On solving fair exchange and related distributed problems in Byzantine environments

Abstract The solvability of the problem of fair exchange in a synchronous system subject to Byzantine failures is investigated in this work. The fair exchange problem arises when a group of processes are required to exchange digital items in a fair manner, which means that either each process obtains the item it was expecting or no process obtains any information on, the inputs of others. After introducing a novel specification of fair exchange that clearly separates safety and liveness, we give an overview of the difficulty of solving such a problem in the context of a fully-connected topology. On one hand, we show that no solution to fair exchange exists in the absence of an identified process that every process can trust a priori; on the other, a well-known solution to fair exchange relying on a trusted third party is recalled. These two results lead us to complete our system model with a flexible representation of the notion of trust. We then show that fair exchange is solvable if and only if a connectivity condition, named the reachable majority condition, is satisfied. The necessity of the condition is proven by an impossibility result and its sufficiency by presenting a general solution to fair exchange relying on a set of trusted processes. The focus is then turned towards a specific network topology in order to provide a fully decentralized, yet realistic, solution to fair exchange. The general solution mentioned above is optimized by reducing the computational load assumed by trusted processes as far as possible. Accordingly, our fair exchange protocol relies on trusted tamperproof modules that have limited communication abilities and are only required in key steps of the algorithm. This modular solution is then implemented in the context of a pedagogical application developed for illustrating and apprehending the complexity of fair exchange. This application, which also includes the implementation of a wide range of Byzantine behaviors, allows executions of the algorithm to be set up and monitored through a graphical display. Surprisingly, some of our results on fair exchange seem contradictory with those found in the literature of secure multiparty computation, a problem from the field of modern cryptography, although the two problems have much in common. Both problems are closely related to the notion of trusted third party, but their approaches and descriptions differ greatly. By introducing a common specification framework, a comparison is proposed in order to clarify their differences and the possible origins of the confusion between them. This leads us to introduce the problem of generalized fair computation, a generalization of fair exchange. Finally, a solution to this new problem is given by generalizing our modular solution to fair exchange

Estudi de les arts del cos en el museu del segle XXI: un art efímer i viu dins del museu

L’objectiu principal d’aquesta investigació és analitzar per què les arts de cos estan tan presents en els museus del segle XXI. Per fer-ho, ens centrarem primer en conèixer la història de les arts del cos des dels seus inicis al carrer o galeries alternatives fins a l’entrada al museu. En segon lloc, farem una aproximació a l’evolució dels museus centrant-nos en els segles XX i XXI. En tercer lloc, investigarem com les arts del cos entren als museus i farem una recerca d’aquestes arts en el museu del segle XXI

Prevention of vascular dysfunction and arterial hypertension in mice generated by assisted reproductive technologies by addition of melatonin to culture media.

Assisted reproductive technologies (ART) induce vascular dysfunction in humans and mice. In mice, ART-induced vascular dysfunction is related to epigenetic alteration of the endothelial nitric oxide synthase (eNOS) gene, resulting in decreased vascular eNOS expression and nitrite/nitrate synthesis. Melatonin is involved in epigenetic regulation, and its administration to sterile women improves the success rate of ART. We hypothesized that addition of melatonin to culture media may prevent ART-induced epigenetic and cardiovascular alterations in mice. We, therefore, assessed mesenteric-artery responses to acetylcholine and arterial blood pressure, together with DNA methylation of the eNOS gene promoter in vascular tissue and nitric oxide plasma concentration in 12-wk-old ART mice generated with and without addition of melatonin to culture media and in control mice. As expected, acetylcholine-induced mesenteric-artery dilation was impaired (P = 0.008 vs. control) and mean arterial blood pressure increased (109.5 ± 3.8 vs. 104.0 ± 4.7 mmHg, P = 0.002, ART vs. control) in ART compared with control mice. These alterations were associated with altered DNA methylation of the eNOS gene promoter (P < 0.001 vs. control) and decreased plasma nitric oxide concentration (10.1 ± 11.1 vs. 29.5 ± 8.0 μM) (P < 0.001 ART vs. control). Addition of melatonin (10(-6) M) to culture media prevented eNOS dysmethylation (P = 0.005, vs. ART + vehicle), normalized nitric oxide plasma concentration (23.1 ± 14.6 μM, P = 0.002 vs. ART + vehicle) and mesentery-artery responsiveness to acetylcholine (P < 0.008 vs. ART + vehicle), and prevented arterial hypertension (104.6 ± 3.4 mmHg, P < 0.003 vs. ART + vehicle). These findings provide proof of principle that modification of culture media prevents ART-induced vascular dysfunction. We speculate that this approach will also allow preventing ART-induced premature atherosclerosis in humans.

