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Sermpezis P.,FORTH | Dimitropoulos X.,University of Crete
Performance Evaluation Review | Year: 2016

The complexity of computer systems, networks and applications, as well as the advancements in computer technology, continue to grow at a rapid pace. Mathematical analysis, modeling and optimization have been playing, and continue to play, an important role in research studies to investigate fundamental issues and tradeoffs at the core of performance problems in the design and implementation of complex computer systems, networks and applications. On June 14, 2016, the 18th Workshop on MAthematical performance Modeling and Analysis (MAMA 2016) was held in Antibes Juan-les-Pins, France, sponsored by ACM SIGMETRICS and IFIP WG 7.3, and held in conjunction with SIGMETRICS/Performance 2016. This workshop seeks to bring together researchers working on the mathematical, methodological and theoretical aspects of performance analysis, modeling and optimization. It is intended to provide a forum at SIGMETRICS/Performance conferences for talks on early research in the more mathematical areas of computer performance analysis. These talks tend to be based on very recent research results (including work in progress) or on new research results that will be otherwise submitted only to a journal (or recently have been submitted to a journal). Thus, part of the goal is to complement and supplement the SIGMETRICS/Performance Conference program with such talks without removing any theoretical contributions from the main technical program. Furthermore, we continue to experience the desired result of having abstracts from previous MAMA workshops appear as full papers in the main program of subsequent SIGMETRICS, Performance and related conferences. All submissions were reviewed by at least 4 members of the program committee, from which a total of 15 were selected for presentation at the MAMA 2016 workshop. This special issue of Performance Evaluation Review includes extended abstracts relating to these presentations (arranged in the order of their presentation), which cover a wide range of topics in the area of mathematical performance analysis, modeling and optimization. The study of Antunes et al. presents a method to detect switches between stationary intervals as part of a probing strategy to estimate time-dependent traffic intensity. Gast provides a mean-field approximation of a system of interacting objects and constructs a Lyapunov function for this model, with applications to caching. The study of Domingues et al. focuses on search and placement in tiered cache networks, proposing and investigating a simple and flexible cache network architecture. Cai et al. consider information spreading forensics, proposing a framework for estimating information spread rates and establishing properties of this framework. The study of Gelenbe introduces a model of mutually influencing individuals who hold one of two opinions about some matter and shows certain properties of this model. Doncel et al. consider the question of whether mean-field games are the limit of finite stochastic games, showing that this convergence does not hold in general. The study of Feinberg and Liang describes the structure of optimal policies for discounted periodic-review single-commodity total-cost stochastic inventory control problems with fixed ordering costs. Fricker et al. investigate the performance of a system under simple resource adaptation algorithms based on the downgrading of requests when certain conditions hold. The study of Lu et al. considers dynamic resource allocation of computing resources to multiple workload classes under uncertainty within the context of a mathematical finance framework. Sermpezis and Dimitropoulos seek to analytically examine the effects of routing centralization on the performance of inter-domain routing and the convergence time of BGP. The study of Gardner et al. proposes a model of redundancy, in which jobs send redundant copies to d servers chosen uniformly at random, and obtains expressions for mean response time in such systems. Mukherjee et al. construct a coupling to bound the difference in queue length processes between the join-the-shortest-queue and power-of-d load balancing schemes. The study of Juneja and Manjunath considers the problem of when to dynamically join the queue in a system that allows customers in the lounge to know the queue, lounge and server occupancy at all times. Stolyar investigates a service system with packing constraints and heterogeneous servers, establishing theoretical properties for two variants of the model in the large-scale asymptotic regime. The study of Lu et al. considers a generalization of the input-queued switch scheduling problem under a linear cost function of delay for each queue and derives optimal solutions and structural properties. I sincerely thank each of the speakers and co-authors for their presentation and participation at the MAMA 2016 workshop, as well as each of the other workshop attendees. I also sincerely thank my fellow program committee members: I. Adan, Y. Baryshnikov, S. Borst, G. Casale, C.S. Chang, E. Coffman, J. Dai, E. de Souza e Silva, A. Dieker, N. Duffield, D. Eager, E. Feinberg, D. Gamarnik, A. Ganesh, D. Gaver, R. Gibbens, L. Golubchik, P. Harrison, A. Jean-Marie, P. Key, G. Latouche, J. van Leeuwaarden, Z. Liu, Y. Lu, J. Lui, M. Mandjes, R. van der Mei, P. Momcilovic, P. Nain, D. Nicol, S. Núñez-Queija, A. Proutiere, A. Radovanovic, K. Ramanan, P. Robert, M. Sharma, E. Smirni, R. Srikant, S. Stolyar, P. Taylor, D. Towsley, B. Van Houdt, A. Wierman, C. Xia, D. Yao, A. Zeevi and B. Zwart. Without all the work and support from both of these groups of people, the MAMA 2016 workshop would not have been possible. I also thank ACM SIGMETRICS and IFIP WG 7.3 for all of their support, and Nidhi Hegde for all of her assistance and support with this special issue of PER.

