Daris, a low-frequency distributed aperture array for radio astronomy in space

DARIS (Distributed Aperture Array for Radio Astronomy in Space) is a radio astronomy space mission concept aimed at observing the low-frequency radio sky in the range 1-10 MHz. Because of the Earth's ionospheric disturbances and opaqueness, this frequency range can only be observed from space. The astronomical science cases include sensitive extragalactic surveys, radio transients such as Jupiter-like burst and Crab-like pulses, and coronal mass ejection tracking. The focus of the DARIS concept study is on feasibility aspects of a distributed aperture synthesis array in space, consisting of small satellite nodes and a mother-ship. The study selected suitable science cases, antenna concepts, communications, signal processing, orbital design, and mission analysis. With current-day technologies a satellite cluster can be built consisting of at least eight satellite nodes and a mother-ship, which could be launched with a Soyuz rocket from Kourou. Such a satellite cluster would open up the last unexplored frequency range for astronomy

'Un Bon Dessin Vaut Mieux Qu'un Long Discours' : the role and impact of cartoons in contemporary France

Cartoons have traditionally occupied an important place in French visual culture, and are now a permanent feature in even the most prestigious publications, including Le Monde, where they appear on the front page. Moreover, there is a long tradition of political cartooning which is firmly situated within the historical context of caricature and lampooning, which over the years has contributed to public debates on key issues such as politics, religion and social change. In this thesis, I focus on political cartoons and argue that the political cartoon is still significant as a cultural product and as a powerful journalistic medium at a time when the existence of the print media is threatened by new technological developments. In order to understand how cartoons remain a powerful mode of expression in the twenty-first century, I begin by examining the historical development of cartooning, tracing its origins in grotesque art, physiognomy and caricature. I then explore a number of events in early modern European history such as the Reformation and the French Revolution to show that the medium was used as a means of mass communication, to inform a largely illiterate public, incite protest and instigate rebellion through propaganda. I show how political graphics were used as effective political weapons against the ruling authorities, in the face of tight regulation such as censorship, and underline the French artists' commitment to defend their right of expression. As I demonstrate, this commitment continues to be pursued by contemporary French cartoonists such as Plantu who is dedicated to fighting for freedom of expression and promoting peace issues, under the banner of Le Monde and the United Nations. In analysing a corpus of Plantu's editorial creations, I underline theoretical perspectives for ‘reading' cartoons and illuminate the visual rhetoric used by cartoonists to communicate serious issues. I conclude with an assessment of the significant role that French cartoonists played during the 2006 Cartoons War to further highlight the impact of cartoons as a vehicle for political communication, and as a catalyst for debate in the twenty first century.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The Disagreement Power of an Adversary

At the heart of distributed computing lies the fundamental result that the level of agreement that can be obtained in an asynchronous shared memory model where t processes can crash is exactly t + 1. In other words, an adversary that can crash any subset of size at most t can prevent the processes from agreeing on t values. But what about the rest (22n − n) adversaries that might crash certain combination of processes and not others? Given any adversary, what is its disagreement power? i.e., the biggest k for which it can prevent processes from agreeing on k values. This paper answers this question. We present a general characterization of adversaries that enables to directly derive their disagreement power. We use our characterization to also close the question of the weakest failure detector for k-set agreement. So far, the result has been obtained for two extreme cases: consensus and n − 1-set agreement. We answer this question for any k and any adversary

The comoving infrared luminosity density: domination of cold galaxies across 0 < z < 1

sIn this paper, we examine the contribution of galaxies with different infrared (IR) spectral energy distributions (SEDs) to the comoving IR luminosity density (IRLD), a proxy for the comoving star formation rate (SFR) density. We characterize galaxies as having either a cold or hot IR SED depending on whether the rest-frame wavelength of their peak IR energy output is above or below 90 mu m. Our work is based on a far-IR selected sample both in the local Universe and at high redshift, the former consisting of IRAS 60 mu m-selected galaxies at z < 0.07 and the latter of Spitzer 70 mu m selected galaxies across 0.1 < z <= 1. We find that the total IR luminosity densities for each redshift/luminosity bin agree well with results derived from other deep mid-/far-IR surveys. At z < 0.07, we observe the previously known results that moderate luminosity galaxies (L-IR < 10(11) L-circle dot) dominate the total luminosity density and that the fraction of cold galaxies decreases with increasing luminosity, becoming negligible at the highest luminosities. Conversely, above z = 0.1, we find that luminous IR galaxies (L-IR > 10(11) L-circle dot), the majority of which are cold, dominate the IRLD. We therefore infer that cold galaxies dominate the IRLD across the whole 0 < z < 1 range, hence appear to be the main driver behind the increase in SFR density up to z similar to 1 whereas local luminous galaxies are not, on the whole, representative of the high-redshift population