Lo que no es nuevo puede ser actual: hacia distintos puntos de mira de la didáctica del arte What is not new can be current - towards different approaches of the didactics of art

With this article we want to present a state of affairs of the didactics of art in our context, and at the same time we want todiscuss on its pluri- and interdisciplinary construction. We check the different disciplines that configure it and we analysethe paradigm of artistic education as a discipline (DBAE) and its passage to post-modernity. This example focuses thediscussion about the opportunity of adapting holistic educative models and the transition of the current educativeinnovation towards skill models

Performance and scalability of isolated DC-DC converter topologies in low voltage, high current applications

Fuel cells are a promising alternative for clean and efficient energy production. A fuel cell is probably the most demanding of all distributed generation power sources. It resembles a solar cell in many ways, but sets strict limits to current ripple, common mode voltages and load variations. The typically low output voltage from the fuel cell stack needs to be boosted to a higher voltage level for grid interfacing. Due to the high electrical efficiency of the fuel cell, there is a need for high efficiency power converters, and in the case of low voltage, high current and galvanic isolation, the implementation of such converters is not a trivial task. This thesis presents galvanically isolated DC-DC converter topologies that have favorable characteristics for fuel cell usage and reviews the topologies from the viewpoint of electrical efficiency and cost efficiency. The focus is on evaluating the design issues when considering a single converter module having large current stresses. The dominating loss mechanism in low voltage, high current applications is conduction losses. In the case of MOSFETs, the conduction losses can be efficiently reduced by paralleling, but in the case of diodes, the effectiveness of paralleling depends strongly on the semiconductor material, diode parameters and output configuration. The transformer winding losses can be a major source of losses if the windings are not optimized according to the topology and the operating conditions. Transformer prototyping can be expensive and time consuming, and thus it is preferable to utilize various calculation methods during the design process in order to evaluate the performance of the transformer. This thesis reviews calculation methods for solid wire, litz wire and copper foil winding losses, and in order to evaluate the applicability of the methods, the calculations are compared against measurements and FEM simulations. By selecting a proper calculation method for each winding type, the winding losses can be predicted quite accurately before actually constructing the transformer. The transformer leakage inductance, the amount of which can also be calculated with reasonable accuracy, has a significant impact on the semiconductor switching losses. Therefore, the leakage inductance effects should also be taken into account when considering the overall efficiency of the converter. It is demonstrated in this thesis that although there are some distinctive differences in the loss distributions between the converter topologies, the differences in the overall efficiency can remain within a range of a few percentage points. However, the optimization effort required in order to achieve the high efficiencies is quite different in each topology. In the presence of practical constraints such as manufacturing complexity or cost, the question of topology selection can become crucial.

Properties and algorithms of the (n, k)-star graphs

The (n, k)-star interconnection network was proposed in 1995 as an attractive alternative to the n-star topology in parallel computation. The (n, k )-star has significant advantages over the n-star which itself was proposed as an attractive alternative to the popular hypercube. The major advantage of the (n, k )-star network is its scalability, which makes it more flexible than the n-star as an interconnection network. In this thesis, we will focus on finding graph theoretical properties of the (n, k )-star as well as developing parallel algorithms that run on this network. The basic topological properties of the (n, k )-star are first studied. These are useful since they can be used to develop efficient algorithms on this network. We then study the (n, k )-star network from algorithmic point of view. Specifically, we will investigate both fundamental and application algorithms for basic communication, prefix computation, and sorting, etc. A literature review of the state-of-the-art in relation to the (n, k )-star network as well as some open problems in this area are also provided.

Le primitivisme et l'art des enfants dans l'oeuvre de Léon Bellefleur (1945-1950)

Les illustrations ont été retirées de la version numérique pour des raisons de droit d'auteur.

