Detection of selfish manipulation of carrier sensing in 802.11 networks

Recently, tuning the clear channel assessment (CCA) threshold in conjunction with power control has been considered for improving the performance of WLANs. However, we show that, CCA tuning can be exploited by selfish nodes to obtain an unfair share of the available bandwidth. Specifically, a selfish entity can manipulate the CCA threshold to ignore ongoing transmissions; this increases the probability of accessing the medium and provides the entity a higher, unfair share of the bandwidth. We experiment on our 802.11 testbed to characterize the effects of CCA tuning on both isolated links and in 802.11 WLAN configurations. We focus on AP-client(s) configurations, proposing a novel approach to detect this misbehavior. A misbehaving client is unlikely to recognize low power receptions as legitimate packets; by intelligently sending low power probe messages, an AP can efficiently detect a misbehaving node. Our key contributions are: 1) We are the first to quantify the impact of selfish CCA tuning via extensive experimentation on various 802.11 configurations. 2) We propose a lightweight scheme for detecting selfish nodes that inappropriately increase their CCAs. 3) We extensively evaluate our system on our testbed; its accuracy is 95 percent while the false positive rate is less than 5 percent. © 2012 IEEE

Grover Mixers for QAOA: Shifting Complexity from Mixer Design to State Preparation

We propose GM-QAOA, a variation of the Quantum Alternating Operator Ansatz (QAOA) that uses Grover-like selective phase shift mixing operators. GM-QAOA works on any NP optimization problem for which it is possible to efficiently prepare an equal superposition of all feasible solutions; it is designed to perform particularly well for constraint optimization problems, where not all possible variable assignments are feasible solutions. GM-QAOA has the following features: (i) It is not susceptible to Hamiltonian Simulation error (such as Trotterization errors) as its operators can be implemented exactly using standard gate sets and (ii) Solutions with the same objective value are always sampled with the same amplitude. We illustrate the potential of GM-QAOA on several optimization problem classes: for permutation-based optimization problems such as the Traveling Salesperson Problem, we present an efficient algorithm to prepare a superposition of all possible permutations of $n$ numbers, defined on $O(n^2)$ qubits; for the hard constraint $k$-Vertex-Cover problem, and for an application to Discrete Portfolio Rebalancing, we show that GM-QAOA outperforms existing QAOA approaches

COMMIT: A Sender-Centric Truthful and Energy-Efficient Routing Protocol for Ad Hoc Networks

In this paper, we consider the problem of establishing a route and sending packets between a source/destination pair in ad hoc networks composed of rational selfish nodes,whose purpose is to maximize their own utility. In order to motivate nodes to follow the protocol specification, we use side payments that are made to the forwarding nodes. Our goal is to design a fully distributed algorithm such that: (i)a node is alwais better off participating in the protocol execution (individual rationality), and (ii) a node is always better off behaving according to the protocol specification (truthfulness). Furthemore, we require that messages are routed along the most energy-efficienth path. We introduce the COMMIT protocol for individually rational, truthful, and energy efficient routing in ad hoc networks. To the best of our knowledge, this is the first ad hoc routing protocol with these features. COMMIT exchanges at most O((|M|^2)*d) messages to find the optimal route, where |M|<= n-2, n is the number of network nodes, and d is the maximum node degree in the communication graph. As anaside, our work demonstrates the advantage of using a cross-layer approach to solving problems: leveraging the exitence of an underlyng topology control, and to reduce its message complessity. On the other hand, our investigation of the routing problem in presence of selfish nodes disclosed a new metric under which topology control protocols can be evaluated: the cost of cooperation

A Framework for Incentive Compatible Topology Control in Non-Cooperative Wireless Multi-Hop Networks

In this paper we consider the problem of building and maintaining a network topology with certain desirable features in a wireless multi-hop network where nodes behave like selfish agents. We first provide examples showing that existing topology control approaches are not resilient to strategic node behavior, indicating the need of considering possible selfish node behavior at the design stage. Given this observation, we propose a general framework that can be used as a guideline in the design of incentive compatible topology control protocols. As examples of application of our framework to specific topology control protocols, we present incentive compatible distributed algorithms for building the minimum spanning tree (MST) and the k-closest neighbors graph, which are very well-known topology control approaches. To the best of our knowledge, the ones presented in this paper are the first incentive compatible realizations of topology control presented in the literature

Helen Bömelburg, Der Arzt und sein Modell. Porträtfotografien aus der deutschen Psychiatrie 1880 bis 1933

Lorsque le genre de la photographie psychiatrique est évoqué, c’est généralement aux portraits des jeunes hystériques de Salpêtrière, rendus célèbres par la publication de Georges Didi-Hubermann (Invention de l’hystérie. Charcot et l’iconographie de la Salpêtrière, Paris, Macula, 1982) que l’on songe en premier. S’il est vrai que les images de Paul Régnard et Albert Londe, construites à l’époque du neurologue Jean-Martin Charcot à la clinique de la Salpêtrière, figurent parmi les plus célèbre..