Visiting Gafni’s Reduction Land: from the BG Simulation to the Extended BG Simulation

Abstract: The Borowsky-Gafni (BG) simulation algorithm is a powerful tool that allows a set of t + 1 asynchronous sequential processes to wait-free simulate (i.e., despite the crash of up to t of them) a large number n of processes under the assumption that at most t of these processes fail (i.e., the simulated algorithm is assumed to be t-resilient). The BG simulation has been used to prove solvability and unsolvability results for crash-prone asynchronous shared memory systems. In its initial form, the BG simulation applies only to colorless decision tasks, i.e., tasks in which nothing prevents processes to decide the same value (e.g., consensus or k-set agreement tasks). Said in another way, it does not apply to decision problems such as renaming where no two processes are allowed to decide the same new name. Very recently (STOC 2009), Eli Gafni has presented an extended BG simulation algorithm (GeBG) that generalizes the basic BG algorithm by extending it to “colored ” decision tasks such as renaming. His algorithm is based on a sequence of sub-protocols where a sub-protocol is either the base agreement protocol that is at the core of BG simulation, or a commit-adopt protocol. This paper presents the core of an extended BG simulation algorithm that is particularly simple. This algorithm is based on two underlying objects: the base agreement object used in the BG simulation (as does GeBG), and (differently from GeBG) a new simple object that we call arbiter. As in GeBG, while each of the n simulated processes is simulated by each simulator, each of the first t + 1 simulated processes is associated with a predetermined simulator that we called its “owner”. The arbiter object is used to ensure that the permanent blocking (crash) of any of these t + 1 simulated processes can only be due to the crash of its owner simulator. After bein

Distributed Universality

International audienceA notion of a universal construction suited to distributed computing has been introduced by M. Herlihy in his celebrated paper “Wait-free synchronization” (ACM TOPLAS, 1991). A universal construction is an algorithm that can be used to wait-free implement any object defined by a sequential specification. Herlihy’s paper shows that the basic system model, which supports only atomic read/write registers, has to be enriched with consensus objects to allow the design of universal constructions. The generalized notion of a k-universal construction has been recently introduced by Gafni and Guerraoui (CONCUR, 2011). A k-universal construction is an algorithm that can be used to simultaneously implement k objects (instead of just one object), with the guarantee that at least one of the k constructed objects progresses forever. While Herlihy’s universal construction relies on atomic registers and consensus objects, a k-universal construction relies on atomic registers and k-simultaneous consensus objects (which are wait-free equivalent to k-set agreement objects in the read/write system model).This paper significantly extends the universality results introduced by Herlihy and Gafni-Guerraoui. In particular, we present a k-universal construction which satisfies the following five desired properties, which are not satisfied by the previous k-universal construction: (1) among the k objects that are constructed, at least ℓ objects (and not just one) are guaranteed to progress forever; (2) the progress condition for processes is wait-freedom, which means that each correct process executes an infinite number of operations on each object that progresses forever; (3) if any of the k constructed objects stops progressing, all its copies (one at each process) stop in the same state; (4) the proposed construction is contention-aware, in the sense that it uses only read/write registers in the absence of contention; and (5) it is generous with respect to the obstruction-freedom progress condition, which means that each process is able to complete any one of its pending operations on the k objects if all the other processes hold still long enough. The proposed construction, which is based on new design principles, is called a (k,ℓ)-universal construction. It uses a natural extension of k-simultaneous consensus objects, called (k,ℓ)-simultaneous consensus objects ((k,ℓ)-SC). Together with atomic registers, (k,ℓ)-SC objects are shown to be necessary and sufficient for building a (k,ℓ)-universal construction, and, in that sense, (k,ℓ)-SC objects are (k,ℓ)-universal