Literatura académica sobre el tema "Pair approach"

In today's network-dependent society, cyber attacks with network worms have become the predominant threat to confidentiality, integrity, and availability of network computing resources. Despite ongoing research efforts, there is still no comprehensive network-security solution aimed at controling large-scale worm propagation. The aim of this work is fivefold: (1) Developing an accurate combinatorial model of worm propagation that can facilitate the analysis of worm control strategies, (2) Building an accurate epidemiological model for the propagation of a worm employing local strategies, (3) Devising distributed architecture and algorithms for detection of worm scanning activities, (4) Designing effective control strategies against the worm, and (5) Simulation of the developed models and strategies on large, scale-free graphs representing real-world communication networks. The proposed pair-approximation model uses the information about the network structure--order, size, degree distribution, and transitivity. The empirical study of propagation on large scale-free graphs is in agreement with the theoretical analysis of the proposed pair-approximation model. We, then, describe a natural generalization of the classical cops-and-robbers game--a combinatorial model of worm propagation and control. With the help of this game on graphs, we show that the problem of containing the worm is NP-hard. Six novel near-optimal control strategies are devised: combination of static and dynamic immunization, reactive dynamic and invariant dynamic immunization, soft quarantining, predictive traffic-blocking, and contact-tracing. The analysis of the predictive dynamic traffic-blocking, employing only local information, shows that the worm can be contained so that 40\% of the network nodes are not affected. Finally, we develop the Detection via Distributed Blackholes architecture and algorithm which reflect the propagation strategy used by the worm and the salient properties of the network. Our distributed detection algorithm can detect the worm scanning activity when only 1.5% of the network has been affected by the propagation. The proposed models and algorithms are analyzed with an individual-based simulation of worm propagation on realistic scale-free topologies.<br>Ph.D.<br>School of Computer Science<br>Engineering and Computer Science<br>Computer Science

In dieser Dissertation werden drei Messungen des Produktionswirkungsquerschnitts von Top-Quark-Antiquark-Paaren in Proton-Proton-Kollisionen bei einer Schwerpunktsenergie von 7 TeV vorgestellt. Die Daten wurden mit dem ATLAS-Experiment am Large Hadron Collider in den Jahren 2010 und 2011 aufgezeichnet. Für die Analyse werden Endzustände mit genau einem Myon oder Elektron, mindestens drei Jets sowie großem fehlenden Tranversalimpuls selektiert. Während eine Analyse ausschließlich kinematische Informationen für die Trennung von Signal- und Untergrundprozessen verwendet, nutzen die anderen beiden zusätzlich Informationen zur Identifizierung von Bottom-Quark-Jets. Mit Hilfe von multivariaten Methoden werden die präzisesten Messungen in dieser Ereignistopologie erreicht. Dies ist für zwei der Analysen insbesondere dank der Profile-Likelihood-Methode möglich, welche sorgfältig untersucht wird. Desweiteren wird zum ersten Mal ein sogenannter sichtbarer Wirkungsquerschnitt in Top-Quark-Ereignissen gemessen. Alle Ergebnisse sind in Übereinstimmung mit den theoretischen Vorhersagen in angenäherter nächstnächstführender Ordnung der Störungstheorie (approx. NNLO).<br>This doctoral thesis presents three measurements of the top quark-antiquark pair production cross section in proton-proton collisions at a centre-of-mass energy of 7TeV recorded in 2010 and 2011 with the ATLAS Experiment at the Large Hadron Collider. Events are selected in the single lepton topology by requiring an electron or muon, large missing transverse momentum and at least three jets. While one analysis relies on kinematic information only to discriminate the top quark-antiquark pair signal from the background processes, the other two also make use of b-tagging information. With the help of multivariate methods the most precise measurements in this topology are obtained. This is for two of the measurements in particular possible due to the use of a profile likelihood method which is studied in detail. For the first time a fiducial inclusive cross section measurement for top quark events is performed allowing a measurement almost independent of theoretical uncertainties. All measurements are in agreement with theory predictions performed in perturbation theory at approximate NNLO.