Sinner E.-K.,Max Planck Institute for Polymer Research | Sinner E.-K.,Johannes Gutenberg University Mainz | Sinner E.-K.,Institute of Materials Research and Engineering of Singapore | Ritz S.,Max Planck Institute for Polymer Research | And 6 more authors.
Materials Today | Year: 2010

This paper summarizes some of our efforts in designing and synthesizing bio-functional layers at solid/solution interfaces, characterizing their structure and dynamics, and optimizing their functional properties. We explore different materials and architectures, focusing here on hydrogels and lipid bilayer membranes. © 2010 Elsevier Ltd. All rights reserved.

Kontopoulos E.,Aristotle University of Thessaloniki | Bassiliades N.,Aristotle University of Thessaloniki | Governatori G.,NICTA | Antoniou G.,FORTH
International Journal on Semantic Web and Information Systems | Year: 2011

Defeasible logic is a non-monotonic formalism that deals with incomplete and conflicting information, whereas modal logic deals with the concepts of necessity and possibility. These types of logics play a significant role in the emerging Semantic Web, which enriches the available Web information with meaning, leading to better cooperation between end-users and applications. Defeasible and modal logics, in general, and, particularly, deontic logic provide means for modeling agent communities, where each agent is characterized by its cognitive profile and normative system, as well as policies, which define privacy requirements, access permissions, and individual rights. Toward this direction, this article discusses the extension of DR-DEVICE, a Semantic Web-aware defeasible reasoner, with a mechanism for expressing modal logic operators, while testing the implementation via deontic logic operators, concerned with obligations, permissions, and related concepts. The motivation behind this work is to develop a practical defeasible reasoner for the Semantic Web that takes advantage of the expressive power offered by modal logics, accompanied by the flexibility to define diverse agent behaviours. A further incentive is to study the various motivational notions of deontic logic and discuss the cognitive state of agents, as well as the interactions among them. Copyright © 2011, IGI Global.

Pandis S.N.,University of Patras | Donahue N.M.,Carnegie Mellon University | Murphy B.N.,Carnegie Mellon University | Riipinen I.,University of Stockholm | And 4 more authors.
Faraday Discussions | Year: 2013