A Shine of Truth in the "universal delusional context of reification" (Theodor W. Adorno)

“A Shine of Truth in the ‘universal delusional context of reification’ (Theodor W. Adorno)” comprend sept chapitres, un prologue et un épilogue. Chaque partie se construit à deux niveaux : (1) à partir des liens qui se tissent entre les phrases contiguës ; et (2) à partir des liens qui se tissent entre les phrases non contiguës. Les incipit des paragraphes forment l’argument principal de la thèse. Le sujet de la thèse, Schein (apparence, illusion, clarté) est abordé de manière non formaliste, c’est à dire, de manière que la forme donne d’elle-même une idée de la chose : illusion comme contradiction imposée. Bien que le sujet de la thèse soit l’illusion, son but est la vérité. Le Chapitre I présente une dialectique de perspectives (celles de Marx, de Lukács, de Hegel, de Horkheimer et d'Adorno) pour arriver à un critère de vérité, compte tenu du contexte d’aveuglement universel de la réification ; c’est la détermination de la dissolution de l’apparence. Le Chapitre II présente le concept d’apparence esthétique—une apparence réversible qui s’oppose à l’apparence sociale générée par l’industrie de la culture. Le Chapitre III cherche à savoir si la vérité en philosophie et la vérité en art sont deux genres distincts de vérités. Le Chapitre IV détermine si l’appel à la vérité comme immédiateté de l’expression, fait par le mouvement expressionniste du 20e siècle, est nouveau, jugé à l’aune d’un important antécédent à l’expressionisme musical : « Der Dichter spricht » de Robert Schumann. Le Chapitre V se penche sur la question à savoir si le montage inorganique est plus avancé que l’expressionisme. Le Chapitre VI reprend là où Peter Bürger clôt son essai Theorie de l’avant-garde : ce chapitre cherche à savoir à quel point l’oeuvre d’art après le Dada et le Surréalisme correspond au modèle hégélien de la « prose ». Le Chapitre VII soutient que Dichterliebe, op. 48, (1840), est une oeuvre d’art vraie. Trois conclusions résultent de cette analyse musicale détaillée : (1) en exploitant, dans certains passages, une ambigüité dans les règles de l’harmonie qui fait en sorte tous les douze tons sont admis dans l’harmonie, l’Opus 48 anticipe sur Schoenberg—tout en restant une musique tonale ; (2) l’Opus 48, no 1 cache une tonalité secrète : à l'oeil, sa tonalité est soit la majeur, soit fa-dièse mineur, mais une nouvelle analyse dans la napolitaine de do-dièse majeur est proposée ici ; (3) une modulation passagère à la napolitaine dans l’Opus 48, no 12 contient l’autre « moitié » de la cadence interrompue à la fin de l’Opus 48, no 1. Considérés à la lumière de la société fausse, l’Allemagne des années 1930, ces trois aspects anti-organiques témoignent d’une conscience avancée. La seule praxis de vie qu’apporte l’art, selon Adorno, est la remémoration. Mais l’effet social ultime de garder la souffrance vécue en souvenir est non négligeable : l’émancipation universelle.

Éclatement des repères artistiques : la philosophie face à la crise de l'art contemporain

L’effondrement des repères artistiques (que plusieurs associent aux premiers ready-made de Marcel Duchamp) dévoile les symptômes d’une crise de l’art. Comme l’histoire de l’art est en quelque sorte la représentation de ce que nous sommes, on peut raisonnablement penser que la crise s’étend bien au-delà de l’art. Toutefois, l’art possède un éclairage puissant, car il illustre, littéralement, plusieurs problèmes notamment au niveau du jugement et de la raison. Faute de repères, le monde contemporain manquerait-il de discernement ? Cette question est tout à fait légitime dans le contexte actuel où tout et n’importe quoi semblent pouvoir être élevés au rang de l’Art. Le culte que l’on voue à l’individu paraît être l’une des causes du problème. On observe qu’en régime de singularité (pour reprendre l’expression de la sociologue de l’art, Nathalie Heinich) les relations du monde de l’art sont de plus en plus conflictuelles : lorsqu’on demande à un artiste de justifier son propre travail, la rationalité devient nécessairement instrumentale ; on rend également caduc le rôle du critique et des institutions. Ce mémoire s’intéresse à analyser, dans une perspective philosophique, les différentes manifestations de la crise de l’art et ses enjeux dans le monde actuel.