Heparin is a sulfated polysaccharide extracted from animal organs, which is successfully used since more than fifty years in clinics as anticoagulant and antithrombotic drug. There is also a growing interest in investigating and exploiting “new” activities of heparin, especially for cancer therapy. Nowadays, a number of non-anticoagulant glycol-split (gs) heparins, obtained by periodate oxidation/borohydride reduction are being considered as potential anticancer due to a potent inhibitory effect on heparanase, overexpressed by tumors. Additionally, the majority of their biological properties are preserved upon glycol-splitting. It is also worth noting that glycol-splitting of glucuronic acid within antithrombin binding region (ATBR) causes a drastic decrease of heparin anticoagulant activity, helping avoiding undesirable effects when being used for clinical therapy. Gs-derivatives of low molecular weight heparins (LMWHs) are of higher interest due to their better bioavailability. In spite of the numerous studies on their biological activity, detailed structural analysis of gs heparins as well as structure–activity relationship have not been reported yet. Their structural characterization remains a very challenging task, firstly, due to the high microheterogeneity of the starting heparin (significantly depending on tissue and animal sources), and to the various side reactions that can occur under sometimes uncontrolled reaction conditions. In the case of more bioavailable and, consequently, more pharmacologically attractive, low molecular weight heparins (LMWHs) used as starting material, the end groups introduced by the depolymerisation processes induce additional heterogeneity of the corresponding gs-derivatives. Evidently, an appropriate analytical approach is required for a pharmaceutical development of these potential drugs. The present study is focused on the development and application of an efficient analytical approach combining advanced techniques, such as NMR and LC-MS methods, for structural characterization of various gs-heparins and gs-LMWHs. The structural information obtained for gs-samples was expected to provide structural details about the sequences of the parent heparin/LMWH material. The long-term aim of this project includes the exploration of structural basis of heparin-related gs-oligosaccharide sequences for their optimal binding motif with heparanase and other target proteins. In Chapter I the state-of-art of the present topic is overviewed. Structural features, biosynthesis and interaction with proteins of heparin and HS as well as structure and bioactivity of LMWHs are discussed. The potential anticancer and anti-inflammation activity of gs-heparins/gs-LMWHs and the main problems in their preparation and structural analysis are also highlighted. In the last part of the Chapter I the main analytical techniques used for analysis of heparin-related samples (NMR, LC-MS, SEC-TDA) are reviewed. The overall goal of the study and the short-term objectives are described in Chapter II. Chapter III is focused on the development of the combined NMR/LC-MS approach using a gs-derivative of a porcine mucosal heparin (PMH) sample as a model. The potentiality of this method for both characterization and differentiation of gs-products originated from heparins of various tissue and animal sources are discussed in terms of average monosaccharide composition determined by NMR as well as LC-MS qualitative and quantitative analysis of the enzymatically digested samples. The advantages of the combination of glycol-splitting and enzymatic depolymerisation for the characterization of gs-products and starting heparin samples are also discussed. A particular attention has been dedicated to the relevance of the diversity of antithrombin binding region (ATBR) in different heparins and to the length of undersulfated domains within their chains. Molecular weight measurements as well as the dependence of the hydrodynamic properties on the introduced glycol-split units (determined by SEC-TDA) are also described. The possible control and monitoring of glycol-splitting reaction (including side-reactions) using the applied techniques is discussed. The applications of the developed approach for the characterization of the more biologically attractive but often more complex gs-LMWHs (gs-tinzaparin, gs-enoxaparin, gs-dalteparin) are reported in Chapter IV. The developed LC-MS method for direct qualitative profiling of gs-LMWHs (possible because of the molecular weight lower than for unfractionated heparins) is discussed as a possible additional analytical tool for their compositional and structural analysis. The studied susceptibility to periodate oxidation/borohydride reduction of particular end-groups (at both reducing and non-reducing ends) of all the three LMWHs is highlighted. Among those, one of the most unexpected result was the oxidation of the enoxaparin 1,6-anhydro-D-mannosamine-N-sulfate, which was studied in detail. The potential application of the LC-MS method for the heparin sequencing is shown for sequences adjacent to the linkage region tetrasaccharide. General conclusions and future perspectives are discussed in Chapter V.