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In public distributed ledger technologies (DLTs), such as Blockchains, nodes can join and leave the network at any time. A major challenge occurs when a new node joining the network wants to retrieve the current state of the ledger. Indeed, that node may receive conflicting information from honest and Byzantine nodes, making it difficult to identify the current state. In this paper, we are interested in protocols that are stateless, i.e., a new joining node should be able to retrieve the current state of the ledger just using a fixed amount of data that characterizes the ledger (such as the genesis block in Bitcoin). We define three variants of stateless DLTs: weak, strong, and probabilistic. Then, we analyze this property for DLTs using different types of consensus.

This paper investigates the problem of Byzantine Agreement in a synchronous system where malicious agents can move from process to process, corrupting their host. Earlier work on the problem are based on biased models which, as we argue in the paper, give an unfair advantage either to the correct processes or to the adversary controlling the malicious agents. Indeed, the earlier studies of the problem assume that, after a malicious agent has left a process, that process, said to be cured, is able to instantly and accurately detect the fact that it was corrupted in earlier rounds, and thus can take local actions to recover a valid state (Garay's model). We found no justification for that assumption which clearly favors correct processes. Under that model, an algorithm is known for n > 4t, where n is the number of processes and t the maximum number of malicious agents. The tightness of the bound is unknown. In contrast, more recent work on the problem remove the assumption on detection and assume instead that a malicious agent may have left corrupted messages in the send queue of a cured process. As a result, the adversary controlling the malicious agents can corrupt the messages sent by cured processes, as well as those sent by the newly corrupted ones, thus doubling the number of effective faults. Under that model, which favors the malicious agents, the problem can be solved if and only if n > 6t. In this paper, we refine the latter model to avoid the above biases. While a cured process may send messages (based on a state corrupted by the malicious agent), it will behave correctly in the way it sends those messages: i.e., send messages according to the algorithm. Surprisingly, in this model we could derive a new non-trivial tight bound for Byzantine Agreement. We prove that at least 5t + 1 processors are needed in order to tolerate t mobile Byzantine agents and provide a time optimal algorithm that matches this lower bound, altogether with a formal specification of the problem., リサーチレポート（北陸先端科学技術大学院大学情報科学研究科）

The spread of a virus and the containment of the spread have been widely studied in the literature. These two problems can be generalized in an abstraction of a two-side problem in which one side tries to spread the infection as much as possible while the other side tries to detect and limit the spread. The spread of a virus and the containment of the spread have been widely studied in the literature. These two problems can be generalized in an abstraction of a two-side problem in which one side tries to spread the infection as much as possible while the other side tries to detect and limit the spread. Three parameters play an important role: (1) the probability of a successful infection, (2) the probability of a successful detection, and (3) the topology of the network. The existing studies consider both sides of this problem separately. They either study the spread without detection or study the containment when detection is perfectly accurate. A natural question that arises when attack detection may possibly be inaccurate, is whether it is possible to contain the spread and, if it is, then under what conditions? This paper studies the two-side problem with defense strategies that can be grouped into two main classes; (1) Killing strategies, where a node decides to sacrifice itself and possibly deactivate some of its neighbors, and (2) Cutting strategies, where a node decides to cut or deactivate some communication links. Both classes aim at containing the epidemic by disconnecting infected nodes from healthy ones., リサーチレポート（北陸先端科学技術大学院大学情報科学研究科）

International audience; In this paper we consider the gathering of oblivious mobile robots in a n-node ring. In this context, the single class of configurations left open in the most recent study [2] is SP4 (a special class of configurations with only four robots).We present an algorithm to solve some of the most intricate configurations in SP4, those that can lead to a change of the axis of symmetry. Our approach lays the methodological bases for closing the remaining open cases for SP4 solvability.

This article investigates discrimination and the interplay of residential and ethnic stigma on the French housing market using two different methods, paired-testing au- dit study of real estate agencies and face-to-face interviews with real estate agents. The juxtaposition of their findings leads to a paradox: interviews reveal high levels of ethnic discrimination but little to none residential discrimination, while the audit study shows that living in deprived suburbs is associated with a lower probability of obtaining an appointment for a housing vacancy but ethnic origin (signaled by the candidate’s name) has no significant discriminatory effect. We have three priors po- tentially consistent with this apparent paradox and re-evaluate their likelihood in light of these findings: (i) agents make use of any statistical information about insolvency, including residency; (ii) there are two distinct and independent taste discriminations, one about space and one about ethnicity; (iii) these two dimensions exist and comple- ment each other.

Access to housing is difficult for minorities in France. An audit study we run in the Paris area showed that minority applicants do not face a strong disadvantage in the first step of the application; however, the fact that applicants come from a deprived area leads to more frequent unfavorable outcome (we call this residential discrimination as opposed to ethnic discrimination). The puzzle and paradox come from the fact that face-to-face interviews with real-estate agents in the city of Paris and the Parisian region DO NOT confirm this result. If anything, all discrimi-nation arise from ethnicity and agents dis-miss residential discrimination. Our paper, forthcoming in Urban Studies, documents this contrast between quantitative and qualitative methods and proposes interpretations.