Mythen und Mythenbildung in Kunst und Werbung

Aufgrund der breiten aktuellen Verwendung des Mythen-Begriffs in Kunst und Werbung, aber darüber hinaus auch in nahezu allen Bereichen gesellschaftlichen Lebens und vor allem in der Philosophie ergibt sich die Notwendigkeit, einen erweiterten Mythos-Begriff über das Historisch-Authentische hinaus zu verfolgen. Ausgehend von einer strukturalen Annäherung an den Mythos-Begriff im Sinne des von Roland Barthes vorgeschlagenen sekundären semiologischen Systems, d.h. einer semiologischen Sinnverschiebung zur Schaffung einer neuen – mythischen – Bedeutung, fordert diese neue Bedeutung eine Analyse, eine Mythenanalyse heraus. Dies ist deshalb so entscheidend, weil eben diese neue Bedeutung ihr mythisches Profil im Sinne von Hans Blumenberg durch forcierte Bedeutsamkeit für Individuen oder für bestimmte gesellschaftliche Gruppierungen unterlegt, z.B. durch bewusst intensive Wiederholung eines Themas oder durch unerwartete Koinzidenzen von Ereignissen oder durch Steigerung bzw. Depotenzierung von Fakten. Der erweiterte Mythen-Begriff verlangt nach einer Strukturierung und führt dabei zu unterschiedlichen Mythen-Ansätzen: zum Ursprungsstoff des authentischen Mythos und darauf basierender Geisteslage, zum Erkennen eines reflektierten Mythos, wenn es um das Verhältnis Mythos/Aufklärung geht, zum Zeitgeist-Mythos mit seinen umfangreichen Ausprägungen ideologischer, affirmativer und kritischer Art oder zu Alltagsmythen, die sich auf Persönlichkeitskulte und Sachverherrlichungen beziehen. Gerade der letztere Typus ist das Terrain der Werbung, die über den Gebrauchswert eines Produktes hinaus Wert steigernde Tauschwerte durch symbolische Zusatzattribute erarbeiten möchte. Hierbei können Markenmythen unterschiedlichster Prägung entstehen, denen wir täglich im Fernsehen oder im Supermarkt begegnen. Die Manifestation des Mythos in der Kunst ist einerseits eine unendliche Transformationsgeschichte mythischer Substanzen und andererseits ein überhöhender Bezug auf Zeitgeisterscheinungen, etwa bei dem Mythos des Künstlers selbst oder der durch ihn vorgenommenen „Verklärung des Gewöhnlichen“. Die Transformationsprozesse können u.a . prototypisch an zwei Beispielketten erläutert werden, die für den Kunst/Werbung-Komplex besonders interessant sind, weil ihr Charakter sich in einem Fall für die Werbung als äußerst Erfolg versprechend erwiesen hat und weil sich im zweiten Fall geradezu das Gegenteil abzeichnet: Zum einen ist es die Mythengestalt der Nymphe, jene jugendliche, erotisch-verführerische Frauengestalt, die über ihre antiken Wurzeln als Sinnbild der Lebensfreude und Fruchtbarkeit hinaus in und nach der Renaissance ihre Eignung als Verbildlichung der Wiederzulassung des Weiblichen in der Kunst beweist und schließlich der Instrumen-talisierung der Werbung dient. Im anderen Fall ist es die Geschichte der Medusa, die man idealtypisch als die andere Seite der Nympha bezeichnen kann. Hier hat Kunst Auf-klärungsarbeit geleistet, vor allem durch die Verschiebung des medusischen Schreckens von ihr weg zu einer allgemein-medusischen Realität, deren neue Träger nicht nur den Schrecken, sondern zugleich ihre Beteiligung an der Schaffung dieses Schreckens auf sich nehmen. Mythosanalyse ist erforderlich, um die Stellungnahmen der Künstler über alle Epochen hinweg und dabei vor allem diese Transformationsprozesse zu erkennen und im Sinne von Ent- oder Remythologisierung einzuordnen. Die hierarchische Zuordnung der dabei erkannten Bedeutungen kann zu einem Grundbestandteil einer praktischen Philosophie werden, wenn sie einen Diskurs durchläuft, der sich an Jürgen Habermas’ Aspekt der Richtigkeit für kommunikatives Handeln unter dem Gesichtspunkt der Toleranz orientiert. Dabei ist nicht nur zu beachten, dass eine verstärkte Mythenbildung in der Kunst zu einem erweiterten Mythen-begriff und damit zu dem erweiterten, heute dominierenden Kunstbegriff postmoderner Prägung geführt hat, sondern dass innerhalb des aktuellen Mythenpakets sich die Darstellungen von Zeitgeist- und Alltagsmythen zu Lasten des authentischen und des reflektierten Mythos entwickelt haben, wobei zusätzlich werbliche Markenmythen ihre Entstehung auf Verfahrensvorbildern der Kunst basieren. Die ökonomische Rationalität der aktuellen Gesellschaft hat die Mythenbildung keines-wegs abgebaut, sie hat sie im Gegenteil gefördert. Der neuerliche Mythenbedarf wurde stimuliert durch die Sinnentleerung der zweckrationalisierten Welt, die Ersatzbedarf anmeldete. Ihre Ordnungsprinzipien durchdringen nicht nur ihre Paradedisziplin, die Ökonomie, sondern Politik und Staat, Wissenschaft und Kunst. Das Umschlagen der Aufklärung wird nur zu vermeiden sein, wenn wir uns Schritt für Schritt durch Mythenanalyse unserer Unmündigkeit entledigen.