QAOA-based Fair Sampling on NISQ Devices

We study the status of fair sampling on Noisy Intermediate Scale Quantum (NISQ) devices, in particular the IBM Q family of backends. Using the recently introduced Grover Mixer-QAOA algorithm for discrete optimization, we generate fair sampling circuits to solve six problems of varying difficulty, each with several optimal solutions, which we then run on ten different backends available on the IBM Q system. For a given circuit evaluated on a specific set of qubits, we evaluate: how frequently the qubits return an optimal solution to the problem, the fairness with which the qubits sample from all optimal solutions, and the reported hardware error rate of the qubits. To quantify fairness, we define a novel metric based on Pearson's $\chi^2$ test. We find that fairness is relatively high for circuits with small and large error rates, but drops for circuits with medium error rates. This indicates that structured errors dominate in this regime, while unstructured errors, which are random and thus inherently fair, dominate in noisier qubits and longer circuits. Our results provide a simple, intuitive means of quantifying fairness in quantum circuits, and show that reducing structured errors is necessary to improve fair sampling on NISQ hardware

Hypnosis at the Parthenon

In the early twentieth century the Genevois photographer Fred Boissonnas took five hundred photographs of the automatic dances of a young woman known as Magdeleine G. These images were commissioned to illustrate the hypnotist émile Magnin’s book L’Art et l’Hypnose. Presented alongside views of ancient Greek sites at an exhibition in 1904, they transformed the visual range of hypnosis photography, previously restricted to occultism and playing with light and shade. Merged with the Hellenizing trend of the turn of the century, the images display a mix of classical references, up-to-date technology, and the exploration of expressivity. Posing outdoor for a telephoto lens or indoor on a pedestal that imbued her with a sculptural quality, Magdeleine G. gave free rein to emotions inspired by the music of Chopin, Wagner, and Schubert. Initially presented as an artist unaware of her own talent, it becomes clear that, hardly culturally impoverished as was claimed, she had been a pupil of émile Jaques-Dalcroze and bore some resemblances to the American dancer Isadora Duncan

L’hypnose au Parthénon. Les photographies de Magdeleine G. par Fred Boissonnas

Au début du xxe siècle, le photographe genevois Fred Boissonnas effectue une série de 500 photographies représentant les danses automatiques de la jeune femme surnommée Magdeleine G., prévues pour illustrer l’ouvrage L’Art et l’Hypnose du magnétiseur Émile Magnin. Présentées parallèlement à des vues sur la Grèce antique lors d’une exposition en 1904, elles renouvellent l’iconographie de l’hypnose, jusqu’alors rattachée à l’occultisme et à des images jouant sur des effets de clair-obscur. Intégrées à l’esthétique hellénisante du tournant du siècle, ces images témoignent d’un mélange de références classiques, de technologie moderne et de recherche expressive. Posant en plein air devant un téléobjectif moderne ou sur un socle qui la rend sculpturale, Magdeleine G. exprime les sentiments que lui inspirent les airs de Chopin, Wagner ou Schubert. Bien que présentée comme une artiste inconsciente de son talent, il s’avère qu’elle était une élève d’emile Jaques-Dalcroze et qu’elle entretenait avec la danseuse américaine Isadora Duncan plusieurs similitudes.In the early twentieth century the Genevois photographer Fred Boissonnas took five hundred photographs of the automatic dances of a young woman known as Magdeleine G. These images were commissioned to illustrate the hypnotist émile Magnin’s book L’Art et l’Hypnose. Presented alongside views of ancient Greek sites at an exhibition in 1904, they transformed the visual range of hypnosis photography, previously restricted to occultism and playing with light and shade. Merged with the Hellenizing trend of the turn of the century, the images display a mix of classical references, up-to-date technology, and the exploration of expressivity. Posing outdoor for a telephoto lens or indoor on a pedestal that imbued her with a sculptural quality, Magdeleine G. gave free rein to emotions inspired by the music of Chopin, Wagner, and Schubert. Initially presented as an artist unaware of her own talent, it becomes clear that, hardly culturally impoverished as was claimed, she had been a pupil of émile Jaques-Dalcroze and bore some resemblances to the American dancer Isadora Duncan