The formation, atmospheric evolution, properties, and removal of organic particulate matter remain some of the least understood aspects of atmospheric chemistry despite the importance of organic aerosol (OA) for both human health and climate change. Here, we summarize our recent efforts to deal with the chemical complexity of the tens of thousands of organic compounds in the atmosphere using the volatility-oxygen content framework (often called the 2D-Volatility Basis Set, 2D-VBS). Our current ability to measure the ambient OA concentration as a function of its volatility and oxygen to carbon (O:C) ratio is evaluated. The combination of a thermodenuder, isothermal dilution and Aerosol Mass Spectrometry (AMS) together with a mathematical aerosol dynamics model is a promising approach. The development of computational modules based on the 2D-VBS that can be used in chemical transport models (CTMs) is described. Approaches of different complexity are tested against ambient observations, showing the challenge of simulating the complex chemical evolution of atmospheric OA. The results of the simplest approach describing the net change due to functionalization and fragmentation are quite encouraging, reproducing both the observed OA levels and O:C in a variety of conditions. The same CTM coupled with source-apportionment algorithms can be used to gain insights into the travel distances and age of atmospheric OA. We estimate that the average age of OA near the ground in continental locations is 1-2 days and most of it was emitted (either as precursor vapors or particles) hundreds of kilometers away. Condensation of organic vapors on fresh particles is critical for the growth of these new particles to larger sizes and eventually to cloud condensation nuclei (CCN) sizes. The semivolatile organics currently simulated by CTMs are too volatile to condense on these tiny particles with high curvature. We show that chemical aging reactions converting these semivolatile compounds to extremely low volatility compounds can explain the observed growth rates of new particles in rural environments. © 2014 The Royal Society of Chemistry.

Spitalsky Z.,FORTH | Tasis D.,University of Patras | Papagelis K.,University of Patras | Galiotis C.,FORTH | Galiotis C.,University of Patras
Progress in Polymer Science (Oxford) | Year: 2010

Carbon nanotubes have long been recognized as the stiffest and strongest man-made material known to date. In addition, their high electrical conductivity has roused interest in the area of electrical appliances and communication related applications. However, due to their miniscule size, the excellent properties of these nanostructures can only be exploited if they are homogeneously embedded into light-weight matrices as those offered by a whole series of engineering polymers. We review the present state of polymer nanocomposites research in which the fillers are carbon nanotubes. In order to enhance their chemical affinity to engineering polymer matrices, chemical modification of the graphitic sidewalls and tips is necessary. In this review, an extended account of the various chemical strategies for grafting polymers onto carbon nanotubes and the manufacturing of carbon nanotube/polymer nanocomposites is given. The mechanical and electrical properties to date of a whole range of nanocomposites of various carbon nanotube contents are also reviewed in an attempt to facilitate progress in this emerging area. © 2009 Elsevier Ltd. All rights reserved.

Liaskos C.,FORTH | Kotronis V.,ETH Zurich | Dimitropoulos X.,FORTH
Proceedings - IEEE INFOCOM | Year: 2016

Distributed link-flooding attacks constitute a new class of attacks with the potential to segment large areas of the Internet. Their distributed nature makes detection and mitigation very hard. This work proposes a novel framework for the analytical modeling and optimal mitigation of such attacks. The detection is modeled as a problem of relational algebra, representing the association of potential attackers (bots) to potential targets. The analysis seeks to optimally dissolve all but the malevolent associations. The framework is implemented at the level of online Traffic Engineering (TE), which is naturally triggered on link-flooding events. The key idea is to continuously re-route traffic in a manner that makes persistent participation to link-flooding events highly improbable for any benign source. Thus, bots are forced to adopt a suspicious behavior to remain effective, revealing their presence. The load-balancing objective of TE is not affected at all. Extensive simulations on various topologies validate our analytical findings. © 2016 IEEE.

Koromilas L.,45 Warren Close | Vasiliadis G.,Qatar Computing Research Institute | Athanasopoulos E.,VU University Amsterdam | Ioannidis S.,FORTH
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2016