Practising Open Education (ART & DESIGN)

Practising
 Open



















 
Education :
 Developing
 the
 Potential 
of 
Open
 Educational
 Resources
 in 
Art,
Design 
and 
Media. A collection of materials uploaded as part of the OER project.


Squirmish at the Oasis: an evening of performance and rant hosted by Agency of Noise at the Kinsgate Workshsops Trust in affiliation with Camden Arts Centre

Squirmish at the Oasis takes its name from Luigi Russolo's fourth noise network 'Skirmish at the Oasis' performed in Milan in 1913. 100 years on the Agency of Noise contemplate changes in technology and the culture industry that provoke new questions around the deliberate use of noise within music and art. Through live acts of enquiry and experimentation five artists unravel paradoxes associated with the use of noise in art, music and the gallery space. The works challenge tensions, contradictions and possible oxymorons that emerge through the use and acceptance of noise within an artistic framework. Featuring: DAISY DIXON / GRAHAM DUNNING / POLLYFIBRE / DANE SUTHERLAND / MARNIE WATTS

Large-scale fields and flows in the magnetosphere-ionosphere system

Advances in our understanding of the large-scale electric and magnetic fields in the coupled magnetosphere-ionosphere system are reviewed. The literature appearing in the period January 1991–June 1993 is sorted into 8 general areas of study. The phenomenon of substorms receives the most attention in this literature, with the location of onset being the single most discussed issue. However, if the magnetic topology in substorm phases was widely debated, less attention was paid to the relationship of convection to the substorm cycle. A significantly new consensus view of substorm expansion and recovery phases emerged, which was termed the ‘Kiruna Conjecture’ after the conference at which it gained widespread acceptance. The second largest area of interest was dayside transient events, both near the magnetopause and the ionosphere. It became apparent that these phenomena include at least two classes of events, probably due to transient reconnection bursts and sudden solar wind dynamic pressure changes. The contribution of both types of event to convection is controversial. The realisation that induction effects decouple electric fields in the magnetosphere and ionosphere, on time scales shorter than several substorm cycles, calls for broadening of the range of measurement techniques in both the ionosphere and at the magnetopause. Several new techniques were introduced including ionospheric observations which yield reconnection rate as a function of time. The magnetospheric and ionospheric behaviour due to various quasi-steady interplanetary conditions was studied using magnetic cloud events. For northward IMF conditions, reverse convection in the polar cap was found to be predominantly a summer hemisphere phenomenon and even for extremely rare prolonged southward IMF conditions, the magnetosphere was observed to oscillate through various substorm cycles rather than forming a steady-state convection bay.

Cheaters in mutualism networks

Mutualism-network studies assume that all interacting species are mutualistic partners and consider that all links are of one kind. However, the influence of different types of links, such as cheating links, on network organization remains unexplored. We studied two flower-visitation networks (Malpighiaceae and Bignoniaceae and their flower visitors), and divide the types of link into cheaters (i.e. robbers and thieves of flower rewards) and effective pollinators. We investigated if there were topological differences among networks with and without cheaters, especially with respect to nestedness and modularity. The Malpighiaceae network was nested, but not modular, and it was dominated by pollinators and had much fewer cheater species than Bignoniaceae network (28% versus 75%). The Bignoniaceae network was mainly a plant-cheater network, being modular because of the presence of pollen robbers and showing no nestedness. In the Malpighiaceae network, removal of cheaters had no major consequences for topology. In contrast, removal of cheaters broke down the modularity of the Bignoniaceae network. As cheaters are ubiquitous in all mutualisms, the results presented here show that they have a strong impact upon network topology.