Feynman Diagrams via Graphical Calculus

This paper is an introduction to the language of Feynman Diagrams. We use Reshetikhin-Turaev graphical calculus to define Feynman diagrams and prove that asymptotic expansions of Gaussian integrals can be written as a sum over a suitable family of graphs. We discuss how different kind of interactions give rise to different families of graphs. In particular, we show how symmetric and cyclic interactions lead to ``ordinary'' and ``ribbon'' graphs respectively. As an example, the 't Hooft-Kontsevich model for 2D quantum gravity is treated in some detail.Comment: 30 pages, AMS-LaTeX, 19 EPS figures + several in-text XY-Pic, PostScript \specials, corrected attributions, 'PROP's instead of 'operads

Matrix Integrals and Feynman Diagrams in the Kontsevich Model

We review some relations occurring between the combinatorial intersection theory on the moduli spaces of stable curves and the asymptotic behavior of the 't Hooft-Kontsevich matrix integrals. In particular, we give an alternative proof of the Witten-Di Francesco-Itzykson-Zuber theorem --which expresses derivatives of the partition function of intersection numbers as matrix integrals-- using techniques based on diagrammatic calculus and combinatorial relations among intersection numbers. These techniques extend to a more general interaction potential.Comment: 52 pages; final versio

Computational techniques in graph homology of the moduli space of curves

The object of this thesis is the automated computation of the rational (co)homology of the moduli spaces of smooth marked Riemann surfaces Mg;n. This is achieved by using a computer to generate a chain complex, known in advance to have the same homology as Mg;n, and explicitly spell out the boundary operators in matrix form. As an application, we compute the Betti numbers of some moduli spaces Mg;n. Our original contribution is twofold. In Chapter 3, we develop algorithms for the enumeration of fatgraphs and their automorphisms, and the computation of the homology of the chain complex formed by fatgraphs of a given genus g and number of boundary components n. In Chapter 4, we describe a new practical parallel algorithm for performing Gaussian elimination on arbitrary matrices with exact computations: projections indicate that the size of the matrices involved in the Betti number computation can easily exceed the computational power of a single computer, so it is necessary to distribute the work over several processing units. Experimental results prove that our algorithm is in practice faster than freely available exact linear algebra codes. An effective implementation of the fatgraph algorithms presented here is available at http://code.google.com/p/fatghol. It has so far been used to compute the Betti numbers of Mg;n for (2g + n) 6 6. The Gaussian elimination code is likewise publicly available as open-source software from http://code.google.com/p/rheinfall

VM-MAD: a cloud/cluster software for service-oriented academic environments

The availability of powerful computing hardware in IaaS clouds makes cloud computing attractive also for computational workloads that were up to now almost exclusively run on HPC clusters. In this paper we present the VM-MAD Orchestrator software: an open source framework for cloudbursting Linux-based HPC clusters into IaaS clouds but also computational grids. The Orchestrator is completely modular, allowing flexible configurations of cloudbursting policies. It can be used with any batch system or cloud infrastructure, dynamically extending the cluster when needed. A distinctive feature of our framework is that the policies can be tested and tuned in a simulation mode based on historical or synthetic cluster accounting data. In the paper we also describe how the VM-MAD Orchestrator was used in a production environment at the FGCZ to speed up the analysis of mass spectrometry-based protein data by cloudbursting to the Amazon EC2. The advantages of this hybrid system are shown with a large evaluation run using about hundred large EC2 nodes.Comment: 16 pages, 5 figures. Accepted at the International Supercomputing Conference ISC13, June 17--20 Leipzig, German

GridCertLib: A Single Sign-on Solution for Grid Web Applications and Portals

This paper describes the design and implementation of GridCertLib, a Java library leveraging a Shibboleth-based authentication infrastructure and the SLCS online certificate signing service, to provide short-lived X.509 certificates and Grid proxies. The main use case envisioned for GridCertLib, is to provide seamless and secure access to Grid X.509 certificates and proxies in web applications and portals: when a user logs in to the portal using SAML-based Shibboleth authentication, GridCertLib uses the SAML assertion to obtain a Grid X.509 certificate from the SLCS service and generate a VOMS proxy from it. We give an overview of the architecture of GridCertLib and briefly describe its programming model. Its application to some deployment scenarios is outlined, as well as a report on practical experience integrating GridCertLib into portals for Bioinformatics and Computational Chemistry applications, based on the popular P-GRADE and Django software

gcodeml: A Grid-enabled Tool for Detecting Positive Selection in Biological Evolution

One of the important questions in biological evolution is to know if certain changes along protein coding genes have contributed to the adaptation of species. This problem is known to be biologically complex and computationally very expensive. It, therefore, requires efficient Grid or cluster solutions to overcome the computational challenge. We have developed a Grid-enabled tool (gcodeml) that relies on the PAML (codeml) package to help analyse large phylogenetic datasets on both Grids and computational clusters. Although we report on results for gcodeml, our approach is applicable and customisable to related problems in biology or other scientific domains.Comment: 10 pages, 4 figures. To appear in the HealthGrid 2012 con

Geopolymer oxygen carriers for chemical-looping combustion

One of the best alternatives to reduce the economic cost of CO2 capture is represented by the chemical looping combustion (CLC). This technology accomplishes indirect fuel combustion by use of a solid oxygen carrier (OC), generally a metal oxide having the capability of transporting the oxygen needed for the combustion from an air reactor to a fuel reactor, usually designed as two coupled fluidized beds. The combustion takes place in the fuel reactor through the reaction between the fuel and the solid OC, which is consequently reduced to a lower oxidation state. The reduced OC is then transferred to the air reactor, where it is regenerated by oxidation in air at high temperature. Therefore, the CLC process enables the inherent separation of the produced CO2, the stream exiting the fuel reactor being only composed of CO2 and H2O, easily separable by water condensation. Please click Additional Files below to see the full abstract