Kernel rootkits can exploit an operating system and enable future accessibility and control, despite all recent advances in software protection. A promising defense mechanism against rootkits is Kernel Integrity Monitor (KIM) systems, which inspect the kernel text and data to discover any malicious changes. A KIM can be implemented either in software, using a hypervisor, or using extra hardware. The latter option is more attractive due to better performance and higher security, since the monitor is isolated from the potentially vulnerable host. To remain under the radar and avoid detection it is paramount for a rootkit to conceal its malicious activities. In order to detect self-hiding rootkits researchers have proposed snooping for inferring suspicious behaviour in kernel memory. This is accomplished by constantly monitoring all memory accesses on the bus and not the actual memory area where the kernel is mapped. In this paper, we present GRIM, an external memory monitor that is built on commodity, off-the-shelf, graphics hardware, and is able to verify OS kernel integrity at a speed that outperforms all so-far published snapshot-based systems. GRIM allows for checking eight thousand 64- bit values simultaneously at a 10 KHz snapshot frequency, which is sufficient to accurately detect a self-hiding loadable kernel module insertion. According to the state-of-the-art, this detection can only happen using a snoop-based monitor. GRIM does not only demonstrate that snapshotbased monitors can be significantly improved, but it additionally offers a fully programmable platform that can be instantly deployed without requiring any modifications to the host it protects. Notice that all snoopbased monitors require substantial changes at the microprocessor level. © Springer International Publishing Switzerland 2016.

Domaschka J.,University of Ulm | Kritikos K.,FORTH | Rossini A.,Sintef
Communications in Computer and Information Science | Year: 2015

The PaaSage project aims at facilitating the specification and execution of cloud-based applications by leveraging upon model-driven engineering (MDE) techniques and methods, and by exploiting multiple cloud infrastructures and platforms. Models are frequently specified using domain-specific languages (DSLs), which are tailored to a specific domain of concern. In order to cover the necessary aspects of the specification and execution of multi-cloud applications, PaaSage encompasses a family of DSLs called Cloud Application Modelling and Execution Language (CAMEL). In this paper, we present one DSL within this family, namely the Scalability Rules Language (SRL), which can be regarded as a first step towards a generic language for specifying scalability rules for multicloud applications. © Springer International Publishing Switzerland 2015.

Tsotsis P.,University of Crete | Eldridge P.S.,FORTH | Gao T.,University of Crete | Tsintzos S.I.,FORTH | And 3 more authors.
New Journal of Physics | Year: 2012

In a polariton, laser coherent monochromatic light is produced by a low-energy state of the system at the bottom of a polariton 'trap', where a condensate of polaritons is formed, requiring no conventional population inversion. Following the recent realization of polariton light-emitting diodes (LEDs) based on GaAs microcavities (MCs) operating up to room temperature, efforts have been directed towards the demonstration of an electrically injected polariton laser. However, until now, low-threshold polariton lasing in GaAs MCs under optical pumping has been reported only at low temperatures. Here, we investigate the temperature dependence of lasing threshold across the border of the strong-to-weak coupling regime transition in high-finesse GaAs MCs under non-resonant optical pumping. Remarkably, we find that although lasing in the strong coupling regime is lost when the temperature is raised from 25 to 70 K, the threshold only doubles, in stark contrast with the expected difference of two orders of magnitude. Our results can be explained by considering temperatureinduced thermalization of carriers to high wavevector states, increasing the reservoir's overall carrier lifetime, resulting in an order of magnitude higher steady-state carrier density at 70K under similar pumping conditions. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Nikolov N.,Sintef | Rossini A.,Sintef | Kritikos K.,FORTH
Procedia Computer Science | Year: 2015

Domain-specific languages (DSLs) are high-level software languages representing concepts in a particular domain. In real-world scenarios, it is common to adopt multiple DSLs to solve different aspects of a specific problem. As any other software artefact, DSLs evolve independently in response to changing requirements, which leads to two challenges. First, the concepts from the DSLs have to be integrated into a single language. Second, models that conform to an old version of the language have to be migrated to conform to its current version. In this paper, we discuss how we tackled the challenge of integrating the DSLs that comprise the Cloud Application Modelling and Execution Language (CAMEL) by leveraging upon Eclipse Modeling Framework (EMF) and Object Constraint Language (OCL). Moreover, we propose a solution to the challenge of persisting and automatically migrating CAMEL models based on Connected Data Objects (CDO) and Edapt. © 2015 The Authors.

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