While phenological shifts and migration of isolated species under climate change have already been observed on alpine summits, very few studies have focused on community composition changes in subalpine grasslands. Here we use permanent plots monitored since 1954 and precisely located phytosociological censuses from 1970 to study compositional changes of subalpine grasslands in two distinct regions of the Swiss Northern Alps. In both areas, warming trends during the monitoring period were associated with changes in land management (abandonment of goat and sheep pasturing or grazing replaced by mowing). Old and recent inventories were compared with correspondence analyses (CA). Ecological indicator values, community-affinities and biological traits of the species were used to infer the factors responsible for triggering the observed changes. In both regions, subalpine grasslands were stable with smaller changes than have previously been observed in alpine environments. Only a few species appeared or disappeared and changes were generally limited to increasing or decreasing frequency and cover of certain taxa. At one site, grazing abandonment favored fallow species. Some of these species were located at their upper altitudinal distribution limits and may have spread because of rising temperatures. In both areas, declining species were predominantly alpine and low-growing species; their decline was probably due to increased competition (e.g., shadow) with more vigorous subalpine taxa no longer limited by grazing. We conclude that vegetation communities can respond rapidly to warming as long as colonization is facilitated by available space or structural change. In the subalpine grasslands studies, changes were mainly driven by land management. These communities have a dense vegetation cover and newly arriving herbaceous species preferring warmer conditions may take some time to establish themselves. However, climate disturbances, such as exceptional drought, may accelerate community changes by opening gaps for new species.

International audience; Since 1993, crime in the United States has fallen to historic lows, seeming to legitimize the country’s mix of welfare reform and mass incarceration. The Upper Limit explains how this unusual mix came about, examining how, beginning in the 1970s, declining living standards for the poor have defined social and penal policy in the United States, making welfare more restrictive and punishment harsher. François Bonnet shows how low-wage work sets the upper limit of social and penal policy, where welfare must be less attractive than low-wage work and criminal life must be less attractive than welfare. In essence, the living standards of the lowest class of workers in a society determine the upper limit for the generosity of welfare and for the humanity of punishment in that society. The Upper Limit explores the local consequences of this punitive adjustment in East New York, a Brooklyn neighborhood where crime fell in the 1990s. Bonnet argues that no meaningful penal reform can happen unless living standards and the minimum wage rise again. Enlightening and provocative, The Upper Limit provides a comprehensive theory of the evolution of social and penal policy.

International audience

International audience; This paper analyzes the changing public/private as well as central/local relationships for the provi-sion of public security in public places in France. It describes the emergence and development of a now frequent public-private mix in policing, based on the hot issue of regulating social behaviours in public places. The significance of the French model in terms of the nature of privatization and pluralization is then discussed and compared to international trends. The rise of a local level public-private mix, while not unique in Europe, appears as a major shift in a French environment traditionally characterized by the structural centralization of its public forces.

What are the implications of Piketty's Capital for sociology and political science? Capital's argument focuses on the evolution of the r/g ratio (capital returns over growth rate) and outlines two modes of economic inequalities. One is characteristic of affluent (g > r) societies and the other is characteristic of patrimonial (r > g) societies. With the current return to a patrimonial society, corporations become political actors; occupational status and education's relevance are declining; the meaning of poverty is transformed, and welfare and punishment become interdependent means to social order; in politics, elitist theories gain traction; immigration is less about assimilation, and more about transnationalism and nationalist politics. We show that some theories are more relevant in an affluent society, and others are more adequate to a patrimonial society.

International audience

International audience

ijur_920 1029..1044 How to rid railway stations of the marginalized people who congregate in them? This is the problem faced by railway companies which are seeking to maximize the commercial drawing power of their spaces. The limitations of a strictly repressive policy are prompting railway companies to fund non-profit community-based organizations to carry out social policies aimed at the marginalized. Based on two studies in the railway stations of Lyon and Milan, the article analyses how this strategy was implemented. Our analysis involves differentiating our work from two hypotheses: the irenic hypothesis, which sets social policies in opposition to security policies, and the malefic hypothesis, which equates social policies with security policies. The work of the non-profit community-based organizations shows that the boundary between social policy and security policy is a tenuous one, since the principal aim is to disperse marginalized people and move them away from the station. Control of marginalized people is based on the use of incentive structures rather than on coercion. The community organizations also have to retain control of their philanthropic legitimacy, which they are selling to the railway companies, but which they are also putting at risk. Focusing on the agency of the actors allows us to avoid both an irenic analysis (in which ‘human’ and ‘just’ social policies come to the aid of the marginalized) and a malefic analysis (in which social policies are merely security policies in disguise).