the EU in the context of its cohesion policy interventions. In the fifth part, we derive some regional policy implications of the dynamised version of the Martin model. We find that there is a case for a “two step regional policy approach” in order to tackle the equity-efficiency trade-off challenge: this approach first aims to support the richer region and thus aggregate growth in the whole integrated area, and then to pursue an equity-oriented cohesion policy by fostering firm creation and innovation in the poorer region.

Non-Adiabatic Vibrational Damping of Molecular Adsorbates: Insights into Electronic Friction and the Role of Electronic Coherence

We present a perturbation approach rooted in time-dependent density-functional theory to calculate electron hole (eh)-pair excitation spectra during the non-adiabatic vibrational damping of adsorbates on metal surfaces. Our analysis for the benchmark systems CO on Cu(100) and Pt(111) elucidates the surprisingly strong influence of rather short electronic coherence times. We demonstrate how in the limit of short electronic coherence times, as implicitly assumed in prevalent quantum nuclear theories for the vibrational lifetimes as well as electronic friction, band structure effects are washed out. Our results suggest that more accurate lifetime or chemicurrent-like experimental measurements could characterize the electronic coherence.Comment: Article as accepted for publication in Physical Review Letter

A horizontally-scalable multiprocessing platform based on Node.js

This paper presents a scalable web-based platform called Node Scala which allows to split and handle requests on a parallel distributed system according to pre-defined use cases. We applied this platform to a client application that visualizes climate data stored in a NoSQL database MongoDB. The design of Node Scala leads to efficient usage of available computing resources in addition to allowing the system to scale simply by adding new workers. Performance evaluation of Node Scala demonstrated a gain of up to 74 % compared to the state-of-the-art techniques.Comment: 8 pages, 7 figures. Accepted for publication as a conference paper for the 13th IEEE International Symposium on Parallel and Distributed Processing with Applications (IEEE ISPA-15

A structural analysis of the A5/1 state transition graph

We describe efficient algorithms to analyze the cycle structure of the graph induced by the state transition function of the A5/1 stream cipher used in GSM mobile phones and report on the results of the implementation. The analysis is performed in five steps utilizing HPC clusters, GPGPU and external memory computation. A great reduction of this huge state transition graph of 2^64 nodes is achieved by focusing on special nodes in the first step and removing leaf nodes that can be detected with limited effort in the second step. This step does not break the overall structure of the graph and keeps at least one node on every cycle. In the third step the nodes of the reduced graph are connected by weighted edges. Since the number of nodes is still huge an efficient bitslice approach is presented that is implemented with NVIDIA's CUDA framework and executed on several GPUs concurrently. An external memory algorithm based on the STXXL library and its parallel pipelining feature further reduces the graph in the fourth step. The result is a graph containing only cycles that can be further analyzed in internal memory to count the number and size of the cycles. This full analysis which previously would take months can now be completed within a few days and allows to present structural results for the full graph for the first time. The structure of the A5/1 graph deviates notably from the theoretical results for random mappings.Comment: In Proceedings GRAPHITE 2012, arXiv:1210.611

Measurement of the Top Quark Mass using Dilepton Events and a Neutrino Weighting Algorithm with the DØ Experiment at the Tevatron (Run II)

Several measurements of the top quark mass in the dilepton final states with the D0 experiment are presented. The theoretical and experimental properties of the top quark are described together with a brief introduction of the Standard Model of particle physics and the physics of hadron collisions. An overview over the experimental setup is given. The Tevatron at Fermilab is presently the highest-energy hadron collider in the world with a center-of-mass energy of 1.96 TeV. There are two main experiments called CDF and D0, A description of the components of the multipurpose D0 detector is given. The reconstruction of simulated events and data events is explained and the criteria for the identification of electrons, muons, jets, and missing transverse energy is given. The kinematics in the dilepton final state is underconstraint. Therefore, the top quark mass is extracted by the so-called Neutrino Weighting method. This method is introduced and several different approaches are described, compared, an d enhanced. Results for the international summer conferences 2006 and winter 2007 are presented. The top quark mass measurement for the combination of all three dilepton channels with a dataset of 1.05 1/fb yields: mtop=172.5+-5.5 (stat.) +- 5.8 (syst.) GeV. This result is presently the most precise top quark mass measurement of the D0 experiment in the dilepton chann el. It entered the top quark mass wold average from March 2007

Electronic friction-based vibrational lifetimes of molecular adsorbates: Beyond the independent atom approximation

We assess the accuracy of vibrational damping rates of diatomic adsorbates on metal surfaces as calculated within the local-density friction approximation (LDFA). An atoms-in-molecules (AIM) type charge partitioning scheme accounts for intra-molecular contributions and overcomes the systematic underestimation of the non-adiabatic losses obtained within the prevalent independent atom approximation. The quantitative agreement obtained with theoretical and experimental benchmark data suggests the LDFA-AIM as an efficient and reliable approach to account for electronic dissipation in ab initio molecular dynamics simulations of surface chemical reactions.Comment: 5 pages including 2 figure